Associations of types of pain with crack-level, tooth-level and patient-level characteristics in posterior teeth with visible cracks: Findings from the National Dental Practice-Based Research Network.

PubMed

Hilton, Thomas J; Funkhouser, Ellen; Ferracane, Jack L; Gordan, Valeria V; Huff, Kevin D; Barna, Julie; Mungia, Rahma; Marker, Timothy; Gilbert, Gregg H

2018-03-01

The objective of this study was to determine which patient traits, behaviors, external tooth and/or crack characteristics correlate with the types of symptoms that teeth with visible cracks exhibit, namely pain on biting, pain due to cold stimuli, or spontaneous pain. Dentists in the National Dental Practice-Based Research Network enrolled a convenience sample of subjects each of whom had a single, vital posterior tooth with at least one observable external crack (cracked teeth); 2858 cracked teeth from 209 practitioners were enrolled. Data were collected at the patient-, tooth-, and crack-level. Generalized estimating equations were used to obtain significant (p < .05) independent odds ratios (OR) associated with teeth that were painful for 10 outcomes based on types of pain and combinations thereof. Overall, 45% of cracked teeth had one or more symptoms. Pain to cold was the most common symptom, which occurred in 37% of cracked teeth. Pain on biting (16%) and spontaneous pain (11%) were less common. Sixty-five percent of symptomatic cracked teeth had only one type of symptom, of these 78% were painful only to cold. No patient-, tooth- or crack-level characteristic was significantly associated with pain to cold alone. Positive associations for various combinations of pain symptoms were present with cracks that: (1) were on molars; (2) were in occlusion; (3) had a wear facet through enamel; (4) had caries; (5) were evident on a radiograph; (6) ran in more than one direction; (7) blocked transilluminated light; (8) connected with another crack; (9) extended onto the root; (10) extended in more than one direction; or (11) were on the distal surface. Persons who were <65 yo or who clench, grind, or press their teeth together also were more likely to have pain symptoms. Pain was less likely in teeth with stained cracks or exposed roots, or in non-Hispanic whites. Although pain to cold was the most commonly noted pain associated with symptomatic cracked teeth, no patient-, tooth- or crack-level characteristic was significantly associated with pain to cold alone. Characteristics were only associated with pain on biting and/or spontaneous pain with or without pain to cold. Although often considered the most reliable diagnosis for a cracked tooth, pain on biting is not the most common symptom of a tooth with a visible crack, but rather pain to cold. Copyright © 2017 Elsevier Ltd. All rights reserved.

Crack-closing of cement mortar beams using NiTi cold-drawn SMA short fibers

NASA Astrophysics Data System (ADS)

Choi, Eunsoo; Kim, Dong Joo; Chung, Young-Soo; Kim, Hee Sun; Jung, Chungsung

2015-01-01

In this study, crack-closing tests of mortar beams reinforced by shape memory alloy (SMA) short fibers were performed. For this purpose, NiTi SMA fibers with a diameter of 0.965 mm and a length of 30 mm were made from SMA wires of 1.0 mm diameter by cold drawing. Four types of SMA fibers were prepared, namely, straight and dog-bone-shaped fiber and the two types of fibers with paper wrapping in the middle of the fibers. The paper provides an unbonded length of 15 mm. For bending tests, six types of mortar beams with the dimensions of 40 mm × 40 mm × 160 mm (B×H×L) were prepared. The SMA fibers were placed at the bottom center of the beams along with an artificial crack of 10 mm depth and 1 mm thickness. This study investigated the influence of SMA fibers on the flexural strength of the beams from the measured force- deflection curves. After cracking, the beams were heated at the bottom by fire to activate the SMA fibers. Then, the beams recovered the deflection, and the cracks were closed. This study evaluated crack-closing capacity using the degree of crack recovery and deflection-recovery factor. The first factor is estimated from the crack-width before and after crack-closing, and the second one is obtained from the downward deflection due to loading and the upward deflection due to the closing force of the SMA fibers.

Effects of Grain Size on the Fatigue Properties in Cold-Expanded Austenitic HNSs

NASA Astrophysics Data System (ADS)

Shin, Jong-Ho; Kim, Young-Deak; Lee, Jong-Wook

2018-05-01

Cold-expanded austenitic high nitrogen steel (HNS) was subjected to investigate the effects of grain size on the stress-controlled high cycle fatigue (HCF) as well as the strain-controlled low cycle fatigue (LCF) properties. The austenitic HNSs with two different grain sizes (160 and 292 μm) were fabricated by the different hot forging strain. The fine-grained (FG) specimen exhibited longer LCF life and higher HCF limit than those of the coarse-grained (CG) specimen. Fatigue crack growth testing showed that crack propagation rate in the FG specimen was the same as that in the CG specimen, implying that crack propagation rate did not affect the discrepancy of LCF life and HCF limit between two cold-expanded HNSs. Therefore, it was estimated that superior LCF and HCF properties in the FG specimen resulted from the retardation of the fatigue crack initiation as compared with the CG specimen. Transmission electron microscopy showed that the effective grain size including twin boundaries are much finer in the FG specimen than that in the CG specimen, which can give favorable contributions to strengthening.

JSC Materials Laboratory Reproduction and Failure Analysis of Cracked Orbiter Reaction Control System Niobium Thruster Injectors

NASA Technical Reports Server (NTRS)

Castner, Willard L.; Jacobs, Jeremy B.

2006-01-01

In April 2004 a Space Shuttle Orbiter Reaction Control System (RCS) thruster was found to be cracked while undergoing a nozzle (niobium/C103 alloy) retrofit. As a failure resulting from an in-flight RCS thruster burn-through (initiated from a crack) could be catastrophic, an official Space Shuttle Program flight constraint was issued until flight safety could be adequately demonstrated. This paper describes the laboratory test program which was undertaken to reproduce the cracking in order to fully understand and bound the driving environments. The associated rationale developed to justify continued safe flight of the Orbiter RCS system is also described. The laboratory testing successfully reproduced the niobium cracking, and established specific bounding conditions necessary to cause cracking in the C103 thruster injectors. Each of the following conditions is necessary in combination together: 1) a mechanically disturbed / cold-worked free surface, 2) an externally applied sustained tensile stress near yield strength, 3) presence of fluorine-containing fluids on exposed tensile / cold-worked free surfaces, and 4) sustained exposure to temperatures greater than 400 F. As a result of this work, it was concluded that fluorine-containing materials (e.g. HF acid, Krytox , Brayco etc.) should be carefully controlled or altogether eliminated during processing of niobium and its alloys.

Sleeve expansion of bolt holes in railroad rail. volume III - field experiment results

DOT National Transportation Integrated Search

1998-02-01

The bolt-hole cold-expansion process has been demonstrated by laboratory tests to significantly affect the initiation and propagation of fatigue cracks from rail bolt holes such that a reduction of the incidence of rail-bolt-holde failure in cold-exp...

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

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.

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

Kruska, Karen; Zhai, Ziqing; Bruemmer, Stephen M.

Due to its superior resistance to corrosion and stress corrosion cracking (SCC), high Cr, Ni-base Alloy 690 is now commonly used in pressurized water reactors (PWRs). Even though highly cold-worked (CW) Alloy 690 has been shown to be susceptible to SCC crack growth in PWR primary water environments, an open question remains whether SCC initiation was possible for these materials under constant load test conditions. Testing has been performed on a series of CW alloy 690 CRDM tubing specimens at constant load for up to 9,220 hours in 360°C simulated PWR primary water. A companion paper will discuss the overallmore » testing approach and describe results on different alloy 690 heats and cold work levels. The focus of the current paper is to illustrate the use of focused ion beam (FIB), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for the high-resolution investigation of precursor damage and intergranular (IG) crack nucleation in these specimens. Three-dimensional (3D) FIB/SEM imaging has been conducted on a series of grain boundary (GB) damage precursors, such as IG small cavities, local corrosion and even shallow cracks observed at the specimen surface. Contrast variations and EDS mapping were used to distinguish oxides, carbides and cavities from the matrix material. Nanometer-sized cavities were observed associated with GB carbides in the highly CW specimens. Shallow IG cracks were present in the 30%CW specimens and exhibited oxidized crack flanks and a higher density of cavities ahead of the oxide front in all cases. The shape and distribution of carbides and cavities in the plane of the cracked GBs was analyzed in 3D to gain a mechanistic understanding of the processes that may be leading to crack initiation in highly CW alloy 690.« less

PFC2D simulation of thermally induced cracks in concrete specimens

NASA Astrophysics Data System (ADS)

Liu, Xinghong; Chang, Xiaolin; Zhou, Wei; Li, Shuirong

2013-06-01

The appearance of cracks exposed to severe environmental conditions can be critical for concrete structures. The research is to validate Particle Flow Code(PFC2D) method in the context of concrete thermally-induced cracking simulations. First, concrete was discreted as meso-level units of aggregate, cement mortar and the interfaces between them. Parallel bonded-particle model in PFC2D was adapted to describe the constitutive relation of the cementing material. Then, the concrete mechanics meso-parameters were obtained through several groups of biaxial tests, in order to make the numerical results comply with the law of the indoor test. The concrete thermal meso-parameters were determined by compared with the parameters in the empirical formula through the simulations imposing a constant heat flow to the left margin of concrete specimens. At last, a case of 1000mm×500mm concrete specimen model was analyzed. It simulated the formation and development process of the thermally-induced cracks under the cold waves of different durations and temperature decline. Good agreements in fracture morphology and process were observed between the simulations, previous studies and laboratory data. The temperature decline limits during cold waves were obtained when its tensile strength was given as 3MPa. And it showed the feasibility of using PFC2D to simulate concrete thermally-induced cracking.

Stress corrosion crack initiation of alloy 600 in PWR primary water

DOE PAGES

Zhai, Ziqing; Toloczko, Mychailo B.; Olszta, Matthew J.; ...

2017-04-27

Stress corrosion crack (SCC) initiation of three mill-annealed alloy 600 heats in simulated pressurized water reactor primary water has been investigated using constant load tests equipped with in-situ direct current potential drop (DCPD) measurement capabilities. SCC initiation times were greatly reduced by a small amount of cold work. Shallow intergranular attack and/or cracks were found on most high-energy grain boundaries intersecting the surface with only a small fraction evolving into larger cracks and intergranular SCC growth. Crack depth profiles were measured and related to DCPD-detected initiation response. Lastly, we discuss processes controlling the SCC initiation in mill-annealed alloy 600.

Stress corrosion crack initiation of alloy 600 in PWR primary water

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

Zhai, Ziqing; Toloczko, Mychailo B.; Olszta, Matthew J.

Stress corrosion crack (SCC) initiation of three mill-annealed alloy 600 heats in simulated pressurized water reactor primary water has been investigated using constant load tests equipped with in-situ direct current potential drop (DCPD) measurement capabilities. SCC initiation times were greatly reduced by a small amount of cold work. Shallow intergranular attack and/or cracks were found on most high-energy grain boundaries intersecting the surface with only a small fraction evolving into larger cracks and intergranular SCC growth. Crack depth profiles were measured and related to DCPD-detected initiation response. Lastly, we discuss processes controlling the SCC initiation in mill-annealed alloy 600.

Cold Spray for Repair of Magnesium Components

DTIC Science & Technology

2011-11-01

powder material. Other advantages of the Cold Spray process include:  It provides extremely dense coatings with virtually no inclusions or cracks ... crack on insertion of Rosan fitting and does not reclaim the mechanical properties of the Mg alloy. It is expected that the use of Cold Spray coating...Spray process include:  Extremely dense coatings with virtually no inclusions or cracks .  Retains properties and microstructure of initial powder

Cold spraying SiC/Al metal matrix composites: effects of SiC contents and heat treatment on microstructure, thermophysical and flexural properties

NASA Astrophysics Data System (ADS)

Gyansah, L.; Tariq, N. H.; Tang, J. R.; Qiu, X.; Feng, B.; Huang, J.; Du, H.; Wang, J. Q.; Xiong, T. Y.

2018-02-01

In this paper, cold spray was used as an additive manufacturing method to fabricate 5 mm thick SiC/Al metal matrix composites with various SiC contents. The effects of SiC contents and heat treatment on the microstructure, thermophysical and flexural properties were investigated. Additionally, the composites were characterized for retention of SiC particulates, splat size, surface roughness and the progressive understanding of strengthening, toughening and cracking mechanisms. Mechanical properties were investigated via three-point bending test, thermophysical analysis, and hardness test. In the as-sprayed state, flexural strength increased from 95.3 MPa to 133.5 MPa, an appreciation of 40% as the SiC contents increased, and the main toughening and strengthening mechanisms were zigzag crack propagation and high retention of SiC particulates respectively. In the heat treatment conditions, flexural strength appreciated significantly compared to the as-sprayed condition and this was as a result of coarsening of pure Al splat. Crack branching, crack deflection and interface delamination were considered as the main toughening mechanisms at the heat treatment conditions. Experimental results were consistent with the measured CTE, hardness, porosity and flexural modulus.

Crack Repair in Aerospace Aluminum Alloy Panels by Cold Spray

NASA Astrophysics Data System (ADS)

Cavaliere, P.; Silvello, A.

2017-04-01

The cold-spray process has recently been recognized as a very useful tool for repairing metallic sheets, achieving desired adhesion strengths when employing optimal combinations of material process parameters. We present herein the possibility of repairing cracks in aluminum sheets by cold spray. A 2099 aluminum alloy panel with a surface 30° V notch was repaired by cold spraying of 2198 and 7075 aluminum alloy powders. The crack behavior of V-notched sheets subjected to bending loading was studied by finite-element modeling (FEM) and mechanical experiments. The simulations and mechanical results showed good agreement, revealing a remarkable K factor reduction, and a consequent reduction in crack nucleation and growth velocity. The results enable prediction of the failure initiation locus in the case of repaired panels subjected to bending loading and deformation. The stress concentration was quantified to show how the residual stress field and failure are affected by the mechanical properties of the sprayed materials and by the geometrical and mechanical properties of the interface. It was demonstrated that the crack resistance increases more than sevenfold in the case of repair using AA2198 and that cold-spray repair can contribute to increased global fatigue life of cracked structures.

Cold Cracking During Direct-Chill Casting

NASA Astrophysics Data System (ADS)

Eskin, D. G.; Lalpoor, M.; Katgerman, L.

Cold cracking phenomenon is the least studied, yet very important defect occurring during direct chill casting. The spontaneous nature of this defect makes its systematic study almost impossible, and the computer simulation of the thermomechanical behavior of the ingot during its cooling after the end of solidification requires constitutive parameters of high-strength aluminum alloys in the as-cast condition, which are not readily available. In this paper we describe constitutive behavior of high strength 7xxx series aluminum alloys in the as-cast condition based on experimentally measured tensile properties at different strain rates and temperatures, plane strain fracture toughness at different temperatures, and thermal contraction. In addition, fracture and structure of the specimens and real cold-cracked billets are examined. As a result a fracture-mechanics-based criterion of cold cracking is suggested based on the critical crack length, and is validated upon pilot-scale billet casting.

Investigations of Low Temperature Time Dependent Cracking

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

Van der Sluys, W A; Robitz, E S; Young, B A

2002-09-30

The objective of this project was to investigate metallurgical and mechanical phenomena associated with time dependent cracking of cold bent carbon steel piping at temperatures between 327 C and 360 C. Boiler piping failures have demonstrated that understanding the fundamental metallurgical and mechanical parameters controlling these failures is insufficient to eliminate it from the field. The results of the project consisted of the development of a testing methodology to reproduce low temperature time dependent cracking in laboratory specimens. This methodology was used to evaluate the cracking resistance of candidate heats in order to identify the factors that enhance cracking sensitivity.more » The resultant data was integrated into current available life prediction tools.« less

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

Zhai, Ziqing; Kruska, Karen; Toloczko, Mychailo B.

Stress corrosion crack initiation of two thermally-treated, cold-worked (CW) alloy 690 materials was investigated in 360oC simulated PWR primary water using constant load tensile (CLT) tests and blunt notch compact tension (BNCT) tests equipped with direct current potential drop (DCPD) for in-situ detection of cracking. SCC initiation was not detected by DCPD for the 21% and 31%CW CLT specimens loaded at their yield stress after ~9,220 h, however intergranular (IG) precursor damage and isolated surface cracks were observed on the specimens. The two 31%CW BNCT specimens loaded at moderate stress intensity after several cyclic loading ramps showed DCPD-indicated crack initiationmore » after 10,400h exposure at constant stress intensity, which resulted from significant growth of IG cracks. The 21%CW BNCT specimens only exhibited isolated small IG surface cracks and showed no apparent DCPD change throughout the test. Interestingly, post-test cross-section examinations revealed many grain boundary (GB) nano-cavities in the bulk of all the CLT and BNCT specimens particularly for the 31%CW materials. Cavities were also found along GBs extending to the surface suggesting an important role in crack nucleation. This paper provides an overview of the evolution of GB cavities and will discuss their effects on crack initiation in CW alloy 690.« less

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.

Stress corrosion crack initiation of alloy 600 in PWR primary water

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

Zhai, Ziqing; Toloczko, Mychailo B.; Olszta, Matthew J.

Stress corrosion crack (SCC) initiation of three mill-annealed (MA) alloy 600 heats in simulated pressurized water reactor primary water has been investigated using constant load tests equipped with in-situ direct current potential drop (DCPD) measurement capabilities. SCC initiation times were greatly reduced by a small amount of cold work. Shallow intergranular (IG) attack and/or cracks were found on most high-energy grain boundaries intersecting the surface with only a small fraction evolving into larger cracks and IGSCC growth. Crack depth profiles were measured and related to DCPD-detected initiation response. Processes controlling the SCC initiation in MA alloy 600 are discussed. INmore » PRESS, CORRECTED PROOF, 05/02/2017 - mfl« less

Evaluation of the Susceptibility to SCC Initiation of Alloy 690 in Simulated PWR Primary Water

NASA Astrophysics Data System (ADS)

Tsutsumi, Kazuya; Couvant, Thierry

Alloy 690 has been widely used in fabricating components of LWR plants as an alternative material to Alloy 600 which has exhibited a significant susceptibility to PWSCC. However, some authors have reported that Alloy 690 can suffer a significant susceptibility to SCC crack growth when highly cold worked. While most of the recent studies emphasize SCC propagation phase, EDF and its partners are focusing on the material's resistance to SCC initiation. This paper summarizes the current work carried out at EDF MAI on the SCC initiation. By means of constant elongation rate tests (CERTs) and constant displacement tests, experimental investigation of the susceptibility to PWSCC were performed. No SCC was observed on either an extruded bar or on two plates, even after 24%-1D cold rolling, confirming the superior PWSCC resistance of Alloy 690 independent of a amount of intergranular precipitation of carbides, and also revealing that such cold rolling does not necessarily decrease the resistance to SCC. On the other hand, a experimental steam generator tube that has a degraded microstructure due to specific heat-treatment revealed its susceptibility to SCC, probably because of the interactive effect of microstructure with heavy intragranular carbide precipitations and the cold worked superficial layer. This phenomenon is in good agreement with results previously published. In this study, the maximal crack depth slightly increased when DH increased from 5 to 60 cc.kg-1H2O. No significant prior ageing effect on the crack depth was observed, even when ageing was combined with high DH.

Experimental Crack Sealing in Asphaltic Concrete Pavements. Thule Air Base. Greenland, 8-24 August 1960

DTIC Science & Technology

1961-07-01

material prgpsr-ed by A"lied ihnterialls Corp., Stroud., VkI.1 th at is supposed to be soft and more pla-stic in cold cliwmtes. ___b. Para- Plastic ...uimenUsed in Tests .11 heeuiprzent, an-I accesscoia *_ e in the w .rk x; eea iso --router, 4-’- ; eJ. jnt =nd crack ’- ’, ir-power-ed wire brush, spIalt E

RSRM TP-H1148 Main Grain Propellant Crack Initiation Evaluation

NASA Technical Reports Server (NTRS)

Earnest, Todd E.

2005-01-01

Pressurized TP-HI 148 propellant fracture toughness testing was performed to assess the potential for initiation of visually undetectable cracks in the RSRM forward segment transition region during motor ignition. Two separate test specimens were used in this evaluation. Testing was performed in cold-gas and hot-fire environments, and under both static and dynamic pressurization conditions. Analysis of test results demonstrates safety factors against initiation of visually undetectable cracks in excess of 8.0. The Reusable Solid Rocket Motor (RSRM) forward segment is cast with PBAN propellant (TP-HI 148) to form T an 1 1-point star configuration that transitions to a tapered center perforated bore (see Figure 1). The geometry of the transition region between the fin valleys and the bore causes a localized area of high strain during horizontal storage. Updated analyses using worst-case mechanical properties at 40 F and improved modeling techniques indicated a slight reduction in safety margins over previous predictions. Although there is no history of strain induced cracks or flaws in the transition region propellant, a proactive test effort was initiated to better understand the implications of the new analysis, primarily the resistance of TP-H1148 propellant to crack initiation' during RSRM ignition.

Investigation of Cold Expansion of Short Edge Margin Holes with Pre-existing Cracks in 2024-T351 Aluminum Alloy

DTIC Science & Technology

2011-12-01

Fractography ............................................................................................................ 57 5. DISCUSSION...small radial cracks (0.03 to 0.07 inch) can be retarded by deep cold expansion (3.5% interference fit cold expansion). Petrak and Stewart (1974) and...the research done by Carlson, 13 and is shown in Fig. 48. 4.6 Fractography Select images were taken for fractography purposes. It should be

Effects of Thermo-Mechanical Treatments on Deformation Behavior and IGSCC Susceptibility of Stainless Steels in Pwr Primary Water Chemistry

NASA Astrophysics Data System (ADS)

Nouraei, S.; Tice, D. R.; Mottershead, K. J.; Wright, D. M.

Field experience of 300 series stainless steels in the primary circuit of PWR plant has been good. Stress Corrosion Cracking of components has been infrequent and mainly associated with contamination by impurities/oxygen in occluded locations. However, some instances of failures have been observed which cannot necessarily be attributed to deviations in the water chemistry. These failures appear to be associated with the presence of cold-work produced by surface finishing and/or by welding-induced shrinkage. Recent data indicate that some heats of SS show an increased susceptibility to SCC; relatively high crack growth rates were observed even when the crack growth direction is orthogonal to the cold-work direction. SCC of cold-worked SS in PWR coolant is therefore determined by a complex interaction of material composition, microstructure, prior cold-work and heat treatment. This paper will focus on the interactions between these parameters on crack propagation in simulated PWR conditions.

Rolling-element fatigue life of AMS 5900 balls

NASA Technical Reports Server (NTRS)

Parker, R. J.

1983-01-01

The rolling-element fatigue life of AMS 5900 12.7-mm (1/2-in.) dia was determined in five-ball fatigue testers. The 10% life with the warm headed AMS 5900 balls was equivalent to that of AMS 5749 and over eight times that of AISI M-50. The AMS balls fabricated by cold heading had small surface cracks which initiated fatigue spalls where these cracks were crossed by running tracks. The cold-headed AMS 5900 balls had a 10% fatigue life an order of magnitude less than that of the warm headed balls even when failures on the cold headed balls at visible surface cracks were omitted.

Research notes : geosynthetic materials in reflective crack prevention.

DOT National Transportation Integrated Search

2007-06-01

Extension of transverse cracks across roadway travel lanes is common in Oregon. Cracks form as a result of shrinkage and brittleness during very cold temperatures. These cracks deteriorate over time, spalling and creating bumpy riding surfaces. Prema...

Cracking of Beams Strengthened with Externally Bonded SRP Tapes

NASA Astrophysics Data System (ADS)

Krzywoń, Rafał

2017-10-01

Paper discusses strengthening efficiency of relatively new kind of SRP composite based on high strength steel wires. They are made of ultra-high strength steel primarily used in cords of car tires. Through advanced treatment, the mechanical properties of SRP steel are similar to other high carbon cold drawn steels used in construction industry. Strength significantly exceed 2000 MPa, there is no perfect plasticity at yield stress level. Almost linear stress-strain relationship makes SRP steel mechanical properties similar to carbon fibers. Also flexibility and weight ratio of the composite overlay is slightly worse than CFRP strip. Despite these advantages SRP is not as popular as other composites reinforced with fibers of high strength. This is due to the small number of studies of SRP behavior and applicability. Paper shows selected results of the laboratory test of beams strengthened with use of SRP and CFRP externally bonded overlays. Attention has been focused primarily on the phenomenon of cracking. Comparison include the cracking moment, crack width and spacing, coverage of crack zone. Despite the somewhat lower rigidity of SRP tapes, they have a much better adhesion to concrete, so that the crack width is comparable in almost the whole load range. The paper also includes an assessment of the common methods of checking the condition of cracking in relation to the tested SRP strengthening. The paper presents actual calculation procedures to determine the crack spacing and crack width. The discussed formulas are verified with results of provided laboratory tests.

Development of methods to control cold temperature and fatigue cracking for asphalt mixtures.

DOT National Transportation Integrated Search

2011-05-01

Pavement distresses caused by low and intermediate temperatures are a significant source of problems : for highway agencies. While many tests have been developed to address this type of distress, few of : them are considered practical for day to day ...

Microstructural Effects on SCC Initiation PWR Primary Water Cold-Worked Alloy 600

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

Zhai, Ziqing; Toloczko, Mychailo B.; Bruemmer, Stephen M.

SCC initiation behavior of one mill annealed alloy 600 plate heat was investigated in simulated PWR primary water under constant load at yield stress with in-situ direct current potential drop (DCPD) monitoring for crack initiation. Twelve specimens were tested at similar cold work levels among which three showed much shorter SCC initiation times (<400 hrs) than the others (>1200 hrs). Post-test examinations revealed that these three specimens all feature an inhomogeneous microstructure where the primary crack always nucleated along the boundary of large elongated grains protruding normally into the gauge. In contrast, such microstructure was either not observed or didmore » not extend deep enough into the gauge in the other specimens exhibiting ~3-6X longer initiation times. In order to better understand the role of this microstructural inhomogeneity in SCC initiation, high-resolution microscopy was performed to compare carbide morphology and strain distribution between the long grains and normal grains, and their potential effects on SCC initiation are discussed in this paper.« less

Stress Corrosion Cracking of Annealed and Cold Worked Titanium Grade 7 and Alloy 22 in 110 C Concentrated Salt Environments

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

P. Andresen

2000-11-08

Stress corrosion crack growth studies have been performed on annealed and cold worked Titanium Grade 7 and Alloy 22 in 110 C, aerated, concentrated, high pH salt environments characteristic of concentrated ground water. Following a very careful transition from fatigue precracking conditions to SCC conditions, the long term behavior under very stable conditions was monitored using reversing dc potential drop. Titanium Grade 7 exhibited continuous crack growth under both near-static and complete static loading conditions. Alloy 22 exhibited similar growth rates, but was less prone to maintain stable crack growth as conditions approached fully static loading.

Below-Ambient and Cryogenic Thermal Testing

NASA Technical Reports Server (NTRS)

Fesmire, James E.

2016-01-01

Thermal insulation systems operating in below-ambient temperature conditions are inherently susceptible to moisture intrusion and vapor drive toward the cold side. The subsequent effects may include condensation, icing, cracking, corrosion, and other problems. Methods and apparatus for real-world thermal performance testing of below-ambient systems have been developed based on cryogenic boiloff calorimetry. New ASTM International standards on cryogenic testing and their extension to future standards for below-ambient testing of pipe insulation are reviewed.

Effect of cold work on the stress corrosion cracking behavior of Alloy 690 in supercritical water environment

NASA Astrophysics Data System (ADS)

Chen, Kai; Du, Donghai; Gao, Wenhua; Guo, Xianglong; Zhang, Lefu; Andresen, Peter L.

2018-01-01

The stress corrosion cracking (SCC) behavior of Alloy 690 with 0, 20% and 30% cold work (CW) was studied in supercritical water (SCW) environment with an emphasis on CW and creep on the CGRs (CGR). SCC and creep CGRs increased with %CW, which correlated hardness very well. Microscopic characterization of the crack tip and fracture surface showed obvious cavity-like features, which is clear evidence of creep attack. The creep CGRs in inert gas were comparable to the SCC CGRs in SCW, indicating that creep is a major factor in crack growth. Increasing level of CW was found to increase the creep susceptibility, and high activation energies for creep crack growth were observed between 500 °C and 550 °C.

Stress Corrosion Cracking Susceptibility of 304L Substrate and 308L Weld Metal Exposed to a Salt Spray

PubMed Central

Hsu, Chia-Hao; Chen, Tai-Cheng; Huang, Rong-Tan; Tsay, Leu-Wen

2017-01-01

304 stainless steels (SS) were considered as the materials for a dry storage canister. In this study, ER (Electrode Rod) 308L was utilized as the filler metal for the groove and overlay welds of a 304L stainless steel substrate, which was prepared via a gas tungsten arc-welding process in multiple passes. The electron backscatter diffraction (EBSD) map was used to identify the inherent microstructures in distinct specimens. U-bend and weight-loss tests were conducted by testing the 304L substrates and welds in a salt spray containing 5 wt % NaCl at 80 °C to evaluate their susceptibility to stress corrosion cracking (SCC). Generally, the weight loss of the ER 308L deposit was higher than that of the 304L substrate in a salt spray in the same sample-prepared condition. The dissolution of the skeletal structure in the fusion zone (FZ) was responsible for a greater weight loss of the 308L deposit, especially for the cold-rolled and sensitized specimen. Cold rolling was detrimental and sensitization after cold rolling was very harmful to the SCC resistance of the 304L substrate and 308L deposit. Overall, the SCC susceptibility of each specimen was correlated with its weight loss in each group. PMID:28772547

[A ten-year clinical study of cracked teeth restored with glass ceramic crowns].

PubMed

Luo, X P; Yuan, Y; Shi, Y J; Qian, D D

2016-10-09

Objective: To evaluate the clinic performance of high strength glass ceramic crowns for the painful cracked teeth during a 10-year observation period. Methods: Forty-two posterior teeth from 36 patients were diagnosed as having a crack, biting painful and sensitivity to cold were selected in the Department of Prosthodontic, Institute and Hospital of Stomatology, Nanjing University Medical School. The lost-wax hot pressed glass ceramic crowns were bonded on the minimally invasive prepared teeth by modern adhesive technology. Patients were interviewed and went through clinic examination after one week, one month, and every six months. Results: The effectiveness of 42 glass ceramic crowns for cracked teeth was evaluated for a mean observation time over 10-year. At the first week, 29(81%) patients were free of pain, three still had sensitivity to cold and chewing pain, three still had sensitivity to cold, one had painful to cold and hot. After one month, two patients still had chewing pain, and one tooth needed endodontic treatment after six months. In 10 years, 2(5%) all ceramic crowns were broken, the other 40 restorations kept good clinical performances with a 10-year survival rate of 95%. Conclusions: The high strength glass ceramic crowns are very effective and successful in treating the cracked teeth and then keep the good mastication function and appearance.

Joining dissimilar stainless steels for pressure vessel components

NASA Astrophysics Data System (ADS)

Sun, Zheng; Han, Huai-Yue

1994-03-01

A series of studies was carried out to examine the weldability and properties of dissimilar steel joints between martensitic and austenitic stainless steels - F6NM (OCr13Ni4Mo) and AISI 347, respectively. Such joints are important parts in, e.g. the primary circuit of a pressurized water reactor (PWR). This kind of joint requires both good mechanical properties, corrosion resistance and a stable magnetic permeability besides good weldability. The weldability tests included weld thermal simulation of the martensitic steel for investigating the influence of weld thermal cycles and post-weld heat treatment (PWHT) on the mechanical properties of the heat-affected zone (HAZ); implant testing for examining the tendency for cold cracking of martensitic steel; rigid restraint testing for determining hot crack susceptibility of the multi-pass dissimilar steel joints. The joints were subjected to various mechanical tests including a tensile test, bending test and impact test at various temperatures, as well as slow strain-rate test for examining the stress corrosion cracking tendency in the simulated environment of a primary circuit of a PWR. The results of various tests indicated that the quality of the tube/tube joints is satisfactory for meeting all the design requirements.

The Effects of Metallurgical Factors on PWSCC Crack Growth Rates in TT Alloy 690 in Simulated PWR Primary Water

NASA Astrophysics Data System (ADS)

Yonezawa, Toshio; Watanabe, Masashi; Hashimoto, Atsushi

2015-06-01

Primary water stress corrosion cracking growth rates (PWSCCGRs) in highly cold-worked thermally treated (TT) Alloy 690 have been recently reported as exhibiting significant heat-to-heat variability. Authors hypothesized that these significant differences could be due to the metallurgical characteristics of each heat. In order to confirm this hypothesis, the effect of fundamental metallurgical characteristics on PWSCCGR measurements in cold-worked TT Alloy 690 has been investigated. The following new observations were made in this study: (1) Microcracks and voids were observed in or near eutectic crystals of grain boundary (GB) M23C6 carbides (primary carbides) after cold rolling, but were not observed before cold rolling. These primary carbides with microcracks and voids were observed in both lightly forged and as-cast and cold-rolled TT Alloy 690 (heat A) as well as in a cold-rolled TT Alloy 690 (heat Y) that simulated the chemical composition and carbide banded structure of the material previously tested by Paraventi and Moshier. However, this was not observed in precipitated (secondary) M23C6 GB carbides in heavily forged and cold-rolled TT Alloy 690 heat A and a cold-rolled commercial TT Alloy 690. (2) From microstructural analyses carried out on the various TT Alloy 690 test materials before and after cold rolling, the amount of eutectic crystals (primary carbides and nitrides) M23C6 and TiN depended on the chemical composition. In particular, the amount of M23C6 depended on the fabrication process. Microcracks and voids in or near the M23C6 and TiN precipitates were generated by the cold rolling process. (3) The PWSCCGRs observed in TT Alloy 690 were different for each heat and fabrication process. The PWSCCGR decreased with increasing Vickers hardness of each heat. However, for the same heats and fabrication processes, the PWSCCGR increased with increasing Vickers hardness due to cold work. Thus, the PWSCCGR must be affected not only by hardness (or equivalently the cold working ratio) but also by grain size, microcracks, and voids of primary M23C6 carbides, etc., which in turn depend on chemical composition and the fabrication process.

Acoustic emission investigation of cold cracking in gas metal-arc welding of AISI 4340 steel

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

Fang, C.K.; Kannatey-Asibu, E. Jr.; Barber, J.R.

1995-06-01

Acoustic emission (AE) has been used to investigate the propagation of a finite crack in a weldment subjected to nonuniform longitudinal residual stresses during gas metal arc welding (GMAW). Cold cracking in selected weldments was accelerated using the electrochemical method to cathodically charge the weldments with hydrogen in order to induce hydrogen embrittlement. Cold cracking was observed about 40 min after charging in the specimen subjected to hydrogen embrittlement, while it was observed two days after welding for the one that was left in the atmosphere. The AE signals were generated as the specimen cracked and were recorded, and themore » effects from structure and instrumentation were removed from the measured signals by deconvolution in the frequency domain. Most of the high-amplitude signal components were found to be clustered in the frequency range below 200 kHz. The experimentally obtained spectrum was compared with theoretical results derived in earlier work, and reasonable agreement with theoretical surface displacement in both time and frequency domains was obtained. The envelopes for both spectra were found to decrease with increasing frequency, while the fluctuations in each curve diminished at high frequencies.« less

Evaluation of cold in-place recycling for rehabilitation of transverse cracking on US 412.

DOT National Transportation Integrated Search

2007-12-01

Successful rehabilitation of transverse cracked hot mix asphalt (HMA) pavements has been a challenge : for state DOTs. Conventional thin HMA overlays allow the rapid return of the existing transverse cracks : and thicker HMA overlays are cost prohibi...

Weldability evaluation of high tensile plates using GMAW process

NASA Astrophysics Data System (ADS)

Datta, R.; Mukerjee, D.; Rohira, K. L.; Veeraraghavan, R.

1999-08-01

High tensile plates, SAILMA-450 high impact (HI) (yield strength, 45 kg/mm2 minimum; ultimate tensile strength, 57 kg/mm2 minimum; elongation, 19% minimum; Charpy impact energy 2.0 kg.m at -20 °C minimum) were successfully developed at the Steel Authority of India Ltd., up to 32 mm plate thickness. Since then the steel has been extensively used for the fabrication of impellers, bridges, excavators, and mining machineries, where welding is an important processing step. The present study deals with the weldability properties of SAILMA-450 HI plates employing the gas metal arc welding process and carbon dioxide gas. Implant and elastic restraint cracking tests were conducted to assess the cold cracking resistance of the weld joint under different welding conditions. The static fatigue limit values were found to be in excess of minimum specified yield strength at higher heat input levels (9.4 and 13.0 kJ/cm), indicating adequate cold cracking resistance. The critical restraint intensities, K cr, were found to vary between 720 and 1280 kg/mm2, indicating that the process can be utilized for fabrication of structures involving moderate to low restraint intensities (200 to 1000 kg/mm2). Lamellar tear tests conducted using full thickness plates at heat input levels ranging from 10 to 27 kJ/cm showed no incidence of lamellar tear upon visual, ultrasonic, and four-section macroexamination. These tests were repeated using machined plates, such that the midthickness of the plates (segregated zone) corresponded to the heat affected zone of the weld. No cracks were observed, indicating good lamellar tear resistance of the weld joint. Optimized welding conditions were formulated based on these tests. The weld joint was subjected to extensive tests to assess the physical properties and soundness of the weld joint. The weld joint exhibited good strength (64.7 kg/mm2) and impact toughness (5.7 and 3.5 kg.m at -20 °C for weld metal and heat affected zone properties. Crack tip opening displacement (CTOD) tests carried out for parent metal, heat-affected zone, and weld metal resulted in δm values of 0.41, 0.40, and 0.34 mm, respectively, which indicates adequate resistance to cleavage fracture. It was concluded that the weld joint conforms to the requirements of SAILMA-450 HI specification and ensures a high integrity of the fabricated products.

Neoproterozoic sand wedges: crack formation in frozen soils under diurnal forcing during a snowball Earth

NASA Astrophysics Data System (ADS)

Maloof, Adam C.; Kellogg, James B.; Anders, Alison M.

2002-11-01

Thermal contraction cracking of permafrost produced sand-wedge polygons at sea level on the paleo-equator during late Neoproterozoic glacial episodes. These sand wedges have been used as evidence for high (≥54°) paleo-obliquity of the Earth's ecliptic, because cracks that form wedges are hypothesized to require deep seasonal cooling so the depth of the stressed layer in the ground reaches ≥1 m, similar to the measured depths of cracks that form wedges. To test the counter hypothesis that equatorial cracks opened under a climate characterized by a strong diurnal cycle and low mean annual temperature (snowball Earth conditions), we examine crack formation in frozen ground subject to periodic temperature variations. We derive analytical expressions relating the Newtonian viscosity to the potential crack depth, concluding that cracks will form only in frozen soils with viscosities greater than ˜10 14 Pa s. We also show numerical calculations of crack growth in frozen soils with stress- and temperature-dependent rheologies and find that fractures may propagate to depths 3-25 times the depth of the thermally stressed layer in equatorial permafrost during a snowball Earth because the mean annual temperature is low enough to keep the ground cold and brittle to relatively great depths.

Experimental Investigation of Bio-Sealants Used for Pavement Preservation and Development of a New Strength Test for Asphalt Binders at Low Temperature

NASA Astrophysics Data System (ADS)

Ghosh, Debaroti

Surface treatment using sealants as a mean of pavement preservation is an important tool for cost-effectively extending service life of pavement. Sealants have become an important tool for cost-effectively extending the service life pavements. Due to the combined negative effects of asphalt aging and thermal cracking, it is always more challenging to choose an appropriate preservation technique for pavements built in cold-regions. Asphalt aging and thermal cracking negatively affect pavements built in cold climates. Therefore, it is important to evaluate the effects of sealants in laboratory conditions before application in the field to ensure effective performance. However, preservation activities cannot effectively address major distresses, such as low-temperature cracking, that can occur when the pavement was built from the very beginning with less durable materials. Therefore, an essential requirement to mitigate low-temperature cracking of pavements for asphalt materials used in the construction of pavement built in cold- regions is ensuring proper fracture properties of the asphalt materials used in construction. This study has two parts. In the first part, a laboratory evaluation of the effects of adding bio-sealants to both asphalt binder and mixture is performed. The goal is to obtain relevant properties of treated asphalt materials to understand the mechanism by which sealants improve pavement performance. For asphalt binders, a dynamic shear rheometer and a bending beam rheometer were used to obtain rheological properties of treated and untreated asphalt binders. For asphalt mixtures, field cores from both untreated and treated sections were collected and thin beam specimens were prepared from the cores to compare the creep and strength properties of the field-treated and laboratory-treated mixture. It is observed that the oil-based sealants have a significant softening effect on the control binder compared to the water-based sealant and traditional emulsion. Oil-based sealants increased rutting and fatigue potential of the binder and helped the low-temperature cracking resistance. For asphalt mixtures, different trends are observed for the field samples compared to the laboratory prepared samples. Similar to binder results, significant differences are observed between the asphalt mixtures treated with oil-based and water-based sealants, respectively. Additional analyses were performed to better understand the sealant effects. Fourier transform infrared spectroscopy (FTIR) analysis showed that the sealant products could not be detected in mixture samples collected from the surface of the treated section. Semi-empirical Hirsch model was able to predict asphalt mixture creep stiffness from binder stiffness. The results of a distress survey of the test sections correlated well with the laboratory findings. In the second part, a news binder strength testing method is proposed with the goal to provide an effective tool for selecting asphalt binders that are crack resistant. A modified Bending Beam Rheometer (BBR) is used to perform three-point bending strength tests, at constant loading rate, on asphalt binder beams at low temperature. Based on the results, a protocol for selecting the most crack resistant material from binders with similar rheological properties is proposed.

Verification of Cold Working and Interference Levels at Fastener Holes

DTIC Science & Technology

2009-02-01

of the Residual Stress Field on the Fatigue Coupons ........................................ 32 3.3.3 Fractography of Fatigue Test Coupons...predictions to fatigue experiment results (none of the literature we reviewed described fractography of cracks propagating through residual stress...ensures continued safety, readiness, and controlled maintenance costs. These methods augment and enhance traditional safe-life and damage tolerance

Enhancement of low pressure cold sprayed copper coating adhesion by laser texturing on aluminum substrates

NASA Astrophysics Data System (ADS)

Knapp, Wolfgang; Gillet, Vincent; Courant, Bruno; Aubignat, Emilie; Costil, Sophie; Langlade, Cécile

2017-02-01

Surface pre-treatment is fundamental in thermal spraying processes to obtain a sufficient bonding strength between substrate and coating. Different pre-treatments can be used, mostly grit-blasting for current industrial applications. This study is focused on Cu-Al2O3 coatings obtained by Low Pressure Cold Spray on AW5083 aluminum alloy substrate. Bonding strength is measured by tensile adhesion test, while deposition efficiency is measured. Substrates are textured by laser, using a pattern of equally spaced grooves with almost constant diameter and variations of depth. Results show that bonding strength is improved up to +81% compared to non-treated substrate, while deposition efficiency remains constant. The study of the samples after rupture reveals a modification of the failure mode, from mixed failure to cohesive failure. A modification of crack propagation is also noticed, the shape of laser textured grooves induces a deviation of cracks inside the coating instead of following the interface between the layers.

Infrared Thermography as a Non-destructive Testing Solution for Thermal Spray Metal Coatings

NASA Astrophysics Data System (ADS)

Santangelo, Paolo E.; Allesina, Giulio; Bolelli, Giovanni; Lusvarghi, Luca; Matikainen, Ville; Vuoristo, Petri

2017-12-01

In this work, an infrared (IR) thermographic procedure was evaluated as a non-destructive testing tool to detect damage in thermal spray metallic coatings. As model systems, polished HVOF- and HVAF-sprayed Fe-based layers deposited onto steel plates were employed. Damage by external-object impingement was simulated through a cyclic impact-test apparatus, which induced circumferential and radial cracks across all model systems, and interface cracks of different sizes in distinct samples. Damaged and undamaged plates were bulk-heated to above 100 °C using an IR lamp; their free-convection cooling was then recorded by an IR thermocamera. The intentionally induced defects were hardly detectable in IR thermograms, due to IR reflection and artificial "hot" spots induced by residuals of transfer material from the impacting counterbody. As a micrometer-thin layer of black paint was applied, surface emissivity got homogenized and any artifacts were effectively suppressed, so that failed coating areas clearly showed up as "cold spots." This effect was more apparent when large interface cracks occurred. Finite-element modeling proved the physical significance of the IR-thermography approach, showing that failed coating areas are cooled by surrounding air faster than they are heated by conduction from the hot substrate, which is due to the insulating effect of cracks.

Multiscale modelling and experimentation of hydrogen embrittlement in aerospace materials

NASA Astrophysics Data System (ADS)

Jothi, Sathiskumar

Pulse plated nickel and nickel based superalloys have been used extensively in the Ariane 5 space launcher engines. Large structural Ariane 5 space launcher engine components such as combustion chambers with complex microstructures have usually been manufactured using electrodeposited nickel with advanced pulse plating techniques with smaller parts made of nickel based superalloys joined or welded to the structure to fabricate Ariane 5 space launcher engines. One of the major challenges in manufacturing these space launcher components using newly developed materials is a fundamental understanding of how different materials and microstructures react with hydrogen during welding which can lead to hydrogen induced cracking. The main objective of this research has been to examine and interpret the effects of microstructure on hydrogen diffusion and hydrogen embrittlement in (i) nickel based superalloy 718, (ii) established and (iii) newly developed grades of pulse plated nickel used in the Ariane 5 space launcher engine combustion chamber. Also, the effect of microstructures on hydrogen induced hot and cold cracking and weldability of three different grades of pulse plated nickel were investigated. Multiscale modelling and experimental methods have been used throughout. The effect of microstructure on hydrogen embrittlement was explored using an original multiscale numerical model (exploiting synthetic and real microstructures) and a wide range of material characterization techniques including scanning electron microscopy, 2D and 3D electron back scattering diffraction, in-situ and ex-situ hydrogen charged slow strain rate tests, thermal spectroscopy analysis and the Varestraint weldability test. This research shows that combined multiscale modelling and experimentation is required for a fundamental understanding of microstructural effects in hydrogen embrittlement in these materials. Methods to control the susceptibility to hydrogen induced hot and cold cracking and to improve the resistance to hydrogen embrittlement in aerospace materials are also suggested. This knowledge can play an important role in the development of new hydrogen embrittlement resistant materials. A novel micro/macro-scale coupled finite element method incorporating multi-scale experimental data is presented with which it is possible to perform full scale component analyses in order to investigate hydrogen embrittlement at the design stage. Finally, some preliminary and very encouraging results of grain boundary engineering based techniques to develop alloys that are resistant to hydrogen induced failure are presented. Keywords: Hydrogen embrittlement; Aerospace materials; Ariane 5 combustion chamber; Pulse plated nickel; Nickel based super alloy 718; SSRT test; Weldability test; TDA; SEM/EBSD; Hydrogen induced hot and cold cracking; Multiscale modelling and experimental methods.

Deformation and damage mechanisms of zinc coatings on hot-dip galvanized steel sheets: Part II. Damage modes

NASA Astrophysics Data System (ADS)

Parisot, Rodolphe; Forest, Samuel; Pineau, André; Grillon, François; Demonet, Xavier; Mataigne, Jean-Michel

2004-03-01

Zinc-based coatings are widely used for protection against corrosion of steel-sheet products in the automotive industry. The objective of the present article is to investigate the damage modes at work in three different microstructures of a zinc coating on an interstitial-free steel substrate under tension, planestrain tension, and expansion loading. Plastic-deformation mechanisms are addressed in the companion article. Two main fracture mechanisms, namely, intergranular cracking and transgranular cleavage fracture, were identified in an untempered cold-rolled coating, a tempered cold-rolled coating, and a recrystallized coating. No fracture at the interface between the steel and zinc coating was observed that could lead to spalling, in the studied zinc alloy. A complex network of cleavage cracks and their interaction with deformation twinning is shown to develop in the material. An extensive quantitative analysis based on systematic image analysis provides the number and cumulative length of cleavage cracks at different strain levels for the three investigated microstructures and three loading conditions. Grain refinement by recrystallization is shown to lead to an improved cracking resistance of the coating. A model for crystallographic cleavage combining the stress component normal to the basal plane and the amount of plastic slip on the basal slip systems is proposed and identified from equibiaxial tension tests and electron backscattered diffraction (EBSD) analysis of the cracked grains. This analysis requires the computation of the nonlinear stress-strain response of each grain using a crystal-plasticity constitutive model. The model is then applied successfully to other loading conditions and is shown to account for the preferred orientations of damaged grains observed in the case of plane-strain tension.

Evaluation of Crack Arrest Toughness ( K IA) of P91 Steel in Various Cold Worked and Thermally Aged Conditions

NASA Astrophysics Data System (ADS)

Sathyanarayanan, S.; Moitra, A.; Sasikala, G.; Bhaduri, A. K.

2015-02-01

K IA is increasingly being regarded as a characteristic fracture toughness below which cleavage fracture does not occur. Its evaluation from small-sized Charpy specimens would be advantageous for applications in power plant industries. In this study, K IA has been evaluated for P91 steel in various cold worked and thermally aged conditions. Evaluation of K IA requires determination of crack arrest load( P arrest) and crack arrest length( a arrest). The main challenge is in the determination of a arrest due to the non-availability of standard methodologies and the absence of unequivocal microstructural signatures on the fracture surface in this steel to identify crack arrest. a arrest has been determined using the analytical Key- Curve methodology which has proven successful for this steel in unaged condition. The applicability of the Key- Curve method is validated by the good agreement of the determined final crack length with that measured optically on unbroken specimens of N&T and subsequently 15% cold-worked P91 steel which had been previously aged at 650 °C for 5000 h. Mean K IA varies from 47.46 MPa√m (NT steel aged at 600 °C for 5000 h) to 69.85 MPa√m(NT + 15% cw steel aged at 650 °C for 10000 h) for the various cold worked and aged datasets. K IA is found to be an average property unlike initiation toughness ( K Jd) which shows statistical scatter. Mean K IA is found to be in reasonable agreement with the lower bound values of cleavage initiation toughness ( K Jd) for the datasets in this study.

Texas cracking performance prediction, simulation, and binder recommendation.

DOT National Transportation Integrated Search

2014-10-01

Recent studies show some mixes with softer binders used outside of Texas (e.g., Minnesotas Cold Weather Road Research Facility mixes) have both good rutting and cracking performance. However, the current binder performance grading (PG) system fail...

Hydrogen-Induced Cold Cracking in High-Frequency Induction Welded Steel Tubes

NASA Astrophysics Data System (ADS)

Banerjee, Kumkum

2016-04-01

Detailed investigation was carried out on 0.4C steel tubes used for the telescopic front fork of two-wheelers to establish the root cause for the occurrence of transverse cracks at the weld heat-affected zone of the tubes. Fractographic and microstructural observations provide evidences of delayed hydrogen-induced cracking. The beneficial microstructure for avoiding the transverse cracks was found to be the bainitic-martensitic, while martensitic structure was noted to be deleterious.

Stress corrosion crack initiation of Zircaloy-4 cladding tubes in an iodine vapor environment during creep, relaxation, and constant strain rate tests

NASA Astrophysics Data System (ADS)

Jezequel, T.; Auzoux, Q.; Le Boulch, D.; Bono, M.; Andrieu, E.; Blanc, C.; Chabretou, V.; Mozzani, N.; Rautenberg, M.

2018-02-01

During accidental power transient conditions with Pellet Cladding Interaction (PCI), the synergistic effect of the stress and strain imposed on the cladding by thermal expansion of the fuel, and corrosion by iodine released as a fission product, may lead to cladding failure by Stress Corrosion Cracking (SCC). In this study, internal pressure tests were conducted on unirradiated cold-worked stress-relieved Zircaloy-4 cladding tubes in an iodine vapor environment. The goal was to investigate the influence of loading type (constant pressure tests, constant circumferential strain rate tests, or constant circumferential strain tests) and test temperature (320, 350, or 380 °C) on iodine-induced stress corrosion cracking (I-SCC). The experimental results obtained with different loading types were consistent with each other. The apparent threshold hoop stress for I-SCC was found to be independent of the test temperature. SEM micrographs of the tested samples showed many pits distributed over the inner surface, which tended to coalesce into large pits in which a microcrack could initiate. A model for the time-to-failure of a cladding tube was developed using finite element simulations of the viscoplastic mechanical behavior of the material and a modified Kachanov's damage growth model. The times-to-failure predicted by this model are consistent with the experimental data.

Thermal behavior of crumb-rubber modified asphalt concrete mixtures

NASA Astrophysics Data System (ADS)

Epps, Amy Louise

Thermal cracking is one of the primary forms of distress in asphalt concrete pavements, resulting from either a single drop in temperature to an extreme low or from multiple temperature cycles above the fracture temperature of the asphalt-aggregate mixture. The first mode described is low temperature cracking; the second is thermal fatigue. The addition of crumb-rubber, manufactured from scrap tires, to the binder in asphalt concrete pavements has been suggested to minimize both types of thermal cracking. Four experiments were designed and completed to evaluate the thermal behavior of crumb-rubber modified (CRM) asphalt-aggregate mixtures. Modified and unmodified mixture response to thermal stresses was measured in four laboratory tests. The Thermal Stress Restrained Specimen Test (TSRST) and the Indirect Tensile Test (IDT) were used to compare mixture resistance to low temperature cracking. Modified mixtures showed improved performance, and cooling rate did not affect mixture resistance according to the statistical analysis. Therefore results from tests with faster rates can predict performance under slower field rates. In comparison, predicted fracture temperatures and stresses (IDT) were generally higher than measured values (TSRST). In addition, predicted fracture temperatures from binder test results demonstrated that binder testing alone is not sufficient to evaluate CRM mixtures. Thermal fatigue was explored in the third experiment using conventional load-induced fatigue tests with conditions selected to simulate daily temperature fluctuations. Test results indicated that thermal fatigue may contribute to transverse cracking in asphalt pavements. Both unmodified and modified mixtures had a finite capacity to withstand daily temperature fluctuations coupled with cold temperatures. Modified mixtures again exhibited improved performance. The fourth experiment examined fracture properties of modified and unmodified mixtures using a common fracture toughness test. Results showed no effect from modification, but the small experiment size may have masked this effect. Reliability concepts were introduced to include risk and uncertainty in a comparison of mixture response measured in the laboratory and estimated environmental conditions. This comparison provided evidence that CRM mixtures exhibit improved resistance to both types of thermal cracking at high levels of reliability. In conclusion, a mix design and analysis framework for evaluating thermal behavior was recommended.

Influence of the Manufacturing Process on Defects in the Galvanized Coating of High Carbon Steel Wires.

PubMed

Gelfi, Marcello; Solazzi, Luigi; Poli, Sandro

2017-03-06

This study is a detailed failure analysis of galvanized high carbon steel wires, which developed coating cracks during the torsion test performed as a quality control at the end of the manufacturing process. Careful visual inspections showed that the cracks are already present in the coating before the torsion test. In order to explain the origin of these cracks, systematic metallographic investigations were performed by means of optical and scanning electron microscope on both the wires and the rods that have been cold drawn to produce the wire. The chemical composition of the galvanized coatings was evaluated by means of energy dispersive spectroscopy. Micro bidimensional X-ray diffraction experiments were also performed to measure the residual stresses in the galvanized coating. The results showed that the failure is related to two main factors: the relatively high content of silicon in the steel and the unsuitable cooling rate of the rods at the exit from the galvanizing bath. The mechanism proposed to explain the origin of the defects was supported by Finite Elements Methods simulations and verified with in-plant tests. The proper countermeasures were then applied and the problem successfully solved.

