On the Use of Equivalent Linearization for High-Cycle Fatigue Analysis of Geometrically Nonlinear Structures

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A.

2003-01-01

The use of stress predictions from equivalent linearization analyses in the computation of high-cycle fatigue life is examined. Stresses so obtained differ in behavior from the fully nonlinear analysis in both spectral shape and amplitude. Consequently, fatigue life predictions made using this data will be affected. Comparisons of fatigue life predictions based upon the stress response obtained from equivalent linear and numerical simulation analyses are made to determine the range over which the equivalent linear analysis is applicable.

Fatigue-Crack-Growth Structural Analysis

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1986-01-01

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

Structural fatigue in the 34-meter HA-Dec antennas

NASA Technical Reports Server (NTRS)

Vanhek, R. A.; Saldua, B. P.

1990-01-01

Structural modifications to the 34-m hour-angle-declination antennas, coupled with the use of the antennas beyond their intended lifespans, have led to structural fatigue, as evidenced by damage to the declination drive gear and cracks on the structural members and gussets. An analysis and simulation were made of the main antenna structural members. The analysis showed that the total stress to the antenna structure substantially exceeds the maximum levels recommended by the American Institute of Steel Construction (AISC). Although each of the separate static conditions of stress is only 50 percent of the total stress and does not reach the AISC reduced yield limit, fatigue can and did occur, causing the material to crack in the weakest places.

A computer program for cyclic plasticity and structural fatigue analysis

NASA Technical Reports Server (NTRS)

Kalev, I.

1980-01-01

A computerized tool for the analysis of time independent cyclic plasticity structural response, life to crack initiation prediction, and crack growth rate prediction for metallic materials is described. Three analytical items are combined: the finite element method with its associated numerical techniques for idealization of the structural component, cyclic plasticity models for idealization of the material behavior, and damage accumulation criteria for the fatigue failure.

Study on Wind-induced Vibration and Fatigue Life of Cable-stayed Flexible Antenna

NASA Astrophysics Data System (ADS)

He, Kongde; He, Xuehui; Fang, Zifan; Zheng, Xiaowei; Yu, Hongchang

2018-03-01

The cable-stayed flexible antenna is a large-span space structure composed of flexible multibody, with low frequency of vibration, vortex-induced resonance can occur under the action of Stochastic wind, and a larger amplitude is generated when resonance occurs. To solve this problem, based on the theory of vortex-induced vibration, this paper analyzes the vortex-induced vibration of a cable-stayed flexible antenna under the action of Wind. Based on the sinusoidal force model and Autoregressive Model (AR) method, the vortex-induced force is simulated, then the fatigue analysis of the structure is based on the linear fatigue cumulative damage principle and the rain-flow method. The minimum fatigue life of the structure is calculated to verify the vibration fatigue performance of the structure.

Structure-phase states evolution in Al-Si alloy under electron-beam treatment and high-cycle fatigue

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

Konovalov, Sergey, E-mail: konovserg@gmail.com; Alsaraeva, Krestina, E-mail: gromov@physics.sibsiu.ru; Gromov, Victor, E-mail: gromov@physics.sibsiu.ru

By methods of scanning and transmission electron diffraction microscopy the analysis of structure-phase states and defect substructure of silumin subjected to high-intensity electron beam irradiation in various regimes and subsequent fatigue loading up to failure was carried out. It is revealed that the sources of fatigue microcracks are silicon plates of micron and submicron size are not soluble in electron beam processing. The possible reasons of the silumin fatigue life increase under electron-beam treatment are discussed.

Fatigue Behavior of a Box-Type Welded Structure of Hydraulic Support Used in Coal Mine

PubMed Central

Zhao, Xiaohui; Li, Fuyong; Liu, Yu; Fan, Yanjun

2015-01-01

Hydraulic support is the main supporting equipment of the coal mining systems, and they are usually subjected to fatigue failure under the high dynamic load. The fracture positions are generally at welded joints where there is a serious stress concentration. In order to investigate and further improve the fatigue strength of hydraulic support, the present work first located the possible position where fatigue failure occurs through finite element analysis, and then fatigue tests were carried out on the different forms of welded joints for the dangerous parts. Finally, Fatigue strength-life (S-N) curves and fracture mechanism were studied. This research will provide a theoretical reference for the fatigue design of welded structures for hydraulic support. PMID:28793586

Fatigue methodology III; Proceedings of the AHS National Technical Specialists' Meeting on Advanced Rotorcraft Structures, Scottsdale, AZ, Oct. 3-5, 1989

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

Not Available

1989-01-01

Papers on rotorcraft and fatigue methodology are presented, covering topics such as reliability design for rotorcraft, a comparison between theory and fatigue test data on stress concentration factors, the retirement lives of rolling element bearings, hydrogen embrittlement risk analysis for high hardness steel parts, and rotating system load monitoring with minimum fixed system instrumentation. Additional topics include usage data collection to improve structural integrity of operational helicopters, usage monitory of military helicopters, improvements to the fatigue substantiation of the H-60 composite tail rotor blade, helicopter surviellance programs, and potential application of automotive fatigue technology in rotorcraft design. Also, consideration ismore » given to fatigue evaluation of C/MH-53 E main rotor damper threaded joints, SH-2F airframe fatigue test program, a ply termination concept for improving fracture and fatigue strength of composite laminates, the analysis and testing of composite panels subject to muzzle blast effects, the certification plan for an all-composite main rotor flexbeam, and the effects of stacking sequence on the flexural strength of composite beams.« less

A Micromechanics-Based Method for Multiscale Fatigue Prediction

NASA Astrophysics Data System (ADS)

Moore, John Allan

An estimated 80% of all structural failures are due to mechanical fatigue, often resulting in catastrophic, dangerous and costly failure events. However, an accurate model to predict fatigue remains an elusive goal. One of the major challenges is that fatigue is intrinsically a multiscale process, which is dependent on a structure's geometric design as well as its material's microscale morphology. The following work begins with a microscale study of fatigue nucleation around non- metallic inclusions. Based on this analysis, a novel multiscale method for fatigue predictions is developed. This method simulates macroscale geometries explicitly while concurrently calculating the simplified response of microscale inclusions. Thus, providing adequate detail on multiple scales for accurate fatigue life predictions. The methods herein provide insight into the multiscale nature of fatigue, while also developing a tool to aid in geometric design and material optimization for fatigue critical devices such as biomedical stents and artificial heart valves.

Fatigue analysis of the bow structure of FPSO

NASA Astrophysics Data System (ADS)

Hu, Zhi-Qiang; Gao, Zhen; Gu, Yong-Ning

2003-06-01

The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring forces, which are induced by wave excitation and transferred by the YOKE and the mooring support frame, may cause fatigue damage to the bow structure. Different from direct wave-induced-forces, the mooring force consists of wave frequency force (WF) and 2nd draft low frequency force (LF)[3], which are represented by two sets of short-term distribution respectively. Based on two sets of short-term distribution of mooring forces obtained by the model test, the fatigue damage of the bow structure of FPSO is analyzed, with emphasis on two points. One is the procedure and position selection for fatigue check, and the other is the application of new formulae for the calculation of accumulative fatigue damage caused by two sets of short-term distribution of hot spot stress range. From the results distinguished features of fatigue damage to the FPSO’s bow structure can be observed.

Fatigue-Induced Damage in Zr-Based Bulk Metallic Glasses

PubMed Central

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

2013-01-01

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

Structural Technology Evaluation Analysis Program (STEAP). Task Order 0029: Thermal Stability of Fatigue Life-Enhanced Structures

DTIC Science & Technology

2012-01-01

and c, we were able to obtain Figure 21: Intensity and Pressure Temporal Profiles Calculated from Pressure Model 0 20 40 60 80 100 0 2 4 6 8...August 2008 – 31 January 2012 4 . TITLE AND SUBTITLE STRUCTURAL TECHNOLOGY EVALUATION ANALYSIS PROGRAM (STEAP) Task Order 0029: Thermal...Stability of Fatigue Life-Enhanced Structures 5a. CONTRACT NUMBER FA8650-04-D-3446-0029 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 62201F 6

Behavioral pattern identification for structural health monitoring in complex systems

NASA Astrophysics Data System (ADS)

Gupta, Shalabh

Estimation of structural damage and quantification of structural integrity are critical for safe and reliable operation of human-engineered complex systems, such as electromechanical, thermofluid, and petrochemical systems. Damage due to fatigue crack is one of the most commonly encountered sources of structural degradation in mechanical systems. Early detection of fatigue damage is essential because the resulting structural degradation could potentially cause catastrophic failures, leading to loss of expensive equipment and human life. Therefore, for reliable operation and enhanced availability, it is necessary to develop capabilities for prognosis and estimation of impending failures, such as the onset of wide-spread fatigue crack damage in mechanical structures. This dissertation presents information-based online sensing of fatigue damage using the analytical tools of symbolic time series analysis ( STSA). Anomaly detection using STSA is a pattern recognition method that has been recently developed based upon a fixed-structure, fixed-order Markov chain. The analysis procedure is built upon the principles of Symbolic Dynamics, Information Theory and Statistical Pattern Recognition. The dissertation demonstrates real-time fatigue damage monitoring based on time series data of ultrasonic signals. Statistical pattern changes are measured using STSA to monitor the evolution of fatigue damage. Real-time anomaly detection is presented as a solution to the forward (analysis) problem and the inverse (synthesis) problem. (1) the forward problem - The primary objective of the forward problem is identification of the statistical changes in the time series data of ultrasonic signals due to gradual evolution of fatigue damage. (2) the inverse problem - The objective of the inverse problem is to infer the anomalies from the observed time series data in real time based on the statistical information generated during the forward problem. A computer-controlled special-purpose fatigue test apparatus, equipped with multiple sensing devices (e.g., ultrasonics and optical microscope) for damage analysis, has been used to experimentally validate the STSA method for early detection of anomalous behavior. The sensor information is integrated with a software module consisting of the STSA algorithm for real-time monitoring of fatigue damage. Experiments have been conducted under different loading conditions on specimens constructed from the ductile aluminium alloy 7075 - T6. The dissertation has also investigated the application of the STSA method for early detection of anomalies in other engineering disciplines. Two primary applications include combustion instability in a generic thermal pulse combustor model and whirling phenomenon in a typical misaligned shaft.

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.

Design for cyclic loading endurance of composites

NASA Technical Reports Server (NTRS)

Shiao, Michael C.; Murthy, Pappu L. N.; Chamis, Christos C.; Liaw, Leslie D. G.

1993-01-01

The application of the computer code IPACS (Integrated Probabilistic Assessment of Composite Structures) to aircraft wing type structures is described. The code performs a complete probabilistic analysis for composites taking into account the uncertainties in geometry, boundary conditions, material properties, laminate lay-ups, and loads. Results of the analysis are presented in terms of cumulative distribution functions (CDF) and probability density function (PDF) of the fatigue life of a wing type composite structure under different hygrothermal environments subjected to the random pressure. The sensitivity of the fatigue life to a number of critical structural/material variables is also computed from the analysis.

Fatigue assessment of an existing steel bridge by finite element modelling and field measurements

NASA Astrophysics Data System (ADS)

Kwad, J.; Alencar, G.; Correia, J.; Jesus, A.; Calçada, R.; Kripakaran, P.

2017-05-01

The evaluation of fatigue life of structural details in metallic bridges is a major challenge for bridge engineers. A reliable and cost-effective approach is essential to ensure appropriate maintenance and management of these structures. Typically, local stresses predicted by a finite element model of the bridge are employed to assess the fatigue life of fatigue-prone details. This paper illustrates an approach for fatigue assessment based on measured data for a connection in an old bascule steel bridge located in Exeter (UK). A finite element model is first developed from the design information. The finite element model of the bridge is calibrated using measured responses from an ambient vibration test. The stress time histories are calculated through dynamic analysis of the updated finite element model. Stress cycles are computed through the rainflow counting algorithm, and the fatigue prone details are evaluated using the standard SN curves approach and the Miner’s rule. Results show that the proposed approach can estimate the fatigue damage of a fatigue prone detail in a structure using measured strain data.

Probabilistic fatigue life prediction of metallic and composite materials

NASA Astrophysics Data System (ADS)

Xiang, Yibing

Fatigue is one of the most common failure modes for engineering structures, such as aircrafts, rotorcrafts and aviation transports. Both metallic materials and composite materials are widely used and affected by fatigue damage. Huge uncertainties arise from material properties, measurement noise, imperfect models, future anticipated loads and environmental conditions. These uncertainties are critical issues for accurate remaining useful life (RUL) prediction for engineering structures in service. Probabilistic fatigue prognosis considering various uncertainties is of great importance for structural safety. The objective of this study is to develop probabilistic fatigue life prediction models for metallic materials and composite materials. A fatigue model based on crack growth analysis and equivalent initial flaw size concept is proposed for metallic materials. Following this, the developed model is extended to include structural geometry effects (notch effect), environmental effects (corroded specimens) and manufacturing effects (shot peening effects). Due to the inhomogeneity and anisotropy, the fatigue model suitable for metallic materials cannot be directly applied to composite materials. A composite fatigue model life prediction is proposed based on a mixed-mode delamination growth model and a stiffness degradation law. After the development of deterministic fatigue models of metallic and composite materials, a general probabilistic life prediction methodology is developed. The proposed methodology combines an efficient Inverse First-Order Reliability Method (IFORM) for the uncertainty propogation in fatigue life prediction. An equivalent stresstransformation has been developed to enhance the computational efficiency under realistic random amplitude loading. A systematical reliability-based maintenance optimization framework is proposed for fatigue risk management and mitigation of engineering structures.

Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations

NASA Technical Reports Server (NTRS)

Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin; Minguet, Pierre J.

2001-01-01

A methodology is presented for determining the fatigue life of composite structures based on fatigue characterization data and geometric nonlinear finite element (FE) analyses. To demonstrate the approach, predicted results were compared to fatigue tests performed on specimens which represented a tapered composite flange bonded onto a composite skin. In a first step, tension tests were performed to evaluate the debonding mechanisms between the flange and the skin. In a second step, a 2D FE model was developed to analyze the tests. To predict matrix cracking onset, the relationship between the tension load and the maximum principal stresses transverse to the fiber direction was determined through FE analysis. Transverse tension fatigue life data were used to -enerate an onset fatigue life P-N curve for matrix cracking. The resulting prediction was in good agreement with data from the fatigue tests. In a third step, a fracture mechanics approach based on FE analysis was used to determine the relationship between the tension load and the critical energy release rate. Mixed mode energy release rate fatigue life data were used to create a fatigue life onset G-N curve for delamination. The resulting prediction was in good agreement with data from the fatigue tests. Further, the prediction curve for cumulative life to failure was generated from the previous onset fatigue life curves. The results showed that the methodology offers a significant potential to Predict cumulative fatigue life of composite structures.

Double Linear Damage Rule for Fatigue Analysis

NASA Technical Reports Server (NTRS)

Halford, G.; Manson, S.

1985-01-01

Double Linear Damage Rule (DLDR) method for use by structural designers to determine fatigue-crack-initiation life when structure subjected to unsteady, variable-amplitude cyclic loadings. Method calculates in advance of service how many loading cycles imposed on structural component before macroscopic crack initiates. Approach eventually used in design of high performance systems and incorporated into design handbooks and codes.

Fatigue and fail-safe design features of the DC-10 airplane

NASA Technical Reports Server (NTRS)

Stone, M. E.

1972-01-01

The philosophy and methods used in the design of the DC-10 aircraft to assure structural reliability against cracks under repeated service loads are described in detail. The approach consists of three complementary parts: (1) the structure is designed to be fatigue resistant for a crack-free life of 60,000 flight hours; (2) inasmuch as small undetected cracks could develop from other sources, such as material flaws and manufacturing preloads, the structure also is designed to arrest and control cracks within a reasonable service-inspection interval; and (3) a meaningful service-inspection program has been defined on the basis of analysis and test experience from the design development program. This service-inspection program closes the loop to assure the structural integrity of the DC-10 airframe. Selected materials, fasteners, and structural arrangements are used to achieve these design features with minimum structural weight and with economy in manufacturing and maintenance. Extensive analyses and testing were performed to develop and verify the design. The basic design considerations for fatigue-resistant structure are illustrated in terms of material selection, design loads spectra, methods for accurate stress and fatigue damage analysis, and proven concepts for efficient detail design.

Analysis of fatigue, fatique-crack propagation, and fracture data. [design of metallic aerospace structural components

NASA Technical Reports Server (NTRS)

Jaske, C. E.; Feddersen, C. E.; Davies, K. B.; Rice, R. C.

1973-01-01

Analytical methods have been developed for consolidation of fatigue, fatigue-crack propagation, and fracture data for use in design of metallic aerospace structural components. To evaluate these methods, a comprehensive file of data on 2024 and 7075 aluminums, Ti-6A1-4V, and 300M and D6Ac steels was established. Data were obtained from both published literature and unpublished reports furnished by aerospace companies. Fatigue and fatigue-crack-propagation analyses were restricted to information obtained from constant-amplitude load or strain cycling of specimens in air at room temperature. Fracture toughness data were from tests of center-cracked tension panels, part-through crack specimens, and compact-tension specimens.

Comparison of fatigue analysis approaches for hot-mix asphalt to ensure a state of good repair.

DOT National Transportation Integrated Search

2013-10-01

Fatigue cracking is a primary form of distress in hot-mix asphalt. The long-term nature of fatigue due to repeated : loading and aging and its required tie to pavement structure present challenges in terms of evaluating mixture : resistance. This pro...

Multidimensional Predictors of Fatigue among Octogenarians and Centenarians

PubMed Central

Cho, Jinmyoung; Martin, Peter; Margrett, Jennifer; MacDonald, Maurice; Johnson, Mary Ann; Poon, Leonard W.

2012-01-01

Background Fatigue is a common and frequently observed complaint among older adults. However, knowledge about the nature and correlates of fatigue in old age is very limited. Objective: This study examined the relationship of functional indicators, psychological and situational factors and fatigue for 210 octogenarians and centenarians from the Georgia Centenarian Study. Methods Three indicators of functional capacity (self-rated health, instrumental activities of daily living, physical activities of daily living), two indicators of psychological well-being (positive and negative affect), two indicators of situational factors (social network and social support), and a multidimensional fatigue scale were used. Blocked multiple regression analyses were computed to examine significant factors related to fatigue. In addition, multi-group analysis in structural equation modeling was used to investigate residential differences (i.e., long-term care facilities vs. private homes) in the relationship between significant factors and fatigue. Results Blocked multiple regression analyses indicated that two indicators of functional capacity, self-rated health and instrumental activities of daily living, both positive and negative affect, and social support were significant predictors of fatigue among oldest-old adults. The multiple group analysis in structural equation modeling revealed a significant difference among oldest-old adults based on residential status. Conclusion The results suggest that we should not consider fatigue as merely an unpleasant physical symptom, but rather adopt a perspective that different factors such as psychosocial aspects can influence fatigue in advanced later life. PMID:22094445

Multidimensional predictors of fatigue among octogenarians and centenarians.

PubMed

Cho, Jinmyoung; Martin, Peter; Margrett, Jennifer; MacDonald, Maurice; Johnson, Mary Ann; Poon, Leonard W; Jazwinski, S M; Green, R C; Gearing, M; Woodard, J L; Tenover, J S; Siegler, I C; Rott, C; Rodgers, W L; Hausman, D; Arnold, J; Davey, A

2012-01-01

Fatigue is a common and frequently observed complaint among older adults. However, knowledge about the nature and correlates of fatigue in old age is very limited. This study examined the relationship of functional indicators, psychological and situational factors and fatigue for 210 octogenarians and centenarians from the Georgia Centenarian Study. Three indicators of functional capacity (self-rated health, instrumental activities of daily living, physical activities of daily living), two indicators of psychological well-being (positive and negative affect), two indicators of situational factors (social network and social support), and a multidimensional fatigue scale were used. Blocked multiple regression analyses were computed to examine significant factors related to fatigue. In addition, multi-group analysis in structural equation modeling was used to investigate residential differences (i.e., long-term care facilities vs. private homes) in the relationship between significant factors and fatigue. Blocked multiple regression analyses indicated that two indicators of functional capacity, self-rated health and instrumental activities of daily living, both positive and negative affect, and social support were significant predictors of fatigue among oldest-old adults. The multiple group analysis in structural equation modeling revealed a significant difference among oldest-old adults based on residential status. The results suggest that we should not consider fatigue as merely an unpleasant physical symptom, but rather adopt a perspective that different factors such as psychosocial aspects can influence fatigue in advanced later life. Copyright © 2011 S. Karger AG, Basel.

Micromechanics Fatigue Damage Analysis Modeling for Fabric Reinforced Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Min, J. B.; Xue, D.; Shi, Y.

2013-01-01

A micromechanics analysis modeling method was developed to analyze the damage progression and fatigue failure of fabric reinforced composite structures, especially for the brittle ceramic matrix material composites. A repeating unit cell concept of fabric reinforced composites was used to represent the global composite structure. The thermal and mechanical properties of the repeating unit cell were considered as the same as those of the global composite structure. The three-phase micromechanics, the shear-lag, and the continuum fracture mechanics models were integrated with a statistical model in the repeating unit cell to predict the progressive damages and fatigue life of the composite structures. The global structure failure was defined as the loss of loading capability of the repeating unit cell, which depends on the stiffness reduction due to material slice failures and nonlinear material properties in the repeating unit cell. The present methodology is demonstrated with the analysis results evaluated through the experimental test performed with carbon fiber reinforced silicon carbide matrix plain weave composite specimens.

The assessment of fatigue: Psychometric qualities and norms for the Checklist individual strength.

PubMed

Worm-Smeitink, M; Gielissen, M; Bloot, L; van Laarhoven, H W M; van Engelen, B G M; van Riel, P; Bleijenberg, G; Nikolaus, S; Knoop, H

2017-07-01

The Checklist Individual Strength (CIS) measures four dimensions of fatigue: Fatigue severity, concentration problems, reduced motivation and activity. On the fatigue severity subscale, a cut-off score of 35 is used. This study 1) investigated the psychometric qualities of the CIS; 2) validated the cut-off score for severe fatigue and 3) provided norms. Representatives of the Dutch general population (n=2288) completed the CIS. The factor structure was investigated using an exploratory factor analysis. Internal consistency and test-retest reliability were determined. Concurrent validity was assessed in two additional samples by correlating the CIS with other fatigue scales (Chalder Fatigue Questionnaire, MOS Short form-36 Vitality subscale, EORTC QLQ-C30 fatigue subscale). To validate the fatigue severity cut-off score, a Receiver Operating Characteristics analysis was performed with patients referred to a chronic fatigue treatment centre (n=5243) and a healthy group (n=1906). Norm scores for CIS subscales were calculated for the general population, patients with chronic fatigue syndrome (CFS; n=1407) and eight groups with other medical conditions (n=1411). The original four-factor structure of the CIS was replicated. Internal consistency (α=0.84-0.95) and test-retest reliability (r=0.74-0.86) of the subscales were high. Correlations with other fatigue scales were moderate to high. The 35 points cut-off score for severe fatigue is appropriate, but, given the 17% false positive rate, should be adjusted to 40 for research in CFS. The CIS is a valid and reliable tool for the assessment of fatigue, with a validated cut-off score for severe fatigue that can be used in clinical practice. Copyright © 2017. Published by Elsevier Inc.

Microtexture Analysis and Modeling of Ambient Fatigue and Creep-Fatigue Damages in Ti-6Al-4V Alloy

NASA Astrophysics Data System (ADS)

Kumar, Jalaj; Singh, A. K.; Raman, S. Ganesh Sundara; Kumar, Vikas

2017-02-01

In the present investigation, microtexture analysis using electron back-scattered diffraction technique has been performed to study fatigue- and creep-fatigue damages and associated deformation structures in Ti-6Al-4V alloy. Special emphasis has been given to low-angle grain boundary configuration and its possible application as a damage indicator. Damage is mostly present in the form of voids as investigated through scanning electron microscopy. Stored deformation energies have been evaluated for the strain-controlled fatigue-, the stress-controlled fatigue-, and the creep-fatigue-tested samples. Stored deformation energies have also been analyzed vis-à-vis total damage energies to quantify the contribution of damages to various samples. A relation between the stored deformation energy and the applied strain amplitude has been proposed in this study.

Computer program to assess impact of fatigue and fracture criteria on weight and cost of transport aircraft

NASA Technical Reports Server (NTRS)

Tanner, C. J.; Kruse, G. S.; Oman, B. H.

1975-01-01

A preliminary design analysis tool for rapidly performing trade-off studies involving fatigue, fracture, static strength, weight, and cost is presented. Analysis subprograms were developed for fatigue life, crack growth life, and residual strength; and linked to a structural synthesis module which in turn was integrated into a computer program. The part definition module of a cost and weight analysis program was expanded to be compatible with the upgraded structural synthesis capability. The resultant vehicle design and evaluation program is named VDEP-2. It is an accurate and useful tool for estimating purposes at the preliminary design stage of airframe development. A sample case along with an explanation of program applications and input preparation is presented.

Fatigue of LiNi0.8Co0.15Al0.05O2 in commercial Li ion batteries

NASA Astrophysics Data System (ADS)

Kleiner, Karin; Dixon, Ditty; Jakes, Peter; Melke, Julia; Yavuz, Murat; Roth, Christina; Nikolowski, Kristian; Liebau, Verena; Ehrenberg, Helmut

2015-01-01

The degradation of LiNi0.8Co0.15Al0.05O2 (LNCAO), a cathode material in lithium-ion-batteries, was studied using in situ powder diffraction and in situ Ni K edge X-ray absorption spectroscopy (XAS). The fatigued material was taken from a 7 Ah battery which was cycled for 34 weeks under defined durability conditions. Meanwhile, a cell was stored, as reference, under controlled conditions without electrochemical treatment. The fatigued LNCAO used in this study showed a capacity loss of 26% ± 9% compared to the non-cycled material. During charge and discharge the local and the overall structure of LNCAO was investigated by X-ray near edge structure (XANES) analysis, the extended X-ray absorption fine structure (EXAFS) analysis and by using Rietveld refinement of in situ powder diffraction patterns. Both powder diffraction and XAS revealed additional, rhombohedral phases which do not change with electrochemical cycling. Moreover, a phase with the lattice parameters of fully lithiated LNCAO was still present in the fatigued material at high potentials, while it was absent in the non-fatigued reference material. The coexistence of these phases is described by domains within the LNCAO particles, in correlation with the observed fatigue.

Fatigue criterion to system design, life and reliability

NASA Technical Reports Server (NTRS)

Zaretsky, E. V.

1985-01-01

A generalized methodology to structural life prediction, design, and reliability based upon a fatigue criterion is advanced. The life prediction methodology is based in part on work of W. Weibull and G. Lundberg and A. Palmgren. The approach incorporates the computed life of elemental stress volumes of a complex machine element to predict system life. The results of coupon fatigue testing can be incorporated into the analysis allowing for life prediction and component or structural renewal rates with reasonable statistical certainty.

Fatigue reliability of deck structures subjected to correlated crack growth

NASA Astrophysics Data System (ADS)

Feng, G. Q.; Garbatov, Y.; Guedes Soares, C.

2013-12-01

The objective of this work is to analyse fatigue reliability of deck structures subjected to correlated crack growth. The stress intensity factors of the correlated cracks are obtained by finite element analysis and based on which the geometry correction functions are derived. The Monte Carlo simulations are applied to predict the statistical descriptors of correlated cracks based on the Paris-Erdogan equation. A probabilistic model of crack growth as a function of time is used to analyse the fatigue reliability of deck structures accounting for the crack propagation correlation. A deck structure is modelled as a series system of stiffened panels, where a stiffened panel is regarded as a parallel system composed of plates and are longitudinal. It has been proven that the method developed here can be conveniently applied to perform the fatigue reliability assessment of structures subjected to correlated crack growth.

A Practical Engineering Approach to Predicting Fatigue Crack Growth in Riveted Lap Joints

NASA Technical Reports Server (NTRS)

Harris, Charles E.; Piascik, Robert S.; Newman, James C., Jr.

1999-01-01

An extensive experimental database has been assembled from very detailed teardown examinations of fatigue cracks found in rivet holes of fuselage structural components. Based on this experimental database, a comprehensive analysis methodology was developed to predict the onset of widespread fatigue damage in lap joints of fuselage structure. Several computer codes were developed with specialized capabilities to conduct the various analyses that make up the comprehensive methodology. Over the past several years, the authors have interrogated various aspects of the analysis methods to determine the degree of computational rigor required to produce numerical predictions with acceptable engineering accuracy. This study led to the formulation of a practical engineering approach to predicting fatigue crack growth in riveted lap joints. This paper describes the practical engineering approach and compares predictions with the results from several experimental studies.

A Practical Engineering Approach to Predicting Fatigue Crack Growth in Riveted Lap Joints

NASA Technical Reports Server (NTRS)

Harris, C. E.; Piascik, R. S.; Newman, J. C., Jr.

2000-01-01

An extensive experimental database has been assembled from very detailed teardown examinations of fatigue cracks found in rivet holes of fuselage structural components. Based on this experimental database, a comprehensive analysis methodology was developed to predict the onset of widespread fatigue damage in lap joints of fuselage structure. Several computer codes were developed with specialized capabilities to conduct the various analyses that make up the comprehensive methodology. Over the past several years, the authors have interrogated various aspects of the analysis methods to determine the degree of computational rigor required to produce numerical predictions with acceptable engineering accuracy. This study led to the formulation of a practical engineering approach to predicting fatigue crack growth in riveted lap joints. This paper describes the practical engineering approach and compares predictions with the results from several experimental studies.

Application of Steinberg vibration fatigue model for structural verification of space instruments

NASA Astrophysics Data System (ADS)

García, Andrés; Sorribes-Palmer, Félix; Alonso, Gustavo

2018-01-01

Electronic components in spaceships are subjected to vibration loads during the ascent phase of the launcher. It is important to verify by tests and analysis that all parts can survive in the most severe load cases. The purpose of this paper is to present the methodology and results of the application of the Steinberg's fatigue model to estimate the life of electronic components of the EPT-HET instrument for the Solar Orbiter space mission. A Nastran finite element model (FEM) of the EPT-HET instrument was created and used for the structural analysis. The methodology is based on the use of the FEM of the entire instrument to calculate the relative displacement RDSD and RMS values of the PCBs from random vibration analysis. These values are used to estimate the fatigue life of the most susceptible electronic components with the Steinberg's fatigue damage equation and the Miner's cumulative fatigue index. The estimations are calculated for two different configurations of the instrument and three different inputs in order to support the redesign process. Finally, these analytical results are contrasted with the inspections and the functional tests made after the vibration tests, concluding that this methodology can adequately predict the fatigue damage or survival of the electronic components.

Biomechanical analysis of fatigue-related foot injury mechanisms in athletes and recruits during intensive marching.

PubMed

Gefen, A

2002-05-01

An integrative analysis, comprising radiographic imaging of the foot, plantar pressure measurements, surface electromyography (EMG) and finite element (FE) modelling of the three-dimensional (3D) foot structure, was used to determine the effects of muscular fatigue induced by intensive athletic or military marching on the structural stability of the foot and on its internal stress state during the stance phase. The medial/lateral (M/L) tendency towards instability of the foot structure during marching in fatigue conditions was experimentally characterised by measuring the M/L deviations of the foot-ground centre of pressure (COP) and correlating these data with fatigue of specific lower-limb muscles, as demonstrated by the EMG spectra. The results demonstrated accelerated fatigue of the peroneus longus muscle in marching conditions (treadmill march of 2 km completed by four subjects at an approximately constant velocity of 8 km h-1). Severe fatigue of the peroneus longus is apparently the dominant cause of lack of foot stability, which was manifested by abnormal lateral deviations of the COP during the stance phase. Under these conditions, ankle sprain injuries are likely to occur. The EMG analysis further revealed substantial fatigue of the pre-tibial and triceps surae muscles during intensive marching (averaged decreases of 36% and 40% in the median frequency of their EMG signal spectra, respectively). Incorporation of this information into the 3D FE model of the foot resulted in a substantial rise in the levels of calcaneal and metatarsal stress concentrations, by 50% and 36%, respectively. This may point to the mechanism by which stress fractures develop and provide the biomechanical tools for future clinical investigations.

Turbine Engine Hot Section Technology, 1984

NASA Technical Reports Server (NTRS)

1984-01-01

Presentations were made concerning the hot section environment and behavior of combustion liners, turbine blades, and waves. The presentations were divided into six sessions: instrumentation, combustion, turbine heat transfer, structural analysis, fatigue and fracture, and surface properties. The principal objective of each session was to disseminate research results to date, along with future plans. Topics discussed included modeling of thermal and fluid flow phenomena, structural analysis, fatigue and fracture, surface protective coatings, constitutive behavior, stress-strain response, and life prediction methods.

Structural optimization procedure of a composite wind turbine blade for reducing both material cost and blade weight

NASA Astrophysics Data System (ADS)

Hu, Weifei; Park, Dohyun; Choi, DongHoon

2013-12-01

A composite blade structure for a 2 MW horizontal axis wind turbine is optimally designed. Design requirements are simultaneously minimizing material cost and blade weight while satisfying the constraints on stress ratio, tip deflection, fatigue life and laminate layup requirements. The stress ratio and tip deflection under extreme gust loads and the fatigue life under a stochastic normal wind load are evaluated. A blade element wind load model is proposed to explain the wind pressure difference due to blade height change during rotor rotation. For fatigue life evaluation, the stress result of an implicit nonlinear dynamic analysis under a time-varying fluctuating wind is converted to the histograms of mean and amplitude of maximum stress ratio using the rainflow counting algorithm Miner's rule is employed to predict the fatigue life. After integrating and automating the whole analysis procedure an evolutionary algorithm is used to solve the discrete optimization problem.

Women's experience of SLE-related fatigue: a focus group interview study.

PubMed

Pettersson, Susanne; Möller, Sonia; Svenungsson, Elisabet; Gunnarsson, Iva; Welin Henriksson, Elisabet

2010-10-01

The aim of this study was to describe women's experience of SLE-related fatigue, how they express the feeling of fatigue, impact on life and strategies developed to manage fatigue in daily living. Seven, semi-structured focus group discussions with 33 women were audio-taped, transcribed verbatim and analysed according to qualitative content analysis. Perceptions of SLE-related fatigue were sorted into four themes. Nature of Fatigue, involved the sensation, occurrence and character. Aspects Affected by Fatigue described emotions that arose together with fatigue as well as aspects of work, family life, social contacts and leisure activities that were affected by fatigue. Striving Towards Power and Control concluded the array of ways used to manage daily life and were categorized into the mental struggle, structure, restrict and provide. Factors Influencing the Perception of Fatigue described understanding from their surroundings and pain as strongly influencing the experience and perception of fatigue. SLE-related fatigue was portrayed as an overwhelming phenomenon with an unpredictable character, resulting in the feeling that fatigue dominates and controls most situations in life. The choice of strategies was described as a balance with implications for how fatigue limited a person's life. Health care professionals are advised to take a more active role to empower people with SLE to find their own balance as a way to achieve a feeling of being in control.

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.

Demonstration of the Application of Composite Load Spectra (CLS) and Probabilistic Structural Analysis (PSAM) Codes to SSME Heat Exchanger Turnaround Vane

NASA Technical Reports Server (NTRS)

Rajagopal, Kadambi R.; DebChaudhury, Amitabha; Orient, George

2000-01-01

This report describes a probabilistic structural analysis performed to determine the probabilistic structural response under fluctuating random pressure loads for the Space Shuttle Main Engine (SSME) turnaround vane. It uses a newly developed frequency and distance dependent correlation model that has features to model the decay phenomena along the flow and across the flow with the capability to introduce a phase delay. The analytical results are compared using two computer codes SAFER (Spectral Analysis of Finite Element Responses) and NESSUS (Numerical Evaluation of Stochastic Structures Under Stress) and with experimentally observed strain gage data. The computer code NESSUS with an interface to a sub set of Composite Load Spectra (CLS) code is used for the probabilistic analysis. A Fatigue code was used to calculate fatigue damage due to the random pressure excitation. The random variables modeled include engine system primitive variables that influence the operating conditions, convection velocity coefficient, stress concentration factor, structural damping, and thickness of the inner and outer vanes. The need for an appropriate correlation model in addition to magnitude of the PSD is emphasized. The study demonstrates that correlation characteristics even under random pressure loads are capable of causing resonance like effects for some modes. The study identifies the important variables that contribute to structural alternate stress response and drive the fatigue damage for the new design. Since the alternate stress for the new redesign is less than the endurance limit for the material, the damage due high cycle fatigue is negligible.

Transitional behaviour of thickness effects in shipbuilding materials (MS plate)

NASA Astrophysics Data System (ADS)

Mahmud, S. M. Ikhtiar; Razib, Amirul Hasan; Rahman, Md. Rabab Raiyatur

2017-12-01

Majority of the crack propagation in ships and offshore structures are caused due to fatigue. Previously, it was known that fatigue strength of notched specimen is dependent on size, but recently it came to light that fatigue strength of some welded joints depends on the thickness. Much investigation is done on the fatigue growth of welded joints. Fatigue often results in fracture accidents, which starts from the sites of structural discontinuities because of the reason that they may induce local stress concentrations. Structural discontinuities include notches, holes, sharp corners, and weld defects. Weld defects include undercut, porosity, lack of fusion, slag inclusion, incomplete weld root penetration, and misalignments. In order to investigate the effects of plate thickness on fatigue strength, semi-elliptical side notches (U and V shaped) in plates are studied in the present research. First consider a simple problem of crack emanating from notches in plates where the solution of stress intensity factor is given by an empirical formula so that the thickness effect on fatigue strength can easily be investigated for a variety of geometrical parameters. The present study aims to investigate the transitional behaviour of thickness effect in plates on fatigue strength. In order to calculate the stress, finite element analysis is carried by using ANSYS.

Validation of the Modified Fatigue Impact Scale in mild to moderate traumatic brain injury.

PubMed

Schiehser, Dawn M; Delano-Wood, Lisa; Jak, Amy J; Matthews, Scott C; Simmons, Alan N; Jacobson, Mark W; Filoteo, J Vincent; Bondi, Mark W; Orff, Henry J; Liu, Lin

2015-01-01

To evaluate the validity of the Modified Fatigue Impact Scale (MFIS) in veterans with a history of mild to moderate traumatic brain injury (TBI). Veterans (N = 106) with mild (92%) or moderate (8%) TBI. Veterans Administration Health System. Factor structure, internal consistency, convergent validity, sensitivity, and specificity of the MFIS were examined. Principal component analysis identified 2 viable MFIS factors: a Cognitive subscale and a Physical/Activities subscale. Item analysis revealed high internal consistency of the MFIS Total scale and subscale items. Strong convergent validity of the MFIS scales was established with 2 Beck Depression Inventory II fatigue items. Receiver operating characteristic curve analysis revealed good to excellent accuracy of the MFIS in classifying fatigued versus nonfatigued individuals. The MFIS is a valid multidimensional measure that can be used to evaluate the impact of fatigue on cognitive and physical functioning in individuals with mild to moderate TBI. The psychometric properties of the MFIS make it useful for evaluating fatigue and provide the potential for improving research on fatigue in this population.

A wireless fatigue monitoring system utilizing a bio-inspired tree ring data tracking technique.

PubMed

Bai, Shi; Li, Xuan; Xie, Zhaohui; Zhou, Zhi; Ou, Jinping

2014-03-05

Fatigue, a hot scientific research topic for centuries, can trigger sudden failure of critical structures such as aircraft and railway systems, resulting in enormous casualties as well as economic losses. The fatigue life of certain structures is intrinsically random and few monitoring techniques are capable of tracking the full life-cycle fatigue damage. In this paper, a novel in-situ wireless real-time fatigue monitoring system using a bio-inspired tree ring data tracking technique is proposed. The general framework, methodology, and verification of this intelligent system are discussed in details. The rain-flow counting (RFC) method is adopted as the core algorithm which quantifies fatigue damages, and Digital Signal Processing (DSP) is introduced as the core module for data collection and analysis. Laboratory test results based on strain gauges and polyvinylidene fluoride (PVDF) sensors have shown that the developed intelligent system can provide a reliable quick feedback and early warning of fatigue failure. With the merits of low cost, high accuracy and great reliability, the developed wireless fatigue sensing system can be further applied to mechanical engineering, civil infrastructures, transportation systems, aerospace engineering, etc.

A transient plasticity study and low cycle fatigue analysis of the Space Station Freedom photovoltaic solar array blanket

NASA Technical Reports Server (NTRS)

Armand, Sasan C.; Liao, Mei-Hwa; Morris, Ronald W.

1990-01-01

The Space Station Freedom photovoltaic solar array blanket assembly is comprised of several layers of materials having dissimilar elastic, thermal, and mechanical properties. The operating temperature of the solar array, which ranges from -75 to +60 C, along with the material incompatibility of the blanket assembly components combine to cause an elastic-plastic stress in the weld points of the assembly. The weld points are secondary structures in nature, merely serving as electrical junctions for gathering the current. The thermal mechanical loading of the blanket assembly operating in low earth orbit continually changes throughout each 90 min orbit, which raises the possibility of fatigue induced failure. A series of structural analyses were performed in an attempt to predict the fatigue life of the solar cell in the Space Station Freedom photovoltaic array blanket. A nonlinear elastic-plastic MSC/NASTRAN analysis followed by a fatigue calculation indicated a fatigue life of 92,000 to 160,000 cycles for the solar cell weld tabs. Additional analyses predict a permanent buckling phenomenon in the copper interconnect after the first loading cycle. This should reduce or eliminate the pulling of the copper interconnect on the joint where it is welded to the silicon solar cell. It is concluded that the actual fatigue life of the solar array blanket assembly should be significantly higher than the calculated 92,000 cycles, and thus the program requirement of 87,500 cycles (orbits) will be met. Another important conclusion that can be drawn from the overall analysis is that, the strain results obtained from the MSC/NASTRAN nonlinear module are accurate to use for low-cycle fatigue analysis, since both thermal cycle testing of solar cells and analysis have shown higher fatigue life than the minimum program requirement of 87,500 cycles.

FAA/NASA International Symposium on Advanced Structural Integrity Methods for Airframe Durability and Damage Tolerance

NASA Technical Reports Server (NTRS)

Harris, Charles E. (Editor)

1994-01-01

International technical experts in durability and damage tolerance of metallic airframe structures were assembled to present and discuss recent research findings and the development of advanced design and analysis methods, structural concepts, and advanced materials. The symposium focused on the dissemination of new knowledge and the peer-review of progress on the development of advanced methodologies. Papers were presented on: structural concepts for enhanced durability, damage tolerance, and maintainability; new metallic alloys and processing technology; fatigue crack initiation and small crack effects; fatigue crack growth models; fracture mechanics failure, criteria for ductile materials; structural mechanics methodology for residual strength and life prediction; development of flight load spectra for design and testing; and advanced approaches to resist corrosion and environmentally assisted fatigue.

Advances in Structural Integrity Analysis Methods for Aging Metallic Airframe Structures with Local Damage

NASA Technical Reports Server (NTRS)

Starnes, James H., Jr.; Newman, James C., Jr.; Harris, Charles E.; Piascik, Robert S.; Young, Richard D.; Rose, Cheryl A.

2003-01-01

Analysis methodologies for predicting fatigue-crack growth from rivet holes in panels subjected to cyclic loads and for predicting the residual strength of aluminum fuselage structures with cracks and subjected to combined internal pressure and mechanical loads are described. The fatigue-crack growth analysis methodology is based on small-crack theory and a plasticity induced crack-closure model, and the effect of a corrosive environment on crack-growth rate is included. The residual strength analysis methodology is based on the critical crack-tip-opening-angle fracture criterion that characterizes the fracture behavior of a material of interest, and a geometric and material nonlinear finite element shell analysis code that performs the structural analysis of the fuselage structure of interest. The methodologies have been verified experimentally for structures ranging from laboratory coupons to full-scale structural components. Analytical and experimental results based on these methodologies are described and compared for laboratory coupons and flat panels, small-scale pressurized shells, and full-scale curved stiffened panels. The residual strength analysis methodology is sufficiently general to include the effects of multiple-site damage on structural behavior.

Psychosocial factors, musculoskeletal disorders and work-related fatigue amongst nurses in Brunei: structural equation model approach.

PubMed

Abdul Rahman, Hanif; Abdul-Mumin, Khadizah; Naing, Lin

2017-09-01

Psychosocial factors, musculoskeletal disorders and work-related fatigue have adverse effects on individual nurses and place a substantial financial burden on health care. Evidence of an association has been reported in the literature, but no theoretical explanation has been published to date. To explore and develop a structural model to provide a theoretical explanation for this relationship. A cross-sectional study using data from 201 valid samples of emergency and critical care nurses across public hospitals in Brunei was performed via self-administered questionnaire. The structural equation model was assessed using partial least squares analysis. A valid and robust structural model was constructed. This revealed that 61.5% of the variance in chronic fatigue could be explained by psychosocial factors and musculoskeletal disorders pathways. Among the psychosocial factors, work-family conflict was identified as a key mediator for progression of musculoskeletal problems and subsequent fatigue through stress and burnout. This report provides a novel theoretical contribution to understanding the relationship between psychosocial factors, musculoskeletal disorders and work-related fatigue. These preliminary results may be useful for future studies on the development of work-related fatigue and musculoskeletal disorders, particularly the central role of work-family conflict. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fatigue assessment for selected connections of structural steel bridge components using the finite elements method

NASA Astrophysics Data System (ADS)

Śledziewski, Krzysztof

2018-01-01

Material fatigue it is one of the most frequent causes of steel bridge failures, particularly the bridges already existing. Thus, the procedure of fatigue life assessment is one of the most relevant procedures in a comprehensive assessment of load-carrying capacity and service life of the structure. A reliable assessment of the fatigue life is predominantly decisive for estimation of the remaining service life. Hitherto, calculation methods of welded joints took into account only stresses occurring in cross sections of whole elements and did not take into account stress concentration occurring in the vicinity of the weld, caused by geometrical aspects of the detail. At present, use of the Finite Element Analysis, makes possible looking for more accurate approach to the fatigue design of steel structures. The method of geometrical stresses is just such approach which is based on definition of stresses which take into account geometry of the detail. The study presents fatigue assessment of a representative type of welded joint in welded bridge structures. The testing covered longitudinal attachments. The main analyses were carried out on the basis of FEM and the method of local stresses, so-called "hot-spot" stresses. The obtained values of stresses were compared with the values obtained in accordance with the method of nominal stress.

Fronto-Parietal Subnetworks Flexibility Compensates For Cognitive Decline Due To Mental Fatigue.

PubMed

Taya, Fumihiko; Dimitriadis, Stavros I; Dragomir, Andrei; Lim, Julian; Sun, Yu; Wong, Kian Foong; Thakor, Nitish V; Bezerianos, Anastasios

2018-04-24

Fronto-parietal subnetworks were revealed to compensate for cognitive decline due to mental fatigue by community structure analysis. Here, we investigate changes in topology of subnetworks of resting-state fMRI networks due to mental fatigue induced by prolonged performance of a cognitively demanding task, and their associations with cognitive decline. As it is well established that brain networks have modular organization, community structure analyses can provide valuable information about mesoscale network organization and serve as a bridge between standard fMRI approaches and brain connectomics that quantify the topology of whole brain networks. We developed inter- and intramodule network metrics to quantify topological characteristics of subnetworks, based on our hypothesis that mental fatigue would impact on functional relationships of subnetworks. Functional networks were constructed with wavelet correlation and a data-driven thresholding scheme based on orthogonal minimum spanning trees, which allowed detection of communities with weak connections. A change from pre- to posttask runs was found for the intermodule density between the frontal and the temporal subnetworks. Seven inter- or intramodule network metrics, mostly at the frontal or the parietal subnetworks, showed significant predictive power of individual cognitive decline, while the network metrics for the whole network were less effective in the predictions. Our results suggest that the control-type fronto-parietal networks have a flexible topological architecture to compensate for declining cognitive ability due to mental fatigue. This community structure analysis provides valuable insight into connectivity dynamics under different cognitive states including mental fatigue. © 2018 Wiley Periodicals, Inc.

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

PubMed

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

2012-07-01

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

New method of determination of spot welding-adhesive joint fatigue life using full field strain evolution

NASA Astrophysics Data System (ADS)

Sadowski, T.; Kneć, M.

2016-04-01

Fatigue tests were conducted since more than two hundred years ago. Despite this long period, as fatigue phenomena are very complex, assessment of fatigue response of standard materials or composites still requires a long time. Quite precise way to estimate fatigue parameters is to test at least 30 standardized specimens for the analysed material and further statistical post processing is required. In case of structural elements analysis like hybrid joints (Figure 1), the situation is much more complex as more factors influence the fatigue load capacity due to much more complicated structure of the joint in comparison to standard materials specimen, i.e. occurrence of: welded hot spots or rivets, adhesive layers, local notches creating the stress concentrations, etc. In order to shorten testing time some rapid methods are known: Locati's method [1] - step by step load increments up to failure, Prot's method [2] - constant increase of the load amplitude up to failure; Lehr's method [2] - seeking for the point during regular fatigue loading when an increase of temperature or strains become non-linear. The present article proposes new method of the fatigue response assessment - combination of the Locati's and Lehr's method.

A Wireless Fatigue Monitoring System Utilizing a Bio-Inspired Tree Ring Data Tracking Technique

PubMed Central

Bai, Shi; Li, Xuan; Xie, Zhaohui; Zhou, Zhi; Ou, Jinping

2014-01-01

Fatigue, a hot scientific research topic for centuries, can trigger sudden failure of critical structures such as aircraft and railway systems, resulting in enormous casualties as well as economic losses. The fatigue life of certain structures is intrinsically random and few monitoring techniques are capable of tracking the full life-cycle fatigue damage. In this paper, a novel in-situ wireless real-time fatigue monitoring system using a bio-inspired tree ring data tracking technique is proposed. The general framework, methodology, and verification of this intelligent system are discussed in details. The rain-flow counting (RFC) method is adopted as the core algorithm which quantifies fatigue damages, and Digital Signal Processing (DSP) is introduced as the core module for data collection and analysis. Laboratory test results based on strain gauges and polyvinylidene fluoride (PVDF) sensors have shown that the developed intelligent system can provide a reliable quick feedback and early warning of fatigue failure. With the merits of low cost, high accuracy and great reliability, the developed wireless fatigue sensing system can be further applied to mechanical engineering, civil infrastructures, transportation systems, aerospace engineering, etc. PMID:24603635

Flexural fatigue life prediction of closed hat-section using materially nonlinear axial fatigue characteristics

NASA Technical Reports Server (NTRS)

Razzaq, Zia

1989-01-01

Straight or curved hat-section members are often used as structural stiffeners in aircraft. For instance, they are employed as stiffeners for the dorsal skin as well as in the aerial refueling adjacent area structure in F-106 aircraft. The flanges of the hat-section are connected to the aircraft skin. Thus, the portion of the skin closing the hat-section interacts with the section itself when resisting the stresses due to service loads. The flexural fatigue life of such a closed section is estimated using materially nonlinear axial fatigue characteristics. It should be recognized that when a structural shape is subjected to bending, the fatigue life at the neutral axis is infinity since the normal stresses are zero at that location. Conversely, the fatigue life at the extreme fibers where the normal bending stresses are maximum can be expected to be finite. Thus, different fatigue life estimates can be visualized at various distances from the neural axis. The problem becomes compounded further when significant portions away from the neutral axis are stressed into plastic range. A theoretical analysis of the closed hat-section subjected to flexural cyclic loading is first conducted. The axial fatigue characteristics together with the related axial fatigue life formula and its inverted form given by Manson and Muralidharan are adopted for an aluminum alloy used in aircraft construction. A closed-form expression for predicting the flexural fatigue life is then derived for the closed hat-section including materially nonlinear action. A computer program is written to conduct a study of the variables such as the thicknesses of the hat-section and the skin, and the type of alloy used. The study has provided a fundamental understanding of the flexural fatigue life characteristics of a practical structural component used in aircraft when materially nonlinear action is present.

Fatigue damage evaluation of short fiber CFRP based on phase information of thermoelastic temperature change

NASA Astrophysics Data System (ADS)

Sakagami, Takahide; Shiozawa, Daiki; Nakamura, Yu; Nonaka, Shinichi; Hamada, Kenichi

2017-05-01

Carbon fiber-reinforced plastic (CFRP) is widely used for structural members of transportation vehicles such as automobile, aircraft or spacecraft, utilizing its excellent specific strength and specific rigidity in contrast with the metal. Short carbon fiber composite materials are receiving a lot of attentions because of their excellent moldability and productivity, however they show complicated behaviors in fatigue fracture due to the random fibers orientation. In this study, thermoelastic stress analysis (TSA) using an infrared thermography was applied to the evaluation of fatigue damage in short carbon fiber composites. The distributions of the thermoelastic temperature change was measured during the fatigue test, as well as the phase difference between the thermoelastic temperature change and applied loading signal. Evolution of fatigue damages was detected from distributions of thermoelastic temperature change according to the thermoelastic damage analysis (TDA) procedure. It was also found that fatigue damage evolution was clearly detected than ever by the newly developed thermoelastic phase damage analysis (TPDA) in which damaged area was emphasized in the differential phase delay images utilizing the nature that carbon fiber show opposite phase thermoelastic temperature change.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a "sandwich structure" as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50-55% of ultimate tensile strength). The dynamic modulus (E(⁎)) was found to stay almost constant at 47GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials. Copyright © 2014 Elsevier Ltd. All rights reserved.

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

PubMed

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

2016-03-01

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

The impact of depression on fatigue in patients with haemodialysis: a correlational study.

