Metal Matrix Composites: Fatigue and Fracture Testing. (Latest citations from the Aerospace Database)

NASA Technical Reports Server (NTRS)

1996-01-01

The bibliography contains citations concerning techniques and results of testing metal matrix composites for fatigue and fracture. Methods include non-destructive testing techniques, and static and cyclic techniques for assessing compression, tensile, bending, and impact characteristics.

Hydrogen effects on materials for CNG/H2 blends.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farese, David; Keller, Jay O.; Somerday, Brian P.

2010-09-01

No concerns for Hydrogen-Enriched Compressed Natural gas (HCNG) in steel storage tanks if material strength is < 950 MPa. Recommend evaluating H{sub 2}-assisted fatigue cracking in higher strength steels at H{sub 2} partial pressure in blend. Limited fatigue testing on higher strength steel cylinders in H{sub 2} shows promising results. Impurities in Compressed Natural Gas (CNG) (e.g., CO) may provide extrinsic mechanism for mitigating H{sub 2}-assisted fatigue cracking in steel tanks.

Design and fabrication of composite wing panels containing a production splice

NASA Technical Reports Server (NTRS)

Reed, D. L.

1975-01-01

Bolted specimens representative of both upper and lower wing surface splices of a transport aircraft were designed and manufactured for static and random load tension and compression fatigue testing including ground-air-ground load reversals. The specimens were fabricated with graphite-epoxy composite material. Multiple tests were conducted at various load levels and the results were used as input to a statistical wearout model. The statically designed specimens performed very well under highly magnified fatigue loadings. Two large panels, one tension and compression, were fabricated for testing by NASA-LRC.

Fatigue behavior of highly porous titanium produced by powder metallurgy with temporary space holders.

PubMed

Özbilen, Sedat; Liebert, Daniela; Beck, Tilmann; Bram, Martin

2016-03-01

Porous titanium cylinders were produced with a constant amount of temporary space holder (70 vol.%). Different interstitial contents were achieved by varying the starting powders (HDH vs. gas atomized) and manufacturing method (cold compaction without organic binders vs. warm compaction of MIM feedstocks). Interstitial contents (O, C, and N) as a function of manufacturing were measured by chemical analysis. Samples contained 0.34-0.58 wt.% oxygen, which was found to have the greatest effect on mechanical properties. Quasi-static mechanical tests under compression at low strain rate were used for reference and to define parameters for cyclic compression tests. Not unexpectedly, increased oxygen content increased the yield strength of the porous titanium. Cyclic compression fatigue tests were conducted using sinusoidal loading in a servo-hydraulic testing machine. Increased oxygen content was concomitant with embrittlement of the titanium matrix, resulting in significant reduction of compression cycles before failure. For samples with 0.34 wt.% oxygen, R, σ(min) and σ(max) were varied systematically to estimate the fatigue limit (~4 million cycles). Microstructural changes induced by cyclic loading were then characterized by optical microscopy, SEM and EBSD. Copyright © 2015 Elsevier B.V. All rights reserved.

Response of resin transfer molded (RTM) composites under reversed cyclic loading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahfuz, H.; Haque, A.; Yu, D.

1996-01-01

Compressive behavior and the tension-compression fatigue response of resin transfer molded IM7 PW/PR 500 composite laminate with a circular notch have been studied. Fatigue damage characteristics have been investigated through the changes in the laminate strength and stiffness by gradually incrementing the fatigue cycles at a preselected load level. Progressive damage in the surface of the laminate during fatigue has been investigated using cellulose replicas. Failure mechanisms during static and cyclic tests have been identified and presented in detail. Extensive debonding of filaments and complete fiber bundle fracture accompanied by delamination were found to be responsible for fatigue failures, whilemore » fiber buckling, partial fiber fracture and delamination were characterized as the failure modes during static tests. Weibull analysis of the static, cyclic and residual tests have been performed and described in detail. Fractured as well as untested specimens were C-scanned, and the progressive damage growth during fatigue is presented. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) for the fractured specimen were also performed and the analysis of the failure behavior is presented.« less

The Effect of Hole Quality on the Fatigue Life of 2024-T3 Aluminum Alloy Sheet

NASA Technical Reports Server (NTRS)

Everett, Richard A., Jr.

2004-01-01

This paper presents the results of a study whose main objective was to determine which type of fabrication process would least affect the fatigue life of an open-hole structural detail. Since the open-hole detail is often the fundamental building block for determining the stress concentration of built-up structural parts, it is important to understand any factor that can affect the fatigue life of an open hole. A test program of constant-amplitude fatigue tests was conducted on five different sets of test specimens each made using a different hole fabrication process. Three of the sets used different mechanical drilling procedures while a fourth and fifth set were mechanically drilled and then chemically polished. Two sets of specimens were also tested under spectrum loading to aid in understanding the effects of residual compressive stresses on fatigue life. Three conclusions were made from this study. One, the residual compressive stresses caused by the hole-drilling process increased the fatigue life by two to three times over specimens that were chemically polished after the holes were drilled. Second, the chemical polishing process does not appear to adversely affect the fatigue life. Third, the chemical polishing process will produce a stress-state adjacent to the hole that has insignificant machining residual stresses.

The fatigue behavior of composite laminates under various mean stresses

NASA Technical Reports Server (NTRS)

Rotem, A.

1991-01-01

A method is developed for predicting the S-N curve of a composite laminate which is subjected to an arbitrary stress ratio, R (minimum stress/maximum stress). The method is based on the measuring of the S-N behavior of two distinct cases, tension-tension and compression-compression fatigue loadings. Using these parameters, expressions are formulated that estimate the fatigue behavior under any stress ratio loading. Experimental results from the testing of graphite/epoxy laminates, with various structures, are compared with the predictions and show good agreement.

Strain-controlled fatigue of acrylic bone cement.

PubMed

Carter, D R; Gates, E I; Harris, W H

1982-09-01

Monotonic tensile tests and tension-compression fatigue tests were conducted of wet acrylic bone cement specimens at 37 degrees C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.

Failure of a laminated composite under tension-compression fatigue loading

NASA Technical Reports Server (NTRS)

Rotem, A.; Nelson, H. G.

1989-01-01

The fatigue behavior of composite laminates under tension-compression loading is analyzed and compared with behavior under tension-tension and compression-compression loading. It is shown that for meaningful fatigue conditions, the tension-compression case is the dominant one. Both tension and compression failure modes can occur under the reversed loading, and failure is dependent on the specific lay-up of the laminate and the difference between the tensile static strength and the absolute value of the compressive static strength. The use of a fatigue failure envelope for determining the fatigue life and mode of failure is proposed and demonstrated.

Stress shielding and fatigue limits of poly-ether-ether-ketone dental implants.

PubMed

Lee, Woo-Taek; Koak, Jai-Young; Lim, Young-Jun; Kim, Seong-Kyun; Kwon, Ho-Beom; Kim, Myung-Joo

2012-05-01

The poly-ether-ether-ketone (PEEK) polymer is of great interest as an alternative to titanium in orthopedics because of its biocompatibility and low elastic modulus. This study evaluated the fatigue limits of PEEK and the effects of the low elastic modulus PEEK in relation to existing dental implants. Compressive loading tests were performed with glass fiber-reinforced PEEK (GFR-PEEK), carbon fiber-reinforced PEEK (CFR-PEEK), and titanium rods. Among these tests, GFR-PEEK fatigue tests were performed according to ISO 14801. For the finite element analysis, three-dimensional models of dental implants and bone were constructed. The implants in the test groups were coated with a 0.5-mm thick and 5-mm long PEEK layer on the upper intrabony area. The strain energy densities (SED) were calculated, and the bone resorption was predicted. The fatigue limits of GFR-PEEK were 310 N and were higher than the static compressive strength of GFR-PEEK. The bone around PEEK-coated implants showed higher levels of SED than the bone in direct contact with the implants, and the wider diameter and stiffer implants showed lower levels of SED. The compressive strength of the GFR-PEEK and CFR-PEEK implants ranged within the bite force of the anterior and posterior dentitions, respectively, and the PEEK implants showed adequate fatigue limits for replacing the anterior teeth. Dental implants with PEEK coatings and PEEK implants may reduce stress shielding effects. Dental implant application of PEEK polymer-fatigue limit and stress shielding. Copyright © 2012 Wiley Periodicals, Inc.

Simplification of Fatigue Test Requirements for Damage Tolerance of Composite Interstage Launch Vehicle Hardware

NASA Technical Reports Server (NTRS)

Nettles, A. T.; Hodge, A. J.; Jackson, J. R.

2010-01-01

The issue of fatigue loading of structures composed of composite materials is considered in a requirements document that is currently in place for manned launch vehicles. By taking into account the short life of these parts, coupled with design considerations, it is demonstrated that the necessary coupon level fatigue data collapse to a static case. Data from a literature review of past studies that examined compressive fatigue loading after impact and data generated from this experimental study are presented to support this finding. Damage growth, in the form of infrared thermography, was difficult to detect due to rapid degradation of compressive properties once damage growth initiated. Unrealistically high fatigue amplitudes were needed to fail 5 of 15 specimens before 10,000 cycles were reached. Since a typical vehicle structure, such as the Ares I interstage, only experiences a few cycles near limit load, it is concluded that static compression after impact (CAI) strength data will suffice for most launch vehicle structures.

Influence of Rare-Earth Additions on Properties of Titanium Alloys - Effects of Yttrium and Erbium Additions on Ti-8Al and Ti-10Al Alloy.

DTIC Science & Technology

1980-08-31

loop generated during the alternate tension-compression fatigue testing of Ti-8A1 alloy at 6000C at a plastic strain amplitude of * 0.5Z...Dependence of peak stress on the number of cycles in the longitudinal orientation of Ti-lOAl-RE alloys deformed in alternate tension-compression at...of cycles in the transverse orientation of Ti-OAl-RE alloys deformed in alternate tension- A compression fatigue at 500 0C at a plastic strain

Compression fatigue behavior and failure mechanism of porous titanium for biomedical applications.

PubMed

Li, Fuping; Li, Jinshan; Huang, Tingting; Kou, Hongchao; Zhou, Lian

2017-01-01

Porous titanium and its alloys are believed to be one of the most attractive biomaterials for orthopedic implant applications. In the present work, porous pure titanium with 50-70% porosity and different pore size was fabricated by diffusion bonding. Compression fatigue behavior was systematically studied along the out-of-plane direction. It resulted that porous pure titanium has anisotropic pore structure and the microstructure is fine-grained equiaxed α phase with a few twins in some α grains. Porosity and pore size have some effect on the S-N curve but this effect is negligible when the fatigue strength is normalized by the yield stress. The relationship between normalized fatigue strength and fatigue life conforms to a power law. The compression fatigue behavior is characteristic of strain accumulation. Porous titanium experiences uniform deformation throughout the entire sample when fatigue cycle is lower than a critical value (N T ). When fatigue cycles exceed N T , strain accumulates rapidly and a single collapse band forms with a certain angle to the loading direction, leading to the sudden failure of testing sample. Both cyclic ratcheting and fatigue crack growth contribute to the fatigue failure mechanism, while the cyclic ratcheting is the dominant one. Porous titanium possesses higher normalized fatigue strength which is in the range of 0.5-0.55 at 10 6 cycles. The reasons for the higher normalized fatigue strength were analyzed based on the microstructure and fatigue failure mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

Improvement on the Fatigue Performance of 2024-T4 Alloy by Synergistic Coating Technology

PubMed Central

Wang, Xi-Shu; Guo, Xing-Wu; Li, Xu-Dong; Ge, Dong-Yun

2014-01-01

In this paper, rotating bending fatigue tests of 2024-T4 Al alloy with different oxide coatings were carried out. Compared to the uncoated and previously reported oxide coatings of aluminum alloys, the fatigue strength is able to be enhanced by using a novel oxide coating with sealing pore technology. These results indicate that the better the coating surface quality is, the more excellent the fatigue performance under rotating bending fatigue loading is. The improvement on the fatigue performance is mainly because the fatigue crack initiation and the early stage of fatigue crack growth at the coating layer can be delayed after PEO coating with pore sealing. Therefore, it is a so-called synergistic coating technology for various uses, including welding thermal cracks and filling micro-pores. The effects of different oxide coatings on surface hardness, compressive residual stress, morphology and fatigue fracture morphology are discussed. A critical compressive residual stress of about 95–100 MPa is proposed. PMID:28788634

Tension-Compression Fatigue of a Nextel™720/alumina Composite at 1200 °C in Air and in Steam

NASA Astrophysics Data System (ADS)

Lanser, R. L.; Ruggles-Wrenn, M. B.

2016-08-01

Tension-compression fatigue behavior of an oxide-oxide ceramic-matrix composite was investigated at 1200 °C in air and in steam. The composite is comprised of an alumina matrix reinforced with Nextel™720 alumina-mullite fibers woven in an eight harness satin weave (8HSW). The composite has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tension-compression fatigue behavior was studied for cyclical stresses ranging from 60 to 120 MPa at a frequency of 1.0 Hz. The R ratio (minimum stress to maximum stress) was -1.0. Fatigue run-out was defined as 105 cycles and was achieved at 80 MPa in air and at 70 MPa in steam. Steam reduced cyclic lives by an order of magnitude. Specimens that achieved fatigue run-out were subjected to tensile tests to failure to characterize the retained tensile properties. Specimens subjected to prior cyclic loading in air retained 100 % of their tensile strength. The steam environment severely degraded tensile properties. Tension-compression cyclic loading was considerably more damaging than tension-tension cyclic loading. Composite microstructure, as well as damage and failure mechanisms were investigated.

Effect of Microstructure on the Mechanical Properties of Extruded Magnesium and a Magnesium Alloy

NASA Astrophysics Data System (ADS)

McGhee, Paul

The main objective of this research was to investigate the relationship between the fatigue behavior and crystallographic texture evolution of magnesium (Mg) alloys with a range of microalloying element content processed under various extrusion conditions. Several Mg alloys were processed under a range of extrusion temperatures, extrusion ratios, and alloying content and tested under monotonic and cyclic fatigue loading conditions: fully-reversed condition tested at strain amplitudes of 0.15% - 1.00% in strain-control mode. After fatigue testing, Mg microstructural analysis was performed using SEM, TEM, optical microscopy, and X-ray diffraction techniques. Microstructural observations revealed significant grain refinement through a combination of zirconium (Zr) addition and hot-extrusion, producing fine equiaxed grain structure with grain sizes ranging between 1-5 microm. Texture analysis and partial compression testing results showed that the initial texture of the extruded alloy gradually evolved upon compressive loading along the c-axes inducing extension twinning creating a strong basal texture along the extrusion direction. Full tensile and compression testing at room temperature showed that the combination of hot extrusion and Zr addition can further refine the grains of the Mg alloys microstructure and enhance the texture while simultaneously enhancing the mechanical properties.

The Effect of Drive Signal Limiting on High Cycle Fatigue Life Analysis

NASA Technical Reports Server (NTRS)

Kihm, Frederic; Rizzi, Stephen A.

2014-01-01

It is common practice to assume a Gaussian distribution of both the input acceleration and the response when modeling random vibration tests. In the laboratory, however, shaker controllers often limit the drive signal to prevent high amplitude peaks. The high amplitudes may either be truncated at a given level (socalled brick wall limiting or abrupt clipping), or compressed (soft limiting), resulting in drive signals which are no longer Gaussian. The paper first introduces several methods for limiting a drive signal, including brick wall limiting and compression. The limited signal is then passed through a linear time-invariant system representing a device under test. High cycle fatigue life predictions are subsequently made using spectral fatigue and rainflow cycle counting schemes. The life predictions are compared with those obtained from unclipped input signals. Some guidelines are provided to help the test engineer decide how clipping should be applied under different test scenarios.

Apparatus and method for fatigue testing of a material specimen in a high-pressure fluid environment

DOEpatents

Wang, Jy-An; Feng, Zhili; Anovitz, Lawrence M; Liu, Kenneth C

2013-06-04

The invention provides fatigue testing of a material specimen while the specimen is disposed in a high pressure fluid environment. A specimen is placed between receivers in an end cap of a vessel and a piston that is moveable within the vessel. Pressurized fluid is provided to compression and tension chambers defined between the piston and the vessel. When the pressure in the compression chamber is greater than the pressure in the tension chamber, the specimen is subjected to a compression force. When the pressure in the tension chamber is greater than the pressure in the compression chamber, the specimen is subjected to a tension force. While the specimen is subjected to either force, it is also surrounded by the pressurized fluid in the tension chamber. In some examples, the specimen is surrounded by hydrogen.

Post-impact fatigue of cross-plied, through-the-thickness reinforced carbon/epoxy composites

NASA Astrophysics Data System (ADS)

Serdinak, Thomas E.

1994-05-01

An experimental investigation of the post-impact fatigue response of integrally woven carbon/epoxy composites was conducted. Five different through-the-thickness (TTT) reinforcing fibers were used in an experimental textile process that produced an integrally woven (0/90/0/90/0/90/0/90/0)(sub T) ply layup with 21K AS4 carbon tow fiber. The resin was Hercules 3501-6, and the five TTT reinforcing fibers were Kevlar, Toray carbon, AS4 carbon, glass, and IM6 carbon. The purpose of this investigation was to study the post-impact fatigue response of these material systems and to identify the optimum TTT fiber. Samples were impacted with one half inch diameter aluminum balls with an average velocity of 543 ft/sec. Post-impact static compression and constant amplitude tension-compression fatigue tests were conducted. Fatigue tests were conducted with a loading ratio of R=-5, and frequency of 4 Hz. Damage growth was monitored using x-radiographic and sectioning techniques and by examining the stress-strain response (across the impact site) throughout the fatigue tests. The static compressive stress versus far-field strain response was nearly linear for all material groups. All the samples had a transverse shear failure mode. The average compressive modulus (from far-field strain) was about 10 Msi. The average post-impact static compressive strength was about 35.5 Ksi. The IM6 carbon sample had a strength of over 40 Ksi, more than 16 percent stronger than average. There was considerable scatter in the S-N data. However, the IM6 carbon samples clearly had the best fatigue response. The response of the other materials, while worse than IM6 carbon, could not be ranked definitively. The initial damage zones caused by the impact loading and damage growth from fatigue loading were similar for all five TTT reinforcing materials. The initial damage zones were circular and consisted of delaminations, matrix cracks and ply cracks.

Post-impact fatigue of cross-plied, through-the-thickness reinforced carbon/epoxy composites. M.S. Thesis - Clemson Univ.

NASA Technical Reports Server (NTRS)

Serdinak, Thomas E.

1994-01-01

An experimental investigation of the post-impact fatigue response of integrally woven carbon/epoxy composites was conducted. Five different through-the-thickness (TTT) reinforcing fibers were used in an experimental textile process that produced an integrally woven (0/90/0/90/0/90/0/90/0)(sub T) ply layup with 21K AS4 carbon tow fiber. The resin was Hercules 3501-6, and the five TTT reinforcing fibers were Kevlar, Toray carbon, AS4 carbon, glass, and IM6 carbon. The purpose of this investigation was to study the post-impact fatigue response of these material systems and to identify the optimum TTT fiber. Samples were impacted with one half inch diameter aluminum balls with an average velocity of 543 ft/sec. Post-impact static compression and constant amplitude tension-compression fatigue tests were conducted. Fatigue tests were conducted with a loading ratio of R=-5, and frequency of 4 Hz. Damage growth was monitored using x-radiographic and sectioning techniques and by examining the stress-strain response (across the impact site) throughout the fatigue tests. The static compressive stress versus far-field strain response was nearly linear for all material groups. All the samples had a transverse shear failure mode. The average compressive modulus (from far-field strain) was about 10 Msi. The average post-impact static compressive strength was about 35.5 Ksi. The IM6 carbon sample had a strength of over 40 Ksi, more than 16 percent stronger than average. There was considerable scatter in the S-N data. However, the IM6 carbon samples clearly had the best fatigue response. The response of the other materials, while worse than IM6 carbon, could not be ranked definitively. The initial damage zones caused by the impact loading and damage growth from fatigue loading were similar for all five TTT reinforcing materials. The initial damage zones were circular and consisted of delaminations, matrix cracks and ply cracks. Post-impact fatigue loading caused delamination growth, ply cracking and fiber bundle failures, typically 45 deg from impact load direction. During the initial 97 percent of fatigue life, delaminations, ply cracks and fiber bundle failures primarily grew at and near the impact site. During the final 3 percent of life, damage grew rapidly transverse to the loading direction as a through-the-thickness transverse shear failure. The stress-strain response was typically linear during the initial 50 percent of life, and stiffness dropped about 20 percent during this period. During the next 47 percent of life, stiffness dropped about 34 percent, and the stress-strain response was no longer linear. The stiffness decreased about 23 percent during the final 3 percent of life. These trends were typical of all the materials tested. Therefore, by monitoring stiffness loss, fatigue failure could be accurately anticipated.

Damage mechanisms in bithermal and thermomechanical fatigue of Haynes 188

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Halford, Gary R.

1992-01-01

Post failure fractographic and metallographic studies were conducted on Haynes 188 specimens fatigued under bithermal and thermomechanical loading conditions between 316 and 760 C. Bithermal fatigue specimens examined included those tested under high strain rate in-phase and out-phase, tensile creep in-phase, and compressive creep out-of-phase loading conditions. Specimens tested under in-phase and out-of-phase thermomechanical fatigue were also examined. The nature of failure mode (transgrandular versus intergranular), the topography of the fracture surface, and the roles of oxidation and metallurgical changes were studied for each type of bithermal and thermomechanical test.

Isothermal Fatigue, Damage Accumulation, and Life Prediction of a Woven PMC

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.

1998-01-01

This dissertation focuses on the characterization of the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin, woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The residual elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed noticeable reductions due to the elevated temperature. The stiffness degradation, as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment composing the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.

Analytical and experimental investigation of fatigue in a sheet specimen with an interference-fit bolt

NASA Technical Reports Server (NTRS)

Crews, J. H., Jr.

1975-01-01

A fatigue analysis, based on finite-element calculations and fatigue tests, was conducted for an aluminum-alloy sheet specimen with a steel interference-fit bolt. The stress analysis of the region near the bolt hole showed that the beneficial effect of an interference-fit bolt can be interpreted as the combined result of two effects: (1) load transfer through the bolt and (2) the compressive interference stresses in the sheet. Results of the fatigue tests show that progressively higher interference levels produced longer fatigue lives. The tests also show that a high level of interference prevents fretting at the bolt-sheet interface and that interferences larger than this level produced little additional improvement in fatigue life.

Fatigue of concrete subjected to biaxial loading in the tension region

NASA Astrophysics Data System (ADS)

Subramaniam, Kolluru V. L.

Rigid airport pavement structures are subjected to repeated high-amplitude loads resulting from passing aircraft. The resulting stress-state in the concrete is a biaxial combination of compression and tension. It is of interest to model the response of plain concrete to such loading conditions and develop accurate fatigue-based material models for implementation in mechanistic pavement design procedures. The objective of this work is to characterize the quasi-static and low-cycle fatigue response of concrete subjected to biaxial stresses in the tensile-compression-tension (t-C-T) region, where the principal tensile stress is larger in magnitude than the principal compressive stress. An experimental investigation of material behavior in the biaxial t-C-T region is conducted. The experimental setup consists of the following test configurations: (a) notched concrete beams tested in three-point bend configuration, and (b) hollow concrete cylinders subjected to torsion with or without superimposed axial tensile force. The damage imparted to the material is examined using mechanical measurements and an independent nondestructive evaluation (NDE) technique based on vibration measurements. The failure of concrete in t-C-T region is shown to be a local phenomenon under quasi-static and fatigue loading, wherein the specimen fails owing to a single crack. The crack propagation is studied using the principles of fracture mechanics. It is shown that the crack propagation resulting from the t-C-T loading can be predicted using mode I fracture parameters. It is observed that crack growth in constant amplitude fatigue loading is a two-phase process: a deceleration phase followed by an acceleration stage. The quasi-static load envelope is shown to predict the crack length at fatigue failure. A fracture-based fatigue failure criterion is proposed, wherein the fatigue failure can be predicted using the critical mode I stress intensity factor. A material model for the damage evolution during fatigue loading of concrete in terms of crack propagation is proposed. The crack growth acceleration stage is shown to follow Paris law. The model parameters obtained from uniaxial fatigue tests are shown to be sufficient for predicting the considered biaxial fatigue response.

Behavior of a centrally notched cross-ply and unidirectional ceramic matrix composite in tension-compression fatigue. Master's thesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weidenaar, W.A.

1992-12-01

Centrally notched (hole), cross-ply, ((0/90) sub 2) sub s, and unidirectional, (0) sub 8 laminates of Silicon Carbide fiber-reinforced Aluminosilicate glass, SiC/1723, were fatigue tested under tension-compression loading with a load ratio of -1. Damage accumulated continuously for both lay-ups, leading to eventual failure and a reduced fatigue life. Critical damage in the cross-ply consisted of longitudinal cracks in the 90 deg plies growing and combining with transverse cracks to effectively eliminate the 90 deg plies' load carrying capability and allowing the specimen to buckle. Critical damage in the unidirectional lay-up consisted of longitudinal cracks which initiated at the shearmore » stress concentration points on the hole periphery. Reversed cyclic loading caused continued crack growth at maximum stresses below the tension-tension fatigue limit. The cross-ply lay-up appeared insensitive to the hole, while critical damage in the unidirectional lay-up was dependent on the shear stress concentrations at the hole.... Ceramic matrix composite, Tension-compression fatigue, Notched specimen.« less

Crystallographic Analysis of Fatigue Crack Initiation Behavior in Coarse-Grained Magnesium Alloy Under Tension-Tension Loading Cycles

NASA Astrophysics Data System (ADS)

Tamada, Kazuhiro; Kakiuchi, Toshifumi; Uematsu, Yoshihiko

2017-07-01

Plane bending fatigue tests are conducted to investigate fatigue crack initiation mechanisms in coarse-grained magnesium alloy, AZ31, under the stress ratios R = -1 and 0.1. The initial crystallographic structures are analyzed by an electron backscatter diffraction method. The slip or twin operation during fatigue tests is identified from the line angle analyses based on Euler angles of the grains. Under the stress ratio R = -1, relatively thick tension twin bands are formed in coarse grains. Subsequently, compression twin or secondary pyramidal slip operates within the tension twin band, resulting in the fatigue crack initiation. On the other hand, under R = 0.1 with tension-tension loading cycles, twin bands are formed on the specimen surface, but the angles of those bands do not correspond to tension twins. Misorientation analyses of c-axes in the matrix grain and twin band reveal that double twins are activated. Under R = 0.1, fatigue crack initiates along the double twin boundaries. The different manners of fatigue crack initiation at R = -1 and 0.1 are related to the asymmetricity of twining under tension and compression loadings. The fatigue strengths under different stress ratios cannot be estimated by the modified Goodman diagram due to the effect of stress ratio on crack initiation mechanisms.

Effects of applied stress ratio on the fatigue behavior of additively manufactured porous biomaterials under compressive loading.

PubMed

de Krijger, Joep; Rans, Calvin; Van Hooreweder, Brecht; Lietaert, Karel; Pouran, Behdad; Zadpoor, Amir A

2017-06-01

Additively manufactured (AM) porous metallic biomaterials are considered promising candidates for bone substitution. In particular, AM porous titanium can be designed to exhibit mechanical properties similar to bone. There is some experimental data available in the literature regarding the fatigue behavior of AM porous titanium, but the effect of stress ratio on the fatigue behavior of those materials has not been studied before. In this paper, we study the effect of applied stress ratio on the compression-compression fatigue behavior of selective laser melted porous titanium (Ti-6Al-4V) based on the diamond unit cell. The porous titanium biomaterial is treated as a meta-material in the context of this work, meaning that R-ratios are calculated based on the applied stresses acting on a homogenized volume. After morphological characterization using micro computed tomography and quasi-static mechanical testing, the porous structures were tested under cyclic loading using five different stress ratios, i.e. R = 0.1, 0.3, 0.5, 0.7 and 0.8, to determine their S-N curves. Feature tracking algorithms were used for full-field deformation measurements during the fatigue tests. It was observed that the S-N curves of the porous structures shift upwards as the stress ratio increases. The stress amplitude was the most important factor determining the fatigue life. Constant fatigue life diagrams were constructed and compared with similar diagrams for bulk Ti-6Al-4V. Contrary to the bulk material, there was limited dependency of the constant life diagrams to mean stress. The notches present in the AM biomaterials were the sites of crack initiation. This observation and other evidence suggest that the notches created by the AM process cause the insensitivity of the fatigue life diagrams to mean stress. Feature tracking algorithms visualized the deformation during fatigue tests and demonstrated the root cause of inclined (45°) planes of specimen failure. In conclusion, the R-ratio behavior of AM porous biomaterials is both quantitatively and qualitatively different from that of bulk materials. Copyright © 2016 Elsevier Ltd. All rights reserved.

Fatigue failure of dentin-composite disks subjected to cyclic diametral compression

PubMed Central

Li, Yuping; Carrera, Carola; Chen, Ruoqiong; Li, Jianying; Chen, Yungchung; Lenton, Patricia; Rudney, Joel. D.; Jones, Robert S.; Aparicio, Conrado; Fok, Alex

2015-01-01

Objective Our aim was to establish the relationship between cyclic loading and fatigue life of the dentin-composite interface using the newly developed disk in diametral compression tests. The results were then used to estimate the fatigue life of restored teeth under occlusal loading. Methods Disk specimens (5mm dia. × 2mm thick) were prepared using bovine incisors and restored with either a methacrylate-based composite Z100™ with Adper Single Bond Plus (Z100) or silorane-based composite Filtek ™ LS with LS System adhesive (LS). The dentin-composite disks were tested under cyclic diametral compression to determine the number of cycles to failure (Nf) at three load levels (n = 3 per group). Finite element analysis (FEA) was used to calculate the interfacial stresses (σ) within the specimen, to establish the σ vs. Nf curves, and those within a restored tooth under normal chewing forces (15N maximum). These were then used to estimate the lifetime of the restored tooth for the two restorative systems. Results The disks restored with LS had a higher fatigue resistance than those restored with Z100. The maximum interfacial stress in the restored tooth determined by FEA was ∼0.5MPa. Based on the estimate of 300,000 cycles of chewing per year, the predicted lifetime under occlusal loading for teeth restored with LS and Z100 was 33 and 10 years, respectively. Significance The disk in cyclic diametral compression has been used successfully to provide fatigue data which allows the lifetime of composite-restored teeth under occlusal loading to be predicted using numerical simulation. PMID:25958269

Effect of Compressive Mode I on the Mixed Mode I/II Fatigue Crack Growth Rate of 42CrMo4

NASA Astrophysics Data System (ADS)

Heirani, Hasan; Farhangdoost, Khalil

2018-01-01

Subsurface cracks in mechanical contact loading components are subjected to mixed mode I/II, so it is necessary to evaluate the fatigue behavior of materials under mixed mode loading. For this purpose, fatigue crack propagation tests are performed with compact tension shear specimens for several stress intensity factor (SIF) ratios of mode I and mode II. The effect of compressive mode I loading on mixed mode I/II crack growth rate and fracture surface is investigated. Tests are carried out for the pure mode I, pure mode II, and two different mixed mode loading angles. On the basis of the experimental results, mixed mode crack growth rate parameters are proposed according to Tanaka and Richard with Paris' law. Results show neither Richard's nor Tanaka's equivalent SIFs are very useful because these SIFs depend strongly on the loading angle, but Richard's equivalent SIF formula is more suitable than Tanaka's formula. The compressive mode I causes the crack closure, and the friction force between the crack surfaces resists against the crack growth. In compressive loading with 45° angle, d a/d N increases as K eq decreases.

Fatigue-Arrestor Bolts

NASA Technical Reports Server (NTRS)

Onstott, Joseph W.; Gilster, Mark; Rodriguez, Sergio; Larson, John E.; Wickham, Mark D.; Schoonover, Kevin E.

1995-01-01

Bolts that arrest (or, more precisely, retard) onset of fatigue cracking caused by inelastic strains developed. Specifically developed to be installed in flange holes of unrestrained rocket engine nozzle. Fanges sometimes used to bolt nozzle to test stand; however, when rocket engine operated without this restraint, region around bolt holes experience severe inelastic strains causing fatigue cracking. Interference fits introduce compressive preloads that retard fatigue by reducing ranges of strains. Principle of these fatigue-arrestor bolts also applicable to holes in plates made of other materials and/or used for different purposes.

High Cycle Fatigue (HCF) Science and Technology Program 2000 Annual Report

DTIC Science & Technology

2000-01-01

in an area of deep compressive stress. • Results of industry and government testing have indicated the ability to stop crack initiation and...fatigue crack nucleation process with the cyclic deformation behavior of the alloy for different microstructures and crystallographic texture ... texture combinations investigated, bimodal fine uni-rolled and lamellar cross-rolled displayed superior fatigue properties to the remaining four

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

NASA Astrophysics Data System (ADS)

Liu, Yi; Dai, Feng; Dong, Lu; Xu, Nuwen; Feng, Peng

2018-01-01

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

Nondestructive evaluation of loading and fatigue effects in Haynes(R) 230(R) alloy

NASA Astrophysics Data System (ADS)

Saleh, Tarik Adel

Nondestructive evaluation is a useful method for studying the effects of deformation and fatigue. In this dissertation I employed neutron and X-ray diffraction, nonlinear resonant ultrasound spectroscopy (NRUS), and infrared thermography to study the effects of deformation and fatigue on two different nickel based superalloys. The alloys studied were HAYNES 230, a solid solution strengthened alloy with 4% M6C carbides, and secondarily HASTELLOY C-2000 a similar single phase alloy. Using neutron and X-ray diffraction, the deformation behavior of HAYNES 230 was revealed to be composite-like during compression, but unusual in tension, where the carbides provide strengthening until just after the macroscopic yield strength and then they begin to debond and crack, creating a tension-compression asymmetry that is revealed clearly by in situ diffraction. In fatigue of HAYNES 230, the hkl elastic strains changed very little in tension-tension fatigue. However, in situ tension-compression studies showed large changes over the initial stages of fatigue. The HAYNES 230 samples studies had two distinct starting textures, measured by neutron diffraction. Some samples were texture free initially and deformed in tension and compression to fiber textures. Other samples started with a bimodal texture due to cross-rolling and incomplete annealing. The final texture of these bimodal samples is shown through modeling to be a superposition of the initial texture and typical FCC deformation mechanisms. The texture-free samples deformed significantly more macroscopically and in internal elastic strains than the samples with the cross-rolled texture. In contrast to the relative insensitivity of neutron diffraction to the effects of tension-tension fatigue, NRUS revealed large differences between as-received and progressively fatigued samples. This showed that microcracking and void formation are the primary mechanisms responsible for fatigue damage in tension-tension fatigue. NRUS is shown to be a useful complimentary technique to neutron diffraction to evaluate fatigue damage. Finally, infrared thermography is used to show temperature changes over the course of fatigue in HASTELLOY C-2000. Four stages of temperature are shown over the course of a single fatigue test. Both empirical and theoretical relationships between steady state temperature and fatigue life are developed and presented.

Experimental studies on fatigue behavior of macro fiber composite (MFC) under mechanical loading

NASA Astrophysics Data System (ADS)

Pandey, Akash; Arockiarajan, A.

2016-04-01

Macro fiber Composite (MFC) finds its application in active control, vibration control and sensing elements. MFC can be laminated to surfaces or embedded in the structures to be used as an actuator and sensors. Due to its attractive properties and applications, it may be subjected to continuous loading, which leads to the deterioration of the properties. This study is focused on the fatigue lifetime of MFC under tensile and compressive loading at room temperature. Experiments were performed using 4 point bending setup, with MFC pasted at the center of the mild steel beam, to maintain constant bending stress along MFC. MFC is pasted using vacuum bagging technique. Sinusoidal loading is given to sample while maintaining R=0.13 (for tensile testing) and R=10 (for compressive testing). For d31 and d33 type of MFC, test was conducted for the strain values of 727 μ strain, 1400 μ strain, 1700 μ strain and 1900 μ strain for fatigue under tensile loading. For fatigue under compressive loading, both d33 and d31, was subjected to minimum strain of -2000 μ strain. Decrease in the slope of dielectric displacement vs. strain is the measure for the degradation. 10 percent decrease in the slope is set as the failure criteria. Experimental results show that MFC is very reliable below 1700 μ strain (R=0.13) at the room temperature.

Crack initiation and propagation in 50.9 at. pct Ni-Ti pseudoelastic shape-memory wires in bending-rotation fatigue

NASA Astrophysics Data System (ADS)

Sawaguchi, Tak Ahiro; Kausträter, Gregor; Yawny, Alejandro; Wagner, Martin; Eggeler, Gunther

2003-12-01

The structural fatigue of pseudoelastic Ni-Ti wires (50.9 at. pct Ni) was investigated using bending-rotation fatigue (BRF) tests, where a bent and otherwise unconstrained wire was forced to rotate at different rotational speeds. The number of cycles to failure ( N f ) was measured for different bending radii and wire thicknesses (1.0, 1.2, and 1.4 mm). The wires consisted of an alloy with a 50-nm grain size, no precipitates, and some TiC inclusions. In BRF tests, the surface of the wire is subjected to tension-compression cycles, and fatigue lives can be related to the maximum tension and compression strain amplitudes ( ɛ a ) in the wire surface. The resulting ɛ a - N f curves can be subdivided into three regimes. At ɛ a > 1 pct rupture occurs early (low N f ) and the fatigue-rupture characteristics were strongly dependent on ɛ a and the rotational speed (regime 1). For 0.75 pct < ɛ a < 1 pct, fatigue lives strongly increase and are characterized by a significant statistical scatter (regime 2). For ɛ a < 0.75 pct, no fatigue rupture occurs up to cycle numbers of 106 (regime 3). Using scanning electron microscopy (SEM), it was shown that surface cracks formed in regions with local stress raisers (such as inclusions and/or scratches). The growth of surface cracks during fatigue loading produced striations on the rupture surface; during final rupture, ductile voids form. The microstructural details of fatigue-damage accumulation during BRF testing are described and discussed.

Micromechanics of fatigue in woven and stitched composites

NASA Technical Reports Server (NTRS)

Cox, B. N.; Dadkhah, M. S.; Inman, R. V.; Mitchell, M. R.; Morris, W. L.; Schroeder, S.

1991-01-01

The goal is to determine how microstructural factors, especially the architecture of microstructural factors, control fatigue damage in 3D reinforced polymer composites. Test materials were fabricated from various preforms, including stitched quasi-isotropic laminates, and through-the-thickness angle interlock, layer-to-layer angle interlock, and through-the-thickness stitching effect weaves. Preforms were impregnated with a tough resin by a special vacuum infiltration method. Most tests are being performed in uniaxial compression/compression loading. In all cases to date, failure has occurred not by delamination, but by shear failure, which occurs suddenly rather than by gradual macroscopic crack growth. Some theoretical aspects of bridging are also examined.

Fatigue Crack Topography.

DTIC Science & Technology

1984-01-01

nominal cycle frequency of 15 Hz. Buckling of the specimens during compression loading was prevented by felt-lined aluminium alloy antibuckling guides...evaluating ciack initiation time and crack propagation, prgram I was used for performing the major fatigue test with the aircraft structure. In...direction of the notch to prevent scratches in the through-the-thickness direction. Prior to testing, the notch surfaces were lightly etched to reveal

The direct-stress fatigue strength of 17S-T aluminum alloy throughout the range from 1/2 to 500,000,000 cycles of stress

NASA Technical Reports Server (NTRS)

Hartmann, E C; Stickley, G W

1942-01-01

Fatigue-test were conducted on six specimens made from 3/4-inch-diameter 17S-T rolled-and-drawn rod for the purpose of obtaining additional data on the fatigue life of the material at stresses up to the static strength. The specimens were tested in direct tension using a stress range from zero to a maximum in tension. A static testing machine was used to apply repeated loads in the case of the first three specimens; the other three specimens were tested in a direct tension-compression fatigue machine. The direct-stress fatigue curve obtained for the material indicates that, in the range of stresses above about two-thirds the tensile strength, the fatigue strength is higher than might be expected by simply extrapolating the ordinary curve of stress plotted against the number of cycles determined at lower stresses.

Fatigue and shear behavior of HPC bulb-tee girders : interim report.

DOT National Transportation Integrated Search

2003-10-01

Three 96-ft (29.3-m) long, 72-in. (1.83-m) deep, precast, pretensioned bulb-tee girders were tested to evaluate behavior under flexural fatigue and static shear loadings. The three girders had a design concrete compressive strength of 10,000 psi (69....

Characterization of multiaxial warp knit composites

NASA Technical Reports Server (NTRS)

Dexter, H. Benson; Hasko, Gregory H.; Cano, Roberto J.

1991-01-01

The objectives were to characterize the mechanical behavior and damage tolerance of two multiaxial warp knit fabrics to determine the acceptability of these fabrics for high performance composite applications. The tests performed included compression, tension, open hole compression, compression after impact and compression-compression fatigue. Tests were performed on as-fabricated fabrics and on multi-layer fabrics that were stitched together with either carbon or Kevlar stitching yarn. Results of processing studies for vacuum impregnation with Hercules 3501-6 epoxy resin and pressure impregnation with Dow Tactix 138/H41 epoxy resin and British Petroleum BP E905L epoxy resin are presented.

Reliability aspects of a composite bolted scarf joint. [in wing skin splice

NASA Technical Reports Server (NTRS)

Reed, D. L.; Eisenmann, J. R.

1975-01-01

The design, fabrication, static test, and fatigue test of both tension and compression graphite-epoxy candidates for a wing splice representative of a next-generation transport aircraft was the objective of the reported research program. A single-scarf bolted joint was selected as the design concept. Test specimens were designed and fabricated to represent an upper-surface and a lower-surface panel containing the splice. The load spectrum was a flight-by-flight random-load history including ground-air-ground loads. The results of the fatigue testing indicate that, for this type of joint, the inherent fatigue resistance of the laminate is reflected in the joint behavior and, consequently, the rate of damage accumulation is very slow under realistic fatigue loadings.

Fatigue resistance and microleakage of CAD/CAM ceramic and composite molar crowns.

PubMed

Kassem, Amr S; Atta, Osama; El-Mowafy, Omar

2012-01-01

The aim of this study was to determine effect of compressive cyclic loading on fatigue resistance and microleakage of monolithic CAD/CAM molar ceramic and composite crowns. Thirty-two extracted molars were prepared to receive CEREC crowns according to manufacturer's guidelines using a special paralleling device (Parallel-A-Prep). Sixteen feldspathic ceramic crowns (VITABLOCS Mark II) (VMII) and 16 resin-composite crowns (Paradigm-MZ100 blocks) (PMZ) were milled using a CEREC-3D machine. Eight crowns of each group were cemented to their respective teeth using self-etching resin cement (Panavia-F-2.0) (PAN), and eight were cemented using self-adhesive resin cement (RelyX-Unicem-Clicker) (RXU). Following storage for 1 week in water, specimens were subjected to uniaxial compressive cyclic loading in an Instron testing machine at 12 Hz for 1,000,000 cycles. Load was applied at the central fossa, and the cycle range was 60-600 N. Specimens were then subjected to microleakage testing. Data were statistically analyzed using factorial ANOVA and Post Hoc (Tukey HSD) tests. All composite crowns survived compressive cyclic loading without fracture, while three ceramic crowns from the subgroup cemented with RXU developed surface cracks at the center of occlusal surfaces, extending laterally. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other three subgroups (p < 0.05). After 1,000,000 cycles of compressive cyclic loading, PMZ composite molar crowns were more fatigue-resistant than VMII ceramic crowns. Cement type had a significant effect on fatigue resistance of the ceramic crowns but not the composite ones. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other subgroups (p < 0.05). © 2011 by The American College of Prosthodontists.

Experimental Evaluation of Fatigue Damage Progression in Postbuckled Single Stringer Composite Specimens

NASA Technical Reports Server (NTRS)

Bisagni, Chiara; Davila, Carlos G.; Rose, Cheryl A.; Zalameda, Joseph N.

2014-01-01

The durability and damage tolerance of postbuckled composite structures are not yet completely understood, and remain difficult to predict due to the nonlinearity of the geometric response and its interaction with local damage modes. A research effort was conducted to investigate experimentally the quasi-static and fatigue damage progression in a single-stringer compression (SSC) specimen. Three specimens were manufactured with a hat-stiffener, and an initial defect was introduced with a Teflon film embedded between one flange of the stringer and the skin. One of the specimens was tested under quasi-static compressive loading, while the remaining two specimens were tested by cycling in postbuckling. The tests were performed at the NASA Langley Research Center under controlled conditions and with instrumentation that allows a precise evaluation of the postbuckling response and of the damage modes. Three-dimensional digital image correlation VIC-3D systems were used to provide full field displacements and strains on the skin and the stringer. Passive thermal monitoring was conducted during the fatigue tests using an infrared camera that showed the location of the delamination front while the specimen was being cycled. The live information from the thermography was used to stop the fatigue tests at critical stages of the damage evolution to allow detailed ultrasonic scans.

Biomechanical Study of the Fixation Strength of Anteromedial Plating for Humeral Shaft Fractures.

PubMed

Zheng, Yin-Feng; Zhou, Jun-Lin; Wang, Xiao-Hong; Shan, Lei; Liu, Yang

2016-08-05

Open reduction and internal fixation with plate and screws are the gold standard for the surgical treatment of humeral shaft fractures, this study was to compare the mechanical properties of anteromedial, anterolateral, and posterior plating for humeral shaft fractures. A distal third humeral shaft fracture model was constructed using fourth-generation sawbones (#3404, composite bone). A total of 24 sawbones with a distal third humeral shaft fracture was randomly divided into three Groups: A, B, and C (n = 8 in each group) for anteromedial, anterolateral, and posterior plating, respectively. All sawbones were subjected to horizontal torsional fatigue tests, horizontal torsional and axial compressive fatigue tests, four-point bending fatigue tests in anteroposterior (AP) and mediolateral (ML) directions and horizontal torsional destructive tests. In the horizontal torsional fatigue tests, the mean torsional angle amplitude in Groups A, B, and C were 6.12°, 6.53°, and 6.81°. In horizontal torsional and axial compressive fatigue tests, the mean torsional angle amplitude in Groups A, B, and C were 5.66°, 5.67°, and 6.36°. The mean plate displacement amplitude was 0.05 mm, 0.08 mm, and 0.10 mm. Group A was smaller than Group C (P < 0.05). In AP four-point bending fatigue tests, the mean plate displacement amplitude was 0.16 mm, 0.13 mm, and 0.20 mm. Group B was smaller than Group C (P < 0.05). In ML four-point bending fatigue tests, the mean plate displacement amplitude were 0.16 mm, 0.19 mm, and 0.17 mm. In horizontal torsional destructive tests, the mean torsional rigidity in Groups A, B, and C was 0.82, 0.75, and 0.76 N·m/deg. The yielding torsional angle was 24.50°, 25.70°, and 23.86°. The mean yielding torque was 18.46, 18.05, and 16.83 N·m, respectively. Anteromedial plating was superior to anterolateral or posterior plating in all mechanical tests except in AP four-point bending fatigue tests compared to the anterolateral plating group. We can suggest that anteromedial plating is a clinically safe and effective way for humeral shaft fractures.

Effects of Control Mode and R-Ratio on the Fatigue Behavior of a Metal Matrix Composite

NASA Technical Reports Server (NTRS)

2005-01-01

Composite Because of their high specific stiffness and strength at elevated temperatures, continuously reinforced metal matrix composites (MMC's) are under consideration for a future generation of aeropropulsion systems. Since components in aeropropulsion systems experience substantial cyclic thermal and mechanical loads, the fatigue behavior of MMC's is of great interest. Almost without exception, previous investigations of the fatigue behavior of MMC's have been conducted in a tension-tension, load-controlled mode. This has been due to the fact that available material is typically less than 2.5-mm thick and, therefore, unable to withstand high compressive loads without buckling. Since one possible use of MMC's is in aircraft skins, this type of testing mode may be appropriate. However, unlike aircraft skins, most engine components are thick. In addition, the transient thermal gradients experienced in an aircraft engine will impose tension-compression loading on engine components, requiring designers to understand how the MMC will behave under fully reversed loading conditions. The increased thickness of the MMC may also affect the fatigue life. Traditionally, low-cycle fatigue (LCF) tests on MMC's have been performed in load control. For monolithic alloys, low-cycle fatigue tests are more typically performed in strain control. Two reasons justify this choice: (1) the critical volume from which cracks initiate and grow is generally small and elastically constrained by the larger surrounding volume of material, and (2) load-controlled, low-cycle fatigue tests of monolithics invariably lead to unconstrained ratcheting and localized necking--an undesired material response because the failure mechanism is far more severe than, and unrelated to, the fatigue mechanism being studied. It is unknown if this is the proper approach to composite testing. However, there is a lack of strain-controlled data on which to base any decisions. Consequently, this study addresses the isothermal, LCF behavior of a [0]_32 MMC tested under strain- and load-controlled conditions for both zero-tension and tension-compression loading conditions. These tests were run at 427 C on thick specimens of SiC-reinforced Ti-15-3. For the fully-reversed tests, no difference was observed in the lives between the load- and strain-controlled tests. However, for the zero-tension tests, the strain-controlled tests had longer lives by a factor of 3 in comparison to the load-controlled tests. This was due to the fact that under strain-control the specimens cyclically softened, reducing the cracking potential. In contrast, the load-controlled tests ratcheted toward larger tensile strains leading to an eventual overload of the fibers. Fatigue tests revealed that specimens tested under fully-reversed conditions had lives approximately an order of magnitude longer than for those specimens tested under zero tension. When examined on a strain-range basis, the fully reversed specimens had similar, but still shorter lives than those of the unreinforced matrix material. However, the composite had a strain limitation at short lives because of the limited strain capacity of the brittle ceramic fiber. The composite also suffered at very high lives because of the lack of an apparent fatigue limit in comparison to the unreinforced matrix. The value of adding fibers to the matrix is apparent when the fatigue lives are plotted as a function of stress range. Here, the composite is far superior to the unreinforced matrix because of the additional load-carrying capacity of the fibers.

Fracture and fatigue behavior of shot-blasted titanium dental implants.

PubMed

Gil, F J; Planell, J A; Padrós, A

2002-01-01

This investigation studies the effect of the shot-blasting treatment on the cyclic deformation behavior of a commercially pure titanium, with two microstructures: equiaxed and acicular. The fatigue tests were carried out in artificial saliva medium at 37 degrees C. Cyclic deformation tests have been carried out up to fracture, and the fatigue crack nucleation and propagation have been analyzed. The results show that the shot-blasting treatment improves the fatigue life in the microstructures studied, and that the equiaxed was better in mechanical properties than the acicular. The cause of this improvement in the mechanical properties is due to the compressive stress on the material surface for the shot-blasted specimens. Hardness tests were carried out to determine the value of these internal stresses.

The ultimate state of polymeric materials and laminated and fibrous composites under asymmetric high-cycle loading

NASA Astrophysics Data System (ADS)

Golub, V. P.; Pogrebniak, A. D.; Kochetkova, E. S.

2008-01-01

The prediction of the high-cycle fatigue strength of polymeric and composite materials in asymmetric loading is considered. The problem is solved on the basis of a nonlinear model of ultimate state allowing us to describe all typical forms of the diagrams of ultimate stresses. The material constants of the model are determined from the results of fatigue tests in symmetric reversed cycling, in a single fatigue test with the minimum stress equal to zero, and in a short-term strength test. The fatigue strength characteristics of some polymers, glass-fiber laminates, glass-fiber-reinforced plastics, organic-fiber-reinforced plastics, and wood laminates in asymmetric tension-compression, bending, and torsion have been calculated and approved experimentally.

Definition and Modeling of Critical Flaws in Graphite Fiber Reinforced Resin Matrix Composite Materials

DTIC Science & Technology

1979-08-28

11 EXPERIMENTAL PROGRAM .......................................*16 SHEAR TESTS ON THICK DISBONDED LAMINATES .... ....... 16 COMPRESSIVE BUCKLING OF...DISBONDED LAMINATES ...... .. 17 MECHANICAL CHARACTERIZATION FOR MOISTURE CONDITIONING EFFECTS .................................. 19 ULTRASONIC WAVE...SHEAR OF THICK LAMINATED BEAMS . . . ....... 24 PROPAGATION OF DISBOND IN FATIGUE ..... ............ .. 26 BUCKLING OF DISBONDED COMPRESSION SKIN

Effect of glucose on fatigue-induced changes in the microstructure and mechanical properties of demineralized bovine cortical bone.

PubMed

Trębacz, Hanna; Zdunek, Artur; Wlizło-Dyś, Ewa; Cybulska, Justyna; Pieczywek, Piotr

2015-10-16

The aim of this study was to test a hypothesis that fatigue-induced weakening of cortical bone was intensified in bone incubated in glucose and that this weakening is revealed in the microstructure and mechanical competence of the bone matrix. Cubic specimens of bovine femoral shaft were incubated in glucose solution (G) or in buffer (NG). One half of G samples and one half of NG were axially loaded in 300 cycles (30 mm/min) at constant deformation (F); the other half was a control (C). Samples from each group (GF, NGF, GC, NGC) were completely demineralized. Slices from demineralized samples were used for microscopic image analysis. A combined effect of glycation and fatigue on demineralized bone was tested in compression (10 mm/min). Damage of samples during the test was examined in terms of acoustic emission analysis (AE). During the fatigue procedure, resistance to loading in glycated samples decreased by 14.5% but only by 8.1% in nonglycated samples. In glycated samples fatigue resulted in increased porosity with pores significantly larger than in the other groups. Under compression, strain at failure in demineralized bone was significantly affected by glucose and fatigue. AE from demineralized bone matrix was considerably related to the largest pores in the tissue. The results confirm the hypothesis that the effect of fatigue on cortical bone tissue was intensified after incubation in glucose, both in the terms of the mechanical competence of bone tissue and the structural changes in the collagenous matrix of bone.

Fuel containment and damage tolerance in large composite primary aircraft structures. Phase 2: Testing

NASA Technical Reports Server (NTRS)

Sandifer, J. P.; Denny, A.; Wood, M. A.

1985-01-01

Technical issues associated with fuel containment and damage tolerance of composite wing structures for transport aircraft were investigated. Material evaluation tests were conducted on two toughened resin composites: Celion/HX1504 and Celion/5245. These consisted of impact, tension, compression, edge delamination, and double cantilever beam tests. Another test series was conducted on graphite/epoxy box beams simulating a wing cover to spar cap joint configuration of a pressurized fuel tank. These tests evaluated the effectiveness of sealing methods with various fastener types and spacings under fatigue loading and with pressurized fuel. Another test series evaluated the ability of the selected coatings, film, and materials to prevent fuel leakage through 32-ply AS4/2220-1 laminates at various impact energy levels. To verify the structural integrity of the technology demonstration article structural details, tests were conducted on blade stiffened panels and sections. Compression tests were performed on undamaged and impacted stiffened AS4/2220-1 panels and smaller element tests to evaluate stiffener pull-off, side load and failsafe properties. Compression tests were also performed on panels subjected to Zone 2 lightning strikes. All of these data were integrated into a demonstration article representing a moderately loaded area of a transport wing. This test combined lightning strike, pressurized fuel, impact, impact repair, fatigue and residual strength.

Electrophysiology of Muscle Fatigue in Cardiopulmonary Resuscitation on Manikin Model.

PubMed

Cobo-Vázquez, Carlos; De Blas, Gemma; García-Canas, Pablo; Del Carmen Gasco-García, María

2018-01-01

Cardiopulmonary resuscitation requires the provider to adopt positions that could be dangerous for his or her spine, specifically affecting the muscles and ligaments in the lumbar zone and the scapular spinal muscles. Increased fatigue caused by muscular activity during the resuscitation could produce a loss of quality and efficacy, resulting in compromising resuscitation. The aim of this study was to evaluate the maximum time a rescuer can perform uninterrupted chest compressions correctly without muscle fatigue. This pilot study was performed at Universidad Complutense de Madrid (Spain) with the population recruited following CONSORT 2010 guidelines. From the 25 volunteers, a total of 14 students were excluded because of kyphoscoliosis (4), lumbar muscle pain (1), anti-inflammatory treatment (3), or not reaching 80% of effective chest compressions during the test (6). Muscle activity at the high spinal and lumbar (L5) muscles was assessed using electromyography while students performed continuous chest compressions on a ResusciAnne manikin. The data from force exerted were analyzed according to side and muscle groups using Student's t test for paired samples. The influence of time, muscle group, and side was analyzed by multivariate analyses ( p ≤ .05). At 2 minutes, high spinal muscle activity (right: 50.82 ± 9.95; left: 57.27 ± 20.85 μV/ms) reached the highest values. Activity decreased at 5 and 15 minutes. At 2 minutes, L5 activity (right: 45.82 ± 9.09; left: 48.91 ± 10.02 μV/ms) reached the highest values. After 5 minutes and at 15 minutes, activity decreased. Fatigue occurred bilaterally and time was the most important factor. Fatigue began at 2 minutes. Rescuers exert muscular countervailing forces in order to maintain effective compressions. This imbalance of forces could determine the onset of poor posture, musculoskeletal pain, and long-term injuries in the rescuer.

Fatigue Damage Mechanisms in Advanced Hybrid Titanium Composite Laminates

NASA Technical Reports Server (NTRS)

Johnson, W. Steven; Rhymer, Donald W.; St.Clair, Terry L. (Technical Monitor)

2000-01-01

Hybrid Titanium Composite Laminates (HTCL) are a type of hybrid composite laminate with promise for high-speed aerospace applications, specifically designed for improved damage tolerance and strength at high-temperature (350 F, 177 C). However, in previous testing, HTCL demonstrated a propensity to excessive delamination at the titanium/PMC interface following titanium cracking. An advanced HTCL has been constructed with an emphasis on strengthening this interface, combining a PETI-5/IM7 PMC with Ti-15-3 foils prepared with an alkaline-perborate surface treatment. This paper discusses how the fatigue capabilities of the "advanced" HTCL compare to the first generation HTCL which was not modified for interface optimization, in both tension-tension (R = 0.1) and tension-compression (R=-0.2). The advanced HTCL under did not demonstrate a significant improvement in fatigue life, in either tension-tension or tension-compression loading. However, the advanced HTCL proved much more damage tolerant. The R = 0.1 tests revealed the advanced HTCL to increase the fatigue life following initial titanium ply damage up to 10X that of the initial HTCL at certain stress levels. The damage progression following the initial ply damage demonstrated the effect of the strengthened PMC/titanium interface. Acetate film replication of the advanced HTCL edges showed a propensity for some fibers in the adjacent PMC layers to fail at the point of titanium crack formation, suppressing delamination at the Ti/PMC interface. The inspection of failure surfaces validated these findings, revealing PMC fibers bonded to the majority of the titanium surfaces. Tension compression fatigue (R = -0.2) demonstrated the same trends in cycles between initial damage and failure, damage progression, and failure surfaces. Moreover, in possessing a higher resistance to delamination, the advanced HTCL did not exhibit buckling following initial titanium ply cracking under compression unlike the initial HTCL.

Procedures for characterizing an alloy and predicting cyclic life with the total strain version of Strainrange Partitioning

NASA Technical Reports Server (NTRS)

Saltsman, James F.; Halford, Gary R.

1989-01-01

Procedures are presented for characterizing an alloy and predicting cyclic life for isothermal and thermomechanical fatigue conditions by using the total strain version of strainrange partitioning (TS-SRP). Numerical examples are given. Two independent alloy characteristics are deemed important: failure behavior, as reflected by the inelastic strainrange versus cyclic life relations; and flow behavior, as indicated by the cyclic stress-strain-time response (i.e., the constitutive behavior). Failure behavior is characterized by conducting creep-fatigue tests in the strain regime, wherein the testing times are reasonably short and the inelastic strains are large enough to be determined accurately. At large strainranges, stress-hold, strain-limited tests are preferred because a high rate of creep damage per cycle is inherent in this type of test. At small strainranges, strain-hold cycles are more appropriate. Flow behavior is characterized by conducting tests wherein the specimen is usually cycled far short of failure and the wave shape is appropriate for the duty cycle of interest. In characterizing an alloy pure fatigue, or PP, failure tests are conducted first. Then depending on the needs of the analyst a series of creep-fatigue tests are conducted. As many of the three generic SRP cycles are featured as are required to characterize the influence of creep on fatigue life (i.e., CP, PC, and CC cycles, respectively, for tensile creep only, compressive creep only, and both tensile and compressive creep). Any mean stress effects on life also must be determined and accounted for when determining the SRP inelastic strainrange versus life relations for cycles featuring creep. This is particularly true for small strainranges. The life relations thus are established for a theoretical zero mean stress condition.

Fatigue resistance of unnotched and post impact(+/- 30 deg/0 deg) 3-D braided composites

NASA Technical Reports Server (NTRS)

Portanova, Marc A.

1994-01-01

The fatigue resistance of a multiaxial braided (3-D) graphite/expoxy composite in both unnotched and post impacted conditions has been evaluated. The material tested is a (+/- 30/0 deg) multiaxial braid constructed from AS4/12K tow graphite fibers and British Petroleum E905L epoxy resin. These materials were braided as dry preforms and the epoxy was added using a resin transfer molding process (RTM). The unnotched and post-impact specimens were tested in compression-compression fatigue at 10 Hz with a stress ratio of R=10. The unnotched tension-tension fatigue specimens were tested at S Hz with a stress ration of R=0.1. Damage initiation and growth was documented through the application of radiography and ultrasonic through transmission (C-scans). Visible inspection of surface and edge damage was also noted to describe the initiation and progression of damage in these materials. The mechanisms leading to damage initiation were established and failure modes were determined. Stiffness and strength degradation were measured as a function of applied cycles. These 3-D braided composite results were compared to strain levels currently used to design primary structure in commercial aircraft composite components made from prepreg tape and autoclave cured.

Biomechanical Study of the Fixation Strength of Anteromedial Plating for Humeral Shaft Fractures

PubMed Central

Zheng, Yin-Feng; Zhou, Jun-Lin; Wang, Xiao-Hong; Shan, Lei; Liu, Yang

2016-01-01

Background: Open reduction and internal fixation with plate and screws are the gold standard for the surgical treatment of humeral shaft fractures, this study was to compare the mechanical properties of anteromedial, anterolateral, and posterior plating for humeral shaft fractures. Methods: A distal third humeral shaft fracture model was constructed using fourth-generation sawbones (#3404, composite bone). A total of 24 sawbones with a distal third humeral shaft fracture was randomly divided into three Groups: A, B, and C (n = 8 in each group) for anteromedial, anterolateral, and posterior plating, respectively. All sawbones were subjected to horizontal torsional fatigue tests, horizontal torsional and axial compressive fatigue tests, four-point bending fatigue tests in anteroposterior (AP) and mediolateral (ML) directions and horizontal torsional destructive tests. Results: In the horizontal torsional fatigue tests, the mean torsional angle amplitude in Groups A, B, and C were 6.12°, 6.53°, and 6.81°. In horizontal torsional and axial compressive fatigue tests, the mean torsional angle amplitude in Groups A, B, and C were 5.66°, 5.67°, and 6.36°. The mean plate displacement amplitude was 0.05 mm, 0.08 mm, and 0.10 mm. Group A was smaller than Group C (P < 0.05). In AP four-point bending fatigue tests, the mean plate displacement amplitude was 0.16 mm, 0.13 mm, and 0.20 mm. Group B was smaller than Group C (P < 0.05). In ML four-point bending fatigue tests, the mean plate displacement amplitude were 0.16 mm, 0.19 mm, and 0.17 mm. In horizontal torsional destructive tests, the mean torsional rigidity in Groups A, B, and C was 0.82, 0.75, and 0.76 N·m/deg. The yielding torsional angle was 24.50°, 25.70°, and 23.86°. The mean yielding torque was 18.46, 18.05, and 16.83 N·m, respectively. Conclusions: Anteromedial plating was superior to anterolateral or posterior plating in all mechanical tests except in AP four-point bending fatigue tests compared to the anterolateral plating group. We can suggest that anteromedial plating is a clinically safe and effective way for humeral shaft fractures. PMID:27453236

Fatigue crack propagation in additively manufactured porous biomaterials.

PubMed

Hedayati, R; Amin Yavari, S; Zadpoor, A A

2017-07-01

Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 10 4 cycles. The test results also showed that for the same load level of 0.5F y , the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45 ° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45 ° direction with respect to the notch direction. Copyright © 2017 Elsevier B.V. All rights reserved.

The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

NASA Astrophysics Data System (ADS)

Winter, L.; Morgenstern, R.; Hockauf, K.; Lampke, T.

2016-03-01

In this work the mean stress influence on the high cycle fatigue behavior of the plasma electrolytic oxidized (PEO) 6082 aluminum alloy (AlSi1MgMn) is investigated. The present study is focused on the fatigue life time and the susceptibility of fatigue-induced cracking of the oxide coating and their dependence on the applied mean stress. Systematic work is done comparing conditions with and without PEO treatment, which have been tested using three different load ratios. For the uncoated substrate the cycles to failure show a significant dependence on the mean stress, which is typical for aluminum alloys. With increased load ratio and therefore increased mean stress, the fatigue strength decreases. The investigation confirms the well-known effect of PEO treatment on the fatigue life: The fatigue strength is significantly reduced by the PEO process, compared to the uncoated substrate. However, also the mean stress sensitivity of the fatigue performance is reduced. The fatigue limit is not influenced by an increasing mean stress for the PEO treated conditions. This effect is firstly shown in these findings and no explanation for this effect can be found in literature. Supposedly the internal compressive stresses and the micro-cracks in the oxide film have a direct influence on the crack initiation and growth from the oxide film through the interface and in the substrate. Contrary to these findings, the susceptibility of fatigue-induced cracking of the oxide coating is influenced by the load ratio. At tension-tension loading a large number of cracks, which grow partially just in the aluminum substrate, are present. With decreasing load ratio to alternating tension-compression stresses, the crack number and length increases and shattering of the oxide film is more pronounced due to the additional effective compressive part of the load cycle.

Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test

NASA Astrophysics Data System (ADS)

Takahashi, Kyouhei; Ogawa, Takeshi

Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×107 cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

On the Crack Bifurcation and Fanning of Crack Growth Data

NASA Technical Reports Server (NTRS)

Forman, Royce G.; Zanganeh, Mohammad

2015-01-01

Crack growth data obtained from ASTM load shedding method for different R values show some fanning especially for aluminum alloys. It is believed by the authors and it has been shown before that the observed fanning is due to the crack bifurcation occurs in the near threshold region which is a function of intrinsic properties of the alloy. Therefore, validity of the ASTM load shedding test procedure and results is confirmed. However, this position has been argued by some experimentalists who believe the fanning is an artifact of the test procedure and thus the obtained results are invalid. It has been shown that using a special test procedure such as using compressively pre-cracked specimens will eliminate the fanning effect. Since not using the fanned data fit can result in a significantly lower calculated cyclic life, design of a component, particularly for rotorcraft and propeller systems will considerably be impacted and therefore this study is of paramount importance. In this effort both test procedures i.e. ASTM load shedding and the proposed compressive pre-cracking have been used to study the fatigue crack growth behavior of compact tension specimens made of aluminum alloy 2524-T3. Fatigue crack growth paths have been closely observed using SEM machines to investigate the effects of compression pre-cracking on the crack bifurcation behavior. The results of this study will shed a light on resolving the existing argument by better understanding of near threshold fatigue crack growth behavior.

Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. II - Low cycle fatigue behavior

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Gayda, J.; Miner, R. V.

1986-01-01

The low cycle fatigue (LCF) properties of a single-crystal nickel-base superalloy Rene N4, have been examined at 760 and 980 C in air. Specimens having crystallographic orientations near the 001, 011, -111, 023, -236, and -145 lines were tested in fully reversed, total-strain-controlled LCF tests at a frequency of 0.1 Hz. At 760 C, this alloy exhibited orientation dependent tension-compression anisotropies of yielding which continued to failure. Also at 760 C, orientations exhibiting predominately single slip exhibited serrated yielding for many cycles. At 980 C, orientation dependencies of yielding behavior were smaller. In spite of the tension-compression anisotropies, cyclic stress range-strain range behavior was not strongly orientation dependent for either test temperature. Fatigue life on a total strain range basis was highly orientation dependent at 760 and 980 C and was related chiefly to elastic modulus, low modulus orientations having longer lives. Stage I crack growth on 111 planes was dominant at 760 C, while Stage II crack growth occurred at 980 C. Crack initiation generally occurred at near-surface micropores, but occasionally at oxidation spikes in the 980 C tests.

Effect of residual stresses induced by prestressing on rolling element fatigue life

NASA Technical Reports Server (NTRS)

Parker, R. J.; Zaretsky, E. V.

1972-01-01

A mechanical prestress cycle suitable to induce compressive stress beneath the surface of the inner race of radially loaded 207-size bearings was determined. Compressive residual stress in excess 0.69 x 10 to the 9th power N/sq m (100,000 psi), as measured by X-ray diffraction, were induced at the depth of maximum shearing stress. The prestress cycle consisted of running the bearings for 25 hours at 2750 rpm at a radial load which produced a maximum Hertz stress of 3.3 x 10 to the 9th power N/sq m (480,000 psi) at the contact of the inner race and the heaviest loaded ball. Bearings subjected to this prestress cycle and subsequently fatigue tested gave a 10 percent fatigue life greater than twice that of a group of baseline bearings.