Influence of the Manufacturing Process on Defects in the Galvanized Coating of High Carbon Steel Wires

PubMed Central

Gelfi, Marcello; Solazzi, Luigi; Poli, Sandro

2017-01-01

This study is a detailed failure analysis of galvanized high carbon steel wires, which developed coating cracks during the torsion test performed as a quality control at the end of the manufacturing process. Careful visual inspections showed that the cracks are already present in the coating before the torsion test. In order to explain the origin of these cracks, systematic metallographic investigations were performed by means of optical and scanning electron microscope on both the wires and the rods that have been cold drawn to produce the wire. The chemical composition of the galvanized coatings was evaluated by means of energy dispersive spectroscopy. Micro bidimensional X-ray diffraction experiments were also performed to measure the residual stresses in the galvanized coating. The results showed that the failure is related to two main factors: the relatively high content of silicon in the steel and the unsuitable cooling rate of the rods at the exit from the galvanizing bath. The mechanism proposed to explain the origin of the defects was supported by Finite Elements Methods simulations and verified with in-plant tests. The proper countermeasures were then applied and the problem successfully solved. PMID:28772623

Cold work study on a 316LN modified alloy for the ITER TF coil conduit

DOE PAGES

Walsh, Robert; Toplosky, V. J.; McRae, D. M.; ...

2012-06-01

The primary structural component of the cable-in-conduit conductor (CICC) magnets, such as the ITER TF coils is the conduit. This function creates requirements for 4 K strength, toughness, fatigue crack resistance, and ductility after exposure to the superconductor's reaction heat treatment. The tensile ductility of a steel is a quality factor related to fatigue and fracture resistance that can be evaluated more economically with tensile tests rather than fatigue and fracture tests. We subject 316LN modified base metal and welds to a range of cold work from 0% to 20% and a subsequent Nb 3Sn reaction heat treatment to evaluatemore » the effects on the tensile properties. With the addition of cold work, the 4 K yield strength increases while tensile elongation decreases in both the base metal and weld. Our results are compared to previously published data on the same alloy to evaluate the use of tensile ductility parameters as a materials qualification specification in magnet design.« less

Cold Regions Environmental Considerations

DTIC Science & Technology

2009-02-03

braided streams, variable discharge, seasonal breakup) limited seasonally limited abundant Hydrology (frozen lakes and bogs) not present seasonally...fuel hoses may crack increasing the potential for fuel spills. Extreme care must be used when handling cables at cold temperatures, protecting the

Effect of Localized Corrosion on Fatigue-Crack Growth in 2524-T3 and 2198-T851 Aluminum Alloys Used as Aircraft Materials

NASA Astrophysics Data System (ADS)

Moreto, J. A.; Broday, E. E.; Rossino, L. S.; Fernandes, J. C. S.; Bose Filho, W. W.

2018-03-01

Corrosion and fatigue of aluminum alloys are major issues for the in-service life assessment of aircraft structures and for the management of aging air fleets. The aim of this work was to evaluate the effect of localized corrosion on fatigue crack growth (FCG) resistance of the AA2198-T851 Al-Li alloy (Solution Heat Treated, Cold Worked, and Artificially Aged), comparing it with the FCG resistance of AA2524-T3 (Solution Heat Treated and Cold Worked), considering the effect of seawater fog environment. Before fatigue tests, the corrosion behavior of 2198-T851 and 2524-T3 aluminum alloys was verified using open circuit potential and potentiodynamic polarization techniques. Fatigue in air and corrosion fatigue tests were performed applying a stress ratio (R) of 0.1, 15 Hz (air) and 0.1 Hz (seawater fog) frequencies, using a sinusoidal waveform in all cases. The results showed that the localized characteristics of the 2198-T851 and 2524-T3 aluminum alloys are essentially related to the existence of intermetallic compounds, which, due to their different nature, may be cathodic or anodic in relation to the aluminum matrix. The corrosive medium has affected the FCG rate of both aluminum alloys, in a quite similar way.

Diffraction-based study of fatigue crack initiation and propagation in aerospace aluminum alloys

NASA Astrophysics Data System (ADS)

Gupta, Vipul K.

The crack initiation sites and microstructure-sensitive growth of small fatigue cracks are experimentally characterized in two precipitation-hardened aluminum alloys, 7075-T651 and 7050-T7451, stressed in ambient temperature moist-air (warm-humid) and -50°C dry N2 (cold-dry) environmental conditions. Backscattered electron imaging (BSE) and energy dispersive spectroscopy (EDS) of the fracture surfaces showed that Fe-Cu rich constituent particle clusters are the most common initiation sites within both alloys stressed in either environment. The crack growth within each alloy, on average, was observed to be slowed in the cold-dry environment than in the warm-humid environment, but only at longer crack lengths. Although no overwhelming effects of grain boundaries and grain orientations on small-crack growth were observed, crack growth data showed local fluctuations within individual grains. These observations are understood as crack propagation through the underlying substructure at the crack surface and frequent interaction with low/high-angle grain and subgrain boundaries, during cyclic loading, and, are further attributed to periodic changes in crack propagation path and multiple occurrences of crack-branching observed in the current study. SEM-based stereology in combination with electron backscattered diffraction (EBSD) established fatigue crack surface crystallography within the region from ˜1 to 50 mum of crack initiating particle clusters. Fatigue crack facets were parallel to a wide variety of crystallographic planes, with pole orientations distributed broadly across the irreducible stereographic triangle between the {001} and {101}-poles within both warm-humid and cold-dry environments. The results indicate environmentally affected fatigue cracking in both cases, given the similarity between the observed morphology and crystallography with that of a variety of aerospace aluminum alloys cracked in the presence of moist-air. There was no evidence of crystallographic {111} slip-plane cracking typical of the Stage I crack growth mode observed in single crystals and high purity polycrystals of face centered cubic metals, and which has presently been assumed for the present materials within fatigue crack initiation models. Rather, the facets tend to have near-Mode I spatial orientation, which is another indicator of the importance of environmentally affected fatigue damage. The results provide a physical basis to develop microstructurally-based next generation multi-stage fatigue (MSF) models that should include a new crack decohesion criteria based upon environmental fatigue cracking mechanisms. EBSD study of small-cracks in alloy 7050-T7451, stressed in warm-humid environment, showed that crack-path orientation changes and crack-branching occurred at both low/high-angle grain and subgrain boundaries. Single surface trace analysis suggests that the crack-path differs substantially from crystallographic slip-planes. EBSD-based observations of small-crack propagation through subgrain structure, either formed by cyclic plastic strain accumulation or pre-existing (typical of unrecrystallized grain structure in the present materials), suggest that subgrain structure plays a crucial role in small fatigue crack propagation. As mentioned earlier, local fluctuations in small-crack growth rates appear to be caused by frequent interaction with subgrain boundaries, and multiple occurrences of crack-branching and crack-path orientation changes at low/high-angle grain and subgrain boundaries. The aforementioned deviation from low-index {001}/{101}-planes and the occurrence of high-index cracking planes observed by EBSD/Stereology, in this study and others, are interpreted as trans-subgranular decohesion or inter-subgranular cracking, due to trapped hydrogen. In summary, the results provide a firmer experimental foundation for, and clearer understanding of, the mechanisms of environmental fatigue cracking of aluminum alloys, especially the role of inter-subgranular cracking, which had previously been advanced based upon fracture surface observations alone.

Experimentally Derived Beta Corrections to Accurately Model the Fatigue Crack Growth Behavior at Cold Expanded Holes in 2024-T351 Aluminum Alloys

DTIC Science & Technology

2008-08-01

was attached to the upper grip and the runout was checked as the lower grip was rotated. The maximum runout was recorded as 0.021 inch. Due to the...difficulties with adjusting the Interlaken test frame, this runout value was noted but considered acceptable. 2.3 Fatigue Testing Procedures...easier to polish the specimen to a mirror finish. The polishing of the specimen was performed using an electric Dremel with a polishing wheel attached

Damage assessment, characterization, and modeling for enhanced design of concrete bridge decks in cold regions : [project brief].

DOT National Transportation Integrated Search

2015-07-01

Freeze-thaw and fatigue-type loading processes degrade concrete materials and reduce the load carrying capacity of concrete decks. Damage to concrete decks is caused by the formation of cracks and micro-cracks during fatigue and freeze-thaw cycles. T...

Method for cold stable biojet fuel

DOEpatents

Seames, Wayne S.; Aulich, Ted

2015-12-08

Plant or animal oils are processed to produce a fuel that operates at very cold temperatures and is suitable as an aviation turbine fuel, a diesel fuel, a fuel blendstock, or any fuel having a low cloud point, pour point or freeze point. The process is based on the cracking of plant or animal oils or their associated esters, known as biodiesel, to generate lighter chemical compounds that have substantially lower cloud, pour, and/or freeze points than the original oil or biodiesel. Cracked oil is processed using separation steps together with analysis to collect fractions with desired low temperature properties by removing undesirable compounds that do not possess the desired temperature properties.

Cyclic stress effect on stress corrosion cracking of duplex stainless steel in chloride and caustic solutions

NASA Astrophysics Data System (ADS)

Yang, Di

Duplex stainless steel (DSS) is a dual-phase material with approximately equal volume amount of austenite and ferrite. It has both great mechanical properties (good ductility and high tensile/fatigue strength) and excellent corrosion resistance due to the mixture of the two phases. Cyclic loadings with high stress level and low frequency are experienced by many structures. However, the existing study on corrosion fatigue (CF) study of various metallic materials has mainly concentrated on relatively high frequency range. No systematic study has been done to understand the ultra-low frequency (˜10-5 Hz) cyclic loading effect on stress corrosion cracking (SCC) of DSSs. In this study, the ultra-low frequency cyclic loading effect on SCC of DSS 2205 was studied in acidified sodium chloride and caustic white liquor (WL) solutions. The research work focused on the environmental effect on SCC of DSS 2205, the cyclic stress effect on strain accumulation behavior of DSS 2205, and the combined environmental and cyclic stress effect on the stress corrosion crack initiation of DSS 2205 in the above environments. Potentiodynamic polarization tests were performed to investigate the electrochemical behavior of DSS 2205 in acidic NaCl solution. Series of slow strain rate tests (SSRTs) at different applied potential values were conducted to reveal the optimum applied potential value for SCC to happen. Room temperature static and cyclic creep tests were performed in air to illustrate the strain accumulation effect of cyclic stresses. Test results showed that cyclic loading could enhance strain accumulation in DSS 2205 compared to static loading. Moreover, the strain accumulation behavior of DSS 2205 was found to be controlled by the two phases of DSS 2205 with different crystal structures. The B.C.C. ferrite phase enhanced strain accumulation due to extensive cross-slips of the dislocations, whereas the F.C.C. austenite phase resisted strain accumulation due to cyclic strain hardening. Cyclic SSRTs were performed under the conditions that SCC occurs in sodium chloride and WL solutions. Test results show that cyclic stress facilitated crack initiations in DSS 2205. Stress corrosion cracks initiated from the intermetallic precipitates in acidic chloride environment, and the cracks initiated from austenite phase in WL environment. Cold-working has been found to retard the crack initiations induced by cyclic stresses.

Assessing Reliability of Cold Spray Sputter Targets in Photovoltaic Manufacturing

NASA Astrophysics Data System (ADS)

Hardikar, Kedar; Vlcek, Johannes; Bheemreddy, Venkata; Juliano, Daniel

2017-10-01

Cold spray has been used to manufacture more than 800 Cu-In-Ga (CIG) sputter targets for deposition of high-efficiency photovoltaic thin films. It is a preferred technique since it enables high deposit purity and transfer of non-equilibrium alloy states to the target material. In this work, an integrated approach to reliability assessment of such targets with deposit weight in excess of 50 lb. is undertaken, involving thermal-mechanical characterization of the material in as-deposited condition, characterization of the interface adhesion on cylindrical substrate in as-deposited condition, and developing means to assess target integrity under thermal-mechanical loads during the physical vapor deposition (PVD) sputtering process. Mechanical characterization of cold spray deposited CIG alloy is accomplished through the use of indentation testing and adaptation of Brazilian disk test. A custom lever test was developed to characterize adhesion along the cylindrical interface between the CIG deposit and cylindrical substrate, overcoming limitations of current standards. A cohesive zone model for crack initiation and propagation at the deposit interface is developed and validated using the lever test and later used to simulate the potential catastrophic target failure in the PVD process. It is shown that this approach enables reliability assessment of sputter targets and improves robustness.

An analytical approach for the Propagation Saw Test

NASA Astrophysics Data System (ADS)

Benedetti, Lorenzo; Fischer, Jan-Thomas; Gaume, Johan

2016-04-01

The Propagation Saw Test (PST) [1, 2] is an experimental in-situ technique that has been introduced to assess crack propagation propensity in weak snowpack layers buried below cohesive snow slabs. This test attracted the interest of a large number of practitioners, being relatively easy to perform and providing useful insights for the evaluation of snow instability. The PST procedure requires isolating a snow column of 30 centimeters of width and -at least-1 meter in the downslope direction. Then, once the stratigraphy is known (e.g. from a manual snow profile), a saw is used to cut a weak layer which could fail, potentially leading to the release of a slab avalanche. If the length of the saw cut reaches the so-called critical crack length, the onset of crack propagation occurs. Furthermore, depending on snow properties, the crack in the weak layer can initiate the fracture and detachment of the overlying slab. Statistical studies over a large set of field data confirmed the relevance of the PST, highlighting the positive correlation between test results and the likelihood of avalanche release [3]. Recent works provided key information on the conditions for the onset of crack propagation [4] and on the evolution of slab displacement during the test [5]. In addition, experimental studies [6] and simplified models [7] focused on the qualitative description of snowpack properties leading to different failure types, namely full propagation or fracture arrest (with or without slab fracture). However, beside current numerical studies utilizing discrete elements methods [8], only little attention has been devoted to a detailed analytical description of the PST able to give a comprehensive mechanical framework of the sequence of processes involved in the test. Consequently, this work aims to give a quantitative tool for an exhaustive interpretation of the PST, stressing the attention on important parameters that influence the test outcomes. First, starting from a pure mechanical point of view, a broad phenomenology of the main failure types of the PST is outlined. Then, the Euler-Bernoulli beam theory is applied to the test setup, allowing an easy description of the snowpack stress state in the quasi-static regime. We assume an elastic-perfectly brittle model as constitutive law for the snow slab. Besides, considering the weak layer as a rigid bed of crystals with an a priori inclination, a local instability problem is formulated in order to take into account the combined effect of compressive and shear loading. As a result, the onset of slab and weak layer fracture is described in terms of cut length, slab dimensions and the main mechanical parameters. A condition on the possible propagation of the crack is proposed as well. References [1] C. Sigrist and J. Schweizer, "Critical energy release rates of weak snowpack layers determined in field experiments", Geophysical Research Letters, Volume 34, L03502, 2007. [2] D. Gauthier and B. Jamieson, "Evaluation of a prototype field test for fracture and failure propagation propensity in weak snowpack layers". Cold Regions Science and Technology, Volume 51, Issue 2, Pages 87-97, 2008. [3] R. Simenhois and K.W. Birkeland. "The extended column test: Test effectiveness, spatial variability, and comparison with the propagation saw test." Cold Regions Science and Technology, Volume 59, Issue 23, Pages 210-216, 2009. [4] J. Heierli, P. Gumbsch, M. Zaiser, "Anticrack Nucleation as Triggering Mecchanism for Snow Slab Avalanches", Science, Volume 321, Pages 240-243, 2008. [5] A. van Herwijnen, J. Schweizer, J. Heierli, "Measurement of the deformation field associated with fracture propagation in weak snowpack layers", Journal of Geophysical Research, Volume 115, F03042, 2010. [6] K. W. Birkeland, A. van Herwijnen, E. Knoff, M. Staples, E. Bair, R. Simenhois, "The role of slabs and weak layers in fracture arrest", Proceedings of the International Snow Science Workshop, Banff, 2014. [7] J. Schweizer, B. Reuter, A. van Herwijnen, B. Jamieson, "On how the tensile strength of the slab affects crack propagation propensity", Proceedings of the International Snow Science Workshop, Banff, 2014. [8] J. Gaume, A. van Herwijnen, G. Chambon, K. W. Birkeland, J. Schweizer. "Modeling of crack propagation in weak snowpack layers using the discrete element method", The Cryosphere, Volume 9, Pages 1915-1932, 2015.

Quantitative Residual Strain Analyses on Strain Hardened Nickel Based Alloy

NASA Astrophysics Data System (ADS)

Yonezawa, Toshio; Maeguchi, Takaharu; Goto, Toru; Juan, Hou

Many papers have reported about the effects of strain hardening by cold rolling, grinding, welding, etc. on stress corrosion cracking susceptibility of nickel based alloys and austenitic stainless steels for LWR pipings and components. But, the residual strain value due to cold rolling, grinding, welding, etc. is not so quantitatively evaluated.

Thermal-Mechanical Stress Analysis of PWR Pressure Vessel and Nozzles under Grid Load-Following Mode: Interim Report on the Effect of Cyclic Hardening Material Properties and Pre-existing Cracks on Stress Analysis Results

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

Mohanty, Subhasish; Soppet, William; Majumdar, Saurin

This report provides an update on an assessment of environmentally assisted fatigue for light water reactor components under extended service conditions. This report is a deliverable under the work package for environmentally assisted fatigue as part of DOE’s Light Water Reactor Sustainability Program. In a previous report (September 2015), we presented tensile and fatigue test data and related hardening material properties for 508 low-alloys steel base metal and other reactor metals. In this report, we present thermal-mechanical stress analysis of the reactor pressure vessel and its hot-leg and cold-leg nozzles based on estimated material properties. We also present results frommore » thermal and thermal-mechanical stress analysis under reactor heat-up, cool-down, and grid load-following conditions. Analysis results are given with and without the presence of preexisting cracks in the reactor nozzles (axial or circumferential crack). In addition, results from validation stress analysis based on tensile and fatigue experiments are reported.« less

Thermal–mechanical stress analysis of pressurized water reactor pressure vessel with/without a preexisting crack under grid load following conditions

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

Mohanty, Subhasish; Soppet, William K.; Majumdar, Saurin

In this paper, we present thermal-mechanical stress analysis of a pressurized water reactor pressure vessel and its hot-leg and cold-leg nozzles. Results are presented from thermal and thermal-mechanical stress analysis under reactor heat-up, cool-down, and grid load-following conditions. Analysis results are given with and without the presence of preexisting crack in the reactor nozzle (axial crack in hot leg nozzle). From the model results it is found that the stress-strain states are significantly higher in case of presence of crack than without crack. In conclusion, the stress-strain state under grid load following condition are more realistic compared to the stress-strainmore » state estimated assuming simplified transients.« less

Thermal–mechanical stress analysis of pressurized water reactor pressure vessel with/without a preexisting crack under grid load following conditions

DOE PAGES

Mohanty, Subhasish; Soppet, William K.; Majumdar, Saurin; ...

2016-10-26

In this paper, we present thermal-mechanical stress analysis of a pressurized water reactor pressure vessel and its hot-leg and cold-leg nozzles. Results are presented from thermal and thermal-mechanical stress analysis under reactor heat-up, cool-down, and grid load-following conditions. Analysis results are given with and without the presence of preexisting crack in the reactor nozzle (axial crack in hot leg nozzle). From the model results it is found that the stress-strain states are significantly higher in case of presence of crack than without crack. In conclusion, the stress-strain state under grid load following condition are more realistic compared to the stress-strainmore » state estimated assuming simplified transients.« less

Cold-workability limits for carbon and alloy steels

NASA Astrophysics Data System (ADS)

El-Domiaty, A.

1999-04-01

In metalforming, the success in accomplishing the required deformation without failure of the forming tools or cracking of the work material represents the major concern for manufacture and design engineers. The degree of deformation that can be achieved in a particular metalworking process without creating an undesirable condition is defined as workability. In the present work, an experimental investigation was carried out to determine the cold-workability limits for five different types of steel: AISI 1018, 1045, 1078, 4140, and 4340. The upset (compression) test was used to determine the workability limit for each type. The upset dies and specimen geometries were designed to give different strain paths covering the range from homogeneous deformation (ɛz/ɛθ=-2.0) to close to plane-strain condition (ɛz/ɛθ=0.0). Grid pattern was printed on the specimen surface in order to measure the axial and hoop strain components during deformation. Specific elements were selected on the specimen surface, and their strain paths were determined. Each strain path was terminated once surface cracking had been observed. The ends of the strain paths, at which macrocracks were observed, were connected to obtain the workability limit on the forming-limit diagram. The workability limit of AISI 1018 is the highest among the other types of steel.

Exploratory Investigation into the Durability of Beneficial Cold Worked Fastener Hole in Aluminum

NASA Technical Reports Server (NTRS)

Johnson, W. S.; Clark, David A.

1999-01-01

Cold working fastener holes in aluminum alloys is a widely used technique in the aerospace industry for improving the fatigue performance of structures. A compressive tangential stress introduced in the material during the cold working of the hole reduces the natural tendency of the material to crack at the holes under cyclic tensile loading. It is a lucrative technique for the aerospace industry in that it provides an increase in performance without any weight cost.

Assessing edge cracking resistance in AHSS automotive parts by the Essential Work of Fracture methodology

NASA Astrophysics Data System (ADS)

Frómeta, D.; Tedesco, M.; Calvo, J.; Lara, A.; Molas, S.; Casellas, D.

2017-09-01

Lightweight designs and demanding safety requirements in automotive industry are increasingly promoting the use of Advanced High Strength Steel (AHSS) sheets. Such steels present higher strength (above 800 MPa) but lower ductility than conventional steels. Their great properties allow the reduction of the thickness of automobile structural components without compromising the safety, but also introduce new challenges to parts manufacturers. The fabrication of most cold formed components starts from shear cut blanks and, due to the lower ductility of AHSS, edge cracking problems can appear during forming operations, forcing the stop of the production and slowing down the industrial process. Forming Limit Diagrams (FLD) and FEM simulations are very useful tools to predict fracture problems in zones with high localized strain, but they are not able to predict edge cracking. It has been observed that the fracture toughness, measured through the Essential Work of Fracture (EWF) methodology, is a good indicator of the stretch flangeability in AHSS and can help to foresee this type of fractures. In this work, a serial production automotive component has been studied. The component showed cracks in some flanged edges when using a dual phase steel. It is shown that the conventional approach to explain formability, based on tensile tests and FLD, fails in the prediction of edge cracking. A new approach, based on fracture mechanics, help to solve the problem by selecting steel grades with higher fracture toughness, measured by means of EWF. Results confirmed that fracture toughness, in terms of EWF, can be readily used as a material parameter to rationalize cracking related problems and select AHSS with improved edge cracking resistance.

The effect of various deformation processes on the corrosion behavior of casing and tubing carbon steels in sweet environment

NASA Astrophysics Data System (ADS)

Elramady, Alyaa Gamal

The aim of this research project is to correlate the plastic deformation and mechanical instability of casing steel materials with corrosion behavior and surface change, in order to identify a tolerable degree of deformation for casing steel materials. While the corrosion of pipeline and casing steels has been investigated extensively, corrosion of these steels in sweet environments with respect to plastic deformation due to bending, rolling, autofrettage, or handling needs more investigation. Downhole tubular expansion of pipes (casings) is becoming standard practice in the petroleum industry to repair damaged casings, shutdown perforations, and ultimately achieve mono-diameter wells. Tubular expansion is a cold-drawing metal forming process, which consists of running conical mandrels through casings either mechanically using a piston or hydraulically by applying a back pressure. This mechanism subjects the pipes to large radial plastic deformations of up to 30 pct. of the inner diameter. It is known that cold-working is a way of strengthening materials such as low carbon steel, but given that this material will be subjected to corrosive environments, susceptibility to stress corrosion cracking (SCC) should be investigated. This research studies the effect of cold-work, in the form of cold-rolling and cold-expansion, on the surface behavior of API 5CT steels when it is exposed to a CO2-containing environment. Cold-work has a pronounced influence on the corrosion behavior of both API 5CT K55 and P110 grade steels. The lowest strength grade steel, API 5CT K55, performed poorly in a corrosive environment in the slow strain rate test. The ductile material exhibited the highest loss in strength and highest susceptibility to stress corrosion cracking in a CO 2-containing environment. The loss in strength declined with cold-rolling, which can be ascribed to the surface compressive stresses induced by cold-work. On the other hand, API 5CT P110 grade steels showed higher susceptibility to SCC when they were cold-rolled and cold-expanded. The research found that surface compressive stresses have an effect on the SCC behavior of casing and tubing steels. The CO2 corrosion behavior and atomic processes at the corroding interface were investigated at laboratory temperature using electrochemical techniques. Cold-work was found to have an influence on the corrosion behavior of both API 5CT K55 and P110 grade steels. These behaviors were found to be material and process dependent. Surface evaluation techniques such as field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) analysis did not detect formation of a protective scale. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) analysis both detected the appearance of a scale that was traced back to magnetite.

Influence of Localized Plasticity on IASCC Sensitivity of Austenitic Stainless Steels under PWR Primary Water

NASA Astrophysics Data System (ADS)

Cissé, Sarata; Tanguy, Benoit; Laffont, Lydia; Lafont, Marie-Christine; Guerre, Catherine; Andrieu, Eric

The sensibility of precipitation-strengthened A286 austenitic stainless steel to Stress Corrosion Cracking (SCC) is studied by means of Slow Strain Rate Tests (SSRT). First, alloy cold working by Low Cycle Fatigue (LCF) is investigated. Fatigue tests under plastic strain control are performed at different strain levels (Δ ɛp/2=0.2%, 0.5% and 0.8%) in order to establish correlation between stress softening and deformation microstructure resulting from LCF tests. Deformed microstructures have been identified through TEM investigations. Three states of cyclic behaviour for precipitation-strengthened A286 have been identified: hardening, cyclic softening and finally saturation of softening. It is shown that the A286 alloy cyclic softening is due to microstructural features such as defects — free deformation bands resulting from dislocations motion along family plans <111>, that swept defects or γ' precipitates and lead to deformation localization. In order to quantify effects of plastic localized deformation on intergranular stress corrosion cracking (IGSCC) of the A286 alloy in PWR primary water, slow strain rate tests are conducted. For each cycling conditions, two specimens at a similar stress level are tested: the first containing free precipitate deformation bands, the other not significant of a localized deformation state. SSRT tests are still in progress.

Feasibility of Steel Fiber-Reinforced Rubberized Concrete in Cold Regions for High Volume Intersections

NASA Astrophysics Data System (ADS)

Abou Eid, Mahear A.

There are many challenges faced with the use of Portland Cement Concrete (PCC) in cold regions, but with the inclusion of new technologies such as steel fibers and recycled tire crumb rubber efficient construction may be possible. Research was conducted on a modified concrete material that included both steel fibers and crumb rubber. The composite material was called Steel Fiber-Reinforced Rubberized Concrete (SFRRC). The objective of this investigation was to provide evidence showing that SFRRC can reduce tire rutting compared to asphaltic pavement. In addition, the research showed that the SFRRC could withstand freeze-thaw cycles and increase service life of roadways. Several tests were performed to determine the characteristics of the material. Freeze-thaw testing was performed to determine compressive strength loss and visual deterioration of the material. Wheel tracker rut testing was performed both with the standard steel wheel and with a modified studded rubber tire to determine plastic deformation and rut resistance. An experimental test slab was cast in place on a public approach to observe the construction procedures, the effects of studded tire wear and the frost actions in cold region conditions. Based on freeze-thaw and wheel tracker test results and observations of the experimental test slab, the SFRRC material shows viability in cold regions for resisting freeze-thaw actions. The freeze-thaw testing resulted in increased compressive strength after 300 freeze-thaw cycles and very low deterioration of material compared to standard PCC. The wheel tracker testing resulted in very low plastic deformation and minor material rutting with use of the studded rubber tire. The test slab showed very minor surface wear, no freeze-thaw cracking and no rutting after one winter of use. It is recommended that further testing of the material be conducted by means of a large-scale trial section. This would provide information with respect to cost analysis and integration of the material into the Department of Transportation construction program.

Comparison of Fatigue Properties and Fatigue Crack Growth Rates of Various Implantable Metals

PubMed Central

Okazaki, Yoshimitsu

2012-01-01

The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P.) grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 107 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK) than Ti alloy.

Report on Status of Shipment of High Fluence Austenitic Steel Samples for Characterization and Stress Corrosion Crack Testing

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

Clark, Scarlett R.; Leonard, Keith J.

The goal of the Mechanisms of Irradiation Assisted Stress Corrosion Cracking (IASCC) task in the LWRS Program is to conduct experimental research into understanding how multiple variables influence the crack initiation and crack growth in materials subjected to stress under corrosive conditions. This includes understanding the influences of alloy composition, radiation condition, water chemistry and metallurgical starting condition (i.e., previous cold work or heat treatments and the resulting microstructure) has on the behavior of materials. Testing involves crack initiation and growth testing on irradiated specimens of single-variable alloys in simulated Light Water Reactor (LWR) environments, tensile testing, hardness testing, microstructuralmore » and microchemical analysis, and detailed efforts to characterize localized deformation. Combined, these single-variable experiments will provide mechanistic understanding that can be used to identify key operational variables to mitigate or control IASCC, optimize inspection and maintenance schedules to the most susceptible materials/locations, and, in the long-term, design IASCC-resistant materials. In support of this research, efforts are currently underway to arrange shipment of “free” high fluence austenitic alloys available through Électricité de France (EDF) for post irradiation testing at the Oak Ridge National Laboratory (ORNL) and IASCC testing at the University of Michigan. These high fluence materials range in damage values from 45 to 125 displacements per atom (dpa). The samples identified for transport to the United States, which include nine, no-cost, 304, 308 and 316 tensile bars, were relocated from the Research Institute of Atomic Reactors (RIAR) in Dimitrovgrad, Ulyanovsk Oblast, Russia, and received at the Halden Reactor in Halden, Norway, on August 23, 2016. ORNL has been notified that a significant amount of work is required to prepare the samples for further shipment to Oak Ridge, Tennessee. The preliminary work for sample shipment between Halden and Oak Ridge includes fabrication of an inner cask sample container, decontamination and preparation of a Type A container, preparation of new activity calculations, all necessary paperwork, and handling. ORNL will continue to work to track progress of sample preparation and shipment status, and to work toward an agreement that covers material shipping costs between the Halden Reactor and the Oak Ridge National Laboratory.« less

Mechanisms of Forming Intergranular Microcracks and Microscopic Surface Discontinuities in Welds

DTIC Science & Technology

1992-06-01

SCC) is defined as slow stable crack extension occurring under static loading in sea water at stress intensity values below KIc (critical stress...preheating on the cold cracking resistance is reflected mainly in a reduction of the degree of localization of microplastic strains, their...deconcentration and an increase of the basis over which microplastic yielding takes place. This increases the amount of energy used for local plastic deformation

Crack Growth in Mercury Embrittled Aluminum Alloys under Cyclic and Static Loading Conditions

DTIC Science & Technology

1983-03-01

STATEMENT (ol the abalract entered In Block 20, It dlHerent from Report) 18. SUPPLEMENTARY NOTES This was a thesis in partial fulfillment of...argued that the strengthening that occurs from cold rolling suppresses crack nucleation at the surface under monotonlc loading. Under cyclic loading...precracking. Copper was chosen because It can be easily electrodeposited on aluminum, easily wet with mercury, and remains wet almost indefinitely

Fatigue properties of type 316LN stainless steel in air and mercury

NASA Astrophysics Data System (ADS)

Strizak, J. P.; Tian, H.; Liaw, P. K.; Mansur, L. K.

2005-08-01

An extensive fatigue testing program on 316LN stainless steel was recently carried out to support the design of the mercury target container for the spallation neutron source (SNS) that is currently under construction at the Oak Ridge National Laboratory in the United States. The major objective was to determine the effects of mercury on fatigue behavior. The S- N fatigue behavior of 316LN stainless steel is characterized by a family of bilinear fatigue curves which are dependent on frequency, environment, mean stress and cold work. Generally, fatigue life increases with decreasing stress and levels off in the high cycle region to an endurance limit below which the material will not fail. For fully reversed loading as well as tensile mean stress loading conditions mercury had no effect on endurance limit. However, at higher stresses a synergistic relationship between mercury and cyclic loading frequency was observed at low frequencies. As expected, fatigue life decreased with decreasing frequency, but the response was more pronounced in mercury compared with air. As a result of liquid metal embrittlement (LME), fracture surfaces of specimens tested in mercury showed widespread brittle intergranular cracking as opposed to typical transgranular cracking for specimens tested in air. For fully reversed loading (zero mean stress) the effect of mercury disappeared as frequency increased to 10 Hz. For mean stress conditions with R-ratios of 0.1 and 0.3, LME was still evident at 10 Hz, but at 700 Hz the effect of mercury had disappeared ( R = 0.1). Further, for higher R-ratios (0.5 and 0.75) fatigue curves for 10 Hz showed no environmental effect. Finally, cold working (20%) increased tensile strength and hardness, and improved fatigue resistance. Fatigue behavior at 10 and 700 Hz was similar and no environmental effect was observed.

The rolling performance of Fe-6.5 wt.% Si sheets edged with stainless steel

NASA Astrophysics Data System (ADS)

Zhang, B.; Ye, F.; Liang, Y. F.; Shi, X. J.; Lin, J. P.

2017-10-01

Compared with common electrical steel, high silicon electrical steel (Fe-6.5 wt.% Si alloy) exhibits excellent soft magnetic properties and a wide application prospect in high frequency electromagnetic fields. In the process of cold rolling Fe-6.5 wt.% Si alloy, edge-crack often occurs on the sheets due to the inadequate ductility and limited formability. It was found that the Fe-6.5 wt.% Si alloy sheet edged with 304 stainless steel by laser welding show an improved rolling performance. The composite sheet could be cold rolled to a thickness of 0.07 mm without observed edge cracks. The mechanical property of the edging material should be in an appropriate window in reference to that of the Fe-6.5 wt.% Si alloy.

75 FR 38061 - Airworthiness Directives; Airbus Model A300 B4-600 Series Airplanes; Model A300 B4-600R Series...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-01

... dimensional measurement of the holes, and doing corrective actions if necessary; doing an eddy current... dimensional measurement of the holes, doing an eddy current inspection of the holes for cracking, doing a cold... the effective date of this AD, prior to doing any cold working process, determine if an eddy current...

PWSCC Susceptibility in Heat Affected Zones of Alloy 600

NASA Astrophysics Data System (ADS)

Couvant, Thierry; Brossier, Thomas; Cossange, Christian

The recent field experience and several experimental results have shown the possible deleterious effect of a heat affected zone (HAZ) induced by welding on the susceptibility to the stress corrosion cracking (SCC) of Alloy 600 of bottom penetrations exposed to primary water of PWRs. This work tried to quantify the increasing susceptibility to initiation and crack propagation in 600/182 HAZ. The rolled plate did not exhibit any susceptibility to SCC except for a cold work higher than 10% typically. By contrast, the weld metal was well known for its high susceptibility to SCC. Metallurgical and mechanical characterizations of the HAZ indicated a slight gradient of Vickers micro hardness close to the fusion line (up to few mm) and a lack of intergranular precipitates up to 500 µm from the fusion line. SCC tests clearly demonstrated that a non-susceptible plate may exhibit a significant susceptibility to SCC propagation in the HAZ. Results of initiation tests did not allow to observe any SCC in the base metal, due to the high susceptibility to SCC of the weld.

Hydrogen Permeation in Cold-Rolled High-Mn Twinning-Induced Plasticity Steels

NASA Astrophysics Data System (ADS)

Han, Do Kyeong; Hwang, A. In; Byeon, Woo Jun; Noh, Seung Jeong; Suh, Dong-Woo

2017-11-01

Hydrogen permeation is investigated in cold-rolled Fe-0.6C-18Mn-(1.5Al) alloys. The hydrogen mobility is lower in cold-rolled alloys compared with annealed alloys. Al-containing alloy shows less deceleration of hydrogen mobility compared with the Al-free alloy. This is attributed to the reduced formation of mechanical twins and dislocations. Mechanical twins trap hydrogen strongly but are vulnerable to crack initiation; suppression of these is thought to be a major favorable influence of Al on hydrogen-induced mechanical degradation.

Saw & seal, airport pavement.

DOT National Transportation Integrated Search

2009-05-01

Due to extreme cold temperatures, hot bituminous pavements on Maines airports are subject to transverse : or thermal cracking. This can lead to poorly performing pavement structure causing heaving and : settlement problems. Studies have shown that...

Effects of Annealing Treatment Prior to Cold Rolling on Delayed Fracture Properties in Ferrite-Austenite Duplex Lightweight Steels

NASA Astrophysics Data System (ADS)

Sohn, Seok Su; Song, Hyejin; Kim, Jung Gi; Kwak, Jai-Hyun; Kim, Hyoung Seop; Lee, Sunghak

2016-02-01

Tensile properties of recently developed automotive high-strength steels containing about 10 wt pct of Mn and Al are superior to other conventional steels, but the active commercialization has been postponed because they are often subjected to cracking during formation or to the delayed fracture after formation. Here, the delayed fracture behavior of a ferrite-austenite duplex lightweight steel whose microstructure was modified by a batch annealing treatment at 1023 K (750 °C) prior to cold rolling was examined by HCl immersion tests of cup specimens, and was compared with that of an unmodified steel. After the batch annealing, band structures were almost decomposed as strong textures of {100}<011> α-fibers and {111}<112> γ-fibers were considerably dissolved, while ferrite grains were refined. The steel cup specimen having this modified microstructure was not cracked when immersed in an HCl solution for 18 days, whereas the specimen having unmodified microstructure underwent the delayed fracture within 1 day. This time delayed fracture was more critically affected by difference in deformation characteristics such as martensitic transformation and deformation inhomogeneity induced from concentration of residual stress or plastic strain, rather than the difference in initial microstructures. The present work gives a promise for automotive applications requiring excellent mechanical and delayed fracture properties as well as reduced specific weight.

Material condition assessment with eddy current sensors

NASA Technical Reports Server (NTRS)

Goldfine, Neil J. (Inventor); Washabaugh, Andrew P. (Inventor); Sheiretov, Yanko K. (Inventor); Schlicker, Darrell E. (Inventor); Lyons, Robert J. (Inventor); Windoloski, Mark D. (Inventor); Craven, Christopher A. (Inventor); Tsukernik, Vladimir B. (Inventor); Grundy, David C. (Inventor)

2010-01-01

Eddy current sensors and sensor arrays are used for process quality and material condition assessment of conducting materials. In an embodiment, changes in spatially registered high resolution images taken before and after cold work processing reflect the quality of the process, such as intensity and coverage. These images also permit the suppression or removal of local outlier variations. Anisotropy in a material property, such as magnetic permeability or electrical conductivity, can be intentionally introduced and used to assess material condition resulting from an operation, such as a cold work or heat treatment. The anisotropy is determined by sensors that provide directional property measurements. The sensor directionality arises from constructs that use a linear conducting drive segment to impose the magnetic field in a test material. Maintaining the orientation of this drive segment, and associated sense elements, relative to a material edge provides enhanced sensitivity for crack detection at edges.

Influence of Cold-Sprayed, Warm-Sprayed, and Plasma-Sprayed Layers Deposition on Fatigue Properties of Steel Specimens

NASA Astrophysics Data System (ADS)

Cizek, J.; Matejkova, M.; Dlouhy, I.; Siska, F.; Kay, C. M.; Karthikeyan, J.; Kuroda, S.; Kovarik, O.; Siegl, J.; Loke, K.; Khor, Khiam Aik

2015-06-01

Titanium powder was deposited onto steel specimens using four thermal spray technologies: plasma spray, low-pressure cold spray, portable cold spray, and warm spray. The specimens were then subjected to strain-controlled cyclic bending test in a dedicated in-house built device. The crack propagation was monitored by observing the changes in the resonance frequency of the samples. For each series, the number of cycles corresponding to a pre-defined specimen cross-section damage was used as a performance indicator. It was found that the grit-blasting procedure did not alter the fatigue properties of the steel specimens (1% increase as compared to as-received set), while the deposition of coatings via all four thermal spray technologies significantly increased the measured fatigue lives. The three high-velocity technologies led to an increase of relative lives to 234% (low-pressure cold spray), 210% (portable cold spray), and 355% (warm spray) and the deposition using plasma spray led to an increase of relative lives to 303%. The observed increase of high-velocity technologies (cold and warm spray) could be attributed to a combination of homogeneous fatigue-resistant coatings and induction of peening stresses into the substrates via the impingement of the high-kinetic energy particles. Given the intrinsic character of the plasma jet (low-velocity impact of semi/molten particles) and the mostly ceramic character of the coating (oxides, nitrides), a hypothesis based on non-linear coatings behavior is provided in the paper.

Urban cool

NASA Astrophysics Data System (ADS)

Ennos, Roland

2010-08-01

The picture-perfect summer for many involves dipping toes into the water's edge on a sandy beach, strolling through a park licking an ice cream or cracking open a bottle of cold beer as gorgeous smells waft from a barbecue nearby.

Hot tensile behaviour in silicon-killed boron microalloyed steels

NASA Astrophysics Data System (ADS)

Chown, Lesley H.; Cornish, Lesley A.

2017-10-01

Low carbon steel for drawing and cold heading applications should have low strength, high ductility and low strain ageing rates. To achieve this, nitrogen must be removed from solid solution, which can be done by low additions of boron. A wire producer had been experiencing occasional problems with severe cracking on silicon-killed, boron steel billets during continuous casting, but the solution was not obvious. Samples from four billets, each from different casts, were removed for analysis and testing. The tested steel compositions were within the specification limits, with boron to nitrogen ratios of 0.40-1.19. Hot ductility testing was performed on a Gleeble 1500 using parameters approximating the capabilities of this particular billet caster. The steel specimens were subjected to in situ melting, then cooled at a rate of 2 C.s-1 to temperatures in the range 750-1250°C, where they were then pulled to failure at a strain rate of 8x10-4 s-1. In this work, it was found that both the boron to nitrogen ratio and the manganese to sulphur ratio influenced the hot ductility and hence the crack susceptibility. Excellent hot ductility was found for B:N ratios above 1.0, which confirmed that the B:N ratio should be above a stoichiometric value of 0.8 to remove all nitrogen from solid solution. TEM analysis showed that coarse BN precipitates nucleated on other precipitates, such as (Fe,Mn)S, which have relatively low melting points, and are detrimental to hot ductility. Low Mn:S ratios of 10 - 12 were shown to promote precipitation of FeS, so a Mn:S > 14 was recommended. A narrower billet surface temperature range for straightening was recommended to prevent transverse surface cracking. Additionally, analysis of industrial casting data showed that the scrap percentage due to transverse cracking increased significantly for Mn:S < 14. An exponential decay relationship between the manganese to sulphur ratio and the average scrap percentage due to transverse cracking was derived as a simple tool to predict, and hence mitigate, scrap levels in the casting plant.

Al-Li Alloy 1441 for Fuselage Applications

NASA Technical Reports Server (NTRS)

Bird, R. K.; Dicus, D. L.; Fridlyander, J. N.; Sandler, V. S.

2000-01-01

A cooperative investigation was conducted to evaluate Al-Cu-Mg-Li alloy 1441 for long service life fuselage applications. Alloy 1441 is currently being used for fuselage applications on the Russian Be-103 amphibious aircraft, and is expected to be used for fuselage skin on a new Tupolev business class aircraft. Alloy 1441 is cold-rollable and has several attributes that make it attractive for fuselage skin applications. These attributes include lower density and higher specific modulus with similar strength as compared to conventional Al-Cu-Mg alloys. Cold-rolled 1441 Al-Li sheet specimens were tested at NASA Langley Research Center (LaRC) and at the All-Russia Institute of Aviation Materials (VIAM) in Russia to evaluate tensile properties, fracture toughness, impact resistance, fatigue life and fatigue crack growth rate. In addition, fuselage panels were fabricated by Tupolev Design Bureau (TDB) using 1441 skins and Al-Zn-Mg-Cu alloy stiffeners. The panels were subjected to cyclic pressurization fatigue tests at TDB and at LaRC to simulate fuselage pressurization/depressurization during aircraft service. This paper discusses the results from this investigation.

Hexagons in Icy Terrain

NASA Image and Video Library

2018-01-23

Ground cemented by ice cover the high latitudes of Mars, much as they do on Earth's cold climates. A common landform that occurs in icy terrain are polygons as shown in this image from NASA's Mars Reconnaissance Orbiter (MRO). Polygonal patterns form by winter cooling and contraction cracking of the frozen ground. Over time these thin cracks develop and coalesce into a honeycomb network, with a few meters spacing between neighboring cracks. Shallow troughs mark the locations of the underground cracks, which are clearly visible form orbit. The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 30.2 centimeters (11.9 inches) per pixel (with 1 x 1 binning); objects on the order of 91 centimeters (35.8 inches) across are resolved.] North is up. https://photojournal.jpl.nasa.gov/catalog/PIA22180

Characterization of microstructure, local deformation and microchemistry in Alloy 690 heat-affected zone and stress corrosion cracking in high temperature water

NASA Astrophysics Data System (ADS)

Lu, Zhanpeng; Chen, Junjie; Shoji, Tetsuo; Takeda, Yoichi; Yamazaki, Seiya

2015-10-01

With increasing the distance from the weld fusion line in an Alloy 690 heat-affected zone, micro-hardness decreases, kernel average misorientation decreases and the fraction of Σ3 boundaries increases. Chromium depletion at grain boundaries in the Alloy 690 heat-affected zone is less significant than that in an Alloy 600 heat-affected zone. Alloy 690 heat-affected zone exhibits much higher IGSCC resistance than Alloy 600 heat-affected zone in simulated pressurized water reactor primary water. Heavily cold worked Alloy 690 exhibits localized intergranular stress corrosion cracking. The effects of metallurgical and mechanical properties on stress corrosion cracking in Alloy 690 are discussed.

Cold spray NDE for porosity and other process anomalies

NASA Astrophysics Data System (ADS)

Glass, S. W.; Larche, M. R.; Prowant, M. S.; Suter, J. D.; Lareau, J. P.; Jiang, X.; Ross, K. A.

2018-04-01

This paper describes a technology review of nondestructive evaluation (NDE) methods that can be applied to cold spray coatings. Cold spray is a process for depositing metal powder at high velocity so that it bonds to the substrate metal without significant heating that would be likely to cause additional residual tensile stresses. Coatings in the range from millimeters to centimeters are possible at relatively high deposition rates. Cold spray coatings that may be used for hydroelectric components that are subject to erosion, corrosion, wear, and cavitation damage are of interest. The topic of cold spray NDE is treated generally, however, but may be considered applicable to virtually any cold spray application except where there are constraints of the hydroelectric component application that bear special consideration. Optical profilometry, eddy current, ultrasound, and hardness tests are shown for one set of good, fair, and poor nickel-chrome (NiCr) on 304 stainless steel (304SS) cold spray samples to demonstrate inspection possibilities. The primary indicator of cold spray quality is the cold spray porosity that is most directly measured with witness-sample destructive examinations (DE)—mostly photo-micrographs. These DE-generated porosity values are correlated with optical profilometry, eddy current, ultrasound, and hardness test NDE methods to infer the porosity and other information of interest. These parameters of interest primarily include: • Porosity primarily caused by improper process conditions (temperature, gas velocity, spray standoff, spray angle, powder size, condition, surface cleanliness, surface oxide, etc.) • Presence/absence of the cold spray coating including possible over-sprayed voids • Coating thicknessOptical profilometry measurements of surface roughness trended with porosity plus, if compared with a reference measurement or reference drawing, would provide information on the coating thickness. Ultrasound could provide similar surface profile information plus attenuation measurements trended with porosity. The ultrasound measurements, however, may be limited to geometries where the substrate back-wall is normal to the cold spray surface and not too thick. Eddy current showed a strong correlation with porosity. Eddy currents can also be sensitive to cracks and do not need fluid coupling to make measurements, but are not sensitive to coating thicknesses in most cases. Vickers hardness measurements also tracked well with porosity; however, these types of hardness measurements are also not sensitive to coating thickness. An NDE program may include multiple measurements.

Development of a 2-stage shear-cutting-process to reduce cut-edge-sensitivity of steels

NASA Astrophysics Data System (ADS)

Gläsner, T.; Sunderkötter, C.; Hoffmann, H.; Volk, W.; Golle, R.

2017-09-01

The edge cracking sensitivity of AHSS and UHSS is a challenging factor in the cold forming process. Expanding cut holes during flanging operations is rather common in automotive components. During these flanging operations the pierced hole is stretched so that its diameter is increased. These flanging operations stretch material that has already been subjected to large amounts of plastic deformation, therefore forming problems may occur. An innovative cutting process decreases micro cracks in the cutting surface and facilitates the subsequent cold forming process. That cutting process consists of two stages, which produces close dimensional tolerance and smooth edges. As a result the hole expanding ratio was increased by nearly 100 % when using thick high strength steels for suspension components. The paper describes the mechanisms of the trimming process at the cut edge, and the positive effect of the 2-stage shear-cutting process on the hole extension capability of multiphase steels.

Hydrogen assisted cracking and CO2 corrosion behaviors of low-alloy steel with high strength used for armor layer of flexible pipe

NASA Astrophysics Data System (ADS)

Liu, Zhenguang; Gao, Xiuhua; Du, Linxiu; Li, Jianping; Zhou, Xiaowei; Wang, Xiaonan; Wang, Yuxin; Liu, Chuan; Xu, Guoxiang; Misra, R. D. K.

2018-05-01

In this study, hydrogen induced cracking (HIC), sulfide stress corrosion cracking (SSCC) and hydrogen embrittlement (HE) were carried out to study hydrogen assisted cracking behavior (HIC, SSCC and HE) of high strength pipeline steel used for armor layer of flexible pipe in ocean. The CO2 corrosion behavior of designed steel with high strength was studied by using immersion experiment. The experimental results demonstrate that the corrosion resistance of designed steel with tempered martensite to HIC, SSCC and HE is excellent according to specific standards, which contributes to the low concentration of dislocation and vacancies previously formed in cold rolling process. The corrosion mechanism of hydrogen induced cracking of designed steel, which involves in producing process, microstructure and cracking behavior, is proposed. The designed steel with tempered martensite shows excellent corrosion resistance to CO2 corrosion. Cr-rich compound was first formed on the coupon surface exposed to CO2-saturated brine condition and chlorine, one of the corrosion ions in solution, was rich in the inner layer of corrosion products.

Study of fatigue crack propagation in Ti-1Al-1Mn based on the calculation of cold work evolution

NASA Astrophysics Data System (ADS)

Plekhov, O. A.; Kostina, A. A.

2017-05-01

The work proposes a numerical method for lifetime assessment for metallic materials based on consideration of energy balance at crack tip. This method is based on the evaluation of the stored energy value per loading cycle. To calculate the stored and dissipated parts of deformation energy an elasto-plastic phenomenological model of energy balance in metals under the deformation and failure processes was proposed. The key point of the model is strain-type internal variable describing the stored energy process. This parameter is introduced based of the statistical description of defect evolution in metals as a second-order tensor and has a meaning of an additional strain due to the initiation and growth of the defects. The fatigue crack rate was calculated in a framework of a stationary crack approach (several loading cycles for every crack length was considered to estimate the energy balance at crack tip). The application of the proposed algorithm is illustrated by the calculation of the lifetime of the Ti-1Al-1Mn compact tension specimen under cyclic loading.

Sensitivity and comparison evaluation of Saturn 5 liquid penetrants

NASA Technical Reports Server (NTRS)

Jones, G. H.

1973-01-01

Results of a sensitivity and comparison evaluation performed on six liquid penetrants that were used on the Saturn 5 vehicle and other space hardware to detect surface discontinuities are described. The relationship between penetrant materials and crack definition capabilities, the optimum penetrant materials evaluation method, and the optimum measurement methods for crack dimensions were investigated. A unique method of precise developer thickness control was envolved, utilizing clear radiographic film and a densitometer. The method of evaluation included five aluminum alloy, 2219-T87, specimens that were heated and then quenched in cold water to produce cracks. The six penetrants were then applied, one at a time, and the crack indications were counted and recorded for each penetrant for comparison purposes. Measurements were made by determining the visual crack indications per linear inch and then sectioning the specimens for a metallographic count of the cracks present. This method provided a numerical approach for assigning a sensitivity index number to the penetrants. Of the six penetrants evaluated, two were not satisfactory (one was not sufficiently sensitive and the other was to sensitive, giving false indications). The other four were satisfactory with approximately the same sensitivity in the range of 78 to 80.5 percent of total cracks detected.

Investigation on the cold rolling and structuring of cold sprayed copper-coated steel sheets

NASA Astrophysics Data System (ADS)

Bobzin, K.; Öte, M.; Wiesner, S.; Gerdt, L.; Senge, S.; Hirt, G.

2017-03-01

A current driving force of research is lightweight design. One of the approaches to reduce the weight of a component without causing an overall stiffness decrease is the use of multi-material components. One of the main challenges of this approach is the low bonding strength between different materials. Focusing on steel-aluminum multi-material components, thermally sprayed copper coatings can come into use as a bonding agent between steel sheets and high pressure die cast aluminum to improve the bonding strength. This paper presents a combination of cold gas spraying of copper coatings and their subsequent structuring by rolling as surface pretreatment method of the steel inserts. Therefore, flat rolling experiments are performed with samples in “as sprayed” and heat treated conditions to determine the influence of the rolling process on the bond strength and the formability of the coating. Furthermore, the influence of the rolling on the roughness and the hardness of the coating was examined. In the next step, the coated surface was structured, to create a surface topology suited for a form closure connection in a subsequent high-pressure die casting process. No cracks were observed after the cold rolling process with a thickness reduction of up to ε = 14 % for heat treated samples. Structuring of heat treated samples could be realized without delamination and cracking.

Experiments on the Effects of Confining Pressure During Reaction-Driven Cracking

NASA Astrophysics Data System (ADS)

Skarbek, R. M.; Savage, H. M.; Kelemen, P. B.; Lambart, S.; Robinson, B.

2016-12-01

Cracking caused by reaction-driven volume increase is an important process in many geological settings. In particular, the interaction of brittle rocks with reactive fluids can create fractures that modify the permeability and reactive surface area, leading to a large variety of feedbacks. The conditions controlling reaction-driven cracking are poorly understood, especially at geologically relevant confining pressures. We conducted two sets of experiments to study the effects of confining pressure on cracking during the formation of gypsum from anhydrite CaSO4 + 2H2O = CaSO4•2H2O, and portlandite from calcium oxide CaO + H2O = Ca(OH)2. In the first set of experiments, we cold-pressed CaSO4, or CaO powder to form cylinders. Samples were confined in steel, and compressed with an axial load of 0.1 to 4 MPa. Water was allowed to infiltrate the initially unsaturated samples through the bottom face via capillary and Darcian flow across a micro-porous frit. The height of the sample was recorded during the experiment, and serves as a measure of volume change due to the hydration reaction. We also recorded acoustic emissions (AEs) using piezoelectric transducers (PZTs), to serve as a measure of cracking during an experiment. Experiments were stopped when the recorded volume change reached 80% - 100% of the stoichiometrically calculated volume change of the reaction. In a second set of experiments, we pressed CaSO4 powder to form cylinders 8.9 cm in length and 3.5 cm in diameter for testing in a tri-axial press with ports for fluid input and output, across the top and bottom faces of the sample. The tri-axial experiments were set up to investigate the reaction-driven cracking process for a range of confining pressures. Cracking during experiments was monitored using strain gauges and PZTs attached to the sample. We measured permeability during experiments by imposing a fluid pressure gradient across the sample. These experiments elucidate the role of cracking caused by crystallization pressure in many important hydration reactions.

ARC-1979-A79-7087

NASA Image and Video Library

1979-07-09

P-21758 BW Range: 246,000 kilometers (152,000 miles) This picture by Voyager 2 is the first close look ever obtained of Jupiter's satellite, Europa. The linear crack-like features had been seen from a much greater distance by Voyager 1 but this image provides a resolution of about four kilometers (2.5 miles). The complicated linear features appear even more like cracks or huge fractures in these images. Also seen are somewhat darker mottled regions which appear to have a slightly pitted appearance, perhaps due to small scale craters. No large craters (more than five kilometers in diameter) are easily identifiable in the Europa photographs to date, suggesting that this satellite has a young surface relative to Ganymede and Callisto, although not perhaps as young as Io's. Various models for Europa's structure will be tested during analysis of these images, including the possibility that the surface is a thin ice crust overlying water or softer ice and that the fracture systems seen are breaks in that crust. Resurfacing mechanisms such as production of fresh ice or snow along the cracks and cold glacier-like flows are being considered as possibilities for removing evidence of impact events. Europa thus appears to truly be a satellite with many properties intermediate between Ganymede and Io.