PubMed

Bai, Yu-Ling; Lai, Liu-Yuan; Lee, Bih-O; Chang, Yong-Yuan; Chiou, Chou-Ping

2015-07-01

To investigate the fatigue levels and important fatigue predictors for patients undergoing haemodialysis. Fatigue is a common symptom for haemodialysis patients. With its debilitating and distressing effects, it impacts patients in terms of their quality of life while also increasing their mortality rate. A descriptive correlational study. Convenience sampling was conducted at six chosen haemodialysis centres in Southern Taiwan. Data were collected via a structured questionnaire from 193 haemodialysis patients. The scales involved in this study were socio-demographic details, the Center for Epidemiologic Studies Depression Scale, and the Fatigue Scale for haemodialysis patients. Data analysis included percentages, means, standard deviations and hierarchical multiple regression analysis. The fatigue level for haemodialysis patients was in the moderate range. Results from the hierarchical multiple regression analysis indicated that age, employment status, types of medications, physical activity and depression were significant. Of those variables, depression had the greatest impact on the patients' fatigue level, accounting for up to 30·6% of the explanatory power. The total explanatory power of the regression model was 64·2%. This study determined that for haemodialysis patients, unemployment, increased age, taking more medications or lower exercise frequencies resulted in more severe depression, which translated in turn to higher levels of fatigue. Among all these factors, depression had the greatest impact on the patients' fatigue levels. Not only is this finding beneficial to future studies on fatigue as a source of reference, it is also helpful in our understanding of important predictors relating to fatigue in the everyday lives of haemodialysis patients. It is recommended that when caring for fatigued patients, more care should be dedicated to their psychological states, and assistance should be provided in a timely way so as to reduce the amount of fatigue suffered. © 2015 John Wiley & Sons Ltd.

Experimental study of crack initiation and propagation in high- and gigacycle fatigue in titanium alloys

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

Bannikov, Mikhail, E-mail: mbannikov@icmm.ru, E-mail: oborin@icmm.ru, E-mail: naimark@icmm.ru; Oborin, Vladimir, E-mail: mbannikov@icmm.ru, E-mail: oborin@icmm.ru, E-mail: naimark@icmm.ru; Naimark, Oleg, E-mail: mbannikov@icmm.ru, E-mail: oborin@icmm.ru, E-mail: naimark@icmm.ru

Fatigue (high- and gigacycle) crack initiation and its propagation in titanium alloys with coarse and fine grain structure are studied by fractography analysis of fracture surface. Fractured specimens were analyzed by interferometer microscope and SEM to improve methods of monitoring of damage accumulation during fatigue test and to verify the models for fatigue crack kinetics. Fatigue strength was estimated for high cycle fatigue regime using the Luong method [1] by “in-situ” infrared scanning of the sample surface for the step-wise loading history for different grain size metals. Fine grain alloys demonstrated higher fatigue resistance for both high cycle fatigue andmore » gigacycle fatigue regimes. Fracture surface analysis for plane and cylindrical samples was carried out using optical and electronic microscopy method. High resolution profilometry (interferometer-profiler New View 5010) data of fracture surface roughness allowed us to estimate scale invariance (the Hurst exponent) and to establish the existence of two characteristic areas of damage localization (different values of the Hurst exponent). Area 1 with diameter ∼300 μm has the pronounced roughness and is associated with damage localization hotspot. Area 2 shows less amplitude roughness, occupies the rest fracture surface and considered as the trace of the fatigue crack path corresponding to the Paris kinetics.« less

Structural Area Inspection Frequency Evaluation (SAIFE). Volume III. Demonstration Input, Inspection Survey, and MRR Data

DTIC Science & Technology

1978-04-01

3 1.7 Production Rate Change Time . . . . 3 1.8 Time of Fatigue Test Start . ..... 3 1.9 Fatigue Test Acceleration Factor . 3 1.10 Corrosion...simulation logic. SAIFE accounts for the following factors : (1) aircraft design analysis; (2) component and full-scale fatigue testing; (3) production ...reliability; production , servi ce,Information Service, Springfield, and corrosion defects; crack or corrosi on Virginia 22151 detection probability; crack

Risk factors and visual fatigue of baggage X-ray security screeners: a structural equation modelling analysis.

PubMed

Yu, Rui-Feng; Yang, Lin-Dong; Wu, Xin

2017-05-01

This study identified the risk factors influencing visual fatigue in baggage X-ray security screeners and estimated the strength of correlations between those factors and visual fatigue using structural equation modelling approach. Two hundred and five X-ray security screeners participated in a questionnaire survey. The result showed that satisfaction with the VDT's physical features and the work environment conditions were negatively correlated with the intensity of visual fatigue, whereas job stress and job burnout had direct positive influences. The path coefficient between the image quality of VDT and visual fatigue was not significant. The total effects of job burnout, job stress, the VDT's physical features and the work environment conditions on visual fatigue were 0.471, 0.469, -0.268 and -0.251 respectively. These findings indicated that both extrinsic factors relating to VDT and workplace environment and psychological factors including job burnout and job stress should be considered in the workplace design and work organisation of security screening tasks to reduce screeners' visual fatigue. Practitioner Summary: This study identified the risk factors influencing visual fatigue in baggage X-ray security screeners and estimated the strength of correlations between those factors and visual fatigue. The findings were of great importance to the workplace design and the work organisation of security screening tasks to reduce screeners' visual fatigue.

On cyclic yield strength in definition of limits for characterisation of fatigue and creep behaviour

NASA Astrophysics Data System (ADS)

Gorash, Yevgen; MacKenzie, Donald

2017-06-01

This study proposes cyclic yield strength as a potential characteristic of safe design for structures operating under fatigue and creep conditions. Cyclic yield strength is defined on a cyclic stress-strain curve, while monotonic yield strength is defined on a monotonic curve. Both values of strengths are identified using a two-step procedure of the experimental stress-strain curves fitting with application of Ramberg-Osgood and Chaboche material models. A typical S-N curve in stress-life approach for fatigue analysis has a distinctive minimum stress lower bound, the fatigue endurance limit. Comparison of cyclic strength and fatigue limit reveals that they are approximately equal. Thus, safe fatigue design is guaranteed in the purely elastic domain defined by the cyclic yielding. A typical long-term strength curve in time-to-failure approach for creep analysis has two inflections corresponding to the cyclic and monotonic strengths. These inflections separate three domains on the long-term strength curve, which are characterised by different creep fracture modes and creep deformation mechanisms. Therefore, safe creep design is guaranteed in the linear creep domain with brittle failure mode defined by the cyclic yielding. These assumptions are confirmed using three structural steels for normal and high-temperature applications. The advantage of using cyclic yield strength for characterisation of fatigue and creep strength is a relatively quick experimental identification. The total duration of cyclic tests for a cyclic stress-strain curve identification is much less than the typical durations of fatigue and creep rupture tests at the stress levels around the cyclic yield strength.

Docetaxel-related fatigue in men with metastatic prostate cancer: a descriptive analysis.

PubMed

Bergin, A R T; Hovey, E; Lloyd, A; Marx, G; Parente, P; Rapke, T; de Souza, P

2017-09-01

Fatigue is a prevalent and debilitating side effect of docetaxel chemotherapy in metastatic prostate cancer. A better understanding of the kinetics and nature of docetaxel-related fatigue may provide a framework for intervention. This secondary analysis was performed using the MOTIF database, from a phase III, randomised, double-blind, placebo-controlled study of modafinil (200 mg/day for 15 days) for docetaxel-related fatigue in men with metastatic prostate cancer [1]. The pattern of fatigue was analysed using the MDASI (MD Anderson Symptom Inventory) score. The impact of modafinil, cumulative docetaxel exposure, age and smoking status on fatigue kinetics were explored. Fatigue-related symptoms were assessed using the SOMA6 (fatigue and related symptoms) subset of the SPHERE (Somatic and Psychological Health Report). Mood was tracked using the short form 36 health survey questionnaire (SF-36). Across four docetaxel cycles, fatigue scores were higher in the first week and decreased over weeks two and three. Whilst men randomised to modafinil had reduced fatigue scores, cumulative docetaxel had little impact. Younger men (55-68 years) had significantly reduced fatigue scores, whereas current and ex-smokers had higher scores. There was no significant change in mood status or haemoglobin across treatment cycles. Men described both 'somnolence' and 'muscle fatigue' contributing significantly to their symptom complex. Assessment and management of docetaxel-related fatigue remains an important challenge. Given the complex, multifactorial nature of fatigue, identification through structured interview and interventions targeted to specific 'at risk' groups may be the most beneficial. Understanding the temporal pattern (kinetics) and nature of fatigue is critical to guide this process.

Fatigue Analysis of Proton Exchange Membrane Fuel Cell Stacks Based on Structural Stress Distribution

NASA Astrophysics Data System (ADS)

Wu, C. W.; Liu, B.; Wei, M. Y.; Liu, L. F.

2017-05-01

Proton exchange membrane fuel cell (PEMFC) stack usually undergoes various vibrations during packing, transportation and serving time, in particular for those used in the automobiles and portable equipment. Based on the Miner fatigue damage theory, the fatigue lives of the fuel cell components are first assessed. Then the component fatigue life contours of the stack are obtained under four working conditions, i.e. the three single-axial (in X-, Y- and Z-axis separately) and multi-axial random vibrations. Accordingly, the component damage under various vibrations is evaluated. The stress distribution on the gasket and PEM will greatly affect their fatigue lives. Finally, we compare the fatigue lives of 4-bolt- and 6-bolt-clamping stacks under the same total clamping force, and find that increasing the bolt number could improve the bolt fatigue lives.

Proceedings of the Air Force Conference on Fatigue and Fracture of Aircraft Structures and Materials Held at Miami Beach, Florida on 15-18 December 1969

DTIC Science & Technology

1970-12-01

a Circular Hole A.S. Kobayashi and D.E. Maiden 217 Fatigue Performance of High Strength An Effective Strain Concept for Steels as Related to Their a ...in AFLC Col. H.B. Morrison, Jr. 899 Results of Analysis, Fatigue Testing and Usage of a High Speed Aircraft Subjected to Combined Peacetime and High ...on the level of the in a recent study of the fatigue performance of some stable elastic limit that can be produced by dislocation pin- high yield

The revised HSE fatigue guidance

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

Stacey, A.; Sharp, J.V.

1995-12-31

Fatigue cracking has been a principal cause of damage to North Sea structures and consequently considerable attention has been given to the development of guidance for the prediction of fatigue performance. The fatigue guidance of the Offshore Safety Division of the Health and Safety Executive (HSE) was recently revised and published, following a significant offshore industry review in the period 1987 to 1990, and is based on the results of a considerable amount of research and development work on the fatigue behavior of welded tubular and plated joints. As a result of this review, the revised fatigue guidance incorporates severalmore » new clauses and recommendations. The revised recommendations apply to joint classification, basic design S-N curves for welded joints and cast or forged steel components, the thickness effect, the effects of environment and the treatment of low and high stress ranges. Additionally, a new appendix on the derivation of stress concentration factors is included. The new clauses cover high strength steels, bolts and threaded connectors, moorings, repaired joints and the use of fracture mechanics analysis. This paper presents an overview of the revisions to the fatigue guidance, the associated background technical information and aspects of the fatigue behavior of offshore structures which are considered to require further investigation. 67 refs., 7 figs., 8 tabs.« less

Structural design of composite rotor blades with consideration of manufacturability, durability, and manufacturing uncertainties

NASA Astrophysics Data System (ADS)

Li, Leihong

A modular structural design methodology for composite blades is developed. This design method can be used to design composite rotor blades with sophisticate geometric cross-sections. This design method hierarchically decomposed the highly-coupled interdisciplinary rotor analysis into global and local levels. In the global level, aeroelastic response analysis and rotor trim are conduced based on multi-body dynamic models. In the local level, variational asymptotic beam sectional analysis methods are used for the equivalent one-dimensional beam properties. Compared with traditional design methodology, the proposed method is more efficient and accurate. Then, the proposed method is used to study three different design problems that have not been investigated before. The first is to add manufacturing constraints into design optimization. The introduction of manufacturing constraints complicates the optimization process. However, the design with manufacturing constraints benefits the manufacturing process and reduces the risk of violating major performance constraints. Next, a new design procedure for structural design against fatigue failure is proposed. This procedure combines the fatigue analysis with the optimization process. The durability or fatigue analysis employs a strength-based model. The design is subject to stiffness, frequency, and durability constraints. Finally, the manufacturing uncertainty impacts on rotor blade aeroelastic behavior are investigated, and a probabilistic design method is proposed to control the impacts of uncertainty on blade structural performance. The uncertainty factors include dimensions, shapes, material properties, and service loads.

Isothermal and thermal-mechanical fatigue of VVER-440 reactor pressure vessel steels

NASA Astrophysics Data System (ADS)

Fekete, Balazs; Trampus, Peter

2015-09-01

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of VVER-440 reactor pressure vessel under completely reserved total strain controlled low cycle fatigue tests were investigated. An advanced test facility was developed for GLEEBLE-3800 physical simulator which was able to perform thermomechanical fatigue experiments under in-service conditions of VVER nuclear reactors. The low cycle fatigue results were evaluated with the plastic strain based Coffin-Manson law, and plastic strain energy based model as well. It was shown that both methods are able to predict the fatigue life of reactor pressure vessel steels accurately. Interrupted fatigue tests were also carried out to investigate the kinetic of the fatigue evolution of the materials. On these samples microstructural evaluation by TEM was performed. The investigated low cycle fatigue behavior can provide reference for remaining life assessment and lifetime extension analysis.

Fatigue Damage Evaluation of Short Carbon Fiber Reinforced Plastics Based on Phase Information of Thermoelastic Temperature Change.

PubMed

Shiozawa, Daiki; Sakagami, Takahide; Nakamura, Yu; Nonaka, Shinichi; Hamada, Kenichi

2017-12-06

Carbon fiber-reinforced plastic (CFRP) is widely used for structural members of transportation vehicles such as automobile, aircraft, or spacecraft, utilizing its excellent specific strength and specific rigidity in contrast with the metal. Short carbon fiber composite materials are receiving a lot of attentions because of their excellent moldability and productivity, however they show complicated behaviors in fatigue fracture due to the random fibers orientation. In this study, thermoelastic stress analysis (TSA) using an infrared thermography was applied to evaluate fatigue damage in short carbon fiber composites. The distribution of the thermoelastic temperature change was measured during the fatigue test, as well as the phase difference between the thermoelastic temperature change and applied loading signal. Evolution of fatigue damage was detected from the distribution of thermoelastic temperature change according to the thermoelastic damage analysis (TDA) procedure. It was also found that fatigue damage evolution was more clearly detected than before by the newly developed thermoelastic phase damage analysis (TPDA) in which damaged area was emphasized in the differential phase delay images utilizing the property that carbon fiber shows opposite phase thermoelastic temperature change.

A conductive grating sensor for online quantitative monitoring of fatigue crack.

PubMed

Li, Peiyuan; Cheng, Li; Yan, Xiaojun; Jiao, Shengbo; Li, Yakun

2018-05-01

Online quantitative monitoring of crack damage due to fatigue is a critical challenge for structural health monitoring systems assessing structural safety. To achieve online quantitative monitoring of fatigue crack, a novel conductive grating sensor based on the principle of electrical potential difference is proposed. The sensor consists of equidistant grating channels to monitor the fatigue crack length and conductive bars to provide the circuit path. An online crack monitoring system is established to verify the sensor's capability. The experimental results prove that the sensor is suitable for online quantitative monitoring of fatigue crack. A finite element model for the sensor is also developed to optimize the sensitivity of crack monitoring, which is defined by the rate of sensor resistance change caused by the break of the first grating channel. Analysis of the model shows that the sensor sensitivity can be enhanced by reducing the number of grating channels and increasing their resistance and reducing the resistance of the conductive bar.

A conductive grating sensor for online quantitative monitoring of fatigue crack

NASA Astrophysics Data System (ADS)

Li, Peiyuan; Cheng, Li; Yan, Xiaojun; Jiao, Shengbo; Li, Yakun

2018-05-01

Online quantitative monitoring of crack damage due to fatigue is a critical challenge for structural health monitoring systems assessing structural safety. To achieve online quantitative monitoring of fatigue crack, a novel conductive grating sensor based on the principle of electrical potential difference is proposed. The sensor consists of equidistant grating channels to monitor the fatigue crack length and conductive bars to provide the circuit path. An online crack monitoring system is established to verify the sensor's capability. The experimental results prove that the sensor is suitable for online quantitative monitoring of fatigue crack. A finite element model for the sensor is also developed to optimize the sensitivity of crack monitoring, which is defined by the rate of sensor resistance change caused by the break of the first grating channel. Analysis of the model shows that the sensor sensitivity can be enhanced by reducing the number of grating channels and increasing their resistance and reducing the resistance of the conductive bar.

The effect of fatigue cracks on fastener flexibility, load distribution, and fatigue crack growth

NASA Astrophysics Data System (ADS)

Whitman, Zachary Layne

Fatigue cracks typically occur at stress risers such as geometry changes and holes. This type of failure has serious safety and economic repercussions affecting structures such as aircraft. The need to prevent catastrophic failure due to fatigue cracks and other discontinuities has led to durability and damage tolerant methodologies influencing the design of aircraft structures. Holes in a plate or sheet filled with a fastener are common fatigue critical locations in aircraft structure requiring damage tolerance analysis (DTA). Often, the fastener is transferring load which leads to a loading condition involving both far-field stresses such as tension and bending, and localized bearing at the hole. The difference between the bearing stress and the tensile field at the hole is known as load transfer. The ratio of load transfer as well as the magnitude of the stresses plays a significant part in how quickly a crack will progress to failure. Unfortunately, the determination of load transfer in a complex joint is far from trivial. Many methods exist in the open literature regarding the analysis of splices, doublers and attachment joints to determine individual fastener loads. These methods work well for static analyses but greater refinement is needed for crack growth analysis. The first fastener in a splice or joint is typically the most critical but different fastener flexibility equations will all give different results. The constraint of the fastener head and shop end, along with the type of fastener, affects the stiffness or flexibility of the fastener. This in turn will determine the load that the fastener will transfer within a given fastener pattern. However, current methods do not account for the change in flexibility at a fastener as the crack develops. It is put forth that a crack does indeed reduce the stiffness of a fastener by changing its constraint, thus lessening the load transfer. A crack growth analysis utilizing reduced load transfer will result in a slower growing crack versus an analysis that ignores the effect.

Equivalent linearization for fatigue life estimates of a nonlinear structure

NASA Technical Reports Server (NTRS)

Miles, R. N.

1989-01-01

An analysis is presented of the suitability of the method of equivalent linearization for estimating the fatigue life of a nonlinear structure. Comparisons are made of the fatigue life of a nonlinear plate as predicted using conventional equivalent linearization and three other more accurate methods. The excitation of the plate is assumed to be Gaussian white noise and the plate response is modeled using a single resonant mode. The methods used for comparison consist of numerical simulation, a probabalistic formulation, and a modification of equivalent linearization which avoids the usual assumption that the response process is Gaussian. Remarkably close agreement is obtained between all four methods, even for cases where the response is significantly linear.

Analysis on mechanics response of long-life asphalt pavement at moist hot heavy loading area

NASA Astrophysics Data System (ADS)

Xu, Xinquan; Li, Hao; Wu, Chuanhai; Li, Shanqiang

2018-04-01

Based on the durability of semi-rigid base asphalt pavement test road in Guangdong Yunluo expressway, by comparing the mechanics response of modified semi-rigid base, RCC base and inverted semi-rigid base with the state of continuous, using four unit five parameter model to evaluate rut depth of asphalt pavement structure, and through commonly used fatigue life prediction model to evaluate fatigue performance of three types of asphalt pavement structure. Theoretical calculation and four years tracking observation results of test road show that rut depth of modified semi-rigid base asphalt pavement is the minimum, the road performance is the best, and the fatigue performance is the optimal.

An investigation of strain cycling behavior of 7075-T6 aluminum under combined state of strain: The effects of out-of-phase, biaxial strain cycling on low cycle fatigue

NASA Technical Reports Server (NTRS)

Zamrik, S. Y.

1972-01-01

The effect of out-of-phase strain cycling on the low cycle fatigue of biaxially loaded specimens is discussed. A method to apply phase angles between two strains imposed in two different directions was developed. The data and the proposed theoretical analysis are part of a research program on biaxial strain cycling effect on fatigue life of structural materials.

Advanced aircraft service life monitoring method via flight-by-flight load spectra

NASA Astrophysics Data System (ADS)

Lee, Hongchul

This research is an effort to understand current method and to propose an advanced method for Damage Tolerance Analysis (DTA) for the purpose of monitoring the aircraft service life. As one of tasks in the DTA, the current indirect Individual Aircraft Tracking (IAT) method for the F-16C/D Block 32 does not properly represent changes in flight usage severity affecting structural fatigue life. Therefore, an advanced aircraft service life monitoring method based on flight-by-flight load spectra is proposed and recommended for IAT program to track consumed fatigue life as an alternative to the current method which is based on the crack severity index (CSI) value. Damage Tolerance is one of aircraft design philosophies to ensure that aging aircrafts satisfy structural reliability in terms of fatigue failures throughout their service periods. IAT program, one of the most important tasks of DTA, is able to track potential structural crack growth at critical areas in the major airframe structural components of individual aircraft. The F-16C/D aircraft is equipped with a flight data recorder to monitor flight usage and provide the data to support structural load analysis. However, limited memory of flight data recorder allows user to monitor individual aircraft fatigue usage in terms of only the vertical inertia (NzW) data for calculating Crack Severity Index (CSI) value which defines the relative maneuver severity. Current IAT method for the F-16C/D Block 32 based on CSI value calculated from NzW is shown to be not accurate enough to monitor individual aircraft fatigue usage due to several problems. The proposed advanced aircraft service life monitoring method based on flight-by-flight load spectra is recommended as an improved method for the F-16C/D Block 32 aircraft. Flight-by-flight load spectra was generated from downloaded Crash Survival Flight Data Recorder (CSFDR) data by calculating loads for each time hack in selected flight data utilizing loads equations. From the comparison of interpolated fatigue life using CSI value and fatigue test results, it is obvious that proposed advanced IAT method via flight-by-flight load spectra is more reliable and accurate than current IAT method. Therefore, the advanced aircraft service life monitoring method based on flight-by-flight load spectra not only monitors the individual aircraft consumed fatigue life for inspection but also ensures the structural reliability of aging aircrafts throughout their service periods.

Lifetime Reliability Evaluation of Structural Ceramic Parts with the CARES/LIFE Computer Program

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.; Gyekenyesi, John P.

1993-01-01

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker equation. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), Weibull's normal stress averaging method (NSA), or Batdorf's theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Two example problems demonstrating cyclic fatigue parameter estimation and component reliability analysis with proof testing are included.

Changes in the flexion relaxation response induced by lumbar muscle fatigue.

PubMed

Descarreaux, Martin; Lafond, Danik; Jeffrey-Gauthier, Renaud; Centomo, Hugo; Cantin, Vincent

2008-01-24

The flexion relaxation phenomenon (FRP) is an interesting model to study the modulation of lumbar stability. Previous investigations have explored the effect of load, angular velocity and posture on this particular response. However, the influence of muscular fatigue on FRP parameters has not been thoroughly examined. The objective of the study is to identify the effect of erector spinae (ES) muscle fatigue and spine loading on myoelectric silence onset and cessation in healthy individuals during a flexion-extension task. Twenty healthy subjects participated in this study and performed blocks of 3 complete trunk flexions under 4 different experimental conditions: no fatigue/no load (1), no fatigue/load (2), fatigue/no load(3), and fatigue/load (4). Fatigue was induced according to the Sorenson protocol, and electromyographic (EMG) power spectral analysis confirmed that muscular fatigue was adequate in each subject. Trunk and pelvis angles and surface EMG of the ES L2 and L5 were recorded during a flexion-extension task. Trunk flexion angle corresponding to the onset and cessation of myoelectric silence was then compared across the different experimental conditions using 2 x 2 repeated-measures ANOVA. Onset of myoelectric silence during the flexion motion appeared earlier after the fatigue task. Additionally, the cessation of myoelectric silence was observed later during the extension after the fatigue task. Statistical analysis also yielded a main effect of load, indicating a persistence of ES myoelectric activity in flexion during the load condition. The results of this study suggest that the presence of fatigue of the ES muscles modifies the FRP. Superficial back muscle fatigue seems to induce a shift in load-sharing towards passive stabilizing structures. The loss of muscle contribution together with or without laxity in the viscoelastic tissues may have a substantial impact on post fatigue stability.

Damage evolution during actuation fatigue in shape memory alloys (SPIE Best Student Paper Award)

NASA Astrophysics Data System (ADS)

Phillips, Francis R.; Wheeler, Robert; Lagoudas, Dimitris C.

2018-03-01

Shape Memory Alloys (SMAs) are unique materials able to undergo a thermomechanically induced, reversible phase transformation. Additionally, SMA are subject to two types of fatigue, that is structural fatigue due to cyclic loading as experienced by most materials, as well as actuation fatigue due to repeated thermally induced phase transformation. The evolution of multiple material characteristics is presented over the actuation fatigue lifetime of NiTiHf actuators, including the accumulation of irrecoverable strain, the evolution of internal voids, and the evolution of the effective modulus of the actuator. The results indicate that all three of these material characteristics are clearly interconnected and careful analysis of each of these characteristics can help to understand the evolution of the others, as well as help to understand how actuation fatigue leads to ultimate failure of the actuator.

Structural and mechanical defects of materials of offshore and onshore main gas pipelines after long-term operation

NASA Astrophysics Data System (ADS)

Maruschak, Pavlo; Panin, Sergey; Danyliuk, Iryna; Poberezhnyi, Lyubomyr; Pyrig, Taras; Bishchak, Roman; Vlasov, Ilya

2015-10-01

The study has established the main regularities of a fatigue failure of offshore gas steel pipes installed using S-lay and J-lay methods.We have numerically analyzed the influence of preliminary deformation on the fatigue life of 09Mn2Si steel at different amplitudes of cyclic loading. The results have revealed the regularities of formation and development of a fatigue crack in 17Mn1Si steel after 40 years of underground operation. The quantitative analysis describes the regularities of occurrence and growth of fatigue cracks in the presence of a stress concentration.

On fatigue crack growth under random loading

NASA Astrophysics Data System (ADS)

Zhu, W. Q.; Lin, Y. K.; Lei, Y.

1992-09-01

A probabilistic analysis of the fatigue crack growth, fatigue life and reliability of a structural or mechanical component is presented on the basis of fracture mechanics and theory of random processes. The material resistance to fatigue crack growth and the time-history of the stress are assumed to be random. Analytical expressions are obtained for the special case in which the random stress is a stationary narrow-band Gaussian random process, and a randomized Paris-Erdogan law is applicable. As an example, the analytical method is applied to a plate with a central crack, and the results are compared with those obtained from digital Monte Carlo simulations.

Turbine Engine Hot Section Technology 1986

NASA Technical Reports Server (NTRS)

1986-01-01

The Turbine Engine Hot Section Technology (HOST) Project of the NASA Lewis Research Center sponsored a workshop to discuss current research pertinent to turbine engine durability problems. Presentations were made concerning the hot section environment and the behavior of combustion liners, turbine blades, and turbine vanes. The presentations were divided into six sessions: Instrumentation, Combustion, Turbine Heat Transfer, Structural Analysis, Fatigue and Fracture, and Surface Protection. Topics discussed included modeling of thermal and fluid-flow phenomena, structural analysis, fatigue and fracture, surface protective coatings, constitutive behavior of materials, stress-strain response, and life-prediction methods. Researchers from industry, academia, and government presented results of their work sponsored by the HOST project.

Factorial invariance of pediatric patient self-reported fatigue across age and gender: a multigroup confirmatory factor analysis approach utilizing the PedsQL™ Multidimensional Fatigue Scale.

PubMed

Varni, James W; Beaujean, A Alexander; Limbers, Christine A

2013-11-01

In order to compare multidimensional fatigue research findings across age and gender subpopulations, it is important to demonstrate measurement invariance, that is, that the items from an instrument have equivalent meaning across the groups studied. This study examined the factorial invariance of the 18-item PedsQL™ Multidimensional Fatigue Scale items across age and gender and tested a bifactor model. Multigroup confirmatory factor analysis (MG-CFA) was performed specifying a three-factor model across three age groups (5-7, 8-12, and 13-18 years) and gender. MG-CFA models were proposed in order to compare the factor structure, metric, scalar, and error variance across age groups and gender. The analyses were based on 837 children and adolescents recruited from general pediatric clinics, subspecialty clinics, and hospitals in which children were being seen for well-child checks, mild acute illness, or chronic illness care. A bifactor model of the items with one general factor influencing all the items and three domain-specific factors representing the General, Sleep/Rest, and Cognitive Fatigue domains fit the data better than oblique factor models. Based on the multiple measures of model fit, configural, metric, and scalar invariance were found for almost all items across the age and gender groups, as was invariance in the factor covariances. The PedsQL™ Multidimensional Fatigue Scale demonstrated strict factorial invariance for child and adolescent self-report across gender and strong factorial invariance across age subpopulations. The findings support an equivalent three-factor structure across the age and gender groups studied. Based on these data, it can be concluded that pediatric patients across the groups interpreted the items in a similar manner regardless of their age or gender, supporting the multidimensional factor structure interpretation of the PedsQL™ Multidimensional Fatigue Scale.

High cycle fatigue in the transmission electron microscope

DOE PAGES

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.; ...

2016-06-28

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

High cycle fatigue in the transmission electron microscope

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

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

Investigation of fatigue assessments accuracy for beam weldments considering material data input and FE-mode type

NASA Astrophysics Data System (ADS)

Gorash, Yevgen; Comlekci, Tugrul; MacKenzie, Donald

2017-05-01

This study investigates the effects of fatigue material data and finite element types on accuracy of residual life assessments under high cycle fatigue. The bending of cross-beam connections is simulated in ANSYS Workbench for different combinations of structural member shapes made of a typical structural steel. The stress analysis of weldments with specific dimensions and loading applied is implemented using solid and shell elements. The stress results are transferred to the fatigue code nCode DesignLife for the residual life prediction. Considering the effects of mean stress using FKM approach, bending and thickness according to BS 7608:2014, fatigue life is predicted using the Volvo method and stress integration rules from ASME Boiler & Pressure Vessel Code. Three different pairs of S-N curves are considered in this work including generic seam weld curves and curves for the equivalent Japanese steel JIS G3106-SM490B. The S-N curve parameters for the steel are identified using the experimental data available from NIMS fatigue data sheets employing least square method and considering thickness and mean stress corrections. The numerical predictions are compared to the available experimental results indicating the most preferable fatigue data input, range of applicability and FE-model formulation to achieve the best accuracy.

Probabilistic analysis for fatigue strength degradation of materials

NASA Technical Reports Server (NTRS)

Royce, Lola

1989-01-01

This report presents the results of the first year of a research program conducted for NASA-LeRC by the University of Texas at San Antonio. The research included development of methodology that provides a probabilistic treatment of lifetime prediction of structural components of aerospace propulsion systems subjected to fatigue. Material strength degradation models, based on primitive variables, include both a fatigue strength reduction model and a fatigue crack growth model. Linear elastic fracture mechanics is utilized in the latter model. Probabilistic analysis is based on simulation, and both maximum entropy and maximum penalized likelihood methods are used for the generation of probability density functions. The resulting constitutive relationships are included in several computer programs, RANDOM2, RANDOM3, and RANDOM4. These programs determine the random lifetime of an engine component, in mechanical load cycles, to reach a critical fatigue strength or crack size. The material considered was a cast nickel base superalloy, one typical of those used in the Space Shuttle Main Engine.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Structurally compliant rocket engine combustion chamber: Experimental and analytical validation

NASA Technical Reports Server (NTRS)

Jankovsky, Robert S.; Arya, Vinod K.; Kazaroff, John M.; Halford, Gary R.

1994-01-01

A new, structurally compliant rocket engine combustion chamber design has been validated through analysis and experiment. Subscale, tubular channel chambers have been cyclically tested and analytically evaluated. Cyclic lives were determined to have a potential for 1000 percent increase over those of rectangular channel designs, the current state of the art. Greater structural compliance in the circumferential direction gave rise to lower thermal strains during hot firing, resulting in lower thermal strain ratcheting and longer predicted fatigue lives. Thermal, structural, and durability analyses of the combustion chamber design, involving cyclic temperatures, strains, and low-cycle fatigue lives, have corroborated the experimental observations.

Thermography Inspection for Early Detection of Composite Damage in Structures During Fatigue Loading

NASA Technical Reports Server (NTRS)

Zalameda, Joseph N.; Burke, Eric R.; Parker, F. Raymond; Seebo, Jeffrey P.; Wright, Christopher W.; Bly, James B.

2012-01-01

Advanced composite structures are commonly tested under controlled loading. Understanding the initiation and progression of composite damage under load is critical for validating design concepts and structural analysis tools. Thermal nondestructive evaluation (NDE) is used to detect and characterize damage in composite structures during fatigue loading. A difference image processing algorithm is demonstrated to enhance damage detection and characterization by removing thermal variations not associated with defects. In addition, a one-dimensional multilayered thermal model is used to characterize damage. Lastly, the thermography results are compared to other inspections such as non-immersion ultrasonic inspections and computed tomography X-ray.

Failure Analysis on Tail Rotor Teeter Pivot Bolt on a Helicopter

NASA Astrophysics Data System (ADS)

Qiang, WANG; Zi-long, DONG

2018-03-01

Tail rotor teeter pivot bolt of a helicopter fractured when in one flight. Failure analysis on the bolt was finished in laboratory. Macroscopic observation of the tailor rotor teeter pivot bolt, macro and microscopic inspection on the fracture surface of the bolt was carried out. Chemical components and metallurgical structure was also carried out. Experiment results showed that fracture mode of the tail rotor teeter pivot bolt is fatigue fracture. Fatigue area is over 80% of the total fracture surface, obvious fatigue band characteristics can be found at the fracture face. According to the results were analyzed from the macroscopic and microcosmic aspects, fracture reasons of the tail rotor teeter pivot bolt were analyzed in detail

Criteria for structural test

NASA Technical Reports Server (NTRS)

1973-01-01

The results of a study to define criteria and techniques of design, analysis and test which permit the use of a single major structural test article for performing dynamic, fatigue, and static testing are presented. The criteria developed is applicable to both space vehicles and aircraft structures operating in the subsonic or supersonic regime. The feasibility of such an approach was demonstrated by defining test interactions, compatibilities and incompatibilities between the three different types of tests. The results of the study indicate that the single test article concept is feasible with a testing sequence of dynamic test followed by a fatigue and static test.

Comparison of structural response and fatigue endurance of aircraft flap-like box structures subjected to acoustic loading

NASA Astrophysics Data System (ADS)

Xiao, Y.; White, R. G.; Aglietti, G. S.

2005-05-01

The results of an extensive test program to characterize the behavior of typical aircraft structures under acoustic loading and to establish their fatigue endurance are presented. The structures tested were the three flap-like box-type of structures. Each structure consisted of one flat (bottom) and one curved (top) stiffener stiffened skin panel, front, and rear spars, and ribs that divided the structures into three bays. The three structures, constructed from three different materials (aircraft standard aluminum alloy, Carbon Fibre Reinforced Plastic, and a Glass Fibre Metal Laminate, i.e., GLARE) had the same size and configuration, with only minor differences due to the use of different materials. A first set of acoustic tests with excitations of intensity ranging from 140 to 160 dB were carried out to obtain detailed data on the dynamic response of the three structures. The FE analysis of the structures is also briefly described and the results compared with the experimental data. The fatigue endurance of the structures was then determined using random acoustic excitation with an overall sound pressure level of 161 dB, and details of crack propagation are reported. .

Development of a structural health monitoring system for the life assessment of critical transportation infrastructure.

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

Roach, Dennis Patrick; Jauregui, David Villegas; Daumueller, Andrew Nicholas

2012-02-01

Recent structural failures such as the I-35W Mississippi River Bridge in Minnesota have underscored the urgent need for improved methods and procedures for evaluating our aging transportation infrastructure. This research seeks to develop a basis for a Structural Health Monitoring (SHM) system to provide quantitative information related to the structural integrity of metallic structures to make appropriate management decisions and ensuring public safety. This research employs advanced structural analysis and nondestructive testing (NDT) methods for an accurate fatigue analysis. Metal railroad bridges in New Mexico will be the focus since many of these structures are over 100 years old andmore » classified as fracture-critical. The term fracture-critical indicates that failure of a single component may result in complete collapse of the structure such as the one experienced by the I-35W Bridge. Failure may originate from sources such as loss of section due to corrosion or cracking caused by fatigue loading. Because standard inspection practice is primarily visual, these types of defects can go undetected due to oversight, lack of access to critical areas, or, in riveted members, hidden defects that are beneath fasteners or connection angles. Another issue is that it is difficult to determine the fatigue damage that a structure has experienced and the rate at which damage is accumulating due to uncertain history and load distribution in supporting members. A SHM system has several advantages that can overcome these limitations. SHM allows critical areas of the structure to be monitored more quantitatively under actual loading. The research needed to apply SHM to metallic structures was performed and a case study was carried out to show the potential of SHM-driven fatigue evaluation to assess the condition of critical transportation infrastructure and to guide inspectors to potential problem areas. This project combines the expertise in transportation infrastructure at New Mexico State University with the expertise at Sandia National Laboratories in the emerging field of SHM.« less

A comparison of reliability and conventional estimation of safe fatigue life and safe inspection intervals

NASA Technical Reports Server (NTRS)

Hooke, F. H.

1972-01-01

Both the conventional and reliability analyses for determining safe fatigue life are predicted on a population having a specified (usually log normal) distribution of life to collapse under a fatigue test load. Under a random service load spectrum, random occurrences of load larger than the fatigue test load may confront and cause collapse of structures which are weakened, though not yet to the fatigue test load. These collapses are included in reliability but excluded in conventional analysis. The theory of risk determination by each method is given, and several reasonably typical examples have been worked out, in which it transpires that if one excludes collapse through exceedance of the uncracked strength, the reliability and conventional analyses gave virtually identical probabilities of failure or survival.

A Novel Approach to Rotorcraft Damage Tolerance

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Everett, Richard A.; Newman, John A.

2002-01-01

Damage-tolerance methodology is positioned to replace safe-life methodologies for designing rotorcraft structures. The argument for implementing a damage-tolerance method comes from the fundamental fact that rotorcraft structures typically fail by fatigue cracking. Therefore, if technology permits prediction of fatigue-crack growth in structures, a damage-tolerance method should deliver the most accurate prediction of component life. Implementing damage-tolerance (DT) into high-cycle-fatigue (HCF) components will require a shift from traditional DT methods that rely on detecting an initial flaw with nondestructive inspection (NDI) methods. The rapid accumulation of cycles in a HCF component will result in a design based on a traditional DT method that is either impractical because of frequent inspections, or because the design will be too heavy to operate efficiently. Furthermore, once a HCF component develops a detectable propagating crack, the remaining fatigue life is short, sometimes less than one flight hour, which does not leave sufficient time for inspection. Therefore, designing a HCF component will require basing the life analysis on an initial flaw that is undetectable with current NDI technology.

Scaling phenomena in fatigue and fracture

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

Barenblatt, G.I.

2004-12-01

The general classification of scaling laws will be presented and the basic concepts of modern similarity analysis--intermediate asymptotics, complete and incomplete similarity--will be introduced and discussed. The examples of scaling laws corresponding to complete similarity will be given. The Paris scaling law in fatigue will be discussed as an instructive example of incomplete similarity. It will be emphasized that in the Paris law the powers are not the material constants. Therefore, the evaluation of the life-time of structures using the data obtained from standard fatigue tests requires some precautions.

Multiscale Fatigue Life Prediction for Composite Panels

NASA Technical Reports Server (NTRS)

Bednarcyk, Brett A.; Yarrington, Phillip W.; Arnold, Steven M.

2012-01-01

Fatigue life prediction capabilities have been incorporated into the HyperSizer Composite Analysis and Structural Sizing Software. The fatigue damage model is introduced at the fiber/matrix constituent scale through HyperSizer s coupling with NASA s MAC/GMC micromechanics software. This enables prediction of the micro scale damage progression throughout stiffened and sandwich panels as a function of cycles leading ultimately to simulated panel failure. The fatigue model implementation uses a cycle jumping technique such that, rather than applying a specified number of additional cycles, a specified local damage increment is specified and the number of additional cycles to reach this damage increment is calculated. In this way, the effect of stress redistribution due to damage-induced stiffness change is captured, but the fatigue simulations remain computationally efficient. The model is compared to experimental fatigue life data for two composite facesheet/foam core sandwich panels, demonstrating very good agreement.

Fatigue in children and adolescents with cancer from the perspective of health professionals 1

PubMed Central

da Silva, Michele Cristina Miyauti; Lopes, Luís Carlos; Nascimento, Lucila Castanheira; de Lima, Regina Aparecida Garcia

2016-01-01

ABSTRACT Objective: to investigate health professionals' knowledge about the concept, assessment and intervention in fatigue in children and adolescents with cancer. Method: exploratory study with qualitative approach, with 53 health professionals (10 nurses, 33 assistant nurses, 3 physicians, 3 nutritionists, 2 psychologists and 2 physical therapists). Semi structured interviews were held, which were recorded and analyzed by means of inductive thematic content analysis. Results: the data were organized around three themes: knowledge of health professionals about fatigue; identification of fatigue and interventions to relieve fatigue. Conclusion: the results indicate the health professionals' limited knowledge about fatigue, as well as the lack of investment in their training and continuing education. Most of all, the lack of research on the theme in the Brazilian context remains a barrier to support improvements in care for this symptom in children and adolescents with cancer. PMID:27579937

Probabilistic finite elements for fatigue and fracture analysis

NASA Astrophysics Data System (ADS)

Belytschko, Ted; Liu, Wing Kam

1993-04-01

An overview of the probabilistic finite element method (PFEM) developed by the authors and their colleagues in recent years is presented. The primary focus is placed on the development of PFEM for both structural mechanics problems and fracture mechanics problems. The perturbation techniques are used as major tools for the analytical derivation. The following topics are covered: (1) representation and discretization of random fields; (2) development of PFEM for the general linear transient problem and nonlinear elasticity using Hu-Washizu variational principle; (3) computational aspects; (4) discussions of the application of PFEM to the reliability analysis of both brittle fracture and fatigue; and (5) a stochastic computational tool based on stochastic boundary element (SBEM). Results are obtained for the reliability index and corresponding probability of failure for: (1) fatigue crack growth; (2) defect geometry; (3) fatigue parameters; and (4) applied loads. These results show that initial defect is a critical parameter.

Probabilistic finite elements for fatigue and fracture analysis

NASA Technical Reports Server (NTRS)

Belytschko, Ted; Liu, Wing Kam

1993-01-01

An overview of the probabilistic finite element method (PFEM) developed by the authors and their colleagues in recent years is presented. The primary focus is placed on the development of PFEM for both structural mechanics problems and fracture mechanics problems. The perturbation techniques are used as major tools for the analytical derivation. The following topics are covered: (1) representation and discretization of random fields; (2) development of PFEM for the general linear transient problem and nonlinear elasticity using Hu-Washizu variational principle; (3) computational aspects; (4) discussions of the application of PFEM to the reliability analysis of both brittle fracture and fatigue; and (5) a stochastic computational tool based on stochastic boundary element (SBEM). Results are obtained for the reliability index and corresponding probability of failure for: (1) fatigue crack growth; (2) defect geometry; (3) fatigue parameters; and (4) applied loads. These results show that initial defect is a critical parameter.

Linear-Elastic 2D and 3D Finite Element Contact Analysis of a Hole Containing a Circular Insert in a Fatigue Test Coupon

DTIC Science & Technology

2015-07-01

circular hole in an aluminium plate fitted with a titanium fastener that were computed using two-dimensional finite element contact analysis. By...used to validate the contact stress distributions associated with a circular hole in an aluminium plate fitted with a titanium fastener that were...fatigue life and aircraft structural integrity management of RAAF airframes. An aluminium coupon has been previously designed in support of the

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

Mandell, John F.; Ashwill, Thomas D.; Wilson, Timothy J.

This report presents an analysis of trends in fatigue results from the Montana State University program on the fatigue of composite materials for wind turbine blades for the period 2005-2009. Test data can be found in the SNL/MSU/DOE Fatigue of Composite Materials Database which is updated annually. This is the fifth report in this series, which summarizes progress of the overall program since its inception in 1989. The primary thrust of this program has been research and testing of a broad range of structural laminate materials of interest to blade structures. The report is focused on current types of infusedmore » and prepreg blade materials, either processed in-house or by industry partners. Trends in static and fatigue performance are analyzed for a range of materials, geometries and loading conditions. Materials include: sixteen resins of three general types, five epoxy based paste adhesives, fifteen reinforcing fabrics including three fiber types, three prepregs, many laminate lay-ups and process variations. Significant differences in static and fatigue performance and delamination resistance are quantified for particular materials and process conditions. When blades do fail, the likely cause is fatigue in the structural detail areas or at major flaws. The program is focused strongly on these issues in addition to standard laminates. Structural detail tests allow evaluation of various blade materials options in the context of more realistic representations of blade structure than do the standard test methods. Types of structural details addressed in this report include ply drops used in thickness tapering, and adhesive joints, each tested over a range of fatigue loading conditions. Ply drop studies were in two areas: (1) a combined experimental and finite element study of basic ply drop delamination parameters for glass and carbon prepreg laminates, and (2) the development of a complex structured resin-infused coupon including ply drops, for comparison studies of various resins, fabrics and pry drop thicknesses. Adhesive joint tests using typical blade adhesives included both generic testing of materials parameters using a notched-lap-shear test geometry developed in this study, and also a series of simulated blade web joint geometries fabricated by an industry partner.« less

Relation between the fracture laws and the fatigue life of a surface-hardened pseudo-α titanium alloy

NASA Astrophysics Data System (ADS)

Bagmutov, V. P.; Vodop'yanov, V. I.; Zakharov, I. N.; Denisevich, D. S.

2016-07-01

The laws of fracture and fatigue life of the PT-3V pseudo-α titanium alloy subjected to surface hardening using electromechanical, ultrasonic, and combined treatment are studied. Fracture mechanisms and the structures of crack nucleation and growth zones are described using the results of metallographic and fractographic analysis of samples after fatigue tests. It is shown that the existence of a thin hardened layer on the sample surface changes the crack nucleation time and the state of fracture surface in the crack nucleation zone. This surface is characterized by signs of brittle or ductile fracture, which substantially affects the fatigue life of the sample.

Validation of the Modified Fatigue Impact Scale in Parkinson's disease.

PubMed

Schiehser, Dawn M; Ayers, Catherine R; Liu, Lin; Lessig, Stephanie; Song, David S; Filoteo, J Vincent

2013-03-01

Fatigue is a common symptom in Parkinson's disease (PD); however, a multidimensional scale that measures the impact of fatigue on functioning has yet to be validated in this population. The aim of this study was to examine the validity of the Modified Fatigue Impact Scale (MFIS), a self-report measure that assesses the effects of fatigue on physical, cognitive, and psychosocial functioning, in a sample of nondemented PD patients. PD patients (N = 100) completed the MFIS, the Positive and Negative Affect Schedule (PANAS-X), and several additional measures of psychosocial, cognitive, and motor functioning. A Principal Component Analysis (PCA) and item analysis using Cronbach's alpha were conducted to determine structural validity and internal consistency of the MFIS. Correlational analyses were performed between the MFIS and the PANAS-X fatigue subscale to evaluate convergent validity and between the MFIS and measures of depression, anxiety, apathy, and disease-related symptoms to determine divergent validity. The PCA identified two viable MFIS subscales: a cognitive subscale and a combination of the original scale's physical and psychosocial subscales as one factor. Item analysis revealed high internal consistency of all 21 items and the items within the two subscales. The MFIS had strong convergent validity with the PANAS-X fatigue subscale and adequate divergent validity with measures of disease stage, motor function, and cognition. Overall, this study demonstrates that the MFIS is a valid multidimensional measure that can be used to evaluate the impact of fatigue on cognitive and physical/social functioning in PD patients without dementia. Published by Elsevier Ltd.

14 CFR 23.572 - Metallic wing, empennage, and associated structures.

Code of Federal Regulations, 2012 CFR

2012-01-01

... principal structural element, and that the remaining structure is able to withstand a static ultimate load... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES... experience: (1) A fatigue strength investigation in which the structure is shown by tests, or by analysis...

14 CFR 23.572 - Metallic wing, empennage, and associated structures.

Code of Federal Regulations, 2013 CFR

2013-01-01

... principal structural element, and that the remaining structure is able to withstand a static ultimate load... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES... experience: (1) A fatigue strength investigation in which the structure is shown by tests, or by analysis...

14 CFR 23.572 - Metallic wing, empennage, and associated structures.

Code of Federal Regulations, 2014 CFR

2014-01-01

... principal structural element, and that the remaining structure is able to withstand a static ultimate load... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES... experience: (1) A fatigue strength investigation in which the structure is shown by tests, or by analysis...

14 CFR 23.572 - Metallic wing, empennage, and associated structures.

Code of Federal Regulations, 2011 CFR

2011-01-01

... principal structural element, and that the remaining structure is able to withstand a static ultimate load... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES... experience: (1) A fatigue strength investigation in which the structure is shown by tests, or by analysis...

14 CFR 23.572 - Metallic wing, empennage, and associated structures.

Code of Federal Regulations, 2010 CFR

2010-01-01

... principal structural element, and that the remaining structure is able to withstand a static ultimate load... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES... experience: (1) A fatigue strength investigation in which the structure is shown by tests, or by analysis...

Fatigue and biological properties of Ti-6Al-4V ELI cellular structures with variously arranged cubic cells made by selective laser melting.

PubMed

Dallago, M; Fontanari, V; Torresani, E; Leoni, M; Pederzolli, C; Potrich, C; Benedetti, M

2018-02-01

Traditional implants made of bulk titanium are much stiffer than human bone and this mismatch can induce stress shielding. Although more complex to produce and with less predictable properties compared to bulk implants, implants with a highly porous structure can be produced to match the bone stiffness and at the same time favor bone ingrowth and regeneration. This paper presents the results of the mechanical and dimensional characterization of different regular cubic open-cell cellular structures produced by Selective Laser Melting (SLM) of Ti6Al4V alloy, all with the same nominal elastic modulus of 3GPa that matches that of human trabecular bone. The main objective of this research was to determine which structure has the best fatigue resistance through fully reversed fatigue tests on cellular specimens. The quality of the manufacturing process and the discrepancy between the actual measured cell parameters and the nominal CAD values were assessed through an extensive metrological analysis. The results of the metrological assessment allowed us to discuss the effect of manufacturing defects (porosity, surface roughness and geometrical inaccuracies) on the mechanical properties. Half of the specimens was subjected to a stress relief thermal treatment while the other half to Hot Isostatic Pressing (HIP), and we compared the effect of the treatments on porosity and on the mechanical properties. Fatigue strength seems to be highly dependent on the surface irregularities and notches introduced during the manufacturing process. In fully reversed fatigue tests, the high performances of stretching dominated structures compared to bending dominated structures are not found. In fact, with thicker struts, such structures proved to be more resistant, even if bending actions were present. Copyright © 2017 Elsevier Ltd. All rights reserved.

30 CFR 250.908 - What are the minimum structural fatigue design requirements?

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 2 2011-07-01 2011-07-01 false What are the minimum structural fatigue design... fatigue design requirements? (a) API RP 2A-WSD, Recommended Practice for Planning, Designing and... the design fatigue life of each joint and member be twice the intended service life of the structure...

Fatigue Life Prediction Based on Crack Closure and Equivalent Initial Flaw Size

PubMed Central

Wang, Qiang; Zhang, Wei; Jiang, Shan

2015-01-01

Failure analysis and fatigue life prediction are necessary and critical for engineering structural materials. In this paper, a general methodology is proposed to predict fatigue life of smooth and circular-hole specimens, in which the crack closure model and equivalent initial flaw size (EIFS) concept are employed. Different effects of crack closure on small crack growth region and long crack growth region are considered in the proposed method. The EIFS is determined by the fatigue limit and fatigue threshold stress intensity factor △Kth. Fatigue limit is directly obtained from experimental data, and △Kth is calculated by using a back-extrapolation method. Experimental data for smooth and circular-hole specimens in three different alloys (Al2024-T3, Al7075-T6 and Ti-6Al-4V) under multiple stress ratios are used to validate the method. In the validation section, Semi-circular surface crack and quarter-circular corner crack are assumed to be the initial crack shapes for the smooth and circular-hole specimens, respectively. A good agreement is observed between model predictions and experimental data. The detailed analysis and discussion are performed on the proposed model. Some conclusions and future work are given. PMID:28793625

Passive detection and localization of fatigue cracking in aluminum plates using Green's function reconstruction from ambient noise.

PubMed

Yang, Yang; Xiao, Li; Qu, Wenzhong; Lu, Ye

2017-11-01

Recent theoretical and experimental studies have demonstrated that a local Green's function can be retrieved from the cross-correlation of ambient noise field. This technique can be used to detect fatigue cracking in metallic structures, owing to the fact that the presence of crack can lead to a change in Green's function. This paper presents a method of structural fatigue cracking characterization method by measuring Green's function reconstruction from noise excitation and verifies the feasibility of crack detection in poor noise source distribution. Fatigue cracks usually generate nonlinear effects, in which different wave amplitudes and frequency compositions can cause different nonlinear responses. This study also undertakes analysis of the capacity of the proposed approach to identify fatigue cracking under different noise amplitudes and frequency ranges. Experimental investigations of an aluminum plate are conducted to assess the cross-correlations of received noise between sensor pairs and finally to detect the introduced fatigue crack. A damage index is proposed according to the variation between cross-correlations obtained from the pristine crack closed state and the crack opening-closure state when sufficient noise amplitude is used to generate nonlinearity. A probability distribution map of damage is calculated based on damage indices. The fatigue crack introduced in the aluminum plate is successfully identified and oriented, verifying that a fatigue crack can be detected by reconstructing Green's functions from an imperfect diffuse field in which ambient noise sources exist locally. Copyright © 2017 Elsevier B.V. All rights reserved.