The Effect of Compressive Loading on the Fatigue Lifetime of Graphite/ Epoxy Laminates

DTIC Science & Technology

1979-10-01

Un-notched 11 3 Specimen Configuration, Notched 12 4 Location of Thickness and Width Measurements 14 5 Overall View of Composite Compression Test...Grips in Universal Testing Machine 24 8 Specimen Positioning Device 26 9 "Full-Fixity" Apparatus, Showing Auxiliary Platens 26 10 Specimen and Restraint...the accumu- lation of a statistically significant data base. * IA previous research study [11 showed that graphite/epoxy composites under constant

High-temperature, low-cycle fatigue of advanced copper-base alloys for rocket nozzles. Part 2: NASA 1.1, Glidcop, and sputtered copper alloys

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1974-01-01

Short-term tensile and low-cycle fatigue data are reported for five advance copper-base alloys: Sputtered Zr-Cu as received, sputtered Zr-Cu heat-treated, Glidcop AL-10, and NASA alloys 1-1A and 1-1B. Tensile tests were performed in argon at 538 C using an axial strain rate of 0.002/sec. Yield strength and ultimate tensile strength data are reported along with reduction in area values. Axial strain controlled low-cycle fatigue tests were performed in argon at 538C using an axial strain rate of 0.002/sec to define the fatigue life over the range from 100 to 3000 cycles for the five materials studied. It was found that the fatigue characteristics of the NASA 1-1A and NASA 1-1B compositions are identical and represent fatique life values which are much greater than those for the other materials tested. The effect of temperature on NASA 1-1B alloy at a strain rate of 0.002/sec was evaluated along with the effect of strain rates of 0.0004 and 0.01/sec at 538 C. Hold-time data are reported for the NASA 1-1B alloy at 538 C using 5 minute hold periods in tension only and compression only at two different strain range values. Hold periods in tension were much more detrimental than hold periods in compression.

How oral environment simulation affects ceramic failure behavior.

PubMed

Lodi, Ediléia; Weber, Kátia R; Benetti, Paula; Corazza, Pedro H; Della Bona, Álvaro; Borba, Márcia

2018-05-01

Investigating the mechanical behavior of ceramics in a clinically simulated scenario contributes to the development of new and tougher materials, improving the clinical performance of restorations. The optimal in vitro environment for testing is unclear. The purpose of this in vitro study was to investigate the failure behavior of a leucite-reinforced glass-ceramic under compression loading and fatigue in different simulated oral environment conditions. Fifty-three plate-shaped ceramic specimens were produced from computer-aided design and computer-aided manufactured (CAD-CAM) blocks and adhesively cemented onto a dentin analog substrate. For the monotonic test (n=23), a gradual compressive load (0.5 mm/min) was applied to the center of the specimens, immersed in 37ºC water, using a universal testing machine. The initial crack was detected with an acoustic system. The fatigue test was performed in a mechanical cycling machine (37ºC water, 2 Hz) using the boundary technique (n=30). Two lifetimes were evaluated (1×10 6 and 2×10 6 cycles). Failure analysis was performed using transillumination. Weibull distribution was used to evaluate compressive load data. A cumulative damage model with an inverse power law (IPL) lifetime-stress relationship was used to fit the fatigue data. A characteristic failure load of 1615 N and a Weibull modulus of 5 were obtained with the monotonic test. The estimated probability of failure (P f ) for 1×10 6 cycles at 100 N was 31%, at 150 N it was 55%, and at 200 N it was 75%. For 2×10 6 cycles, the P f increased approximately 20% in comparison with the values predicted for 1×10 6 cycles, which was not significant. The most frequent failure mode was a radial crack from the intaglio surface. For fatigue, combined failure modes were also found (radial crack combined with cone crack or chipping). Fatigue affects the fracture load and failure mode of leucite-reinforced glass-ceramic. Copyright © 2017 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

EVALUATION OF THE MECHANICAL PROPERTIES OF 9NI-4CO FORGINGS.

DTIC Science & Technology

FORGING, MECHANICAL PROPERTIES, STEEL , QUENCHING, SPECIFICATIONS, TENSILE PROPERTIES, COMPRESSIVE PROPERTIES, FATIGUE(MECHANICS), TOUGHNESS, STRESS...CORROSION, THERMAL STABILITY, STRAIN(MECHANICS), BAINITE , TEST METHODS, HEAT TREATMENT, CRACK PROPAGATION.

Influences of Processing and Fatigue Cycling on Residual Stresses in a NiCrY-Coated Powder Metallurgy Disk Superalloy

NASA Astrophysics Data System (ADS)

Gabb, T. P.; Rogers, R. B.; Nesbitt, J. A.; Miller, R. A.; Puleo, B. J.; Johnson, D.; Telesman, J.; Draper, S. L.; Locci, I. E.

2017-11-01

Oxidation and corrosion can attack superalloy disk surfaces exposed to increasing operating temperatures in some turbine engine environments. Any potential protective coatings must also be resistant to harmful fatigue cracking during service. The objective of this study was to investigate how residual stresses evolve in one such coating. Fatigue specimens of a powder metallurgy-processed disk superalloy were coated with a NiCrY coating, shot peened, and then subjected to fatigue in air at room and high temperatures. The effects of this processing and fatigue cycling on axial residual stresses and other aspects of the coating were assessed. While shot peening did induce beneficial compressive residual stresses in the coating and substrate, these stresses relaxed in the coating with subsequent heating. Several cast alloys having compositions near the coating were subjected to thermal expansion and tensile stress relaxation tests to help explain this response of residual stresses in the coating. For the coated fatigue specimens, this response contributed to earlier cracking of the coating than for the uncoated surface during long intervals of cycling at 760 °C. Yet, substantial compressive residual stresses still remained in the substrate adjacent to the coating, which were sufficient to suppress fatigue cracking there. The coating continued to protect the substrate from hot corrosion pitting, even after fatigue cracks initiated in the coating.

Fatigue pre-cracking and fracture toughness in polycrystalline tungsten and molybdenum

NASA Astrophysics Data System (ADS)

Taguchi, Katsuya; Nakadate, Kazuhito; Matsuo, Satoru; Tokunaga, Kazutoshi; Kurishita, Hiroaki

2018-01-01

Fatigue pre-cracking performance and fracture toughness in polycrystalline tungsten (W) and molybdenum (Mo) have been investigated in relation to grain boundary (GB) configuration with respect to the crack advance direction. Sub-sized, single edge notched bend (SENB) specimens with three different orientations, R-L (ASTM notation) for a forged Mo rod and L-S and T-S for a rolled W plate, were pre-cracked in two steps: fully uniaxial compression fatigue loading to provoke crack initiation and its stable growth from the notch root, and subsequent 3-point bend (3PB) fatigue loading to extend the crack. The latter step intends to minimize the influence of the residual tensile stresses generated during compression fatigue by moving the crack tip away from the plastic zone. It is shown that fatigue pre-cracking performance, especially pre-crack extension behavior, is significantly affected by the specimen orientation. The R-L orientation, giving the easiest cracking path, permitted crack extension completely beyond the plastic zone, while the L-S and T-S orientations with the thickness cracking direction of the rolled plate sustained the crack lengths around or possibly within the plastic zone size due to difficulty in crack advance through an aligned grain structure. Room temperature fracture toughness tests revealed that the 3PB fatigued specimens exhibited appreciably higher fracture toughness by about 30% for R-L, 40% for L-S and 60% for T-S than the specimens of each orientation pre-cracked by compression fatigue only. This indicates that 3PB fatigue provides the crack tip front out of the residual tensile stress zone by crack extension or leads to reduction in the residual stresses at the crack tip front. Strong dependence of fracture toughness on GB configuration was evident. The obtained fracture toughness values are compared with those in the literature and its strong GB configuration dependence is discussed in connection with the appearance of pop-in.

Fatigue characteristics of carbon nanotube blocks under compression

NASA Astrophysics Data System (ADS)

Suhr, J.; Ci, L.; Victor, P.; Ajayan, P. M.

2008-03-01

In this paper we investigate the mechanical response from repeated high compressive strains on freestanding, long, vertically aligned multiwalled carbon nanotube membranes and show that the arrays of nanotubes under compression behave very similar to soft tissue and exhibit viscoelastic behavior. Under compressive cyclic loading, the mechanical response of nanotube blocks shows initial preconditioning and hysteresis characteristic of viscoeleastic materials. Furthermore, no fatigue failure is observed even at high strain amplitudes up to half million cycles. The outstanding fatigue life and extraordinary soft tissue-like mechanical behavior suggest that properly engineered carbon nanotube structures could mimic artificial muscles.

Cyclic Inelastic Deformation and Fatigue Resistance of a Rail Steel : Experimental Results and Mathematical Models

DOT National Transportation Integrated Search

1981-10-01

Experimental results developed from tests of uniaxial, smooth specimens obtained from the head of an unused section of rail have been reported. Testing encompassed a broad range of conditions - monotonic tension, monotonic compression, and fully reve...

High temperature fatigue behavior of tungsten copper composites

NASA Technical Reports Server (NTRS)

Verrilli, Michael J.; Kim, Yong-Suk; Gabb, Timothy P.

1989-01-01

The high temperature fatigue behavior of a 9 vol percent, tungsten fiber reinforced copper matrix composite was investigated. Load-controlled isothermal fatigue experiments at 260 and 560 C and thermomechanical fatigue (TMF) experiments, both in phase and out of phase between 260 and 560 C, were performed. The stress-strain response displayed considerable inelasticity under all conditions. Also, strain ratcheting was observed during all the fatigue experiments. For the isothermal fatigue and in-phase TMF tests, the ratcheting was always in a tensile direction, continuing until failure. The ratcheting during the out-of-phase TMF test shifted from a tensile direction to a compressive direction. This behavior was thought to be associated with the observed bulging and the extensive cracking of the out-of-phase specimen. For all cases, the fatigue lives were found to be controlled by damage to the copper matrix. Grain boundary cavitation was the dominant damage mechanism of the matrix. On a stress basis, TMF loading reduced lives substantially, relative to isothermal cycling. In-phase cycling resulted in the shortest lives, and isothermal fatigue at 260 C, the longest.

Materials research for high-speed civil transport and generic hypersonics: Composites durability

NASA Technical Reports Server (NTRS)

Allen-Lilly, Heather; Cregger, Eric; Hoffman, Daniel; Mccool, Jim

1995-01-01

This report covers a portion of an ongoing investigation of the durability of composites for the High Speed Civil Transport (HSCT) program. Candidate HSCT composites need to possess the high-temperature capability required for supersonic flight. This program was designed to initiate the design, analysis, fabrication, and testing of equipment intended for use in validating the long-term durability of materials for the HSCT. This equipment includes thermally actuated compression and tension fixtures, hydraulic-actuated reversible load fixtures, and thermal chambers. This equipment can be used for the durability evaluation of both composite and adhesive materials. Thermally actuated fixtures are recommended for fatigue cycling when long-term thermomechanical fatigue (TMF) data are required on coupon-sized tension or compression specimens. Long term durability testing plans for polymer matrix composite specimens are included.

The influence of cell morphology on the compressive fatigue behavior of Ti-6Al-4V meshes fabricated by electron beam melting.

PubMed

Zhao, S; Li, S J; Hou, W T; Hao, Y L; Yang, R; Misra, R D K

2016-06-01

Additive manufacturing technique is a promising approach for fabricating cellular bone substitutes such as trabecular and cortical bones because of the ability to adjust process parameters to fabricate different shapes and inner structures. Considering the long term safe application in human body, the metallic cellular implants are expected to exhibit superior fatigue property. The objective of the study was to study the influence of cell shape on the compressive fatigue behavior of Ti-6Al-4V mesh arrays fabricated by electron beam melting. The results indicated that the underlying fatigue mechanism for the three kinds of meshes (cubic, G7 and rhombic dodecahedron) is the interaction of cyclic ratcheting and fatigue crack growth on the struts, which is closely related to cumulative effect of buckling and bending deformation of the strut. By increasing the buckling deformation on the struts through cell shape design, the cyclic ratcheting rate of the meshes during cyclic deformation was decreased and accordingly, the compressive fatigue strength was increased. With increasing bending deformation of struts, fatigue crack growth in struts contributed more to the fatigue damage of meshes. Rough surface and pores contained in the struts significantly deteriorated the compressive fatigue strength of the struts. By optimizing the buckling and bending deformation through cell shape design, Ti-6Al-4V alloy cellular solids with high fatigue strength and low modulus can be fabricated by the EBM technique. Copyright © 2016 Elsevier Ltd. All rights reserved.

[Evaluation of mechanical properties of four kinds of composite resins for inlay].

PubMed

Jiang, Ling-ling; Liu, Hong; Wang, Jin-rui

2011-04-01

To evaluate the compressive strength, wear resistance, hardness, and soaking fatigue of four composite resins for inlay, which were Ceramage, Surefil, Solitaire 2, and Filtek(TM) Z350. Scanning electron microscope (SEM) was used to analyze the microstructures of the wear surface of the samples. The samples for the compression test, hardness test and wear were prepared. The samples were respectively immersed in the artificial saliva for 2 months for immersed test. The electronic universal testing machine was used to test the compression strength. Hardness was quantified by micro-Vickers hardness test. The wear tester was used for the wear test. SEM was used to analyze the microstructures of the wear surface of samples. All the data was analyzed by using SPSS17.0 software package. The compressive strength of Surefil was the biggest which was significantly higher than the other three resins before soaking (P<0.05). After soaking, there was no significant difference between the composite resins (P>0.05). The hardness of Surefil was the best, and significant difference was found between the hardness of the materials before soaking (P<0.05). After soaking, no significant difference was obtained between the hardness of Surefil and Filtek(TM) Z350 (P>0.05).The compressive strength and hardness of 4 materials decreased after soaking in artificial saliva. But only the compressive strength of Filtek(TM) Z350 had no significant change after immersion (P>0.05). Except Filtek(TM) Z350, there was significant difference between the other three materials (P<0.05). Significant relationship was observed between wear and hardness of three materials (P<0.05). According to SEM observation, abrasive wear occurred in four materials. In addition to Ceramage, other composite resins had adhesive wear. The mechanical property of Surefil is the best, and it is suitable for fabrication of posterior inlay. Filtek(TM) Z350's ability to resist fatigue is the best.

Improvements of mechanical fatigue reliability of Cu interconnects on flexible substrates through MoTi alloy under-layer

NASA Astrophysics Data System (ADS)

Lee, Young-Joo; Shin, Hae-A.-Seul; Nam, Dae-Hyun; Yeon, Han-Wool; Nam, Boae; Woo, Kyoohee; Joo, Young-Chang

2015-01-01

The mechanical fatigue of Cu films and lines on flexible substrates was investigated, and an improvement in the structures through the use of a MoTi alloy under-layer was proposed. Fatigue reliability was decreased by 3-fold in lines compared with films in the tensile condition and by 6-fold in the compressive condition. Crack formation was observed to be more detrimental for lines than for films. With a MoTi under-layer, the fatigue limit was increased by 2 times that of a structure without MoTi in the tensile condition and by 15 times in the compressive bending condition. The suppression of delamination through the use of a MoTi under-layer improved the fatigue reliability under compressive bending.

The fatigue growth of internal delaminations under compressive loading of cross-ply composite plates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pelegri, A.A.; Kardomateas, G.A.; Malik, B.U.

1997-12-31

This study focuses on the mode dependence of delamination growth under cyclic compressive loads in cross-ply composite plates. The model proposed makes use of an initial postbuckling solution derived from a perturbation procedure. A mode-dependent crack growth criterion is introduced. Expressions describing the fatigue crack growth are derived in terms of the distribution of the mode adjusted energy release rate. The resulting crack growth laws are numerically integrated to produce delamination growth versus number of cycles diagrams. The model does not impose any restrictive assumptions on the relative thickness of the delaminated and the base plates, although transverse shear stressmore » effects are not considered. Experimental results are presented for cross-ply graphite/epoxy specimens, and the results are compared with experimental results for unidirectional specimens. The test data are obtained for different delamination locations and for different values of applied compressive strain.« less

Tension and compression fatigue response of unnotched 3D braided composites

NASA Technical Reports Server (NTRS)

Portanova, M. A.

1992-01-01

The unnotched compression and tension fatigue response of a 3-D braided composite was measured. Both gross compressive stress and tensile stress were plotted against cycles to failure to evaluate the fatigue life of these materials. Damage initiation and growth was monitored visually and by tracking compliance change during cycle loading. The intent was to establish by what means the strength of a 3-D architecture will start to degrade, at what point will it degrade beyond an acceptable level, and how this material will typically fail.

Proceedings of the Annual Mechanics of Composites Review (8th) Held at Wright-Patterson AFB, Ohio on 5-7 October 1982.

DTIC Science & Technology

1983-04-01

Spectrum Fatigue Behavior of Postbuckled Shear Panels; PO01 246 Development of Analysis for Predicting Compression Fatigt Life and Residual Strength in...Lazyup and Frequency Effects on Fatigue Life of Composites, POOl 256 Effect of Stress Ratio on Fatigue Life of Composites,’ POOl 257 High-Load Transfer...L. Agerwall, Northrop Corporation 0950-1020 BREAK 1020-1100 DEVELOPMENT OF ANALYSIS FOR PREDICTING COMPRESSION 34 FATIGUE LIFE AND RESIDUAL STRENGTH

Fatigue Life of Postbuckled Structures with Indentation Damage

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Bisagni, Chiara

2016-01-01

The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of the stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 37 millimeters to 56 millimeters were tested in fatigue and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

High temperature fatigue behavior of Haynes 188

NASA Technical Reports Server (NTRS)

Halford, Gary R.; Saltsman, James F.; Kalluri, Sreeramesh

1988-01-01

The high temperature, creep-fatigue behavior of Haynes 188 was investigated as an element in a broader thermomechanical fatigue life prediction model development program at the NASA-Lewis. The models are still in the development stage, but the data that were generated possess intrinsic value on their own. Results generated to date is reported. Data were generated to characterize isothermal low cycle fatigue resistance at temperatures of 316, 704, and 927 C with cyclic failure lives ranging from 10 to more than 20,000. These results follow trends that would be predicted from a knowledge of tensile properties, i.e., as the tensile ductility varies with temperature, so varies the cyclic inelastic straining capacity. Likewise, as the tensile strength decreases, so does the high cyclic fatigue resistance. A few two-minute hold-time cycles at peak compressive strain were included in tests at 760 C. These results were obtained in support of a redesign effort for the Orbital Maneuverable System engine. No detrimental effects on cyclic life were noted despite the added exposure time for creep and oxidation. Finally, a series of simulated thermal fatigue tests, referred to as bithermal fatigue tests, were conducted using 316 C as the minimum and 760 C as the maximum temperature. Only out-of-phase bithermal tests were conducted to date. These test results are intended for use as input to a more general thermomechanical fatigue life prediction model based on the concepts of the total strain version of Strainrange Partitioning.

Atomistic origin of size effects in fatigue behavior of metallic glasses

NASA Astrophysics Data System (ADS)

Sha, Zhendong; Wong, Wei Hin; Pei, Qingxiang; Branicio, Paulo Sergio; Liu, Zishun; Wang, Tiejun; Guo, Tianfu; Gao, Huajian

2017-07-01

While many experiments and simulations on metallic glasses (MGs) have focused on their tensile ductility under monotonic loading, the fatigue mechanisms of MGs under cyclic loading still remain largely elusive. Here we perform molecular dynamics (MD) and finite element simulations of tension-compression fatigue tests in MGs to elucidate their fatigue mechanisms with focus on the sample size effect. Shear band (SB) thickening is found to be the inherent fatigue mechanism for nanoscale MGs. The difference in fatigue mechanisms between macroscopic and nanoscale MGs originates from whether the SB forms partially or fully through the cross-section of the specimen. Furthermore, a qualitative investigation of the sample size effect suggests that small sample size increases the fatigue life while large sample size promotes cyclic softening and necking. Our observations on the size-dependent fatigue behavior can be rationalized by the Gurson model and the concept of surface tension of the nanovoids. The present study sheds light on the fatigue mechanisms of MGs and can be useful in interpreting previous experimental results.

Low strain, long life creep fatigue of AF2-1DA and INCO 718

NASA Technical Reports Server (NTRS)

Thakker, A. B.; Cowles, B. A.

1983-01-01

Two aircraft turbine disk alloys, GATORIZED AF2-DA and INCO 718 were evaluated for their low strain long life creep-fatigue behavior. Static (tensile and creep rupture) and cyclic properties of both alloys were characterized. The cntrolled strain LCF tests were conducted at 760 C (1400 F) and 649 C (1200 F) for AF2-1DA and INCO 718, respectively. Hold times were varied for tensile, compressive and tensile/compressive strain dwell (relaxation) tests. Stress (creep) hold behavior of AF2-1DA was also evaluated. Generally, INCO 718 exhibited more pronounced reduction in cyclic life due to hold than AF2-1DA. The percent reduction in life for both alloys for strain dwell tests was greater at low strain ranges (longer life regime). Changing hold time from 0 to 0.5, 2.0 and 15.0 min. resulted in corresponding reductions in life. The continuous cycle and cyclic/dwell initiation failure mechanism was predominantly transgranular for AF2-1DA and intergranular for INCO 718.

Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material

NASA Technical Reports Server (NTRS)

Vandermey, Nancy E.; Morris, Don H.; Masters, John E.

1991-01-01

Damage initiation and growth under compression-compression fatigue loading were investigated for a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic layup. Performance of unnotched specimens having stitch rows at either 0 degree or 90 degrees to the loading direction was compared. Special attention was given to the effects of stitching related manufacturing defects. Damage evaluation techniques included edge replication, stiffness monitoring, x-ray radiography, residual compressive strength, and laminate sectioning. It was found that the manufacturing defect of inclined stitches had the greatest adverse effect on material performance. Zero degree and 90 degree specimen performances were generally the same. While the stitches were the source of damage initiation, they also slowed damage propagation both along the length and across the width and affected through-the-thickness damage growth. A pinched layer zone formed by the stitches particularly affected damage initiation and growth. The compressive failure mode was transverse shear for all specimens, both in static compression and fatigue cycling effects.

Low cycle fatigue and creep fatigue interaction behavior of 9Cr-0.5Mo-1.8W-V-Nb heat-resistant steel at high temperature

NASA Astrophysics Data System (ADS)

Wang, Xiaowei; Zhang, Wei; Gong, Jianming; Wahab, Magd Abdel

2018-07-01

In this paper, Low Cycle Fatigue (LCF) and Creep-Fatigue Interaction (CFI) behavior of 9Cr-0.5Mo-1.8 W-V-Nb heat-resistant steel (ASME Grade P92 steel) at elevated temperature of 600 °C are investigated. Strain controlled LCF tests are conducted in fully reversed triangular waveform at different strain amplitudes ranging from 0.2% to 0.8%. CFI tests are conducted at 0.4% strain amplitude in trapezoid waveform with tensile hold time varying from 1 min to 60 min and compressive hold time varying from 1 min to 10 min. During LCF and CFI loadings, the evolution of cyclic stress, mean stress and stress relaxation behavior are investigated. It turns out that the softening behavior and lifetime degradation are dependent on strain amplitude, hold time and hold direction. In addition, the microstructure evolution and fracture behavior are characterized by optical, scanning and transmission electron microscope. The initial rapid softening behavior is attributed to the quick elimination of low angle boundaries, whereas no obvious microstructure alteration appears in the stable stage. Fracture behavior analysis reveals creep voids in long-term CFI tests facilitates the initiation and propagation of secondary cracks. The different responses of outer surface oxidation layer during cycling provides an explanation for severer damage of compressive hold and also accounts for the observed various fracture behavior of failed samples.

Fatigue acceptance test limit criterion for larger diameter rolled thread fasteners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kephart, A.R.

1997-05-01

This document describes a fatigue lifetime acceptance test criterion by which studs having rolled threads, larger than 1.0 inches in diameter, can be assured to meet minimum quality attributes associated with a controlled rolling process. This criterion is derived from a stress dependent, room temperature air fatigue database for test studs having a 0.625 inch diameter threads of Alloys X-750 HTH and direct aged 625. Anticipated fatigue lives of larger threads are based on thread root elastic stress concentration factors which increase with increasing thread diameters. Over the thread size range of interest, a 30% increase in notch stress ismore » equivalent to a factor of five (5X) reduction in fatigue life. The resulting diameter dependent fatigue acceptance criterion is normalized to the aerospace rolled thread acceptance standards for a 1.0 inch diameter, 0.125 inch pitch, Unified National thread with a controlled Root radius (UNR). Testing was conducted at a stress of 50% of the minimum specified material ultimate strength, 80 Ksi, and at a stress ratio (R) of 0.10. Limited test data for fastener diameters of 1.00 to 2.25 inches are compared to the acceptance criterion. Sensitivity of fatigue life of threads to test nut geometry variables was also shown to be dependent on notch stress conditions. Bearing surface concavity of the compression nuts and thread flank contact mismatch conditions can significantly affect the fastener fatigue life. Without improved controls these conditions could potentially provide misleading acceptance data. Alternate test nut geometry features are described and implemented in the rolled thread stud specification, MIL-DTL-24789(SH), to mitigate the potential effects on fatigue acceptance data.« less

Advanced Gear Alloys for Ultra High Strength Applications

NASA Technical Reports Server (NTRS)

Shen, Tony; Krantz, Timothy; Sebastian, Jason

2011-01-01

Single tooth bending fatigue (STBF) test data of UHS Ferrium C61 and C64 alloys are presented in comparison with historical test data of conventional gear steels (9310 and Pyrowear 53) with comparable statistical analysis methods. Pitting and scoring tests of C61 and C64 are works in progress. Boeing statistical analysis of STBF test data for the four gear steels (C61, C64, 9310 and Pyrowear 53) indicates that the UHS grades exhibit increases in fatigue strength in the low cycle fatigue (LCF) regime. In the high cycle fatigue (HCF) regime, the UHS steels exhibit better mean fatigue strength endurance limit behavior (particularly as compared to Pyrowear 53). However, due to considerable scatter in the UHS test data, the anticipated overall benefits of the UHS grades in bending fatigue have not been fully demonstrated. Based on all the test data and on Boeing s analysis, C61 has been selected by Boeing as the gear steel for the final ERDS demonstrator test gearboxes. In terms of potential follow-up work, detailed physics-based, micromechanical analysis and modeling of the fatigue data would allow for a better understanding of the causes of the experimental scatter, and of the transition from high-stress LCF (surface-dominated) to low-stress HCF (subsurface-dominated) fatigue failure. Additional STBF test data and failure analysis work, particularly in the HCF regime and around the endurance limit stress, could allow for better statistical confidence and could reduce the observed effects of experimental test scatter. Finally, the need for further optimization of the residual compressive stress profiles of the UHS steels (resulting from carburization and peening) is noted, particularly for the case of the higher hardness C64 material.

Effects of Wearing a Compression Garment During Night Sleep on Recovery From High-Intensity Eccentric-Concentric Quadriceps Muscle Fatigue.

PubMed

Shimokochi, Yohei; Kuwano, Satoshi; Yamaguchi, Taichi; Abutani, Hiroyuki; Shima, Norihiro

2017-10-01

This study aimed to investigate the effects of wearing a compression garment (CG) during night sleep on muscle fatigue recovery after high-intensity eccentric and concentric knee extensor exercises. Seventeen male college students participated in 2 experimental sessions under CG and non-CG (NCG) wearing conditions. Before night sleep under CG or NCG wearing conditions, the subjects performed a fatiguing protocol consisting of 10 sets of 10 repetitions of maximal isokinetic eccentric and concentric knee extensor contractions, with 30-second rest intervals between the sets. Immediately before and after and 24 hours after the fatiguing protocol, maximum voluntary isometric contraction (MVIC) force for knee extensor muscles was measured; surface electromyographic data from the vastus medialis and rectus femoris were also measured. A 2-way repeated-measure analysis of variance followed by Bonferroni pairwise comparisons were used to analyze the differences in each variable. Paired-sample t-tests were used to analyze the mean differences between the conditions at the same time points for each variable. The MVIC 24 hours after the fatiguing protocol was approximately 10% greater in the CG than in the NCG condition (p = 0.033). Changes in the electromyographic variables over time did not significantly differ between the conditions. Thus, it was concluded that wearing a CG during night sleep may promote localized muscle fatigue recovery but does not influence neurological factors after the fatiguing exercise.

Corrosion and Fatigue Behavior of High-Strength Steel Treated with a Zn-Alloy Thermo-diffusion Coating

NASA Astrophysics Data System (ADS)

Mulligan, C. P.; Vigilante, G. N.; Cannon, J. J.

2017-11-01

High and low cycle fatigue tests were conducted on high-strength steel using four-point bending. The materials tested were ASTM A723 steel in the as-machined condition, grit-blasted condition, MIL-DTL-16232 heavy manganese phosphate-coated condition, and ASTM A1059 Zn-alloy thermo-diffusion coated (Zn-TDC). The ASTM A723 steel base material exhibits a yield strength of 1000 MPa. The effects of the surface treatments versus uncoated steel were examined. The fatigue life of the Zn-TDC specimens was generally reduced on as-coated specimens versus uncoated or phosphate-coated specimens. Several mechanisms are examined including the role of compressive residual stress relief with the Zn-TDC process as well as fatigue crack initiation from the hardened Zn-Fe alloy surface layer produced in the gas-metal reaction. Additionally, the effects of corrosion pitting on the fatigue life of coated specimens are explored as the Zn-TDC specimens exhibit significantly improved corrosion resistance over phosphate-coated and oiled specimens.

Improvement in Fatigue Performance of Aluminium Alloy Welded Joints by Laser Shock Peening in a Dynamic Strain Aging Temperature Regime.

PubMed

Su, Chun; Zhou, Jianzhong; Meng, Xiankai; Huang, Shu

2016-09-26

As a new treatment process after welding, the process parameters of laser shock peening (LSP) in dynamic strain aging (DSA) temperature regimes can be precisely controlled, and the process is a non-contact one. The effects of LSP at elevated temperatures on the distribution of the surface residual stress of AA6061-T6 welded joints were investigated by using X-ray diffraction technology with the sin² ϕ method and Abaqus software. The fatigue life of the welded joints was estimated by performing tensile fatigue tests. The microstructural evolution in surface and fatigue fractures of the welded joints was presented by means of surface integrity and fracture surface testing. In the DSA temperature regime of AA6061-T6 welded joints, the residual compressive stress was distributed more stably than that of LSP at room temperature. The thermal corrosion resistance and fatigue properties of the welded joints were also improved. The experimental results and numerical analysis were in mutual agreement.

Improvement in Fatigue Performance of Aluminium Alloy Welded Joints by Laser Shock Peening in a Dynamic Strain Aging Temperature Regime

PubMed Central

Su, Chun; Zhou, Jianzhong; Meng, Xiankai; Huang, Shu

2016-01-01

As a new treatment process after welding, the process parameters of laser shock peening (LSP) in dynamic strain aging (DSA) temperature regimes can be precisely controlled, and the process is a non-contact one. The effects of LSP at elevated temperatures on the distribution of the surface residual stress of AA6061-T6 welded joints were investigated by using X-ray diffraction technology with the sin2ϕ method and Abaqus software. The fatigue life of the welded joints was estimated by performing tensile fatigue tests. The microstructural evolution in surface and fatigue fractures of the welded joints was presented by means of surface integrity and fracture surface testing. In the DSA temperature regime of AA6061-T6 welded joints, the residual compressive stress was distributed more stably than that of LSP at room temperature. The thermal corrosion resistance and fatigue properties of the welded joints were also improved. The experimental results and numerical analysis were in mutual agreement. PMID:28773920

Delivery of cardiopulmonary resuscitation in the microgravity environment

NASA Technical Reports Server (NTRS)

Barratt, M. R.; Billica, R. D.

1992-01-01

The microgravity environment presents several challenges for delivering effective cardiopulmonary resuscitation (CPR). Chest compressions must be driven by muscular force rather than by the weight of the rescuer's upper torso. Airway stabilization is influenced by the neutral body posture. Rescuers will consist of crew members of varying sizes and degrees of physical deconditioning from space flight. Several methods of CPR designed to accommodate these factors were tested in the one G environment, in parabolic flight, and on a recent shuttle flight. Methods: Utilizing study participants of varying sizes, different techniques of CPR delivery were evaluated using a recording CPR manikin to assess adequacy of compressive force and frequency. Under conditions of parabolic flight, methods tested included conventional positioning of rescuer and victim, free floating 'Heimlich type' compressions, straddling the patient with active and passive restraints, and utilizing a mechanical cardiac compression assist device (CCAD). Multiple restrain systems and ventilation methods were also assessed. Results: Delivery of effective CPR was possible in all configurations tested. Reliance on muscular force alone was quickly fatiguing to the rescuer. Effectiveness of CPR was dependent on technique, adequate restraint of the rescuer and patient, and rescuer size and preference. Free floating CPR was adequate but rapidly fatiguing. The CCAD was able to provide adequate compressive force but positioning was problematic. Conclusions: Delivery of effective CPR in microgravity will be dependent on adequate resuer and patient restraint, technique, and rescuer size and preference. Free floating CPR may be employed as a stop gap method until patient restraint is available. Development of an adequate CCAD would be desirable to compensate for the effects of deconditioning.

Influence of creep damage on the low cycle thermal-mechanical fatigue behavior of two tantalum base alloys

NASA Technical Reports Server (NTRS)

Sheffler, K. D.; Doble, G. S.

1972-01-01

Low cycle fatigue tests have been performed on the tantalum base alloys T-111 and ASTAR 811C with synchronized, independently programmed temperature and strain cycling. The thermal-mechanical cycles applied fell into three basic categories: these were isothermal cycling, in-phase thermal cycling, and out-of-phase thermal cycling. In-phase cycling was defined as tensile deformation associated with high temperature and compressive deformation with low temperature, while out-of-phase thermal cycling was defined as the reverse case. The in-phase thermal cycling had a pronounced detrimental influence on the fatigue life of both alloys, with the life reduction being greater in the solid solution strengthened T-111 alloy than in the carbide strengthened ASTAR 811C alloy. The out-of-phase tests also showed pronounced effects on the fatigue life of both alloys, although not as dramatic.

Characterization and damage evaluation of advanced materials

NASA Astrophysics Data System (ADS)

Mitrovic, Milan

Mechanical characterization of advanced materials, namely magnetostrictive and graphite/epoxy composite materials, is studied in this dissertation, with an emphasis on damage evaluation of composite materials. Consequently, the work in this dissertation is divided into two parts, with the first part focusing on characterization of the magneto-elastic response of magnetostrictlve materials, while the second part of this dissertation describes methods for evaluating the fatigue damage in composite materials. The objective of the first part of this dissertation is to evaluate a nonlinear constitutive relation which more closely depict the magneto-elastic response of magnetostrictive materials. Correlation between experimental and theoretical values indicate that the model adequately predicts the nonlinear strain/field relations in specific regimes, and that the currently employed linear approaches are inappropriate for modeling the response of this material in a structure. The objective of the second part of this dissertation is to unravel the complexities associated with damage events associated with polymeric composite materials. The intent is to characterize and understand the influence of impact and fatigue induced damage on the residual thermo-mechanical properties and compressive strength of composite systems. The influence of fatigue generated matrix cracking and micro-delaminations on thermal expansion coefficient (TEC) and compressive strength is investigated for woven graphite/epoxy composite system. Experimental results indicate that a strong correlation exists between TEC and compressive strength measurements, indicating that TEC measurements can be used as a damage metric for this material systems. The influence of delaminations on the natural frequencies and mode shapes of a composite laminate is also investigated. Based on the changes of these parameters as a function of damage, a methodology for determining the size and location of damage is suggested. Finally, the influence of loading parameters on impact damage growth is investigated experimentally though constant amplitude and spectrum loading fatigue tests. Based on observed impact damage growth during these tests it is suggested that the low load levels can be deleted from the standardized test sequence without significant influence on impact damage propagation.

High-Cycle Fatigue Resistance of Si-Mo Ductile Cast Iron as Affected by Temperature and Strain Rate

NASA Astrophysics Data System (ADS)

Matteis, Paolo; Scavino, Giorgio; Castello, Alessandro; Firrao, Donato

2015-09-01

Silicon-molybdenum ductile cast irons are used to fabricate exhaust manifolds of internal combustion engines of large series cars, where the maximum pointwise temperature at full engine load may be higher than 973 K (700 °C). In this application, high-temperature oxidation and thermo-mechanical fatigue (the latter being caused by the engine start and stop and by the variation of its power output) have been the subject of several studies and are well known, whereas little attention has been devoted to the high-cycle fatigue, arising from the engine vibration. Therefore, the mechanical behavior of Si-Mo cast iron is studied here by means of stress-life fatigue tests up to 10 million cycles, at temperatures gradually increasing up to 973 K (700 °C). The mechanical characterization is completed by tensile and compressive tests and ensuing fractographic examinations; the mechanical test results are correlated with the cast iron microstructure and heat treatment.

Steady-state temperature determination on the base of hysteresis loop energy for CuZn37 brass

NASA Astrophysics Data System (ADS)

Lipski, Adam; Skibicki, Dariusz; Pejkowski, Łukasz

2017-03-01

This paper presents the verification of the relationship between the temperature and the hysteresis loop energy for the CuZn37 brass under multiaxial fatigue loading. Fatigue tests were performed on the hollow specimens subjected to fully reversed tension-compression, torsion, proportional loading, 90° out-of-phase non-proportional loading and two another non-proportional loadings with frequency differences. All test were strain-controlled. Calculations of a plastic strain energy were based on midlife strain hysteresis loops data. The calculated specimen temperatures were compared with temperatures observed by thermographic camera.

Fatigue-Induced Damage in Zr-Based Bulk Metallic Glasses

PubMed Central

Chuang, Chih-Pin; Yuan, Tao; Dmowski, Wojciech; Wang, Gong-Yao; Freels, Matt; Liaw, Peter K.; Li, Ran; Zhang, Tao

2013-01-01

In the present work, we investigate the effect of “fatigue” on the fatigue behavior and atomic structure of Zr-based BMGs. Fatigue experiments on the failed-by-fatigue samples indicate that the remnants generally have similar or longer fatigue life than the as-cast samples. Meanwhile, the pair-distribution-function (PDF) analysis of the as-cast and post-fatigue samples showed very small changes of local atomic structures. These observations suggest that the fatigue life of the 6-mm in-diameter Zr-based BMG is dominated by the number of pre-existing crack-initiation sites in the sample. Once the crack initiates in the specimen, the fatigue-induced damage is accumulated locally on these initiated sites, while the rest of the region deforms elastically. The results suggest that the fatigue failure of BMGs under compression-compression fatigue experiments is a defect-controlled process. The present work indicates the significance of the improved fatigue resistance with decreasing the sample size. PMID:23999496

DETERMINATION OF THE CREEP–FATIGUE INTERACTION DIAGRAM FOR ALLOY 617

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wright, J. K.; Carroll, L. J.; Sham, T. -L.

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, creep-fatigue testing was performed. Testing has been performed primarily on a single heat of material at 850 and 950°C for total strain ranges of 0.3 to 1% and tensile hold times as long as 240 minutes. At 850°C, increases in the tensile hold duration degraded the creep fatigue resistance, at least to the investigated strain-controlled hold time of up to 60 minutes at the 0.3% strain range and 240 minutesmore » at the 1.0% strain range. At 950°C, the creep-fatigue cycles to failure becomes constant with increasing hold times, indicating saturation occurs at relatively short hold times. The creep and fatigue damage fractions have been calculated and plotted on a creep-fatigue interaction D-diagram. Results from earlier creep-fatigue tests at 800 and 1000°C on an additional heat of Alloy 617 are also plotted on the D-diagram. The methodology for calculating the damage fractions will be presented, and the effects of strain rate, strain range, temperature, hold time, and strain profile (i.e. holds in tension, compression or both) on the creep-fatigue damage will be explored.« less

Bystander fatigue and CPR quality by older bystanders: a randomized crossover trial comparing continuous chest compressions and 30:2 compressions to ventilations.

PubMed

Liu, Shawn; Vaillancourt, Christian; Kasaboski, Ann; Taljaard, Monica

2016-11-01

This study sought to measure bystander fatigue and cardiopulmonary resuscitation (CPR) quality after five minutes of CPR using the continuous chest compression (CCC) versus the 30:2 chest compression to ventilation method in older lay persons, a population most likely to perform CPR on cardiac arrest victims. This randomized crossover trial took place at three tertiary care hospitals and a seniors' center. Participants were aged ≥55 years without significant physical limitations (frailty score ≤3/7). They completed two 5-minute CPR sessions (using 30:2 and CCC) on manikins; sessions were separated by a rest period. We used concealed block randomization to determine CPR method order. Metronome feedback maintained a compression rate of 100/minute. We measured heart rate (HR), mean arterial pressure (MAP), and Borg Exertion Scale. CPR quality measures included total number of compressions and number of adequate compressions (depth ≥5 cm). Sixty-three participants were enrolled: mean age 70.8 years, female 66.7%, past CPR training 60.3%. Bystander fatigue was similar between CPR methods: mean difference in HR -0.59 (95% CI -3.51-2.33), MAP 1.64 (95% CI -0.23-3.50), and Borg 0.46 (95% CI 0.07-0.84). Compared to 30:2, participants using CCC performed more chest compressions (480.0 v. 376.3, mean difference 107.7; p<0.0001) and more adequate chest compressions (381.5 v. 324.9, mean difference. 62.0; p=0.0001), although good compressions/minute declined significantly faster with the CCC method (p=0.0002). CPR quality decreased significantly faster when performing CCC compared to 30:2. However, performing CCC produced more adequate compressions overall with a similar level of fatigue compared to the 30:2 method.

Insights into the effects of tensile and compressive loadings on human femur bone.

PubMed

Havaldar, Raviraj; Pilli, S C; Putti, B B

2014-01-01

Fragile fractures are most likely manifestations of fatigue damage that develop under repetitive loading conditions. Numerous microcracks disperse throughout the bone with the tensile and compressive loads. In this study, tensile and compressive load tests are performed on specimens of both the genders within 19 to 83 years of age and the failure strength is estimated. Fifty five human femur cortical samples are tested. They are divided into various age groups ranging from 19-83 years. Mechanical tests are performed on an Instron 3366 universal testing machine, according to American Society for Testing and Materials International (ASTM) standards. The results show that stress induced in the bone tissue depends on age and gender. It is observed that both tensile and compression strengths reduces as age advances. Compressive strength is more than tensile strength in both the genders. The compression and tensile strength of human femur cortical bone is estimated for both male and female subjecting in the age group of 19-83 years. The fracture toughness increases till 35 years in male and 30 years in female and reduces there after. Mechanical properties of bone are age and gender dependent.

Rolling contact fatigue strengths of shot-peened and crack-healed ceramics

NASA Astrophysics Data System (ADS)

Takahashi, K.; Oki, T.

2018-06-01

The effects of shot-peening (SP) and crack-healing on the rolling contact fatigue (RCF) strengths of Al2O3/SiC composite ceramics were investigated. Non-shot-peened, shot- peened, and shot-peened + crack-healed specimens were prepared. SP was performed using ZrO2 beads. The shot-peened + crack-healed specimen was crack-healed after SP. X-ray diffraction clearly showed that SP induced a compressive residual stress up to 300 MPa at the specimen surfaces. Furthermore, the shot-peened + crack-healed specimen retained a compressive residual stress of 200 MPa. The apparent surface fracture toughness of the shot- peened specimens increased owing to the positive effects of the compressive residual stress. RCF tests were performed using a thrust load-bearing test device. The RCF lives of the shot- peened specimens did not improve compared to that of the non-shot-peened specimen, because the numerous SP-introduced surface cracks could act as crack initiation sites during the RCF tests. However, the RCF life of the shot-peened + crack-healed specimen did improve compared to those of non-shot-peened and shot-peened specimens, implying that combining SP and crack-healing was an effective strategy for improving the RCF lives of Al2O3/SiC composite ceramics.

Up-Down Hand Position Switch May Delay the Fatigue of Non-Dominant Hand Position Rescuers and Improve Chest Compression Quality during Cardiopulmonary Resuscitation: A Randomized Crossover Manikin Study

PubMed Central

Xu, Bing; Wang, Huang-Lei; Xiong, Dan; Sheng, Li-Pin; Yang, Qi-Sheng; Jiang, Shan; Xu, Peng; Chen, Zhi-Qiao; Zhao, Yan

2015-01-01

Previous studies have shown improved external chest compression (ECC) quality and delayed rescuer fatigue when the dominant hand (DH) was in contact with the sternum. However, many rescuers prefer placing the non-dominant hand (NH) in contact with the sternum during ECC. We aimed to investigate the effects of up-down hand position switch on the quality of ECC and the fatigue of rescuers during cardiopulmonary resuscitation (CPR). After completion of a review of the standard adult basic life support (BLS) course, every candidate performed 10 cycles of single adult CPR twice on an adult manikin with either a constant hand position (CH) or a switched hand position (SH) in random order at 7-day intervals. The rescuers’ general characteristics, hand positions, physiological signs, fatigue appearance and ECC qualities were recorded. Our results showed no significant differences in chest compression quality for the DH position rescuers between the CH and SH sessions (p>0.05, resp.). And also no significant differences were found for Borg score (p = 0.437) or cycle number (p = 0.127) of fatigue appearance after chest compressions between the two sessions. However, for NH position rescuers, the appearance of fatigue was delayed (p = 0.046), with a lower Borg score in the SH session (12.67 ± 2.03) compared to the CH session (13.33 ± 1.95) (p = 0.011). Moreover, the compression depth was significantly greater in the SH session (39.3 ± 7.2 mm) compared to the CH session (36.3 ± 8.1 mm) (p = 0.015). Our data suggest that the up-down hand position switch during CPR may delay the fatigue of non-dominant hand position rescuers and improve the quality of chest compressions. PMID:26267353

Effects of Range of Stress and of Special Notches on Fatigue Properties of Aluminum Alloys Suitable for Airplane Propellers

NASA Technical Reports Server (NTRS)

Dolan, Thomas J

1942-01-01

Laboratory tests were made to obtain information on the load-resisting properties of X76S-T aluminum alloy when subjected to static, impact, and repeated loads. Results are presented from static-load test of unnotched specimens in tension and in torsion and of notched specimens in tension. Charpy impact values obtained from bend tests on notched specimens and tension impact values for both notched and unnotched specimens tested at several different temperatures are included. The endurance limits obtained from repeated bending fatigue tests made on three different types of testing machine are given for unnotched polished specimens, and the endurance limits of notched specimens subjected to six different ranges of bending stress are also reported. The results indicated that: (a) polished rectangular specimens had an endurance limit about 30 percent less than that obtained for round specimens; (b) a comparison of endurance limits obtained from tests on three different types of machine indicated that there was no apparent effect of speed of testing on the endurance limit for the range of speeds used (1,750 to 13,000 rpm). (c) the fatigue strength (endurance limit) of the X76S-T alloy was greatly decreased by the presence of a notch in the specimens; (d) no complete fractures of the entire specimens occurred in notched fatigue specimens when subjected to stress cycles for which the mean stress at the notch during the cycle was a compressive stress; for this test condition a microscopic cracking occurred near the root of the notch and was used as a criterion of failure of the specimen. (e) as the mean stress at the notch was decreased from a tensile (+) stress to a compressive (-) stress, it was found that the alternating stress that could be superimposed on the mean stress in the cycle without causing failure of the specimens was increased.

Super-elastic and fatigue resistant carbon material with lamellar multi-arch microstructure

NASA Astrophysics Data System (ADS)

Gao, Huai-Ling; Zhu, Yin-Bo; Mao, Li-Bo; Wang, Feng-Chao; Luo, Xi-Sheng; Liu, Yang-Yi; Lu, Yang; Pan, Zhao; Ge, Jin; Shen, Wei; Zheng, Ya-Rong; Xu, Liang; Wang, Lin-Jun; Xu, Wei-Hong; Wu, Heng-An; Yu, Shu-Hong

2016-09-01

Low-density compressible materials enable various applications but are often hindered by structure-derived fatigue failure, weak elasticity with slow recovery speed and large energy dissipation. Here we demonstrate a carbon material with microstructure-derived super-elasticity and high fatigue resistance achieved by designing a hierarchical lamellar architecture composed of thousands of microscale arches that serve as elastic units. The obtained monolithic carbon material can rebound a steel ball in spring-like fashion with fast recovery speed (~580 mm s-1), and demonstrates complete recovery and small energy dissipation (~0.2) in each compress-release cycle, even under 90% strain. Particularly, the material can maintain structural integrity after more than 106 cycles at 20% strain and 2.5 × 105 cycles at 50% strain. This structural material, although constructed using an intrinsically brittle carbon constituent, is simultaneously super-elastic, highly compressible and fatigue resistant to a degree even greater than that of previously reported compressible foams mainly made from more robust constituents.

Muscle Performance Investigated With a Novel Smart Compression Garment Based on Pressure Sensor Force Myography and Its Validation Against EMG.

PubMed

Belbasis, Aaron; Fuss, Franz Konstantin

2018-01-01

Muscle activity and fatigue performance parameters were obtained and compared between both a smart compression garment and the gold-standard, a surface electromyography (EMG) system during high-speed cycling in seven participants. The smart compression garment, based on force myography (FMG), comprised of integrated pressure sensors that were sandwiched between skin and garment, located on five thigh muscles. The muscle activity was assessed by means of crank cycle diagrams (polar plots) that displayed the muscle activity relative to the crank cycle. The fatigue was assessed by means of the median frequency of the power spectrum of the EMG signal; the fractal dimension (FD) of the EMG signal; and the FD of the pressure signal. The smart compression garment returned performance parameters (muscle activity and fatigue) comparable to the surface EMG. The major differences were that the EMG measured the electrical activity, whereas the pressure sensor measured the mechanical activity. As such, there was a phase shift between electrical and mechanical signals, with the electrical signals preceding the mechanical counterparts in most cases. This is specifically pronounced in high-speed cycling. The fatigue trend over the duration of the cycling exercise was clearly reflected in the fatigue parameters (FDs and median frequency) obtained from pressure and EMG signals. The fatigue parameter of the pressure signal (FD) showed a higher time dependency ( R 2 = 0.84) compared to the EMG signal. This reflects that the pressure signal puts more emphasis on the fatigue as a function of time rather than on the origin of fatigue (e.g., peripheral or central fatigue). In light of the high-speed activity results, caution should be exerted when using data obtained from EMG for biomechanical models. In contrast to EMG data, activity data obtained from FMG are considered more appropriate and accurate as an input for biomechanical modeling as they truly reflect the mechanical muscle activity. In summary, the smart compression garment based on FMG is a valid alternative to EMG-garments and provides more accurate results at high-speed activity (avoiding the electro-mechanical delay), as well as clearly measures the progress of muscle fatigue over time.

Muscle Performance Investigated With a Novel Smart Compression Garment Based on Pressure Sensor Force Myography and Its Validation Against EMG

PubMed Central

Belbasis, Aaron; Fuss, Franz Konstantin

2018-01-01

Muscle activity and fatigue performance parameters were obtained and compared between both a smart compression garment and the gold-standard, a surface electromyography (EMG) system during high-speed cycling in seven participants. The smart compression garment, based on force myography (FMG), comprised of integrated pressure sensors that were sandwiched between skin and garment, located on five thigh muscles. The muscle activity was assessed by means of crank cycle diagrams (polar plots) that displayed the muscle activity relative to the crank cycle. The fatigue was assessed by means of the median frequency of the power spectrum of the EMG signal; the fractal dimension (FD) of the EMG signal; and the FD of the pressure signal. The smart compression garment returned performance parameters (muscle activity and fatigue) comparable to the surface EMG. The major differences were that the EMG measured the electrical activity, whereas the pressure sensor measured the mechanical activity. As such, there was a phase shift between electrical and mechanical signals, with the electrical signals preceding the mechanical counterparts in most cases. This is specifically pronounced in high-speed cycling. The fatigue trend over the duration of the cycling exercise was clearly reflected in the fatigue parameters (FDs and median frequency) obtained from pressure and EMG signals. The fatigue parameter of the pressure signal (FD) showed a higher time dependency (R2 = 0.84) compared to the EMG signal. This reflects that the pressure signal puts more emphasis on the fatigue as a function of time rather than on the origin of fatigue (e.g., peripheral or central fatigue). In light of the high-speed activity results, caution should be exerted when using data obtained from EMG for biomechanical models. In contrast to EMG data, activity data obtained from FMG are considered more appropriate and accurate as an input for biomechanical modeling as they truly reflect the mechanical muscle activity. In summary, the smart compression garment based on FMG is a valid alternative to EMG-garments and provides more accurate results at high-speed activity (avoiding the electro-mechanical delay), as well as clearly measures the progress of muscle fatigue over time. PMID:29725306

Influence of residual welding stresses, overload and specimen preparation on fatigue crack growth under axial compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greasley, A.

1995-02-01

Double edge notched axial compression specimens taken from thick welded steel joints have been used to grow fatigue cracks under pulsating compressive loads at mean stresses up to 55% of that needed for general yielding. The redistribution of residual stresses during specimen preparation and during crack growth influences the nucleation, growth rate and extent of fatigue cracks. Crack growth rates which are comparable to the equivalent tensile situation have been observed in as-welded, welded plus overloaded and stress relieved plus overloaded joints. Multiple nucleation and curved crack profiles have been observed in all cases. 5 refs.

Fatigue Life of Postbuckled Structures with Indentation Damages

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Bisagni, Chiara

2016-01-01

The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of each stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 32 millimeters to 56 millimeters were tested quasi-statically and in fatigue, and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

Effects of Cyclic Loading on the Deformation and Elastic-Plastic Fracture Behavior of a Cast Stainless Steel

DTIC Science & Technology

1991-10-01

23 8. High Cycle Fatigue Crack Growth Data for Cast Stainless Steel Showing Comparison with Rolfe and Barsom Fit .......... 24 9. Cyclic Load...compared to the Rolfe /Barsom4 fatigue crack propagation equation for austenitic stainless steels in Fig. 8. ELASTIC-PLASTIC Cyclic J-testing was...place during both the compression and tensile loadings. The J-integral was calculated on each cycle using the Merkle -Corten 9 J equation as modified by

Analysis of SNL/MSU/DOE Fatigue Database Trends for Wind Turbine Blade Materials 2010-2015.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandell, John F.; Samborsky, Daniel D.; Miller, David A.

Wind turbine blades are designed to several major structural conditions, including tip deflection, strength and b uckling during severe loading, as well as very high numbers of fatigue cycles and various service environments. The MSU Database Program has, since 1989, addressed the broad range of properties needed for current and potential blade materials through stati c and fatigue testing and test development in cooperation with Sandia National Laboratories and wind industry and supplier partners. This report is the latest in a series, giving test results and analysis for the period 2010 - 2015. Program data are compiled in a publicmore » database [1] and other reports and publications given in the cited references. The report begins with an executive summary and introductory material including background discussion of previous related studies. Section 3 describes experimental methods including processing, test methods, instrumentation and test development. Section 4 provides static tension, compression and shear stress - strain properties in three directions using coupons sectioned from a thick infused unidirectional glass/epoxy laminate. The nonlinear, shear dominated static properties were characterized with loading - u nloading - reloading (LUR) tests in tension and compression to increasing load levels, for +-45O laminates. Section 5 explores the origins of tensile fatigue sensitivity in glass fiber dominated laminates with variations in fabric architecture including speci ally prepared fabrics and aligned strand laminates. Several types of resins are considered, with variations in resin toughness and bonding to fibers, as well as cure cycle variations for an epoxy. Conclusions are drawn as to the limits of tensile fatigue r esistance and the effects of resin type and fabric architecture, including the behavior of a commercial aligned glass strand product. Interactions between cyclic fatigue response and creep are addressed for off - axis (+-45O) glass/epoxy laminates in Sectio n 6. The nonlinear fatigue and creep stress - strain and cumulative strain response are characterized in tension and compression as a function of stress level, cycles and cumulative time, using square and sinewave loading over a broad range of frequency. The results are analyzed in terms of the cycles and cumulative time under load. A cumulative strain failure criterion is established, and used to construct shear and tension constant life diagrams (CLD's) with data for nine R - values. The effects of a more duc tile urethne resin are also explored. A previous study of thick adhesives testing is extended to mixed mode fracture mechanics testing in Section 7. Mechanisms of static and fatigue crack extension near the laminate adherend interface are reported in deta il. Data are presented for mixed mode adhesive fracture, compared to mixed mode fracture in ply delamination. Fatigue crack growth exponents are also developed for a mixed mode cracked lap shear coupon. The data for fatigue trends and relative failure stra ins and exponents are compared for various blade component materials in Section 8. The effects of temperature and seawater saturation are considered for selected materials of interest for wind and hydrokinetic turbine blades in Section 9. Section 10 gives detailed conclusions for each section. A cknowledgements The research presented in this report was carried out under Sandia National Laboratories purchase orders 1325028 an d 1543945 between 2010 and 2015, with support from the DOE Wind and Water Technologies Office . In addition to the authors listed, significant contributions were made by Patrick Flaherty, Pancastya Agastra, Michael Schuster, and Michael Voth. Industry m aterials suppliers include Vectorply, Saertex, OCV, AGY, Bayer, Ashland, 3M and Nextel. Industry suppliers with significant contributions to the study were Hexion, PPG, Reichhold, Gurit and NEPTCO. Intentionally Left Blank« less

Effect of moisture on the fatigue behavior of graphite/epoxy composite laminates

NASA Technical Reports Server (NTRS)

Ramani, S. V.; Nelson, H. G.

1979-01-01

The form of the moisture distribution in the specimen (gradient and flat profile) was considered to establish the influence of accelerated moisture conditioning on fatigue behavior. For the gradient specimens having an average moisture content of 1.4 percent, fatigue life was reduced by a factor of 8 at all stress levels investigated. Corresponding reduction in fatigue life for the flat moisture profile specimens at the same average moisture content was comparatively smaller, being about a factor of 5 from the value in dry specimens. X-ray radiographic analysis of damage accumulation in compression-compression fatigue revealed interlaminar cracking to be the dominant mode of failure responsible for the observed enhanced cyclic degradation of moisture-conditioned specimens. This finding was corroborated by the observed systematic reduction in interlaminar shear strength as a function of moisture content, which, in turn, increased the propensity for delamination under cyclic compressive loads. Residual strength measurements on cycled specimens indicated significant strength reductions at long lives, particularly in moisture conditioned specimens.

Microstructure-sensitive plasticity and fatigue modeling of extruded 6061 aluminum alloys

NASA Astrophysics Data System (ADS)

McCullough, Robert Ross

In this study, the development of fatigue failure and stress anisotropy in light weight ductile metal alloys, specifically Al-Mg-Si aluminum alloys, was investigated. The experiments were carried out on an extruded 6061 aluminum alloy. Reverse loading experiments were performed up to a prestrain of 5% in both tension-followed-by-compression and compression-followed-by-tension. The development of isotropic and kinematic hardening and subsequent anisotropy was indicated by the observation of the Bauschinger effect phenomenon. Experimental results show that 6061 aluminum alloy exhibited a slight increase in the kinematic hardening versus applied prestrain. However, the ratio of kinematic-to-isotropic hardening remained near unity. An internal state variable (ISV) plasticity and damage model was used to capture the evolution of the anisotropy for the as-received T6 and partially annealed conditions. Following the stress anisotropy experiments, the same extruded 6061 aluminum alloy was tested under fully reversing, strain-controlled low cycle fatigue at up to 2.5% strain amplitudes and two heat treatment conditions. Observations were made of the development of striation fields up to the point of nucleation at cracked and clustered precipitants and free surfaces through localized precipitant slip band development. A finite element enabled micro-mechanics study of fatigue damage development of local strain field in the presence of hard phases was conducted. Both the FEA and experimental data sets were utilized in the implementation of a multi-stage fatigue model in order to predict the microstructure response, including fatigue nucleation and propagation contributions on the total fatigue life in AA6061. Good correlation between experimental and predicted results in the number of cycles to final failure was observed. The AA6061 material maintained relatively consistent low cycle fatigue performance despite two different heat treatments.

Neuromuscular fatigue and tibiofemoral joint biomechanics when transitioning from non-weight bearing to weight bearing.

PubMed

Schmitz, Randy J; Kim, Hyunsoo; Shultz, Sandra J

2015-01-01

Fatigue is suggested to be a risk factor for anterior cruciate ligament injury. Fatiguing exercise can affect neuromuscular control and laxity of the knee joint, which may render the knee less able to resist externally applied loads. Few authors have examined the effects of fatiguing exercise on knee biomechanics during the in vivo transition of the knee from non-weight bearing to weight bearing, the time when anterior cruciate ligament injury likely occurs. To investigate the effect of fatiguing exercise on tibiofemoral joint biomechanics during the transition from non-weight bearing to early weight bearing. Cross-sectional study. Research laboratory. Ten participants (5 men and 5 women; age = 25.3 ± 4.0 years) with no previous history of knee-ligament injury to the dominant leg. Participants were tested before (preexercise) and after (postexercise) a protocol consisting of repeated leg presses (15 repetitions from 10°-40° of knee flexion, 10 seconds' rest) against a 60% body-weight load until they were unable to complete a full bout of repetitions. Electromagnetic sensors measured anterior tibial translation and knee-flexion excursion during the application of a 40% body-weight axial compressive load to the bottom of the foot, simulating weight acceptance. A force transducer recorded axial compressive force. The axial compressive force (351.8 ± 44.3 N versus 374.0 ± 47.9 N; P = .018), knee-flexion excursion (8.0° ± 4.0° versus 10.2° ± 3.7°; P = .046), and anterior tibial translation (6.7 ± 1.7 mm versus 8.2 ± 1.9 mm; P < .001) increased from preexercise to postexercise. No significant correlations were noted. Neuromuscular fatigue may impair initial knee-joint stabilization during weight acceptance, leading to greater accessory motion at the knee and the potential for greater anterior cruciate ligament loading.

National Transonic Facility Fan Blade prepreg material characterization tests

NASA Technical Reports Server (NTRS)

Klich, P. J.; Richards, W. H.; Ahl, E. L., Jr.

1981-01-01

The test program for the basic prepreg materials used in process development work and planned fabrication of the national transonic facility fan blade is presented. The basic prepreg materials and the design laminate are characterized at 89 K, room temperature, and 366 K. Characterization tests, test equipment, and test data are discussed. Material tests results in the warp direction are given for tensile, compressive, fatigue (tension-tension), interlaminar shear and thermal expansion.

Research on fatigue cracking growth parameters in asphaltic mixtures using computed tomography

NASA Astrophysics Data System (ADS)

Braz, D.; Lopes, R. T.; Motta, L. M. G.

2004-01-01

Distress of asphalt concrete pavement due to repeated bending from traffic loads has been a well-recognized problem in Brazil. If it is assumed that fatigue cracking growth is governed by the conditions at the crack tip, and that the crack tip conditions can be characterized by the stress intensity factor, then fatigue cracking growth as a function of stress intensity range Δ K can be determined. Computed tomography technique is used to detect crack evolution in asphaltic mixtures which were submitted to fatigue tests. Fatigue tests under conditions of controlled stress were carried out using diametral compression equipment and repeat loading. The aim of this work is imaging several specimens at different stages of the fatigue tests. In preliminary studies it was noted that the trajectory of a crack was influenced by the existence of voids in the originally unloaded specimens. Cracks would first be observed in the central region of a specimen, propagating in the direction of the extremities. Analyzing the graphics, that represent the fatigue cracking growth (d c/d N) as a function of stress intensity factor (Δ K), it is noticed that the curve has practically shown the same behavior for all specimens at the same level of the static tension rupture stress. The experimental values obtained for the constants A and n (of the Paris-Erdogan Law) present good agreement with the results obtained by Liang and Zhou.

The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.; Matthews, W. T.; Prabhakaran, R.; Newman, J. C., Jr.; Dubberly, M. J.

2001-01-01

Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

Thermal-Fatigue Crack-Growth Characteristics and Mechanical Strain Cycling Behavior of A-286 Discaloy, and 16-25-6 Austenitic Steels

NASA Technical Reports Server (NTRS)

Smith, Robert W.; Smith, Gordon T.

1960-01-01

Thermal-fatigue crack-growth characteristics of notched- and unnotched-disk specimens of A-286, Discaloy, hot-cold worked 16-25-6, and overaged 16-25-6 were experimentally studied. Separately controlled variables were total strain range (0.0043 to 0.0079 in./in.), maximum cycle temperature (1300 and 1100 F), and hold time at maximum temperature (O and 5 min). A limited number of mechanical, push-pull, constant-strain cycle tests at room temperature were made using notched and un-notched bars of the same materials. In these tests the number of cycles to failure as well as the variation of load change with accumulated cycles was measured, and the effects of mean stress were observed. Constant-strain-range mechanical-fatigue tests at room temperature revealed notched-bar fatigue life to be strongly influenced by mean stress. For a specific strain range, the longest fatigue life was always found to be associated with the least-tensile (or most compressive) mean stress. By defining thermal-fatigue life as the number of cycles required to produce a crack area of 6000 square mils, the relative thermal-fatigue resistances of the test materials were established. Notched-disk specimens of A-286 and Discaloy steels exhibited longer fatigue lives than either hot-cold worked or overaged 16-25-6. On the other hand, unnotched-disk specimens of Discaloy and hot-cold worked 16-25-6 had longer lives than A-286 and overaged 16-25-6. Separation of the crack-growth data into microstage and macrostage periods revealed that the macrostage period accounted for the greatest part of the difference among materials when tested in the notched configuration, while the microstage was largely responsible for the differences encountered in unnotched disks.

Evolution of Residual-Strain Distribution through an Overload-Induced Retardation Period during Fatigue Crack Growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, S. Y.; Sun, Yinan; An, Ke

2010-01-01

Neutron diffraction was employed to investigate the crack-growth retardation phenomenon after a single tensile overload by mapping both one-dimensional and two-dimensional residual-strain distributions around the crack tip in a series of compact-tension specimens representing various crack-growth stages through an overload-induced retardation period. The results clearly show a large compressive residual-strain field near the crack tip immediately after the overload. As the fatigue crack propagates through the overload-induced plastic zone, the compressive residual strains are gradually relaxed, and a new compressive residual-strain field is developed around the propagating crack tip, illustrating that the subsequent fatigue-induced plastic zone grows out of themore » large plastic zone caused by the overloading. The relationship between the overload-induced plastic zone and subsequent fatigue-induced plastic zone, and its influence on the residual-strain distributions in the perturbed plastic zone are discussed.« less

Retention of Compressive Residual Stresses Introduced by Shot Peening in a Powder Metal Disk Superalloy

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Danetti, Andrew; Draper, Susan L.; Locci, Ivan E.; Telesman, Jack

2016-01-01

The fatigue lives of disk superalloys can be increased by shot peening their surfaces, to induce compressive residual stresses near the surface that impede cracking there. As disk application temperatures increase for improved efficiency, the persistence of these beneficial stresses could be impaired, especially with continued fatigue cycling. The objective of this work was to study the retention of residual stresses introduced by shot peening, when subjected to fatigue and high temperatures. Fatigue specimens of powder metallurgy processed nickel-base disk superalloy ME3 were prepared with consistent processing and heat treatment. They were then shot peened using varied conditions. Strain-controlled fatigue cycles were run at room temperature and 704 C, to allow re-assessment of residual stresses.

Gear crack propagation investigations

NASA Technical Reports Server (NTRS)

Lewicki, David G.; Ballarini, Roberto

1996-01-01

Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.

Effects of Accumulating Work Shifts on Performance-Based Fatigue Using Multiple Strength Measurements in Day and Night Shift Nurses and Aides.

PubMed

Thompson, Brennan J; Stock, Matt S; Banuelas, Victoria K

2017-05-01

Objective This study aimed to examine the effects of accumulating nursing work on maximal and rapid strength characteristics in female nurses and compare these effects in day versus night shift workers. Background Nurses exhibit among the highest nonfatal injury rates of all occupations, which may be a consequence of long, cumulative work shift schedules. Fatigue may accumulate across multiple shifts and lead to performance impairments, which in turn may be linked to injury risks. Method Thirty-seven nurses and aides performed isometric strength-based performance testing of three muscle groups, including the knee extensors, knee flexors, and wrist flexors (hand grip), as well as countermovement jumps, at baseline and following exposure to three 12-hour work shifts in a four-day period. Variables included peak torque (PT) and rate of torque development (RTD) from isometric strength testing and jump height and power output. Results The rigorous work period resulted in significant decreases (-7.2% to -19.2%) in a large majority (8/9) of the isometric strength-based measurements. No differences were noted for the day versus night shift workers except for the RTD at 200 millisecond variable, for which the night shift had greater work-induced decreases than the day shift workers. No changes were observed for jump height or power output. Conclusions A compressed nursing work schedule resulted in decreases in strength-based performance abilities, being indicative of performance fatigue. Application Compressed work schedules involving long shifts lead to functional declines in nurse performance capacities that may pose risks for both the nurse and patient quality of care. Fatigue management plans are needed to monitor and regulate increased levels of fatigue.

Real Time Fatigue Damage Growth Assessment of a Composite Three-Stringer Panel Using Passive Thermography

NASA Technical Reports Server (NTRS)

Zalameda, Joseph N.; Burke, Eric R.; Horne, Michael R.; Bly, James B.