Forecasting Frost Damage: Follow the Water

NASA Astrophysics Data System (ADS)

Rempel, A. W.

2015-12-01

Frost damage takes place when the pressure exerted against pore walls exceeds the cohesive strength of water-infiltrated rock and causes cracks to extend. Elegant theoretical treatments supported by meticulous field and laboratory observations have combined to unravel the basic mechanical and thermodynamic controls in idealized systems. Frost damage is most vigorous when conditions are cold enough that the net pressure exerted against the pore walls can cause crack extension, yet warm enough to enable the flow that supplies further ice growth in the newly opened space. This insight is applied here to develop practical geomorphic process laws for the effects of frost damage at the larger scales that are relevant for describing the evolution of landscapes. To this end, a direct connection is made between the intensity of frost damage and the porosity increase that results from gradients in water flux under conditions that are cold enough for ice-rock interactions to propagate cracks. This implies that the annual temperature variation at the ground surface can be combined with considerations of heat and mass transport to derive rigorous forecasts of the potential for frost damage that are tied to the increases in water mass that accompany solidification in porous rock. As an example, the image shows the depth-integrated porosity change λ promoted by crack growth at temperatures colder than -ΔTc over an annual cycle for different choices of mean annual temperature MAT and surface amplitude A (assuming a thermal diffusivity of 1 mm2/s and a power-law relationship between permeability and undercooling with exponent α=4, such that a base value of 10-14m2 is reached at a reference undercooling of 0.1 ºC). The abrupt onset in cracking once MAT decreases below a threshold is produced by the requirement that undercooling surpass ΔTc in order to generate sufficient pressures to propagate cracks. The eventual reduction and gradual tail in λ at colder MAT is produced by the clogging of the permeable pathways needed to supply additional water to propmote crack growth.

Evaluation and ranking of candidate ceramic wafer engine seal materials

NASA Technical Reports Server (NTRS)

Steinetz, Bruce M.

1991-01-01

Modern engineered ceramics offer high temperature capabilities not found in even the best superalloy metals. The high temperature properties of several selected ceramics including aluminum oxide, silicon carbide, and silicon nitride are reviewed as they apply to hypersonic engine seal design. A ranking procedure is employed to objectively differentiate among four different monolithic ceramic materials considered, including: a cold-pressed and sintered aluminum oxide; a sintered alpha-phase silicon carbide; a hot-isostatically pressed silicon nitride; and a cold-pressed and sintered silicon nitride. This procedure is used to narrow the wide range of potential ceramics considered to an acceptable number for future detailed and costly analyses and tests. The materials are numerically scored according to their high temperature flexural strength; high temperature thermal conductivity; resistance to crack growth; resistance to high heating rates; fracture toughness; Weibull modulus; and finally according to their resistance to leakage flow, where materials having coefficients of thermal expansion closely matching the engine panel material resist leakage flow best. The cold-pressed and sintered material (Kyocera SN-251) ranked the highest in the overall ranking especially when implemented in engine panels made of low expansion rate materials being considered for the engine, including Incoloy and titanium alloys.

Synthesis, Characterization and Cold Workability of Cast Copper-Magnesium-Tin Alloys

NASA Astrophysics Data System (ADS)

Bravo Bénard, Agustín Eduardo; Martínez Hernández, David; González Reyes, José Gonzalo; Ortiz Prado, Armando; Schouwenaars Franssens, Rafael

2014-02-01

The use of Mg as an alloying element in copper alloys has largely been overlooked in scientific literature and technological applications. Its supposed tribological compatibility with iron makes it an interesting option to replace Pb in tribological alloys. This work describes the casting process of high-quality thin slabs of Cu-Mg-Sn alloys with different compositions by means of conventional methods. The resulting phases were analyzed using X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray spectroscopy techniques. Typical dendritic α-Cu, eutectic Cu2Mg(Sn) and eutectoid non-equilibrium microstructures were found. Tensile tests and Vickers microhardness show the excellent hardening capability of Mg as compared to other copper alloys in the as-cast condition. For some of the slabs and compositions, cold rolling reductions of over 95 pct have been easily achieved. Other compositions and slabs have failed during the deformation process. Failure analysis after cold rolling reveals that one cause for brittleness is the presence of casting defects such as microshrinkage and inclusions, which can be eliminated. However, for high Mg contents, a high volume fraction of the intermetallic phase provides a contiguous path for crack propagation through the connected interdendritic regions.

Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

NASA Astrophysics Data System (ADS)

Cissé, Sarata; Laffont, Lydia; Lafont, Marie-Christine; Tanguy, Benoit; Andrieu, Eric

2013-02-01

The sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δɛp/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown.

Elimination of Dual Slope from the Coffin Manson Relationship of Low-Cycle Fatigue in the Titanium Alloy Timetal 834, by Cold Rolling

NASA Astrophysics Data System (ADS)

Sai Srinadh, K. V.; Singh, Vakil

2007-08-01

Cold rolling of the titanium alloy Timetal 834 was found to cause marked enhancement in low-cycle fatigue (LCF) life at low strain amplitude and to eliminate bilinear behavior from the Coffin Manson (C-M) relationship. It was due to work hardening of surface grains of soft orientation and consequent increase in resistance of the material against crack initiation. The observed effect was not associated with texture.

Novel Method of Aluminum to Copper Bonding by Cold Spray

NASA Astrophysics Data System (ADS)

Fu, Si-Lin; Li, Cheng-Xin; Wei, Ying-Kang; Luo, Xiao-Tao; Yang, Guan-Jun; Li, Chang-Jiu; Li, Jing-Long

2018-04-01

Cold spray bonding (CSB) has been proposed as a new method for joining aluminum and copper. At high speeds, solid Al particles impacted the groove between the two substrates to form a bond between Al and Cu. Compared to traditional welding technologies, CSB does not form distinct intermetallic compounds. Large stainless steel particles were introduced into the spray powders as in situ shot peen particles to create a dense Al deposit and to improve the bond strength of joints. It was discovered that introducing shot peen particles significantly improved the flattening ratio of the deposited Al particles. Increasing the proportion of shot peen particles from 0 to 70 vol.% decreased the porosity of the deposits from 12.4 to 0.2%, while the shear strength of joints significantly increased. The tensile test results of the Al-Cu joints demonstrated that cracks were initiated at the interface between the Al and the deposit. The average tensile strength was 71.4 MPa and could reach 81% of the tensile strength of pure Al.

Enhanced bonding property of cold-sprayed Zn-Al coating on interstitial-free steel substrate with a nanostructured surface layer

NASA Astrophysics Data System (ADS)

Liang, Y. L.; Wang, Z. B.; Zhang, J.; Zhang, J. B.; Lu, K.

2016-11-01

By means of surface mechanical attrition treatment (SMAT), a gradient nanostructured surface layer was fabricated on a hot-rolled interstitial-free steel plate. A Zn-Al coating was subsequently deposited on the SMAT sample by using cold spray process. The bonding property of the coating on the SMAT substrate was compared with that on the coarse-grained (CG) sample. Stud-pull tests showed that the bonding strength in the as-sprayed SMAT sample is ∼30% higher than that in the as-sprayed CG sample. No further improvement in bonding strength was achieved in the coated SMAT sample after annealing at 400 °C, mostly due to the formation of cracks and intermetallic compounds at the coating/substrate interface in an earlier stage (<30 min) and in a final stage (>90 min), respectively. The enhanced bonding property of the Zn-Al coating on the SMAT sample might be related with the promoted atomic diffusion and hardness in the nanostructured surface layer.

Shear fatigue crack growth - A literature survey

NASA Technical Reports Server (NTRS)

Liu, H. W.

1985-01-01

Recent studies of shear crack growth are reviewed, emphasizing test methods and data analyses. The combined mode I and mode II elastic crack tip stress fields are considered. The development and design of the compact shear specimen are described, and the results of fatigue crack growth tests using compact shear specimens are reviewed. The fatigue crack growth tests are discussed and the results of inclined cracks in tensile panels, center cracks in plates under biaxial loading, cracked beam specimens with combined bending and shear loading, center-cracked panels and double edge-cracked plates under cyclic shear loading are examined and analyzed in detail.

Air Quality Aspects of Traffic Management

DOT National Transportation Integrated Search

2000-12-20

Roads don't last as long as they should. Potholes, cracks, crumbling, stress and strain - these are all symptoms of a failing pavement, and they're more frequent nowadays as the weight and volume of traffic on our roads continues to rise. And in cold...

Direct observation of the residual plastic deformation caused by a single tensile overload

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

Bichler, C.; Pippan, R.

1999-07-01

The fatigue crack growth behavior following single tensile overloads at high stress intensity ranges in a cold-rolled austenitic steel has been studied experimentally. After tensile overloads, fatigue cracks initially accelerate, followed by significant retardation, before the growth rates return to their baseline level. The initial acceleration was attributed to an immediate reduction in near-tip closure. Scanning electron micrography and stereophotogrammetric reconstruction of the fracture surface were applied to study the residual plastic deformation caused by a single tensile overload in the mid-thickness of the specimen. The measured residual opening displacement of the crack as a function of the overload ismore » presented and compared with simple estimations. Also, free specimen surface observations of the residual plastic deformation and crack growth rate were performed. In the midsection of the specimens the striation spacing-length, i.e., the microscopic growth rates, were measured before and after the applied overload. It will be shown that the measured plasticity-induced wedges from the single overload and the observed propagation behavior support the significance of the concept of crack closure.« less

Stable tearing behavior of a thin-sheet material with multiple cracks

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Newman, J. C., Jr.; Sutton, M. A.; Amstutz, B. E.

1994-01-01

Fracture tests were conducted on 2.3mm thick, 305mm wide sheets of 2024-T3 aluminum alloy with 1-5 collinear cracks. The cracks were introduced (crack history) into the specimens by three methods: (1) saw cutting; (2) fatigue precracking at a low stress range; and (3) fatigue precracking at a high stress range. For the single crack tests, the initial crack history influenced the stress required for the onset of stable crack growth and the first 10mm of crack growth. The effect on failure stress was about 4 percent or less. For the multiple crack tests, the initial crack history was shown to cause differences of more than 20 percent in the link-up stress and 13 percent in failure stress. An elastic-plastic finite element analysis employing the Crack Tip Opening Angle (CTOA) fracture criterion was used to predict the fracture behavior of the single and multiple crack tests. The numerical predictions were within 7 percent of the observed link-up and failure stress in all the tests.

Influence of crack history on the stable tearing behavior of a thin-sheet material with multiple cracks

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Newman, J. C., Jr.; Sutton, M. A.; Amstutz, B. E.

1994-01-01

Fracture tests were conducted on 2.3mm thick, 305mm wide sheets of 2024-T3 aluminum alloy with from one to five collinear cracks. The cracks were introduced (crack history) into the specimens by three methods: saw cutting, fatigue precracking at a low stress range, and fatigue precracking at a high stress range. For the single crack tests, the initial crack history influenced the stress required for the onset of stable crack growth and the first 10mm of crack growth. The effect on failure stress was about 4 percent or less. For the multiple crack tests, the initial crack history was shown to cause differences of more than 20 percent in the link-up stress and 13 percent in failure stress. An elastic-plastic finite element analysis employing the CTOA fracture criterion was used to predict the fracture behavior of the single and multiple crack tests. The numerical predictions were within 7 percent of the observed link-up and failure stress in all the tests.

Reasonable Temperature Schedules for Cold or Hot Charging of Continuously Cast Steel Slabs

NASA Astrophysics Data System (ADS)

Li, Yang; Chen, Xin; Liu, Ke; Wang, Jing; Wen, Jin; Zhang, Jiaquan

2013-12-01

Some continuously cast steel slabs are sensitive to transverse fracture problems during transportation or handling away from their storage state, while some steel slabs are sensitive to surface transverse cracks during the following rolling process in a certain hot charging temperature range. It is revealed that the investigated steel slabs with high fracture tendency under room cooling condition always contain pearlite transformation delayed elements, which lead to the internal brittle bainitic structure formation, while some microalloyed steels exhibit high surface crack susceptibility to hot charging temperatures due to carbonitride precipitation. According to the calculated internal cooling rates and CCT diagrams, the slabs with high fracture tendency during cold charging should be slowly cooled after cutting to length from hot strand or charged to the reheating furnace directly above their bainite formation temperatures. Based on a thermodynamic calculation for carbonitride precipitation in austenite, the sensitive hot charging temperature range of related steels was revealed for the determination of reasonable temperature schedules.

Epitaxial Growth and Cracking Mechanisms of Thermally Sprayed Ceramic Splats

NASA Astrophysics Data System (ADS)

Chen, Lin; Yang, Guan-jun

2018-02-01

In the present study, the epitaxial growth and cracking mechanisms of thermally sprayed ceramic splats were explored. We report, for the first time, the epitaxial growth of various splat/substrate combinations at low substrate temperatures (100 °C) and large lattice mismatch (- 11.26%). Our results suggest that thermal spray deposition was essentially a liquid-phase epitaxy, readily forming chemical bonding. The interface temperature was also estimated. The results convincingly demonstrated that atoms only need to diffuse and rearrange over a sufficiently short range during extremely rapid solidification. Concurrently, severe cracking occurred in the epitaxial splat/substrate systems, which indicated high tensile stress was produced during splat deposition. The origin of the tensile stress was attributed to the strong constraint of the locally heated substrate by its cold surroundings.

Fatigue Crack Closure Analysis Using Digital Image Correlation

NASA Technical Reports Server (NTRS)

Leser, William P.; Newman, John A.; Johnston, William M.

2010-01-01

Fatigue crack closure during crack growth testing is analyzed in order to evaluate the critieria of ASTM Standard E647 for measurement of fatigue crack growth rates. Of specific concern is remote closure, which occurs away from the crack tip and is a product of the load history during crack-driving-force-reduction fatigue crack growth testing. Crack closure behavior is characterized using relative displacements determined from a series of high-magnification digital images acquired as the crack is loaded. Changes in the relative displacements of features on opposite sides of the crack are used to generate crack closure data as a function of crack wake position. For the results presented in this paper, remote closure did not affect fatigue crack growth rate measurements when ASTM Standard E647 was strictly followed and only became a problem when testing parameters (e.g., load shed rate, initial crack driving force, etc.) greatly exceeded the guidelines of the accepted standard.

Fracture Property of Y-Shaped Cracks of Brittle Materials under Compression

PubMed Central

Zhang, Xiaoyan; Zhu, Zheming; Liu, Hongjie

2014-01-01

In order to investigate the properties of Y-shaped cracks of brittle materials under compression, compression tests by using square cement mortar specimens with Y-shaped crack were conducted. A true triaxial loading device was applied in the tests, and the major principle stresses or the critical stresses were measured. The results show that as the branch angle θ between the branch crack and the stem crack is 75°, the cracked specimen has the lowest strength. In order to explain the test results, numerical models of Y-shaped cracks by using ABAQUS code were established, and the J-integral method was applied in calculating crack tip stress intensity factor (SIF). The results show that when the branch angle θ increases, the SIF K I of the branch crack increases from negative to positive and the absolute value K II of the branch crack first increases, and as θ is 50°, it is the maximum, and then it decreases. Finally, in order to further investigate the stress distribution around Y-shaped cracks, photoelastic tests were conducted, and the test results generally agree with the compressive test results. PMID:25013846

Small crack test program for helicopter materials

NASA Technical Reports Server (NTRS)

Annigeri, Bal; Schneider, George

1994-01-01

Crack propagation tests were conducted to determine crack growth behavior in five helicopter materials for surface cracks between 0.005 to 0.020 inches in depth. Constant amplitude tests were conducted at stress ratios R equals 0.1 and 0.5, and emphasis was placed on near threshold data (i.e., 10-8 to 10-6 inches/cycle). Spectrum tests were conducted using a helicopter spectrum. The test specimen was an unnotched tension specimen, and cracks were initiated from a small EDM notch. An optical/video system was used to monitor crack growth. The material for the test specimens was obtained from helicopter part forgings. Testing was conducted at stresses below yield to reflect actual stresses in helicopter parts.

Photographer: JPL P-21758 BW Range: 246,000 kilometers (152,000 miles) This picture by Voyager 2 is

NASA Technical Reports Server (NTRS)

1979-01-01

Photographer: JPL P-21758 BW Range: 246,000 kilometers (152,000 miles) This picture by Voyager 2 is the first close look ever obtained of Jupiter's satellite, Europa. The linear crack-like features had been seen from a much greater distance by Voyager 1 but this image provides a resolution of about four kilometers (2.5 miles). The complicated linear features appear even more like cracks or huge fractures in these images. Also seen are somewhat darker mottled regions which appear to have a slightly pitted appearance, perhaps due to small scale craters. No large craters (more than five kilometers in diameter) are easily identifiable in the Europa photographs to date, suggesting that this satellite has a young surface relative to Ganymede and Callisto, although not perhaps as young as Io's. Various models for Europa's structure will be tested during analysis of these images, including the possibility that the surface is a thin ice crust overlying water or softer ice and that the fracture systems seen are breaks in that crust. Resurfacing mechanisms such as production of fresh ice or snow along the cracks and cold glacier-like flows are being considered as possibilities for removing evidence of impact events. Europa thus appears to truly be a satellite with many properties intermediate between Ganymede and Io.

Europa Linear Features from 246,000 kilometers

NASA Technical Reports Server (NTRS)

1979-01-01

The first close look ever obtained of Jupiter's satellite, Europa, was taken today, July 9, by Voyager 2 as the spacecraft approached the planet. The linear crack-like features had been seen from a much greater distance last March by Voyager 1. This picture was made at a range of 246,000 kilometers (152,000 miles) and provides a resolution of about four kilometers (2.5 miles). The complicated linear features appear even more like cracks or huge fractures in these images. Also seen are somewhat darker mottled regions which appear to have a slightly pitted appearance, perhaps due to small scale craters. No large craters (more than five kilometers in diameter) are easily identifiable in the Europa photographs to date, suggesting that this satellite has a young surface relative to Ganymede and Callisto, although not perhaps as young as Io's. Various models for Europa's structure will be tested during analysis of these images, including the possibility that the surface is a thin ice crust overlying water or softer ice and that the fracture systems seen are breaks in that crust. Resurfacing mechanisms such as production of fresh ice or snow along the cracks and cold glacier-like flows are being considered as possibilities for removing evidence of impact events. Europa thus appears to truly be a satellite with many properties intermediate between Ganymede and Io.

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.

Crack-tip-opening angle measurements and crack tunneling under stable tearing in thin sheet 2024-T3 aluminum alloy

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Sutton, M. A.

1993-01-01

The stable tearing behavior of thin sheets 2024-T3 aluminum alloy was studied for middle crack tension specimens having initial cracks that were: flat cracks (low fatigue stress) and 45 degrees through-thickness slant cracks (high fatigue stress). The critical crack-tip-opening angle (CTOA) values during stable tearing were measured by two independent methods, optical microscopy and digital image correlation. Results from the two methods agreed well. The CTOA measurements and observations of the fracture surfaces showed that the initial stable tearing behavior of low and high fatigue stress tests is significantly different. The cracks in the low fatigue stress tests underwent a transition from flat-to-slant crack growth, during which the CTOA values were high and significant crack tunneling occurred. After crack growth equal to about the thickness, CTOA reached a constant value of 6 deg and after crack growth equal to about twice the thickness, crack tunneling stabilized. The initial high CTOA values, in the low fatigue crack tests, coincided with large three-dimensional crack front shape changes due to a variation in the through-thickness crack tip constraint. The cracks in the high fatigue stress tests reach the same constant CTOA value after crack growth equal to about the thickness, but produced only a slightly higher CTOA value during initial crack growth. For crack growth on the 45 degree slant, the crack front and local field variables are still highly three-dimensional. However, the constant CTOA values and stable crack front shape may allow the process to be approximated with two-dimensional models.

Eddy current crack detection capability assessment approach using crack specimens with differing electrical conductivity

NASA Astrophysics Data System (ADS)

Koshti, Ajay M.

2018-03-01

Like other NDE methods, eddy current surface crack detectability is determined using probability of detection (POD) demonstration. The POD demonstration involves eddy current testing of surface crack specimens with known crack sizes. Reliably detectable flaw size, denoted by, a90/95 is determined by statistical analysis of POD test data. The surface crack specimens shall be made from a similar material with electrical conductivity close to the part conductivity. A calibration standard with electro-discharged machined (EDM) notches is typically used in eddy current testing for surface crack detection. The calibration standard conductivity shall be within +/- 15% of the part conductivity. This condition is also applicable to the POD demonstration crack set. Here, a case is considered, where conductivity of the crack specimens available for POD testing differs by more than 15% from that of the part to be inspected. Therefore, a direct POD demonstration of reliably detectable flaw size is not applicable. Additional testing is necessary to use the demonstrated POD test data. An approach to estimate the reliably detectable flaw size in eddy current testing for part made from material A using POD crack specimens made from material B with different conductivity is provided. The approach uses additional test data obtained on EDM notch specimens made from materials A and B. EDM notch test data from the two materials is used to create a transfer function between the demonstrated a90/95 size on crack specimens made of material B and the estimated a90/95 size for part made of material A. Two methods are given. For method A, a90/95 crack size for material B is given and POD data is available. Objective of method A is to determine a90/95 crack size for material A using the same relative decision threshold that was used for material B. For method B, target crack size a90/95 for material A is known. Objective is to determine decision threshold for inspecting material A.

Eddy current testing for blade edge micro cracks of aircraft engine

NASA Astrophysics Data System (ADS)

Zhang, Wei-min; Xu, Min-dong; Gao, Xuan-yi; Jin, Xin; Qin, Feng

2017-10-01

Based on the problems of low detection efficiency in the micro cracks detection of aircraft engine blades, a differential excitation eddy current testing system was designed and developed. The function and the working principle of the system were described, the problems which contained the manufacture method of simulated cracks, signal generating, signal processing and the signal display method were described. The detection test was carried out by taking a certain model aircraft engine blade with simulated cracks as a tested specimen. The test data was processed by digital low-pass filter in the computer and the crack signals of time domain display and Lissajous figure display were acquired. By comparing the test results, it is verified that Lissajous figure display shows better performance compared to time domain display when the crack angle is small. The test results show that the eddy current testing system designed in this paper is feasible to detect the micro cracks on the aeroengine blade and can effectively improve the detection efficiency of micro cracks in the practical detection work.

Short-crack growth behaviour in an aluminum alloy: An AGARD cooperative test program

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Edwards, P. R.

1988-01-01

An AGARD Cooperative Test Program on the growth of short fatigue cracks was conducted to define the significance of the short-crack effect, to compare test results from various laboratories, and to evaluate an existing analytical crack-growth prediction model. The initiation and growth of short fatigue cracks (5 micrometer to 2 mm) from the surface of a semi-circular notch in 2024-T3 aluminum alloy sheet material were monitored under various load histories. The cracks initiated from inclusion particle clusters or voids on the notch surface and generally grew as surface cracks. Tests were conducted under several constant-amplitude (stress ratios of -2, -1, 0, and 0.5) and spectrum (FALSTAFF and Gaussian) loading conditions at 3 stress levels each. Short crack growth was recorded using a plastic-replica technique. Over 250 edge-notched specimens were fatigue tested and nearly 950 cracks monitored by 12 participants from 9 countries. Long crack-growth rate data for cracks greater than 2 mm in length were obtained over a wide range in rates (10 to the -8 to 10 to the -1 mm/cycle) for all constant-amplitude loading conditions. Long crack-growth rate data for the FALSTAFF and Gaussian load sequences were also obtained.

Formation of Hot Tear Under Controlled Solidification Conditions

NASA Astrophysics Data System (ADS)

Subroto, Tungky; Miroux, Alexis; Bouffier, Lionel; Josserond, Charles; Salvo, Luc; Suéry, Michel; Eskin, Dmitry G.; Katgerman, Laurens

2014-06-01

Aluminum alloy 7050 is known for its superior mechanical properties, and thus finds its application in aerospace industry. Vertical direct-chill (DC) casting process is typically employed for producing such an alloy. Despite its advantages, AA7050 is considered as a "hard-to-cast" alloy because of its propensity to cold cracking. This type of cracks occurs catastrophically and is difficult to predict. Previous research suggested that such a crack could be initiated by undeveloped hot tears (microscopic hot tear) formed during the DC casting process if they reach a certain critical size. However, validation of such a hypothesis has not been done yet. Therefore, a method to produce a hot tear with a controlled size is needed as part of the verification studies. In the current study, we demonstrate a method that has a potential to control the size of the created hot tear in a small-scale solidification process. We found that by changing two variables, cooling rate and displacement compensation rate, the size of the hot tear during solidification can be modified in a controlled way. An X-ray microtomography characterization technique is utilized to quantify the created hot tear. We suggest that feeding and strain rate during DC casting are more important compared with the exerted force on the sample for the formation of a hot tear. In addition, we show that there are four different domains of hot-tear development in the explored experimental window—compression, microscopic hot tear, macroscopic hot tear, and failure. The samples produced in the current study will be used for subsequent experiments that simulate cold-cracking conditions to confirm the earlier proposed model.

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.

Some important considerations in the development of stress corrosion cracking test methods.

NASA Technical Reports Server (NTRS)

Wei, R. P.; Novak, S. R.; Williams, D. P.

1972-01-01

Discussion of some of the precaution needs the development of fracture-mechanics based test methods for studying stress corrosion cracking involves. Following a review of pertinent analytical fracture mechanics considerations and of basic test methods, the implications for test corrosion cracking studies of the time-to-failure determining kinetics of crack growth and life are examined. It is shown that the basic assumption of the linear-elastic fracture mechanics analyses must be clearly recognized and satisfied in experimentation and that the effects of incubation and nonsteady-state crack growth must also be properly taken into account in determining the crack growth kinetics, if valid data are to be obtained from fracture-mechanics based test methods.

Monitoring crack extension in fracture toughness tests by ultrasonics

NASA Technical Reports Server (NTRS)

Klima, S. J.; Fisher, D. M.; Buzzard, R. J.

1975-01-01

An ultrasonic method was used to observe the onset of crack extension and to monitor continued crack growth in fracture toughness specimens during three point bend tests. A 20 MHz transducer was used with commercially available equipment to detect average crack extension less than 0.09 mm. The material tested was a 300-grade maraging steel in the annealed condition. A crack extension resistance curve was developed to demonstrate the usefulness of the ultrasonic method for minimizing the number of tests required to generate such curves.

Thermo-Mechanical Fatigue Crack Growth of RR1000

PubMed Central

Pretty, Christopher John; Whitaker, Mark Thomas; Williams, Steve John

2017-01-01

Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles. PMID:28772394

Periodic Overload and Transport Spectrum Fatigue Crack Growth Tests of Ti62222STA and Al2024T3 Sheet

NASA Technical Reports Server (NTRS)

Phillips, Edward P.

1999-01-01

Variable amplitude loading crack growth tests have been conducted to provide data that can be used to evaluate crack growth prediction codes. Tests with periodic overloads or overloads followed by underloads were conducted on titanium alloy Ti-6Al-2Sn-2Zr-2Mo-2Cr solution treated and aged (Ti62222STA) material at room temperature and at 350 F. Spectrum fatigue crack growth tests were conducted on two materials (Ti62222STA and aluminum alloy 2024-T3) using two transport lower-wing test spectra at two temperatures (room temperature and 350 F (Ti only)). Test lives (growth from an initial crack half-length of 0.15 in. to failure) were recorded in all tests and the crack length against cycles (or flights) data were recorded in many of the tests. The following observations were made regarding the test results: (1) in tests of the Ti62222STA material, the tests at 350 F had longer lives than those at room temperature, (2) in tests to the MiniTwist spectrum, the Al2024T3 material showed much greater crack growth retardations due to the highest stresses in the spectrum than did the Ti62222STA material, and (3) comparisons of material crack growth performances on an "equal weight" basis were spectrum dependent.

Storage temperature and 1-MCP treatment affect storage disorders and physiological attributes of ‘Royal Gala’ apples

USDA-ARS?s Scientific Manuscript database

‘Royal Gala’ apples [Malus domestica (Borkh.) Mansf.] can develop postharvest disorders such as flesh browning, senescent breakdown, peeling, cracking, or shriveling during and after cold storage. The objective of this study was to examine the effects of storage temperature and a range of 1-methylc...

76 FR 58094 - Airworthiness Directives; 328 Support Services GmbH (Type Certificate Previously Held by AvCraft...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-20

... subsequent Eddy Current inspection (NDI) [non-destructive inspection] of the same area to detect cracks... inspections are eddy current inspections. The modification includes cold expansion of the former lower wing... with consequent loss of control. * * * * * The new inspections are eddy current inspections. The...

Preliminary research on eddy current bobbin quantitative test for heat exchange tube in nuclear power plant

NASA Astrophysics Data System (ADS)

Qi, Pan; Shao, Wenbin; Liao, Shusheng

2016-02-01

For quantitative defects detection research on heat transfer tube in nuclear power plants (NPP), two parts of work are carried out based on the crack as the main research objects. (1) Production optimization of calibration tube. Firstly, ASME, RSEM and homemade crack calibration tubes are applied to quantitatively analyze the defects depth on other designed crack test tubes, and then the judgment with quantitative results under crack calibration tube with more accuracy is given. Base on that, weight analysis of influence factors for crack depth quantitative test such as crack orientation, length, volume and so on can be undertaken, which will optimize manufacture technology of calibration tubes. (2) Quantitative optimization of crack depth. Neural network model with multi-calibration curve adopted to optimize natural crack test depth generated in in-service tubes shows preliminary ability to improve quantitative accuracy.

Super-formable pure magnesium at room temperature.

PubMed

Zeng, Zhuoran; Nie, Jian-Feng; Xu, Shi-Wei; H J Davies, Chris; Birbilis, Nick

2017-10-17

Magnesium, the lightest structural metal, is difficult to form at room temperature due to an insufficient number of deformation modes imposed by its hexagonal structure and a strong texture developed during thermomechanical processes. Although appropriate alloying additions can weaken the texture, formability improvement is limited because alloying additions do not fundamentally alter deformation modes. Here we show that magnesium can become super-formable at room temperature without alloying. Despite possessing a strong texture, magnesium can be cold rolled to a strain at least eight times that possible in conventional processing. The resultant cold-rolled sheet can be further formed without cracking due to grain size reduction to the order of one micron and inter-granular mechanisms becoming dominant, rather than the usual slip and twinning. These findings provide a pathway for developing highly formable products from magnesium and other hexagonal metals that are traditionally difficult to form at room temperature.Replacing steel or aluminium vehicle parts with magnesium would result in reduced emissions, but shaping magnesium without cracking remains challenging. Here, the authors successfully extrude and roll textured magnesium into ductile foil at low temperatures by activating intra-granular mechanisms.

Cold in-place recycling characterization framework for single or multiple component binder systems

NASA Astrophysics Data System (ADS)

Cox, Benjamin C.

Cold in-place recycling (CIR) is a pavement rehabilitation technique which has gained momentum in recent years. This momentum is due partly to its economic and sustainability characteristics, which has led to CIR market expansion. When pavement network deterioration is considered alongside increasing material costs, it is not beyond reason to expect demands on CIR to continue to increase. Historically, single component binder (SCB) systems, those with one stabilization binder (or two if the secondary binder dosage is 1% or less), have dominated the CIR market and could be considered the general state of practice. Common stabilization binders are either bituminous or cementitious. Two example SCB systems would be: 1) 3% portland cement, or 2) 3% asphalt emulsion with 1% hydrated lime. While traditional SCB systems have demonstrated positive economic and sustainability impacts, this dissertation focuses on multiple component binder (MCB) systems (bituminous and cementitious combined) which exhibit the potential to provide better overall economics and performance. Use of MCBs has the potential to alleviate SCB issues to some extent (e.g. cracking with cementitious SCBs, rutting with bituminous SCBs). Furthermore, to fairly represent both binders in an MCB system a universal design method which can accommodate multiple binder types is needed. The main objectives of this dissertation are to develop a universal CIR design framework and, using this framework, characterize multiple SCB and MCB systems. Approximately 1500 CIR specimens were tested herein along with approximately 300 asphalt concrete specimens which serve as a reference data set for CIR characterization. A case study of a high-traffic Mississippi CIR project which included cement SCB and emulsion SCB sections is also presented to support laboratory efforts. Individual components needed to comprise a universal design framework, such as curing protocols, were developed. SCB and MCB characterization indicated that cement SCBs yielded low cracking resistance, high rutting resistance, and lower costs. Emulsion SCBs yielded the opposite. MCBs demonstrated the ability to balance rutting, cracking, and economics. Overall, the universal framework presented appears promising as it could offer agencies flexibility and, in some cases, improved overall performance beyond that of current SCB design methods.

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.

Investigation of Low-Cycle Bending Fatigue of AISI 9310 Steel Spur Gears

NASA Technical Reports Server (NTRS)

Handschuh, Robert F.; Krantz, Timothy L.; Lerch, Bradley A.; Burke, Christopher S.

2007-01-01

An investigation of the low-cycle bending fatigue of spur gears made from AISI 9310 gear steel was completed. Tests were conducted using the single-tooth bending method to achieve crack initiation and propagation. Tests were conducted on spur gears in a fatigue test machine using a dedicated gear test fixture. Test loads were applied at the highest point of single tooth contact. Gear bending stresses for a given testing load were calculated using a linear-elastic finite element model. Test data were accumulated from 1/4 cycle to several thousand cycles depending on the test stress level. The relationship of stress and cycles for crack initiation was found to be semi-logarithmic. The relationship of stress and cycles for crack propagation was found to be linear. For the range of loads investigated, the crack propagation phase is related to the level of load being applied. Very high loads have comparable crack initiation and propagation times whereas lower loads can have a much smaller number of cycles for crack propagation cycles as compared to crack initiation.

Investigation of Low-Cycle Bending Fatigue of AISI 9310 Steel Spur Gears

NASA Technical Reports Server (NTRS)

Handschuh, Robert F.; Krantz, Timothy L.; Lerch, Bradley A.; Burke, Christopher S.

2007-01-01

An investigation of the low-cycle bending fatigue of spur gears made from AISI 9310 gear steel was completed. Tests were conducted using the single-tooth bending method to achieve crack initiation and propagation. Tests were conducted on spur gears in a fatigue test machine using a dedicated gear test fixture. Test loads were applied at the highest point of single tooth contact. Gear bending stresses for a given testing load were calculated using a linear-elastic finite element model. Test data were accumulated from 1/4 cycle to several thousand cycles depending on the test stress level. The relationship of stress and cycles for crack initiation was found to be semilogarithmic. The relationship of stress and cycles for crack propagation was found to be linear. For the range of loads investigated, the crack propagation phase is related to the level of load being applied. Very high loads have comparable crack initiation and propagation times whereas lower loads can have a much smaller number of cycles for crack propagation cycles as compared to crack initiation.

Fatigue crack growth in 2024-T3 aluminum under tensile and transverse shear stresses

NASA Technical Reports Server (NTRS)

Viz, Mark J.; Zehnder, Alan T.

1994-01-01

The influence of transverse shear stresses on the fatigue crack growth rate in thin 2024-T3 aluminum alloy sheets is investigated experimentally. The tests are performed on double-edge cracked sheets in cyclic tensile and torsional loading. This loading generates crack tip stress intensity factors in the same ratio as the values computed for a crack lying along a lap joint in a pressurized aircraft fuselage. The relevant fracture mechanics of cracks in thin plates along with the details of the geometrically nonlinear finite element analyses used for the test specimen calibration are developed and discussed. Preliminary fatigue crack growth data correlated using the fully coupled stress intensity factor calibration are presented and compared with fatigue crack growth data from pure delta K(sub I)fatigue tests.

Fracture Behavior of Ceramics Under Displacement Controlled Loading

NASA Technical Reports Server (NTRS)

Calomino, Anthony; Brewer, David; Ghosn, Louis

1994-01-01

A Mode I fracture specimen and loading method has been developed which permits the observation of stable crack extension in monolithic and in situ toughened ceramics. The developed technique was used to conduct room temperature tests on commercial grade alumina (Coors' AD-995) and silicon nitride (Norton NC-132). The results of these tests are reported. Crack growth for the alumina remained subcritical throughout testing revealing possible effects of environmental stress corrosion. The crack growth resistance curve for the alumina is presented. The silicon nitride tests displayed a series of stable (slow) crack growth segments interrupted by dynamic (rapid) crack extension. Crack initiation and arrest stress intensity factors, K(sub Ic) and K(sub Ia), for silicon nitride are reported. The evolution of the specimen design through testing is briefly discussed.

Laboratory Reproduction and Failure Analysis of Cracked Orbiter Reaction Control System Niobium Thruster Injectors

NASA Technical Reports Server (NTRS)

Jacobs, Jeremy B.; Castner, Willard L.

2007-01-01

A viewgraph presentation describing cracks and failure analysis of an orbiter reaction control system is shown. The topics include: 1) Endeavour STS-113 Landing; 2) RCS Thruster; 3) Thruster Cross-Section; 4) RCS Injector; 5) RCS Thruster, S/N 120l 6) Counterbore Cracks; 7) Relief Radius Cracks; 8) RCS Thruster Cracking History; 9) Thruster Manufacturing Timelines; 10) Laboratory Reproduction of Injector Cracking; 11) The Brownfield Specimen; 12) HF EtchantTests/Specimen Loading; 13) Specimen #3 HF + 600F; 14) Specimen #3 IG Fracture; 15) Specimen #5 HF + 600F; 16) Specimen #5 Popcorn ; 17) Specimen #5 Cleaned and Bent; 18) HF Exposure Test Matrix; 19) Krytox143AC Tests; 20) KrytoxTests/Specimen Loading; 21) Specimen #13 Krytox + 600F; and 22) KrytoxExposure Test Matrix.

Initiation and growth of multiple-site damage in the riveted lap joint of a curved stiffened fuselage panel: An experimental and analytical study

NASA Astrophysics Data System (ADS)

Ahmed, Abubaker Ali

As part of the structural integrity research of the National Aging Aircraft Research Program, a comprehensive study on multiple-site damage (MSD) initiation and growth in a pristine lap-joint fuselage panel has been conducted. The curved stiffened fuselage panel was tested at the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration William J. Hughes Technical Center. A strain survey test was conducted to verify proper load application. The panel was then subjected to a fatigue test with constant-amplitude cyclic loading. The applied loading spectrum included underload marker cycles so that crack growth history could be reconstructed from post-test fractographic examinations. Crack formation and growth were monitored via nondestructive and high-magnification visual inspections. Strain gage measurements recorded during the strain survey tests indicated that the inner surface of the skin along the upper rivet row of the lap joint experienced high tensile stresses due to local bending. During the fatigue loading, cracks were detected by eddy-current inspections at multiple rivet holes along the upper rivet row. Through-thickness cracks were detected visually after about 80% of the fatigue life. Once MSD cracks from two adjacent rivet holes linked up, there was a quick deterioration in the structural integrity of the lap joint. The linkup resulted in a 2.87" (72.9-mm) lead fatigue crack that rapidly propagated across 12 rivet holes and crossed over into the next skin bay, at which stage the fatigue test was terminated. A post-fatigue residual strength test was then conducted by loading the panel quasi-statically up to final failure. The panel failed catastrophically when the crack extended instantaneously across three additional bays. Post-test fractographic examinations of the fracture surfaces in the lap joint of the fuselage panel were conducted to characterize subsurface crack initiation and growth. Results showed evidence of fretting damage and crack initiation at multiple locations near the rivet holes along the faying surface of the skin. The subsurface cracks grew significantly along the faying surface before reaching the outer surface of the skin, forming elliptical crack fronts. A finite element model (FE) of the panel was constructed and geometrically-nonlinear analyses conducted to determine strain distribution under the applied loads. The FE model was validated by comparing the analysis results with the strain gage measurements recorded during the strain survey test. The validated FE model was then used to determine stress-intensity factors at the crack tips. Stress-intensity factor results indicated that crack growth in the lap joint was under mixed-mode; however, the opening-mode stress intensity factor was dominant. The stress-intensity factors computed from the FE analysis were used to conduct cycle-by-cycle integration of fatigue crack growth. In the cycle-by-cycle integration, the NASGRO crack growth model was used with its parameters selected to account for the effects of plasticity-induced crack closure and the test environment on crack growth rate. Fatigue crack growth predictions from cycle-by-cycle computation were in good agreement with the experimental measured crack growth data. The results of the study provide key insights into the natural development and growth of MSD cracks in the pristine lap joint. The data provided by the study represent a valuable source for the evaluation and validation of analytical methodologies used for predicting MSD crack initiation and growth.

A preliminary study of crack initiation and growth at stress concentration sites

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Gallagher, J. P.; Hartman, G. A.; Rajendran, A. M.

1982-01-01

Crack initiation and propagation models for notches are examined. The Dowling crack initiation model and the E1 Haddad et al. crack propagation model were chosen for additional study. Existing data was used to make a preliminary evaluation of the crack propagation model. The results indicate that for the crack sizes in the test, the elastic parameter K gave good correlation for the crack growth rate data. Additional testing, directed specifically toward the problem of small cracks initiating and propagating from notches is necessary to make a full evaluation of these initiation and propagation models.

Mode I and mixed I/III crack initiation and propagation behavior of V-4Cr-4Ti alloy at 25{degrees}C

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

Li, H.X.; Kurtz, R.J.; Jones, R.H.

1997-04-01

The mode I and mixed-mode I/III fracture behavior of the production-scale heat (No. 832665) of V-4Cr-4Ti has been investigated at 25{degrees}C using compact tension (CT) specimens for a mode I crack and modified CT specimens for a mixed-mode I/III crack. The mode III to mode I load ratio was 0.47. Test specimens were vacuum annealed at 1000{degrees}C for 1 h after final machining. Both mode I and mixed-mode I/III specimens were fatigue cracked prior to J-integral testing. It was noticed that the mixed-mode I/III crack angle decreased from an initial 25 degrees to approximately 23 degrees due to crack planemore » rotation during fatigue cracking. No crack plane rotation occurred in the mode I specimen. The crack initiation and propagation behavior was evaluated by generating J-R curves. Due to the high ductility of this alloy and the limited specimen thickness (6.35 mm), plane strain requirements were not met so valid critical J-integral values were not obtained. However, it was found that the crack initiation and propagation behavior was significantly different between the mode I and the mixed-mode I/III specimens. In the mode I specimen crack initiation did not occur, only extensive crack tip blunting due to plastic deformation. During J-integral testing the mixed-mode crack rotated to an increased crack angle (in contrast to fatigue precracking) by crack blunting. When the crack initiated, the crack angle was about 30 degrees. After crack initiation the crack plane remained at 30 degrees until the test was completed. Mixed-mode crack initiation was difficult, but propagation was easy. The fracture surface of the mixed-mode specimen was characterized by microvoid coalescence.« less

Photomultiplier tube failure under hydrostatic pressure in future neutrino detectors

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

Chambliss, K.; Diwan, M.; Simos, N.

Failure of photomultiplier tubes (PMTs) under hydrostatic pressure is a concern in neutrino detection, specifically, in the proposed Long-Baseline Neutrino Experiment project. Controlled hydrostatic implosion tests were performed on prototypic PMT bulbs of 10-inch diameter and recorded using high speed filming techniques to capture failures in detail. These high-speed videos were analyzed frame-by-frame in order to identify the origin of a crack, measure the progression of individual crack along the surface of the bulb as it propagates through the glass, and estimate crack velocity. Crack velocity was calculated for each individual crack, and an average velocity was determined for allmore » measurable cracks on each bulb. Overall, 32 cracks were measured in 9 different bulbs tested. Finite element modeling (FEM) of crack formation and growth in prototypic PMT shows stress concentration near the middle section of the PMT bulbs that correlates well with our crack velocity measurements in that section. The FEM model predicts a crack velocity value that is close to the terminal crack velocity reported. Our measurements also reveal significantly reduced crack velocities compared to terminal crack velocities measured in glasses using fracture mechanics testing and reported in literature.« less

Photomultiplier tube failure under hydrostatic pressure in future neutrino detectors

DOE PAGES

Chambliss, K.; Diwan, M.; Simos, N.; ...

2014-10-09

Failure of photomultiplier tubes (PMTs) under hydrostatic pressure is a concern in neutrino detection, specifically, in the proposed Long-Baseline Neutrino Experiment project. Controlled hydrostatic implosion tests were performed on prototypic PMT bulbs of 10-inch diameter and recorded using high speed filming techniques to capture failures in detail. These high-speed videos were analyzed frame-by-frame in order to identify the origin of a crack, measure the progression of individual crack along the surface of the bulb as it propagates through the glass, and estimate crack velocity. Crack velocity was calculated for each individual crack, and an average velocity was determined for allmore » measurable cracks on each bulb. Overall, 32 cracks were measured in 9 different bulbs tested. Finite element modeling (FEM) of crack formation and growth in prototypic PMT shows stress concentration near the middle section of the PMT bulbs that correlates well with our crack velocity measurements in that section. The FEM model predicts a crack velocity value that is close to the terminal crack velocity reported. Our measurements also reveal significantly reduced crack velocities compared to terminal crack velocities measured in glasses using fracture mechanics testing and reported in literature.« less

Moisture contamination and welding parameter effects on flux cored arc welding diffusible hydrogen

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

Kiefer, J.J.

1994-12-31

Gas metal arc (GMAW) and flux cored arc (FCAW) welding are gas shielded semiautomatic processes widely used for achieving high productivity in steel fabrication. Contamination of the shielding has can occur due to poorly maintained gas distribution systems. Moisture entering as a gas contaminant is a source of hydrogen that can cause delayed cold cracking in welds. Limiting heat-affected zone hardness is one method of controlling cracking. Even this is based on some assumptions about the hydrogen levels in the weld. A study was conducted to investigate the effect of shielding gas moisture contamination and welding parameters on the diffusiblemore » hydrogen content of gas shielded flux cored arc welding. The total wire hydrogen of various electrodes was also tested and compared to the diffusible weld hydrogen. An empirical equation has been developed that estimates the diffusible hydrogen in weld metal for gas shielded flux cored arc welding. The equation is suitable for small diameter electrodes and welding parameter ranges commonly used for out-of-position welding. by combining this with the results from the total wire hydrogen tests, it is possible to estimate diffusible hydrogen directly from measured welding parameters, shielding gas dew point, and total hydrogen of the consumable. These equations are also useful for evaluating the effect of welding procedure variations from known baseline conditions.« less

A method for evaluating the fatigue crack growth in spiral notch torsion fracture toughness test

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

Wang, Jy -An John; Tan, Ting

The spiral notch torsion test (SNTT) has been a recent breakthrough in measuring fracture toughness for different materials, including metals, ceramics, concrete, and polymers composites. Due to its high geometry constraint and unique loading condition, SNTT can be used to measure the fracture toughness with smaller specimens without concern of size effects. The application of SNTT to brittle materials has been proved to be successful. The micro-cracks induced by original notches in brittle materials could ensure crack growth in SNTT samples. Therefore, no fatigue pre-cracks are needed. The application of SNTT to the ductile material to generate valid toughness datamore » will require a test sample with sufficient crack length. Fatigue pre-crack growth techniques are employed to introduce sharp crack front into the sample. Previously, only rough calculations were applied to estimate the compliance evolution in the SNTT crack growth process, while accurate quantitative descriptions have never been attempted. This generates an urgent need to understand the crack evolution during the SNTT fracture testing process of ductile materials. Here, the newly developed governing equations for SNTT crack growth estimate are discussed in the paper.« less

A method for evaluating the fatigue crack growth in spiral notch torsion fracture toughness test

DOE PAGES

Wang, Jy -An John; Tan, Ting

2018-05-21

The spiral notch torsion test (SNTT) has been a recent breakthrough in measuring fracture toughness for different materials, including metals, ceramics, concrete, and polymers composites. Due to its high geometry constraint and unique loading condition, SNTT can be used to measure the fracture toughness with smaller specimens without concern of size effects. The application of SNTT to brittle materials has been proved to be successful. The micro-cracks induced by original notches in brittle materials could ensure crack growth in SNTT samples. Therefore, no fatigue pre-cracks are needed. The application of SNTT to the ductile material to generate valid toughness datamore » will require a test sample with sufficient crack length. Fatigue pre-crack growth techniques are employed to introduce sharp crack front into the sample. Previously, only rough calculations were applied to estimate the compliance evolution in the SNTT crack growth process, while accurate quantitative descriptions have never been attempted. This generates an urgent need to understand the crack evolution during the SNTT fracture testing process of ductile materials. Here, the newly developed governing equations for SNTT crack growth estimate are discussed in the paper.« less

The Effect of the Laboratory Specimen on Fatigue Crack Growth Rate

NASA Technical Reports Server (NTRS)

Forth, S. C.; Johnston, W. M.; Seshadri, B. R.

2006-01-01

Over the past thirty years, laboratory experiments have been devised to develop fatigue crack growth rate data that is representative of the material response. The crack growth rate data generated in the laboratory is then used to predict the safe operating envelope of a structure. The ability to interrelate laboratory data and structural response is called similitude. In essence, a nondimensional term, called the stress intensity factor, was developed that includes the applied stresses, crack size and geometric configuration. The stress intensity factor is then directly related to the rate at which cracks propagate in a material, resulting in the material property of fatigue crack growth response. Standardized specimen configurations and experimental procedures have been developed for laboratory testing to generate crack growth rate data that supports similitude of the stress intensity factor solution. In this paper, the authors present laboratory fatigue crack growth rate test data and finite element analyses that show similitude between standard specimen configurations tested using the constant stress ratio test method is unobtainable.

The effects of shot-peening residual stresses on the fracture and crack growth properties of D6AC steel

NASA Technical Reports Server (NTRS)

Elber, W.

1973-01-01

The fracture strength and cyclic crack-growth properties of surface-flawed, shot-peened D6AC steel plate were investigated. For short crack lengths (up to 1.5mm) simple linear elastic fracture mechanics - based only on applied loading - did not predict the fracture strengths. Also, Paris' Law for cyclic crack growth did not correlate the crack-growth behavior. To investigate the effect of shot-peening, additional fracture and crack-growth tests were performed on material which was precompressed to remove the residual stresses left by the shot-peening. Both tests and analysis show that the shot-peening residual stresses influence the fracture and crack-growth properties of the material. The analytical method of compensating for residual stresses and the fracture and cyclic crack-growth test results and predictions are presented.

Effects of shot-peening residual stresses on the fracture and crack-growth properties of D6AC steel

NASA Technical Reports Server (NTRS)

Elber, W.

1974-01-01

The fracture strength and cyclic crack-growth properties of surface-flawed, shot-peened D6AC steel plate were investigated. For short crack lengths (up to 1.5 mm) simple linear elastic fracture mechanics - based only on applied loading - did not predict the fracture strengths. Also, Paris' Law for cyclic crack growth did not correlate the crack-growth behavior. To investigate the effect of shot-peening, additional fracture and crack-growth tests were performed on material which was precompressed to remove the residual stresses left by the shot-peening. Both tests and analysis show that shot-peening residual stresses influence the fracture and crack-growth properties of the material. This report presents the analytical method of compensating for residual stresses and the fracture and cyclic crack-growth test results and predictions.

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.

Mix design of asphalt mixture used for the waterproof and anti-cracking layer in the rainy area of South China.

PubMed

Liu, Fuming; Dong, Aixia; Liu, Chaoqun; Wu, Wenqing

2018-01-01

In this study, the asphalt mixture (porosity <2%) was tested for use between the upper and middle layers of the asphalt pavement to improve its interlayer structure and to enhance its related waterproof and anti-cracking ability. Considering the weather characteristics and traffic conditions in Jiangxi Province, appropriate raw materials were selected. Based on the technical indexes of the raw materials, expected porosity (<2%), and AC-5 standard for the asphalt mixture, experiments were conducted to determine the best gradation range of the waterproof and anti-cracking layer, and to obtain the optimum amount of the asphalt and fiber used based on Marshall tests. The high-temperature rutting test, low-temperature cracking test, and water stability test were conducted to evaluate the pavement performance of the waterproof and anti-cracking layer. A waterproof and anti-cracking layer was added between the upper and middle layers of the asphalt pavement, which has excellent performance for avoiding cracks and water damage.

Fracture and crack growth resistance studies of 304 stainless steel weldments relating to retesting of cryogenic vessels

NASA Technical Reports Server (NTRS)

Hall, L. R.; Finger, R. W.

1972-01-01

Fracture and crack growth resistance characteristics of 304 stainless steel alloy weldments as relating to retesting of cryogenic vessels were examined. Welding procedures were typical of those used in full scale vessel fabrication. Fracture resistance survey tests were conducted in room temperature air, liquid nitrogen and liquid hydrogen. In air, both surface-flawed and center-cracked panels containing cracks in weld metal, fusion line, heat-affected zone, or parent metal were tested. In liquid nitrogen and liquid hydrogen, tests were conducted using center-cracked panels containing weld centerline cracks. Load-unload, sustained load, and cyclic load tests were performed in air or hydrogen gas, liquid nitrogen, and liquid hydrogen using surface-flawed specimens containing weld centerline cracks. Results were used to evaluate the effectiveness of periodic proof overloads in assuring safe and reliable operation of over-the-road cryogenic dewars.

Kinetics and microscopic processes of long term fracture in polyethylene piping materials

NASA Astrophysics Data System (ADS)

Brown, N.; Lu, X.

1992-07-01

The report contains 9 completed works as follows: The Dependence of Slow Crack Growth in a Polyethylene Copolymer on Testing Temperature and Morphology; A Test of Slow Crack Growth Failure of PE Under Constant Load; Effect of Annealing on Slow Crack Growth in an Ethylene-Hexene Copolymer; The Fundamental Material Parameters that Govern Slow Crack Growth in Linear Polyethylene; Slow Crack Growth in Blends of HDPE and UHMWPE; The Mechanism of Fatigue Failure in a Polyethylene Copolymer; PENT Quality Control Test for PE Gas Pipes and Resins; International Round Robin Study of a Fatigue Test Approach to the Ranking of Polyethylene Pipe Material; and Proposed ASTM Specification for ASTM F17.40 Test Methods Committee.

Characteristics of lead induced stress corrosion cracking of alloy 690 in high temperature

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

Chung, K.K.; Lim, J.K.; Watanabe, Yutaka

1996-10-01

Slow strain rate tests (SSRT) were conducted on alloy 690 in various lead chloride solutions and metal lead added to 100 ppm chloride solution at 288 C. The corrosion potential (rest potential) for the alloy was measured with SSRT tests. The cracking was observed by metallographic examination and electron probe micro analyzer. Also, the corrosion behavior of the alloy was evaluated by anodic polarized measurement at 30 C. Resulting from the tests, cracking was characterized by cracking behavior, crack length and crack growth rate, and lead effects on cracking. The cracking was mainly intergranular in mode, approximately from 60 ummore » to 450 um in crack length, and approximately 10{sup {minus}6} to 10{sup {minus}7} mmS-1 in crack velocity. The cracking was evaluated through the variation the corrosion potential in potential-time and lead behavior during SSRTs. The lead effect in corrosion was evaluated through active to passive transition behavior in anodic polarized curves. The corrosion reactions in the cracking region were confirmed by electron probe microanalysis. Alloy 690 is used for steam generation tubes in pressurized water reactors.« less

Crack networks in damaged glass

NASA Astrophysics Data System (ADS)

Mallet, Celine; Fortin, Jerome; Gueguen, Yves

2013-04-01

We investigate how cracks develop and propagate in synthetic glass samples. Cracks are introduced in glass by a thermal shock of 300oC. Crack network is documented from optical and electronic microscopy on these samples that have been submitted to a thermal shock only. Samples are cylinder of 80 mm length and 40 mm diameter. Sections were cut along the cylinder axis and perpendicular to it. Using SEM, crack lengths and apertures can be measured. Optical microscopy allows to get the crack distribution over the entire sample. The sample average crack length is 3 mm. The average aperture is 6 ± 3μm. There is however a clear difference between the sample core, where the crack network has approximatively a transverse isotrope symmetry and the outer ring, where cracks are smaller and more numerous. By measuring before and after the thermal treatment the radial P and S wave velocities in room conditions, we can determine the total crack density which is 0.24. Thermally cracked samples, as described above, were submitted to creep tests. Constant axial stress and lateral stress were applied. Several experiments were performed at different stress values. Samples are saturated for 48 hours (to get an homogeneous pore fluid distribution), the axial stress is increased up to 80% of the sample strength. Stress step tests were performed in order to get creep data. The evolution of strain (axial and radial strain) is measured using strain gages, gap sensors (for the global axial strain) and pore volume change (for the volumetric strain). Creep data are interpreted as evidence of sub-critical crack growth in the cracked glass samples. The above microstructural observations are used, together with a crack propagation model, to account for the creep behavior. Assuming that (i) the observed volumetric strain rate is due to crack propagation and (ii) crack aspect ratio is constant we calculate the creep rate. We obtain some value on the crack propagation during a 24 hours of constant stress test. At each of these test, crack propagate of 0.3 to 0.4 mm. From the initial average crack length of 3 mm, the crack reach the size of 5.8 mm at the end of a complete creep test (with 8 constant stress step of 24 hours).