Al-Li alloy AA2198's very high cycle fatigue crack initiation mechanism and its fatigue thermal effect

NASA Astrophysics Data System (ADS)

Xu, Luopeng; Cao, Xiaojian; Chen, Yu; Wang, Qingyuan

2015-10-01

AA2198 alloy is one of the third generation Al-Li alloys which have low density, high elastic modulus, high specific strength and specific stiffness. Compared With the previous two generation Al-Li alloys, the third generation alloys have much improved in alloys strength, corrosion resistance and weldable characteristic. For these advantages, the third generation Al-Li alloys are used as aircraft structures, such as C919 aviation airplane manufactured by China and Russia next generation aviation airplane--MS-21. As we know, the aircraft structures are usually subjected to more than 108 cycles fatigue life during 20-30 years of service, however, there is few reported paper about the third generation Al-Li alloys' very high cycle fatigue(VHCF) which is more than 108 cycles fatigue. The VHCF experiment of AA2198 have been carried out. The two different initiation mechanisms of fatigue fracture have been found in VHCF. The cracks can initiate from the interior of the testing material with lower stress amplitude and more than 108 cycles fatigue life, or from the surface or subsurface of material which is the dominant reason of fatigue failures. During the experiment, the infrared technology is used to monitor the VHCF thermal effect. With the increase of the stress, the temperature of sample is also rising up, increasing about 15 °C for every 10Mpa. The theoretical thermal analysis is also carried out.

Parallel computing for probabilistic fatigue analysis

NASA Technical Reports Server (NTRS)

Sues, Robert H.; Lua, Yuan J.; Smith, Mark D.

1993-01-01

This paper presents the results of Phase I research to investigate the most effective parallel processing software strategies and hardware configurations for probabilistic structural analysis. We investigate the efficiency of both shared and distributed-memory architectures via a probabilistic fatigue life analysis problem. We also present a parallel programming approach, the virtual shared-memory paradigm, that is applicable across both types of hardware. Using this approach, problems can be solved on a variety of parallel configurations, including networks of single or multiprocessor workstations. We conclude that it is possible to effectively parallelize probabilistic fatigue analysis codes; however, special strategies will be needed to achieve large-scale parallelism to keep large number of processors busy and to treat problems with the large memory requirements encountered in practice. We also conclude that distributed-memory architecture is preferable to shared-memory for achieving large scale parallelism; however, in the future, the currently emerging hybrid-memory architectures will likely be optimal.

Structural Performance of Inconel 625 Superalloy Brazed Joints

NASA Astrophysics Data System (ADS)

Chen, Jianqiang; Demers, Vincent; Cadotte, Eve-Line; Turner, Daniel; Bocher, Philippe

2017-02-01

The purpose of this work was to investigate tensile and fatigue behaviors of Inconel 625 superalloy brazed joints after transient liquid-phase bonding process. Brazing was performed in a vacuum furnace using a nickel-based filler metal in a form of paste to join wrought Inconel 625 plates. Mechanical tests were carried out on single-lap joints under various lap distance-to-thickness ratios. The fatigue crack initiation and crack growth modes were examined via metallographic analysis, and the effect of local stress on fatigue life was assessed by finite element simulations. The fatigue results show that fatigue strength and endurance limit increase with overlap distance, leading to a relatively large scatter of results. Fatigue cracks nucleated in the high-stressed region of the weld fillets from brittle eutectic phases or from internal brazing cavities. The present work proposes to rationalize the results by using the local stress at the brazing fillet. When using this local stress, all fatigue-obtained results find themselves on a single S- N curve, providing a design curve for any joint configuration in fatigue solicitation.

Psychometric properties of the Polish version of the Multidimensional Fatigue Inventory-20 in cancer patients.

PubMed

Buss, Tomasz; Kruk, Agnieszka; Wiśniewski, Piotr; Modlinska, Aleksandra; Janiszewska, Justyna; Lichodziejewska-Niemierko, Monika

2014-10-01

Multidimensional questionnaires estimating cancer-related fatigue (CRF) as a symptom cluster or a clinical syndrome primarily have been used and validated in English-speaking populations. However, cultural issues and language peculiarities can affect CRF assessment The main aims of this study were to evaluate the psychometric properties of the Polish version of the Multidimensional Fatigue Inventory-20 (MFI-20) and to deliver to clinicians a multidimensional tool for CRF assessment in Polish-speaking patients with cancer. After forward-backward translation procedures, the Polish version of MFI-20 was administered to 340 cancer patients. The Polish MFI-20 was appraised in terms of acceptability, reliability, and validity. Internal consistency was assessed by calculating Cronbach's alpha coefficients. Structural validity was evaluated with confirmatory factor analysis. The translated MFI-20 was well accepted; 90% of subjects fully completed the questionnaire. The overall Cronbach's alpha coefficient was 0.9, ranging from 0.57 to 0.81. All correlation coefficients among Numeric Rating Scale-fatigue, fatigue-related items from the European Organization for Research and Treatment of Cancer Quality of Life Core-30 questionnaire, and the MFI--20 were statistically significant (P < 0.001). Confirmatory factor analysis demonstrated good structural validity and revealed only three dimensions in the Polish version of the MFI-20-physical and mental fatigue as well as reduced motivation. The Polish version of the MFI-20 is well accepted by patients, reliable, and a valid instrument to assess CRF in Polish cancer patients. Copyright © 2014 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.

Three-dimensional elastic-plastic finite-element analysis of fatigue crack propagation

NASA Technical Reports Server (NTRS)

Goglia, G. L.; Chermahini, R. G.

1985-01-01

Fatigue cracks are a major problem in designing structures subjected to cyclic loading. Cracks frequently occur in structures such as aircraft and spacecraft. The inspection intervals of many aircraft structures are based on crack-propagation lives. Therefore, improved prediction of propagation lives under flight-load conditions (variable-amplitude loading) are needed to provide more realistic design criteria for these structures. The main thrust was to develop a three-dimensional, nonlinear, elastic-plastic, finite element program capable of extending a crack and changing boundary conditions for the model under consideration. The finite-element model is composed of 8-noded (linear-strain) isoparametric elements. In the analysis, the material is assumed to be elastic-perfectly plastic. The cycle stress-strain curve for the material is shown Zienkiewicz's initial-stress method, von Mises's yield criterion, and Drucker's normality condition under small-strain assumptions are used to account for plasticity. The three-dimensional analysis is capable of extending the crack and changing boundary conditions under cyclic loading.

14 CFR 29.571 - Fatigue Tolerance Evaluation of Metallic Structure.

Code of Federal Regulations, 2013 CFR

2013-01-01

... Structure. 29.571 Section 29.571 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... Evaluation § 29.571 Fatigue Tolerance Evaluation of Metallic Structure. (a) A fatigue tolerance evaluation of... Administrator. (d) Considering all rotorcraft structure, structural elements, and assemblies, each PSE must be...

14 CFR 29.571 - Fatigue Tolerance Evaluation of Metallic Structure.

Code of Federal Regulations, 2014 CFR

2014-01-01

... Structure. 29.571 Section 29.571 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... Evaluation § 29.571 Fatigue Tolerance Evaluation of Metallic Structure. (a) A fatigue tolerance evaluation of... Administrator. (d) Considering all rotorcraft structure, structural elements, and assemblies, each PSE must be...

Analysis of cold worked holes for structural life extension

NASA Technical Reports Server (NTRS)

Wieland, David H.; Cutshall, Jon T.; Burnside, O. Hal; Cardinal, Joseph W.

1994-01-01

Cold working holes for improved fatigue life of fastener holes are widely used on aircraft. This paper presents methods used by the authors to determine the percent of cold working to be applied and to analyze fatigue crack growth of cold worked fastener holes. An elastic, perfectly-plastic analysis of a thick-walled tube is used to determine the stress field during the cold working process and the residual stress field after the process is completed. The results of the elastic/plastic analysis are used to determine the amount of cold working to apply to a hole. The residual stress field is then used to perform damage tolerance analysis of a crack growing out of a cold worked fastener hole. This analysis method is easily implemented in existing crack growth computer codes so that the cold worked holes can be used to extend the structural life of aircraft. Analytical results are compared to test data where appropriate.

Reliability analysis applied to structural tests

NASA Technical Reports Server (NTRS)

Diamond, P.; Payne, A. O.

1972-01-01

The application of reliability theory to predict, from structural fatigue test data, the risk of failure of a structure under service conditions because its load-carrying capability is progressively reduced by the extension of a fatigue crack, is considered. The procedure is applicable to both safe-life and fail-safe structures and, for a prescribed safety level, it will enable an inspection procedure to be planned or, if inspection is not feasible, it will evaluate the life to replacement. The theory has been further developed to cope with the case of structures with initial cracks, such as can occur in modern high-strength materials which are susceptible to the formation of small flaws during the production process. The method has been applied to a structure of high-strength steel and the results are compared with those obtained by the current life estimation procedures. This has shown that the conventional methods can be unconservative in certain cases, depending on the characteristics of the structure and the design operating conditions. The suitability of the probabilistic approach to the interpretation of the results from full-scale fatigue testing of aircraft structures is discussed and the assumptions involved are examined.

Evaluation of Inelastic Constitutive Models for Nonlinear Structural Analysis

NASA Technical Reports Server (NTRS)

Kaufman, A.

1983-01-01

The influence of inelastic material models on computed stress-strain states, and therefore predicted lives, was studied for thermomechanically loaded structures. Nonlinear structural analyses were performed on a fatigue specimen which was subjected to thermal cycling in fluidized beds and on a mechanically load cycled benchmark notch specimen. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic-kinematic, combined plus transient creep) were exercised. Of the plasticity models, kinematic hardening gave results most consistent with experimental observations. Life predictions using the computed strain histories at the critical location with a Strainrange Partitioning approach considerably overpredicted the crack initiation life of the thermal fatigue specimen.

Fatigue risks in the connections of sign support structures : [technical brief].

DOT National Transportation Integrated Search

2013-07-01

The latest edition of the AASHTO design specifications (AASHTO 2001) introduced provisions for fatigue design. However, many structures presently in service were designed before fatigue provisions were part of the design specifications. The fatigue d...

Analysis of Lightweight Materials for the AM2 System

DTIC Science & Technology

2014-06-01

and fatigue behavior in magnesium alloys . Materials Science & Engineering A (Structural Materials: Properties , Microstructure and Processing ), v 434...Table 7. Tensile properties of the alloys AA2024 or the T3 and T81 temper designations (Kuo et al . 2005...using a powder metallurgy technique, such as a standard cold compacting press and sintering process . However, the fatigue life of the liquid-based

30 CFR 250.908 - What are the minimum structural fatigue design requirements?

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 2 2010-07-01 2010-07-01 false What are the minimum structural fatigue design... Platform Approval Program § 250.908 What are the minimum structural fatigue design requirements? (a) API RP... (incorporated by reference as specified in 30 CFR 250.198), requires that the design fatigue life of each joint...

14 CFR 23.571 - Metallic pressurized cabin structures.

Code of Federal Regulations, 2012 CFR

2012-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Structure... the following: (a) A fatigue strength investigation in which the structure is shown by tests, or by analysis supported by test evidence, to be able to withstand the repeated loads of variable magnitude...

Above-knee prosthesis design based on fatigue life using finite element method and design of experiment.

PubMed

Phanphet, Suwattanarwong; Dechjarern, Surangsee; Jomjanyong, Sermkiat

2017-05-01

The main objective of this work is to improve the standard of the existing design of knee prosthesis developed by Thailand's Prostheses Foundation of Her Royal Highness The Princess Mother. The experimental structural tests, based on the ISO 10328, of the existing design showed that a few components failed due to fatigue under normal cyclic loading below the required number of cycles. The finite element (FE) simulations of structural tests on the knee prosthesis were carried out. Fatigue life predictions of knee component materials were modeled based on the Morrow's approach. The fatigue life prediction based on the FE model result was validated with the corresponding structural test and the results agreed well. The new designs of the failed components were studied using the design of experimental approach and finite element analysis of the ISO 10328 structural test of knee prostheses under two separated loading cases. Under ultimate loading, knee prosthesis peak von Mises stress must be less than the yield strength of knee component's material and the total knee deflection must be lower than 2.5mm. The fatigue life prediction of all knee components must be higher than 3,000,000 cycles under normal cyclic loading. The design parameters are the thickness of joint bars, the diameter of lower connector and the thickness of absorber-stopper. The optimized knee prosthesis design meeting all the requirements was recommended. Experimental ISO 10328 structural test of the fabricated knee prosthesis based on the optimized design confirmed the finite element prediction. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

Structural analysis of a reflux pool-boiler solar receiver

NASA Astrophysics Data System (ADS)

Hoffman, E. L.; Stone, C. M.

1991-06-01

Coupled thermal-structural finite element calculations of a reflux pool-boiler solar receiver were performed to characterize the operating stresses and to address issues affecting the service life of the receiver. Analyses performed using shell elements provided information for receiver material selection and design optimization. Calculations based on linear elastic fracture mechanics principles were performed using continuum elements to assess the vulnerability of a seam-weld to fatigue crack growth. All calculations were performed using ABAQUS, a general purpose finite element code, and elements specifically formulated for coupled thermal-structural analysis. Two materials were evaluated: 316L SS and Haynes 230 alloys. The receiver response was simulated for a combination of structural and thermal loads that represent the startup and operating conditions of the receiver. For both materials, maximum stresses in the receiver developed shortly after startup due to uneven temperature distribution across the receiver surface. The largest effective stress was near yield in the 316L SS receiver and below 39 percent of yield in the Haynes 230 receiver. The calculations demonstrated that stress reductions of over 25 percent could be obtained by reducing the aft dome thickness to one closer to the absorber. The fatigue calculations demonstrated that the stress distribution near the seam-weld notch depends primarily on the structural load created by internal pressurization of the receiver rather than the thermal, indicating that the thermal loads can be neglected when assessing the stress intensity near the seam-weld notch. The stress intensity factor, computed using the J-integral method and crack opening-displacement field equations, was significantly below the fatigue threshold for most steels. The calculations indicated that the weld notch was always loaded in compression, a condition which is not conducive to fatigue crack growth.

High Sensitive Methods for Health Monitoring of Compressor Blades and Fatigue Detection

PubMed Central

Witoś, Mirosław

2013-01-01

The diagnostic and research aspects of compressor blade fatigue detection have been elaborated in the paper. The real maintenance and overhaul problems and characteristic of different modes of metal blade fatigue (LCF, HCF, and VHCF) have been presented. The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, are taken into account. The three experimental methods of structural health assessment are considered. The metal magnetic memory (MMM), experimental modal analysis (EMA) and tip timing (TTM) methods provide information on the damage of diagnosed objects, for example, compressor blades. Early damage symptoms, that is, magnetic and modal properties of material strengthening and weakening phases (change of local dislocation density and grain diameter, increase of structural and magnetic anisotropy), have been described. It has been proven that the shape of resonance characteristic gives abilities to determine if fatigue or a blade crack is concerned. The capabilities of the methods for steel and titanium alloy blades have been illustrated in examples from active and passive experiments. In the conclusion, the MMM, EMA, and TTM have been verified, and the potential for reliable diagnosis of the compressor blades using this method has been confirmed. PMID:24191135

Factors associated with multidimensional aspect of post-stroke fatigue in acute stroke period.

PubMed

Mutai, Hitoshi; Furukawa, Tomomi; Houri, Ayumi; Suzuki, Akihito; Hanihara, Tokiji

2017-04-01

Post-stroke fatigue (PSF) is a frequent and distressing consequence of stroke, and can be both acute and long lasting. We aimed to investigate multidimensional aspects of acute PSF and to determine the clinical factors relevant to acute PSF. We collected data of 101 patients admitted to the hospital for acute stroke. PSF was assessed using the Multidimensional Fatigue Inventory within 2 weeks of stroke. Measures included Mini-Mental State Examination, Hospital Anxiety and Depression Scale, and Functional Independence Measure. Stroke character, lesion location, and clinical variables that potentially influence PSF were also collected. The prevalence of pathological fatigue is 56.4% within 2 weeks of stroke. Binary logistic regression analysis revealed that anxiety was the only predictor for presence of PSF (OR=1.32, 95% CI: 1.13-1.53, P<0.001). Multivariate stepwise regression analysis showed anxiety, right lesion side, thalamus, and/or brainstem were independently associated with general fatigue, right lesion side, depression, diabetes mellitus, and anxiety with physical fatigue, depression with reduced activity, depression, and BMI with reduced motivation, depression, and diabetes mellitus with mental fatigue. PSF was highly prevalent in the acute phase, and specific factors including lesion location (right side lesion, thalamic and brainstem lesion), anxiety, and depression were independently associated with multidimensional aspects of PSF. Further study is needed to elucidate how specific structural lesions and anxiety symptoms relate to the development of early fatigue following stroke. Copyright © 2016 Elsevier B.V. All rights reserved.

Fatigue behavior of porous biomaterials manufactured using selective laser melting.

PubMed

Yavari, S Amin; Wauthle, R; van der Stok, J; Riemslag, A C; Janssen, M; Mulier, M; Kruth, J P; Schrooten, J; Weinans, H; Zadpoor, A A

2013-12-01

Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S-N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S-N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S-N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S-N curves. It is shown that the measured data points conform to the fitted power law very well, R(2)=0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (<0.2) is lower than that of corresponding solid material (c.a. 0.4). © 2013.

Multidimensional daily diary of fatigue-fibromyalgia-17 items (MDF-fibro-17): part 2 psychometric evaluation in fibromyalgia patients.

PubMed

Li, Y; Morris, S; Cole, J; Dube', S; Smith, J A M; Burbridge, C; Symonds, T; Hudgens, S; Wang, W

2017-05-18

The Multidimensional Daily Diary of Fatigue-Fibromyalgia-17 instrument (MDF-Fibro-17) has been developed for use in fibromyalgia (FM) clinical studies and includes 5 domains: Global Fatigue Experience, Cognitive Fatigue, Physical Fatigue, Motivation, and Impact on Function. Psychometric properties of the MDF-Fibro-17 needed to demonstrate the appropriateness of using this instrument in clinical studies are presented. Psychometric analyses were conducted to evaluate the factor structure, reliability, validity, and responsiveness of the MDF-Fibro-17 using data from a Phase 2 clinical study of FM patients (N = 381). Confirmatory factor analyses (CFA) were performed to ensure understanding of the multidimensional domain structure, and a secondary factor analysis of the domains examined the appropriateness of calculating a total score in addition to domain scores. Longitudinal psychometric analyses (test-retest reliability and responder analysis) were also conducted on the data from Baseline to Week 6. The CFA supported the 17-item, 5 domain structure of this instrument as the best fit of the data: comparative fit index (CFI) and non-normed fit index (NNFI) were 0.997 and 0.992 respectively, standardized root mean square residual (SRMR) was 0.010 and the root mean square error of approximation (RMSEA) was 0.06. In addition, total score (CFI and NNFI both 0.95) met required standards. For the total and 5 domain scores, reliability and validity data were acceptable: test-retest and internal consistency were above 0.9; correlations were as expected with the Global Fatigue Index (GFI) (0.62-0.75), Fibromyalgia Impact Questionnaire (FIQ) Total (0.59-0.71), and 36-Item Short Form Health Survey (SF-36) vitality (VT) (0.43-0.53); and discrimination was shown using quintile scores for the GFI, FIQ Total, and Pain Numeric Rating Scale (NRS) quartiles. In addition, sensitivity to change was demonstrated with an overall mean responder score of -2.59 using anchor-based methods. The MDF-Fibro-17 reliably measures 5 domains of FM-related fatigue and psychometric evaluation confirms that this measure meets or exceeds each of the predefined acceptable thresholds for evidence of reliability, validity, and responsiveness to changes in clinical status. This suggests that the MDF-Fibro-17 is an appropriate and responsive measure of FM-related fatigue in clinical studies.

Futurepath: The Story of Research and Technology at NASA Lewis Research Center. Structures for Flight Propulsion, ARC Sprayed Monotape, National Aero-Space Plane

NASA Technical Reports Server (NTRS)

1989-01-01

The story of research and technology at NASA Lewis Research Center's Structures Division is presented. The job and designs of the Structures Division needed for flight propulsion is described including structural mechanics, structural dynamics, fatigue, and fracture. The video briefly explains why properties of metals used in structural mechanics need to be tested. Examples of tests and simulations used in structural dynamics (bodies in motion) are briefly described. Destructive and non-destructive fatigue/fracture analysis is also described. The arc sprayed monotape (a composite material) is explained, as are the programs in which monotape plays a roll. Finally, the National Aero-Space Plane (NASP or x-30) is introduced, including the material development and metal matrix as well as how NASP will reduce costs for NASA.

Psychometric Properties of the Chinese Version of the Occupational Fatigue Exhaustion/Recovery Scale: A Test in a Nursing Population.

PubMed

Fang, Jin-Bo; Zhou, Chun-Fen; Huang, Jing; Qiu, Chang-Jian

2018-06-01

The Occupational Fatigue Exhaustion/Recovery Scale (OFER) was designed to assess occupational fatigue in nurses. Although the original English version of this instrument has shown high degrees of reliability and validity, a Chinese version of this scale has yet to be verified. The aim of this study was to evaluate the psychometric properties of the OFER in a population of Chinese nurses. The scale was translated using translation and back-translation. The validities and reliabilities were evaluated on 923 qualified participants using content validity index, concurrent validity, factorial validity, internal consistency reliability, and test-retest reliability. The content validity index for the OFER was .92. The correlation coefficients between the scores of the OFER subscales and the criteria in this study (varying from -.498 to .705) verified that the OFER has acceptable concurrent validity. Principal component analysis and confirmatory factor analysis revealed that three factors correspond to the structure of the original instrument and that recovery mediates the relationship between acute and chronic fatigue. The Cronbach's alpha for the chronic fatigue, acute fatigue, and intershift recovery subscales were .83, .85, and .86, respectively. Test-retest reliabilities with correlation coefficients from .61 to .78 were found in the three subscales. OFER is a reliable and valid instrument for assessing work-related fatigue in Chinese nurses. However, further improvement of the acute fatigue subscale is recommended. The OFER has the potential to elicit information that is useful for assessing fatigue in nurses in China. Furthermore, as it differentiates between acute and chronic fatigue, OFER may be an effective tool for guiding the development and implementation of various, related intervention measures.

Exploring the potential role of the advanced nurse practitioner within a care path for patients with chronic fatigue syndrome.

PubMed

Ryckeghem, Hannah; Delesie, Liesbeth; Tobback, Els; Lievens, Stefaan; Vogelaers, Dirk; Mariman, An

2017-07-01

To explore the experiences and expectations of patients with chronic fatigue syndrome and general practitioners to develop the potential role of an advanced nurse practitioner at the diagnostic care path of abnormal fatigue developed for regional transmural implementation in the Belgian provinces of East and West Flanders. Patients with chronic fatigue syndrome experience an incapacitating chronic fatigue that is present for at least 6 months. Since many uncertainties exist about the causes and progression of the disease, patients have to cope with disbelief and scepticism. Access to health care may be hampered, which could lead to inappropriate treatments and guidance. Qualitative design. Individual semi-structured interviews were conducted with patients with chronic fatigue syndrome and general practitioners in Belgium. Data were collected over 9 months in 2014-2015. All interviews were audio recorded and transcribed for qualitative analysis using open explorative thematic coding. Fifteen patients and 15 general practitioners were interviewed. Three themes were identified: mixed feelings with the diagnosis, lack of one central intermediator and insufficient coordination. Participants stressed the need for education, knowledge and an intermediator to provide relevant information at the right time and to build up a trust relationship. This qualitative exploration underscores some clear deficiencies in the guidance of patients suffering from chronic fatigue syndrome and abnormal fatigue. An advanced nurse practitioner as a central intermediator in the transmural care of these patients could promote interdisciplinary/multidisciplinary collaboration and effective communication, provide education and ensure a structured and coordinated approach. © 2016 John Wiley & Sons Ltd.

Structural Damage Identification in Stiffened Plate Fatigue Specimens Using Piezoelectric Active Sensing

DTIC Science & Technology

2011-09-01

isolated AO mode first arrival, recorded at PZT 2, is shown at 3 different fatigue levels. Figure 5. The area under the PSD curve, calculated twice...Structural Damage Identification in Stiffened Plate Fatigue Specimens Using Piezoelectric Active Sensing B. L. GRISSO, G. PARK, L. W. SALVINO...with several challenges including limited performance knowledge of the materials, aluminum sensitization, structural fatigue performance, and

14 CFR 121.1109 - Supplemental inspections.

Code of Federal Regulations, 2010 CFR

2010-01-01

... damage-tolerance-based inspections and procedures for airplane structure susceptible to fatigue cracking... termed “fatigue critical structure.” (2) Adverse effects of repairs, alterations, and modifications. The..., and modifications may have on fatigue critical structure and on inspections required by paragraph (c...

The Influence of Work-Related Fatigue, Work Conditions, and Personal Characteristics on Intent to Leave Among New Nurses.

PubMed

Liu, Yi; Wu, Li-Min; Chou, Pi-Ling; Chen, Mei-Hsin; Yang, Li-Chien; Hsu, Hsin-Tien

2016-01-01

This study aimed to (a) test the fit of the hypothesized model for new nurses' intent to leave and (b) determine the extent to which personal characteristics, work conditions, and work-related fatigue predict intent to leave among new nurses. This study was a cross-sectional survey study. A total of 162 new nurses were recruited. A hypothesized model was proposed for model testing. Structural equation modelling was used for data analysis. Work conditions only had an effect through work-related fatigue on new nurses' intent to leave. Personal characteristics did not have a significant effect on new nurses' intent to leave. The final model showed a good fit. Work-related fatigue, work conditions, and health explained 65% of the variance in new nurses' intent to leave. Work-related fatigue was a major determinant of new nurses' intent to leave. More attention should be paid to fatigue reduction strategies among new nurses. Work-related fatigue should be monitored, particularly for new nurses who work more than 10 hr per day and who have greater workloads. © 2015 Sigma Theta Tau International.

Fatigue damage monitoring for basalt fiber reinforced polymer composites using acoustic emission technique

NASA Astrophysics Data System (ADS)

Wang, Wentao; Li, Hui; Qu, Zhi

2012-04-01

Basalt fiber reinforced polymer (BFRP) is a structural material with superior mechanical properties. In this study, unidirectional BFRP laminates with 14 layers are made with the hand lay-up method. Then, the acoustic emission technique (AE) combined with the scanning electronic microscope (SEM) technique is employed to monitor the fatigue damage evolution of the BFRP plates in the fatigue loading tests. Time-frequency analysis using the wavelet transform technique is proposed to analyze the received AE signal instead of the peak frequency method. A comparison between AE signals and SEM images indicates that the multi-frequency peaks picked from the time-frequency curves of AE signals reflect the accumulated fatigue damage evolution and fatigue damage patterns. Furthermore, seven damage patterns, that is, matrix cracking, delamination, fiber fracture and their combinations, are identified from the time-frequency curves of the AE signals.

Analysis of fatigue reliability for high temperature and high pressure multi-stage decompression control valve

NASA Astrophysics Data System (ADS)

Yu, Long; Xu, Juanjuan; Zhang, Lifang; Xu, Xiaogang

2018-03-01

Based on stress-strength interference theory to establish the reliability mathematical model for high temperature and high pressure multi-stage decompression control valve (HMDCV), and introduced to the temperature correction coefficient for revising material fatigue limit at high temperature. Reliability of key dangerous components and fatigue sensitivity curve of each component are calculated and analyzed by the means, which are analyzed the fatigue life of control valve and combined with reliability theory of control valve model. The impact proportion of each component on the control valve system fatigue failure was obtained. The results is shown that temperature correction factor makes the theoretical calculations of reliability more accurate, prediction life expectancy of main pressure parts accords with the technical requirements, and valve body and the sleeve have obvious influence on control system reliability, the stress concentration in key part of control valve can be reduced in the design process by improving structure.

Time-dependent reliability analysis of ceramic engine components

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.

1993-01-01

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing either the power or Paris law relations. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Two example problems demonstrating proof testing and fatigue parameter estimation are given.

Fatigue of reinforcing bars during hydro-demolition

NASA Astrophysics Data System (ADS)

Hyland, C. W. K.; Ouwejan, A.

2017-05-01

Reinforcing steel fractured during hydro-demolition of a reinforced concrete pier head due to low cycle flexural fatigue from vibration caused by impact of the high pressure water jet on the exposed length of the bars. Research into the fatigue performance of steel reinforcing steel tends to focus on the high cycle axial performance in reinforced concrete members and re-bending behaviour. However with the increasing use of hydro-demolition of concrete structures as part of remediation works care is required to ensure the steel reinforcement exposed to the high pressure jet of water is not going to suffer relatively low cycle flexural damage that may compromise the designed performance of the completed reinforced concrete structure. This paper describes the failure assessment, fatigue analysis, and metallographic examination that was undertaken. It was found that the rib to flank transition radius on the reinforcement steel was small enough to cause a significant stress concentration effect and was the location of fatigue crack growth. A relatively simple analysis using the maximum unrestrained cantilevered bar length and force exerted by the water jet was used to calculate the maximum expected bending moment. This was compared to the bending capacity at initiation of yielding at the rib flank transition accounting for stress concentration effects. This showed that the observed cyclic reversing ductile crack growth and fracture of the H25 bars was consistent with the loading applied. A method is proposed based on these observations to assess suitable limits for unrestrained bar lengths or maximum working offset of the water jet from the point of bar restraint when undertaking hydro-demolition work. The fatigue critical performance requirements of AS/NZS4671 500E bars are also therefore compared with those of BS4449:2005 and PN EN/ISO 15630-1:2011 for comparable 500C bars

FAA/NASA International Symposium on Advanced Structural Integrity Methods for Airframe Durability and Damage Tolerance, part 2

NASA Technical Reports Server (NTRS)

Harris, Charles E. (Editor)

1994-01-01

The international technical experts in the areas of durability and damage tolerance of metallic airframe structures were assembled to present and discuss recent research findings and the development of advanced design and analysis methods, structural concepts, and advanced materials. The principal focus of the symposium was on the dissemination of new knowledge and the peer-review of progress on the development of advanced methodologies. Papers were presented on the following topics: structural concepts for enhanced durability, damage tolerance, and maintainability; new metallic alloys and processing technology; fatigue crack initiation and small crack effects; fatigue crack growth models; fracture mechanics failure criteria for ductile materials; structural mechanics methodology for residual strength and life prediction; development of flight load spectra for design and testing; and corrosion resistance.

14 CFR 27.571 - Fatigue evaluation of flight structure.

Code of Federal Regulations, 2010 CFR

2010-01-01

... § 27.309, except that maneuvering load factors need not exceed the maximum values expected in operation... paragraph (a)(3) of this section. (b) Fatigue tolerance evaluation. It must be shown that the fatigue tolerance of the structure ensures that the probability of catastrophic fatigue failure is extremely remote...

Review of fatigue and fracture research at NASA Langley Research Center

NASA Technical Reports Server (NTRS)

Everett, Richard A., Jr.

1988-01-01

Most dynamic components in helicopters are designed with a safe-life constant-amplitude testing approach that has not changed in many years. In contrast, the fatigue methodology in other industries has advanced significantly in the last two decades. Recent research at the NASA Langley Research Center and the U.S. Army Aerostructures Directorate at Langley are reviewed relative to fatigue and fracture design methodology for metallic components. Most of the Langley research was directed towards the damage tolerance design approach, but some work was done that is applicable to the safe-life approach. In the areas of testing, damage tolerance concepts are concentrating on the small-crack effect in crack growth and measurement of crack opening stresses. Tests were conducted to determine the effects of a machining scratch on the fatigue life of a high strength steel. In the area of analysis, work was concentrated on developing a crack closure model that will predict fatigue life under spectrum loading for several different metal alloys including a high strength steel that is often used in the dynamic components of helicopters. Work is also continuing in developing a three-dimensional, finite-element stress analysis for cracked and uncracked isotropic and anisotropic structures. A numerical technique for solving simultaneous equations called the multigrid method is being pursued to enhance the solution schemes in both the finite-element analysis and the boundary element analysis. Finally, a fracture mechanics project involving an elastic-plastic finite element analysis of J-resistance curve is also being pursued.

Nonlinear Fatigue Damage Model Based on the Residual Strength Degradation Law

NASA Astrophysics Data System (ADS)

Yongyi, Gao; Zhixiao, Su

In this paper, a logarithmic expression to describe the residual strength degradation process is developed in order to fatigue test results for normalized carbon steel. The definition and expression of fatigue damage due to symmetrical stress with a constant amplitude are also given. The expression of fatigue damage can also explain the nonlinear properties of fatigue damage. Furthermore, the fatigue damage of structures under random stress is analyzed, and an iterative formula to describe the fatigue damage process is deduced. Finally, an approximate method for evaluating the fatigue life of structures under repeated random stress blocking is presented through various calculation examples.

Fatigue based design and analysis of wheel hub for Student formula car by Simulation Approach

NASA Astrophysics Data System (ADS)

Gowtham, V.; Ranganathan, A. S.; Satish, S.; Alexis, S. John; Siva kumar, S.

2016-09-01

In the existing design of Wheel hub used for Student formula cars, the brake discs cannot be removed easily since the disc is mounted in between the knuckle and hub. In case of bend or any other damage to the disc, the replacement of the disc becomes difficult. Further using OEM hub and knuckle that are used for commercial vehicles will result in increase of unsprung mass, which should be avoided in Student formula cars for improving the performance. In this design the above mentioned difficulties have been overcome by redesigning the hub in such a way that the brake disc could be removed easily by just removing the wheel and the caliper and also it will have reduced weight when compared to existing OEM hub. A CAD Model was developed based on the required fatigue life cycles. The forces acting on the hub were calculated and linear static structural analysis was performed on the wheel hub for three different materials using ANSYS Finite Element code V 16.2. The theoretical fatigue strength was compared with the stress obtained from the structural analysis for each material.

77 FR 4890 - Damage Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures, and Damage Tolerance...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-01

...-AJ52, 2120-AJ51 Damage Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures, and Damage... Tolerance and Fatigue Evaluation for Composite Rotorcraft Structures'' (76 FR 74655), published December 1... December 2, 2011. In the ``Composite Rotorcraft Structures'' rule, the FAA amended its regulations to...

Fatigue crack detection and identification by the elastic wave propagation method

NASA Astrophysics Data System (ADS)

Stawiarski, Adam; Barski, Marek; Pająk, Piotr

2017-05-01

In this paper the elastic wave propagation phenomenon was used to detect the initiation of the fatigue damage in isotropic plate with a circular hole. The safety and reliability of structures mostly depend on the effectiveness of the monitoring methods. The Structural Health Monitoring (SHM) system based on the active pitch-catch measurement technique was proposed. The piezoelectric (PZT) elements was used as an actuators and sensors in the multipoint measuring system. The comparison of the intact and defected structures has been used by damage detection algorithm. One part of the SHM system has been responsible for detection of the fatigue crack initiation. The second part observed the evolution of the damage growth and assess the size of the defect. The numerical results of the wave propagation phenomenon has been used to present the effectiveness and accuracy of the proposed method. The preliminary experimental analysis has been carried out during the tension test of the aluminum plate with a circular hole to determine the efficiency of the measurement technique.

14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

Code of Federal Regulations, 2014 CFR

2014-01-01

... contribute to a catastrophic failure (such as wing, empennage, control surfaces and their systems, the... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25... of similar structural design and sonic excitation environment, that— (1) Sonic fatigue cracks are not...

14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

Code of Federal Regulations, 2012 CFR

2012-01-01

... contribute to a catastrophic failure (such as wing, empennage, control surfaces and their systems, the... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25... of similar structural design and sonic excitation environment, that— (1) Sonic fatigue cracks are not...

14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

Code of Federal Regulations, 2013 CFR

2013-01-01

... contribute to a catastrophic failure (such as wing, empennage, control surfaces and their systems, the... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25... of similar structural design and sonic excitation environment, that— (1) Sonic fatigue cracks are not...

Fatigue Resistant Design Criteria for MD SHA Cantilevered Mast Arm Signal Structure

DOT National Transportation Integrated Search

2017-12-01

The fatigue design of the mast arm structures and connections vary significantly based on the Category of Importance factor adopted and the load cases for fatigue design loads. Consideration should include the cost and size of the structures for both...

Creep-Fatigue Damage Investigation and Modeling of Alloy 617 at High Temperatures

NASA Astrophysics Data System (ADS)

Tahir, Fraaz

The Very High Temperature Reactor (VHTR) is one of six conceptual designs proposed for Generation IV nuclear reactors. Alloy 617, a solid solution strengthened Ni-base superalloy, is currently the primary candidate material for the tubing of the Intermediate Heat Exchanger (IHX) in the VHTR design. Steady-state operation of the nuclear power plant at elevated temperatures leads to creep deformation, whereas loading transients including startup and shutdown generate fatigue. A detailed understanding of the creep-fatigue interaction in Alloy 617 is necessary before it can be considered as a material for nuclear construction in ASME Boiler and Pressure Vessel Code. Current design codes for components undergoing creep-fatigue interaction at elevated temperatures require creep-fatigue testing data covering the entire range from fatigue-dominant to creep-dominant loading. Classical strain-controlled tests, which produce stress relaxation during the hold period, show a saturation in cycle life with increasing hold periods due to the rapid stress-relaxation of Alloy 617 at high temperatures. Therefore, applying longer hold time in these tests cannot generate creep-dominated failure. In this study, uniaxial isothermal creep-fatigue tests with non-traditional loading waveforms were designed and performed at 850 and 950°C, with an objective of generating test data in the creep-dominant regime. The new loading waveforms are hybrid strain-controlled and force-controlled testing which avoid stress relaxation during the creep hold. The experimental data showed varying proportions of creep and fatigue damage, and provided evidence for the inadequacy of the widely-used time fraction rule for estimating creep damage under creep-fatigue conditions. Micro-scale damage features in failed test specimens, such as fatigue cracks and creep voids, were quantified using a Scanning Electron Microscope (SEM) to find a correlation between creep and fatigue damage. Quantitative statistical imaging analysis showed that the microstructural damage features (cracks and voids) are correlated with a new mechanical driving force parameter. The results from this image-based damage analysis were used to develop a phenomenological life-prediction methodology called the effective time fraction approach. Finally, the constitutive creep-fatigue response of the material at 950°C was modeled using a unified viscoplastic model coupled with a damage accumulation model. The simulation results were used to validate an energy-based constitutive life-prediction model, as a mechanistic model for potential component and structure level creep-fatigue analysis.

Fatigue: a distressing symptom for patients with irritable bowel syndrome.

PubMed

Frändemark, Å; Jakobsson Ung, E; Törnblom, H; Simrén, M; Jakobsson, S

2017-01-01

Fatigue is a frequent symptom in patients with irritable bowel syndrome (IBS), and is associated with poor quality of life. However, few studies have evaluated its impact on daily life or the perceived distress it can cause. Using a multi-methods approach, this study describes the impact and manifestations of fatigue in patients with IBS and investigates the relationship between fatigue severity and illness-related and health-promoting factors. A total of 160 patients with IBS completed self-reported questionnaires assessing fatigue, gastrointestinal symptoms, psychological distress, and sense of coherence. Fatigue was assessed with the Fatigue Impact Scale, which also includes structured and open-ended questions which were analyzed with a deductive qualitative analysis. Patients were classified as having severe, moderate, or mild fatigue based on frequency, distress and impact on daily life. The open-ended questions revealed a multidimensional impact on life. Fatigue mainly interfered with the ability to perform physical activities, work, and domestic work, and the ability to interact socially. Decreased stamina was evident, along with strategies to limit the bodily consequences of tiredness. Severe fatigue was accompanied by more severe IBS symptoms, anxiety and depression and lower sense of coherence. Fatigue is a distressing symptom which occurs in a sizeable proportion of patients with IBS. It affects life in a multidimensional way, with poor bodily stamina being the most prominent feature. Fatigue, along with sense of coherence, depression and anxiety, needs to be assessed, confirmed and targeted for interventions. © 2016 John Wiley & Sons Ltd.

Fatigue performance of variable message sign & luminaire support structures : volume II, fatigue related wind loads on highway support structures.

DOT National Transportation Integrated Search

1998-05-01

In Order to determine equivalent static pressures for fatigue loads on cantilevered highway support structures a : cantilevered Variable Message Sign(VMS) located along Interstate westbound at mile marker 48.5 in northern : New Jersey was continuousl...

77 FR 50576 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures; OMB Approval of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-22

... Composite Rotorcraft Structures; OMB Approval of Information Collection AGENCY: Federal Aviation... requirement contained in the FAA's final rule, ``Damage Tolerance and Fatigue Evaluation of Composite... and Fatigue Evaluation of Composite Rotorcraft Structures,'' published in the Federal Register (76 FR...

Fatigue performance of variable message sign & luminaire support structures : volume I, fatigue related wind loads on highway support structures

DOT National Transportation Integrated Search

1998-04-01

In Order to determine equivalent static pressures for fatigue loads on cantilevered highway support structures a : cantilevered Variable Message Sign(VMS) located along Interstate westbound at mile marker 48.5 in northern : New Jersey was continuousl...

Fatigue testing of galvanized and ungalvanized socket connections.

DOT National Transportation Integrated Search

2014-09-01

The fatigue resistance of welded traffic signal support structure details is an ongoing research topic being : addressed at multiple universities primarily through state funding mechanisms. Fatigue problems with these : structures have plagued multip...

Patients with primary biliary cholangitis and fatigue present with depressive symptoms and selected cognitive deficits, but with normal attention performance and brain structure.

PubMed

Zenouzi, Roman; von der Gablentz, Janina; Heldmann, Marcus; Göttlich, Martin; Weiler-Normann, Christina; Sebode, Marcial; Ehlken, Hanno; Hartl, Johannes; Fellbrich, Anja; Siemonsen, Susanne; Schramm, Christoph; Münte, Thomas F; Lohse, Ansgar W

2018-01-01

In primary biliary cholangitis (PBC) fatigue is a major clinical challenge of unknown etiology. By demonstrating that fatigue in PBC is associated with an impaired cognitive performance, previous studies have pointed out the possibility of brain abnormalities underlying fatigue in PBC. Whether structural brain changes are present in PBC patients with fatigue, however, is unclear. To evaluate the role of structural brain abnormalities in PBC patients severely affected from fatigue we, therefore, performed a case-control cerebral magnetic resonance imaging (cMRI) study and correlated changes of white and grey brain matter with the cognitive and attention performance. 20 female patients with PBC and 20 female age-matched controls were examined in this study. The assessment of fatigue, psychological symptoms, cognitive and attention performance included clinical questionnaires, established cognition tests and a computerized test battery of attention performance. T1-weighted cMRI and diffusion tensor imaging (DTI) scans were acquired with a 3 Tesla scanner. Structural brain alterations were investigated with voxel-based morphometry (VBM) and DTI analyses. Results were correlated to the cognitive and attention performance. Compared to healthy controls, PBC patients had significantly higher levels of fatigue and associated psychological symptoms. Except for an impairment of verbal fluency, no cognitive or attention deficits were found in the PBC cohort. The VBM and DTI analyses revealed neither major structural brain abnormalities in the PBC cohort nor correlations with the cognitive and attention performance. Despite the high burden of fatigue and selected cognitive deficits, the attention performance of PBC patients appears to be comparable to healthy people. As structural brain alterations do not seem to be present in PBC patients with fatigue, fatigue in PBC must be regarded as purely functional. Future studies should evaluate, whether functional brain changes underlie fatigue in PBC.

Life extension of Structural Repairs – A statistical approach towards efficiency improvement

NASA Astrophysics Data System (ADS)

Deepashri, N. V.; Kalaiyappan, Mohan

2018-05-01

The life extension program of aircraft is taken up whenever aircraft’s intended life reaches close to its DSG (Design Service Goal). The Extended Service Goal (ESG) of an aircraft, in general, and structural repairs, in particular, is arrived at on the basis of F&DT (Fatigue & Damage Tolerance) analysis. Life extension program of aircraft consists of assessment of remaining life of all parts of the aircrafts including structural, mechanical, and electrical and avionics equipment and structural repairs. For life extension of stringer repair, as an example, it is required to re-assess the fatigue life of stringer in the presence of coupling under modified load spectrum. This is achieved by assessing the fatigue life of Web and Outer Flange (OF) part of stringers separately as per F&DT justification philosophy. Assessment of the fatigue life requires determination of stress concentration factor (Kt) for different combination of width, pitch, stringer thickness, coupling thickness and pad-up thickness of all stringer profiles available in different sections of fuselage. Determination of stress concentration factor for Web and Outer Flange of stringer profile covering entire ranges involves substantial number of Finite Element (FE) analysis. In order to optimise the number of FE runs, stress concentration factor is determined under worst repair factors combination (max. plate width; max. thickness; max. pitch; min. rivet dia.; and min. No. of rivets) resulting in conservative value. A parametric study of Web and Outer Flange data across stringer profiles were carried out and proven statistical techniques were used to find the optimal equation to predict stress concentration factor. This in turn reduced number of FE runs substantially for a given range of width, pitch, stringer thickness and so on. The use of optimal equation obtained through regression analysis is able to predict Kt within reasonable accuracy for a given range of inputs.

14 CFR 129.109 - Supplemental inspections for U.S.-registered aircraft.

Code of Federal Regulations, 2010 CFR

2010-01-01

... for airplane structure susceptible to fatigue cracking that could contribute to a catastrophic failure. For the purpose of this section, this structure is termed “fatigue critical structure.” (2) Adverse... means for addressing the adverse effects repairs, alterations, and modifications may have on fatigue...

77 FR 42547 - Agency Information Collection Activities: Requests for Comments; Clearance of Renewed Approval of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-07-19

... and Fatigue Evaluation of Composite Rotorcraft Structures AGENCY: Federal Aviation Administration (FAA... Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures. Form Numbers: There are no FAA forms... ``Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures'' final rule (76 FR 74655...

14 CFR 26.43 - Holders of and applicants for type certificates-Repairs.

Code of Federal Regulations, 2014 CFR

2014-01-01

... payload capacity of 7,500 pounds or more. (b) List of fatigue critical baseline structure. For airplanes...) Identify fatigue critical baseline structure for all airplane model variations and derivatives approved... affects fatigue critical baseline structure identified under paragraph (b)(1) of this section; (2) Perform...

14 CFR 26.43 - Holders of and applicants for type certificates-Repairs.

Code of Federal Regulations, 2011 CFR

2011-01-01

... payload capacity of 7,500 pounds or more. (b) List of fatigue critical baseline structure. For airplanes...) Identify fatigue critical baseline structure for all airplane model variations and derivatives approved... affects fatigue critical baseline structure identified under paragraph (b)(1) of this section; (2) Perform...

14 CFR 26.43 - Holders of and applicants for type certificates-Repairs.

Code of Federal Regulations, 2012 CFR

2012-01-01

... payload capacity of 7,500 pounds or more. (b) List of fatigue critical baseline structure. For airplanes...) Identify fatigue critical baseline structure for all airplane model variations and derivatives approved... affects fatigue critical baseline structure identified under paragraph (b)(1) of this section; (2) Perform...

14 CFR 26.43 - Holders of and applicants for type certificates-Repairs.

Code of Federal Regulations, 2013 CFR

2013-01-01

... payload capacity of 7,500 pounds or more. (b) List of fatigue critical baseline structure. For airplanes...) Identify fatigue critical baseline structure for all airplane model variations and derivatives approved... affects fatigue critical baseline structure identified under paragraph (b)(1) of this section; (2) Perform...

14 CFR 26.43 - Holders of and applicants for type certificates-Repairs.

Code of Federal Regulations, 2010 CFR

2010-01-01

... payload capacity of 7,500 pounds or more. (b) List of fatigue critical baseline structure. For airplanes...) Identify fatigue critical baseline structure for all airplane model variations and derivatives approved... affects fatigue critical baseline structure identified under paragraph (b)(1) of this section; (2) Perform...

Static, Dynamic, and Fatigue Analysis of the Mechanical System of Ultrasonic Scanner for Inservice Inspection of Research Reactors

NASA Astrophysics Data System (ADS)

Awwaluddin, Muhammad; Kristedjo, K.; Handono, Khairul; Ahmad, H.

2018-02-01

This analysis is conducted to determine the effects of static and dynamic loads of the structure of mechanical system of Ultrasonic Scanner i.e., arm, column, and connection systems for inservice inspection of research reactors. The analysis is performed using the finite element method with 520 N static load. The correction factor of dynamic loads used is the Gerber mean stress correction (stress life). The results of the analysis show that the value of maximum equivalent von Mises stress is 1.3698E8 Pa for static loading and value of the maximum equivalent alternating stress is 1.4758E7 Pa for dynamic loading. These values are below the upper limit allowed according to ASTM A240 standards i.e. 2.05E8 Pa. The result analysis of fatigue life cycle are at least 1E6 cycle, so it can be concluded that the structure is in the high life cycle category.

Dynamic and Fatigue Analysis of an 18th Century Steel Arch Bridge

NASA Astrophysics Data System (ADS)

Boumechra, Nadir; Hamdaoui, Karim

2008-07-01

Within the "Oran-Tlemcen" railway line realization project (159 km), several bridges were built by the Railroads Algerian West Company. 7 km from the east of Tlemcen city, this railway line must cross a very broken mountainous collar, that's why the French engineer "Gustave Eiffel" was solicited to construct a 68 m length bridge. In 1890, an arch steel truss bridge was realized. The bridge presents 300 m of apron curvature radius and, currently, is considered as one of the most important monuments of the Algerian historical heritage. Considering the age of the bridge and the evolution of the railway loads in time, it was essential to check the good behavior of the studied structure. For that, analyses to verify the physical and mechanical properties of the growth iron members are made. A finite element model of the bridge was built and numerical simulations were drawn. The structural vibration conducted analysis permit to understand the behavior of this particular structure, then to evaluate (in detail) the rate of the structure fatigue.

Fast prediction of the fatigue behavior of short-fiber-reinforced thermoplastics based on heat build-up measurements: application to heterogeneous cases

NASA Astrophysics Data System (ADS)

Serrano, Leonell; Marco, Yann; Le Saux, Vincent; Robert, Gilles; Charrier, Pierre

2017-09-01

Short-fiber-reinforced thermoplastics components for structural applications are usually very complex parts as stiffeners, ribs and thickness variations are used to compensate the quite low material intrinsic stiffness. These complex geometries induce complex local mechanical fields but also complex microstructures due to the injection process. Accounting for these two aspects is crucial for the design in regard to fatigue of these parts, especially for automotive industry. The aim of this paper is to challenge an energetic approach, defined to evaluate quickly the fatigue lifetime, on three different heterogeneous cases: a classic dog-bone sample with a skin-core microstructure and two structural samples representative of the thickness variations observed for industrial components. First, a method to evaluate dissipated energy fields from thermal measurements is described and is applied to the three samples in order to relate the cyclic loading amplitude to the fields of cyclic dissipated energy. Then, a local analysis is detailed in order to link the energy dissipated at the failure location to the fatigue lifetime and to predict the fatigue curve from the thermomechanical response of one single sample. The predictions obtained for the three cases are compared successfully to the Wöhler curves obtained with classic fatigue tests. Finally, a discussion is proposed to compare results for the three samples in terms of dissipation fields and fatigue lifetime. This comparison illustrates that, if the approach is leading to a very relevant diagnosis on each case, the dissipated energy field is not giving a straightforward access to the lifetime cartography as the relation between fatigue failure and dissipated energy seems to be dependent on the local mechanical and microstructural state.

Probabilistic finite elements for fatigue and fracture analysis

NASA Astrophysics Data System (ADS)

Belytschko, Ted; Liu, Wing Kam

Attenuation is focused on the development of Probabilistic Finite Element Method (PFEM), which combines the finite element method with statistics and reliability methods, and its application to linear, nonlinear structural mechanics problems and fracture mechanics problems. The computational tool based on the Stochastic Boundary Element Method is also given for the reliability analysis of a curvilinear fatigue crack growth. The existing PFEM's have been applied to solve for two types of problems: (1) determination of the response uncertainty in terms of the means, variance and correlation coefficients; and (2) determination the probability of failure associated with prescribed limit states.

Probabilistic finite elements for fatigue and fracture analysis

NASA Technical Reports Server (NTRS)

Belytschko, Ted; Liu, Wing Kam

1992-01-01

Attenuation is focused on the development of Probabilistic Finite Element Method (PFEM), which combines the finite element method with statistics and reliability methods, and its application to linear, nonlinear structural mechanics problems and fracture mechanics problems. The computational tool based on the Stochastic Boundary Element Method is also given for the reliability analysis of a curvilinear fatigue crack growth. The existing PFEM's have been applied to solve for two types of problems: (1) determination of the response uncertainty in terms of the means, variance and correlation coefficients; and (2) determination the probability of failure associated with prescribed limit states.

Reference-free fatigue crack detection using nonlinear ultrasonic modulation under various temperature and loading conditions

NASA Astrophysics Data System (ADS)

Lim, Hyung Jin; Sohn, Hoon; DeSimio, Martin P.; Brown, Kevin

2014-04-01

This study presents a reference-free fatigue crack detection technique using nonlinear ultrasonic modulation. When low frequency (LF) and high frequency (HF) inputs generated by two surface-mounted lead zirconate titanate (PZT) transducers are applied to a structure, the presence of a fatigue crack can provide a mechanism for nonlinear ultrasonic modulation and create spectral sidebands around the frequency of the HF signal. The crack-induced spectral sidebands are isolated using a combination of linear response subtraction (LRS), synchronous demodulation (SD) and continuous wavelet transform (CWT) filtering. Then, a sequential outlier analysis is performed on the extracted sidebands to identify the crack presence without referring any baseline data obtained from the intact condition of the structure. Finally, the robustness of the proposed technique is demonstrated using actual test data obtained from simple aluminum plate and complex aircraft fitting-lug specimens under varying temperature and loading variations.

Computational predictive methods for fracture and fatigue

NASA Technical Reports Server (NTRS)

Cordes, J.; Chang, A. T.; Nelson, N.; Kim, Y.