2015-01-01

Fatigue testing of advanced composite structures is critical to validate both structural designs and damage prediction models. In-situ inspection methods are necessary to track damage onset and growth as a function of load cycles. Passive thermography is a large area, noncontact inspection technique that is used to detect composite damage onset and growth in real time as a function of fatigue cycles. The thermal images are acquired in synchronicity to the applied compressive load using a dual infrared camera acquisition system for full (front and back) coverage. Image processing algorithms are investigated to increase defect contrast areas. The thermal results are compared to non-immersion ultrasound inspections and acoustic emission data.

An in vitro biomechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: an axial positioned dynamic compression plate and two abaxial transarticular cortical screws inserted in lag fashion versus three parallel transarticular cortical screws inserted in lag fashion.

PubMed

Sod, Gary A; Riggs, Laura M; Mitchell, Colin F; Hubert, Jeremy D; Martin, George S

2010-01-01

To compare in vitro monotonic biomechanical properties of an axial 3-hole, 4.5 mm narrow dynamic compression plate (DCP) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion (DCP-TLS) with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion (3-TLS) for the equine proximal interphalangeal (PIP) joint arthrodesis. Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Cadaveric adult equine forelimbs (n=15 pairs). For each forelimb pair, 1 PIP joint was stabilized with an axial 3-hole narrow DCP (4.5 mm) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion and 1 with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion. Five matching pairs of constructs were tested in single cycle to failure under axial compression, 5 construct pairs were tested for cyclic fatigue under axial compression, and 5 construct pairs were tested in single cycle to failure under torsional loading. Mean values for each fixation method were compared using a paired t-test within each group with statistical significance set at P<.05. Mean yield load, yield stiffness, and failure load under axial compression and torsion, single cycle to failure, of the DCP-TLS fixation were significantly greater than those of the 3-TLS fixation. Mean cycles to failure in axial compression of the DCP-TLS fixation was significantly greater than that of the 3-TLS fixation. The DCP-TLS was superior to the 3-TLS in resisting the static overload forces and in resisting cyclic fatigue. The results of this in vitro study may provide information to aid in the selection of a treatment modality for arthrodesis of the equine PIP joint.

Prestraining and Its Influence on Subsequent Fatigue Life

NASA Technical Reports Server (NTRS)

Halford, Gary R.; Mcgaw, Michael A.; Kalluri, Sreeramesh

1995-01-01

An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully-reversed strain-control. Additional specimens were prestrained to 2 percent, 5 percent, and 10 percent (engineering strains) in the tensile direction and to 2 percent (engineering strain) in the compressive direction under stroke-control, and were subsequently fatigued to failure under fully-reversed strain-control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the Linear Damage Rule; (2) the Linear Strain and Life Fraction Rule; and (3) the nonlinear Damage Curve Approach. The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, best remaining fatigue life predictions were obtained with the nonlinear Damage Curve Approach.

Evaluation of an injectable hydrogel and polymethyl methacrylate in restoring mechanics to compressively fractured spine motion segments.

PubMed

Balkovec, Christian; Vernengo, Andrea J; Stevenson, Peter; McGill, Stuart M

2016-11-01

Compressive fracture can produce profound changes to the mechanical profile of a spine segment. Minimally invasive repair has the potential to restore both function and structural integrity to an injured spine. Use of both hydrogels to address changes to the disc, combined with polymethyl methacrylate (PMMA) to address changes to the vertebral body, has the potential to facilitate repair. The purpose of this investigation was to determine if the combined use of hydrogel injection and PMMA could restore the mechanical profile of an axially injured spinal motion segment. This is a basic science study evaluating a combination of hydrogel injection and vertebroplasty on restoring mechanics to compressively injured porcine spine motion segments. Fourteen porcine spine motion segments were subject to axial compression until fracture using a dynamic servohydraulic testing apparatus. Rotational and compressive stiffness was measured for each specimen under the following conditions: initial undamaged, fractured, fatigue loading under compression, hydrogel injection, PMMA injection, and fatigue loading under compression. Group 1 received hydrogel injection followed by PMMA injection, whereas Group 2 received PMMA injection followed by hydrogel injection. This study was funded under a Natural Sciences and Engineering Research Council of Canada discovery grant. PMMA injection was found to alter the compressive stiffness properties of axially injured spine motion segments, restoring values from Groups 1 and 2 to 89.3%±29.3% and 81%±27.9% of initial values respectively. Hydrogel injection was found to alter the rotational stiffness properties, restoring specimens in Groups 1 and 2 to 151.5%±81% and 177.2%±54.9% of initial values respectively. Prolonged restoration of function was not possible, however, after further fatigue loading. Using this repair technique, replication of the mechanism of injury appears to cause a rapid deterioration in function of the motion segments. Containment of the hydrogel appears to be an issue with large breaches in the end plate, as it is posited to migrate into the cancellous bone of the vertebral body. Future work should attempt to evaluate methods in fully sealing the disc space. Copyright © 2016 Elsevier Inc. All rights reserved.

Boron/aluminum skins for the DC-10 aft pylon

NASA Technical Reports Server (NTRS)

Elliott, S. Y.

1975-01-01

Boron/aluminum pylon boat tail skins were designed and fabricated and installed on the DC-10 aircraft for a 5-year flight service demonstration test. Inspection and tests of the exposed skins will establish the ability of the boron/aluminum composite to withstand long time flight service conditions, which include exposure to high temperatures, sonic fatigue, and flutter. The results of a preliminary testing program yield room temperature and elevated temperature data on the tension, compression, in-plane shear, interlaminar shear, bolt bearing, and tension fatigue properties of the boron/aluminum laminates. Present technology was used in the fabrication of the skins. Although maximum weight saving was not sought, weight of the constant thickness boron/aluminum skin is 26% less than the chemically milled titanium skin.

Improving the fatigue performance of porous metallic biomaterials produced by Selective Laser Melting.

PubMed

Van Hooreweder, Brecht; Apers, Yanni; Lietaert, Karel; Kruth, Jean-Pierre

2017-01-01

This paper provides new insights into the fatigue properties of porous metallic biomaterials produced by additive manufacturing. Cylindrical porous samples with diamond unit cells were produced from Ti6Al4V powder using Selective Laser Melting (SLM). After measuring all morphological and quasi-static properties, compression-compression fatigue tests were performed to determine fatigue strength and to identify important fatigue influencing factors. In a next step, post-SLM treatments were used to improve the fatigue life of these biomaterials by changing the microstructure and by reducing stress concentrators and surface roughness. In particular, the influence of stress relieving, hot isostatic pressing and chemical etching was studied. Analytical and numerical techniques were developed to calculate the maximum local tensile stress in the struts as function of the strut diameter and load. With this method, the variability in the relative density between all samples was taken into account. The local stress in the struts was then used to quantify the exact influence of the applied post-SLM treatments on the fatigue life. A significant improvement of the fatigue life was achieved. Also, the post-SLM treatments, procedures and calculation methods can be applied to different types of porous metallic structures and hence this paper provides useful tools for improving fatigue performance of metallic biomaterials. Additive Manufacturing (AM) techniques such as Selective Laser Melting (SLM) are increasingly being used for producing customized porous metallic biomaterials. These biomaterials are regularly used for biomedical implants and hence a long lifetime is required. In this paper, a set of post-built surface and heat treatments is presented that can be used to significantly improve the fatigue life of porous SLM-Ti6Al4V samples. In addition, a novel and efficient analytical local stress method was developed to accurately quantify the influence of the post-built treatments on the fatigue life. Also numerical simulation techniques were used for validation. The developed methods and techniques can be applied to other types of porous biomaterials and hence provide new and useful tools for improving and predicting the fatigue life of porous biomaterials. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Mechanical Testing of IN718 Lattice Block Structures

NASA Technical Reports Server (NTRS)

Krause, David L.; Whittenberger, John D.; Kantzos, Pete T.; Hebsur, Mohan G.

2002-01-01

Lattice block construction produces a flat, structurally rigid panel composed of thin ligaments of material arranged in a three-dimensional triangulated truss-like structure. Low-cost methods of producing cast metallic lattice block panels are now available that greatly expand opportunities for using this unique material system in today's high-performance structures. Additional advances are being made in NASA's Ultra Efficient Engine Technology (UEET) program to extend the lattice block concept to superalloy materials. Advantages offered by this combination include high strength, light weight, high stiffness, and elevated temperature capabilities. Recently under UEET, the nickel-based superalloy Inconel 718 (IN718) was investment cast into lattice block panels with great success. To evaluate casting quality and lattice block architecture merit, individual ligaments, and structural subelement specimens were extracted from the panels. Tensile tests, structural compression, and bending strength tests were performed on these specimens. Fatigue testing was also completed for several bend test specimens. This paper first presents metallurgical and optical microscopy analysis of the castings. This is followed by mechanical test results for the tensile ligament tests and the subelement compression and bending strength tests, as well as for the fatigue tests that were performed. These tests generally showed comparable properties to base IN718 with the same heat treatment, and they underscored the benefits offered by lattice block materials. These benefits might be extended with improved architecture such as face sheets.

The specific effect of metronome guidance on the quality of one-person cardiopulmonary resuscitation and rescuer fatigue.

PubMed

Chung, Tae Nyoung; Kim, Sun Wook; You, Je Sung; Cho, Young Soon; Chung, Sung Phil; Park, Incheol; Kim, Seung Ho

2012-12-01

Metronome guidance is a simple and economic feedback method of guiding cardiopulmonary resuscitation (CPR). It has been proven for its usefulness in regulating the rate of chest compression and ventilation, but it is not yet clear how metronome use may affect compression depth or rescuer fatigue. The aim of this study was to assess the specific effect that metronome guidance has on the quality of CPR and rescuer fatigue. One-person CPRs were performed by senior medical students on Resusci Anne® manikins (Laerdal, Stavanger, Norway) with personal-computer skill-reporting systems. Half of the students performed CPR with metronome guidance and the other half without. CPR performance data, duration, and before-after trial differences in mean arterial pressure (MAP) and heart rate (HR) were compared between groups. Average compression depth (ACD) of the first five cycles, compression rate, no-flow fraction, and ventilation count were significantly lower in the metronome group (p=0.028, < 0.001, 0.001, and 0.041, respectively). Total CPR duration, total work (ACD × total compression count), and the before-after trial differences of the MAP and HR did not differ between the two groups. Metronome guidance is associated with lower chest compression depth of the first five cycles, while shortening the no-flow fraction and the ventilation count in a simulated one-person CPR model. Metronome guidance does not have an obvious effect of intensifying rescuer fatigue. Copyright © 2012 Elsevier Inc. All rights reserved.

Study of the influence of hole quality on composite materials

NASA Technical Reports Server (NTRS)

Pengra, J. J.

1980-01-01

The influence of hole quality on the structural behavior of composite materials was investigated. From an industry survey it was determined that the most frequent imperfections encountered during hole fabrication are chipout, delamination, and oversize conditions. These hole flaw types were generated in critical areas of static, compression, and fatigue specimens fabricated from T300/5208 graphite/epoxy system. The specimens were tested in static and cyclic pin bearing modes in addition to compression loading. Results of these tests are presented and discussed. The hole chipout defect reduced the static and cyclic endurance characteristics. Oversize holes also lowered the cyclic pin bearing endurance, but had no influence of the static pin bearing characteristics. Delamination had no insignificant influence on the static tension and cyclic pin bearing characteristics. Compression tests demonstrated a deleterious effect for chipout of delamination defects. Hole quality requirements proposed are discussed.

Effect of 3 Weeks Use of Compression Garments on Stride and Impact Shock during a Fatiguing Run.

PubMed

Lucas-Cuevas, A G; Priego-Quesada, J I; Aparicio, I; Giménez, J V; Llana-Belloch, S; Pérez-Soriano, P

2015-10-01

Excessive and prolonged exposure to impact acceleration during running is associated with increased injury rate. Acute use of compressive garments has been speculated to improve attenuation. However, it is unknown how longer interventions of compressive garments influence attenuation in running. 40 runners trained with compressive and placebo stockings for 3 weeks. Perception of comfort, stride parameters (rate, length) and impact acceleration (head and tibial peak acceleration, magnitude, acceleration rate and attenuation) were measured every 5 min during a fatigue run (30 min at 80% of the individual's maximal aerobic speed). Compressive stockings reduced tibial peak acceleration and magnitude compared to placebo stockings at every minute (p<0.05) except for the initial measurement (p>0.05). Moreover, compressive stockings led to a lower rate of increase in tibial peak acceleration (14%, p<0.005) and magnitude (16%, p<0.001) as a result of the development of fatigue compared to placebo stockings (24% and 26% increase, p=0.014 and p=0.003, respectively). Similar perception of comfort was reported for both garments. Training with compressive stockings for 3 weeks reduced impact acceleration and the rate of increase in acceleration compared to placebo stockings. These findings suggest that compressive stockings may play a protective role by reducing impact accelerations during running. © Georg Thieme Verlag KG Stuttgart · New York.

Fracture toughness of SiC/Al metal matrix composite

NASA Technical Reports Server (NTRS)

Flom, Yury; Parker, B. H.; Chu, H. P.

1989-01-01

An experimental study was conducted to evaluate fracture toughness of SiC/Al metal matrix composite (MMC). The material was a 12.7 mm thick extrusion of 6061-T6 aluminum alloy with 40 v/o SiC particulates. Specimen configuration and test procedure conformed to ASTM E399 Standard for compact specimens. It was found that special procedures were necessary to obtain fatigue cracks of controlled lengths in the preparation of precracked specimens for the MMC material. Fatigue loading with both minimum and maximum loads in compression was used to start the precrack. The initial precracking would stop by self-arrest. Afterwards, the precrack could be safely extended to the desired length by additional cyclic tensile loading. Test results met practically all the E399 criteria for the calculation of plane strain fracture toughness of the material. A valid K sub IC value of the SiC/Al composite was established as K sub IC = 8.9 MPa square root of m. The threshold stress intensity under which crack would cease to grow in the material was estimated as delta K sub th = 2MPa square root of m for R = 0.09 using the fatigue precracking data. Fractographic examinations show that failure occurred by the micromechanism involved with plastic deformation although the specimens broke by brittle fracture. The effect of precracking by cyclic loading in compression on fracture toughness is included in the discussion.

A Muscle Fibre Conduction Velocity Tracking ASIC for Local Fatigue Monitoring.

PubMed

Koutsos, Ermis; Cretu, Vlad; Georgiou, Pantelis

2016-12-01

Electromyography analysis can provide information about a muscle's fatigue state by estimating Muscle Fibre Conduction Velocity (MFCV), a measure of the travelling speed of Motor Unit Action Potentials (MUAPs) in muscle tissue. MFCV better represents the physical manifestations of muscle fatigue, compared to the progressive compression of the myoelectic Power Spectral Density, hence it is more suitable for a muscle fatigue tracking system. This paper presents a novel algorithm for the estimation of MFCV using single threshold bit-stream conversion and a dedicated application-specified integrated circuit (ASIC) for its implementation, suitable for a compact, wearable and easy to use muscle fatigue monitor. The presented ASIC is implemented in a commercially available AMS 0.35 [Formula: see text] CMOS technology and utilizes a bit-stream cross-correlator that estimates the conduction velocity of the myoelectric signal in real time. A test group of 20 subjects was used to evaluate the performance of the developed ASIC, achieving good accuracy with an error of only 3.2% compared to Matlab.

Low-cycle fatigue of Type 347 stainless steel and Hastelloy alloy X in hydrogen gas and in air at elevated temperatures

NASA Technical Reports Server (NTRS)

Jaske, C. E.; Rice, R. C.; Buchheit, R. D.; Roach, D. B.; Porfilio, T. L.

1976-01-01

An investigation was conducted to assess the low-cycle fatigue resistance of two alloys, Type 347 stainless steel and Hastelloy Alloy X, that were under consideration for use in nuclear-powered rocket vehicles. Constant-amplitude, strain-controlled fatigue tests were conducted under compressive strain cycling at a constant strain rate of 0.001/sec and at total axial strain ranges of 1.5, 3.0, and 5.0 %, in both laboratory-air and low-pressure hydrogen-gas environments at temperatures from 538 to 871 C. Specimens were obtained from three heats of Type 347 stainless steel bar and two heats of Hastelloy Alloy X. The tensile properties of each heat were determined at 21, 538, 649, and 760 C. The continuous cycling fatigue resistance was determined for each heat at temperatures of 538, 760, and 871 C. The Type 347 stainless steel exhibited equal or superior fatigue resistance to the Hastelloy Alloy X at all conditions of this study.

Influence of mean stress on fatigue strength of ferritic-pearlite ductile cast iron with small defects

NASA Astrophysics Data System (ADS)

Deguchi, T.; Kim, H. J.; Ikeda, T.; Yanase, K.

2017-05-01

Because of their excellent mechanical properties, low cost and good workability, the application of ductile cast iron has been increased in various industries such as the automotive, construction and rail industries. For safety designing of the ductile cast iron component, it is necessary to understand the effect of stress ratio, R, on fatigue limit of ductile cast iron in the presence of small defects. Correspondingly in this study, rotating bending fatigue tests at R = -1 and tension-compression fatigue tests at R = -1 and 0.1 were performed by using a ferritic-pearlitic ductile cast iron. To study the effects of small defects, we introduced a small drilled hole at surface of a specimen. The diameter and depth of a drilled hole were 50, 200 and 500 μm, respectively. The non-propagating cracks emanating from graphite particles and holes edge were observed at fatigue limit, irrespective of the value of stress ratio. From the microscopic observation of crack propagation behavior, it can be concluded that the fatigue limit is determined by the threshold condition for propagation of a small crack. It was found that the effect of stress ratio on the fatigue limit of ductile cast iron with small defects can be successfully predicted based on \\sqrt {area} parameter model. Furthermore, a use of the tensile strength, σ B, instead of the Vickers hardness, HV, is effective for fatigue limit prediction.

The influence of modifications of a fatigue loading history program on fatigue lifetime

NASA Technical Reports Server (NTRS)

Branger, J.

1972-01-01

Rectangular specimens of 7075 and 2014 aluminum alloys with two holes (stress concentration factor of 3.24) have been tested under axial fatigue loading on a six-rod test bed with modifications of the loading program, the surface particulars, and the frequency. The length of the precrack stage was investigated by use of a new crack detector. In most cases the two alloys behaved similarly, with similar life to crack start under the same loading. Some overloads lengthened the life. Truncation by omission of the lowest peak loads should be limited to about 20 percent of the ultimate load. Simplifying counting methods gave misleading results. Very thin surface layers of anodizing, protection by vinyl, dry nitrogen atmosphere, as well as stepwise reaming or grinding the surface of the holes, lengthened the life; thick anodized layers shortened the life. Compressing the hole surface by rolling had no influence. Frequencies at about 210 to 240 cpm produced shorter lives than those at 40 cpm. At 5.4 cpm the life was considerably longer. A model to better understand the precrack-stage fatigue mechanism is discussed.

Effect of shot peening on surface fatigue life of carburized and hardened AISI 9310 spur gears

NASA Technical Reports Server (NTRS)

Townsend, D. P.; Zaretsky, E. V.

1982-01-01

Surface fatigue tests were conducted on two groups of AISI 9310 spur gears. Both groups were manufactured with standard ground tooth surfaces, with the second group subjected to an additional shot peening process on the gear tooth flanks. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a gear temperature of 350 K (170 F), a maximum Hertz stress of 1.71 billion N/sq m (248,000 psi), and a speed of 10,000 rpm. The shot peened gears exhibited pitting fatigue lives 1.6 times the life of standard gears without shot peening. Residual stress measurements and analysis indicate that the longer fatigue life is the result of the higher compressive stress produced by the shot peening. The life for the shot peened gear was calculated to be 1.5 times that for the plain gear by using the measured residual stress difference for the standard and shot peened gears. The measured residual stress for the shot peened gears was much higher than that for the standard gears.

Very high-cycle fatigue failure in micron-scale polycrystalline silicon films: Effects of environment and surface oxide thickness

NASA Astrophysics Data System (ADS)

Alsem, D. H.; Timmerman, R.; Boyce, B. L.; Stach, E. A.; De Hosson, J. Th. M.; Ritchie, R. O.

2007-01-01

Fatigue failure in micron-scale polycrystalline silicon structural films, a phenomenon that is not observed in bulk silicon, can severely impact the durability and reliability of microelectromechanical system devices. Despite several studies on the very high-cycle fatigue behavior of these films (up to 1012cycles), there is still an on-going debate on the precise mechanisms involved. We show here that for devices fabricated in the multiuser microelectromechanical system process (MUMPs) foundry and Sandia Ultra-planar, Multi-level MEMS Technology (SUMMiT V™) process and tested under equi-tension/compression loading at ˜40kHz in different environments, stress-lifetime data exhibit similar trends in fatigue behavior in ambient room air, shorter lifetimes in higher relative humidity environments, and no fatigue failure at all in high vacuum. The transmission electron microscopy of the surface oxides in the test samples shows a four- to sixfold thickening of the surface oxide at stress concentrations after fatigue failure, but no thickening after overload fracture in air or after fatigue cycling in vacuo. We find that such oxide thickening and premature fatigue failure (in air) occur in devices with initial oxide thicknesses of ˜4nm (SUMMiT V™) as well as in devices with much thicker initial oxides ˜20nm (MUMPs). Such results are interpreted and explained by a reaction-layer fatigue mechanism. Specifically, moisture-assisted subcritical cracking within a cyclic stress-assisted thickened oxide layer occurs until the crack reaches a critical size to cause catastrophic failure of the entire device. The entirety of the evidence presented here strongly indicates that the reaction-layer fatigue mechanism is the governing mechanism for fatigue failure in micron-scale polycrystalline silicon thin films.

Behavior of sandwich panels subjected to bending fatigue, axial compression loading and in-plane bending

NASA Astrophysics Data System (ADS)

Mathieson, Haley Aaron

This thesis investigates experimentally and analytically the structural performance of sandwich panels composed of glass fibre reinforced polymer (GFRP) skins and a soft polyurethane foam core, with or without thin GFRP ribs connecting skins. The study includes three main components: (a) out-of-plane bending fatigue, (b) axial compression loading, and (c) in-plane bending of sandwich beams. Fatigue studies included 28 specimens and looked into establishing service life (S-N) curves of sandwich panels without ribs, governed by soft core shear failure and also ribbed panels governed by failure at the rib-skin junction. Additionally, the study compared fatigue life curves of sandwich panels loaded under fully reversed bending conditions (R=-1) with panels cyclically loaded in one direction only (R=0) and established the stiffness degradation characteristics throughout their fatigue life. Mathematical models expressing fatigue life and stiffness degradation curves were calibrated and expanded forms for various loading ratios were developed. Approximate fatigue thresholds of 37% and 23% were determined for non-ribbed panels loaded at R=0 and -1, respectively. Digital imaging techniques showed significant shear contribution significantly (90%) to deflections if no ribs used. Axial loading work included 51 specimens and examined the behavior of panels of various lengths (slenderness ratios), skin thicknesses, and also panels of similar length with various rib configurations. Observed failure modes governing were global buckling, skin wrinkling or skin crushing. In-plane bending involved testing 18 sandwich beams of various shear span-to-depth ratios and skin thicknesses, which failed by skin wrinkling at the compression side. The analytical modeling components of axially loaded panels include; a simple design-oriented analytical failure model and a robust non-linear model capable of predicting the full load-displacement response of axially loaded slender sandwich panels, accounting for P-Delta effects, inherent out-of-straightness profile of any shape at initial conditions, and the excessive shear deformation of soft core and its effect on buckling capacity. Another model was developed to predict the load-deflection response and failure modes of in-plane loaded sandwich beams. After successful verification of the models using experimental results, comprehensive parametric studies were carried out using these models to cover parameters beyond the limitations of the experimental program.

Fatigue Analysis of Notched Laminates: A Time-Efficient Macro-Mechanical Approach

NASA Technical Reports Server (NTRS)

Naghipour, P.; Pineda, E. J.; Bednarcyk, B. A.; Arnold, S. M.; Waas, A. M.

2016-01-01

A coupled transversely isotropic deformation and damage fatigue model is implemented within the finite element method and was utilized along with a static progressive damage model to predict the fatigue life, stiffness degradation as a function of number of cycles, and post-fatigue tension and compression response of notched, multidirectional laminates. Initially, the material parameters for the fatigue model were obtained utilizing micromechanics simulations and the provided [0], [90] and [plus or minus 45] experimental composite laminate S-N (stress-cycle) data. Within the fatigue damage model, the transverse and shear properties of the plies were degraded with an isotropic scalar damage variable. The damage in the longitudinal (fiber) ply direction was suppressed, and only the strength of the fiber was degraded as a function of fatigue cycles. A maximum strain criterion was used to capture the failure in each element, and once this criterion was satisfied, the longitudinal stiffness of the element was decreased by a factor of 10 (sup 4). The resulting, degraded properties were then used to calculate the new stress state. This procedure was repeated until final failure of the composite laminate was achieved or a specified number of cycles reached. For post-fatigue tension and compression behavior, four internal state variables were used to control the damage and failure. The predictive capability of the above-mentioned approach was assessed by performing blind predictions of the notched multidirectional IM7/977-3 composite laminates response under fatigue and post-fatigue tensile and compressive loading, followed by a recalibration phase. Although three different multidirectional laminates were analyzed in the course of this study, only detailed results (i.e., stiffness degradation and post-fatigue stress-train curves as well as damage evolution states for a single laminate ([30/60/90/minus 30/minus 60] (sub 2s)) are discussed in detail here.

Passive Orbital Disconnect Strut (PODS 3) structural test program

NASA Technical Reports Server (NTRS)

Parmley, R. T.

1985-01-01

A passive orbital disconnect strut (PODS-3) was analyzed structurally and thermally. Development tests on a graphite/epoxy orbit tube and S glass epoxy launch tube provided the needed data to finalize the design. A detailed assembly procedure was prepared. One strut was fabricated. Shorting loads in both the axial and lateral direction (vs. load angle and location) were measured. The strut was taken to design limit loads at both ambient and 78 K (cold end only). One million fatigue cycles were performed at predicted STS loads (half in tension, half in compression) with the cold end at 78 K. The fatigue test was repeated at design limit loads. Six struts were then fabricated and tested as a system. Axial loads, side loads, and simulated asymmetric loads due to temperature gradients around the vacuum shell were applied. Shorting loads were measured for all tests.

Repetitive lifting tasks fatigue the back muscles and increase the bending moment acting on the lumbar spine.

PubMed

Dolan, P; Adams, M A

1998-08-01

During manual handling, the back muscles protect the spine from excessive flexion, but in doing so impose a high compressive force on it. Epidemiological links between back pain and repetitive lifting suggest that fatigued muscles may adversely affect the balance between bending and compression. Fifteen volunteers lifted and lowered a 10 kg weight from floor to waist height 100 times. Throughout this task, the bending moment acting on the osteoligamentous lumbar spine was estimated from continuous measurements of lumbar flexion, obtained using the 3-Space Isotrak. Spinal compression was estimated from the electromyographic (EMG) activity of the erector spinae muscles, recorded from skin-surface electrodes at the levels of T10 and L3. EMG signals were calibrated against force when subjects pulled up on a load cell, and correction factors were applied to account for changes in muscle length and contraction velocity. Fatigue in the erector spinae muscles was quantified by comparing the frequency content of their EMG signal during static contractions performed before, and immediately after, the 100 lifts. Results showed that peak lumbar flexion increased during the 100 lifts from 83.3 +/- 14.8% to 90.4 +/- 14.3%, resulting in a 36% increase in estimated peak bending moment acting on the lumbar spine (P = 0.008). Peak spinal compression fell by 11% (p = 0.007). The median frequency of the EMG signal at L3 decreased by 5.5% following the 100 lifts (p = 0.042) confirming that the erector spinae were fatigued, but measures of fatigue showed no significant correlation with increased bending. We conclude that repetitive lifting induces measurable fatigue in the erector spinae muscles, and substantially increases the bending moment acting on the lumbar spine.

Computational Study of Axial Fatigue for Peripheral Nitinol Stents

NASA Astrophysics Data System (ADS)

Meoli, Alessio; Dordoni, Elena; Petrini, Lorenza; Migliavacca, Francesco; Dubini, Gabriele; Pennati, Giancarlo

2014-07-01

Despite their success as primary treatment for vascular diseases, Nitinol peripheral stents are still affected by complications related to fatigue failure. Hip and knee movements during daily activities produce large and cyclic deformations of the superficial femoral artery, that concomitant to the effects of pulsatile blood pressure, may cause fatigue failure in the stent. Fatigue failure typically occurs in cases of very extended lesions, which often require the use of two or more overlapping stents. In this study, finite element models were used to study the fatigue behavior of Nitinol stents when subjected to cyclic axial compression in different conditions. A specific commercial Nitinol stent was chosen for the analysis and subjected to cyclic axial compression typical of the femoral vascular region. Three different configurations were investigated: stent alone, stent deployed in a tube, and two overlapping stents deployed in a tube. Results confirm that stent oversizing has an influence in determining both the mean and amplitude strains induced in the stent and plays an important role in determining the fatigue response of Nitinol stents. In case of overlapping stents, numerical results suggest higher amplitude strains concentrate in the region close to the overlapping portion where the abrupt change in stiffness causes higher cyclic compression. These findings help to explain the high incidence of stent fractures observed in various clinical trials located close to the overlapping portion.

Effet Bauschinger lors de la plasticité cyclique de l'aluminium pur monocristallin

NASA Astrophysics Data System (ADS)

Alhamany, A.; Chicois, J.; Fougères, R.; Hamel, A.

1992-08-01

This paper is concerned with the study of microscopic mechanisms which control the cyclic deformation of pure aluminium and especially with the analysis of the Bauschinger effect which appears in aluminium single crystals deformed by cyclic straining. Fatigue tests are performed on Al single crystals with the crystal axis parallel to [ overline{1}23] at room temperature, at plastic shear strain amplitudes in the range from 10^{-4} to 3× 10^{-3}. Mechanical saturation is not obtained at any strain level. Instead, a hardening-softening-secondary hardening sequence is found. The magnitude of the Bauschinger effect as the difference between yield stresses in traction and in compression, changes all along the fatigue loop and during the fatigue test. The Bauschinger effect disappears at two points of the fatigue loop, one in the traction part, the other in the compression one. At these points, the Bauschinger effect is inverted. Dislocation arrangement evolutions with fatigue conditions can explain the cyclic behaviour of Al single crystals. An heterogeneous dislocation distribution can be observed in the cyclically strained metal : dislocation tangles, long dislocation walls and dislocation cell walls, separated by dislocation poor channels appear in the material as a function of the cycle number. The long range internal stress necessary to ensure the compatibility of deformation between the hard and soft regions controls the observed Bauschinger effect. Ce travail s'inscrit dans le cadre de l'étude des mécanismes microsocopiques intervenant lors de la déformation cyclique de l'aluminium pur et concerne en particulier l'analyse de l'effet Bauschinger apparaissant au cours de la solliciation cyclique des monocristaux. L'étude a été menée à température ambiante sur des monocristaux d'aluminium pur orientés pour un glissement simple (axe [ overline{1}23] ), à des amplitudes de déformation plastique comprise entre 10^{-4} et quelques 10^{-3}. Nous n'avons pas obtenu de véritable saturation mécanique. Nous sommes en présence d'une séquence durcissement-adoucissement-durcissement secondaire. L'amplitude de l'effet Bauschinger considéré comme la différence entre les limites élastiques en traction et en compression mesurées selon une procédure appropriée, évolue le long d'une boucle de fatigue, s'annule pour deux points particuliers l'un en traction l'autre en compression. De part et d'autre de ces points, le signe de l'effet Bauschinger est inversé. Les microstructures des états fatigués sont caractérisés par une répartition hétérogène des dislocations constituée d'amas, de murs ou des parois, suivant le degré de déformation cyclique, séparés par des zones à faible densité de dislocations. Les contraintes internes liées aux incompatibilités de déformation résultant de cette répartition hétérogène des dislocations sont à l'origine de l'effet Bauschinger observé dans les monocristaux. Ces contraintes et l'évolution de la quantité de cellules de dislocations avec la fatigue expliquent le durcissement secondaire.

Plasma immersion ion implantation on 15-5PH stainless steel: influence on fatigue strength and wear resistance

NASA Astrophysics Data System (ADS)

Bonora, R.; Cioffi, M. O. H.; Voorwald, H. J. C.

2017-05-01

Surface improvement in steels is of great interest for applications in industry. The aim of this investigation is to study the effect of nitrogen ion implantation on the axial fatigue strength and wear resistance of 15-5 PH stainless steel. It is well know that electroplated coatings, which are used to improve abrasive wear and corrosion properties, affects negatively the fatigue strength. It is also important to consider requirements to reduce the use of coated materials with electroplated chromium and cadmium, that produce waste, which is harmful to health and environment. The HVOF (High velocity oxygen fuel) process provides hardness, wear strength and higher fatigue resistance in comparison to electroplated chromium. Plasma immersion ion implantation has been used to enhance the hardness, wear, fatigue and corrosion properties of metals and alloys. In the present research the fatigue life increased twice for 15-5 PH three hours PIII treated in comparison to base material. From the abrasive wear tests a lower pin mass reduction was observed, associated to the superficial treatments. The improvement of fatigue and mechanical performance is attributed to a combination of nitrides phase structure and compressive residual stresses during the PIII treatment.

Effects of bionic units on the fatigue wear of gray cast iron surface with different shapes and distributions

NASA Astrophysics Data System (ADS)

Chen, Zhi-kai; Lu, Shu-chao; Song, Xi-bin; Zhang, Haifeng; Yang, Wan-shi; Zhou, Hong

2015-03-01

To improve the fatigue wear resistance of gray cast iron (GCI), GCI samples were modified by a laser to imitate the unique structure of some soil animals alternating between soft and hard phases; the hard phase resists the deformation and the soft phase releases the deformation. Using the self-controlled fatigue wear test method, the fatigue wear behaviors of treated and untreated samples were investigated and compared experimentally. The results show that the bionic non-smooth surface obtains a beneficial effect on improving the fatigue wear resistance of a sample, and the fatigue wear resistance of the bionic sample assembled with reticulate units (60°+0°), whose mass loss was reduced by 62%, was superior to the others. Meanwhile, a finite element (FE) was used to simulate the compression and the distributions of strain and stress on the non-smooth surface was inferred. From these results, we understood that the functions of the bionic unit such as reducing strain and stress, and also obstructing the closure and propagation of cracks were the main reasons for improving the fatigue wear property of GCI.

Damage morphology study of high cycle fatigued as-cast Mg–3.0Nd–0.2Zn–Zr (wt.%) alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yue, Haiyan; Fu, Penghuai, E-mail: fph112sjtu@sjtu.edu.cn; Peng, Liming

Laser scanning confocal microscopy (LSCM) and Electron back-scattered diffraction (EBSD) were applied to the study of surface morphology variation of as-cast Mg–3.0Nd–0.2Zn–Zr (NZ30K) (wt.%) alloy under tension-compression fatigue test at room temperature. Two kinds of typical damage morphologies were observed in fatigued NZ30K alloy: One was parallel lines on basal planes led by the cumulation of basal slips, called persistent slip markings (PSMs), and the other was lens shaped, thicker and in less density, led by the formation of twinning. The surface fatigue damage morphology evolution was analyzed in a statistical way. The influences of stress amplitude and grain orientationmore » on fatigue deformation mechanisms were discussed and the non-uniform deformation among grains and the PSMs, within twinning were described quantitatively. - Highlights: • Fatigue morphology evolution was studied by Laser Scanning Confocal Microscopy. • 3D morphology of persistent slip markings and twins was characterized. • Non-uniform deformation among grains, the PSMs and twins were quantified. • Initiations of fatigue crack were clearly investigated.« less

Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-standing Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

2003-01-01

Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma-sprayed ZrO2-8wt % Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness, and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material's unique constitutive relations.

Dynamic strain aging behavior of 10Cr steel under low cycle fatigue at 650°C

NASA Astrophysics Data System (ADS)

Mishnev, Roman; Dudova, Nadezhda; Kaibyshev, Rustam

2017-12-01

The low cycle fatigue behavior of a 10Cr-2W-0.7Mo-3Co-NbV steel with 80 ppm of B additions was studied at elevated temperatures of 600 and 650°C. The steel after normalizing and tempering at 770°C was tested under fully reversed tension-compression loading with the total strain amplitude controlled from ±0.2 to ±1.0% at temperatures of 600 and 650°C. It was revealed that the steel exhibits a positive temperature dependence of both the cyclic strain hardening exponent n' and the cyclic strength coefficient K ' during cyclic loading at 650°C. It was suggested that dynamic strain aging causes fatigue resistance degradation through facilitating microcrack initiation.

Piezoelectric Bolt Breakers and Bolt Fatigue Testers

NASA Technical Reports Server (NTRS)

Sherrit, Stewart; Badescu, Mircea; Bar-Cohen, Yoseph; Barengoltz, Jack; Heckman, Vanessa

2008-01-01

A proposed family of devices for inducing fatigue in bolts in order to break the bolts would incorporate piezoelectric actuators into resonant fixtures as in ultrasonic/ sonic drills/corers and similar devices described in numerous prior NASA Tech Briefs articles. These devices were originally intended primarily for use as safer, more-reliable, more-versatile alternatives to explosive bolts heretofore used to fasten spacecraft structures that must subsequently be separated from each other quickly on command during flight. On Earth, these devices could be used for accelerated fatigue testing of bolts. Fatigue theory suggests that a bolt subjected to both a constant-amplitude dynamic (that is, oscillatory) stress and a static tensile stress below the ultimate strength of the bolt material will fail faster than will a bolt subjected to only the dynamic stress. This suggestion would be applied in a device of the proposed type. The device would be designed so that the device and the bolt to be fatigue-tested or broken would be integral parts of an assembly (see figure). The static tension in the tightened bolt would apply not only the clamping force to hold the joined structures (if any) together but also the compression necessary for proper operation of the piezoelectric actuators as parts of a resonant structural assembly. The constant-amplitude dynamic stress would be applied to the bolt by driving the piezoelectric actuators with a sinusoidal voltage at the resonance frequency of longitudinal vibration of the assembly. The amplitude of the excitation would be made large enough so that the vibration would induce fatigue in the bolt within an acceptably short time. In the spacecraft applications or in similar terrestrial structural-separation applications, devices of the proposed type would offer several advantages over explosive bolts: Unlike explosive bolts, the proposed devices would be reusable, could be tested before final use, and would not be subject to catastrophic misfire. In fatigue-testing applications, devices of the proposed type would offer advantages of compactness and low cost, relative to conventional fatigue- testing apparatuses. In both structural- separation and fatigue-testing applications, bolts to be broken or tested could be instrumented with additional ultrasonic transducers for monitoring of pertinent physical properties and of fatigue failure processes.

Myoelectric manifestations of jaw elevator muscle fatigue and recovery in healthy and TMD subjects.

PubMed

Castroflorio, T; Falla, D; Tartaglia, G M; Sforza, C; Deregibus, A

2012-09-01

The effects of muscle pain and fatigue on the control of jaw elevator muscles are not well known. Furthermore, the myoelectric manifestations of fatigue and recovery from fatigue in the masticatory muscles are not reported in literature. The main aims of this study were (i) to evaluate the possible use of surface electromyography (sEMG) as an objective measure of fatigue of the jaw elevator muscles, (ii) to compare the myoelectric manifestations of fatigue in the temporalis anterior and masseter muscles bilaterally, (iii) to assess recovery of the investigated muscles after an endurance test and (iv) to compare fatigue and recovery of the jaw elevator muscles in healthy subjects and patients with muscle-related temporomandibular disorders (TMD). The study was performed on twenty healthy volunteers and eighteen patients with muscle-related TMD. An intra-oral compressive-force sensor was used to measure the voluntary contraction forces close to the intercuspal position and to provide visual feedback of submaximal forces to the subject. Surface EMG signals were recorded with linear electrode arrays during isometric contractions at 20%, 40%, 60% and 80% of the maximum voluntary contraction force, during an endurance test and during the recovery phase. The results showed that (i) the slope of the mean power spectral frequency (MNF) and the initial average rectified value (ARV) could be used to monitor fatigue of the jaw elevators, (ii) the temporalis anterior and masseter muscle show the same myoelectric manifestations of fatigue and recovery and (iii) the initial values of MNF and ARV were lower in patients with muscle-related TMD. The assessment of myoelectric manifestations of fatigue in the masticatory muscles may assist in the clinical assessment of TMDs. © 2012 Blackwell Publishing Ltd.

COMPRESSIVE FATIGUE IN TITANIUM DENTAL IMPLANTS SUBMITTED TO FLUORIDE IONS ACTION

PubMed Central

Ribeiro, Ana Lúcia Roselino; Noriega, Jorge Roberto; Dametto, Fábio Roberto; Vaz, Luís Geraldo

2007-01-01

The aim of this study was to assess the influence of a fluoridated medium on the mechanical properties of an internal hexagon implant-abutment set, by means of compression, mechanical cycling and metallographic characterization by scanning electronic microscopy. Five years of regular use of oral hygiene with a sodium fluoride solution content of 1500 ppm were simulated, immersing the samples in this medium for 184 hours, with the solutions being changed every 12 hours. Data were analyzed at a 95% confidence level with Fisher's exact test. After the action of fluoride ions, a negative influence occurred in the mechanical cycling test performed in a servohydraulic machine (Material Test System-810) set to a frequency of 15 Hz with 100,000 cycles and programmed to 60% of the maximum resistance of static compression test. The sets tended to fracture by compression on the screw, characterized by mixed ruptures with predominance of fragile fracture, as observed by microscopy. An evidence of corrosion by pitting on sample surfaces was found after the fluoride ions action. It may be concluded that prolonged contact with fluoride ions is harmful to the mechanical properties of commercially pure titanium structures. PMID:19089148

Investigation of a ceramic matrix composite under strain controlled fatigue condition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gudaitis, J.J.; Mall, S.

The fatigue behavior along with damage mechanisms and failure modes of a fiber reinforced ceramic matrix composite with a cross-ply lay-up was investigated under strain controlled mode. Two fatigue conditions involving tension-tension and tension-compression cycling were employed. The strain range versus fatigue life curves for both fatigue conditions were in agreement with each other. However, damage mechanisms and failure modes were different for both cases.

Oxidation-Assisted Crack Growth in Single-Crystal Superalloys during Fatigue with Compressive Holds

NASA Astrophysics Data System (ADS)

Lafata, M. A.; Rettberg, L. H.; He, M. Y.; Pollock, T. M.

2018-01-01

The mechanism of oxidation-assisted growth of surface cracks during fatigue with compressive holds has been studied experimentally and via a model that describes the role of oxide and substrate properties. The creep-based finite element model has been employed to examine the role of material parameters in the damage evolution in a Ni-base single-crystal superalloy René N5. Low-cycle fatigue experiments with compressive holds were conducted at 1255 K and 1366 K (982 °C and 1093 °C). Interrupted and failed specimens were characterized for crack depth and spacing, oxide thickness, and microstructural evolution. Comparison of experimental to modeled hysteresis loops indicates that transient creep drives the macroscopic stress-strain response. Crack penetration rates are strongly influenced by growth stresses in the oxide, structural evolution in the substrate, and the development of γ ^' } denuded zones. Implications for design of alloys resistant to this mode of degradation are discussed.

Case Studies of Fatigue Life Improvement Using Low Plasticity Burnishing in Gas Turbine Engine Applications

NASA Technical Reports Server (NTRS)

Prevey, Paul S.; Shepard, Michael; Ravindranath, Ravi A.; Gabb, Timothy

2003-01-01

Surface enhancement technologies such as shot peening, laser shock peening (LSP), and low plasticity burnishing (LPB) can provide substantial fatigue life improvement. However, to be effective, the compressive residual stresses that increase fatigue strength must be retained in service. For successful integration into turbine design, the process must be affordable and compatible with the manufacturing environment. LPB provides thermally stable compression of comparable magnitude and even greater depth than other methods, and can be performed in conventional machine shop environments on CNC machine tools. LPB provides a means to extend the fatigue lives of both new and legacy aircraft engines and ground-based turbines. Improving fatigue performance by introducing deep stable layers of compressive residual stress avoids the generally cost prohibitive alternative of modifying either material or design. The X-ray diffraction based background studies of thermal and mechanical stability of surface enhancement techniques are briefly reviewed, demonstrating the importance of minimizing cold work. The LPB process, tooling, and control systems are described. An overview of current research programs conducted for engine OEMs and the military to apply LPB to a variety of engine and aging aircraft components are presented. Fatigue performance and residual stress data developed to date for several case studies are presented including: * The effect of LPB on the fatigue performance of the nickel based super alloy IN718, showing fatigue benefit of thermal stability at engine temperatures. * An order of magnitude improvement in damage tolerance of LPB processed Ti-6-4 fan blade leading edges. * Elimination of the fretting fatigue debit for Ti-6-4 with prior LPB. * Corrosion fatigue mitigation with LPB in Carpenter 450 steel. *Damage tolerance improvement in 17-4PH steel. Where appropriate, the performance of LPB is compared to conventional shot peening after exposure to engine operating temperatures.

Fatigue limit prediction of ferritic-pearlitic ductile cast iron considering stress ratio and notch size

NASA Astrophysics Data System (ADS)

Deguchi, T.; Kim, H. J.; Ikeda, T.

2017-05-01

The mechanical behavior of ductile cast iron is governed by graphite particles and casting defects in the microstructures, which can significantly decrease the fatigue strength. In our previous study, the fatigue limit of ferritic-pearlitic ductile cast iron specimens with small defects ((\\sqrt{{area}}=80˜ 1500{{μ }}{{m}})) could successfully be predicted based on the \\sqrt{{area}} parameter model by using \\sqrt{{area}} as a geometrical parameter of defect as well as the tensile strength as a material parameter. In addition, the fatigue limit for larger defects could be predicted based on the conventional fracture mechanics approach. In this study, rotating bending and tension-compression fatigue tests with ferritic-pearlitic ductile cast iron containing circumferential sharp notches as well as smooth specimens were performed to investigate quantitatively the effects of defect. The notch depths ranged 10 ˜ 2500 μm and the notch root radii were 5 and 50 μm. The stress ratios were R = -1 and 0.1. The microscopic observation of crack propagation near fatigue limit revealed that the fatigue limit was determined by the threshold condition for propagation of a small crack emanating from graphite particles. The fatigue limit could be successfully predicted as a function of R using a method proposed in this study.

A Predictive Framework for Thermomechanical Fatigue Life of High Silicon Molybdenum Ductile Cast Iron Based on Considerations of Strain Energy Dissipation

NASA Astrophysics Data System (ADS)

Avery, Katherine R.

Isothermal low cycle fatigue (LCF) and anisothermal thermomechanical fatigue (TMF) tests were conducted on a high silicon molybdenum (HiSiMo) cast iron for temperatures up to 1073K. LCF and out-of-phase (OP) TMF lives were significantly reduced when the temperature was near 673K due to an embrittlement phenomenon which decreases the ductility of HiSiMo at this temperature. In this case, intergranular fracture was predominant, and magnesium was observed at the fracture surface. When the thermal cycle did not include 673K, the failure mode was predominantly transgranular, and magnesium was not present on the fracture surface. The in-phase (IP) TMF lives were unaffected when the thermal cycle included 673K, and the predominant failure mode was found to be transgranular fracture, regardless of the temperature. No magnesium was present on the IP TMF fracture surfaces. Thus, the embrittlement phenomenon was found to contribute to fatigue damage only when the temperature was near 673K and a tensile stress was present. To account for the temperature- and stress-dependence of the embrittlement phenomenon on the TMF life of HiSiMo cast iron, an original model based on the cyclic inelastic energy dissipation is proposed which accounts for temperature-dependent differences in the rate of fatigue damage accumulation in tension and compression. The proposed model has few empirical parameters. Despite the simplicity of the model, the predicted fatigue life shows good agreement with more than 130 uniaxial low cycle and thermomechanical fatigue tests, cyclic creep tests, and tests conducted at slow strain rates and with hold times. The proposed model was implemented in a multiaxial formulation and applied to the fatigue life prediction of an exhaust manifold subjected to severe thermal cycles. The simulation results show good agreement with the failure locations and number of cycles to failure observed in a component-level experiment.

Strength and fatigue properties of three-step sintered dense nanocrystal hydroxyapatite bioceramics

NASA Astrophysics Data System (ADS)

Guo, Wen-Guang; Qiu, Zhi-Ye; Cui, Han; Wang, Chang-Ming; Zhang, Xiao-Jun; Lee, In-Seop; Dong, Yu-Qi; Cui, Fu-Zhai

2013-06-01

Dense hydroxyapatite (HA) ceramic is a promising material for hard tissue repair due to its unique physical properties and biologic properties. However, the brittleness and low compressive strength of traditional HA ceramics limited their applications, because previous sintering methods produced HA ceramics with crystal sizes greater than nanometer range. In this study, nano-sized HA powder was employed to fabricate dense nanocrystal HA ceramic by high pressure molding, and followed by a three-step sintering process. The phase composition, microstructure, crystal dimension and crystal shape of the sintered ceramic were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical properties of the HA ceramic were tested, and cytocompatibility was evaluated. The phase of the sintered ceramic was pure HA, and the crystal size was about 200 nm. The compressive strength and elastic modulus of the HA ceramic were comparable to human cortical bone, especially the good fatigue strength overcame brittleness of traditional sintered HA ceramics. Cell attachment experiment also demonstrated that the ceramics had a good cytocompatibility.

Constitutive Relations of Randomly Oriented Steel Fiber Reinforced Concrete under Multiaxial Compressive Loadings,

DTIC Science & Technology

1981-12-01

This was done to observe the effect of specimen age on strength after the curing period of 7 days in the humidity room and the remaining time in air in... fatigue resistance. Although the compressive strength is not much improved, the brittle behavior that would occur in plain concrete after peak strength...such as fracture toughness, fatigue resistance, impact resistance and flexural strength (82). The idea of fiber reinforcement applications is not new

Effect of load, cadence, and fatigue on tibio-femoral joint force during a half squat.

PubMed

Hattin, H C; Pierrynowski, M R; Ball, K A

1989-10-01

Ten male university student volunteers were selected to investigate the 3D articular force at the tibio-femoral joint during a half squat exercise, as affected by cadence, different barbell loads, and fatigue. Each subject was required to perform a half squat exercise with a barbell weight centered across the shoulders at two different cadences (1 and 2 s intervals) and three different loads (15, 22 and 30% of the one repetition maximum). Fifty repetitions at each experimental condition were recorded with an active optoelectronic kinematic data capture system (WATSMART) and a force plate (Kistler). Processing the data involved a photogrammetric technique to obtain subject tailored anthropometric data. The findings of this study were: 1) the maximal antero-posterior shear and compressive force consistently occurred at the lowest position of the weight, and the forces were very symmetrically disposed on either side of this halfway point; 2) the medio-lateral shear forces were small over the squat cycle with few peaks and troughs; 3) cadence increased the antero-posterior shear (50%) and the compressive forces (28%); 4) as a subject fatigues, load had a significant effect on the antero-posterior shear force; 5) fatigue increased all articular force components but it did not manifest itself until about halfway through the 50 repetitions of the exercise; 6) the antero-posterior shear force was most affected by fatigue; 7) cadence had a significant effect on fatigue for the medio-lateral shear and compressive forces.

A new application of Fe-28Mn-6Si-5Cr (mass%) shape memory alloy, for self-adjustable axial preloading of ball bearings

NASA Astrophysics Data System (ADS)

Paleu, V.; Gurău, G.; Comăneci, R. I.; Sampath, V.; Gurău, C.; Bujoreanu, L. G.

2018-07-01

A new application of Fe-Mn-Si based shape memory alloys (SMAs) was developed under the form of truncated cone-shaped module, for self-adaptive axial preload control in angular contact bearings. The modules were processed by high-speed high-pressure torsion (HS-HPT), from circular crowns cut from axially drilled ingots of Fe-28Mn-6Si-9Cr (mass%) SMA. The specimens were mechanically tested in the hot rolled state, prior to HS-HPT processing, demonstrating free-recovery shape memory effect (SME) and high values for ultimate tensile stress and strain as well as low cycle fatigue life. The HS-HPT modules were subjected to static loading–unloading compression, without/with lubrication at specimen-tool interface, both individually and in different coupling modes. Dry compression cycles revealed reproducible stress plateaus both during loading and unloading stages, being associated with hardness gradient, along cone generator, caused by HS-HPT processing. Constrained recovery tests, performed using compressed modules, emphasized the continuous generation of stress during heating, by one way SME, at a rate of ∼9.3 kPa/%. Dynamic compression tests demonstrated the capability of modules to develop closed stress–strain loops after 50 000 cycles, without visible signs of fatigue. HS-HPT caused the fragmentation of crystalline grains, while compression cycles enabled the formation of ε hexagonal close-packed stress-induced martensite (ε), which is characterized by a high density of stacking faults. Using an experimental setup, specifically designed and manufactured for this purpose, both feasibility and functionality tests were performed using HS-HPT modules. The feasibility tests proved the existence of a general tendency of both axial force and friction torque to increase in time, favoured by the increase of initial preloading force and the augmentation of rotation speed. Functionality tests, performed on two pairs of HS-HPT modules fastened in base-to-base coupling mode, demonstrated the capacity of modules to accommodate high preloads while maintaining both axial force and friction torque at constant values in time. These preliminary results suggest that, for the time being, the modules can operate only as single use applications, more effective during the running-in period. This bevahior recommends HS-HPT modules as a new application of Fe-Mn-Si SMAs, with the potential to be used for the development of new temperature-responsive compression displacement systems.

Mechanical properties of a fiberglass prepreg system at cryogenic and other temperatures

NASA Technical Reports Server (NTRS)

Klich, P. J.; Cockrell, C. E.

1982-01-01

The compressor driving the flow in the National Transonic Facility, which is nearing completion at the Langley Research Center, has 25 fiberglass blades. E-glass cloth with a pre-impregnated epoxy resin has been selected as the material for the fan blades because of its low cost, high damping, and fatigue resistance. A complete characterization is presented of this fan blade fiberglass system at temperatures of 367 K, room temperature, and 89 K. The characterization test results suggest that the material follows the general trends of metals and other glass-reinforced plastics at cryogenic temperatures. A slight diminution in strength was observed at the elevated temperature. The tests included the following: tensile, compression, fatigue, inplane shear, interlaminar shear, thermal expansion, creep, and thermal cycle.

High Cycle Fatigue Performance in Laser Shock Peened TC4 Titanium Alloys Subjected to Foreign Object Damage

NASA Astrophysics Data System (ADS)

Luo, Sihai; Nie, Xiangfan; Zhou, Liucheng; Li, Yiming; He, Weifeng

2018-03-01

During their service, titanium alloys are likely to suffer from the foreign object damage (FOD), resulting in a decrease in their fatigue strength. Laser shock peening (LSP) has been proved to effectively increase the damage tolerance of military engine components by introducing a magnitude compressive residual stress in the near-surface layer of alloys. In this paper, smooth specimens of a TC4 titanium alloy were used and treated by LSP and subsequently exposed to FOD, which was simulated by firing a steel sphere with a nominal velocity of 300 m/s, at 90° with the leading edge of the LSP-treated region using a light gas gun. All impacted specimens were then subjected to fatigue loading. The results showed that LSP could effectively improve the fatigue strength of the damaged specimens. The effect of LSP on the fatigue strength was assessed through fracture observations, microhardness tests and residual stress analyses. The residual stresses due to the plastic deformation caused by LSP and the FOD impact, which were found to play a crucial role on the fatigue strength, were determined using the commercial software ABAQUS.

Full-Scale Fatigue Testing of a Wind Turbine Blade in Flapwise Direction and Examining the Effect of Crack Propagation on the Blade Performance.

PubMed

Al-Khudairi, Othman; Hadavinia, Homayoun; Little, Christian; Gillmore, Gavin; Greaves, Peter; Dyer, Kirsten

2017-10-03

In this paper, the sensitivity of the structural integrity of wind turbine blades to debonding of the shear web from the spar cap was investigated. In this regard, modal analysis, static and fatigue testing were performed on a 45.7 m blade for three states of the blade: (i) as received blade (ii) when a crack of 200 mm was introduced between the web and the spar cap and (iii) when the crack was extended to 1000 mm. Calibration pull-tests for all three states of the blade were performed to obtain the strain-bending moment relationship of the blade according to the estimated target bending moment (BM) which the blade is expected to experience in its service life. The resultant data was used to apply appropriate load in the fatigue tests. The blade natural frequencies in flapwise and edgewise directions over a range of frequency domain were found by modal testing for all three states of the blade. The blade first natural frequency for each state was used for the flapwise fatigue tests. These were performed in accordance with technical specification IEC TS 61400-23. The fatigue results showed that, for a 200 mm crack between the web and spar cap at 9 m from the blade root, the crack did not propagate at 50% of the target BM up to 62,110 cycles. However, when the load was increased to 70% of target BM, some damages were detected on the pressure side of the blade. When the 200 mm crack was extended to 1000 mm, the crack began to propagate when the applied load exceeded 100% of target BM and the blade experienced delaminations, adhesive joint failure, compression failure and sandwich core failure.

Full-Scale Fatigue Testing of a Wind Turbine Blade in Flapwise Direction and Examining the Effect of Crack Propagation on the Blade Performance

PubMed Central

Al-Khudairi, Othman; Little, Christian; Gillmore, Gavin; Greaves, Peter; Dyer, Kirsten

2017-01-01

In this paper, the sensitivity of the structural integrity of wind turbine blades to debonding of the shear web from the spar cap was investigated. In this regard, modal analysis, static and fatigue testing were performed on a 45.7 m blade for three states of the blade: (i) as received blade (ii) when a crack of 200 mm was introduced between the web and the spar cap and (iii) when the crack was extended to 1000 mm. Calibration pull-tests for all three states of the blade were performed to obtain the strain-bending moment relationship of the blade according to the estimated target bending moment (BM) which the blade is expected to experience in its service life. The resultant data was used to apply appropriate load in the fatigue tests. The blade natural frequencies in flapwise and edgewise directions over a range of frequency domain were found by modal testing for all three states of the blade. The blade first natural frequency for each state was used for the flapwise fatigue tests. These were performed in accordance with technical specification IEC TS 61400-23. The fatigue results showed that, for a 200 mm crack between the web and spar cap at 9 m from the blade root, the crack did not propagate at 50% of the target BM up to 62,110 cycles. However, when the load was increased to 70% of target BM, some damages were detected on the pressure side of the blade. When the 200 mm crack was extended to 1000 mm, the crack began to propagate when the applied load exceeded 100% of target BM and the blade experienced delaminations, adhesive joint failure, compression failure and sandwich core failure. PMID:28972548

Tension-Compression Fatigue Behavior of 2D and 3D Polymer Matrix Composites at Elevated Temperature

DTIC Science & Technology

2015-09-21

temperature calibrations, tests procedures and optical microscopy used in this research. 4.1 Mechanical Testing Equipment A Model 810 MTS servo -hydraulic...Composite Materials”. Oxford University Press , New York, NY, 2nd edition, 1994. 4. F.C. Campbell. “Structural Composite Materials” ASM International...M. “Mechanics of Composite Materials”. CRC Press , second Edition, ISBN-10: 156032712x, July 1998. 13. Ruggles-Wrenn, M. B., D. T. Christensen, A. L

High temperature, low-cycle fatigue of copper-base alloys in argon. Part 2: Zirconium-copper at 482, 538 and 593 C

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1973-01-01

Zirconium-copper (1/2 hard) was tested in argon over the temperature range from 482 to 593 C in an evaluation of short-term tensile and low-cycle fatigue behavior. The effect of strain rate on the tensile properties was evaluated at 538 C and in general it was found that the yield and ultimate strengths increased as the strain rate was increased from 0.0004 to 0.01/sec. Ductility was essentially insensitive to strain rate in the case of the zirconium-copper alloy. Strain-rate and hold-time effects on the low cycle fatigue behavior of zirconium-copper were evaluated in argon at 538 C. These effects were as expected in that decreased fatigue life was noted as the strain rate decreased and when hold times were introduced into the tension portion of the strain-cycle. Hold times in compression were much less detrimental than hold times in tension.

Fracture strength and fatigue resistance of all-ceramic molar crowns manufactured with CAD/CAM technology.

PubMed

Zahran, Mohammed; El-Mowafy, Omar; Tam, Laura; Watson, Philip A; Finer, Yoav

2008-07-01

All-ceramic crowns are subject to fracture during function, especially in the posterior area. The use of yttrium-stabilized zirconium-oxide ceramic as a substructure for all-ceramic crowns to improve fracture resistance is unproven. The aim of this study was to compare fracture strength and fatigue resistance of new zirconium-oxide and feldspathic all-ceramic crowns made with computer-aided design/computer-aided manufacturing (CAD/CAM). An ivorine molar was prepared to receive an all-ceramic crown. Using epoxy resin, 40 replication dies were made of the prepared tooth. Twenty feldspathic all-ceramic crowns (Vita Mark II) (VMII) and 20 zirconium-oxide crown copings (In-Ceram YZ) (YZ) were made using CAD/CAM technique (CEREC-3D). The YZ copings were sintered and veneered manually with a fine-particle ceramic (VM9). All crowns were cemented to their respective dies using resin cement (Panavia F 2.0). Ten crowns in each group were subjected to compressive fatigue loading in a universal testing machine (instron). The other ten crowns from each group were loaded to fracture at a crosshead speed of 1 mm/min. Data were statistically analyzed using independent t-test and Fisher's exact test at alpha= 0.05. There was a significant difference between the survival rates of the two materials during the fatigue test (p < 0.001). All VMII crowns survived without any crack formation, while all YZ crowns fractured (40%) or developed cracks (60%). All the YZ crown fractures occurred within the veneering layer during the fatigue test. There was no significant difference in mean fracture load between the two materials (p= 0.268). Mean fracture loads (standard deviation) in N were: 1459 (492) for YZ crowns and 1272 (109) for VMII crowns. The performance of VMII crowns was superior to YZ crowns in the fatigue test. The premature fractures and cracks of the YZ crowns were attributed to weakness in the YZ veneer layer or in the core/veneer bond.

Fatigue damage prognosis of internal delamination in composite plates under cyclic compression loadings using affine arithmetic as uncertainty propagation tool

NASA Astrophysics Data System (ADS)

Gbaguidi, Audrey J.-M.

Structural health monitoring (SHM) has become indispensable for reducing maintenance costs and increasing the in-service capacity of a structure. The increased use of lightweight composite materials in aircraft structures drastically increased the effects of fatigue induced damage on their critical structural components and thus the necessity to predict the remaining life of those components. Damage prognosis, one of the least investigated fields in SHM, uses the current damage state of the system to forecast its future performance by estimating the expected loading environments. A successful damage prediction model requires the integration of technologies in areas like measurements, materials science, mechanics of materials, and probability theories, but most importantly the quantification of uncertainty in all these areas. In this study, Affine Arithmetic is used as a method for incorporating the uncertainties due to the material properties into the fatigue life prognosis of composite plates subjected to cyclic compressive loadings. When loadings are compressive in nature, the composite plates undergo repeated buckling-unloading of the delaminated layer which induces mixed modes I and II states of stress at the tip of the delamination in the plates. The Kardomateas model-based prediction law is used to predict the growth of the delamination, while the integration of the effects of the uncertainties for modes I and II coefficients in the fatigue life prediction model is handled using Affine arithmetic. The Mode I and Mode II interlaminar fracture toughness and fatigue characterization of the composite plates are first experimentally studied to obtain the material coefficients and fracture toughness, respectively. Next, these obtained coefficients are used in the Kardomateas law to predict the delamination lengths in the composite plates while using Affine Arithmetic to handle their uncertainties. At last, the fatigue characterization of the composite plates during compressive-buckling loadings is experimentally studied, and the delamination lengths obtained are compared with the predicted values to check the performance of Affine Arithmetic as an uncertainty propagation tool.

Suggested techniques, equipment, and standards for the testing of hand insecticide-spraying equipment

PubMed Central

Hall, Lawrence B.

1955-01-01

The new demands placed upon application equipment by the introduction of modern insecticides have revealed the deficiencies of this equipment when required for continuous use on a large scale. If adequate equipment is to be produced, specifications must be based not only on basic materials tests but also on “use” tests, in which the conditions of field use are simulated. The author outlines suggested techniques to be followed and standards to be adopted in testing the performance of compression sprayers and allied equipment, with reference to the following features: compression-sprayer tank fatigue; tank impact; pump resistance to bursting; pump resistance to collapse; pump friction; cut-off valve durability; constant-pressure valves; cut-off valve actuation; hose flexure; hose tension and bursting-pressure; hose friction; gaskets, valve faces, and similar non-metallic parts; nozzle-orifice erosion; and nozzle pattern. ImagesFIG. 1FIG. 14FIG. 20 PMID:14364189

Compact and portable digitally controlled device for testing footwear materials: technical note.

PubMed

Foto, James G

2008-01-01

Little or no practical decision-making data are available to the foot-care provider regarding the selection of orthotic materials used in therapeutic footwear. A device for simulating in-shoe forefoot conditions for the testing of orthosis materials is described. Materials are tested for their effectiveness by evaluating and comparing stress-strain and dynamic compression fatigue characteristics. The device, called the Cyclical Compression Tester (CCT), has been optimized for size, simplicity of construction, and cost. Application of the device ranges from the clinician deciding the useful life of single- and multidensity orthosis materials to the researcher characterizing materials for finite-element analysis modeling. This real-time CCT device and custom user interface combine to make an evaluation tool useful for testing how the pressure distribution of in-shoe materials changes over time in therapeutic footwear for those with peripheral neuropathy at risk for foot injury.

Improvement of fatigue resistance for multilayer lead zirconate titanate (PZT)-based ceramic actuators by external mechanical loads

NASA Astrophysics Data System (ADS)

Yang, Gang; Yue, Zhenxing; Ji, Ye; Chu, Xiangcheng; Li, Longtu

2008-12-01

The influence of external compressive loads, applied along a direction perpendicular to polarization, on fatigue behaviors of multilayer lead zirconate titanate (PZT)-based ceramic actuators was investigated. Under no external mechanical load, a normal fatigue behavior was observed, demonstrating that both switching polarization (Pswitching) and remnant polarization (Pr) progressively decreased with increasing switching cycles due to domain pinning by charge point defects. However, an anomalous enhancement in both switching and remnant polarizations was observed upon application of the external compressive loads. After 5×106 cycles of polarization switching, Pswitching and Pr increase by about 13% and 6% at 40 MPa, respectively, while Pswitching and Pr increase by about 11% and 21% at 60 MPa, respectively. The improvement of fatigue resistance can be attributed to non-180° domain switching and suppression of microcracking, triggered by external mechanical loads.

The compression of perceived time in a hot environment depends on physiological and psychological factors.

PubMed

Tamm, Maria; Jakobson, Ainika; Havik, Merle; Burk, Andres; Timpmann, Saima; Allik, Jüri; Oöpik, Vahur; Kreegipuu, Kairi

2014-01-01

The human perception of time was observed under extremely hot conditions. Young healthy men performed a time production task repeatedly in 4 experimental trials in either a temperate (22 °C, relative humidity 35%) or a hot (42 °C, relative humidity 18%) environment and with or without a moderate-intensity treadmill exercise. Within 1 hour, the produced durations indicated a significant compression of short intervals (0.5 to 10 s) in the combination of exercising and high ambient temperature, while neither variable/condition alone was enough to yield the effect. Temporal judgement was analysed in relation to different indicators of arousal, such as critical flicker frequency (CFF), core temperature, heart rate, and subjective ratings of fatigue and exertion. The arousal-sensitive internal clock model (originally proposed by Treisman) is used to explain the temporal compression while exercising in heat. As a result, we suggest that the psychological response to heat stress, the more precisely perceived fatigue, is important in describing the relationship between core temperature and time perception. Temporal compression is related to higher core temperature, but only if a certain level of perceived fatigue is accounted for, implying the existence of a thermoemotional internal clock.

Towards a damage tolerance philosophy for composite materials and structures

NASA Technical Reports Server (NTRS)

O'Brien, T. Kevin

1990-01-01

A damage-threshold/fail-safe approach is proposed to ensure that composite structures are both sufficiently durable for economy of operation, as well as adequately fail-safe or damage tolerant for flight safety. Matrix cracks are assumed to exist throughout the off-axis plies. Delamination onset is predicted using a strain energy release rate characterization. Delamination growth is accounted for in one of three ways: either analytically, using delamination growth laws in conjunction with strain energy release rate analyses incorporating delamination resistance curves; experimentally, using measured stiffness loss; or conservatively, assuming delamination onset corresponds to catastrophic delamination growth. Fail-safety is assessed by accounting for the accumulation of delaminations through the thickness. A tension fatigue life prediction for composite laminates is presented as a case study to illustrate how this approach may be implemented. Suggestions are made for applying the damage-threshold/fail-safe approach to compression fatigue, tension/compression fatigue, and compression strength following low velocity impact.

Towards a damage tolerance philosophy for composite materials and structures

NASA Technical Reports Server (NTRS)

Obrien, T. Kevin

1988-01-01

A damage-threshold/fail-safe approach is proposed to ensure that composite structures are both sufficiently durable for economy of operation, as well as adequately fail-safe or damage tolerant for flight safety. Matrix cracks are assumed to exist throughout the off-axis plies. Delamination onset is predicted using a strain energy release rate characterization. Delamination growth is accounted for in one of three ways: either analytically, using delamination growth laws in conjunction with strain energy release rate analyses incorporating delamination resistance curves; experimentally, using measured stiffness loss; or conservatively, assuming delamination onset corresponds to catastrophic delamination growth. Fail-safety is assessed by accounting for the accumulation of delaminations through the thickness. A tension fatigue life prediction for composite laminates is presented as a case study to illustrate how this approach may be implemented. Suggestions are made for applying the damage-threshold/fail-safe approach to compression fatigue, tension/compression fatigue, and compression strength following low velocity impact.