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.

Fabrication of boron articles

DOEpatents

Benton, Samuel T.

1976-01-01

This invention is directed to the fabrication of boron articles by a powder metallurgical method wherein the articles are of a density close to the theoretical density of boron and are essentially crackfree. The method comprises the steps of admixing 1 to 10 weight percent carbon powder with amorphous boron powder, cold pressing the mixture and then hot pressing the cold pressed compact into the desired article. The addition of the carbon to the mixture provides a pressing aid for inhibiting the cracking of the hot pressed article and is of a concentration less than that which would cause the articles to possess significant concentrations of boron carbide.

Miniature quadrupole mass spectrometer having a cold cathode ionization source

DOEpatents

Felter, Thomas E.

2002-01-01

An improved quadrupole mass spectrometer is described. The improvement lies in the substitution of the conventional hot filament electron source with a cold cathode field emitter array which in turn allows operating a small QMS at much high internal pressures then are currently achievable. By eliminating of the hot filament such problems as thermally "cracking" delicate analyte molecules, outgassing a "hot" filament, high power requirements, filament contamination by outgas species, and spurious em fields are avoid all together. In addition, the ability of produce FEAs using well-known and well developed photolithographic techniques, permits building a QMS having multiple redundancies of the ionization source at very low additional cost.

Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

NASA Astrophysics Data System (ADS)

Moradian, Zabihallah; Einstein, Herbert H.; Ballivy, Gerard

2016-03-01

Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress-strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.

Fracture Testing of Integral Stiffened Structure

NASA Technical Reports Server (NTRS)

Newman, John A.; Smith, Stephen W.; Piascik, Robert S.; Dawicke, David S.; Johnston, William M.; Willard, Scott A.

2008-01-01

Laboratory testing was conducted to evaluate safety concerns for integrally-stiffened tanks that were found to have developed cracks during pressurization testing. Cracks occurred at fastener holes where additional stiffeners were attached to the integrally-stiffened tank structure. Tests were conducted to obtain material properties and to reproduce the crack morphologies that were observed in service to help determine if the tanks are safe for operation. Reproducing the cracking modes observed during pressurization testing required a complex loading state involving both a tensile load in the integrally-stiffened structure and a pin-load at a fastener hole.

The overlay tester (OT) : comparison with other crack test methods and recommendations for surrogate crack tests.

DOT National Transportation Integrated Search

2012-10-01

Presently, one of the principal performance concerns of hot-mix asphalt (HMA) pavements is premature : cracking, particularly of HMA surfacing mixes. Regrettably, however, while many USA transportation agencies have : implemented design-level tests t...

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.

On Generating Fatigue Crack Growth Thresholds

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James, Jr.; Forman, Royce G.

2003-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. These experimental procedures can induce load history effects that result in crack closure. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake or blunt at the crack tip, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor range, Delta K, will increase, as will the crack growth rate. da/dN. A fatigue crack growth threshold test procedure is experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R. The authors have chosen to study a ductile aluminum alloy where the plastic deformations generated during testing may be of the magnitude to impact the crack opening.

Effect of water vapor on fatigue crack growth in 7475-T651 aluminum alloy plate. [for aerospace applications

NASA Technical Reports Server (NTRS)

Dicus, D. L.

1984-01-01

The effects of water vapor on fatigue crack growth in 7475-T651 aluminum alloy plate at frequencies of 1 Hz and 10 Hz were investigated. Twenty-five mm thick compact specimens were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Fatigue crack growth rates were calculated from effective crack lengths determined using a compliance method. Tests were conducted in hard vacuum and at water vapor partial pressures ranging from 94 Pa to 3.8 kPa. Fatigue crack growth rates were frequency insensitive under all environment conditions tested. For constant stress intensity factor ranges crack growth rate transitions occurred at low and high water vapor pressures. Crack growth rates at intermediate pressures were relatively constant and showed reasonable agreement with published data for two Al-Cu-Mg alloys. The existence of two crack growth rate transitions suggests either a change in rate controlling kinetics or a change in corrosion fatigue mechanism as a function of water vapor pressure. Reduced residual deformation and transverse cracking specimens tested in water vapor versus vacuum may be evidence of embrittlement within the plastic zone due to environmental interaction.

The effect of water vapor on fatigue crack Growth in 7475-t651 aluminum alloy plate. [for aerospace applications

NASA Technical Reports Server (NTRS)

Dicus, D. L.

1982-01-01

The effects of water vapor on fatigue crack growth in 7475-T651 aluminum alloy plate at frequencies of 1 Hz and 10 Hz were investigated. Twenty-five mm thick compact specimens were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Fatigue crack growth rates were calculated from effective crack lengths determined using a compliance method. Tests were conducted in hard vacuum and at water vapor partial pressures ranging from 94 Pa to 3.8 kPa. Fatigue crack growth rates were frequency insensitive under all environment conditions tested. For constant stress intensity factor ranges crack growth rate transitions occurred at low and high water vapor pressures. Crack growth rates at intermediate pressures were relatively constant and showed reasonable agreement with published data for two Al-Cu-Mg alloys. The existence of two crack growth rate transitions suggests either a change in rate controlling kinetics or a change in corrosion fatigue mechanism as a function of water vapor pressure. Reduced residual deformation and transverse cracking specimens tested in water vapor versus vacuum may be evidence of embrittlement within the plastic zone due to environmental interaction.

Fatigue Crack Propagation from Notched Specimens of 304 SS in elevated Temperature Aqueous Environment

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

Wire, G. L.; Mills, W. J.

2002-08-01

Fatigue crack propagation (FCP) rates for 304 stainless steel (304SS) were determined in 24 degree C and 288 degree C air and 288 degree C water using double-edged notch (DEN) specimens of 304 stainless steel (304 SS). Test performed at matched loading conditions in air and water at 288 degree C with 20-6- cc h[sub]2/kg h[sub]2O provided a direct comparison of the relative crack growth rates in air and water over a wide range of crack growth rates. The DEN crack extension ranged from short cracks (0.03-0.25 mm) to long cracks up to 4.06 mm, which are consistent with conventionalmore » deep crack tests. Crack growth rates of 304 SS in water were about 12 times the air rate. This 12X environmental enhancement persisted to crack extensions up to 4.06 mm, far outside the range associated with short crack effects. The large environmental degradation for 304 SS crack growth is consistent with the strong reduction of fatigue life in high hydrogen water. Further, very similar environmental effects w ere reported in fatigue crack growth tests in hydrogen water chemistry (HWC). Most literature data in high hydrogen water show only a mild environmental effect for 304 SS, of order 2.5 times air or less, but the tests were predominantly performed at high cyclic stress intensity or equivalently, high air rates. The environmental effect in low oxygen environments at low stress intensity depends strongly on both the stress ratio, R, and the load rise time, T[sub]r, as recently reported for austenitic stainless steel in BWR water. Fractography was performed for both tests in air and water. At 288 degree C in water, the fracture surfaces were crisply faceted with a crystallographic appearance, and showed striations under high magnification. The cleavage-like facets on the fracture surfaces suggest that hydrogen embrittlement is the primary cause of accelerated cracking.« less

Effects of δ phase and cold drawing ratio on the LCF properties of alloy 718 wire

NASA Astrophysics Data System (ADS)

Jeong, Yong-Kwon; Jo, Chang-Yong; Kim, In-Bae

2000-10-01

The effects of the amount and distribution of δ particles on the low cycle fatigue (LCF) properties of alloy 718 wire were investigated. The amount and distribution of δ particles were controlled by cold drawing followed by a variety of agings. As the cold drawing ratio and aging time at 1116K increased, the well developed granular δ particles increased in amount and their distribution at grain/twin boundaries became more uniform. Regardless of the aging conditions, the LCF life increased as the cold drawing ratio increased. The granular particles precipitated along the grain boundary also improved the LCF life of alloy 718 wire since they inhibited crack propagation. After Merrick heat treatment, 50% of the cold drawn wire displayed lower 698K tensile and yield strength than 30% of the cold drawn wire. This was because the higher strain induced by the cold drawing prior to the first aging at 1116K appeared to promote the precipitation of the δ phase during aging, which has no influence on the strength of the material but has same stoichiometry with the γ phase as Ni3Nb and, as a result, the higher strain precipitated a smaller quantity of γ particles with subsequent aging, which is a major hardening phase of the alloy. Cold drawing also lowered the precipitation temperature of the δ phase.

New Surface-Treatment Technique of Concrete Structures Using Crack Repair Stick with Healing Ingredients

PubMed Central

Ahn, Tae-Ho; Kim, Hong-gi; Ryou, Jae-Suk

2016-01-01

This study focused on the development of a crack repair stick as a new repair method along with self-healing materials that can be used to easily repair the cracks in a concrete structure at the construction site. In developing this new repair technique, the self-healing efficiency of various cementitious materials was considered. Likewise, a crack repair stick was developed to apply to concrete structures with 0.3 mm or lower crack widths. The crack repair stick was made with different materials, such as cement, an expansive material (C12A7), a swelling material, and calcium carbonate, to endow it with a self-healing property. To verify the performance of the crack repair stick for concrete structures, two types of procedures (field experiment and field absorption test) were carried out. As a result of such procedures, it was concluded that the developed crack repair stick could be used on concrete structures to reduce repair expenses and for the improved workability, usability, and serviceability of such structures. On the other hand, to evaluate the self-healing performance of the crack repair stick, various tests were conducted, such as the relative dynamic modulus of elasticity test, the water tightness test, the water permeability test, observation via a microscope, and scanning electron microscope (SEM) analysis. From the results, it is found that water leakage can be prevented and that the durability of a concrete structure can be improved through self-healing. Also, it was verified that the cracks were perfectly closed after 28 days due to application of the crack repair stick. These results indicate the usability of the crack repair stick for concrete structures, and its self-healing efficiency. PMID:28773776

Using Peer-Referral Chains with Incentives to Promote HIV Testing and Identify Undiagnosed HIV Infections Among Crack Users in San Salvador

PubMed Central

Glasman, Laura R.; Dickson-Gomez, Julia; Lechuga, Julia; Tarima, Sergey; Bodnar, Gloria; de Mendoza, Lorena Rivas

2016-01-01

In El Salvador, crack users are at high risk for HIV but they are not targeted by efforts to promote early HIV diagnosis. We evaluated the promise of peer-referral chains with incentives to increase HIV testing and identify undiagnosed HIV infections among networks of crack users in San Salvador. For 14 months, we offered HIV testing in communities with a high prevalence of crack use. For the following 14 months, we promoted chains in which crack users from these communities referred their peers to HIV testing and received a small monetary incentive. We recorded the monthly numbers of HIV testers, and their crack use, sexual risk behaviors and test results. After launching the referral chains, the monthly numbers of HIV testers increased significantly (Z = 6.90, p < .001) and decayed more slowly (Z = 5.93, p < .001), and the total number of crack-using testers increased nearly fourfold. Testers in the peer-referral period reported fewer HIV risk behaviors, but a similar percentage (~5 %) tested HIV positive in both periods. More women than men received an HIV-positive diagnosis throughout the study (χ2(1, N = 799) = 4.23, p = .040). Peer-referral chains with incentives can potentially increase HIV testing among networks of crack users while retaining a focus on high-risk individuals. PMID:26687093

Critical assessment of precracked specimen configuration and experimental test variables for stress corrosion testing of 7075-T6 aluminum alloy plate

NASA Technical Reports Server (NTRS)

Domack, M. S.

1985-01-01

A research program was conducted to critically assess the effects of precracked specimen configuration, stress intensity solutions, compliance relationships and other experimental test variables for stress corrosion testing of 7075-T6 aluminum alloy plate. Modified compact and double beam wedge-loaded specimens were tested and analyzed to determine the threshold stress intensity factor and stress corrosion crack growth rate. Stress intensity solutions and experimentally determined compliance relationships were developed and compared with other solutions available in the literature. Crack growth data suggests that more effective crack length measurement techniques are necessary to better characterize stress corrosion crack growth. Final load determined by specimen reloading and by compliance did not correlate well, and was considered a major source of interlaboratory variability. Test duration must be determined systematically, accounting for crack length measurement resolution, time for crack arrest, and experimental interferences. This work was conducted as part of a round robin program sponsored by ASTM committees G1.06 and E24.04 to develop a standard test method for stress corrosion testing using precracked specimens.

Behavior of Fatigue Crack Tip Opening in Air and Corrosive Atmosphere

NASA Astrophysics Data System (ADS)

Hayashi, Morihito; Toeda, Kazunori

In the study, a formula for predicting fatigue crack tip opening displacement is deduced firstly. And then, due to comparing actual crack growth rate with the deduced formula, the crack tip configuration factor is defined to figure out the crack tip opening configuration that is useful to clarify the behavior of fatigue crack tip formation apparently. Applying the concept, the crack growth of 7/3 brass and 6/4 brass is predicted from the formula, by replacing material properties such as plastic flow resistance, Young modulus, the Poisson ratio, and fatigue toughness, and fatigue test conditions such as the stress intensity factor range, the load ratio, and cycle frequency. Furthermore, the theoretically expected results are verified with the fatigue tests which were carried out on CT specimens under different load conditions of load ratio, cycle frequency, and cyclic peak load, in different environments of air or corrosive ammonia atmosphere, for various brasses. And by comparing and discussing the calculated crack growth rate with attained experimental results, the apparent configuration factor at the crack tip is determined. And through the attained factor which changes along with crack growth, the behaviors of fatigue crack tip formation under different test conditions have been found out.

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.

Testing and analysis of flat and curved panels with multiple cracks

NASA Technical Reports Server (NTRS)

Broek, David; Jeong, David Y.; Thomson, Douglas

1994-01-01

An experimental and analytical investigation of multiple cracking in various types of test specimens is described in this paper. The testing phase is comprised of a flat unstiffened panel series and curved stiffened and unstiffened panel series. The test specimens contained various configurations for initial damage. Static loading was applied to these specimens until ultimate failure, while loads and crack propagation were recorded. This data provides the basis for developing and validating methodologies for predicting linkup of multiple cracks, progression to failure, and overall residual strength. The results from twelve flat coupon and ten full scale curved panel tests are presented. In addition, an engineering analysis procedure was developed to predict multiple crack linkup. Reasonable agreement was found between predictions and actual test results for linkup and residual strength for both flat and curved panels. The results indicate that an engineering analysis approach has the potential to quantitatively assess the effect of multiple cracks in the arrest capability of an aircraft fuselage structure.

Study on underclad cracking in nuclear reactor vessel steels

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

Horiya, T.; Takeda, T.; Yamato, K.

1985-02-01

Susceptibility to underclad cracking in nuclear reactor vessel steels, such as SA533 Grade B Class 1 and SA508 Class 2, was studied in detail. A convenient simulation test method using simulated HAZ specimens of small size has been developed for quantitative evaluation of susceptibility to underclad cracks. The method can predict precisely the cracking behavior in weldments of steels with relative low crack susceptibility. The effect of chemical compositions on susceptibility to the cracking was examined systematically using the developed simulation test method and the following index was obtained from the test results: U = 20(V) + 7(C) + 4(Mo)more » + (Cr) + (Cu) - 0.5(Mn) + 1.5 log(X) X = Al . . . Al/2N less than or equal to 1 X = 2N . . . Al/2N > 1 It was confirmed that the new index (U) is useful for the prediction of crack susceptibility of the nuclear vessel steels; i.e., no crack initiation is detected in weldments in the roller bend test for steels having U value below 0.90.« less

Crack sealer fill characteristics.

DOT National Transportation Integrated Search

2010-06-01

Laboratory testing was conducted to determine the extent of crack fill for crack sealers composed of methyl methacrylate, : epoxy, urethane, and high molecular weight methacrylate. The test specimens consisted of eight-inch long concrete : cylinders ...

Up-going Red Water in the Ice at the Bottom of the World: Picture Taking Boxes and Listening Boxes Tell Us How and Why

NASA Astrophysics Data System (ADS)

Carr, C. G.; Pettit, E. C.

2017-12-01

Blood Falls is a place where red water comes out from under ice to the top of the ice and makes a strange red water fall. This ice is part of the big ice at the bottom of the world. The red water only comes out at some times and not every year, but it always comes out at the same place. The red water is important because it has tiny tiny not-animal life that tells us how life could be on other worlds. Knowing about the ice and red water is important because this ice is cold, colder than other ice in other places, and we want to know how water can get through. We didn't know why the red water comes up from under the ice when it does or how. We wanted to understand how the ice breaks and we watched the ice by taking pictures all year to see when the red water comes out. We found out that in the cold part of one year, the red water came out even though the air was not warm enough for water to be water! We think the red water comes out because the red water is blocked under the heavy ice and gets pushed tight. In the cold part of the year, cracks break down from the air into the ice and other cracks break up from under the ice because the red water is so pushed. The cracks from the top and bottom of the ice join, and the red water comes out. We used listening boxes that can feel how the ground moves to understand that the ice is breaking at the bottom and we can see that it breaks at the top of the ice. The red water can stay water and not ice inside the big ice because the red water has tiny pieces of the same stuff that can turn ice into water on the roads. If the ice breaks in the cold time, no water can get in from the top of the ice, so the red water under the ice stays clean from the air water. If the ice breaks in the warm time of year, water could get in from the top of the ice and make the red water under the ice not clean from the air. Since we saw in our pictures that the red water came out in the cold time of year, this means the red water could stay clean from the air. Maybe we can use this to tell us how life on other worlds could stay clean and safe under ice. It can also tell us how water can get through very cold ice.

Creep Behavior and Durability of Cracked CMC

NASA Technical Reports Server (NTRS)

Bhatt, R. T.; Fox, Dennis; Smith, Craig

2015-01-01

To understand failure mechanisms and durability of cracked Ceramic matrix composites (CMCs), Melt Infiltration (MI) SiCSiC composites with Sylramic-iBN fibers and full Chemical vapour infiltration SiCSiC composites with Sylramic-ion bombarded BN (iBN) and Hi-Nicalon -S fibers were pre-cracked between 150 to 200 megapascal and then creep and Sustained Peak Low Cycle Fatigue (SPLCF) tested at 13150 C at stress levels from 35 to 103 megapascal for up to 200 hours under furnace and burner rig conditions. In addition creep testing was also conducted on pre-cracked full Chemical vapour infiltration SiCSiC composites at 14500 C between 35 and 103 megapascal for up to 200 hours under furnace conditions. If the specimens survived the 200 hour durability tests, then they were tensile tested at room temperature to determine their residual tensile properties. The failed specimens were examined by Scanning electron microscope (SEM) to determine the failure modes and mechanisms. The influence of crack healing matrix, fiber types, crack density, testing modes and interface oxidation on durability of cracked Ceramic matrix composites (CMCs) will be discussed.

Overload and Underload Effects on the Fatigue Crack Growth Behavior of the 2024-T3 Aluminum Alloy

NASA Technical Reports Server (NTRS)

Dawicke, David S.

1997-01-01

Fatigue crack growth tests were conducted on 0.09 inch thick, 3.0 inch wide middle-crack tension specimens cut from sheets of 2024-T3 aluminum alloy. The tests were conducted using a load sequence that consisted of a single block of 2,500 cycles of constant amplitude loading followed by an overload/underload combination. The largest fatigue crack growth life occurred for the tests with the overload stress equal to 2 times the constant amplitude stress and the underload stress equal to the constant amplitude minimum stress. For the tests with compressive underloads, the fatigue crack growth life decreased with increasing compressive underload stress.

Hot-crack test for aluminium alloys welds using TIG process

NASA Astrophysics Data System (ADS)

Niel, A.; Deschaux-Beaume, F.; Bordreuil, C.; Fras, G.

2010-06-01

Hot cracking is a critical defect frequently observed during welding of aluminium alloys. In order to better understand the interaction between cracking phenomenon, process parameters, mechanical factors and microstructures resulting from solidification after welding, an original hot-cracking test during welding is developed. According to in-situ observations and post mortem analyses, hot cracking mechanisms are investigated, taking into account the interaction between microstructural parameters, depending on the thermal cycles, and mechanical parameters, depending on geometry and clamping conditions of the samples and on the thermal field on the sample. Finally, a process map indicating the limit between cracking and non-cracking zones according to welding parameters is presented.

Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Seshadri, Banavara R.; Newman, John A.

2015-01-01

The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms.

An investigation of the elevated temperature cracking susceptibility of alloy C-22 weld-metal

NASA Astrophysics Data System (ADS)

Gallagher, Morgan Leo

Alloy C-22 is one of the most corrosion resistant Ni-Cr-Mo alloys available today, and is particularly versatile. As a result, Alloy C-22 is being considered for use in the construction of storage canisters for permanent disposal of radioactive waste in the Yucca Mountain Project. However, in such a critical application, weld related defects (such as these two forms of cracking) are simply unacceptable. Solidification cracking occurs when weld shrinkage strains are applied to liquid films that result from microsegregation during solidification. Many nickel-base alloys are susceptible to solidification cracking since they solidify as austenite and many of their alloying additions partition during solidification and form low melting eutectic constituents. The transvarestraint test was used to quantify the susceptibility of Alloy C-22 to solidification cracking. The solidification cracking temperature range (SCTR) was found to be approximately 50°C (90°F); this SCTR predicts that Alloy-C-22 will have only slightly higher susceptibility than known crack-resistant alloys, such as duplex stainless-steel 2205 and austenitic stainless-steel Type 304 (FN6). Ductility-dip cracking (DDC) is a solid-state cracking phenomenon that occurs below the effective solidus temperature in highly restrained austenitic alloys. Although this type of cracking is relatively uncommon, it can be costly in critical applications where there is a low tolerance for defects. This investigation used two separate tests to quantify the susceptibility of the alloy to DDC: the hot-ductility test and the strain-to-fracture (STF) test. The hot-ductility test revealed that Alloy C-22 weld-metal exhibits an intermediate temperature ductility-dip, with ductility recovery at the upper end of the testing temperature range. The ductility minimum in the hot-ductility tests occurred around 950°C (1742°F) in both the on-heating and on-cooling tests. The strain-to-fracture test also revealed Alloy C-22 to be susceptible to ductility-dip cracking. Alloy C-22 displayed a low threshold strain necessary to initiate cracking, a wide temperature range over which cracking occurred, and no recovery of ductility at the upper end of the testing temperature range. The recovery of ductility at the upper end of the testing temperature range in the hotductility test, and the absence of this recovery in the STF test, is explained by the recrystallization behavior of the metal. Alloy C-22 has a low stacking-fault-energy, as compared to other DDC susceptible nickel-base alloys, and accordingly requires higher levels of deformation before recrystallization begins. With the relatively low strains experienced by the samples in the STF test (less than ten-percent), cracking will occur before enough strain is accumulated to cause recrystallization. In the hot-ductility test, where the sample is pulled to failure, sufficient strain (forty-percent or greater) is applied such that recrystallization occurs. This recrystallization is responsible for the recovery of ductility at the high end of the testing temperature range in the hot-ductility test. The low threshold strain that is observed in the STF test is in part explained by the behavior of the metal during the thermal cycle of the test. Experimental observations indicate that tortuous (wavy) solidification grain boundaries (SGB) migrate, or straighten, during the temperature upslope and hold period of the STF test. This migration of the grain boundaries reduces the mechanical locking effect that tortuous grain boundaries provide, allowing cracking to occur at lower applied strains. Button-melting experiments were conducted to examine the effect of compositional variation on both solidification cracking and ductility-dip cracking susceptibility of the alloy. Molybdenum, tungsten, and iron were selected for variation, as previous research has shown these three elements to be significantly enriched or depleted in the terminal solidification products of Alloy C-22 weld-metal. The solidification temperature range and volume fraction of secondary phases were used as indicators of the susceptibility of the experimental alloys to solidification cracking and ductility-dip cracking, respectively. Previous research on nickel-base alloys has demonstrated that the solidification temperature range of an alloy is directly proportional to the susceptibility of the alloy to solidification cracking. Experiments conducted within this investigation indicate that increasing the volume fraction of secondary phases in Alloy C-22 acts to increase the elevated temperature cracking-resistance and ductility of the alloy. The solidification temperature ranges of the Alloy C-22 variants examined within the button-melting experiments did not significantly widen or narrow with increases in composition. These same compositional variations demonstrated that increasing amounts of molybdenum, tungsten, and iron increased the volume fraction of secondary phases, with each element having relatively the same potency. Based on the button melting experiments and thermodynamic simulations, it is expected that Alloy C-22 will have good resistance to weld solidification cracking over its entire composition range. (Abstract shortened by UMI.)

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.

Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels

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

Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.

Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impededmore » hydrogen diffusion across the banded pearlite.« less

Effects of microstructure banding on hydrogen assisted fatigue crack growth in X65 pipeline steels

DOE PAGES

Ronevich, Joseph A.; Somerday, Brian P.; San Marchi, Chris W.

2015-09-10

Banded ferrite-pearlite X65 pipeline steel was tested in high pressure hydrogen gas to evaluate the effects of oriented pearlite on hydrogen assisted fatigue crack growth. Test specimens were oriented in the steel pipe such that cracks propagated either parallel or perpendicular to the banded pearlite. The ferrite-pearlite microstructure exhibited orientation dependent behavior in which fatigue crack growth rates were significantly lower for cracks oriented perpendicular to the banded pearlite compared to cracks oriented parallel to the bands. Thus the reduction of hydrogen assisted fatigue crack growth across the banded pearlite is attributed to a combination of crack-tip branching and impededmore » hydrogen diffusion across the banded pearlite.« less

Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD

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

Laureys, A., E-mail: Aurelie.Laureys@UGent.be; Depover, T.; Petrov, R.

2016-02-15

The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses justmore » after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of phases on the crack path.« less

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.

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.

Pre-processing of data coming from a laser-EMAT system for non-destructive testing of steel slabs.

PubMed

Sgarbi, Mirko; Colla, Valentina; Cateni, Sivia; Higson, Stuart

2012-01-01

Non destructive test systems are increasingly applied in the industrial context for their strong potentialities in improving and standardizing quality control. Especially in the intermediate manufacturing stages, early detection of defects on semi-finished products allow their direction towards later production processes according to their quality, with consequent considerable savings in time, energy, materials and work. However, the raw data coming from non destructive test systems are not always immediately suitable for sophisticated defect detection algorithms, due to noise and disturbances which are unavoidable, especially in harsh operating conditions, such as the ones which are typical of the steelmaking cycle. The paper describes some pre-processing operations which are required in order to exploit the data coming from a non destructive test system. Such a system is based on the joint exploitation of Laser and Electro-Magnetic Acoustic Transducer technologies and is applied to the detection of surface and sub-surface cracks in cold and hot steel slabs. Copyright © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

Investigation of the ElectroPuls E3000 Test Machine for Fatigue Testing of Structural Materials

DTIC Science & Technology

2016-12-01

sharpening of the crack tip and deformation of a portion of the newly formed surface (the surface created during loading portion of the cycle) during...cracking process is that the size of the final plastic zone formed by pre-cracking can affect the crack growth rate in subsequent testing. To...similar. In other structural materials, such as aluminium , striations are often well-defined. Typically, fatigue striations on an aluminium fracture

A Comparison of Single-Cycle Versus Multiple-Cycle Proof Testing Strategies

NASA Technical Reports Server (NTRS)

McClung, R. C.; Chell, G. G.; Millwater, H. R.; Russell, D. A.; Millwater, H. R.

1999-01-01

Single-cycle and multiple-cycle proof testing (SCPT and MCPT) strategies for reusable aerospace propulsion system components are critically evaluated and compared from a rigorous elastic-plastic fracture mechanics perspective. Earlier MCPT studies are briefly reviewed. New J-integral estimation methods for semielliptical surface cracks and cracks at notches are derived and validated. Engineering methods are developed to characterize crack growth rates during elastic-plastic fatigue crack growth (FCG) and the tear-fatigue interaction near instability. Surface crack growth experiments are conducted with Inconel 718 to characterize tearing resistance, FCG under small-scale yielding and elastic-plastic conditions, and crack growth during simulated MCPT. Fractography and acoustic emission studies provide additional insight. The relative merits of SCPT and MCPT are directly compared using a probabilistic analysis linked with an elastic-plastic crack growth computer code. The conditional probability of failure in service is computed for a population of components that have survived a previous proof test, based on an assumed distribution of initial crack depths. Parameter studies investigate the influence of proof factor, tearing resistance, crack shape, initial crack depth distribution, and notches on the MCPT versus SCPT comparison. The parameter studies provide a rational basis to formulate conclusions about the relative advantages and disadvantages of SCPT and MCPT. Practical engineering guidelines are proposed to help select the optimum proof test protocol in a given application.

A Comparison of Single-Cycle Versus Multiple-Cycle Proof Testing Strategies

NASA Technical Reports Server (NTRS)

McClung, R. C.; Chell, G. G.; Millwater, H. R.; Russell, D. A.; Orient, G. E.

1996-01-01

Single-cycle and multiple-cycle proof testing (SCPT and MCPT) strategies for reusable aerospace propulsion system components are critically evaluated and compared from a rigorous elastic-plastic fracture mechanics perspective. Earlier MCPT studies are briefly reviewed. New J-integral estimation methods for semi-elliptical surface cracks and cracks at notches are derived and validated. Engineering methods are developed to characterize crack growth rates during elastic-plastic fatigue crack growth (FCG) and the tear-fatigue interaction near instability. Surface crack growth experiments are conducted with Inconel 718 to characterize tearing resistance, FCG under small-scale yielding and elastic-plastic conditions, and crack growth during simulated MCPT. Fractography and acoustic emission studies provide additional insight. The relative merits of SCPT and MCPT are directly compared using a probabilistic analysis linked with an elastic-plastic crack growth computer code. The conditional probability of failure in service is computed for a population of components that have survived a previous proof test, based on an assumed distribution of initial crack depths. Parameter studies investigate the influence of proof factor, tearing resistance, crack shape, initial crack depth distribution, and notches on the MCPT vs. SCPT comparison. The parameter studies provide a rational basis to formulate conclusions about the relative advantages and disadvantages of SCPT and MCPT. Practical engineering guidelines are proposed to help select the optimum proof test protocol in a given application.

Ultrasonic infrared thermal wave nondestructive evaluation for crack detection of several aerospace materials

NASA Astrophysics Data System (ADS)

Xu, Weichao; Shen, Jingling; Zhang, Cunlin; Tao, Ning; Feng, Lichun

2008-03-01

The applications of ultrasonic infrared thermal wave nondestructive evaluation for crack detection of several materials, which often used in aviation alloy. For instance, steel and carbon fiber. It is difficult to test cracks interfacial or vertical with structure's surface by the traditional nondestructive testing methods. Ultrasonic infrared thermal wave nondestructive testing technology uses high-power and low-frequency ultrasonic as heat source to excite the sample and an infrared video camera as a detector to detect the surface temperature. The ultrasonic emitter launch pulses of ultrasonic into the skin of the sample, which causes the crack interfaces to rub and dissipate energy as heat, and then caused local increase in temperature at one of the specimen surfaces. The infrared camera images the returning thermal wave reflections from subsurface cracks. A computer collects and processes the thermal images according to different properties of samples to get the satisfied effect. In this paper, a steel plate with fatigue crack we designed and a juncture of carbon fiber composite that has been used in a space probe were tested and get satisfying results. The ultrasonic infrared thermal wave nondestructive detection is fast, sensitive for cracks, especially cracks that vertical with structure's surface. It is significative for nondestructive testing in manufacture produce and application of aviation, cosmography and optoelectronics.

Residual Strength Pressure Tests and Nonlinear Analyses of Stringer- and Frame-Stiffened Aluminum Fuselage Panels with Longitudinal Cracks

NASA Technical Reports Server (NTRS)

Young, Richard D.; Rouse, Marshall; Ambur, Damodar R.; Starnes, James H., Jr.

1999-01-01

The results of residual strength pressure tests and nonlinear analyses of stringer- and frame-stiffened aluminum fuselage panels with longitudinal cracks are presented. Two types of damage are considered: a longitudinal crack located midway between stringers, and a longitudinal crack adjacent to a stringer and along a row of fasteners in a lap joint that has multiple-site damage (MSD). In both cases, the longitudinal crack is centered on a severed frame. The panels are subjected to internal pressure plus axial tension loads. The axial tension loads are equivalent to a bulkhead pressure load. Nonlinear elastic-plastic residual strength analyses of the fuselage panels are conducted using a finite element program and the crack-tip-opening-angle (CTOA) fracture criterion. Predicted crack growth and residual strength results from nonlinear analyses of the stiffened fuselage panels are compared with experimental measurements and observations. Both the test and analysis results indicate that the presence of MSD affects crack growth stability and reduces the residual strength of stiffened fuselage shells with long cracks.

Residual Strength Pressure Tests and Nonlinear Analyses of Stringer-and Frame-Stiffened Aluminum Fuselage Panels with Longitudinal Cracks

NASA Technical Reports Server (NTRS)

Young, Richard D.; Rouse, Marshall; Ambur, Damodar R.; Starnes, James H., Jr.

1998-01-01

The results of residual strength pressure tests and nonlinear analyses of stringer- and frame-stiffened aluminum fuselage panels with longitudinal cracks are presented. Two types of damage are considered: a longitudinal crack located midway between stringers, and a longitudinal crack adjacent to a stringer and along a row of fasteners in a lap joint that has multiple-site damage (MSD). In both cases, the longitudinal crack is centered on a severed frame. The panels are subjected to internal pressure plus axial tension loads. The axial tension loads are equivalent to a bulkhead pressure load. Nonlinear elastic-plastic residual strength analyses of the fuselage panels are conducted using a finite element program and the crack-tip-opening-angle (CTOA) fracture criterion. Predicted crack growth and residual strength results from nonlinear analyses of the stiffened fuselage panels are compared with experimental measurements and observations. Both the test and analysis results indicate that the presence of MSD affects crack growth stability and reduces the residual strength of stiffened fuselage shells with long cracks.

Fracture mechanics life analytical methods verification testing

NASA Technical Reports Server (NTRS)

Favenesi, J. A.; Clemons, T. G.; Riddell, W. T.; Ingraffea, A. R.; Wawrzynek, P. A.

1994-01-01

The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

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

Beushausen, Hans, E-mail: hans.beushausen@uct.ac.za; Chilwesa, Masuzyo

2013-11-15

Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing wasmore » found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus. -- Highlights: •Parameter study on material characteristics influencing overlay cracking. •Analytical model gives good quantitative indication of overlay cracking. •Ring test presents good qualitative indication of overlay cracking. •Curing duration has little effect on overlay cracking.« less

Using Peer-Referral Chains with Incentives to Promote HIV Testing and Identify Undiagnosed HIV Infections Among Crack Users in San Salvador.

PubMed

Glasman, Laura R; Dickson-Gomez, Julia; Lechuga, Julia; Tarima, Sergey; Bodnar, Gloria; de Mendoza, Lorena Rivas

2016-06-01

In El Salvador, crack users are at high risk for HIV but they are not targeted by efforts to promote early HIV diagnosis. We evaluated the promise of peer-referral chains with incentives to increase HIV testing and identify undiagnosed HIV infections among networks of crack users in San Salvador. For 14 months, we offered HIV testing in communities with a high prevalence of crack use. For the following 14 months, we promoted chains in which crack users from these communities referred their peers to HIV testing and received a small monetary incentive. We recorded the monthly numbers of HIV testers, and their crack use, sexual risk behaviors and test results. After launching the referral chains, the monthly numbers of HIV testers increased significantly (Z = 6.90, p < .001) and decayed more slowly (Z = 5.93, p < .001), and the total number of crack-using testers increased nearly fourfold. Testers in the peer-referral period reported fewer HIV risk behaviors, but a similar percentage (~5 %) tested HIV positive in both periods. More women than men received an HIV-positive diagnosis throughout the study (χ(2)(1, N = 799) = 4.23, p = .040). Peer-referral chains with incentives can potentially increase HIV testing among networks of crack users while retaining a focus on high-risk individuals.

A nonlinear fracture mechanics approach to the growth of small cracks

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1983-01-01

An analytical model of crack closure is used to study the crack growth and closure behavior of small cracks in plates and at notches. The calculated crack opening stresses for small and large cracks, together with elastic and elastic plastic fracture mechanics analyses, are used to correlate crack growth rate data. At equivalent elastic stress intensity factor levels, calculations predict that small cracks in plates and at notches should grow faster than large cracks because the applied stress needed to open a small crack is less than that needed to open a large crack. These predictions agree with observed trends in test data. The calculations from the model also imply that many of the stress intensity factor thresholds that are developed in tests with large cracks and with load reduction schemes do not apply to the growth of small cracks. The current calculations are based upon continuum mechanics principles and, thus, some crack size and grain structure exist where the underlying fracture mechanics assumptions become invalid because of material inhomogeneity (grains, inclusions, etc.). Admittedly, much more effort is needed to develop the mechanics of a noncontinuum. Nevertheless, these results indicate the importance of crack closure in predicting the growth of small cracks from large crack data.

Crack Growth Simulation and Residual Strength Prediction in Airplane Fuselages

NASA Technical Reports Server (NTRS)

Chen, Chuin-Shan; Wawrzynek, Paul A.; Ingraffea, Anthony R.

1999-01-01

The objectives were to create a capability to simulate curvilinear crack growth and ductile tearing in aircraft fuselages subjected to widespread fatigue damage and to validate with tests. Analysis methodology and software program (FRANC3D/STAGS) developed herein allows engineers to maintain aging aircraft economically, while insuring continuous airworthiness, and to design more damage-tolerant aircraft for the next generation. Simulations of crack growth in fuselages were described. The crack tip opening angle (CTOA) fracture criterion, obtained from laboratory tests, was used to predict fracture behavior of fuselage panel tests. Geometrically nonlinear, elastic-plastic, thin shell finite element crack growth analyses were conducted. Comparisons of stress distributions, multiple stable crack growth history, and residual strength between measured and predicted results were made to assess the validity of the methodology. Incorporation of residual plastic deformations and tear strap failure was essential for accurate residual strength predictions. Issue related to predicting crack trajectory in fuselages were also discussed. A directional criterion, including T-stress and fracture toughness orthotropy, was developed. Curvilinear crack growth was simulated in coupon and fuselage panel tests. Both T-stress and fracture toughness orthotropy were essential to predict the observed crack paths. Flapping of fuselages were predicted. Measured and predicted results agreed reasonable well.

Adhesion testing procedure for hot-poured crack sealants.

DOT National Transportation Integrated Search

2008-11-01

Crack sealing is a common pavement maintenance treatment because it extends pavement service life significantly. : However, crack sealant often fails prematurely due to a loss of adhesion. Because current test methods are mostly : empirical and only ...

Effect of Particle Morphology on Cold Spray Deposition of Chromium Carbide-Nickel Chromium Cermet Powders

NASA Astrophysics Data System (ADS)

Fernandez, Ruben; Jodoin, Bertrand

2017-08-01

Nickel chromium-chromium carbide coatings provide good corrosion and wear resistance at high temperatures, making them ideal for applications where a harsh environment and high temperatures are expected. Thermal spray processes are preferred as deposition technique of cermets, but the high process temperatures can lead to decarburization and reduction of the coatings properties. Cold spray uses lower temperatures preventing decarburization. Since the metallic phase remains solid, the feedstock powder morphology becomes crucial on the deposition behavior. Six commercially available powders were studied, varying in morphology and metal/ceramic ratios. The powders were categorized into 4 groups depending on their morphology. Spherical powders lead to substrate erosion due to their limited overall ductility. Porous agglomerated and sintered powders lead to severely cracked coatings. For dense agglomerated and sintered powders, the outcome depended on the initial metal/ceramic ratio: powders with 25 wt.% NiCr led to substrate erosion while 35 wt.% NiCr powders led to dense coatings. Finally, blended ceramic-metal mixtures also lead to dense coatings. All coatings obtained had lower ceramic content than the initial feedstock powders. Interrupted spray tests, combined with FEA, helped drawing conclusions on the deposition behavior to explain the obtained results.

Effects of Preprocessing on Multi-Direction Properties of Aluminum Alloy Cold-Spray Deposits

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nardi, A. T.; Champagne, V. K.; Nutt, S. R.

2018-05-01

The effects of powder preprocessing (degassing at 400 °C for 6 h) on microstructure and mechanical properties of 5056 aluminum deposits produced by high-pressure cold spray were investigated. To investigate directionality of the mechanical properties, microtensile coupons were excised from different directions of the deposit, i.e., longitudinal, short transverse, long transverse, and diagonal and then tested. The results were compared to properties of wrought 5056 and the coating deposited with as-received 5056 Al powder and correlated with the observed microstructures. Preprocessing softened the particles and eliminated the pores within them, resulting in more extensive and uniform deformation upon impact with the substrate and with underlying deposited material. Microstructural characterization and finite element simulation indicated that upon particle impact, the peripheral regions experienced more extensive deformation and higher temperatures than the central contact zone. This led to more recrystallization and stronger bonding at peripheral regions relative to the contact zone area and yielded superior properties in the longitudinal direction compared with the short transverse direction. Fractography revealed that crack propagation takes place along the particle-particle interfaces in the transverse directions (caused by insufficient bonding and recrystallization), whereas through the deposited particles, fracture is dominant in the longitudinal direction.

Inspecting cracks in foam insulation

NASA Technical Reports Server (NTRS)

Cambell, L. W.; Jung, G. K.

1979-01-01

Dye solution indicates extent of cracking by penetrating crack and showing original crack depth clearly. Solution comprised of methylene blue in denatured ethyl alcohol penetrates cracks completely and evaporates quickly and is suitable technique for usage in environmental or structural tests.

Fatigue Crack Growth Behavior of 2099-T83 Extrusions in two Different Environments

NASA Astrophysics Data System (ADS)

Goma, Franck Armel Tchitembo; Larouche, Daniel; Bois-Brochu, Alexandre; Blais, Carls; Boselli, Julien; Brochu, Mathieu

Aluminum-lithium alloy 2099-T83 is an advanced material with superior mechanical properties, as compared to traditional alloys used in structural applications, and has been selected for use in the latest generation of airplanes. While this alloy exhibits improved fatigue crack growth (FCG) performance over non-Li alloys, it is of interest to simulate the impact of fluctuating loads under variable temperature during airplane service, particularly in terms of the potential effects of material processing history. In the present paper, the FCG behavior in an Integrally Stiffened Panel (ISP) has been investigated both at room temperature and at 243 K. It has been shown that the resistance to crack growth in a cold environment was higher than in ambient laboratory air. Results of this investigation are discussed from the microfractographic point of view, with regard to the variation of the local extrusion aspect ratio, a parameter which correlates with both the crystallographic texture and the grain structure.

Intelligent detection of cracks in metallic surfaces using a waveguide sensor loaded with metamaterial elements.

PubMed

Ali, Abdulbaset; Hu, Bing; Ramahi, Omar

2015-05-15

This work presents a real life experiment of implementing an artificial intelligence model for detecting sub-millimeter cracks in metallic surfaces on a dataset obtained from a waveguide sensor loaded with metamaterial elements. Crack detection using microwave sensors is typically based on human observation of change in the sensor's signal (pattern) depicted on a high-resolution screen of the test equipment. However, as demonstrated in this work, implementing artificial intelligence to classify cracked from non-cracked surfaces has appreciable impact in terms of sensing sensitivity, cost, and automation. Furthermore, applying artificial intelligence for post-processing data collected from microwave sensors is a cornerstone for handheld test equipment that can outperform rack equipment with large screens and sophisticated plotting features. The proposed method was tested on a metallic plate with different cracks and the obtained experimental results showed good crack classification accuracy rates.

Intelligent Detection of Cracks in Metallic Surfaces Using a Waveguide Sensor Loaded with Metamaterial Elements

PubMed Central

Ali, Abdulbaset; Hu, Bing; Ramahi, Omar M.

2015-01-01

This work presents a real-life experiment implementing an artificial intelligence model for detecting sub-millimeter cracks in metallic surfaces on a dataset obtained from a waveguide sensor loaded with metamaterial elements. Crack detection using microwave sensors is typically based on human observation of change in the sensor's signal (pattern) depicted on a high-resolution screen of the test equipment. However, as demonstrated in this work, implementing artificial intelligence to classify cracked from non-cracked surfaces has appreciable impacts in terms of sensing sensitivity, cost, and automation. Furthermore, applying artificial intelligence for post-processing the data collected from microwave sensors is a cornerstone for handheld test equipment that can outperform rack equipment with large screens and sophisticated plotting features. The proposed method was tested on a metallic plate with different cracks, and the experimental results showed good crack classification accuracy rates. PMID:25988871

Crack identification for reinforced concrete using PZT based smart rebar active sensing diagnostic network

NASA Astrophysics Data System (ADS)

Song, N. N.; Wu, F.

2016-04-01

An active sensing diagnostic system using PZT based smart rebar for SHM of RC structure has been currently under investigation. Previous test results showed that the system could detect the de-bond of concrete from reinforcement, and the diagnostic signals were increased exponentially with the de-bonding size. Previous study also showed that the smart rebar could function well like regular reinforcement to undertake tension stresses. In this study, a smart rebar network has been used to detect the crack damage of concrete based on guided waves. Experimental test has been carried out for the study. In the test, concrete beams with 2 reinforcements have been built. 8 sets of PZT elements were mounted onto the reinforcement bars in an optimized way to form an active sensing diagnostic system. A 90 kHz 5-cycle Hanning-windowed tone burst was used as input. Multiple cracks have been generated on the concrete structures. Through the guided bulk waves propagating in the structures from actuators and sensors mounted from different bars, crack damage could be detected clearly. Cases for both single and multiple cracks were tested. Different crack depths from the surface and different crack numbers have been studied. Test result shows that the amplitude of sensor output signals is deceased linearly with a propagating crack, and is decreased exponentially with increased crack numbers. From the study, the active sensing diagnostic system using PZT based smart rebar network shows a promising way to provide concrete crack damage information through the "talk" among sensors.

Microstructural examination of fatigue crack tip in high strength steel

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

Fukuoka, C.; Yoshizawa, H.; Nakagawa, Y.G.

1993-10-01

Fatigue tests were performed to examine how microstructural conditioning influences crack initiation and propagation in SA508 class 3 low-carbon steel. A 3-mm-long crack was introduced in compact tension (CT) fatigue test specimens under four different loads in order to obtain crack tip plastic zones at different stress intensity factor ranges, [Delta]K = 18, 36, 54, and 72 MPa[radical]m. The microstructure of the plastic zones around the crack tip were examined by transmission electron microscopy (TEM) and selected area electron diffraction (SAD). Micro-orientation of the dislocation cells in the plastic zones of all of the CT samples increased to 4 degmore » from the level of an as-received sample. Four-point bending fatigue tests were performed for plate shape samples with a large cyclic strain range. The SAD value of the bending samples was also 4 deg in the damaged area where cracks already initiated at an early stage of the fatigue process. These test results indicate that the microstructural conditioning is a prerequisite for the fatigue crack initiation and propagation in SA508. These observations may lead to better understanding of how fatigue initiation processes transit to cracks.« less

An evaluation of the pressure proof test concept for thin sheet 2024-T3

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Poe, C. C., Jr.; Newman, J. C., Jr.; Harris, C. E.

1990-01-01

The concept of pressure proof testing of fuselage structures with fatigue cracks to insure structural integrity was evaluated from a fracture mechanics viewpoint. A generic analytical and experimental investigation was conducted on uniaxially loaded flat panels with crack configurations and stress levels typical of longitudinal lap-splice joints in commercial transport aircraft fuselage. The results revealed that the remaining fatigue life after a proof test was longer than that without the proof test because of crack growth retardation due to increased crack closure. However, based on a crack length that is slightly less than the critical value at the maximum proof test stress, the minimum assured life or proof test interval must be no more than 550 pressure cycles for a 1.33 proof factor and 1530 pressure cycles for a 1.5 proof factor to prevent in-flight failures.

An evaluation of the pressure proof test concept for thin sheet 2024-T3

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Poe, C. C., Jr.; Newman, James C., Jr.; Harris, Charles E.

1990-01-01

The concept of pressure proof testing of fuselage structures with fatigue cracks to insure structural integrity was evaluated from a fracture mechanics viewpoint. A generic analytical and experimental investigation was conducted on uniaxially loaded flat panels with crack configurations and stress levels typical of longitudinal lap splice joints in commercial transport aircraft fuselages. The results revealed that the remaining fatigue life after a proof test was longer than that without the proof test because of crack growth retardation due to increased crack closure. However, based on a crack length that is slightly less than the critical value at the maximum proof test stress, the minimum assured life or proof test interval must be no more than 550 pressure cycles for a 1.33 proof factor and 1530 pressure cycles for a 1.5 proof factor to prevent in-flight failures.

Residual strength and crack propagation tests on C-130 airplane center wings with service-imposed fatigue damage

NASA Technical Reports Server (NTRS)

Snider, H. L.; Reeder, F. L.; Dirkin, W. J.

1972-01-01

Fourteen C-130 airplane center wings, each containing service-imposed fatigue damage resulting from 4000 to 13,000 accumulated flight hours, were tested to determine their fatigue crack propagation and static residual strength characteristics. Eight wings were subjected to a two-step constant amplitude fatigue test prior to static testing. Cracks up to 30 inches long were generated in these tests. Residual static strengths of these wings ranged from 56 to 87 percent of limit load. The remaining six wings containing cracks up to 4 inches long were statically tested as received from field service. Residual static strengths of these wings ranged from 98 to 117 percent of limit load. Damage-tolerant structural design features such as fastener holes, stringers, doublers around door cutouts, and spanwise panel splices proved to be effective in retarding crack propagation.

Near-Threshold Fatigue Crack Growth Behavior of Fine-Grain Nickel-Based Alloys

NASA Technical Reports Server (NTRS)

Newman, John A.; Piascik, Robert S.

2003-01-01

Constant-Kmax fatigue crack growth tests were performed on two finegrain nickel-base alloys Inconel 718 (DA) and Ren 95 to determine if these alloys exhibit near-threshold time-dependent crack growth behavior observed for fine-grain aluminum alloys in room-temperature laboratory air. Test results showed that increases in K(sub max) values resulted in increased crack growth rates, but no evidence of time-dependent crack growth was observed for either nickel-base alloy at room temperature.

Development of Standard Methods of Testing and Analyzing Fatigue Crack Growth Rate Data

DTIC Science & Technology

1978-05-01

nitrogen cooled cryostat; high temperature tests were conducted using resistance heating tapes . An automatic controller maintained test temperatures...Cracking," Int. J. Fracture, Vol. 9, 1973, pp. 63-74. 87. P. Paris and F. Erdogan , "A Critical Analysis of Crack Propagation Laws," Trans. ASME, Ser. D: J...requirements of Sec. 7.2 and Appendix B. 200 REFERENCES 1. P. C. Paris and F. Erdogan , "A Critical Analysis of Crack Propagation Laws", Trans. ASME, Ser. D: 3

Influence of bitumen type on cracking resistance of asphalt mixtures used in pavement overlays

NASA Astrophysics Data System (ADS)

Jaskula, P.; Szydlowski, C.; Stienss, M.

2018-05-01

Cracking is one of the predominant distresses occurring in flexible pavements, especially in old pavements that were rehabilitated with an asphalt overlay. In such cases asphalt mixtures should be designed to ensure high resistance to reflective cracking because new asphalt layers are exposed to existing cracks of the old pavement. The nature of these cracks can be various (transverse, longitudinal as well as crazy cracking). One factor that minimizes this type of distress is the proper mix design process, which should involve selection of specific bitumen binder and mineral mix gradation. However, still there is no universally adopted laboratory test method that would allow to clearly assess resistance of asphalt mixtures to reflective cracking. This paper describes the usage of one of the devices developed to test asphalt mixtures in terms of such distress – Texas Overlay Tester. For this test, samples prepared in laboratory conditions (i.e. compacted with the use of Superpave Gyratory Compactor) as well as obtained in the field (by core drilling) can be used. The results are obtained not only quickly and easily, but also with sufficient repeatability. The described method characterizes both crack initiation and crack propagation properties of asphalt mixtures. In this work one type of mineral mixture was tested with 4 different types of bitumen (one neat bitumen, two ordinary polymer-modified and one polymer-modified with high polymer content). For selected cases extra additives (rubber and loose fibres) were also tested. In total, six asphalt mixtures were tested. A ranking of the used binders was created on the basis of the results in order to conclude which bitumen would ensure the best performance characteristics in terms of reflective cracking. The results have clearly shown that deliberate choice of the binder used in the asphalt mixture for the overlay will significantly improve its reflective cracking resistance or even fatigue resistance.

Fabrication and testing of prestressed composite rotor blade spar specimens

NASA Technical Reports Server (NTRS)

Gleich, D.

1974-01-01

Prestressed composite spar specimens were fabricated and evaluated by crack propagation and ballistic penetration tests. The crack propagation tests on flawed specimens showed that the prestressed composite spar construction significantly suppresses crack growth. Damage from three high velocity 30 caliber projectile hits was confined to three small holes in the ballistic test specimen. No fragmentation or crack propagation was observed indicating good ballistic damage resistance. Rotor attachment approaches and improved structural performance configurations were identified. Design theory was verified by tests. The prestressed composite spar configuration consisted of a compressively prestressed high strength ARDEFORM 301 stainless steel liner overwrapped with pretensioned S-994 fiberglass.

Use of Marker Bands for Determination of Fatigue Crack Growth Rates and Crack Front Shapes in Pre-Corroded Coupons

NASA Technical Reports Server (NTRS)

Willard, S. A.

1997-01-01

Groups of striations called marker bands generated on a fatigue fracture surface can be used to mark the position of an advancing fatigue crack at known intervals. A technique has been developed that uses the distance between multiple sets of marker bands to obtain a vs. N, crack front shape, and fatigue crack growth rate data for small cracks. This technique is particularly usefull for specimens that require crack length measurements during testing that cannot be obtained because corrosion obscures the surface of the specimen. It is also useful for specimens with unusual or non-symmetric shapes where it is difficult to obtain accurate crack lengths using traditional methods such as compliance or electric potential difference in the early stages of testing.

Test program to provide confidence in liquid oxygen cooling of hydrocarbon fueled rocket thrust chambers

NASA Technical Reports Server (NTRS)

Armstrong, E. S.

1986-01-01

An experimental program has been planned at the NASA Lewis Research Center to build confidence in the feasibility of liquid oxygen cooling for hydrocarbon fueled rocket engines. Although liquid oxygen cooling has previously been incorporated in test hardware, more runtime is necessary to gain confidence in this concept. In the previous tests, small oxygen leaks developed at the throat of the thrust chamber and film cooled the hot-gas side of the chamber wall without resulting in catastrophic failure. However, more testing is necessary to demonstrate that a catastrophic failure would not occur if cracks developed further upstream between the injector and the throat, where the boundary layer has not been established. Since under normal conditions cracks are expected to form in the throat region of the thrust chamber, cracks must be initiated artificially in order to control their location. Several methods of crack initiation are discussed in this report. Four thrust chambers, three with cracks and one without, should be tested. The axial location of the cracks should be varied parametrically. Each chamber should be instrumented to determine the effects of the cracks, as well as the overall performance and durability of the chambers.