1994-01-01

The damage-tolerant design philosophy as used by aircraft industries enables aircraft components and aircraft structures to operate safely with minor damage, small cracks, and flaws. Maintenance and inspection procedures insure that damages developed during service remain below design values. When damage is found, repairs or design modifications are implemented and flight is resumed. Design and redesign guidelines, such as military specifications MIL-A-83444, have successfully reduced the incidence of damage and cracks. However, fatigue cracks continue to appear in aircraft well before the design life has expired. The F16 airplane, for instance, developed small cracks in the engine mount, wing support, bulk heads, the fuselage upper skin, the fuel shelf joints, and along the upper wings. Some cracks were found after 600 hours of the 8000 hour design service life and design modifications were required. Tests on the F16 plane showed that the design loading conditions were close to the predicted loading conditions. Improvements to analytic methods for predicting fatigue crack growth adjacent to holes, when multiple damage sites are present, and in corrosive environments would result in more cost-effective designs, fewer repairs, and fewer redesigns. The overall objective of the research described in this paper is to develop, verify, and extend the computational efficiency of analysis procedures necessary for damage tolerant design. This paper describes an elastic/plastic fracture method and an associated fatigue analysis method for damage tolerant design. Both methods are unique in that material parameters such as fracture toughness, R-curve data, and fatigue constants are not required. The methods are implemented with a general-purpose finite element package. Several proof-of-concept examples are given. With further development, the methods could be extended for analysis of multi-site damage, creep-fatigue, and corrosion fatigue problems.

Computational predictive methods for fracture and fatigue

NASA Astrophysics Data System (ADS)

Cordes, J.; Chang, A. T.; Nelson, N.; Kim, Y.

1994-09-01

The damage-tolerant design philosophy as used by aircraft industries enables aircraft components and aircraft structures to operate safely with minor damage, small cracks, and flaws. Maintenance and inspection procedures insure that damages developed during service remain below design values. When damage is found, repairs or design modifications are implemented and flight is resumed. Design and redesign guidelines, such as military specifications MIL-A-83444, have successfully reduced the incidence of damage and cracks. However, fatigue cracks continue to appear in aircraft well before the design life has expired. The F16 airplane, for instance, developed small cracks in the engine mount, wing support, bulk heads, the fuselage upper skin, the fuel shelf joints, and along the upper wings. Some cracks were found after 600 hours of the 8000 hour design service life and design modifications were required. Tests on the F16 plane showed that the design loading conditions were close to the predicted loading conditions. Improvements to analytic methods for predicting fatigue crack growth adjacent to holes, when multiple damage sites are present, and in corrosive environments would result in more cost-effective designs, fewer repairs, and fewer redesigns. The overall objective of the research described in this paper is to develop, verify, and extend the computational efficiency of analysis procedures necessary for damage tolerant design. This paper describes an elastic/plastic fracture method and an associated fatigue analysis method for damage tolerant design. Both methods are unique in that material parameters such as fracture toughness, R-curve data, and fatigue constants are not required. The methods are implemented with a general-purpose finite element package. Several proof-of-concept examples are given. With further development, the methods could be extended for analysis of multi-site damage, creep-fatigue, and corrosion fatigue problems.

Computational simulation of acoustic fatigue for hot composite structures

NASA Technical Reports Server (NTRS)

Singhal, S. N.; Nagpal, V. K.; Murthy, P. L. N.; Chamis, C. C.

1991-01-01

This paper presents predictive methods/codes for computational simulation of acoustic fatigue resistance of hot composite structures subjected to acoustic excitation emanating from an adjacent vibrating component. Select codes developed over the past two decades at the NASA Lewis Research Center are used. The codes include computation of (1) acoustic noise generated from a vibrating component, (2) degradation in material properties of the composite laminate at use temperature, (3) dynamic response of acoustically excited hot multilayered composite structure, (4) degradation in the first-ply strength of the excited structure due to acoustic loading, and (5) acoustic fatigue resistance of the excited structure, including propulsion environment. Effects of the laminate lay-up and environment on the acoustic fatigue life are evaluated. The results show that, by keeping the angled plies on the outer surface of the laminate, a substantial increase in the acoustic fatigue life is obtained. The effect of environment (temperature and moisure) is to relieve the residual stresses leading to an increase in the acoustic fatigue life of the excited panel.

Computational simulation of acoustic fatigue for hot composite structures

NASA Technical Reports Server (NTRS)

Singhal, Surendra N.; Murthy, Pappu L. N.; Chamis, Christos C.; Nagpal, Vinod K.; Sutjahjo, Edhi

1991-01-01

Predictive methods/computer codes for the computational simulation of acoustic fatigue resistance of hot composite structures subjected to acoustic excitation emanating from an adjacent vibrating component are discussed. Select codes developed over the past two decades at the NASA Lewis Research Center are used. The codes include computation of acoustic noise generated from a vibrating component, degradation in material properties of a composite laminate at use temperature, dynamic response of acoustically excited hot multilayered composite structure, degradation in the first ply strength of the excited structure due to acoustic loading, and acoustic fatigue resistance of the excited structure, including the propulsion environment. Effects of the laminate lay-up and environment on the acoustic fatigue life are evaluated. The results show that, by keeping the angled plies on the outer surface of the laminate, a substantial increase in the acoustic fatigue life is obtained. The effect of environment (temperature and moisture) is to relieve the residual stresses leading to an increase in the acoustic fatigue life of the excited panel.

Microstructural Influence on Deformation and Fatigue Life of Composites Using the Generalized Method of Cells

NASA Technical Reports Server (NTRS)

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

2015-01-01

A fully coupled deformation and damage approach to modeling the response of composite materials and composite laminates is presented. It is based on the semi-­-analytical generalized method of cells (GMC) micromechanics model as well as its higher fidelity counterpart, HFGMC, both of which provide closed-form constitutive equations for composite materials as well as the micro scale stress and strain fields in the composite phases. The provided constitutive equations allow GMC and HFGMC to function within a higher scale structural analysis (e.g., finite element analysis or lamination theory) to represent a composite material point, while the availability of the micro fields allow the incorporation of lower scale sub­-models to represent local phenomena in the fiber and matrix. Further, GMC's formulation performs averaging when applying certain governing equations such that some degree of microscale field accuracy is surrendered in favor of extreme computational efficiency, rendering the method quite attractive as the centerpiece in a integrated computational material engineering (ICME) structural analysis; whereas HFGMC retains this microscale field accuracy, but at the price of significantly slower computational speed. Herein, the sensitivity of deformation and the fatigue life of graphite/epoxy PMC composites, with both ordered and disordered microstructures, has been investigated using this coupled deformation and damage micromechanics based approach. The local effects of fiber breakage and fatigue damage are included as sub-models that operate on the microscale for the individual composite phases. For analysis of laminates, classical lamination theory is employed as the global or structural scale model, while GMC/HFGMC is embedded to operate on the microscale to simulate the behavior of the composite material within each laminate layer. A key outcome of this study is the statistical influence of microstructure and micromechanics idealization (GMC or HFGMC) on the overall accuracy of unidirectional and laminated composite deformation and fatigue response.

Structure-property relations and modeling of small crack fatigue behavior of various magnesium alloys

NASA Astrophysics Data System (ADS)

Bernard, Jairus Daniel

Lightweight structural components are important to the automotive and aerospace industries so that better fuel economy can be realized. Magnesium alloys in particular are being examined to fulfill this need due to their attractive stiffness- and strength-to-weight ratios when compared to other materials. However, when introducing a material into new roles, one needs to properly characterize its mechanical properties. Fatigue behavior is especially important considering aerospace and automotive component applications. Therefore, quantifying the structure-property relationships and accurately predicting the fatigue behavior for these materials are vital. This study has two purposes. The first is to quantify the structure-property relationships for the fatigue behavior in an AM30 magnesium alloy. The second is to use the microstructural-based MultiStage Fatigue (MSF) model in order to accurately predict the fatigue behavior of three magnesium alloys: AM30, Elektron 21, and AZ61. While some studies have previously quantified the MSF material constants for several magnesium alloys, detailed research into the fatigue regimes, notably the microstructurally small crack (MSC) region, is lacking. Hence, the contribution of this work is the first of its kind to experimentally quantify the fatigue crack incubation and MSC regimes that are used for the MultiStage Fatigue model. Using a multi-faceted experimental approach, these regimes were explored with a replica method that used a dual-stage silicone based compound along with previously published in situ fatigue tests. These observations were used in calibrating the MultiStage Fatigue model.

The Characteristics of Fatigue Damage in the Fuselage Riveted Lap Splice Joint

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Willard, Scott A.

1997-01-01

An extensive data base has been developed to form the physical basis for new analytical methodology to predict the onset of widespread fatigue damage in the fuselage lap splice joint. The results of detailed destructive examinations have been cataloged to describe the physical nature of MSD in the lap splice joint. ne catalog includes a detailed description, e.g., crack initiation, growth rates, size, location, and fracture morphology, of fatigue damage in the fuselage lap splice joint structure. Detailed examinations were conducted on a lap splice joint panel removed from a full scale fuselage test article after completing a 60,000 cycle pressure test. The panel contained a four bay region that exhibited visible outer skin cracks and regions of crack link-up along the upper rivet row. Destructive examinations revealed undetected fatigue damage in the outer skin, inner skin, and tear strap regions. Outer skin fatigue cracks were found to initiate by fretting damage along the faying surface. The cracks grew along the faying surface to a length equivalent to two to three skin thicknesses before penetrating the outboard surface of the outer skin. Analysis of fracture surface marker bands produced during full scale testing revealed that all upper rivet row fatigue cracks contained in a dim bay region grow at similar rates; this important result suggests that fracture mechanics based methods can be used to predict the growth of outer skin fatigue cracks in lap splice structure. Results are presented showing the affects of MSD and out-of-plane pressure loads on outer skin crack link-up.

TTK Chitra tilting disc heart valve model TC2: An assessment of fatigue life and durability.

PubMed

Subhash, N N; Rajeev, Adathala; Sujesh, Sreedharan; Muraleedharan, C V

2017-08-01

Average age group of heart valve replacement in India and most of the Third World countries is below 30 years. Hence, the valve for such patients need to be designed to have a service life of 50 years or more which corresponds to 2000 million cycles of operation. The purpose of this study was to assess the structural performance of the TTK Chitra tilting disc heart valve model TC2 and thereby address its durability. The TC2 model tilting disc heart valves were assessed to evaluate the risks connected with potential structural failure modes. To be more specific, the studies covered the finite element analysis-based fatigue life prediction and accelerated durability testing of the tilting disc heart valves for nine different valve sizes. First, finite element analysis-based fatigue life prediction showed that all nine valve sizes were in the infinite life region. Second, accelerated durability test showed that all nine valve sizes remained functional for 400 million cycles under experimental conditions. The study ensures the continued function of TC2 model tilting disc heart valves over duration in excess of 50 years. The results imply that the TC2 model valve designs are structurally safe, reliable and durable.

Reliability Quantification of the Flexure: A Critical Stirling Convertor Component

NASA Technical Reports Server (NTRS)

Shah, Ashwin R.; Korovaichuk, Igor; Zampino, Edward J.

2004-01-01

Uncertainties in the manufacturing, fabrication process, material behavior, loads, and boundary conditions results in the variation of the stresses and strains induced in the flexures and its fatigue life. Past experience and the test data at material coupon levels revealed a significant amount of scatter of the fatigue life. Owing to these facts, the design of the flexure, using conventional approaches based on safety factor or traditional reliability based on similar equipment considerations does not provide a direct measure of reliability. Additionally, it may not be feasible to run actual long term fatigue tests due to cost and time constraints. Therefore it is difficult to ascertain material fatigue strength limit. The objective of the paper is to present a methodology and quantified results of numerical simulation for the reliability of flexures used in the Stirling convertor for their structural performance. The proposed approach is based on application of finite element analysis method in combination with the random fatigue limit model, which includes uncertainties in material fatigue life. Additionally, sensitivity of fatigue life reliability to the design variables is quantified and its use to develop guidelines to improve design, manufacturing, quality control and inspection design process is described.

Fatigue of restorative materials.

PubMed

Baran, G; Boberick, K; McCool, J

2001-01-01

Failure due to fatigue manifests itself in dental prostheses and restorations as wear, fractured margins, delaminated coatings, and bulk fracture. Mechanisms responsible for fatigue-induced failure depend on material ductility: Brittle materials are susceptible to catastrophic failure, while ductile materials utilize their plasticity to reduce stress concentrations at the crack tip. Because of the expense associated with the replacement of failed restorations, there is a strong desire on the part of basic scientists and clinicians to evaluate the resistance of materials to fatigue in laboratory tests. Test variables include fatigue-loading mode and test environment, such as soaking in water. The outcome variable is typically fracture strength, and these data typically fit the Weibull distribution. Analysis of fatigue data permits predictive inferences to be made concerning the survival of structures fabricated from restorative materials under specified loading conditions. Although many dental-restorative materials are routinely evaluated, only limited use has been made of fatigue data collected in vitro: Wear of materials and the survival of porcelain restorations has been modeled by both fracture mechanics and probabilistic approaches. A need still exists for a clinical failure database and for the development of valid test methods for the evaluation of composite materials.

Experimental Evaluation of Fatigue Crack Initiation from Corroded Hemispherical Notches in Aerospace Structural Materials

NASA Technical Reports Server (NTRS)

Garcia, Daniel B.; Forman, Royce; Shindo, David

2010-01-01

A test program was developed and executed to evaluate the influence of corroded hemispherical notches on the fatigue crack initiation and propagation in aluminum 7075-T7351, 4340 steel, and D6AC steel. Surface enhancements such as shot peening and laser shock peening were also incorporated as part of the test effort with the intent of improving fatigue performance. In addition to the testing, fracture mechanics and endurance limit based analysis methods were evaluated to characterize the results with the objective of challenging typical assumptions used in modeling fatigue cracks from corrosion pits. The results specifically demonstrate that the aluminum and steel alloys behave differently with respect to fatigue crack initiation from hemispherical corrosion pits. The aluminum test results were bounded by the fracture mechanics and endurance limit models while exhibiting a general insensitivity to the residual stress field generated by shot peening. The steel specimens were better characterized by the endurance limit fatigue properties and did exhibit sensitivities to residual stresses from the shot peening and laser shock peening

The Boeing 747 fatigue integrity program

NASA Technical Reports Server (NTRS)

Spencer, M. M.

1972-01-01

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

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

NASA Astrophysics Data System (ADS)

Tamada, Kazuhiro; Kakiuchi, Toshifumi; Uematsu, Yoshihiko

2017-07-01

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

Impact of Fatigue in Rheumatic Diseases in the Work Environment: A Qualitative Study.

PubMed

Connolly, Deirdre; Fitzpatrick, Clodagh; O'Toole, Lynn; Doran, Michele; O'Shea, Finbar

2015-10-28

Fatigue is a symptom of arthritis that causes difficulty at work. An improved understanding of this symptom could assist its management in the work environment. The aim of this study was to explore people with rheumatic diseases' experiences of fatigue in work. A qualitative descriptive design was used with semi-structured interviews and a constant comparative method of data analysis. There were 18 participants, the majority of them female with Rheumatoid Arthritis (RA) and working full-time. Three themes were identified: "Impact of fatigue on work performance" with cognition, mood and physical abilities being the main difficulties reported. In the second theme "Disclosure at Work" participants discussed disclosing their disease to employers but reported a lack of understanding of fatigue from colleagues. The final theme "work-based fatigue management strategies" included cognitive strategies and energy management techniques, which were mainly self-taught. In this study, fatigue was reported to impact on many areas of work performance with limited understanding from colleagues and employers. Interventions from health professionals to assist with development of work-related self-management skills are required to assist with symptom management in the work place. Such interventions should include education to employers and colleagues on the nature of fatigue in Rheumatic diseases.

Impact of Fatigue in Rheumatic Diseases in the Work Environment: A Qualitative Study

PubMed Central

Connolly, Deirdre; Fitzpatrick, Clodagh; O’Toole, Lynn; Doran, Michele; O’Shea, Finbar

2015-01-01

Fatigue is a symptom of arthritis that causes difficulty at work. An improved understanding of this symptom could assist its management in the work environment. The aim of this study was to explore people with rheumatic diseases’ experiences of fatigue in work. A qualitative descriptive design was used with semi-structured interviews and a constant comparative method of data analysis. There were 18 participants, the majority of them female with Rheumatoid Arthritis (RA) and working full-time. Three themes were identified: “Impact of fatigue on work performance” with cognition, mood and physical abilities being the main difficulties reported. In the second theme “Disclosure at Work” participants discussed disclosing their disease to employers but reported a lack of understanding of fatigue from colleagues. The final theme “work-based fatigue management strategies” included cognitive strategies and energy management techniques, which were mainly self-taught. In this study, fatigue was reported to impact on many areas of work performance with limited understanding from colleagues and employers. Interventions from health professionals to assist with development of work-related self-management skills are required to assist with symptom management in the work place. Such interventions should include education to employers and colleagues on the nature of fatigue in Rheumatic diseases. PMID:26516896

Evaluating Changes in Tendon Crimp with Fatigue Loading as an ex vivo Structural Assessment of Tendon Damage

PubMed Central

Freedman, Benjamin R.; Zuskov, Andrey; Sarver, Joseph J.; Buckley, Mark R.; Soslowsky, Louis J.

2015-01-01

The complex structure of tendons relates to their mechanical properties. Previous research has associated the waviness of collagen fibers (crimp) during quasi-static tensile loading to tensile mechanics, but less is known about the role of fatigue loading on crimp properties. In this study (IACUC approved), mouse patellar tendons were fatigue loaded while an integrated plane polariscope simultaneously assessed crimp properties. We demonstrate a novel structural mechanism whereby tendon crimp amplitude and frequency are altered with fatigue loading. In particular, fatigue loading increased the crimp amplitude across the tendon width and length, and these structural alterations were shown to be both region and load dependent. The change in crimp amplitude was strongly correlated to mechanical tissue laxity (defined as the ratio of displacement and gauge length relative to the first cycle of fatigue loading assessed at constant load throughout testing), at all loads and regions evaluated. Together, this study highlights the role of fatigue loading on tendon crimp properties as a function of load applied and region evaluated, and offers an additional structural mechanism for mechanical alterations that may lead to ultimate tendon failure. PMID:25773654

Rapid Assessment of the Role of Microstructural Variability in the Fatigue Behavior of Structural Alloys using Ultrasonic Fatigue

DTIC Science & Technology

2007-06-23

6 %AI-2%Sn- 4 %Zr- 6 %Mo in the very high cycle regime. The microstructure is a two-phase structure with primary a grains (ap grains) in a transformed [3...aluminum [2], magnesium [3], nickel-based [ 4 ], and titanium [5,6] alloy systems. Fatigue crack initiation is known to consume the majority of fatigue...microstructural neighborhood affects this process. In fatigue studies of alpha + beta titanium alloys, [ 6 -9] cyclic deformation localization is first observed in

A Model of Fatigue Following Traumatic Brain Injury.

PubMed

Ponsford, Jennie; Schönberger, Michael; Rajaratnam, Shantha M W

2015-01-01

Fatigue is one of the most frequent sequelae of traumatic brain injury (TBI), although its causes are poorly understood. This study investigated the interrelationships between fatigue and sleepiness, vigilance performance, depression, and anxiety, using a structural equation modeling approach. Seventy-two participants with moderate to severe TBI (78% males) were recruited a median of 305 days postinjury. They completed the Fatigue Severity Scale, a vigilance task, the Epworth Sleepiness Scale, and Hospital Anxiety and Depression Scale. A model of the interrelationships between the study variables was developed, tested, and modified with path analysis. The modified model had a good overall fit (χ2 = 1.3, P = .54; comparative fit index = 1.0; root-mean square error of approximation = 0.0; standardized root-mean square residual = 0.02). Most paths in this model were significant (P < .05). Fatigue predicted anxiety, depression, and daytime sleepiness. Depression predicted daytime sleepiness and poor vigilance, whereas anxiety tended to predict reduced daytime sleepiness. This model confirms the complexity of fatigue experience. It supports the hypothesis that fatigue after TBI is a cause, not a consequence, of anxiety, depression, and daytime sleepiness, which, in turn (especially depression), may exacerbate fatigue by affecting cognitive functioning. These findings suggest that to alleviate fatigue, it is important to address each of these factors. However, the findings need to be confirmed with a longitudinal research design.

Experimental and theoretical investigation of fatigue life in reusable rocket thrust chambers

NASA Technical Reports Server (NTRS)

Hannum, N. P.; Kasper, H. J.; Pavli, A. J.

1976-01-01

During a test program to investigate low-cycle thermal fatigue, 13 rocket combustion chambers were fabricated and cyclically test fired to failure. Six oxygen-free, high-conductivity (OFHC) copper and seven Amzirc chambers were tested. The chamber liners were fabricated of copper or copper alloy and contained milled coolant channels. The chambers were completed by means of an electroformed nickel closeout. The oxidant/fuel ratio for the liquid oxygen and gaseous hydrogen propellants was 6.0. The failures in the OFHC copper chambers were not typical fatigue failures but are described as creep rupture enhanced by ratcheting. The coolant channels bulged toward the chamber centerline, resulting in progressive thinning of the wall during each cycle. The failures in the Amzirc alloy chambers were caused by low-cycle thermal fatigue. The lives were much shorter than were predicted by an analytical structural analysis computer program used in conjunction with fatigue life data from isothermal test specimens, due to the uneven distribution of Zr in the chamber material.

Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties

NASA Astrophysics Data System (ADS)

Wycisk, Eric; Solbach, Andreas; Siddique, Shafaqat; Herzog, Dirk; Walther, Frank; Emmelmann, Claus

Laser Additive Manufacturing (LAM) enables economical production of complex lightweight structures as well as patient individual implants. Due to these possibilities the additive manufacturing technology gains increasing importance in the aircraft and the medical industry. Yet these industries obtain high quality standards and demand predictability of material properties for static and dynamic load cases. However, especially fatigue and crack propagation properties are not sufficiently determined. Therefore this paper presents an analysis and simulation of crack propagation behavior considering Laser Additive Manufacturing specific defects, such as porosity and surface roughness. For the mechanical characterization of laser additive manufactured titanium alloy Ti-6Al-4V, crack propagation rates are experimentally determined and used for an analytical modeling and simulation of fatigue. Using experimental results from HCF tests and simulated data, the fatigue and crack resistance performance is analyzed considering material specific defects and surface roughness. The accumulated results enable the reliable prediction of the defects influence on fatigue life of laser additive manufactured titanium components.

Simulation of Delamination Propagation in Composites Under High-Cycle Fatigue by Means of Cohesive-Zone Models

NASA Technical Reports Server (NTRS)

Turon, Albert; Costa, Josep; Camanho, Pedro P.; Davila, Carlos G.

2006-01-01

A damage model for the simulation of delamination propagation under high-cycle fatigue loading is proposed. The basis for the formulation is a cohesive law that links fracture and damage mechanics to establish the evolution of the damage variable in terms of the crack growth rate dA/dN. The damage state is obtained as a function of the loading conditions as well as the experimentally-determined coefficients of the Paris Law crack propagation rates for the material. It is shown that by using the constitutive fatigue damage model in a structural analysis, experimental results can be reproduced without the need of additional model-specific curve-fitting parameters.

Composite structural materials

NASA Technical Reports Server (NTRS)

Loewy, Robert G.; Wiberley, Stephen E.

1988-01-01

A decade long program to develop critical advanced composite technology in the areas of physical properties, structural concept and analysis, manufacturing, reliability, and life predictions is reviewed. Specific goals are discussed. The status of the chemical vapor deposition effects on carbon fiber properties; inelastic deformation of metal matrix laminates; fatigue damage in fibrous MMC laminates; delamination fracture toughness in thermoplastic matrix composites; and numerical analysis of composite micromechanical behavior are presented.

High-temperature low cycle fatigue behavior of a gray cast iron

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

Fan, K.L., E-mail: 12klfan@tongji.edu.cn; He, G.Q.; She, M.

The strain controlled low cycle fatigue properties of the studied gray cast iron for engine cylinder blocks were investigated. At the same total strain amplitude, the low cycle fatigue life of the studied material at 523 K was higher than that at 423 K. The fatigue behavior of the studied material was characterized as cyclic softening at any given total strain amplitude (0.12%–0.24%), which was attributed to fatigue crack initiation and propagation. Moreover, this material exhibited asymmetric hysteresis loops due to the presence of the graphite lamellas. Transmission electron microscopy analysis suggested that cyclic softening was also caused by themore » interactions of dislocations at 423 K, such as cell structure in ferrite, whereas cyclic softening was related to subgrain boundaries and dislocation climbing at 523 K. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain amplitudes. It showed that the higher the temperature, the rougher the crack face of the examined gray cast iron at the same total strain amplitude. Additionally, the microcracks were readily blunted during growth inside the pearlite matrix at 423 K, whereas the microcracks could easily pass through pearlite matrix along with deflection at 523 K. The results of fatigue experiments consistently showed that fatigue damage for the studied material at 423 K was lower than that at 523 K under any given total strain amplitude. - Highlights: • The low cycle fatigue behavior of the HT250 for engine cylinder blocks was investigated. • TEM investigations were conducted to explain the cyclic deformation response. • The low cycle fatigue cracks of HT250 GCI were studied by SEM. • The fatigue life of the examined material at 523 K is higher than that at 423 K.« less

A procedure for utilization of a damage-dependent constitutive model for laminated composites

NASA Technical Reports Server (NTRS)

Lo, David C.; Allen, David H.; Harris, Charles E.

1992-01-01

Described here is the procedure for utilizing a damage constitutive model to predict progressive damage growth in laminated composites. In this model, the effects of the internal damage are represented by strain-like second order tensorial damage variables and enter the analysis through damage dependent ply level and laminate level constitutive equations. The growth of matrix cracks due to fatigue loading is predicted by an experimentally based damage evolutionary relationship. This model is incorporated into a computer code called FLAMSTR. This code is capable of predicting the constitutive response and matrix crack damage accumulation in fatigue loaded laminated composites. The structure and usage of FLAMSTR are presented along with sample input and output files to assist the code user. As an example problem, an analysis of crossply laminates subjected to two stage fatigue loading was conducted and the resulting damage accumulation and stress redistribution were examined to determine the effect of variations in fatigue load amplitude applied during the first stage of the load history. It was found that the model predicts a significant loading history effect on damage evolution.

Modal Frequency Detection in Composite Beams Using Fiber Optic Sensors

DTIC Science & Technology

1997-04-18

Structures 4, 270-280 (1995). [35] Chen-Jung Li and Ray Asok , "Neural Network Representation of Fatigue Damage Dynamics," Smart Materials and Structures 3...37] Roland Ray Kilcher, "Modal Analysis and Impact Damage Assessment of Composite Laminates: an Experimental Study," M.S. thesis, University of

Coupled modeling of a directly heated tubular solar receiver for supercritical carbon dioxide Brayton cycle: Structural and creep-fatigue evaluation

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

Ortega, Jesus; Khivsara, Sagar; Christian, Joshua

A supercritical carbon dioxide (sCO 2) Brayton cycle is an emerging high energy-density cycle undergoing extensive research due to the appealing thermo-physical properties of sCO 2 and single phase operation. Development of a solar receiver capable of delivering sCO 2 at 20 MPa and 700 °C is required for implementation of the high efficiency (~50%) solar powered sCO 2 Brayton cycle. In this work, extensive candidate materials are review along with tube size optimization using the ASME Boiler and Pressure Vessel Code. Moreover, temperature and pressure distribution obtained from the thermal-fluid modeling (presented in a complementary publication) are used tomore » evaluate the thermal and mechanical stresses along with detailed creep-fatigue analysis of the tubes. The lifetime performance of the receiver tubes were approximated using the resulting body stresses. A cyclic loading analysis is performed by coupling the Strain-Life approach and the Larson-Miller creep model. The structural integrity of the receiver was examined and it was found that the stresses can be withstood by specific tubes, determined by a parametric geometric analysis. Furthermore, the creep-fatigue analysis displayed the damage accumulation due to cycling and the permanent deformation on the tubes showed that the tubes can operate for the full lifetime of the receiver.« less

Coupled modeling of a directly heated tubular solar receiver for supercritical carbon dioxide Brayton cycle: Structural and creep-fatigue evaluation

DOE PAGES

Ortega, Jesus; Khivsara, Sagar; Christian, Joshua; ...

2016-06-06

A supercritical carbon dioxide (sCO 2) Brayton cycle is an emerging high energy-density cycle undergoing extensive research due to the appealing thermo-physical properties of sCO 2 and single phase operation. Development of a solar receiver capable of delivering sCO 2 at 20 MPa and 700 °C is required for implementation of the high efficiency (~50%) solar powered sCO 2 Brayton cycle. In this work, extensive candidate materials are review along with tube size optimization using the ASME Boiler and Pressure Vessel Code. Moreover, temperature and pressure distribution obtained from the thermal-fluid modeling (presented in a complementary publication) are used tomore » evaluate the thermal and mechanical stresses along with detailed creep-fatigue analysis of the tubes. The lifetime performance of the receiver tubes were approximated using the resulting body stresses. A cyclic loading analysis is performed by coupling the Strain-Life approach and the Larson-Miller creep model. The structural integrity of the receiver was examined and it was found that the stresses can be withstood by specific tubes, determined by a parametric geometric analysis. Furthermore, the creep-fatigue analysis displayed the damage accumulation due to cycling and the permanent deformation on the tubes showed that the tubes can operate for the full lifetime of the receiver.« less

High Speed Research Program Sonic Fatigue

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A. (Technical Monitor); Beier, Theodor H.; Heaton, Paul

2005-01-01

The objective of this sonic fatigue summary is to provide major findings and technical results of studies, initiated in 1994, to assess sonic fatigue behavior of structure that is being considered for the High Speed Civil Transport (HSCT). High Speed Research (HSR) program objectives in the area of sonic fatigue were to predict inlet, exhaust and boundary layer acoustic loads; measure high cycle fatigue data for materials developed during the HSR program; develop advanced sonic fatigue calculation methods to reduce required conservatism in airframe designs; develop damping techniques for sonic fatigue reduction where weight effective; develop wing and fuselage sonic fatigue design requirements; and perform sonic fatigue analyses on HSCT structural concepts to provide guidance to design teams. All goals were partially achieved, but none were completed due to the premature conclusion of the HSR program. A summary of major program findings and recommendations for continued effort are included in the report.

Estimation of Sonic Fatigue by Reduced-Order Finite Element Based Analyses

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A.; Przekop, Adam

2006-01-01

A computationally efficient, reduced-order method is presented for prediction of sonic fatigue of structures exhibiting geometrically nonlinear response. A procedure to determine the nonlinear modal stiffness using commercial finite element codes allows the coupled nonlinear equations of motion in physical degrees of freedom to be transformed to a smaller coupled system of equations in modal coordinates. The nonlinear modal system is first solved using a computationally light equivalent linearization solution to determine if the structure responds to the applied loading in a nonlinear fashion. If so, a higher fidelity numerical simulation in modal coordinates is undertaken to more accurately determine the nonlinear response. Comparisons of displacement and stress response obtained from the reduced-order analyses are made with results obtained from numerical simulation in physical degrees-of-freedom. Fatigue life predictions from nonlinear modal and physical simulations are made using the rainflow cycle counting method in a linear cumulative damage analysis. Results computed for a simple beam structure under a random acoustic loading demonstrate the effectiveness of the approach and compare favorably with results obtained from the solution in physical degrees-of-freedom.

Progress in Developing Transfer Functions for Surface Scanning Eddy Current Inspections

NASA Astrophysics Data System (ADS)

Shearer, J.; Heebl, J.; Brausch, J.; Lindgren, E.

2009-03-01

As US Air Force (USAF) aircraft continue to age, additional inspections are required for structural components. The validation of new inspections typically requires a capability demonstration of the method using representative structure with representative damage. To minimize the time and cost required to prepare such samples, Electric Discharge machined (EDM) notches are commonly used to represent fatigue cracks in validation studies. However, the sensitivity to damage typically changes as a function of damage type. This requires a mathematical relationship to be developed between the responses from the two different flaw types to enable the use of EDM notched samples to validate new inspections. This paper reviews progress to develop transfer functions for surface scanning eddy current inspections of aluminum and titanium alloys found in structural aircraft components. Multiple samples with well characterized grown fatigue cracks and master gages with EDM notches, both with a range of flaw sizes, were used to collect flaw signals with USAF field inspection equipment. Analysis of this empirical data was used to develop a transfer function between the response from the EDM notches and grown fatigue cracks.

Simplified rotor load models and fatigue damage estimates for offshore wind turbines.

PubMed

Muskulus, M

2015-02-28

The aim of rotor load models is to characterize and generate the thrust loads acting on an offshore wind turbine. Ideally, the rotor simulation can be replaced by time series from a model with a few parameters and state variables only. Such models are used extensively in control system design and, as a potentially new application area, structural optimization of support structures. Different rotor load models are here evaluated for a jacket support structure in terms of fatigue lifetimes of relevant structural variables. All models were found to be lacking in accuracy, with differences of more than 20% in fatigue load estimates. The most accurate models were the use of an effective thrust coefficient determined from a regression analysis of dynamic thrust loads, and a novel stochastic model in state-space form. The stochastic model explicitly models the quasi-periodic components obtained from rotational sampling of turbulent fluctuations. Its state variables follow a mean-reverting Ornstein-Uhlenbeck process. Although promising, more work is needed on how to determine the parameters of the stochastic model and before accurate lifetime predictions can be obtained without comprehensive rotor simulations. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Very High Cycle Fatigue Failure Analysis and Life Prediction of Cr-Ni-W Gear Steel Based on Crack Initiation and Growth Behaviors.

PubMed

Deng, Hailong; Li, Wei; Sakai, Tatsuo; Sun, Zhenduo

2015-12-02

The unexpected failures of structural materials in very high cycle fatigue (VHCF) regime have been a critical issue in modern engineering design. In this study, the VHCF property of a Cr-Ni-W gear steel was experimentally investigated under axial loading with the stress ratio of R = -1, and a life prediction model associated with crack initiation and growth behaviors was proposed. Results show that the Cr-Ni-W gear steel exhibits the constantly decreasing S-N property without traditional fatigue limit, and the fatigue strength corresponding to 10⁸ cycles is around 485 MPa. The inclusion-fine granular area (FGA)-fisheye induced failure becomes the main failure mechanism in the VHCF regime, and the local stress around the inclusion play a key role. By using the finite element analysis of representative volume element, the local stress tends to increase with the increase of elastic modulus difference between inclusion and matrix. The predicted crack initiation life occupies the majority of total fatigue life, while the predicted crack growth life is only accounts for a tiny fraction. In view of the good agreement between the predicted and experimental results, the proposed VHCF life prediction model involving crack initiation and growth can be acceptable for inclusion-FGA-fisheye induced failure.

Data-Driven Correlation Analysis Between Observed 3D Fatigue-Crack Path and Computed Fields from High-Fidelity, Crystal-Plasticity, Finite-Element Simulations

NASA Astrophysics Data System (ADS)

Pierson, Kyle D.; Hochhalter, Jacob D.; Spear, Ashley D.

2018-05-01

Systematic correlation analysis was performed between simulated micromechanical fields in an uncracked polycrystal and the known path of an eventual fatigue-crack surface based on experimental observation. Concurrent multiscale finite-element simulation of cyclic loading was performed using a high-fidelity representation of grain structure obtained from near-field high-energy x-ray diffraction microscopy measurements. An algorithm was developed to parameterize and systematically correlate the three-dimensional (3D) micromechanical fields from simulation with the 3D fatigue-failure surface from experiment. For comparison, correlation coefficients were also computed between the micromechanical fields and hypothetical, alternative surfaces. The correlation of the fields with hypothetical surfaces was found to be consistently weaker than that with the known crack surface, suggesting that the micromechanical fields of the cyclically loaded, uncracked microstructure might provide some degree of predictiveness for microstructurally small fatigue-crack paths, although the extent of such predictiveness remains to be tested. In general, gradients of the field variables exhibit stronger correlations with crack path than the field variables themselves. Results from the data-driven approach implemented here can be leveraged in future model development for prediction of fatigue-failure surfaces (for example, to facilitate univariate feature selection required by convolution-based models).

Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes

NASA Technical Reports Server (NTRS)

Miles, R. N.

1992-01-01

This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for performing fatigue life estimates for structures that exhibit nonlinear vibration behavior and that have numerous resonant modes contributing to the response.

Assessment of fatigue in rheumatoid arthritis: a psychometric comparison of single-item, multiitem, and multidimensional measures.

PubMed

Oude Voshaar, Martijn A H; Ten Klooster, Peter M; Bode, Christina; Vonkeman, Harald E; Glas, Cees A W; Jansen, Tim; van Albada-Kuipers, Iet; van Riel, Piet L C M; van de Laar, Mart A F J

2015-03-01

To compare the psychometric functioning of multidimensional disease-specific, multiitem generic, and single-item measures of fatigue in patients with rheumatoid arthritis (RA). Confirmatory factor analysis (CFA) and longitudinal item response theory (IRT) modeling were used to evaluate the measurement structure and local reliability of the Bristol RA Fatigue Multi-Dimensional Questionnaire (BRAF-MDQ), the Medical Outcomes Study Short Form-36 (SF-36) vitality scale, and the BRAF Numerical Rating Scales (BRAF-NRS) in a sample of 588 patients with RA. A 1-factor CFA model yielded a similar fit to a 5-factor model with subscale-specific dimensions, and the items from the different instruments adequately fit the IRT model, suggesting essential unidimensionality in measurement. The SF-36 vitality scale outperformed the BRAF-MDQ at lower levels of fatigue, but was less precise at moderate to higher levels of fatigue. At these levels of fatigue, the living, cognition, and emotion subscales of the BRAF-MDQ provide additional precision. The BRAF-NRS showed a limited measurement range with its highest precision centered on average levels of fatigue. The different instruments appear to access a common underlying domain of fatigue severity, but differ considerably in their measurement precision along the continuum. The SF-36 vitality scale can be used to measure fatigue severity in samples with relatively mild fatigue. For samples expected to have higher levels of fatigue, the multidimensional BRAF-MDQ appears to be a better choice. The BRAF-NRS are not recommended if precise assessment is required, for instance in longitudinal settings.

Turbine Engine Hot Section Technology, 1987

NASA Technical Reports Server (NTRS)

1987-01-01

Presentations were made concerning the development of design analysis tools for combustor liners, turbine vanes, and turbine blades. Presentations were divided into six sections: instrumentation, combustion, turbine heat transfer, structural analysis, fatigue and fracture, surface protective coatings, constitutive behavior of materials, stress-strain response and life prediction methods.

Experimental characterization of fatigue strength in butt welded joint considering the geometry and the effect of cooling rate of the weld

NASA Astrophysics Data System (ADS)

Arzola, Nelson; Hernández, Edgar

2017-05-01

In this work the experimental characterization of fatigue strength in butt welded joints considering the geometry and the post-weld cooling cycle was performed. ASTM A-36 structural steel was used as the base metal for the shielded metal arc welding process, with welding electrode E6013. Two experimental factors were established: weld bead geometry and the post-weld cooling rate. Two levels for each factor, the welding reinforcement (1 and 3 mm), and the rate of cooling, slow (quiet air) and fast (immersion in water) are evaluated respectively. For the uniaxial fatigue tests, 8 samples were selected for each treatment for a total of 32 specimens. The mechanical and fractomechanical properties of fusion zone, heat affected zone and base metal in relation to the analysis of failure mechanisms were analysed. The fatigue crack growth rates were estimated based on the counting of microstrations. Furthermore, experimental tests, such as uniaxial tension, microindentation hardness, Charpy impact and metallographic analysis, were made to know the influence of the experimental factors in the fatigue strength. On this research, about the 78.13% of the samples obtained a resistance higher than the recommended one by class FAT 100. The results showed that the geometry of the joint is the factor of greatest influence on fatigue strength for butt welded joints; the greater the weld reinforcement the lower the fatigue strength of the joint. Although it is also important to consider other geometric factors of less impact as it is the weld toe radius and the welding chord width.

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

PubMed

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

2015-10-16

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

A new methodology for automating acoustic emission detection of metallic fatigue fractures in highly demanding aerospace environments: An overview

NASA Astrophysics Data System (ADS)

Holford, Karen M.; Eaton, Mark J.; Hensman, James J.; Pullin, Rhys; Evans, Sam L.; Dervilis, Nikolaos; Worden, Keith

2017-04-01

The acoustic emission (AE) phenomenon has many attributes that make it desirable as a structural health monitoring or non-destructive testing technique, including the capability to continuously and globally monitor large structures using a sparse sensor array and with no dependency on defect size. However, AE monitoring is yet to fulfil its true potential, due mainly to limitations in location accuracy and signal characterisation that often arise in complex structures with high levels of background noise. Furthermore, the technique has been criticised for a lack of quantitative results and the large amount of operator interpretation required during data analysis. This paper begins by introducing the challenges faced in developing an AE based structural health monitoring system and then gives a review of previous progress made in addresing these challenges. Subsequently an overview of a novel methodology for automatic detection of fatigue fractures in complex geometries and noisy environments is presented, which combines a number of signal processing techniques to address the current limitations of AE monitoring. The technique was developed for monitoring metallic landing gear components during pre-flight certification testing and results are presented from a full-scale steel landing gear component undergoing fatigue loading. Fracture onset was successfully identify automatically at 49,000 fatigue cycles prior to final failure (validated by the use of dye penetrant inspection) and the fracture position was located to within 10 mm of the actual location.

Decision fatigue: A conceptual analysis.

PubMed

Pignatiello, Grant A; Martin, Richard J; Hickman, Ronald L

2018-03-01

Decision fatigue is an applicable concept to healthcare psychology. Due to a lack of conceptual clarity, we present a concept analysis of decision fatigue. A search of the term "decision fatigue" was conducted across seven research databases, which yielded 17 relevant articles. The authors identified three antecedent themes (decisional, self-regulatory, and situational) and three attributional themes (behavioral, cognitive, and physiological) of decision fatigue. However, the extant literature failed to adequately describe consequences of decision fatigue. This concept analysis provides needed conceptual clarity for decision fatigue, a concept possessing relevance to nursing and allied health sciences.

Numerical prediction of mechanical properties of Pb-Sn solder alloys containing antimony, bismuth and or silver ternary trace elements

NASA Astrophysics Data System (ADS)

Gadag, Shiva P.; Patra, Susant

2000-12-01

Solder joint interconnects are mechanical means of structural support for bridging the various electronic components and providing electrical contacts and a thermal path for heat dissipation. The functionality of the electronic device often relies on the structural integrity of the solder. The dimensional stability of solder joints is numerically predicted based on their mechanical properties. Algorithms to model the kinetics of dissolution and subsequent growth of intermetallic from the complete knowledge of a single history of time-temperature-reflow profile, by considering equivalent isothermal time intervals, have been developed. The information for dissolution is derived during the heating cycle of reflow and for the growth process from cooling curve of reflow profile. A simple and quick analysis tool to derive tensile stress-strain maps as a function of the reflow temperature of solder and strain rate has been developed by numerical program. The tensile properties are used in modeling thermal strain, thermal fatigue and to predict the overall fatigue life of solder joints. The numerical analysis of the tensile properties as affected by their composition and rate of testing, has been compiled in this paper. A numerical model using constitutive equation has been developed to evaluate the interfacial fatigue crack growth rate. The model can assess the effect of cooling rate, which depends on the level of strain energy release rate. Increasing cooling rate from normalizing to water-quenching, enhanced the fatigue resistance to interfacial crack growth by up to 50% at low strain energy release rate. The increased cooling rates enhanced the fatigue crack growth resistance by surface roughening at the interface of solder joint. This paper highlights salient features of process modeling. Interfacial intermetallic microstructure is affected by cooling rate and thereby affects the mechanical properties.

Structure analysis and anti-fatigue activity of a polysaccharide from Lepidium meyenii Walp.

PubMed

Tang, Yun; Zhu, Zhen-Yuan; Pan, Li-Chao; Sun, Huiqing; Song, Qiao-Ying; Zhang, Yongmin

2018-03-16

A polysaccharide was obtained from Lepidium meyenii Walp by hot water extraction and purification by Millipore (100 kD) and Sephadex G-200. The content of polysaccharide was examined to be 89.9% with phenol-sulfuric acid method. Its average molecular weight was estimated to be 2.213 × 10 6  Da by High Performance Gel Permeation Chromatography (HPGPC). Monosaccharide analysis showed that the polysaccharide was composed of arabinose, mannose, glucose and galactose with the molar ratio of 2.134: 1: 2.78: 2.82. After Smith degradation, methylation, infrared spectroscopy and NMR, the primary structure of the polysaccharide was identified. The backbone of the polysaccharide was composed of →4)-β-D-Galp-(1→ and →4)-α-D-Galp-(1→, while the branches were comprised of →6)-β-D-Glup-(1→, →5)- β-D-Araf-(1→, →3,6)-α-D-Manp-(1→, →3)-α-D-Galp-(1→, and α-D-Glup-(1→. The anti-fatigue effect of the polysaccharide was evaluated using exhaustive swimming test and biochemical indexes. The results indicated the polysaccharide has anti-fatigue effect.

FEM Techniques for High Stress Detection in Accelerated Fatigue Simulation

NASA Astrophysics Data System (ADS)

Veltri, M.

2016-09-01

This work presents the theory and a numerical validation study in support to a novel method for a priori identification of fatigue critical regions, with the aim to accelerate durability design in large FEM problems. The investigation is placed in the context of modern full-body structural durability analysis, where a computationally intensive dynamic solution could be required to identify areas with potential for fatigue damage initiation. The early detection of fatigue critical areas can drive a simplification of the problem size, leading to sensible improvement in solution time and model handling while allowing processing of the critical areas in higher detail. The proposed technique is applied to a real life industrial case in a comparative assessment with established practices. Synthetic damage prediction quantification and visualization techniques allow for a quick and efficient comparison between methods, outlining potential application benefits and boundaries.

14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

Code of Federal Regulations, 2010 CFR

2010-01-01

... contribute to a catastrophic failure (such as wing, empennage, control surfaces and their systems, the... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25... and sonic excitation environment, that— (1) Sonic fatigue cracks are not probable in any part of the...

Engineering Evaluation of International Low Impact Docking System Latch Hooks

NASA Technical Reports Server (NTRS)

Martinez, J.; Patin, R.; Figert, J.

2013-01-01

The international Low Impact Docking System (iLIDS) provides a structural arrangement that allows for visiting vehicles to dock with the International Space Station (ISS) (Fig 1). The iLIDS docking units are mechanically joined together by a series of active and passive latch hooks. In order to preserve docking capability at the existing Russian docking interfaces, the iLIDS latch hooks are required to conform to the existing Russian design. The latch hooks are classified as being fail-safe. Since the latch hooks are fail-safe, the hooks are not fracture critical and a fatigue based service life assessment will satisfy the structural integrity requirements. Constant amplitude fatigue testing to failure on four sets of active/passive iLIDS latch hooks was performed at load magnitudes of 10, 11, and 12 kips. Failure analysis of the hook fatigue failures identified multi-site fatigue initiation that was effectively centered about the hook mid-plane (consistent with the 3D model results). The fatigue crack initiation distribution implies that the fatigue damage accumulation effectively results in a very low aspect ratio surface crack (which can be simulated as thru-thickness crack). Fatigue damage progression resulted in numerous close proximity fatigue crack initiation sites. It was not possible to determine if fatigue crack coalescence occurs during cyclic loading or as result of the fast fracture response. The presence of multiple fatigue crack initiation sites on different planes will result in the formation of ratchet marks as the cracks coalesce. Once the stable fatigue crack becomes unstable and the fast fracture advances across the remaining ligament and the plane stress condition at a free-surface will result in failure along a 45 deg. shear plane (slant fracture) and the resulting inclined edge is called a shear lip. The hook thickness on the plane of fatigue crack initiation is 0.787". The distance between the shear lips on this plane was on the order of 0.48" and it was effectively centered about the mid-plane of the section. The numerous ratchet marks between the shear lips on the fracture initiation plane are indicative of multiple fatigue initiation sites within this region. The distribution of the fatigue damage about the centerline of the hook is consistent with the analytical results that demonstrate peak stress/strain response at the mid-plane that decreases in the direction of the hook outer surfaces. Scanning electron microscope images of the failed sections detected fatigue crack striations in close proximity to the free surface of the hook radius. These findings were documented at three locations on the fracture surface : 1) adjacent to the left shear lip, 2) adjacent to the right shear lip, and 3) near the centerline of the section. The features of the titanium fracture surface did not allow for a determination of a critical crack size via identification of the region where the fatigue crack propagation became unstable. The fracture based service life projections where benchmarked with strain-life analyses. The strainrange response in the hook radius was defined via the correlated finite element models and the modified method of universal slopes was incorporated to define the strain-life equation for the titanium alloy. The strain-life assessment confirmed that the fracture based projections were reasonable for the loading range of interest. Based upon the analysis and component level fatigue test data a preliminary service life capability for the iLIDS active and passive hooks of 2 lifetimes is projected (includes a scatter factor of 4).

The Development of Lightweight Commercial Vehicle Wheels Using Microalloying Steel

NASA Astrophysics Data System (ADS)

Lu, Hongzhou; Zhang, Lilong; Wang, Jiegong; Xuan, Zhaozhi; Liu, Xiandong; Guo, Aimin; Wang, Wenjun; Lu, Guimin

Lightweight wheels can reduce weight about 100kg for commercial vehicles, and it can save energy and reduce emission, what's more, it can enhance the profits for logistics companies. The development of lightweight commercial vehicle wheels is achieved by the development of new steel for rim, the process optimization of flash butt welding, and structure optimization by finite element methods. Niobium micro-alloying technology can improve hole expansion rate, weldability and fatigue performance of wheel steel, and based on Niobium micro-alloying technology, a special wheel steel has been studied whose microstructure are Ferrite and Bainite, with high formability and high fatigue performance, and stable mechanical properties. The content of Nb in this new steel is 0.025% and the hole expansion rate is ≥ 100%. At the same time, welding parameters including electric upsetting time, upset allowance, upsetting pressure and flash allowance are optimized, and by CAE analysis, an optimized structure has been attained. As a results, the weight of 22.5in×8.25in wheel is up to 31.5kg, which is most lightweight comparing the same size wheels. And its functions including bending fatigue performance and radial fatigue performance meet the application requirements of truck makers and logistics companies.

75 FR 27419 - Airworthiness Directives; BAE Systems (Operations) Limited Model BAe 146 and Avro 146-RJ70A, 146...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-05-17

... environmental and fatigue inspections would not have detected the corrosion or fatigue damage. Corrosion or fatigue damage in this area, if not detected and corrected, could lead to degradation of the structural... fatigue inspections would not have detected the corrosion or fatigue damage. Corrosion or fatigue damage...

Development of a clinician-administered National Institutes of Health-Brief Fatigue Inventory: A measure of fatigue in the context of depressive disorders.

PubMed

Saligan, Leorey N; Luckenbaugh, David A; Slonena, Elizabeth E; Machado-Vieira, Rodrigo; Zarate, Carlos A

2015-09-01

Fatigue is a complex, multidimensional condition. Although it is often associated with depression, it is not known whether it has a distinct network from depression or whether it can be clinically evaluated, separately. This study describes preliminary findings in the development of a brief, clinician-administered instrument to measure fatigue in the context of depressive disorders using items from existing clinician-administered depression and mania scales. Based on items from prior fatigue measurements, items were selected from the Hamilton Depression Rating Scale (HDRS), Montgomery-Asberg Depression Rating Scale (MADRS), Young Mania Rating Scale, and Structured Interview Guide for HDRS with Atypical Depression. The final items composed the NIH-Brief Fatigue Inventory (NIH-BFI). Responses from 89 depressed adults collected pre- and post-antidepressant therapy (ADT) determined the reliability and consistency of the NIH-BFI using Cronbach's alpha and principal components analysis (PCA). Correlations of the NIH-BFI and fatigue items from other scales before and after ADT explored validity. The 7-item NIH-BFI had Cronbach alphas ranging from 0.81 to 0.88 and PCA indicating a single dimension. The NIH-BFI score was strongly correlated (r = 0.73, p < 0.001) with fatigue items from Beck Depression Index, with MADRS without fatigue items (r = 0.77, p < 0.001), and HDRS without fatigue items (pre: r = 0.69, p < 0.001). Preliminary findings show support for internal consistency reliability and validity of the NIH-BFI, a clinician-administered measure of fatigue. Further testing in other clinical populations is recommended to obtain additional information on reliability and validity. The NIH-BFI provides a method for clinician-rated fatigue that may be a separate from depression. Published by Elsevier Ltd.

Recent developments of the NESSUS probabilistic structural analysis computer program

NASA Technical Reports Server (NTRS)

Millwater, H.; Wu, Y.-T.; Torng, T.; Thacker, B.; Riha, D.; Leung, C. P.

1992-01-01

The NESSUS probabilistic structural analysis computer program combines state-of-the-art probabilistic algorithms with general purpose structural analysis methods to compute the probabilistic response and the reliability of engineering structures. Uncertainty in loading, material properties, geometry, boundary conditions and initial conditions can be simulated. The structural analysis methods include nonlinear finite element and boundary element methods. Several probabilistic algorithms are available such as the advanced mean value method and the adaptive importance sampling method. The scope of the code has recently been expanded to include probabilistic life and fatigue prediction of structures in terms of component and system reliability and risk analysis of structures considering cost of failure. The code is currently being extended to structural reliability considering progressive crack propagation. Several examples are presented to demonstrate the new capabilities.

Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

NASA Astrophysics Data System (ADS)

Ranjan, Srikant

2005-11-01

Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the resolved shear stress on primary slip planes. The maximum value of Krss and DeltaKrss was found to determine the crack growth direction and the fatigue crack growth rate respectively. The fatigue crack driving force parameter, DeltaK rss, forms an important multiaxial fatigue damage parameter that can be used to predict life in superalloy components.