In-situ neutron diffraction study on the tension-compression fatigue behavior of a twinning induced plasticity steel

DOE PAGES

Xie, Qingge; Liang, Jiangtao; Stoica, Alexandru Dan; ...

2017-05-17

Grain orientation dependent behavior during tension-compression type of fatigue loading in a TWIP steel was studied using in-situ neutron diffraction. Orientation zones with dominant behavior of (1) twinning-de-twinning, (2) twinning-re-twinning followed by twinning-de-twinning, (3) twinning followed by dislocation slip and (4) dislocation slip were identified. Jumps of the orientation density were evidenced in neutron diffraction peaks which explains the macroscopic asymmetric behavior. The asymmetric behavior in early stage of fatigue loading is mainly due to small volume fraction of twins in comparison with that at later stage. As a result, easy activation of the de-twin makes the macroscopically unloading behaviormore » nonlinear.« less

In-situ neutron diffraction study on the tension-compression fatigue behavior of a twinning induced plasticity steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Qingge; Liang, Jiangtao; Stoica, Alexandru Dan

Grain orientation dependent behavior during tension-compression type of fatigue loading in a TWIP steel was studied using in-situ neutron diffraction. Orientation zones with dominant behavior of (1) twinning-de-twinning, (2) twinning-re-twinning followed by twinning-de-twinning, (3) twinning followed by dislocation slip and (4) dislocation slip were identified. Jumps of the orientation density were evidenced in neutron diffraction peaks which explains the macroscopic asymmetric behavior. The asymmetric behavior in early stage of fatigue loading is mainly due to small volume fraction of twins in comparison with that at later stage. As a result, easy activation of the de-twin makes the macroscopically unloading behaviormore » nonlinear.« less

Effects of Different R ratios on Fatigue Crack Growth in Laser Peened Friction Stir Welds

NASA Technical Reports Server (NTRS)

Hatamleh, Omar; Hackel, Lloyd; Forth, Scott

2007-01-01

The influence of laser peening on the fatigue crack growth behavior of friction stir welded (FSW) Aluminum Alloy (AA) 7075-T7351 sheets was investigated. The surface modification resulting from the peening process on the fatigue crack growth of FSW was assessed for two different R ratios. The investigation indicated a significant decrease in fatigue crack growth rates resulting from using laser shock peening compared with unpeened, welded and unwelded specimens. The slower fatigue crack growth rate was attributed to the compressive residual stresses induced by the peening.

Mechanical behavior and fatigue performance of SMA short fiber reinforced MMC

NASA Astrophysics Data System (ADS)

Al-Matar, Basem Jawad

The mechanical behavior and performance of Shape Memory Alloy (SMA) short fiber NiTi reinforced Al was experimentally investigated for monotonic and fatigue test Al 6061 NiTi-SiC T6 was superior to unreinforced materials as well as to the reinforced Al T4. Taya three-dimensional model was performed on the monotonic tensile test at room temperature. It showed good agreement with experimental results. In order to utilize the compressive criterion for SMA, the NiTi reinforced Al composite was cooled at -10°C and prestrained at 1.2%. Beyond this limit composite suffered from damage. The net enhancement of SMA effect was around 10 MPa on composite yield stress. Results showed that the elastic constant for the composite did not change with loading and unloading suggesting that the inelastic behavior is plasticity. Further investigation on the inelastic behavior model as damage and/or plasticity by evaluating Poisson's ratio during loading was carried out by Adaptive Image Correlation Technique for Full-Field Strain Measurement. Poisson's ratio increased from around 0.33 to 0.5 demonstrating that it is plasticity that is responsible for the inelastic behavior. Scanning electron microscopy was also used and confirmed model results. The overall damage-behavior was quantified in terms of the post fatigue failure strength for low-cycle fatigue tests. Power law model was best to fit experimental findings.

Residual Stresses in a NiCrY-Coated Powder Metallurgy Disk Superalloy

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Rogers, Richard B.; Nesbitt, James A.; Puleo, Bernadette J.; Miller, Robert A.; Telesman, Ignacy; Draper, Susan L.; Locci, Ivan E.

2017-01-01

Protective ductile coatings will be necessary to mitigate oxidation and corrosion attack on superalloy disks exposed to increasing operating temperatures in some turbine engine environments. However, such coatings must be resistant to harmful surface cracking during service. The objective of this study was to investigate how residual stresses evolve in such coatings. Cylindrical gage fatigue specimens of powder metallurgy-processed disk superalloy LSHR were coated with a NiCrY coating, shot peened, and then subjected to fatigue in air at room and high temperatures. The effects of shot peening and fatigue cycling on average residual stresses and other aspects of the coating were assessed. Shot peening did induce beneficial compressive residual stresses in the coating and substrate. However, these stresses became more tensile in the coating with subsequent heating and contributed to cracking of the coating in long intervals of cycling at 760 C. Substantial compressive residual stresses remained in the substrate adjacent to the coating, sufficient to suppress fatigue cracking. The coating continued to protect the substrate from hot corrosion pitting, even after fatigue cracks initiated in the coating.

Open Screw Placement in a 1.5 mm LCP Over a Fracture Gap Decreases Fatigue Life

PubMed Central

Alwen, Sarah G. J.; Kapatkin, Amy S.; Garcia, Tanya C.; Milgram, Joshua; Stover, Susan M.

2018-01-01

Objective To investigate the influence of plate and screw hole position on the stability of simulated radial fractures stabilized with a 1.5 mm condylar locking compression plate (LCP). Study Design In vitro mechanical testing of paired cadaveric limbs. Sample Population Paired radii (n = 7) stabilized with a 1.5 mm condylar LCP with an open screw hole positioned either proximal to (PG), or over (OG), a simulated small fracture gap. Methods Constructs were cycled in axial compression at a simulated trot load until failure or a maximum of 200,000 cycles. Specimens that sustained 200,000 cycles without failure were then loaded in axial compression in a single cycle to failure. Construct cyclic axial stiffness and gap strain, fatigue life, and residual strength were evaluated and compared between constructs using analysis of variance. Results Of pairs that had a failure during cyclic loading, OG constructs survived fewer cycles (54,700 ± 60,600) than PG (116,800 ± 49,300). OG constructs had significantly lower initial stiffness throughout cyclic loading and higher gap strain range within the first 1,000 cycles than PG constructs. Residual strength variables were not significantly different between constructs, however yield loads occurred at loads only marginally higher than approximated trot loads. Fatigue life decreased with increasing body weight. Conclusion Fracture fixation stability is compromised by an open screw hole directly over a fracture gap compared to the open screw hole being buttressed by bone in the model studied. The 1.5 mm condylar LCP may be insufficient stabilization in dogs with appropriate radial geometry but high body weights. PMID:29876361

Fatigue tests of YBCO coated conductors

NASA Astrophysics Data System (ADS)

Bamba, S.; Tanaka, Y.; Ando, T.; Ueda, H.; Ishiyama, A.; Yamada, Y.; Shiohara, Y.

2008-02-01

In this paper, we report the fatigue characteristics of IBAD/PLD YBCO coated conductors. A YBCO coated conductor used in the superconducting coil of a SMES system is repeatedly subjected to mechanical tensile or compressive strain due to the Lorentz force during electrical charging or discharging. The superconducting characteristic of this conductor may deteriorate because of this cyclic strain. Therefore, it is necessary to investigate the effect of cyclic strain on the superconducting characteristics of YBCO coated conductors that have a laminated structure. We developed an experimental apparatus with a U-shaped sample holder in order to apply cyclic strain to the sample tape. This apparatus was used to perform the fatigue tests on YBCO coated conductors in liquid nitrogen in the absence of an external magnetic field. The strain cycles with the maximum strain epsilonmax (zero external strain → epsilonmax → zero external strain) were applied and repeated up to 5000 times, and the Ic measurements were performed at epsilonmax. Therefore, the application of cyclic strain with epsilonmax ranging from 0.3% to 0.5% did not result in any significant deterioration of the superconducting characteristics of the conductor.

Corrosion-fatigue of laser-repaired commercially pure titanium and Ti-6Al-4V alloy under different test environments.

PubMed

Zavanelli, R A; Guilherme, A S; Pessanha-Henriques, G E; de Arruda Nóbilo, M Antônio; Mesquita, M F

2004-10-01

This study evaluated the corrosion-fatigue life of laser-repaired specimens fabricated from commercially pure titanium (CP Ti) and Ti-6Al-4V alloy, tested under different storage conditions. For each metal, 30 dumbbell rods with a central 2.3 mm diameter were prepared by lost-wax casting with the Rematitan System. Simulating the failure after service, corrosion-fatigue life in different media at room temperature (air, synthetic saliva and fluoride synthetic saliva) was determined at a testing frequency of 10 Hz for intact specimens and after laser repairing, using a square waveform with equal maximum tensile and compressive stress that was 30% lower than the 0.2% offset yield strength. For laser welding, the fractured specimens were rejoined using a jig to align the sections invested in type-IV dental stone. The adjacent areas of the gap was air-abraded with 100 microm aluminum oxide, laser welded and retested under the same conditions as the initial intact specimens. The number of cycles at failure was recorded, and the fracture surface was examined with a scanning electron microscope (SEM). The number of cycles for failure of the welded and intact specimens was compared by anova and the Tukey test at a 5% probability level. Within the limitations of this study, the number of cycles required for fracture decreased in wet environments and the laser repairing process adversely affected the life of both metals under the corrosion-fatigue conditions.

THE EFFECT OF LASER SHOCK PEENING ON THE LIFE AND FAILURE MODE OF A COLD PILGER DIE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavender, Curt A.; Hong, Sung-tae; Smith, Mark T.

2008-08-11

The laser shock peening process was used to increase fatigue life of pilger dies made of A2 tool steel by imparting compressive residual stresses to fatigue prone areas of the dies. The result of X-Ray diffraction analysis indicated that deep, high- magnitude compressive residual stresses were generated by the laser shock peening process, and the peened dies exhibited a significant increase of in-service life. Fractography of the failed dies indicates that the fracture mechanism was altered by the peening process.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

The effect of surface treatment on the stress/life fatigue behavior of a titanium Ti-6Al-4V turbine fan blade alloy is investigated in the regime of 102 to 106 cycles to failure under fully reversed stress-controlled isothermal push-pull loading between 25? and 550?C at a frequency of 5 Hz. Specifically, the fatigue behavior was examined in specimens in the deep-rolled and laser-shock peened surface conditions, and compared to results on samples in the untreated (machined and stress annealed) condition. Although the fatigue resistance of the Ti-6Al-4V alloy declined with increasing test temperature regardless of surface condition, deep-rolling and laser-shock peening surface treatmentsmore » were found to extend the fatigue lives by factors of more than 30 and 5-10, respectively, in the high-cycle and low-cycle fatigue regimes at temperatures as high as 550?C. At these temperatures, compressive residual stresses are essentially relaxed; however, it is the presence of near-surface work hardened layers, with a nanocystalline structure in the case of deep-rolling and dense dislocation tangles in the case of laser-shock peening, which remain fairly stable even after cycling at 450?-550?C, that provide the basis for the beneficial role of mechanical surface treatments on the fatigue strength of Ti-6Al-4V at elevated temperatures.« less

Advantages of Residual Stresses in Dynamically Riveted Joints.

DTIC Science & Technology

1978-02-01

strain distribution around a rivet hole, and describes an experimental method for measuring the radial velocity of an expanding rivet. The advantages of... benefits of compressive residual stresses in riveted joints, fatigue specimens made of 2024-T81 aluminum were used. The specimens were tested at constant...concentration of in-service tensile stresses near the hole surfaze. Substan;Aal and significant benefits in design life and structural weight can be

Experimental Investigation of the Influence of Joint Geometric Configurations on the Mechanical Properties of Intermittent Jointed Rock Models Under Cyclic Uniaxial Compression

NASA Astrophysics Data System (ADS)

Liu, Yi; Dai, Feng; Fan, Pengxian; Xu, Nuwen; Dong, Lu

2017-06-01

Intermittent joints in rock mass are quite sensitive to cyclic loading conditions. Understanding the fatigue mechanical properties of jointed rocks is beneficial for rational design and stability analysis of rock engineering projects. This study experimentally investigated the influences of joint geometry (i.e., dip angle, persistency, density and spacing) on the fatigue mechanism of synthetic jointed rock models. Our results revealed that the stress-strain curve of jointed rock under cyclic loadings is dominated by its curve under monotonic uniaxial loadings; the terminal strain in fatigue curve is equal to the post-peak strain corresponding to the maximum cyclic stress in the monotonic stress-strain curve. The four joint geometrical parameters studied significantly affect the fatigue properties of jointed rocks, including the irreversible strains, the fatigue deformation modulus, the energy evolution, the damage variable and the crack coalescence patterns. The higher the values of the geometrical parameters, the lower the elastic energy stores in this jointed rock, the higher the fatigue damage accumulates in the first few cycles, and the lower the fatigue life. The elastic energy has certain storage limitation, at which the fatigue failure occurs. Two basic micro-cracks, i.e., tensile wing crack and shear crack, are observed in cyclic loading and unloading tests, which are controlled principally by joint dip angle and persistency. In general, shear cracks only occur in the jointed rock with higher dip angle or higher persistency, and the jointed rock is characterized by lower fatigue strength, larger damage variable and lower fatigue life.

EFFECTS OF CYCLIC FLEXURAL FATIGUE ON PORCINE BIOPROSTHETIC HEART VALVE HETEROGRAFT BIOMATERIALS

PubMed Central

Mirnajafi, Ali; Zubiate, Brett; Sacks, Michael S.

2009-01-01

While bioprosthetic heart valves (BHV) remain the primary treatment modality for adult heart valve replacement, continued problems with durability remain. Several studies have implicated flexure as a major damage mode in porcine-derived heterograft biomaterials used in BHV fabrication. While conventional accelerated wear testing can provide valuable insights into BHV damage phenomena, the constituent tissues are subjected to complex, time-varying deformation modes (i.e. tension and flexure), that do not allow for the control of the amount, direction, and location of flexure. Thus, in the present study customized fatigue testing devices were developed to subject circumferentially oriented porcine BHV tissue strips to controlled cyclic flexural loading. By using this approach, we were able to study layer-specific structural damage induced by cyclic flexural tensile and compressive stresses alone. 10×106, 25×106 and 50×106 cycle levels were used, with resulting changes in flexural stiffness and collagen structure assessed. Results indicated that flexural rigidity was markedly reduced after only 10×106 cycles, and progressively decayed at a lower rate with cycle number thereafter. Moreover, the against-curvature fatigue direction induced the most damage, suggesting that the ventricularis and fibrosa layers have low resistance to cyclic flexural compressive and tensile loads, respectively. The histological analyses indicated progressive collagen fiber delamination as early as 10×106 cycles, but otherwise no change in gross collagen orientation. Our results underscore that porcine-derived heterograft biomaterials are very sensitive to flexural fatigue, with delamination of the tissue layers the primary underlying mechanism. This appears to be in contrast to pericardial BHV, wherein high tensile stresses are considered to be the major cause of structural failure. These findings point towards the need for the development of chemical fixation technologies that minimize flexure induced damage to extend porcine heterograft biomaterial durability. PMID:20166221

Holographic evaluation of fatigue cracks by a compressive stress (HYSTERESIS) technique

NASA Technical Reports Server (NTRS)

Freska, S. A.; Rummel, W. D.

1974-01-01

Holographic interferometry compares unknown field of optical waves with known one. Differences are displayed as interference bands or fringes. Technique was evaluated on fatigue-cracked 2219-T87 aluminum-alloy panels. Small cracks were detected when specimen was incrementally unloaded.

Multiple Fatigue Failure Behaviors and Long-Life Prediction Approach of Carburized Cr-Ni Steel with Variable Stress Ratio

PubMed Central

Deng, Hailong; Li, Wei; Zhao, Hongqiao; Sakai, Tatsuo

2017-01-01

Axial loading tests with stress ratios R of −1, 0 and 0.3 were performed to examine the fatigue failure behavior of a carburized Cr-Ni steel in the long-life regime from 104 to 108 cycles. Results show that this steel represents continuously descending S-N characteristics with interior inclusion-induced failure under R = −1, whereas it shows duplex S-N characteristics with surface defect-induced failure and interior inclusion-induced failure under R = 0 and 0.3. The increasing tension eliminates the effect of compressive residual stress and promotes crack initiation from the surface or interior defects in the carburized layer. The FGA (fine granular area) formation greatly depends on the number of loading cycles, but can be inhibited by decreasing the compressive stress. Based on the evaluation of the stress intensity factor at the crack tip, the surface and interior failures in the short life regime can be characterized by the crack growth process, while the interior failure with the FGA in the long life regime can be characterized by the crack initiation process. In view of the good agreement between predicted and experimental results, the proposed approach can be well utilized to predict fatigue lives associated with interior inclusion-FGA-fisheye induced failure, interior inclusion-fisheye induced failure, and surface defect induced failure. PMID:28906454

Bending cyclic load test for crystalline silicon photovoltaic modules

NASA Astrophysics Data System (ADS)

Suzuki, Soh; Doi, Takuya; Masuda, Atsushi; Tanahashi, Tadanori

2018-02-01

The failures induced by thermomechanical fatigue within crystalline silicon photovoltaic modules are a common issue that can occur in any climate. In order to understand these failures, we confirmed the effects of compressive or tensile stresses (which were cyclically loaded on photovoltaic cells and cell interconnect ribbons) at subzero, moderate, and high temperatures. We found that cell cracks were induced predominantly at low temperatures, irrespective of the compression or tension applied to the cells, although the orientation of cell cracks was dependent on the stress applied. The fracture of cell interconnect ribbons was caused by cyclical compressive stress at moderate and high temperatures, and this failure was promoted by the elevation of temperature. On the basis of these results, the causes of these failures are comprehensively discussed in relation to the viscoelasticity of the encapsulant.

Influence of chest compression rate guidance on the quality of cardiopulmonary resuscitation performed on manikins.

PubMed

Jäntti, H; Silfvast, T; Turpeinen, A; Kiviniemi, V; Uusaro, A

2009-04-01

The adequate chest compression rate during CPR is associated with improved haemodynamics and primary survival. To explore whether the use of a metronome would affect also chest compression depth beside the rate, we evaluated CPR quality using a metronome in a simulated CPR scenario. Forty-four experienced intensive care unit nurses participated in two-rescuer basic life support given to manikins in 10min scenarios. The target chest compression to ventilation ratio was 30:2 performed with bag and mask ventilation. The rescuer performing the compressions was changed every 2min. CPR was performed first without and then with a metronome that beeped 100 times per minute. The quality of CPR was analysed with manikin software. The effect of rescuer fatigue on CPR quality was analysed separately. The mean compression rate between ventilation pauses was 137+/-18compressions per minute (cpm) without and 98+/-2cpm with metronome guidance (p<0.001). The mean number of chest compressions actually performed was 104+/-12cpm without and 79+/-3cpm with the metronome (p<0.001). The mean compression depth during the scenario was 46.9+/-7.7mm without and 43.2+/-6.3mm with metronome guidance (p=0.09). The total number of chest compressions performed was 1022 without metronome guidance, 42% at the correct depth; and 780 with metronome guidance, 61% at the correct depth (p=0.09 for difference for percentage of compression with correct depth). Metronome guidance corrected chest compression rates for each compression cycle to within guideline recommendations, but did not affect chest compression quality or rescuer fatigue.

Influence of the height of the external hexagon and surface treatment on fatigue life of commercially pure titanium dental implants.

PubMed

Gil, Francisco Javier; Aparicio, Conrado; Manero, Jose M; Padros, Alejandro

2009-01-01

This study evaluated the effect of external hexagon height and commonly applied surface treatments on the fatigue life of titanium dental implants. Electropolished commercially pure titanium dental implants (seven implants per group) with three different external hexagon heights (0.6, 1.2, and 1.8 mm) and implants with the highest external hexagon height (1.8 mm) and different surface treatments (electropolishing, grit blasting with aluminium oxide, and acid etching with sulfuric acid) were tested to evaluate their mechanical fatigue life. To do so, 10-Hz triangular flexural load cycles were applied at 37 degrees C in artificial saliva, and the number of load cycles until implant fracture was determined. Tolerances of the hexagon/abutment fit and implant surface roughness were analyzed by scanning electron microscopy and light interferometry. Transmission electron microscopy and electron diffraction analyses of titanium hydrides were performed. First, the fatigue life of implants with the highest hexagon (8,683 +/- 978 load cycles) was more than double that of the implants with the shortest hexagons (3,654 +/- 789 load cycles) (P < .02). Second, the grit-blasted implants had the longest fatigue life of the tested materials (21,393 +/- 2,356 load cycles), which was significantly greater than that of the other surfaces (P < .001). The compressive surface residual stresses induced when blasting titanium are responsible for this superior mechanical response. Third, precipitation of titanium hydrides in grain boundaries of titanium caused by hydrogen adsorption from the acid solution deteriorates the fatigue life of acid-etched titanium dental implants. These implants had the shortest fatigue life (P < .05). The fatigue life of threaded root-form dental implants varies with the height of the external hexagon and/or the surface treatment of the implant. An external hexagon height of 1.8 mm and/or a blasting treatment appear to significantly increase fatigue life of dental implants.

Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted

NASA Technical Reports Server (NTRS)

Krause, David L.; Whittenberger, J. Daniel

2002-01-01

The first mechanical tests of superalloy lattice block structures produced promising results for this exciting new lightweight material system. The testing was performed in-house at NASA Glenn Research Center's Structural Benchmark Test Facility, where small subelement-sized compression and beam specimens were loaded to observe elastic and plastic behavior, component strength levels, and fatigue resistance for hundreds of thousands of load cycles. Current lattice block construction produces a flat panel composed of thin ligaments arranged in a three-dimensional triangulated trusslike structure. Investment casting of lattice block panels has been developed and greatly expands opportunities for using this unique architecture in today's high-performance structures. In addition, advances made in NASA's Ultra-Efficient Engine Technology Program have extended the lattice block concept to superalloy materials. After a series of casting iterations, the nickel-based superalloy Inconel 718 (IN 718, Inco Alloys International, Inc., Huntington, WV) was successfully cast into lattice block panels; this combination offers light weight combined with high strength, high stiffness, and elevated-temperature durability. For tests to evaluate casting quality and configuration merit, small structural compression and bend test specimens were machined from the 5- by 12- by 0.5-in. panels. Linear elastic finite element analyses were completed for several specimen layouts to predict material stresses and deflections under proposed test conditions. The structural specimens were then subjected to room-temperature static and cyclic loads in Glenn's Life Prediction Branch's material test machine. Surprisingly, the test results exceeded analytical predictions: plastic strains greater than 5 percent were obtained, and fatigue lives did not depreciate relative to the base material. These assets were due to the formation of plastic hinges and the redundancies inherent in lattice block construction, which were not considered in the simplified computer models. The fatigue testing proved the value of redundancies since specimen strength was maintained even after the fracture of one or two ligaments. This ongoing test program is planned to continue through high-temperature testing. Also scheduled for testing are IN 718 lattice block panels with integral face sheets, as well as specimens cast from a higher temperature alloy. The initial testing suggests the value of this technology for large panels under low and moderate pressure loadings and for high-risk, damage-tolerant structures. Potential aeropropulsion uses for lattice blocks include turbine-engine actuated panels, exhaust nozzle flaps, and side panel structures.

Fatigue response of notched laminates subjected to tension-compression cyclic loads

NASA Technical Reports Server (NTRS)

Bakis, C. E.; Stinchcomb, W. W.

1986-01-01

The fatigue response of a ((0/45/90/-45)(sub s))(sub 4) T300-5208 graphite-epoxy laminate with a drilled center-hole subjected to various components of tensile and compressive cyclic loads was investigated. Damage evaluation techniques such as stiffness monitoring, penetrant-enhanced X-ray radiography, C-scan, laminate deply and residual strength measurement were used to establish the mechanisms of damage development as well as the effect of such damage on the laminate strength, stiffness and life. Damage modes consisted of transverse matrix cracks, initiating at the hole, in all plies, followed by delamination between plies of different orientation. A characteristic stiffness repsonse during cyclic loading at two load levels was identified and utilized a more reliable indicator of material and residual properties than accumulated cycles. For the load ratios of tension-compression loading, residual tensile strength increased significantly above the virgin strength early in the fatigue life and remained approximately constant to near the end of life. A technique developed for predicting delamination initiation sites along the hole boundary correlated well with experimental evidence.

Planum sphenoidale meningioma leading to visual disturbance

PubMed Central

Lutwak, Nancy; Dill, Curt; Wieczorek, Rosemary

2011-01-01

A 60-year-old male presented with complaints of dizziness, which worsened with fatigue and a sense his balance was ‘off’. Initial physical examination was negative and the laboratory testing was unremarkable. Within weeks, the patient developed bilateral visual field deficits. MRI revealed an extra-axial mass which extended into the pituitary fossa and caused compression of the pituitary gland. The pituitary stalk was displaced posteriorly and the optic chiasm was compressed with displacement superiorly and posteriorly. The patient underwent a surgical resection. Diabetes insipidus developed postoperatively requiring a vasopressin drip. He also developed hypopituitarism after the resection with hypothyroidism, hypoadrenalism and hypogonadism. The patient requires testosterone, levothyroxine and hydrocortisone replacement and has mild residual bitemporal hemianopsia. PMID:22679053

Planum sphenoidale meningioma leading to visual disturbance.

PubMed

Lutwak, Nancy; Dill, Curt; Wieczorek, Rosemary

2011-08-31

A 60-year-old male presented with complaints of dizziness, which worsened with fatigue and a sense his balance was 'off'. Initial physical examination was negative and the laboratory testing was unremarkable. Within weeks, the patient developed bilateral visual field deficits. MRI revealed an extra-axial mass which extended into the pituitary fossa and caused compression of the pituitary gland. The pituitary stalk was displaced posteriorly and the optic chiasm was compressed with displacement superiorly and posteriorly. The patient underwent a surgical resection. Diabetes insipidus developed postoperatively requiring a vasopressin drip. He also developed hypopituitarism after the resection with hypothyroidism, hypoadrenalism and hypogonadism. The patient requires testosterone, levothyroxine and hydrocortisone replacement and has mild residual bitemporal hemianopsia.

Relationship between weight of rescuer and quality of chest compression during cardiopulmonary resuscitation

PubMed Central

2014-01-01

Background According to the guidelines for cardiopulmonary resuscitation (CPR), the rotation time for chest compression should be about 2 min. The quality of chest compressions is related to the physical fitness of the rescuer, but this was not considered when determining rotation time. The present study aimed to clarify associations between body weight and the quality of chest compression and physical fatigue during CPR performed by 18 registered nurses (10 male and 8 female) assigned to light and heavy groups according to the average weight for each sex in Japan. Methods Five-minute chest compressions were then performed on a manikin that was placed on the floor. Measurement parameters were compression depth, heart rate, oxygen uptake, integrated electromyography signals, and rating of perceived exertion. Compression depth was evaluated according to the ratio (%) of adequate compressions (at least 5 cm deep). Results The ratio of adequate compressions decreased significantly over time in the light group. Values for heart rate, oxygen uptake, muscle activity defined as integrated electromyography signals, and rating of perceived exertion were significantly higher for the light group than for the heavy group. Conclusion Chest compression caused increased fatigue among the light group, which consequently resulted in a gradual fall in the quality of chest compression. These results suggested that individuals with a lower body weight should rotate at 1-min intervals to maintain high quality CPR and thus improve the survival rates and neurological outcomes of victims of cardiac arrest. PMID:24957919

The Impact of a Rigorous Multiple Work Shift Schedule and Day Versus Night Shift Work on Reaction Time and Balance Performance in Female Nurses: A Repeated Measures Study.

PubMed

Thompson, Brennan J; Stock, Matt S; Banuelas, Victoria K; Akalonu, Chibuzo C

2016-07-01

The aim of this study was to determine the impact of a demanding work schedule involving long, cumulative work shifts on response time and balance-related performance outcomes and to evaluate the prevalence of musculoskeletal disorders between day and night shift working nurses. A questionnaire was used to identify the prevalence of past (12-month) and current (7-day) musculoskeletal disorders. Nurses worked three 12-hour work shifts in a 4-day period. Reaction time and balance tests were conducted before and after the work period. The work period induced impairments for reaction time, errors on reaction time tasks, and balance performance, independent of shift type. Musculoskeletal symptom prevalence was high in workers of both work shifts. Compressed work shifts caused performance-based fatigue in nurses. Reaction time and balance tests may be sensitive fatigue identification markers in nurses.

Scanning electron microscope fractography of induced fatigue-damaged saline breast implants.

PubMed

Brandon, H J; Jerina, K L; Savoy, T L; Wolf, C J

2006-01-01

Breast implant strength and durability is presently an important topic in biomaterials science. Research studies are being conducted to determine the mechanisms and rates of failure in order to assess the in vivo performance of breast implants. Fatigue life is a measure of breast implant durability since fatigue failure is a potential in vivo failure mechanism. This study describes the characterization of the fracture surface morphology of breast implant shell regions that have failed due to cyclic fatigue. Saline breast implants were fatigue tested to failure using a laboratory apparatus in which flat plates cyclically compressed the implants. The implants were unimplanted control devices of both textured and smooth saline implants. The failure surfaces of the fatigued shells were examined using scanning electron microscopy (SEM). The morphological features of the failure surfaces are described for implants with short and long fatigue lifetimes. The details of both the inside and outside surfaces of the shell at the failure location are described. Two different modes of failure were observed in both the textured and smooth shells. These modes depend on the magnitude of the cyclic load and corresponding number of fatigue cycles at failure. The first mode is a tear in the shell of about 18 mm in length, and the second mode is a pinhole approximately 1 mm in diameter. Details of the surface morphology for these two types of failure modes and shell thickness data are presented herein. There was no significant change in the crosslink density of the shell as a result of fatigue.

Functional Fatigue and Tension-Compression Asymmetry in [001]-Oriented Co49Ni21Ga30 High-Temperature Shape Memory Alloy Single Crystals

NASA Astrophysics Data System (ADS)

Krooß, P.; Niendorf, T.; Kadletz, P. M.; Somsen, C.; Gutmann, M. J.; Chumlyakov, Y. I.; Schmahl, W. W.; Eggeler, G.; Maier, H. J.

2015-03-01

Conventional shape memory alloys cannot be employed for applications in the elevated temperature regime due to rapid functional degradation. Co-Ni-Ga has shown the potential to be used up to temperatures of about 400 °C due to a fully reversible superelastic stress-strain response. However, available results only highlight the superelastic response for single cycle tests. So far, no data addressing cyclic loading and functional fatigue are available. In order to close this gap, the current study reports on the cyclic degradation behavior and tension-compression asymmetry in [001]-oriented Co49Ni21Ga30 single crystals at elevated temperatures. The cyclic stress-strain response of the material under displacement controlled superelastic loading conditions was found to be dictated by the number of active martensite variants and different resulting stabilization effects. Co-Ni-Ga shows a large superelastic temperature window of about 400 °C under tension and compression, but a linear Clausius-Clapeyron relationship could only be observed up to a temperature of 200 °C. In the present experiments, the samples were subjected to 1000 cycles at different temperatures. Degradation mechanisms were characterized by neutron diffraction and transmission electron microscopy. The results in this study confirm the potential of these alloys for damping applications at elevated temperatures.

An Evidence-Based Approach for Choosing Post-exercise Recovery Techniques to Reduce Markers of Muscle Damage, Soreness, Fatigue, and Inflammation: A Systematic Review With Meta-Analysis

PubMed Central

Dupuy, Olivier; Douzi, Wafa; Theurot, Dimitri; Bosquet, Laurent; Dugué, Benoit

2018-01-01

Introduction: The aim of the present work was to perform a meta-analysis evaluating the impact of recovery techniques on delayed onset muscle soreness (DOMS), perceived fatigue, muscle damage, and inflammatory markers after physical exercise. Method: Three databases including PubMed, Embase, and Web-of-Science were searched using the following terms: (“recovery” or “active recovery” or “cooling” or “massage” or “compression garment” or “electrostimulation” or “stretching” or “immersion” or “cryotherapy”) and (“DOMS” or “perceived fatigue” or “CK” or “CRP” or “IL-6”) and (“after exercise” or “post-exercise”) for randomized controlled trials, crossover trials, and repeated-measure studies. Overall, 99 studies were included. Results: Active recovery, massage, compression garments, immersion, contrast water therapy, and cryotherapy induced a small to large decrease (−2.26 < g < −0.40) in the magnitude of DOMS, while there was no change for the other methods. Massage was found to be the most powerful technique for recovering from DOMS and fatigue. In terms of muscle damage and inflammatory markers, we observed an overall moderate decrease in creatine kinase [SMD (95% CI) = −0.37 (−0.58 to −0.16), I2 = 40.15%] and overall small decreases in interleukin-6 [SMD (95% CI) = −0.36 (−0.60 to −0.12), I2 = 0%] and C-reactive protein [SMD (95% CI) = −0.38 (−0.59 to−0.14), I2 = 39%]. The most powerful techniques for reducing inflammation were massage and cold exposure. Conclusion: Massage seems to be the most effective method for reducing DOMS and perceived fatigue. Perceived fatigue can be effectively managed using compression techniques, such as compression garments, massage, or water immersion. PMID:29755363

Experimental Study on Fatigue Behaviour of Shot-Peened Open-Hole Steel Plates

PubMed Central

Wang, Zhi-Yu; Wang, Qing-Yuan; Cao, Mengqin

2017-01-01

This paper presents an experimental study on the fatigue behaviour of shot-peened open-hole plates with Q345 steel. The beneficial effects induced by shot peening on the fatigue life improvement are highlighted. The characteristic fatigue crack initiation and propagation modes of open-hole details under fatigue loading are revealed. The surface hardening effect brought by the shot peening is analyzed from the aspects of in-depth micro-hardness and compressive residual stress. The fatigue life results are evaluated and related design suggestions are made as a comparison with codified detail categories. In particular, a fracture mechanics theory-based method is proposed and demonstrated its validity in predicting the fatigue life of studied shot-peened open-hole details. PMID:28841160

Fatigue life improvements of the AISI 304 stainless steel ground surfaces by wire brushing

NASA Astrophysics Data System (ADS)

Ben Fredj, Nabil; Ben Nasr, Mohamed; Ben Rhouma, Amir; Sidhom, Habib; Braham, Chedly

2004-10-01

The surface and subsurface integrity of metallic ground components is usually characterized by an induced tensile residual stress, which has a detrimental effect on the fatigue life of these components. In particular, it tends to accelerate the initiation and growth of the fatigue cracks. In this investigation, to deliberately generate compressive residual stresses into the ground surfaces of the AISI 304 stainless steel (SS), wire brushing was applied. It was found that under the experimental conditions selected in this investigation, while the surface roughness was slightly improved by the brushing process, the surface residual stress shifted from a tensile stress (σ‖=+450 MPa) to a compressive stress (σ‖=-435 MPa). On the other hand, the work-hardened deformation layer was almost two times deeper after wire brushing. Concerning the fatigue life, an improvement of 26% in terms of endurance limit at 2×106 cycles was realized. Scanning electron microscope (SEM) observations of the fatigue fracture location and size were carried out to explain the fatigue life improvement. It was found that the enhancement of the fatigue strength could be correlated with the distribution and location of the fatigue fracture nucleation sites. Concerning the ground surfaces, it was seen that the fatigue cracks initiated at the bottom of the grinding grooves and were particularly long (150-200 µm). However, the fatigue cracks at the brushed surfaces were shorter (20-40 µm) and appeared to initiate sideways to the plowed material caused by the wire brushing. The results of the wire-brushed surface characterization have shown that significant advantages can be realized regarding surface integrity by the application of this low-cost process compared to shot peening.

Compression-after-Impact and Bend Fatigue Results of Glass/Epoxy Composites with Compliant Interlayer and Needling Interlaminar Enhancements

DTIC Science & Technology

2017-05-22

velocity impact of 2-D woven fabric panels displacement response with various interlaminar enhancements ............................... 7 Fig. 3 Low...various interlaminar enhancements ............. 9 Fig. 8 Low-velocity impact displacement response for 3-D TPU interlayer composites...The results for the impact testing of the panels with 2-D woven glass fabrics are provided in Figs. 2–6 for displacement versus time, energy versus

The effects of simulated bone loss on the implant-abutment assembly and likelihood of fracture: an in vitro study.

PubMed

Manzoor, Behzad; Suleiman, Mahmood; Palmer, Richard M

2013-01-01

The crestal bone level around a dental implant may influence its strength characteristics by offering protection against mechanical failures. Therefore, the present study investigated the effect of simulated bone loss on modes, loads, and cycles to failure in an in vitro model. Different amounts of bone loss were simulated: 0, 1.5, 3.0, and 4.5 mm from the implant head. Forty narrow-diameter (3.0-mm) implant-abutment assemblies were tested using compressive bending and cyclic fatigue testing. Weibull and accelerated life testing analysis were used to assess reliability and functional life. Statistical analyses were performed using the Fisher-Exact test and the Spearman ranked correlation. Compressive bending tests showed that the level of bone loss influenced the load-bearing capacity of implant-abutment assemblies. Fatigue testing showed that the modes, loads, and cycles to failure had a statistically significant relationship with the level of bone loss. All 16 samples with bone loss of 3.0 mm or more experienced horizontal implant body fractures. In contrast, 14 of 16 samples with 0 and 1.5 mm of bone loss showed abutment and screw fractures. Weibull and accelerated life testing analysis indicated a two-group distribution: the 0- and 1.5-mm bone loss samples had better functional life and reliability than the 3.0- and 4.5-mm samples. Progressive bone loss had a significant effect on modes, loads, and cycles to failure. In addition, bone loss influenced the functional life and reliability of the implant-abutment assemblies. Maintaining crestal bone levels is important in ensuring biomechanical sustainability and predictable long-term function of dental implant assemblies.

Benchmark notch test for life prediction

NASA Technical Reports Server (NTRS)

Domas, P. A.; Sharpe, W. N.; Ward, M.; Yau, J. F.

1982-01-01

The laser Interferometric Strain Displacement Gage (ISDG) was used to measure local strains in notched Inconel 718 test bars subjected to six different load histories at 649 C (1200 F) and including effects of tensile and compressive hold periods. The measurements were compared to simplified Neuber notch analysis predictions of notch root stress and strain. The actual strains incurred at the root of a discontinuity in cyclically loaded test samples subjected to inelastic deformation at high temperature where creep deformations readily occur were determined. The steady state cyclic, stress-strain response at the root of the discontinuity was analyzed. Flat, double notched uniaxially loaded fatigue specimens manufactured from the nickel base, superalloy Inconel 718 were used. The ISDG was used to obtain cycle by cycle recordings of notch root strain during continuous and hold time cycling at 649 C. Comparisons to Neuber and finite element model analyses were made. The results obtained provide a benchmark data set in high technology design where notch fatigue life is the predominant component service life limitation.

High temperature tension-compression fatigue behavior of a tungsten copper composite

NASA Technical Reports Server (NTRS)

Verrilli, Michael J.; Gabb, Timothy P.

1990-01-01

The high temperature fatigue of a (O)12 tungsten fiber reinforced copper matrix composite was investigated. Specimens having fiber volume percentages of 10 and 36 were fatigued under fully-reversed, strain-controlled conditions at both 260 and 560 C. The fatigue life was found to be independent of fiber volume fraction because fatigue damage preferentially occurred in the matrix. Also, the composite fatigue lives were shorter at 560 C as compared to 260 C due to changes in mode of matrix failure. On a total strain basis, the fatigue life of the composite at 560 C was the same as the life of unreinforced copper, indicating that the presence of the fibers did not degrade the fatigue resistance of the copper matrix in this composite system. Comparison of strain-controlled fatigue data to previously-generated load-controlled data revealed that the strain-controlled fatigue lives were longer because of mean strain and mean stress effects.

The prevalence of chest compression leaning during in-hospital cardiopulmonary resuscitation

PubMed Central

Fried, David A.; Leary, Marion; Smith, Douglas A.; Sutton, Robert M.; Niles, Dana; Herzberg, Daniel L.; Becker, Lance B.; Abella, Benjamin S.

2011-01-01

Objective Successful resuscitation from cardiac arrest requires the delivery of high-quality chest compressions, encompassing parameters such as adequate rate, depth, and full recoil between compressions. The lack of compression recoil (“leaning” or “incomplete recoil”) has been shown to adversely affect hemodynamics in experimental arrest models, but the prevalence of leaning during actual resuscitation is poorly understood. We hypothesized that leaning varies across resuscitation events, possibly due to rescuer and/or patient characteristics and may worsen over time from rescuer fatigue during continuous chest compressions. Methods This was an observational clinical cohort study at one academic medical center. Data were collected from adult in-hospital and Emergency Department arrest events using monitor/defibrillators that record chest compression characteristics and provide real-time feedback. Results We analyzed 112,569 chest compressions from 108 arrest episodes from 5/2007 to 2/2009. Leaning was present in 98/108 (91%) cases; 12% of all compressions exhibited leaning. Leaning varied widely across cases: 41/108 (38%) of arrest episodes exhibited <5% leaning yet 20/108 (19%) demonstrated >20% compression leaning. When evaluating blocks of continuous compressions (>120 sec), only 4/33 (12%) had an increase in leaning over time and 29/33 (88%) showed a decrease (p<0.001). Conclusions Chest compression leaning was common during resuscitation care and exhibited a wide distribution, with most leaning within a subset of resuscitations. Leaning decreased over time during continuous chest compression blocks, suggesting that either leaning may not be a function of rescuer fatiguing, or that it may have been mitigated by automated feedback provided during resuscitation episodes. PMID:21482010

Stress corrosion cracking and corrosion fatigue characterisation of MgZn1Ca0.3 (ZX10) in a simulated physiological environment.

PubMed

Jafari, Sajjad; Raman, R K Singh; Davies, Chris H J; Hofstetter, Joelle; Uggowitzer, Peter J; Löffler, Jörg F

2017-01-01

Magnesium (Mg) alloys have attracted great attention as potential materials for biodegradable implants. It is essential that an implant material possesses adequate resistance to cracking/fracture under the simultaneous actions of corrosion and mechanical stresses, i.e., stress corrosion cracking (SCC) and/or corrosion fatigue (CF). This study investigates the deformation behaviour of a newly developed high-strength low-alloy Mg alloy, MgZn1Ca0.3 (ZX10), processed at two different extrusion temperatures of 325 and 400°C (named E325 and E400, respectively), under slow strain tensile and cyclic tension-compression loadings in air and modified simulated body fluid (m-SBF). Extrusion resulted in a bimodal grain size distribution with recrystallised grain sizes of 1.2 μm ± 0.8 μm and 7 ± 5 μm for E325 and E400, respectively. E325 possessed superior tensile and fatigue properties to E400 when tested in air. This is mainly attributed to a grain-boundary strengthening mechanism. However, both E325 and E400 were found to be susceptible to SCC at a strain rate of 3.1×10 -7 s -1 in m-SBF. Moreover, both E325 and E400 showed similar fatigue strength when tested in m-SBF. This is explained on the basis of crack initiation from localised corrosion following tests in m-SBF. Crown Copyright © 2016. Published by Elsevier Ltd. All rights reserved.

Fatigue behavior of thermal sprayed WC-CoCr- steel systems: Role of process and deposition parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vackel, Andrew; Sampath, Sanjay

Thermal spray deposited WC-CoCr coatings are extensively used for surface protection of wear prone components in a variety of applications. Although the primary purpose of the coating is wear and corrosion protection, many of the coated components are structural systems (aero landing gear, hydraulic cylinders, drive shafts etc.) and as such experience cyclic loading during service and are potentially prone to fatigue failure. It is of interest to ensure that the coating and the application process does not deleteriously affect the fatigue strength of the parent structural metal. It has long been appreciated that the relative fatigue life of amore » thermal sprayed component can be affected by the residual stresses arising from coating deposition. The magnitude of these stresses can be managed by torch processing parameters and can also be influenced by deposition effects, particularly the deposition temperature. In this study, the effect of both torch operating parameters (particle states) and deposition conditions (notably substrate temperature) were investigated through rotating bending fatigue studies. The results indicate a strong influence of process parameters on relative fatigue life, including credit or debit to the substrate's fatigue life measured via rotating bend beam studies. Damage progression within the substrate was further explored by stripping the coating off part way through fatigue testing, revealing a delay in the onset of substrate damage with more fatigue resistant coatings but no benefit with coatings with inadequate properties. Finally, the results indicate that compressive residual stress and adequate load bearing capability of the coating (both controlled by torch and deposition parameters) delay onset of substrate damage, enabling fatigue credit of the coated component.« less

Fatigue behavior of thermal sprayed WC-CoCr- steel systems: Role of process and deposition parameters

DOE PAGES

Vackel, Andrew; Sampath, Sanjay

2017-02-27

Thermal spray deposited WC-CoCr coatings are extensively used for surface protection of wear prone components in a variety of applications. Although the primary purpose of the coating is wear and corrosion protection, many of the coated components are structural systems (aero landing gear, hydraulic cylinders, drive shafts etc.) and as such experience cyclic loading during service and are potentially prone to fatigue failure. It is of interest to ensure that the coating and the application process does not deleteriously affect the fatigue strength of the parent structural metal. It has long been appreciated that the relative fatigue life of amore » thermal sprayed component can be affected by the residual stresses arising from coating deposition. The magnitude of these stresses can be managed by torch processing parameters and can also be influenced by deposition effects, particularly the deposition temperature. In this study, the effect of both torch operating parameters (particle states) and deposition conditions (notably substrate temperature) were investigated through rotating bending fatigue studies. The results indicate a strong influence of process parameters on relative fatigue life, including credit or debit to the substrate's fatigue life measured via rotating bend beam studies. Damage progression within the substrate was further explored by stripping the coating off part way through fatigue testing, revealing a delay in the onset of substrate damage with more fatigue resistant coatings but no benefit with coatings with inadequate properties. Finally, the results indicate that compressive residual stress and adequate load bearing capability of the coating (both controlled by torch and deposition parameters) delay onset of substrate damage, enabling fatigue credit of the coated component.« less

Time-Dependent Material Data Essential for the Durability Analysis of Composite Flywheels Provided by Compressive Experiments

NASA Technical Reports Server (NTRS)

Thesken, John C.; Bowman, Cheryl L.; Arnold, Steven M.

2003-01-01

Successful spaceflight operations require onboard power management systems that reliably achieve mission objectives for a minimal launch weight. Because of their high specific energies and potential for reduced maintenance and logistics, composite flywheels are an attractive alternative to electrochemical batteries. The Rotor Durability Team, which comprises members from the Ohio Aerospace Institute (OAI) and the NASA Glenn Research Center, completed a program of elevated temperature testing at Glenn' s Life Prediction Branch's Fatigue Laboratory. The experiments provided unique design data essential to the safety and durability of flywheel energy storage systems for the International Space Station and other manned spaceflight applications. Analysis of the experimental data (ref. 1) demonstrated that the compressive stress relaxation of composite flywheel rotor material is significantly greater than the commonly available tensile stress relaxation data. Durability analysis of compression preloaded flywheel rotors is required for accurate safe-life predictions for use in the International Space Station.

In vitro biomechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: prototype equine spoon plate versus axially positioned dynamic compression plate and two abaxial transarticular cortical screws inserted in lag fashion.

PubMed

Sod, Gary A; Mitchell, Colin F; Hubert, Jeremy D; Martin, George S; Gill, Marjorie S

2007-12-01

To compare in vitro monotonic biomechanical properties of an equine spoon plate (ESP) with an axial 3-hole, 4.5 mm narrow dynamic compression plate (DCP) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws (DCP-TLS) inserted in lag fashion for equine proximal interphalangeal (PIP) joint arthrodesis. Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Cadaveric adult equine forelimbs (n=18 pairs). For each forelimb pair, 1 PIP joint was stabilized with an ESP (8 hole, 4.5 mm) and 1 with an axial 3-hole narrow DCP (4.5 mm) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion. Six matching pairs of constructs were tested in single cycle to failure under axial compression with load applied under displacement control at a constant rate of 5 cm/s. Six construct pairs were tested for cyclic fatigue under axial compression with cyclic load (0-7.5 kN) applied at 6 Hz; cycles to failure were recorded. Six construct pairs were tested in single cycle to failure under torsional loading applied at a constant displacement rate (0.17 radians/s) until rotation of 0.87 radians occurred. Mean values for each fixation method were compared using a paired t-test within each group with statistical significance set at P<.05. Mean yield load, yield stiffness, and failure load for ESP fixation were significantly greater (for axial compression and torsion) than for DCP-TLS fixation. Mean (+/- SD) values for the ESP and DCP-TLS fixation techniques, respectively, in single cycle to failure under axial compression were: yield load 123.9 +/- 8.96 and 28.5 +/- 3.32 kN; stiffness, 13.11 +/- 0.242 and 2.60 +/- 0.17 kN/cm; and failure load, 144.4 +/- 13.6 and 31.4 +/- 3.8 kN. In single cycle to failure under torsion, mean (+/- SD) values for ESP and DCP-TLS, respectively, were: stiffness 2,022 +/- 26.2 and 107.9 +/- 11.1 N m/rad; and failure load: 256.4 +/- 39.2 and 87.1 +/- 11.5 N m. Mean cycles to failure in axial compression of ESP fixation (622,529 +/- 65,468) was significantly greater than DCP-TLS (95,418 +/- 11,037). ESP was superior to an axial 3-hole narrow DCP with 2 abaxial transarticular screws inserted in lag fashion in resisting static overload forces and cyclic fatigue. In vitro results support further evaluation of ESP for PIP joint arthrodesis in horses. Its specific design may provide increased stability without need for external coaptation support.

Drilling the near cortex with elongated figure-of-8 holes to reduce the stiffness of a locking compression plate construct.

PubMed

Chen, Jerry Yongqiang; Zhou, Zhihong; Ang, Benjamin Fu Hong; Yew, Andy Khye Soon; Chou, Siaw Meng; Chia, Shi-Lu; Koh, Joyce Suang Bee; Howe, Tet Sen

2015-12-01

To compare the stiffness of locking compression plate (LCP) constructs with or without drilling the near cortex with elongated figure-of-8 holes. 24 synthetic bones were sawn to create a 10-mm gap and were fixed with a 9-hole 4.5-mm narrow LCP. In 12 bones, the near cortex of the adjacent holes to the LCP holes was drilled to create elongated figure-of-8 holes before screw insertion. The stiffness of LCP constructs under axial loading or 4-point bending was assessed by (1) dynamic quasi-physiological testing for fatigue strength, (2) quasi-static testing for stiffness, and (3) testing for absolute strength to failure. None of the 24 constructs had subcatastrophic or catastrophic failure after 10 000 cycles of fatigue loading (p=1.000). The axial stiffness reduced by 16% from 613±62 to 517±44 N/mm (p=0.012) in the case group, whereas the bending stiffness was 16±1 Nm2 in both groups (p=1.000). The maximum axial load to catastrophic failure was 1596±84 N for the control group and 1627±48 N for the case group (p=0.486), whereas the maximum bending moment to catastrophic failure was 79±12 and 80±10 Nm, respectively (p=0.919). Drilling the near cortex with elongated figure-of-8 holes reduces the axial stiffness of the LCP construct, without compromising its bending stiffness or strength.

Accelerated fatigue testing of dentin-composite bond with continuously increasing load.

PubMed

Li, Kai; Guo, Jiawen; Li, Yuping; Heo, Young Cheul; Chen, Jihua; Xin, Haitao; Fok, Alex

2017-06-01

The aim of this study was to evaluate an accelerated fatigue test method that used a continuously increasing load for testing the dentin-composite bond strength. Dentin-composite disks (ϕ5mm×2mm) made from bovine incisor roots were subjected to cyclic diametral compression with a continuously increasingly load amplitude. Two different load profiles, linear and nonlinear with respect to the number of cycles, were considered. The data were then analyzed by using a probabilistic failure model based on the Weakest-Link Theory and the classical stress-life function, before being transformed to simulate clinical data of direct restorations. All the experimental data could be well fitted with a 2-parameter Weibull function. However, a calibration was required for the effective stress amplitude to account for the difference between static and cyclic loading. Good agreement was then obtained between theory and experiments for both load profiles. The in vitro model also successfully simulated the clinical data. The method presented will allow tooth-composite interfacial fatigue parameters to be determined more efficiently. With suitable calibration, the in vitro model can also be used to assess composite systems in a more clinically relevant manner. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance

PubMed Central

Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

2015-01-01

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding. PMID:26067176

Parametric study on single shot peening by dimensional analysis method incorporated with finite element method

NASA Astrophysics Data System (ADS)

Wu, Xian-Qian; Wang, Xi; Wei, Yan-Peng; Song, Hong-Wei; Huang, Chen-Guang

2012-06-01

Shot peening is a widely used surface treatment method by generating compressive residual stress near the surface of metallic materials to increase fatigue life and resistance to corrosion fatigue, cracking, etc. Compressive residual stress and dent profile are important factors to evaluate the effectiveness of shot peening process. In this paper, the influence of dimensionless parameters on maximum compressive residual stress and maximum depth of the dent were investigated. Firstly, dimensionless relations of processing parameters that affect the maximum compressive residual stress and the maximum depth of the dent were deduced by dimensional analysis method. Secondly, the influence of each dimensionless parameter on dimensionless variables was investigated by the finite element method. Furthermore, related empirical formulas were given for each dimensionless parameter based on the simulation results. Finally, comparison was made and good agreement was found between the simulation results and the empirical formula, which shows that a useful approach is provided in this paper for analyzing the influence of each individual parameter.

In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance.

PubMed

Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

2015-06-11

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding.

In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance

NASA Astrophysics Data System (ADS)

Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

2015-06-01

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding.

The cyclic stress-strain behavior of a nickel-base superalloy at 650 C

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Welsch, G. E.

1986-01-01

It is pointed out that examinations of the monotonic tensile and fatigue behaviors of single crystal nickel-base superalloys have disclosed orientation-dependent tension-compression anisotropies and significant differences in the mechanical response of octahedral and cube slip at intermediate temperatures. An examination is conducted of the cyclic hardening response of the single crystal superalloy PWA 1480 at 650 C. In the considered case, tension-compression anisotropy is present, taking into account primarily conditions under which a single slip system is operative. Aspects of a deformation by single slip are considered along with cyclic hardening anisotropy in tension and compression. It is found that specimens deforming by octahedral slip on a single slip system have similar hardening responses in tensile and low cycle fatigue loading. Cyclic strain hardening is very low for specimens displaying single slip.

In vitro biomechanical comparison of multistrand cables with conventional cervical stabilization.

PubMed

Weis, J C; Cunningham, B W; Kanayama, M; Parker, L; McAfee, P C

1996-09-15

The biomechanical stability of six different methods of cervical spine stabilization, three using multistrand cables, were evaluated in a bovine model. To quantify and compare the in vitro biomechanical properties of multistrand cables used for posterior cervical wiring to standard cervical fixation techniques. Fixation of the posterior cervical spine with monofilament stainless steel wire is a proven technique for stabilization of the cervical spine. Recently, multistrand braided cables have been used as a substitute for monofilament stainless steel wires. These cables, made of stainless steel, titanium, or polyethylene, are reported to be stronger, more flexible, and fatigue resistant than are monofilament wire based on mechanical testing. However, no in vitro biomechanical studies have been performed testing a standard posterior cervical wiring technique using multistrand cables. Thirty-six fresh frozen cervical calf spines consistent in size and age were mounted and fixed rigidly to isolate the C4-C5 motion segment. Six different reconstruction techniques were evaluated for Rogers' posterior cervical wiring technique using: 1) 20-gauge stainless steel monofilament wire, 2) stainless steel cable, 3) titanium cable, 4) polyethylene cables, 5) anterior locking plate construct with interbody graft, and 6) posterior plate construct. Six cervical spines were included in each group (n = 6), with each specimen statically evaluated under three stability conditions: 1) intact, 2) reconstructed, and 3) postfatigue. The instability model created before the reconstruction consisted of a distractive flexion Stage 3 injury at C4-C5. Nondestructive static biomechanical testing, performed on an material testing machine (MTS 858 Bionix test system, Minneapolis, MN), included axial compression, axial rotation, flexion-extension, and lateral bending. After reconstruction and static analysis, the specimens were fatigued for 1500 cycles and then statically retested. Data analysis included normalization of the reconstructed and postfatigue data to the intact condition. The calculated static parameters included operative functional unit stiffness and range of motion. Posterior cervical reconstruction with stainless steel monofilament wire proved inadequate under fatigue testing. Two of the six specimens failed with fatigue, and this construct permitted the greatest degree of flexion-extension motion after fatigue in comparison with all other constructs (P < 0.05). There were no significant differences in flexural stiffness or range of motion between stainless steel, titanium, or polyethylene cable constructs before or after fatigue testing. The posterior cervical plate constructs were the stiffest constructs under flexion, extension, and lateral bending modes, before and after fatigue testing (P < 0.05). Multistrand cables were superior to monofilament wire with fatigue testing using an in vitro calf cervical spine model. There were no failures or detectable differences in elongation after fatigue testing between the stainless steel, titanium, and polyethylene cables, as shown by the flexion-extension range of motion. The posterior cervical plate construct offered the greatest stability compared with all other constructs.

[Cement augmentation on the spine : Biomechanical considerations].

PubMed

Kolb, J P; Weiser, L; Kueny, R A; Huber, G; Rueger, J M; Lehmann, W

2015-09-01

Vertebral compression fractures are the most common osteoporotic fractures. Since the introduction of vertebroplasty and screw augmentation, the management of osteoporotic fractures has changed significantly. The biomechanical characteristics of the risk of adjacent fractures and novel treatment modalities for osteoporotic vertebral fractures, including pure cement augmentation by vertebroplasty, and cement augmentation of screws for posterior instrumentation, are explored. Eighteen human osteoporotic lumbar spines (L1-5) adjacent to vertebral bodies after vertebroplasty were tested in a servo-hydraulic machine. As augmentation compounds we used standard cement and a modified low-strength cement. Different anchoring pedicle screws were tested with and without cement augmentation in another cohort of human specimens with a simple pull-out test and a fatigue test that better reflects physiological conditions. Cement augmentation in the osteoporotic spine leads to greater biomechanical stability. However, change in vertebral stiffness resulted in alterations with the risk of adjacent fractures. By using a less firm cement compound, the risk of adjacent fractures is significantly reduced. Both screw augmentation techniques resulted in a significant increase in the withdrawal force compared with the group without cement. Augmentation using perforated screws showed the highest stability in the fatigue test. The augmentation of cement leads to a significant change in the biomechanical properties. Differences in the stability of adjacent vertebral bodies increase the risk of adjacent fractures, which could be mitigated by a modified cement compound with reduced strength. Screws that were specifically designed for cement application displayed greatest stability in the fatigue test.

The Mechanical Properties and Biometrical Effect of 3D Preformed Titanium Membrane for Guided Bone Regeneration on Alveolar Bone Defect

PubMed Central

Lee, So-Hyoun; Moon, Jong-Hoon; Jeong, Chang-Mo; Bae, Eun-Bin; Park, Chung-Eun; Jeon, Gye-Rok; Lee, Jin-Ju; Jeon, Young-Chan

2017-01-01

The purpose of this study is to evaluate the effect of three-dimensional preformed titanium membrane (3D-PFTM) to enhance mechanical properties and ability of bone regeneration on the peri-implant bone defect. 3D-PFTMs by new mechanically compressive molding technology and manually shaped- (MS-) PFTMs by hand manipulation were applied in artificial peri-implant bone defect model for static compressive load test and cyclic fatigue load test. In 12 implants installed in the mandibular of three beagle dogs, six 3D-PFTMs, and six collagen membranes (CM) randomly were applied to 2.5 mm peri-implant buccal bone defect with particulate bone graft materials for guided bone regeneration (GBR). The 3D-PFTM group showed about 7.4 times higher mechanical stiffness and 5 times higher fatigue resistance than the MS-PFTM group. The levels of the new bone area (NBA, %), the bone-to-implant contact (BIC, %), distance from the new bone to the old bone (NB-OB, %), and distance from the osseointegration to the old bone (OI-OB, %) were significantly higher in the 3D-PFTM group than the CM group (p < .001). It was verified that the 3D-PFTM increased mechanical properties which were effective in supporting the space maintenance ability and stabilizing the particulate bone grafts, which led to highly efficient bone regeneration. PMID:29018818

The Effects of the Compressed Workweek: A Review of the Evidence.

ERIC Educational Resources Information Center

Dawkins, Peter; Tulsi, Narmon

1990-01-01

A literature review showed substantial growth in the use of compressed work weeks. Employees benefited from increased leisure but suffered from increased fatigue and work disruption. Organizations might experience enhanced morale and less absenteeism as well as work coordination and communication problems. (SK)

Perspective for Fibre-Hybrid Composites in Wind Energy Applications

PubMed Central

2017-01-01

Increasing the efficiency of wind turbines will be vital for the wind energy sector to continue growing. The drive for increased efficiency is pushing turbine manufacturers to shift from glass fibre composite blades towards carbon/glass fibre-hybrid composite blades. This shift brings significant challenges in terms of optimising the design and understanding the failure of these new blade materials. This review therefore surveys the literature on fibre-hybrid composites, with an emphasis on aspects that are relevant for turbine blade materials. The literature on tensile, flexural, compressive, and fatigue performance is critically assessed and areas for future research are identified. Numerical simulations of fibre-hybrid composites have reached a reasonable maturity for tensile failure, but significant progress is required for flexural, compressive, and fatigue failure. Fatigue failure of fibre-hybrid composites in particular, requires more careful attention from both a modelling and experimental point of view. PMID:29117126

Perspective for Fibre-Hybrid Composites in Wind Energy Applications.

PubMed

Swolfs, Yentl

2017-11-08

Increasing the efficiency of wind turbines will be vital for the wind energy sector to continue growing. The drive for increased efficiency is pushing turbine manufacturers to shift from glass fibre composite blades towards carbon/glass fibre-hybrid composite blades. This shift brings significant challenges in terms of optimising the design and understanding the failure of these new blade materials. This review therefore surveys the literature on fibre-hybrid composites, with an emphasis on aspects that are relevant for turbine blade materials. The literature on tensile, flexural, compressive, and fatigue performance is critically assessed and areas for future research are identified. Numerical simulations of fibre-hybrid composites have reached a reasonable maturity for tensile failure, but significant progress is required for flexural, compressive, and fatigue failure. Fatigue failure of fibre-hybrid composites in particular, requires more careful attention from both a modelling and experimental point of view.

Experimental investigation of fatigue behavior of carbon fiber composites using fully-reversed four-point bending test

NASA Astrophysics Data System (ADS)

Amiri, Ali

Carbon fiber reinforced polymers (CFRP) have become an increasingly notable material for use in structural engineering applications. Some of their advantages include high strength-to-weight ratio, high stiffness-to-weight ratio, and good moldability. Prediction of the fatigue life of composite laminates has been the subject of various studies due to the cyclic loading experienced in many applications. Both theoretical studies and experimental tests have been performed to estimate the endurance limit and fatigue life of composite plates. One of the main methods to predict fatigue life is the four-point bending test. In most previous works, the tests have been done in one direction (load ratio, R, > 0). In the current work, we have designed and manufactured a special fixture to perform a fully reversed bending test (R = -1). Static four-point bending tests were carried out on three (0°/90°)15 and (± 45°)15 samples to measure the mechanical properties of CFRP. Testing was displacement-controlled at the rate of 10 mm/min until failure. In (0°/90°)15 samples, all failed by cracking/buckling on the compressive side of the sample. While in (± 45°)15 all three tests, no visual fracture or failure of the samples was observed. 3.4 times higher stresses were reached during four-point static bending test of (0° /90°)15 samples compared to (± 45°)15. Same trend was seen in literature for similar tests. Four-point bending fatigue tests were carried out on (0° /90°)15 sample with stress ratio, R = -1 and frequency of 5 Hz. Applied maximum stresses were approximately 45%, 56%, 67%, 72% and 76% of the measured yield stress for (0° /90°)15 samples. There was visible cracking through the thickness of the samples. The expected downward trend in fatigue life with increasing maximum applied stress was observed in S-N curves of samples. There appears to be a threshold for ‘infinite’ life, defined as 1.7 million cycles in the current work, at a maximum stress of about 200 MPa. The decay in flexural modulus of the beam as it goes under cyclic loading was calculated and it was seen that flexural modulus shows an exponential decay which can be expressed as: E = E0e AN. Four-point bending fatigue tests were carried out on three (±45°)15 samples with stress ratio, R = -1 and frequency of 5 Hz. Maximum applied stress was 85% of the measured yield stress of (±45°)15 samples. None of the samples failed, nor any sign of crack was seen. Tests were stopped once the number of cycles passed 1.7×106. In general, current study provided additional insight into the fatigue and static behavior of polymer composites and effect of fiber orientation in their mechanical behavior.

77 FR 26948 - Airworthiness Directives; Fokker Services B.V. Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-08

... sliding member cracks is high compressive stress during braking at higher deceleration levels outside the regular fatigue load spectrum. Starting at deceleration stress levels somewhat below limit load, the high compressive stress locally exceeds the elasticity limit of the material, leaving a residual tensile stress at...

Influences of semiconductor morphology on the mechanical fatigue behavior of flexible organic electronics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Young-Joo; Yeon, Han-Wool; Shin, Hae-A-Seul

2013-12-09

The influence of crystalline morphology on the mechanical fatigue of organic semiconductors (OSCs) was investigated using 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as a crystalline OSC and poly(triarylamine) (PTAA) as an amorphous OSC. During cyclic bending, resistances of the OSCs were monitored using the transmission-line method on a metal-semiconductor-metal structure. The resistance of the TIPS-pentacene increased under fatigue damage in tensile-stress mode, but no such degradation was observed in the PTAA. Both OSCs were stable under compressive bending fatigue. The formation of intergranular cracks at the domain boundaries of the TIPS-pentacene was responsible for the degradation of its electrical properties under tensile bending fatigue.

Healing of Fatigue Crack in 1045 Steel by Using Eddy Current Treatment

PubMed Central

Yang, Chuan; Xu, Wenchen; Guo, Bin; Shan, Debin; Zhang, Jian

2016-01-01

In order to investigate the methods to heal fatigue cracks in metals, tubular specimens of 1045 steel with axial and radial fatigue cracks were treated under the eddy current. The optical microscope was employed to examine the change of fatigue cracks of specimens before and after the eddy current treatment. The results show that the fatigue cracks along the axial direction of the specimen could be healed effectively in the fatigue crack initiation zone and the crack tip zone under the eddy current treatment, and the healing could occur within a very short time. The voltage breakdown and the transient thermal compressive stress caused by the detouring of eddy current around the fatigue crack were the main factors contributing to the healing in the fatigue crack initiation zone and the crack tip zone, respectively. Eddy current treatment may be a novel and effective method for crack healing. PMID:28773761

Healing of Fatigue Crack in 1045 Steel by Using Eddy Current Treatment.

PubMed

Yang, Chuan; Xu, Wenchen; Guo, Bin; Shan, Debin; Zhang, Jian

2016-07-29

In order to investigate the methods to heal fatigue cracks in metals, tubular specimens of 1045 steel with axial and radial fatigue cracks were treated under the eddy current. The optical microscope was employed to examine the change of fatigue cracks of specimens before and after the eddy current treatment. The results show that the fatigue cracks along the axial direction of the specimen could be healed effectively in the fatigue crack initiation zone and the crack tip zone under the eddy current treatment, and the healing could occur within a very short time. The voltage breakdown and the transient thermal compressive stress caused by the detouring of eddy current around the fatigue crack were the main factors contributing to the healing in the fatigue crack initiation zone and the crack tip zone, respectively. Eddy current treatment may be a novel and effective method for crack healing.

The interaction of fatigue cracks with a residual stress field using thermoelastic stress analysis and synchrotron X-ray diffraction experiments

PubMed Central

Amjad, Khurram; Asquith, David; Sebastian, Christopher M.; Wang, Wei-Chung

2017-01-01

This article presents an experimental study on the fatigue behaviour of cracks emanating from cold-expanded holes utilizing thermoelastic stress analysis (TSA) and synchrotron X-ray diffraction (SXRD) techniques with the aim of resolving the long-standing ambiguity in the literature regarding potential relaxation, or modification, of beneficial compressive residual stresses as a result of fatigue crack propagation. The crack growth rates are found to be substantially lower as the crack tip moved through the residual stress zone induced by cold expansion. The TSA results demonstrated that the crack tip plastic zones were reduced in size by the presence of the residual compressive stresses induced by cold expansion. The crack tip plastic zones were found to be insignificant in size in comparison to the residual stress zone resulting from cold expansion, which implied that they were unlikely to have had a notable impact on the surrounding residual stresses induced by cold expansion. The residual stress distributions measured along the direction of crack growth, using SXRD, showed no signs of any significant stress relaxation or redistribution, which validates the conclusions drawn from the TSA data. Fractographic analysis qualitatively confirmed the influence on crack initiation of the residual stresses induced by the cold expansion. It was found that the application of single compressive overload caused a relaxation, or reduction in the residual stresses, which has wider implications for improving the fatigue life. PMID:29291095

Fatigue characteristics of SAE52100 steel via ultrasonic nanocrystal surface modification technology.