Evaluation of Environmentally Assisted Cracking of Armour Wires in Flexible Pipes, Power Cables and Umbilicals

NASA Astrophysics Data System (ADS)

Zhang, Zhiying

Environmentally assisted cracking (EAC) of armour wires in flexible pipes, power cables and umbilicals is a major concern with the development of oil and gas fields and wind farms in harsh environments. Hydrogen induced cracking (HIC) or hydrogen embrittlement (HE) of steel armour wires used in deep-water and ultra-deep-water has been evaluated. Simulated tests have been carried out in simulated sea water, under conditions where the susceptibility is the highest, i.e. at room temperature, at the maximum negative cathodic potential and at the maximum stress level expected in service for 150 hours. Examinations of the tested specimens have not revealed cracking or blistering, and measurement of hydrogen content has confirmed hydrogen charging. In addition, sulphide stress cracking (SSC) and chloride stress cracking (CSC) of nickel-based alloy armour wires used in harsh down-hole environments has been evaluated. Simulated tests have been carried out in simulated solution containing high concentration of chloride, with high hydrogen sulphide partial pressure, at high stress level and at 120 °C for 720 hours. Examinations of the tested specimens have not revealed cracking or blistering. Subsequent tensile tests of the tested specimens at ambient pressure and temperature have revealed properties similar to the as-received specimens.

Method for analyzing the mass of a sample using a cold cathode ionization source mass filter

DOEpatents

Felter, Thomas E.

2003-10-14

An improved quadrupole mass spectrometer is described. The improvement lies in the substitution of the conventional hot filament electron source with a cold cathode field emitter array which in turn allows operating a small QMS at much high internal pressures then are currently achievable. By eliminating of the hot filament such problems as thermally "cracking" delicate analyte molecules, outgassing a "hot" filament, high power requirements, filament contamination by outgas species, and spurious em fields are avoid all together. In addition, the ability of produce FEAs using well-known and well developed photolithographic techniques, permits building a QMS having multiple redundancies of the ionization source at very low additional cost.

Long-Term Corrosion Fatigue of Welded Marine Steels.

DTIC Science & Technology

1984-01-01

MPa ksi MPa I C API 5L Grade B 35 240 60 min. 415 mrin. ASTM A53 Grade B 35 240 60 min. 415 min. ASTM A135 Grade B 35 240 60 min. 415 min. ASTM A139...2% max. cold expansion 42 290 60 min. 415 min. API 5LX Grade X52 2% max. cold expansion 52 360 66 min. 455 min. ASTM AS00 Grade B 42-46 290-320 58 mi...Environments 3.38 " 3.5 Influence of Load Ratio on the Corrosion Fatigue Crack Growth Rates in API X-70 Linepipe Steel in 3.5% NaCl (From (3.30]) 3.39 3.6

Composite material reinforced with atomized quasicrystalline particles and method of making same

DOEpatents

Biner, Suleyman B.; Sordelet, Daniel J.; Lograsso, Barbara K.; Anderson, Iver E.

1998-12-22

A composite material comprises an aluminum or aluminum alloy matrix having generally spherical, atomized quasicrystalline aluminum-transition metal alloy reinforcement particles disposed in the matrix to improve mechanical properties. A composite article can be made by consolidating generally spherical, atomized quaiscrystalline aluminum-transition metal alloy particles and aluminum or aluminum alloy particles to form a body that is cold and/or hot reduced to form composite products, such as composite plate or sheet, with interfacial bonding between the quasicrystalline particles and the aluminum or aluminum alloy matrix without damage (e.g. cracking or shape change) of the reinforcement particles. The cold and/or hot worked compositehibits substantially improved yield strength, tensile strength, Young's modulus (stiffness).

Fatigue crack propagation behavior of stainless steel welds

NASA Astrophysics Data System (ADS)

Kusko, Chad S.

The fatigue crack propagation behavior of austenitic and duplex stainless steel base and weld metals has been investigated using various fatigue crack growth test procedures, ferrite measurement techniques, light optical microscopy, stereomicroscopy, scanning electron microscopy, and optical profilometry. The compliance offset method has been incorporated to measure crack closure during testing in order to determine a stress ratio at which such closure is overcome. Based on this method, an empirically determined stress ratio of 0.60 has been shown to be very successful in overcoming crack closure for all da/dN for gas metal arc and laser welds. This empirically-determined stress ratio of 0.60 has been applied to testing of stainless steel base metal and weld metal to understand the influence of microstructure. Regarding the base metal investigation, for 316L and AL6XN base metals, grain size and grain plus twin size have been shown to influence resulting crack growth behavior. The cyclic plastic zone size model has been applied to accurately model crack growth behavior for austenitic stainless steels when the average grain plus twin size is considered. Additionally, the effect of the tortuous crack paths observed for the larger grain size base metals can be explained by a literature model for crack deflection. Constant Delta K testing has been used to characterize the crack growth behavior across various regions of the gas metal arc and laser welds at the empirically determined stress ratio of 0.60. Despite an extensive range of stainless steel weld metal FN and delta-ferrite morphologies, neither delta-ferrite morphology significantly influence the room temperature crack growth behavior. However, variations in weld metal da/dN can be explained by local surface roughness resulting from large columnar grains and tortuous crack paths in the weld metal.

Prediction of Low-Temperature Cracking Using Superpave Binder Specifications

DOT National Transportation Integrated Search

1996-02-01

Six different AC-20 asphalt cements were used in a Pennsylvania project in September 1976. Two of the six test pavements developed low-temperature cracking in January 1977. The remaining four test pavements started to develop cracks to different degr...

Microstructural examination of

NASA Astrophysics Data System (ADS)

Fukuoka, C.; Yoshizawa, H.; Nakagawa, Y. G.; Lapides, M. E.

1993-10-01

Fatigue tests were performed to examine how microstructural conditioning influences crack initiation and propagation in SA508 class 3 low-carbon steel. A 3-mm-long crack was introduced in compact tension (CT) fatigue test specimens under four different loads in order to obtain crack tip plastic zones at different stress intensity factor ranges, ΔK = 18, 36, 54, and 72 MPa√m. The microstructure of the plastic zones around the crack tip were examined by trans- mission electron microscopy (TEM) and selected area electron diffraction (SAD). Micro- orientation of the dislocation cells in the plastic zones of all of the CT samples increased to 4 deg from the level of an as-received sample. Four-point bending fatigue tests were performed for plate shape samples with a large cyclic strain range. The SAD value of the bending samples was also 4 deg in the damaged area where cracks already initiated at an early stage of the fatigue process. These test results indicate that the microstructural conditioning is a prerequisite for the fatigue crack initiation and propagation in SA508. These observations may lead to better under- standing of how fatigue initiation processes transit to cracks.

Experimental studies of rock fracture behavior related to hydraulic fracture

NASA Astrophysics Data System (ADS)

Ma, Zifeng

The objective of this experimental investigation stems from the uncontrollable of the hydraulic fracture shape in the oil and gas production field. A small-scale laboratory investigation of crack propagation in sandstone was first performed with the objective to simulate the field fracture growth. Test results showed that the fracture resistance increased with crack extension, assuming that there was an interaction between crack faces (bridging, interlocking, and friction). An acoustic emission test was conducted to examine the existence of the interaction by locating AE events and analyzing waveform. Furthermore, the effects of confining stress, loading rate, stress field, and strength heterogeneous on the tortuosity of the fracture surface were experimentally investigated in the study. Finally, a test was designed and conducted to investigate the crack propagation in a stratified media with permeability contrast. Crack was observed to arrested in an interface. The phenomenon of delamination along an interface between layers with permeability contrast was observed. The delamination was proposed to be the cause of crack arrest and crack jump in the saturated stratified materials under confinement test.

A Statistics-Based Cracking Criterion of Resin-Bonded Silica Sand for Casting Process Simulation

NASA Astrophysics Data System (ADS)

Wang, Huimin; Lu, Yan; Ripplinger, Keith; Detwiler, Duane; Luo, Alan A.

2017-02-01

Cracking of sand molds/cores can result in many casting defects such as veining. A robust cracking criterion is needed in casting process simulation for predicting/controlling such defects. A cracking probability map, relating to fracture stress and effective volume, was proposed for resin-bonded silica sand based on Weibull statistics. Three-point bending test results of sand samples were used to generate the cracking map and set up a safety line for cracking criterion. Tensile test results confirmed the accuracy of the safety line for cracking prediction. A laboratory casting experiment was designed and carried out to predict cracking of a cup mold during aluminum casting. The stress-strain behavior and the effective volume of the cup molds were calculated using a finite element analysis code ProCAST®. Furthermore, an energy dispersive spectroscopy fractographic examination of the sand samples confirmed the binder cracking in resin-bonded silica sand.

Fatigue crack growth rates in a pressure vessel steel under various conditions of loading and the environment

NASA Astrophysics Data System (ADS)

Hicks, P. D.; Robinson, F. P. A.

1986-10-01

Corrosion fatigue (CF) tests have been carried out on SA508 Cl 3 pressure vessel steel, in simulated P.W.R. environments. The test variables investigated included air and P.W.R. water environments, frequency variation over the range 1 Hz to 10 Hz, transverse and longitudinal crack growth directions, temperatures of 20 °C and 50 °C, and R-ratios of 0.2 and 0.7. It was found that decreasing the test frequency increased fatigue crack growth rates (FCGR) in P.W.R. environments, P.W.R. environment testing gave enhanced crack growth (vs air tests), FCGRs were greater for cracks growing in the longitudinal direction, slight increases in temperature gave noticeable accelerations in FCGR, and several air tests gave FCGR greater than those predicted by the existing ASME codes. Fractographic evidence indicates that FCGRs were accelerated by a hydrogen embrittlement mechanism. The presence of elongated MnS inclusions aided both mechanical fatigue and hydrogen embrittlement processes, thus producing synergistically fast FCGRs. Both anodic dissolution and hydrogen embrittlement mechanisms have been proposed for the environmental enhancement of crack growth rates. Electrochemical potential measurements and potentiostatic tests have shown that sample isolation of the test specimens from the clevises in the apparatus is not essential during low temperature corrosion fatigue testing.

Effects of powder characteristics on injection molding and burnout cracking

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

Bandyopadhyay, G.; French, K.W.

Silicon nitride particle size and size distributions were varied widely to determine their effects on burnout cracking of injection-molded test parts containing thick and thin sections. Elimination of internal cracking required significant burnout shrinkage, which did not occur by changes of particle size and size distribution. However, isopressing of test parts after burnout provided the dimensional shrinkage necessary for producing crack-free components.

A study of creep crack growth in 2219-T851

NASA Astrophysics Data System (ADS)

Bensussan, Philippe L.; Jablonski, David A.; Pelloux, Regis M.

1984-01-01

Creep crack growth rates were measured in high strength 2219-T851 aluminum alloy with a computerized fully automated test procedure. Crack growth tests were performed on CT specimens with side grooves. The experimental set-up is described. During a test, the specimen is cyclically loaded on a servohydraulic testing machine under computer control, maintained at maximum load for a given hold time at each cycle, unloaded, and then reloaded. Crack lengths are obtained from compliance measurements recorded during each unloading. It is shown that the measured crack growth rates per cycle do represent creep crack growth rates per unit time for hold times longer than 10 seconds. The validity of LEFM concepts for side-grooved specimens is reviewed, and compliance and stress intensity factor calibrations for such specimens are reported. For the range of testing conditions of this study, 2219-T851 is shown to be creep brittle in terms of concepts of fracture mechanics of creeping solids. It is found that, under these testing conditions, a correlation exists between the creep crack growth rates under plane strain conditions and the stress intensity factor ( da/dt = A K 3.8 at 175 °C) for simple K histories in a regime of steady or quasi-steady state crack growth. The micromechanisms of fracture are determined to be of complex nature. The fracture mode is observed to be mixed inter- and transgranular, the relative amount of intergranular fracture decreasing as K and da/dt increase.

Cyclic Crack Growth Testing of an A.O. Smith Multilayer Pressure Vessel with Modal Acoustic Emission Monitoring and Data Assessment

NASA Technical Reports Server (NTRS)

Ziola, Steven M.

2014-01-01

Digital Wave Corp. (DWC) was retained by Jacobs ATOM at NASA Ames Research Center to perform cyclic pressure crack growth sensitivity testing on a multilayer pressure vessel instrumented with DWC's Modal Acoustic Emission (MAE) system, with captured wave analysis to be performed using DWCs WaveExplorerTM software, which has been used at Ames since 2001. The objectives were to document the ability to detect and characterize a known growing crack in such a vessel using only MAE, to establish the sensitivity of the equipment vs. crack size and / or relevance in a realistic field environment, and to obtain fracture toughness materials properties in follow up testing to enable accurate crack growth analysis. This report contains the results of the testing.

Failure Pressure and Leak Rate of Steam Generator Tubes With Stress Corrosion Cracks

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

Majumdar, S.; Kasza, K.; Park, J.Y.

2002-07-01

This paper illustrates the use of an 'equivalent rectangular crack' approach to predict leak rates through laboratory generated stress corrosion cracks. A comparison between predicted and observed test data on rupture and leak rate from laboratory generated stress corrosion cracks are provided. Specimen flaws were sized by post-test fractography in addition to pre-test advanced eddy current technique. The test failure pressures and leak rates are shown to be closer to those predicted on the basis of fractography than on NDE. However, the predictions based on NDE results are encouraging, particularly because they have the potential to determine a more detailedmore » geometry of ligamentous cracks from which more accurate predictions of failure pressure and leak rate can be made in the future. (authors)« less

Crack Initiation and Growth Behavior at Corrosion Pit in 2024-T3 Aluminum Alloy

DTIC Science & Technology

2014-09-01

63 Figure B.1: The crack length vs. number of cycles during fatigue testing for the 2AI-01 specimen...number of cycles during fatigue testing for the the 2AI- 02 specimen...64 Figure B.3: The crack length vs. number of cycles during fatigue testing for the 2Sl-01 specimen

Autogenous healing of sea-water exposed mortar: Quantification through a simple and rapid permeability test

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

Palin, D., E-mail: d.palin@tudelft.nl; Jonkers, H. M.; Wiktor, V.

Concrete has an autogenous ability to heal cracks potentially contributing to its functional water tightness and durability. Here, we quantify the crack-healing capacity of sea-water submerged mortar specimens through a simple and rapid permeability test. Defined crack width geometries were created in blast furnace slag cement specimens allowing healed specimens to be quantified against unhealed specimens. Specimens with 0.2 mm wide cracks were not permeable after 28 days submersion. Specimens with 0.4 mm cracks had decreases in permeability of 66% after 28 days submersion, and 50–53% after 56 days submersion. Precipitation of aragonite and brucite in the cracks was themore » main cause of crack healing. Healing potential was dependent on the initial crack width, thermodynamic considerations and the amount of ions available in the crack. To our knowledge, this is the first study to quantify the functional autogenous healing capacity of cracked sea-water exposed cementitious specimens.« less

Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

NASA Technical Reports Server (NTRS)

Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

1998-01-01

The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

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.

Monitoring the corrosion process of reinforced concrete using BOTDA and FBG sensors.

PubMed

Mao, Jianghong; Chen, Jiayun; Cui, Lei; Jin, Weiliang; Xu, Chen; He, Yong

2015-04-15

Expansion and cracking induced by the corrosion of reinforcement concrete is the major factor in the failure of concrete durability. Therefore, monitoring of concrete cracking is critical for evaluating the safety of concrete structures. In this paper, we introduce a novel monitoring method combining Brillouin optical time domain analysis (BOTDA) and fiber Bragg grating (FBG), based on mechanical principles of concrete expansion cracking. BOTDA monitors concrete expansion and crack width, while FBG identifies the time and position of cracking. A water-pressure loading simulation test was carried out to determine the relationship between fiber strain, concrete expansion and crack width. An electrical accelerated corrosion test was also conducted to evaluate the ability of this novel sensor to monitor concrete cracking under practical conditions.

Test Method Variability in Slow Crack Growth Properties of Sealing Glasses

NASA Technical Reports Server (NTRS)

Salem, J. A.; Tandon, R.

2010-01-01

The crack growth properties of several sealing glasses were measured by using constant stress rate testing in 2 and 95 percent RH (relative humidity). Crack growth parameters measured in high humidity are systematically smaller (n and B) than those measured in low humidity, and crack velocities for dry environments are 100x lower than for wet environments. The crack velocity is very sensitive to small changes in RH at low RH. Biaxial and uniaxial stress states produced similar parameters. Confidence intervals on crack growth parameters that were estimated from propagation of errors solutions were comparable to those from Monte Carlo simulation. Use of scratch-like and indentation flaws produced similar crack growth parameters when residual stresses were considered.

Firing test of propellant-cracked solid motor under X-ray TV

NASA Astrophysics Data System (ADS)

Fujiwara, Tsutomu; Tanemura, Toshiharu; Itoh, Katsuya; Kakuta, Yoshiaki; Shimizu, Morio; Takahashi, Michio

This paper presents the effects of a big crack on the combustion behaviors of the scaled-down Japanese H-I upper stage motors of the National Space Development Agency (NASDA). The big crack was generated by cooling down the propellant grain below -100 C; the crack was identified and measured with the X-ray computer tomography (CT) system designed for medical use. It was found that the crack spread widely from inner bore to liner and fore-and-aft of the motor. The firing test of the propellant-cracked solid motor was performed under X-ray TV observation, and the motor exploded just after the ignition because of the abrupt chamber pressure increase due to flame propagation into the crack.

Elevated Temperature Crack Propagation

NASA Technical Reports Server (NTRS)

Orange, Thomas W.

1994-01-01

This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.

STRESS CORROSION CRACK GROWTH RESPONSE FOR ALLOY 152/52 DISSIMILAR METAL WELDS IN PWR PRIMARY WATER

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

Toloczko, Mychailo B.; Olszta, Matthew J.; Overman, Nicole R.

2015-08-15

As part of ongoing research into primary water stress corrosion cracking (PWSCC) susceptibility of alloy 690 and its welds, SCC tests have been conducted on alloy 152/52 dissimilar metal (DM) welds with cracks positioned with the goal to assess weld dilution and fusion line effects on SCC susceptibility. No increased crack growth rate was found when evaluating a 20% Cr dilution zone in alloy 152M joined to carbon steel (CS) that had not undergone a post-weld heat treatment (PWHT). However, high SCC crack growth rates were observed when the crack reached the fusion line of that material where it propagatedmore » both on the fusion line and in the heat affected zone (HAZ) of the carbon steel. Crack surface and crack profile examinations of the specimen revealed that cracking in the weld region was transgranular (TG) with weld grain boundaries not aligned with the geometric crack growth plane of the specimen. The application of a typical pressure vessel PWHT on a second set of alloy 152/52 – carbon steel DM weld specimens was found to eliminate the high SCC susceptibility in the fusion line and carbon steel HAZ regions. PWSCC tests were also performed on alloy 152-304SS DM weld specimens. Constant K crack growth rates did not exceed 5x10-9 mm/s in this material with post-test examinations revealing cracking primarily on the fusion line and slightly into the 304SS HAZ.« less

Crack identification and evolution law in the vibration failure process of loaded coal

NASA Astrophysics Data System (ADS)

Li, Chengwu; Ai, Dihao; Sun, Xiaoyuan; Xie, Beijing

2017-08-01

To study the characteristics of coal cracks produced in the vibration failure process, we set up a static load and static and dynamic combination load failure test simulation system, prepared with different particle size, formation pressure, and firmness coefficient coal samples. Through static load damage testing of coal samples and then dynamic load (vibration exciter) and static (jack) combination destructive testing, the crack images of coal samples under the load condition were obtained. Combined with digital image processing technology, an algorithm of crack identification with high precision and in real-time is proposed. With the crack features of the coal samples under different load conditions as the research object, we analyzed the distribution of cracks on the surface of the coal samples and the factors influencing crack evolution using the proposed algorithm and a high-resolution industrial camera. Experimental results showed that the major portion of the crack after excitation is located in the rear of the coal sample where the vibration exciter cannot act. Under the same disturbance conditions, crack size and particle size exhibit a positive correlation, while crack size and formation pressure exhibit a negative correlation. Soft coal is more likely to lead to crack evolution than hard coal, and more easily causes instability failure. The experimental results and crack identification algorithm provide a solid basis for the prevention and control of instability and failure of coal and rock mass, and they are helpful in improving the monitoring method of coal and rock dynamic disasters.

AE characteristic for monitoring of fatigue crack in steel bridge members

NASA Astrophysics Data System (ADS)

Yoon, Dong-Jin; Jung, Juong-Chae; Park, Philip; Lee, Seung-Seok

2000-06-01

Acoustic emission technique was employed for the monitoring of crack activity in both steel bridge members and laboratory specimen. Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact tension specimen. The relationship between a stress intensity factor and AE signals activity as well as conventional AE parameter analysis was discussed. A field test was also conducted on a railway bridge, which contain several fatigue cracks. Crack activities were investigated while in service with strain measurement. From the results, in the laboratory tests, the features of three parameters such as the length of crack growth, the AE energy, and the cumulative AE events, showed the almost same trend in their increase as the number of fatigue cycle increased. From the comparisons of peak amplitude and AE energy with stress intensity factor, it was verified that the higher stress intensity factors generated AE signals with higher peak amplitude and a large number of AE counts. In the field test, real crack propagation signals were captured and the crack activity was verified in two cases.

Evaluation of the fuselage lap joint fatigue and terminating action repair

NASA Technical Reports Server (NTRS)

Samavedam, Gopal; Thomson, Douglas; Jeong, David Y.

1994-01-01

Terminating action is a remedial repair which entails the replacement of shear head countersunk rivets with universal head rivets which have a larger shank diameter. The procedure was developed to eliminate the risk of widespread fatigue damage (WFD) in the upper rivet row of a fuselage lap joint. A test and evaluation program has been conducted by Foster-Miller, Inc. (FMI) to evaluate the terminating action repair of the upper rivet row of a commercial aircraft fuselage lap splice. Two full scale fatigue tests were conducted on fuselage panels using the growth of fatigue cracks in the lap joint. The second test was performed to evaluate the effectiveness of the terminating action repair. In both tests, cyclic pressurization loading was applied to the panels while crack propagation was recorded at all rivet locations at regular intervals to generate detailed data on conditions of fatigue crack initiation, ligament link-up, and fuselage fracture. This program demonstrated that the terminating action repair substantially increases the fatigue life of a fuselage panel structure and effectively eliminates the occurrence of cracking in the upper rivet row of the lap joint. While high cycle crack growth was recorded in the middle rivet row during the second test, failure was not imminent when the test was terminated after cycling to well beyond the service life. The program also demonstrated that the initiation, propagation, and linkup of WFD in full-scale fuselage structures can be simulated and quantitatively studied in the laboratory. This paper presents an overview of the testing program and provides a detailed discussion of the data analysis and results. Crack distribution and propagation rates and directions as well as frequency of cracking are presented for both tests. The progression of damage to linkup of adjacent cracks and to eventual overall panel failure is discussed. In addition, an assessment of the effectiveness of the terminating action repair and the occurrence of cracking in the middle rivet row is provided, and conclusions of practical interest are drawn.

Test methods for environment-assisted cracking

NASA Astrophysics Data System (ADS)

Turnbull, A.

1992-03-01

The test methods for assessing environment assisted cracking of metals in aqueous solution are described. The advantages and disadvantages are examined and the interrelationship between results from different test methods is discussed. The source of differences in susceptibility to cracking occasionally observed from the varied mechanical test methods arises often from the variation between environmental parameters in the different test conditions and the lack of adequate specification, monitoring, and control of environmental variables. Time is also a significant factor when comparing results from short term tests with long exposure tests. In addition to these factors, the intrinsic difference in the important mechanical variables, such as strain rate, associated with the various mechanical tests methods can change the apparent sensitivity of the material to stress corrosion cracking. The increasing economic pressure for more accelerated testing is in conflict with the characteristic time dependence of corrosion processes. Unreliable results may be inevitable in some cases but improved understanding of mechanisms and the development of mechanistically based models of environment assisted cracking which incorporate the key mechanical, material, and environmental variables can provide the framework for a more realistic interpretation of short term data.

Evaluation of Stress Corrosion Resistance Properties of 15CrMoR(H) in H2S Environment

NASA Astrophysics Data System (ADS)

Zhang, Yiliang; Wang, Jing; Wu, Mingyao; Li, Shurui; Liu, Wenbin

To evaluate the hydrogen resistant properties of the 15CrMoR(H) with new smelting process, according to NACE and National Standards, three tests including NACE standard tensile test, NACE standard bent-beam test and hydrogen induced cracking test are executed in saturated hydrogen sulfide(H2S) environment. Stress-life mathematical model of this material is given by analyzing and fitting the results of tensile test. Test results show that the threshold sth of tensile test is 0.7R eL(252MPa); the threshold nominal stress SC of bent-beam is higher than 4.5 R eL (1620MPa); for HIC test, the crack length rate CLR is 4.40%, the crack thickness rate CTR is 0.87% and the crack sensitive rate CSR is 0.04%. Compare with EFC standard, the safety margin of HIC test is 3.4, 3.4 and 37.5 times respectively. All the experimental results show that the new 15CrMoR(H) material has excellent H2S environmental cracking resistance properties.

Improved method for determining the stress relaxation at the crack tip

NASA Astrophysics Data System (ADS)

Grinevich, A. V.; Erasov, V. S.; Avtaev, V. V.

2017-10-01

A technique is suggested to determine the stress relaxation at the crack tip during tests of a specimen of a new type at a constant crack opening fixed by a stay bolt. The shape and geometry of the specimen make it possible to set the load and to determine the crack closure force after long-term exposure using the force transducer of a tensile-testing machine. The stress relaxation at the crack tip is determined in a V95pchT2 alloy specimen at elevated temperatures.

Hydrogen accelerated fatigue crack growth of friction stir welded X52 steel pipe

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

Ronevich, Joseph Allen; Somerday, Brian P.; Feng, Zhili

Friction stir welded steel pipelines were tested in high pressure hydrogen gas to examine the effects of hydrogen accelerated fatigue crack growth. Fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationships were measured for an X52 friction stir welded pipe tested in 21 MPa hydrogen gas at a frequency of 1 Hz and R = 0.5. Tests were performed on three regions: base metal (BM), center of friction stir weld (FSW), and 15 mm off-center of the weld. For all three material regions, tests in hydrogen exhibited accelerated fatigue crack growth rates that exceeded an order of magnitudemore » compared to companion tests in air. Among tests in hydrogen, fatigue crack growth rates were modestly higher in the FSW than the BM and 15 mm off-center tests. Select regions of the fracture surfaces associated with specified ΔK levels were examined which revealed intergranular fracture in the BM and 15 mm off-center specimens but an absence of intergranular features in the FSW specimens. In conclusion, the X52 friction stir weld and base metal tested in hydrogen exhibited fatigue crack growth rate relationships that are comparable to those for conventional arc welded steel pipeline of similar strength found in the literature.« less

Hydrogen accelerated fatigue crack growth of friction stir welded X52 steel pipe

DOE PAGES

Ronevich, Joseph Allen; Somerday, Brian P.; Feng, Zhili

2016-11-17

Friction stir welded steel pipelines were tested in high pressure hydrogen gas to examine the effects of hydrogen accelerated fatigue crack growth. Fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationships were measured for an X52 friction stir welded pipe tested in 21 MPa hydrogen gas at a frequency of 1 Hz and R = 0.5. Tests were performed on three regions: base metal (BM), center of friction stir weld (FSW), and 15 mm off-center of the weld. For all three material regions, tests in hydrogen exhibited accelerated fatigue crack growth rates that exceeded an order of magnitudemore » compared to companion tests in air. Among tests in hydrogen, fatigue crack growth rates were modestly higher in the FSW than the BM and 15 mm off-center tests. Select regions of the fracture surfaces associated with specified ΔK levels were examined which revealed intergranular fracture in the BM and 15 mm off-center specimens but an absence of intergranular features in the FSW specimens. In conclusion, the X52 friction stir weld and base metal tested in hydrogen exhibited fatigue crack growth rate relationships that are comparable to those for conventional arc welded steel pipeline of similar strength found in the literature.« less

Reliability analysis of structures under periodic proof tests in service

NASA Technical Reports Server (NTRS)

Yang, J.-N.

1976-01-01

A reliability analysis of structures subjected to random service loads and periodic proof tests treats gust loads and maneuver loads as random processes. Crack initiation, crack propagation, and strength degradation are treated as the fatigue process. The time to fatigue crack initiation and ultimate strength are random variables. Residual strength decreases during crack propagation, so that failure rate increases with time. When a structure fails under periodic proof testing, a new structure is built and proof-tested. The probability of structural failure in service is derived from treatment of all the random variables, strength degradations, service loads, proof tests, and the renewal of failed structures. Some numerical examples are worked out.

Remote monitoring and prognosis of fatigue cracking in steel bridges with acoustic emission

NASA Astrophysics Data System (ADS)

Yu, Jianguo Peter; Ziehl, Paul; Pollock, Adrian

2011-04-01

Acoustic emission (AE) monitoring is desirable to nondestructively detect fatigue damage in steel bridges. Investigations of the relationship between AE signals and crack growth behavior are of paramount importance prior to the widespread application of passive piezoelectric sensing for monitoring of fatigue crack propagation in steel bridges. Tests have been performed to detect AE from fatigue cracks in A572G50 steel. Noise induced AE signals were filtered based on friction emission tests, loading pattern, and a combined approach involving Swansong II filters and investigation of waveforms. The filtering methods based on friction emission tests and load pattern are of interest to the field evaluation using sparse datasets. The combined approach is suitable for data filtering and interpretation of actual field tests. The pattern recognition program NOESIS (Envirocoustics) was utilized for the evaluation of AE data quality. AE parameters are associated with crack length, crack growth rate, maximum stress intensity and stress intensity range. It is shown that AE hits, counts, absolute energy, and signal strength are able to provide warnings at the critical cracking level where cracking progresses from stage II (stable propagation) to stage III (unstable propagation which may result in failure). Absolute energy rate and signal strength rate may be better than count rate to assess the remaining fatigue life of inservice steel bridges.

Use of Slow Strain Rate Tensile Testing to Assess the Ability of Several Superalloys to Resist Environmentally-Assisted Intergranular Cracking

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Telesman, Jack; Banik, Anthony; McDevitt, Erin

2014-01-01

Intergranular fatigue crack initiation and growth due to environmental degradation, especially at notched features, can often limit the fatigue life of disk superalloys at high temperatures. For clear comparisons, the effects of alloy composition on cracking in air needs to be understood and compared separately from variables associated with notches and cracks such as effective stress concentration, plastic flow, stress relaxation, and stress redistribution. The objective of this study was to attempt using simple tensile tests of specimens with uniform gage sections to compare the effects of varied alloy composition on environment-assisted cracking of several powder metal and cast and wrought superalloys including ME3, LSHR, Udimet 720(TradeMark) ATI 718Plus(Registered TradeMark) alloy, Haynes 282(Trademark), and Inconel 740(TradeMark) Slow and fast strain-rate tensile tests were found to be a useful tool to compare propensities for intergranular surface crack initiation and growth. The effects of composition and heat treatment on tensile fracture strain and associated failure modes were compared. Environment interactions were determined to often limit ductility, by promoting intergranular surface cracking. The response of various superalloys and heat treatments to slow strain rate tensile testing varied substantially, showing that composition and microstructure can significantly influence environmental resistance to cracking.

Fracture analysis of stiffened panels under biaxial loading with widespread cracking

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Dawicke, D. S.

1995-01-01

An elastic-plastic finite-element analysis with a critical crack-tip-opening angle (CTOA) fracture criterion was used to model stable crack growth and fracture of 2024-T3 aluminum alloy (bare and clad) panels for several thicknesses. The panels had either single or multiple-site damage (MSD) cracks subjected to uniaxial or biaxial loading. Analyses were also conducted on cracked stiffened panels with single or MSD cracks. The critical CTOA value for each thickness was determined by matching the failure load on a middle-crack tension specimen. Comparisons were made between the critical angles determined from the finite-element analyses and those measured with photographic methods. Predicted load-against-crack extension and failure loads for panels under biaxial loading, panels with MSD cracks, and panels with various number of stiffeners were compared with test data, whenever possible. The predicted results agreed well with the test data even for large-scale plastic deformations. The analyses were also able to predict stable tearing behavior of a large lead crack in the presence of MSD cracks. The analyses were then used to study the influence of stiffeners on residual strength in the presence of widespread fatigue cracking. Small MSD cracks were found to greatly reduce the residual strength for large lead cracks even for stiffened panels.

Fracture analysis of stiffened panels under biaxial loading with widespread cracking

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1995-01-01

An elastic-plastic finite-element analysis with a critical crack-tip opening angle (CTOA) fracture criterion was used to model stable crack growth and fracture of 2024-T3 aluminum alloy (bare and clad) panels for several thicknesses. The panels had either single or multiple-site damage (MSD) cracks subjected to uniaxial or biaxial loading. Analyses were also conducted on cracked stiffened panels with single or MSD cracks. The critical CTOA value for each thickness was determined by matching the failure load on a middle-crack tension specimen. Comparisons were made between the critical angles determined from the finite-element analyses and those measured with photographic methods. Predicted load-against-crack extension and failure loads for panels under biaxial loading, panels with MSD cracks, and panels with various numbers of stiffeners were compared with test data whenever possible. The predicted results agreed well with the test data even for large-scale plastic deformations. The analyses were also able to predict stable tearing behavior of a large lead crack in the presence of MSD cracks. The analyses were then used to study the influence of stiffeners on residual strength in the presence of widespread fatigue cracking. Small MSD cracks were found to greatly reduce the residual strength for large lead cracks even for stiffened panels.

The characterization of widespread fatigue damage in fuselage structure

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Willard, Scott A.; Miller, Matthew

1994-01-01

The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this were to establish an experimental data base for validating emerging WSFD analytical prediction methodology and to identify first order effects that contribute to fatigue crack initiation and growth. Detailed examinations were performed on a test panel containing four bays of a riveted lap splice joint. The panel was removed from a full scale fuselage test article after receiving 60,000 full pressurization cycles. The results of in situ examinations document the progression of fuselage skin fatigue crack growth through crack linkup. Detailed tear down examinations and fractography of the lap splice joint region revealed fatigue crack initiation sites, crack morphology, and crack linkup geometry. From this large data base, distributions of crack size and locations are presented and discussions of operative damage mechanisms are offered.

The characterization of widespread fatigue damage in fuselage structure

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Willard, Scott A.; Miller, Matthew

1994-01-01

The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this work were to establish an experimental data base for validating emerging WSFD analytical prediction methodology and to identify first order effects that contribute to fatigue crack initiation and growth. Detailed examinations were performed on a test panel containing four bays of a riveted lap splice joint. The panel was removed from a full scale fuselage test article after receiving 60,000 full pressurization cycles. The results of in situ examinations document the progression of fuselage skin fatigue crack growth through crack linkup. Detailed tear down examinations and fractography of the lap splice joint region revealed fatigue crack initiation sites, crack morphology and crack linkup geometry. From this large data base, distributions of crack size and locations are presented and discussions of operative damage mechanisms are offered.

Fatigue and Fracture Characterization of GlasGridRTM Reinforced Asphalt Concrete Pavement

NASA Astrophysics Data System (ADS)

Safavizadeh, Seyed Amirshayan

The purpose of this research is to develop an experimental and analytical framework for describing, modeling, and predicting the reflective cracking patterns and crack growth rates in GlasGridRTM-reinforced asphalt pavements. In order to fulfill this objective, the effects of different interfacial conditions (mixture and tack coat type, and grid opening size) on reflective cracking-related failure mechanisms and the fatigue and fracture characteristics of fiberglass grid-reinforced asphalt concrete beams were studied by means of four- and threepoint bending notched beam fatigue tests (NBFTs) and cyclic and monotonic interface shear tests. The digital image correlation (DIC) technique was utilized for obtaining the displacement and strain contours of specimen surfaces during each test. The DIC analysis results were used to develop crack tip detection methods that were in turn used to determine interfacial crack lengths in the shear tests, and vertical and horizontal (interfacial) crack lengths in the notched beam fatigue tests. Linear elastic fracture mechanics (LEFM) principles were applied to the crack length data to describe the crack growth. In the case of the NBFTs, a finite element (FE) code was developed and used for modeling each beam at different stages of testing and back-calculating the stress intensity factors (SIFs) for the vertical and horizontal cracks. The local effect of reinforcement on the stiffness of the system at a vertical crack-interface intersection or the resistance of the grid system to the deflection differential at the joint/crack (hereinafter called joint stiffness) for GlasGrid-reinforced asphalt concrete beams was determined by implementing a joint stiffness parameter into the finite element code. The strain level dependency of the fatigue and fracture characteristics of the GlasGrid-reinforced beams was studied by performing four-point bending notched beam fatigue tests at strain levels of 600, 750, and 900 microstrain. These beam tests were conducted at 15°C, 20°C, and 23°C, with the main focus being to find the characteristics at 20°C. The results obtained from the tests at the different temperatures were used to investigate the effects of temperature on the reflective cracking performance of the gridreinforced beam specimens. The temperature tests were also used to investigate the validity of the time-temperature superposition (t-TS) principle in shear and the beam fatigue performance of the grid-reinforced specimens. The NBFT results suggest that different interlayer conditions do not reflect a unique failure mechanism, and thus, in order to predict and model the performance of grid-reinforced pavement, all the mechanisms involved in weakening its structural integrity, including damage within the asphalt layers and along the interface, must be considered. The shear and beam fatigue test results suggest that the grid opening size, interfacial bond quality, and mixture type play important roles in the reflective cracking performance of GlasGrid-reinforced asphalt pavements. According to the NBTF results, GlasGrid reinforcement retards reflective crack growth by stiffening the composite system and introducing a joint stiffness parameter. The results also show that the higher the bond strength and interlayer stiffness values, the higher the joint stiffness and retardation effects. The t-TS studies proved the validity of this principle in terms of the reflective crack growth of the grid-reinforced beam specimens and the shear modulus and shear strength of the grid-reinforced interfaces.

KSC-2010-5934

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- Work platforms inside the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida begin to surround space shuttle Discovery, its solid rocket boosters and external fuel tank at dawn. The shuttle rolled back from Launch Pad 39A so technicians can examine the external tank and re-apply foam where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5887

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5933

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- Space shuttle Discovery enters the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, from Launch Pad 39A began at 10:48 p.m. yesterday and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5923

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery, secured to a crawler-transporter, begins its 3.4-mile trek, known as rollback, from Launch Pad 39A to the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Rollback began at 10:48 p.m. and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5932

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- The bright lights inside the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida invite space shuttle Discovery inside. The 3.4-mile trek, called rollback, from Launch Pad 39A began at 10:48 p.m. yesterday and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5927

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery, secured to a crawler-transporter, slowly moves away from Launch Pad 39A at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, to the Vehicle Assembly Building began at 10:48 p.m. and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5925

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery, secured to a crawler-transporter, slowly moves away from Launch Pad 39A at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, to the Vehicle Assembly Building began at 10:48 p.m. and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5924

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery, secured to a crawler-transporter, begins its 3.4-mile trek, known as rollback, from Launch Pad 39A to the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. Rollback began at 10:48 p.m. and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5888

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5928

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- Space shuttle Discovery slowly moves down the crawlerway at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, from Launch Pad 39A to the Vehicle Assembly Building began at 10:48 p.m. yesterday and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5926

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery, secured to a crawler-transporter, slowly moves away from Launch Pad 39A at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, to the Vehicle Assembly Building began at 10:48 p.m. and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5929

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- Space shuttle Discovery slowly moves down the crawlerway at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, from Launch Pad 39A to the Vehicle Assembly Building began at 10:48 p.m. yesterday and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5930

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- Space shuttle Discovery approached the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, from Launch Pad 39A began at 10:48 p.m. yesterday and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5922

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery, secured to a crawler-transporter, slowly moves away from Launch Pad 39A at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, to the Vehicle Assembly Building began at 10:48 p.m. and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5931

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- Space shuttle Discovery begins to enter the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, from Launch Pad 39A began at 10:48 p.m. yesterday and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5935

NASA Image and Video Library

2010-12-22

CAPE CANAVERAL, Fla. -- Work platforms inside the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida begin to surround space shuttle Discovery, its solid rocket boosters and external fuel tank. The shuttle rolled back from Launch Pad 39A so technicians can examine the external tank and re-apply foam where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5921

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery, secured to a crawler-transporter, slowly moves away from Launch Pad 39A at NASA's Kennedy Space Center in Florida. The 3.4-mile trek, called rollback, to the Vehicle Assembly Building began at 10:48 p.m. and took about eight hours. Next, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

Pretensioned concrete girder end crack control : research brief.

DOT National Transportation Integrated Search

2017-02-01

Research Objectives: : Prove through physical testing and observation that debonding strands can reduce or eliminate critical girder end cracking : Eliminate cracking in the bottom flange of the girders, where cracks could allow moisture to r...

Adhesion mechanisms of bituminous crack sealant to aggregate and laboratory test development

NASA Astrophysics Data System (ADS)

Hajialiakbari Fini, Elham

Crack sealing is a common pavement maintenance treatment because it extends pavement service life. However, crack sealant often fails prematurely due to a loss of adhesion. Since current test methods are mostly empirical and only provide a qualitative measure of bond strength, they cannot predict sealant adhesive failure accurately. Hence, there is an urgent need for test methods based on bituminous sealant rheology that can better predict sealant field performance. This study introduces three laboratory tests aimed to assess the bond property of hot-poured crack sealant to pavement crack walls. The three tests are designed to serve the respective needs of producers, engineers, and researchers. The first test implements the principle of surface energy to measure the thermodynamic work of adhesion, which is the energy spent in separating the two materials at the interface. The work of adhesion is reported as a measure of material compatibility at an interface. The second test is a direct adhesion test, a mechanical test which is designed to closely resemble both the installation process and the crack expansion due to thermal loading. This test uses the Direct Tension Test (DTT) device. The principle of the test is to apply a tensile force to detach the sealant from its aggregate counterpart. The maximum load, Pmax, and the energy to separation, E, are calculated and reported to indicate interface bonding. The third test implements the principles of fracture mechanics in a pressurized circular blister test. The apparatus is specifically designed to conduct the test for bituminous crack sealant, asphalt binder, or other bitumen-based materials. In this test, a fluid is injected at a constant rate at the interface between the substrate (aggregate or a standard material) and the adhesive (crack sealant) to create a blister. The fluid pressure and blister height are measured as functions of time; the data is used to calculate Interfacial Fracture Energy (IFE), which is a fundamental property that can be used to predict adhesion. The stable interface debonding process makes this test attractive. This test also may be used to estimate the optimum annealing time, and to quantify other interface characteristics, such as the moisture susceptibility of a bond. In addition, the elastic modulus of the sealant and its residual stresses can be determined analytically. While the direct adhesion test is proposed as part of newly-developed performance-based guidelines for the selection of hot-poured crack sealant, the blister test may be used to estimate the optimum annealing time, in addition to IFE determination.

Crack-growth behavior in thick welded plates of Inconel 718 at room and cryogenic temperatures

NASA Technical Reports Server (NTRS)

Forman, R. G.

1974-01-01

Results of mechanical-properties and axial-load fatigue and fracture tests performed on thick welded plates of Inconel 718 superalloy are presented. The test objectives were to determine the tensile strength properties and the crack-growth behavior in electron-beam, plasma-arc, and gas tungsten are welds for plates 1.90 cm (0.75 in) thick. Base-metal specimens were also tested to determine the flaw-growth behavior. The tests were performed in room-temperature-air and liquid nitrogen environments. The experimental crack-growth-rate data are correlated with theoretical crack-growth-rate predictions for semielliptical surface flaws.

Double torsion fracture mechanics testing of shales under chemically reactive conditions

NASA Astrophysics Data System (ADS)

Chen, X.; Callahan, O. A.; Holder, J. T.; Olson, J. E.; Eichhubl, P.

2015-12-01

Fracture properties of shales is vital for applications such as shale and tight gas development, and seal performance of carbon storage reservoirs. We analyze the fracture behavior from samples of Marcellus, Woodford, and Mancos shales using double-torsion (DT) load relaxation fracture tests. The DT test allows the determination of mode-I fracture toughness (KIC), subcritical crack growth index (SCI), and the stress-intensity factor vs crack velocity (K-V) curves. Samples are tested at ambient air and aqueous conditions with variable ionic concentrations of NaCl and CaCl2, and temperatures up to 70 to determine the effects of chemical/environmental conditions on fracture. Under ambient air condition, KIC determined from DT tests is 1.51±0.32, 0.85±0.25, 1.08±0.17 MPam1/2 for Marcellus, Woodford, and Mancos shales, respectively. Tests under water showed considerable change of KIC compared to ambient condition, with 10.6% increase for Marcellus, 36.5% decrease for Woodford, and 6.7% decrease for Mancos shales. SCI under ambient air condition is between 56 and 80 for the shales tested. The presence of water results in a significant reduction of the SCI from 70% to 85% compared to air condition. Tests under chemically reactive solutions are currently being performed with temperature control. K-V curves under ambient air conditions are linear with stable SCI throughout the load-relaxation period. However, tests conducted under water result in an initial cracking period with SCI values comparable to ambient air tests, which then gradually transition into stable but significantly lower SCI values of 10-20. The non-linear K-V curves reveal that crack propagation in shales is initially limited by the transport of chemical agents due to their low permeability. Only after the initial cracking do interactions at the crack tip lead to cracking controlled by faster stress corrosion reactions. The decrease of SCI in water indicates higher crack propagation velocity due to faster stress corrosion rate in water than in ambient air. The experimental results are applicable for the prediction of fracture initiation based on KIC, modeling fracture pattern based on SCI, and the estimation of dynamic fracture propagation such as crack growth velocity and crack re-initiation.

Fracture behavior of large-scale thin-sheet aluminum alloy

NASA Technical Reports Server (NTRS)

Dewit, Roland; Fields, Richard J.; Mordfin, Leonard; Low, Samuel R.; Harne, Donald

1994-01-01

A series of fracture tests on large-scale, pre-cracked, aluminum alloy panels is being carried out to examine and to characterize the process by which cracks propagate and link up in this material. Extended grips and test fixtures were specially designed to enable the panel specimens to be loaded in tension, in a 1780-kN-capacity universal testing machine. Twelve panel specimens, each consisting of a single sheet of bare 2024-T3 aluminum alloy, 3988 mm high, 2286 mm wide, and 1.016 mm thick are being fabricated with simulated through-cracks oriented horizontally at mid-height. Using existing information, a test matrix has been set up that explores regions of failure that are controlled by fracture mechanics, with additional tests near the boundary between plastic collapse and fracture. In addition, a variety of multiple site damage (MSD) configurations have been included to distinguish between various proposed linkage mechanisms. All tests but one use anti-buckling guides. At this writing seven specimens have been tested. Three were fabricated with a single central crack, three others had multiple cracks on each side of the central crack, and one had a single crack but no anti-buckling guides. Each fracture event was recorded on film, video, computer, magnetic tape, and occasionally optical microscopy. The visual showed the crack tip with a load meter in the field of view, using motion picture film for one tip and SVHS video tape for the other. The computer recorded the output of the testing machine load cell, the stroke, and twelve strain gages at 1.5 second intervals. A wideband FM magnetic tape recorder was used to record data from the same sources. The data were analyzed by two different procedures: (1) the plastic zone model based on the residual strength diagram; and (2) the R-curve. The first three tests were used to determine the basic material properties, and these results were then used in the analysis of the two subsequent tests with MSD cracks. There is good agreement between measured values and results obtained from the model.

Evaluation of Elber's Crack Closure Model as an Explanation of Train Load Sequence Effects on Crack Growth Rates

DOT National Transportation Integrated Search

1990-06-01

Elber's crack closure model is studied in relation to the results of laboratory spectrum crack growth tests on compact tension specimens (CTS) fabricated from rail effected by mean of an analysis of a center cracked panel (CCP) subjected to an equiva...

Observation of Intralaminar Cracking in the Edge Crack Torsion Specimen

NASA Technical Reports Server (NTRS)

Czabaj, Michael W.; Ratcliffe, James G.; Davidson, Barry D.

2013-01-01

The edge crack torsion (ECT) test is evaluated to determine its suitability for measuring fracture toughness associated with mode III delamination growth onset. A series of ECT specimens with preimplanted inserts with different lengths is tested and examined using nondestructive and destructive techniques. Ultrasonic inspection of all tested specimens reveals that delamination growth occurs at one interface ply beneath the intended midplane interface. Sectioning and optical microscopy suggest that the observed delamination growth results from coalescence of angled intralaminar matrix cracks that form and extend across the midplane plies. The relative orientation of these cracks is approximately 45 deg with respect to the midplane, suggesting their formation is caused by resolved principal tensile stresses arising due to the global mode-III shear loading. Examination of ECT specimens tested to loads below the level corresponding to delamination growth onset reveals that initiation of intralaminar cracking approximately coincides with the onset of nonlinearity in the specimen's force-displacement response. The existence of intralaminar cracking prior to delamination growth onset and the resulting delamination extension at an unintended interface render the ECT test, in its current form, unsuitable for characterization of mode III delamination growth onset. The broader implications of the mechanisms observed in this study are also discussed with respect to the current understanding of shear-driven delamination in tape-laminate composites.

Fatigue crack growth in 7475-T651 aluminum alloy plate in hard vacuum and water vapor. M.S. Thesis - George Washington Univ.

NASA Technical Reports Server (NTRS)

Dicus, D. L.

1981-01-01

Compact specimens of 25 mm thick aluminum alloy plate were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Crack growth rates were determined at frequencies of 1 Hz and 10 Hz in hard vacuum and laboratory air, and in mixtures of water vapor and nitrogen at water vapor partial pressures ranging from 94 Pa to 3.8 kPa. A significant effect of water vapor on fatigue crack growth rates was observed at the lowest water vapor pressure tested. Crack rates changed little for pressures up to 1.03 kPa, but abruptly accelerated at higher pressures. At low stress intensity factor ranges, cracking rates at the lowest and highest water vapor pressure tested were, respectively, two and five times higher than rates in vacuum. Although a frequency was observed in laboratory air, cracking rates in water vapor and vacuum are insensitive to a ten-fold change in frequency. Surfaces of specimens tested in water vapor and vacuum exhibited different amounts of residual deformation. Reduced deformation on the fracture surfaces of the specimens tested in water vapor suggests embrittlement of the plastic zone ahead of the crack tip as a result of environmental interaction.

Analytical Round Robin for Elastic-Plastic Analysis of Surface Cracked Plates, Phase II Results

NASA Technical Reports Server (NTRS)

Allen, P. A.; Wells, D. N.

2017-01-01

The second phase of an analytical round robin for the elastic-plastic analysis of surface cracks in flat plates was conducted under the auspices of ASTM Interlaboratory Study 732. The interlaboratory study (ILS) had 10 participants with a broad range of expertise and experience, and experimental results from a surface crack tension test in 4142 steel plate loaded well into the elastic-plastic regime provided the basis for the study. The participants were asked to evaluate a surface crack tension test according to the version of the surface crack initiation toughness testing standard published at the time of the ILS, E2899-13. Data were provided to each participant that represent the fundamental information that would be provided by a mechanical test laboratory prior to evaluating the test result. Overall, the participant’s test analysis results were in good agreement and constructive feedback was received that has resulted in an improved published version of the standard E2899-15.

Monitoring the Corrosion Process of Reinforced Concrete Using BOTDA and FBG Sensors

PubMed Central

Mao, Jianghong; Chen, Jiayun; Cui, Lei; Jin, Weiliang; Xu, Chen; He, Yong

2015-01-01

Expansion and cracking induced by the corrosion of reinforcement concrete is the major factor in the failure of concrete durability. Therefore, monitoring of concrete cracking is critical for evaluating the safety of concrete structures. In this paper, we introduce a novel monitoring method combining Brillouin optical time domain analysis (BOTDA) and fiber Bragg grating (FBG), based on mechanical principles of concrete expansion cracking. BOTDA monitors concrete expansion and crack width, while FBG identifies the time and position of cracking. A water-pressure loading simulation test was carried out to determine the relationship between fiber strain, concrete expansion and crack width. An electrical accelerated corrosion test was also conducted to evaluate the ability of this novel sensor to monitor concrete cracking under practical conditions. PMID:25884790

Orientation effects on the measurement and analysis of critical CTOA in an aluminum alloy sheet

NASA Technical Reports Server (NTRS)

Sutton, M. A.; Dawicke, D. S.; Newman, J. C., Jr.

1994-01-01

Fracture tests were conducted on 76.2mm wide, 2.3mm thick middle crack tension (M(T)) specimens machined from 2024-T3 aluminum sheet. The specimens were tested on the T-L orientation and comparisons were made to similar tests conducted in the L-T orientation. Measurement of critical crack tip opening angle (CTOA), applied stress, and crack front shape were made as a function of crack extension. A two-dimensional, elastic-plastic finite element analysis was used to simulate the fracture behavior for both orientations. The results indicate that the T-L orientation had a 10 percent lower stress at fracture than similar tests conducted in the L-T orientation. Correspondingly, the critical CTOA in the T-L tests reached a constant value of 4.7 degrees after 2-3mm of crack extension and the L-T tests reached a value of 6 degrees. The fracture surfaces of the T-L specimens were observed to remain flat, while those of the L-T specimens transitioned to a 45 degree slant fracture after about 2-3mm of crack extension. The tunneling behavior of the two orientations also differed; the T-L specimens reached a deeply tunneled stabilized crack front shape while, the L-T specimens were observed to have only a small amount of tunneling once the crack began to grow on the 45 degree slant. The two-dimensional, elastic-plastic finite element analysis was able to simulate the fracture behavior for both the T-L and L-T orientations.

Experimental Study on the Growth, Coalescence and Wrapping Behaviors of 3D Cross-Embedded Flaws Under Uniaxial Compression

NASA Astrophysics Data System (ADS)

Zhou, Xiao-Ping; Zhang, Jian-Zhi; Wong, Louis Ngai Yuen

2018-05-01

The crack initiation, growth, wrapping and coalescence of two 3D pre-existing cross-embedded flaws in PMMA specimens under uniaxial compression are investigated. The stress-strain curves of PMMA specimens with 3D cross-embedded flaws are obtained. The tested PMMA specimens exhibit dominant elastic deformation and eventual brittle failure. The experimental results show that four modes of crack initiation and five modes of crack coalescence are observed. The initiations of oblique secondary crack and anti-wing crack in 3D cracking behaviors are first reported as well as the coalescence of anti-wing cracks. Moreover, two types of crack wrapping are found. Substantial wrapping of petal cracks, which includes open and closed modes of wrapping, appears to be the major difference between 2D and 3D cracking behaviors of pre-existing flaws, which are also first reported. Petal crack wraps symmetrically from either the propagated wing cracks or the coalesced wing cracks. Besides, only limited growth of petal cracks is observed, and ultimate failure of specimens is induced by the further growth of the propagated wing crack. The fracture mechanism of the tested PMMA specimens is finally revealed. In addition, the initiation stress and the peak stress versus the geometry of two 3D pre-existing cross-embedded flaws are also investigated in detail.

The role of cyclic plastic zone size on fatigue crack growth behavior in high strength steels

NASA Astrophysics Data System (ADS)

Korda, Akhmad A.; Miyashita, Y.; Mutoh, Y.

2015-09-01

The role of cyclic plastic zone in front of the crack tip was studied in high strength steels. Estimated plastic zone size would be compared with actual observation. Strain controlled fatigue tests of the steels were carried out to obtain cyclic stress-strain curves for plastic zone estimation. Observations of plastic zone were carried out using in situ SEM fatigue crack growth tests under a constant-ΔK. Hard microstructures in structural steels showed to inhibit the extent of plastic deformation around the crack tip. The rate of crack growth can be correlated with the size of plastic zone. The smaller the plastic zone size, the slower the fatigue crack growth.