A fundamental study on the structural integrity of magnesium alloys joined by friction stir welding

NASA Astrophysics Data System (ADS)

Rao, Harish Mangebettu

The goal of this research is to study the factors that influence the physical and mechanical properties of lap-shear joints produced using friction stir welding. This study focuses on understanding the effect of tool geometry and weld process parameters including the tool rotation rate, tool plunge depth and dwell time on the mechanical performance of similar magnesium alloy and dissimilar magnesium to aluminum alloy weld joints. A variety of experimental activities were conducted including tensile and fatigue testing, fracture surface and failure analysis, microstructure characterization, hardness measurements and chemical composition analysis. An investigation on the effect of weld process conditions in friction stir spot welding of magnesium to magnesium produced in a manner that had a large effective sheet thickness and smaller interfacial hook height exhibited superior weld strength. Furthermore, in fatigue testing of friction stir spot welded of magnesium to magnesium alloy, lap-shear welds produced using a triangular tool pin profile exhibited better fatigue life properties compared to lap-shear welds produced using a cylindrical tool pin profile. In friction stir spot welding of dissimilar magnesium to aluminum, formation of intermetallic compounds in the stir zone of the weld had a dominant effect on the weld strength. Lap-shear dissimilar welds with good material mixture and discontinues intermetallic compounds in the stir zone exhibited superior weld strength compared to lap-shear dissimilar welds with continuous formation of intermetallic compounds in the stir zone. The weld structural geometry like the interfacial hook, hook orientation and bond width also played a major role in influencing the weld strength of the dissimilar lap-shear friction stir spot welds. A wide scatter in fatigue test results was observed in friction stir linear welds of aluminum to magnesium alloys. Different modes of failure were observed under fatigue loading including crack propagation into the top sheet, into the bottom sheet, and interfacial separation. Investigation of the tested welds revealed that the voids in the weld nugget reduced the weld strength, resulting in lower fatigue life. A thin layer of IMCs formed along the faying surface which accelerated the fatigue failure.

Developing a Data Set and Processing Methodology for Fluid/Structure Interaction Code Validation

DTIC Science & Technology

2007-06-01

50 29. 9-Probe Wake Survey Rake Configurations...structural stability and fatigue in test article components and, in general, in facility support structures and rotating machinery blading . Both T&E... blade analysis and simulations. To ensure the accuracy of the U of CO technology, validation using flight-test data and test data from a wind tunnel

Lifetime Reliability Prediction of Ceramic Structures Under Transient Thermomechanical Loads

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Jadaan, Osama J.; Gyekenyesi, John P.

2005-01-01

An analytical methodology is developed to predict the probability of survival (reliability) of ceramic components subjected to harsh thermomechanical loads that can vary with time (transient reliability analysis). This capability enables more accurate prediction of ceramic component integrity against fracture in situations such as turbine startup and shutdown, operational vibrations, atmospheric reentry, or other rapid heating or cooling situations (thermal shock). The transient reliability analysis methodology developed herein incorporates the following features: fast-fracture transient analysis (reliability analysis without slow crack growth, SCG); transient analysis with SCG (reliability analysis with time-dependent damage due to SCG); a computationally efficient algorithm to compute the reliability for components subjected to repeated transient loading (block loading); cyclic fatigue modeling using a combined SCG and Walker fatigue law; proof testing for transient loads; and Weibull and fatigue parameters that are allowed to vary with temperature or time. Component-to-component variation in strength (stochastic strength response) is accounted for with the Weibull distribution, and either the principle of independent action or the Batdorf theory is used to predict the effect of multiaxial stresses on reliability. The reliability analysis can be performed either as a function of the component surface (for surface-distributed flaws) or component volume (for volume-distributed flaws). The transient reliability analysis capability has been added to the NASA CARES/ Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code. CARES/Life was also updated to interface with commercially available finite element analysis software, such as ANSYS, when used to model the effects of transient load histories. Examples are provided to demonstrate the features of the methodology as implemented in the CARES/Life program.

Collagen fibrils in functionally distinct tendons have differing structural responses to tendon rupture and fatigue loading.

PubMed

Herod, Tyler W; Chambers, Neil C; Veres, Samuel P

2016-09-15

In this study we investigate relationships between the nanoscale structure of collagen fibrils and the macroscale functional response of collagenous tissues. To do so, we study two functionally distinct classes of tendons, positional tendons and energy storing tendons, using a bovine forelimb model. Molecular-level assessment using differential scanning calorimetry (DSC), functional crosslink assessment using hydrothermal isometric tension (HIT) analysis, and ultrastructural assessment using scanning electron microscopy (SEM) were used to study undamaged, ruptured, and cyclically loaded samples from the two tendon types. HIT indicated differences in both crosslink type and crosslink density, with flexor tendons having more thermally stable crosslinks than the extensor tendons (higher TFmax of >90 vs. 75.1±2.7°C), and greater total crosslink density than the extensor tendons (higher t1/2 of 11.5±1.9 vs. 3.5±1.0h after NaBH4 treatment). Despite having a lower crosslink density than flexor tendons, extensor tendons were significantly stronger (37.6±8.1 vs. 23.1±7.7MPa) and tougher (14.3±3.6 vs. 6.8±3.4MJ/m(3)). SEM showed that collagen fibrils in the tougher, stronger extensor tendons were able to undergo remarkable levels of plastic deformation in the form of discrete plasticity, while those in the flexor tendons were not able to plastically deform. When cyclically loaded, collagen fibrils in extensor tendons accumulated fatigue damage rapidly in the form of kink bands, while those in flexor tendons did not accumulate significant fatigue damage. The results demonstrate that collagen fibrils in functionally distinct tendons respond differently to mechanical loading, and suggests that fibrillar collagens may be subject to a strength vs. fatigue resistance tradeoff. Collagen fibrils-nanoscale biological cables-are the fundamental load-bearing elements of all structural human tissues. While all collagen fibrils share common features, such as being composed of a precise quarter-staggered polymeric arrangement of triple-helical collagen molecules, their structure can vary significantly between tissue types, and even between different anatomical structures of the same tissue type. To understand normal function, homeostasis, and disease of collagenous tissues requires detailed knowledge of collagen fibril structure-function. Using anatomically proximate but structurally distinct tendons, we show that collagen fibrils in functionally distinct tendons have differing susceptibilities to damage under both tensile overload and cyclic fatigue loading. Our results suggest that the structure of collagen fibrils may lead to a strength versus fatigue resistance tradeoff, where high strength is gained at the expense of fatigue resistance, and vice versa. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

CARES/LIFE Ceramics Analysis and Reliability Evaluation of Structures Life Prediction Program

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.; Gyekenyesi, John P.

2003-01-01

This manual describes the Ceramics Analysis and Reliability Evaluation of Structures Life Prediction (CARES/LIFE) computer program. The program calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. CARES/LIFE is an extension of the CARES (Ceramic Analysis and Reliability Evaluation of Structures) computer program. The program uses results from MSC/NASTRAN, ABAQUS, and ANSYS finite element analysis programs to evaluate component reliability due to inherent surface and/or volume type flaws. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker law. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled by using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. The probabilistic time-dependent theories used in CARES/LIFE, along with the input and output for CARES/LIFE, are described. Example problems to demonstrate various features of the program are also included.

Review on stress corrosion and corrosion fatigue failure of centrifugal compressor impeller

NASA Astrophysics Data System (ADS)

Sun, Jiao; Chen, Songying; Qu, Yanpeng; Li, Jianfeng

2015-03-01

Corrosion failure, especially stress corrosion cracking and corrosion fatigue, is the main cause of centrifugal compressor impeller failure. And it is concealed and destructive. This paper summarizes the main theories of stress corrosion cracking and corrosion fatigue and its latest developments, and it also points out that existing stress corrosion cracking theories can be reduced to the anodic dissolution (AD), the hydrogen-induced cracking (HIC), and the combined AD and HIC mechanisms. The corrosion behavior and the mechanism of corrosion fatigue in the crack propagation stage are similar to stress corrosion cracking. The effects of stress ratio, loading frequency, and corrosive medium on the corrosion fatigue crack propagation rate are analyzed and summarized. The corrosion behavior and the mechanism of stress corrosion cracking and corrosion fatigue in corrosive environments, which contain sulfide, chlorides, and carbonate, are analyzed. The working environments of the centrifugal compressor impeller show the behavior and the mechanism of stress corrosion cracking and corrosion fatigue in different corrosive environments. The current research methods for centrifugal compressor impeller corrosion failure are analyzed. Physical analysis, numerical simulation, and the fluid-structure interaction method play an increasingly important role in the research on impeller deformation and stress distribution caused by the joint action of aerodynamic load and centrifugal load.

Probability of failure prediction for step-stress fatigue under sine or random stress

NASA Technical Reports Server (NTRS)

Lambert, R. G.

1979-01-01

A previously proposed cumulative fatigue damage law is extended to predict the probability of failure or fatigue life for structural materials with S-N fatigue curves represented as a scatterband of failure points. The proposed law applies to structures subjected to sinusoidal or random stresses and includes the effect of initial crack (i.e., flaw) sizes. The corrected cycle ratio damage function is shown to have physical significance.

Probabilistic Multi-Scale, Multi-Level, Multi-Disciplinary Analysis and Optimization of Engine Structures

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Abumeri, Galib H.

2000-01-01

Aircraft engines are assemblies of dynamically interacting components. Engine updates to keep present aircraft flying safely and engines for new aircraft are progressively required to operate in more demanding technological and environmental requirements. Designs to effectively meet those requirements are necessarily collections of multi-scale, multi-level, multi-disciplinary analysis and optimization methods and probabilistic methods are necessary to quantify respective uncertainties. These types of methods are the only ones that can formally evaluate advanced composite designs which satisfy those progressively demanding requirements while assuring minimum cost, maximum reliability and maximum durability. Recent research activities at NASA Glenn Research Center have focused on developing multi-scale, multi-level, multidisciplinary analysis and optimization methods. Multi-scale refers to formal methods which describe complex material behavior metal or composite; multi-level refers to integration of participating disciplines to describe a structural response at the scale of interest; multidisciplinary refers to open-ended for various existing and yet to be developed discipline constructs required to formally predict/describe a structural response in engine operating environments. For example, these include but are not limited to: multi-factor models for material behavior, multi-scale composite mechanics, general purpose structural analysis, progressive structural fracture for evaluating durability and integrity, noise and acoustic fatigue, emission requirements, hot fluid mechanics, heat-transfer and probabilistic simulations. Many of these, as well as others, are encompassed in an integrated computer code identified as Engine Structures Technology Benefits Estimator (EST/BEST) or Multi-faceted/Engine Structures Optimization (MP/ESTOP). The discipline modules integrated in MP/ESTOP include: engine cycle (thermodynamics), engine weights, internal fluid mechanics, cost, mission and coupled structural/thermal, various composite property simulators and probabilistic methods to evaluate uncertainty effects (scatter ranges) in all the design parameters. The objective of the proposed paper is to briefly describe a multi-faceted design analysis and optimization capability for coupled multi-discipline engine structures optimization. Results are presented for engine and aircraft type metrics to illustrate the versatility of that capability. Results are also presented for reliability, noise and fatigue to illustrate its inclusiveness. For example, replacing metal rotors with composites reduces the engine weight by 20 percent, 15 percent noise reduction, and an order of magnitude improvement in reliability. Composite designs exist to increase fatigue life by at least two orders of magnitude compared to state-of-the-art metals.

Johnson Space Center Overview

NASA Technical Reports Server (NTRS)

Gafka, Tammy; Terrier, Doug; Smith, James

2011-01-01

This slide presentation is a review of the work of Johnson Space Center. It includes a section on technology development areas, (i.e., composite structures, non-destructive evaluation, applied nanotechnology, additive manufacturing, and fracture and fatigue analytical methods), a section on structural analysis capabilities within NASA/JSC and a section on Friction stir welding and laser peening.

Dynamic and Fatigue Analysis of an 18{sup th} Century Steel Arch Bridge

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

Boumechra, Nadir; Hamdaoui, Karim

2008-07-08

Within the 'Oran-Tlemcen' railway line realization project (159 km), several bridges were built by the Railroads Algerian West Company. 7 km from the east of Tlemcen city, this railway line must cross a very broken mountainous collar, that's why the French engineer 'Gustave Eiffel' was solicited to construct a 68 m length bridge. In 1890, an arch steel truss bridge was realized. The bridge presents 300 m of apron curvature radius and, currently, is considered as one of the most important monuments of the Algerian historical heritage. Considering the age of the bridge and the evolution of the railway loadsmore » in time, it was essential to check the good behavior of the studied structure. For that, analyses to verify the physical and mechanical properties of the growth iron members are made. A finite element model of the bridge was built and numerical simulations were drawn. The structural vibration conducted analysis permit to understand the behavior of this particular structure, then to evaluate (in detail) the rate of the structure fatigue.« less

Strain-cycling fatigue behavior of ten structural metals tested in liquid helium (4 K), in liquid nitrogen (78 K), and in ambient air (300 K)

NASA Technical Reports Server (NTRS)

Nachtigall, A. J.

1974-01-01

Strain-cycling fatigue behavior of 10 different structural alloys and metals was investigated in liquid helium (4 K), in liquid nitrogen (78 K), and in ambient air (300 K). At high cyclic lives, fatigue resistance increased with decreasing temperature for all the materials investigated. At low cyclic lives, fatigue resistance generally decreased with decreasing temperature for the materials investigated. Only for Inconel 718 did fatigue resistance increase with decreasing temperature over the entire life range investigated. Comparison of the experimental fatigue behavior with that predicted by the Manson method of universal slopes showed that the fatigue behavior of these materials can be predicted for cryogenic temperatures by using material tensile properties obtained at those same temperatures.

Creep-Fatigue Interaction Testing

NASA Technical Reports Server (NTRS)

Halford, Gary R.

2001-01-01

Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher temperatures, fatigue lives are altered due to time-dependent, thermally activated creep. Conversely, creep rates are altered by super. imposed fatigue loading. Creep and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-temperature structures such as nuclear reactors, reusable rocket engines, gas turbine engines, terrestrial steam turbines, pressure vessel and piping components, casting dies, molds for plastics, and pollution control devices. Safety and lifecycle costs force designers to quantify these interactions. Analytical and experimental approaches to creep-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing creep-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.

Monitoring Poisson's Ratio Degradation of FRP Composites under Fatigue Loading Using Biaxially Embedded FBG Sensors.

PubMed

Akay, Erdem; Yilmaz, Cagatay; Kocaman, Esat S; Turkmen, Halit S; Yildiz, Mehmet

2016-09-19

The significance of strain measurement is obvious for the analysis of Fiber-Reinforced Polymer (FRP) composites. Conventional strain measurement methods are sufficient for static testing in general. Nevertheless, if the requirements exceed the capabilities of these conventional methods, more sophisticated techniques are necessary to obtain strain data. Fiber Bragg Grating (FBG) sensors have many advantages for strain measurement over conventional ones. Thus, the present paper suggests a novel method for biaxial strain measurement using embedded FBG sensors during the fatigue testing of FRP composites. Poisson's ratio and its reduction were monitored for each cyclic loading by using embedded FBG sensors for a given specimen and correlated with the fatigue stages determined based on the variations of the applied fatigue loading and temperature due to the autogenous heating to predict an oncoming failure of the continuous fiber-reinforced epoxy matrix composite specimens under fatigue loading. The results show that FBG sensor technology has a remarkable potential for monitoring the evolution of Poisson's ratio on a cycle-by-cycle basis, which can reliably be used towards tracking the fatigue stages of composite for structural health monitoring purposes.

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

PubMed

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

2017-06-01

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

Monitoring Poisson’s Ratio Degradation of FRP Composites under Fatigue Loading Using Biaxially Embedded FBG Sensors

PubMed Central

Akay, Erdem; Yilmaz, Cagatay; Kocaman, Esat S.; Turkmen, Halit S.; Yildiz, Mehmet

2016-01-01

The significance of strain measurement is obvious for the analysis of Fiber-Reinforced Polymer (FRP) composites. Conventional strain measurement methods are sufficient for static testing in general. Nevertheless, if the requirements exceed the capabilities of these conventional methods, more sophisticated techniques are necessary to obtain strain data. Fiber Bragg Grating (FBG) sensors have many advantages for strain measurement over conventional ones. Thus, the present paper suggests a novel method for biaxial strain measurement using embedded FBG sensors during the fatigue testing of FRP composites. Poisson’s ratio and its reduction were monitored for each cyclic loading by using embedded FBG sensors for a given specimen and correlated with the fatigue stages determined based on the variations of the applied fatigue loading and temperature due to the autogenous heating to predict an oncoming failure of the continuous fiber-reinforced epoxy matrix composite specimens under fatigue loading. The results show that FBG sensor technology has a remarkable potential for monitoring the evolution of Poisson’s ratio on a cycle-by-cycle basis, which can reliably be used towards tracking the fatigue stages of composite for structural health monitoring purposes. PMID:28773901

Advances in Fatigue and Fracture Mechanics Analyses for Aircraft Structures

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1999-01-01

This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

Advances in Fatigue and Fracture Mechanics Analyses for Metallic Aircraft Structures

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

2000-01-01

This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked metallic structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

Enhancing fatigue life of cylinder-crown integrated structure by optimizing dimension

NASA Astrophysics Data System (ADS)

Zhang, Weiwei; Wang, Xiaosong; Wang, Zhongren; Yuan, Shijian

2015-03-01

Cylinder-crown integrated hydraulic press (CCIHP) is a new press structure. The hemispherical hydraulic cylinder also functions as a main portion of crown, which has lower weight and higher section modulus compared with the conventional hydraulic cylinder and press crown. As a result, the material strength capacity is better utilized. During the engineering design of cylinder-crown integrated structure, in order to increase the fatigue life, structural optimization on the basis of the adaptive macro genetic algorithms (AMGA) is first conducted to both reduce weight and decrease peak stress. It is shown that the magnitude of the maximum principal stress is decreased by 28.6%, and simultaneously the total weight is reduced by 4.4%. Subsequently, strain-controlled fatigue test is carried out, and the stress-strain hysteresis loops and cyclic hardening curve are obtained. Based on linear fit, the fatigue properties are calculated and used for the fatigue life prediction. It is shown that the predicted fatigue life is significantly increased from 157000 to 1070000 cycles after structural optimization. Finally, according to the optimization design, a 6300 kN CCIHP has been manufactured, and priority application has been also suggested.

The impact of job and family demands on partner's fatigue: A study of Japanese dual-earner parents.

PubMed

Watanabe, Mayumi; Shimazu, Akihito; Bakker, Arnold B; Demerouti, Evangelia; Shimada, Kyoko; Kawakami, Norito

2017-01-01

This study of Japanese dual-earner couples examined the impact of family and job demands on one's own and one's partner's fatigue as well as gender differences in these effects. A total of 2,502 parents (1,251 couples) were surveyed using a self-administered questionnaire. A crossover model was tested using structural equation modeling. The results of structural equation modeling analyses showed that both job and family demands independently exacerbated fatigue. There was an indirect effect of job and family demands on partner fatigue through one's own fatigue only from husbands to wives. An indirect effect of job demands on partner fatigue through partner's family demands was identified only from wives to husbands. Furthermore, there were gender differences in the crossover of fatigue. This study shows that job and family demands influence family circumstances. When considering means to reduce employees' fatigue, gender differences in the mechanism of fatigue need to be taken into account.

Study on the Effect of Secondary Banded Structure on the Fatigue Property of Non-Quenched and Tempered Micro Alloyed Steel

NASA Astrophysics Data System (ADS)

Yajie, Cheng; Qingliang, Liao; Yue, Zhang

Due to composition segregation and cooling speed, streamline or banded structure were often obtained in the thermal forming parts along the direction of parts forming. Generally speaking, banded structure doesn't decrease the longitudinal mechanical properties, so the secondary banded structure can't get enough attention. The effect of secondary banded structure on the fatigue properties of micro alloyed DG20Mn and 35CrMo steel was investigated using the axial tensile fatigue test of stress ratio of 0.1. The result shows that secondary banded structure was obtained in the center of the steel parts, because of the composition segregation and the lower cooling rate in center part of steel. Secondary banded structure has no significant effect on axial tensile properties of both DG20Mn and 35CrMo, but decreases the axial tensile fatigue performance of DG20Mn steel. This study suggests that under the high cyclic tensile stress, multi-source damage cracks in steel initiated by large strain of pearlite of secondary banded structure, which is larger than damage strain, is the major factor of the decrease of fatigue life of steel.

Fatigue crack initiation of magnesium alloys under elastic stress amplitudes: A review

NASA Astrophysics Data System (ADS)

Wang, B. J.; Xu, D. K.; Wang, S. D.; Han, E. H.

2017-12-01

The most advantageous property of magnesium (Mg) alloys is their density, which is lower compared with traditional metallic materials. Mg alloys, considered the lightest metallic structural material among others, have great potential for applications as secondary load components in the transportation and aerospace industries. The fatigue evaluation of Mg alloys under elastic stress amplitudes is very important in ensuring their service safety and reliability. Given their hexagonal close packed structure, the fatigue crack initiation of Mg and its alloys is closely related to the deformation mechanisms of twinning and basal slips. However, for Mg alloys with shrinkage porosities and inclusions, fatigue cracks will preferentially initiate at these defects, remarkably reducing the fatigue lifetime. In this paper, some fundamental aspects about the fatigue crack initiation mechanisms of Mg alloys are reviewed, including the 3 followings: 1) Fatigue crack initiation of as-cast Mg alloys, 2) influence of microstructure on fatigue crack initiation of wrought Mg alloys, and 3) the effect of heat treatment on fatigue initiation mechanisms. Moreover, some unresolved issues and future target on the fatigue crack initiation mechanism of Mg alloys are also described.

Prediction of Fatigue Crack Growth of Repaired Al-alloy Structures with Double Sides

NASA Astrophysics Data System (ADS)

Benachour, M.; Benachour, N.; Benguediab, M.; Seriari, F. Z.

During navigation, aircrafts are subject to fatigue damage. In order to rehabilitate damaged structures some techniques are often used to resolve this problem. Efficient repair technique, called composite patch repair, was used to reinforce the damaged structures and stop cracks. In this paper, effect of composite patch repair (Boron/Epoxy) on fatigue crack growth (FCG) was investigated on 2219 T62 Al-alloy. Effects of double patch repair in single notch tensile specimen (SENT) on FCG were studied and compared to single patch repair. Results show beneficial effect of patch repair on fatigue life and FCGR in comparison with the un-patched specimen. In addition, effect of mean stress characterized by stress ratio was highlighted. Fatigue behavior of investigated Al-alloy was compared.

Wavelet multiresolution complex network for decoding brain fatigued behavior from P300 signals

NASA Astrophysics Data System (ADS)

Gao, Zhong-Ke; Wang, Zi-Bo; Yang, Yu-Xuan; Li, Shan; Dang, Wei-Dong; Mao, Xiao-Qian

2018-09-01

Brain-computer interface (BCI) enables users to interact with the environment without relying on neural pathways and muscles. P300 based BCI systems have been extensively used to achieve human-machine interaction. However, the appearance of fatigue symptoms during operation process leads to the decline in classification accuracy of P300. Characterizing brain cognitive process underlying normal and fatigue conditions constitutes a problem of vital importance in the field of brain science. We in this paper propose a novel wavelet decomposition based complex network method to efficiently analyze the P300 signals recorded in the image stimulus test based on classical 'Oddball' paradigm. Initially, multichannel EEG signals are decomposed into wavelet coefficient series. Then we construct complex network by treating electrodes as nodes and determining the connections according to the 2-norm distances between wavelet coefficient series. The analysis of topological structure and statistical index indicates that the properties of brain network demonstrate significant distinctions between normal status and fatigue status. More specifically, the brain network reconfiguration in response to the cognitive task in fatigue status is reflected as the enhancement of the small-worldness.

Postpartum fatigue, baby-care activities, and maternal-infant attachment of vaginal and cesarean births following rooming-in.

PubMed

Lai, Ya-Ling; Hung, Chich-Hsiu; Stocker, Joel; Chan, Te-Fu; Liu, Yi

2015-05-01

This study compares women's postpartum fatigue, baby-care activities, and maternal-infant attachment following vaginal and cesarean births in rooming-in settings. Postpartum women admitted to baby-friendly hospitals are asked to stay with their babies 24 hours a day and to breastfeed on demand regardless of the type of childbirth. The study used a descriptive cross-sectional study design. A total of 120 postpartum women were recruited from two accredited baby-friendly hospitals in southern Taiwan. Three structured questionnaires were used to collect data, on which an analysis of covariance was conducted. Women who experienced a cesarean birth had higher postpartum fatigue scores than women who had given birth vaginally. Higher postpartum fatigue scores were correlated with greater difficulty in baby-care activities, which in turn resulted in weaker maternal-infant attachment as measured in the first 2 to 3 days postpartum. Hospitals should implement rooming-in in a more flexible way by taking women's postpartum fatigue and physical functioning into consideration. Copyright © 2014 Elsevier Inc. All rights reserved.

Fatigue Crack Growth Database for Damage Tolerance Analysis

NASA Technical Reports Server (NTRS)

Forman, R. G.; Shivakumar, V.; Cardinal, J. W.; Williams, L. C.; McKeighan, P. C.

2005-01-01

The objective of this project was to begin the process of developing a fatigue crack growth database (FCGD) of metallic materials for use in damage tolerance analysis of aircraft structure. For this initial effort, crack growth rate data in the NASGRO (Registered trademark) database, the United States Air Force Damage Tolerant Design Handbook, and other publicly available sources were examined and used to develop a database that characterizes crack growth behavior for specific applications (materials). The focus of this effort was on materials for general commercial aircraft applications, including large transport airplanes, small transport commuter airplanes, general aviation airplanes, and rotorcraft. The end products of this project are the FCGD software and this report. The specific goal of this effort was to present fatigue crack growth data in three usable formats: (1) NASGRO equation parameters, (2) Walker equation parameters, and (3) tabular data points. The development of this FCGD will begin the process of developing a consistent set of standard fatigue crack growth material properties. It is envisioned that the end product of the process will be a general repository for credible and well-documented fracture properties that may be used as a default standard in damage tolerance analyses.

USAF Damage Tolerant Design Handbook: Guidelines for the analysis and Design of Damage Tolerant Aircraft Structures. Revision A

DTIC Science & Technology

1979-03-01

Fatigue Crack Growth (Schr~matic) 5.12 Sustained Load Crack Growth Rate Data for 7075-f651,7079- T651, and 2024 - T351 Aluminum Plate (Ref...Block Programming and Block Size on Crack Growth Life (All histories Have Same Cycle Content) Alloy : 2024 -T3 Aluminum (Ref. 38) 5.21 Yield Zone Due to...4340 Steel in Humid Air," ASM Trans 58, 46-53 (1965). 20. Meyn, D.A., "Frequency and Amplitude Effects on Corrosion Fatigue Cracks in a Titanium Alloy

Structural Health Monitoring System Trade Space Analysis Tool with Consideration for Crack Growth, Sensor Degradation and a Variable Detection Threshold

DTIC Science & Technology

2014-09-18

Erdogan , 1963). 26 Paris’s Law Under a fatigue stress regime Paris’s Law relates sub-critical crack growth to stress intensity factor. The basic...Paris and Erdogan , 1963). After takeoff, the model generates a probability distribution for the crack length in that specific sortie based on the...Law is one of the most widely used fatigue crack growth models and was used in this research effort (Paris and Erdogan , 1963). Paris’s Law Under a

The Response of a Mechanical Oscillator Due to Swept and Dithered Excitation

NASA Technical Reports Server (NTRS)

Davis, R. Benjamin; Durham, R. Caitlyn; Brown, Andrew M.

2010-01-01

A single degree-of-freedom oscillator subject to linearly swept and/or dithered excitation is considered. Dither refers to the variation of an excitation frequency about a given nominal, or primary, frequency. Dither in rocket engine turbopump shaft speeds can be an important consideration when analyzing the dynamic response of turbomachinery components such as turbine blades. Results indicate that the incorporation of dithered excitation into a fatigue analysis may extend the predicted fatigue life of the structure by a factor of two or more.

Fatigue evaluation for Tsing Ma Bridge using structural health monitoring data

NASA Astrophysics Data System (ADS)

Chan, Hung-tin Tommy; Ko, Jan Ming; Li, Zhao-Xia

2001-08-01

Fatigue assessment for the Tsing Ma Bridge (TMB) are presented based on the British standard BS5400 and the real-time structural health monitoring data under railway loading. TMB, as an essential portion of transport network for the Hong Kong airport, is the longest suspension bridge in the world carrying both highway and railway traffic. The bridge design has been mainly based on BS5400. A structural health monitoring system - Wind and Structural Health Monitoring System (WASHMS) for TMB has been operated since the bridge commissioning in May 1997. In order to assess the fatigue behavior of TMB under railway loading, strain gauges were installed on the bridge deck to measure the strain-time histories as soon as the bridge is loaded by a standard railway loading due to the service of an actual train. The strain-time history data at the critical members are then used to determine the stress spectrum, of which the rainflow method recommended for railway bridges by BS5400 is applied to count cycles of stress range. Miner's law is employed to evaluate fatigue damage and remaining service life of the bridge. The evaluated results of fatigue damage and remaining service life would help us to well understand about the fatigue design of the bridge and status in fatigue accumulation.

An Investigation of High-Cycle Fatigue Models for Metallic Structures Exhibiting Snap-Through Response

NASA Technical Reports Server (NTRS)

Przekop, Adam; Rizzi, Stephen A.; Sweitzer, Karl A.

2007-01-01

A study is undertaken to develop a methodology for determining the suitability of various high-cycle fatigue models for metallic structures subjected to combined thermal-acoustic loadings. Two features of this problem differentiate it from the fatigue of structures subject to acoustic loading alone. Potentially large mean stresses associated with the thermally pre- and post-buckled states require models capable of handling those conditions. Snap-through motion between multiple post-buckled equilibrium positions introduces very high alternating stress. The thermal-acoustic time history response of a clamped aluminum beam structure with geometric and material nonlinearities is determined via numerical simulation. A cumulative damage model is employed using a rainflow cycle counting scheme and fatigue estimates are made for 2024-T3 aluminum using various non-zero mean fatigue models, including Walker, Morrow, Morrow with true fracture strength, and MMPDS. A baseline zero-mean model is additionally considered. It is shown that for this material, the Walker model produces the most conservative fatigue estimates when the stress response has a tensile mean introduced by geometric nonlinearity, but remains in the linear elastic range. However, when the loading level is sufficiently high to produce plasticity, the response becomes more fully reversed and the baseline, Morrow, and Morrow with true fracture strength models produce the most conservative fatigue estimates.

Fatigue damage evaluation of austenitic stainless steel using nonlinear ultrasonic waves in low cycle regime

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

Zhang, Jianfeng; Xuan, Fu-Zhen, E-mail: fzxuan@ecust.edu.cn

The interrupted low cycle fatigue test of austenitic stainless steel was conducted and the dislocation structure and fatigue damage was evaluated subsequently by using both transmission electron microscope and nonlinear ultrasonic wave techniques. A “mountain shape” correlation between the nonlinear acoustic parameter and the fatigue life fraction was achieved. This was ascribed to the generation and evolution of planar dislocation structure and nonplanar dislocation structure such as veins, walls, and cells. The “mountain shape” correlation was interpreted successfully by the combined contribution of dislocation monopole and dipole with an internal-stress dependent term of acoustic nonlinearity.

Fatigue of Ti6Al4V Structural Health Monitoring Systems Produced by Selective Laser Melting.

PubMed

Strantza, Maria; Vafadari, Reza; de Baere, Dieter; Vrancken, Bey; van Paepegem, Wim; Vandendael, Isabelle; Terryn, Herman; Guillaume, Patrick; van Hemelrijck, Danny

2016-02-11

Selective laser melting (SLM) is an additive manufacturing (AM) process which is used for producing metallic components. Currently, the integrity of components produced by SLM is in need of improvement due to residual stresses and unknown fracture behavior. Titanium alloys produced by AM are capable candidates for applications in aerospace and industrial fields due to their fracture resistance, fatigue behavior and corrosion resistance. On the other hand, structural health monitoring (SHM) system technologies are promising and requested from the industry. SHM systems can monitor the integrity of a structure and during the last decades the research has primarily been influenced by bionic engineering. In that aspect a new philosophy for SHM has been developed: the so-called effective structural health monitoring (eSHM) system. The current system uses the design freedom provided by AM. The working principle of the system is based on crack detection by means of a network of capillaries that are integrated in a structure. The main objective of this research is to evaluate the functionality of Ti6Al4V produced by the SLM process in the novel SHM system and to confirm that the eSHM system can successfully detect cracks in SLM components. In this study four-point bending fatigue tests on Ti6Al4V SLM specimens with an integrated SHM system were conducted. Fractographic analysis was performed after the final failure, while finite element simulations were used in order to determine the stress distribution in the capillary region and on the component. It was proven that the SHM system does not influence the crack initiation behavior during fatigue. The results highlight the effectiveness of the eSHM on SLM components, which can potentially be used by industrial and aerospace applications.

Fatigue Performance of Ti-6Al-4V Additively Manufactured Specimens with Integrated Capillaries of an Embedded Structural Health Monitoring System

PubMed Central

Hinderdael, Michaël; Strantza, Maria; De Baere, Dieter; Devesse, Wim; De Graeve, Iris; Terryn, Herman; Guillaume, Patrick

2017-01-01

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored. PMID:28841186

Fatigue Performance of Ti-6Al-4V Additively Manufactured Specimens with Integrated Capillaries of an Embedded Structural Health Monitoring System

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

Hinderdael, Michaël; Strantza, Maria; De Baere, Dieter

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the referencemore » specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.« less

Fatigue Performance of Ti-6Al-4V Additively Manufactured Specimens with Integrated Capillaries of an Embedded Structural Health Monitoring System

DOE PAGES

Hinderdael, Michaël; Strantza, Maria; De Baere, Dieter; ...

2017-08-25

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the referencemore » specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.« less

Fatigue Performance of Ti-6Al-4V Additively Manufactured Specimens with Integrated Capillaries of an Embedded Structural Health Monitoring System.

PubMed

Hinderdael, Michaël; Strantza, Maria; De Baere, Dieter; Devesse, Wim; De Graeve, Iris; Terryn, Herman; Guillaume, Patrick

2017-08-25

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.

Translation and adaptation of the fatigue severity scale for use in Portugal.

PubMed

Laranjeira, Carlos António

2012-08-01

The Fatigue Severity Scale (FSS) is a widely used instrument to measure the impact of fatigue on specific types of functioning. This study aims to translate and test the reliability and validity of the Portuguese version of the FSS. The questionnaire was administered to a worker sample of 424 nurses. Reliability analysis showed satisfactory results (Cronbach's alpha coefficient = .87). The test-retest reliability was .85. The principal component analysis showed that the FSS was a measure with a one-factor structure. The construct validity of the total FSS score was assessed by correlation with Maslach Burnout Inventory (MBI) score, Depression Anxiety Stress Scale (DASS) score, and Visual Analogue Scale (VAS) score. Each of the corresponding correlation coefficients among the total FSS score and MBI score, DASS score, and perceived fatigue score (VAS) were .55 (p < .01), .62 (p < .01), and .68 (p < .01), respectively, which shows sufficient construct validity. To measure the discriminant validity of FSS, we examined the differences in scores between groups in terms of the number of hours of sleep and overtime. The less nurses slept and the longer they worked, the higher their total FSS score became. This preliminary validation study of the Portuguese version of FSS proved that it is an acceptable, reliable, and valid measure of fatigue in the working population. Copyright © 2012 Elsevier Inc. All rights reserved.

Experimental Study on Surrogate Nuclear Fuel Rods under Reversed Cyclic Bending

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

Wang, Hong; Wang, Jy-An John

The mechanical behavior of spent nuclear fuel (SNF) rods under reversed cyclic bending or bending fatigue must be understood to evaluate their vibration integrity in a transportation environment. This is especially important for high-burnup fuels (>45 GWd/MTU), which have the potential for increased structural damage. It has been demonstrated that the bending fatigue of SNF rods can be effectively studied using surrogate rods. In this investigation, surrogate rods made of stainless steel (SS) 304 cladding and aluminum oxide pellets were tested under load or moment control at a variety of amplitude levels at 5 Hz using the Cyclic Integrated Reversible-Bendingmore » Fatigue Tester developed at Oak Ridge National Laboratory. The behavior of the rods was further characterized using flexural rigidity and hysteresis data, and fractography was performed on the failed rods. The proposed surrogate rods captured many of the characteristics of deformation and failure mode observed in SNF, including the linear-to-nonlinear deformation transition and large residual curvature in static tests, PPI and PCMI failure mechanisms, and large variation in the initial structural condition. Rod degradation was measured and characterized by measuring the flexural rigidity; the degradation of the rigidity depended on both the moment amplitude applied and the initial structural condition of the rods. It was also shown that a cracking initiation site can be located on the internal surface or the external surface of cladding. Finally, fatigue damage to the bending rods can be described in terms of flexural rigidity, and the fatigue life of rods can be predicted once damage model parameters are properly evaluated. The developed experimental approach, test protocol, and analysis method can be used to study the vibration integrity of SNF rods in the future.« less

Thermographic Analysis of Stress Distribution in Welded Joints

NASA Astrophysics Data System (ADS)

Piršić, T.; Krstulović Opara, L.; Domazet, Ž.

2010-06-01

The fatigue life prediction of welded joints based on S-N curves in conjunction with nominal stresses generally is not reliable. Stress distribution in welded area affected by geometrical inhomogeneity, irregular welded surface and weld toe radius is quite complex, so the local (structural) stress concept is accepted in recent papers. The aim of this paper is to determine the stress distribution in plate type aluminum welded joints, to analyze the reliability of TSA (Thermal Stress Analysis) in this kind of investigations, and to obtain numerical values for stress concentration factors for practical use. Stress distribution in aluminum butt and fillet welded joints is determined by using the three different methods: strain gauges measurement, thermal stress analysis and FEM. Obtained results show good agreement - the TSA mutually confirmed the FEM model and stresses measured by strain gauges. According to obtained results, it may be stated that TSA, as a relatively new measurement technique may in the future become a standard tool for the experimental investigation of stress concentration and fatigue in welded joints that can help to develop more accurate numerical tools for fatigue life prediction.

Fatigue Life Methodology for Bonded Composite Skin/Stringer Configurations

NASA Technical Reports Server (NTRS)

Krueger, Ronald; Paris, Isabelle L.; OBrien, T. Kevin

2000-01-01

A methodology is presented for determining the fatigue life of bonded composite skin/stringer structures based on delamination fatigue characterization data and geometric nonlinear finite element analyses. Results were compared to fatigue tests on stringer flange/skin specimens to verify the approach.

Preliminary metallographic studies of ball fatigue under rolling-contact conditions

NASA Technical Reports Server (NTRS)

Bear, H Robert; Butler, Robert H

1957-01-01

The metallurgical results produced on balls tested in the rolling-contact fatigue spin rig were studied by metallographic examination. Origin and progression of fatigue failures were observed. These evaluations were made on SAE 52100 and AISI M-1 balls fatigue tested at room temperature (80 F) and 200 to 250 F. Most failures originated subsurface in shear; inclusions, structure changes, and directionalism adversely affected ball fatigue life. Structures in the maximum-shear-stress region of the balls of both materials were stable at room temperature and unstable at 200 to 250 F. Failures were of the same type as those found in full-scale bearings.

Ventromedial prefrontal cortex modulates fatigue after penetrating traumatic brain injury

PubMed Central

Pardini, Matteo; Krueger, Frank; Raymont, Vanessa; Grafman, Jordan

2010-01-01

Background: Fatigue is a common and disabling symptom in neurologic disorders including traumatic penetrating brain injury (PBI). Despite fatigue's prevalence and impact on quality of life, its pathophysiology is not understood. Studies on effort perception in healthy subjects, animal behavioral paradigms, and recent evidence in different clinical populations suggest that ventromedial prefrontal cortex could play a significant role in fatigue pathophysiology in neurologic conditions. Methods: We enrolled 97 PBI patients and 37 control subjects drawn from the Vietnam Head Injury Study registry. Fatigue was assessed with a self-report questionnaire and a clinician-rated instrument; lesion location and volume were evaluated on CT scans. PBI patients were divided in 3 groups according to lesion location: a nonfrontal lesion group, a ventromedial prefrontal cortex lesion (vmPFC) group, and a dorso/lateral prefrontal cortex (d/lPFC) group. Fatigue scores were compared among the 3 PBI groups and the healthy controls. Results: Individuals with vmPFC lesions were significantly more fatigued than individuals with d/lPFC lesions, individuals with nonfrontal lesions, and healthy controls, while these 3 latter groups were equally fatigued. VmPFC volume was correlated with fatigue scores, showing that the larger the lesion volume, the higher the fatigue scores. Conclusions: We demonstrated that ventromedial prefrontal cortex lesion (vmPFC) plays a critical role in penetrating brain injury–related fatigue, providing a rationale to link fatigue to different vmPFC functions such as effort and reward perception. The identification of the anatomic and cognitive basis of fatigue can contribute to developing pathophysiology-based treatments for this disabling symptom. GLOSSARY AAL = Automated Anatomic Labeling; ANOVA = analysis of variance; BDI = Beck Depression Inventory; d/lPFC = dorso/lateral prefrontal cortex; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, 4th edition; NBRS = Neurobehavioral Rating Scale; NF = nonfrontal lesion; PBI = penetrating brain injury; ROI = region of interest; SCID-I = Structured Clinical Interview for DSM-IV, Axis I; VHIS = Vietnam Head Injury Study; vmPFC = ventromedial prefrontal cortex lesion. PMID:20194914

Fatigue crack monitoring with coupled piezoelectric film acoustic emission sensors

NASA Astrophysics Data System (ADS)

Zhou, Changjiang

Fatigue-induced cracking is a commonly seen problem in civil infrastructures reaching their original design life. A number of high-profile accidents have been reported in the past that involved fatigue damage in structures. Such incidences often happen without prior warnings due to lack of proper crack monitoring technique. In order to detect and monitor the fatigue crack, acoustic emission (AE) technique, has been receiving growing interests recently. AE can provide continuous and real-time monitoring data on damage progression in structures. Piezoelectric film AE sensor measures stress-wave induced strain in ultrasonic frequency range and its feasibility for AE signal monitoring has been demonstrated recently. However, extensive work in AE monitoring system development based on piezoelectric film AE sensor and sensor characterization on full-scale structures with fatigue cracks, have not been done. A lack of theoretical formulations for understanding the AE signals also hinders the use of piezoelectric film AE sensors. Additionally, crack detection and source localization with AE signals is a very important area yet to be explored for this new type of AE sensor. This dissertation presents the results of both analytical and experimental study on the signal characteristics of surface stress-wave induced AE strain signals measured by piezoelectric film AE sensors in near-field and an AE source localization method based on sensor couple theory. Based on moment tensor theory, generalized expression for AE strain signal is formulated. A special case involving the response of piezoelectric film AE sensor to surface load is also studied, which could potentially be used for sensor calibration of this type of sensor. A new concept of sensor couple theory based AE source localization technique is proposed and validated with both simulated and experimental data from fatigue test and field monitoring. Two series of fatigue tests were conducted to perform fatigue crack monitoring on large-scale steel test specimens using piezoelectric film AE sensors. Continuous monitoring of fatigue crack growth in steel structures is demonstrated in these fatigue test specimens. The use of piezoelectric film AE sensor for field monitoring of existing fatigue crack is also demonstrated in a real steel I-girder bridge located in Maryland. The sensor couple theory based AE source localization is validated using a limited number of piezoelectric film AE sensor data from both fatigue test specimens and field monitoring bridge. Through both laboratory fatigue test and field monitoring of steel structures with active fatigue cracks, the signal characteristics of piezoelectric film AE sensor have been studied in real-world environment.

Effect of welding structure and δ-ferrite on fatigue properties for TIG welded austenitic stainless steels at cryogenic temperatures

NASA Astrophysics Data System (ADS)

Yuri, Tetsumi; Ogata, Toshio; Saito, Masahiro; Hirayama, Yoshiaki

2000-04-01

High-cycle and low-cycle fatigue properties of base and weld metals for SUS304L and SUS316L and the effects of welding structure and δ-ferrite on fatigue properties were investigated at cryogenic temperatures in order to evaluate the long-life reliability of the structural materials to be used in liquid hydrogen supertankers and storage tanks and to develop a welding process for these applications. The S-N curves of the base and weld metals shifted towards higher levels, i.e., the longer life side, with decreasing test temperatures. High-cycle fatigue tests demonstrated the ratios of fatigue strength at 10 6 cycles to tensile strength of the weld metals to be 0.35-0.7, falling below those of base metals with decreasing test temperatures. Fatigue crack initiation sites in SUS304L weld metals were mostly at blowholes with diameters of 200-700 μm, and those of SUS316L weld metals were at weld pass interface boundaries. Low-cycle fatigue tests revealed the fatigue lives of the weld metals to be somewhat lower than those of the base metals. Although δ-ferrite reduces the toughness of austenitic stainless steels at cryogenic temperatures, the effects of δ-ferrite on high-cycle and low-cycle fatigue properties are not clear or significant.

Fatigue behavior of ULTIMETRTM alloy: Experiment and theoretical modeling

NASA Astrophysics Data System (ADS)

Jiang, Liang

ULTIMETRTM alloy is a commercial Co-26Cr-9Ni (weight percent) superalloy, which possesses excellent resistance to both wear and corrosion. In order to extend the structural applications of this alloy and improve the fundamental understanding of the fatigue damage mechanisms, stress- and strain-controlled fatigue tests were performed at various temperatures and in different environments. The stress- and strain-life data were developed for the structural design and engineering applications of this material. Fractographic studies characterized the crack-initiation and propagation behavior of the alloy. Microstructure evolution during fatigue was revealed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Specifically, it was found that the metastable face-centered-cubic structure of this alloy in the as-received condition could be transformed into a hexagonal-close-packed structure either under the action of plastic deformation at room temperature, or due to the aging and cyclic deformation at intermediate temperatures. This interesting observation constructed a sound basis for the alloy development. The dominant mechanisms, which control the fatigue behavior of ULTIMET alloy, were characterized. High-speed, high-resolution infrared (IR) thermography, as a non-contact, full-field, and nondestructive technique, was used to characterize the damage during fatigue. The temperature variations during each fatigue cycle, which were due to the thermal-elastic-plastic effect, were observed and related to stress-strain analyses. The temperature evolution during fatigue manifested the cumulative fatigue damage process. A constitutive model was developed to predict thermal and mechanical responses of ULTIMET alloy subjected to cyclic deformation. The predicted cyclic stress-strain responses and temperature variations were found to be in good agreement with the experimental results. In addition, a fatigue life prediction model was developed based on the strain-energy consideration, and the measured temperature could be utilized as an index for fatigue-life prediction.

Probabilistic Fatigue Damage Program (FATIG)

NASA Technical Reports Server (NTRS)

Michalopoulos, Constantine

2012-01-01

FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.

Investigation of Fuselage Structure Subject to Widespread Fatigue Damage

DOT National Transportation Integrated Search

1996-01-01

This report documents the results of the "Investigation of Fuselage Structure Subject to Widespread Fatigue Damage" contract. The primary program objective was to obtain data on airplane fuselage structures subject to multiple site damage (MSD) in an...

Remaining life assessment of in-service luminaire support structures : final report, January 2010.

DOT National Transportation Integrated Search

2010-01-01

Recent fatigue failures of in-service luminaire support structures in Washington and around the country have : prompted concern about their fatigue resistance. Most luminaire support structures in Washington were designed : without attention to fatig...

Estimation of fatigue life using electromechanical impedance technique

NASA Astrophysics Data System (ADS)

Lim, Yee Yan; Soh, Chee Kiong

2010-04-01

Fatigue induced damage is often progressive and gradual in nature. Structures subjected to large number of fatigue load cycles will encounter the process of progressive crack initiation, propagation and finally fracture. Monitoring of structural health, especially for the critical components, is therefore essential for early detection of potential harmful crack. Recent advent of smart materials such as piezo-impedance transducer adopting the electromechanical impedance (EMI) technique and wave propagation technique are well proven to be effective in incipient damage detection and characterization. Exceptional advantages such as autonomous, real-time and online, remote monitoring may provide a cost-effective alternative to the conventional structural health monitoring (SHM) techniques. In this study, the main focus is to investigate the feasibility of characterizing a propagating fatigue crack in a structure using the EMI technique as well as estimating its remaining fatigue life using the linear elastic fracture mechanics (LEFM) approach. Uniaxial cyclic tensile load is applied on a lab-sized aluminum beam up to failure. Progressive shift in admittance signatures measured by the piezo-impedance transducer (PZT patch) corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression. With the use of LEFM, prediction of the remaining life of the structure at different cycles of loading is possible.

The Reorganization of Human Brain Networks Modulated by Driving Mental Fatigue.

PubMed

Chunlin Zhao; Min Zhao; Yong Yang; Junfeng Gao; Nini Rao; Pan Lin

2017-05-01

The organization of the brain functional network is associated with mental fatigue, but little is known about the brain network topology that is modulated by the mental fatigue. In this study, we used the graph theory approach to investigate reconfiguration changes in functional networks of different electroen-cephalography (EEG) bands from 16 subjects performing a simulated driving task. Behavior and brain functional networks were compared between the normal and driving mental fatigue states. The scores of subjective self-reports indicated that 90 min of simulated driving-induced mental fatigue. We observed that coherence was significantly increased in the frontal, central, and temporal brain regions. Furthermore, in the brain network topology metric, significant increases were observed in the clustering coefficient (Cp) for beta, alpha, and delta bands and the character path length (Lp) for all EEG bands. The normalized measures γ showed significant increases in beta, alpha, and delta bands, and λ showed similar patterns in beta and theta bands. These results indicate that functional network topology can shift the network topology structure toward a more economic but less efficient configuration, which suggests low wiring costs in functional networks and disruption of the effective interactions between and across cortical regions during mental fatigue states. Graph theory analysis might be a useful tool for further understanding the neural mechanisms of driving mental fatigue.

The impact of job and family demands on partner’s fatigue: A study of Japanese dual-earner parents

PubMed Central

Shimazu, Akihito; Bakker, Arnold B.; Demerouti, Evangelia; Shimada, Kyoko; Kawakami, Norito

2017-01-01

Objectives This study of Japanese dual-earner couples examined the impact of family and job demands on one’s own and one’s partner’s fatigue as well as gender differences in these effects. Methods A total of 2,502 parents (1,251 couples) were surveyed using a self-administered questionnaire. A crossover model was tested using structural equation modeling. Results The results of structural equation modeling analyses showed that both job and family demands independently exacerbated fatigue. There was an indirect effect of job and family demands on partner fatigue through one’s own fatigue only from husbands to wives. An indirect effect of job demands on partner fatigue through partner’s family demands was identified only from wives to husbands. Furthermore, there were gender differences in the crossover of fatigue. Conclusions This study shows that job and family demands influence family circumstances. When considering means to reduce employees’ fatigue, gender differences in the mechanism of fatigue need to be taken into account. PMID:28235008

Supervised exercise reduces cancer-related fatigue: a systematic review.

PubMed

Meneses-Echávez, José F; González-Jiménez, Emilio; Ramírez-Vélez, Robinson

2015-01-01

Does supervised physical activity reduce cancer-related fatigue? Systematic review with meta-analysis of randomised trials. People diagnosed with any type of cancer, without restriction to a particular stage of diagnosis or treatment. Supervised physical activity interventions (eg, aerobic, resistance and stretching exercise), defined as any planned or structured body movement causing an increase in energy expenditure, designed to maintain or enhance health-related outcomes, and performed with systematic frequency, intensity and duration. The primary outcome measure was fatigue. Secondary outcomes were physical and functional wellbeing assessed using the Functional Assessment of Cancer Therapy Fatigue Scale, European Organisation for Research and Treatment of Cancer Quality of Life QUESTIONnaire, Piper Fatigue Scale, Schwartz Cancer Fatigue Scale and the Multidimensional Fatigue Inventory. Methodological quality, including risk of bias of the studies, was evaluated using the PEDro Scale. Eleven studies involving 1530 participants were included in the review. The assessment of quality showed a mean score of 6.5 (SD 1.1), indicating a low overall risk of bias. The pooled effect on fatigue, calculated as a standardised mean difference (SMD) using a random-effects model, was -1.69 (95% CI -2.99 to -0.39). Beneficial reductions in fatigue were also found with combined aerobic and resistance training with supervision (SMD=-0.41, 95% CI -0.70 to -0.13) and with combined aerobic, resistance and stretching training with supervision (SMD=-0.67, 95% CI -1.17 to -0.17). Supervised physical activity interventions reduce cancer-related fatigue. These findings suggest that combined aerobic and resistance exercise regimens with or without stretching should be included as part of rehabilitation programs for people who have been diagnosed with cancer. PROSPERO CRD42013005803. Copyright © 2014 Australian Physiotherapy Association. Published by Elsevier B.V. All rights reserved.

A survey of forest workers in New Zealand. Do hours of work, rest, and recovery play a role in accidents and injury?

PubMed

Lilley, Rebbecca; Feyer, Anne-Marie; Kirk, Patrick; Gander, Philippa

2002-01-01

A number of structural and organizational changes have occurred recently within the New Zealand Forestry Industry, with concerns being raised about the impact of these changes on the forestry worker in terms of fatigue, sleepiness, and compromised safety. This study explored the relationship of fatigue, and some of its key determinants, with accidents and injuries in a group of forestry industry workers in New Zealand. A total of 367 forestry workers responded to a self-administered questionnaire. Fatigue was found to be commonly experienced at work in the forest, with 78% of workers reporting that they experienced fatigue at least "sometimes." This study found that certain groups of workers reported long working hours, reduced sleep, compromised recovery time, and intensely paced work. The results of logistic regression analysis showed that recent sleep, number of breaks taken during the workday, and specific job/tasks were independently associated with reporting of high fatigue levels at work. Near-miss injury events were significantly more common among those reporting a high level of fatigue at work. Accidents and lost-time injury were associated with length of time at work, ethnicity, and having had near-miss injury events. Together, these results suggest that fatigue and aspects of work organization, which are likely to be fatiguing, may be associated with compromised safety for forest workers. With an already slim margin of error present in forest operations, an impairment due to increased fatigue may constitute a significant risk factor for accidents and injuries in this workforce. The results indicate the need for further examination of shift and workload management among forestry workers, as well as a role for improving industry awareness about the causes and consequences of fatigue.