PubMed

Pyun, Young Sik; Suh, Chang Min; Yamaguchi, Tokutaro; Im, Jong Soon; Kim, Jun Hyong; Amanov, Auezhan; Park, Jeong Hyeon

2012-07-01

Ultrasonic nanocrystal surface modification (UNSM) technology is a novel surface modification technology that can improve the mechanical and tribological properties of interacting surfaces in relative motion. UNSM treatment was utilized to improve the wear resistance fatigue strength of slim bearing rings made of SAE52100 bearing steel without damaging the raceway surfaces. In this study, wear and fatigue results that were subjected to different impact loads of the UNSM treatment were investigated and compared with those of the untreated specimen. The microhardness of the UNSM-treated specimens increased by about 20%, higher than that of the untreated specimens. The X-ray diffraction analysis showed that a compressive residual stress of more than 1,000 MPa was induced after the UNSM treatment. Also, electron backscatter diffraction analysis was used to study the surface structure and nanograin refinement. The results showed that the rolling contact fatigue life and the rotary bending fatigue strength of the UNSM-treated specimens increased by about 80% and 31%, respectively, compared to those of the untreated specimen. These results might be attributed to the increased microhardness, the induced compressive residual stress, and the nanocrystal structure modification after the UNSM treatment. In addition, the fracture surface analysis showed that the fish eye crack initiation phenomenon was observed after the UNSM treatment.

Effects of wearing lower leg compression sleeves on locomotion economy.

PubMed

Kurz, Eduard; Anders, Christoph

2018-09-01

The purpose of this investigation was to assess the effect of compression sleeves on muscle activation cost during locomotion. Twenty-two recreationally active men (age: 25 ± 3 years) ran on a treadmill at four different speeds (ordered sequence of 2.8, 3.3, 2.2, and 3.9 m/s). The tests were performed without (control situation, CON) and while wearing specially designed lower leg compression sleeves (SL). Myoelectric activity of five lower leg muscles (tibialis anterior, fibularis longus, lateral and medial head of gastrocnemius, and soleus) was captured using Surface EMG. To assess muscle activation cost, the cumulative muscle activity per distance travelled (CMAPD) of the CON and SL situations was determined. Repeated measures analyses of variance were performed separately for each muscle. The analyses revealed a reduced lower leg muscle activation cost with respect to test situation for SL for all muscles (p < 0.05, η p 2  > 0.18). The respective significant reductions of CMAPD values during SL ranged between 4% and 16% and were largest at 2.8 m/s. The findings presented point towards an improved muscle activation cost while wearing lower leg compression sleeves during locomotion that have potential to postpone muscle fatigue.

Fatigue-Crack-Growth Structural Analysis

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1986-01-01

Elastic and plastic deformations calculated under variety of loading conditions. Prediction of fatigue-crack-growth lives made with FatigueCrack-Growth Structural Analysis (FASTRAN) computer program. As cyclic loads are applied to initial crack configuration, FASTRAN predicts crack length and other parameters until complete break occurs. Loads are tensile or compressive and of variable or constant amplitude. FASTRAN incorporates linear-elastic fracture mechanics with modifications of load-interaction effects caused by crack closure. FASTRAN considered research tool, because of lengthy calculation times. FASTRAN written in FORTRAN IV for batch execution.

Effects of combined plasma chromizing and shot peening on the fatigue properties of a Ti6Al4V alloy

NASA Astrophysics Data System (ADS)

Yu, Shouming; Liu, Daoxin; Zhang, Xiaohua; Du, Dongxing

2015-10-01

A plasma chromizing treatment was conducted on Ti6Al4V samples by employing the recently developed double glow plasma surface alloying technology. The Cr-alloyed layer consisted of four sub-layers, namely the Cr deposition, Cr2Ti, CrTi4, and Cr-Ti solid-solution layers. The local hardness and moduli were determined via nanoindentation. In addition, the fatigue properties of the samples were evaluated by using a rotating-bending fatigue machine under a given load. The results showed that the hardness or elastic moduli of the adjacent sub-layers differed significantly and the fatigue properties of the Ti6Al4V alloy deteriorated with the plasma chromizing treatment. This deterioration stemmed mainly from cracks initiated at the interfaces between the sub-layers and the microstructural changes of the substrate; these changes were induced by the high temperature used in the plasma chromizing process. However, the fatigue life of the plasma-chromized samples was increased by a shot peening post-treatment. The fatigue life of the samples resulting from this combination of treatments was slightly higher than that of the single-shot-peened Ti6Al4V substrate. In fact, the sample retaining only the Cr-Ti solid-solution layer (that is, the first three sub-layers were removed), when shot-peened, exhibited the highest fatigue life among all the tested samples; this was attributed to that sample having the highest residual compressive stress, the significant work hardening, and the good hardness to toughness balance.

The effect of muscle fatigue on in vivo tibial strains.

PubMed

Milgrom, Charles; Radeva-Petrova, Denitsa R; Finestone, Aharon; Nyska, Meir; Mendelson, Stephen; Benjuya, Nisim; Simkin, Ariel; Burr, David

2007-01-01

Stress fracture is a common musculoskeletal problem affecting athletes and soldiers. Repetitive high bone strains and strain rates are considered to be its etiology. The strain level necessary to cause fatigue failure of bone ex vivo is higher than the strains recorded in humans during vigorous physical activity. We hypothesized that during fatiguing exercises, bone strains may increase and reach levels exceeding those measured in the non-fatigued state. To test this hypothesis, we measured in vivo tibial strains, the maximum gastrocnemius isokinetic torque and ground reaction forces in four subjects before and after two fatiguing levels of exercise: a 2km run and a 30km desert march. Strains were measured using strain-gauged staples inserted percutaneously in the medial aspect of their mid-tibial diaphysis. There was a decrease in the peak gastrocnemius isokinetic torque of all four subjects' post-march as compared to pre-run (p=0.0001), indicating the presence of gastrocnemius muscle fatigue. Tension strains increased 26% post-run (p=0.002, 95 % confidence interval (CI) and 29% post-march (p=0.0002, 95% CI) as compared to the pre-run phase. Tension strain rates increased 13% post-run (p=0.001, 95% CI) and 11% post-march (p=0.009, 95% CI) and the compression strain rates increased 9% post-run (p=0.0004, 95% CI) and 17% post-march (p=0.0001, 95% CI). The fatigue state increases bone strains well above those recorded in rested individuals and may be a major factor in the stress fracture etiology.

Impact of physical fitness and biometric data on the quality of external chest compression: a randomised, crossover trial

PubMed Central

2011-01-01

Background During circulatory arrest, effective external chest compression (ECC) is a key element for patient survival. In 2005, international emergency medical organisations changed their recommended compression-ventilation ratio (CVR) from 15:2 to 30:2 to acknowledge the vital importance of ECC. We hypothesised that physical fitness, biometric data and gender can influence the quality of ECC. Furthermore, we aimed to determine objective parameters of physical fitness that can reliably predict the quality of ECC. Methods The physical fitness of 30 male and 10 female healthcare professionals was assessed by cycling and rowing ergometry (focussing on lower and upper body, respectively). During ergometry, continuous breath-by-breath ergospirometric measurements and heart rate (HR) were recorded. All participants performed two nine-minute sequences of ECC on a manikin using CVRs of 30:2 and 15:2. We measured the compression and decompression depths, compression rates and assessed the participants' perception of exhaustion and comfort. The median body mass index (BMI; male 25.4 kg/m2 and female 20.4 kg/m2) was used as the threshold for subgroup analyses of participants with higher and lower BMI. Results HR during rowing ergometry at 75 watts (HR75) correlated best with the quality of ECC (r = -0.57, p < 0.05). Participants with a higher BMI and better physical fitness performed better and showed less fatigue during ECC. These results are valid for the entire cohort, as well as for the gender-based subgroups. The compressions of female participants were too shallow and more rapid (mean compression depth was 32 mm and rate was 117/min with a CVR of 30:2). For participants with a lower BMI and higher HR75, the compression depth decreased over time, beginning after four minutes for the 15:2 CVR and after three minutes for the 30:2 CVR. Although found to be more exhausting, a CVR of 30:2 was rated as being more comfortable. Conclusion The quality of the ECC and fatigue can both be predicted by BMI and physical fitness. An evaluation focussing on the upper body may be a more valid predictor of ECC quality than cycling based tests. Our data strongly support the recommendation to relieve ECC providers after two minutes. PMID:22053981

76 FR 68668 - Airworthiness Directives; Fokker Services B.V. Model F.28 Mark 0100 Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-07

... compressive stress during braking at higher deceleration levels outside the regular fatigue load spectrum. [T]he high compressive stress locally exceeds the elasticity limit of the material, leaving a residual tensile stress at release of the heavy braking load. Subsequently, this local residual tensile stress...

Effect of phase lag on cyclic durability of laminated composite

NASA Astrophysics Data System (ADS)

Andersons, Janis; Limonov, V.; Tamuzs, Vitants

1992-07-01

Theoretical and experimental results on fatigue of laminated fiber reinforced composites under out-of-phase, biaxial cyclic loading are presented. Experiments were carried out on tubular filament wound samples of epoxy matrix/organic (Kevlar type) fiber composites. Fatigue strength under two different loading modes, namely cyclic torsion combined with axial tension or compression, was investigated for phase lags psi = 0, pi/2, and pi. Durability was shown to decrease with increasing phase shift both for axial tension (R = 0.1) and compression (R = 10). A matrix failure criterion was proposed for a unidirectionally reinforced ply, and the ply discount method was modified to account for phase lag. Calculated S-N curves agree reasonably well with experimental data.

Composite materials: Fatigue and fracture. Vol. 3

NASA Technical Reports Server (NTRS)

O'Brien, T. K. (Editor)

1991-01-01

The present volume discusses topics in the fields of matrix cracking and delamination, interlaminar fracture toughness, delamination analysis, strength and impact characteristics, and fatigue and fracture behavior. Attention is given to cooling rate effects in carbon-reinforced PEEK, the effect of porosity on flange-web corner strength, mode II delamination in toughened composites, the combined effect of matrix cracking and free edge delamination, and a 3D stress analysis of plain weave composites. Also discussed are the compression behavior of composites, damage-based notched-strength modeling, fatigue failure processes in aligned carbon-epoxy laminates, and the thermomechanical fatigue of a quasi-isotropic metal-matrix composite.

Hydrogen Assisted Cracking in Pearlitic Steel Rods: The Role of Residual Stresses Generated by Fatigue Precracking

PubMed Central

Toribio, Jesús; Aguado, Leticia; Lorenzo, Miguel; Kharin, Viktor

2017-01-01

Stress corrosion cracking (SCC) of metals is an issue of major concern in engineering since this phenomenon causes many catastrophic failures of structural components in aggressive environments. SCC is even more harmful under cathodic conditions promoting the phenomenon known as hydrogen assisted cracking (HAC), hydrogen assisted fracture (HAF) or hydrogen embrittlement (HE). A common way to assess the susceptibility of a given material to HAC, HAF or HE is to subject a cracked rod to a constant extension rate tension (CERT) test until it fractures in this harsh environment. This paper analyzes the influence of a residual stress field generated by fatigue precracking on the sample’s posterior susceptibility to HAC. To achieve this goal, numerical simulations were carried out of hydrogen diffusion assisted by the stress field. Firstly, a mechanical simulation of the fatigue precracking was developed for revealing the residual stress field after diverse cyclic loading scenarios and posterior stress field evolution during CERT loading. Afterwards, a simulation of hydrogen diffusion assisted by stress was carried out considering the residual stresses after fatigue and the superposed rising stresses caused by CERT loading. Results reveal the key role of the residual stress field after fatigue precracking in the HAC phenomena in cracked steel rods as well as the beneficial effect of compressive residual stress. PMID:28772845

Creep fatigue of low-cobalt superalloys: Waspalloy, PM U 700 and wrought U 700

NASA Technical Reports Server (NTRS)

Leis, B. N.; Rungta, R.; Hopper, A. T.

1983-01-01

The influence of cobalt content on the high temperature creep fatigue crack initiation resistance of three primary alloys was evaluated. These were Waspalloy, Powder U 700, and Cast U 700, with cobalt contents ranging from 0 up to 17 percent. Waspalloy was studied at 538 C whereas the U 700 was studied at 760 C. Constraints of the program required investigation at a single strain range using diametral strain control. The approach was phenomenological, using standard low cycle fatigue tests involving continuous cycling tension hold cycling, compression hold cycling, and symmetric hold cycling. Cycling in the absence of or between holds was done at 0.5 Hz, whereas holds when introduced lasted 1 minute. The plan was to allocate two specimens to the continuous cycling, and one specimen to each of the hold time conditions. Data was taken to document the nature of the cracking process, the deformation response, and the resistance to cyclic loading to the formation of small cracks and to specimen separation. The influence of cobalt content on creep fatigue resistance was not judged to be very significant based on the results generated. Specific conclusions were that the hold time history dependence of the resistance is as significant as the influence of cobalt content and increased cobalt content does not produce increased creep fatigue resistance on a one to one basis.

Effects of Loading Frequency and Film Thickness on the Mechanical Behavior of Nanoscale TiN Film

NASA Astrophysics Data System (ADS)

Liu, Jin-na; Xu, Bin-shi; Wang, Hai-dou; Cui, Xiu-fang; Jin, Guo; Xing, Zhi-guo

2017-09-01

The mechanical properties of a nanoscale-thickness film material determine its reliability and service life. To achieve quantitative detection of film material mechanical performance based on nanoscale mechanical testing methods and to explore the influence of loading frequency of the cycle load on the fatigue test, a TiN film was prepared on monocrystalline silicon by magnetron sputtering. The microstructure of the nanoscale-thickness film material was characterized by using scanning electron microscopy and high-resolution transmission electron microscopy. The residual stress distribution of the thin film was obtained by using an electronic film stress tester. The hardness values and the fatigue behavior were measured by using a nanomechanical tester. Combined with finite element simulation, the paper analyzed the influence of the film thickness and loading frequency on the deformation, as well as the equivalent stress and strain. The results showed that the TiN film was a typical face-centered cubic structure with a large amount of amorphous. The residual compressive stress decreased gradually with increasing thin film thickness, and the influence of the substrate on the elastic modulus and hardness was also reduced. A greater load frequency would accelerate the dynamic fatigue damage that occurs in TiN films.

Characterization of the mechanical and physical properties of TD-NiCr (Ni-20Cr-2ThO2) alloy sheet

NASA Technical Reports Server (NTRS)

Fritz, L. J.; Koster, W. P.; Taylor, R. E.

1973-01-01

Sheets of TD-NiCr processed using techniques developed to produce uniform material were tested to supply mechanical and physical property data. Two heats each of 0.025 and 0.051 cm thick sheet were tested. Mechanical properties evaluated included tensile, modulus of elasticity, Poisson's Ratio, compression, creep-rupture, creep strength, bearing strength, shear strength, sharp notch and fatigue strength. Test temperatures covered the range from ambient to 1589K. Physical properties were also studied as a function of temperature. The physical properties measured were thermal conductivity, linear thermal expansion, specific heat, total hemispherical emittance, thermal diffusivity, and electrical conductivity.

[Utility of nickel-titanium shape memory alloys of vertebral body reduction fixator with assisted distraction bar].

PubMed

Man, Yi; Zheng, Yue-huan; Cao, Peng; Chen, Bo; Zheng, Tao; Sun, Chang-hui; Lu, Jiong

2011-06-07

To test the nickel-titanium (Ni-Ti) shape memory alloys of vertebral body reduction fixator with assisted distraction bar for the treatment of traumatic and osteoporotic vertebral body fracture. A Ni-Ti shape memory alloys of vertebral body reduction fixator with assisted distraction bar was implanted into the compressed fracture specimens through vertebral pedicle with the radiographic monitoring to reduce the collapsed endplate as well as distract the compressed vertebral fracture. Radiographic film and computed tomographic reconstruction technique were employed to evaluate the effects of reduction and distraction. A biomechanic test machine was used to measure the fatigue and the stability of deformation of fixation segments. Relying on the effect of temperature shape memory, such an assembly could basically reduce the collapsed endplate as well as distract the compressed vertebral fracture. And when unsatisfied results of reduction and distraction occurred, its super flexibility could provide additional distraction strength. A Ni-Ti shape memory alloys of vertebral body reduction fixator with assisted distraction bar may provide effective endplate reduction, restore the vertebral height and the immediate biomechanic spinal stability. So the above assembly is indicated for the treatment of traumatic and osteoporotic vertebral body fracture.

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wei; An, Ke

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

DOE PAGES

Wu, Wei; An, Ke

2015-10-03

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

Performance of cardiopulmonary resuscitation during prolonged basic life support in military medical university students: A manikin study.

PubMed

Wang, Juan; Zhuo, Chao-Nan; Zhang, Lei; Gong, Yu-Shun; Yin, Chang-Lin; Li, Yong-Qin

2015-01-01

The quality of chest compressions can be significantly improved after training of rescuers according to the latest national guidelines of China. However, rescuers may be unable to maintain adequate compression or ventilation throughout a response of average emergency medical services because of increased rescuer fatigue. In the present study, we evaluated the performance of cardiopulmonary resuscitation (CPR) in training of military medical university students during a prolonged basic life support (BLS). A 3-hour BLS training was given to 120 military medical university students. Six months after the training, 115 students performed single rescuer BLS on a manikin for 8 minutes. The qualities of chest compressions as well as ventilations were assessed. The average compression depth and rate were 53.7±5.3 mm and 135.1±15.7 compressions per minute respectively. The proportion of chest compressions with appropriate depth was 71.7%±28.4%. The average ventilation volume was 847.2±260.4 mL and the proportion of students with adequate ventilation was 63.5%. Compared with male students, significantly lower compression depth (46.7±4.8 vs. 54.6±4.8 mm, P<0.001) and adequate compression rate (35.5%±26.5% vs. 76.1%±25.1%, P<0.001) were observed in female students. CPR was found to be related to gender, body weight, and body mass index of students in this study. The quality of chest compressions was well maintained in male students during 8 minutes of conventional CPR but declined rapidly in female students after 2 minutes according to the latest national guidelines. Physical fitness and rescuer fatigue did not affect the quality of ventilation.

Performance of cardiopulmonary resuscitation during prolonged basic life support in military medical university students: A manikin study

PubMed Central

Wang, Juan; Zhuo, Chao-nan; Zhang, Lei; Gong, Yu-shun; Yin, Chang-lin; Li, Yong-qin

2015-01-01

BACKGROUND: The quality of chest compressions can be significantly improved after training of rescuers according to the latest national guidelines of China. However, rescuers may be unable to maintain adequate compression or ventilation throughout a response of average emergency medical services because of increased rescuer fatigue. In the present study, we evaluated the performance of cardiopulmonary resuscitation (CPR) in training of military medical university students during a prolonged basic life support (BLS). METHODS: A 3-hour BLS training was given to 120 military medical university students. Six months after the training, 115 students performed single rescuer BLS on a manikin for 8 minutes. The qualities of chest compressions as well as ventilations were assessed. RESULTS: The average compression depth and rate were 53.7±5.3 mm and 135.1±15.7 compressions per minute respectively. The proportion of chest compressions with appropriate depth was 71.7%±28.4%. The average ventilation volume was 847.2±260.4 mL and the proportion of students with adequate ventilation was 63.5%. Compared with male students, significantly lower compression depth (46.7±4.8 vs. 54.6±4.8 mm, P<0.001) and adequate compression rate (35.5%±26.5% vs. 76.1%±25.1%, P<0.001) were observed in female students. CONCLUSIONS: CPR was found to be related to gender, body weight, and body mass index of students in this study. The quality of chest compressions was well maintained in male students during 8 minutes of conventional CPR but declined rapidly in female students after 2 minutes according to the latest national guidelines. Physical fitness and rescuer fatigue did not affect the quality of ventilation. PMID:26401177

Effects of Loading Frequency on Fatigue Behavior, Residual Stress, and Microstructure of Deep-Rolled Stainless Steel AISI 304 at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Nikitin, I.; Juijerm, P.

2018-02-01

The effects of loading frequency on the fatigue behavior of non-deep-rolled (NDR) and deep-rolled (DR) austenitic stainless steel AISI 304 were systematically clarified at elevated temperatures, especially at temperatures exhibiting the dynamic strain aging (DSA) phenomena. Tension-compression fatigue tests were performed isothermally at temperatures of 573 K and 773 K (300 °C and 500 °C) with different loading frequencies of 5, 0.5, 0.05, and 0.005 Hz. For the DR condition, the residual stresses and work-hardening states will be presented. It was found that DSA would be detected at appropriate temperatures and deformation rates. The cyclic deformation curves and the fatigue lives of the investigated austenitic stainless steel AISI 304 are considerably affected by the DSA, especially on the DR condition having high dislocation densities at the surface and in near-surface regions. In the temperature range of the DSA, residual stresses and work-hardening states of the DR condition seem to be stabilized. The microstructural alterations were investigated by transmission electron microscopy (TEM). At an appropriate temperature with low loading frequency, the plastic deformation mechanism shifted from a wavy slip manner to a planar slip manner in the DSA regimes, whereas the dislocation movements were obstructed.

Strength, Fatigue, and Fracture Toughness of Ti-6Al-4V Liner from a Composite Over-Wrapped Pressure Vessel

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Lerch, Brad; Thesken, John C.; Sutter, Jim; Russell, Richard

2008-01-01

It was demonstrated by way of experiment that Composite Over-wrapped Pressure Vessel (COPV) Ti-6Al-4V liner material can sustain the expected service loads and cycles. The experiments were performed as part of investigations on the residual life of COPV tanks being used in Space Shuttle Orbiters. Measured properties included tensile strength, compressive strength, reversed loading cycles to simulate liner proof strains, and cyclic fatigue loading to demonstrate the ability to sustain 1000 cycles after liner buckling. The liner material came from a salvaged 40 in. Columbia (orbiter 102) tank (SN029), and tensile strength measurements were made on both boss-transition (thick) and membrane regions (thin). The average measured yield strength was 131 ksi in the boss-transition and membrane regions, in good agreement with measurements made on 1970 s vintage forged plate stock. However, Young s modulus was 17.4+/-0.3 Msi, somewhat higher than typical handbook values (approx.16 Msi). The fracture toughness, as estimated from a failed fatigue specimen, was 74 ksi/sq in, in reasonable agreement with standardized measurements made on 1970 s vintage forged plate stock. Low cycle fatigue of a buckled test specimen implied that as-imprinted liners can sustain over 4000 load cycles.

Enhanced fatigue performance of porous coated Ti6Al4V biomedical alloy

NASA Astrophysics Data System (ADS)

Apachitei, I.; Leoni, A.; Riemslag, A. C.; Fratila-Apachitei, L. E.; Duszczyk, J.

2011-05-01

Biofunctional coatings are necessary to improve integration of titanium implants in the host tissue but they may be detrimental for the implant fatigue properties. This study presents an attempt towards enhancement of the in vitro fatigue strength of plasma electrolytic oxidation coated Ti6Al4V alloy by applying shot peening process prior to coating. The electrolytic oxidation was performed in calcium acetate and calcium glycerophosphate electrolytes that allowed formation of porous oxide coatings with high surface free energy and apatite like ability. A deformed surface layer coupled with induced residual compressive stresses seem to affect oxide growth rate and fatigue behavior of the titanium alloy.

Microfracture and changes in energy absorption to fracture of young vertebral cancellous bone following physiological fatigue loading.

PubMed

Lu, W W; Luk, K D K; Cheung, K C M; Gui-Xing, Qiu; Shen, J X; Yuen, L; Ouyang, J; Leong, J C Y

2004-06-01

Fifty-five human thoracolumbar vertebrae were randomly fatigue loaded and analyzed. The purpose of this study was to explore the relationship between fatigue loading, trabecular microfracture, and energy absorption to fracture in human cadaveric thoracolumbar vertebrae. Although trabecular microfractures are found in vivo and have been produced by fatigue loading in vitro, the effect of the level of physiologic fatigue loading on microfracture and energy absorption has not been investigated. Fifty-five human thoracolumbar vertebrae (T11-L4) were randomly divided into 5 groups: 1) control (no loading, n = 6); 2) axial compression to yield (n = 7); and 3-5) 20,000 cycles of fatigue loading at 2 Hz (each n = 14). The level of fatigue loading was determined as a proportion of the yield load of Group 2 as follows: 10% (Group 3), 20% (Group 4), and 30% (Group 5). Half of the specimens in groups 3 to 5 were used for radiographic and histomorphometric analysis to determine microfracture density and distribution, whereas the other half were tested to determine the energy absorption to yield failure. No radiographic evidence of gross fracture was found in any of the groups following fatigue loading. A mean 7.5% increase in stiffness was found in specimens subject to cyclic loading at 10% of yield stress (Group 3). Fatigue at 20% (Group 4) and 30% of yield stress (Group 5) caused significantly higher (P < 0.05) increases in mean stiffness of 23.6% and 24.2%, respectively. Microfracture density increased from 0.46/mm in Group 3 to 0.66/mm in Group 4 and 0.94/mm in Group 5 (P < 0.05). The energy absorbed to failure decreased from 21.9 J in Group 3 to 18.1 J and 19.6 J in Groups 4 and 5, respectively (P < 0.05). Fatigue loading at physiologic levels produced microfractures that are not detectable by radiography. Increased fatigue load results in an increase in microfracture density and decrease energy absorbed to fracture, indicating a reduced resistance to further fatigue loading.

Performance of Diffusion Aluminide Coatings Applied on Alloy CF8C-Plus at 800oC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Deepak; Dryepondt, Sebastien N; Zhang, Ying

2012-01-01

High performance cast stainless steel, CF8C-Plus, is a low cost alloy with prospective applications ranging from covers and casings of small and medium size gas turbines to turbocharger housing and manifolds in internal combustion engines. Diffusion aluminide coatings were applied on this alloy as a potential strategy for improved oxidation resistance, particularly in wet air and steam. In this paper the performance of the aluminide coatings evaluated by cyclic oxidation experiments in air containing 10 vol.% H2O at 800 C and conventional tension-compression low-cycle-fatigue tests in air at 800 C with a strain range of 0.5% is presented. The resultsmore » show that specimens coated by a chemical vapor deposition process provide better oxidation resistance than those coated by an Al-slurry coating process. The application of a coating by pack cementation reduced the fatigue life by 15%.« less

Stable interstitial layer to alleviate fatigue fracture of high nickel cathode for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Yang, Chengkai; Shao, Ruiwen; Mi, Yingying; Shen, Lanyao; Zhao, Binglu; wang, Qian; Wu, Kai; Lui, Wen; Gao, Peng; Zhou, Henghui

2018-02-01

High nickel cathodes can deliver higher capacity with lower cost than conventional LiCoO2, however, the irreversible structural and morphology degradation with long-term cycling hinder their further application. In this paper, LiNi0.815Co0.15Al0.035O2 agglomerates are treated by LiNi0.333Co0.333Mn0.333O2 coating to get a stable interstitial layer without capacity loss. The interstitial layer is about 10 nm in thickness and has a layered (R-3m) structure, which can improve the chemical and mechanical stability of cathode materials with capacity retention of 88.5% after 200 cycles. The structural analysis and in-situ compression test proves that the morphology degradation is a fatigue process within long-term electrochemical reaction, and the coated sample has an excellent elastic recovery capacity thus leading to long cycle life.

A study of spectrum fatigue crack propagation in two aluminum alloys. 1: Spectrum simplification

NASA Technical Reports Server (NTRS)

Telesman, J.; Antolovich, S. D.

1985-01-01

The fatigue crack propagation behavior of two commercial Al alloys was studied using spectrum loading conditions characteristics of those encountered at critical locations in high performance fighter aircraft. A tension dominated (TD) and tension compression (TC) spectrum were employed for each alloy. Using a mechanics-based analysis, it was suggested that negative loads could be eliminated for the TC spectrum for low to intermediate maximum stress intensities. The suggestion was verified by subsequent testing. Using fractographic evidence, it was suggested that a further similification in the spectra could be accomplished by eliminating low and intermediate peak load points resulting in near or below threshold maximum peak stress intensity values. It is concluded that load interactions become more important at higher stress intensities and more plasticity at the crack tip. These results suggest that a combined mechanics/fractographic mechanisms approach can be used to simplify other complex spectra.

Low Cycle Fatigue Properties of Extruded Mg10GdxNd Alloys

NASA Astrophysics Data System (ADS)

Tober, Gerhard; Maier, Petra; Müller, Sören; Hort, Norbert

The Rare Earth (RE) containing magnesium alloys Mg10Gd and Mg10Gd1Nd show after extrusion very good low cycle fatigue (LCF) properties. Considering extruded AZ31 as a possible benchmark alloy, life times as a function of LCF stress values are similar to the alloys investigated in this study. Mechanical properties determined in tension and compression show smaller values for both RE containing alloys. Therefore the LCF behavior is analyzed by the stress-strain hysteresis evaluation resulting in cyclic creep and plastic hardening or softening. LCF tests were strain controlled with amplitude of 0.5 % and 0.8 % at a frequency of 5Hz. The fracture surfaces are examined by SEM, where the area of crack propagation and overload were of main interest. Micrographs of longitudinal cross sections reveal twinning along the region of crack propagation. The correlation between the amount of twins and the number of cycles is discussed.

Cushing disease

MedlinePlus

... Fatigue Frequent infections Headache Increased thirst and urination High blood pressure Diabetes ... Cushing disease include: Compression fractures in the spine Diabetes High blood pressure Infections Kidney stones Mood or other psychiatric problems

Experimental and analytical study of fatigue damage in notched graphite/epoxy laminates

NASA Technical Reports Server (NTRS)

Whitcomb, J. D.

1979-01-01

Both tension and compression fatigue behaviors were investigated in four notched graphite/epoxy laminates. After fatigue loading, specimens were examined for damage type and location using visual inspection, light microscopy, scanning electron microscopy, ultrasonic C-scans, and X-radiography. Delamination and ply cracking were found to be the dominant types of fatigue damage. In general, ply cracks did not propagate into adjacent plies of differing fiber orientation. To help understand the varied fatigue observations, the interlaminar stress distribution was calculated with finite element analysis for the regions around the hole and along the straight free edge. Comparison of observed delamination locations with the calculated stresses indicated that both interlaminar shear and peel stresses must be considered when predicting delamination. The effects of the fatigue cycling on residual strength and stiffness were measured for some specimens of each laminate type. Fatigue loading generally caused only small stiffness losses. In all cases, residual strengths were greater than or equal to the virgin strengths.

Post-fatigue fracture resistance of metal core crowns: press-on metal ceramic versus a conventional veneering system

PubMed Central

Agustín-Panadero, Rubén; Campos-Estellés, Carlos; Labaig-Rueda, Carlos

2015-01-01

Background The aim of this in vitro study was to compare the mechanical failure behavior and to analyze fracture characteristics of metal ceramic crowns with two veneering systems – press-on metal (PoM) ceramic versus a conventional veneering system – subjected to static compressive loading. Material and Methods Forty-six crowns were constructed and divided into two groups according to porcelain veneer manufacture. Group A: 23 metal copings with porcelain IPS-InLine veneering (conventional metal ceramic). Group B: 23 metal copings with IPS-InLine PoM veneering porcelain. After 120,000 fatigue cycles, the crowns were axially loaded to the moment of fracture with a universal testing machine. The fractured specimens were examined under optical stereomicroscopy and scanning electron microscope. Results Fracture resistance values showed statistically significant differences (Student’s t-test) regarding the type of ceramic veneering technique (p=0.001): Group A (conventional metal ceramics) obtained a mean fracture resistance of 1933.17 N, and Group B 1325.74N (Press-on metal ceramics). The most common type of fracture was adhesive failure (with metal exposure) (p=0.000). Veneer porcelain fractured on the occlusal surface following a radial pattern. Conclusions Metal ceramic crowns made of IPS InLine or IPS InLine PoM ceramics with different laboratory techniques all achieved above-average values for clinical survival in the oral environment according to ISO 6872. Crowns made with IPS InLine by conventional technique resisted fracture an average of 45% more than IPS InLine PoM fabricated with the press-on technique. Key words:Mechanical failure, conventional feldspathic, pressable ceramic, chewing simulator, thermocycling, compressive testing, fracture types, scanning electron microscope. PMID:26155346

Effects of temperature and humidity cycling on the strengths of textile reinforced carbon/epoxy composite materials

NASA Technical Reports Server (NTRS)

Cano, Roberto J.; Furrow, Keith W.

1993-01-01

Results are presented from an experimental evaluation of the combined effects of temperature and humidity cycling on AS4/3501-6 composites (unstitched, Kevlar 29 stitched, and S-2 glass stitched uniweave fabric) and AS4/E905L composites (2-D, S-2 glass stitched 2-D, and 3-D braided fabric). The AS4/3501-6 uniweave material had a quasi-isotropic layup, whereas the AS4/E905L materials were braided in a (+/-30 deg/0 deg)(sub s) orientation. Data presented include compression strengths and compression-compression fatigue results for uncycled composites and cycled composites (160, 480, 720, and 1280 cycles from 140 deg F at 95 percent relative humidity to -67 deg F). To observe the presence of microcracking within the laminates, photomicrographs were taken of each material type at the end of each cycling period. Microcracks were found to be more prevalent within stitched laminates, predominantly around individual stitches. The glass stitched laminates showed significant microcracking even before cycling. Less microcracking was evident in the Kevlar stitched materials, whereas the unstitched uniweave material developed microcracks only after cycling. The 3-D braid did not develop microcracks. The static compression strengths of the unstitched and Kevlar stitched uniweave materials were degraded by about 10 percent after 1280 temperature/humidity cycles, whereas the reduction in compression strength for the glass stitched uniweave was less than 3 percent. The reduction in compression strength for the glass stitched 2-D braid was less than 8 percent. The unstitched 2-D and 3-D braids did not lose strength from temperature/humidity cycling. The compression-compression fatigue properties of all six material types were not affected by temperature/humidity cycling.

Relation Between Residual and Hoop Stresses and Rolling Bearing Fatigue Life

NASA Technical Reports Server (NTRS)

Oswald, Fred B.; Zaretsky, Erwin V.; Poplawski, Joseph V.

2015-01-01

Rolling-element bearings operated at high speed or high vibration may require a tight interference fit between the bore of the bearing and shaft to prevent rotation of the bearing bore around the shaft and fretting damage at the interfaces. Previous work showed that the hoop stresses resulting from tight interference fits can reduce bearing lives by as much as 65 percent. Where tight interference fits are required, case-carburized steel such as AISI 9310 or M50 NiL is often used because the compressive residual stresses inhibit subsurface crack formation and the ductile core inhibits inner-ring fracture. The presence of compressive residual stress and its combination with hoop stress also modifies the Hertz stress-life relation. This paper analyzes the beneficial effect of residual stresses on rolling-element bearing fatigue life in the presence of high hoop stresses for three bearing steels. These additional stresses were superimposed on Hertzian principal stresses to calculate the inner-race maximum shearing stress and the resulting fatigue life of the bearing. The load-life exponent p and Hertz stress-life exponent n increase in the presence of compressive residual stress, which yields increased life, particularly at lower stress levels. The Zaretsky life equation is described and is shown to predict longer bearing lives and greater load- and stress-life exponents, which better predicts observed life of bearings made from vacuum-processed steel.

Characterization of Cracking and Crack Growth Properties of the C5A Aircraft Tie-Box Forging

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Smith, Stephen W.; Newman, John A.; Willard, Scott A.

2003-01-01

Detailed destructive examinations were conducted to characterize the integrity and material properties of two aluminum alloy (7075-T6) horizontal stabilizer tie box forgings removed.from US. Air Force C5A and C5B transport aircraft. The C5B tie box forging was,found to contain no evidence of cracking. Thirteen cracks were found in the CSA,forging. All but one of the cracks observed in the C5A component were located along the top cap region (one crack was located in the bottom cap region). The cracks in the C5A component initiated at fastener holes and propagated along a highly tunneled intergranular crack path. The tunneled crack growth configuration is a likelv result of surface compressive stress produced during peening of the .forging suijace. The tie box forging ,fatigue crack growth, fracture and stress corrosion cracking (SCC) properties were characterized. Reported herein are the results of laboratory air ,fatigue crack growth tests and 95% relative humidity SCC tests conducted using specimens machined from the C5A ,forging. SCC test results revealed that the C5A ,forging material was susceptible to intergranular environmental assisted cracking: the C5A forging material exhibited a SCC crack-tip stress-intensity factor threshold of less than 6 MPadn. Fracture toughness tests revealed that the C5A forging material exhibited a fracture toughness that was 25% less than the C5B forging. The C5A forging exhibited rapid laboratory air fatigue crack growth rates having a threshold crack-tip stress-intensity factor range of less than 0.8 MPa sup m. Detailed fractographic examinations revealed that the ,fatigue crack intergranular growth crack path was similar to the cracking observed in the C5A tie box forging. Because both fatigue crack propagation and SCC exhibit similar intergranular crack path behavior, the damage mechanism resulting in multi-site cracking of tie box forgings cannot be determined unless local cyclic stresses can be quantified.

Deformation history and load sequence effects on cumulative fatigue damage and life predictions

NASA Astrophysics Data System (ADS)

Colin, Julie

Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless steel is a material with strong deformation history effects and phase transformation resulting from plastic straining, such load sequence and variable amplitude loading effects are significant to its fatigue behavior and life predictions. The goal of this study was to investigate the effects of cyclic deformation on fatigue behavior of stainless steel 304L as a deformation history sensitive material and determine how to quantify and accumulate fatigue damage to enable life predictions under variable amplitude loading conditions for such materials. A comprehensive experimental program including testing under fully-reversed, as well as mean stress and/or mean strain conditions, with initial or periodic overloads, along with step testing and random loading histories was conducted on two grades of stainless steel 304L, under both strain-controlled and load-controlled conditions. To facilitate comparisons with a material without deformation history effects, similar tests were also carried out on aluminum 7075-T6. Experimental results are discussed, including peculiarities observed with stainless steel behavior, such as a phenomenon, referred to as secondary hardening characterized by a continuous increase in the stress response in a strain-controlled test and often leading to runout fatigue life. Possible mechanisms for secondary hardening observed in some tests are also discussed. The behavior of aluminum is shown not to be affected by preloading, whereas the behavior of stainless steel is greatly influenced by prior loading. Mean stress relaxation in strain control and ratcheting in load control and their influence on fatigue life are discussed. Some unusual mean strain test results are presented for stainless steel 304L, where in spite of mean stress relaxation fatigue lives were significantly longer than fully-reversed tests. Prestraining indicated no effect on either deformation or fatigue behavior of aluminum, while it induced considerable hardening in stainless steel 304L and led to different results on fatigue life, depending on the test control mode. In step tests for stainless steel 304L, strong hardening induced by the first step of a high-low sequence significantly affects the fatigue behavior, depending on the test control mode used. For periodic overload tests of stainless steel 340L, hardening due to the overloads was progressive throughout life and more significant than in high-low step tests. For aluminum, no effect on deformation behavior was observed due to periodic overloads. However, the direction of the overloads was found to affect fatigue life, as tensile overloads led to longer lives, while compressive overloads led to shorter lives. Deformation and fatigue behaviors under random loading conditions are also presented and discussed for the two materials. The applicability of a common cumulative damage rule, the linear damage rule, is assessed for the two types of material, and for various loading conditions. While the linear damage rule associated with a strain-life or stress-life curve is shown to be fairly accurate for life predictions for aluminum, it is shown to poorly represent the behavior of stainless steel, especially in prestrained and high-low step tests, in load control. In order to account for prior deformation effects and achieve accurate fatigue life predictions for stainless steel, parameters including both stress and strain terms are required. The Smith-Watson-Topper and Fatemi-Socie approaches, as such parameters, are shown to correlate most test data fairly accurately. For damage accumulation under variable amplitude loading, the linear damage rule associated with strain-life or stress-life curves can lead to inaccurate fatigue life predictions, especially for materials presenting strong deformation memory effect, such as stainless steel 304L. The inadequacy of this method is typically attributed to the linear damage rule itself. On the contrary, this study demonstrates that damage accumulation using the linear damage rule can be accurate, provided that the linear damage rule is used in conjunction with parameters including both stress and strain terms. By including both loading history and response of the material in damage quantification, shortcomings of the commonly used linear damage rule approach can be circumvented in an effective manner. In addition, cracking behavior was also analyzed under various loading conditions. Results on microcrack initiation and propagation are presented in relation to deformation and fatigue behaviors of the materials. Microcracks were observed to form during the first few percent of life, indicating that most of the fatigue life of smooth specimens is spent in microcrack formation and growth. Analyses of fractured specimens showed that microcrack formation and growth is dependent on the loading history, and less important in aluminum than stainless steel 304L, due to the higher toughness of this latter material.

The strainrange conversion principle for treating cumulative fatigue damage in the creep range

NASA Technical Reports Server (NTRS)

Manson, S. S.

1983-01-01

A formula is derived for combining effects of successive hysteresis loops in the creep range of materials when one loop has excess tensile creep, while the other contains excess compressive creep. The resultant effect resembles single loops involving balanced tensile and compressive creep. The attempt to use the Interaction Damage Rule as a tool in combining loops of non-equal size and complex strainrange content has led to important new concepts useful in future studies of creep-fatigue. It turns out that the Interaction Damage Rule is basically an expression of how a set of hysteresis loops involving only single generic strains can combine to produce the same micromechanistic damage as the loop containing the combined strainranges which it analyzes. Making use of the underlying concept of Strainrange Partitioning that only the strainrange content of a hysteresis loop governs fatigue life, not order of introducing strainranges, a rational derivation of the Interaction Damage Rule is provided, showing also how it can effectively be used to synthesize independent loops and determine both damaging and healing effects.

The compressed work week as organizational change: behavioral and attitudinal outcomes.

PubMed

Ronen, S; Primps, S B

1981-01-01

The results from recent studies on the compressed work week have been compiled and categorized in order to provide some basis for generalizing the effects of the work schedule on employee attitudes and behavior. It appears that attitudes toward the compressed week are favorable, with some generalization to job attitudes. Performance outcomes are ambiguous, although there are no reported decreases; fatigue seems to be the only negative aspect of the longer day. An examination of mediating variables suggests more complex relationships between the implementation of the compressed work week and potential outcomes. These relationships are described and directions are indicated for future research.

Reporting the Fatigue Life of 316L Stainless Steel Locking Compression Plate Implants: The Role of the Femoral and Tibial Biomechanics During the Gait.

PubMed

Rice, Devyn; Shaat, Mohamed

2017-10-01

In this study, the fatigue characteristics of femoral and tibial locking compression plate (LCP) implants are determined accounting for the knee biomechanics during the gait. A biomechanical model for the kinematics and kinetics of the knee joint during the complete gait cycle is proposed. The rotations of the femur, tibia, and patella about the knee joint during the gait are determined. Moreover, the patellar-tendon force (PT), quadriceps-tendon force (QT), the tibiofemoral joint force (TFJ), and the patellofemoral joint force (PFJ) through the standard gait cycle are obtained as functions of the body weight (BW). On the basis of the derived biomechanics of the knee joint, the fatigue factors of safety along with the fatigue life of 316L stainless steel femoral and tibial LCP implants are reported as functions of the BW and bone fracture location, for the first time. The reported results reveal that 316L stainless steel LCP implants for femoral surgeries are preferred for conditions in which the bone fracture is close to the knee joint and the BW is less than 80 kg. For tibial surgeries, 316L stainless steel LCP implants can be used for conditions in which the bone fracture is close to the knee joint and the BW is less than 100 kg. This study presents a critical guide for the determination of the fatigue characteristics of LCP implants. The obtained results reveal that the fatigue analyses should be performed on the basis of the body biomechanics to guarantee accurate designs of LCP implants for femoral and tibial orthopedic surgeries.

Production and mechanical properties of Al-SiC metal matrix composites

NASA Astrophysics Data System (ADS)

Karvanis, K.; Fasnakis, D.; Maropoulos, A.; Papanikolaou, S.

2016-11-01

The usage of Al-SiC Metal Matrix Composites is constantly increasing in the last years due to their unique properties such as light weight, high strength, high specific modulus, high fatigue strength, high hardness and low density. Al-SiC composites of various carbide compositions were produced using a centrifugal casting machine. The mechanical properties, tensile and compression strength, hardness and drop-weight impact strength were studied in order to determine the optimum carbide % in the metal matrix composites. Scanning electron microscopy was used to study the microstructure-property correlation. It was observed that the tensile and the compressive strength of the composites increased as the proportion of silicon carbide became higher in the composites. Also with increasing proportion of silicon carbide in the composite, the material became harder and appeared to have smaller values for total displacement and total energy during impact testing.

Effect of one-rescuer compression/ventilation ratios on cardiopulmonary resuscitation in infant, pediatric, and adult manikins.

PubMed

Srikantan, Shoba Krishnan; Berg, Robert A; Cox, Tim; Tice, Lisa; Nadkarni, Vinay M

2005-05-01

Optimal chest compression to ventilation ratio (C:V) for one-rescuer cardiopulmonary resuscitation (CPR) is not known, with current American Heart Association recommendations 3:1 for newborns, 5:1 for children, and 15:2 for adults. C:V ratios influence effectiveness of CPR, but memorizing different ratios is educationally cumbersome. We hypothesized that a 10:2 ratio might provide adequate universal application for all age arrest victims. Clinical study. Tertiary care children's hospital. Thirty-five health care providers. Thirty-five health care providers performed 5-min epochs of one-rescuer CPR at C:V ratios of 3:1, 5:1, 10:2, and 15:2 in random order on infant, pediatric, and adult manikins. Compressions were paced at 100/min by metronome. The number of effective compressions and ventilations delivered per minute was recorded by a trained basic life support instructor. Subjective assessments of fatigue (self-report) and exertion (change in rescuer pulse rate compared with baseline) were assessed. Analysis was by repeated measures analysis of variance and paired Student's t-test. Effective infant compressions per minute did not differ by C:V ratio, but ventilations per minute were greater at 3:1 vs. 5:1, 10:2, and 15:2 (p < .05). Effective pediatric compressions per minute were less at 3:1 vs. 5:1, 10:2, and 15:2 (p < .05) and not different between 5:1, 10:2, and 15:2 ratios. Effective pediatric ventilations per minute were greater at 3:1 than all other ratios and both 5:1 and 10:2 were >15:2 (p < .05). Effective adult compressions per minute were progressively greater with 3:1 vs. 5:1 vs. 10:2 vs. 15:2 (p < .05). Self-efficacy was assessed, and rescuers always subjectively rated 10:2 and 15:2 ratios as easier than 5:1 or 3:1 ratios for all manikins. Rescuer pulse change (exertion) was greater after pediatric and adult vs. infant CPR (p < .05), with no significant difference by C:V ratio. C:V ratio and manikin size have a significant influence on the number of effective compressions and ventilations delivered during ideal, metronome-paced, one-rescuer CPR. Low ratios of 3:1, 5:1, and 10:2 favor ventilation, and high ratios of 15:2 favor compression, especially in adult manikins. Rescuers subjectively preferred C:V ratios of 10:2 and 15:2 over 3:1 or 5:1. Infant CPR caused less exertion and subjective fatigue than pediatric or adult CPR technique, without significant difference by C:V ratio. We speculate that a universal 10:2 C:V ratio for one-rescuer layperson CPR is physiologically reasonable but warrants further study with particular attention to educational value and technique retention.

Rolling Contact Fatigue Performances of Carburized and High-C Nanostructured Bainitic Steels.

PubMed

Wang, Yanhui; Zhang, Fucheng; Yang, Zhinan; Lv, Bo; Zheng, Chunlei

2016-11-25

In the present work, the nanostructured bainitic microstructures were obtained at the surfaces of a carburized steel and a high-C steel. The rolling contact fatigue (RCF) performances of the two alloy steels with the same volume fraction of undissolved carbide were studied under lubrication. Results show that the RCF life of the carburized nanostructured bainitic steel is superior to that of the high-C nanostructured bainitic steel in spite of the chemical composition, phase constituent, plate thickness of bainitic ferrite, hardness, and residual compressive stress value of the contact surfaces of the two steels under roughly similar conditions. The excellent RCF performance of the carburized nanostructured bainitic steel is mainly attributed to the following reasons: finer carbide dispersion distribution in the top surface, the higher residual compressive stress values in the carburized layer, the deeper residual compressive stress layer, the higher work hardening ability, the larger amount of retained austenite transforming into martensite at the surface and the more stable untransformed retained austenite left in the top surface of the steel.

Rolling Contact Fatigue Performances of Carburized and High-C Nanostructured Bainitic Steels

PubMed Central

Wang, Yanhui; Zhang, Fucheng; Yang, Zhinan; Lv, Bo; Zheng, Chunlei

2016-01-01

In the present work, the nanostructured bainitic microstructures were obtained at the surfaces of a carburized steel and a high-C steel. The rolling contact fatigue (RCF) performances of the two alloy steels with the same volume fraction of undissolved carbide were studied under lubrication. Results show that the RCF life of the carburized nanostructured bainitic steel is superior to that of the high-C nanostructured bainitic steel in spite of the chemical composition, phase constituent, plate thickness of bainitic ferrite, hardness, and residual compressive stress value of the contact surfaces of the two steels under roughly similar conditions. The excellent RCF performance of the carburized nanostructured bainitic steel is mainly attributed to the following reasons: finer carbide dispersion distribution in the top surface, the higher residual compressive stress values in the carburized layer, the deeper residual compressive stress layer, the higher work hardening ability, the larger amount of retained austenite transforming into martensite at the surface and the more stable untransformed retained austenite left in the top surface of the steel. PMID:28774081

Process and application of shock compression by nanosecond pulses of frequency-doubled Nd:YAG laser

NASA Astrophysics Data System (ADS)

Sano, Yuji; Kimura, Motohiko; Mukai, Naruhiko; Yoda, Masaki; Obata, Minoru; Ogisu, Tatsuki

2000-02-01

The authors have developed a new process of laser-induced shock compression to introduce a residual compressive stress on material surface, which is effective for prevention of stress corrosion cracking (SCC) and enhancement of fatigue strength of metal materials. The process developed is unique and beneficial. It requires no pre-conditioning for the surface, whereas the conventional process requires that the so-called sacrificial layer is made to protect the surface from damage. The new process can be freely applied to water- immersed components, since it uses water-penetrable green light of a frequency-doubled Nd:YAG laser. The process developed has the potential to open up new high-power laser applications in manufacturing and maintenance technologies. The laser-induced shock compression process (LSP) can be used to improve a residual stress field from tensile to compressive. In order to understand the physics and optimize the process, the propagation of a shock wave generated by the impulse of laser irradiation and the dynamic response of the material were analyzed by time-dependent elasto-plastic calculations with a finite element program using laser-induced plasma pressure as an external load. The analysis shows that a permanent strain and a residual compressive stress remain after the passage of the shock wave with amplitude exceeding the yield strength of the material. A practical system materializing the LSP was designed, manufactured, and tested to confirm the applicability to core components of light water reactors (LWRs). The system accesses the target component and remotely irradiates laser pulses to the heat affected zone (HAZ) along weld lines. Various functional tests were conducted using a full-scale mockup facility, in which remote maintenance work in a reactor vessel could be simulated. The results showed that the system remotely accessed the target weld lines and successfully introduced a residual compressive stress. After sufficient training for operational personnel, the system was applied to the core shroud of an existing nuclear power plant.

An in vitro study to compare the transverse strength of thermopressed and conventional compression-molded polymethylmethacrylate polymers.

PubMed

Raut, Anjana; Rao, Polsani Laxman; Vikas, B V J; Ravindranath, T; Paradkar, Archana; Malakondaiah, G

2013-01-01

Acrylic resins have been in the center stage of Prosthodontics for more than half a century. The flexural fatigue failure of denture base materials is the primary mode of clinical failure. Hence there is a need for superior physical and mechanical properties. This in vitro study compared the transverse strength of specimens of thermopressed injection-molded and conventional compression-molded polymethylmethacrylate polymers and examined the morphology and microstructure of fractured acrylic specimens. The following denture base resins were examined: Brecrystal (Thermopressed injection-molded, modified polymethylmethacrylate) and Pyrax (compression molded, control group). Specimens of each material were tested according to the American Society for Testing and Materials standard D790-03 for flexural strength testing of reinforced plastics and subsequently examined under SEM. The data was analyzed with Student unpaired t test. Flexural strength of Brecrystal (82.08 ± 1.27 MPa) was significantly higher than Pyrax (72.76 ± 0.97 MPa). The tested denture base materials fulfilled the requirements regarding flexural strength (>65 MPa). The scanning electron microscopy image of Brecrystal revealed a ductile fracture with crazing. The fracture pattern of control group specimens exhibited poorly defined crystallographic planes with a high degree of disorganization. Flexural strength of Brecrystal was significantly higher than the control group. Brecrystal showed a higher mean transverse strength value of 82.08 ± 1.27 MPa and a more homogenous pattern at microscopic level. Based on flexural strength properties and handling characteristics, Brecrystal may prove to be an useful alternative to conventional denture base resins.

Fabrication and investigation on field-dependent properties of natural rubber based magneto-rheological elastomer isolator

NASA Astrophysics Data System (ADS)

Ain Abd Wahab, Nurul; Amri Mazlan, Saiful; Ubaidillah; Kamaruddin, Shamsul; Intan Nik Ismail, Nik; Choi, Seung-Bok; Haziq Rostam Sharif, Amirul

2016-10-01

This study presents a laminated magnetorheological elastomer (MRE) isolator which applies to vibration control in practice. The proposed isolator is fabricated with multilayer MRE sheets associated with the natural rubber (NR) as a matrix, and steel plates. The fabricated MRE isolator is then magnetically analysed to achieve high magnetic field intensity which can produce high damping force required for effective vibration control. Subsequently, the NR-based MRE specimen is tested to identify the field-dependent rheological properties such as storage modulus with 60 weight percentage of carbonyl iron particles. It is shown from this test that the MR effect of MRE specimen is quantified to reach up to 120% at 0.8 T. Following the design stage, the electromagnetic simulation using the finite element method magnetic (FEMM) software is carried out for analysing the magnetic flux distribution in the laminated MRE isolator. The laminated MRE isolator is then examined to a series of compression for static and dynamic test under various applied currents using the dynamic fatigue machine and biaxial dynamic testing machine. It is shown that the static compression force is increased by 14.5% under strong magnetic field compared to its off-state. Meanwhile, the dynamic compression test results show that the force increase of the laminated MRE isolator is up to 16% and 7% for low and high frequency respectively. From the results presented in this work, it is demonstrated that the full-scale concept of the MRE isolator can be one of the potential candidates for vibration control applications by tunability of the dynamic stiffness.

Comparison of the cohesive and delamination fatigue properties of atomic-layer-deposited alumina and titania ultrathin protective coatings deposited at 200 °C

PubMed Central

Sadeghi-Tohidi, Farzad; Samet, David; Graham, Samuel; Pierron, Olivier N

2014-01-01

The fatigue properties of ultrathin protective coatings on silicon thin films were investigated. The cohesive and delamination fatigue properties of 22 nm-thick atomic-layered-deposited (ALD) titania were characterized and compared to that of 25 nm-thick alumina. Both coatings were deposited at 200 °C. The fatigue rates are comparable at 30 °C, 50% relative humidity (RH) while they are one order of magnitude larger for alumina compared to titania at 80 °C, 90% RH. The improved fatigue performance is believed to be related to the improved stability of the ALD titania coating with water compared to ALD alumina, which may in part be related to the fact that ALD titania is crystalline, while ALD alumina is amorphous. Static fatigue crack nucleation and propagation was not observed. The underlying fatigue mechanism is different from previously documented mechanisms, such as stress corrosion cracking, and appears to result from the presence of compressive stresses and a rough coating–substrate interface. PMID:27877645

Increased Antibiotic Release from a Bone Cement Containing Bacterial Cellulose

PubMed Central

Nakai, Takahisa; Enomoto, Koichi; Uchio, Yuji; Yoshino, Katsumi

2010-01-01

Background Major disadvantages of antibiotic bone cements include limited drug release and reduced strength resulting from the addition of high doses of antibiotics. Bacterial cellulose, a three-dimensional hydrophilic mesh, may retain antibiotics and release them gradually. We hypothesized that the addition of cellulose to antibiotic bone cement would improve mechanical strength and antibiotic release. Questions/purposes We therefore examined the mechanical strength and antibiotic release of cellulose antibiotic cement. Methods A high dose of antibiotics (5 g per 40 g cement powder) was incorporated into bacterial cellulose and then mixed with bone cement. We compared the compression strength, fracture toughness, fatigue life, and elution kinetics of this formulation with those of plain cement and a traditional antibiotic cement. Results The average values for compression strength, fracture toughness, and fatigue life of the cellulose antibiotic cement were 97%, 97%, and 78% of the values obtained for plain cement, respectively. The corresponding values for the traditional antibiotic cement were 79%, 82%, and 17%, respectively. The cumulative elution over 35 days was 129% greater from the cellulose antibiotic cement than from the traditional antibiotic cement. Conclusions With a high dose of antibiotics, incorporating cellulose into the bone cement prevented compression and fracture fragility, improved fatigue life, and increased antibiotic elution. Clinical Relevance Antibiotic cements containing cellulose may have applications in clinical situations that require high levels of antibiotic release and preservation of the mechanical properties of the cement. PMID:20945120

The strengthening mechanism of a nickel-based alloy after laser shock processing at high temperatures

PubMed Central

Li, Yinghong; Zhou, Liucheng; He, Weifeng; He, Guangyu; Wang, Xuede; Nie, Xiangfan; Wang, Bo; Luo, Sihai; Li, Yuqin

2013-01-01

We investigated the strengthening mechanism of laser shock processing (LSP) at high temperatures in the K417 nickel-based alloy. Using a laser-induced shock wave, residual compressive stresses and nanocrystals with a length of 30–200 nm and a thickness of 1 μm are produced on the surface of the nickel-based alloy K417. When the K417 alloy is subjected to heat treatment at 900 °C after LSP, most of the residual compressive stress relaxes while the microhardness retains good thermal stability; the nanocrystalline surface has not obviously grown after the 900 °C per 10 h heat treatment, which shows a comparatively good thermal stability. There are several reasons for the good thermal stability of the nanocrystalline surface, such as the low value of cold hardening of LSP, extreme high-density defects and the grain boundary pinning of an impure element. The results of the vibration fatigue experiments show that the fatigue strength of K417 alloy is enhanced and improved from 110 to 285 MPa after LSP. After the 900 °C per 10 h heat treatment, the fatigue strength is 225 MPa; the heat treatment has not significantly reduced the reinforcement effect. The feature of the LSP strengthening mechanism of nickel-based alloy at a high temperature is the co-working effect of the nanocrystalline surface and the residual compressive stress after thermal relaxation. PMID:27877617

Mechanisms of High-Temperature Fatigue Failure in Alloy 800H

NASA Technical Reports Server (NTRS)

BhanuSankaraRao, K.; Schuster, H.; Halford, G. R.

1996-01-01

The damage mechanisms influencing the axial strain-controlled Low-Cycle Fatigue (LCF) behavior of alloy 800H at 850 C have been evaluated under conditions of equal tension/compression ramp rates (Fast-Fast (F-F): 4 X 10(sup -3)/s and Slow-Slow (S-S): 4 X 10(sup -5)/s) and asymmetrical ramp rates (Fast-Slow (F-S): 4 x 10(sup -3)/s / 4 X 10(sup -5/s and Slow-Fast (S-F): 4 X 10(sup -5) / 4 X 10(sup -3)/s) in tension and compression. The fatigue life, cyclic stress response, and fracture modes were significantly influenced by the waveform shape. The fatigue lives displayed by different loading conditions were in the following order: F-F greater than S-S greater than F-S greater than S-F. The fracture mode was dictated by the ramp rate adopted in the tensile direction. The fast ramp rate in the tensile direction led to the occurrence of transgranular crack initiation and propagation, whereas the slow ramp rate caused intergranular initiation and propagation. The time-dependent processes and their synergistic interactions, which were at the basis of observed changes in cyclic stress response and fatigue life, were identified. Oxidation, creep damage, dynamic strain aging, massive carbide precipitation, time-dependent creep deformation, and deformation ratcheting were among the several factors influencing cyclic life. Irrespective of the loading condition, the largest effect on life was exerted by oxidation processes. Deformation ratcheting had its greatest influence on life under asymmetrical loading conditions. Creep damage accumulated the greatest amount during the slow tensile ramp under S-F conditions.

Uniaxial and Multiaxial Fatigue Life Prediction of the Trabecular Bone Based on Physiological Loading: A Comparative Study.

PubMed

Fatihhi, S J; Harun, M N; Abdul Kadir, Mohammed Rafiq; Abdullah, Jaafar; Kamarul, T; Öchsner, Andreas; Syahrom, Ardiyansyah

2015-10-01

Fatigue assessment of the trabecular bone has been developed to give a better understanding of bone properties. While most fatigue studies are relying on uniaxial compressive load as the method of assessment, in various cases details are missing, or the uniaxial results are not very realistic. In this paper, the effect of three different load histories from physiological loading applied on the trabecular bone were studied in order to predict the first failure surface and the fatigue lifetime. The fatigue behaviour of the trabecular bone under uniaxial load was compared to that of multiaxial load using a finite element simulation. The plastic strain was found localized at the trabecular structure under multiaxial load. On average, applying multiaxial loads reduced more than five times the fatigue life of the trabecular bone. The results provide evidence that multiaxial loading is dominated in the low cycle fatigue in contrast to the uniaxial one. Both bone volume fraction and structural model index were best predictors of failure (p < 0.05) in fatigue for both types of loading, whilst uniaxial loading has indicated better values in most cases.

Fretting Fatigue with Cylindrical-On-Flat Contact: Crack Nucleation, Crack Path and Fatigue Life

PubMed Central

Noraphaiphipaksa, Nitikorn; Manonukul, Anchalee; Kanchanomai, Chaosuan

2017-01-01

Fretting fatigue experiments and finite element analysis were carried out to investigate the influence of cylindrical-on-flat contact on crack nucleation, crack path and fatigue life of medium-carbon steel. The location of crack nucleation was predicted using the maximum shear stress range criterion and the maximum relative slip amplitude criterion. The prediction using the maximum relative slip amplitude criterion gave the better agreement with the experimental result, and should be used for the prediction of the location of crack nucleation. Crack openings under compressive bulk stresses were found in the fretting fatigues with flat-on-flat contact and cylindrical-on-flat contacts, i.e., fretting-contact-induced crack openings. The crack opening stress of specimen with flat-on-flat contact was lower than those of specimens with cylindrical-on-flat contacts, while that of specimen with 60-mm radius contact pad was lower than that of specimen with 15-mm radius contact pad. The fretting fatigue lives were estimated by integrating the fatigue crack growth curve from an initial propagating crack length to a critical crack length. The predictions of fretting fatigue life with consideration of crack opening were in good agreement with the experimental results. PMID:28772522

Influence of High Cycle Thermal Loads on Thermal Fatigue Behavior of Thick Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Miller, Robert A.

1997-01-01

Thick thermal barrier coating systems in a diesel engine experience severe thermal Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF) during engine operation. In the present study, the mechanisms of fatigue crack initiation and propagation, as well as of coating failure, under thermal loads which simulate engine conditions, are investigated using a high power CO2 laser. In general, surface vertical cracks initiate early and grow continuously under LCF and HCF cyclic stresses. It is found that in the absence of interfacial oxidation, the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. Experiments show that the HCF cycles are very damaging to the coating systems. The combined LCF and HCF tests produced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. It is suggested that the HCF component cannot only accelerate the surface crack initiation, but also interact with the LCF by contributing to the crack growth at high temperatures. The increased LCF stress intensity at the crack tip due to the HCF component enhances the subsequent LCF crack growth. Conversely, since a faster HCF crack growth rate will be expected with lower effective compressive stresses in the coating, the LCF cycles also facilitate the HCF crack growth at high temperatures by stress relaxation process. A surface wedging model has been proposed to account for the HCF crack growth in the coating system. This mechanism predicts that HCF damage effect increases with increasing temperature swing, the thermal expansion coefficient and the elastic modulus of the ceramic coating, as well as the HCF interacting depth. A good agreement has been found between the analysis and experimental evidence.

Biomechanical investigation of an alternative concept to angular stable plating using conventional fixation hardware.

PubMed

Windolf, Markus; Klos, Kajetan; Wähnert, Dirk; van der Pol, Bas; Radtke, Roman; Schwieger, Karsten; Jakob, Roland P

2010-05-21

Angle-stable locking plates have improved the surgical management of fractures. However, locking implants are costly and removal can be difficult. The aim of this in vitro study was to evaluate the biomechanical performance of a newly proposed crossed-screw concept ("Fence") utilizing conventional (non-locked) implants in comparison to conventional LC-DCP (limited contact dynamic compression plate) and LCP (locking compression plate) stabilization, in a human cadaveric diaphyseal gap model. In eight pairs of human cadaveric femora, one femur per pair was randomly assigned to receive a Fence construct with either elevated or non-elevated plate, while the contralateral femur received either an LCP or LC-DCP instrumentation. Fracture gap motion and fatigue performance under cyclic loading was evaluated successively in axial compression and in torsion. Results were statistically compared in a pairwise setting. The elevated Fence constructs allowed significantly higher gap motion compared to the LCP instrumentations (axial compression: p

Contribution a l'etude du comportement en fatigue des aciers inoxydables 13%Cr-4%Ni: Contraintes residuelles de soudage et transformation sous contrainte de l'austenite de reversion

NASA Astrophysics Data System (ADS)

Thibault, Denis

The objectives of the present study are to characterize some of the main parameters affecting fatigue behaviour of 13%Cr-4%Ni martensitic stainless steels used for hydraulic turbines manufacturing. Two aspects are studied: the residual stresses left after autogenous welding of these steels and the stress-assisted transformation of the reformed austenite contained in this alloy. The residual stresses induced by welding were characterized by four different methods: the hole-drilling method, X-ray diffraction, neutron diffraction and the contour method. The state of stress was characterized in two different joints geometries, both using 41ONiMo weld filler metal. The characterization was made before and after post-weld heat treatment. A stress distribution completely different of the stress distribution commonly found in structural steels was measured. Triaxial compression was found in the last bead with a maximum value of approximately 400 MPa. Tensile stress was measured around the heat-affected zone and just below the last weld layer. The low temperature martensitic transformation occuring during weld cooling (˜300°C) explains this unusual stress distribution. The results also showed that the post-weld heat treatment commonly used in the industry is efficient in lowering residual stresses. A maximum stress of about 150 MPa was found after heat treament. The austenite formed during this post-weld heat treatment is mechanically unstable. The results presented in this thesis show that after fatigue crack propagation testing, all the reformed austenite found near the fracture surface has transformed to martensite under cyclic stress loading. These measurements made by X-ray diffraction are confirmed by low-cycle fatigue tests showing that the reformed austenite found in this alloy transforms gradually to martensite during strain cycling. The transformation is completed after 100 cycles. The fatigue crack growth behaviour of the tested alloys does not seem to be influenced by this phenomenon occuring at all values of stress intensity factor. The practical implications of this work on fabrication and repair of hydraulic turbines made of 13%Cr-4%Ni are also discussed in this thesis. Keywords: martensitic stainless steel, fatigue, residual stress, welding

Hydrostatic Stress Effect on the Yield Behavior of Inconel 100

NASA Technical Reports Server (NTRS)

Allen, Phillip A.; Wilson, Christopher D.

2003-01-01

Classical metal plasticity theory assumes that hydrostatic stress has negligible effect on the yield and postyield behavior of metals. Recent reexaminations of classical theory have revealed a significant effect of hydrostatic stress on the yield behavior of various geometries. Fatigue tests and nonlinear finite element analyses (FEA) of Inconel 100 (IN100) equal-arm bend specimens and new monotonic tests and nonlinear finite element analyses of IN100 smooth tension, smooth compression, and double-edge notch tension (DENT) test specimens have revealed the effect of internal hydrostatic tensile stresses on yielding. Nonlinear FEA using the von Mises (yielding is independent of hydrostatic stress) and the Drucker-Prager (yielding is linearly dependent on hydrostatic stress) yield functions were performed. A new FEA constitutive model was developed that incorporates a pressure-dependent yield function with combined multilinear kinematic and multilinear isotropic hardening using the ABAQUS user subroutine (UMAT) utility. In all monotonic tensile test cases, the von Mises constitutive model, overestimated the load for a given displacement or strain. Considering the failure displacements or strains for the DENT specimen, the Drucker-Prager FEM s predicted loads that were approximately 3% lower than the von Mises values. For the failure loads, the Drucker Prager FEM s predicted strains that were up to 35% greater than the von Mises values. Both the Drucker-Prager model and the von Mises model performed equally-well in simulating the equal-arm bend fatigue test.

Stress state during fixation determines susceptibility to fatigue-linked biodegradation in bioprosthetic heart valve materials.