Plastic Faulting in Ice: Shear Localization under Elevated Pressure

NASA Astrophysics Data System (ADS)

Golding, N.; Durham, W. B.

2013-12-01

Ice exhibits, at least, two distinct kinds of shear faults when loaded triaxially under compression. Under moderate levels of confinement, brittle failure follows crack growth, crack coalescence and the development of a fault oriented about 30 degrees from the direction of maximum compression. The mechanism governing this mode of failure, termed frictional or Coulombic faulting, has previously been discussed for ice and rocks in connection with the comb-crack model. Under higher levels of confinement, where frictional sliding is suppressed by confining pressure, failure is characterized by sudden brittle-like loss in load bearing capacity and the development of a narrow shear band, comprised of recrystallized grains, oriented about 45 degrees from the direction of maximum compression, i.e. along the direction of maximum shear. This mode of failure, referred to here as plastic faulting, has previously been discussed for warm ice, T = 233 - 263 K, in connection with adiabatic shear heating and has been discussed for cold ice, T = 77 - 163 K, in connection with phase transformation. Here, new results are presented that examine the mechanical behavior and microstructural properties of plastic faulting in polycrystalline ice loaded at temperatures from T = 175 - 210 K and confining pressures up to P = 200 MPa. The results are reviewed in context of previous work and possible mechanisms to account for shear localization in ice under high pressure, including 1) adiabatic shear heating, 2) grain refinement and 3) phase transformation, are discussed. The present observations highlight the similarities in the behavior of plastic faulting under both warm and cold conditions and suggest adiabatic shear heating as a possible mechanism to account for shear instability and plastic faulting at temperatures ranging from T = 77 - 263 K.

Redistribution of Welding Residual Stresses of Crack Tip Opening Displacement Specimen by Local Compression.

PubMed

Kim, Young-Gon; Song, Kuk-Hyun; Lee, Dong-Hoon; Joo, Sung-Min

2018-03-01

The demand of crack tip opening displacement (CTOD) test which evaluates fracture toughness of a cracked material is very important to ensure the stability of structure under severe service environment. The validity of the CTOD test result is judged using several criterions of the specification standards. One of them is the artificially generated fatigue pre-crack length inside the specimen. For acceptable CTOD test results, fatigue pre-crack must have a reasonable sharp crack front. The propagation of fatigue crack started from the tip of the machined notch, which might have propagated irregularly due to residual stress field. To overcome this problem, test codes suggest local compression method, reversed bending method and stepwise high-R ratio method to reduce the disparity of residual stress distribution inside the specimen. In this paper, the relation between the degree of local compression and distribution of welding residual stress has been analyzed by finite element analyses in order to determine the amount of effective local compression of the test piece. Analysis results show that initial welding residual stress is dramatically varied three-dimensionally while cutting, notch machining and local compressing due to the change of internal restraint force. From the simulation result, the authors find that there is an optimum amount of local compression to modify regularly for generating fatigue pre-crack propagation. In the case of 0.5% compressions of the model width is the most effective for uniforming residual stress distribution.

Characterization of crack growth under combined loading

NASA Technical Reports Server (NTRS)

Feldman, A.; Smith, F. W.; Holston, A., Jr.

1977-01-01

Room-temperature static and cyclic tests were made on 21 aluminum plates in the shape of a 91.4x91.4-cm Maltese cross with 45 deg flaws to develop crack growth and fracture toughness data under mixed-mode conditions. During cyclic testing, it was impossible to maintain a high proportion of shear-mode deformation on the crack tips. Cracks either branched or turned. Under static loading, cracks remained straight if shear stress intensity exceeded normal stress intensity. Mixed-mode crack growth rate data compared reasonably well with published single-mode data, and measured crack displacements agreed with the straight and branched crack analyses. Values of critical strain energy release rate at fracture for pure shear were approximately 50% higher than for pure normal opening, and there was a large reduction in normal stress intensity at fracture in the presence of high shear stress intensity. Net section stresses were well into the inelastic range when fracture occurred under high shear on the cracks.

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.

Micromechanisms of fatigue crack growth in polycarbonate polyurethane: Time dependent and hydration effects.

PubMed

Ford, Audrey C; Gramling, Hannah; Li, Samuel C; Sov, Jessica V; Srinivasan, Amrita; Pruitt, Lisa A

2018-03-01

Polycarbonate polyurethane has cartilage-like, hygroscopic, and elastomeric properties that make it an attractive material for orthopedic joint replacement application. However, little data exists on the cyclic loading and fracture behavior of polycarbonate polyurethane. This study investigates the mechanisms of fatigue crack growth in polycarbonate polyurethane with respect to time dependent effects and conditioning. We studied two commercially available polycarbonate polyurethanes, Bionate® 75D and 80A. Tension testing was performed on specimens at variable time points after being removed from hydration and variable strain rates. Fatigue crack propagation characterized three aspects of loading. Study 1 investigated the impact of continuous loading (24h/day) versus intermittent loading (8-10h/day) allowing for relaxation overnight. Study 2 evaluated the effect of frequency and study 3 examined the impact of hydration on the fatigue crack propagation in polycarbonate polyurethane. Samples loaded intermittently failed instantaneously and prematurely upon reloading while samples loaded continuously sustained longer stable cracks. Crack growth for samples tested at 2 and 5Hz was largely planar with little crack deflection. However, samples tested at 10Hz showed high degrees of crack tip deflection and multiple crack fronts. Crack growth in hydrated samples proceeded with much greater ductile crack mouth opening displacement than dry samples. An understanding of the failure mechanisms of this polymer is important to assess the long-term structural integrity of this material for use in load-bearing orthopedic implant applications. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effects of Changing Stress Amplitude on the Rate of Fatigue-Crack Propagation in Two Aluminum Alloys

NASA Technical Reports Server (NTRS)

Hudson, C. Michael; Hardrath, Herbert F.

1961-01-01

A series of fatigue tests with specimens subjected to constant amplitude and two-step axial loads were conducted on 12-inch-wide sheet specimens of 2024-T3 and 7075-T6 aluminum alloy to study the effects of a change in stress level on fatigue-crack propagation. Comparison of the results of the tests in which the specimens were tested at first a high and then a low stress level with those of the constant-stress- amplitude tests indicated that crack propagation was generally delayed after the transition to the lower stress level. In the tests in which the specimens were tested at first a low and then a high stress level, crack propagation continued at the expected rate after the change in stress levels.

New methods to quantify the cracking performance of cementitious systems made with internal curing

NASA Astrophysics Data System (ADS)

Schlitter, John L.

The use of high performance concretes that utilize low water-cement ratios have been promoted for use in infrastructure based on their potential to increase durability and service life because they are stronger and less porous. Unfortunately, these benefits are not always realized due to the susceptibility of high performance concrete to undergo early age cracking caused by shrinkage. This problem is widespread and effects federal, state, and local budgets that must maintain or replace deterioration caused by cracking. As a result, methods to reduce or eliminate early age shrinkage cracking have been investigated. Internal curing is one such method in which a prewetted lightweight sand is incorporated into the concrete mixture to provide internal water as the concrete cures. This action can significantly reduce or eliminate shrinkage and in some cases causes a beneficial early age expansion. Standard laboratory tests have been developed to quantify the shrinkage cracking potential of concrete. Unfortunately, many of these tests may not be appropriate for use with internally cured mixtures and only provide limited amounts of information. Most standard tests are not designed to capture the expansive behavior of internally cured mixtures. This thesis describes the design and implementation of two new testing devices that overcome the limitations of current standards. The first device discussed in this thesis is called the dual ring. The dual ring is a testing device that quantifies the early age restrained shrinkage performance of cementitious mixtures. The design of the dual ring is based on the current ASTM C 1581-04 standard test which utilizes one steel ring to restrain a cementitious specimen. The dual ring overcomes two important limitations of the standard test. First, the standard single ring test cannot restrain the expansion that takes place at early ages which is not representative of field conditions. The dual ring incorporates a second restraining ring which is located outside of the sample to provide restraint against expansion. Second, the standard ring test is a passive test that only relies on the autogenous and drying shrinkage of the mixture to induce cracking. The dual ring test can be an active test because it has the ability to vary the temperature of the specimen in order to induce thermal stress and produce cracking. This ability enables the study of the restrained cracking capacity as the mixture ages in order to quantify crack sensitive periods of time. Measurements made with the dual ring quantify the benefits from using larger amounts of internal curing. Mixtures that resupplied internal curing water to match that of chemical shrinkage could sustain three times the magnitude of thermal change before cracking. The second device discussed in this thesis is a large scale slab testing device. This device tests the cracking potential of 15' long by 4" thick by 24" wide slab specimens in an environmentally controlled chamber. The current standard testing devices can be considered small scale and encounter problems when linking their results to the field due to size effects. Therefore, the large scale slab testing device was developed in order to calibrate the results of smaller scale tests to real world field conditions such as a pavement or bridge deck. Measurements made with the large scale testing device showed that the cracking propensity of the internally cured mixtures was reduced and that a significant benefit could be realized.

Corrosion of NiTi Wires with Cracked Oxide Layer

NASA Astrophysics Data System (ADS)

Racek, Jan; Šittner, Petr; Heller, Luděk; Pilch, Jan; Petrenec, Martin; Sedlák, Petr

2014-07-01

Corrosion behavior of superelastic NiTi shape memory alloy wires with cracked TiO2 surface oxide layers was investigated by electrochemical corrosion tests (Electrochemical Impedance Spectroscopy, Open Circuit Potential, and Potentiodynamic Polarization) on wires bent into U-shapes of various bending radii. Cracks within the oxide on the surface of the bent wires were observed by FIB-SEM and TEM methods. The density and width of the surface oxide cracks dramatically increase with decreasing bending radius. The results of electrochemical experiments consistently show that corrosion properties of NiTi wires with cracked oxide layers (static load keeps the cracks opened) are inferior compared to the corrosion properties of the straight NiTi wires covered by virgin uncracked oxides. Out of the three methods employed, the Electrochemical Impedance Spectroscopy seems to be the most appropriate test for the electrochemical characterization of the cracked oxide layers, since the impedance curves (Nyquist plot) of differently bent NiTi wires can be associated with increasing state of the surface cracking and since the NiTi wires are exposed to similar conditions as the surfaces of NiTi implants in human body. On the other hand, the potentiodynamic polarization test accelerates the corrosion processes and provides clear evidence that the corrosion resistance of bent superelastic NiTi wires degrades with oxide cracking.

The effectiveness of an adhesively bonded composite patch repair as applied to a transport aircraft lower wing skin

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

Ruschau, J.J.; Coate, J.E.

1996-12-31

Specimens were machined from lower wing skin extrusions of a transport aircraft, precracked under fatigue loading, repaired with a boron/epoxy patch, and subsequently fatigue tested under simulated flight loading conditions to evaluate the effectiveness of an adhesively bonded repair patch. Testing was performed at RT and -54{degrees}C for two configurations: one with the crack running up the integral stiffener (riser), the other running down the riser towards the outer skin surface. Cracks were initiated from a single 6.35 mm diameter hole located in the riser portion of the 7075-T6 wing skin material. Ultrasonic inspections were performed during fatigue loading tomore » determine crack growth and damage underneath the patch. Limited results show the adhesively bonded patch was successful in stopping or greatly reducing any further crack growth. Under laboratory air conditions, no crack growth occurred following 30,000 equivalent flight hours, double the expected life of the patched structure. Similarly at -54{degrees}C, no crack growth was observed for a patched crack growing up the riser following 15,000 EFH. For the case of a crack growing down the riser at the lower test temperature, some crack growth was measured, though at a greatly reduced rate.« less

Preliminary results on the fracture analysis of multi-site cracking of lap joints in aircraft skins

NASA Astrophysics Data System (ADS)

Beuth, J. L., Jr.; Hutchinson, John W.

1992-07-01

Results of a fracture mechanics analysis relevant to fatigue crack growth at rivets in lap joints of aircraft skins are presented. Multi-site damage (MSD) is receiving increased attention within the context of problems of aging aircraft. Fracture analyses previously carried out include small-scale modeling of rivet/skin interactions, larger-scale two-dimensional models of lap joints similar to that developed here, and full scale three-dimensional models of large portions of the aircraft fuselage. Fatigue testing efforts have included flat coupon specimens, two-dimensional lap joint tests, and full scale tests on specimens designed to closely duplicate aircraft sections. Most of this work is documented in the proceedings of previous symposia on the aging aircraft problem. The effect MSD has on the ability of skin stiffeners to arrest the growth of long skin cracks is a particularly important topic that remains to be addressed. One of the most striking features of MSD observed in joints of some test sections and in the joints of some of the older aircraft fuselages is the relative uniformity of the fatigue cracks from rivet to rivet along an extended row of rivets. This regularity suggests that nucleation of the cracks must not be overly difficult. Moreover, it indicates that there is some mechanism which keeps longer cracks from running away from shorter ones, or, equivalently, a mechanism for shorter cracks to catch-up with longer cracks. This basic mechanism has not been identified, and one of the objectives of the work is to see to what extent the mechanism is revealed by a fracture analysis of the MSD cracks. Another related aim is to present accurate stress intensity factor variations with crack length which can be used to estimate fatigue crack growth lifetimes once cracks have been initiated. Results are presented which illustrate the influence of load shedding from rivets with long cracks to neighboring rivets with shorter cracks. Results are also included for the effect of residual stress due to the riveting process itself.

Preliminary results on the fracture analysis of multi-site cracking of lap joints in aircraft skins

NASA Technical Reports Server (NTRS)

Beuth, J. L., Jr.; Hutchinson, John W.

1992-01-01

Results of a fracture mechanics analysis relevant to fatigue crack growth at rivets in lap joints of aircraft skins are presented. Multi-site damage (MSD) is receiving increased attention within the context of problems of aging aircraft. Fracture analyses previously carried out include small-scale modeling of rivet/skin interactions, larger-scale two-dimensional models of lap joints similar to that developed here, and full scale three-dimensional models of large portions of the aircraft fuselage. Fatigue testing efforts have included flat coupon specimens, two-dimensional lap joint tests, and full scale tests on specimens designed to closely duplicate aircraft sections. Most of this work is documented in the proceedings of previous symposia on the aging aircraft problem. The effect MSD has on the ability of skin stiffeners to arrest the growth of long skin cracks is a particularly important topic that remains to be addressed. One of the most striking features of MSD observed in joints of some test sections and in the joints of some of the older aircraft fuselages is the relative uniformity of the fatigue cracks from rivet to rivet along an extended row of rivets. This regularity suggests that nucleation of the cracks must not be overly difficult. Moreover, it indicates that there is some mechanism which keeps longer cracks from running away from shorter ones, or, equivalently, a mechanism for shorter cracks to catch-up with longer cracks. This basic mechanism has not been identified, and one of the objectives of the work is to see to what extent the mechanism is revealed by a fracture analysis of the MSD cracks. Another related aim is to present accurate stress intensity factor variations with crack length which can be used to estimate fatigue crack growth lifetimes once cracks have been initiated. Results are presented which illustrate the influence of load shedding from rivets with long cracks to neighboring rivets with shorter cracks. Results are also included for the effect of residual stress due to the riveting process itself.

Cold Expansion Effects on Cracked Fastener Holes Under Constant Amplitude and Spectrum Loading in the 2024-T351 Aluminum Alloy

DTIC Science & Technology

2012-05-01

1 1.2. History of Fatigue Designs ................................................................................... 2 1.3...of design . 1.2. History of Fatigue Designs 1.2.1. Safe Life Design The United States Air Force (USAF) has primarily used two design paradigms...for fatigue thus far. These paradigms are the Safe Life, and the Damage Tolerance fatigue designs . The American Society for Metals (ASM) Handbook

Some observations on loss of static strength due to fatigue cracks

NASA Technical Reports Server (NTRS)

Illg, Walter; Hardrath, Herbert F

1955-01-01

Static tensile tests were performed on simple notched specimens containing fatigue cracks. Four types of aluminum alloys were investigated: 2024-T3(formerly 24S-T3) and 7075-T6(formerly 75S-T6) in sheet form, and 2024-T4(formerly 24S-T4) and 7075-T6(formerly 75S-T6) in extruded form. The cracked specimens were tested statically under four conditions: unmodified and with reduced eccentricity of loading by three methods. Results of static tests on C-46 wings containing fatigue cracks are also reported.

Fracture Test Methods for Plastically Responding COPV Liners

NASA Technical Reports Server (NTRS)

Dawicke, David S.; Lewis, Joseph C.

2009-01-01

An experimental procedure for evaluating the validity of using uniaxial tests to provide a conservative bound on the fatigue crack growth rate behavior small cracks in bi-axially loaded Composite Overwrapped Pressure Vessel (COPV) liners is described. The experimental procedure included the use of a laser notch to quickly generate small surface fatigue cracks with the desired size and aspect ratios. An out-of-plane constraint system was designed to allow fully reversed, fully plastic testing of thin sheet uniaxial coupons. Finally, a method was developed to determine to initiate small cracks in the liner of COPVs.

Residual Strength Analyses of Riveted Lap-Splice Joints

NASA Technical Reports Server (NTRS)

Seshadri, B. R.; Newman, J. C., Jr.

2000-01-01

The objective of this paper was to analyze the crack-linkup behavior in riveted-stiffened lap-splice joint panels with small multiple-site damage (MSD) cracks at several adjacent rivet holes. Analyses are based on the STAGS (STructural Analysis of General Shells) code with the critical crack-tip-opening angle (CTOA) fracture criterion. To account for high constraint around a crack front, the "plane strain core" option in STAGS was used. The importance of modeling rivet flexibility with fastener elements that accurately model load transfer across the joint is discussed. Fastener holes are not modeled but rivet connectivity is accounted for by attaching rivets to the sheet on one side of the cracks that simulated both the rivet diameter and MSD cracks. Residual strength analyses made on 2024-T3 alloy (1.6-mm thick) riveted-lap-splice joints with a lead crack and various size MSD cracks were compared with test data from Boeing Airplane Company. Analyses were conducted for both restrained and unrestrained buckling conditions. Comparison of results from these analyses and results from lap-splice-joint test panels, which were partially restrained against buckling indicate that the test results were bounded by the failure loads predicted by the analyses with restrained and unrestrained conditions.

7075-T6 and 2024-T351 Aluminum Alloy Fatigue Crack Growth Rate Data

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Wright, Christopher W.; Johnston, William M., Jr.

2005-01-01

Experimental test procedures for the development of fatigue crack growth rate data has been standardized by the American Society for Testing and Materials. Over the past 30 years several gradual changes have been made to the standard without rigorous assessment of the affect these changes have on the precision or variability of the data generated. Therefore, the ASTM committee on fatigue crack growth has initiated an international round robin test program to assess the precision and variability of test results generated using the standard E647-00. Crack growth rate data presented in this report, in support of the ASTM roundrobin, shows excellent precision and repeatability.

Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels.

PubMed

Papula, Suvi; Sarikka, Teemu; Anttila, Severi; Talonen, Juho; Virkkunen, Iikka; Hänninen, Hannu

2017-06-03

Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α'-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α'-martensite increases the hydrogen-induced cracking susceptibility.

Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels

PubMed Central

Papula, Suvi; Sarikka, Teemu; Anttila, Severi; Talonen, Juho; Virkkunen, Iikka; Hänninen, Hannu

2017-01-01

Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility. PMID:28772975

High-Temperature Slow Crack Growth of Silicon Carbide Determined by Constant-Stress-Rate and Constant-Stress Testing

NASA Technical Reports Server (NTRS)

Choi, Sung H.; Salem, J. A.; Nemeth, N. N.

1998-01-01

High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate ("dynamic fatigue") and constant-stress ("static fatigue") testing in flexure at 1300 C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation methods were used to determine the slow crack growth parameters. The four estimation methods were in good agreement for the constant-stress-rate testing with a small variation in the slow-crack-growth parameter, n, ranging from 28 to 36. By contrast, the variation in n between the four estimation methods was significant in the constant-stress testing with a somewhat wide range of n= 16 to 32.

Composite material reinforced with atomized quasicrystalline particles and method of making same

DOEpatents

Biner, S.B.; Sordelet, D.J.; Lograsso, B.K.; Anderson, I.E.

1998-12-22

A composite material comprises an aluminum or aluminum alloy matrix having generally spherical, atomized quasicrystalline aluminum-transition metal alloy reinforcement particles disposed in the matrix to improve mechanical properties. A composite article can be made by consolidating generally spherical, atomized quasicrystalline aluminum-transition metal alloy particles and aluminum or aluminum alloy particles to form a body that is cold and/or hot reduced to form composite products, such as composite plate or sheet, with interfacial bonding between the quasicrystalline particles and the aluminum or aluminum alloy matrix without damage (e.g. cracking or shape change) of the reinforcement particles. The cold and/or hot worked composite exhibits substantially improved yield strength, tensile strength, Young`s modulus (stiffness). 3 figs.

Mitigation of Crack Damage in Metallic Materials

NASA Technical Reports Server (NTRS)

Leser, Patrick E.; Newman, John A.; Smith, Stephen W.; Leser, William P.; Wincheski, Russell A.; Wallace, Terryl A.; Glaessgen, Edward H.; Piascik, Robert S.

2014-01-01

A system designed to mitigate or heal crack damage in metallic materials has been developed where the protected material or component is coated with a low-melting temperature film. After a crack is formed, the material is heated, melting the film which then infiltrates the crack opening through capillary action. Upon solidification, the healing material inhibits further crack damage in two ways. While the crack healing material is intact, it acts like an adhesive that bonds or bridges the crack faces together. After fatigue loading damages, the healing material in the crack mouth inhibits further crack growth by creating artificially-high crack closure levels. Mechanical test data show that this method sucessfully arrests or retards crack growth in laboratory specimens.

Fatigue crack growth under general-yielding cyclic-loading

NASA Technical Reports Server (NTRS)

Minzhong, Z.; Liu, H. W.

1986-01-01

In low cycle fatigue, cracks are initiated and propagated under general yielding cyclic loading. For general yielding cyclic loading, Dowling and Begley have shown that fatigue crack growth rate correlates well with the measured delta J. The correlation of da/dN with delta J was also studied by a number of other investigators. However, none of thse studies have correlated da/dN with delta J calculated specifically for the test specimens. Solomon measured fatigue crack growth in specimens in general yielding cyclic loading. The crack tips fields for Solomon's specimens are calculated using the finite element method and the J values of Solomon's tests are evaluated. The measured crack growth rate in Solomon's specimens correlates very well with the calculated delta J.

Statistical analysis of 59 inspected SSME HPFTP turbine blades (uncracked and cracked)

NASA Technical Reports Server (NTRS)

Wheeler, John T.

1987-01-01

The numerical results of statistical analysis of the test data of Space Shuttle Main Engine high pressure fuel turbopump second-stage turbine blades, including some with cracks are presented. Several statistical methods use the test data to determine the application of differences in frequency variations between the uncracked and cracked blades.

Applications of infrared thermography for nondestructive testing of fatigue cracks in steel bridges

NASA Astrophysics Data System (ADS)

Sakagami, Takahide; Izumi, Yui; Kobayashi, Yoshihiro; Mizokami, Yoshiaki; Kawabata, Sunao

2014-05-01

In recent years, fatigue crack propagations in aged steel bridge which may lead to catastrophic structural failures have become a serious problem. For large-scale steel structures such as orthotropic steel decks in highway bridges, nondestructive inspection of deteriorations and fatigue damages are indispensable for securing their safety and for estimating their remaining strength. As conventional NDT techniques for steel bridges, visual testing, magnetic particle testing and ultrasonic testing have been commonly employed. However, these techniques are time- and labor- consuming techniques, because special equipment is required for inspection, such as scaffolding or a truck mount aerial work platform. In this paper, a new thermography NDT technique, which is based on temperature gap appeared on the surface of structural members due to thermal insulation effect of the crack, is developed for detection of fatigue cracks. The practicability of the developed technique is demonstrated by the field experiments for highway steel bridges in service. Detectable crack size and factors such as measurement time, season or spatial resolution which influence crack detectability are investigated.

An investigation on die crack detection using Temperature Sensitive Parameter for high speed LED mass production

NASA Astrophysics Data System (ADS)

Annaniah, Luruthudass; Devarajan, Mutharasu; San, Teoh Kok

To ensure the highest quality & long-term reliability of LED components it is necessary to examine LED dice that have sustained mechanical damage during the manufacturing process. This paper has demonstrated that detection of die crack in mass manufactured LEDs can be achieved by measuring Temperature Sensitive Parameters (TSPs) during final testing. A newly-designed apparatus and microcontroller was used for this investigation in order to achieve the millisecond switching time needed for detecting thermal transient effects and at the same time meet the expected speed for mass manufacturing. Evaluations conducted at lab scale shows that thermal transient behaviour of cracked die is significantly different than that of an undamaged die. Having an established test limits to differentiate cracked dice, large volume tests in a production environment were used to confirm the effectiveness of this test method. Failure Bin Analysis (FBA) of this high volume experiment confirmed that all the cracked die LEDs were detected and the undamaged LEDs passed this test without over-rejection. The work verifies that tests based on TSP are effective in identifying die cracks and it is believed that the method could be extended to other types of rejects that have thermal transient signatures such as die delamination.

A comparison of fatigue life prediction methodologies for rotorcraft

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.

1990-01-01

Because of the current U.S. Army requirement that all new rotorcraft be designed to a 'six nines' reliability on fatigue life, this study was undertaken to assess the accuracy of the current safe life philosophy using the nominal stress Palmgrem-Miner linear cumulative damage rule to predict the fatigue life of rotorcraft dynamic components. It has been shown that this methodology can predict fatigue lives that differ from test lives by more than two orders of magnitude. A further objective of this work was to compare the accuracy of this methodology to another safe life method called the local strain approach as well as to a method which predicts fatigue life based solely on crack growth data. Spectrum fatigue tests were run on notched (k(sub t) = 3.2) specimens made of 4340 steel using the Felix/28 tests fairly well, being slightly on the unconservative side of the test data. The crack growth method, which is based on 'small crack' crack growth data and a crack-closure model, also predicted the fatigue lives very well with the predicted lives being slightly longer that the mean test lives but within the experimental scatter band. The crack growth model was also able to predict the change in test lives produced by the rainflow reconstructed spectra.

An Experimental Study of Fatigue Crack Growth in Aluminum Sheet Subjected to Combined Bending and Membrane Stresses

NASA Technical Reports Server (NTRS)

Phillips, Edward P.

1997-01-01

An experimental study was conducted to determine the effects of combined bending and membrane cyclic stresses on the fatigue crack growth behavior of aluminum sheet material. The materials used in the tests were 0.040-in.- thick 2024-T3 alclad and 0.090-in.-thick 2024-T3 bare sheet. In the tests, the membrane stresses were applied as a constant amplitude loading at a stress ratio (minimum to maximum stress) of 0.02, and the bending stresses were applied as a constant amplitude deflection in phase with the membrane stresses. Tests were conducted at ratios of bending to membrane stresses (B/M) of 0, 0.75, and 1.50. The general trends of the results were for larger effects of bending for the higher B/M ratios, the lower membrane stresses, and the thicker material. The addition of cyclic bending stresses to a test with cyclic membrane stresses had only a small effect on the growth rates of through-thickness cracks in the thin material, but had a significant effect on the crack growth rates of through-thickness cracks in the thick material. Adding bending stresses to a test had the most effect on the initiation and early growth of cracks and had less effect on the growth of long through-thickness cracks.

Fracture of concrete caused by the reinforcement corrosion products

NASA Astrophysics Data System (ADS)

Nguyen, Q. T.; Millard, A.; Caré, S.; L'Hostis, V.; Berthaud, Y.

2006-11-01

One of the most current degradations in reinforced concrete structures is related to the corrosion of the reinforcements. The corrosion products during active corrosion induce a mechanical pressure on the surrounding concrete that leads to cover cracking along the rebar. The objective of this work is to study the cracking of concrete due to the corrosion of the reinforcements. The phenomenon of corrosion/cracking is studied in experiments through tests of accelerated corrosion on plate and cylindrical specimens. A CCD camera is used to take images every hour and the pictures are analyzed by using the intercorrelation image technique (Correli^LMT) to derive the displacement and strain field. Thus the date of appearance of the first through crack is detected and the cinematic crack initiations are observed during the test. A finite element model that allows prediction of the mechanical consequences of the corrosion of steel in reinforced concrete structures is proposed. From the comparison between the test results and numerical simulations, it may be concluded that the model is validated in term of strains up to the moment when the crack becomes visible, and in terms of crack pattern.

Flexural Behavior of HPFRCC Members with Inhomogeneous Material Properties.

PubMed

Shin, Kyung-Joon; Jang, Kyu-Hyeon; Choi, Young-Cheol; Lee, Seong-Cheol

2015-04-21

In this paper, the flexural behavior of High-performance Fiber-Reinforced Cementitious Composite (HPFRCC) has been investigated, especially focusing on the localization of cracks, which significantly governs the flexural behavior of HPFRCC members. From four points bending tests with HPFRCC members, it was observed that almost evenly distributed cracks formed gradually, followed by a localized crack that determined the failure of the members. In order to investigate the effect of a localized crack on the flexural behavior of HPFRCC members, an analytical procedure has been developed with the consideration of intrinsic inhomogeneous material properties of HPFRCC such as cracking and ultimate tensile strengths. From the comparison, while the predictions with homogeneous material properties overestimated flexural strength and ductility of HPFRCC members, it was found that the analysis results considering localization effect with inhomogeneous material properties showed good agreement with the test results, not only the flexural strength and ductility but also the crack widths. The test results and the developed analysis procedure presented in this paper can be usefully applied for the prediction of flexural behaviors of HPFRCC members by considering the effect of localized cracking behavior.

Influence of Crack-Tip Configurations on the Fracture Response of 0.04-Inch Thick 2024-T3 Aluminum Alloy Sheet

NASA Technical Reports Server (NTRS)

Johnston, William M.; Newman, James C. (Technical Monitor)

2002-01-01

A series of fracture tests were conducted on Middle-crack tension M(T) and compact tension C(T) specimens to determine the effects of specimen type, specimen width, notch tip sharpness and buckling on the fracture behavior of cracked thin sheet (0.04 inch thick) 2024-T3 aluminum alloy material. A series of M(T) specimens were tested with three notch tip configurations: (1) a fatigue pre-cracked notch, (2) a 0.010-inch-diameter wire electrical discharge machined (EDM) notch, and (3) a EDM notch sharpened with a razor blade. The test procedures are discussed and the experimental results for failure stress, load vs. crack extension and the material stress-strain response are reported.

Characterization of low temperature mechanical properties of crack sealants utilizing direct tension test.

DOT National Transportation Integrated Search

2008-11-01

Crack sealing has been widely used as a routine preventative maintenance practice. Given its proper : installation, crack sealants can extend pavement service life by three to five years. However, current : specifications for the selection of crack s...

Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

NASA Technical Reports Server (NTRS)

Forman, R. G.; Zanganeh, M.

2014-01-01

This paper describes the results of a research program conducted to improve the understanding of fatigue crack growth rate behavior in the threshold growth rate region and to answer a question on the validity of threshold region test data. The validity question relates to the view held by some experimentalists that using the ASTM load shedding test method does not produce valid threshold test results and material properties. The question involves the fanning behavior observed in threshold region of da/dN plots for some materials in which the low R-ratio data fans out from the high R-ratio data. This fanning behavior or elevation of threshold values in the low R-ratio tests is generally assumed to be caused by an increase in crack closure in the low R-ratio tests. Also, the increase in crack closure is assumed by some experimentalists to result from using the ASTM load shedding test procedure. The belief is that this procedure induces load history effects which cause remote closure from plasticity and/or roughness changes in the surface morphology. However, experimental studies performed by the authors have shown that the increase in crack closure is a result of extensive crack tip bifurcations that can occur in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the fanning behavior which occurs in aluminum alloys is a function of intrinsic dislocation property of the alloy, and therefore, the fanned data does represent the true threshold properties of the material. However, for the corrosion sensitive steel alloys tested in laboratory air, the occurrence of fanning results from fretting corrosion at the crack tips, and these results should not be considered to be representative of valid threshold properties because the fanning is eliminated when testing is performed in dry air.

Humidity Testing of PME and BME Ceramic Capacitors with Cracks

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander A.; Herzberger, Jaemi

2014-01-01

Cracks in ceramic capacitors are one of the major causes of failures during operation of electronic systems. Humidity testing has been successfully used for many years to verify the absence of cracks and assure quality of military grade capacitors. Traditionally, only precious metal electrode (PME) capacitors were used in high reliability applications and the existing requirements for humidity testing were developed for this type of parts. With the advance of base metal electrode (BME) capacitors, there is a need for assessment of the applicability of the existing techniques for the new technology capacitors. In this work, variety of different PME and BME capacitors with introduced cracks were tested in humid environments at different voltages and temperatures. Analysis of the test results indicates differences in the behavior and failure mechanisms for BME and PME capacitors and the need for different testing conditions.

Aspects of fracture mechanics in cryogenic model design. Part 2: NTF materials

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Lisagor, W. B.

1983-01-01

Results of fatigue crack growth and fracture toughness tests conducted on three candidate materials are presented. Fatigue crack growth and fracture toughness tests were conducted on NITRONIC 40 at room temperature and -275 F. Fracture toughness tests were also conducted on Vascomax 200 and 250 maraging steel from room temperature to -320 F. NITRONIC 40 was used to make the Pathfinder 1 model. The fatigue crack growth rate tests were conducted at room temperature and -275 F on three-point notch bend specimens. The fracture toughness tests on the as received and stress relieved materials at -275 F were conducted on the center crack tension specimens. Toughness tests were also conducted on Vascomax CVM-200 and CVM-250 maraging steel from room temperature to -320 F using round and rectangular compact specimens.

Proof-test-based life prediction of high-toughness pressure vessels

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

Panontin, T.L.; Hill, M.R.

1996-02-01

The paper examines the problems associated with applying proof-test-based life prediction to vessels made of high-toughness metals. Two A106 Gr B pipe specimens containing long, through-wall circumferential flaws were tested. One failed during hydrostatic testing and the other during tension-tension cycling following a hydrostatic test. Quantitative fractography was used to verify experimentally obtained fatigue crack growth rates and a variety of LEFM and EPFM techniques were used to analyze the experimental results. The results show that: plastic collapse analysis provides accurate predictions of screened (initial) crack size when the flow stress is determined experimentally; LEFM analysis underestimates the crack sizemore » screened by the proof test and overpredicts the subsequent fatigue life of the vessel when retardation effects are small (i.e., low proof levels); and, at a high proof-test level (2.4 {times} operating pressure), the large retardation effect on fatigue crack growth due to the overload overwhelmed the deleterious effect on fatigue life from stable tearing during the proof test and alleviated the problem of screening only long cracks due to the high toughness of the metal.« less

Application of Self Nulling Eddy Current Probe Technique to the Detection of Fatigue Crack Initiation and Control of Test Procedures

NASA Technical Reports Server (NTRS)

Namkung, M.; Nath, S.; Wincheski, B.; Fulton, J. P.

1994-01-01

A major part of fracture mechanics is concerned with studying the initiation and propagation of fatigue cracks. This typically requires constant monitoring of crack growth during fatigue cycles and the knowledge of the precise location of the crack tip at any given time. One technique currently available for measuring fatigue crack length is the Potential Drop method. The method, however, may be inaccurate if the direction of crack growth deviates considerably from what was assumed initially or the curvature of the crack becomes significant. Another popular approach is to optically view the crack using a high magnification microscope, but this entails a person constantly monitoring it. The present proposed technique uses an automated scheme, in order to eliminate the need for a person to constantly monitor the experiment. Another technique under development elsewhere is to digitize an optical image of the test specimen surface and then apply a pattern recognition algorithm to locate the crack tip. A previous publication showed that the self nulling eddy current probe successfully tracked a simulated crack in an aluminum sample. This was the impetus to develop an online real time crack monitoring system. An automated system has been developed which includes a two axis scanner mounted on the tensile testing machine, the probe and its instrumentation and a personal computer (PC) to communicate and control all the parameters. The system software controls the testing parameters as well as monitoring the fatigue crack as it propagates. This paper will discuss the experimental setup in detail and demonstrate its capabilities. A three dimensional finite element model is utilized to model the magnetic field distribution due to the probe and how the probe voltage changes as it scans the crack. Experimental data of the probe for different samples under zero load, static load and high cycle fatigue load will be discussed. The final section summarizes the major accomplishments of the present work, the elements of the future R&D needs and the advantages and disadvantages of using this system in the laboratory and field.

The static breaking technique for sustainable and eco-environmental coal mining.

PubMed

Bing-yuan, Hao; Hui, Huang; Zi-jun, Feng; Kai, Wang

2014-01-01

The initiating explosive devices are prohibited in rock breaking near the goaf of the highly gassy mine. It is effective and applicable to cracking the hard roof with static cracking agent. By testing the static cracking of cubic limestone (size: 200 × 200 × 200 mm) with true triaxial rock mechanics testing machine under the effect of bidirectional stress and by monitoring the evolution process of the cracks generated during the acoustic emission experiment of static cracking, we conclude the following: the experiment results of the acoustic emission show that the cracks start from the lower part of the hole wall until they spread all over the sample. The crack growth rate follows a trend of "from rapidness to slowness." The expansion time is different for the two bunches of cracks. The growth rates can be divided into the rapid increasing period and the rapid declining period, of which the growth rate in declining period is less than that in the increasing period. Also, the growth rate along the vertical direction is greater than that of the horizontal direction. Then the extended model for the static cracking is built according to the theories of elastic mechanics and fracture mechanics. Thus the relation formula between the applied forces of cracks and crack expansion radius is obtained. By comparison with the test results, the model proves to be applicable. In accordance with the actual geological situation of Yangquan No. 3 Mine, the basic parameters of manpower manipulated caving breaking with static crushing are settled, which reaps bumper industrial effects.

Single-Specimen Technique to Establish the J-Resistance of Linear Viscoelastic Solids with Constant Poisson's Ratio

NASA Technical Reports Server (NTRS)

Gutierrez-Lemini, Danton; McCool, Alex (Technical Monitor)

2001-01-01

A method is developed to establish the J-resistance function for an isotropic linear viscoelastic solid of constant Poisson's ratio using the single-specimen technique with constant-rate test data. The method is based on the fact that, for a test specimen of fixed crack size under constant rate, the initiation J-integral may be established from the crack size itself, the actual external load and load-point displacement at growth initiation, and the relaxation modulus of the viscoelastic solid, without knowledge of the complete test record. Since crack size alone, of the required data, would be unknown at each point of the load-vs-load-point displacement curve of a single-specimen test, an expression is derived to estimate it. With it, the physical J-integral at each point of the test record may be established. Because of its basis on single-specimen testing, not only does the method not require the use of multiple specimens with differing initial crack sizes, but avoids the need for tracking crack growth as well.

Residual Strength Analyses of Monolithic Structures

NASA Technical Reports Server (NTRS)

Forth, Scott (Technical Monitor); Ambur, Damodar R. (Technical Monitor); Seshadri, B. R.; Tiwari, S. N.

2003-01-01

Finite-element fracture simulation methodology predicts the residual strength of damaged aircraft structures. The methodology uses the critical crack-tip-opening-angle (CTOA) fracture criterion to characterize the fracture behavior of the material. The CTOA fracture criterion assumes that stable crack growth occurs when the crack-tip angle reaches a constant critical value. The use of the CTOA criterion requires an elastic- plastic, finite-element analysis. The critical CTOA value is determined by simulating fracture behavior in laboratory specimens, such as a compact specimen, to obtain the angle that best fits the observed test behavior. The critical CTOA value appears to be independent of loading, crack length, and in-plane dimensions. However, it is a function of material thickness and local crack-front constraint. Modeling the local constraint requires either a three-dimensional analysis or a two-dimensional analysis with an approximation to account for the constraint effects. In recent times as the aircraft industry is leaning towards monolithic structures with the intention of reducing part count and manufacturing cost, there has been a consistent effort at NASA Langley to extend critical CTOA based numerical methodology in the analysis of integrally-stiffened panels.In this regard, a series of fracture tests were conducted on both flat and curved aluminum alloy integrally-stiffened panels. These flat panels were subjected to uniaxial tension and during the test, applied load-crack extension, out-of-plane displacements and local deformations around the crack tip region were measured. Compact and middle-crack tension specimens were tested to determine the critical angle (wc) using three-dimensional code (ZIP3D) and the plane-strain core height (hJ using two-dimensional code (STAGS). These values were then used in the STAGS analysis to predict the fracture behavior of the integrally-stiffened panels. The analyses modeled stable tearing, buckling, and crack branching at the integral stiffener using different values of critical CTOA for different material thicknesses and orientation. Comparisons were made between measured and predicted load-crack extension, out-of-plane displacements and local deformations around the crack tip region. Simultaneously, three-dimensional capabilities to model crack branching and to monitor stable crack growth of multiple cracks in a large thick integrally-stiffened flat panels were implemented in three-dimensional finite element code (ZIP3D) and tested by analyzing the integrally-stiffened panels tested at Alcoa. The residual strength of the panels predicted from STAGS and ZP3D code compared very well with experimental data. In recent times, STAGS software has been updated with new features and now one can have combinations of solid and shell elements in the residual strength analysis of integrally-stiffened panels.

Simplified moment tensor analysis and unified decomposition of acoustic emission source: Application to in situ hydrofracturing test

NASA Astrophysics Data System (ADS)

Ohtsu, Masayasu

1991-04-01

An application of a moment tensor analysis to acoustic emission (AE) is studied to elucidate crack types and orientations of AE sources. In the analysis, simplified treatment is desirable, because hundreds of AE records are obtained from just one experiment and thus sophisticated treatment is realistically cumbersome. Consequently, a moment tensor inversion based on P wave amplitude is employed to determine six independent tensor components. Selecting only P wave portion from the full-space Green's function of homogeneous and isotropic material, a computer code named SiGMA (simplified Green's functions for the moment tensor analysis) is developed for the AE inversion analysis. To classify crack type and to determine crack orientation from moment tensor components, a unified decomposition of eigenvalues into a double-couple (DC) part, a compensated linear vector dipole (CLVD) part, and an isotropic part is proposed. The aim of the decomposition is to determine the proportion of shear contribution (DC) and tensile contribution (CLVD + isotropic) on AE sources and to classify cracks into a crack type of the dominant motion. Crack orientations determined from eigenvectors are presented as crack-opening vectors for tensile cracks and fault motion vectors for shear cracks, instead of stereonets. The SiGMA inversion and the unified decomposition are applied to synthetic data and AE waveforms detected during an in situ hydrofracturing test. To check the accuracy of the procedure, numerical experiments are performed on the synthetic waveforms, including cases with 10% random noise added. Results show reasonable agreement with assumed crack configurations. Although the maximum error is approximately 10% with respect to the ratios, the differences on crack orientations are less than 7°. AE waveforms detected by eight accelerometers deployed during the hydrofracturing test are analyzed. Crack types and orientations determined are in reasonable agreement with a predicted failure plane from borehole TV observation. The results suggest that tensile cracks are generated first at weak seams and then shear cracks follow on the opened joints.

A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis.

PubMed

Peloquin, John M; Elliott, Dawn M

2016-04-01

Cracks in fibrous soft tissue, such as intervertebral disc annulus fibrosus and knee meniscus, cause pain and compromise joint mechanics. A crack concentrates stress at its tip, making further failure and crack extension (fracture) more likely. Ex vivo mechanical testing is an important tool for studying the loading conditions required for crack extension, but prior work has shown that it is difficult to reproduce crack extension. Most prior work used edge crack specimens in uniaxial tension, with the crack 90° to the edge of the specimen. This configuration does not necessarily represent the loading conditions that cause in vivo crack extension. To find a potentially better choice for experiments aiming to reproduce crack extension, we used finite element analysis to compare, in factorial combination, (1) center crack vs. edge crack location, (2) biaxial vs. uniaxial loading, and (3) crack-fiber angles ranging from 0° to 90°. The simulated material was annulus fibrosus fibrocartilage with a single fiber family. We hypothesized that one of the simulated test cases would produce a stronger stress concentration than the commonly used uniaxially loaded 90° crack-fiber angle edge crack case. Stress concentrations were compared between cases in terms of fiber-parallel stress (representing risk of fiber rupture), fiber-perpendicular stress (representing risk of matrix rupture), and fiber shear stress (representing risk of fiber sliding). Fiber-perpendicular stress and fiber shear stress concentrations were greatest in edge crack specimens (of any crack-fiber angle) and center crack specimens with a 90° crack-fiber angle. However, unless the crack is parallel to the fiber direction, these stress components alone are insufficient to cause crack opening and extension. Fiber-parallel stress concentrations were greatest in center crack specimens with a 45° crack-fiber angle, either biaxially or uniaxially loaded. We therefore recommend that the 45° center crack case be tried in future experiments intended to study crack extension by fiber rupture. Copyright © 2015 Elsevier Ltd. All rights reserved.

The application of Newman crack-closure model to predicting fatigue crack growth

NASA Astrophysics Data System (ADS)

Si, Erjian

1994-09-01

Newman crack-closure model and the relevant crack growth program were applied to the analysis of crack growth under constant amplitude and aircraft spectrum loading on a number of aluminum alloy materials. The analysis was performed for available test data of 2219-T851, 2024-T3, 2024-T351, 7075-T651, 2324-T39, and 7150-T651 aluminum materials. The results showed that the constraint factor is a significant factor in the method. The determination of the constraint factor is discussed. For constant amplitude loading, satisfactory crack growth lives could be predicted. For the above aluminum specimens, the ratio of predicted to experimental lives, Np/Nt, ranged from 0.74 to 1.36. The mean value of Np/Nt was 0.97. For a specified complex spectrum loading, predicted crack growth lives are not in very good agreement with the test data. Further effort is needed to correctly simulate the transition between plane strain and plane stress conditions, existing near the crack tip.

Slow crack growth in spinel in water

NASA Technical Reports Server (NTRS)

Schwantes, S.; Elber, W.

1983-01-01

Magnesium aluminate spinel was tested in a water environment at room temperature to establish its slow crack-growth behavior. Ring specimens with artificial flaws on the outside surface were loaded hydraulically on the inside surface. The time to failure was measured. Various precracking techniques were evaluated and multiple precracks were used to minimize the scatter in the static fatigue tests. Statistical analysis techniques were developed to determine the strength and crack velocities for a single flaw. Slow crack-growth rupture was observed at stress intensities as low as 70 percent of K sub c. A strengthening effect was observed in specimens that had survived long-time static fatigue tests.

DUCTILE-PHASE TOUGHENED TUNGSTEN FOR PLASMA-FACING MATERIALS IN FUSION REACTORS

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

Henager, Charles H.; Setyawan, Wahyu; Roosendaal, Timothy J.

2017-05-01

Tungsten (W) and W-alloys are the leading candidates for plasma-facing components in nuclear fusion reactor designs because of their high melting point, strength retention at high temperatures, high thermal conductivity, and low sputtering yield. However, tungsten is brittle and does not exhibit the required fracture toughness for licensing in nuclear applications. A promising approach to increasing fracture toughness of W-alloys is by ductile-phase toughening (DPT). In this method, a ductile phase is included in a brittle matrix to prevent on inhibit crack propagation by crack blunting, crack bridging, crack deflection, and crack branching. Model examples of DPT tungsten are exploredmore » in this study, including W-Cu and W-Ni-Fe powder product composites. Three-point and four-point notched and/or pre-cracked bend samples were tested at several strain rates and temperatures to help understand deformation, cracking, and toughening in these materials. Data from these tests are used for developing and calibrating crack-bridging models. Finite element damage mechanics models are introduced as a modeling method that appears to capture the complexity of crack growth in these materials.« less

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.

Fracture modes in human teeth.

PubMed

Lee, J J-W; Kwon, J-Y; Chai, H; Lucas, P W; Thompson, V P; Lawn, B R

2009-03-01

The structural integrity of teeth under stress is vital to functional longevity. We tested the hypothesis that this integrity is limited by fracture of the enamel. Experiments were conducted on molar teeth, with a metal rod loaded onto individual cusps. Fracture during testing was tracked with a video camera. Two longitudinal modes of cracking were observed: median cracking from the contact zone, and margin cracking along side walls. Median cracks initiated from plastic damage at the contact site, at first growing slowly and then accelerating to the tooth margin. Margin cracks appeared to originate from the cemento-enamel junction, and traversed the tooth wall adjacent to the loaded cusp from the gingival to the occlusal surface. All cracks remained confined within the enamel shell up to about 550 N. At higher loads, additional crack modes--such as enamel chipping and delamination--began to manifest themselves, leading to more comprehensive failure of the tooth structure.

Numerical and experimental study on buckling and postbuckling behavior of cracked cylindrical shells

NASA Astrophysics Data System (ADS)

Saemi, J.; Sedighi, M.; Shariati, M.

2015-09-01

The effect of crack on load-bearing capacity and buckling behavior of cylindrical shells is an essential consideration in their design. In this paper, experimental and numerical buckling analysis of steel cylindrical shells of various lengths and diameters with cracks have been studied using the finite element method, and the effect of crack position, crack orientation and the crack length-to-cylindrical shell perimeter ( λ = a/(2 πr)) and shell length-to-diameter ( L/ D) ratios on the buckling and post-buckling behavior of cylindrical shells has been investigated. For several specimens, buckling test was performed using an INSTRON 8802 servo hydraulic machine, and the results of experimental tests were compared to numerical results. A very good correlation was observed between numerical simulation and experimental results. Finally, based on the experimental and numerical results, sensitivity of the buckling load to the shell length, crack length and orientation has also been investigated.

Fatigue crack growth in unidirectional and cross-ply SCS-6/Timetal 21S titanium matrix composite

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

Herrmann, D.J.

1994-01-01

Fatigue crack growth in unidirectional and cross-ply SCS-6/ Timetal(R) 21S titanium matrix composite was investigated. Fatigue crack growth tests were performed on (0){sub 4}, (90){sub 4}, and (0/90){sub s} center notch specimens. The (0){sub 4} and (0/90){sub s} fatigue crack growth rates decreased initially. Specimens removed prior to failure were polished to the first row of fibers and intact fibers in the wake of the matrix crack were observed. These bridging fibers reduced the stress intensity range that the matrix material was subjected to, thus reducing the crack growth rate. The crack growth rate eventually increased as fibers failed inmore » the crack wake but the fatigue crack growth rate was still much slower than that of unreinforced Timetal(R) 21S. A model was developed to study the mechanics of a cracked unidirectional composite with any combination of intact and broken fibers in the wake of a matrix crack. The model was correlated to fatigue crack growth rate tests. The model was verified by comparing predicted displacements near the crack surface with Elber gage (1.5 mm gage length extensometer) measurements. The fatigue crack growth rate for the (90){sub 4} specimens was faster than that of unreinforced Timetal(registered trademark) 21S. Elber gage displacement measurements were in agreement with linear elastic fracture mechanics predictions, suggesting that linear elastic fracture mechanics may be applicable to transversely loaded titanium matrix composites.« less

Small-crack effects in high-strength aluminum alloys

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Wu, X. R.; Venneri, S. L.; Li, C. G.

1994-01-01

The National Aeronautics and Space Administration and the Chinese Aeronautical Establishment participated in a Fatigue and Fracture Mechanics Cooperative Program. The program objectives were to identify and characterize crack initiation and growth of small cracks (10 microns to 2 mm long) in commonly used US and PRC aluminum alloys, to improve fracture mechanics analyses of surface- and corner-crack configurations, and to develop improved life-prediction methods. Fatigue and small-crack tests were performed on single-edgenotch tension (SENT) specimens and large-crack tests were conducted on center-crack tension specimens for constant-amplitude (stress ratios of -1, 0, and 0.5) and Mini-TWIST spectrum loading. The plastic replica method was used to monitor the initiation and growth of small fatigue cracks at the semicircular notch. Crack growth results from each laboratory on 7075-T6 bare and LC9cs clad aluminum alloys agreed well and showed that fatigue life was mostly crack propagation from a material defect (inclusion particles or void) or from the cladding layer. Finite-element and weight-function methods were used to determine stress intensity factors for surface and corner cracks in the SENT specimens. Equations were then developed and used in a crack growth and crack-closure model to correlate small- and large-crack data and to make life predictions for various load histories. The cooperative program produced useful experimental data and efficient analysis methods for improving life predictions. The results should ultimately improve aircraft structural reliability and safety.

A fracture criterion for widespread cracking in thin-sheet aluminum alloys

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Dawicke, D. S.; Sutton, M. A.; Bigelow, C. A.

1993-01-01

An elastic-plastic finite-element analysis was used with a critical crack-tip-opening angle (CTOA) fracture criterion to model stable crack growth in thin-sheet 2024-T3 aluminum alloy panels with single and multiple-site damage (MSD) cracks. Comparisons were made between critical angles determined from the analyses and those measured with photographic methods. Calculated load against crack extension and load against crack-tip displacement on single crack specimens agreed well with test data even for large-scale plastic deformations. The analyses were also able to predict the stable tearing behavior of large lead cracks in the presence of stably tearing MSD cracks. Small MSD cracks significantly reduced the residual strength for large lead cracks.

Automotive and Construction Equipment for Arctic Use: Heating and Cold Starting

DTIC Science & Technology

1991-04-01

heater. Catalytic combustion heaters similar to that shown in Figure 12 produce flameless heat using gasoline, benzene or a similar fuel and have... combustion chamber; physical scientist, is a • engine compartment air; and member of CRREL’s * personnel and cargo compartments. Applied Research Wind...component warping and thermal cracking. When coolant is pumped, heat is not only provided to the cylinders, thereby warming the combustion cha iber and the

In-vitro characterization of stress corrosion cracking of aluminium-free magnesium alloys for temporary bio-implant applications.

PubMed

Choudhary, Lokesh; Singh Raman, R K; Hofstetter, Joelle; Uggowitzer, Peter J

2014-09-01

The complex interaction between physiological stresses and corrosive human body fluid may cause premature failure of metallic biomaterials due to the phenomenon of stress corrosion cracking. In this study, the susceptibility to stress corrosion cracking of biodegradable and aluminium-free magnesium alloys ZX50, WZ21 and WE43 was investigated by slow strain rate tensile testing in a simulated human body fluid. Slow strain rate tensile testing results indicated that each alloy was susceptible to stress corrosion cracking, and this was confirmed by fractographic features of transgranular and/or intergranular cracking. However, the variation in alloy susceptibility to stress corrosion cracking is explained on the basis of their electrochemical and microstructural characteristics. Copyright © 2014 Elsevier B.V. All rights reserved.

Fractography and mechanisms of environmentally enhanced fatigue crack propagation of a reactor pressure vessel steel

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

Torronen, K.; Kemppainen, M.

1981-10-01

This paper describes the findings and interpretations of the fractographic survey conducted for the International Cyclic Crack Growth Rate (ICCGR) cooperative group round-robin specimens. Specimens of A533B pressure vessel steel were tested at several laboratories in the United States and elsewhere with the same nominal test parameters. A rather wide scatter of the results was found. A fractographic and metallographic survey was carried out in order to clarify the scatter and to evaluate the micromechanism of the crack growth. The fractographic findings are reported in detail and correlated to the crack growth behavior. A hydrogen-assisted crack propagation mechanism based onmore » the fractography is proposed and applied to the observed crack growth behavior.« less

CHROMIUM PLATING FOR PROTECTION AGAINST STRESS CORROSION CRACKING OF HARDENED AISI 410 STEEL

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

Suss, H.

1958-04-22

Because of its high corrosion resistance properties, chromium electroplate should offer protection to AISI 419 steel against stress corrosion cracking. Tests have been made (KAPL and Bettis) on chromium plates on test specimens as deposited by two different sources in conformance with Bettis and USMC specifications. These deposits either offered protection to hardened (RC36- 42) AISI 410 against stress corrosion cracking, or caused accelerated stress corrosion cracking under conditions which did not crack unplated material. At present there is no significant data which could give definite clues for these extreme differences in the corrosive protective values. The results of testsmore » so far strongly question tbe value of chromium plate as a means to protect AISI 410 against stress corrosion cracking. (A.C.)« less

Reaction Control System Thruster Cracking Consultation: NASA Engineering and Safety Center (NESC) Materials Super Problem Resolution Team (SPRT) Findings

NASA Technical Reports Server (NTRS)

MacKay, Rebecca A.; Smith, Stephen W.; Shah, Sandeep R.; Piascik, Robert S.