14 CFR 29.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

Code of Federal Regulations, 2012 CFR

2012-01-01

... Composite Rotorcraft Structures. 29.573 Section 29.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance..., types, and sizes of damage, considering fatigue, environmental effects, intrinsic and discrete flaws...

14 CFR 27.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

Code of Federal Regulations, 2012 CFR

2012-01-01

... Composite Rotorcraft Structures. 27.573 Section 27.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance..., types, and sizes of damage, considering fatigue, environmental effects, intrinsic and discrete flaws...

14 CFR 27.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

Code of Federal Regulations, 2013 CFR

2013-01-01

... Composite Rotorcraft Structures. 27.573 Section 27.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance..., types, and sizes of damage, considering fatigue, environmental effects, intrinsic and discrete flaws...

14 CFR 29.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

Code of Federal Regulations, 2013 CFR

2013-01-01

... Composite Rotorcraft Structures. 29.573 Section 29.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance..., types, and sizes of damage, considering fatigue, environmental effects, intrinsic and discrete flaws...

14 CFR 27.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

Code of Federal Regulations, 2014 CFR

2014-01-01

... Composite Rotorcraft Structures. 27.573 Section 27.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance..., types, and sizes of damage, considering fatigue, environmental effects, intrinsic and discrete flaws...

14 CFR 29.573 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures.

Code of Federal Regulations, 2014 CFR

2014-01-01

... Composite Rotorcraft Structures. 29.573 Section 29.573 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... Structures. (a) Each applicant must evaluate the composite rotorcraft structure under the damage tolerance..., types, and sizes of damage, considering fatigue, environmental effects, intrinsic and discrete flaws...

Ion beam sputter etching of orthopedic implanted alloy MP35N and resulting effects on fatigue

NASA Technical Reports Server (NTRS)

Wintucky, E. G.; Christopher, M.; Bahnuik, E.; Wang, S.

1981-01-01

The effects of two types of argon ion sputter etched surface structures on the tensile stress fatigue properties of orthopedic implant alloy MP35N were investigated. One surface structure was a natural texture resulting from direct bombardment by 1 keV argon ions. The other structure was a pattern of square holes milled into the surface by a 1 keV argon ion beam through a Ni screen mask. The etched surfaces were subjected to tensile stress only in fatigue tests designed to simulate the cyclic load conditions experienced by the stems of artificial hip joint implants. Both types of sputter etched surface structures were found to reduce the fatigue strength below that of smooth surface MP35N.

14 CFR 23.627 - Fatigue strength.

Code of Federal Regulations, 2010 CFR

2010-01-01

... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service. ...

14 CFR 23.627 - Fatigue strength.

Code of Federal Regulations, 2013 CFR

2013-01-01

... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service. ...

14 CFR 23.627 - Fatigue strength.

Code of Federal Regulations, 2014 CFR

2014-01-01

... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service. ...

14 CFR 23.627 - Fatigue strength.

Code of Federal Regulations, 2012 CFR

2012-01-01

... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service. ...

14 CFR 23.627 - Fatigue strength.

Code of Federal Regulations, 2011 CFR

2011-01-01

... Fatigue strength. The structure must be designed, as far as practicable, to avoid points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service. ...

Gamma Radiation Sterilization Reduces the High-cycle Fatigue Life of Allograft Bone.

PubMed

Islam, Anowarul; Chapin, Katherine; Moore, Emily; Ford, Joel; Rimnac, Clare; Akkus, Ozan

2016-03-01

Sterilization by gamma radiation impairs the mechanical properties of bone allografts. Previous work related to radiation-induced embrittlement of bone tissue has been limited mostly to monotonic testing which does not necessarily predict the high-cycle fatigue life of allografts in vivo. We designed a custom rotating-bending fatigue device to answer the following questions: (1) Does gamma radiation sterilization affect the high-cycle fatigue behavior of cortical bone; and (2) how does the fatigue life change with cyclic stress level? The high-cycle fatigue behavior of human cortical bone specimens was examined at stress levels related to physiologic levels using a custom-designed rotating-bending fatigue device. Test specimens were distributed among two treatment groups (n = 6/group); control and irradiated. Samples were tested until failure at stress levels of 25, 35, and 45 MPa. At 25 MPa, 83% of control samples survived 30 million cycles (run-out) whereas 83% of irradiated samples survived only 0.5 million cycles. At 35 MPa, irradiated samples showed an approximately 19-fold reduction in fatigue life compared with control samples (12.2 × 10(6) ± 12.3 × 10(6) versus 6.38 × 10(5) ± 6.81 × 10(5); p = 0.046), and in the case of 45 MPa, this reduction was approximately 17.5-fold (7.31 × 10(5) ± 6.39 × 10(5) versus 4.17 × 10(4) ± 1.91 × 10(4); p = 0.025). Equations to estimate high-cycle fatigue life of irradiated and control cortical bone allograft at a certain stress level were derived. Gamma radiation sterilization severely impairs the high cycle fatigue life of structural allograft bone tissues, more so than the decline that has been reported for monotonic mechanical properties. Therefore, clinicians need to be conservative in the expectation of the fatigue life of structural allograft bone tissues. Methods to preserve the fatigue strength of nonirradiated allograft bone tissue are needed. As opposed to what monotonic tests might suggest, the cyclic fatigue life of radiation-sterilized structural allografts is likely severely compromised relative to the nonirradiated condition and therefore should be taken into consideration. Methods to reduce the effect of irradiation or to recover structural allograft bone tissue fatigue strength are important to pursue.

Designing for fiber composite structural durability in hygrothermomechanical environment

NASA Technical Reports Server (NTRS)

Chamis, C. C.

1985-01-01

A methodology is described which can be used to design/analyze fiber composite structures subjected to complex hygrothermomechanical environments. This methodology includes composite mechanics and advanced structural analysis methods (finite element). Select examples are described to illustrate the application of the available methodology. The examples include: (1) composite progressive fracture; (2) composite design for high cycle fatigue combined with hot-wet conditions; and (3) general laminate design.

High Speed Research Program Structural Acoustics Multi-Year Summary Report

NASA Technical Reports Server (NTRS)

Beier, Theodor H.; Bhat, Waman V.; Rizzi, Stephen A.; Silcox, Richard J.; Simpson, Myles A.

2005-01-01

This report summarizes the work conducted by the Structural Acoustics Integrated Technology Development (ITD) Team under NASA's High Speed Research (HSR) Phase II program from 1993 to 1999. It is intended to serve as a reference for future researchers by documenting the results of the interior noise and sonic fatigue technology development activities conducted during this period. For interior noise, these activities included excitation modeling, structural acoustic response modeling, development of passive treatments and active controls, and prediction of interior noise. For sonic fatigue, these activities included loads prediction, materials characterization, sonic fatigue code development, development of response reduction techniques, and generation of sonic fatigue design requirements. Also included are lessons learned and recommendations for future work.

The Dopamine Imbalance Hypothesis of Fatigue in Multiple Sclerosis and Other Neurological Disorders

PubMed Central

Dobryakova, Ekaterina; Genova, Helen M.; DeLuca, John; Wylie, Glenn R.

2015-01-01

Fatigue is one of the most pervasive symptoms of multiple sclerosis (MS), and has engendered hundreds of investigations on the topic. While there is a growing literature using various methods to study fatigue, a unified theory of fatigue in MS is yet to emerge. In the current review, we synthesize findings from neuroimaging, pharmacological, neuropsychological, and immunological studies of fatigue in MS, which point to a specific hypothesis of fatigue in MS: the dopamine imbalance hypothesis. The communication between the striatum and prefrontal cortex is reliant on dopamine, a modulatory neurotransmitter. Neuroimaging findings suggest that fatigue results from the disruption of communication between these regions. Supporting the dopamine imbalance hypothesis, structural and functional neuroimaging studies show abnormalities in the frontal and striatal regions that are heavily innervated by dopamine neurons. Further, dopaminergic psychostimulant medication has been shown to alleviate fatigue in individuals with traumatic brain injury, chronic fatigue syndrome, and in cancer patients, also indicating that dopamine might play an important role in fatigue perception. This paper reviews the structural and functional neuroimaging evidence as well as pharmacological studies that suggest that dopamine plays a critical role in the phenomenon of fatigue. We conclude with how specific aspects of the dopamine imbalance hypothesis can be tested in future research. PMID:25814977

Development and characterization of fatigue resistant Aramid reinforced aluminium laminates (ARALL) for fatigue Critical aircraft components

NASA Astrophysics Data System (ADS)

Qaiser, M. H.; Umar, S.; Nauman, S.

2014-06-01

The structural weight of an aircraft has always been a controlling parameter that governs its fuel efficiency and transport capacity. In pursuit of achieving light-weight aircraft structures, high design stress levels have to be adopted and materials with high specific strength such as Aluminum etc. are to be deployed. However, an extensive spectrum of fatigue load exists at the aircraft wings and other aerodynamic components that may cause initiation and propagation of fatigue cracks and concludes in a catastrophic rupture. Fatigue is therefore the limiting design parameter in such cases and materials with high fatigue resistance are then required. A major improvement in the fatigue behavior was observed by laminating Kevlar fibers with Aluminum using epoxy. ARALL (Aramid Reinforced ALuminum Laminates) is a fatigue resistant hybrid composite that consists of layers of thin high strength aluminum alloy sheets surface bonded with aramid fibers. The intact aramid fibers tie up the fatigue cracks, thus reducing the stress intensity factor at the crack tip as a result of which the fatigue properties of can be enhanced with orders of magnitude as compared to monolithic high strength Aluminum alloy sheets. Significant amount of weight savings can be achieved in fatigue critical components in comparison with the traditional materials used in aircraft.

Anatomical Thin Titanium Mesh Plate Structural Optimization for Zygomatic-Maxillary Complex Fracture under Fatigue Testing.

PubMed

Wang, Yu-Tzu; Huang, Shao-Fu; Fang, Yu-Ting; Huang, Shou-Chieh; Cheng, Hwei-Fang; Chen, Chih-Hao; Wang, Po-Fang; Lin, Chun-Li

2018-01-01

This study performs a structural optimization of anatomical thin titanium mesh (ATTM) plate and optimal designed ATTM plate fabricated using additive manufacturing (AM) to verify its stabilization under fatigue testing. Finite element (FE) analysis was used to simulate the structural bending resistance of a regular ATTM plate. The Taguchi method was employed to identify the significance of each design factor in controlling the deflection and determine an optimal combination of designed factors. The optimal designed ATTM plate with patient-matched facial contour was fabricated using AM and applied to a ZMC comminuted fracture to evaluate the resting maxillary micromotion/strain under fatigue testing. The Taguchi analysis found that the ATTM plate required a designed internal hole distance to be 0.9 mm, internal hole diameter to be 1 mm, plate thickness to be 0.8 mm, and plate height to be 10 mm. The designed plate thickness factor primarily dominated the bending resistance up to 78% importance. The averaged micromotion (displacement) and strain of the maxillary bone showed that ZMC fracture fixation using the miniplate was significantly higher than those using the AM optimal designed ATTM plate. This study concluded that the optimal designed ATTM plate with enough strength to resist the bending effect can be obtained by combining FE and Taguchi analyses. The optimal designed ATTM plate with patient-matched facial contour fabricated using AM provides superior stabilization for ZMC comminuted fractured bone segments.

Fatigue in the Presence of Corrosion (Fatigue sous corrosion)

DTIC Science & Technology

1999-03-01

Fatigue Crack Growth Propagation of Aluminum Lithium cycle managers to safely delay repairs to a more appropriate Alloys " described the effect of... effects of service corrosion on fatigue lab tests with 2024 -T3, because 7178 life , if any, can be established in this was not available. However, we did not... life and the fatigue crack growth behavior of the cases where a structural member is the 2024 alloy was studied as well. stressed or fatigued

Thermo-Vibro-Acoustic Loads and Fatigue of Hypersonic Flight Vehicle Structure

DTIC Science & Technology

2009-06-01

on the title page or on the first page of thiS document. 3 FORM NO. 6531-0 standards: 20 Btu/ft2-sec alang the lawer surface ramp at Mach 20 and Q...exceed ather laads alang their line af shack-skin interactian. ANALYSIS AND RESULTS Three panels were chasen for detailed finite analysis: the

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

Fatigue disbonding analysis of wide composite panels by means of Lamb waves

NASA Astrophysics Data System (ADS)

Michalcová, Lenka; Rechcígel, Lukáš; Bělský, Petr; Kucharský, Pavel

2018-03-01

Guided wave-based monitoring of composite structures plays an important role in the area of structural health monitoring (SHM) of aerospace structures. Adhesively bonded joints have not yet fulfilled current airworthiness requirements; hence, assemblies of carbon fibre-reinforced parts still require mechanical fasteners, and a verified SHM method with reliable disbonding/delamination detection and propagation assessment is needed. This study investigated the disbonding/delamination propagation in adhesively bonded panels using Lamb waves during fatigue tests. Analyses focused on the proper frequency and mode selection, sensor placement and selection of parameter sensitive to the growth of disbonding areas. Piezoelectric transducers placed across the bonded area were used as actuators and sensors. Lamb wave propagation was investigated considering the actual shape of the crack front and the mode of the crack propagation. The actual cracked area was determined by ultrasonic A-scans. A correlation between the crack propagation rate and the A0 mode velocity was found.

Composite structural materials

NASA Technical Reports Server (NTRS)

Ansell, G. S.; Loewy, R. G.; Wiberley, S. E.

1983-01-01

Transverse properties of fiber constituents in composites, fatigue in composite materials, matrix dominated properties of high performance composites, numerical investigation of moisture effects, numerical investigation of the micromechanics of composite fracture, advanced analysis methods, compact lug design, and the RP-1 and RP-2 sailplanes projects are discussed.

Thermomechanical fatigue life prediction for several solders

NASA Astrophysics Data System (ADS)

Wen, Shengmin

Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage is the eventual percolation result of such local events. Fine's dislocation energy density concept and Mura's microcrack initiation theory are adopted to derive the fatigue formula for an individual grain. A physical damage metric is introduced to describe the material with damage. A unified creep and plasticity constitutive model is adopted to simulate the mechanical behavior of solders. The model is cast into a continuum damage mechanics framework to simulate material with damage. The model gives good agreement with the experimental results of 96.5Pb-3.5Sn and 96.5Sn-3.5Ag solders under uniaxial strain-controlled cyclic loading. The model is convenient for implementation into commercial computational packages. Also presented is a fatigue theory with its failure criterion for solders based on physical damage mechanism. By introducing grain orientation into the fatigue formula, an m-N curve (m is Schmid factor) at constant loading condition is suggested for fatigue of grains with different orientations. A solder structure is defined as fatigued when the damage metric reaches a critical threshold, since at this threshold the failed grains may form a cluster and percolate through the structure according to percolation theory. Fatigue data of 96.5Pb-3.5Sn solder bulk specimens under various uniaxial tension tests were analyzed. Results show that the theory gives consistent predictions under broad conditions, while inelastic strain theory does not. The theory is anisotropic with no size limitation to its application, which could be suitable for anisotropic small-scale (micron or nano scale) solder joints. More importantly, the theory is materials science based so that the parameters of the fatigue formula can be worked out by testing of bulk specimens while the formula can be applicable to small-scale structures. The theory suggests metallurgical control in the manufacturing process to optimize the fatigue life of solder structures.

Cyclic fatigue analysis of rocket thrust chambers. Volume 1: OFHC copper chamber low cycle fatigue

NASA Technical Reports Server (NTRS)

Miller, R. W.

1974-01-01

A three-dimensional finite element elasto-plastic strain analysis was performed for the throat section of a regeneratively cooled rocket combustion chamber. The analysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the chamber operating cycle. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen combustion chamber which was fatigue tested to failure. The computed strain range at typical chamber operating conditions was used in conjunction with oxygen-free, high-conductivity (OHFC) copper isothermal fatigue test data to predict chamber low-cycle fatigue life.

Improved aircraft dynamic response and fatigue life during ground operations using an active control landing gear system

NASA Technical Reports Server (NTRS)

Mcgehee, J. R.; Carden, H. D.; Edson, R.

1978-01-01

A three-degree-of-freedom aircraft landing analysis incorporating a series-hydraulic active control main landing gear has been developed and verified using preliminary experimental data from drop tests of a modified main landing gear from a 2722 kg (6000 lbm) class of airplane. The verified analysis was also employed to predict the landing dynamics of a supersonic research airplane with an active control main landing gear system. The results of this investigation have shown that this type of active gear is feasible and indicate a potential for improving airplane dynamic response and reducing structural fatigue damage during ground operations by approximately 90% relative to that incurred with the passive gear.

Reliability analysis of different structure parameters of PCBA under drop impact

NASA Astrophysics Data System (ADS)

Liu, P. S.; Fan, G. M.; Liu, Y. H.

2018-03-01

The establishing process of PCBA is modelled by finite element analysis software ABAQUS. Firstly, introduce the Input-G method and the fatigue life under drop impact are introduced and the mechanism of the solder joint failure in the process of drop is analysed. The main reason of solder joint failure is that the PCB component is suffering repeated tension and compression stress during the drop impact. Finally, the equivalent stress and peel stress of different solder joint and plate-level components under different impact acceleration are also analysed. The results show that the reliability of tin-silver copper joint is better than that of tin- lead solder joint, and the fatigue life of solder joint expectancy decrease as the impact pulse amplitude increases.

Sleep-deprivation effect on human performance: a meta-analysis approach

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

Candice D. Griffith; Candice D. Griffith; Sankaran Mahadevan

Human fatigue is hard to define since there is no direct measure of fatigue, much like stress. Instead fatigue must be inferred from measures that are affected by fatigue. One such measurable output affected by fatigue is reaction time. In this study the relationship of reaction time to sleep deprivation is studied. These variables were selected because reaction time and hours of sleep deprivation are straightforward characteristics of fatigue to begin the investigation of fatigue effects on performance. Meta-analysis, a widely used procedure in medical and psychological studies, is applied to the variety of fatigue literature collected from various fieldsmore » in this study. Meta-analysis establishes a procedure for coding and analyzing information from various studies to compute an effect size. In this research the effect size reported is the difference between standardized means, and is found to be -0.6341, implying a strong relationship between sleep deprivation and performance degradation.« less

Excitation, response, and fatigue life estimation methods for the structural design of externally blown flaps

NASA Technical Reports Server (NTRS)

Ungar, E. E.; Chandiramani, K. L.; Barger, J. E.

1972-01-01

Means for predicting the fluctuating pressures acting on externally blown flap surfaces are developed on the basis of generalizations derived from non-dimensionalized empirical data. Approaches for estimation of the fatigue lives of skin-stringer and honeycomb-core sandwich flap structures are derived from vibration response analyses and panel fatigue data. Approximate expressions for fluctuating pressures, structural response, and fatigue life are combined to reveal the important parametric dependences. The two-dimensional equations of motion of multi-element flap systems are derived in general form, so that they can be specialized readily for any particular system. An introduction is presented of an approach to characterizing the excitation pressures and structural responses which makes use of space-time spectral concepts and promises to provide useful insights, as well as experimental and analytical savings.

14 CFR 25.571 - Damage-tolerance and fatigue evaluation of structure.

Code of Federal Regulations, 2011 CFR

2011-01-01

... catastrophic failure (such as wing, empennage, control surfaces and their systems, the fuselage, engine... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Fatigue Evaluation § 25..., or by the service history of airplanes of similar structural design and sonic excitation environment...

On the Use of 3dB Qualification Margin for Structural Parts on Expendable Launch Vehicles

NASA Technical Reports Server (NTRS)

Yunis, Isam

2007-01-01

The standard random vibration qualification test used for Expendable Launch Vehicle components is Maximum Predicted Environment (MPE) + 6dB for a duration of 4 times the service life of the part. This can be a severe qualification test for these fatigue-sensitive structures. This paper uses flight data from several launch vehicles to establish that reducing the qualification approach to MPE+3dB for the duration of the peak environment (1x life) is valid for fatigue-sensitive structural components. Items that can be classified as fatigue-sensitive are probes, ducts, tubing, bellows, hoses, and any non-functional structure. Non-functional structure may be flight critical or carry fluid, but it cannot include any moving parts or electronics. This reduced qualification approach does not include primary or secondary structure which would be exclusively designed by peak loads, either transient or quasi-static, that are so large and of so few cycles as to make fatigue a moot point.

Initial dynamic load estimates during configuration design

NASA Technical Reports Server (NTRS)

Schiff, Daniel

1987-01-01

This analysis includes the structural response to shock and vibration and evaluates the maximum deflections and material stresses and the potential for the occurrence of elastic instability, fatigue and fracture. The required computations are often performed by means of finite element analysis (FEA) computer programs in which the structure is simulated by a finite element model which may contain thousands of elements. The formulation of a finite element model can be time consuming, and substantial additional modeling effort may be necessary if the structure requires significant changes after initial analysis. Rapid methods for obtaining rough estimates of the structural response to shock and vibration are presented for the purpose of providing guidance during the initial mechanical design configuration stage.

Development of a wireless nonlinear wave modulation spectroscopy (NWMS) sensor node for fatigue crack detection

NASA Astrophysics Data System (ADS)

Liu, Peipei; Yang, Suyoung; Lim, Hyung Jin; Park, Hyung Chul; Ko, In Chang; Sohn, Hoon

2014-03-01

Fatigue crack is one of the main culprits for the failure of metallic structures. Recently, it has been shown that nonlinear wave modulation spectroscopy (NWMS) is effective in detecting nonlinear mechanisms produced by fatigue crack. In this study, an active wireless sensor node for fatigue crack detection is developed based on NWMS. Using PZT transducers attached to a target structure, ultrasonic waves at two distinctive frequencies are generated, and their modulation due to fatigue crack formation is detected using another PZT transducer. Furthermore, a reference-free NWMS algorithm is developed so that fatigue crack can be detected without relying on history data of the structure with minimal parameter adjustment by the end users. The algorithm is embedded into FPGA, and the diagnosis is transmitted to a base station using a commercial wireless communication system. The whole design of the sensor node is fulfilled in a low power working strategy. Finally, an experimental verification has been performed using aluminum plate specimens to show the feasibility of the developed active wireless NWMS sensor node.

Probabilistic Sensitivity Analysis of Fretting Fatigue (Preprint)

DTIC Science & Technology

2009-04-01

AFRL-RX-WP-TP-2009-4091 PROBABILISTIC SENSITIVITY ANALYSIS OF FRETTING FATIGUE (Preprint) Patrick J. Golden, Harry R. Millwater , and...Sensitivity Analysis of Fretting Fatigue Patrick J. Golden * Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 Harry R. Millwater † and

Space Shuttle Crawler Transporter Vibration Analysis in Support of Rollout Fatigue Load Spectra Verification Program

NASA Technical Reports Server (NTRS)

Margasahayam, Ravi N.; Meyer, Karl A.; Nerolich, Shaun M.; Burton, Roy C.; Gosselin, Armand M.

2004-01-01

The Crawler Transporter (CT), designed and built for the Apollo Program in the 1960's and surpassing its initial operational life, has become an integral part of the Space Shuttle Program (SSP). The CT transports the Space Shuttle Vehicle (SSV) stack, atop the Mobile Launch Platform (MLP), from the Vehicle Assembly Building (VAB) to the launch pad. This support structure provides hydraulic jacking, leveling and load equalization for the 12 million pound stack on its 3.5-5.0 mile rollout to the launch pad. Major elements of the SSV, consisting of the orbiter, solid rocket boosters (SRB) and external tank (ET) have required fatigue analyses as part of the mission life certification. Compared to rollout vibration, the SSV sees relatively high vibration loads during launch, ascent, descent and landing phases of the mission. Although preliminary measured SRB vibration levels during rollout were of low amplitude and frequency, the duration of the rollout phase is typically high, from 5-6 hours. As part of an expanded mission life assessment, additional certification effort was initiated to define fatigue load spectra for rollout. This study addresses the CT vibration analyses in support of the rollout fatigue study. Structural models developed for modal and vibration analyses were used to identify unique CT, CT/MLP and CT/MLP/SRB vibration characteristics for comparison to instrumented rollout tests. Whereas the main structural and vibration characteristics of the SSV are well defined, minimum analytical and vibration test data on the Crawler Transporter were available. Unique vibration characteristics of the CT are attributable to the drive mechanism, hydraulic jacking system, structural framing and the CT-to-MLP support pad restraints. Initial tests performed on the CT/MLP/SRB configuration showed reasonable correlation with predicted mode shapes and frequencies.

75 FR 30284 - Airworthiness Directives; Empresa Brasileira de Aeronautica S.A. (EMBRAER) Model ERJ 170 Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-01

... condition as: During ERJ 170 airplane full scale fatigue test, cracks were found in some structural... intervals, could prevent a timely detection of fatigue cracks. Undetected fatigue cracks in these areas... unsafe condition for the specified products. The MCAI states: During ERJ 170 airplane full scale fatigue...

Fatigue strength degradation of metals in corrosive environments

NASA Astrophysics Data System (ADS)

Adasooriya, N. D.; Hemmingsen, T.; Pavlou, D.

2017-12-01

Structures exposed to aggressive environmental conditions are often subjected to time-dependent loss of coating and loss of material due to corrosion; this causes reduction in the cross-sectional properties of the members, increased surface roughness, surface irregularities and corrosion pits, and degradation of material strengths. These effects have been identified and simulated in different research studies. However, time and corrosive media dependent fatigue strength curves for materials have not been discussed in the design or assessment guidelines for structures. This paper attempts to review the corrosion degradation process and available approaches/models used to determine the fatigue strength of corroded materials and to interpolate corrosion deterioration data. High cycle fatigue and full range fatigue life formulae for fatigue strength of corroded materials are proposed. The above formulae depend on the endurance limit of corroded material, in addition to the stress-life fatigue curve parameters of the uncorroded material. The endurance limit of corroded material can either be determined by a limited number of tests in the very high-cycle fatigue region or predicted by an analytical approach. Comparison with experimentally measured corrosion fatigue behavior of several materials is provided and discussed.

a Study on the Fretting Fatigue Life of Zircaloy Alloys

NASA Astrophysics Data System (ADS)

Kwon, Jae-Do; Park, Dae-Kyu; Woo, Seung-Wan; Chai, Young-Suck

Studies on the strength and fatigue life of machines and structures have been conducted in accordance with the development of modern industries. In particular, fine and repetitive cyclic damage occurring in contact regions has been known to have an impact on fretting fatigue fractures. The main component of zircaloy alloy is Zr, and it possesses good mechanical characteristics at high temperatures. This alloy is used in the fuel rod material of nuclear power plants because of its excellent resistance. In this paper, the effect of the fretting damage on the fatigue behavior of the zircaloy alloy is studied. Further, various types of mechanical tests such as tension and plain fatigue tests are performed. Fretting fatigue tests are performed with a flat-flat contact configuration using a bridge-type contact pad and plate-type specimen. Through these experiments, it is found that the fretting fatigue strength decreases by about 80% as compared to the plain fatigue strength. Oblique cracks are observed in the initial stage of the fretting fatigue, in which damaged areas are found. These results can be used as the basic data for the structural integrity evaluation of corrosion-resisting alloys considering the fretting damages.

A Rasch Analysis of Assessments of Morning and Evening Fatigue in Oncology Patients Using the Lee Fatigue Scale.

PubMed

Lerdal, Anners; Kottorp, Anders; Gay, Caryl; Aouizerat, Bradley E; Lee, Kathryn A; Miaskowski, Christine

2016-06-01

To accurately investigate diurnal variations in fatigue, a measure needs to be psychometrically sound and demonstrate stable item function in relationship to time of day. Rasch analysis is a modern psychometric approach that can be used to evaluate these characteristics. To evaluate, using Rasch analysis, the psychometric properties of the Lee Fatigue Scale (LFS) in a sample of oncology patients. The sample comprised 587 patients (mean age 57.3 ± 11.9 years, 80% women) undergoing chemotherapy for breast, gastrointestinal, gynecological, or lung cancer. Patients completed the 13-item LFS within 30 minutes of awakening (i.e., morning fatigue) and before going to bed (i.e., evening fatigue). Rasch analysis was used to assess validity and reliability. In initial analyses of differential item function, eight of the 13 items functioned differently depending on whether the LFS was completed in the morning or in the evening. Subsequent analyses were conducted separately for the morning and evening fatigue assessments. Nine of the morning fatigue items and 10 of the evening fatigue items demonstrated acceptable goodness-of-fit to the Rasch model. Principal components analyses indicated that both morning and evening assessments demonstrated unidimensionality. Person-separation indices indicated that both morning and evening fatigue scales were able to distinguish four distinct strata of fatigue severity. Excluding four items from the morning fatigue scale and three items from the evening fatigue scale improved the psychometric properties of the LFS for assessing diurnal variations in fatigue severity in oncology patients. Copyright © 2016 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.

Probabilistic Assessment of National Wind Tunnel

NASA Technical Reports Server (NTRS)

Shah, A. R.; Shiao, M.; Chamis, C. C.

1996-01-01

A preliminary probabilistic structural assessment of the critical section of National Wind Tunnel (NWT) is performed using NESSUS (Numerical Evaluation of Stochastic Structures Under Stress) computer code. Thereby, the capabilities of NESSUS code have been demonstrated to address reliability issues of the NWT. Uncertainties in the geometry, material properties, loads and stiffener location on the NWT are considered to perform the reliability assessment. Probabilistic stress, frequency, buckling, fatigue and proof load analyses are performed. These analyses cover the major global and some local design requirements. Based on the assumed uncertainties, the results reveal the assurance of minimum 0.999 reliability for the NWT. Preliminary life prediction analysis results show that the life of the NWT is governed by the fatigue of welds. Also, reliability based proof test assessment is performed.

Probabilistic fracture finite elements

NASA Technical Reports Server (NTRS)

Liu, W. K.; Belytschko, T.; Lua, Y. J.

1991-01-01

The Probabilistic Fracture Mechanics (PFM) is a promising method for estimating the fatigue life and inspection cycles for mechanical and structural components. The Probability Finite Element Method (PFEM), which is based on second moment analysis, has proved to be a promising, practical approach to handle problems with uncertainties. As the PFEM provides a powerful computational tool to determine first and second moment of random parameters, the second moment reliability method can be easily combined with PFEM to obtain measures of the reliability of the structural system. The method is also being applied to fatigue crack growth. Uncertainties in the material properties of advanced materials such as polycrystalline alloys, ceramics, and composites are commonly observed from experimental tests. This is mainly attributed to intrinsic microcracks, which are randomly distributed as a result of the applied load and the residual stress.

Probabilistic fracture finite elements

NASA Astrophysics Data System (ADS)

Liu, W. K.; Belytschko, T.; Lua, Y. J.

1991-05-01

The Probabilistic Fracture Mechanics (PFM) is a promising method for estimating the fatigue life and inspection cycles for mechanical and structural components. The Probability Finite Element Method (PFEM), which is based on second moment analysis, has proved to be a promising, practical approach to handle problems with uncertainties. As the PFEM provides a powerful computational tool to determine first and second moment of random parameters, the second moment reliability method can be easily combined with PFEM to obtain measures of the reliability of the structural system. The method is also being applied to fatigue crack growth. Uncertainties in the material properties of advanced materials such as polycrystalline alloys, ceramics, and composites are commonly observed from experimental tests. This is mainly attributed to intrinsic microcracks, which are randomly distributed as a result of the applied load and the residual stress.

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.

Power Law Versus Exponential Form of Slow Crack Growth of Advanced Structural Ceramics: Dynamic Fatigue

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2002-01-01

The life prediction analysis based on an exponential crack velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress-rate ("dynamic fatigue") and preload testing at ambient and elevated temperatures. The data fit to the strength versus In (stress rate) relation was found to be very reasonable for most of the materials. It was also found that preloading technique was equally applicable for the case of slow crack growth (SCG) parameter n > 30. The major limitation in the exponential crack velocity formulation, however, was that an inert strength of a material must be known priori to evaluate the important SCG parameter n, a significant drawback as compared to the conventional power-law crack velocity formulation.

The course of cancer related fatigue up to ten years in early breast cancer patients: What impact in clinical practice?

PubMed

Fabi, Alessandra; Falcicchio, Chiara; Giannarelli, Diana; Maggi, Gabriella; Cognetti, Francesco; Pugliese, Patrizia

2017-08-01

Little is known about the cancer related fatigue (CRF) along cancer course and risk factors that could predict CRF development and persistence in breast cancer (BC) survivors. This prospective study detected incidence, timing of onset, duration of CRF, impact on QoL and psychological distress. Seventy-eight early BC patients, undergoing chemotherapy (CT) followed or not by hormonal therapy were assessed for QoL and psychological distress by EORTC QLQC30 and HADs questionnaires. Fatigue was investigated with mix methods, structured interview and psychometric measures. A qualitative analysis was added to assess the behavioral pattern of CRF. Low fatigue levels were identified after surgery (9%), increasing during (49%) and at the end of CT (47%), maintaining after 1 year (31%) and declining up to ten years of follow-up. Prevalence of CRF was higher at the end of CT and lower at follow-up. At the end and after 1 and 2 years from CT, persistence of CRF was associated to anxiety in 20%, 11% and 5% and to depression in 15%, 10% and 5% respectively. A relationship between CRF and psychological distress was observed; patients presenting depression and anxiety before CT were at higher risk for fatigue onset at a later period. A relationship between fatigue and QoL was noted at the end of CT. Our study shows the fatigue timely trend in early BC patients from surgery, CT and follow-up. Identification of biological, psychological, social predictor factors related to fatigue could be helpful for early interventions in patients at higher risk of developing fatigue. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Re-assessment of offshore structures using the revised HSE fatigue guidance

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

Stacey, A.; Sharp, J.V.

1995-12-31

The re-assessment of existing North Sea structures is an increasingly important issue as the age of platforms increases. Over 50 from a total of approximately 180 fixed installations in the UK sector are now over 15 years old. Fatigue damage has been the main reason for repairs to North Sea structures and the risk of this continues. The fatigue guidance of the Offshore Safety Division of the Health and Safety Executive (HSE) has recently been revised and published. Fundamental changes have been made to this guidance with several new recommendations including joint classification, basic design S-N curves for welded joints,more » the thickness effect, the effects of environment and the treatment of low and high stress ranges. To quantify the effects of the new guidance on the fatigue life assessment of offshore strictures, the HSE commissioned a study which included a deep water and a shallow water fixed steel structure and a twin-pontoon semi-submersible. These structures are typical of those operating in the North Sea. These were re-assessed with respect to fatigue lives and the results compared with predictions based on the 1990 guidance. The results and general conclusions are presented in this paper.« less

X-ray fractography on fatigue fractured surface of austenitic stainless steel

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

Yajima, Zenjiro; Tokuyama, Hideki; Kibayashi, Yasuo

1995-12-31

X-ray diffraction observation of the material internal structure beneath fracture surfaces provide fracture analysis with useful information to investigate the conditions and mechanisms of fracture. X-ray fractography is a generic name given to this technique. In the present study, X-ray fractography was applied to fatigue fracture surfaces of austenitic stainless steel (AISI 304) which consisted of solution treatment. The fatigue tests were carried out on compact tension (CT) specimens. The plastic strain on the fracture surface was estimated from measuring the line broadening of X-ray diffraction profiles. The line broadening of X-ray diffraction profiles was measured on and beneath fatiguemore » fracture surfaces. The depth of the plastic zone left on fracture surfaces was evaluated from the line broadening. The results are discussed on the basis of fracture mechanics.« less

Three-Dimensional Geometric Nonlinear Contact Stress Analysis of Riveted Joints

NASA Technical Reports Server (NTRS)

Shivakumar, Kunigal N.; Ramanujapuram, Vivek

1998-01-01

The problems associated with fatigue were brought into the forefront of research by the explosive decompression and structural failure of the Aloha Airlines Flight 243 in 1988. The structural failure of this airplane has been attributed to debonding and multiple cracking along the longitudinal lap splice riveted joint in the fuselage. This crash created what may be termed as a minor "Structural Integrity Revolution" in the commercial transport industry. Major steps have been taken by the manufacturers, operators and authorities to improve the structural airworthiness of the aging fleet of airplanes. Notwithstanding, this considerable effort there are still outstanding issues and concerns related to the formulation of Widespread Fatigue Damage which is believed to have been a contributing factor in the probable cause of the Aloha accident. The lesson from this accident was that Multiple-Site Damage (MSD) in "aging" aircraft can lead to extensive aircraft damage. A strong candidate in which MSD is highly probable to occur is the riveted lap joint.

Multiaxial and Thermomechanical Fatigue of Materials: A Historical Perspective and Some Future Challenges

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh

2013-01-01

Structural materials used in engineering applications routinely subjected to repetitive mechanical loads in multiple directions under non-isothermal conditions. Over past few decades, several multiaxial fatigue life estimation models (stress- and strain-based) developed for isothermal conditions. Historically, numerous fatigue life prediction models also developed for thermomechanical fatigue (TMF) life prediction, predominantly for uniaxial mechanical loading conditions. Realistic structural components encounter multiaxial loads and non-isothermal loading conditions, which increase potential for interaction of damage modes. A need exists for mechanical testing and development verification of life prediction models under such conditions.

Inspection Correlation Study of Ultrasonic-Based In Situ Structural Health Monitoring Monthly Report for December 2014-January 2015

DTIC Science & Technology

2015-05-01

fatigue an induced ultrasonic elastic vibration (via piezoelectric transducers [ PZTs ]) propagates through the dogbone specimen. A receiver PZT picks up...inspection of fatigue crack growth in aluminum 7075-T6 dogbone specimens. Acellent Technologies, Inc., is supporting this project through providing...January 2015. 15. SUBJECT TERMS structural health monitoring, probabilistics, fatigue damage, guided waves, Lamb waves 16. SECURITY CLASSIFICATION OF

In Situ Estimation of Applied Biaxial Loads with Lamb Waves (Preprint)

DTIC Science & Technology

2012-07-01

be correct. IV. EXPERIMENTS AND RESULTS Fatigue tests were conducted for an array of six surface-bonded PZT transducers permanently attached to...because of their cumulative effects on the fatigue life of the structures. Waves propagating between array elements are directly affected by applied loads...their cumulative effects on the fatigue life of the structures. Waves propagating between array elements are directly affected by applied loads

On the role of the amygdala for experiencing fatigue in patients with multiple sclerosis.

PubMed

Hanken, Katrin; Francis, Yoselin; Kastrup, Andreas; Eling, Paul; Klein, Jan; Hildebrandt, Helmut

2018-02-01

Recently, we proposed a model explaining the origin of fatigue in multiple sclerosis (MS) patients. This model assumes that the feeling of fatigue results from inflammation-induced information processing within interoceptive brain areas. To investigate the association between self-reported cognitive fatigue and structural integrity of interoceptive brain areas in MS patients. 95 MS patients and 28 healthy controls participated in this study. All participants underwent diffusion tensor MRI and fractional anisotropy data were calculated for the amygdala, the stria terminalis and the corpus callosum, a non-interoceptive brain area. Based on the cognitive fatigue score of the Fatigue Scale for Motor and Cognition, patients were divided into moderately cognitively fatigued (cognitive fatigue score ≥ 28) and cognitively non-fatigued (cognitive fatigue score < 28) MS patients. Healthy controls were recruited as a third group. Repeated measures analyses of covariance, controlling for age, depression and brain atrophy, were performed to investigate whether the factor Group had a significant effect on the fractional anisotropy data. A significant effect of Group was observed for the amygdala (F = 3.389, p = 0.037). MS patients without cognitive fatigue presented lower values of the amygdala than MS patients with cognitive fatigue and healthy controls. For the stria terminalis and the corpus callosum, no main effect of Group was observed. The structural integrity of the amygdala in non-fatigued MS patients appears to be reduced. According to our model this might indicate that the absence of fatigue in non-fatigued MS patients might result from disturbed inflammation-induced information processing in the amygdala. Copyright © 2017 Elsevier B.V. All rights reserved.

Fatigue and post-fatigue performance of Fabry-Perot FOS installed on CFRP-strengthened RC-beams

NASA Astrophysics Data System (ADS)

Gheorghiu, Catalin; Labossiere, Pierre; Proulx, Jean

2004-07-01

There is a growing need for built-in monitoring systems for civil engineering infrastructures, due to problems such as increasing traffic loads and rising costs of maintenance and repair. Fibre optic sensors (FOS), capable of reading various parameters are promising candidates for life-long health monitoring of these structures. However, since FOS have only been introduced recently into the field of structural monitoring, their acceptance and widespread implementation will be conditioned by their durability under severe climatic and loading conditions. This paper reports on the performance of strain extrinsic FOS attached to carbon fibre reinforced polymer (CFRP) plates used to strengthen concrete structures. The specimens tested in this project are reinforced concrete (RC) beams with an additional external CFRP reinforcement. The FOS-instrumented beams were first subjected to fatigue loading for various numbers of cycles and load amplitudes. Then, they were tested monotonically to failure under four-point-bending. The test results provide an insight on the fatigue and post-fatigue behaviour of FOS used for monitoring reinforced concrete structures.

Active sensing of fatigue damage using embedded ultrasonics

NASA Astrophysics Data System (ADS)

Zagrai, Andrei; Kruse, Walter A.; Gigineishvili, Vlasi

2009-03-01

Embedded ultrasonics has demonstrated considerable utility in structural health monitoring of aeronautical vehicle. This active sensing approach has been widely used to detect and monitor cracks, delaminations, and disbonds in a broad spectrum of metallic and composite structures. However, application of the embedded ultrasonics for active sensing of incipient damage before fracture has received limited attention. The aim of this study was to investigate the suitability of embedded ultrasonics and nonlinear acoustic signatures for monitoring pre-crack fatigue damage in aerospace structural material. A harmonic load was applied to structural specimens in order to induce fatigue damage accumulation and growth. Specimens of simple geometry were considered and piezoelectric active sensors were employed for generation and reception of elastic waves. The elastic wave signatures were analyzed in the frequency domain using nonlinear impedance and nonlinear resonance methods. A relationship between fatigue severity and linear as well as nonlinear acoustic signatures was investigated and considered in the damage classification procedure. Practical aspects of the active sensing of the fatigue damage before fracture were discussed and prospective avenues for future research were suggested.

Analytical and experimental investigation of aircraft metal structures reinforced with filamentary composites. Phase 2: Structural fatigue, thermal cycling, creep, and residual strength

NASA Technical Reports Server (NTRS)

Blichfeldt, B.; Mccarty, J. E.

1972-01-01

Specimens representative of metal aircraft structural components reinforced with boron filamentary composites were manufactured and tested under cyclic loading, cyclic temperature, or continuously applied loading to evaluate some of the factors that affect structural integrity under cyclic conditions. Bonded, stepped joints were used throughout to provide composite-to-metal transition regions at load introduction points. Honeycomb panels with titanium or aluminum faces reinforced with unidirectional boron composite were fatigue tested at constant amplitude under completely reversed loading. Results indicated that the matrix material was the most fatigue-sensitive part of the design, with debonding initiating in the stepped joints. However, comparisons with equal weight all-metal specimens show a 10 to 50 times improved fatigue life. Fatigue crack propagation and residual strength were studied for several different stiffened panel concepts, and were found to vary considerably depending on the configuration. Composite-reinforced metal specimens were also subjected to creep and thermal cycling tests. Thermal cycling of stepped joint tensile specimens resulted in a ten percent decrease in residual strength after 4000 cycles.

Surface Irregularity Factor as a Parameter to Evaluate the Fatigue Damage State of CFRP

PubMed Central

Zuluaga-Ramírez, Pablo; Frövel, Malte; Belenguer, Tomás; Salazar, Félix

2015-01-01

This work presents an optical non-contact technique to evaluate the fatigue damage state of CFRP structures measuring the irregularity factor of the surface. This factor includes information about surface topology and can be measured easily on field, by techniques such as optical perfilometers. The surface irregularity factor has been correlated with stiffness degradation, which is a well-accepted parameter for the evaluation of the fatigue damage state of composite materials. Constant amplitude fatigue loads (CAL) and realistic variable amplitude loads (VAL), representative of real in- flight conditions, have been applied to “dog bone” shaped tensile specimens. It has been shown that the measurement of the surface irregularity parameters can be applied to evaluate the damage state of a structure, and that it is independent of the type of fatigue load that has caused the damage. As a result, this measurement technique is applicable for a wide range of inspections of composite material structures, from pressurized tanks with constant amplitude loads, to variable amplitude loaded aeronautical structures such as wings and empennages, up to automotive and other industrial applications. PMID:28793655

Analysis of Global Ultrasonic Sensor Data from a Full Scale Wing Panel Test

NASA Astrophysics Data System (ADS)

Michaels, Jennifer E.; Michaels, Thomas E.; Martin, Ramaldo S.

2009-03-01

A full scale wing panel fatigue test was undertaken in 2007 as a part of the DARPA Structural Integrity Prognosis System (SIPS) program. Both local and global ultrasonic sensors were installed on the wing panel and data were recorded periodically over a period of about seven weeks. The local ultrasonic sensors interrogated a small number of selected fastener holes, and the global ultrasonic sensors were arranged in a spatially distributed array surrounding an area encompassing multiple fastener holes of interest. The global ultrasonic sensor data is the focus of the work reported here. Waveforms were recorded from all pitch-catch sensor pairs as a function of static load while fatiguing was paused. The time windows over which the waveforms were recorded were long enough to include most of the reverberating energy. Partway through the test simulated defects were temporarily introduced by gluing masses onto the surface of the wing panel, and waveforms were recorded immediately before their attachment and after their removal. The overall fatigue test was terminated while cracks originating from the fastener holes were still relatively small and before they reached the surface of the wing panel. Both detection and localization results are shown for the artificial damage, and the overall repeatability and stability of the signals are analyzed. Also shown is an analysis of how the reverberating signals change as a function of applied load. The fastener hole fatigue cracks were not detected by the global transducer array, which is not surprising given the final sizes of the cracks as determined by later destructive analysis. However, signals were stable throughout the entire fatigue test, and effects of load on the received signals were significant, both in the short-time and long-time signal regimes.

Influence of sleep disturbance, fatigue, vitality on oral health and academic performance in indian dental students

PubMed Central

ASAWA, KAILASH; SEN, NANDINI; BHAT, NAGESH; TAK, MRIDULA; SULTANE, PRATIBHA; MANDAL, ARITRA

2017-01-01

Background Oral health and academic performance are important contributing factors for a student’s professional life. Countless factors affect both, among which sleep, vitality and fatigue are less explored areas that also have a strong impact. Objective The objective of the study was to assess the association of sleep disturbances, fatigue and vitality with self reported oral health status, oral hygiene habits and academic performance of dental students of Udaipur. Methods A descriptive cross-sectional study was conducted among undergraduate and postgraduate dental students of Udaipur. Self-administered structured questionnaire was used to assess the psychological factors, vitality, sleep quality, fatigue, self reported oral health status, habits and academic performance. Analysis of variance and stepwise multiple linear regression were utilized for statistical analysis with 95% confidence level and 5% level of significance. Results Of the 230 participants, 180 (78.3%) were undergraduates and 50 (21.7%) were postgraduates. Among them, females showed higher scores in disturbed sleep index (2.69±2.14) as compared to males (2.45±1.91). Respondents who had “Poor” dental health, scored more in disturbed sleep index (3.15±1.64) and fatigue scale (20.00±4.88). Subjects who flossed “everyday”, were found to have good sleep and more energy (p=0.01) and those who assessed themselves as excellent students scored more in the Vitality Scale (p=0.01) and less in the Sleep index (p=0.01). Conclusion The present study confirms that disturbed sleep, aliveness and fatigue, all are interlinked with each other and are imperative factors having the potential to alter the oral health status, habits and academics of dental students. PMID:28781530

Unified risk analysis of fatigue failure in ductile alloy components during all three stages of fatigue crack evolution process.

PubMed

Patankar, Ravindra

2003-10-01

Statistical fatigue life of a ductile alloy specimen is traditionally divided into three stages, namely, crack nucleation, small crack growth, and large crack growth. Crack nucleation and small crack growth show a wide variation and hence a big spread on cycles versus crack length graph. Relatively, large crack growth shows a lesser variation. Therefore, different models are fitted to the different stages of the fatigue evolution process, thus treating different stages as different phenomena. With these independent models, it is impossible to predict one phenomenon based on the information available about the other phenomenon. Experimentally, it is easier to carry out crack length measurements of large cracks compared to nucleating cracks and small cracks. Thus, it is easier to collect statistical data for large crack growth compared to the painstaking effort it would take to collect statistical data for crack nucleation and small crack growth. This article presents a fracture mechanics-based stochastic model of fatigue crack growth in ductile alloys that are commonly encountered in mechanical structures and machine components. The model has been validated by Ray (1998) for crack propagation by various statistical fatigue data. Based on the model, this article proposes a technique to predict statistical information of fatigue crack nucleation and small crack growth properties that uses the statistical properties of large crack growth under constant amplitude stress excitation. The statistical properties of large crack growth under constant amplitude stress excitation can be obtained via experiments.

Development of an in situ fatigue sensor.

DOT National Transportation Integrated Search

2011-01-01

A prototype in situ fatigue sensor has been designed, constructed and evaluated experimentally for its ability to monitor the accumulation of fatigue damage in a cyclically loaded steel structure, e.g., highway bridge. The sensor consists of multiple...

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.

Fatigue life estimation of a 1D aluminum beam under mode-I loading using the electromechanical impedance technique

NASA Astrophysics Data System (ADS)

Lim, Yee Yan; Kiong Soh, Chee

2011-12-01

Structures in service are often subjected to fatigue loads. Cracks would develop and lead to failure if left unnoticed after a large number of cyclic loadings. Monitoring the process of fatigue crack propagation as well as estimating the remaining useful life of a structure is thus essential to prevent catastrophe while minimizing earlier-than-required replacement. The advent of smart materials such as piezo-impedance transducers (lead zirconate titanate, PZT) has ushered in a new era of structural health monitoring (SHM) based on non-destructive evaluation (NDE). This paper presents a series of investigative studies to evaluate the feasibility of fatigue crack monitoring and estimation of remaining useful life using the electromechanical impedance (EMI) technique employing a PZT transducer. Experimental tests were conducted to study the ability of the EMI technique in monitoring fatigue crack in 1D lab-sized aluminum beams. The experimental results prove that the EMI technique is very sensitive to fatigue crack propagation. A proof-of-concept semi-analytical damage model for fatigue life estimation has been developed by incorporating the linear elastic fracture mechanics (LEFM) theory into the finite element (FE) model. The prediction of the model matches closely with the experiment, suggesting the possibility of replacing costly experiments in future.

Severe fatigue in type 1 diabetes: Exploring its course, predictors and relationship with HbA1c in a prospective study.

PubMed

Menting, Juliane; Nikolaus, Stephanie; van der Veld, William M; Goedendorp, Martine M; Tack, Cees J; Knoop, Hans

2016-11-01

To prospectively identify the course of severe fatigue, its predictors and the relationship with HbA 1c in patients with type 1 diabetes. 214 adult patients completed questionnaires on fatigue severity and fatigue-related factors at baseline. HbA 1c was retrieved from medical records. After 43months, fatigue severity and HbA 1c were reassessed in 194 patients. A logistic regression analysis was used to determine predictors of severe fatigue at follow-up with various cognitive-behavioral and clinical factors as potential predictors. The relationship between fatigue and HbA 1c was investigated in a sub-analysis by differentiating between patients with suboptimal glucose control [HbA 1c >7% (53mmol/mol)] and optimal glucose control [HbA 1c ⩽7% (53mmol/mol)]. The prevalence of severe fatigue was 40% at baseline and 42% at follow-up. In three out of four severely fatigued patients at baseline (76%), severe fatigue persisted over time. More depressive symptoms, more pain, sleep disturbances, lower self-efficacy concerning fatigue, less confidence in diabetes self-care, more fatigue severity at baseline and more diabetes complications predicted severe fatigue at follow-up. Over time, HbA 1c at baseline was positively associated with fatigue severity at follow-up in both groups (suboptimal glucose control: r=.18, p<.05; optimal glucose control: r=.09, p<.05). About three quarters of fatigued[corrected] patients with type 1 diabetes suffer from persistent fatigue. Aside from the number of diabetes complications, no clinical factors explained the persistence of fatigue. HbA 1c and fatigue were weakly associated in a sub-analysis. Since the strongest predictors of severe fatigue were cognitive-behavioral factors, behavioral interventions might be effective in decreasing fatigue. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Damage Tolerant Analysis of Cracked Al 2024-T3 Panels repaired with Single Boron/Epoxy Patch

NASA Astrophysics Data System (ADS)

Mahajan, Akshay D.; Murthy, A. Ramachandra; Nanda Kumar, M. R.; Gopinath, Smitha

2018-06-01

It is known that damage tolerant analysis has two objectives, namely, remaining life prediction and residual strength evaluation. To achieve the these objectives, determination of accurate and reliable fracture parameter is very important. XFEM methodologies for fatigue and fracture analysis of cracked aluminium panels repaired with different patch shapes made of single boron/epoxy have been developed. Heaviside and asymptotic crack tip enrichment functions are employed to model the crack. XFEM formulations such as displacement field formulation and element stiffness matrix formulation are presented. Domain form of interaction integral is employed to determine Stress Intensity Factor of repaired cracked panels. Computed SIFs are incorporated in Paris crack growth model to predict the remaining fatigue life. The residual strength has been computed by using the remaining life approach, which accounts for both crack growth constants and no. of cycles to failure. From the various studies conducted, it is observed that repaired panels have significant effect on reduction of the SIF at the crack tip and hence residual strength as well as remaining life of the patched cracked panels are improved significantly. The predicted remaining life and residual strength will be useful for design of structures/components under fatigue loading.

Scanning electron microscope fractography in failure analysis of steels

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

Wouters, R.; Froyen, L.