PubMed

Margueratt, Sean D; Lee, J Michael

2002-01-01

Mechanical loading contributes to the structural deterioration of bioprosthetic heart valves. The influence of stress state during fixation may play a substantial role in their failure, linking fatigue damage caused by buckling and tension and the enzymatic degradation of glutaraldehyde-crosslinked collagen. Bovine pericardia were obtained immediately postmortem and 100 mm x 15 mm samples were cut in the base-to-apex direction. Half the samples were subjected to a uniaxial tensile stress of 250 kPa and half remained unloaded during a crosslinking treatment in 0.5% glutaraldehyde. Tissue samples were rinsed and cut into 16 mm x 4 mm test strips. Half of these strips were exposed to cyclic compressive buckling and alternating tension at 30 Hz for 20 million cycles (approx. 7.5 days) using a custom-built multi-sample fatigue system. Fatigue-damaged and non-damaged samples were subsequently incubated at 37 C for 48 hrs in: (i) Type I bacterial collagenase (20 U/ml) buffered in 0.05 M Tris, 10 mM CaCl2 2H2O (pH 7.4) or (ii) 0.05 M Tris buffer (pH 7.4) only. In both cases, the samples were loaded sinusoidally between 40 and 80 g using a previously described microtensile culture system. Tissue removed from the bath was rinsed in 0.1 M EDTA solution and mounted in a servo-hydraulic mechanical testing system (MTS). Ultimate tensile strength (UTS), maximum tissue modulus, and fracture strain were determined. The percent collagen solubilized was assessed by a colourmetric hydroxyproline assay of the enzyme bath and tissue sample. All data were analyzed by analysis of variance (ANOVA). The results confirmed the synergy between fatigue damage and collagenase proteolysis in these materials; however, there were no significant differences in this effect between simple fixation and stress-fixation up to 20 million cycles. There were significant decreases in the mechanical properties and an increase in the amount of collagen solubilized with increased exposure to fatigue cycling.

Numerical simulation of the fatigue behavior of additive manufactured titanium porous lattice structures.

PubMed

Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S

2016-03-01

In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1-0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. Copyright © 2015 Elsevier B.V. All rights reserved.

A comprehensive characterization of asphalt mixtures in compression.

DOT National Transportation Integrated Search

2013-08-01

Permanent deformation (i.e., rutting) is one of the major distresses in asphalt pavements, and it consists of : irrecoverable deformation due to viscoplastic flow and viscofracture fatigue damage. The mechanisms of rutting have not : been well addres...

Microstructure and Mechanical Properties of Extruded Gamma Met PX

NASA Technical Reports Server (NTRS)

Draper, S. L.; Das, G.; Locci, I.; Whittenberger, J. D.; Lerch, B. A.; Kestler, H.

2003-01-01

A gamma TiAl alloy with a high Nb content is being assessed as a compressor blade material. The microstructure and mechanical properties of extruded Ti-45Al-X(Nb,B,C) (at %) were evaluated in both an as-extruded condition and after a lamellar heat treatment. Tensile behavior of both as-extruded and lamellar heat treated specimens was studied in the temperature range of RT to 926 C. In general, the yield stress and ultimate tensile strength reached relatively high values at room temperature and decreased with increasing deformation temperature. The fatigue strength of both microstructures was characterized at 650 C and compared to a baseline TiAl alloy and to a Ni-base superalloy. Tensile and fatigue specimens were also exposed to 800 C for 200 h in air to evaluate the alloy's environmental resistance. A decrease in ductility was observed at room temperature due to the 800 C exposure but the 650 C fatigue properties were unaffected. Compressive and tensile creep testing between 727 and 1027 C revealed that the creep deformation was reproducible and predictable. Creep strengths reached superalloy-like levels at fast strain rates and lower temperatures but deformation at slower strain rates and/or higher temperature indicated significant weakening for the as-extruded condition. At high temperatures and low stresses, the lamellar microstructure had improved creep properties when compared to the as-extruded material. Microstructural evolution during heat treatment, identification of various phases, and the effect of microstructure on the tensile, fatigue, and creep behaviors is discussed.

Microstructure and Mechanical Properties of Extruded Gamma Microstructure Met PX

NASA Technical Reports Server (NTRS)

Draper, S. L.; Das, G.; Locci, J.; Whittenberger, J. D.; Lerch, B. A.; Kestler, H.

2003-01-01

A gamma TiAl alloy with a high Nb content is being assessed as a compressor blade material. The microstructure and mechanical properties of extruded Ti-45Al-X(Nb,B,C) (at.%) were evaluated in both an as-extruded condition and after a lamellar heat treatment. Tensile behavior of both as-extruded and lamellar heat treated specimens was studied in the temperature range of RT to 926 C. In general, the yield stress and ultimate tensile strength reached relatively high values at room temperature and decreased with increasing deformation temperature. The fatigue strength of both microstructures was characterized at 650 C and compared to a baseline TiAl alloy and to a Ni-base superalloy. Tensile and fatigue specimens were also exposed to 800 C for 200 h in air to evaluate the alloy's environmental resistance. A decrease in ductility was observed at room temperature due to the 800 C. exposure but the 650 C fatigue properties were unaffected. Compressive and tensile creep testing between 727 and 1027 C revealed that the creep deformation was reproducible and predictable. Creep strengths reached superalloy-like levels at fast strain rates and lower temperatures but deformation at slower strain rates and/or higher temperature indicated significant weakening for the as-extruded condition. At high temperatures and low stresses, the lamellar microstructure had improved creep properties when compared to the as-extruded material. Microstructural evolution during heat treatment, identification of various phases, and the effect of microstructure on the tensile, fatigue, and creep behaviors is discussed.

Numerical simulation of unmanned aerial vehicle under centrifugal load and optimization of milling and planing

NASA Astrophysics Data System (ADS)

Chen, Yunsheng; Lu, Xinghua

2018-05-01

The mechanical parts of the fuselage surface of the UAV are easily fractured by the action of the centrifugal load. In order to improve the compressive strength of UAV and guide the milling and planing of mechanical parts, a numerical simulation method of UAV fuselage compression under centrifugal load based on discrete element analysis method is proposed. The three-dimensional discrete element method is used to establish the splitting tensile force analysis model of the UAV fuselage under centrifugal loading. The micro-contact connection parameters of the UAV fuselage are calculated, and the yield tensile model of the mechanical components is established. The dynamic and static mechanical model of the aircraft fuselage milling is analyzed by the axial amplitude vibration frequency combined method. The correlation parameters of the cutting depth on the tool wear are obtained. The centrifugal load stress spectrum of the surface of the UAV is calculated. The meshing and finite element simulation of the rotor blade of the unmanned aerial vehicle is carried out to optimize the milling process. The test results show that the accuracy of the anti - compression numerical test of the UAV is higher by adopting the method, and the anti - fatigue damage capability of the unmanned aerial vehicle body is improved through the milling and processing optimization, and the mechanical strength of the unmanned aerial vehicle can be effectively improved.

Effect of Multi-Pass Ultrasonic Surface Rolling on the Mechanical and Fatigue Properties of HIP Ti-6Al-4V Alloy

PubMed Central

Li, Gang; Qu, Shengguan; Xie, Mingxin; Ren, Zhaojun; Li, Xiaoqiang

2017-01-01

The main purpose of this paper was to investigate the effect of a surface plastic deformation layer introduced by multi-pass ultrasonic surface rolling (MUSR) on the mechanical and fatigue properties of HIP Ti-6Al-4V alloys. Some microscopic analysis methods (SEM, TEM and XRD) were used to characterize the modified microstructure in the material surface layer. The results indicated that the material surface layer experienced a certain extent plastic deformation, accompanied by some dense dislocations and twin generation. Moreover, surface microhardness, residual stress and roughness values of samples treated by MUSR were also greatly improved compared with that of untreated samples. Surface microhardness and compressive residual stress were increased to 435 HV and −1173 MPa, respectively. The minimum surface roughness was reduced to 0.13 μm. The maximum depth of the surface hardening layer was about 55 μm. However, the practical influence depth was about 450 μm judging from the tensile and fatigue fracture surfaces. The ultimate tensile strength of the MUSR-treated sample increased to 990 MPa from the initial 963 MPa. The fatigue strength of the MUSR-treated sample was increased by about 25% on the base of 107 cycles, and the lifetime was prolonged from two times to two orders of magnitude at the applied stress amplitudes of 650–560 MPa. The improved mechanical and fatigue properties of MUSR-treated samples should be attributed to the combined effects of the increased microhardness and compressive residual stress, low surface roughness, grain refinement and micro-pore healing in the material surface-modified layer. PMID:28772494

Effects of Fine Particle Peening Conditions on the Rotational Bending Fatigue Strength of a Vacuum-Carburized Transformation-Induced Plasticity-Aided Martensitic Steel

NASA Astrophysics Data System (ADS)

Sugimoto, Koh-ichi; Hojo, Tomohiko; Mizuno, Yuta

2018-02-01

The effects of fine particle peening conditions on the rotational bending fatigue strength of a vacuum-carburized transformation-induced plasticity-aided martensitic steel with a chemical composition of 0.20 pct C, 1.49 pct Si, 1.50 pct Mn, 0.99 pct Cr, 0.02 pct Mo, and 0.05 pct Nb were investigated for the fabrication of automotive drivetrain parts. The maximum fatigue limit, resulting from high hardness and compressive residual stress in the surface-hardened layer caused by the severe plastic deformation and the strain-induced martensite transformation of the retained austenite during fine particle peening, was obtained by fine particle peening at an arc height of 0.21 mm (N). The high fatigue limit was also a result of the increased martensite fraction and the active plastic relaxation via the strain-induced martensite transformation during fatigue deformation, as well as preferential crack initiation on the surface or at the subsurface.

Effect of laser shock processing on fatigue life of 2205 duplex stainless steel notched specimens

NASA Astrophysics Data System (ADS)

Vázquez Jiménez, César A.; Gómez Rosas, Gilberto; Rubio González, Carlos; Granados Alejo, Vignaud; Hereñú, Silvina

2017-12-01

The effect laser shock processing (LSP) on high cycle fatigue behavior of 2205 duplex stainless steel (DSS) notched samples was investigated. The swept direction parallel (LSP 1) and perpendicular (LSP 2) to rolling were used in order to examine the sensitivity of LSP to manufacturing process since this steel present significantly anisotropy. The Nd:YAG pulsed laser operating at 10 Hz frequency and 1064 nm wavelength was utilized. The LSP configuration was the water jet mode without protective coating. Notched specimens 4 mm thick were treated on both sides, and then fatigue loading was applied with R = 0.1. The results showed that the LSP 2 condition induces higher compressive residual stresses as well as a higher fatigue life than the LSP 1 condition. By applying LSP 2 condition, an enhancement of fatigue life up to 402% is reported. In addition, the microhardness profiles showed different depths of hardening layer for each direction, according to the anisotropy observed.

Special Test Methods for Batteries

NASA Technical Reports Server (NTRS)

Gross, S.

1984-01-01

Various methods are described for measuring heat generation in primary and secondary batteries as well as the specific heat of batteries and cell thermal conductance. Problems associated with determining heat generation in large batteries are examined. Special attention is given to monitoring temperature gradients in nickel cadmium cells, the use of auxiliary electrodes for conducting tests on battery charge control, evaluating the linear sweep of current from charge to discharge, and determining zero current voltage. The fast transient behavior of batteries in the microsecond range, and the electrical conductance of nickel sinters in the thickness direction are also considered. Mechanical problems experienced in the vibration of Ni-Cd batteries and tests to simulate cyclic fatigue of the steel table connecting the plates to the comb are considered. Methods of defining the distribution of forces when cells are compressed during battery packaging are also explored.

Special test methods for batteries

NASA Astrophysics Data System (ADS)

Gross, S.

1984-09-01

Various methods are described for measuring heat generation in primary and secondary batteries as well as the specific heat of batteries and cell thermal conductance. Problems associated with determining heat generation in large batteries are examined. Special attention is given to monitoring temperature gradients in nickel cadmium cells, the use of auxiliary electrodes for conducting tests on battery charge control, evaluating the linear sweep of current from charge to discharge, and determining zero current voltage. The fast transient behavior of batteries in the microsecond range, and the electrical conductance of nickel sinters in the thickness direction are also considered. Mechanical problems experienced in the vibration of Ni-Cd batteries and tests to simulate cyclic fatigue of the steel table connecting the plates to the comb are considered. Methods of defining the distribution of forces when cells are compressed during battery packaging are also explored.

High Fidelity Simulations for Unsteady Flow Through the Orbiter LH2 Feedline Flowliner

NASA Technical Reports Server (NTRS)

Kiris, Cetin C.; Kwak, Dochan; Chan, William; Housman, Jeffrey

2005-01-01

High fidelity computations were carried out to analyze the orbiter M2 feedline flowliner. Various computational models were used to characterize the unsteady flow features in the turbopump, including the orbiter Low-Pressure-Fuel-Turbopump (LPFTP) inducer, the orbiter manifold and a test article used to represent the manifold. Unsteady flow originating from the orbiter LPFTP inducer is one of the major contributors to the high frequency cyclic loading that results in high cycle fatigue damage to the gimbal flowliners just upstream of the LPFTP. The flow fields for the orbiter manifold and representative test article are computed and analyzed for similarities and differences. An incompressible Navier-Stokes flow solver INS3D, based on the artificial compressibility method, was used to compute the flow of liquid hydrogen in each test article.

Spinoff From a Moon Suit

NASA Technical Reports Server (NTRS)

1991-01-01

Al Gross transferred expertise obtained as an ILC engineer for NASA's Apollo program to the manufacture of athletic shoes. Gross substituted DuPont's Hytrel plastic for foam materials in the shoe's midsole, eliminating cushioning loss caused by body weight. An external pressurized shell applied from space suit technology was incorporated into the shoe. Stiffness and cushioning properties of the midsole were "tuned" by varying material thickness and styling lines. A stress free "blow molding" process adapted from NASA space suit design was also utilized. The resulting compression chamber midsole performed well in tests. It allows AVIA to re-configure for specific sports and is a "first step" toward a durable, foamless, non-fatiguing midsole.

Surface modification and fatigue behavior of nitinol for load bearing implants

NASA Astrophysics Data System (ADS)

Bernard, Sheldon A.

Musculoskeletal disorders are recognized amongst the most significant human health problems that exist today. Even though considerable research and development has gone towards understanding musculoskeletal disorders, there is still lack of bone replacement materials that are appropriate for restoring lost structures and functions, particularly for load-bearing applications. Many materials on the market today, such as titanium and stainless steel, suffer from significantly higher modulus than natural bone and low bioactivity leading to stress shielding and implant loosening over longer time use. Nitinol (NiTi) is an equiatomic intermetallic compound of nickel and titanium whose unique biomechanical and biological properties contributed to its increasing use as a biomaterial. An innovative method for creating dense and porous net shape NiTi alloy parts has been developed to improve biological properties while maintaining comparable or better mechanical properties than commercial materials that are currently in use. Laser engineered net shaping (LENS(TM)) and surface electrochemistry modification was used to create dense/porous samples and micro textured surfaces on NiTi parts, respectively. Porous implants are known to promote cell adhesion and have a low elastic modulus, a combination that can significantly increase the life of an implant. However, porosity can significantly reduce the fatigue life of an implant, and very little work has been reported on the fatigue behavior of bulk porous metals, specifically on porous nitinol alloy. High-cycle rotating bending and compression-compression fatigue behavior of porous NiTi fabricated using LENS(TM) were studied. In cyclic compression loading, plastic strain increased with increasing porosity and it was evident that maximum strain was achieved during the first 50000 cycles and remained constant throughout the remaining loading. No failures were observed due to loading up to 150% of the yield strength. When subjected to rotary bending fatigue, samples demonstrated a high tolerance to failure, up to 50% of the yield stress. Using anodization, improvements to the surface wettability were made by lowering the contact angle from 32° to less than 5°, which prove to enhance the bioactivity of the nitinol surface in the cell study. The surface free energy was also calculated to show comparable properties to that of cpTi. Ni ion release was studied over a 8 week duration and found that anodization not only reduces the amount of metal ion release but also decreases the rate of release as well. This work was aimed at understanding the effects of porosity characteristics, microstructure, surface morphology and fatigue behavior of nitinol on its mechanical and biological properties.

A study of stiffness, residual strength and fatigue life relationships for composite laminates

NASA Technical Reports Server (NTRS)

Ryder, J. T.; Crossman, F. W.

1983-01-01

Qualitative and quantitative exploration of the relationship between stiffness, strength, fatigue life, residual strength, and damage of unnotched, graphite/epoxy laminates subjected to tension loading. Clarification of the mechanics of the tension loading is intended to explain previous contradictory observations and hypotheses; to develop a simple procedure to anticipate strength, fatigue life, and stiffness changes; and to provide reasons for the study of more complex cases of compression, notches, and spectrum fatigue loading. Mathematical models are developed based upon analysis of the damage states. Mathematical models were based on laminate analysis, free body type modeling or a strain energy release rate. Enough understanding of the tension loaded case is developed to allow development of a proposed, simple procedure for calculating strain to failure, stiffness, strength, data scatter, and shape of the stress-life curve for unnotched laminates subjected to tension load.

Damage Tolerance of Composite Laminates from an Empirical Perspective

NASA Technical Reports Server (NTRS)

Nettles, Alan T.

2009-01-01

Damage tolerance consists of analysis and experimentation working together. Impact damage is usually of most concern for laminated composites. Once impacted, the residual compression strength is usually of most interest. Other properties may be of more interest than compression (application dependent). A damage tolerance program is application specific (not everyone is building aircraft). The "Building Block Approach" is suggested for damage tolerance. Advantage can be taken of the excellent fatigue resistance of damaged laminates to save time and costs.

[Belated diagnosis of medullar compression in a case of post-polio syndrome].

PubMed

Boulay, C; Hamonet, C; Galaup, N; Djindjian, M; Montagne, A; Vivant, R

2001-03-01

The physiatrist observes about his practice individuals with sequela of old poliomyelitics. A part of them have unusual fatigue and muscular pains and weakness. The hypothesis of an evolution of neuro-biological mechanism suggested by few authors isn't, actually, demonstrated. More probably, the modifications of lesional and, functional changes with disability observed are the consequence of elderly effects and decreasing of physical activites. We report a case of spinal cord compression by intramedullar tumor, associated with a post-polio syndrome.

Hydraulic Fatigue-Testing Machine

NASA Technical Reports Server (NTRS)

Hodo, James D.; Moore, Dennis R.; Morris, Thomas F.; Tiller, Newton G.

1987-01-01

Fatigue-testing machine applies fluctuating tension to number of specimens at same time. When sample breaks, machine continues to test remaining specimens. Series of tensile tests needed to determine fatigue properties of materials performed more rapidly than in conventional fatigue-testing machine.

Evaluation on Compressive Characteristics of Medical Stents Applied by Mesh Structures

NASA Astrophysics Data System (ADS)

Hirayama, Kazuki; He, Jianmei

2017-11-01

There are concerns about strength reduction and fatigue fracture due to stress concentration in currently used medical stents. To address these problems, meshed stents applied by mesh structures were interested for achieving long life and high strength perfromance of medical stents. The purpose of this study is to design basic mesh shapes to obatin three dimensional (3D) meshed stent models for mechanical property evaluation. The influence of introduced design variables on compressive characteristics of meshed stent models are evaluated through finite element analysis using ANSYS Workbench code. From the analytical results, the compressive stiffness are changed periodically with compressive directions, average results need to be introduced as the mean value of compressive stiffness of meshed stents. Secondly, compressive flexibility of meshed stents can be improved by increasing the angle proportional to the arm length of the mesh basic shape. By increasing the number of basic mesh shapes arranged in stent’s circumferential direction, compressive rigidity of meshed stent tends to be increased. Finaly reducing the mesh line width is found effective to improve compressive flexibility of meshed stents.

Study to determine and analyze the strength of high modulus glass in epoxy-matrix composites

NASA Technical Reports Server (NTRS)

Bacon, J. F.

1974-01-01

Glass composition research was conducted to produce a high modulus, high strength beryllium-free glass fiber. This program was built on the previous research for developing high modulus, high strength glass fibers which had a 5 weight percent beryllia content. The fibers resulting from the composition program were then used to produce fiber reinforced-epoxy resin composites which were compared with composites reinforced by commercial high modulus glass fibers, Thornel S graphite fiber, and hybrids where the external quarters were reinforced with Thornel S graphite fiber and the interior half with glass fiber as well as the reverse hybrid. The composites were given tensile strength, compressive strength, short-beam shear strength, creep and fatigue tests. Comments are included on the significance of the test data.

In vitro mechanical fatigue behavior of poly-ɛ-caprolactone macroporous scaffolds for cartilage tissue engineering: Influence of pore filling by a poly(vinyl alcohol) gel.

PubMed

Panadero, J A; Vikingsson, L; Gomez Ribelles, J L; Lanceros-Mendez, S; Sencadas, V

2015-07-01

Polymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and submitted to repeated loading cycles. In the case of articular cartilage engineering, an implanted scaffold is typically subjected to long-term dynamic compression. The evolution of the mechanical properties of the scaffold during bioresorption has been deeply studied in the past, but the possibility of failure due to mechanical fatigue has not been properly addressed. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. In this work fatigue studies of polycaprolactone scaffolds were carried by subjecting the scaffold to repeated compression cycles in conditions simulating the scaffold implanted in the articular cartilage. The behavior of the polycaprolactone sponge with the pores filled with a poly(vinyl alcohol) gel simulating the new formed tissue within the pores was compared with that of the material immersed in water. Results were analyzed with Morrow's criteria for failure and accurate fittings are obtained just up to 200 loading cycles. It is also shown that the presence of poly(vinyl alcohol) increases the elastic modulus of the scaffolds, the effect being more pronounced with increasing the number of freeze/thawing cycles. © 2014 Wiley Periodicals, Inc.

In-situ X-ray CT results of damage evolution in L6 ordinary chondrite meteorites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuadra, Jefferson A.; Hazeli, Kavan; Ramesh, K. T.

2016-06-17

These are slides about in-situ X-ray CT results of damage evolution in L6 ordinary chondrite meteorites. The following topics are covered: mechanical and thermal damage characterization, list of Grosvenor Mountain (GRO) meteorite samples, in-situ x-ray compression test setup, GRO-chipped reference at 0 N - existing cracks, GRO-chipped loaded at 1580 N, in-situ x-ray thermal fatigue test setup, GRO-B14 room temperature reference, GRO-B14 Cycle 47 at 200°C, GRO-B14 Cycle 47 at room temperature, conclusions from qualitative analysis, future work and next steps. Conclusions are the following: Both GRO-Chipped and GRO-B14 had existing voids and cracks within the volume. These sites withmore » existing damage were selected for CT images from mechanically and thermally loaded scans since they are prone to damage initiation. The GRO-Chipped sample was loaded to 1580 N which resulted in a 14% compressive engineering strain, calculated using LVDT. Based on the CT cross sectional images, the GRO-B14 sample at 200°C has a thermal expansion of approximately 96 μm in height (i.e. ~1.6% engineering strain).« less

Fatigue behaviour of NiTi shape memory alloy scaffolds produced by SLM, a unit cell design comparison.

PubMed

Speirs, M; Van Hooreweder, B; Van Humbeeck, J; Kruth, J-P

2017-06-01

Selective laser melting (SLM) is an additive manufacturing technique able to produce complex functional parts via successively melting layers of metal powder. This process grants the freedom to design highly complex scaffold components to allow bone ingrowth and aid mechanical anchorage. This paper investigates the compression fatigue behaviour of three different unit cells (octahedron, cellular gyroid and sheet gyroid) of SLM nitinol scaffolds. It was found that triply periodic minimal surfaces display superior static mechanical properties in comparison to conventional octahedron beam lattice structures at identical volume fractions. Fatigue resistance was also found to be highly geometry dependent due to the effects of AM processing techniques on the surface topography and notch sensitivity. Geometries minimising nodal points and the staircase effect displayed the greatest fatigue resistance when normalized to yield strength. Furthermore oxygen analysis showed a large oxygen uptake during SLM processing which must be altered to meet ASTM medical grade standards and may significantly reduce fatigue life. These achieved fatigue properties indicate that NiTi scaffolds produced via SLM can provide sufficient mechanical support over an implants lifetime within stress range values experienced in real life. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fatigue, Creep-Fatigue, and Thermomechanical Fatigue Life Testing of Alloys

NASA Technical Reports Server (NTRS)

Halford, Gary R.; Lerch, Bradley A.; McGaw, Michael A.

2000-01-01

The fatigue crack initiation resistance of an alloy is determined by conducting a series of tests over a range of values of stress amplitude or strain range. The observed number of cycles to failure is plotted against the stress amplitude or strain range to obtain a fatigue curve. The fatigue properties quoted for an alloy are typically the constants used in the equation(s) that describe the fatigue curve. Fatigue lives of interest may be as low as 10(exp 2) or higher than 10(exp 9) cycles. Because of the enormous scatter associated with fatigue, dozens of tests may be needed to confidently establish a fatigue curve, and the cost may run into several thousands of dollars. To further establish the effects on fatigue life of the test temperature, environment, alloy condition, mean stress effects, creep-fatigue effects, thermomechanical cycling, etc. requires an extraordinarily large and usually very costly test matrix. The total effort required to establish the fatigue resistance of an alloy should not be taken lightly. Fatigue crack initiation tests are conducted on relatively small and presumed to be initially crack-free, samples of an alloy that are intended to be representative of the alloy's metallurgical and physical condition. Generally, samples are smooth and have uniformly polished surfaces within the test section. Some may have intentionally machined notches of well-controlled geometry, but the surface at the root of the notch is usually not polished. The purpose of polishing is to attain a reproducible surface finish. This is to eliminate surface finish as an uncontrolled variable. Representative test specimen geometries will be discussed later. Test specimens are cyclically loaded until macroscopically observable cracks initiate and eventually grow to failure. Normally, the fatigue failure life of a specimen is defined as the number of cycles to separation of the specimen into two pieces. Alternative definitions are becoming more common, particularly for low-cycle fatigue testing, wherein some prescribed indication of impending failure due to cracking is adopted. Specific criteria will be described later. As a rule, cracks that develop during testing are not measured nor are the test parameters intentionally altered owing to the presence of cracking.

Fatigue Test Design: Scenarios for Biaxial Fatigue Testing of a 60-Meter Wind Turbine Blade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Post, Nathan

Current practice in commercial certification of wind turbine blades is to perform separate flap and lead-lag fatigue tests. The National Renewable Energy Laboratory has been researching and evaluating biaxial fatigue testing techniques and demonstrating various options, typically on smaller-scale test articles at the National Wind Technology Center. This report evaluates some of these biaxial fatigue options in the context of application to a multimegawatt blade certification test program at the Wind Technology Testing Center in Charlestown, Massachusetts.

Assessment of reliability of CAD-CAM tooth-colored implant custom abutments.

PubMed

Guilherme, Nuno Marques; Chung, Kwok-Hung; Flinn, Brian D; Zheng, Cheng; Raigrodski, Ariel J

2016-08-01

Information is lacking about the fatigue resistance of computer-aided design and computer-aided manufacturing (CAD-CAM) tooth-colored implant custom abutment materials. The purpose of this in vitro study was to investigate the reliability of different types of CAD-CAM tooth-colored implant custom abutments. Zirconia (Lava Plus), lithium disilicate (IPS e.max CAD), and resin-based composite (Lava Ultimate) abutments were fabricated using CAD-CAM technology and bonded to machined titanium-6 aluminum-4 vanadium (Ti-6Al-4V) alloy inserts for conical connection implants (NobelReplace Conical Connection RP 4.3×10 mm; Nobel Biocare). Three groups (n=19) were assessed: group ZR, CAD-CAM zirconia/Ti-6Al-4V bonded abutments; group RC, CAD-CAM resin-based composite/Ti-6Al-4V bonded abutments; and group LD, CAD-CAM lithium disilicate/Ti-6Al-4V bonded abutments. Fifty-seven implant abutments were secured to implants and embedded in autopolymerizing acrylic resin according to ISO standard 14801. Static failure load (n=5) and fatigue failure load (n=14) were tested. Weibull cumulative damage analysis was used to calculate step-stress reliability at 150-N and 200-N loads with 2-sided 90% confidence limits. Representative fractured specimens were examined using stereomicroscopy and scanning electron microscopy to observe fracture patterns. Weibull plots revealed β values of 2.59 for group ZR, 0.30 for group RC, and 0.58 for group LD, indicating a wear-out or cumulative fatigue pattern for group ZR and load as the failure accelerating factor for groups RC and LD. Fractographic observation disclosed that failures initiated in the interproximal area where the lingual tensile stresses meet the compressive facial stresses for the early failure specimens. Plastic deformation of titanium inserts with fracture was observed for zirconia abutments in fatigue resistance testing. Significantly higher reliability was found in group ZR, and no significant differences in reliability were determined between groups RC and LD. Differences were found in the failure characteristics of group ZR between static and fatigue loading. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Cumulative fatigue damage behavior of MAR M-247

NASA Technical Reports Server (NTRS)

Mcgaw, Michael A.; Halford, Gary R.; Kalluri, Sreeramesh

1991-01-01

The objective was to examine the room temperature fatigue and nonlinear cumulative fatigue damage behavior of the cast nickel-based superalloy, MAR M-247. The fatigue test matrix consisted of single-level, fully reversed fatigue experiments. Two series of tests were performed: one of the two baseline fatigue LCF (Low-Cycle Fatigue) life levels was used in the first loading block, and the HCF (High-Cycle Fatigue) baseline loading level was used in the second block in each series. For each series, duplicate tests were performed at each applied LCF life fraction.

Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition

NASA Technical Reports Server (NTRS)

Phillips, E. P.

1974-01-01

Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.

A randomized controlled trial of manual therapy and pneumatic compression for recovery from prolonged running - an extended study.

PubMed

Heapy, Amanda M; Hoffman, Martin D; Verhagen, Heidie H; Thompson, Samuel W; Dhamija, Pavitra; Sandford, Fiona J; Cooper, Mary C

2018-03-07

Manual therapy (MT) and intermittent pneumatic compression (IPC) are recovery methods used by endurance athletes with little evidence supporting effectiveness. This randomized controlled trial evaluated effectiveness of four daily post-race treatments of a specific MT protocol and IPC compared with supine rest on recovery following an ultramarathon among 56 ultramarathoners. Groups were comparable across all characteristics examined, including post-race plasma creatine kinase concentration. Subject completed timed 400 m runs before the race and on days three, five, seven and 14 post- race, and also provided muscle pain and soreness ratings and fatigue scores immediately before and after treatments, and during the 14 days post- race. Daily subjective measures and 400 m run times were not improved by either treatment, but both treatments reduced (p < .05) muscular fatigue scores acutely after treatment following the race and on post-race day 1, and MT improved (p < .05) muscle pain and soreness acutely following the race.

High Fidelity Simulations of Unsteady Flow through Turbopumps and Flowliners

NASA Technical Reports Server (NTRS)

Kiris, Cetin C.; Kwak, dochan; Chan, William; Housman, Jeff

2006-01-01

High fidelity computations were carried out to analyze the orbiter LH2 feedline flowliner. Computations were performed on the Columbia platform which is a 10,240-processor supercluster consisting of 20 Altix nodes with 512 processor each. Various computational models were used to characterize the unsteady flow features in the turbopump, including the orbiter Low-Pressure-Fuel-Turbopump (LPFTP) inducer, the orbiter manifold and a test article used to represent the manifold. Unsteady flow originating from the orbiter LPFTP inducer is one of the major contributors to the high frequency cyclic loading that results in high cycle fatigue damage to the gimbal flowliners just upstream of the LPFTP. The flow fields for the orbiter manifold and representative test article are computed and analyzed for similarities and differences. The incompressible Navier-Stokes flow solver INS3D, based on the artificial compressibility method, was used to compute the flow of liquid hydrogen in each test article.

Development of a high-frequency and large-stroke fatigue testing system for rubber

NASA Astrophysics Data System (ADS)

Chen, Gang; Wu, Hao; Gao, Jianwen; Lin, Qiang

2017-04-01

The limited capabilities of current fatigue testing machines have resulted in studies on the fatigue behavior of rubber under large-displacement amplitude and high frequency being very sparse. In this study, a fatigue testing system that can carry out large-displacement amplitude and high-frequency fatigue tests on rubber was developed using a moving magnet voice coil motor (MMVCM) actuator, with finite element analysis applied to analyze the thrust of the MMVCM actuator. The results of a series of cyclic tension tests conducted on vulcanized natural rubber specimens using the developed fatigue testing system verify that it has high precision, low noise, large-stroke, and high-frequency characteristics. Further, the load frame with the developed MMVCM actuator is feasible for material testing, especially for large-stroke and high-frequency fatigue tests.

Fatigue tests on big structure assemblies of concorde aircraft

NASA Technical Reports Server (NTRS)

Nguyen, V. P.; Perrais, J. P.

1972-01-01

Fatigue tests on structural assemblies of the Concorde supersonic transport aircraft are reported. Two main sections of the aircraft were subjected to pressure, mechanical load, and thermal static tests. The types of fatigue tests conducted and the results obtained are discussed. It was concluded that on a supersonic aircraft whose structural weight is a significant part of the weight analysis, many fatigue and static strength development tests should be made and fatigue and thermal tests of the structures are absolutely necessary.

Hygrothermomechanical evaluation of transverse filament tape epoxy/polyester fiberglass composites

NASA Technical Reports Server (NTRS)

Lark, R. L.; Chamis, C. C.

1983-01-01

The static and cyclic load behavior of transverse filament tape (TFT) fiberglass/epoxy and TFY fiberglass/polyester composites, intended for use in the design of low-cost wind turbine blades, are presented. The data behavior is also evaluated with respect to predicted properties based on an integrated hygrothermomechanical response theory. Experimental TFT composite data were developed by the testing of laminates made by using composite layups typical of those used for the fabrication of TFT fiberglass wind turbine blades. Static properties include tension, compression, and interlaminar shear strengths at ambient conditions and at high humidity/elevated temperature conditions after a 500 hour exposure. Cyclic fatigue data were obtained using similar environmental conditions and a range of cyclic stresses. The environmental (temperature and moisture) and cyclic load effects on composite strength degradation are subsequently compared with the predictions obtained by using the composite life/durability theory. The results obtained show that the predicted hygrothermomechanical environmental effects on TFT composites are in good agreement with measured data for various properties including fatigue at different cyclic stresses.

Time-lapsed investigation of three-dimensional failure and damage accumulation in trabecular bone using synchrotron light.

PubMed

Thurner, P J; Wyss, P; Voide, R; Stauber, M; Stampanoni, M; Sennhauser, U; Müller, R

2006-08-01

Synchrotron radiation micro-computed tomography (SRmicroCT) is a very useful technique when it comes to three-dimensional (3D) imaging of complex internal and external geometries. Being a fully non-destructive technique, SRmicroCT can be combined with other experiments in situ for functional imaging. We are especially interested in the combination of SRmicroCT with mechanical testing in order to gain new insights in the failure mechanism of trabecular bone. This interest is motivated by the immense costs in health care due to patients suffering from osteoporosis, a systemic skeletal disease resulting in decreased bone stability and increased fracture risk. To better investigate the different failure mechanisms on the microlevel, we have developed a novel in situ mechanical compression device, capable of exerting both static and dynamic displacements on experimental samples. The device was calibrated for mechanical testing using solid aluminum and bovine trabecular bone samples. To study different failure mechanisms in trabecular bone, we compared a fatigued and a non-fatigued bovine bone sample with respect to failure initiation and propagation. The fatigued sample failed in a burst-like fashion in contrast to the non-fatigued sample, which exhibited a distinct localized failure band. Moreover, microscopic cracks - microcracks and microfractures - were uncovered in a 3D fashion illustrating the failure process in great detail. The majority of these cracks were connected to a bone surface. The data also showed that the classification of microcracks and -fractures from 2D section can sometimes be ambiguous, which is also true for the distinction of diffuse and distinct microdamage. Detailed investigation of the failure mechanism in these samples illustrated that trabecular bone often fails in delamination, providing a mechanism for energy dissipation while conserving trabecular bone architecture. In the future, this will allow an even better understanding of bone mechanics related to its hierarchical structural organization.

The Effects of Hot Corrosion Pits on the Fatigue Resistance of a Disk Superalloy

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Telesman, Jack; Hazel, Brian; Mourer, David P.

2009-01-01

The effects of hot corrosion pits on low cycle fatigue life and failure modes of the disk superalloy ME3 were investigated. Low cycle fatigue specimens were subjected to hot corrosion exposures producing pits, then tested at low and high temperatures. Fatigue lives and failure initiation points were compared to those of specimens without corrosion pits. Several tests were interrupted to estimate the fraction of fatigue life that fatigue cracks initiated at pits. Corrosion pits significantly reduced fatigue life by 60 to 98 percent. Fatigue cracks initiated at a very small fraction of life for high temperature tests, but initiated at higher fractions in tests at low temperature. Critical pit sizes required to promote fatigue cracking were estimated, based on measurements of pits initiating cracks on fracture surfaces.

Improved chest recoil using an adhesive glove device for active compression–decompression CPR in a pediatric manikin model☆

PubMed Central

Udassi, Jai P.; Udassi, Sharda; Lamb, Melissa A.; Lamb, Kenneth E.; Theriaque, Douglas W.; Shuster, Jonathan J.; Zaritsky, Arno L.; Haque, Ikram U.

2013-01-01

Objective We developed an adhesive glove device (AGD) to perform ACD-CPR in pediatric manikins, hypothesizing that AGD-ACD-CPR provides better chest decompression compared to standard (S)-CPR. Design Split-plot design randomizing 16 subjects to test four manikin-technique models in a crossover fashion to AGD-ACD-CPR vs. S-CPR. Healthcare providers performed 5 min of CPR with 30:2 compression:ventilation ratio in the four manikin models: (1) adolescent; (2) child two-hand; (3) child one-hand; and (4) infant two-thumb. Methods Modified manikins recorded compression pressure (CP), compression depth (CD) and decompression depth (DD). The AGD consisted of a modified oven mitt with an adjustable strap; a Velcro patch was sewn to the palmer aspect. The counter Velcro patch was bonded to the anterior chest wall. For infant CPR, the thumbs of two oven mitts were stitched together with Velcro. Subjects were asked to actively pull up during decompression. Subjects’ heart rate (HR), respiratory rate (RR) and recovery time (RT) for HR/RR to return to baseline were recorded. Subjects were blinded to data recordings. Data (mean ± SEM) were analyzed using a two-tailed paired t-test. Significance was defined qualitatively as P ≤ 0.05. Results Mean decompression depth difference was significantly greater with AGD-ACD-CPR compared to S-CPR; 38–75% of subjects achieved chest decompression to or beyond baseline. AGD-ACD-CPR provided 6–12% fewer chest compressions/minute than S-CPR group. There was no significant difference in CD, CP, HR, RR and RT within each group comparing both techniques. Conclusion A simple, inexpensive glove device for ACD-CPR improved chest decompression with emphasis on active pull in manikins without excessive rescuer fatigue. The clinical implication of fewer compressions/minute in the AGD group needs to be evaluated. PMID:19683849

Customized fiber glass posts. Fatigue and fracture resistance.

PubMed

Costa, Rogério Goulart; De Morais, Eduardo Christiano Caregnatto; Campos, Edson Alves; Michel, Milton Domingos; Gonzaga, Carla Castiglia; Correr, Gisele Maria

2012-02-01

To evaluate the root fracture strength of human single-rooted premolars restored with customized fiberglass post-core systems after fatigue simulation. 40 human premolars had their crowns cut and the root length was standardized to 13 mm. The teeth were endodontically treated and embedded in acrylic resin. The specimens were distributed into four groups (n=10) according to the restorative material used: prefabricated fiber post (PFP), PFP+accessory fiber posts (PFPa), PFP+unidirectional fiberglass (PFPf), and unidirectional fiberglass customized post (CP). All posts were luted using resin cement and the cores were built up with a resin composite. The samples were stored for 24 hours at 37 degrees C and 100% relative humidity and then submitted to mechanical cycling. The specimens were then compressive-loaded in a universal testing machine at a crosshead speed of 0.5 mm/minute until fracture. The failure patterns were analyzed and classified. Data was submitted to one-way ANOVA and Tukey's test (alpha = 0.05). The mean values of maximum load (N) were: PFP - 811.4 +/- 124.3; PFPa - 729.2 +/- 157.2; PFPf- 747.5 +/- 204.7; CP - 762.4 +/- 110. Statistical differences were not observed among the groups. All groups showed favorable restorable failures. Fiberglass customized post did not show improved fracture resistance or differences in failure patterns when compared to prefabricated glass fiber posts.

Rocketdyne automated dynamics data analysis and management system

NASA Technical Reports Server (NTRS)

Tarn, Robert B.

1988-01-01

An automated dynamics data analysis and management systems implemented on a DEC VAX minicomputer cluster is described. Multichannel acquisition, Fast Fourier Transformation analysis, and an online database have significantly improved the analysis of wideband transducer responses from Space Shuttle Main Engine testing. Leakage error correction to recover sinusoid amplitudes and correct for frequency slewing is described. The phase errors caused by FM recorder/playback head misalignment are automatically measured and used to correct the data. Data compression methods are described and compared. The system hardware is described. Applications using the data base are introduced, including software for power spectral density, instantaneous time history, amplitude histogram, fatigue analysis, and rotordynamics expert system analysis.

Fatigue Characterization of Alloy 10: a 1300F Disk Alloy for Small Gas Turbine Engines

NASA Technical Reports Server (NTRS)

Gayda, John

2000-01-01

A detailed fatigue characterization of Alloy 10, a high strength nickel-based disk alloy, was conducted on test coupons machined from a 'pancake' forging. Smooth bar, strain controlled fatigue testing at various R-ratios was run at representative bore, 750 F, and rim, 1300 F, temperatures. This was followed by notch fatigue testing (Kt=2) run under load control. Analysis of the fatigue data using a Smith-Watson-Topper approach and finite element analysis of the notch root was employed to understand material behavior in these tests. Smooth bar fatigue data showed a significant R-ratio dependence at either test temperature which could be accounted for using a Smith-Watson-Topper parameter (SWT). In general, fatigue life was longer at 750 F than 1300 F for a given SWT. For notch fatigue tests, life was longer at 750 F than 1300 F but only at higher stresses. This was attributed to differences in alloy strength. At lower stresses, finite element analysis suggested that convergence of fatigue life at both temperatures resulted from relaxation of stresses at the notch root in the 1300 F tests.

The Boeing 747 fatigue integrity program

NASA Technical Reports Server (NTRS)

Spencer, M. M.

1972-01-01

The fatigue integrity program which was established to insure economic operations and to provide foundation data for inspection and maintenance is discussed. Significant features of the 747 fatigue integrity program are: (1) fatigue analyses which are continually updated to reflect design changes, fatigue test results, and static and flight load survey measurements; (2) material selection and detail design by using initial fatigue analyses, service experience, and testing; and (3) fatigue testing to check detail design quality and to verify the analyses, culminated by the test of a structurally complete airframe. Fatigue stress analyses were performed with the aid of experimental as well as analytical procedures. Extensive application was made of the stress severity factor, developed at Boeing, for evaluating peak stresses in complex joints. A frame of reference was established by families of structural fatigue performance curves (S-N curves) encompassing the range of materials and fatigue qualities anticipated for the 747 airplane design.

Performance and durability testing of parabolic trough receivers

NASA Astrophysics Data System (ADS)

Lei, Dongqiang; Fu, Xuqiang; Zhao, Dongming; Yuan, Guofeng; Wang, Zhifeng; Guo, Minghuan

2017-06-01

The paper describes the key performance and durability testing facilities of the parabolic trough receiver developed by Institute of Electrical Engineering, Chinese Academy of Sciences. The indoor heat loss test can be applied at 4-7 different temperature levels within 200-550 on receivers. The optical efficiency test bench consists of 12 metal halide lamps as the solar simulator and a 5 m length half-elliptical cylinder reflector with flat end reflectors. 3 ultra-precision temperature sensors are used in receiver each end to get the temperature difference. The residual gas analysis test bench is applied to analyze and predict the vacuum lifetime of the receiver. It can test the variations of composition and partial pressure of residual gases with temperature and time in the receiver annulus space by a high sensitivity quadrupole mass spectrometer gas analyzer. A coating accelerated ageing test bench, which is also used to test the thermal cycle, has been developed. This test bench uses the absorber tube of the recevier as the resistance heater to heat up the whole receiver. The coating lifetime can be predicted by the Arrhenius parameters. For the cycling test, the compressed air is used to directly cool the inner surface of the absorber tube. The thermal cycling test is performed with temperature cycles from 150 °C to 450 °C for 160 cycles. The maximum thermal cycling frequency is 8 cycles per day. The mechanical fatigue test bench is used to test the bellows and the glass-to-metal seals durability at the same time. Both bellows are expanded and compressed to 6.5 mm in turn with 10,000 cycles. A new rotating test bench was also developed to test the thermal efficiency of the receiver.

Low visual information-processing speed and attention are predictors of fatigue in elementary and junior high school students

PubMed Central

2011-01-01

Background Fatigue is a common complaint among elementary and junior high school students, and is known to be associated with reduced academic performance. Recently, we demonstrated that fatigue was correlated with decreased cognitive function in these students. However, no studies have identified cognitive predictors of fatigue. Therefore, we attempted to determine independent cognitive predictors of fatigue in these students. Methods We performed a prospective cohort study. One hundred and forty-two elementary and junior high school students without fatigue participated. They completed a variety of paper-and-pencil tests, including list learning and list recall tests, kana pick-out test, semantic fluency test, figure copying test, digit span forward test, and symbol digit modalities test. The participants also completed computerized cognitive tests (tasks A to E on the modified advanced trail making test). These cognitive tests were used to evaluate motor- and information-processing speed, immediate and delayed memory function, auditory and visual attention, divided and switching attention, retrieval of learned material, and spatial construction. One year after the tests, a questionnaire about fatigue (Japanese version of the Chalder Fatigue Scale) was administered to all the participants. Results After the follow-up period, we confirmed 40 cases of fatigue among 118 students. In multivariate logistic regression analyses adjusted for grades and gender, poorer performance on visual information-processing speed and attention tasks was associated with increased risk of fatigue. Conclusions Reduced visual information-processing speed and poor attention are independent predictors of fatigue in elementary and junior high school students. PMID:21672212

Low visual information-processing speed and attention are predictors of fatigue in elementary and junior high school students.

PubMed

Mizuno, Kei; Tanaka, Masaaki; Fukuda, Sanae; Yamano, Emi; Shigihara, Yoshihito; Imai-Matsumura, Kyoko; Watanabe, Yasuyoshi

2011-06-14

Fatigue is a common complaint among elementary and junior high school students, and is known to be associated with reduced academic performance. Recently, we demonstrated that fatigue was correlated with decreased cognitive function in these students. However, no studies have identified cognitive predictors of fatigue. Therefore, we attempted to determine independent cognitive predictors of fatigue in these students. We performed a prospective cohort study. One hundred and forty-two elementary and junior high school students without fatigue participated. They completed a variety of paper-and-pencil tests, including list learning and list recall tests, kana pick-out test, semantic fluency test, figure copying test, digit span forward test, and symbol digit modalities test. The participants also completed computerized cognitive tests (tasks A to E on the modified advanced trail making test). These cognitive tests were used to evaluate motor- and information-processing speed, immediate and delayed memory function, auditory and visual attention, divided and switching attention, retrieval of learned material, and spatial construction. One year after the tests, a questionnaire about fatigue (Japanese version of the Chalder Fatigue Scale) was administered to all the participants. After the follow-up period, we confirmed 40 cases of fatigue among 118 students. In multivariate logistic regression analyses adjusted for grades and gender, poorer performance on visual information-processing speed and attention tasks was associated with increased risk of fatigue. Reduced visual information-processing speed and poor attention are independent predictors of fatigue in elementary and junior high school students. © 2011 Mizuno et al; licensee BioMed Central Ltd.

Pre-stressed/pre-compressed gas turbine nozzle

DOEpatents

Jang, Hoyle; Itzel, Gary Michael; Yu, Yufeng Phillip

2002-01-01

A method of increasing low cycle fatigue life of a turbine nozzle comprising a plurality of stationary airfoils extending between radially inner and outer ring segments comprising a) providing at least one radial passage in each of the plurality of airfoils; b) installing a rod in the radial passage extending between the radially inner and outer ring segments and fixing one end of the rod to one of the inner and outer rings; and c) pre-loading the rod to compress the airfoil between the inner and outer ring segments.

Numerical Investigation of the Dynamic Properties of Intermittent Jointed Rock Models Subjected to Cyclic Uniaxial Compression

NASA Astrophysics Data System (ADS)

Liu, Yi; Dai, Feng; Zhao, Tao; Xu, Nu-wen

2017-01-01

Intermittent jointed rocks, which exist in a myriad of engineering projects, are extraordinarily susceptible to cyclic loadings. Understanding the dynamic fatigue properties of jointed rocks is necessary for evaluating the stability of rock engineering structures. This study numerically investigated the influences of cyclic loading conditions (i.e., frequency, maximum stress and amplitude) and joint geometric configurations (i.e., dip angle, persistency and interspace) on the dynamic fatigue mechanisms of jointed rock models. A reduction model of stiffness and strength was first proposed, and then, sixteen cyclic uniaxial loading tests with distinct loading parameters and joint geometries were simulated. Our results indicate that the reduction model can effectively reproduce the hysteresis loops and the accumulative plastic deformation of jointed rocks in the cyclic process. Both the loading parameters and the joint geometries significantly affect the dynamic properties, including the irreversible strain, damage evolution, dynamic residual strength and fatigue life. Three failure modes of jointed rocks, which are principally controlled by joint geometries, occur in the simulations: splitting failure through the entire rock sample, sliding failure along joint planes and mixed failure, which are principally controlled by joint geometries. Furthermore, the progressive failure processes of the jointed rock samples are numerically observed, and the different loading stages can be distinguished by the relationship between the number of broken bonds and the axial stress.

Investigation on Residual Stress Induced by Shot Peening

NASA Astrophysics Data System (ADS)

Zhao, Chunmei; Gao, Yukui; Guo, Jing; Wang, Qiang; Fu, Lichao; Yang, Qingxiang

2015-03-01

The high strength steel widely used in the aviation industry was chosen in this paper. The shot peening (SP) tests with different technical parameters were carried out, and compressive residual stress (CRS) distribution along the depth was determined. The phase structures before and after SP were analyzed by XRD and TEM. Microhardness and fatigue life were measured, and the morphology of fatigue fracture was also observed. The effects of different technical parameters on CRS field were investigated, and the CRS features with the characteristic parameters were analyzed deeply to summarize the rules. The results show that the CRS field induced by SP can be expressed by four characteristic parameters: the surface CRS σsrs, the maximum CRS σmrs, the depth of maximum CRS ξm and the depth of CRS (strengthened depth) ξ0. Martensite matrix is not changed by SP, while its boundary changes ambiguous with the formation of dislocations. After SP, the microhardness of the specimen increase, and the fatigue crack source moves inwards. The SP saturated time is 1 min. With the increase of SP intensity, σsrs, σmrs, ξm, and ξ0 all increase. While with the increase of SP angle, ξ0 grows gradually. The strengthen effect behaves more obviously as the shot size increases, and the shot material with larger hardness cause higher level of CRS field. Dual SP mainly increases σsrs value.

Fatigue Crack Growth in Peened Friction Stir Welds

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Hatamleh, Omar

2008-01-01

Friction stir welding induces residual stresses that accelerates fatigue crack growth in the weld nugget. Shot peening over the weld had little effect on growth rate. Laser peening over the weld retarded the growth rate: Final crack growth rate was comparable to the base, un-welded material. Crack tunneling evident from residual compressive stresses. 2195-T8 fracture surfaces were highly textured. Texturing makes comparisons difficult as the material system is affecting the data as much as the processing. Material usage becoming more common in space applications requiring additional work to develop useful datasets for damage tolerance analyses.

Recovery interventions and strategies for improved tennis performance

PubMed Central

Kovacs, Mark S; Baker, Lindsay B

2014-01-01

Improving the recovery capabilities of the tennis athlete is receiving more emphasis in the research communities, and also by practitioners (coaches, physical trainers, tennis performance specialists, physical therapists, etc). The purpose of this article was to review areas of recovery to limit the severity of fatigue and/or speed recovery from fatigue. This review will cover four broad recovery techniques commonly used in tennis with the belief that the interventions may improve athlete recovery and therefore improve adaptation and future performance. The four areas covered are: (1) temperature-based interventions, (2) compressive clothing, (3) electronic interventions and (4) nutritional interventions. PMID:24668374

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skochko, G.W.; Herrmann, T.P.

Axial load cycling fatigue tests of threaded fasteners are useful in determining fastener fatigue failure or design properties. By using appropriate design factors between the failure and design fatigue strengths, such tests are used to establish fatigue failure and design parameters of fasteners for axial and bending cyclic load conditions. This paper reviews the factors which influence the fatigue strength of low Alloy steel threaded fasteners, identifies those most significant to fatigue strength, and provides design guidelines based on the direct evaluation of fatigue tests of threaded fasteners. Influences on fatigue strength of thread manufacturing process (machining and rolling ofmore » threads), effect of fastener membrane and bending stresses, thread root radii, fastener sizes, fastener tensile strength, stress relaxation, mean stress, and test temperature are discussed.« less

Assessing fatigue in inflammatory bowel disease: comparison of three fatigue scales.

PubMed

Norton, C; Czuber-Dochan, W; Bassett, P; Berliner, S; Bredin, F; Darvell, M; Forbes, A; Gay, M; Ream, E; Terry, H

2015-07-01

Fatigue is commonly reported by patients with inflammatory bowel disease (IBD), both in quiescent and active disease. Few fatigue scales have been tested in IBD. To assess three fatigue assessment scales in IBD and to determine correlates of fatigue. Potential participants (n = 2131) were randomly selected from an IBD organisation's members' database; 605 volunteered and were posted three fatigue scales: Inflammatory Bowel Disease Fatigue scale, Multidimensional Fatigue Inventory and Multidimensional Assessment Fatigue scale and questionnaires assessing anxiety, depression, quality of life (QoL) and IBD activity. The questionnaires were tested for stability over time with another group (n = 70) of invited participants. Internal consistency was measured by Cronbach's alpha and test-retest reliability by the intraclass correlation coefficient (ICC). Four hundred and sixty-five of 605 (77%) questionnaires were returned; of 70 invited, 48/70 returned test (68.6%) and 41/70 (58.6%) returned retest. The three scales are highly correlated (P < 0.001). Test-retest suggests reasonable agreement with ICC values between 0.65 and 0.84. Lower age, female gender, IBD diagnosis, anxiety, depression and QoL were associated with fatigue (P < 0.001) on univariable analysis. However, on multivariable analysis only depression and low QoL were consistently associated with fatigue, while female gender was associated on most scales. IBD diagnosis, age and other factors were not consistently associated with severity or impact of fatigue once other variables were controlled for. All three fatigue scales are likely to measure IBD fatigue adequately. Responsiveness to change has not been tested. Depression, poorer QoL and probably female gender are the major associations of fatigue in IBD. © 2015 John Wiley & Sons Ltd.

Fatigue Behavior Degradation due to the Interlaminar Conditions in Lightweight Piezoelectric Composite Actuator (lipca)

NASA Astrophysics Data System (ADS)

Kim, Cheol-Woong; Yoon, Kwang-Joon

The advanced piezoelectric ceramic composite actuator, which is called LIPCA (LIghtweight Piezoelectric Composite Actuator), replaced the Al foil and stainless steel in THUNDER with the FRP and the optimization of the laminate configuration was performed to maximize the stress transfer and the fiber bridging effect. This study evaluated the fatigue characteristics in LIPCA under the resonance frequency, and the changes of its interlaminar phase were also evaluated. Beside, the residual stress distribution was estimated. In conclusions, firstly, comparing with the fatigue life of LIPCA without the artificial delamination (intact LIPCA), the fatigue life of LIPCA embedded by the artificial delamination was decreased up to 50%. Secondly, the micro void growth and the coalescence of epoxy were actively made at the interlaminar phase subject to the large tensile stress. Finally, it was known that the harmonic configuration between the compressive residuals stress and the tensile one was made. The requirement of the performance displacement increment was satisfied.

Microstructural variation through weld thickness and mechanical properties of peened friction stir welded 6061 aluminum alloy joints

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdulstaar, Mustafa A., E-mail: mustafa.abdulstaar

The current study examined the effect of microstructure variation on the development of mechanical properties in friction stir welded joints of 6061-T6 aluminum alloy, which were subsequently processed by shot peening (SP). Following to FSW, fatigue specimens were extracted perpendicularly to the welding direction. Surface Skimming to 0.5 mm from crown and root sides of the joint was made and SP was later applied on the two sides using ceramic shots of two different Almen intensities of 0.18 mmA and 0.24 mmA. Microstructural examination by electron back scattered diffraction (EBSD) indicated variation in the grain refinement of the weld zone,more » with coarsest grains (5 μm) at the crown side and finest grains (2 μm) at the root side. Reduction of microhardness to 60 HV occurred in the weld zone for samples in FSW condition. Application of SP promoted significant strain hardening at the crown side, with Almen intensities of 0.24 mmA providing maximum increase in microhardness to 120 HV. On the contrary, only a maximum microhardness of 75 HV was obtained at the root side. The difference in strain hardening capability at the two sides was strongly dependent on grain size. The two Almen intensities produced similar distribution of compressive residual stresses in the subsurface regions that led to enhance the fatigue strength to the level of base metal for N ≥ 10{sup 5} cycles. Yet, the increase in fatigue strength was more pronounced with increasing Almen intensity to 0.24 mmA, demonstrating further enhancement by strain hardening. - Highlights: • Grain refinement was observed after friction stir welding of AA 6061-T6. • Reduction in microhardness and fatigue strength were obtained after welding. • Variation in grain refinement led to different hardening behavior after peening. • Shot peening induced beneficial compressive residual stresses. • Shot peening and surface skimming markedly improved the fatigue performance.« less

Biomechanical stability according to different configurations of screws and rods.

PubMed

Ha, Kee-Yong; Hwang, Sung-Chul; Whang, Tae-Hyuk

2013-05-01

Comparison of biomechanical strength according to 2 different configurations of screws and rods. To compare the biomechanical strength of different configurations of screws and rods composed of the same material and of the same size. Many complications related to instrumentation have been reported. The incidence of metallic failure would differ according to the materials and configurations of the assembly of the screws and rods used. However, to our knowledge, the biomechanical effects of implant assembly rods and screws with different configurations and different contours have not been reported. Biomechanical testing was conducted to compare top tightening (TT) screw-rod configuration with side tightening (ST) screw-rod configuration. All tests were conducted using a hydraulic all-purpose testing machine. All data were acquired at a rate of 10 Hz. Both screw systems used spinal rods of 6 mm diameter and were made of TiAl4V ELI material. Among 5 types of tests, 3 were conducted on the basis of American Society for Testing and Materials (ASTM) F 1798 to 97 and F1717-10. The other 2 tests were conducted for comparing the characteristics between TT and ST pedicle screws according to modified methods from ASTM F 1717-10 and ASTM F 1798-97. All results including axial gripping capacity and yield forces were obtained using the same methods on the basis of the mentioned ASTM standards. In the axial gripping capacity test, the mean axial gripping capacity of the TT screw-rod configuration was 3332 ± 118 N and that of ST was 2222 ± 147 N in straight rods (P = 0.019). In 15-degree contoured rods, TT was 2988 ± 199 N and ST was 2116 ± 423 N (P = 0.014). In 30-degree contoured rods, TT was 2227 ± 408 N and ST was 1814 ± 285 N (P = 0.009). In the pulling-out test, the pulling-out force of ST was 8695 ± 1616 N and that of TT was 6106 ± 195 N (P = 0.014). In the rod-pushing test, the failure force of ST was 4131 ± 205 N and that of TT was 5639 ± 105 N. In the compressive fatigue test, the maximum load was 145 N in ST and 119 N in TT. In the cycle fatigue test, the fatigue strength of ST was higher than that of TT. In the rod-pushing test, the failure force of ST was 4131 ± 205 N and that of TT was 5639 ± 105 N (P=0.046). Two different configurations of rod-screw systems found statistically significant differences with axial gripping, pulling out, and fatigue failures. ST constructs improved fixation stability over TT constructs. It was concluded that ST configuration may reduce complications related to implantation.

Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weakermore » regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.« less

Effect of Different Levels of Localized Muscle Fatigue on Knee Position Sense

PubMed Central

Gear, William S.

2011-01-01

There is little information available regarding how proprioceptive abilities decline as the amount of exertion increases during exercise. The purpose of this study was to determine the role of different levels of fatigue on knee joint position sense. A repeated measures design was used to examine changes in active joint reposition sense (AJRS) prior to and following three levels of fatigue. Eighteen participants performed knee extension and flexion isokinetic exercise until torque output was 90%, 70%, or 50% of the peak hamstring torque for three consecutive repetitions. Active joint reposition sense at 15, 30, or 45 degrees was tested following the isokinetic exercise session. Following testing of the first independent measure, participants were given a 20 minute rest period. Testing procedures were repeated for two more exercise sessions following the other levels of fatigue. Testing of each AJRS test angle was conducted on three separate days with 48 hours between test days. Significant main effect for fatigue was indicated (p = 0.001). Pairwise comparisons indicated a significant difference between the pre-test and following 90% of peak hamstring torque (p = 0.02) and between the pre-test and following 50% of peak hamstring torque (p = 0.02). Fatigue has long been theorized to be a contributing factor in decreased proprioceptive acuity, and therefore a contributing factor to joint injury. The findings of the present study indicate that fatigue may have an effect on proprioception following mild and maximum fatigue. Key points A repeated measures design was used to examine the effect of different levels of fatigue on active joint reposition sense (AJRS) of the knee at joint angles of 15°, 30° and 45° of flexion. A statistically significant main effect for fatigue was found, specifically between no fatigue and mild fatigue and no fatigue and maximum fatigue. A statistically significant interaction effect between AJRS and fatigue was not found. Secondary analysis of the results indicated a potential plateau effect of AJRS as fatigue continues to increase. Further investigation of the effect of increasing levels of fatigue on proprioception is warranted. PMID:24149565

Effect of different levels of localized muscle fatigue on knee position sense.

PubMed

Gear, William S

2011-01-01

There is little information available regarding how proprioceptive abilities decline as the amount of exertion increases during exercise. The purpose of this study was to determine the role of different levels of fatigue on knee joint position sense. A repeated measures design was used to examine changes in active joint reposition sense (AJRS) prior to and following three levels of fatigue. Eighteen participants performed knee extension and flexion isokinetic exercise until torque output was 90%, 70%, or 50% of the peak hamstring torque for three consecutive repetitions. Active joint reposition sense at 15, 30, or 45 degrees was tested following the isokinetic exercise session. Following testing of the first independent measure, participants were given a 20 minute rest period. Testing procedures were repeated for two more exercise sessions following the other levels of fatigue. Testing of each AJRS test angle was conducted on three separate days with 48 hours between test days. Significant main effect for fatigue was indicated (p = 0.001). Pairwise comparisons indicated a significant difference between the pre-test and following 90% of peak hamstring torque (p = 0.02) and between the pre-test and following 50% of peak hamstring torque (p = 0.02). Fatigue has long been theorized to be a contributing factor in decreased proprioceptive acuity, and therefore a contributing factor to joint injury. The findings of the present study indicate that fatigue may have an effect on proprioception following mild and maximum fatigue. Key pointsA repeated measures design was used to examine the effect of different levels of fatigue on active joint reposition sense (AJRS) of the knee at joint angles of 15°, 30° and 45° of flexion.A statistically significant main effect for fatigue was found, specifically between no fatigue and mild fatigue and no fatigue and maximum fatigue.A statistically significant interaction effect between AJRS and fatigue was not found.Secondary analysis of the results indicated a potential plateau effect of AJRS as fatigue continues to increase.Further investigation of the effect of increasing levels of fatigue on proprioception is warranted.

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading

PubMed Central

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-01-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress–strain responses for each cycle, and the hysteresis stress–strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given. PMID:26937465

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading.

PubMed

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-03-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress-strain responses for each cycle, and the hysteresis stress-strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given.

Recovery in soccer : part ii-recovery strategies.

PubMed

Nédélec, Mathieu; McCall, Alan; Carling, Chris; Legall, Franck; Berthoin, Serge; Dupont, Gregory

2013-01-01

In the formerly published part I of this two-part review, we examined fatigue after soccer matchplay and recovery kinetics of physical performance, and cognitive, subjective and biological markers. To reduce the magnitude of fatigue and to accelerate the time to fully recover after completion, several recovery strategies are now used in professional soccer teams. During congested fixture schedules, recovery strategies are highly required to alleviate post-match fatigue, and then to regain performance faster and reduce the risk of injury. Fatigue following competition is multifactorial and mainly related to dehydration, glycogen depletion, muscle damage and mental fatigue. Recovery strategies should consequently be targeted against the major causes of fatigue. Strategies reviewed in part II of this article were nutritional intake, cold water immersion, sleeping, active recovery, stretching, compression garments, massage and electrical stimulation. Some strategies such as hydration, diet and sleep are effective in their ability to counteract the fatigue mechanisms. Providing milk drinks to players at the end of competition and a meal containing high-glycaemic index carbohydrate and protein within the hour following the match are effective in replenishing substrate stores and optimizing muscle-damage repair. Sleep is an essential part of recovery management. Sleep disturbance after a match is common and can negatively impact on the recovery process. Cold water immersion is effective during acute periods of match congestion in order to regain performance levels faster and repress the acute inflammatory process. Scientific evidence for other strategies reviewed in their ability to accelerate the return to the initial level of performance is still lacking. These include active recovery, stretching, compression garments, massage and electrical stimulation. While this does not mean that these strategies do not aid the recovery process, the protocols implemented up until now do not significantly accelerate the return to initial levels of performance in comparison with a control condition. In conclusion, scientific evidence to support the use of strategies commonly used during recovery is lacking. Additional research is required in this area in order to help practitioners establish an efficient recovery protocol immediately after matchplay, but also for the following days. Future studies could focus on the chronic effects of recovery strategies, on combinations of recovery protocols and on the effects of recovery strategies inducing an anti-inflammatory or a pro-inflammatory response.

Predicting Fatigue Lives Of Metal-Matrix/Fiber Composites

NASA Technical Reports Server (NTRS)

Bartolotta, Paul A.

1994-01-01

Method of prediction of fatigue lives of intermetallic-matrix/fiber composite parts at high temperatures styled after method of universal slopes. It suffices to perform relatively small numbers of fatigue tests. Data from fatigue tests correlated with tensile-test data by fitting universal-slopes equation to both sets of data. Thereafter, universal-slopes equation used to predict fatigue lives from tensile properties.

Experimental and modeling results of creep fatigue life of Inconel 617 and Haynes 230 at 850 C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiang; Sokolov, Mikhail A; Sham, Sam

Creep fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure formore » both materials decreased under creep fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep fatigue life. The linear damage summation could predict the creep fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep fatigue life prediction results for both materials.« less

Evaluation of fatigue life of CRM-reinforced SMA and its relationship to dynamic stiffness.

PubMed

Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati; Koting, Suhana

2014-01-01

Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture.

Experimental and modeling results of creep-fatigue life of Inconel 617 and Haynes 230 at 850 °C

NASA Astrophysics Data System (ADS)

Chen, Xiang; Sokolov, Mikhail A.; Sham, Sam; Erdman, Donald L., III; Busby, Jeremy T.; Mo, Kun; Stubbins, James F.

2013-01-01

Creep-fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 °C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep-fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep-fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure for both materials decreased under creep-fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep-fatigue life. The linear damage summation could predict the creep-fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep-fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep-fatigue life prediction results for both materials.

A coupled creep plasticity model for residual stress relaxation of a shot-peened nickel-based superalloy

NASA Astrophysics Data System (ADS)

Buchanan, Dennis J.; John, Reji; Brockman, Robert A.; Rosenberger, Andrew H.

2010-01-01

Shot peening is a commonly used surface treatment process that imparts compressive residual stresses into the surface of metal components. Compressive residual stresses retard initiation and growth of fatigue cracks. During component loading history, shot-peened residual stresses may change due to thermal exposure, creep, and cyclic loading. In these instances, taking full credit for compressive residual stresses would result in a nonconservative life prediction. This article describes a methodical approach for characterizing and modeling residual stress relaxation under elevated temperature loading, near and above the monotonic yield strength of INI 00. The model incorporates the dominant creep deformation mechanism, coupling between the creep and plasticity models, and effects of prior plastic strain to simulate surface treatment deformation.

Fatigue crack identification method based on strain amplitude changing

NASA Astrophysics Data System (ADS)

Guo, Tiancai; Gao, Jun; Wang, Yonghong; Xu, Youliang

2017-09-01

Aiming at the difficulties in identifying the location and time of crack initiation in the castings of helicopter transmission system during fatigue tests, by introducing the classification diagnostic criteria of similar failure mode to find out the similarity of fatigue crack initiation among castings, an engineering method and quantitative criterion for detecting fatigue cracks based on strain amplitude changing is proposed. This method is applied on the fatigue test of a gearbox housing, whose results indicates: during the fatigue test, the system alarms when SC strain meter reaches the quantitative criterion. The afterwards check shows that a fatigue crack less than 5mm is found at the corresponding location of SC strain meter. The test result proves that the method can provide accurate test data for strength life analysis.

Health and efficiency in trimix versus air breathing in compressed air workers.