2005-01-01

The shuttle orbiter s reaction control system (RCS) primary thruster serial number 120 was found to contain cracks in the counter bores and relief radius after a chamber repair and rejuvenation was performed in April 2004. Relief radius cracking had been observed in the 1970s and 1980s in seven thrusters prior to flight; however, counter bore cracking had never been seen previously in RCS thrusters. Members of the Materials Super Problem Resolution Team (SPRT) of the NASA Engineering and Safety Center (NESC) conducted a detailed review of the relevant literature and of the documentation from the previous RCS thruster failure analyses. It was concluded that the previous failure analyses lacked sufficient documentation to support the conclusions that stress corrosion cracking or hot-salt cracking was the root cause of the thruster cracking and lacked reliable inspection controls to prevent cracked thrusters from entering the fleet. The NESC team identified and performed new materials characterization and mechanical tests. It was determined that the thruster intergranular cracking was due to hydrogen embrittlement and that the cracking was produced during manufacturing as a result of processing the thrusters with fluoride-containing acids. Testing and characterization demonstrated that appreciable environmental crack propagation does not occur after manufacturing.

Fatigue of Self-Healing Nanofiber-based Composites: Static Test and Subcritical Crack Propagation.

PubMed

Lee, Min Wook; Sett, Soumyadip; Yoon, Sam S; Yarin, Alexander L

2016-07-20

Here, we studied the self-healing of composite materials filled with epoxy-containing nanofibers. An initial incision in the middle of a composite sample stretched in a static fatigue test can result in either crack propagation or healing. In this study, crack evolution was observed in real time. A binary epoxy, which acted as a self-healing agent, was encapsulated in two separate types of interwoven nano/microfibers formed by dual-solution blowing, with the core containing either epoxy or hardener and the shell being formed from poly(vinylidene fluoride)/ poly(ethylene oxide) mixture. The core-shell fibers were encased in a poly(dimethylsiloxane) matrix. When the fibers were damaged by a growing crack in this fiber-reinforced composite material because of static stretching in the fatigue test, they broke and released the healing agent into the crack area. The epoxy used in this study was cured and solidified for approximately an hour at room temperature, which then conglutinated and healed the damaged location. The observations were made for at least several hours and in some cases up to several days. It was revealed that the presence of the healing agent (the epoxy) in the fibers successfully prevented the propagation of cracks in stretched samples subjected to the fatigue test. A theoretical analysis of subcritical cracks was performed, and it revealed a jumplike growth of subcritical cracks, which was in qualitative agreement with the experimental results.

Effect of Measured Welding Residual Stresses on Crack Growth

NASA Technical Reports Server (NTRS)

Hampton, Roy W.; Nelson, Drew; Doty, Laura W. (Technical Monitor)

1998-01-01

Welding residual stresses in thin plate A516-70 steel and 2219-T87 aluminum butt weldments were measured by the strain-gage hole drilling and X-ray diffraction methods. The residual stress data were used to construct 3D strain fields which were modeled as thermally induced strains. These 3D strain fields were then analyzed with the WARP31) FEM fracture analysis code in order to predict their effect on fatigue and on fracture. For analyses of fatigue crack advance and subsequent verification testing, fatigue crack growth increments were simulated by successive saw-cuts and incremental loading to generate, as a function of crack length, effects on crack growth of the interaction between residual stresses and load induced stresses. The specimen experimental response was characterized and compared to the WARM linear elastic and elastic-plastic fracture mechanics analysis predictions. To perform the fracture analysis, the plate material's crack tearing resistance was determined by tests of thin plate M(T) specimens. Fracture analyses of these specimen were performed using WARP31D to determine the critical Crack Tip Opening Angle [CTOA] of each material. These critical CTOA values were used to predict crack tearing and fracture in the weldments. To verify the fracture predictions, weldment M(T) specimen were tested in monotonic loading to fracture while characterizing the fracture process.

Search for a test for fracture potential of asphalt mixes : close out meeting.

DOT National Transportation Integrated Search

2012-08-01

Presentation Outline : 1)Part A Introduction : 2)Part B The OT test method : 3)Part C Surrogate crack tests (6 No.) : 4)Part D Comparison of the crack test methods : 5)Part E Summary & recommendations : 6)Miscellaneous & discussions

Stress-Corrosion Cracking in Martensitic PH Stainless Steels

NASA Technical Reports Server (NTRS)

Humphries, T.; Nelson, E.

1984-01-01

Precipitation-hardening alloys evaluated in marine environment tests. Report describes marine-environment stress-corrosion cracking (SCC) tests of three martensitic precipitation hardening (PH) stainless-steel alloys.

Acoustic Emission Methodology to Evaluate the Fracture Toughness in Heat Treated AISI D2 Tool Steel

NASA Astrophysics Data System (ADS)

Mostafavi, Sajad; Fotouhi, Mohamad; Motasemi, Abed; Ahmadi, Mehdi; Sindi, Cevat Teymuri

2012-10-01

In this article, fracture toughness behavior of tool steel was investigated using Acoustic Emission (AE) monitoring. Fracture toughness ( K IC) values of a specific tool steel was determined by applying various approaches based on conventional AE parameters, such as Acoustic Emission Cumulative Count (AECC), Acoustic Emission Energy Rate (AEER), and the combination of mechanical characteristics and AE information called sentry function. The critical fracture toughness values during crack propagation were achieved by means of relationship between the integral of the sentry function and cumulative fracture toughness (KICUM). Specimens were selected from AISI D2 cold-work tool steel and were heat treated at four different tempering conditions (300, 450, 525, and 575 °C). The results achieved through AE approaches were then compared with a methodology proposed by compact specimen testing according to ASTM standard E399. It was concluded that AE information was an efficient method to investigate fracture characteristics.

Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth

NASA Technical Reports Server (NTRS)

Telesman, Jack; Gabb, Tim; Ghosn, Louis J.

2016-01-01

Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress intensity parameter, Kmax, was developed by incorporating into the formulation the remaining stress level concept as measured by simple stress relaxation tests. The newly proposed parameter, Ksrf, did an excellent job in correlating the dwell crack growth rates for the four heat treatments which were shown to have similar intrinsic environmental cyclic fatigue crack growth resistance.

Mixed-mode stress intensity factors for kink cracks with finite kink length loaded in tension and bending: application to dentin and enamel.

PubMed

Bechtle, Sabine; Fett, Theo; Rizzi, Gabriele; Habelitz, Stefan; Schneider, Gerold A

2010-05-01

Fracture toughness resistance curves describe a material's resistance against crack propagation. These curves are often used to characterize biomaterials like bone, nacre or dentin as these materials commonly exhibit a pronounced increase in fracture toughness with crack extension due to co-acting mechanisms such as crack bridging, crack deflection and microcracking. The knowledge of appropriate stress intensity factors which depend on the sample and crack geometry is essential for determining these curves. For the dental biomaterials enamel and dentin it was observed that, under bending and tensile loading, crack propagation occurs under certain constant angles to the initial notch direction during testing procedures used for fracture resistance curve determination. For this special crack geometry (a kink crack of finite length in a finite body) appropriate geometric function solutions are missing. Hence, we present in this study new mixed-mode stress intensity factors for kink cracks with finite kink length within samples of finite dimensions for two loading cases (tension and bending) which were derived from a combination of mixed-mode stress intensity factors of kink cracks with infinitely small kinks and of slant cracks. These results were further applied to determine the fracture resistance curves of enamel and dentin by testing single edge notched bending (SENB) specimens. It was found that kink cracks with finite kink length exhibit identical stress fields to slant cracks as soon as the kink length exceeds 0.15 times the initial straight crack or notch length. The use of stress intensity factor solutions for infinitely small kink cracks for the determination of dentin fracture resistance curves (as was done by other researchers) leads to an overestimation of dentin's fracture resistance of up to 30%. Copyright 2010 Elsevier Ltd. All rights reserved.

A total life prediction model for stress concentration sites

NASA Technical Reports Server (NTRS)

Hartman, G. A.; Dawicke, D. S.

1983-01-01

Fatigue crack growth tests were performed on center crack panels and radial crack hole samples. The data were reduced and correlated with the elastic parameter K taking into account finite width and corner crack corrections. The anomalous behavior normally associated with short cracks was not observed. Total life estimates for notches were made by coupling an initiation life estimate with a propagation life estimate.

A total life prediction model for stress concentration sites

NASA Technical Reports Server (NTRS)

Hartman, G. A.; Dawicke, D. S.

1983-01-01

Fatigue crack growth tests were performed on center crack panels and radial crack hole samples. The data were reduced and correlated with the elastic parameter-K taking into account finite width and corner crack corrections. The anomalous behavior normally associated with short cracks was not observed. Total life estimates for notches were made by coupling an initiation life estimate with a propagation life estimate.

Detection of fatigue cracks by nondestructive testing methods

NASA Technical Reports Server (NTRS)

Anderson, R. T.; Delacy, T. J.; Stewart, R. C.

1973-01-01

The effectiveness was assessed of various NDT methods to detect small tight cracks by randomly introducing fatigue cracks into aluminum sheets. The study included optimizing NDT methods calibrating NDT equipment with fatigue cracked standards, and evaluating a number of cracked specimens by the optimized NDT methods. The evaluations were conducted by highly trained personnel, provided with detailed procedures, in order to minimize the effects of human variability. These personnel performed the NDT on the test specimens without knowledge of the flaw locations and reported on the flaws detected. The performance of these tests was measured by comparing the flaws detected against the flaws present. The principal NDT methods utilized were radiographic, ultrasonic, penetrant, and eddy current. Holographic interferometry, acoustic emission monitoring, and replication methods were also applied on a reduced number of specimens. Generally, the best performance was shown by eddy current, ultrasonic, penetrant and holographic tests. Etching provided no measurable improvement, while proof loading improved flaw detectability. Data are shown that quantify the performances of the NDT methods applied.

Sonic environment tests of an insulator/ablator material

NASA Technical Reports Server (NTRS)

Jackson, L. R.; Taylor, A. H.; Rucker, C. E.

1977-01-01

A 50.8 cm (20 inch) square panel of perpyrolized insulator/ablator was subjected to six 30-minute tests at 160 and 158 dB in the Langley Thermo-Acoustic Fatigue Apparatus (TAFA). This environment simulates the aerodynamic and engine noise encountered by a research airplane while in captive flight on the B-52 pylon during takeoff and climb. The pyrolized layer sustained damage in the form of three chips and numerous cracks. The chips occurred during the first test. Some cracking resulted during aerodynamic heating tests, and additional cracking resulted from the sonic environment tests.

Evaluation of sonic IR for NDE at Lawrence Livermore National Laboratory

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

Miller, W O

2001-02-01

Sonic IR was evaluated as an NDE technique at LLNL using a commercial ThermoSoniX system from Indigo Systems Corp. The main effort was to detect small cracks in aluminum oxide, a dense stiff ceramic. Test coupons were made containing 0.2-mm cracks by surface grinding, 1-mm cracks by compression with a Vickers bit, and 4-mm cracks by 3-point bending. Only the 3-point bend cracks produced thermal images. Several parts shattered during testing, perhaps by being forced at resonance by the 20-kHz acoustic probe. Tests on damaged carbon composite coupons produced thermal images that were in excellent agreement with ultrasonic inspection. Themore » composite results also showed some dependence on contact location of the acoustic probe, and on the method of support. Tests on glass with surface damage produced weak images at the pits. Tests on metal ballistic targets produced thermal images at the impact sites. Modal analyses suggest that the input frequency should be matched to the desired response, and also that forced resonance damaged some parts.« less

Subcritical crack growth of selected aerospace pressure vessel materials

NASA Technical Reports Server (NTRS)

Hall, L. R.; Bixler, W. D.

1972-01-01

This experimental program was undertaken to determine the effects of combined cyclic/sustained loads, stress level, and crack shape on the fatigue crack growth rate behavior of cracks subjected to plane strain conditions. Material/environment combinations tested included: 2219-T87 aluminum plate in gaseous helium, room air, and 3.5% NaCl solution at room temperature, liquid nitrogen, and liquid hydrogen; 5Al-2.5 Sn (ELI) titanium plate in liquid nitrogen and liquid hydrogen and 6AL-4V (ELI) STA titanium plate in gaseous helium and methanol at room temperature. Most testing was accomplished using surface flawed specimens instrumented with a clip gage to continuously monitor crack opening displacements at the specimen surface. Tapered double cantilever beam specimens were also tested. Static fracture and ten hour sustained load tests were conducted to determine fracture toughness and apparent threshold stress intensity values. Cyclic tests were performed using sinusoidal loading profiles at 333 MHz (20 cpm) and trapezoidal loading profiles at both 8.3 MHz (0.5 cpm) and 3.3 MHz (0.2 cpm). Data were evaluated using modified linear elastic fracture mechanics parameters.

Results of the second Round Robin on opening-load measurement conducted by ASTM Task Group E24.04.04 on crack closure measurement and analysis

NASA Technical Reports Server (NTRS)

Phillips, E. P.

1993-01-01

A second experimental Round Robin on the measurement of the crack opening load in fatigue crack growth tests has been completed by the ASTM Task Group E24.04.04 on Crack Closure Measurement and Analysis. Fourteen laboratories participated in the testing of aluminum alloy compact tension specimens. Opening-load measurements were made at three crack lengths during constant Delta K, constant stress ratio tests by most of the participants. Four participants made opening-load measurements during threshold tests. All opening-load measurements were based on the analysis of specimens compliance behavior, where the displacement/strain was measured either at the crack mouth or the mid-height back face location. The Round Robin data were analyzed for opening load using two non-subjective analysis methods: the compliance offset and the correlation coefficient methods. The scatter in the opening load results was significantly reduced when some of the results were excluded from the analysis population based on an accept/reject criterion for raw data quality. The compliance offset and correlation coefficient opening load analysis methods produced similar results for data populations that had been screened to eliminate poor quality data.

Grainex Mar-M 247 Turbine Disk Life Study for NASA's High Temperature High Speed Turbine Seal Test Facility

NASA Technical Reports Server (NTRS)

Delgado, Irebert R.

2015-01-01

An experimental and analytical fatigue life study was performed on the Grainex Mar-M 247 disk used in NASA s Turbine Seal Test Facility. To preclude fatigue cracks from growing to critical size in the NASA disk bolt holes due to cyclic loading at severe test conditions, a retirement-for-cause methodology was adopted to detect and monitor cracks within the bolt holes using eddy-current inspection. For the NASA disk material that was tested, the fatigue strain-life to crack initiation at a total strain of 0.5 percent, a minimum to maximum strain ratio of 0, and a bolt hole temperature of 649 C was calculated to be 665 cycles using -99.95 percent prediction intervals. The fatigue crack propagation life was calculated to be 367 cycles after implementing a safety factor of 2 on life. Thus, the NASA disk bolt hole total life or retirement life was determined to be 1032 cycles at a crack depth of 0.501 mm. An initial NASA disk bolt hole inspection at 665 cycles is suggested with 50 cycle inspection intervals thereafter to monitor fatigue crack growth.

Behavior and influence of desiccation cracking in loess landfill covers

NASA Astrophysics Data System (ADS)

Wu, Tao; Lan, Ji-wu; Qiu, Qing-wen; He, Hai-jie; Li, He

2017-11-01

In the northwest region of China, loess was the main closure cover material of local landfills. Tests in a full-scale testing facility were conducted to investigate the behavior and influence of desiccation cracking in loess landfill covers. The desiccation cracks in the loess landfill cover intersected with T-shape, and the intersection angles were close to 90 degrees. The desiccation cracks formed as a result of drying, and would heal with the increase of moisture content of the loess. In addition, desiccation cracking in loess covers would promote the formation of preferential flow channels. As a consequence, the gas permeability of the loess cover was improved, and methane emissions increased obviously.

Visualization of Lamb Wave Interaction with a 5 mm Fatigue Crack using 1D Ultra High Frequency Laser Doppler Vibrometry

DTIC Science & Technology

2011-09-01

detection of a fatigue crack via 3D LDV measurements, both in aluminum plates. All the referenced LDV/guided wave studies made use of PZT or similar...Figure 1a). (b) (a) (c) Figure 1: (a) Test specimen in MTS fatigue test machine, (b) hole with 5 mm crack, (c) PZT placement with...mm thick aluminum plates with a small (1.59 mm) center hole added to facilitate growth of a fatigue crack. One plate was left undamaged while the

Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

NASA Technical Reports Server (NTRS)

Forman, Royce G.; Zanganehgheshlaghi, Mohannad

2014-01-01

The research results described in this paper presents a new understanding of the behavior of fatigue crack growth in the threshold region. It is believed by some crack growth experts that the ASTM load shedding test method does not produce true or valid threshold properties. The concern involves the observed fanning of threshold region da/dN data plots for some materials in which the low R-ratio data fans out or away from the high R-ratio data. This data fanning or elevation of threshold values is obviously caused by an increase in crack closure in the low R-ratio tested specimens. This increase in crack closure is assumed by some investigators to be caused by a plastic wake on the crack surfaces that was created during the load shedding test phase. This study shows that the increase in crack closure is the result of an extensive occurrence of crack bifurcation behavior in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the particular fanning behavior in aluminum alloys is a function of intrinsic dislocation property of the materials and that the fanned data represents valid material properties. However, for corrosion sensitive steel alloys used in this study the fanning was caused by a build-up of iron oxide at the crack tip from fretting corrosion.

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.

Replacement/Refurbishment of JSC/NASA POD Specimens

NASA Technical Reports Server (NTRS)

Castner, Willard L.

2010-01-01

The NASA Special NDE certification process requires demonstration of NDE capability by test per NASA-STD-5009. This test is performed with fatigue cracked specimens containing very small cracks. The certification test results are usually based on binomial statistics and must meet a 90/95 Probability of Detection (POD). The assumption is that fatigue cracks are tightly closed, difficult to detect, and inspectors and processes passing such a test are well qualified for inspecting NASA fracture critical hardware. The JSC NDE laboratory has what may be the largest inventory that exists of such fatigue cracked NDE demonstration specimens. These specimens were produced by the hundreds in the late 1980s and early 1990s. None have been produced since that time and the condition and usability of the specimens are questionable.

1. VIEW NORTHEAST, LEFT TO RIGHT COLD CALIBRATION TEST STAND ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. VIEW NORTHEAST, LEFT TO RIGHT COLD CALIBRATION TEST STAND COLD CALIBRATION BLOCKHOUSE IN FOREGROUND. - Marshall Space Flight Center, East Test Area, Cold Calibration Test Stand, Huntsville, Madison County, AL

Rolling contact fatigue of low hardness steel for slewing ring application

NASA Astrophysics Data System (ADS)

Knuth, Jason A.

This thesis discusses the rolling contact fatigue of steel utilized in anti-friction bearings, also referred to as slewing bearings. These slewing bearings are utilized in cranes, excavators, wind turbines and other similar applications. Five materials composed of two different material types were tested. The two material types were high carbon steel and medium carbon alloy steel. The test specimens were processed from forged rolled rings. Two machines were evaluated a ZF-RCF and 3-Ball test machine. The evaluation was to determine which machine can best simulate the application in which the slewing bearing is utilized. Initially, each specimen will be pretested to determine the appropriate testing direction from within the forged rolled rings. Pretesting is needed in order to establish consistent failure modes between samples. The primary goal of the test is to understand the life differences and failure modes between high carbon steel and medium carbon alloy steel. The high carbon steel ring was cut into two sections, one of which was stress relieved and the other was quenched and tempered. The medium carbon alloy steel was cut into three sections, all of which were quenched and tempered to different hardness levels. The test program was dynamically adjusted based upon the previous sample's life and load. An S-N curve was then established from the 5 materials tested at two target loads. The samples were run until the first sign of a crack was detected by an eddy current. At the completion of the rolling contact test, select sample's microstructure was evaluated for crack initiation location. The selected samples were divided into four groups which represent different maximum shear stress levels. These samples displayed indications of material deformation in which the high carbon steel experienced an increased amount of cold work when compared to medium carbon alloy steel. The life of the high carbon steel was nearly equivalent to the expected life of the medium carbon alloy. The work hardening of the high carbon steel increased the surface hardness that exceeded the medium carbon alloy steel surface hardness.

Fracture Mechanics Testing of Titanium 6AL-4V in AF-M315E

NASA Technical Reports Server (NTRS)

Sampson, J. W.; Martinez, J.; McLean, C.

2016-01-01

The Green Propellant Infusion Mission (GPIM) will demonstrate the performance of AF-M315E monopropellant on orbit. Flight certification requires a safe-life analysis of the titanium alloy fuel tank to ensure inherent processing flaws will not cause failure during the design life of the tank. Material property inputs for this analysis require testing to determine the stress intensity factor for environment-assisted cracking (KEAC) of Ti 6Al-4V in combination with the AF-M315E monopropellant. Testing of single-edge notched, or SE(B), specimens representing the bulk tank membrane and weld material were performed in accordance with ASTM E1681. Specimens with fatigue pre-cracks were loaded into test fixtures so that the crack tips were exposed to AF-M315E at 50 C for a duration of 1,000 hours. Specimens that did not fail during exposure were opened to inspect the crack surfaces for evidence of crack growth. The threshold stress intensity value, KEAC, is the highest applied stress intensity that produced neither a failure of the specimen during the exposure nor showed evidence of crack growth. The threshold stress intensity factor for environment-assisted cracking of the Ti 6Al-4V forged tank material was found to be at least 22 ksivin and at least 31 ksivin for the weld material when exposed to AF-M315E monopropellant.

Axial crack propagation and arrest in pressurized fuselage

NASA Technical Reports Server (NTRS)

Kosai, M.; Shimamoto, A.; Yu, C.-T.; Walker, S. I.; Kobayashi, A. S.; Tan, P.

1994-01-01

The crack arrest capability of a tear strap in a pressurized precracked fuselage was studied through instrumented axial rupture tests of small scale models of an idealized fuselage. Upon pressurization, rapid crack propagation initiated at an axial through crack along the stringer and immediately kinked due to the mixed modes 1 and 2 state caused by the one-sided opening of the crack flap. The diagonally running crack further turned at the tear straps. Dynamic finite element analysis of the rupturing cylinder showed that the crack kinked and also ran straight in the presence of a mixed mode state according to a modified two-parameter crack kinking criterion.

Thermal fatigue performance of integrally cast automotive turbine wheels

NASA Technical Reports Server (NTRS)

Humphreys, V. E.; Hofer, K. E.

1980-01-01

Fluidized bed thermal fatigue testing was conducted on 16 integrally cast automotive turbine wheels for 1000-10,000 (600 sec total) thermal cycles at 935/50 C. The 16 wheels consisted of 14 IN-792 + 1% Hf and 2 gatorized AF2-1DA wheels; 6 of the IN-792 + Hf wheels contained crack arrest pockets inside the blade root flange. Temperature transients during the thermal cycling were measured in three calibration tests using either 18 or 30 thermocouples per wheel. Thermal cracking based on crack length versus accumulated cycles was greatest for unpocketed wheels developing cracks in 8-13 cycles compared to 75-250 cycles for unpocketed wheels. However, pocketed wheels survived up to 10,000 cycles with crack lengths less than 20 mm, whereas two unpocketed wheels developed 45 mm long cracks in 1000-2000 cycles.

Fatigue crack closure behavior at high stress ratios

NASA Technical Reports Server (NTRS)

Turner, C. Christopher; Carman, C. Davis; Hillberry, Ben M.

1988-01-01

Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

The detection of tightly closed flaws by nondestructive testing (NDT) methods. [fatigue crack formation in aluminum alloy test specimens

NASA Technical Reports Server (NTRS)

Rummel, W. D.; Rathke, R. A.; Todd, P. H., Jr.; Mullen, S. J.

1975-01-01

Liquid penetrant, ultrasonic, eddy current and X-radiographic techniques were optimized and applied to the evaluation of 2219-T87 aluminum alloy test specimens in integrally stiffened panel, and weld panel configurations. Fatigue cracks in integrally stiffened panels, lack-of-fusion in weld panels, and fatigue cracks in weld panels were the flaw types used for evaluation. A 2319 aluminum alloy weld filler rod was used for all welding to produce the test specimens. Forty seven integrally stiffened panels containing a total of 146 fatigue cracks, ninety three lack-of-penetration (LOP) specimens containing a total of 239 LOP flaws, and one-hundred seventeen welded specimens containing a total of 293 fatigue cracks were evaluated. Nondestructive test detection reliability enhancement was evaluated during separate inspection sequences in the specimens in the 'as-machined or as-welded', post etched and post proof loaded conditions. Results of the nondestructive test evaluations were compared to the actual flaw size obtained by measurement of the fracture specimens after completing all inspection sequences. Inspection data were then analyzed to provide a statistical basis for determining the flaw detection reliability.

Fatigue damage assessment of high-usage in-service aircraft fuselage structure

NASA Astrophysics Data System (ADS)

Mosinyi, Bao Rasebolai

As the commercial and military aircraft fleets continue to age, there is a growing concern that multiple-site damage (MSD) can compromise structural integrity. Multiple site damage is the simultaneous occurrence of many small cracks at independent structural locations, and is the natural result of fatigue, corrosion, fretting and other possible damage mechanisms. These MSD cracks may linkup and form a fatigue lead crack of critical length. The presence of MSD also reduces the structure's ability to withstand longer cracks. The objective of the current study is to assess, both experimentally and analytically, MSD formation and growth in the lap joint of curved panels removed from a retired aircraft. A Boeing 727-232 airplane owned and operated by Delta Air Lines, and retired at its design service goal, was selected for the study. Two panels removed from the left-hand side of the fuselage crown, near stringer 4L, were subjected to extended fatigue testing using the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration (FAA) William J. Hughes Technical Center. The state of MSD was continuously assessed using several nondestructive inspection (NDI) methods. Damage to the load attachment points of the first panel resulted in termination of the fatigue test at 43,500 fatigue cycles, before cracks had developed in the lap joint. The fatigue test for the second panel was initially conducted under simulated in-service loading conditions for 120,000 cycles, and no cracks were detected in the skin of the panel test section. Artificial damage was then introduced into the panel at selected rivets in the critical (lower) rivet row, and the fatigue loads were increased. Visually detectable crack growth from the artificial notches was first seen after 133,000 cycles. The resulting lead crack grew along the lower rivet row, eventually forming an 11.8" long unstable crack after 141,771 cycles, at which point the test was terminated. Posttest fractograpic examinations of the crack surfaces were conducted, revealing the presence of subsurface MSD at the critical rivet row of the lap joint. Special attention was also given to the stringer clips that attach the fuselage frames to the stringers, since they also experienced cracking during the fatigue tests. The performance of the different conventional and emerging NDI methods was also assessed, and some of the emerging NDI methods were quite effective in detecting and measuring the length of subsurface cracks. Delta Air Lines conducted a separate destructive investigation on the state of damage along the right-hand side of the fuselage, near stringer 4R. A comparison of these two studies showed that the lap joint on the left hand-side of the aircraft, along stringer 4L, had better fatigue life than the one on the opposite side, along stringer 4R. The cause of the difference in fatigue life was investigated by close examination of the rivet installation qualities, and was found to be a result of better rivet installation along the lap joint at stringer 4L. Finite element models for both the skin and substructures of the panels were developed and geometrically nonlinear finite element analyses were conducted to verify the loading conditions and to determine near-field parameters governing MSD initiation and growth. Fatigue crack growth predictions based on the NASGRO equation were in good agreement with the experimental crack growth data for through-the-thickness cracks. For subsurface cracks, simulation of crack growth was found to correlate better with fractography data when an empirical crack growth model was used. The results of the study contribute to the understanding of the initiation and growth of MSD in the inner skin layer of a lap joint, and provide valuable data for the evaluation and validation of analytical methodologies to predict MSD initiation and growth and a better understanding on the effect of manufacturing quality on damage accumulation along the lap joint.

An evaluation of the pressure proof test concept for 2024-T3 aluminium alloy sheet

NASA Technical Reports Server (NTRS)

Dawicke, D. S.; Poe, C. C., Jr.; Newman, J. C.; Harris, C. E.

1991-01-01

The concept of pressure proof testing of fuselage structures with fatigue cracks to insure structural integrity was evaluated from a fracture mechanics viewpoint. A generic analytical and experimental investigation was conducted on uniaxially loaded flat panels with crack configurations and stress levels typical of longitudinal lap splice joints in commercial transport aircraft fuselages. The results revealed that the remaining fatigue life after a proof cycle was longer than that without the proof cycle because of crack growth retardation due to increased crack closure. However, based on a crack length that is slightly less than the critical value at the maximum proof stress, the minimum assured life or proof test interval must be no more than 550 pressure cycles for a 1.33 proof factor and 1530 pressure cycles for a 1.5 proof factor to prevent in-flight failures.

Testing and analysis of flat and curved panels with multiple cracks

DOT National Transportation Integrated Search

1994-08-01

An experimental and analytical investigation of multiple cracking in various types of test specimens is described in this paper. The testing phase is comprised of a flat unstiffened panel series and curved stiffened and unstiffened panel series. The ...

A robust signal processing method for quantitative high-cycle fatigue crack monitoring using soft elastomeric capacitor sensors

NASA Astrophysics Data System (ADS)

Kong, Xiangxiong; Li, Jian; Collins, William; Bennett, Caroline; Laflamme, Simon; Jo, Hongki

2017-04-01

A large-area electronics (LAE) strain sensor, termed soft elastomeric capacitor (SEC), has shown great promise in fatigue crack monitoring. The SEC is able to monitor strain changes over a mesoscale structural surface and endure large deformations without being damaged under cracking. Previous tests verified that the SEC is able to detect, localize, and monitor fatigue crack activities under low-cycle fatigue loading. In this paper, to examine the SEC's capability of monitoring high-cycle fatigue cracks, a compact specimen is tested under cyclic tension, designed to ensure realistic crack opening sizes representative of those in real steel bridges. To overcome the difficulty of low signal amplitude and relatively high noise level under high-cycle fatigue loading, a robust signal processing method is proposed to convert the measured capacitance time history from the SEC sensor to power spectral densities (PSD) in the frequency domain, such that signal's peak-to-peak amplitude can be extracted at the dominant loading frequency. A crack damage indicator is proposed as the ratio between the square root of the amplitude of PSD and load range. Results show that the crack damage indicator offers consistent indication of crack growth.

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

Crack growth through the thickness of thin-sheet Hydrided Zircaloy-4

NASA Astrophysics Data System (ADS)

Raynaud, Patrick A. C.

In recent years, the limits on fuel burnup have been increased to allow an increase in the amount of energy produced by a nuclear fuel assembly thus reducing waste volume and allowing greater capacity factors. As a result, it is paramount to ensure safety after longer reactor exposure times in the case of design-basis accidents, such as reactivity-initiated accidents (RIA). Previously proposed failure criteria do not directly address the particular cladding failure mechanism during a RIA, in which crack initiation in brittle outer-layers is immediately followed by crack growth through the thickness of the thin-wall tubing. In such a case, the fracture toughness of hydrided thin-wall cladding material must be known for the conditions of through-thickness crack growth in order to predict the failure of high-burnup cladding. The fracture toughness of hydrided Zircaloy-4 in the form of thin-sheet has been examined for the condition of through-thickness crack growth as a function of hydride content and distribution at 25°C, 300°C, and 375°C. To achieve this goal, an experimental procedure was developed in which a linear hydride blister formed across the width of a four-point bend specimen was used to inject a sharp crack that was subsequently extended by fatigue pre-cracking. The electrical potential drop method was used to monitor the crack length during fracture toughness testing, thus allowing for correlation of the load-displacement record with the crack length. Elastic-plastic fracture mechanics were used to interpret the experimental test results in terms of fracture toughness, and J-R crack growth resistance curves were generated. Finite element modeling was performed to adapt the classic theories of fracture mechanics applicable to thick-plate specimens to the case of through-thickness crack growth in thin-sheet materials, and to account for non-uniform crack fronts. Finally, the hydride microstructure was characterized in the vicinity of the crack tip by means of digital image processing, so as to understand the influence of the hydride microstructure on fracture toughness, at the various test temperatures. Crack growth occurred through a microstructure which varied within the thickness of the thin-sheet Zircaloy-4 such that the hydrogen concentration and the radial hydride content decreased with increasing distance from the hydride blister. At 25°C, the fracture toughness was sensitive to the changes in hydride microstructure, such that the toughness KJi decreased from 39 MPa√m to 24 MPa√m with increasing hydrogen content and increasing the fraction of radial hydrides. The hydride particles present in the Zircaloy-4 substrate fractured ahead of the crack tip, and crack growth occurred by linking the crack-tip with the next hydride-induced primary void ahead of it. Unstable crack growth was observed at 25°C prior to any stable crack growth in the specimens where the hydrogen content was the highest. At 375°C as well as in most cases at 300°C, the hydride particles were resistant to cracking and the resistance to crack-growth initiation was very high. As a result, for this bend test procedure, crack extension was solely due to crack-tip blunting instead of crack growth in all tests at 375°C and in most cases at 300°C. The lower bound for fracture toughness at these temperatures, the parameter KJPmax, had values of K JPmax˜54MPa√m at both 300°C and 375°C. For cases where stable crack growth occurred at 300°C, the fracture toughness was K Ji˜58MPa√m and the tearing modulus was twice as high as that at 25°C. It is believed that the failure of hydrided Zircaloy-4 thin-wall cladding can be predicted using fracture mechanics analyses when failure occurs by crack growth. This failure mechanism was observed to occur in all cases at 25°C and in some cases at 300°C. However, at more elevated temperatures, such as 375°C, failure will likely occur by a mechanism other than crack growth, possibly by an imperfection-induced shear instability.

Analysis of small crack behavior for airframe applications

NASA Technical Reports Server (NTRS)

Mcclung, R. C.; Chan, K. S.; Hudak, S. J., Jr.; Davidson, D. L.

1994-01-01

The small fatigue crack problem is critically reviewed from the perspective of airframe applications. Different types of small cracks-microstructural, mechanical, and chemical-are carefully defined and relevant mechanisms identified. Appropriate analysis techniques, including both rigorous scientific and practical engineering treatments, are briefly described. Important materials data issues are addressed, including increased scatter in small crack data and recommended small crack test methods. Key problems requiring further study are highlighted.

Comparative Study on Prediction Effects of Short Fatigue Crack Propagation Rate by Two Different Calculation Methods

NASA Astrophysics Data System (ADS)

Yang, Bing; Liao, Zhen; Qin, Yahang; Wu, Yayun; Liang, Sai; Xiao, Shoune; Yang, Guangwu; Zhu, Tao

2017-05-01

To describe the complicated nonlinear process of the fatigue short crack evolution behavior, especially the change of the crack propagation rate, two different calculation methods are applied. The dominant effective short fatigue crack propagation rates are calculated based on the replica fatigue short crack test with nine smooth funnel-shaped specimens and the observation of the replica films according to the effective short fatigue cracks principle. Due to the fast decay and the nonlinear approximation ability of wavelet analysis, the self-learning ability of neural network, and the macroscopic searching and global optimization of genetic algorithm, the genetic wavelet neural network can reflect the implicit complex nonlinear relationship when considering multi-influencing factors synthetically. The effective short fatigue cracks and the dominant effective short fatigue crack are simulated and compared by the Genetic Wavelet Neural Network. The simulation results show that Genetic Wavelet Neural Network is a rational and available method for studying the evolution behavior of fatigue short crack propagation rate. Meanwhile, a traditional data fitting method for a short crack growth model is also utilized for fitting the test data. It is reasonable and applicable for predicting the growth rate. Finally, the reason for the difference between the prediction effects by these two methods is interpreted.

Crack closure, a literature study

NASA Astrophysics Data System (ADS)

Holmgren, M.

1993-08-01

In this report crack closure is treated. The state of the art is reviewed. Different empirical formulas for determining the crack closure are compared with each other, and their benefits are discussed. Experimental techniques for determining the crack closure stress are discussed, and some results from fatigue tests are also reported. Experimental data from the literature are reported.

NASA-Langley Research Center's participation in a round-robin comparison between some current crack-propagation prediction methods

NASA Technical Reports Server (NTRS)

Hudson, C. M.; Lewis, P. E.

1979-01-01

A round-robin study was conducted which evaluated and compared different methods currently in practice for predicting crack growth in surface-cracked specimens. This report describes the prediction methods used by the Fracture Mechanics Engineering Section, at NASA-Langley Research Center, and presents a comparison between predicted crack growth and crack growth observed in laboratory experiments. For tests at higher stress levels, the correlation between predicted and experimentally determined crack growth was generally quite good. For tests at lower stress levels, the predicted number of cycles to reach a given crack length was consistently higher than the experimentally determined number of cycles. This consistent overestimation of the number of cycles could have resulted from a lack of definition of crack-growth data at low values of the stress intensity range. Generally, the predicted critical flaw sizes were smaller than the experimentally determined critical flaw sizes. This underestimation probably resulted from using plane-strain fracture toughness values to predict failure rather than the more appropriate values based on maximum load.

Environmentally assisted cracking in light water reactors. Semiannual report, July 1998-December 1998.

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

Chopra, O. K.; Chung, H. M.; Gruber, E. E.

This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors from July 1998 to December 1998. Topics that have been investigated include (a) environmental effects on fatigue S-N behavior of primary pressure boundary materials, (b) irradiation-assisted stress corrosion cracking of austenitic stainless steels (SSs), and (c) EAC of Alloys 600 and 690. Fatigue tests have been conducted to determine the crack initiation and crack growth characteristics of austenitic SSs in LWR environments. Procedures are presented for incorporating the effects of reactor coolant environments on the fatigue life of pressure vesselmore » and piping steels. Slow-strain-rate tensile tests and posttest fractographic analyses were conducted on several model SS alloys irradiated to {approx}0.3 and 0.9 x 10{sup 21} n {center_dot} cm{sup -2} (E > 1 MeV) in helium at 289 C in the Halden reactor. The results have been used to determine the influence of alloying and impurity elements on the susceptibility of these steels to irradiation-assisted stress corrosion cracking. Fracture toughness J-R curve tests were also conducted on two heats of Type 304 SS that were irradiated to {approx}0.3 x 10{sup 21} n {center_dot} cm{sup -2} in the Halden reactor. Crack-growth-rate tests have been conducted on compact-tension specimens of Alloys 600 and 690 under constant load to evaluate the resistance of these alloys to stress corrosion cracking in LWR environments.« less

What Happens Where the Water and the Rock Touch in Small Space Bodies

NASA Astrophysics Data System (ADS)

Byrne, P. K.; Regensburger, P. V.; Klimczak, C.; Bohnenstiehl, D. R.; Dombard, A. J.; Hauck, S. A., II

2017-12-01

There are several small space bodies that go around bigger worlds that might have a layer of water under a layer of ice. Lots of study has been done to understand the outside ice layer of these small space bodies, because the ice can tells us important things about the big water layer under it. Some of these small space bodies are very interesting because the right things for life—water, hot rock, and food—might be at the bottom of the water layer, where it touches the top of the next layer down, which is made of rock. But it is very hard to understand what this rock at the bottom of the water is like, because we can't see it. So, we are imagining what this rock is like by thinking about what the rock is like under the water layer on our own world. If hot rock comes out of the rock layer through cracks under the water, the cold of the water makes the hot rock go very cold very fast, and it makes funny rolls as it does so. This might happen on some small space bodies that are hot enough on the inside to make hot rock. We know that on our own world the rock layer under the water is wet to as far down as cracks can go, so it makes sense that this is true for small space bodies, too. We did some thinking about numbers and found out that the cracks can go a few ten hundred steps into the rock layer on small space bodies, but for bigger (well, not quite so small) space bodies, the cracks can go at least tens of ten hundred steps into the rock layer. This means that water goes into the rock layer this much, too. But get this: some small bodies are not really that small—one of them is bigger than the first world from the Sun! And on a few of these big (small) bodies, the layer of water is so heavy that the bottom of that water is pushed together from all sides and turns into a type of hot ice. This means that, for these big (small) worlds, the water can't get into the rock layer through cracks (since there is a layer of hot ice in the way), and so these bodies are not such good places to think about where life might be.

Natural Crack Sizing Based on Eddy Current Image and Electromagnetic Field Analyses

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

Endo, H.; Uchimoto, T.; Takagi, T.

2006-03-06

An eddy current testing (ECT) system with multi-coil type probes is applied to size up cracks fabricated on austenite stainless plates. We have developed muti-channel ECT system to produce data as digital images. The probes consist of transmit-receive type sensors as elements to classify crack directions, working as two scan direction modes simultaneously. Template matching applied to the ECT images determines regions of interest in sizing up cracks. Finite element based inversion sizes up the crack depth from the measured ECT signal. The present paper demonstrates this approach for fatigue crack and stress corrosion cracking.

Controlled crack shapes for indentation fracture of soda-lime glass

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

Smith, S.M.; Scattergood, R.O.

1992-01-01

Radial cracks for indented soda-lime glass aged in distilled water were highly elliptical because of truncation by lateral cracks. Indentation in silicone oil minimized radial/lateral crack interaction but still produced cracks having nominally constant ellipticity during bend testing. Analysis of applied stress/indentation crack length data using stress intensity factors based on half-penny crack shape resulted in apparent R-curve behavior and/or overestimation of the fracture toughness. Incorporation of elliptical shape factors eliminated the R-curve behavior and reduced measured toughness to near the accepted value for soda-lime glass.

On fractography of shallow and deep HY-100 cracked bend specimens

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

Yuan, D.W.; Zarzour, J.F.; Kleinosky, M.J.

1994-12-01

The influence of shallow cracks on the fracture behavior of structural components has been studied extensively in recent years. Finite element analyses have indicated dramatic differences in the crack-tip stress states between shallow and deep cracked bend specimens. In this study, an experimental program was carried out to investigate the fracture behavior of HY-100 steel containing various initial flaw depths. Four a/w ratios ranging from 0.05 to 0.5 were chosen for the notched three-point bend tests. Test results showed that higher fracture toughness values are associated with specimens having shorter surface cracks. Also, fractographic studies indicated that two sets ofmore » dimples are present for a/w = 0.5 specimen, one set of equiaxed dimple for a/w = 0.05 specimen near the crack initiation zone. As the crack grows, increase in the volume fraction of the small dimple were observed. Finally, it showed that the characteristic features of the fracture surfaces can be correlated with the previous numerical predictions.« less

Local delamination in laminates with angle ply matrix cracks. Part 1: Tension tests and stress analysis

NASA Technical Reports Server (NTRS)

Obrien, T. Kevin; Hooper, S. J.

1991-01-01

Quasi-static tension tests were conducted on AS4/3501-6 graphite epoxy laminates. Dye penetrant enhanced x-radiography was used to document the onset of matrix cracking and the onset of local delaminations at the intersection of the matrix cracks and the free edge. Edge micrographs taken after the onset of damage were used to verify the location of the matrix cracks and local delamination through the laminate thickness. A quasi-3D finite element analysis was conducted to calculate the stresses responsible for matrix cracking in the off-axis plies. Laminated plate theory indicated that the transverse normal stresses were compressive. However, the finite element analysis yielded tensile transverse normal stresses near the free edge. Matrix cracks formed in the off-axis plies near the free edge where in-plane transverse stresses were tensile and had their greatest magnitude. The influence of the matrix crack on interlaminar stresses is also discussed.

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.

Surface-crack growth: Models, experiments, and structures; Proceedings of the Symposium, Sparks, NV, Apr. 25, 1988

NASA Technical Reports Server (NTRS)

Reuter, Walter G. (Editor); Underwood, John H. (Editor); Newman, James C., Jr. (Editor)

1990-01-01

The present volume on surface-crack growth modeling, experimental methods, and structures, discusses elastoplastic behavior, the fracture analysis of three-dimensional bodies with surface cracks, optical measurements of free-surface effects on natural surfaces and through cracks, an optical and finite-element investigation of a plastically deformed surface flaw under tension, fracture behavior prediction for rapidly loaded surface-cracked specimens, and surface cracks in thick laminated fiber composite plates. Also discussed are a novel study procedure for crack initiation and growth in thermal fatigue testing, the growth of surface cracks under fatigue and monotonically increasing load, the subcritical growth of a surface flaw, surface crack propagation in notched and unnotched rods, and theoretical and experimental analyses of surface cracks in weldments.

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

Mechanical properties of low-nickel stainless steel

NASA Technical Reports Server (NTRS)

Montano, J. W.

1978-01-01

Demand for improved corrosion-resistant steels, coupled with increased emphasis on conserving strategic metals, has led to development of family of stainless steels in which manganese and nitrogen are substituted for portion of usual nickel content. Advantages are approximately-doubled yield strength in annealed condition, better resistance to stress-corrosion cracking, retention of low magnetic permeability even after severe cold working, excellent strength and ductility at cryogenic temperatures, superior resistance to wear and galling, and excellent high-temperature properties.

Polyfibroblast: A Self-Healing and Galvanic Protection Additive

DTIC Science & Technology

2013-03-22

polyurethane-urea (MCPU). When scratched, the foaming action of a propellant ejects the resin from the broken tubes and completely fills the crack . No...Resistivities of Control NCP and Enhanced NCP primers are 5xl06 and UxlO6 Ohm/sq respectively indicating we may be able to use simple enamel rater...instrumentation to evaluate self-healing. 1. Enamel rater evaluation underway. 2. 1 |im films of OTS prepared on Cold Rolled Steel and Blasted Steel panels

Development and Application of the High Bandwidth Powered Resonance Tube

DTIC Science & Technology

2005-11-09

arises in practical situations. In laser cutting, it is a common practice to remove the molten mass of metal with the help of high speed jet of air...cleaner and straighter laser cuts[Masuda and Nakamura, 19921. Thin glass sheets are prone to cracks when tempered by a cold air jet with impingement...Alvi, F. S., Shish, C., Elavarasan, R., Garg, G., and Krothapalli, A., 2003. Control of supersonic impinging jet flows using supersonic microjets

The detection of fatigue cracks by nondestructive testing methods

NASA Technical Reports Server (NTRS)

Rummel, W. D.; Todd, P. H., Jr.; Frecska, S. A.; Rathke, R. A.

1974-01-01

X-radiographic penetrant, ultrasonic, eddy current, holographic, and acoustic emission techniques were optimized and applied to the evaluation of 2219-T87 aluminum alloy test specimens. One hundred eighteen specimens containing a total of 328 fatigue cracks were evaluated. The cracks ranged in length from 0.500 inch (1.27 cm) to 0.007 inch (0.018 cm) and in depth from 0.178 inch (0.451 cm) and 0.001 inch (0.003 cm). Specimen thicknesses were nominally 0.060 inch (0.152 cm) and 0.210 inch (0.532 cm) and surface finishes were nominally 32 and 125 rms and 64 and 200 rms respectively. Specimens were evaluated in the as-milled surface condition, in the chemically milled surface condition and, after proof loading, in a randomized inspection sequence. Results of the nondestructive test (NDT) evaluations were compared with actual crack size obtained by measurement of the fractured specimens. Inspection data was then analyzed to provide a statistical basis for determinating the threshold crack detection sensitivity (the largest crack size that would be missed) for each of the inspection techniques at a 95% probability and 95% confidence level.

Effect of pre-strain on creep of three AISI 316 austenitic stainless steels in relation to reheat cracking of weld-affected zones

NASA Astrophysics Data System (ADS)

Auzoux, Q.; Allais, L.; Caës, C.; Monnet, I.; Gourgues, A. F.; Pineau, A.

2010-05-01

Microstructural modifications induced by welding of 316 stainless steels and their effect on creep properties and relaxation crack propagation were examined. Cumulative strain due to multi-pass welding hardens the materials by increasing the dislocation density. Creep tests were conducted on three plates from different grades of 316 steel at 600 °C, with various carbon and nitrogen contents. These plates were tested both in the annealed condition and after warm rolling, which introduced pre-strain. It was found that the creep strain rate and ductility after warm rolling was reduced compared with the annealed condition. Moreover, all steels exhibited intergranular crack propagation during relaxation tests on Compact Tension specimens in the pre-strained state, but not in the annealed state. These results confirmed that the reheat cracking risk increases with both residual stress triaxiality and pre-strain. On the contrary, high solute content and strain-induced carbide precipitation, which are thought to increase reheat cracking risk of stabilised austenitic stainless steels did not appear as key parameters in reheat cracking of 316 stainless steels.

Crack Growth Simulation and Residual Strength Prediction in Airplane Fuselages

NASA Technical Reports Server (NTRS)

Chen, Chuin-Shan; Wawrzynek, Paul A.; Ingraffea, Anthony R.

1999-01-01

This is the final report for the NASA funded project entitled "Crack Growth Prediction Methodology for Multi-Site Damage." The primary objective of the project was to create a capability to simulate curvilinear fatigue crack growth and ductile tearing in aircraft fuselages subjected to widespread fatigue damage. The second objective was to validate the capability by way of comparisons to experimental results. Both objectives have been achieved and the results are detailed herein. In the first part of the report, the crack tip opening angle (CTOA) fracture criterion, obtained and correlated from coupon tests to predict fracture behavior and residual strength of built-up aircraft fuselages, is discussed. Geometrically nonlinear, elastic-plastic, thin shell finite element analyses are used to simulate stable crack growth and to predict residual strength. Both measured and predicted results of laboratory flat panel tests and full-scale fuselage panel tests show substantial reduction of residual strength due to the occurrence of multi-site damage (MSD). Detailed comparisons of n stable crack growth history, and residual strength between the predicted and experimental results are used to assess the validity of the analysis methodology. In the second part of the report, issues related to crack trajectory prediction in thin shells; an evolving methodology uses the crack turning phenomenon to improve the structural integrity of aircraft structures are discussed, A directional criterion is developed based on the maximum tangential stress theory, but taking into account the effect of T-stress and fracture toughness orthotropy. Possible extensions of the current crack growth directional criterion to handle geometrically and materially nonlinear problems are discussed. The path independent contour integral method for T-stress evaluation is derived and its accuracy is assessed using a p- and hp-version adaptive finite element method. Curvilinear crack growth is simulated in coupon tests and in full-scale fuselage panel tests. Both T-stress and fracture toughness orthotropy are found to be essential to predict the observed crack paths. The analysis methodology and software program (FRANC3D/STAGS) developed herein allows engineers to maintain aging aircraft economically while insuring continuous airworthiness. Consequently, it will improve the technology to support the safe operation of the current aircraft fleet as well as the design of more damage-tolerant aircraft for the next generation fleet.

Environmentally assisted cracking in light water reactors.

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

Chopra, O. K.; Chung, H. M.; Clark, R. W.

2007-11-06

This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from January to December 2002. Topics that have been investigated include: (a) environmental effects on fatigue crack initiation in carbon and low-alloy steels and austenitic stainless steels (SSs), (b) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs in BWRs, (c) evaluation of causes and mechanisms of irradiation-assisted cracking of austenitic SS in PWRs, and (d) cracking in Ni-alloys and welds. A critical review of the ASME Code fatigue design margins and an assessment of the conservation in the currentmore » choice of design margins are presented. The existing fatigue {var_epsilon}-N data have been evaluated to define the effects of key material, loading, and environmental parameters on the fatigue lives of carbon and low-alloy steels and austenitic SSs. Experimental data are presented on the effects of surface roughness on fatigue crack initiation in these materials in air and LWR environments. Crack growth tests were performed in BWR environments on SSs irradiated to 0.9 and 2.0 x 10{sup 21} n x cm{sup -2}. The crack growth rates (CGRs) of the irradiated steels are a factor of {approx}5 higher than the disposition curve proposed in NUREG-0313 for thermally sensitized materials. The CGRs decreased by an order of magnitude in low-dissolved oxygen (DO) environments. Slow-strain-rate tensile (SSRT) tests were conducted in high-purity 289 C water on steels irradiated to {approx}3 dpa. The bulk S content correlated well with the susceptibility to intergranular SCC in 289 C water. The IASCC susceptibility of SSs that contain >0.003 wt. % S increased drastically. bend tests in inert environments at 23 C were conducted on broken pieces of SSRT specimens and on unirradiated specimens of the same materials after hydrogen charging. The results of the tests and a review of other data in the literature indicate that IASCC in 289 C water is dominated by a crack-tip grain-boundary process that involves S. An initial IASCC model has been proposed. A crack growth test was completed on mill annealed Alloy 600 in high-purity water at 289 C and 320 C under various environmental and loading conditions. The results from this test are compared with data obtained earlier on several other heats of Alloy 600.« less

Fractography of a bis-GMA resin.

PubMed

Davis, D M; Waters, N E

1989-07-01

The fracture behavior of a bis-GMA resin was studied by means of the double-torsion test. The fracture parameter measured was the stress-intensity factor. Fracture occurred in either a stick-slip (unstable) or continuous (stable) manner, depending upon the test conditions. When stick-slip propagation occurred, the fracture surfaces showed characteristic crack-arrest lines. The fracture surfaces were examined by use of a reflected-light optical microscope. The stress-intensity factor for crack initiation was found to be related to the size of the crack-arrest line which, in turn, could be related to the Dugdale model for plastic zone size. The evidence supported the concept that the behavior of the crack during propagation was controlled by the amount of plastic deformation occurring at the crack tip.

Material Characterization for the Analysis of Skin/Stiffener Separation

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Leone, Frank A.; Song, Kyongchan; Ratcliffe, James G.; Rose, Cheryl A.

2017-01-01

Test results show that separation failure in co-cured skin/stiffener interfaces is characterized by dense networks of interacting cracks and crack path migrations that are not present in standard characterization tests for delamination. These crack networks result in measurable large-scale and sub-ply-scale R curve toughening mechanisms, such as fiber bridging, crack migration, and crack delving. Consequently, a number of unknown issues exist regarding the level of analysis detail that is required for sufficient predictive fidelity. The objective of the present paper is to examine some of the difficulties associated with modeling separation failure in stiffened composite structures. A procedure to characterize the interfacial material properties is proposed and the use of simplified models based on empirical interface properties is evaluated.