1996-04-01

For many failure cases, macroscopic examination of the fracture surface permits discrimination of fatigue fractures from overload fractures. For clarifying fatigue fractures, the practical significance of microfractography is limited to an investigation of the crack initiation areas. Scanning electron microscopy is successfully used in tracing local material abnormalities that act as fatigue crack initiators. The task for the scanning electron microscope, however, is much more substantial in failure analysis of overload fractures, especially for steels. By revealing specific fractographic characteristics, complemented by information about the material and the loading conditions, scanning electron microscopy provides a strong indication of the probablemore » cause of failure. A complete dimple fracture is indicative of acceptable bulk material properties; overloading, by subdimensioning or excessive external loading, has to be verified. The presence of cleavage fracture makes the material properties questionable if external conditions causing embrittlement are absent. Intergranular brittle fracture requires verification of grain-boundary weakening conditions--a sensitized structure, whether or not combined with a local stress state or a specific environment. The role of scanning electron microscopy in failure analysis is illustrated by case histories of the aforementioned fracture types.« less

Full-scale 3-D finite element modeling of a two-loop pressurized water reactor for heat transfer, thermal–mechanical cyclic stress analysis, and environmental fatigue life estimation

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

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

This paper discusses a system-level finite element model of a two-loop pressurized water reactor (PWR). Based on this model, system-level heat transfer analysis and subsequent sequentially coupled thermal-mechanical stress analysis were performed for typical thermal-mechanical fatigue cycles. The in-air fatigue lives of example components, such as the hot and cold legs, were estimated on the basis of stress analysis results, ASME in-air fatigue life estimation criteria, and fatigue design curves. Furthermore, environmental correction factors and associated PWR environment fatigue lives for the hot and cold legs were estimated by using estimated stress and strain histories and the approach described inmore » US-NRC report: NUREG-6909.« less

Fatigue risks in the connections of sign support structures.

DOT National Transportation Integrated Search

2013-05-01

This research effort develops a reliability-based approach for prescribing inspection intervals for mast-arm sign support : structures corresponding to user-specified levels of fatigue-induced fracture risk. The resulting level of risk for a : partic...

A pilot mixed-methods evaluation of MS INFoRm: a self-directed fatigue management resource for individuals with multiple sclerosis.

PubMed

Akbar, Nadine; Turpin, Karen; Petrin, Julie; Smyth, Penny; Finlayson, Marcia

2018-06-01

Fatigue management interventions for individuals with multiple sclerosis (MS) often feature structured programmes requiring repeated, in-person attendance that is not possible for all individuals. We sought to determine whether MS INFoRm, a self-directed fatigue management resource for individuals with MS, was worth further, more rigorous evaluation. Our indicators of worthiness were actual use of the resource by participants over 3 months, reductions in fatigue impact and increases in self-efficacy, and participant reports of changes in fatigue management knowledge and behaviours. This was a single-group, mixed-methods, before-after pilot study in individuals with MS reporting mild to moderate fatigue. Thirty-five participants were provided with MS INFoRm by a USB flash drive to use at home for 3 months, on their own volition. Twenty-three participants completed all standardized questionnaires, semi-structured interviews and study process measures. Participants reported actively using MS INFoRm over the 3-month study period (median total time spent using MS INFoRm=315 min) as well as significantly lower overall fatigue impact (Modified Fatigue Impact Scale: t=2.6, P=0.01), increased knowledge of MS fatigue (z=-2.8, P=0.01) and greater confidence in managing MS fatigue (z=-3.3, P=0.001). Individuals with significant reductions in fatigue impact also reported behavioural changes including tracking fatigue, better communication with others, greater awareness, improved quality of life and being more proactive. This study provides evidence that further rigorous evaluation of MS INFoRm, a self-directed resource for managing fatigue, is worth pursuing.

Energy Based Multiscale Modeling with Non-Periodic Boundary Conditions

DTIC Science & Technology

2013-05-13

below in Figure 8. At each incremental step in the analysis , the user material defined subroutine (UMAT) was utilized to perform the communication...initiation and modeling using XFEM. Appropriate localization schemes will be developed to allow for deformations conducive for crack opening...REFERENCES 1. Talreja R., 2006, “Damage analysis for structural integrity and durability of composite materials ,” Fatigue & Fracture of

Composite structural materials. [aircraft structures

NASA Technical Reports Server (NTRS)

Ansell, G. S.; Loewy, R. G.; Wiberley, S. E.

1980-01-01

The use of filamentary composite materials in the design and construction of primary aircraft structures is considered with emphasis on efforts to develop advanced technology in the areas of physical properties, structural concepts and analysis, manufacturing, and reliability and life prediction. The redesign of a main spar/rib region on the Boeing 727 elevator near its actuator attachment point is discussed. A composite fabrication and test facility is described as well as the use of minicomputers for computer aided design. Other topics covered include (1) advanced structural analysis methids for composites; (2) ultrasonic nondestructive testing of composite structures; (3) optimum combination of hardeners in the cure of epoxy; (4) fatigue in composite materials; (5) resin matrix characterization and properties; (6) postbuckling analysis of curved laminate composite panels; and (7) acoustic emission testing of composite tensile specimens.

Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism.

PubMed

Gludovatz, Bernd; Demetriou, Marios D; Floyd, Michael; Hohenwarter, Anton; Johnson, William L; Ritchie, Robert O

2013-11-12

Bulk-metallic glasses (BMGs) are now candidate materials for structural applications due to their exceptional strength and toughness. However, their fatigue resistance can be poor and inconsistent, severely limiting their potential as reliable structural materials. As fatigue limits are invariably governed by the local arrest of microscopically small cracks at microstructural features, the lack of microstructure in monolithic glasses, often coupled with other factors, such as the ease of crack formation in shear bands or a high susceptibility to corrosion, can lead to low fatigue limits (some ~1/20 of their tensile strengths) and highly variable fatigue lives. BMG-matrix composites can provide a solution here as their duplex microstructures can arrest shear bands at a second phase to prevent cracks from exceeding critical size; under these conditions, fatigue limits become comparable with those of crystalline alloys. Here, we report on a Pd-based glass that similarly has high fatigue resistance but without a second phase. This monolithic glass displays high intrinsic toughness from extensive shear-band proliferation with cavitation and cracking effectively obstructed. We find that this property can further promote fatigue resistance through extrinsic crack-tip shielding, a mechanism well known in crystalline metals but not previously reported in BMGs, whereby cyclically loaded cracks propagate in a highly "zig-zag" manner, creating a rough "staircase-like" profile. The resulting crack-surface contact (roughness-induced crack closure) elevates fatigue properties to those comparable to crystalline alloys, and the accompanying plasticity helps to reduce flaw sensitivity in the glass, thereby promoting structural reliability.

Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism

PubMed Central

Gludovatz, Bernd; Demetriou, Marios D.; Floyd, Michael; Hohenwarter, Anton; Johnson, William L.; Ritchie, Robert O.

2013-01-01

Bulk-metallic glasses (BMGs) are now candidate materials for structural applications due to their exceptional strength and toughness. However, their fatigue resistance can be poor and inconsistent, severely limiting their potential as reliable structural materials. As fatigue limits are invariably governed by the local arrest of microscopically small cracks at microstructural features, the lack of microstructure in monolithic glasses, often coupled with other factors, such as the ease of crack formation in shear bands or a high susceptibility to corrosion, can lead to low fatigue limits (some ∼1/20 of their tensile strengths) and highly variable fatigue lives. BMG-matrix composites can provide a solution here as their duplex microstructures can arrest shear bands at a second phase to prevent cracks from exceeding critical size; under these conditions, fatigue limits become comparable with those of crystalline alloys. Here, we report on a Pd-based glass that similarly has high fatigue resistance but without a second phase. This monolithic glass displays high intrinsic toughness from extensive shear-band proliferation with cavitation and cracking effectively obstructed. We find that this property can further promote fatigue resistance through extrinsic crack-tip shielding, a mechanism well known in crystalline metals but not previously reported in BMGs, whereby cyclically loaded cracks propagate in a highly “zig-zag” manner, creating a rough “staircase-like” profile. The resulting crack-surface contact (roughness-induced crack closure) elevates fatigue properties to those comparable to crystalline alloys, and the accompanying plasticity helps to reduce flaw sensitivity in the glass, thereby promoting structural reliability. PMID:24167284

System-Level Heat Transfer Analysis, Thermal- Mechanical Cyclic Stress Analysis, and Environmental Fatigue Modeling of a Two-Loop Pressurized Water Reactor. A Preliminary Study

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 in April 2015 under the work package for environmentally assisted fatigue under DOE's Light Water Reactor Sustainability program. In this report, updates are discussed related to a system level preliminary finite element model of a two-loop pressurized water reactor (PWR). Based on this model, system-level heat transfer analysis and subsequent thermal-mechanical stress analysis were performed for typical design-basis thermal-mechanical fatigue cycles. The in-air fatigue lives of components, such as the hot and cold legs,more » were estimated on the basis of stress analysis results, ASME in-air fatigue life estimation criteria, and fatigue design curves. Furthermore, environmental correction factors and associated PWR environment fatigue lives for the hot and cold legs were estimated by using estimated stress and strain histories and the approach described in NUREG-6909. The discussed models and results are very preliminary. Further advancement of the discussed model is required for more accurate life prediction of reactor components. This report only presents the work related to finite element modelling activities. However, in between multiple tensile and fatigue tests were conducted. The related experimental results will be presented in the year-end report.« less

Investigation into Z-Pin Reinforced Composite Skin/Stiffener Debond under Monotonic and Cyclic Bending

NASA Astrophysics Data System (ADS)

Zhang, Xiangyang; Li, Yong; Van Hoa, Suong; Xiao, Jun; Chu, Qiyi

2018-02-01

Skin/stiffener debonding has been a longstanding concern for the users of stiffened composite panels in long-term service. Z-pinning technology is an emerging solution to reinforce the composite assembly joints. This work experimentally characterizes the progressive debonding of Z-pinned skin/stiffener interface with the skin under static bend loading. The three-stage failure process is identified as: flange edge debonding, pin/laminate debonding, and ultimate structural failure. Three different distribution patterns were compared in terms of the static debonding properties revealed the affirmative fact that locating pins in high normal stress regions, that is close to the flange edges in skin/stiffener structures, is more beneficial to utilize the full potential of Z-pinning reinforcement. The unit strip FE model was developed and demonstrated effective to analysis the effect of Z-pin distribution on the ultimate debond load. On the other hand, the evolution of fatigue cracks at Z-pinned skin/flange interface was investigated with a series of displacement-controlled fatigue bending tests and microscopic observations. Results show that Z-pinning postpones crack initiations at low displacement levels, and the remarkable crack-arresting function of pins enables the structure a prolonged fatigue life. However, pins become less effective when the maximum displacement exceeds the crack initiation level due to gradually pullout of pins.

Probabilistic evaluation of uncertainties and risks in aerospace components

NASA Technical Reports Server (NTRS)

Shah, A. R.; Shiao, M. C.; Nagpal, V. K.; Chamis, C. C.

1992-01-01

This paper summarizes a methodology developed at NASA Lewis Research Center which computationally simulates the structural, material, and load uncertainties associated with Space Shuttle Main Engine (SSME) components. The methodology was applied to evaluate the scatter in static, buckling, dynamic, fatigue, and damage behavior of the SSME turbo pump blade. Also calculated are the probability densities of typical critical blade responses, such as effective stress, natural frequency, damage initiation, most probable damage path, etc. Risk assessments were performed for different failure modes, and the effect of material degradation on the fatigue and damage behaviors of a blade were calculated using a multi-factor interaction equation. Failure probabilities for different fatigue cycles were computed and the uncertainties associated with damage initiation and damage propagation due to different load cycle were quantified. Evaluations on the effects of mistuned blades on a rotor were made; uncertainties in the excitation frequency were found to significantly amplify the blade responses of a mistuned rotor. The effects of the number of blades on a rotor were studied. The autocorrelation function of displacements and the probability density function of the first passage time for deterministic and random barriers for structures subjected to random processes also were computed. A brief discussion was included on the future direction of probabilistic structural analysis.

Composite structural materials

NASA Technical Reports Server (NTRS)

Ansell, G. S.; Loewy, R. G.; Wiberley, S. E.

1979-01-01

A multifaceted program is described in which aeronautical, mechanical, and materials engineers interact to develop composite aircraft structures. Topics covered include: (1) the design of an advanced composite elevator and a proposed spar and rib assembly; (2) optimizing fiber orientation in the vicinity of heavily loaded joints; (3) failure mechanisms and delamination; (4) the construction of an ultralight sailplane; (5) computer-aided design; finite element analysis programs, preprocessor development, and array preprocessor for SPAR; (6) advanced analysis methods for composite structures; (7) ultrasonic nondestructive testing; (8) physical properties of epoxy resins and composites; (9) fatigue in composite materials, and (10) transverse thermal expansion of carbon/epoxy composites.

Survival of resin infiltrated ceramics under influence of fatigue.

PubMed

Aboushelib, Moustafa N; Elsafi, Mohamed H

2016-04-01

to evaluate influence of cyclic fatigue on two resin infiltrated ceramics and three all-ceramic crowns manufactured using CAD/CAM technology. CAD/CAM anatomically shaped crowns were manufactured using two resin infiltrated ceramics (Lava Ultimate and Vita Enamic), two reinforced glass ceramic milling blocks ((IPS)Empress CAD and (IPS)e.max CAD) and a veneered zirconia core ((IPS)Zir CAD). (IPS)e.max CAD and (IPS)Zir CAD were milled into 0.5mm thick anatomically shaped core structure which received standardized press-on veneer ceramic. The manufactured crowns were cemented on standardized resin dies using a resin adhesive (Panavia F2.0). Initial fracture strength of half of the specimens was calculated using one cycle load to failure in a universal testing machine. The remaining crowns were subjected to 3.7 million chewing cycles (load range 50-200N at 3s interval) in a custom made pneumatic fatigue tester. Survival statistics were calculated and Weibull modulus was measured from fitted load-cycle-failure diagrams. Scanning electron microscopy was performed to fractographically analyze fractured surfaces. Data were analyzed using two way analysis of variance and Bonferroni post hoc tests (α=0.05). Dynamic fatigue resulted in significant reduction (F=7.54, P<0.005) of the initial fracture strength of the tested specimens. Zirconia showed the highest deterioration percent (34% reduction in strength) followed by (IPS)Empress (32.2%), (IPS)e.max (27.1%) while Lava Ultimate and Vita Enamic showed the lowest percent of reduction in strength. The two types of resin infiltrated ceramics and (IPS)Empress demonstrated the highest percent of fracture incidences under the influence of fatigue (35-45% splitting). None of the tested veneered zirconia restorations were fractured during testing, however, chipping of the veneer ceramics was observed in 6 crowns. The lowest percent of failure was observed for (IPS)e.max crowns manifested as 3 cases of minor chipping in addition to two complete fracture incidences. SEM images demonstrated the internal structure of the tested materials and detected location and size of the critical crack. The internal structure of the tested materials significantly influenced their fatigue behavior. Resin infiltrated ceramics were least influenced by fatigue while the characteristic strength of zirconia prevented core fracture but failure still occurred from the weaker veneer ceramic. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Thermal-mechanical fatigue of high temperature structural materials

NASA Astrophysics Data System (ADS)

Renauld, Mark Leo

Experimental and analytical methods were developed to address the effect of thermal-mechanical strain cycling on high temperature structural materials under uniaxial and biaxial stress states. Two materials were used in the investigation, a nickel-base superalloy of low ductility, IN-738LC and a high ductility material, 316 stainless steel. A uniaxial life prediction model for the IN-738LC material was based on tensile hysteresis energy measured in stabilized, mid-life hysteresis loops. Hold-time effects and temperature cycling were incorporated in the hysteresis energy approach. Crack growth analysis was also included in the model to predict the number of TMF cycles to initiate and grow a fatigue crack through the coating. The nickel-base superalloy, IN-738LC, was primarily tested in out-of-phase (OP) TMF with a temperature range from 482-871sp°C (900-1600sp°F) under continuous and compressive hold-time cycling. IN-738LC fatigue specimens were coated either with an aluminide, NiCoCrAlHfSi overlay or CoNiCrAlY overlay coating on the outer surface of the specimen. Metallurgical failure analysis via optical and scanning electron microscopy, was used to characterize failure behavior of both substrate and coating materials. Type 316 SS was subjected to continuous biaxial strain cycling with an in-phase (IP) TMF loading and a temperature range from 399-621sp°C (750-1150sp°F). As a result, a biaxial TMF life prediction model was proposed on the basis of an extended isothermal fatigue model. The model incorporates a frequency effect and phase factors to assess the different damage mechanisms observed during TMF loading. The model was also applied to biaxial TMF data generated on uncoated IN-738LC.

A survey of the prevalence of fatigue, its precursors and individual coping mechanisms among U.S. manufacturing workers.

PubMed

Lu, Lin; Megahed, Fadel M; Sesek, Richard F; Cavuoto, Lora A

2017-11-01

Advanced manufacturing has resulted in significant changes on the shop-floor, influencing work demands and the working environment. The corresponding safety-related effects, including fatigue, have not been captured on an industry-wide scale. This paper presents results of a survey of U.S. manufacturing workers for the: prevalence of fatigue, its root causes and significant factors, and adopted individual fatigue coping methods. The responses from 451 manufacturing employees were analyzed using descriptive data analysis, bivariate analysis and Market Basket Analysis. 57.9% of respondents indicated that they were somewhat fatigued during the past week. They reported the ankles/feet, lower back and eyes were frequently affected body parts and a lack of sleep, work stress and shift schedule were top selected root causes for fatigue. In order to respond to fatigue when it is present, respondents reported coping by drinking caffeinated drinks, stretching/doing exercises and talking with coworkers. Frequent combinations of fatigue causes and individual coping methods were identified. These results may inform the design of fatigue monitoring and mitigation strategies and future research related to fatigue development. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

NASA Technical Reports Server (NTRS)

Gayda, John

2000-01-01

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

Full-scale fatigue tests of CX-100 wind turbine blades. Part II: analysis

NASA Astrophysics Data System (ADS)

Taylor, Stuart G.; Jeong, Hyomi; Jang, Jae Kyeong; Park, Gyuhae; Farinholt, Kevin M.; Todd, Michael D.; Ammerman, Curtt M.

2012-04-01

This paper presents the initial analysis results of several structural health monitoring (SHM) methods applied to two 9- meter CX-100 wind turbine blades subjected to fatigue loading at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC). The first blade was a pristine blade, manufactured to standard CX-100 design specifications. The second blade was manufactured for the University of Massachusetts, Lowell (UMass), with intentional simulated defects within the fabric layup. Each blade was instrumented with a variety of sensors on its surface. The blades were subject to harmonic excitation at their first natural frequency with steadily increasing loading until ultimately reaching failure. Data from the sensors were collected between and during fatigue loading sessions. The data were measured at multi-scale frequency ranges using a variety of data acquisition equipment, including off-the-shelf systems and prototype data acquisition hardware. The data were analyzed to identify fatigue damage initiation and to assess damage progression. Modal response, diffuse wave-field transfer functions in time and frequency domains, and wave propagation methods were applied to assess the condition of the turbine blade. The analysis methods implemented were evaluated in conjunction with hardware-specific performance for their efficacy in enabling the assessment of damage progression in the blade. The results of this assessment will inform the selection of specific data to be collected and analysis methods to be implemented for a CX-100 flight test to be conducted in collaboration with Sandia National Laboratory at the U.S. Department of Agriculture's (USDA) Conservation and Production Research Laboratory (CPRL) in Bushland, Texas.

Development of a patient reported outcome scale for fatigue in multiple sclerosis: The Neurological Fatigue Index (NFI-MS)

PubMed Central

2010-01-01

Background Fatigue is a common and debilitating symptom in multiple sclerosis (MS). Best-practice guidelines suggest that health services should repeatedly assess fatigue in persons with MS. Several fatigue scales are available but concern has been expressed about their validity. The objective of this study was to examine the reliability and validity of a new scale for MS fatigue, the Neurological Fatigue Index (NFI-MS). Methods Qualitative analysis of 40 MS patient interviews had previously contributed to a coherent definition of fatigue, and a potential 52 item set representing the salient themes. A draft questionnaire was mailed out to 1223 people with MS, and the resulting data subjected to both factor and Rasch analysis. Results Data from 635 (51.9% response) respondents were split randomly into an 'evaluation' and 'validation' sample. Exploratory factor analysis identified four potential subscales: 'physical', 'cognitive', 'relief by diurnal sleep or rest' and 'abnormal nocturnal sleep and sleepiness'. Rasch analysis led to further item reduction and the generation of a Summary scale comprising items from the Physical and Cognitive subscales. The scales were shown to fit Rasch model expectations, across both the evaluation and validation samples. Conclusion A simple 10-item Summary scale, together with scales measuring the physical and cognitive components of fatigue, were validated for MS fatigue. PMID:20152031

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

NASA Technical Reports Server (NTRS)

Forman, Royce G.; Figert, J.; Beek, J.; Ventura, J.; Martinez, J.; Samonski, F.

2011-01-01

This presentation describes results obtained from a research project conducted at the NASA Johnson Space Center (JSC) that was jointly supported by the FAA Technical Center and JSC. The JSC effort was part of a multi-task FAA program involving several U.S. laboratories and initiated for the purpose of developing enhanced analysis tools to assess damage tolerance of rotorcraft and aircraft propeller systems. The research results to be covered in this presentation include a new understanding of the behavior of fatigue crack growth in the threshold region. This behavior is important for structural life analysis of aircraft propeller systems and certain rotorcraft structural components (e.g., the mast). These components are often designed to not allow fatigue crack propagation to exceed an experimentally determined fatigue crack growth threshold value. During the FAA review meetings for the program, disagreements occurred between the researchers regarding the observed fanning (spread between the da/dN curves of constant R) in the threshold region at low stress ratios, R. Some participants believed that the fanning was a result of the ASTM load shedding test method for threshold testing, and thus did not represent the true characteristics of the material. If the fanning portion of the threshold value is deleted or not included in a life analysis, a significant penalty in the calculated life and design of the component would occur. The crack growth threshold behavior was previously studied and reported by several research investigators in the time period: 1970-1980. Those investigators used electron microscopes to view the crack morphology of the fatigue fracture surfaces. Their results showed that just before reaching threshold, the crack morphology often changed from a striated to a faceted or cleavage-like morphology. This change was reported to have been caused by particular dislocation properties of the material. Based on the results of these early investigations, a program was initiated at JSC to repeat these examinations on a number of aircraft structural alloys that were currently being tested for obtaining fatigue crack growth properties. These new scanning electron microscope (SEM) examinations of the fatigue fracture faces confirmed the change in crack morphology in the threshold crack tip region. In addition, SEM examinations were further performed in the threshold crack-tip region before breaking the specimens open (not done in the earlier published studies). In these examinations, extensive crack forking and even 90-degree crack bifurcations were found to have occurred in the final threshold crack-tip region. The forking and bifurcations caused numerous closure points to occur that prevented full crack closure in the threshold region, and thus were the cause of the fanning at low-R values. Therefore, we have shown that the fanning behavior was caused by intrinsic dislocation properties of the different alloy materials and were not the result of a plastic wake that remains from the load-shedding test phase. Also, to accommodate the use of da/dN data which includes fanning at low R-values, an updated fanning factor term has been developed and will be implemented into the NASGRO fatigue crack growth software. The term can be set to zero if it is desired that the fanning behavior is not be modeled for particular cases, such as when fanning is not a result of the intrinsic properties of a material.

A Review on Strengthening Steel Beams Using FRP under Fatigue

PubMed Central

Jumaat, Mohd Zamin; Ramli Sulong, N. H.

2014-01-01

In recent decades, the application of fibre-reinforced polymer (FRP) composites for strengthening structural elements has become an efficient option to meet the increased cyclic loads or repair due to corrosion or fatigue cracking. Hence, the objective of this study is to explore the existing FRP reinforcing techniques to care for fatigue damaged structural steel elements. This study covers the surface treatment techniques, adhesive curing, and support conditions under cyclic loading including fatigue performance, crack propagation, and failure modes with finite element (FE) simulation of the steel bridge girders and structural elements. FRP strengthening composites delay initial cracking, reduce the crack growth rate, extend the fatigue life, and decrease the stiffness decay with residual deflection. Prestressed carbon fibre-reinforced polymer (CFRP) is the best strengthening option. End anchorage prevents debonding of the CRRP strips at the beam ends by reducing the local interfacial shear and peel stresses. Hybrid-joint, nanoadhesive, and carbon-flex can also be attractive for strengthening systems. PMID:25243221

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

NASA Technical Reports Server (NTRS)

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

2010-01-01

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

A review on strengthening steel beams using FRP under fatigue.

PubMed

Kamruzzaman, Mohamed; Jumaat, Mohd Zamin; Sulong, N H Ramli; Islam, A B M Saiful

2014-01-01

In recent decades, the application of fibre-reinforced polymer (FRP) composites for strengthening structural elements has become an efficient option to meet the increased cyclic loads or repair due to corrosion or fatigue cracking. Hence, the objective of this study is to explore the existing FRP reinforcing techniques to care for fatigue damaged structural steel elements. This study covers the surface treatment techniques, adhesive curing, and support conditions under cyclic loading including fatigue performance, crack propagation, and failure modes with finite element (FE) simulation of the steel bridge girders and structural elements. FRP strengthening composites delay initial cracking, reduce the crack growth rate, extend the fatigue life, and decrease the stiffness decay with residual deflection. Prestressed carbon fibre-reinforced polymer (CFRP) is the best strengthening option. End anchorage prevents debonding of the CRRP strips at the beam ends by reducing the local interfacial shear and peel stresses. Hybrid-joint, nanoadhesive, and carbon-flex can also be attractive for strengthening systems.

Analysis of cancer-related fatigue based on smart bracelet devices.

PubMed

Shen, Hong; Hou, Honglun; Tian, Wei; Wu, MingHui; Chen, Tianzhou; Zhong, Xian

2016-01-01

Fatigue is the most common symptom associated with cancer and its treatment, and profoundly affects all aspects of quality of life for cancer patients. It is very important to measure and manage cancer-related fatigue. Usually, the cancer-related fatigue scores, which estimate the degree of fatigue, are self-reported by cancer patients using standardized assessment tools. But most of the classical methods used for measurement of fatigue are subjective and inconvenient. In this study, we try to establish a new method to assess cancer-related fatigue objectively and accurately by using smart bracelet. All patients with metastatic pancreatic cancer wore smart bracelet for recording the physical activity including step count and sleep time before and after chemotherapy. Meantime, their psychological state was assessed by completing questionnaire tables as cancer-related fatigue scores. Step count record by smart bracelet reflecting the physical performance dramatically decreased in the initial days of chemotherapy and recovered in the next few days. Statistical analysis showed a strong and significant correlation between self-reported cancer-related fatigue and physical performance (P= 0.000, r=-0.929). Sleep time was also significantly correlated with fatigue (P= 0.000, r= 0.723). Multiple regression analysis showed that physical performance and sleep time are significant predictors of fatigue. Measuring activity using smart bracelets may be an appropriate method for quantitative and objective measurement of cancer-related fatigue by using smart bracelet devices.

Effects of foot reflexology on fatigue, sleep and pain: a systematic review and meta-analysis.

PubMed

Lee, Jeongsoon; Han, Misook; Chung, Younghae; Kim, Jinsun; Choi, Jungsook

2011-12-01

The purpose of this study was to evaluate the effectiveness of foot reflexology on fatigue, sleep and pain. A systematic review and meta-analysis were conducted. Electronic database and manual searches were conducted on all published studies reporting the effects of foot reflexology on fatigue, sleep, and pain. Forty four studies were eligible including 15 studies associated with fatigue, 18 with sleep, and 11 with pain. The effects of foot reflexology were analyzed using Comprehensive Meta-Analysis Version 2.0. The homogeneity and the fail-safe N were calculated. Moreover, a funnel plot was used to assess publication bias. The effects on fatigue, sleep, and pain were not homogeneous and ranged from 0.63 to 5.29, 0.01 to 3.22, and 0.43 to 2.67, respectively. The weighted averages for fatigue, sleep, and pain were 1.43, 1.19, and 1.35, respectively. No publication bias was detected as evaluated by fail-safe N. Foot reflexology had a larger effect on fatigue and sleep and a smaller effect on pain. This meta-analysis indicates that foot reflexology is a useful nursing intervention to relieve fatigue and to promote sleep. Further studies are needed to evaluate the effects of foot reflexology on outcome variables other than fatigue, sleep and pain.

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

NASA Astrophysics Data System (ADS)

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

2015-01-01

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

Development of a realistic stress analysis for fatigue analysis of notched composite laminates

NASA Technical Reports Server (NTRS)

Humphreys, E. A.; Rosen, B. W.

1979-01-01

A finite element stress analysis which consists of a membrane and interlaminar shear spring analysis was developed. This approach was utilized in order to model physically realistic failure mechanisms while maintaining a high degree of computational economy. The accuracy of the stress analysis predictions is verified through comparisons with other solutions to the composite laminate edge effect problem. The stress analysis model was incorporated into an existing fatigue analysis methodology and the entire procedure computerized. A fatigue analysis is performed upon a square laminated composite plate with a circular central hole. A complete description and users guide for the computer code FLAC (Fatigue of Laminated Composites) is included as an appendix.

Effect of Fatigue Training on Safety, Fatigue, and Sleep in Emergency Medical Services Personnel and Other Shift Workers: A Systematic Review and Meta-Analysis

DOT National Transportation Integrated Search

2018-01-11

Background: Fatigue training may be an effective way to mitigate fatigue-related risk. We aimed to critically review and synthesize existing literature on the impact of fatigue training on fatigue-related outcomes for Emergency Medical Services (EMS)...

14 CFR 29.571 - Fatigue evaluation of structure.

Code of Federal Regulations, 2011 CFR

2011-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Strength Requirements Fatigue Evaluation... fatigue, considering the effects of environment, intrinsic/discrete flaws, or accidental damage will be avoided. Parts to be evaluated include, but are not limited to, rotors, rotor drive systems between the...

14 CFR 29.571 - Fatigue evaluation of structure.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Strength Requirements Fatigue Evaluation... fatigue, considering the effects of environment, intrinsic/discrete flaws, or accidental damage will be avoided. Parts to be evaluated include, but are not limited to, rotors, rotor drive systems between the...

The role of neuroticism, perfectionism and depression in chronic fatigue syndrome. A structural equation modeling approach.

PubMed

Valero, Sergi; Sáez-Francàs, Naia; Calvo, Natalia; Alegre, José; Casas, Miquel

2013-10-01

Previous studies have reported consistent associations between Neuroticism, maladaptive perfectionism and depression with severity of fatigue in Chronic Fatigue Syndrome (CFS). Depression has been considered a mediator factor between maladaptive perfectionism and fatigue severity, but no studies have explored the role of neuroticism in a comparable theoretical framework. This study aims to examine for the first time, the role of neuroticism, maladaptive perfectionism and depression on the severity of CFS, analyzing several explanation models. A sample of 229 CFS patients were studied comparing four structural equation models, testing the role of mediation effect of depression severity in the association of Neuroticism and/or Maladaptive perfectionism on fatigue severity. The model considering depression severity as mediator factor between Neuroticism and fatigue severity is the only one of the explored models where all the structural modeling indexes have fitted satisfactorily (Chi square=27.01, p=0.079; RMSE=0.047, CFI=0.994; SRMR=0.033). Neuroticism is associated with CFS by the mediation effect of depression severity. This personality variable constitutes a more consistent factor than maladaptive perfectionism in the conceptualization of CFS severity. Copyright © 2013 Elsevier Inc. All rights reserved.

Modeling Delamination in Postbuckled Composite Structures Under Static and Fatigue Loads

NASA Technical Reports Server (NTRS)

Bisagni, Chiara; Brambilla, Pietro; Bavila, Carlos G.

2013-01-01

The ability of the Abaqus progressive Virtual Crack Closure Technique (VCCT) to model delamination in composite structures was investigated for static, postbuckling, and fatigue loads. Preliminary evaluations were performed using simple Double Cantilever Beam (DCB) and Mixed-Mode Bending (MMB) specimens. The nodal release sequences that describe the propagation of the delamination front were investigated. The effect of using a sudden or a gradual nodal release was evaluated by considering meshes aligned with the crack front as well as misaligned meshes. Fatigue simulations were then performed using the Direct Cyclic Fatigue (DCF) algorithm. It was found that in specimens such as the DCB, which are characterized by a nearly linear response and a pure fracture mode, the algorithm correctly predicts the Paris Law rate of propagation. However, the Abaqus DCF algorithm does not consider different fatigue propagation laws in different fracture modes. Finally, skin/stiffener debonding was studied in an aircraft fuselage subcomponent in which debonding occurs deep into post-buckling deformation. VCCT was shown to be a robust tool for estimating the onset propagation. However, difficulties were found with the ability of the current implementation of the Abaqus progressive VCCT to predict delamination propagation within structures subjected to postbuckling deformations or fatigue loads.

Piezoelectric Bolt Breakers and Bolt Fatigue Testers

NASA Technical Reports Server (NTRS)

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

2008-01-01

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

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

PubMed

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

2015-10-01

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

The fatigue evaluation method for a structural stainless steel using the magnetic sensor composed of three pancake coils

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

Oka, M.; Tsuchida, Y.; Enokizono, M.

May metallic structural materials, such as stainless steels, are currently used in our surroundings. If external force is repeatedly added for many years, it is thought that fatigue damage accumulates in stainless steels. When excessive fatigue damage accumulates in these metals, there is a possibility that they are destroyed by fatigue damage accumulation. Therefore, it is important to know the amount of the fatigue damage they have suffered in order to prevent them from being destroyed. We are developing the fatigue evaluation method for stainless steels with a magnetic sensor composed of three pancake type coils. In this research, themore » inspection object is ferritic stainless steels such as SUS430. The method of fatigue evaluation for ferritic stainless steels uses the three coil type sensor, and shows a good correlation between the number of stress cycles and the output signal of the sensor, even though the correlation between the output signal and an added stress is not completely accurate. This paper describes the evaluation method of fatigue damage in ferritic stainless steel using a magnetic sensor composed of three pancake-type coils.« less

Guidelines for VCCT-Based Interlaminar Fatigue and Progressive Failure Finite Element Analysis

NASA Technical Reports Server (NTRS)

Deobald, Lyle R.; Mabson, Gerald E.; Engelstad, Steve; Prabhakar, M.; Gurvich, Mark; Seneviratne, Waruna; Perera, Shenal; O'Brien, T. Kevin; Murri, Gretchen; Ratcliffe, James;

Probabilistic Structural Analysis Methods (PSAM) for Select Space Propulsion System Components

NASA Technical Reports Server (NTRS)

1999-01-01

Probabilistic Structural Analysis Methods (PSAM) are described for the probabilistic structural analysis of engine components for current and future space propulsion systems. Components for these systems are subjected to stochastic thermomechanical launch loads. Uncertainties or randomness also occurs in material properties, structural geometry, and boundary conditions. Material property stochasticity, such as in modulus of elasticity or yield strength, exists in every structure and is a consequence of variations in material composition and manufacturing processes. Procedures are outlined for computing the probabilistic structural response or reliability of the structural components. The response variables include static or dynamic deflections, strains, and stresses at one or several locations, natural frequencies, fatigue or creep life, etc. Sample cases illustrates how the PSAM methods and codes simulate input uncertainties and compute probabilistic response or reliability using a finite element model with probabilistic methods.

Characterization of fatigue crack growth behavior in LENS fabricated Ti-6Al-4V using high-energy synchrotron x-ray microtomography

DOE PAGES

Sandgren, Hayley R.; Zhai, Yuwei; Lados, Diana A.; ...

2016-09-28

Laser Engineered Net Shaping (LENS) is an additive manufacturing technique that belongs to the ASTM standardized directed energy deposition category. To date, very limited work has been conducted towards understanding the fatigue crack growth behavior of LENS fabricated materials, which hinders the widespread adoption of this technology for high-integrity structural applications. In this study, the propagation of a 20 μm initial crack in LENS fabricated Ti-6Al-4V was captured in-situ, using high-energy synchrotron x-ray microtomography. Fatigue crack growth (FCG) data were then determined from 2D and 3D tomography reconstructions, as well as from fracture surface striation measurements using SEM. The generatedmore » data were compared to those obtained from conventional FCG tests that used compliance and direct current potential drop (DCPD) techniques to measure long and small crack growth. In conclusion, the observed agreement demonstrates that x-ray microtomography and fractographic analysis using SEM can be successfully combined to study the propagation behavior of fatigue cracks.« less

Creep-Fatigue Relationsihps in Electroactive Polymer Systems and Predicted Effects in an Actuator Design

NASA Technical Reports Server (NTRS)

Vinogradov, Aleksandra M.; Ihlefeld, Curtis M.; Henslee, Issac

2009-01-01

The paper concerns the time-dependent behavior of electroactive polymers (EAP) and their use in advanced intelligent structures for space exploration. Innovative actuator design for low weight and low power valves required in small plants planned for use on the moon for chemical analysis is discussed. It is shown that in-depth understanding of cyclic loading effects observed through accelerated creep rates due to creep-fatigue interaction in polymers is critical in terms of proper functioning of EAP based actuator devices. In the paper, an overview of experimental results concerning the creep properties and cyclic creep response of a thin film piezoelectric polymer polyvinylidene fluoride (PVDF) is presented. The development of a constitutive creep-fatigue interaction model to predict the durability and service life of electroactive polymers is discussed. A novel method is proposed to predict damage accumulation and fatigue life of polymers under oyclic loading conditions in the presence of creep. The study provides a basis for ongoing research initiatives at the NASA Kennedy Space Center in the pursuit of new technologies using EAP as active elements for lunar exploration systems.

Characterization of fatigue crack growth behavior in LENS fabricated Ti-6Al-4V using high-energy synchrotron x-ray microtomography

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

Sandgren, Hayley R.; Zhai, Yuwei; Lados, Diana A.

Laser Engineered Net Shaping (LENS) is an additive manufacturing technique that belongs to the ASTM standardized directed energy deposition category. To date, very limited work has been conducted towards understanding the fatigue crack growth behavior of LENS fabricated materials, which hinders the widespread adoption of this technology for high-integrity structural applications. In this study, the propagation of a 20 μm initial crack in LENS fabricated Ti-6Al-4V was captured in-situ, using high-energy synchrotron x-ray microtomography. Fatigue crack growth (FCG) data were then determined from 2D and 3D tomography reconstructions, as well as from fracture surface striation measurements using SEM. The generatedmore » data were compared to those obtained from conventional FCG tests that used compliance and direct current potential drop (DCPD) techniques to measure long and small crack growth. In conclusion, the observed agreement demonstrates that x-ray microtomography and fractographic analysis using SEM can be successfully combined to study the propagation behavior of fatigue cracks.« less

The role of appraisal and coping style in relation with societal participation in fatigued patients with multiple sclerosis: a cross-sectional multiple mediator analysis.

PubMed

van den Akker, Lizanne Eva; Beckerman, Heleen; Collette, Emma Hubertine; Bleijenberg, Gijs; Dekker, Joost; Knoop, Hans; de Groot, Vincent

2016-10-01

To determine the relationship between appraisal and societal participation in fatigued patients with Multiple Sclerosis (MS), and whether this relation is mediated by coping styles. 265 severely-fatigued MS patients. Appraisal, a latent construct, was created from the General Self-Efficacy Scale and the helplessness and acceptance subscales of the Illness Cognition Questionnaire. Coping styles were assessed using the Coping Inventory Stressful Situations (CISS21) and societal participation was assessed using the Impact on Participation and Autonomy. A multiple mediator model was developed and tested by structural equation modeling on cross-sectional data. We corrected for confounding by disease-related factors. Mediation was determined using a product-of-coefficients approach. A significant relationship existed between appraisal and participation (β = 0.21, 95 % CI 0.04-0.39). The pathways via coping styles were not significant. In patients with severe MS-related fatigue, appraisal and societal participation show a positive relationship that is not mediated by coping styles.

Compassion fatigue and burnout amongst clinicians: a medical exploratory study.

PubMed

Bhutani, Jaikrit; Bhutani, Sukriti; Balhara, Yatan Pal Singh; Kalra, Sanjay

2012-10-01

Compassion fatigue is a broad term comprising of two components - burnout and secondary traumatic stress. The current study is aimed at identifying 'burnout' and 'compassion fatigue' among clinicians involved in care of individuals suffering from medical illness. A total of 60 clinicians were included in the study. A semi-structured questionnaire was administered to gather information related to personal, professional, anthropometric, and metabolic profile of the study participants. Professional Quality of Life Scale (ProQoL Version V) was used to assess burnout, compassion satisfaction and secondary traumatic stress. Analysis was carried out using the SPSS version 19.0. The mean age of clinicians was 46.68±11.06 (range 26-67 years). Burnout score was significantly higher in those involved in diabetology practice. Similarly, compassion satisfaction score was greater among those with greater years of practice as well as among those in private practice. Clinicians who reported a poor working condition, as opposed to good, had more burnout and less compassion satisfaction. The current study suggests that it is important to find out ways of decreasing burnout and compassion fatigue among clinicians.

Fatigue of titanium alloys in a supersonic-cruise airplane environment

NASA Technical Reports Server (NTRS)

Imig, L. A.

1976-01-01

The test programs conducted by several aerospace companies and NASA, summarized in this paper, studied several titanium materials previously identified as having high potential for application to supersonic cruise airplane structures. These studies demonstrate that the temperature (560 K) by itself produced no significant degradation of the materials. However, the fatigue resistance of titanium-alloy structures, in which thermal and loading effects are combined, has been studied insufficiently. The predominant topic for future study of fatigue problems in Mach 3 structures should be the influences of thermal stress particularly, the effects of thermal stress on failure location.

Optimal periodic proof test based on cost-effective and reliability criteria

NASA Technical Reports Server (NTRS)

Yang, J.-N.

1976-01-01

An exploratory study for the optimization of periodic proof tests for fatigue-critical structures is presented. The optimal proof load level and the optimal number of periodic proof tests are determined by minimizing the total expected (statistical average) cost, while the constraint on the allowable level of structural reliability is satisfied. The total expected cost consists of the expected cost of proof tests, the expected cost of structures destroyed by proof tests, and the expected cost of structural failure in service. It is demonstrated by numerical examples that significant cost saving and reliability improvement for fatigue-critical structures can be achieved by the application of the optimal periodic proof test. The present study is relevant to the establishment of optimal maintenance procedures for fatigue-critical structures.

A Multi-Scale Structural Health Monitoring Approach for Damage Detection, Diagnosis and Prognosis in Aerospace Structures

DTIC Science & Technology

2012-01-20

ultrasonic Lamb waves to plastic strain and fatigue life. Theory was developed and validated to predict second harmonic generation for specific mode... Fatigue and damage generation and progression are processes consisting of a series of interrelated events that span large scales of space and time...strain and fatigue life A set of experiments were completed that worked to relate the acoustic nonlinearity measured with Lamb waves to both the

Interim Report on Fatigue Characteristics of a Typical Metal Wing

NASA Technical Reports Server (NTRS)

Kepert, J L; Payne, A O

1956-01-01

Constant amplitude fatigue tests of seventy-two P-51D "Mustang" wings are reported. The tests were performed by a vibrational loading system and by an hydraulic loading device for conditions with and without varying amounts of pre-load. The results indicate that: (a) the frequency of occurrence of fatigue at any one location is related to the range of the loads applied, (b) the rate of propagation of visible cracks is more or less constant for a large portion of the life of the specimen, (c) the fatigue strength of the structure is similar to that of notched material having a theoretical stress concentration factor of more than 3.0, (d) the frequency distribution of fatigue life is approximately logarithmic normal, (e) the relative increase in fatigue life for a given pre-load depends on the maximum load of the loading cycle only, while the optimum pre-load value is approximately 85 percent of the ultimate failing load, and (f) that normal design procedure will not permit the determination of local stress levels with sufficient accuracy to determine the fatigue strength of an element of a redundant structure.

A Review of Spectral Methods for Variable Amplitude Fatigue Prediction and New Results

NASA Technical Reports Server (NTRS)

Larsen, Curtis E.; Irvine, Tom

2013-01-01

A comprehensive review of the available methods for estimating fatigue damage from variable amplitude loading is presented. The dependence of fatigue damage accumulation on power spectral density (psd) is investigated for random processes relevant to real structures such as in offshore or aerospace applications. Beginning with the Rayleigh (or narrow band) approximation, attempts at improved approximations or corrections to the Rayleigh approximation are examined by comparison to rainflow analysis of time histories simulated from psd functions representative of simple theoretical and real world applications. Spectral methods investigated include corrections by Wirsching and Light, Ortiz and Chen, the Dirlik formula, and the Single-Moment method, among other more recent proposed methods. Good agreement is obtained between the spectral methods and the time-domain rainflow identification for most cases, with some limitations. Guidelines are given for using the several spectral methods to increase confidence in the damage estimate.

Fatigue of Chinese railway employees and its influential factors: Structural equation modelling.

PubMed

Tsao, Liuxing; Chang, Jing; Ma, Liang

2017-07-01

Fatigue is an identifiable and preventable cause of accidents in transport operations. Regarding the railway sector, incident logs and simulation studies show that employee fatigue leads to lack of alertness, impaired performance, and occurrence of incidents. China has one of the largest rail systems in the world, and Chinese railway employees work under high fatigue risks; therefore, it is important to assess their fatigue level and find the major factors leading to fatigue. We designed a questionnaire that uses Multidimensional Fatigue Instrument (MFI-20), NASA-TLX and subjective rating of work overtime feelings to assess employee fatigue. The contribution of each influential factor of fatigue was analysed using structural equation modelling. In total, 297 employees from the rail maintenance department and 227 employees from the locomotive department returned valid responses. The average scores and standard deviations for the five subscales of MFI-20, namely General Fatigue, Physical Fatigue, Reduced Activity, Reduced Motivation, and Mental Fatigue, were 2.9 (0.8), 2.8 (0.8), 2.5 (0.8), 2.5 (0.7), and 2.4 (0.8) among the rail maintenance employees and 3.5 (0.8), 3.5 (0.7), 3.3 (0.7), 3.0 (0.6), and 3.1 (0.7), respectively, among the locomotive employees. The fatigue of the locomotive employees was influenced by feelings related to working overtime (standardized r = 0.22) and workload (standardized r = 0.27). The work overtime control and physical working environment significantly influenced subjective feelings (standardized r = -0.25 and 0.47, respectively), while improper work/rest rhythms and an adverse physical working environment significantly increased the workload (standardized r = 0.48 and 0.33, respectively). Copyright © 2017 Elsevier Ltd. All rights reserved.

Response of plain concrete to a state of biaxial fatigue loading : equipment and technique.

DOT National Transportation Integrated Search

1974-01-01

The fatigue strength of concrete is an important factor in the design of certain structures, particularly those associated with transportation functions. A considerable body of research has been developed on fatigue using specimens subjected to uniax...

Investigation of the effect of vacuum environment on the fatigue and fracture behavior of 7075-T6.

NASA Technical Reports Server (NTRS)

Hudson, C. M.

1972-01-01

Axial-load fatigue-life, fatigue-crack propagation, and fracture-toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at air pressures ranging from 101 kN/sq m to 7 micronewtons/sq m to determine the effect of air pressure on fatigue behavior. Analysis of the results from the fatigue-life experiments indicated that for a given stress level, the lower the air pressure was the longer the fatigue life. At a pressure of 7 micronewtons/sq m, fatigue lives were 15 to 30 times longer than at 101 kN/sq m. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue-crack-growth rates were approximately twice as high at atmospheric pressure as in vacuum. However, at higher values of stress-intensity range, the fatigue-crack-growth rates were nominally the same in vacuum and at atmospheric pressure.

49 CFR 228.407 - Analysis of work schedules; submissions; FRA review and approval of submissions; fatigue...

Code of Federal Regulations, 2012 CFR

2012-10-01

... TRANSPORTATION HOURS OF SERVICE OF RAILROAD EMPLOYEES; RECORDKEEPING AND REPORTING; SLEEPING QUARTERS Substantive... fatigue mitigation tools to reduce the risk for fatigue to a level that does not violate the fatigue... mitigation tools so as to present a risk for a level of fatigue that does not violate the applicable fatigue...

49 CFR 228.407 - Analysis of work schedules; submissions; FRA review and approval of submissions; fatigue...

Code of Federal Regulations, 2013 CFR

2013-10-01

... TRANSPORTATION HOURS OF SERVICE OF RAILROAD EMPLOYEES; RECORDKEEPING AND REPORTING; SLEEPING QUARTERS Substantive... fatigue mitigation tools to reduce the risk for fatigue to a level that does not violate the fatigue... mitigation tools so as to present a risk for a level of fatigue that does not violate the applicable fatigue...

49 CFR 228.407 - Analysis of work schedules; submissions; FRA review and approval of submissions; fatigue...

Code of Federal Regulations, 2014 CFR

2014-10-01

... TRANSPORTATION HOURS OF SERVICE OF RAILROAD EMPLOYEES; RECORDKEEPING AND REPORTING; SLEEPING QUARTERS Substantive... fatigue mitigation tools to reduce the risk for fatigue to a level that does not violate the fatigue... mitigation tools so as to present a risk for a level of fatigue that does not violate the applicable fatigue...

Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure

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

Zhou, J; Huang, M; Niu, X

In this paper, we investigated the effects of substrate creep on the fatigue behavior of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 grit or 600 grit sand papers before bonding to create different sub-surface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the sub-surfaces.more » They were also significantly reduced by the substrate creep when tested at relatively low load levels i.e. P{sub m} < 60 N (Pm is the maximum magnitude of cyclic load). But at relatively high load levels i.e. P{sub m} > 65 N, slow crack growth (SCG) was the major failure mechanisms. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect (SCE).« less

Detailed finite element analysis and preliminary study of the effects of friction and fastener pre-tension on the mechanical behavior of fastened built-up members

NASA Astrophysics Data System (ADS)

Bonachera Martin, Francisco Javier

The characterization of fatigue resistance is one of the main concerns in structural engineering, a concern that is particularly important in the evaluation of existing bridge members designed or erected before the development of fatigue design provisions. The ability of a structural member to develop alternate load paths after the failure of a component is known as member-level or internal redundancy. In fastened built-up members, these alternate load paths are affected by the combination of fastener pre-tension and friction between the structural member components in contact. In this study, a finite element methodology to model and analyze riveted and bolted built-up members was developed in ABAQUS and validated with experimental results. This methodology was used to created finite element models of three fastened plates subjected to tension, in which the middle plate had failed, in order to investigate the fundamental effects of combined fastener pre-tension and friction on their mechanical behavior. Detailed finite element models of riveted and bolted built-up flexural members were created and analyze to understand the effect of fastener pre-tension in member-level redundancy and resistance to fatigue and fracture. The obtained results showed that bolted members are able to re-distribute a larger portion of the load away from the failing component into the rest of the member than riveted members, and that this transfer of load also took place over a smaller length. Superior pre-tension of bolts, in comparison to rivets, results in larger frictional forces that develop at the contact interfaces between components and constitute additional alternate load paths that increase member-level redundancy which increase the fatigue and fracture resistance of the structural member during the failure of one of its components. Although fatigue and fracture potential may be mitigated by compressive stresses developing around the fastener hole due to fastener pre-tension, it was also observed, that at the surface of the fastener hole and at the contact interface with another plate, tensional stresses could develop; however, further computational and experimental work should be performed to verify this claim.

The revised Bristol Rheumatoid Arthritis Fatigue measures and the Rheumatoid Arthritis Impact of Disease scale: validation in six countries

PubMed Central

Kirwan, John; Bode, Christina; Cramp, Fiona; Carmona, Loreto; Dures, Emma; Englbrecht, Matthias; Fransen, Jaap; Greenwood, Rosemary; Hagel, Sofia; van de Laar, Maart; Molto, Anna; Nicklin, Joanna; Petersson, Ingemar F; Redondo, Marta; Schett, Georg; Gossec, Laure

2018-01-01

Abstract Objective To evaluate the Bristol Rheumatoid Arthritis Fatigue Multidimensional Questionnaire (BRAF-MDQ), the revised Bristol Rheumatoid Arthritis Numerical Rating Scales (BRAF-NRS V2) and the Rheumatoid Arthritis Impact of Disease (RAID) scale in six countries. Methods We surveyed RA patients in France, Germany, The Netherlands, Spain, Sweden and the UK, including the HAQ, 36-item Short Form Health Survey (SF-36) and potential revisions of the BRAF-NRS coping and Spanish RAID coping items. Factor structure and internal consistency were examined by factor analysis and Cronbach’s α and construct validity by Spearman’s correlation. Results A total of 1276 patients participated (76% female, 25% with a disease duration <5 years, median HAQ 1.0). The original BRAF-MDQ four-factor structure and RAID single-factor structure were confirmed in every country with ⩾66% of variation in items explained by each factor and all item factor loadings of 0.71–0.98. Internal consistency for the BRAF-MDQ total and subscales was a Cronbach’s α of 0.75–0.96 and for RAID, 0.93–0.96. Fatigue construct validity was shown for the BRAF-MDQ and BRAF-NRS severity and effect scales, correlated internally with SF-36 vitality and with RAID fatigue (r = 0.63–0.93). Broader construct validity for the BRAFs and RAID was shown by correlation with each other, HAQ and SF-36 domains (r = 0.46–0.82), with similar patterns in individual countries. The revised BRAF-NRS V2 Coping item had stronger validity than the original in all analyses. The revised Spanish RAID coping item performed as well as the original. Conclusion Across six European countries, the BRAF-MDQ identifies the same four aspects of fatigue, and along with the RAID, shows strong factor structure and internal consistency and moderate–good construct validity. The revised BRAF-NRS V2 shows improved construct validity and replaces the original. PMID:29087507

The revised Bristol Rheumatoid Arthritis Fatigue measures and the Rheumatoid Arthritis Impact of Disease scale: validation in six countries.