PubMed

Van Rees Vellinga, T P; Verhoeven, A C; Van Dijk, F J H; Sterk, W

2006-01-01

The Western Scheldt Tunneling Project in the Netherlands provided a unique opportunity to evaluate the effects of trimix usage on the health of compressed air workers and the efficiency of the project. Data analysis addressed 318 exposures to compressed air at 3.9-4.4 bar gauge and 52 exposures to trimix (25% oxygen, 25% helium, and 50% nitrogen) at 4.6-4.8 bar gauge. Results revealed three incidents of decompression sickness all of which involved the use of compressed air. During exposure to compressed air, the effects of nitrogen narcosis were manifested in operational errors and increased fatigue among the workers. When using trimix, less effort was required for breathing, and mandatory decompression times for stays of a specific duration and maximum depth were considerably shorter. We conclude that it might be rational--for both medical and operational reasons--to use breathing gases with lower nitrogen fractions (e.g., trimix) for deep-caisson work at pressures exceeding 3 bar gauge, although definitive studies are needed.

Non-destructive measurement and role of surface residual stress monitoring in residual life assessment of a steam turbine blading material

NASA Astrophysics Data System (ADS)

Prabhu-Gaunkar, Gajanana; Rawat, M. S.; Prasad, C. R.

2014-02-01

Steam turbine blades in power generation equipment are made from martensitic stainless steels having high strength, good toughness and corrosion resistance. However, these steels are susceptible to pitting which can promote early failures of blades in the turbines, particularly in the low pressure dry/wet areas by stress corrosion and corrosion fatigue. Presence of tensile residual stresses is known to accelerate failures whereas compressive stresses can help in delaying failures. Shot peening has been employed as an effective tool to induce compressive residual stresses which offset a part of local surface tensile stresses in the surface layers of components. Maintaining local stresses at stress raisers, such as pits formed during service, below a threshold level can help in preventing the initiation microcracks and failures. The thickness of the layer in compression will, however, depend of the shot peening parameters and should extend below the bottom of corrosion pits. The magnitude of surface compressive drops progressively during service exposure and over time the effectiveness of shot peening is lost making the material susceptible to micro-crack initiation once again. Measurement and monitoring of surface residual stress therefore becomes important for assessing residual life of components in service. This paper shows the applicability of surface stress monitoring to life assessment of steam turbine blade material based on data generated in laboratory on residual surface stress measurements in relation to fatigue exposure. An empirical model is proposed to calculate the remaining life of shot peened steam turbine blades in service.

The Biomechanical Properties of Pedicle Screw Fixation Combined With Trajectory Bone Cement Augmentation in Osteoporotic Vertebrae.

PubMed

Fan, Haitao T; Zhang, Renjie J; Shen, Cailiang L; Dong, Fulong L; Li, Yong; Song, Peiwen W; Gong, Chen; Wang, Yijin J

2016-03-01

The biomechanics of pedicle screw fixation combined with trajectory cement augmentation with various filling volumes were measured by pull-out, periodic antibending, and compression fatigue tests. To investigate the biomechanical properties of the pedicle screw fixation combined with trajectory bone cement (polymethylmethacrylate) augmentation in osteoporotic vertebrae and to explore the optimum filling volume of the bone cement. Pedicle screw fixation is considered to be the most effective posterior fixation method. The decrease of the bone mineral density apparently increases the fixation failure risk caused by screw loosening and displacement. Trajectory bone cement augmentation has been confirmed to be an effective method to increase the bone intensity and could markedly increase the stability of the fixation interface. Sixteen elderly cadaveric 1-5 lumbar vertebral specimens were diagnosed with osteoporosis. The left and right vertebral pedicles were alternatively randomized for treatment in all groups, with the contralateral pedicles as control. The study groups included: group A (pedicle screw fixation with full trajectory bone cement augmentation), group B (75% filling), group C (50% filling), and group D (25% filling). Finally, the bone cement leakage and dispersion were assessed and the mechanical testing was conducted. The bone cement was well dispersed around the pedicle screw. The augmented bone intensity, pull-out strength, periodic loading times, and compression fatigue performance were markedly higher than those of the control groups. With the increase in trajectory bone cement, the leakage was also increased (P<0.05). The pull-out strength of the pedicle screw was increased with an increase in bone mineral density and trajectory bone cement. It peaked at 75% filling, with the largest power consumption. The optimal filling volume of the bone cement was 75% of the trajectory volume (about 1.03 mL). The use of excessive bone cement did not increase the fixation intensity but increased the risk of leakage.

Is There Evidence that Runners can Benefit from Wearing Compression Clothing?

PubMed

Engel, Florian Azad; Holmberg, Hans-Christer; Sperlich, Billy

2016-12-01

Runners at various levels of performance and specializing in different events (from 800 m to marathons) wear compression socks, sleeves, shorts, and/or tights in attempt to improve their performance and facilitate recovery. Recently, a number of publications reporting contradictory results with regard to the influence of compression garments in this context have appeared. To assess original research on the effects of compression clothing (socks, calf sleeves, shorts, and tights) on running performance and recovery. A computerized research of the electronic databases PubMed, MEDLINE, SPORTDiscus, and Web of Science was performed in September of 2015, and the relevant articles published in peer-reviewed journals were thus identified rated using the Physiotherapy Evidence Database (PEDro) Scale. Studies examining effects on physiological, psychological, and/or biomechanical parameters during or after running were included, and means and measures of variability for the outcome employed to calculate Hedges'g effect size and associated 95 % confidence intervals for comparison of experimental (compression) and control (non-compression) trials. Compression garments exerted no statistically significant mean effects on running performance (times for a (half) marathon, 15-km trail running, 5- and 10-km runs, and 400-m sprint), maximal and submaximal oxygen uptake, blood lactate concentrations, blood gas kinetics, cardiac parameters (including heart rate, cardiac output, cardiac index, and stroke volume), body and perceived temperature, or the performance of strength-related tasks after running. Small positive effect sizes were calculated for the time to exhaustion (in incremental or step tests), running economy (including biomechanical variables), clearance of blood lactate, perceived exertion, maximal voluntary isometric contraction and peak leg muscle power immediately after running, and markers of muscle damage and inflammation. The body core temperature was moderately affected by compression, while the effect size values for post-exercise leg soreness and the delay in onset of muscle fatigue indicated large positive effects. Our present findings suggest that by wearing compression clothing, runners may improve variables related to endurance performance (i.e., time to exhaustion) slightly, due to improvements in running economy, biomechanical variables, perception, and muscle temperature. They should also benefit from reduced muscle pain, damage, and inflammation.

Space Shuttle Crawler Transporter Truck Shoe Qualification Tests and Analyses for Return-to-Flight

NASA Technical Reports Server (NTRS)

Margasahayam, Ravi N.; Meyer, Karl A.; Burton, Roy C.; Gosselin, Armand M.

2005-01-01

A vital element to Launch Complex 39 (LC39) and NASA's Kennedy Space Center (KSC) mobile launch transfer operation is a 3 million kilogram behemoth known as the Crawler Transporter (CT). Built in the 1960's, two CT's have accumulated over 1700+ miles each and have been used for the Apollo and the Space Shuttle programs. Recent observation of fatigue cracks on the CT shoes led to a comprehensive engineering, structural and metallurgical evaluation to assess the root cause that necessitated procurement of over 1000 new shoes. This paper documents the completed dynamic and compression tests on the old and new shoes respectively, so as to certify them for Space Shuttle's return-to-flight (RTF). Measured strain data from the rollout tests was used to develop stress/loading spectra and static equivalent load for qualification testing of the new shoes. Additionally, finite element analysis (FEA) was used to conduct sensitivity analyses of various contact parameters and structural characteristics for acceptance of new shoes.

Influence of fatiguing noise on auditory evoked responses to stimuli of various levels in a beluga whale, Delphinapterus leucas.

PubMed

Popov, Vladimir V; Sysueva, Evgeniya V; Nechaev, Dmitry I; Rozhnov, Viatcheslav V; Supin, Alexander Ya

2017-03-15

The negative impact of man-made noise on the hearing of odontocetes has attracted considerable recent attention. In the majority of studies, permanent or temporary reductions in sensitivity, known as permanent or temporary threshold shift (PTS or TTS, respectively), have been investigated. In the present study, the effects of a fatiguing sound on the hearing of a beluga whale, Delphinapterus leucas , within a wide range of levels of test signals was investigated. The fatiguing noise was half-octave band-limited noise centered at 32 kHz. Post-exposure effects of this noise on the evoked responses to test stimuli (rhythmic pip trains with a 45-kHz center frequency) at various levels (from threshold to 60 dB above threshold) were measured. For baseline (pre-exposure) responses, the magnitude-versus-level function featured a segment of steep magnitude dependence on level (up to 30 dB above threshold) that was followed by a plateau segment that featured little dependence on level (30 to 55 dB above threshold). Post-exposure, the function shifted upward along the level scale. The shift was 23 dB at the threshold and up to 33 dB at the supra-threshold level. Owing to the plateau in the magnitude-versus-level function, post-exposure suppression of responses depended on the stimulus level such that higher levels corresponded to less suppression. The experimental data may be modeled based on the compressive non-linearity of the cochlea. According to the model, post-exposure responses of the cochlea to high-level stimuli are minimally suppressed compared with the pre-exposure responses, despite a substantially increased threshold. © 2017. Published by The Company of Biologists Ltd.

Effects of Acute Fatigue of the Hip Flexor Muscles on Hamstring Muscle Extensibility.

PubMed

Muyor, José M; Arrabal-Campos, Francisco M

2016-12-01

The purpose of the present study was to evaluate the influence of acute fatigue of the hip flexor muscles on scores attained in tests frequently used in literature to measure hamstring muscle extensibility, namely the passive straight leg raise (PSLR), active straight leg raise (ASLR), passive knee extension (PKE), active knee extension (AKE), sit-and-reach (SR) and toe-touch (TT) tests. A total of seventy-five healthy and recreationally active adults voluntarily participated in this study. To reach fatigue, the participants actively lifted their legs alternately as many times as possible. In the passive tests, the results were 7.10 ± 5.21° and 5.68 ± 4.54° higher (p < 0.01) for PSLR and PKE tests, respectively, after acute fatigue. However, in the ASLR test, the results were lower post-fatigue than pre-fatigue (mean difference = -5.30° ± 9.51°; p < 0.01). The AKE, SR and TT tests did not show significant differences between pre- and post-fatigue (p > 0.05). Moderate (r = 0.40) to high (r = 0.97) correlation coefficients were found, which were statistically significant among all the measured flexibility tests both pre- and post-fatigue. In conclusion, the active implication of the hip flexor muscles until reaching fatigue had acute influences on the results of the PSLR, PKE and ASLR tests, but not on the results of the AKE, SR and TT tests. It is recommended to use the AKE test to assess hamstring muscle extensibility in situations where athletes show fatigue in their hip flexor muscles.

Strain energy release rate as a function of temperature and preloading history utilizing the edge delamination fatique test method

NASA Technical Reports Server (NTRS)

Zimmerman, Richard S.; Adams, Donald F.

1989-01-01

Static laminate and tension-tension fatigue tests of IM7/8551-7 composite materials was performed. The Edge Delamination Test (EDT) was utilized to evaluate the temperature and preloading history effect on the critical strain energy release rate. Static and fatigue testing was performed at room temperature and 180 F (82 C). Three preloading schemes were used to precondition fatigue test specimens prior to performing the normal tension-tension fatigue EDT testing. Computer software was written to perform all fatigue testing while monitoring the dynamic modulus to detect the onset of delamination and record the test information for later retrieval and reduction.

Is the Sørensen test valid to assess muscle fatigue of the trunk extensor muscles?

PubMed

Demoulin, Christophe; Boyer, Mathieu; Duchateau, Jacques; Grosdent, Stéphanie; Jidovtseff, Boris; Crielaard, Jean-Michel; Vanderthommen, Marc

2016-01-01

Very few studies have quantified the degree of fatigue characterized by the decline in the maximal voluntary contraction (MVC) force of the trunk extensors induced by the widely used Sørensen test. Measure the degree of fatigue of the trunk extensor muscles induced by the Sørensen test. Eighty young healthy subjects were randomly divided into a control group (CG) and an experimental group (EG), each including 50% of the two genders. The EG performed an isometric MVC of the trunk extensors (pre-fatigue test) followed by the Sørensen test, the latter being immediately followed by another MVC (post-fatigue test). The CG performed only the pre- and post-fatigue tests without any exertion in between. The comparison of the pre- and post-fatigue tests revealed a significant (P< 0.05) decrease in MVC force normalized by body mass (-13%) in the EG, whereas a small increase occurred in the CG (+2.7%, P= 0.001). This study shows that the Sørensen test performed until failure in a young healthy population results in a reduced ability of the trunk extensor muscles to generate maximal force, and indicates that this test is valid for the assessment of fatigue in trunk extensor muscles.

Full title: Biomechanical comparison between stainless steel, titanium and carbon-fiber reinforced polyetheretherketone volar locking plates for distal radius fractures.

PubMed

Mugnai, Raffaele; Tarallo, Luigi; Capra, Francesco; Catani, Fabio

2018-05-25

As the popularity of volar locked plate fixation for distal radius fractures has increased, so have the number and variety of implants, including variations in plate design, the size and angle of the screws, the locking screw mechanism, and the material of the plates. carbon-fiber reinforced polyetheretherketone (CFR-PEEK) plate features similar biomechanical properties to metallic plates, representing, therefore, an optimal alternative for the treatment of distal radius fractures. three different materials-composed plates were evaluated: stainless steel volar lateral column (Zimmer); titanium DVR (Hand Innovations); CFR-PEEK DiPHOS-RM (Lima Corporate). Six plates for each type were implanted in sawbones and an extra-articular rectangular osteotomy was created. Three plates for each material were tested for load to failure and bending stiffness in axial compression. Moreover, 3 constructs for each plate were evaluated after dynamically loading for 6000 cycles of fatigue. the mean bending stiffness pre-fatigue was significantly higher for the stainless steel plate. The titanium plate yielded the higher load to failure both pre and post fatigue. After cyclic loading, the bending stiffness increased by a mean of 24% for the stainless steel plate; 33% for the titanium; and 17% for the CFR-PEEK plate. The mean load to failure post-fatigue increased by a mean of 10% for the stainless steel and 14% for CFR-PEEK plates, whereas it decreased (-16%) for the titanium plate. Statistical analysis between groups reported significant values (p <.001) for all comparisons except for Hand Innovations vs. Zimmer bending stiffness post fatigue (p = .197). the significant higher load to failure of the titanium plate, makes it indicated for patients with higher functional requirements or at higher risk of trauma in the post-operative period. The CFR-PEEK plate showed material-specific disadvantages, represented by little tolerance to plastic deformation, and lower load to failure. N/A. Copyright © 2018. Published by Elsevier Masson SAS.

Weibull models of fracture strengths and fatigue behavior of dental resins in flexure and shear.

PubMed

Baran, G R; McCool, J I; Paul, D; Boberick, K; Wunder, S

1998-01-01

In estimating lifetimes of dental restorative materials, it is useful to have available data on the fatigue behavior of these materials. Current efforts at estimation include several untested assumptions related to the equivalence of flaw distributions sampled by shear, tensile, and compressive stresses. Environmental influences on material properties are not accounted for, and it is unclear if fatigue limits exist. In this study, the shear and flexural strengths of three resins used as matrices in dental restorative composite materials were characterized by Weibull parameters. It was found that shear strengths were lower than flexural strengths, liquid sorption had a profound effect on characteristic strengths, and the Weibull shape parameter obtained from shear data differed for some materials from that obtained in flexure. In shear and flexural fatigue, a power law relationship applied for up to 250,000 cycles; no fatigue limits were found, and the data thus imply only one flaw population is responsible for failure. Again, liquid sorption adversely affected strength levels in most materials (decreasing shear strengths and flexural strengths by factors of 2-3) and to a greater extent than did the degree of cure or material chemistry.

Evaluation of Fatigue Life of CRM-Reinforced SMA and Its Relationship to Dynamic Stiffness

PubMed Central

Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati

2014-01-01

Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406

Thermal-mechanical fatigue of high temperature structural materials

NASA Astrophysics Data System (ADS)

Renauld, Mark Leo

Experimental and analytical methods were developed to address the effect of thermal-mechanical strain cycling on high temperature structural materials under uniaxial and biaxial stress states. Two materials were used in the investigation, a nickel-base superalloy of low ductility, IN-738LC and a high ductility material, 316 stainless steel. A uniaxial life prediction model for the IN-738LC material was based on tensile hysteresis energy measured in stabilized, mid-life hysteresis loops. Hold-time effects and temperature cycling were incorporated in the hysteresis energy approach. Crack growth analysis was also included in the model to predict the number of TMF cycles to initiate and grow a fatigue crack through the coating. The nickel-base superalloy, IN-738LC, was primarily tested in out-of-phase (OP) TMF with a temperature range from 482-871sp°C (900-1600sp°F) under continuous and compressive hold-time cycling. IN-738LC fatigue specimens were coated either with an aluminide, NiCoCrAlHfSi overlay or CoNiCrAlY overlay coating on the outer surface of the specimen. Metallurgical failure analysis via optical and scanning electron microscopy, was used to characterize failure behavior of both substrate and coating materials. Type 316 SS was subjected to continuous biaxial strain cycling with an in-phase (IP) TMF loading and a temperature range from 399-621sp°C (750-1150sp°F). As a result, a biaxial TMF life prediction model was proposed on the basis of an extended isothermal fatigue model. The model incorporates a frequency effect and phase factors to assess the different damage mechanisms observed during TMF loading. The model was also applied to biaxial TMF data generated on uncoated IN-738LC.

Fatigue Strength and Related Characteristics of Aircraft Joints I : Comparison of Spot-Weld and Rivet Patterns in 24s-t Alclad and 75s-t Alclad

NASA Technical Reports Server (NTRS)

Russell, H W; Jackson, L R; Grover, H J; Beaver, W W

1944-01-01

Report contains detailed results of a number of fatigue tests on spot-welded joints in aluminum alloys. The tests described include: (1) fatigue tests on spot-welded lap joints in sheets of unequal thickness of alclad 24s-t. These tests indicate that the fatigue strength of a spot-welded joint in sheets of two different gages is slightly higher than that of a similar joint in two sheets of the thinner gage but definitely lower than that of a similar joint in two sheets of the thicker gage. (2) Fatigue tests on spot-welded alclad 75s-t spot-welded lap-joint specimens of alclad 75s-t were not any stronger in fatigue than similar specimens of alclad 24s-t. (3) Fatigue tests on lap-joint specimens spot -welded after various surface preparations--these included ac welding wire-brushed surfaces, dc welding wire-brushed surfaces, and dc welding chemically cleaned surfaces. While the ac welds were strongest statically, the dc welds on wire-brushed surfaces were strongest in fatigue. Specimens prepared in this way were very nearly as strong as the best riveted specimens tested for comparison. (4) Fatigue tests on specimens spot-welded with varying voltage so as to include a wide range of static spot-weld strengths. The fatigue strengths were in the same order as the static strengths but showed less range. (author)

Simulation of Fatigue Crack Initiation at Corrosion Pits With EDM Notches

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Newman, John A.; Piascik, Robert S.

2003-01-01

Uniaxial fatigue tests were conducted to compare the fatigue life of laboratory produced corrosion pits, similar to those observed in the shuttle main landing gear wheel bolt-hole, and an electro-discharged-machined (EDM) flaw. EDM Jaws are used to simulate corrosion pits during shuttle wheel (dynamometer) testing. The aluminum alloy, (AA 7050) laboratory fatigue tests were conducted to simulate the local stress level contained in the wheel bolt-hole. Under this high local stress condition, the EDM notch produced a fatigue life similar to test specimens containing corrosion pits of similar size. Based on the laboratory fatigue test results, the EDM Jaw (semi-circular disc shaped) produces a local stress state similar to corrosion pits and can be used to simulate a corrosion pit during the shuttle wheel dynamometer tests.

High temperature, low-cycle fatigue of copper-base alloys for rocket nozzles. Part 2: Strainrange partitioning and low-cycle fatigue results at 538 deg C

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1976-01-01

Low-cycle fatigue tests of 1/2 Hard AMZIRC Copper and NARloy Z were performed in argon at 538 C to determine partitioned strain range versus life relationships. Strain-controlled low-cycle fatigue tests of a Zr-Cr-Mg copper-base alloy were also performed. Strain ranges, lower than those employed in previous tests, were imposed in order to extend the fatigue life curve out to approximately 400,000 cycles. An experimental copper alloy and an experimental silver alloy were also studied. Tensile tests were performed in air at room temperature and in argon at 538 C. Strain-controlled low-cycle fatigue tests were performed at 538 C in argon to define the fatigue life over the regime from 300 to 3,000 cycles. For the silver alloy, three additional heat treatments were introduced, and a limited evaluation of the short-term tensile and low-cycle fatigue behavior at 538 C was performed.

Notched fatigue of single crystal PWA 1480 at turbine attachment temperatures

NASA Technical Reports Server (NTRS)

Meyer, T. G.; Nissley, D. M.; Swanson, G. A.

1989-01-01

The focus is on the lower temperature, uncoated and notched features of gas turbine blades. Constitutive and fatigue life prediction models applicable to these regions are being developed. Fatigue results are presented which were obtained thus far. Fatigue tests are being conducted on PWA 1480 single crystal material using smooth strain controlled specimens and three different notched specimens. Isothermal fatigue tests were conducted at 1200, 1400, and 1600 F. The bulk of the tests were conducted at 1200 F. The strain controlled tests were conducted at 0.4 percent per second strain rate and the notched tests were cycled at 1.0 cycle per second. A clear orientation dependence is observed in the smooth strain controlled fatigue results. The fatigue lifes of the thin, mild notched specimens agree fairly well with this smooth data when elastic stress range is used as a correlating parameter. Finite element analyses were used to calculate notch stresses. Fatigue testing will continue to further explore the trends observed thus far. Constitutive and life prediction models are being developed.

Prediction of Mean and Design Fatigue Lives of Self Compacting Concrete Beams in Flexure

NASA Astrophysics Data System (ADS)

Goel, S.; Singh, S. P.; Singh, P.; Kaushik, S. K.

2012-02-01

In this paper, result of an investigation conducted to study the flexural fatigue characteristics of self compacting concrete (SCC) beams in flexure are presented. An experimental programme was planned in which approximately 60 SCC beam specimens of size 100 × 100 × 500 mm were tested under flexural fatigue loading. Approximately 45 static flexural tests were also conducted to facilitate fatigue testing. The flexural fatigue and static flexural strength tests were conducted on a 100 kN servo-controlled actuator. The fatigue life data thus obtained have been used to establish the probability distributions of fatigue life of SCC using two-parameter Weibull distribution. The parameters of the Weibull distribution have been obtained by different methods of analysis. Using the distribution parameters, the mean and design fatigue lives of SCC have been estimated and compared with Normally vibrated concrete (NVC), the data for which have been taken from literature. It has been observed that SCC exhibits higher mean and design fatigue lives compared to NVC.

Detecting Gear Tooth Fatigue Cracks in Advance of Complete Fracture

NASA Technical Reports Server (NTRS)

Zakrajsek, James J.; Lewicki, David G.

1996-01-01

Results of using vibration-based methods to detect gear tooth fatigue cracks are presented. An experimental test rig was used to fail a number of spur gear specimens through bending fatigue. The gear tooth fatigue crack in each test was initiated through a small notch in the fillet area of a tooth on the gear. The primary purpose of these tests was to verify analytical predictions of fatigue crack propagation direction and rate as a function of gear rim thickness. The vibration signal from a total of three tests was monitored and recorded for gear fault detection research. The damage consisted of complete rim fracture on the two thin rim gears and single tooth fracture on the standard full rim test gear. Vibration-based fault detection methods were applied to the vibration signal both on-line and after the tests were completed. The objectives of this effort were to identify methods capable of detecting the fatigue crack and to determine how far in advance of total failure positive detection was given. Results show that the fault detection methods failed to respond to the fatigue crack prior to complete rim fracture in the thin rim gear tests. In the standard full rim gear test all of the methods responded to the fatigue crack in advance of tooth fracture; however, only three of the methods responded to the fatigue crack in the early stages of crack propagation.

Thermal cycling reliability of Cu/SnAg double-bump flip chip assemblies for 100 μm pitch applications

NASA Astrophysics Data System (ADS)

Son, Ho-Young; Kim, Ilho; Lee, Soon-Bok; Jung, Gi-Jo; Park, Byung-Jin; Paik, Kyung-Wook

2009-01-01

A thick Cu column based double-bump flip chip structure is one of the promising alternatives for fine pitch flip chip applications. In this study, the thermal cycling (T/C) reliability of Cu/SnAg double-bump flip chip assemblies was investigated, and the failure mechanism was analyzed through the correlation of T/C test and the finite element analysis (FEA) results. After 1000 thermal cycles, T/C failures occurred at some Cu/SnAg bumps located at the edge and corner of chips. Scanning acoustic microscope analysis and scanning electron microscope observations indicated that the failure site was the Cu column/Si chip interface. It was identified by a FEA where the maximum stress concentration was located during T/C. During T/C, the Al pad between the Si chip and a Cu column bump was displaced due to thermomechanical stress. Based on the low cycle fatigue model, the accumulation of equivalent plastic strain resulted in thermal fatigue deformation of the Cu column bumps and ultimately reduced the thermal cycling lifetime. The maximum equivalent plastic strains of some bumps at the chip edge increased with an increased number of thermal cycles. However, equivalent plastic strains of the inner bumps did not increase regardless of the number of thermal cycles. In addition, the z-directional normal plastic strain ɛ22 was determined to be compressive and was a dominant component causing the plastic deformation of Cu/SnAg double bumps. As the number of thermal cycles increased, normal plastic strains in the perpendicular direction to the Si chip and shear strains were accumulated on the Cu column bumps at the chip edge at low temperature region. Thus it was found that the Al pad at the Si chip/Cu column interface underwent thermal fatigue deformation by compressive normal strain and the contact loss by displacement failure of the Al pad, the main T/C failure mode of the Cu/SnAg flip chip assembly, then occurred at the Si chip/Cu column interface shear strain deformation during T/C.

Investigating the effects of maximal anaerobic fatigue on dynamic postural control using the Y-Balance Test.

PubMed

Johnston, William; Dolan, Kara; Reid, Niamh; Coughlan, Garrett F; Caulfield, Brian

2018-01-01

The Y Balance Test is one of the most commonly used dynamic balance assessments, providing an insight into the integration of the sensorimotor subsystems. In recent times, there has been an increase in interest surrounding it's use in various clinical populations demonstrating alterations in motor function. Therefore, it is important to examine the effect physiological influences such as fatigue play in dynamic postural control, and establish a timeframe for its recovery. Descriptive laboratory study. Twenty male and female (age 23.75±4.79years, height 174.12±8.45cm, mass 69.32±8.76kg) partaking in competitive sport, completed the Y Balance Test protocol at 0, 10 and 20min, prior to a modified 60s Wingate fatiguing protocol. Post-fatigue assessments were then completed at 0, 10 and 20 min post-fatiguing intervention. Intraclass correlation coefficients demonstrated excellent intra-session reliability (0.976-0.982) across the three pre-fatigue YBT tests. Post-hoc paired sample t-tests demonstrated that all three reach directions demonstrated statistically significant differences between pre-fatigue and the first post-fatigue measurement (anterior; p=0.019, posteromedial; p=0.019 & posterolateral; p=0.003). The anterior reach direction returned to pre-fatigue levels within 10min (p=0.632). The posteromedial reach direction returned to pre-fatigue levels within 20min (p=0.236), while the posterolateral direction maintained a statistically significant difference at 20min (p=0.023). Maximal anaerobic fatigue has a negative effect on normalised Y balance test scores in all three directions. Following the fatiguing protocol, dynamic postural control returns to pre-fatigue levels for the anterior (<10min), posteromedial (<20min) and posterolateral (>20min). Copyright © 2017 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Crack branching in cross-ply composites

NASA Astrophysics Data System (ADS)

La Saponara, Valeria

2001-10-01

The purpose of this research work is to examine the behavior of an interface crack in a cross-ply laminate which is subject to static and fatigue loading. The failure mechanism analyzed here is crack branching (or crack kinking or intra-layer crack): the delamination located between two different plies starts growing as an interface crack and then may branch into the less tough ply. The specimens were manufactured from different types of Glass/Epoxy and Graphite/Epoxy, by hand lay-up, vacuum bagging and cure in autoclave. Each specimen had a delamination starter. Static mixed mode tests and compressive fatigue tests were performed. Experiments showed the scale of the problem, one ply thickness, and some significant features, like contact in the branched crack. The amount of scatter in the experiments required use of statistics. Exploratory Data Analysis and a factorial design of experiments based on a 8 x 8 Hadamard matrix were used. Experiments and statistics show that there is a critical branching angle above which crack growth is greatly accelerated. This angle seems: (1) not to be affected by the specimens' life; (2) not to depend on the specimen geometry and loading conditions; (3) to strongly depend on the amount of contact in the branched crack. Numerical analysis was conducted to predict crack propagation based on the actual displacement/load curves for static tests. This method allows us to predict the total crack propagation in 2D conditions, while neglecting branching. Finally, the existence of a solution based on analytic continuation is discussed.

Comments on the origin of acoustic emission in fatigue testing of aluminum alloys

NASA Astrophysics Data System (ADS)

Heiple, C. R.; Carpenter, S. H.; Armentrout, D. L.

The size of acoustic emission (AE) signals expected from inclusion fracture during fatigue testing of 7075 aluminum has been estimated on the basis of previous measurements of AE produced by the fracture of boron particles incorporated into 2219 aluminum. The AF signal size expected from deformation in the plastic zone ahead of the fatigue crack was estimated from the results of tensile tests on 7075 aluminum. The signals predicted from both processes are near or below the noise level in the fatigue experiments and are therefore far too small to account for the signals actually observed. Nearly simultaneous fracture of multiple inclusions could produce signals as large as those observed in fatigue tests of 7075 aluminum, however, fatigue tests of 7050 aluminum produced signals as large or larger than in 7075. Since 7050 has substantially fewer inclusions than 7075, the simultaneous failure of multiple inclusions is unlikely to be a major AE source in fatigue testing of either aluminum alloy. Thus, the most probable source of acoustic emission during fatigue testing of 7075 and 7050 aluminum is the crack advance itself. The measured crack advance per cycle is large enough to release sufficient elastic energy to account for the AE signals observed.

Supermacroprous chitosan–agarose–gelatin cryogels: in vitro characterization and in vivo assessment for cartilage tissue engineering

PubMed Central

Bhat, Sumrita; Tripathi, Anuj; Kumar, Ashok

2011-01-01

The study focuses on the synthesis of a novel polymeric scaffold having good porosity and mechanical characteristics synthesized by using natural polymers and their optimization for application in cartilage tissue engineering. The scaffolds were synthesized via cryogelation technology using an optimized ratio of the polymer solutions (chitosan, agarose and gelatin) and cross-linker followed by the incubation at sub-zero temperature (−12°C). Microstructure examination of the chitosan–agarose–gelatine (CAG) cryogels was done using scanning electron microscopy (SEM) and fluorescent microscopy. Mechanical analysis, such as the unconfined compression test, demonstrated that cryogels with varying chitosan concentrations, i.e. 0.5–1% have a high compression modulus. In addition, fatigue tests revealed that scaffolds are suitable for bioreactor studies where gels are subjected to continuous cyclic strain. In order to confirm the stability, cryogels were subjected to high frequency (5 Hz) with 30 per cent compression of their original length up to 1 × 105 cycles, gels did not show any significant changes in their mass and dimensions during the experiment. These cryogels have exhibited degradation capacity under aseptic conditions. CAG cryogels showed good cell adhesion of primary goat chondrocytes examined by SEM. Cytotoxicity of the material was checked by MTT assay and results confirmed the biocompatibility of the material. In vivo biocompatibility of the scaffolds was checked by the implantation of the scaffolds in laboratory animals. These results suggest the potential of CAG cryogels as a good three-dimensional scaffold for cartilage tissue engineering. PMID:20943683

Development of a remote-controlled fatigue test machine using a laser extensometer for investigation of irradiation effect on fatigue properties

NASA Astrophysics Data System (ADS)

Yonekawa, M.; Ishii, T.; Ohmi, M.; Takada, F.; Hoshiya, T.; Niimi, M.; Ioka, I.; Miwa, Y.; Tsuji, H.

2002-12-01

In order to investigate effects of neutron irradiation on fatigue properties of nuclear materials, a remote-controlled high temperature fatigue test machine was developed at the hot laboratory of the Japan Materials Testing Reactor (JMTR) in the Japan Atomic Energy Research Institute (JAERI). A small-sized fatigue specimen having double blades to measure strain with a laser extensometer was designed for this machine. A strain amplitude in fatigue tests of a completely reversed push-pull type using a triangular wave was controlled with an accuracy of ±3% of the total strain range during test. Low cycle fatigue tests of type 304 stainless steel irradiated in JMTR at 823 K up to a fast neutron fluence of 1×10 25 n/m 2 ( E>1 MeV) were performed in total strain ranges of 0.7-1.4% at 823 K using the designed small-sized specimens.

75 FR 75882 - Airworthiness Directives; British Aerospace Regional Aircraft Models Jetstream Series 3101 and...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-07

... describes the unsafe condition as: As a result of the fatigue-testing programme on the Jetstream fatigue... result of the fatigue-testing programme on the Jetstream fatigue test specimen, it has been identified....S. registry. We also estimate that it will take about 15 work-hours per product to comply with the...

A literature review and inventory of the effects of environment on the fatigue behavior of metals

NASA Technical Reports Server (NTRS)

Hudson, C. M.; Seward, S. K.

1976-01-01

The current state of knowledge of the effects of gas environments (at atmospheric pressure and below) on the fatigue behavior of metals is reviewed. Among the topics considered are the mechanisms proposed to explain the differences observed in the fatigue behavior of vacuum- and air-tested specimens, the effects of environment on the surface topography of fatigue cycled specimens, the effect of environment on the various phases of the fatigue phenomenon, the effect of prolonged exposure to vacuum on fatigue life, the variation of fatigue life with decreasing gas pressure, and gas evolution during fatigue cycling. Analysis of the findings of this review indicates that hydrogen embrittlement is primarily responsible for decreased fatigue resistance in humid environments, and that dislocations move more easily during tests in vacuum than during test in air. It was found that fatigue cracks generally initiated and propagated more rapidly in air than in vacuum. Prolonged exposure to vacuum does not adversely affect fatigue resistance. The variation of fatigue life with decreasing gas pressure is sometimes stepped and sometimes continuous.

Fatigue Behavior of Steel Fiber Reinforced High-Strength Concrete under Different Stress Levels

NASA Astrophysics Data System (ADS)

Zhang, Chong; Gao, Danying; Gu, Zhiqiang

2017-12-01

The investigation was conducted to study the fatigue behavior of steel fiber reinforced high-strength concrete (SFRHSC) beams. A series of 5 SFRHSC beams was conducted flexural fatigue tests at different stress level S of 0.5, 0.55, 0.6, 0.7 and 0.8 respectively. Static test was conducted to determine the ultimate static capacity prior to fatigue tests. Fatigue modes and S-N curves were analyzed. Besides, two fatige life prediction model were analyzed and compared. It was found that stress level S significantly influenced the fatigue life of SFRHSC beams and the fatigue behavior of SFRHSC beams was mainly determined by the tensile reinforcement.

Tension and fatigue behavior of 316LVM 1x7 multi-strand cables used as implantable electrodes.

PubMed

Lewandowski, John J; Varadarajan, Ravikumar; Smith, Brian; Tuma, Chris; Shazly, Mostafa; Vatamanu, Luciano O

2008-07-15

The mechanical behavior of 316LVM 1x7 cables were evaluated in uniaxial tension, and in cyclic strain-controlled fatigue with the use of a Flex tester operated to provide fully reversed bending fatigue. The magnitude of cyclic strains imparted to each cable tested was controlled via the use of different diameter mandrels. Smaller diameter mandrels produced higher values of cyclic strain and lower fatigue life. Multiple samples were tested and analyzed via scanning electron microscopy. The fatigue results were analyzed via a Coffin-Manson-Basquin approach and compared to fatigue data obtained from the literature where testing was conducted on similar materials, but under rotating bending fatigue conditions.

Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations

NASA Technical Reports Server (NTRS)

Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin; Minguet, Pierre J.

2001-01-01

A methodology is presented for determining the fatigue life of composite structures based on fatigue characterization data and geometric nonlinear finite element (FE) analyses. To demonstrate the approach, predicted results were compared to fatigue tests performed on specimens which represented a tapered composite flange bonded onto a composite skin. In a first step, tension tests were performed to evaluate the debonding mechanisms between the flange and the skin. In a second step, a 2D FE model was developed to analyze the tests. To predict matrix cracking onset, the relationship between the tension load and the maximum principal stresses transverse to the fiber direction was determined through FE analysis. Transverse tension fatigue life data were used to -enerate an onset fatigue life P-N curve for matrix cracking. The resulting prediction was in good agreement with data from the fatigue tests. In a third step, a fracture mechanics approach based on FE analysis was used to determine the relationship between the tension load and the critical energy release rate. Mixed mode energy release rate fatigue life data were used to create a fatigue life onset G-N curve for delamination. The resulting prediction was in good agreement with data from the fatigue tests. Further, the prediction curve for cumulative life to failure was generated from the previous onset fatigue life curves. The results showed that the methodology offers a significant potential to Predict cumulative fatigue life of composite structures.

Intramedullary nailing in opening wedge high tibial osteotomy-in vitro test for validation of a method of fixation.

PubMed

Burchard, Rene; Katerla, Denise; Hammer, Marina; Pahlkötter, Anke; Soost, Christian; Dietrich, Gerhard; Ohrndorf, Arne; Richter, Wolfgang; Lengsfeld, Markus; Christ, Hans-Jürgen; Graw, Jan Adriaan; Fritzen, Claus-Peter

2018-02-01

Opening wedge high tibial osteotomy (HTO) as a treatment in unicompartimental osteoarthritis of the knee can significantly relieve pain and prevent or at least delay an early joint replacement. The fixation of the osteotomy has undergone development and refinements during the last years. The angle-stable plate fixator is currently one of the most commonly used plates in HTOs. The angular stable fixation between screws and the plate offers a high primary stability to retain the correction with early weight-bearing protocols. This surgical technique is performed as a standard of care and generally well tolerated by the patients. Nevertheless, some studies observed that many patients complained about discomfort related to the implant. Therefore, the stability of two different intramedullary nails, a short implant used in humeral fractures and a long device used in tibial fractures for stabilization in valgus HTOs, was investigated as an alternative fixation technique. The plate fixator was defined as reference standard. Nine synthetic tibia models were standardly osteotomized and stabilized by one of the fixation devices. Axial compression was realized using a special testing machine and two protocols were performed: a multi-step fatigue test and a load-to-failure test. Overall motion, medial, and lateral displacements were documented. Fractures always occurred at the lateral cortex. Axial cyclic loading up to 800 N was tolerated by all implants without failure. The tibia nail provided highest fatigue strength under the load-to-failure conditions. The results suggest that intramedullary nailing might be used as an alternative concept in HTO.

Strain isolated ceramic coatings

NASA Technical Reports Server (NTRS)

Tolokan, R. P.; Brady, J. B.; Jarrabet, G. P.

1985-01-01

Plasma sprayed ceramic coatings are used in gas turbine engines to improve component temperature capability and cooling air efficiency. A compliant metal fiber strain isolator between a plasma sprayed ceramic coating and a metal substrate improves ceramic durability while allowing thicker coatings for better insulation. Development of strain isolated coatings has concentrated on design and fabrication of coatings and coating evaluation via thermal shock testing. In thermal shock testing, five types of failure are possible: buckling failure im compression on heat up, bimetal type failure, isothermal expansion mismatch failure, mudflat cracking during cool down, and long term fatigue. A primary failure mode for thermally cycled coatings is designated bimetal type failure. Bimetal failure is tensile failure in the ceramic near the ceramic-metal interface. One of the significant benefits of the strain isolator is an insulating layer protecting the metal substrate from heat deformation and thereby preventing bimetal type failure.

Texture studies of hot compressed near alpha titanium alloy (IMI 834) at 1000°C with different strain rates

NASA Astrophysics Data System (ADS)

Kodli, B. K.; Saxena, K. K.; Dey, S. R.; Pancholi, V.; Bhattacharjee, A.

2015-04-01

IMI 834 Titanium alloy is a near alpha (hcp) titanium alloy used for high temperature applications with the service temperature up to 600°C. Generally, this alloy is widely used in gas turbine engine applications such as low pressure compressor discs. For these applications, good fatigue and creep properties are required, which have been noticed better in a bimodal microstructure, containing 15-20% volume fraction of primary alpha grains (αp) and remaining bcc beta (β) grains transformed secondary alpha laths (αs). The bimodal microstructure is achieved during processing of IMI 834 in the high temperature α+β region. The major issue of bimodal IMI 834 during utilization is its poor dwell fatigue life time caused by textured macrozones. Textured macrozone is the spatial accumulation of similar oriented grains in the microstructure generated during hot processing in the high temperature α+β region. Textured macrozone can be mitigated by controlling the hot deformation with certain strain rate under stable plastic conditions having β grains undergoing dynamic recrystallization. Hence, a comprehensive study is required to understand the deformation behavior of α and β grains at different strain rates in that region. Hot compression tests up to 5°% strain of the samples are performed with five different strain rates i.e. 10-3 s-1, 10-2 s-1, 10-1 s-1, 1 s-1 and 10 s-1 at 1000°C using Gleeble 3800. The resultant bimodal microstructure and the texture studies of primary alpha grains (αp) and secondary alpha laths (αs) are carried out using scanning electron microscopy (SEM)-electron back scattered diffraction (EBSD) method.

Benefits of Compression Garments Worn During Handball-Specific Circuit on Short-Term Fatigue in Professional Players.

PubMed

Ravier, Gilles; Bouzigon, Romain; Beliard, Samuel; Tordi, Nicolas; Grappe, Frederic

2018-04-04

Ravier, G, Bouzigon, R, Beliard, S, Tordi, N, and Grappe, F. Benefits of compression garments worn during handball-specific circuit on short-term fatigue in professional players. J Strength Cond Res XX(X): 000-000, 2016-The purpose of this study was to investigate the benefits of full-leg length compression garments (CGs) worn during a handball-specific circuit exercises on athletic performance and acute fatigue-induced changes in strength and muscle soreness in professional handball players. Eighteen men (mean ± SD: age 23.22 ± 4.97 years; body mass: 82.06 ± 9.69 kg; height: 184.61 ± 4.78 cm) completed 2 identical sessions either wearing regular gym short or CGs in a randomized crossover design. Exercise circuits of explosive activities included 3 periods of 12 minutes of sprints, jumps, and agility drills every 25 seconds. Before, immediately after and 24 hours postexercise, maximal voluntary knee extension (maximal voluntary contraction, MVC), rate of force development (RFD), and muscle soreness were assessed. During the handball-specific circuit sprint and jump performances were unchanged in both conditions. Immediately after performing the circuit exercises MVC, RFD, and PPT decreased significantly compared with preexercise with CGs and noncompression clothes. Decrement was similar in both conditions for RFD (effect size, ES = 0.40) and PPT for the soleus (ES = 0.86). However, wearing CGs attenuated decrement in MVC (p < 0.001) with a smaller decrease (ES = 1.53) in CGs compared with regular gym shorts condition (-5.4 vs. -18.7%, respectively). Full recovery was observed 24 hours postexercise in both conditions for muscle soreness, MVC, and RFD. These findings suggest that wearing CGs during a handball-specific circuit provides benefits on the impairment of the maximal muscle force characteristics and is likely to be worthwhile for handball players involved in activities such as tackles.

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

NASA Astrophysics Data System (ADS)

Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

2016-03-01

This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

Spectrum Fatigue of 7075-T651 Aluminum Alloy under Overloading and Underloading

DTIC Science & Technology

2016-03-15

underload, stress ratio, and environment on fatigue crack growth. Fatigue crack growth tests were conducted with a 7075-T651 aluminum alloy under constant...the UniGrow equation, the variation of crack length with number of loading cycle was predicted. The prediction and the fatigue test life were found to...Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18 REPORT NO. NAWCADPAX/TIM-2015/282 ii SUMMARY Fatigue tests of 7075-T651

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE PAGES

Gao, Yanfei

2015-11-30

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Yanfei

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Investigation of Gear and Bearing Fatigue Damage Using Debris Particle Distributions

NASA Technical Reports Server (NTRS)

Dempsey, Paula J.; Lewicki, David G.; Decker, Harry J.

2004-01-01

A diagnostic tool was developed for detecting fatigue damage to spur gears, spiral bevel gears, and rolling element bearings. This diagnostic tool was developed and evaluated experimentally by collecting oil debris data from fatigue tests performed in the NASA Glenn Spur Gear Fatigue Rig, Spiral Bevel Gear Test Facility, and the 500hp Helicopter Transmission Test Stand. During each test, data from an online, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results indicate oil debris alone cannot discriminate between bearing and gear fatigue damage.

Influence of sustained submaximal clenching fatigue test on electromyographic activity and maximum voluntary bite forces in healthy subjects and patients with temporomandibular disorders.

PubMed

Xu, L; Fan, S; Cai, B; Fang, Z; Jiang, X

2017-05-01

This study aimed to investigate whether the fatigue induced by sustained motor task in the jaw elevator muscles differed between healthy subjects and patients with temporomandibular disorder (TMD). Fifteen patients with TMD and thirteen age- and sex-matched healthy controls performed a fatigue test consisting of sustained clenching contractions at 30% maximal voluntary clenching intensity until test failure (the criterion for terminating the fatigue test was when the biting force decreased by 10% or more from the target force consecutively for >3 s). The pre- and post-maximal bite forces (MBFs) were measured. Surface electromyographic signals were recorded from the superficial masseter muscles and anterior temporal muscles bilaterally, and the median frequency at the beginning, middle and end of the fatigue test was calculated. The duration of the fatigue test was also quantified. Both pre- and post-MBFs were lower in patients with TMD than in controls (P < 0·01). No significant difference was found in the percentage change in MBF between groups. The duration of the fatigue test in TMD patients was significantly shorter than that of the controls (P < 0·05). Our results suggest that, compared to healthy subjects, patients with TMD become more easily fatigued, but the electromyographic activation process during the fatigue test is similar between healthy subjects and patients with TMD. However, the mechanisms involved in this process remain unclear, and further research is warranted. © 2017 John Wiley & Sons Ltd.

Thermal-Mechanical Fatigue Testing of a Titanium-Aluminide Alloy.

DTIC Science & Technology

1987-12-01

DIMSTRIBUTION STA Approved for pubi robing e% dQ *- AFIT/GAB/AA/87D-18 THERMAL-MECHANICAL FATIGUE TESTING OF A TITANIUM - ALUMINIDE ALLOY THESIS John J...THERMAL-MECHANICAL FATIGUE TESTING OF A TITANIUM - ALUMINIDE ALLOY THESIS Presented to the Faculty of the School of Engineering of the Air Force Institute...develop a Thermal-Mechanical Fatigue (TMF) testing system for titanium - aluminide compact tension specimens. I could not have accomplished this without the

Single-leg hop testing following fatiguing exercise: reliability and biomechanical analysis.

PubMed

Augustsson, J; Thomeé, R; Lindén, C; Folkesson, M; Tranberg, R; Karlsson, J

2006-04-01

A fatiguing exercise protocol was combined with single-leg hop testing to improve the possibilities of evaluating the effects of training or rehabilitation interventions. In the first test-retest experiment, 11 healthy male subjects performed two trials of single-leg hops under three different test conditions: non-fatigued and following fatiguing exercise, which consisted of unilateral weight machine knee extensions at 80% and 50%, respectively, of 1 repetition maximum (1 RM) strength. Intraclass correlation coefficients ranged from 0.75 to 0.98 for different hop test conditions, indicating that all tests were reliable. For the second experiment, eight healthy male subjects performed the fatiguing exercise protocol to investigate how fatigue influences lower-extremity joint kinematics and kinetics during single-leg hops. Hip, knee and ankle joint angles, moments and powers, as well as ground-reaction forces were recorded with a six-camera, motion-capture system and a force platform. Recovery of hop performance following the fatiguing exercise was also measured. During the take-off for the single-leg hops, hip and knee flexion angles, generated powers for the knee and ankle joints, and ground-reaction forces decreased for the fatigued hop conditions compared with the non-fatigued condition (P<0.05). Compared with landing during the non-fatigued condition, hip moments and ground-reaction forces were lower for the fatigued hop conditions (P<0.05). The negative joint power was two to three times greater for the knee than for the hip and five to 10 times greater for the knee than for the ankle during landing for all test conditions (P<0.05). Most measured variables had recovered three minutes post-exercise. It is concluded that the fatiguing exercise protocol combined with single-leg hop testing was a reliable method for investigating functional performance under fatigued test conditions. Further, subjects utilized an adapted hop strategy, which employed less hip and knee flexion and generated powers for the knee and ankle joints during take-off, and less hip joint moments during landing under fatigued conditions. The large negative power values observed at the knee joint during the landing phase of the single-leg hop, during which the quadriceps muscle activates eccentrically, indicate that not only hop distance but also the ability to perform successful landings should be investigated when assessing dynamic knee function.

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2011-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Probabilistic Simulation for Combined Cycle Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2010-01-01

A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multifactor interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2010-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Effect of Cyclic Thermo-Mechanical Loads on Fatigue Reliability in Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Shah, A. R.; Murthy, P. L. N.; Chamis, C. C.

1996-01-01

A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multi-factor interaction relationship developed at NASA Lewis Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability- based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)(sub s) graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Experimental Investigation and Finite Element Analysis on Fatigue Behavior of Aluminum Alloy 7050 Single-Lap Joints

NASA Astrophysics Data System (ADS)

Zhou, Bing; Cui, Hao; Liu, Haibo; Li, Yang; Liu, Gaofeng; Li, Shujun; Zhang, Shangzhou

2018-03-01

The fatigue behavior of single-lap four-riveted aluminum alloy 7050 joints was investigated by using high-frequency fatigue test and scanning electron microscope (SEM). Stress distributions obtained by finite element (FE) analysis help explain the fatigue performance. The fatigue test results showed that the fatigue lives of the joints depend on cold expansion and applied cyclic loads. FE analysis and fractography indicated that the improved fatigue lives can be attributed to the reduction in maximum stress and evolution of fatigue damage at the critical location. The beneficial effects of strengthening techniques result in tearing ridges or lamellar structure on fracture surface, decrease in fatigue striations spacing, delay of fatigue crack initiation, crack deflection in fatigue crack propagation and plasticity-induced crack closure.

Fatigue Lives Of Laser-Cut Metals

NASA Technical Reports Server (NTRS)

Martin, Michael R.

1988-01-01

Fatigue lives made to approach those attainable by traditional grinding methods. Fatigue-test specimens prepared from four metallic alloys, and material removed from specimens by manual grinding, by Nd:glass laser, and by Nd:YAG laser. Results of fatigue tests of all specimens indicated reduction of fatigue strengths of laser-fired specimens. Laser machining holds promise for improved balancing of components of gas turbines.

Acid-resistant calcium silicate-based composite implants with high-strength as load-bearing bone graft substitutes and fracture fixation devices.

PubMed

Wei, Chung-Kai; Ding, Shinn-Jyh

2016-09-01

To achieve the excellent mechanical properties of biodegradable materials used for cortical bone graft substitutes and fracture fixation devices remains a challenge. To this end, the biomimetic calcium silicate/gelatin/chitosan oligosaccharide composite implants were developed, with an aim of achieving high strength, controlled degradation, and superior osteogenic activity. The work focused on the effect of gelatin on mechanical properties of the composites under four different kinds of mechanical stresses including compression, tensile, bending, and impact. The evaluation of in vitro degradability and fatigue at two simulated body fluid (SBF) of pH 7.4 and 5.0 was also performed, in which the pH 5.0 condition simulated clinical conditions caused by bacterial induced local metabolic acidosis or tissue inflammation. In addition, human mesenchymal stem cells (hMSCs) were sued to examine osteogenic activity. Experimental results showed that the appropriate amount of gelatin positively contributed to failure enhancement in compressive and impact modes. The 10wt% gelatin-containing composite exhibits the maximum value of the compressive strength (166.1MPa), which is within the reported compressive strength for cortical bone. The stability of the bone implants was apparently affected by the in vitro fatigue, but not by the initial pH environments (7.4 or 5.0). The gelatin not only greatly enhanced the degradation of the composite when soaked in the dynamic SBF solution, but effectively promoted attachment, proliferation, differentiation, and formation of mineralization of hMSCs. The 10wt%-gelatin composite with high initial strength may be a potential implant candidate for cortical bone repair and fracture fixation applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Chest Compression With Personal Protective Equipment During Cardiopulmonary Resuscitation: A Randomized Crossover Simulation Study.

PubMed

Chen, Jie; Lu, Kai-Zhi; Yi, Bin; Chen, Yan

2016-04-01

Following a chemical, biological, radiation, and nuclear incident, prompt cardiopulmonary resuscitation (CPR) procedure is essential for patients who suffer cardiac arrest. But CPR when wearing personal protection equipment (PPE) before decontamination becomes a challenge for healthcare workers (HCW). Although previous studies have assessed the impact of PPE on airway management, there is little research available regarding the quality of chest compression (CC) when wearing PPE.A present randomized cross-over simulation study was designed to evaluate the effect of PPE on CC performance using mannequins.The study was set in one university medical center in the China.Forty anesthesia residents participated in this randomized cross-over study.Each participant performed 2 min of CC on a manikin with and without PPE, respectively. Participants were randomized into 2 groups that either performed CC with PPE first, followed by a trial without PPE after a 180-min rest, or vice versa.CPR recording technology was used to objectively quantify the quality of CC. Additionally, participants' physiological parameters and subjective fatigue score values were recorded.With the use of PPE, a significant decrease of the percentage of effective compressions (41.3 ± 17.1% with PPE vs 67.5 ± 15.6% without PPE, P < 0.001) and the percentage of adequate compressions (67.7 ± 18.9% with PPE vs 80.7 ± 15.5% without PPE, P < 0.001) were observed. Furthermore, the increases in heart rate, mean arterial pressure, and subjective fatigue score values were more obvious with the use of PPE (all P < 0.01).We found significant deterioration of CC performance in HCW with the use of a level-C PPE, which may be a disadvantage for enhancing survival of cardiac arrest.

Metal Additive Manufacturing: A Review of Mechanical Properties

NASA Astrophysics Data System (ADS)

Lewandowski, John J.; Seifi, Mohsen

2016-07-01

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test orientation/build direction on properties, when available, are also provided, along with discussion of the potential source(s) (e.g., texture, microstructure changes, defects) of anisotropy in properties. Recommendations for additional work are also provided.

Cumulative Axial and Torsional Fatigue: An Investigation of Load-Type Sequencing Effects

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Bonacuse, Peter J.

2000-01-01

Cumulative fatigue behavior of a wrought cobalt-base superalloy, Haynes 188 was investigated at 538 C under various single-step sequences of axial and torsional loading conditions. Initially, fully-reversed, axial and torsional fatigue tests were conducted under strain control at 538 C on thin-walled tubular specimens to establish baseline fatigue life relationships. Subsequently, four sequences (axial/axial, torsional/torsional, axial/torsional, and torsional/axial) of two load-level fatigue tests were conducted to characterize both the load-order (high/low) and load-type sequencing effects. For the two load-level tests, summations of life fractions and the remaining fatigue lives at the second load-level were computed by the Miner's Linear Damage Rule (LDR) and a nonlinear Damage Curve Approach (DCA). In general, for all four cases predictions by LDR were unconservative. Predictions by the DCA were within a factor of two of the experimentally observed fatigue lives for a majority of the cumulative axial and torsional fatigue tests.

Rolling-element fatigue life of AMS 5749 corrosion resistant, high temperature bearing steel

NASA Technical Reports Server (NTRS)

Parker, R. J.; Hodder, R. S.

1977-01-01

The rolling element fatigue lives of AMS 5749 and AISI M-50 were compared in tests run in the five ball fatigue tester and the rolling contact fatigue tester. The effects of double vacuum melting and retained austenite on the life of AMS 5749 were determined in five ball fatigue tests. The double vacuum melting process consisted of induction vacuum melting followed by vacuum arc remelting (VIM-VAR). In the five ball tests, VIM-VAR AMS 5749 gave lives at least six times that of VIM-VAR AISI M-50. Similar tests in the rolling contact fatigue tester showed no significant difference in the lives of the two materials. The rolling element fatigue life of VIM-VAR AMS 5749 was at least 14 times that of vacuum induction melted AMS 5749. A trend toward increased rolling element fatigue life with decreased retained austenite is apparent, but the confidence that all experimental differences are significant is not great.

Fatigue and physical fitness of mildly disabled persons with multiple sclerosis: a cross-sectional study.

PubMed

Valet, Maxime; Lejeune, Thierry; Glibert, Yumiko; Hakizimana, Jean C; Van Pesch, Vincent; El Sankari, Souraya; Detrembleur, Christine; Stoquart, Gaëtan

2017-09-01

Fatigue is frequent and disabling in persons with multiple sclerosis (pwMS) with mild neurological disability. These patients also have impaired physical fitness. Whether mildly disabled pwMS are deconditioned, and this deconditioning is linked to fatigue, remains unknown. Our aim is to determine the physical fitness of mildly disabled patients with multiple sclerosis and study its relationship with perceived fatigue and to link perceived fatigue with other parameters. Twenty patients (14 women; mean age: 45.5 years) with mild disability (Expanded Disability Status Scale 0-4) underwent a 2-min walking test, Timed Up-and-Go test, aerobic capacity testing, and isometric knee extension testing to assess strength and neuromuscular fatigability. They completed questionnaires assessing perceived fatigue, psychological status, and physical activity. Correlation coefficients and multivariate regression were used to analyze the relationships among variables. Seventeen (85%) patients reported a high level of fatigue. Thirteen (65%) patients had subnormal aerobic capacity. Fatigue was weakly to moderately associated with aerobic capacity, mobility, walking capacity, depression, and neuromuscular fatigability. An association of disease duration, aerobic capacity, and the neuromuscular fatigability index explained 65.1% of fatigue. A high proportion of pwMS with mild neurological disability are fatigued and deconditioned. Perceived fatigue is linked to aerobic capacity, neuromuscular fatigability, depression, mobility, and walking capacity. Focusing on these parameters could help in the management of fatigue.

Research on the Fatigue Flexural Performance of RC Beams Attacked by Salt Spray

NASA Astrophysics Data System (ADS)

Mao, Jiang-hong; Xu, Fang-yuan; Jin, Wei-liang; Zhang, Jun; Wu, Xi-xi; Chen, Cai-sheng

2018-04-01

The fatigue flexural performance of RC beams attacked by salt spray was studied. A testing method involving electro osmosis, electrical accelerated corrosion and salt spray was proposed. This corrosion process method effectively simulates real-world salt spray and fatigue loading exerted by RC components on sea bridges. Four RC beams that have different stress amplitudes were tested. It is found that deterioration by corrosion and fatigue loading reduces the fatigue life of the RC and decreases the ability of deformation. The fatigue life and deflection ability could be reduced by increasing the stress amplitude and the corrosion duration time. The test result demonstrates that this experimental method can couple corrosion deterioration and fatigue loading reasonably. This procedure may be applied to evaluate the fatigue life and concrete durability of RC components located in a natural salt spray environment.

Assessment of corrosion fatigue damage by acoustic emission and periodic proof tests

NASA Astrophysics Data System (ADS)

Mehdizadeh, P.

1976-03-01

The development of a better nondestructive inspection method for detecting corrosion fatigue damage based on acoustic emission (AE) and periodic proof testing (PPT) is studied for corrosion fatigue tests in salt water solution under tension-tension loading. It is shown that PPT combined with AE monitoring can be a sensitive method for assessing the progress of corrosion fatigue damage as the continuous AE monitoring method. The AE-PPT technique is shown to be dependent on the geometry and size of the crack relative to the test specimen. A qualitative method based on plateauing of acoustic emission counts during proof tests due to changes in the fracture mode is used to predict the remaining fatigue life up to 70% of the actual values. PPT is shown to have no adverse effect on fatigue performance in salt water.

Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

NASA Technical Reports Server (NTRS)

Lerch, Brad; Draper, Sue; Pereira, J. Mike

2002-01-01

High cycle fatigue strength testing of gamma TiAl by the step test method is investigated. A design of experiments was implemented to determine if the coaxing effect occurred during testing. Since coaxing was not observed, step testing was deemed a suitable method to define the fatigue strength at 106 cycles.

Oxygen uptake during peak graded exercise and single-stage fatigue tests of wheelchair propulsion in manual wheelchair users and the able-bodied.

PubMed

Keyser, R E; Rodgers, M M; Gardner, E R; Russell, P J

1999-10-01

To determine if a single-stage, submaximal fatigue test on a wheelchair ergometer would result in higher than expected energy expenditure. An experimental survey design contrasting physiologic responses during peak graded exercise tests and fatigue tests. A rehabilitation science laboratory that included a prototypical wheelchair ergometer, open-circuit spirometry system, and heart rate monitor. Nine able-bodied non-wheelchair users (the NWC group: 6 men and 3 women, mean +/- SD age 30 +/- 7yrs) and 15 manual wheelchair users (the WC group: 12 men and 3 women, age 40 +/- 9yrs, time in wheelchair 16 +/- 9yrs). No subject had any disease, medication regimen, or upper body neurologic, orthopedic, or other condition that would limit wheelchair exercise. Peak oxygen uptake (VO2) for graded exercise testing and during fatigue testing, using a power output corresponding to 75% peak aerobic capacity on graded exercise test. In the WC group, VO2 at 6 minutes of fatigue testing was not significantly different from peak VO2. In the NWC group, VO2 was similar to the expected level throughout fatigue testing. Energy expenditure was higher than expected in the WC group but not in the NWC group. Fatigue testing may provide a useful evaluation of cardiorespiratory status in manual wheelchair users.

Repeatability of testing procedures for resilient modulus and fatigue : appendices.

DOT National Transportation Integrated Search

1989-04-01

The article is the appendices of "Repeatability of testing procedures for resilient modulus and fatigue". : Extensive use of diametral resilient modulus and fatigue testing is made by the Oregon State Highway Division to evaluate asphaltic concrete m...

Electromagnetic induction sensor for dynamic testing of coagulation process.

PubMed

Wang, Zhe; Yu, Yuanhua; Yu, Zhanjiang; Chen, Qimeng

2018-03-01

With the increasing demand for coagulation POCT for patients in the surgery department or the ICU, rapid coagulation testing techniques and methods have drawn widespread attention from scholars and businessmen. This paper proposes the use of electromagnetic induction sensor probe for detection of dynamic process causing changes in the blood viscosity and density before and after coagulation based on the damped vibration principle, in order to evaluate the coagulation status. Utilizing the dynamic principle, the differential equation of vibration system comprising elastic support and electromagnetic induction device is established through sensor dynamic modeling. The structural parameters of elastic support are optimized, and the circular sheet spring is designed. Furthermore, harmonic response analysis and vibration fatigue coupling analysis are performed on the elastic support of the sensor by considering the natural frequency of the system, and the electromagnetic induction sensor testing device is set up. Using the device and coagulation reagent, the standard curve for coagulation POCT is plotted, and the blood sample application in clinical patients is established, which are methodologically compared with the imported POCT coagulation analyzer. The results show that the sensor designed in this paper has a first-order natural frequency of 11.368 Hz, which can withstand 5.295 × 10 2 million times of compressions and rebounds. Its correlation with the results of SONOCLOT analyzer reaches 0.996, and the reproducibility 0.002. The electromagnetic induction coagulation testing sensor designed has good elasticity and anti-fatigue, which can meet the accuracy requirement of clinical detection. This study provides the core technology for developing the electromagnetic induction POCT instrument for dynamic testing of coagulation process.

Three-dimensional measurements of fatigue crack closure

NASA Technical Reports Server (NTRS)

Ray, S. K.; Grandt, A. F., Jr.

1984-01-01

Fatigue crack growth and retardation experiments conducted in polycarbonate test specimen are described. The transparent test material allows optical interferometry measurements of the fatigue crack opening (and closing) profiles. Crack surface displacements are obtained through the specimen thickness and three dimensional aspects of fatigue crack closure are discussed.

Critical flaw size in silicon nitride ball bearings

NASA Astrophysics Data System (ADS)

Levesque, George Arthur

Aircraft engine and bearing manufacturers have been aggressively pursuing advanced materials technology systems solutions to meet main shaft-bearing needs of advanced military aircraft engines. Ceramic silicon nitride hybrid bearings are being developed for such high performance applications. Though silicon nitride exhibits many favorable properties such as high compressive strength, high hardness, a third of the density of steel, low coefficient of thermal expansion, and high corrosion and temperature resistance, they also have low fracture toughness and are susceptible to failure from fatigue spalls emanating from pre-existing surface flaws that can grow under rolling contact fatigue (RCF). Rolling elements and raceways are among the most demanding components in aircraft engines due to a combination of high cyclic contact stresses, long expected component lifetimes, corrosive environment, and the high consequence of fatigue failure. The cost of these rolling elements increases exponentially with the decrease in allowable flaw size for service applications. Hence the range of 3D non-planar surface flaw geometries subject to RCF is simulated to determine the critical flaw size (CFS) or the largest allowable flaw that does not grow under service conditions. This dissertation is a numerical and experimental investigation of surface flaws in ceramic balls subjected to RCF and has resulted in the following analyses: Crack Shape Determination: the nucleation of surface flaws from ball impact that occurs during the manufacturing process is simulated. By examining the subsurface Hertzian stresses between contacting spheres, their applicability to predicting and characterizing crack size and shape is established. It is demonstrated that a wide range of cone and partial cone cracks, observed in practice, can be generated using the proposed approaches. RCF Simulation: the procedure and concerns in modeling nonplanar 3D cracks subject to RCF using FEA for stress intensity factor (SIF) trends observed from parametrically varying different physical effects are plotted and discussed. Included are developments in contact algorithms for 3D nonplanar cracks, meshing of nonplanar cracks for SIFs, parametric studies via MATLAB and other subroutines in python and FORTRAN. Establishing Fracture Parameters: the fracture toughness, K c, is determined by using numerical techniques on experimental tests namely the Brazilian disc test and a novel compression test on an indented ball. The fatigue threshold for mixed-mode loading, Keff, is determined by using a combination of numerical modeling and results from the V-ring single ball RCF test. CFS Determination: the range of 3D non-planar surface flaw geometries subject to RCF are simulated to calculate mixed mode SIFs to determine the critical flaw size, or the largest allowable flaw that does not grow under service conditions. The CFS results are presented as a function of Hertzian contact stress, traction magnitude, and crack size. Empirical Equations: accurate empirical equations (response functions) for the KI, KII, and K III SIFs for semi-elliptical surface cracks subjected to RCF as a function of the contact patch diameter, angle of crack to the surface, max pressure, position along the crack front, and aspect ratio of the crack are developed via parametric 3D FEA. Statistical Probability of Failure: since the variability in mechanical properties for brittle materials is high a probabilistic investigation of variations in flaw size, flaw orientation, fracture toughness, and Hertzian load on failure probability is conducted to statistically determine the probability of ball failure for an existing flaw subjected to the service conditions. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)

Plate Versus Intramedullary Nail Fixation of Anterior Tibial Stress Fractures: A Biomechanical Study.

PubMed

Markolf, Keith L; Cheung, Edward; Joshi, Nirav B; Boguszewski, Daniel V; Petrigliano, Frank A; McAllister, David R

2016-06-01

Anterior midtibial stress fractures are an important clinical problem for patients engaged in high-intensity military activities or athletic training activities. When nonoperative treatment has failed, intramedullary (IM) nail and plate fixation are 2 surgical options used to arrest the progression of a fatigue fracture and allow bone healing. A plate will be more effective than an IM nail in preventing the opening of a simulated anterior midtibial stress fracture from tibial bending. Controlled laboratory study. Fresh-frozen human tibias were loaded by applying a pure bending moment in the sagittal plane. Thin transverse saw cuts, 50% and 75% of the depth of the anterior tibial cortex, were created at the midtibia to simulate a fatigue fracture. An extensometer spanning the defect was used to measure the fracture opening displacement (FOD) before and after the application of IM nail and plate fixation constructs. IM nails were tested without locking screws, with a proximal screw only, and with proximal and distal screws. Plates were tested with unlocked bicortical screws (standard compression plate) and locked bicortical screws; both plate constructs were tested with the plate edge placed 1 mm from the anterior tibial crest (anterior location) and 5 mm posterior to the crest. For the 75% saw cut depth, the mean FOD values for all IM nail constructs were 13% to 17% less than those for the saw cut alone; the use of locking screws had no significant effect on the FOD. The mean FOD values for all plate constructs were significantly less than those for all IM nail constructs. The mean FOD values for all plates were 28% to 46% less than those for the saw cut alone. Anterior plate placement significantly decreased mean FOD values for both compression and locked plate constructs, but the mean percentage reductions for locked and unlocked plates were not significantly different from each other for either plate placement. The percentage FOD reductions for all plate constructs and the unlocked IM nail were significantly less with a 50% saw cut depth. Plate fixation was superior to IM nail fixation in limiting the opening of a simulated midtibial stress fracture, and anterior-posterior placement of the plate was an important variable for this construct. Results from these tests can help guide the selection of fixation hardware for patients requiring surgical treatment for a midtibial stress fracture. © 2016 The Author(s).