An investigation of reheat cracking in the weld heat affected zone of type 347 stainless steel

NASA Astrophysics Data System (ADS)

Phung-On, Isaratat

2007-12-01

Reheat cracking has been a persistent problem for welding of many alloys such as the stabilized stainless steels: Types 321 and 347 as well as Cr-Mo-V steels. Similar problem occurs in Ni-base superalloys termed "strain-age cracking". Cracking occurs during the post weld heat treatment. The HAZ is the most susceptible area due to metallurgical reactions in solid state during both heating and cooling thermal cycle. Many investigations have been conducted to understand the RHC mechanism. There is still no comprehensive mechanism to explain its underlying mechanism. In this study, there were two proposed cracking mechanisms. The first is the formation of a PFZ resulting in local weakening and strain localization. The second is the creep-like grain boundary sliding that causes microvoid formation at the grain boundaries and the triple point junctions. Cracking occurs due to the coalescence of the microvoids that form. In this study, stabilized grade stainless steel, Type 347, was selected for investigation of reheat cracking mechanism due to the simplicity of its microstructure and understanding of its metallurgical behavior. The Gleeble(TM) 3800 system was employed due to its capability for precise control of both thermal and mechanical simulation. Cylindrical samples were subjected to thermal cycles for the HAZ simulation followed by PWHT as the reheat cracking test. "Susceptibility C-curves" were plotted as a function of PWHT temperatures and time to failure at applied stress levels of 70% and 80% yield strength. These C-curves show the possible relationship of the reheat cracking susceptibility and carbide precipitation behavior. To identify the mechanism, the sample shape was modified containing two flat surfaces at the center section. These flat surfaces were electro-polished and subjected to the HAZ simulation followed by the placement of the micro-indentation arrays. Then, the reheat cracking test was performed. The cracking mechanism was identified by tracing the shifting of the micro-indentations compared to their original locations. At the 80% stress level, the cracking mechanism was identified as the PFZ weakening, while at the 70% stress as the creep-like grain boundary sliding. A design of experiment (DOE) using a D-optimal design was successfully employed in this study to investigate the effects of microstructures on the reheat cracking susceptibility. The microstructures were modified by heat treatment prior to the reheat cracking test. The grain size and cooling rate were found to have moderate effects on cracking susceptibility. The amount (volume fraction) of MC carbide (NbC) had a significant effect on time to failure. The more NbC formed prior to test, the longer time to failure, and the more resistance to reheat cracking. On the other hand, the amount of GB carbide (M23C6) had an insignificant effect. The statistical interaction between MC carbide with other testing parameters also had strong effect. The PWHT temperature also had significant effect as can be predicted from the susceptibility C-curves. The heat treatment schedules, during cooling and during heating schedules, were also investigated. During cooling schedule was the same schedule done earlier in this study. On the other hand, during heating schedule allowed the sample cool to room temperature prior microstructure modification followed by the reheat cracking test. During heating schedule showed an improvement in resistance to reheat cracking. Microstructure of the crack samples showed the intergranular cracking path and wedge shapes along cracking boundaries. There was also the evidence of grain boundary sliding as a result of the creep-like grain boundary sliding cracking mechanism. SEM showed the intergranular cracking and grain separation with precipitates decorated on the fracture surfaces. The precipitates were identified as Nb-rich, MC carbide (NbC). The fracture surfaces showed micro-ductility and microvoid coalescence. The size of microvoid corresponds to the size of precipitate that forms. In addition, there was intragranular cracking in some location indicating that another failure mechanism may also be possible. It was believed that failure may occur along a precipitate free zone. However, the distinct PFZ could not be detected. A SS-DTA technique was also implemented in order to determine precipitation temperatures of the material. The results showed the possible precipitation temperatures in the range of 850°C to 650°C. However, the results were not confidently reliable due to the small amount of carbide formed that affects the sensitivity of the SS-DTA. A simple grain boundary sliding model was generated proposing that the sliding is operated by the shear stress resulting from the formation of precipitate in the grain interior. Then, the sliding results in the microvoid formation and coalescence followed by cracking. In addition, a simple finite element model was generated to provide the illustration of the shear stress built up by the formation of precipitate. The model showed that shear stress can cause the grain boundary movement/sliding. Based on the results from this study, the recommendation for the selection of post weld heat treatment schedule as well as welding procedures can be determined for the prevention of the reheat cracking. A residual stress should be kept below the critical value during welding and post weld heat treating. The testing procedures used in this study can be applied as the guidelines to conduct the reheat cracking susceptibility test for material selection.

Distribution of Inclusion-Initiated Fatigue Cracking in Powder Metallurgy Udimet 720 Characterized

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kantzos, Pete T.; Barrie, Robert; Telesman, Jack; Ghosn, Louis J.; Gabb, Timothy P.

2004-01-01

In the absence of extrinsic surface damage, the fatigue life of metals is often dictated by the distribution of intrinsic defects. In powder metallurgy (PM) alloys, relatively large defects occur rarely enough that a typical characterization with a limited number of small volume fatigue test specimens will not adequately sample inclusion-initiated damage. Counterintuitively, inclusion-initiated failure has a greater impact on the distribution in PM alloy fatigue lives because they tend to have fewer defects than their cast and wrought counterparts. Although the relative paucity of defects in PM alloys leads to higher mean fatigue lives, the distribution in observed lives tends to be broader. In order to study this important failure initiation mechanism without expending an inordinate number of specimens, a study was undertaken at the NASA Glenn Research Center where known populations of artificial inclusions (seeds) were introduced to production powder. Fatigue specimens were machined from forgings produced from the seeded powder. Considerable effort has been expended in characterizing the crack growth rate from inclusion-initiated cracks in seeded PM alloys. A rotating and translating positioning system, with associated software, was devised to map the surface inclusions in low-cycle fatigue (LCF) test bars and to monitor the crack growth from these inclusions. The preceding graph illustrates the measured extension in fatigue cracks from inclusions on a seeded LCF test bar subjected to cyclic loading at a strain range of 0.8 percent and a strain ratio (max/min) of zero. Notice that the observed inclusions fall into three categories: some do not propagate at all (arrest), some propagate with a decreasing crack growth rate, and a few propagate at increasing rates that can be modeled by fracture mechanics. The following graph shows the measured inclusion-initiated crack growth rates from 10 interrupted LCF tests plotted against stress intensities calculated for semi-elliptical cracks with the observed surface lengths. The expected scatter in the crack growth rates for stress intensity ranges near threshold is observed. These data will be used to help determine the distribution in growth rates of cracks emanating from inclusions as well as the proportion of cracks that arrest under various loading conditions.

Test Standard Developed for Determining the Slow Crack Growth of Advanced Ceramics at Ambient Temperature

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Salem, Jonathan A.

1998-01-01

The service life of structural ceramic components is often limited by the process of slow crack growth. Therefore, it is important to develop an appropriate testing methodology for accurately determining the slow crack growth design parameters necessary for component life prediction. In addition, an appropriate test methodology can be used to determine the influences of component processing variables and composition on the slow crack growth and strength behavior of newly developed materials, thus allowing the component process to be tailored and optimized to specific needs. At the NASA Lewis Research Center, work to develop a standard test method to determine the slow crack growth parameters of advanced ceramics was initiated by the authors in early 1994 in the C 28 (Advanced Ceramics) committee of the American Society for Testing and Materials (ASTM). After about 2 years of required balloting, the draft written by the authors was approved and established as a new ASTM test standard: ASTM C 1368-97, Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-Rate Flexural Testing at Ambient Temperature. Briefly, the test method uses constant stress-rate testing to determine strengths as a function of stress rate at ambient temperature. Strengths are measured in a routine manner at four or more stress rates by applying constant displacement or loading rates. The slow crack growth parameters required for design are then estimated from a relationship between strength and stress rate. This new standard will be published in the Annual Book of ASTM Standards, Vol. 15.01, in 1998. Currently, a companion draft ASTM standard for determination of the slow crack growth parameters of advanced ceramics at elevated temperatures is being prepared by the authors and will be presented to the committee by the middle of 1998. Consequently, Lewis will maintain an active leadership role in advanced ceramics standardization within ASTM. In addition, the authors have been and are involved with several international standardization organizations including the Versailles Project on Advanced Materials and Standards (VAMAS), the International Energy Agency (IEA), and the International Organization for Standardization (ISO). The associated standardization activities involve fracture toughness, strength, elastic modulus, and the machining of advanced ceramics.

Comparison of two computer codes for crack growth analysis: NASCRAC Versus NASA/FLAGRO

NASA Technical Reports Server (NTRS)

Stallworth, R.; Meyers, C. A.; Stinson, H. C.

1989-01-01

Results are presented from the comparison study of two computer codes for crack growth analysis - NASCRAC and NASA/FLAGRO. The two computer codes gave compatible conservative results when the part through crack analysis solutions were analyzed versus experimental test data. Results showed good correlation between the codes for the through crack at a lug solution. For the through crack at a lug solution, NASA/FLAGRO gave the most conservative results.

Time-dependent crack growth behavior of alloy 617 and alloy 230 at elevated temperatures

NASA Astrophysics Data System (ADS)

Roy, Shawoon Kumar

2011-12-01

Two Ni-base solid-solution-strengthened superalloys: INCONEL 617 and HAYNES 230 were studied to check sustained loading crack growth (SLCG) behavior at elevated temperatures appropriate for Next Generation Nuclear Plant (NGNP) applictaions with constant stress intensity factor (Kmax= 27.75 MPa✓m) in air. The results indicate a time-dependent rate controlling process which can be characterized by a linear elastic fracture mechanics (LEFM) parameter -- stress intensity factor (K). At elevated temperatures, the crack growth mechanism was best described using a damage zone concept. Based on results and study, SAGBOE (stress accelerated grain boundary oxidation embrittlement) is considered the primary reason for time-dependent SLCG. A thermodynamic equation was considered to correlate all the SLCG results to determine the thermal activation energy in the process. A phenomenological model based on a time-dependent factor was developed considering the previous researcher's time-dependent fatigue crack propagation (FCP) results and current SLCG results to relate cycle-dependent and time-dependent FCP for both alloys. Further study includes hold time (3+300s) fatigue testing and no hold (1s) fatigue testing with various load ratios (R) at 700°C with a Kmax of 27.75 MPa✓m. Study results suggest an interesting point: crack growth behavior is significantly affected with the change in R value in cycle-dependent process whereas in time-dependent process, change in R does not have any significant effect. Fractography study showed intergranular cracking mode for all time-dependent processes and transgranular cracking mode for cycle-dependent processes. In Alloy 230, SEM images display intergranular cracking with carbide particles, dense oxides and dimple mixed secondary cracks for time-dependent 3+300s FCP and SLCG test. In all cases, Alloy 230 shows better crack growth resistance compared to Alloy 617.

Caustic stress corrosion tests for the LLTR

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

Indig, M.E.

1976-05-01

A series of tests have been performed in order to determine the effects of the caustic resulting from the Na/H/sub 2/O reaction on the materials used in the LLTR-MSG series of testing. Stainless steel, 2 /sup 1///sub 4/ Cr--1 Mo and carbon steel have been evaluated. Stress corrosion cracking susceptibility and general corrosion are reported. Over the range of temperature, caustic concentration and heating rate tested the stainless steel stressed to 90% of yield or above suffered cracking. Whereas, the 2-/sup 1///sub 4/ Cr--1 Mo and carbon steel were not cracked.

Effect of temperature on crack growth rates of stress corrosion cracks in metal alloys exposed to water

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

Vogt, H.; Speidel, M.O.

1996-12-01

The effect of temperature on stress corrosion crack growth rates was studied using four commercial alloys: an Al-Mg-Zn alloy (7000-Series), an Al-Cu alloy (2000-Series), a Mg-rare earth alloy and a Zr 2.5% Nb alloy. Stress Corrosion crack growth rate data were obtained using fracture mechanic specimens which were tested in high purity water in the temperature range of {minus}10 C to 320 C, depending on the alloy. Attention was directed towards region 2 behavior, where the crack propagation rate is independent of stress intensity but sensitive to test temperature. The experimental activation energies of the different alloys were compared withmore » literature on rate-controlling steps in order to identify the possible stress corrosion cracking mechanisms. The results were also compared with the activation energies obtained from general corrosion and hydrogen diffusion experiments.« less

Nonlinear ultrasonic fatigue crack detection using a single piezoelectric transducer

NASA Astrophysics Data System (ADS)

An, Yun-Kyu; Lee, Dong Jun

2016-04-01

This paper proposes a new nonlinear ultrasonic technique for fatigue crack detection using a single piezoelectric transducer (PZT). The proposed technique identifies a fatigue crack using linear (α) and nonlinear (β) parameters obtained from only a single PZT mounted on a target structure. Based on the different physical characteristics of α and β, a fatigue crack-induced feature is able to be effectively isolated from the inherent nonlinearity of a target structure and data acquisition system. The proposed technique requires much simpler test setup and less processing costs than the existing nonlinear ultrasonic techniques, but fast and powerful. To validate the proposed technique, a real fatigue crack is created in an aluminum plate, and then false positive and negative tests are carried out under varying temperature conditions. The experimental results reveal that the fatigue crack is successfully detected, and no positive false alarm is indicated.

Strain rate effects in stress corrosion cracking

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

Parkins, R.N.

Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this maymore » be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.« less

Fracture Toughness of Thin Plates by the Double-Torsion Test Method

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Radovic, Miladin; Lara-Curzio, Edgar; Nelson, George

2006-01-01

Double torsion testing can produce fracture toughness values without crack length measurement that are comparable to those measured via standardized techniques such as the chevron-notch, surface-crack-in-flexure and precracked beam if the appropriate geometry is employed, and the material does not exhibit increasing crack growth resistance. Results to date indicate that 8 < W/d < 80 and L/W > 2 are required if crack length is not considered in stress intensity calculations. At L/W = 2, the normalized crack length should be 0.35 < a/L < 0.65; whereas for L/W = 3, 0.2 < a/L < 0.75 is acceptable. In addition, the load-points need to roll to reduce friction. For an alumina exhibiting increasing crack growth resistance, values corresponding to the plateau of the R-curve were measured. For very thin plates (W/d > 80) nonlinear effects were encountered.

Evaluation of shrinkage and cracking in concrete of ring test by acoustic emission method

NASA Astrophysics Data System (ADS)

Watanabe, Takeshi; Hashimoto, Chikanori

2015-03-01

Drying shrinkage of concrete is one of the typical problems related to reduce durability and defilation of concrete structures. Lime stone, expansive additive and low-heat Portland cement are used to reduce drying shrinkage in Japan. Drying shrinkage is commonly evaluated by methods of measurement for length change of mortar and concrete. In these methods, there is detected strain due to drying shrinkage of free body, although visible cracking does not occur. In this study, the ring test was employed to detect strain and age cracking of concrete. The acoustic emission (AE) method was adopted to detect micro cracking due to shrinkage. It was recognized that in concrete using lime stone, expansive additive and low-heat Portland cement are effective to decrease drying shrinkage and visible cracking. Micro cracking due to shrinkage of this concrete was detected and evaluated by the AE method.

Development of an Improved Crack Propagation Model for Corrosion-Induced Cover Cracking in RC Structures

NASA Astrophysics Data System (ADS)

Hilyati, S.; Nizam, Z. M.; Zurisman, M. A. A.; Azhar, A. T. S.

2017-06-01

During the last two decades, reinforced concrete (RC) has been extensively used in most of the world as one of the common construction material due to its advantages and durability. However, RC structures exposed to marine environments are subjected to chloride attack. Chlorides from seawater penetrate into RC structures are not only causing severe corrosion problems but also affect the durability and serviceability of such structures. This paper investigates the influence of transverse reinforcement and spacing of reinforcing bars on concrete cover cracking of two-way RC slab specimens using accelerated corrosion tests. The experimental program involved the testing of four RC slab specimens and was generally designed to observe the crack width and the time of crack to propagate. An improved model for predicting the timing of crack propagation based on the experimental data was then developed.

Investigation of the effects of manufacturing variations and materials on fatigue crack detection methods in gear teeth

NASA Technical Reports Server (NTRS)

Wheitner, Jeffrey A.; Houser, Donald R.

1994-01-01

The fatigue life of a gear tooth can be thought of as the sum of the number of cycles required to initiate a crack, N(sub i), plus the number of cycles required to propagate the crack to such a length that fracture occurs, N(sub p). The factors that govern crack initiation are thought to be related to localized stress or strain at a point, while propagation of a fatigue crack is a function of the crack tip parameters such as crack shape, stress state, and stress intensity factor. During a test there is no clear transition between initiation and propagation. The mechanisms of initiation and propagation are quite different and modeling them separately produces a higher degree of accuracy, but then the question that continually arises is 'what is a crack?' The total life prediction in a fracture mechanics model presently hinges on the assumption of an initial crack length, and this length can significantly affect the total life prediction. The size of the initial crack is generally taken to be in the range of 0.01 in. to 0.2 in. Several researchers have used various techniques to determine the beginning of the crack propagation stage. Barhorst showed the relationship between dynamic stiffness changes and crack propagation. Acoustic emissions, which are stress waves produced by the sudden movement of stressed materials, have also been successfully used to monitor the growth of cracks in tensile and fatigue specimens. The purpose of this research is to determine whether acoustic emissions can be used to define the beginning of crack propagation in a gear using a single-tooth bending fatigue test.

Crack classification in concrete beams using AE parameters

NASA Astrophysics Data System (ADS)

Bahari, N. A. A. S.; Shahidan, S.; Abdullah, S. R.; Ali, N.; Zuki, S. S. Mohd; Ibrahim, M. H. W.; Rahim, M. A.

2017-11-01

The acoustic emission (AE) technique is an effective tool for the evaluation of crack growth. The aim of this study is to evaluate crack classification in reinforced concrete beams using statistical analysis. AE has been applied for the early monitoring of reinforced concrete structures using AE parameters such as average frequency, rise time, amplitude counts and duration. This experimental study focuses on the utilisation of this method in evaluating reinforced concrete beams. Beam specimens measuring 150 mm × 250 mm × 1200 mm were tested using a three-point load flexural test using Universal Testing Machines (UTM) together with an AE monitoring system. The results indicated that RA value can be used to determine the relationship between tensile crack and shear movement in reinforced concrete beams.

Thermal Analysis in Support of the Booster Separation Motor Crack Investigation

NASA Technical Reports Server (NTRS)

Davis, Darrell; Prickett, Terry; Turner, Larry D. (Technical Monitor)

2001-01-01

During a post-test inspection of a Booster Separation Motor (BSM) from a Lot Acceptance Test (LAT), a crack was noticed in the graphite throat. Since this was an out-of-family occurrence, an investigation team was formed to determine the cause of the crack. This paper will describe thermal analysis techniques used in support of this investigation. Models were generated to predict gradients in nominal motor conditions, as well as potentially anomalous conditions. Analysis was also performed on throats that were tested in the Laser Hardened Material Evaluation Laboratory (LHMEL). Some of these throats were pre-cracked, while others represented configurations designed to amplify effects of thermal stresses. Results from these analyses will be presented in this paper.

Thermal Analysis in Support of the Booster Separation Motor Crack Investigation

NASA Technical Reports Server (NTRS)

Davis, Darrell; Prickett, Terry

2002-01-01

During a post-test inspection of a Booster Separation Motor (BSM) from a Lot Acceptance Test (LAT), a crack was noticed in the graphite throat. Since this was an out-of-family occurrence, an investigation team was formed to determine the cause of the crack. This paper will describe thermal analysis techniques used in support of this investigation. Models were generated to predict gradients in nominal motor conditions, as well as potentially anomalous conditions. Analysis was also performed on throats that were tested in the Laser Hardened Material Evaluation Laboratory (LHMEL). Some of these throats were pre-cracked, while others represented configurations designed to amplify effects of thermal stresses. Results from these analyses will be presented in this paper.

A computerized test system for thermal-mechanical fatigue crack growth

NASA Technical Reports Server (NTRS)

Marchand, N.; Pelloux, R. M.

1986-01-01

A computerized testing system to measure fatigue crack growth under thermal-mechanical fatigue conditions is described. Built around a servohydraulic machine, the system is capable of a push-pull test under stress-controlled or strain-controlled conditions in the temperature range of 25 to 1050 C. Temperature and mechanical strain are independently controlled by the closed-loop system to simulate the complex inservice strain-temperature relationship. A d-c electrical potential method is used to measure crack growth rates. The correction procedure of the potential signal to take into account powerline and RF-induced noises and thermal changes is described. It is shown that the potential drop technique can be used for physical mechanism studies and for modelling crack tip processes.

Behavior of Ti-5Al-2.5Sn ELI titanium alloy sheet parent and weld metal in the presence of cracks at 20 K

NASA Technical Reports Server (NTRS)

Sullivan, T. L.

1971-01-01

Through- and surface-cracked specimens of two thicknesses were tested in uniaxial tension. Surface-cracked specimens were generally found to be stronger than through-cracked specimens with the same crack length. Apparent surface-crack fracture toughness calculated using the Anderson modified Irwin equation remained relatively constant for cracks as deep as 90 percent of the sheet thickness. Subcritical growth of surface cracks was investigated. Comparison of chamber and open air welds showed chamber welds to be slightly tougher. Both methods produced welds with toughness that compared favorably with that of the parent metal. Weld efficiencies were above 94 percent.

Further Development of Crack Growth Detection Techniques for US Test and Research Reactors

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

Kohse, Gordon; Carpenter, David M.; Ostrovsky, Yakov

One of the key issues facing Light Water Reactors (LWRs) in extending lifetimes beyond 60 years is characterizing the combined effect of irradiation and water chemistry on material degradation and failure. Irradiation Assisted Stress Corrosion Cracking (IASCC), in which a crack propagates in a susceptible material under stress in an aggressive environment, is a mechanism of particular concern. Full understanding of IASCC depends on real time crack growth data acquired under relevant irradiation conditions. Techniques to measure crack growth in actively loaded samples under irradiation have been developed outside the US - at the Halden Boiling Water Reactor, for example.more » Several types of IASCC tests have also been deployed at the MITR, including passively loaded crack growth measurements and actively loaded slow strain rate tests. However, there is not currently a facility available in the US to measure crack growth on actively loaded, pre-cracked specimens in LWR irradiation environments. A joint program between the Idaho National Laboratory (INL) and the Massachusetts Institute of Technology (MIT) Nuclear Reactor Laboratory (NRL) is currently underway to develop and demonstrate such a capability for US test and research reactors. Based on the Halden design, the samples will be loaded using miniature high pressure bellows and a compact loading mechanism, with crack length measured in real time using the switched Direct Current Potential Drop (DCPD) method. The basic design and initial mechanical testing of the load system and implementation of the DCPD method have been previously reported. This paper presents the results of initial autoclave testing at INL and the adaptation of the design for use in the high pressure, high temperature water loop at the MITR 6 MW research reactor, where an initial demonstration is planned in mid-2015. Materials considerations for the high pressure bellows are addressed. Design modifications to the loading mechanism required by the size constraints of the MITR water loop are described. The safety case for operation of the high pressure gas-driven bellows mechanism is also presented. Key issues are the design and response of systems to limit gas flow in the event of a high pressure gas leak in the in-core autoclave. Integrity of the autoclave must be maintained and reactivity effects due to voiding of the loop coolant must be shown to be within the reactor technical specifications. The technical development of the crack growth monitor for application in the INL Advanced Test Reactor or the MITR can act as a template for adaptation of this technology in other reactors. (authors)« less

KSC-2010-5891

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- The moon shines brightly over space shuttle Discovery following a total lunar eclipse as the spacecraft waits to roll back from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The move was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5917

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter, which is in front of the shuttle. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5913

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter, which is in front of the shuttle. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5905

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5890

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- The beginning of a total lunar eclipse hovers over the top of space shuttle Discovery as the spacecraft waits to roll back from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The move was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5910

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter, which is in front of the shuttle. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5892

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- The moon shines brightly over space shuttle Discovery following a total lunar eclipse as the spacecraft waits to roll back from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The move was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5894

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery shares the stage with the moon following a total lunar eclipse as the spacecraft waits to roll back from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The move was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5904

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5907

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5916

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter, which is in front of the shuttle. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5914

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5912

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter, which is in front of the shuttle. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5903

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5889

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- The beginning of a total lunar eclipse illuminates the top of space shuttle Discovery as the spacecraft waits to roll back from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The move was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5911

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter, which is in front of the shuttle. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

KSC-2010-5893

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- The moon shines brightly over space shuttle Discovery following a total lunar eclipse as the spacecraft waits to roll back from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The move was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett

KSC-2010-5915

NASA Image and Video Library

2010-12-21

CAPE CANAVERAL, Fla. -- Space shuttle Discovery awaits its move, called rollback, from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. Rollback was scheduled for 12:30 a.m., but was postponed until 10 p.m. so technicians could resolve an issue with a leveling system on the crawler-transporter, which is in front of the shuttle. Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity to the International Space Station on the STS-133 mission is no earlier than Feb. 3, 2011. For more information on STS-133, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Frank Michaux

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2000-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case 1 loading), constant stress/constant stress-rate testing (Case 2 loading), and cyclic stress/constant stress-rate testing (Case 2 loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case 1 loading history, and alumina for the Case 3 loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test materials.

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2000-01-01

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth arid/or damage accumulation was determined numerically as a Function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test material&

Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments.

PubMed

Schlappal, Thomas; Schweigler, Michael; Gmainer, Susanne; Peyerl, Martin; Pichler, Bernhard

2017-01-01

Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

Fracture mechanics analysis for various fiber/matrix interface loadings

NASA Technical Reports Server (NTRS)

Naik, R. A.; Crews, J. H., Jr.

1991-01-01

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Fracture mechanics analysis for various fiber/matrix interface loadings

NASA Technical Reports Server (NTRS)

Naik, Rajiv A.; Crews, John H., Jr.

1992-01-01

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, theory avoiding fractional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Fracture mechanics analysis for various fiber/matrix interface loadings

NASA Technical Reports Server (NTRS)

Naik, R. A.; Crews, J. H., Jr.

1991-01-01

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. An F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

A comparison of single-cycle versus multiple-cycle proof testing strategies

NASA Technical Reports Server (NTRS)

Hudak, S. J., Jr.; Mcclung, R. C.; Bartlett, M. L.; Fitzgerald, J. H.; Russell, D. A.

1990-01-01

An evaluation of single-cycle and multiple-cycle proof testing (MCPT) strategies for SSME components is described. Data for initial sizes and shapes of actual SSME hardware defects are analyzed statistically. Closed-form estimates of the J-integral for surface flaws are derived with a modified reference stress method. The results of load- and displacement-controlled stable crack growth tests on thin IN-718 plates with deep surface flaws are summarized. A J-resistance curve for the surface-cracked configuration is developed and compared with data from thick compact tension specimens. The potential for further crack growth during large unload/reload cycles is discussed, highlighting conflicting data in the literature. A simple model for ductile crack growth during MCPT based on the J-resistance curve is used to study the potential effects of key variables. The projected changes in the crack size distribution during MCPT depend on the interactions between several key parameters, including the number of proof cycles, the nature of the resistance curve, the initial crack size distribution, the component boundary conditions (load vs. displacement control), and the magnitude of the applied load or displacement. The relative advantages of single-cycle and multiple-cycle proof testing appear to be specific, therefore, to individual component geometry, material, and loading.

Cascaded image analysis for dynamic crack detection in material testing

NASA Astrophysics Data System (ADS)

Hampel, U.; Maas, H.-G.

Concrete probes in civil engineering material testing often show fissures or hairline-cracks. These cracks develop dynamically. Starting at a width of a few microns, they usually cannot be detected visually or in an image of a camera imaging the whole probe. Conventional image analysis techniques will detect fissures only if they show a width in the order of one pixel. To be able to detect and measure fissures with a width of a fraction of a pixel at an early stage of their development, a cascaded image analysis approach has been developed, implemented and tested. The basic idea of the approach is to detect discontinuities in dense surface deformation vector fields. These deformation vector fields between consecutive stereo image pairs, which are generated by cross correlation or least squares matching, show a precision in the order of 1/50 pixel. Hairline-cracks can be detected and measured by applying edge detection techniques such as a Sobel operator to the results of the image matching process. Cracks will show up as linear discontinuities in the deformation vector field and can be vectorized by edge chaining. In practical tests of the method, cracks with a width of 1/20 pixel could be detected, and their width could be determined at a precision of 1/50 pixel.

Investigation of Dynamic Crack Coalescence Using a Gypsum-Like 3D Printing Material

NASA Astrophysics Data System (ADS)

Jiang, Chao; Zhao, Gao-Feng; Zhu, Jianbo; Zhao, Yi-Xin; Shen, Luming

2016-10-01

Dynamic crack coalescence attracts great attention in rock mechanics. However, specimen preparation in experimental study is a time-consuming and difficult procedure. In this work, a gypsum-like material by powder bed and inkjet 3D printing technique was applied to produce specimens with preset cracks for split Hopkinson pressure bar (SHPB) test. From micro X-ray CT test, it was found that the 3D printing technique could successfully prepare specimens that contain preset cracks with width of 0.2 mm. Basic mechanical properties of the 3D printing material, i.e., the elastic modulus, the Poisson's ratio, the density, the compressive strength, the indirect tensile strength, and the fracture toughness, were obtained and reported. Unlike 3D printed specimens using polylactic acid, these gypsum-like specimens can produce failure patterns much closer to those observed in classical rock mechanical tests. Finally, the dynamic crack coalescence of the 3D printed specimens with preset cracks were captured using a high-speed camera during SHPB tests. Failure patterns of these 3D printed specimens are similar to the specimens made by Portland cement concrete. Our results indicate that sample preparation by 3D printing is highly competitive due to its quickness in prototyping, precision and flexibility on the geometry, and high material homogeneity.

Generating Fatigue Crack Growth Thresholds with Constant Amplitude Loads

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Newman, James C., J.; Forman, Royce G.

2002-01-01

The fatigue crack growth threshold, defining crack growth as either very slow or nonexistent, has been traditionally determined with standardized load reduction methodologies. Some experimental procedures tend to induce load history effects that result in remote crack closure from plasticity. This history can affect the crack driving force, i.e. during the unloading process the crack will close first at some point along the wake, reducing the effective load at the crack tip. One way to reduce the effects of load history is to propagate a crack under constant amplitude loading. As a crack propagates under constant amplitude loading, the stress intensity factor, K, will increase, as will the crack growth rate, da/dN. A fatigue crack growth threshold test procedure is developed and experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R.

Prediction of stress corrosion of carbon steel by nuclear process liquid wastes

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

Ondrejcin, R.S.

1978-08-01

Radioactive liquid wastes are produced as a consequence of processing fuel from Savannah River Plant (SRP) production reactors. These wastes are stored in mild steel waste tanks, some of which have developed cracks from stress corrosion. A laboratory test was developed to determine the relative agressiveness of the wastes for stress corrosion cracking of mild steel. Tensile samples were strained to fracture in synthetic waste solutions in an electrochemical cell with the sample as the anode. Crack initiation is expected if total elongation of the steel in the test is less than its uniform elongation in air. Cracking would bemore » anticipated in a plant waste tank if solution conditions were equivalent to test conditions that cause a total elongation that is less than uniform elongation. The electrochemical tensile tests showed that the supernates in salt receiver tanks at SRP have the least aggressive compositions, and wastes newly generated during fuel repocessing have the most aggressive ones. Test data also verified that ASTM A 516-70 steel used in the fabrication of the later design waste tanks is less susceptible to cracking than the ASTM A 285-B steel used in earlier designs.« less

Study of the Corrosion Resistance of Austenitic Stainless Steels during Conversion of Waste to Biofuel

PubMed Central

Cabrini, Marina; Lorenzi, Sergio; Pastore, Tommaso; Pellegrini, Simone; Burattini, Mauro; Miglio, Roberta

2017-01-01

The paper deals with the corrosion behavior of stainless steels as candidate materials for biofuel production plants by liquefaction process of the sorted organic fraction of municipal solid waste. Corrosion tests were carried out on AISI 316L and AISI 304L stainless steels at 250 °C in a batch reactor during conversion of raw material to bio-oil (biofuel precursor), by exposing specimens either to water/oil phase or humid gas phase. General corrosion rate was measured by weight loss tests. The susceptibility to stress corrosion cracking was evaluated by means of U-bend specimens and slow stress rate tests at 10−6 or 10−5 s−1 strain rate. After tests, scanning electron microscope analysis was carried out to detect cracks and localized attacks. The results are discussed in relation with exposure conditions. They show very low corrosion rates strictly dependent upon time and temperature. No stress corrosion cracking was observed on U-bend specimens, under constant loading. Small cracks confined in the necking cone of specimens prove that stress corrosion cracking only occurred during slow strain rate tests at stresses exceeding the yield strength. PMID:28772682

Hot-cracking studies of Inconel 718 weld- heat-affected zones

NASA Technical Reports Server (NTRS)

Thompson, E. G.

1969-01-01

Hot ductility tests, gas-tungsten-arc fillerless fusion tests, and circle patch-weld-restraint tests were conducted on Inconel 718 to better understand and correlate the weldability /resistance to hot cracking/ of the alloy. A correlation of the test results with composition, heat-treat condition, grain size, and microstructure was made.

Comparative Stress Corrosion Cracking and General Corrosion Resistance of Annealed and Hardened 440 C Stainless Steel - New Techniques in Stress Corrosion Testing

NASA Technical Reports Server (NTRS)

Mendreck, M. J.; Hurless, B. E.; Torres, P. D.; Danford, M. D.

1998-01-01

The corrosion and stress corrosion cracking (SCC) characteristics of annealed and hardened 440C stainless steel were evaluated in high humidity and 3.5-percent NaCl solution. Corrosion testing consisted of an evaluation of flat plates, with and without grease, in high humidity, as well as electrochemical testing in 3.5-percent NaCl. Stress corrosion testing consisted of conventional, constant strain, smooth bar testing in high humidity in addition to two relatively new techniques under evaluation at MSFC. These techniques involve either incremental or constant rate increases in the load applied to a precracked SE(B) specimen, monitoring the crack-opening-displacement response for indications of crack growth. The electrochemical corrosion testing demonstrated an order of magnitude greater general corrosion rate in the annealed 440C. All techniques for stress corrosion testing showed substantially better SCC resistance in the annealed material. The efficacy of the new techniques for stress corrosion testing was demonstrated both by the savings in time and the ability to better quantify SCC data.

Virtual hybrid test control of sinuous crack

NASA Astrophysics Data System (ADS)

Jailin, Clément; Carpiuc, Andreea; Kazymyrenko, Kyrylo; Poncelet, Martin; Leclerc, Hugo; Hild, François; Roux, Stéphane

2017-05-01

The present study aims at proposing a new generation of experimental protocol for analysing crack propagation in quasi brittle materials. The boundary conditions are controlled in real-time to conform to a predefined crack path. Servo-control is achieved through a full-field measurement technique to determine the pre-set fracture path and a simple predictor model based on linear elastic fracture mechanics to prescribe the boundary conditions on the fly so that the actual crack path follows at best the predefined trajectory. The final goal is to identify, for instance, non-local damage models involving internal lengths. The validation of this novel procedure is performed via a virtual test-case based on an enriched damage model with an internal length scale, a prior chosen sinusoidal crack path and a concrete sample. Notwithstanding the fact that the predictor model selected for monitoring the test is a highly simplified picture of the targeted constitutive law, the proposed protocol exhibits a much improved sensitivity to the sought parameters such as internal lengths as assessed from the comparison with other available experimental tests.

Crack propagation analysis and fatigue life prediction for structural alloy steel based on metal magnetic memory testing

NASA Astrophysics Data System (ADS)

Ni, Chen; Hua, Lin; Wang, Xiaokai

2018-09-01

To monitor the crack propagation and predict the fatigue life of ferromagnetic material, the metal magnetic memory (MMM) testing was carried out to the single edge notched specimen made from structural alloy steel under three-point bending fatigue experiment in this paper. The variation of magnetic memory signal Hp (y) in process of fatigue crack propagation was investigated. The gradient K of Hp (y) was investigated and compared with the stress of specimen obtained by finite element analysis. It indicated that the gradient K can qualitatively reflect the distribution and variation of stress. The maximum gradient Kmax and crack size showed a good linear relationship, which indicated that the crack propagation can be estimated by MMM testing. Furthermore, the damage model represented by magnetic memory characteristic was created and a fatigue life prediction method was developed. The fatigue life can be evaluated by the relationship between damage parameter and normalized life. The method was also verified by another specimen. Because of MMM testing, it provided a new approach for predicting fatigue life.

Strain-age cracking in Rene 41 alloy

NASA Technical Reports Server (NTRS)

Prager, M.; Thompson, E. G.

1969-01-01

Weldability test determines the effects of material and process variables on the occurrence of strain-age cracking, and demonstrates effective and practical means for its reduction. Studies consist of tensile, impact, and stress-rupture tests.

Ultrasonic detection of plate cracks in railway wheels

DOT National Transportation Integrated Search

1976-07-31

The results of experimental efforts established the feasibility of the detection of railway wheel plate cracks by an ultrasonic pulse echo testing technique from the tread surface. Feasibility and test sensitivities were established using artificial ...

Crack propagation life of detail fractures in rails

DOT National Transportation Integrated Search

1988-10-01

The results of a comprehensive study of the crack propagation behavior of detail fractures in railroad rails are presented. The study includes full-scale crack growth experiments in a test track under simulated heavy freight train service, similar fi...

Research notes : reflective cracking : year 3 report.

DOT National Transportation Integrated Search

2001-10-01

Transverse cracking is a major problem on US Highway 97. The design life of the pavement is shortened due to premature cracking, thus increasing maintenance costs. : In September 1998, a test section near Chemult was established to study the effectiv...

Development of the crack sealant adhesion test.

DOT National Transportation Integrated Search

2009-04-01

Crack sealants are widely used in Texas to prevent water from entering into lower structural layers thereby : extending pavement life. However, most current crack sealants have been reported to have a very short life mainly due : to adhesive failures...

Research notes : the war on reflective cracking.

DOT National Transportation Integrated Search

1999-08-01

Transverse cracking is a major problem on Highway 97. The design life of the pavement is shortened due to premature cracking, thus increasing maintenance costs. In September 1998, a test section near Chemult was established to study the effectiveness...

Evaluation of a Small-Crack Monitoring System

NASA Technical Reports Server (NTRS)

Newman, John A.; Johnston, William M.

2010-01-01

A new system has been developed to obtain fatigue crack growth rate data from a series of images acquired during fatigue testing of specimens containing small surface cracks that initiate at highly-polished notches. The primary benefit associated with replica-based crack growth rate data methods is preserving a record of the crack configuration during the life of the specimen. Additionally, this system has the benefits of both reducing time and labor, and not requiring introduction of surface replica media into the crack. Fatigue crack growth rate data obtained using this new system are found to be in good agreement with similar results obtained from surface replicas.

Crack-shape effects for indentation fracture toughness measurements

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

Smith, S.M.; Scattergood, R.O.

1992-02-01

Various methods to measure fracture toughness using indentation precracks were compared using soda-lime glass as a test material. In situ measurements of crack size as a function of applied stress allow both the toughness K[sub c] and the residual-stress factor [chi] to be independently determined. Analysis of the data showed that stress intensity factors based on classical half-penny crack shapes overestimate toughness values and produce an apparent R-curve effect. This is due to a constraint on crack shape imposed by primary lateral cracks in soda-lime glass. Models based on elliptical cracks were developed to account for the crack-shape effects.

Fatigue failure of regenerator screens in a high frequency Stirling engine

NASA Technical Reports Server (NTRS)

Hull, David R.; Alger, Donald L.; Moore, Thomas J.; Scheuermann, Coulson M.

1988-01-01

Failure of Stirling Space Power Demonstrator Engine (SPDE) regenerator screens was investigated. After several hours of operation the SPDE was shut down for inspection and on removing the regenator screens, debris of unknown origin was discovered along with considerable cracking of the screens in localized areas. Metallurgical analysis of the debris determined it to be cracked-off-deformed pieces of the 41 micron thickness Type 304 stainless steel wire screen. Scanning electron microscopy of the cracked screens revealed failures occurring at wire crossovers and fatigue striations on the fracture surface of the wires. Thus, the screen failure can be characterized as a fatigue failure of the wires. The crossovers were determined to contain 30 percent reduction in wire thickness and a highly worked microstructure occurring from the manufacturing process of the wire screens. Later it was found that reduction in wire thickness occurred because the screen fabricator had subjected it to a light cold-roll process after weaving. Installation of this screen left a clearance in the regenerator allowing the screens to move. The combined effects of the reduction in wire thickness, stress concentration (caused by screen movement), and highly worked microstructure at the wire crossovers led to the fatigue failure of the screens.

Thermal-mechanical fatigue behavior of nickel-base superalloys

NASA Technical Reports Server (NTRS)

Pelloux, R. M.; Marchand, N.

1986-01-01

The main achievements of a 36-month research program are presented. The main objective was to gain more insight into the problem of crack growth under thermal mechanical fatigue (TMF) conditions. This program was conducted at M.I.T. for the period of September 1982 to September 1985. The program was arranged into five technical tasks. Under Task I, the literature of TMF data was reviewed. The goal was to identify the crack propagation conditions in aircraft engines (hot section) and to assess the validity of conventional fracture mechanics parameters to address TMF crack growth. The second task defined the test facilities, test specimen and the testing conditions needed to establish the effectiveness of data correlation parameters identified in Task I. Three materials (Inconel X-750, Hastelloy-X, and B-1900) were chosen for the program. Task II was accomplished in collaboration with Pratt & Whitney Aircraft engineers. Under Task III, a computerized testing system to measure the TMF behavior (LCF and CG behaviors) of various alloys systems was built. The software used to run isothermal and TMF tests was also developed. Built around a conventional servohydraulic machine, the system is capable of push-pull tests under stress or strain and temperature controlled conditions in the temperature range of 25C to 1050C. A crack propagation test program was defined and conducted under Task IV. The test variables included strain range, strain rate (frequency) and temperature. Task V correlated and generalized the Task IV data for isothermal and variable temperature conditions so that several crack propagation parameters could be compared and evaluated. The structural damage (mode of cracking and dislocation substructure) under TMF cycling was identified and contrasted with the isothermal damage to achieve a sound fundamental mechanistic understanding of TMF.

Updated Fatigue-Crack-Growth And Fracture-Mechanics Software

NASA Technical Reports Server (NTRS)

Forman, Royce G.; Shivakumar, Venkataraman; Newman, James C., Jr.

1995-01-01

NASA/FLAGRO 2.0 developed as analytical aid in predicting growth and stability of preexisting flaws and cracks in structural components of aerospace systems. Used for fracture-control analysis of space hardware. Organized into three modules to maximize efficiency in operation. Useful in: (1) crack-instability/crack-growth analysis, (2) processing raw crack-growth data from laboratory tests, and (3) boundary-element analysis to determine stresses and stress-intensity factors. Written in FORTRAN 77 and ANSI C.

Crack Branching and Fracture Mirror Data of Glasses and Advanced Ceramics

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

1998-01-01

The fracture mirror and crack branching constants were determined from three glasses and nine advanced ceramics tested under various loading and specimen configurations in an attempt to use the constants as a data base for fractography. The ratios of fracture mirror or crack branching constant to fracture toughness were found to be approximately two for most ceramic materials tested. A demonstration of how to use the two constants as a tool for verifying stress measurements was presented for silicon nitride disk specimens subjected to high-temperature, constant stress-rate biaxial flexure testing.

Fatigue Crack Growth Behavior and Microstructural Mechanisms in Ti-6Al-4V Manufactured by Laser Engineered Net Shaping

DTIC Science & Technology

2015-12-01

hardening heat treatment were the controlling factors of the fatigue resistance, while testing directions have the least impact. Leuders et al. [16...radius. The microstructurally-small fatigue crack growth test was run under load control at constant stress ratio R=0.1 and a cyclic frequency of 20 Hz...not been thoroughly investigated. In this study, long fatigue crack growth tests were conducted at two stress ratios (R=0.1 and 0.8), using Ti-6Al

Development of Carbon Nanotube-Based Sensor to Monitor Crack Growth in Cracked Aluminum Structures Underneath Composite Patching

DTIC Science & Technology

2014-06-01

layer of epoxy and ensure crack is filled in. Let sit for at least 1 hour, but no longer than 3 hours. (Do not allow base layer to harden before...10 mmHg and hold for 8 hours. • Once hardened remove excess epoxy and test sample. C. TENSILE TESTING For the purpose of this study, total fracture...hardened remove excess epoxy and test sample. 2. Final Changes Changes were made from this initial sample preparation to the final one shown in the

Detection and Location of Transverse Matrix Cracks in Cross-Ply Gr/Ep Composites Using Acoustic Emission

NASA Technical Reports Server (NTRS)

Prosser, W. H.; Jackson, K. E.; Kellas, S.; Smith, B. T.; McKeon, J.; Friedman, A.

1995-01-01

Transverse matrix cracking in cross-ply gr/ep laminates was studied with advanced acoustic emission (AE) techniques. The primary goal of this research was to measure the load required to initiate the first transverse matrix crack in cross-ply laminates of different thicknesses. Other methods had been previously used for these measurements including penetrant enhanced radiography, optical microscopy, and audible acoustic microphone measurements. The former methods required that the mechanical test be paused for measurements at load intervals. This slowed the test procedure and did not provide the required resolution in load. With acoustic microphones, acoustic signals from cracks could not be clearly differentiated from other noise sources such as grip damage, specimen slippage, or test machine noise. A second goal for this work was to use the high resolution source location accuracy of the advanced acoustic emission techniques to determine whether the crack initiation site was at the specimen edge or in the interior of the specimen.In this research, advanced AE techniques using broad band sensors, high capture rate digital waveform acquisition, and plate wave propagation based analysis were applied to cross-ply composite coupons with different numbers of 0 and 90 degree plies. Noise signals, believed to be caused by grip damage or specimen slipping, were eliminated based on their plate wave characteristics. Such signals were always located outside the sensor gage length in the gripped region of the specimen. Cracks were confirmed post-test by microscopic analysis of a polished specimen edge, backscatter ultrasonic scans, and in limited cases, by penetrant enhanced radiography. For specimens with three or more 90 degree plies together, there was an exact 1-1 correlation between AE crack signals and observed cracks. The ultrasonic scans and some destructive sectioning analysis showed that the cracks extended across the full width of the specimen. Furthermore, the locations of the cracks from the AE data were in excellent agreement with the locations measured with the microscope. The high resolution source location capability of this technique, combined with an array of sensors, was able to determine that the cracks initiated at the specimen edges, rather than in the interior. For specimens with only one or two 90 degree plies, the crack-like signals were significantly smaller in amplitude and there was not a 1-1 correlation to observed cracks. This was similar to previous results. In this case, however, ultrasonic and destructive sectioning analysis revealed that the cracks did not extend across the specimen. They initiated at the edge, but did not propagate any appreciable distance into the specimen. This explains the much smaller AE signal amplitudes and the difficulty in correlating these signals to actual cracks in this, as well as in the previous study.

Small-scale martian polygonal terrain: Implications for liquid surface water

USGS Publications Warehouse

Seibert, N.M.; Kargel, J.S.

2001-01-01

Images from the Mars Orbiter Camera (MOC) through August 1999 were analyzed for the global distribution of small-scale polygonal terrain not clearly resolved in Viking Orbiter imagery. With very few exceptions, small-scale polygonal terrain occurs at middle to high latitudes of the northern and southern hemisphere in Hesperian-age geologic units. The largest concentration of this terrain occurs in the Utopia basin in close association with scalloped depressions (interpreted as thermokarst) and appears to represent an Amazonia event. The morphology and occurence of small polygonal terrain suggest they are either mud desiccation cracks or ice-wedge polygons. Because the small-scale polygons in Utopia and Argyre Planitiae are associated with other cold-climate permafrost or glacial features, an ice-wedge model is preferred for these areas. Both cracking mechanisms work most effectively in water- or ice-rich finegrained material and may imply the seasonal or episodic existence of liquid water at the surface.

[Moisture and mold on the inner walls of prefabricated building slabs--investigating a strange cause].

PubMed

Kaufhold, T; Fiedler, K; Jung, G; Lindner, M; Gassel, R P

1997-04-01

Reasons for indoor-moisture beyond the normal level can be caused by penetrating dampness, condensation-water, and apartment misuse. A fall in the air temperature below the dew point in connection with moulding inside buildings becomes evident mostly at places like badly insulated outer-walls or room-corners. In a number of houses built between 1980 and 1983 in the so called "Plattenbauweise" (prefabricated slabs), exclusively the inner-walls were covered in mould around cracks in the walls. Examinations showed connections between the apartment and the outer-corridor with a slight exchange of air through the cracks. Warm, wet air escaped from the apartment into the outer-corridor, and cold air entered the apartment from the outer-corridor. This temporary fall below the dewpoint caused by suitable variation of temperature probably resulted in the building materials and wallpapers becoming damp, as well as the growth of mould.

Stress corrosion resistant fasteners

NASA Technical Reports Server (NTRS)

Roach, T. A.

1985-01-01

A family of high performance aerospace fasteners made from corrosion resistant alloys for use in applications where corrosion and stress-corrosion cracking are of major concern are discussed. The materials discussed are mainly A-286, Inconel 718, MP35N and MP159. Most of the fasteners utilize cold worked and aged materials to achieve the desired properties. The fasteners are unique in that they provide a combination of high strength and immunity to stress corrosion cracking not previously attainable. A discussion of fastener stress corrosion failures is presented including a review of the history and a description of the mechanism. Case histories are presented to illustrate the problems which can arise when material selection is made without proper regard for the environmental conditions. Mechanical properties and chemical compositions are included for the fasteners discussed. Several aspects of the application of high performance corrosion resistant fasteners are discussed including galvanic compatibility and torque-tension relationships.

Measurement and interpretation of threshold stress intensity factors for steels in high-pressure hydrogen gas.

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

Dadfarnia, Mohsen; Nibur, Kevin A.; San Marchi, Christopher W.

2010-07-01

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K{sub THi}* is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; K{sub THa} ismore » the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K{sub JH} is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K{sub THi}*, and the crack arrest threshold, K{sub THa}, were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustained-load cracking tests under constant displacement. In contrast, K{sub JH}, which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that is relevant to structural components in which sub-critical crack extension is driven by internal hydrogen gas pressure.« less

Measurement and interpretation of threshold stress intensity factors for steels in high-pressure hydrogen gas.

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

Nibur, Kevin A.

2010-11-01

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K{sub THi}* is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; K{sub THa} ismore » the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K{sub JH} is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K{sub THi}*, and the crack arrest threshold, K{sub THa}, were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustained-load cracking tests under constant displacement. In contrast, K{sub JH}, which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that is relevant to structural components in which sub-critical crack extension is driven by internal hydrogen gas pressure.« less

Effect of initial contact surface condition on the friction and wear properties of bearing steel in cyclic reciprocating sliding contact

NASA Astrophysics Data System (ADS)

Tanaka, Y.; Endo, M.; Moriyama, S.

2017-05-01

Delamination failure is one of the most important engineering problems. This failure can frequently be detrimental to rolling contact machine elements such as bearings, gear wheels, etc. This phenomenon, called rolling contact fatigue, has a close relationship not only with opening-mode but also with shear-mode fatigue crack growth. The crack face interference is known to significantly affect the shear-mode fatigue crack propagation and its threshold behavior. Quantitative investigation on friction and wear at fatigue crack faces in the material is essentially impossible. Previously, thus, a novel ring-on-ring test by making use of fatigue testing machine was proposed to simulate a cyclic reciprocating sliding contact of crack surfaces. However, this test procedure had some problems. For instance, in order to achieve the uniform contact at the start of test, the rubbing of specimens must be conducted in advance. By this treatment, the specimen surfaces were already damaged before the test. In this study, an improvement of experimental method was made to perform the test using the damage-free specimens. The friction and wear properties for heat-treated high carbon-chromium bearing steel were investigated with this new method and the results were compared to the results obtained by using the initially damaged specimens.

Sensing sheets based on large area electronics for fatigue crack detection

NASA Astrophysics Data System (ADS)

Yao, Yao; Glisic, Branko

2015-03-01

Reliable early-stage damage detection requires continuous structural health monitoring (SHM) over large areas of structure, and with high spatial resolution of sensors. This paper presents the development stage of prototype strain sensing sheets based on Large Area Electronics (LAE), in which thin-film strain gauges and control circuits are integrated on the flexible electronics and deposited on a polyimide sheet that can cover large areas. These sensing sheets were applied for fatigue crack detection on small-scale steel plates. Two types of sensing-sheet interconnects were designed and manufactured, and dense arrays of strain gauge sensors were assembled onto the interconnects. In total, four (two for each design type) strain sensing sheets were created and tested, which were sensitive to strain at virtually every point over the whole sensing sheet area. The sensing sheets were bonded to small-scale steel plates, which had a notch on the boundary so that fatigue cracks could be generated under cyclic loading. The fatigue tests were carried out at the Carleton Laboratory of Columbia University, and the steel plates were attached through a fixture to the loading machine that applied cyclic fatigue load. Fatigue cracks then occurred and propagated across the steel plates, leading to the failure of these test samples. The strain sensor that was close to the notch successfully detected the initialization of fatigue crack and localized the damage on the plate. The strain sensor that was away from the crack successfully detected the propagation of fatigue crack based on the time history of measured strain. Overall, the results of the fatigue tests validated general principles of the strain sensing sheets for crack detection.

Micro-indentation fracture behavior of human enamel.

PubMed

Padmanabhan, Sanosh Kunjalukkal; Balakrishnan, Avinash; Chu, Min-Cheol; Kim, Taik Nam; Cho, Seong Jai

2010-01-01

The purpose of this study was to determine the crack resistance behavior (K(R)) of human enamel in relation to its microstructure. Human molar teeth were precision cut, polished and tested using Vickers micro-indentation at different loads ranging from 0.98 to 9.8 N. Five indentation load levels were considered, 20 indentation cracks for each load level were introduced on the surface of the test specimen (10 indentations per tooth) and their variability was evaluated using Weibull statistics and an empirical model. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the crack morphology and propagation mechanisms involved. The results showed that enamel exhibited increasing cracking resistance (K(R)) with increasing load. It was found that the crack propagation mainly depended on the location and the microstructure it encountered. SEM showed the formation of crack bridges and crack deflection near the indentation crack tip. The crack mode was of Palmqvist type even at larger loads of 9.8 N. This was mainly attributed to the large process zone created by the interwoven lamellar rod like microstructure exhibited by the enamel surface. This study shows that there are still considerable prospects for improving dental ceramics and for mimicking the enamel structure developed by nature.

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 and fracture assessment of cracks in steel elements using acoustic emission

NASA Astrophysics Data System (ADS)

Nemati, Navid; Metrovich, Brian; Nanni, Antonio

2011-04-01

Single edge notches provide a very well defined load and fatigue crack size and shape environment for estimation of the stress intensity factor K, which is not found in welded elements. ASTM SE(T) specimens do not appear to provide ideal boundary conditions for proper recording of acoustic wave propagation and crack growth behavior observed in steel bridges, but do provide standard fatigue crack growth rate data. A modified versions of the SE(T) specimen has been examined to provide small scale specimens with improved acoustic emission(AE) characteristics while still maintaining accuracy of fatigue crack growth rate (da/dN) versus stress intensity factor (ΔK). The specimens intend to represent a steel beam flange subjected to pure tension, with a surface crack growing transverse to a uniform stress field. Fatigue test is conducted at low R ratio. Analytical and numerical studies of stress intensity factor are developed for single edge notch test specimens consistent with the experimental program. ABAQUS finite element software is utilized for stress analysis of crack tips. Analytical, experimental and numerical analysis were compared to assess the abilities of AE to capture a growing crack.

Characterization of cracking behavior using posttest fractographic analysis

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

Kobayashi, T.; Shockey, D.A.

A determination of time to initiation of stress corrosion cracking in structures and test specimens is important for performing structural failure analysis and for setting inspection intervals. Yet it is seldom possible to establish how much of a component's lifetime represents the time to initiation of fracture and how much represents postinitiation crack growth. This exploratory research project was undertaken to examine the feasibility of determining crack initiation times and crack growth rates from posttest examination of fracture surfaces of constant-extension-rate-test (CERT) specimens by using the fracture reconstruction applying surface topography analysis (FRASTA) technique. The specimens used in this studymore » were Type 304 stainless steel fractured in several boiling water reactor (BWR) aqueous environments. 2 refs., 25 figs., 2 tabs.« less

Socio-demographic Characteristics of Individuals with History of Crack Cocaine Use in the US General Population.

PubMed

Yur'yev, Andriy; Akerele, Evaristo

2016-11-01

This study explores socio-demographic characteristics of individuals with history of crack cocaine use. Data from the 29th Round of General Social Survey was used. Respondents with history of crack cocaine use were compared to respondents without such history. T test was applied to identify differences between groups. Approximately 6 % of respondents reported lifetime history of crack cocaine use. Groups with and without history of crack cocaine use differed significantly in gender, marital status, education, income distribution, employment, health perception, family and financial satisfaction, criminal history, happiness, sexual history, history of injection drug use, and HIV testing. There were no significant differences for race. The study provides insights that could improve identification and prevention of substance use disorders.

A test procedure for determining the influence of stress ratio on fatigue crack growth

NASA Technical Reports Server (NTRS)

Fitzgerald, J. H.; Wei, R. P.

1974-01-01

A test procedure is outlined by which the rate of fatigue crack growth over a range of stress ratios and stress intensities can be determined expeditiously using a small number of specimens. This procedure was developed to avoid or circumvent the effects of load interactions on fatigue crack growth, and was used to develop data on a mill annealed Ti-6Al-4V alloy plate. Experimental data suggest that the rates of fatigue crack growth among the various stress ratios may be correlated in terms of an effective stress intensity range at given values of K max. This procedure is not to be used, however, for determining the corrosion fatigue crack growth characteristics of alloys when nonsteady-state effects are significant.