High Frequency Vibration Based Fatigue Testing of Developmental Alloys

NASA Astrophysics Data System (ADS)

Holycross, Casey M.; Srinivasan, Raghavan; George, Tommy J.; Tamirisakandala, Seshacharyulu; Russ, Stephan M.

Many fatigue test methods have been previously developed to rapidly evaluate fatigue behavior. This increased test speed can come at some expense, since these methods may require non-standard specimen geometry or increased facility and equipment capability. One such method, developed by George et al, involves a base-excited plate specimen driven into a high frequency bending resonant mode. This resonant mode is of sufficient frequency (typically 1200 to 1700 Hertz) to accumulate 107 cycles in a few hours. One of the main limitations of this test method is that fatigue cracking is almost certainly guaranteed to be surface initiated at regions of high stress. This brings into question the validity of the fatigue test results, as compared to more traditional uniaxial, smooth-bar testing, since high stresses are subjecting only a small volume to fatigue damage. This limitation also brings into question the suitability of this method to screen developmental alloys, should their initiation life be governed by subsurface flaws. However, if applicable, the rapid generation of fatigue data using this method would facilitate faster design iterations, identifying more quickly, material and manufacturing process deficiencies. The developmental alloy used in this study was a powder metallurgy boron-modified Ti-6Al-4V, a new alloy currently being considered for gas turbine engine fan blades. Plate specimens were subjected to fully reversed bending fatigue. Results are compared with existing data from commercially available Ti-6Al-4V using both vibration based and more traditional fatigue test methods.

Spot-Welding Gun Is Easy To Use

NASA Technical Reports Server (NTRS)

Morgan, Gene E.; Nguyen, Francis H.

1991-01-01

Electrical-resistance spot-welding gun designed to produce more welds per unit time by decreasing technician's effort and fatigue. Vacuum cups on frame secure welding gun to workpiece while compressed air drives welding tip against workpiece to make spot resistance weld. When weld completed, vacuum in frame cups released so frame and gun moved to position of next spot weld.

Fatigue Behavior of a Cross-Ply Ceramic Matrix Composite Under Tension-Tension and Tension-Compression Loading.

DTIC Science & Technology

1992-12-01

Majidi [5] had experimented with cross-ply Nicalon/CAS and varied the number of plies. They theorized that the number of plies affected when the transverse...74, No 11, November 1991, p 2851 - 2858 5. Wang, S.-W., and Parvizi- Majidi , A., "Mechanical Behavior of Nicalon Fiber-Reinforced Calcium

Effect of fatigue loading on critical current in stainless steel-laminated DI-BSCCO superconducting composite tape

NASA Astrophysics Data System (ADS)

Hojo, M.; Osawa, K.; Adachi, T.; Inoue, Y.; Osamura, K.; Ochiai, S.; Ayai, N.; Hayashi, K.

2010-11-01

Tensile strain tolerance of the critical current in (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) composite superconductor is dramatically improved when the tape is laminated with stainless steel. For practical applications, it is important to understand whether this reinforcement by lamination is effective under fatigue loading. In the present study, we carried out fatigue tests in LN2 and measured the critical current at the specific fatigue cycles to clarify the strain tolerance of the critical current in stainless steel-laminated drastically innovative Bi2223 (DI-BSCCO®) tapes. The fatigue tests were carried out using a computer-controlled 10 kN servo-hydraulic fatigue testing machine with a load cell capacity of 2.5 kN. Tests under static loading showed that the irreversible stress at which the critical current is reduced by 1% from the original value (tensile stress at Ic/Ic0 = 0.99) was 315 MPa when measured at unloading state. The present fatigue tests results indicated that the critical current was maintained at over 98% of the original value at unloading state after stress cycles of 106 when the static irreversible stress was selected as the maximum stress under fatigue loading. Thus, laminated DI-BSCCO tapes showed excellent mechanical properties even under fatigue loading.

Axial-Load Fatigue Tests on 17-7 PH Stainless Steel Under Constant-Amplitude Loading

NASA Technical Reports Server (NTRS)

Leybold, Herbert A.

1960-01-01

Axial-load fatigue tests were conducted at room temperature on notched and unnotched sheet specimens of 17-7 PH stainless steel in Condition TH 1050. The notched specimens had theoretical stress-concentration factors of 2.32, 4.00, and 5.00. All specimens were tested under completely reversed loading. S-N curves are presented for each specimen configuration and ratios of fatigue strengths of unnotched specimens to those of notched specimens are given. Predictions of the fatigue behavior of notched specimens near the fatigue limit were made.

Characterization of fatigue behavior of 2-D woven fabric reinforced ceramic matrix composite at elevated temperature. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Groner, D.J.

This study investigated the fatigue behavior and associated damage mechanisms in notched and unnotched enhanced SiC/SiC ceramic matrix composite specimens at 1100 deg C. Stiffness degradation, strain variation, and hysteresis were evaluated to characterize material behavior. Microscopic examination was performed to characterize damage mechanisms. During high cycle/low stress fatigue tests, far less fiber/matrix interface debond was evident than in low cycle/high stress fatigue tests. Notched specimens exhibited minimal stress concentration during monotonic tensile testing and minimal notch sensitivity during fatigue testing. Damage mechanisms were also similar to unnotched.

Comparison of Mode II and III Monotonic and Fatigue Delamination Onset Behavior for Carbon/Toughened Epoxy Composites

NASA Technical Reports Server (NTRS)

Li, Jian; OBrien, T. Kevin; Lee, Shaw Ming

1997-01-01

Monotonic and fatigue tests were performed to compare the Mode II and III interlaminar fracture toughness and fatigue delamination onset for Tenax-HTA/R6376 carbon/toughened epoxy composites. The Mode II interlaminar fracture toughness and fatigue delamination onset were characterized using the end-notched flexure (ENF) test while the Mode III interlaminar fracture toughness and fatigue delamination onset were characterized by using the edge crack torsion (ECT) test. Monotonic tests show that the Mode III fracture toughness is higher than the Mode II fracture toughness. Both Mode II and III cyclic loading greatly increases the tendency for a delamination to grow relative to a single monotonically increasing load. Under fatigue loading, the Mode III specimen also has a longer life than the Mode II specimen.

Analysis of methods for determining high cycle fatigue strength of a material with investigation of titanium-aluminum-vanadium gigacycle fatigue behavior

NASA Astrophysics Data System (ADS)

Pollak, Randall D.

Today, aerospace engineers still grapple with the qualitative and quantitative understanding of fatigue behavior in the design and testing of turbine-driven jet engines. The Department of Defense has taken a very active role in addressing this problem with the formation of the National High Cycle Fatigue Science & Technology Program in 1994. The primary goal of this program is to further the understanding of high cycle fatigue (HCF) behavior and develop methods in order to mitigate the negative impact of HCF on aerospace operations. This research supports this program by addressing the fatigue strength testing guidance currently provided by the DoD to engine manufacturers, with the primary goal to investigate current methods and recommend a test strategy to characterize the fatigue strength of a material at a specified number of cycles, such as the 109 design goal specified by MIL-HDBK-1783B, or range of cycles. The research utilized the benefits of numerical simulation to initially investigate the staircase method for use in fatigue strength testing. The staircase method is a commonly used fatigue strength test, but its ability to characterize fatigue strength variability is extremely suspect. A modified staircase approach was developed and shown to significantly reduce bias and scatter in estimates for fatigue strength variance. Experimental validation of this proposed test strategy was accomplished using a dual-phase Ti-6Al-4V alloy. The HCF behavior of a second material with a very different microstructure (beta annealed Ti-6Al-4V) was also investigated. The random fatigue limit (RFL) model, a recently developed analysis tool, was investigated to characterize stress-life behavior but found to have difficulty representing fatigue life curves with sharp transitions. Two alternative models (bilinear and hyperbolic) were developed based on maximum likelihood methods to better characterize the Ti-6Al-4V fatigue life behavior. These models provided a good fit to the experimental data for the dual-phase Ti-6Al-4V and were applied to the beta annealed variant in order to estimate stress-life behavior using a small-sample approach. Based on this research, designers should be better able to make reliable estimates of fatigue strength parameters using small-sample testing.

Fatigue injury risk in anterior cruciate ligament of target side knee during golf swing.

PubMed

Purevsuren, Tserenchimed; Kwon, Moon Seok; Park, Won Man; Kim, Kyungsoo; Jang, Seung Ho; Lim, Young-Tae; Kim, Yoon Hyuk

2017-02-28

A golf-related ACL injury can be linked with excessive golf play or practice because such over-use by repetitive golf swing motions can increase damage accumulation to the ACL bundles. In this study, joint angular rotations, forces, and moments, as well as the forces and strains on the ACL of the target-side knee joint, were investigated for ten professional golfers using the multi-body lower extremity model. The fatigue life of the ACL was also predicted by assuming the estimated ACL force as a cyclic load. The ACL force and strain reached their maximum values within a short time just after ball-impact in the follow-through phase. The smaller knee flexion, higher internal tibial rotation, increase of the joint compressive force and knee abduction moment in the follow-through phase were shown as to lead an increased ACL loading. The number of cycles to fatigue failure (fatigue life) in the ACL might be several thousands. It is suggested that the excessive training or practice of swing motion without enough rest may be one of factors to lead to damage or injury in the ACL by the fatigue failure. The present technology can provide fundamental information to understand and prevent the ACL injury for golf players. Copyright © 2017. Published by Elsevier Ltd.

Intrinsic Compressive Stress in Polycrystalline Films is Localized at Edges of the Grain Boundaries.

PubMed

Vasco, Enrique; Polop, Celia

2017-12-22

The intrinsic compression that arises in polycrystalline thin films under high atomic mobility conditions has been attributed to the insertion or trapping of adatoms inside grain boundaries. This compression is a consequence of the stress field resulting from imperfections in the solid and causes the thermomechanical fatigue that is estimated to be responsible for 90% of mechanical failures in current devices. We directly measure the local distribution of residual intrinsic stress in polycrystalline thin films on nanometer scales, using a pioneering method based on atomic force microscopy. Our results demonstrate that, at odds with expectations, compression is not generated inside grain boundaries but at the edges of gaps where the boundaries intercept the surface. We describe a model wherein this compressive stress is caused by Mullins-type surface diffusion towards the boundaries, generating a kinetic surface profile different from the mechanical equilibrium profile by the Laplace-Young equation. Where the curvatures of both profiles differ, an intrinsic stress is generated in the form of Laplace pressure. The Srolovitz-type surface diffusion that results from the stress counters the Mullins-type diffusion and stabilizes the kinetic surface profile, giving rise to a steady compression regime. The proposed mechanism of competition between surface diffusions would explain the flux and time dependency of compressive stress in polycrystalline thin films.

Intrinsic Compressive Stress in Polycrystalline Films is Localized at Edges of the Grain Boundaries

NASA Astrophysics Data System (ADS)

Vasco, Enrique; Polop, Celia

2017-12-01

The intrinsic compression that arises in polycrystalline thin films under high atomic mobility conditions has been attributed to the insertion or trapping of adatoms inside grain boundaries. This compression is a consequence of the stress field resulting from imperfections in the solid and causes the thermomechanical fatigue that is estimated to be responsible for 90% of mechanical failures in current devices. We directly measure the local distribution of residual intrinsic stress in polycrystalline thin films on nanometer scales, using a pioneering method based on atomic force microscopy. Our results demonstrate that, at odds with expectations, compression is not generated inside grain boundaries but at the edges of gaps where the boundaries intercept the surface. We describe a model wherein this compressive stress is caused by Mullins-type surface diffusion towards the boundaries, generating a kinetic surface profile different from the mechanical equilibrium profile by the Laplace-Young equation. Where the curvatures of both profiles differ, an intrinsic stress is generated in the form of Laplace pressure. The Srolovitz-type surface diffusion that results from the stress counters the Mullins-type diffusion and stabilizes the kinetic surface profile, giving rise to a steady compression regime. The proposed mechanism of competition between surface diffusions would explain the flux and time dependency of compressive stress in polycrystalline thin films.

Risk of Anterior Cruciate Ligament Fatigue Failure Is Increased by Limited Internal Femoral Rotation During In Vitro Repeated Pivot Landings

PubMed Central

Beaulieu, Mélanie L.; Wojtys, Edward M.; Ashton-Miller, James A.

2015-01-01

Background A reduced range of hip internal rotation is associated with increased peak anterior cruciate ligament (ACL) strain and risk for injury. It is unknown, however, whether limiting the available range of internal femoral rotation increases the susceptibility of the ACL to fatigue failure. Hypothesis Risk of ACL failure is significantly greater in female knee specimens with a limited range of internal femoral rotation, smaller femoral-ACL attachment angle, and smaller tibial eminence volume during repeated in vitro simulated single-leg pivot landings. Study Design Controlled laboratory study. Methods A custom-built testing apparatus was used to simulate repeated single-leg pivot landings with a 4×-body weight impulsive load that induces knee compression, knee flexion, and internal tibial torque in 32 paired human knee specimens from 8 male and 8 female donors. These test loads were applied to each pair of specimens, in one knee with limited internal femoral rotation and in the contralateral knee with femoral rotation resisted by 2 springs to simulate the active hip rotator muscles’ resistance to stretch. The landings were repeated until ACL failure occurred or until a minimum of 100 trials were executed. The angle at which the ACL originates from the femur and the tibial eminence volume were measured on magnetic resonance images. Results The final Cox regression model (P = .024) revealed that range of internal femoral rotation and sex of donor were significant factors in determining risk of ACL fatigue failure. The specimens with limited range of internal femoral rotation had a failure risk 17.1 times higher than did the specimens with free rotation (P = .016). The female knee specimens had a risk of ACL failure 26.9 times higher than the male specimens (P = .055). Conclusion Limiting the range of internal femoral rotation during repetitive pivot landings increases the risk of an ACL fatigue failure in comparison with free rotation in a cadaveric model. Clinical Relevance Screening for restricted internal rotation at the hip in ACL injury prevention programs as well as in individuals with ACL injuries and/or reconstructions is warranted. PMID:26122384

Risk of anterior cruciate ligament fatigue failure is increased by limited internal femoral rotation during in vitro repeated pivot landings.

PubMed

Beaulieu, Mélanie L; Wojtys, Edward M; Ashton-Miller, James A

2015-09-01

A reduced range of hip internal rotation is associated with increased peak anterior cruciate ligament (ACL) strain and risk for injury. It is unknown, however, whether limiting the available range of internal femoral rotation increases the susceptibility of the ACL to fatigue failure. Risk of ACL failure is significantly greater in female knee specimens with a limited range of internal femoral rotation, smaller femoral-ACL attachment angle, and smaller tibial eminence volume during repeated in vitro simulated single-leg pivot landings. Controlled laboratory study. A custom-built testing apparatus was used to simulate repeated single-leg pivot landings with a 4×-body weight impulsive load that induces knee compression, knee flexion, and internal tibial torque in 32 paired human knee specimens from 8 male and 8 female donors. These test loads were applied to each pair of specimens, in one knee with limited internal femoral rotation and in the contralateral knee with femoral rotation resisted by 2 springs to simulate the active hip rotator muscles' resistance to stretch. The landings were repeated until ACL failure occurred or until a minimum of 100 trials were executed. The angle at which the ACL originates from the femur and the tibial eminence volume were measured on magnetic resonance images. The final Cox regression model (P = .024) revealed that range of internal femoral rotation and sex of donor were significant factors in determining risk of ACL fatigue failure. The specimens with limited range of internal femoral rotation had a failure risk 17.1 times higher than did the specimens with free rotation (P = .016). The female knee specimens had a risk of ACL failure 26.9 times higher than the male specimens (P = .055). Limiting the range of internal femoral rotation during repetitive pivot landings increases the risk of an ACL fatigue failure in comparison with free rotation in a cadaveric model. Screening for restricted internal rotation at the hip in ACL injury prevention programs as well as in individuals with ACL injuries and/or reconstructions is warranted. © 2015 The Author(s).

Fatigue-environment interactions in a SiC/Ti-15-3 composite

NASA Technical Reports Server (NTRS)

Gayda, J.; Gabb, T. P.; Lerch, B. A.

1993-01-01

Load-controlled isothermal and nonisothermal fatigue lives of a (0-deg)s SiC/Ti-15-3 were evaluated at temperatures between 150 and 550 C and a target strain range of about 0.45 percent. In nonisothermal fatigue tests, load was first cycled at minimum temperature and then temperature was cycled at zero load. For fatigue tests with peak temperatures at or above 300 C, fatigue life was dramatically reduced compared to that at 150 C. The shortest life was produced by the nonisothermal test with the greatest temperature range (Delta T = 400 C) and highest peak temperature (T(max) = 550 C). Vacuum testing showed that much of the life reduction under isothermal and nonisothermal conditions was related to environmental effects, although the nature of the fatigue-environment interaction was decidedly different for the isothermal and nonisothermal test cycles which were studied.

Sonic fatigue testing of an advanced composite aileron

NASA Technical Reports Server (NTRS)

Soovere, J.

1982-01-01

The sonic fatigue test program to verify the design of the composite inboard aileron for the L-1011 airplane is described. The composite aileron is fabricated from graphite/epoxy minisandwich covers which are attached to graphite/epoxy front spar and ribs, and to an aluminum rear spar with fasteners. The program covers the development of random fatigue data by means of coupon testing and modal studies on a representative section of the composite aileron, culminating in the accelerated sonic fatigue proof test. The composite aileron sustained nonlinear panel vibration during the proof test without failure. Viscous damping coefficients as low as 0.4% were measured on the panels. The effects of moisture conditioning and elevated temperature on the random fatigue life of both undamaged and impact damaged coupons were investigated. The combination of impact damage, moisture, and a 180 F temperature could reduce the random fatigue life by 50%.

Isothermal and thermal-mechanical fatigue of VVER-440 reactor pressure vessel steels

NASA Astrophysics Data System (ADS)

Fekete, Balazs; Trampus, Peter

2015-09-01

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of VVER-440 reactor pressure vessel under completely reserved total strain controlled low cycle fatigue tests were investigated. An advanced test facility was developed for GLEEBLE-3800 physical simulator which was able to perform thermomechanical fatigue experiments under in-service conditions of VVER nuclear reactors. The low cycle fatigue results were evaluated with the plastic strain based Coffin-Manson law, and plastic strain energy based model as well. It was shown that both methods are able to predict the fatigue life of reactor pressure vessel steels accurately. Interrupted fatigue tests were also carried out to investigate the kinetic of the fatigue evolution of the materials. On these samples microstructural evaluation by TEM was performed. The investigated low cycle fatigue behavior can provide reference for remaining life assessment and lifetime extension analysis.

Corrosion fatigue of high strength fastener materials in seawater. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tipton, D.G.

1983-12-01

Environmental effects can significantly reduce the fatigue life of metals. As such, corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L40 high strength steel blade-to-hub attachment bolt at the MOD-0A 200 kW wind turbine generator in Oahu, Hawaii prompted the current test program. Tests were undertaken to confirm the dramatic reduction of fatigue strength of AISI 41L40 in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials. AISI 41L40, AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35Nmore » were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data were fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.« less

Fatigue limit and Hysteresis Behavior of Type 304L Stainless Steel in Air and PWR Water, at 150°C and 300°C

NASA Astrophysics Data System (ADS)

Solomon, H. D.; Amzallag, C.; Vallee, A. J.; DeLair, R. E.

This is a study of the 107 cycle fatigue limit of Type 304L Stainless Steel, as measured in fully reversed (R=-1) load-controlled tests, at 150°C and 300°C, in air and PWR water. The staircase method was used to determine the fatigue limit. The tests run here utilized a cycle frequency of 1.818Hz and are compared to other tests from the literature that were run at 30Hz. The fatigue limit measured in the tests run at the high frequency was higher than that measured here. This is explained by measurements of the strain developed during cycling, using the different cycle frequencies. The tests run at the higher frequencies yielded lower strains for a given stress and, as expected, this resulted in higher fatigue limits. Using 107 cycles to define a run-out also led to a lower fatigue limit. These results are important as most previous fatigue limit measurements utilized 106 cycles or less to define a run-out, and when lives as long as 107 cycles are used the tests are generally run at high cycle frequencies, thus leading to higher fatigue limits than those measured here.

The mechanical behaviour of NBR/FEF under compressive cyclic stress strain

NASA Astrophysics Data System (ADS)

Mahmoud, W. E.; El-Eraki, M. H. I.; El-Lawindy, A. M. Y.; Hassan, H. H.

2006-06-01

Acrylonitrile butadiene rubber compounds filled with different concentrations of fast extrusion furnace (FEF) carbon black were experimentally investigated. The stress-strain curves of the composites were studied, which suggest good filler-matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non-spherical particles. The effect of FEF carbon black on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress-strain relationships for any cycle were described by applying Ogden's model for rubber samples. The dissipation energy that indicates the vibration damping capacity for all samples was determined. A simple model was proposed, to investigate the relation between maximum stress and the number of cyclic fatigue.

Experimental Behavior of Fatigued Single Stiffener PRSEUS Specimens

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.

2009-01-01

NASA, the Air Force Research Laboratory and The Boeing Company have worked to develop new low-cost, light-weight composite structures for aircraft. A Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept has been developed which offers advantages over traditional metallic structure. In this concept a stitched carbon-epoxy material system has been developed with the potential for reducing the weight and cost of transport aircraft structure by eliminating fasteners, thereby reducing part count and labor. By adding unidirectional carbon rods to the top of stiffeners, the panel becomes more structurally efficient. This combination produces a more damage tolerant design. This document describes the results of experimentation on PRSEUS specimens loaded in unidirectional compression in fatigue and to failure.

Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA's High Temperature, High Speed Turbine Seal Test Rig

NASA Technical Reports Server (NTRS)

Delgado, Irebert R.; Steinetz, Bruce M.; Rimnac, Clare M.; Lewandowski, John J.

2008-01-01

The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA s Turbine Seal Test Facility. The facility is used to test air-to-air seals primarily for use in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work, an inspection interval is determined for the test disk. The fatigue crack growth life of the NASA disk bolt holes is found to be 367 cycles at a crack depth of 0.501 mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032 cycles at a crack depth of 0.501 mm. Eddy-current inspections are suggested starting at 665 cycles since eddy current detection thresholds are currently at 0.381 mm. Inspection intervals are recommended every 50 cycles when operated at maximum operating conditions.

Tibiotalocalcaneal Arthrodesis Nails: A Comparison of Nails With and Without Internal Compression.

PubMed

Taylor, James; Lucas, Douglas E; Riley, Aimee; Simpson, G Alex; Philbin, Terrence M

2016-03-01

Hindfoot arthrodesis with tibiotalocalcaneal (TTC) intramedullary nails is used commonly when treating ankle and subtalar arthritis and other hindfoot pathology. Adequate compression is paramount to avoid nonunion and fatigue fracture of the hardware. Arthrodesis systems with internal compression have demonstrated superior compression to systems relying on external methods. This study examined the speed of union with TTC fusion nails with internal compression over nails without internal compression. A retrospective review was performed identifying nail type and time to union of the subtalar joint (STJ) and tibiotalar joint (TTJ). A total of 198 patients were included from 2003 to 2011. The median time to STJ fusion without internal compression was 104 days compared to 92 days with internal compression (P = .044). The median time to TTJ fusion without internal compression was 111 days compared to 93 days with internal compression (P = .010). Adjusting for diabetes, there was no significant difference in fusion speed with or without internal compression for the STJ (P = .561) or TTJ (P = .358). Nonunion rates were 24.5% for the STJ and 17.0% for the TTJ with internal compression, and 43.4% for the STJ and 42.1% for the TTJ without internal compression. This difference remained statistically significant after adjusting for diabetes for the TTJ (P = .001) but not for the STJ (P = .194). The intramedullary hindfoot arthrodesis nail was a viable treatment option in degenerative joint disease of the TTC joint. There appeared to be an advantage using systems with internal compression; however, there was no statistically significant difference after controlling for diabetes. Level III, retrospective comparative series. © The Author(s) 2015.

Proof test and fatigue crack growth modeling on 2024-T3 aluminum alloy

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Poe, C. C., Jr.; Dawicke, D. S.

1990-01-01

Pressure proof testing of aircraft fuselage structures has been suggested as a means of screening critical crack sizes and of extending their useful life. The objective of this paper is to study the proof-test concept and to model the crack-growth process on a ductile material. Simulated proof and operational fatigue life tests have been conducted on cracked panels made of 2024-T3 aluminum alloy sheet material. A fatigue crack-closure model was modified to simulate the proof test and operational fatigue cycling. Using crack-growth rate and resistance-curve data, the model was able to predict crack growth during and after the proof load. These tests and analyses indicate that the proof test increases fatigue life; but the beneficial life, after a 1.33 or 1.5 proof, was less than a few hundred cycles.

Improved High-Cycle Fatigue (HCF) Life Prediction

DTIC Science & Technology

2001-01-01

fatigue in 2024 - T351 aluminum alloy ’, Wear 221, 24-36. Appendix 6C CHARACTERIZATION OF FRETTING FATIGUE INITIATED CRACKS P.J. Golden A.F...0.8. To evaluate the effects of surface residual stresses on notch fatigue life , shot peened specimens were tested at R = -1.0 and 0.1. Data in...Behavior - Response • The undamaged fatigue test program demonstrates the sensitivity of surface effects (for different

Factors Influencing Dwell Fatigue Cracking in Notches of Powder Metallurgy Superalloys

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Telesman, J.; Ghosn, L.; Garg, A.; Gayda, J.

2011-01-01

The influences of heat treatment and cyclic dwells on the notch fatigue resistance of powder metallurgy disk superalloys were investigated for low solvus high refractory (LSHR) and ME3 disk alloys. Disks were processed to produce material conditions with varied microstructures and associated mechanical properties. Notched specimens were first subjected to baseline dwell fatigue cycles having a dwell at maximum load, as well as tensile, stress relaxation, creep rupture, and dwell fatigue crack growth tests at 704 C. Several material heat treatments displayed a bimodal distribution of fatigue life with the lives varying by two orders-of-magnitude, while others had more consistent fatigue lives. This response was compared to other mechanical properties, in search of correlations. The wide scatter in baseline dwell fatigue life was observed only for material conditions resistant to stress relaxation. For selected materials and conditions, additional tests were then performed with the dwells shifted in part or in total to minimum tensile load. The tests performed with dwells at minimum load exhibited lower fatigue lives than max dwell tests, and also exhibited early crack initiation and a substantial increase in the number of initiation sites. These results could be explained in part by modeling evolution of peak stresses in the notch with continued dwell fatigue cycling. Fatigue-environment interactions were determined to limit life for the fatigue cycles with dwells.

The influence of cyclic shear fatigue on the bracket-adhesive-enamel complex: an in vitro study.

PubMed

Daratsianos, Nikolaos; Musabegovic, Ena; Reimann, Susanne; Grüner, Manfred; Jäger, Andreas; Bourauel, Christoph

2013-05-01

To describe the effect of fatigue on the strength of the bracket-adhesive-enamel complex and characterize the fatigue behavior of the materials tested. Upper central incisor brackets (Discovery(®), Dentaurum) were bonded with a light-curing (Transbond XT™, 3M Unitek) and a chemically-curing adhesive (Concise™, 3M Unitek) on bovine teeth embedded in cylindrical resign bases and stored in water at 37(±2)°C for 24 (±2)h. The first 15 specimens were tested with a universal testing machine ZMART.PRO(®) (Zwick GmbH & Co. KG, Ulm, Germany) for ultimate shear bond strength according to the DIN-13990-2-standard. The remaining three groups of 20 specimens underwent fatigue staircase testing of 100, 1000 and 3000 cycles at 1Hz with a self-made testing machine. The survived specimens were subjected to shear strength testing. The fatigued specimens showed decreased shear strength with both adhesives at all cycle levels. The shear strength after fatigue for 100, 1000 and 3000 cycles was in the Concise™-groups 34.8%, 59.0%, 47.3% and in the Transbond™ XT-groups 33.6%, 23.1%, 27.3% relative to the ultimate shear strength. The fatigue life of the Concise™-groups decreased with increasing stress and Transbond™ XT showed lower fatigue ratio with no obvious trend. The specimens bonded with Transbond™ XT showed typically favorable fracture modes in contrary to Concise™. Fatigue of the bracket-adhesive-enamel complex decreased its shear strength. The staircase method can provide a standardized experimental protocol for fatigue studies, however testing at various cycle numbers is recommended. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Experimental Study on Fatigue Performance of Foamed Lightweight Soil

NASA Astrophysics Data System (ADS)

Qiu, Youqiang; Yang, Ping; Li, Yongliang; Zhang, Liujun

2017-12-01

In order to study fatigue performance of foamed lightweight soil and forecast its fatigue life in the supporting project, on the base of preliminary tests, beam fatigue tests on foamed lightweight soil is conducted by using UTM-100 test system. Based on Weibull distribution and lognormal distribution, using the mathematical statistics method, fatigue equations of foamed lightweight soil are obtained. At the same time, according to the traffic load on real road surface of the supporting project, fatigue life of formed lightweight soil is analyzed and compared with the cumulative equivalent axle loads during the design period of the pavement. The results show that even the fatigue life of foamed lightweight soil has discrete property, the linear relationship between logarithmic fatigue life and stress ratio still performs well. Especially, the fatigue life of Weibull distribution is more close to that derived from the lognormal distribution, in the instance of 50% guarantee ratio. In addition, the results demonstrated that foamed lightweight soil as subgrade filler has good anti-fatigue performance, which can be further adopted by other projects in the similar research domain.

Bithermal fatigue: A simplified alternative to thermomechanical fatigue

NASA Technical Reports Server (NTRS)

Verrilli, Michael J.

1988-01-01

A bithermal fatigue test technique was proposed as a simplified alternative to the thermomechanical fatigue test. Both the thermomechanical cycle and the bithermal technique can be used to study nonisothermal fatigue behavior. The difference between the two cycles is that in a conventional thermomechanical fatigue cycle the temperature is continuously varied concurrently with the applied mechanical strains, but in the bithermal fatigue cycle the specimen is held at zero load during the temperature excursions and all the loads are applied at the two extreme temperatures of the cycle. Experimentally, the bithermal fatigue test technique offers advantages such as ease in synchronizing the temperature and mechanical strain waveforms, in minimizing temperature gradients in the specimen gauge length, and in reducing and interpreting thermal fatigue such as the influence of alternate high and low temperatures on the cyclic stress-strain response characteristics, the effects of thermal state, and the possibility of introducing high- and low-temperature deformation mechanisms within the same cycle. The bithermal technique was used to study nonisothermal fatigue behavior of alloys such as single-crystal PWA 1480, single-crystal Rene N4, cast B1900+Hf, and wrought Haynes 188.

Identification marking by means of laser peening

DOEpatents

Hackel, Lloyd A.; Dane, C. Brent; Harris, Fritz

2002-01-01

The invention is a method and apparatus for marking components by inducing a shock wave on the surface that results in an indented (strained) layer and a residual compressive stress in the surface layer. One embodiment of the laser peenmarking system rapidly imprints, with single laser pulses, a complete identification code or three-dimensional pattern and leaves the surface in a state of deep residual compressive stress. A state of compressive stress in parts made of metal or other materials is highly desirable to make them resistant to fatigue failure and stress corrosion cracking. This process employs a laser peening system and beam spatial modulation hardware or imaging technology that can be setup to impress full three dimensional patterns into metal surfaces at the pulse rate of the laser, a rate that is at least an order of magnitude faster than competing marking technologies.

Corrosion fatigue in nitrocarburized quenched and tempered steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karim Khani, M.; Dengel, D.

1996-05-01

In order to investigate the fatigue strength and fracture mechanism of salt bath nitrocarburized steels, specimens of the steels SAE 4135 and SAE 4140, in a quenched and tempered state, and additionally in a salt bath nitrocarburized and oxidizing cooled state as well as in a polished (after the oxidizing cooling) and renewed oxidized state, were subjected to comparative rotating bending fatigue tests in inert oil and 5 pct NaCl solution. In addition, some of the quenched and tempered specimens of SAE 4135 material were provided with an approximately 50-{mu}m-thick electroless Ni-P layer, in order to compare corrosion fatigue behaviormore » between the Ni-P layer and the nitride layers. Long-life corrosion fatigue tests of SAE 4135 material were carried out under small stresses in the long-life range up to 10{sup 8} cycles with a test frequency of 100 Hz. Fatigue tests of SAE 4140 material were carried out in the range of finite life (low-cycle range) with a test frequency of 13 Hz. The results show that the 5 pct NaCl environment drastically reduced fatigue life, but nitrocarburizing plus oxidation treatment was found to improve the corrosion fatigue life over that of untreated and Ni-P coated specimens. The role of inclusions in initiating fatigue cracks was investigated. It was found that under corrosion fatigue conditions, the fatigue cracks started at cavities along the interfaces of MnS inclusions and matrix in the case of quenched and tempered specimens. The nitrocarburized specimens, however, showed a superposition of pitting corrosion and corrosion fatigue in which pores and nonmetallic inclusions in the compound layer play a predominant role concerning the formation of pits in the substrate.« less

Investigation of fatigue failure in bituminous base mixes.

DOT National Transportation Integrated Search

1980-01-01

A correlation between the results obtained with the fatigue test and those from the indirect tensile test on two base mixes was attempted in anticipation of the possible use of the latter test to design base mixes for maximum fatigue life. Two base m...

Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

NASA Technical Reports Server (NTRS)

Jones, David J.; Kurath, Peter

1988-01-01

Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.

Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life

NASA Technical Reports Server (NTRS)

Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.

2008-01-01

Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.

Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life

NASA Technical Reports Server (NTRS)

Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.

2012-01-01

Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.

Cognitive and Physical Fatigue Tasks Enhance Pain, Cognitive Fatigue and Physical Fatigue in People with Fibromyalgia

PubMed Central

Dailey, Dana L; Keffala, Valerie J; Sluka, Kathleen A

2014-01-01

Objective Fibromyalgia is a condition characterized by chronic widespread muscle pain and fatigue. The primary objective of this study was to determine if pain, perceived cognitive fatigue, and perceived physical fatigue were enhanced in participants with fibromyalgia compared to healthy controls during a cognitive fatigue task, a physical fatigue task and a dual fatigue task. Methods Twenty four people with fibromyalgia and 33 healthy controls completed pain, fatigue and function measures. A cognitive fatigue task (Controlled Oral Word Association Test) and physical fatigue task (Valpar peg test) were done individually and combined for a dual fatigue task. Resting pain, perceived cognitive fatigue and perceived physical fatigue were assessed during each task using visual analogue scales. Function was assessed with shoulder range of motion and grip. Results People with fibromyalgia had significantly higher increases in pain, cognitive fatigue and physical fatigue when compared to healthy controls after completion of a cognitive fatigue task, a physical fatigue task, or a dual fatigue task (p<0.01). People with fibromyalgia performed equivalently on measures of physical performance and cognitive performance on the physical and cognitive fatigue tasks, respectively. Conclusions These data show that people with fibromyalgia show larger increases in pain, perceived cognitive fatigue and perceived physical fatigue to both cognitive and physical fatigue tasks compared to healthy controls. The increases in pain and fatigue during cognitive and physical fatigue tasks could influence subject participation in daily activities and rehabilitation. PMID:25074583

Laboratory Study on the Fatigue Resistance of Asphaltic Concrete Containing Titanium Dioxide

NASA Astrophysics Data System (ADS)

Buhari, Rosnawati; Ezree Abdullah, Mohd; Khairul Ahmad, Mohd; Azhar Tajudin, Saiful; Khatijah Abu Bakar, Siti

2018-03-01

This study aims to evaluate the fatigue performance of modified asphalt mixture using Indirect Tensile Fatigue Test. Titanium Dioxide (TiO2) powder in a form of rutile was used for producing asphalt concrete with lower mixing and compaction temperature compared to conventional hot mix asphalt without reducing its physical and mechanical also resistance to fatigue. The characteristic of the asphalt and modified asphalt was evaluated using penetration test, softening test and rotational viscosity test. Titanium dioxide of 2%, 4%, 6%, 8% and 10% by weight of asphalt has been incorporated into unaged 80/100 asphalt mix in order to improvise its performance and to fulfill the objectives of this experimental study. As a result, TiO2 as an additive is potential to decrease the penetration and increasing the softening point of the asphalt. In terms of fatigue performance testing, addition TiO2 additive does help in improving the fatigue properties as it shows greater result than the control asphalt. In conclusion, TiO2 is great in improving fatigue properties.

High temperature, low cycle fatigue of copper-base alloys in argon. Part 3: Zirconium-copper; thermal-mechanical strain cycling, hold-time and notch fatigue results

NASA Technical Reports Server (NTRS)

Conway, J. B.; Stentz, R. H.; Berling, J. T.

1973-01-01

The low-cycle fatigue characteristics of smooth bar and notched bar specimens (hourglass shape) of zirconium-copper, 1/2 Hard, material (R-2 Series) were evaluated at room temperature in axial strain control. Over the fatigue life range from about 300 to 3000 cycles the ratio of fatigue life for smooth bar to fatigue life for notched bar remained constant at a value of about 6.0. Some additional hold-time data for the R-2 alloy tested in argon at 538 C are reported. An analysis of the relaxation data obtained in these hold-time tests is also reported and it is shown that these data yield a fairly consistent correlation in terms of instantaneous stress rate divided by instantaneous stress. Two thermal-mechanical strain cycling tests were also performed using a cyclic frequency of 4.5 cycles per hour and a temperature cycling interval from 260 to 538 C. The fatigue life values in these tests were noticeably lower than that observed in isothermal tests at 538 C.

Review of specimen heating in mechanical tests at cryogenic temperatures

NASA Astrophysics Data System (ADS)

Ogata, T.; Yuri, T.; Ono, Y.

2014-01-01

At cryogenic temperatures near 4 K, a discontinuous deformation produces a large amount of specimen temperature rise that might bring significant changes in mechanical properties. The authors measured the specimen heating in tensile tests, fatigue test, and other tests in liquid helium for stainless steels and other materials. In this paper, we have measured the specimen temperature in high-cycle and low-cycle fatigue tests for stainless steels at various frequencies and stress levels and evaluated the testing conditions to keep the specimen at a specified temperature. We proposed maximum frequency in load-controlled fatigue tests for specified loading variables and a maximum strain rate in strain-controlled fatigue tests.

Rolling-element fatigue life with two synthetic cycloaliphatic traction fluids

NASA Technical Reports Server (NTRS)

Loewenthal, S. H.; Parker, R. J.

1976-01-01

The life potential of two synthetic cycloaliphatic hydrocarbon traction fluids in rolling element fatigue was evaluated in a five ball fatigue tester. Life comparisons with a MIL-L-23699 qualified tetraester oil showed that the traction test oils had good fatigue life performance, comparable to that of the tetraester oil. No statistically significant life differences between the traction fluids and the tetraester oil were exhibited under the accelerated fatigue test conditions. Erratic operating behavior was occasionally encountered during tests with the antiwear additive containing traction fluid for reasons thought to be related to excessive chemical activity under high contact pressure. This behavior occasionally resulted in premature test termination due to excessive surface distress and overheating.

Effects of Total SAT® Test Time on Performance and Fatigue. Research Notes. RN-37

ERIC Educational Resources Information Center

Ackerman, Phillip L.; Kanfer, Ruth; Wolman, Stacey D.

2005-01-01

The current study was designed to examine performance effects and fatigue effects associated with different total SAT testing times. In addition, the researchers examined personality, motivation, and other determinants of individual differences in examinee fatigue before, during, and after testing.

Ultrasonic Fatigue Endurance of Thin Carbon Fiber Sheets

NASA Astrophysics Data System (ADS)

Domínguez Almaraz, Gonzalo M.; Ruiz Vilchez, Julio A.; Dominguez, Aymeric; Meyer, Yann

2016-04-01

Ultrasonic fatigue tests were carried out on thin carbon fiber sheets (0.3 mm of thickness) to determine the fatigue endurance under very high-frequency loading (20 kHz). This material, called the gas diffusion layer (GDL), plays a major role in the overall performances of proton exchange membrane fuel cells (PEMFCs). The study of its physical-chemical properties is an on-going subject in the literature; nevertheless, no knowledge is available concerning the high-frequency fatigue endurance. A principal difficulty in carrying out ultrasonic fatigue tests on this material was to determine the dimensions of testing specimen to fit the resonance condition. This aspect was solved by modal numerical simulation: The testing specimen has been a combination of a low-strength steel frame (to facilitate the attachment to the ultrasonic machine and to increase the mass of the specimen), and the carbon fiber hourglass-shape profile. Under resonance condition, a stationary elastic wave is generated along the specimen that induces high stress at the neck section and high displacements at the ends. Results show that fatigue life was close to 3 × 108 cycles when the high Von Misses stress at the neck section was 170 MPa, whereas fatigue life attains the 4.5 × 109 cycles when stress decreases to 117 MPa. Crack initiation and propagation were analyzed, and conclusions were drawn concerning the fatigue endurance of these fiber carbon sheets under ultrasonic fatigue testing.

Fatigue analysis and testing of wind turbine blades

NASA Astrophysics Data System (ADS)

Greaves, Peter Robert

This thesis focuses on fatigue analysis and testing of large, multi MW wind turbine blades. The blades are one of the most expensive components of a wind turbine, and their mass has cost implications for the hub, nacelle, tower and foundations of the turbine so it is important that they are not unnecessarily strong. Fatigue is often an important design driver, but fatigue of composites is poorly understood and so large safety factors are often applied to the loads. This has implications for the weight of the blade. Full scale fatigue testing of blades is required by the design standards, and provides manufacturers with confidence that the blade will be able to survive its service life. This testing is usually performed by resonating the blade in the flapwise and edgewise directions separately, but in service these two loads occur at the same time.. A fatigue testing method developed at Narec (the National Renewable Energy Centre) in the UK in which the flapwise and edgewise directions are excited simultaneously has been evaluated by comparing the Palmgren-Miner damage sum around the blade cross section after testing with the damage distribution caused by the service life. A method to obtain the resonant test configuration that will result in the optimum mode shapes for the flapwise and edgewise directions was then developed, and simulation software was designed to allow the blade test to be simulated so that realistic comparisons between the damage distributions after different test types could be obtained. During the course of this work the shortcomings with conventional fatigue analysis methods became apparent, and a novel method of fatigue analysis based on multi-continuum theory and the kinetic theory of fracture was developed. This method was benchmarked using physical test data from the OPTIDAT database and was applied to the analysis of a complete blade. A full scale fatigue test method based on this new analysis approach is also discussed..

Resistance Spot Welding Characteristics and High Cycle Fatigue Behavior of DP 780 Steel Sheet

NASA Astrophysics Data System (ADS)

Pal, Tapan Kumar; Bhowmick, Kaushik

2012-02-01

Resistance spot welding characteristics of DP 780 steel was investigated using peel test, microhardness test, tensile shear test, and fatigue test. Tensile shear test provides better spot weld quality than conventional peel test and hardness is not a good indicator of the susceptibility to interfacial fracture. The results of high-cycle fatigue behavior of spot welded DP 780 steel under two different parameters show that at high load low cycle range a significant difference in the S- N curve and almost similar fatigue behavior of spot welds at low load high cycle range are obtained. However, when applied load was converted to stress intensity factor, the difference in the fatigue behavior between welds diminished. Furthermore, a transition in fracture mode, i.e., interfacial and plug and hole-type at about 50% of yield load is observed.

Synergistic Effects of Temperature, Oxidation and Stress Level on Fatigue Damage Evolution and Lifetime Prediction of Cross-Ply SiC/CAS Ceramic-Matrix Composites Through Hysteresis-Based Parameters

NASA Astrophysics Data System (ADS)

Li, Longbiao

2017-12-01

The damage development and cyclic fatigue lifetime of cross-ply SiC/CAS ceramic-matrix composites have been investigated at different testing temperatures in air atmosphere. The relationships between the fatigue hysteresis-based damage parameters, i.e., fatigue hysteresis dissipated energy, fatigue hysteresis modulus and fatigue peak strain and the damage mechanisms of matrix multicracking, fiber/matrix interface debonding, interface sliding and fibers failure, have been established. With the increase in the cycle number, the evolution of the fatigue hysteresis modulus, fatigue peak strain and fatigue hysteresis dissipated energy depends upon the fatigue peak stress levels, interface and fibers oxidation and testing temperature. The fatigue life S-N curves of cross-ply SiC/CAS composite at room and elevated temperatures have been predicted, and the fatigue limit stresses at room temperature, 750 and 850 °C, are 50, 36 and 30% of the tensile strength, respectively.

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2014 CFR

2014-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2012 CFR

2012-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2013 CFR

2013-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

14 CFR 35.37 - Fatigue limits and evaluation.

Code of Federal Regulations, 2011 CFR

2011-01-01

... AIRWORTHINESS STANDARDS: PROPELLERS Tests and Inspections § 35.37 Fatigue limits and evaluation. This section does not apply to fixed-pitch wood propellers of conventional design. (a) Fatigue limits must be established by tests, or analysis based on tests, for propeller: (1) Hubs. (2) Blades. (3) Blade retention...

Corrosion fatigue in nitrocarburized quenched and tempered steels

NASA Astrophysics Data System (ADS)

Khani, M. Karim; Dengel, D.

1996-05-01

In order to investigate the fatigue strength and fracture mechanism of salt bath nitrocarburized steels, specimens of the steels SAE 4135 and SAE 4140, in a quenched and tempered state, and additionally in a salt bath nitrocarburized and oxidizing cooled state as well as in a polished (after the oxidizing cooling) and renewed oxidized state, were subjected to comparative rotating bending fatigue tests in inert oil and 5 pct NaCl solution. In addition, some of the quenched and tempered specimens of SAE 4135 material were provided with an approximately 50-μm-thick electroless Ni-P layer, in order to compare corrosion fatigue behavior between the Ni-P layer and the nitride layers. Long-life corrosion fatigue tests of SAE 4135 material were carried out under small stresses in the long-life range up to 108 cycles with a test frequency of 100 Hz. Fatigue tests of SAE 4140 material were carried out in the range of finite life (low-cycle range) with a test frequency of 13 Hz. The results show that the 5 pct NaCl environment drastically reduced fatigue life, but nitrocarburizing plus oxidation treatment was found to improve the corrosion fatigue life over that of untreated and Ni-P coated specimens. The beneficial effect of nitrocarburizing followed by oxidation treatment on cor-rosion fatigue life results from the protection rendered by the compound layer by means of a well-sealed oxide layer, whereby the pores present in the compound layer fill up with oxides. The role of inclusions in initiating fatigue cracks was investigated. It was found that under corrosion fatigue conditions, the fatigue cracks started at cavities along the interfaces of MnS inclusions and matrix in the case of quenched and tempered specimens. The nitrocarburized specimens, however, showed a superposition of pitting corrosion and corrosion fatigue in which pores and nonmetallic inclusions in the compound layer play a predominant role concerning the formation of pits in the substrate.

Characterization of hydroxyapatite whisker reinforced composites and scaffolds for mechanical and biological function in orthopaedic and spinal implants

NASA Astrophysics Data System (ADS)

Conrad, Timothy L.

The overall objective of this study was to investigate the mechanical and biological properties of HA whisker reinforced polyaryletherketone (PAEK) composites and scaffolds which are key to clinical translation for orthopedic and spinal implants. The fatigue behavior of polyetherketoneketone (PEKK) reinforced with 0, 20, and 40 vol% hydroxyapatite (HA) was investigated in four-point bending fatigue. The fatigue life decreased with increasing HA reinforcement. However, PEKK reinforced with 40 vol% HA whiskers exhibited a fatigue life greater than 2.106 cycles at 40 MPa. Moreover, HA whisker reinforcement resulted in decreased creep deformation and minimal modulus degradation. The effects of the mold temperature and polyetheretherketone (PEEK) powder were investigated on the mechanical properties and crystallinity of HA whisker reinforced PEEK scaffolds prepared using compression molding and porogen leaching. The mechanical properties of the scaffolds increased while the PEEK crystallinity decreased, with increasing mold temperature and suggested an optimal mold temperature of 370--375°C for PEEK scaffolds comprising of 75% porosity and 20 vol% HA whisker reinforcement, regardless of the PEEK powder size. The effects of the porogen morphology on the architecture, mechanical properties, and permeability of HA whisker reinforced PEEK scaffolds were investigated in 75--90% porous scaffolds. HA whisker reinforced PEEK scaffolds prepared with an ellipsoidal porogen exhibited a greater permeability than scaffolds prepared with a cubic porogen. The compressive modulus, yield strength, and yield strain were not affected by the porogen morphology. The effects of HA reinforcement morphology and content was investigated on the behavior of primary osteoblasts on dense HA reinforced PEEK substrates in vitro. At day 7, the number of osteoblasts attached to PEEK substrate surfaces increased with increasing HA content and for HA whiskers compared to equiaxed HA powder reinforcement. This suggests that the HA reinforcement content morphology can promote cellular attachment and proliferation at early time points.

Fatigue crack growth in an aluminum alloy-fractographic study

NASA Astrophysics Data System (ADS)

Salam, I.; Muhammad, W.; Ejaz, N.

2016-08-01

A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.

Statistical characterization of the fatigue behavior of composite lamina

NASA Technical Reports Server (NTRS)

Yang, J. N.; Jones, D. L.

1979-01-01

A theoretical model was developed to predict statistically the effects of constant and variable amplitude fatigue loadings on the residual strength and fatigue life of composite lamina. The parameters in the model were established from the results of a series of static tensile tests and a fatigue scan and a number of verification tests were performed. Abstracts for two other papers on the effect of load sequence on the statistical fatigue of composites are also presented.

The neural effects of positively and negatively re-experiencing mental fatigue sensation: a magnetoencephalography study.

PubMed

Ishii, Akira; Ishizuka, Takuya; Muta, Yuki; Tanaka, Masaaki; Yamano, Emi; Watanabe, Yasuyoshi

2018-06-01

Fatigue sensation is an essential biological alarm that urges us to take rest to avoid disrupting homeostasis and thus plays an important role in maintaining well-being. However, there are situations in which the anticipation of unpleasant fatigue sensation undesirably reduces motivation for activity. The aim of this study was to examine whether thinking positively about the fatigue sensation would increase motivation to accomplish the workload. Fourteen healthy male volunteers participated in this study and performed a two-back test for 30 min to induce mental fatigue sensation. After their subjective level of fatigue had recovered to the baseline level, they re-experienced the fatigue sensation experienced in the two-back test positively, negatively, and without any modification (i.e., re-experienced the fatigue sensation as it was). The level of motivation to perform another two-back test they felt during the re-experiencing was assessed. The neural activity related to the re-experiencing was recorded using magnetoencephalography. The level of the motivation to perform another two-back test was increased by positively re-experiencing the fatigue sensation. The increase in delta band power in Brodmann area 7 was positively associated with the increase in motivation. These results show that positive thinking about fatigue sensation can enhance motivation and suggest that this enhanced motivation may have some effects on visual attention system.

Characterization of Transformation-Induced Defects in Nickel Titanium Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Bowers, Matthew L.

Shape memory alloys have remarkable strain recovery properties that make them ideal candidates for many applications that include devices in the automotive, aerospace, medical, and MEMS industries. Although these materials are widely used today, their performance is hindered by poor dimensional stability resulting from cyclic degradation of the martensitic transformation behavior. This functional fatigue results in decreased work output and cyclic accumulation of permanent strain. To date, few studies have taken a fundamental approach to investigating the interaction between plasticity and martensite growth and propagation, which is vitally important to mitigating functional fatigue in future alloy development. The current work focuses on understanding the interplay of these deformation mechanisms in NiTi-based shape memory alloys under a variety of different thermomechanical test conditions. Micron-scale compression testing of NiTi shape memory alloy single crystals is undertaken in an effort to probe the mechanism of austenite dislocation generation. Mechanical testing is paired with post mortem defect analysis via diffraction contrast scanning transmission electron microscopy (STEM). Accompanied by micromechanics-based modeling of local stresses surrounding a martensite plate, these results demonstrate that the previously existing martensite and resulting austenite dislocation substructure are intimately related. A mechanism of transformation-induced dislocation generation is described in detail. A study of pure and load-biased thermal cycling of bulk polycrystalline NiTi is done for comparison of the transformation behavior and resultant defects to the stress-induced case. Post mortem and in situ STEM characterization demonstrate unique defect configurations in this test mode and STEM-based orientation mapping reveals local crystal rotation with increasing thermal cycles. Changes in both martensite and austenite microstructures are explored. The results for several different thermomechanical histories are discussed and a new mechanism of austenite grain refinement is proposed with support from ab initio calculations and crystallographic theory.

Effects of sour crude oil on fatigue properties of steel plates for shipbuilding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouchi, H.; Kobayashi, J.; Ishikawa, T.

1994-12-31

The concentration of diffusible hydrogen introduced into steel was measured, and fatigue crack growth tests and fatigue life tests were carried out in sour crude oil containing a high concentration of hydrogen sulfide and under electrolytic hydrogen-charging conditions in neutral solution, using a high strength steel produced by the thermo-mechanical control process (TMCP) and a mild steel which are steels for hull plates. Comparison of the results demonstrated that a very small amount of hydrogen such as that introduced into steel from sour crude oil under atmospheric pressure accelerated the fatigue crack growth in the high {Delta}K regime and shortenedmore » the fatigue life in the high stress range region, but did not shorten the fatigue life in the low stress region. The electrolytic hydrogen-charging condition appeared to be appropriate as a fatigue-crack-growth test environment to simulate sour crude oil. The deterioration of fatigue characteristics of the TMCP high strength steel was similar with that of the mild steel.« less

Fretting Fatigue Experiment and Analysis of AlSi9Cu2Mg Alloy

PubMed Central

Wang, Jun; Xu, Hong; Su, Tiexiong; Zhang, Yi; Guo, Zhen; Mao, Huping; Zhang, Yangang

2016-01-01

An investigation was carried out in order to study the fretting fatigue behavior of an AlSi9Cu2Mg aluminum alloy. The fretting fatigue tests of AlSi9Cu2Mg were performed using a specially designed testing machine. The failure mechanism of fretting fatigue was explored by studying the fracture surfaces, fretting scars, fretting debris, and micro-hardness of fretting fatigue specimens using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and micro Vickers hardness test techniques. The experimental results show that the fretting fatigue limit (42 MPa) is significantly reduced to approximately 47% of the plain fatigue limit (89 MPa) under 62.5 MPa contact pressure. Furthermore, the fretting fatigue life decreases with increasing alternating stress and increasing contact pressure. The examination results suggest that the stress concentrates induced by oxidation-assisted wear on the contact interface led to the earlier initiation and propagation of crack under the fretting condition. PMID:28774103

Fretting Fatigue Experiment and Analysis of AlSi9Cu2Mg Alloy.

PubMed

Wang, Jun; Xu, Hong; Su, Tiexiong; Zhang, Yi; Guo, Zhen; Mao, Huping; Zhang, Yangang

2016-12-05

An investigation was carried out in order to study the fretting fatigue behavior of an AlSi9Cu2Mg aluminum alloy. The fretting fatigue tests of AlSi9Cu2Mg were performed using a specially designed testing machine. The failure mechanism of fretting fatigue was explored by studying the fracture surfaces, fretting scars, fretting debris, and micro-hardness of fretting fatigue specimens using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and micro Vickers hardness test techniques. The experimental results show that the fretting fatigue limit (42 MPa) is significantly reduced to approximately 47% of the plain fatigue limit (89 MPa) under 62.5 MPa contact pressure. Furthermore, the fretting fatigue life decreases with increasing alternating stress and increasing contact pressure. The examination results suggest that the stress concentrates induced by oxidation-assisted wear on the contact interface led to the earlier initiation and propagation of crack under the fretting condition.

The fatigue experience for women with human immunodeficiency virus.

PubMed

Lee, K A; Portillo, C J; Miramontes, H

1999-01-01

To examine fatigue as a symptom experienced by women with human immunodeficiency virus (HIV). A convenience sample of 100 women with HIV. Independent sample t-tests were used to test for mean differences in fatigue related to variables in the women's sociocultural and home environment (ethnicity, employment, marital status, and parenting). Pearson product moment correlations were used to examine significant relationships between fatigue and physiologic variables (age, CD4 cell count, and sleep). Lower CD4 cell counts were related to more daytime sleep, higher evening fatigue, and higher morning fatigue. Morning fatigue was related to duration of wake episodes during the night, napping, and perception of sleep disturbance during the past week. The number of awakenings during the first night predicted the severity of fatigue the next evening. To understand the fatigue experienced by women with HIV, researchers and clinicians must focus on the relative contributions of sociocultural, home, and physiologic environments within which these women live. Additional research is ongoing to identify the strategies these women use to manage daily activities such that gender-relevant and culturally relevant interventions for alleviating fatigue can be tested in women with a variety of chronic illnesses, including HIV and acquired immune deficiency syndrome.

Thermomechanical and bithermal fatigue behavior of cast B1900 + Hf and wrought Haynes 188

NASA Technical Reports Server (NTRS)

Halford, G. R.; Verrilli, M. J.; Kalluri, S.; Ritzert, F. J.; Duckert, R. E.; Holland, F. A.

1992-01-01

A thermomechanical fatigue (TMF) high-temperature life prediction method has been evaluated using the experimental data. Bithermal fatigue (BTF), bithermal creep-fatigue (BTC-F), and TMF experiments were performed using two aerospace structural alloys, cast B1900 + Hf and wrought Haynes 188. The method which is based on the total strain version of strain range partitioning and unified cyclic constitutive modeling requires, as an input, information on the flow and failure behavior of the material of interest. Bithermal temperatures of 483 and 871 C were used for the cast B1900 + Hf nickel-base alloy and 316 and 760 C for the wrought Haynes 188 cobalt-base alloy. Maximum and minimum temperatures were also used in both TMF and BTF tests. Comparisons were made between the results of these tests and isothermal tensile and fatigue test data obtained previously. Qualitative correlations were observed between tensile and isothermal fatigue tests.

A proposed USAF fatigue evaluation program based upon recent systems experience

NASA Technical Reports Server (NTRS)

Haviland, G. P.; Purkey, G. F.

1972-01-01

The United States Air Force has published a document entitled Aircraft Structural Integrity Program. One phase of the program is concerned with the fatigue life certification of all types of military aircraft. The document describes the criteria, analyses, and tests that are necessary in order to satisfy the USAF fatigue life requirement. Some recent and valid criticism has been directed toward the document, particularly the fatigue-life requirements contained in it. Some changes are proposed based on surveys conducted in the United States and abroad as well as some recent systems' experience. The surveys covered both military and civilian organizations. The fatigue certification case histories of selected military and commercial aircraft are presented. The design development element tests, preproduction design verification tests, and full-scale fatigue tests of each are described. A brief status report on the revisions to the MIL-A-008860 series specifications is included.

Biomechanical modelling and evaluation of construction jobs for performance improvement.

PubMed

Parida, Ratri; Ray, Pradip Kumar

2012-01-01

Occupational risk factors, such as awkward posture, repetition, lack of rest, insufficient illumination and heavy workload related to construction-related MMH activities may cause musculoskeletal disorders and poor performance of the workers, ergonomic design of construction worksystems was a critical need for improving their health and safety wherein a dynamic biomechanical models were required to be empirically developed and tested at a construction site of Tata Steel, the largest steel making company of India in private sector. In this study, a comprehensive framework is proposed for biomechanical evaluation of shovelling and grinding under diverse work environments. The benefit of such an analysis lies in its usefulness in setting guidelines for designing such jobs with minimization of risks of musculoskeletal disorders (MSDs) and enhancing correct methods of carrying out the jobs leading to reduced fatigue and physical stress. Data based on direct observations and videography were collected for the shovellers and grinders over a number of workcycles. Compressive forces and moments for a number of segments and joints are computed with respect to joint flexion and extension. The results indicate that moments and compressive forces at L5/S1 link are significant for shovellers while moments at elbow and wrist are significant for grinders.

Novel Electrochemical Test Bench for Evaluating the Functional Fatigue Life of Biomedical Alloys

NASA Astrophysics Data System (ADS)

Ijaz, M. F.; Dubinskiy, S.; Zhukova, Y.; Korobkova, A.; Pustov, Y.; Brailovski, V.; Prokoshkin, S.

2017-08-01

The aim of the present work was first to develop and validate a test bench that simulates the in vitro conditions to which the biomedical implants will be actually subjected in vivo. For the preliminary application assessments, the strain-controlled fatigue tests of biomedically pure Ti and Ti-Nb-Zr alloy in simulated body fluid were undertaken. The in situ open-circuit potential measurements from the test bench demonstrated a strong dependence on the dynamic cycling and kind of material under testing. The results showed that during fatigue cycling, the passive oxide film formed on the surface of Ti-Nb-Zr alloy was more resistant to fatigue degradation when compared with pure Ti. The Ti-Nb-Zr alloy exhibited prolonged fatigue life when compared with pure Ti. The fractographic features of both materials were also characterized using scanning electron microscopy. The electrochemical results and the fractographic evidence confirmed that the prolonged functional fatigue life of the Ti-Nb-Zr alloy is apparently ascribable to the reversible martensitic phase transformation.

Taltirelin alleviates fatigue-like behavior in mouse models of cancer-related fatigue.

PubMed

Dougherty, John P; Wolff, Brian S; Cullen, Mary J; Saligan, Leorey N; Gershengorn, Marvin C

2017-10-01

Fatigue affects most cancer patients and has numerous potential causes, including cancer itself and cancer treatment. Cancer-related fatigue (CRF) is not relieved by rest, can decrease quality of life, and has no FDA-approved therapy. Thyrotropin-releasing hormone (TRH) has been proposed as a potential novel treatment for CRF, but its efficacy against CRF remains largely untested. Thus, we tested the TRH analog, taltirelin (TAL), in mouse models of CRF. To model fatigue, we used a mouse model of chemotherapy, a mouse model of radiation therapy, and mice bearing colon 26 carcinoma tumors. We used the treadmill fatigue test to assess fatigue-like behavior after treatment with TAL. Additionally, we used wild-type and TRH receptor knockout mice to determine which TRH receptor was necessary for the actions of TAL. Tumor-bearing mice displayed muscle wasting and all models caused fatigue-like behavior, with mice running a shorter distance in the treadmill fatigue test than controls. TAL reversed fatigue-like behavior in all three models and the mouse TRH 1 receptor was necessary for the effects of TAL. These data suggest that TAL may be useful in alleviating fatigue in all cancer patients and provide further support for evaluating TAL as a potential therapy for CRF in humans. Published by Elsevier Ltd.

The effect of matrix mechanical properties on (0)8 unidirectional SiC/Ti composite fatigue resistance

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Gayda, J.; Lerch, B. A.; Halford, G. R.

1991-01-01

The relationship between constituent and MMC properties in fatigue loading is investigated with low-cycle fatigue-resistance testing of an alloy Ti-15-3 matrix reinforced with SiC SCS-6 fibers. The fabrication of the composite is described, and specimens are generated that are weak and ductile (WD), strong and moderately ductile (SM), or strong and brittle (SB). Strain is measured during MMC fatigue tests at a constant load amplitude with a load-controlled waveform and during matrix-alloy fatigue tests at a constant strain amplitude using a strain-controlled waveform. The fatigue resistance of the (0)8 SiC/Ti-15-3 composite is found to be slightly influenced by matrix mechanical properties, and the composite- and matrix-alloy fatigue lives are not correlated. This finding is suggested to relate to the different crack-initiation and -growth processes in MMCs and matrix alloys.

Design of Fatigue Resistant Heusler-strengthened PdTi-based Shape Memory Alloys for Biomedical Applications

NASA Astrophysics Data System (ADS)

Frankel, Dana J.

The development of non-surgical transcatheter aortic valve implantation (TAVI) techniques, which utilize collapsible artificial heart valves with shape memory alloy (SMA)-based frames, pushes performance requirements for biomedical SMAs beyond those for well-established vascular stent applications. Fatigue life for these devices must extend into the ultra-high cycle fatigue (UHCF) regime (>600M cycles) with zero probability of failure predicted at applied strain levels. High rates of Ni-hypersensitivity raise biocompatibility concerns, driving the development of low-Ni and Ni-free SMAs. This work focuses on the development of biocompatible, precipitation-strengthened, fatigue-resistant PdTi-based SMAs for biomedical applications. Functional and structural fatigue are both manifestations of cyclic instability resulting in accumulation of slip and eventual structural damage. While functional fatigue is easily experimentally evaluated, structural fatigue is more difficult to measure without the proper equipment. Therefore, in this work a theoretical approach using a model well validated in steels is utilized to investigate structural fatigue behavior in NiTi in the UHCF regime, while low cycle functional fatigue is evaluated in order to monitor the core phenomena of the cyclic instability. Results from fatigue simulations modeling crack nucleation at non-metallic inclusions in commercial NiTi underscore the importance of increasing yield strength for UHCF performance. Controlled precipitation of nanoscale, low-misfit, L21 Heusler aluminides can provide effective strengthening. Phase relations, precipitation kinetics, transformation temperature, transformation strain, cyclic stability, and mechanical properties are characterized in both Ni-free (Pd,Fe)(Ti,Al) and low-Ni high-strength "hybrid" (Pd,Ni)(Ti,Zr,Al) systems. Atom probe tomography is employed to measure phase compositions and particle sizes used to calibrate LSW models for coarsening kinetics and Gibbs-Thompson models for composition trajectories for systems under evolving unstable equilibrium. Mechanical and thermal cyclic stability are investigated using compression testing and differential scanning calorimetry. Mechanical properties are characterized using room temperature and high temperature Vickers microhardness as well as nanoindentation. A superelastic Ni-free (Pd,Fe)(Ti,Al) alloy with near-ambient transformation temperatures, low hysteresis, a highly stable cyclic response, and reversible transformation strains of 3.2% was designed. Due to Pd softening, the addition of Zr is considered to improve strength in a low-Ni "hybrid" (Pd,Ni)(Ti,Zr,Al) alloy. Aging studies at 600°C result in unusually fast coarsening kinetics, while low-temperature aging studies at 500-530°C reveal the presence of a Zr-rich phase in association with the matrix and Heusler phase. A strengthening study on a nontransforming hybrid prototype shows lower than expected precipitation strengthening at 600°C but significant strengthening when aged at 500°C due to the Zr-rich phase. Transformation temperatures, transformation strain, and cyclic stability are characterized in a set of transforming hybrid prototypes.

Room Temperature and Elevated Temperature Composite Sandwich Joint Testing

NASA Technical Reports Server (NTRS)

Walker, Sandra P.

1998-01-01

Testing of composite sandwich joint elements has been completed to verify the strength capacity of joints designed to carry specified running loads representative of a high speed civil transport wing. Static tension testing at both room and an elevated temperature of 350 F and fatigue testing at room temperature were conducted to determine strength capacity, fatigue life, and failure modes. Static tension test results yielded failure loads above the design loads for the room temperature tests, confirming the ability of the joint concepts tested to carry their design loads. However, strength reductions as large as 30% were observed at the elevated test temperature, where all failure loads were below the room temperature design loads for the specific joint designs tested. Fatigue testing resulted in lower than predicted fatigue lives.

Fatigue test results of the rotating steel blades of steam turbine K-25-0.6 GEO with ion-plasma coating

NASA Astrophysics Data System (ADS)

Kachalin, G. V.; Mednikov, A. F.; Tkhabisimov, A. B.; Arkad'ev, D. A.; Temkin, S. G.; Senina, N. A.

2016-12-01

Fatigue test results of the rotating steel blades of the fourth stage of the K-25-0.6 low pressure cylinder Geo steam turbine manufactured in the Kaluga Turbine Plant (hereinafter, KTP) with the ion-plasma coating were presented. Coating formation was carried out at the National Research University (MPEI) on the Gefest vacuum pilot plant by the magnetron sputtering method. Characteristics of the obtained coating were analyzed with the use of the scientific-research equipment of the National Research University (MPEI). Fatigue tests of the rotating blades and determination of the fatigue strength of the material with the ion-plasma coating were carried out on the electrodynamic vibration machines VEDS-400A in the KTP structural laboratory. The following characteristics were obtained after tests: Ti-TiN composition, 10-11 μm thickness, 1200 HV 0.05 microhardness. Fatigue tests showed that destruction, regardless of availability or nonavailability of the coating, took place by cross-section in the root zone both on the leading and trailing edges of the blade, i.e., in the most stressed zones. It was found out that the maximum stresses during tests were revealed in the root section along the trailing edge on the blade pressure side, and the less stresses were on the leading edge. Fatigue strength of the working blades after coating formation increased by 12% minimum. Results of the fatigue tests prove the previously obtained data concerning 10-12% increase of the fatigue strength of the blade steel with the ion-plasma coating and allow claiming that the process of their formation exerts the positive influence on the fatigue characteristics of the blade materials.

Study on Determination Method of Fatigue Testing Load for Wind Turbine Blade

NASA Astrophysics Data System (ADS)

Liao, Gaohua; Wu, Jianzhong

2017-07-01

In this paper, the load calculation method of the fatigue test was studied for the wind turbine blade under uniaxial loading. The characteristics of wind load and blade equivalent load were analyzed. The fatigue property and damage theory of blade material were studied. The fatigue load for 2MW blade was calculated by Bladed, and the stress calculated by ANSYS. Goodman modified exponential function S-N curve and linear cumulative damage rule were used to calculate the fatigue load of wind turbine blades. It lays the foundation for the design and experiment of wind turbine blade fatigue loading system.