PubMed

Hewlett, Sarah; Kirwan, John; Bode, Christina; Cramp, Fiona; Carmona, Loreto; Dures, Emma; Englbrecht, Matthias; Fransen, Jaap; Greenwood, Rosemary; Hagel, Sofia; van de Laar, Maart; Molto, Anna; Nicklin, Joanna; Petersson, Ingemar F; Redondo, Marta; Schett, Georg; Gossec, Laure

2018-02-01

To evaluate the Bristol Rheumatoid Arthritis Fatigue Multidimensional Questionnaire (BRAF-MDQ), the revised Bristol Rheumatoid Arthritis Numerical Rating Scales (BRAF-NRS V2) and the Rheumatoid Arthritis Impact of Disease (RAID) scale in six countries. We surveyed RA patients in France, Germany, The Netherlands, Spain, Sweden and the UK, including the HAQ, 36-item Short Form Health Survey (SF-36) and potential revisions of the BRAF-NRS coping and Spanish RAID coping items. Factor structure and internal consistency were examined by factor analysis and Cronbach's α and construct validity by Spearman's correlation. A total of 1276 patients participated (76% female, 25% with a disease duration <5 years, median HAQ 1.0). The original BRAF-MDQ four-factor structure and RAID single-factor structure were confirmed in every country with ⩾66% of variation in items explained by each factor and all item factor loadings of 0.71-0.98. Internal consistency for the BRAF-MDQ total and subscales was a Cronbach's α of 0.75-0.96 and for RAID, 0.93-0.96. Fatigue construct validity was shown for the BRAF-MDQ and BRAF-NRS severity and effect scales, correlated internally with SF-36 vitality and with RAID fatigue (r = 0.63-0.93). Broader construct validity for the BRAFs and RAID was shown by correlation with each other, HAQ and SF-36 domains (r = 0.46-0.82), with similar patterns in individual countries. The revised BRAF-NRS V2 Coping item had stronger validity than the original in all analyses. The revised Spanish RAID coping item performed as well as the original. Across six European countries, the BRAF-MDQ identifies the same four aspects of fatigue, and along with the RAID, shows strong factor structure and internal consistency and moderate-good construct validity. The revised BRAF-NRS V2 shows improved construct validity and replaces the original. © The Author 2017. Published by Oxford University Press on behalf of the British Society for Rheumatology.

Application of a symbolic motion structure representation algorithm to identify upper extremity kinematic changes during a repetitive task.

PubMed

Whittaker, Rachel L; Park, Woojin; Dickerson, Clark R

2018-04-27

Efficient and holistic identification of fatigue-induced movement strategies can be limited by large between-subject variability in descriptors of joint angle data. One promising alternative to traditional, or computationally intensive methods is the symbolic motion structure representation algorithm (SMSR), which identifies the basic spatial-temporal structure of joint angle data using string descriptors of temporal joint angle trajectories. This study attempted to use the SMSR to identify changes in upper extremity time series joint angle data during a repetitive goal directed task causing muscle fatigue. Twenty-eight participants (15 M, 13 F) performed a seated repetitive task until fatigued. Upper extremity joint angles were extracted from motion capture for representative task cycles. SMSRs, averages and ranges of several joint angles were compared at the start and end of the repetitive task to identify kinematic changes with fatigue. At the group level, significant increases in the range of all joint angle data existed with large between-subject variability that posed a challenge to the interpretation of these fatigue-related changes. However, changes in the SMSRs across participants effectively summarized the adoption of adaptive movement strategies. This establishes SMSR as a viable, logical, and sensitive method of fatigue identification via kinematic changes, with novel application and pragmatism for visual assessment of fatigue development. Copyright © 2018 Elsevier Ltd. All rights reserved.

Cyclic plasticity models and application in fatigue analysis

NASA Technical Reports Server (NTRS)

Kalev, I.

1981-01-01

An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a crack plane stress panel under several cyclic loading conditions.

An Experimental Investigation of the Effects of Vacuum Environment on the Fatigue Life, Fatigue-Crack-Growth Behavior, and Fracture Toughness of 7075-T6 Aluminum Alloy. Ph.D. Thesis - North Carolina State Univ.

NASA Technical Reports Server (NTRS)

Hudson, C. M.

1972-01-01

Axial load fatigue life, fatigue-crack propagation, and fracture toughness tests were conducted on 0.090-inch thick specimens made of 7075-T6 aluminum alloy. The fatigue life and fatigue-crack propagation experiments were conducted at a stress ratio of 0.02. Maximum stresses ranged from 33 to 60 ksi in the fatigue life experiments, and from 10 to 40 ksi in the fatigue-crack propagation experiments, and fatigue life experiments were conducted at gas pressures of 760, 0.5, 0.05, and 0.00000005 torr. Fatigue-crack-growth and fracture toughness experiments were conducted at gas pressures of 760 and 5 x 10 to the minus 8th power torr. Residual stress measurements were made on selected fatigue life specimens to determine the effect of such stresses on fatigue life. Analysis of the results from the fatigue life experiments indicated that fatigue life progressively increased as the gas pressure decreased. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue crack growth rates were approximately twice as high in air as in vacuum. Fracture toughness data showed there was essentially no difference in the fracture toughness of 7075-T6 in vacuum and in air.

The Effect of Weld Reinforcement and Post-Welding Cooling Cycles on Fatigue Strength of Butt-Welded Joints under Cyclic Tensile Loading.

PubMed

Araque, Oscar; Arzola, Nelson; Hernández, Edgar

2018-04-12

This research deals with the fatigue behavior of butt-welded joints, by considering the geometry and post-welding cooling cycles, as a result of cooling in quiet air and immersed in water. ASTM A-36 HR structural steel was used as the base metal for the shielded metal arc welding (SMAW) process with welding electrode E6013. The welding reinforcement was 1 mm and 3 mm, respectively; axial fatigue tests were carried out to determine the life and behavior in cracks propagation of the tested welded joints, mechanical characterization tests of properties in welded joints such as microhardness, Charpy impact test and metallographic analysis were carried out. The latter were used as input for the analysis by finite elements which influence the initiation and propagation of cracks and the evaluation of stress intensity factors (SIF). The latter led to obtaining the crack propagation rate and the geometric factor. The tested specimens were analyzed, by taking photographs of the cracks at its beginning in order to make a count of the marks at the origin of the crack. From the results obtained and the marks count, the fatigue crack growth rate and the influence of the cooling media on the life of the welded joint are validated, according to the experimental results. It can be concluded that the welded joints with a higher weld reinforcement have a shorter fatigue life. This is due to the stress concentration that occurs in the vicinity of the weld toe.

The Effect of Weld Reinforcement and Post-Welding Cooling Cycles on Fatigue Strength of Butt-Welded Joints under Cyclic Tensile Loading

PubMed Central

Arzola, Nelson; Hernández, Edgar

2018-01-01

This research deals with the fatigue behavior of butt-welded joints, by considering the geometry and post-welding cooling cycles, as a result of cooling in quiet air and immersed in water. ASTM A-36 HR structural steel was used as the base metal for the shielded metal arc welding (SMAW) process with welding electrode E6013. The welding reinforcement was 1 mm and 3 mm, respectively; axial fatigue tests were carried out to determine the life and behavior in cracks propagation of the tested welded joints, mechanical characterization tests of properties in welded joints such as microhardness, Charpy impact test and metallographic analysis were carried out. The latter were used as input for the analysis by finite elements which influence the initiation and propagation of cracks and the evaluation of stress intensity factors (SIF). The latter led to obtaining the crack propagation rate and the geometric factor. The tested specimens were analyzed, by taking photographs of the cracks at its beginning in order to make a count of the marks at the origin of the crack. From the results obtained and the marks count, the fatigue crack growth rate and the influence of the cooling media on the life of the welded joint are validated, according to the experimental results. It can be concluded that the welded joints with a higher weld reinforcement have a shorter fatigue life. This is due to the stress concentration that occurs in the vicinity of the weld toe. PMID:29649117

Air Vehicles Division Computational Structural Analysis Facilities Policy and Guidelines for Users

DTIC Science & Technology

2005-05-01

34 Thermal " as appropriate and the tolerance set to "default". b) Create the model geometry. c) Create the finite elements. d) Create the...linear, non-linear, dynamic, thermal , acoustic analysis. The modelling of composite materials, creep, fatigue and plasticity are also covered...perform professional, high quality finite element analysis (FEA). FE analysts from many tasks within AVD are using the facilities to conduct FEA with

Probabilistic fatigue methodology for six nines reliability

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.; Bartlett, F. D., Jr.; Elber, Wolf

1990-01-01

Fleet readiness and flight safety strongly depend on the degree of reliability that can be designed into rotorcraft flight critical components. The current U.S. Army fatigue life specification for new rotorcraft is the so-called six nines reliability, or a probability of failure of one in a million. The progress of a round robin which was established by the American Helicopter Society (AHS) Subcommittee for Fatigue and Damage Tolerance is reviewed to investigate reliability-based fatigue methodology. The participants in this cooperative effort are in the U.S. Army Aviation Systems Command (AVSCOM) and the rotorcraft industry. One phase of the joint activity examined fatigue reliability under uniquely defined conditions for which only one answer was correct. The other phases were set up to learn how the different industry methods in defining fatigue strength affected the mean fatigue life and reliability calculations. Hence, constant amplitude and spectrum fatigue test data were provided so that each participant could perform their standard fatigue life analysis. As a result of this round robin, the probabilistic logic which includes both fatigue strength and spectrum loading variability in developing a consistant reliability analysis was established. In this first study, the reliability analysis was limited to the linear cumulative damage approach. However, it is expected that superior fatigue life prediction methods will ultimately be developed through this open AHS forum. To that end, these preliminary results were useful in identifying some topics for additional study.

Damage tolerance of bonded composite aircraft repairs for metallic structures

NASA Astrophysics Data System (ADS)

Clark, Randal John

This thesis describes the development and validation of methods for damage tolerance substantiation of bonded composite repairs applied to cracked plates. This technology is used to repair metal aircraft structures, offering improvements in fatigue life, cost, manufacturability, and inspectability when compared to riveted repairs. The work focuses on the effects of plate thickness and bending on repair life, and covers fundamental aspects of fracture and fatigue of cracked plates and bonded joints. This project falls under the UBC Bonded Composite Repair Program, which has the goal of certification and widespread use of bonded repairs in civilian air transportation. This thesis analyses the plate thickness and transverse stress effects on fracture of repaired plates and the related problem of induced geometrically nonlinear bending in unbalanced (single-sided) repairs. The author begins by developing a classification scheme for assigning repair damage tolerance substantiation requirements based upon stress-based adhesive fracture/fatigue criteria and the residual strength of the original structure. The governing equations for bending of cracked plates are then reformulated and line-spring models are developed for linear and nonlinear coupled bending and extension of reinforced cracks. The line-spring models were used to correct the Wang and Rose energy method for the determination of the long-crack limit stress intensity, and to develop a new interpolation model for repaired cracks of arbitrary length. The analysis was validated using finite element models and data from mechanical tests performed on hybrid bonded joints and repair specimens that are representative of an in-service repair. This work will allow designers to evaluate the damage tolerance of the repaired plate, the adhesive, and the composite patch, which is an airworthiness requirement under FAR (Federal Aviation Regulations) 25.571. The thesis concludes by assessing the remaining barriers to certification of bonded repairs, discussing the results of the analysis, and making suggestions for future work. The developed techniques should also prove to be useful for the analysis of fibre-reinforced metal laminates and other layered structures. Some concepts are general and should be useful in the analysis of any plate with large in-plane stress gradients that lead to significant transverse stresses.

Effects of Corrosion and Fatigue on the Load-Carrying Capacity of Structural and Reinforcing Steel

DOT National Transportation Integrated Search

1994-03-01

Pitting and crevice corrosion have profound effects on the fatigue life of structural and reinforcing steels used in bridge construction. Stress concentration factors were measured on actual corroded plates with strain gage instrumentation. Using cor...

Fatigue Resistant Design Criteria for MD SHA Cantilevered Mast Arm Signal Structure : Research Summary

DOT National Transportation Integrated Search

2017-12-01

Over the past two decades, wind induced fatigue cracking of highway signs, luminaires, and traffic signal support structures have been increasingly reported all over the United States. While fatalities associated with these failures have been limited...

Fatigue impact on Mod-1 wind turbine design

NASA Technical Reports Server (NTRS)

Stahle, C. V., Jr.

1978-01-01

Fatigue is a key consideration in the design of a long-life Wind Turbine Generator (WTG) system. This paper discusses the fatigue aspects of the large Mod-1 horizontal-axis WTG design starting with the characterization of the environment and proceeding through the design. Major sources of fatigue loading are discussed and methods of limiting fatigue loading are described. NASTRAN finite element models are used to determine dynamic loading and internal cyclic stresses. Recent developments in determining the allowable fatigue stress consistent with present construction codes are discussed relative to their application to WTG structural design.

Fatigue in hospital nurses - 'Supernurse' culture is a barrier to addressing problems: A qualitative interview study.

PubMed

Steege, Linsey M; Rainbow, Jessica G

2017-02-01

Fatigue in hospital nurses is associated with decreased nurse satisfaction, increased turnover and negative patient outcomes. Addressing fatigue in nurses has been identified as a priority by many organizations worldwide in an effort to promote both a culture of patient safety and a healthy nursing workforce. The overall aim of this study was to explore barriers and facilitators within the hospital nurse work system to nurse coping and fatigue. The purpose of this paper is to describe emergent themes that offer new insight describing the relationships among nurse perceptions of fatigue, nursing professional culture, and implications for the nursing workforce. A qualitative exploratory study was used to explore nurse identified sources, barriers to addressing, and consequences of fatigue. Twenty-two nurses working in intensive care and medical-surgical units within a large academic medical center in the United States participated in the interviews. Interviews with the participants followed a semi-structured interview guide that included questions eliciting participants' views on nurse fatigue levels, consequences of fatigue, and barriers to addressing fatigue. The interview transcripts were analyzed using directed content analysis guided by the Systems Engineering Initiative for Patient Safety (SEIPS) model. Additional themes that did not directly align with the SEIPS model were also identified. All nurses in the current study experienced fatigue; yet they had varying perspectives on the importance of addressing fatigue in relation to other health systems challenges. A new construct related to nursing professional culture was identified and defined as "Supernurse". Identified subthemes of Supernurse include: extraordinary powers used for good; cloak of invulnerability; no sidekick; Kryptonite, and an alterego. These values, beliefs, and behaviors define the specific aspects of nursing professional culture that can act as barriers to fatigue risk management programs and achieving safety culture in hospital organizations. Nurse fatigue and attributes of nurse professional culture also have implications for nurse satisfaction and retention. Findings from this study further support the role of nursing professional culture as an important barrier to effectively addressing fatigue in nursing work systems. Future work is needed to identify and evaluate innovative culture change models and strategies to target these barriers. Copyright © 2016 Elsevier Ltd. All rights reserved.

Helicopter Fatigue Life Assessment

DTIC Science & Technology

1981-03-01

is made to bring together alternative statistical opinions. 1. INTRODUCTION In almost arn paper on helicopter fatigue (references 1-15) a diagram is...of fatigue life calculations. In the excercise of the A.H.S., mentioned in the introduction the ratios of fatljue life, based on a cycle counting...monitoring. I INTRODUCTION The requirements for the design of structures of United Kingdom Military aeroplanes against fatigue are contained in Aviation

Fatigue Crack Detection via Load-Differential Guided Wave Methods (Preprint)

DTIC Science & Technology

2011-11-01

AFRL-RX-WP-TP-2011-4362 FATIGUE CRACK DETECTION VIA LOAD- DIFFERENTIAL GUIDED WAVE METHODS (PREPRINT) Jennifer E. Michaels, Sang Jun Lee...November 2011 Technical Paper 1 November 2011 – 1 November 2011 4. TITLE AND SUBTITLE FATIGUE CRACK DETECTION VIA LOAD-DIFFERENTIAL GUIDED WAVE...document contains color. 14. ABSTRACT Detection of fatigue cracks originating from fastener holes is an important application for structural health

Developing the Stroke Exercise Preference Inventory (SEPI)

PubMed Central

Bonner, Nicholas S.; O’Halloran, Paul D.; Bernhardt, Julie; Cumming, Toby B.

2016-01-01

Background Physical inactivity is highly prevalent after stroke, increasing the risk of poor health outcomes including recurrent stroke. Tailoring of exercise programs to individual preferences can improve adherence, but no tools exist for this purpose in stroke. Methods We identified potential questionnaire items for establishing exercise preferences via: (i) our preliminary Exercise Preference Questionnaire in stroke, (ii) similar tools used in other conditions, and (iii) expert panel consultations. The resulting 35-item questionnaire (SEPI-35) was administered to stroke survivors, along with measures of disability, depression, anxiety, fatigue and self-reported physical activity. Exploratory factor analysis was used to identify a factor structure in exercise preferences, providing a framework for item reduction. Associations between exercise preferences and personal characteristics were analysed using multivariable regression. Results A group of 134 community-dwelling stroke survivors (mean age 64.0, SD 13.3) participated. Analysis of the SEPI-35 identified 7 exercise preference factors (Supervision-support, Confidence-challenge, Health-wellbeing, Exercise context, Home-alone, Similar others, Music-TV). Item reduction processes yielded a 13-item version (SEPI-13); in analysis of this version, the original factor structure was maintained. Lower scores on Confidence-challenge were significantly associated with disability (p = 0.002), depression (p = 0.001) and fatigue (p = 0.001). Self-reported barriers to exercise were particularly prevalent in those experiencing fatigue and anxiety. Conclusions The SEPI-13 is a brief instrument that allows assessment of exercise preferences and barriers in the stroke population. This new tool can be employed by health professionals to inform the development of individually tailored exercise interventions. PMID:27711242

Fatigue Behavior and Deformation Mechanisms in Inconel 718 Superalloy Investigated

NASA Technical Reports Server (NTRS)

2005-01-01

The nickel-base superalloy Inconel 718 (IN 718) is used as a structural material for a variety of components in the space shuttle main engine (SSME) and accounts for more than half of the total weight of this engine. IN 718 is the bill-of-material for the pressure vessels of nickel-hydrogen batteries for the space station. In the case of the space shuttle main engine, structural components are typically subjected to startup and shutdown load transients and occasional overloads in addition to high-frequency vibratory loads from routine operation. The nickel-hydrogen battery cells are prooftested before service and are subjected to fluctuating pressure loads during operation. In both of these applications, the structural material is subjected to a monotonic load initially, which is subsequently followed by fatigue. To assess the life of these structural components, it is necessary to determine the influence of a prior monotonic load on the subsequent fatigue life of the superalloy. An insight into the underlying deformation and damage mechanisms is also required to properly account for the interaction between the prior monotonic load and the subsequent fatigue loading. An experimental investigation was conducted to establish the effect of prior monotonic straining on the subsequent fatigue behavior of wrought, double-aged, IN 718 at room temperature. First, monotonic strain tests and fully-reversed, strain-controlled fatigue tests were conducted on uniform-gage-section IN 718 specimens. Next, fully reversed fatigue tests were conducted under strain control on specimens that were monotonically strained in tension. Results from this investigation indicated that prior monotonic straining reduced the fatigue resistance of the superalloy particularly at the lowest strain range. Some of the tested specimens were sectioned and examined by transmission electron microscopy to reveal typical microstructures as well as the active deformation and damage mechanisms under each of the loading conditions. In monotonically strained specimens, deformation during the subsequent fatigue loading was mainly confined to the deformation bands initiated during the prior monotonic straining. This can cause dislocations to move more readily along the previously activated deformation bands and to pile up near grain boundaries, eventually making the grain boundaries susceptible to fatigue crack initiation. The mechanisms inferred from the microstructural investigation were extremely valuable in interpreting the influence of prior monotonic straining on the subsequent fatigue life of Inconel 718 superalloy.

Fatigue design procedure for the American SST prototype

NASA Technical Reports Server (NTRS)

Doty, R. J.

1972-01-01

For supersonic airline operations, significantly higher environmental temperature is the primary new factor affecting structural service life. Methods for incorporating the influence of temperature in detailed fatigue analyses are shown along with current test indications. Thermal effects investigated include real-time compared with short-time testing, long-time temperature exposure, and stress-temperature cycle phasing. A method is presented which allows designers and stress analyzers to check fatigue resistance of structural design details. A communicative rating system is presented which defines the relative fatigue quality of the detail so that the analyst can define cyclic-load capability of the design detail by entering constant-life charts for varying detail quality. If necessary then, this system allows the designer to determine ways to improve the fatigue quality for better life or to determine the operating stresses which will provide the required service life.

Effect of Light Water Reactor Water Environments on the Fatigue Life of Reactor Materials

DOE PAGES

Chopra, O. K.; Stevens, G. L.; Tregoning, R.; ...

2017-10-06

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) provides rules for the design of Class 1 components of nuclear power plants. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify fatigue design curves for applicable structural materials. However, the Code design curves do not explicitly address the effects of light water reactor (LWR) water environments. Existing fatigue strain-vs.-life (ε-N) laboratory data illustrate potentially significant effects of LWR water environments on the fatigue resistance of pressure vessel and piping steels. Extensive studies have been conducted at Argonne National Laboratory and elsewheremore » since 1990 to investigate the effects of LWR environments on the fatigue life of piping and pressure vessel steels. This article summarizes the results of these studies. Existing fatigue ε-N data were evaluated to identify the various material, environmental, and loading conditions that influence fatigue crack initiation; a methodology for estimating fatigue lives as a function of these parameters was developed. The effects were incorporated into the ASME Code Section III fatigue evaluations in terms of an environmental correction factor, F en, which is defined as the ratio of fatigue life in air at room temperature to the fatigue life in the LWR water environment at reactor operating temperatures. Available fatigue data were used to develop fatigue design curves for carbon and low-alloy steels, austenitic stainless steels, and nickel-chromium-iron (NiCr-Fe) alloys and their weld metals in air at room temperature. A review of the Code Section III fatigue adjustment factors of 2 on strain and 20 on life is also presented and the possible conservatism inherent in the choice of these adjustment factors is evaluated. A brief description of potential effects of neutron irradiation on fatigue crack initiation for these structural materials is also presented.« less

Effect of Light Water Reactor Water Environments on the Fatigue Life of Reactor Materials

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

Chopra, O. K.; Stevens, G. L.; Tregoning, R.

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) provides rules for the design of Class 1 components of nuclear power plants. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify fatigue design curves for applicable structural materials. However, the Code design curves do not explicitly address the effects of light water reactor (LWR) water environments. Existing fatigue strain-vs.-life (ε-N) laboratory data illustrate potentially significant effects of LWR water environments on the fatigue resistance of pressure vessel and piping steels. Extensive studies have been conducted at Argonne National Laboratory and elsewheremore » since 1990 to investigate the effects of LWR environments on the fatigue life of piping and pressure vessel steels. This article summarizes the results of these studies. Existing fatigue ε-N data were evaluated to identify the various material, environmental, and loading conditions that influence fatigue crack initiation; a methodology for estimating fatigue lives as a function of these parameters was developed. The effects were incorporated into the ASME Code Section III fatigue evaluations in terms of an environmental correction factor, F en, which is defined as the ratio of fatigue life in air at room temperature to the fatigue life in the LWR water environment at reactor operating temperatures. Available fatigue data were used to develop fatigue design curves for carbon and low-alloy steels, austenitic stainless steels, and nickel-chromium-iron (NiCr-Fe) alloys and their weld metals in air at room temperature. A review of the Code Section III fatigue adjustment factors of 2 on strain and 20 on life is also presented and the possible conservatism inherent in the choice of these adjustment factors is evaluated. A brief description of potential effects of neutron irradiation on fatigue crack initiation for these structural materials is also presented.« less

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.

Low-cycle fatigue analysis of a cooled copper combustion chamber

NASA Technical Reports Server (NTRS)

Miller, R. W.

1974-01-01

A three-dimensional finite element elastoplastic strain analysis was performed for the throat section of regeneratively cooled rocket engine combustion chamber. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the engine operating cycle. The strain range was used in conjunction with OFHC copper isothermal fatigue test data to predict engine low-cycle fatigue life. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen chamber which was fatigue tested to failure at the NASA Lewis Research Center.

Neural basis of exertional fatigue in the heat: A review of magnetic resonance imaging methods.

PubMed

Tan, X R; Low, I C C; Stephenson, M C; Soong, T W; Lee, J K W

2018-03-01

The central nervous system, specifically the brain, is implicated in the development of exertional fatigue under a hot environment. Diverse neuroimaging techniques have been used to visualize the brain activity during or after exercise. Notably, the use of magnetic resonance imaging (MRI) has become prevalent due to its excellent spatial resolution and versatility. This review evaluates the significance and limitations of various brain MRI techniques in exercise studies-brain volumetric analysis, functional MRI, functional connectivity MRI, and arterial spin labeling. The review aims to provide a summary on the neural basis of exertional fatigue and proposes future directions for brain MRI studies. A systematic literature search was performed where a total of thirty-seven brain MRI studies associated with exercise, fatigue, or related physiological factors were reviewed. The findings suggest that with moderate dehydration, there is a decrease in total brain volume accompanied with expansion of ventricular volume. With exercise fatigue, there is increased activation of sensorimotor and cognitive brain areas, increased thalamo-insular activation and decreased interhemispheric connectivity in motor cortex. Under passive hyperthermia, there are regional changes in cerebral perfusion, a reduction in local connectivity in functional brain networks and an impairment to executive function. Current literature suggests that the brain structure and function are influenced by exercise, fatigue, and related physiological perturbations. However, there is still a dearth of knowledge and it is hoped that through understanding of MRI advantages and limitations, future studies will shed light on the central origin of exertional fatigue in the heat. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Construct validity of the Swedish version of the revised piper fatigue scale in an oncology sample--a Rasch analysis.

PubMed

Lundgren-Nilsson, Asa; Dencker, Anna; Jakobsson, Sofie; Taft, Charles; Tennant, Alan

2014-06-01

Fatigue is a common and distressing symptom in cancer patients due to both the disease and its treatments. The concept of fatigue is multidimensional and includes both physical and mental components. The 22-item Revised Piper Fatigue Scale (RPFS) is a multidimensional instrument developed to assess cancer-related fatigue. This study reports on the construct validity of the Swedish version of the RPFS from the perspective of Rasch measurement. The Swedish version of the RPFS was answered by 196 cancer patients fatigued after 4 to 5 weeks of curative radiation therapy. Data from the scale were fitted to the Rasch measurement model. This involved testing a series of assumptions, including the stochastic ordering of items, local response dependency, and unidimensionality. A series of fit statistics were computed, differential item functioning (DIF) was tested, and local response dependency was accommodated through testlets. The Behavioral, Affective and Sensory domains all satisfied the Rasch model expectations. No DIF was observed, and all domains were found to be unidimensional. The Mood/Cognitive scale failed to fit the model, and substantial multidimensionality was found. Splitting the scale between Mood and Cognitive items resolved fit to the Rasch model, and new domains were unidimensional without DIF. The current Rasch analyses add to the evidence of measurement properties of the scale and show that the RPFS has good psychometric properties and works well to measure fatigue. The original four-factor structure, however, was not supported. Copyright © 2014 International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc. All rights reserved.

Brainstem dose is associated with patient-reported acute fatigue in head and neck cancer radiation therapy.

PubMed

Ferris, Matthew J; Zhong, Jim; Switchenko, Jeffrey M; Higgins, Kristin A; Cassidy, Richard J; McDonald, Mark W; Eaton, Bree R; Patel, Kirtesh R; Steuer, Conor E; Baddour, H Michael; Miller, Andrew H; Bruner, Deborah W; Xiao, Canhua; Beitler, Jonathan J

2018-01-01

Radiation (RT) dose to the central nervous system (CNS) has been implicated as a contributor to treatment-related fatigue in head and neck cancer (HNC) patients undergoing radiation therapy (RT). This study evaluates the association of RT dose to CNS structures with patient-reported (PRO) fatigue scores in a population of HNC patients. At pre-RT (baseline), 6th week of RT, and 1-month post-RT time points, Multidimensional Fatigue Inventory (MFI-20) scores were prospectively obtained from 124 patients undergoing definitive treatment for HNC. Medulla, pons, midbrain, total brainstem, cerebellum, posterior fossa, and pituitary dosimetry were evaluated using summary statistics and dose-volume histograms, and associations with MFI-20 scores were analyzed. Maximum dose (Dmax) to the brainstem and medulla was significantly associated with MFI-20 scores at 6th week of RT and 1-month post-RT time points, after controlling for baseline scores (p<0.05). Each 1Gy increase in medulla Dmax resulted in an increase in total MFI-20 score over baseline of 0.30 (p=0.026), and 0.25 (p=0.037), at the 6th week of RT and 1-month post-RT, respectively. Each 1Gy increase in brainstem Dmax resulted in an increase in total MFI-20 score over baseline of 0.30 (p=0.027), and 0.25 (p=0.037) at the 6th week of RT, 1-month post-RT, respectively. Statistically significant associations were not found between dosimetry for the other CNS structures and MFI-20 scores. In this analysis of PRO fatigue scores from a population of patients undergoing definitive RT for HNC, maximum dose to the brainstem and medulla was associated with a significantly increased risk of acute patient fatigue. Copyright © 2017 Elsevier B.V. All rights reserved.

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.

Recent and Future Enhancements in NDI for Aircraft Structures

DTIC Science & Technology

2015-09-10

1]. Four of the B-47 losses were attributed to fatigue , which led to a probabilistic approach for establishing the aircraft service life...sufficient to preclude in-service structural failures attributable to fatigue . The safe- life approach was the basis for all new designs during the 1960s...and was also used to establish the safe-life of earlier designs that were subjected to a fatigue test. Losses of an F-111 in December 1969 and an F-5

Recent and Future Enhancements in NDI for Aircraft Structures (Postprint)

DTIC Science & Technology

2015-09-10

1]. Four of the B-47 losses were attributed to fatigue , which led to a probabilistic approach for establishing the aircraft service life...sufficient to preclude in-service structural failures attributable to fatigue . The safe- life approach was the basis for all new designs during the 1960s...and was also used to establish the safe-life of earlier designs that were subjected to a fatigue test. Losses of an F-111 in December 1969 and an F-5

RECENT AND FUTURE ENHANCEMENTS IN NDI FOR AIRCRAFT STRUCTURES POSTPRINT

DTIC Science & Technology

2015-09-10

1]. Four of the B-47 losses were attributed to fatigue , which led to a probabilistic approach for establishing the aircraft service life...sufficient to preclude in-service structural failures attributable to fatigue . The safe- life approach was the basis for all new designs during the 1960s...and was also used to establish the safe-life of earlier designs that were subjected to a fatigue test. Losses of an F-111 in December 1969 and an F-5

Recent and Future Enhancements in NDI for Aircraft Structures (Postprint)

DTIC Science & Technology

2015-11-01

1]. Four of the B-47 losses were attributed to fatigue , which led to a probabilistic approach for establishing the aircraft service life...sufficient to preclude in-service structural failures attributable to fatigue . The safe- life approach was the basis for all new designs during the 1960s...and was also used to establish the safe-life of earlier designs that were subjected to a fatigue test. Losses of an F-111 in December 1969 and an F-5

RECENT AND FUTURE ENHANCEMENTS IN NDI FOR AIRCRAFT STRUCTURES (POSTPRINT)

DTIC Science & Technology

2015-09-10

1]. Four of the B-47 losses were attributed to fatigue , which led to a probabilistic approach for establishing the aircraft service life...sufficient to preclude in-service structural failures attributable to fatigue . The safe- life approach was the basis for all new designs during the 1960s...and was also used to establish the safe-life of earlier designs that were subjected to a fatigue test. Losses of an F-111 in December 1969 and an F-5

Fatigue Technology Assessment and Strategies for Fatigue Avoidance in Marine Structures

DTIC Science & Technology

1992-06-01

time history. xii MODELING ERROR (Xme) : Typically defined as the ratio of actual behavior of the structure to the one predicted by the model. It is...and temperature changes may be important to fatigue in a local component, these loadings are not a major concern in the global behavior of typical...Reference 3.1) to assess fracture behavior in a low toughness HAZ indicated that a small low- toughness area in the HAZ can be masked by the higher

Fatigue life prediction of bonded primary joints

NASA Technical Reports Server (NTRS)

Knauss, J. F.

1979-01-01

The validation of a proposed fatigue life prediction methodology was sought through the use of aluminum butt and scarf joint and graphite/epoxy butt joint specimens in a constant amplitude fatigue environment. The structural properties of the HYSOL 9313 adhesive system were obtained by mechanical test of molded heat adhesive specimens. Aluminum contoured double cantilever beam specimens were used to generate crack velocity versus stress intensity factor data. The specific objectives were: (1) to ascertain the feasibility of predicting fatigue failure of an adhesive in a primary bonded composite structure by incorporating linear elastic crack growth behavior; and (2) to ascertain if acoustic emission and/or compliance measurement techniques can be used to detect flaws.

Finite element analysis of container ship's cargo hold using ANSYS and POSEIDON software

NASA Astrophysics Data System (ADS)

Tanny, Tania Tamiz; Akter, Naznin; Amin, Osman Md.

2017-12-01

Nowadays ship structural analysis has become an integral part of the preliminary ship design providing further support for the development and detail design of ship structures. Structural analyses of container ship's cargo holds are carried out for the balancing of their safety and capacity, as those ships are exposed to the high risk of structural damage during voyage. Two different design methodologies have been considered for the structural analysis of a container ship's cargo hold. One is rule-based methodology and the other is a more conventional software based analyses. The rule based analysis is done by DNV-GL's software POSEIDON and the conventional package based analysis is done by ANSYS structural module. Both methods have been applied to analyze some of the mechanical properties of the model such as total deformation, stress-strain distribution, Von Mises stress, Fatigue etc., following different design bases and approaches, to indicate some guidance's for further improvements in ship structural design.

Fatigue Is Associated With Global and Regional Thalamic Morphometry in Veterans With a History of Mild Traumatic Brain Injury.

PubMed

Clark, Alexandra L; Sorg, Scott F; Holiday, Kelsey; Bigler, Erin D; Bangen, Katherine J; Evangelista, Nicole D; Bondi, Mark W; Schiehser, Dawn M; Delano-Wood, Lisa

2018-01-30

Fatigue is a complex, multidimensional phenomenon that commonly occurs following traumatic brain injury (TBI). The thalamus-a structure vulnerable to both primary and secondary injuries in TBI-is thought to play a pivotal role in the manifestation of fatigue. We explored how neuroimaging markers of local and global thalamic morphometry relate to the subjective experience of fatigue post-TBI. Sixty-three Veterans with a history of mild TBI underwent structural magnetic resonance imaging and completed questionnaires related to fatigue and psychiatric symptoms. FMRIB's Software (FSL) was utilized to obtain whole brain and thalamic volume estimates, as well as to perform regional thalamic morphometry analyses. Independent of age, sex, intracranial volume, posttraumatic stress disorder, and depressive symptoms, greater levels of self-reported fatigue were significantly associated with decreased right (P = .026) and left (P = .046) thalamic volumes. Regional morphometry analyses revealed that fatigue was significantly associated with reductions in the anterior and dorsomedial aspects of the right thalamic body (P < .05). Similar trends were observed for the left thalamic body (P < .10). Both global and regional thalamic morphometric changes are associated with the subjective experience of fatigue in Veterans with a history of mild TBI. These findings support a theory in which disruption of thalamocorticostriatal circuitry may result in the manifestation of fatigue in individuals with a history of neurotrauma.

Relationship between unit cell type and porosity and the fatigue behavior of selective laser melted meta-biomaterials.

PubMed

Amin Yavari, S; Ahmadi, S M; Wauthle, R; Pouran, B; Schrooten, J; Weinans, H; Zadpoor, A A

2015-03-01

Meta-materials are structures when their small-scale properties are considered, but behave as materials when their homogenized macroscopic properties are studied. There is an intimate relationship between the design of the small-scale structure and the homogenized properties of such materials. In this article, we studied that relationship for meta-biomaterials that are aimed for biomedical applications, otherwise known as meta-biomaterials. Selective laser melted porous titanium (Ti6Al4V ELI) structures were manufactured based on three different types of repeating unit cells, namely cube, diamond, and truncated cuboctahedron, and with different porosities. The morphological features, static mechanical properties, and fatigue behavior of the porous biomaterials were studied with a focus on their fatigue behavior. It was observed that, in addition to static mechanical properties, the fatigue properties of the porous biomaterials are highly dependent on the type of unit cell as well as on porosity. None of the porous structures based on the cube unit cell failed after 10(6) loading cycles even when the applied stress reached 80% of their yield strengths. For both other unit cells, higher porosities resulted in shorter fatigue lives for the same level of applied stress. When normalized with respect to their yield stresses, the S-N data points of structures with different porosities very well (R(2)>0.8) conformed to one single power law specific to the type of the unit cell. For the same level of normalized applied stress, the truncated cuboctahedron unit cell resulted in a longer fatigue life as compared to the diamond unit cell. In a similar comparison, the fatigue lives of the porous structures based on both truncated cuboctahedron and diamond unit cells were longer than that of the porous structures based on the rhombic dodecahedron unit cell (determined in a previous study). The data presented in this study could serve as a basis for design of porous biomaterials as well as for corroboration of relevant analytical and computational models. Copyright © 2014 Elsevier Ltd. All rights reserved.

Methods of Collection of Biological Information for Fatigue Evaluation during Visual Display Terminals (VDT) Operation

NASA Astrophysics Data System (ADS)

Hachiya, Yuriko; Ogai, Harutoshi; Okazaki, Hiroko; Fujisaki, Takeshi; Uchida, Kazuhiko; Oda, Susumu; Wada, Futoshi; Mori, Koji

A method for the analysis of fatigue parameters has been rarely researched in VDT operation. Up to now, fatigue was evaluated by changing of biological information. If signals regarding fatigue are detected, fatigue can be measured. The purpose of this study proposed experiment and analysis method to extract parameters related to fatigue from the biological information during VDT operation using the Independent Component Analysis (ICA). An experiment had 11 subjects. As for the experiment were light loaded VDT operation and heavy loaded VDT operation. A measurement item were amount of work, a mistake number, subjective symptom, surface skin temperature (forehead and apex nasi), heart rate, skin blood flow of forearm and respiratory rate. In the heavy loaded operation group, mistake number and subjective symptom score were increased to compare with the other. And Two-factor ANOVA was used for analysis. The result of mistake number was confirmed that heavy loaded. After the moving averages of waveshape were calculated, it was made to extract independent components by using the ICA. The results of the ICA suggest that the independent components increase according to accumulation of fatigue. Thus, the independent components would be a possible parameter of fatigue. However, further experiments should continue in order to obtain the conclusive finding of our research.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a “sandwich structure” as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50–55% of ultimate tensile strength). The dynamic modulus (E⁎) was found to stay almost constant at 47 GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials.

Acoustic fatigue: Overview of activities at NASA Langley

NASA Technical Reports Server (NTRS)

Mixson, John S.; Roussos, Louis A.

1987-01-01

A number of aircraft and spacecraft configurations are being considered for future development. These include high-speed turboprop aircraft, advanced vertical take-off and landing fighter aircraft, and aerospace planes for hypersonic intercontinental cruise or flight to orbit and return. Review of the acoustic environment expected for these vehicles indicates levels high enough that acoustic fatigue must be considered. Unfortunately, the sonic fatique design technology used for current aircraft may not be adequate for these future vehicles. This has resulted in renewed emphasis on acoustic fatigue research at the NASA Langley Research Center. The overall objective of the Langley program is to develop methods and information for design of aerospace vehicles that will resist acoustic fatigue. The program includes definition of the acoustic loads acting on structures due to exhaust jets of boundary layers, and subsequent determination of the stresses within the structure due to these acoustic loads. Material fatigue associated with the high frequency structural stress reversal patterns resulting from acoustic loadings is considered to be an area requiring study, but no activity is currently underway.

Analyzing Aeroelasticity in Turbomachines

NASA Technical Reports Server (NTRS)

Reddy, T. S. R.; Srivastava, R.

2003-01-01

ASTROP2-LE is a computer program that predicts flutter and forced responses of blades, vanes, and other components of such turbomachines as fans, compressors, and turbines. ASTROP2-LE is based on the ASTROP2 program, developed previously for analysis of stability of turbomachinery components. In developing ASTROP2- LE, ASTROP2 was modified to include a capability for modeling forced responses. The program was also modified to add a capability for analysis of aeroelasticity with mistuning and unsteady aerodynamic solutions from another program, LINFLX2D, that solves the linearized Euler equations of unsteady two-dimensional flow. Using LINFLX2D to calculate unsteady aerodynamic loads, it is possible to analyze effects of transonic flow on flutter and forced response. ASTROP2-LE can be used to analyze subsonic, transonic, and supersonic aerodynamics and structural mistuning for rotors with blades of differing structural properties. It calculates the aerodynamic damping of a blade system operating in airflow so that stability can be assessed. The code also predicts the magnitudes and frequencies of the unsteady aerodynamic forces on the airfoils of a blade row from incoming wakes. This information can be used in high-cycle fatigue analysis to predict the fatigue lives of the blades.

An engineering approach to the prediction of fatigue behavior of unnotched/notched fiber reinforced composite laminates

NASA Technical Reports Server (NTRS)

Kulkarni, S. V.; Mclaughlin, P. V., Jr.

1978-01-01

An engineering approach is proposed for predicting unnotched/notched laminate fatigue behavior from basic lamina fatigue data. The fatigue analysis procedure was used to determine the laminate property (strength/stiffness) degradation as a function of fatigue cycles in uniaxial tension and in plane shear. These properties were then introduced into the failure model for a notched laminate to obtain damage growth, residual strength, and failure mode. The approach is thus essentially a combination of the cumulative damage accumulation (akin to the Miner-Palmgren hypothesis and its derivatives) and the damage growth rate (similar to the fracture mechanics approach) philosophies. An analysis/experiment correlation appears to confirm the basic postulates of material wearout and the predictability of laminate fatigue properties from lamina fatigue data.

Nondestructive Evaluation of Metal Fatigue Using Nonlinear Acoustics

NASA Technical Reports Server (NTRS)

Cantrell, John H., Jr.

2008-01-01

Safe-life and damage-tolerant design philosophies of high performance structures have driven the development of various methods to evaluate nondestructively the accumulation of damage in such structures resulting from cyclic loading. Although many techniques have proven useful, none has been able to provide an unambiguous, quantitative assessment of damage accumulation at each stage of fatigue from the virgin state to fracture. A method based on nonlinear acoustics is shown to provide such a means to assess the state of metal fatigue. The salient features of an analytical model are presented of the microelastic-plastic nonlinearities resulting from the interaction of an acoustic wave with fatigue-generated dislocation substructures and cracks that predictably evolve during the metal fatigue process. The interaction is quantified by the material (acoustic) nonlinearity parameter extracted from acoustic harmonic generation measurements. The parameters typically increase monotonically by several hundred percent over the fatigue life of the metal, thus providing a unique measure of the state of fatigue. Application of the model to aluminum alloy 2024-T4, 410Cb stainless steel, and IN100 nickel-base superalloy specimens fatigued using different loading conditions yields good agreement between theory and experiment. Application of the model and measurement technique to the on-site inspection of steam turbine blades is discussed.

Exploring nurse leader fatigue: a mixed methods study.

PubMed

Steege, Linsey M; Pinekenstein, Barbara J; Arsenault Knudsen, Élise; Rainbow, Jessica G

2017-05-01

To describe hospital nurse leaders' experiences of fatigue. Fatigue is a critical challenge in nursing. Existing literature focuses on staff nurse fatigue, yet nurse leaders are exposed to high demands that may contribute to fatigue and associated risks to patient, nurse and organisational outcomes. A mixed method approach comprising semi-structured interviews and the Occupational Fatigue Exhaustion Recovery scale with 21 nurse administrators (10 nurse managers and 11 nurse executives) from hospitals in a Midwestern state. Most nurse leaders experience fatigue; nurse managers reported higher levels of chronic fatigue. Participants identified multiple sources of fatigue including 24 h accountability and intensity of role expectations, and used a combination of wellness, restorative, social support and boundary setting strategies to cope with fatigue. The consequences of nurse leader fatigue include an impact on decision-making, work-life balance and turnover intent. The high prevalence of nurse leader fatigue could impact the turnover intent of nurse administrators and quality of care. This study highlights the significance and consequences of nurse leader fatigue. As health care organisations continue to raise awareness and establish systems to reduce nurse fatigue, policies and programmes must be adapted to address nurse leader fatigue. © 2017 John Wiley & Sons Ltd.

Sleep Disturbance, Daytime Symptoms, and Functional Performance in Patients With Stable Heart Failure: A Mediation Analysis.

PubMed

Jeon, Sangchoon; Redeker, Nancy S

2016-01-01

Sleep disturbance is common among patients with heart failure (HF) who also experience symptom burden and poor functional performance. We evaluated the extent to which sleep-related, daytime symptoms (fatigue, excessive daytime sleepiness, and depressive symptoms) mediate the relationship between sleep disturbance and functional performance among patients with stable HF. We recruited patients with stable HF for this secondary analysis of data from a cross-sectional, observational study. Participants completed unattended ambulatory polysomnography from which the Respiratory Disturbance Index was calculated, along with a Six-Minute Walk Test, questionnaires to elicit sleep disturbance (Pittsburgh Sleep Quality Index, Insomnia Symptoms from the Sleep Habits Questionnaire), daytime symptoms (Center for Epidemiologic Studies Depression Scale, Global Fatigue Index, Epworth Sleepiness Scale), and self-reported functional performance (Medical Outcomes Study SF36 V2 Physical Function Scale). We used structural equation modeling with latent variables for the key analysis. Follow-up, exploratory regression analysis with bootstrapped samples was used to examine the extent to which individual daytime symptoms mediated effects of sleep disturbance on functional performance after controlling for clinical and demographic covariates. The sample included 173 New York Heart Association Class I-IV HF patients (n = 60/34.7% women; M = 60.7, SD = 16.07 years of age). Daytime symptoms mediated the relationship between sleep disturbance and functional performance. Fatigue and depression mediated the relationship between insomnia symptoms and self-reported functional performance, whereas fatigue and sleepiness mediated the relationship between sleep quality and functional performance. Sleepiness mediated the relationship between the respiratory index and self-reported functional performance only in people who did not report insomnia. Daytime symptoms explain the relationships between sleep disturbance and functional performance in stable HF.

A study of fatigue and fracture in 7075-T6 aluminum alloy in vacuum and air environments

NASA Technical Reports Server (NTRS)

Hudson, C. M.

1973-01-01

Axial load fatigue life, fatigue-crack propagation, and fracture toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at pressures ranging from atmospheric to 5 x 10 to the minus 8th torr. Analysis of the results from the fatigue life experiments indicated that for a given stress level, lower air pressures produced longer fatigue lives. At a pressure of 5 x 10 to the minus 8th torr fatigue lives were 15 or more times as long as at atmospheric pressure. Analysis of the results from the fatigue crack propagation experiments indicated that for small stress intensity factor ranges the fatigue crack propagation rates were up to twice as high at atmospheric pressure as in vacuum. The fracture toughness of 7075-T6 was unaffected by the vacuum environment. Fractographic examination showed that specimens tested in both vacuum and air developed fatigue striations. Considerably more striations developed on specimens tested at atmospheric pressure, however.

New optomechanical approach to quantitative characterization of fatigue behavior of dynamically loaded structures

NASA Astrophysics Data System (ADS)

Furlong, Cosme; Pryputniewicz, Ryszard J.

1995-06-01

The basic relationships between stress and strain under cyclic conditions of loading are not at present well understood. It would seem that information of this type is vital for a fundamental approach to understand the fatigue behavior of dynamically loaded structures. In this paper, experimental and computational methods are utilized to study the fatigue behavior of a thin aluminum cantilever plate subjected to dynamic loading. The studies are performed by combining optomechanical and finite element methods. The cantilever plate is loaded periodically by excitation set at a fixed amplitude and at a specific resonance frequency of the plate. By continuously applying this type of loading and using holographic interferometry, the behavior of the plate during a specific period of time is investigated. Quantitative information is obtained from laser vibrometry data which are utilized by a finite element program to calculate strains and stresses assuming a homogeneous and isotropic material and constant strain elements. It is shown that the use of experimental and computational hybrid methodologies allows identification of different zones of the plate that are fatigue critical. This optomechanical approach proves to be a viable tool for understanding of fatigue behavior of mechanical components and for performing optimization of structures subjected to fatigue conditions.

Effects of bio-functionalizing surface treatments on the mechanical behavior of open porous titanium biomaterials.

PubMed

Amin Yavari, S; Ahmadi, S M; van der Stok, J; Wauthle, R; Riemslag, A C; Janssen, M; Schrooten, J; Weinans, H; Zadpoor, A A

2014-08-01

Bio-functionalizing surface treatments are often applied for improving the bioactivity of biomaterials that are based on otherwise bioinert titanium alloys. When applied on highly porous titanium alloy structures intended for orthopedic bone regeneration purposes, such surface treatments could significantly change the static and fatigue properties of these structures and, thus, affect the application of the biomaterial as bone substitute. Therefore, the interplay between biofunctionalizing surface treatments and mechanical behavior needs to be controlled. In this paper, we studied the effects of two bio-functionalizing surface treatments, namely alkali-acid heat treatment (AlAcH) and acid-alkali (AcAl), on the static and fatigue properties of three different highly porous titanium alloy implants manufactured using selective laser melting. It was found that AlAcH treatment results in minimal mass loss. The static and fatigue properties of AlAcH specimens were therefore not much different from as-manufactured (AsM) specimens. In contrast, AcAl resulted in substantial mass loss and also in significantly less static and fatigue properties particularly for porous structures with the highest porosity. The ratio of the static mechanical properties of AcAl specimens to that of AsM specimen was in the range of 1.5-6. The fatigue lives of AcAl specimens were much more severely affected by the applied surface treatments with fatigue lives up to 23 times smaller than that of AsM specimens particularly for the porous structures with the highest porosity. In conclusion, the fatigue properties of surface treated porous titanium are dependent not only on the type of applied surface treatment but also on the porosity of the biomaterial. Copyright © 2014 Elsevier Ltd. All rights reserved.

77 FR 60167 - Agency Information Collection Activities: Requests for Comments; Clearance of Renewed Approval of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-02

... and Fatigue Evaluation of Composite Rotorcraft Structures AGENCY: Federal Aviation Administration (FAA... Control Number: 2120-0753. Title: Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft... technology for composite rotorcraft structures. In order to show compliance and obtain type certification...

Combining Passive Thermography and Acoustic Emission for Large Area Fatigue Damage Growth Assessment of a Composite Structure

NASA Technical Reports Server (NTRS)

Zalameda, Joseph N.; Horne, Michael R.; Madaras, Eric I.; Burke, Eric R.

2016-01-01

Passive thermography and acoustic emission data were obtained for improved real time damage detection during fatigue loading. A strong positive correlation was demonstrated between acoustic energy event location and thermal heating, especially if the structure under load was nearing ultimate failure. An image processing routine was developed to map the acoustic emission data onto the thermal imagery. This required removing optical barrel distortion and angular rotation from the thermal data. The acoustic emission data were then mapped onto thermal data, revealing the cluster of acoustic emission event locations around the thermal signatures of interest. By combining both techniques, progression of damage growth is confirmed and areas of failure are identified. This technology provides improved real time inspections of advanced composite structures during fatigue testing.Keywords: Thermal nondestructive evaluation, fatigue damage detection, aerospace composite inspection, acoustic emission, passive thermography

Influence of the creep ageing process on the fatigue properties of components from V95pchT2 (analog 7175T76) and V95ochT2 (analog 7475) aluminium alloys

NASA Astrophysics Data System (ADS)

Larichkin, A.; Zakharchenko, K.; Gorev, B.; Kapustin, V.; Maksimovskiy, E.

2017-10-01

Influence of conditions of technological process of forming thick panels of a given geometry on fatigue limit of flat specimens from the V95ochT2 and V95pchT2 (analogues 7475 and 7175T76) alloys (Al-Mg-Cu-Zn) has been analysed. The process has been simulated experimentally on flat samples for temperatures 20, 165 and 420°C. The process includes: non-elastic strain in the range 10-5 - 10-2 s-1 up to 2% of total strain, followed by heat treatment according to T2 mode (quenching and aging). Fatigue life tests were carried out both on solid samples and on samples with a hole. It has been shown that resistance to fatigue of the observed alloys after forming at the annealing temperature (420°C) is comparable to the basic material resistance to fatigue. Meso-structure analysis showed absence of stress in grains. It is established that, on average, the shape of the grains is the same for a series of samples for different temperatures and loading rates. The results of testing samples with a hole showed that fatigue limit slightly decreases in samples which were previously deformed at (420°C), with respect to the durability of samples from the material in basic state. With an increase in rate of pre-strain, the relative number of cycles before destruction occurs increased.

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

Code of Federal Regulations, 2014 CFR

2014-01-01

... evaluation of commuter category airplanes. 23.574 Section 23.574 Aeronautics and Space FEDERAL AVIATION... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category airplanes. For commuter category airplanes— (a) Metallic damage tolerance. An...

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

Code of Federal Regulations, 2012 CFR

2012-01-01

... evaluation of commuter category airplanes. 23.574 Section 23.574 Aeronautics and Space FEDERAL AVIATION... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category airplanes. For commuter category airplanes— (a) Metallic damage tolerance. An...

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

Code of Federal Regulations, 2013 CFR

2013-01-01

... evaluation of commuter category airplanes. 23.574 Section 23.574 Aeronautics and Space FEDERAL AVIATION... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category airplanes. For commuter category airplanes— (a) Metallic damage tolerance. An...

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

Code of Federal Regulations, 2011 CFR

2011-01-01

... evaluation of commuter category airplanes. 23.574 Section 23.574 Aeronautics and Space FEDERAL AVIATION... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category airplanes. For commuter category airplanes— (a) Metallic damage tolerance. An...

14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

Code of Federal Regulations, 2010 CFR

2010-01-01

... evaluation of commuter category airplanes. 23.574 Section 23.574 Aeronautics and Space FEDERAL AVIATION... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue evaluation of commuter category airplanes. For commuter category airplanes— (a) Metallic damage tolerance. An...

Multidimensional daily diary of fatigue-fibromyalgia-17 items (MDF-fibro-17). part 1: development and content validity.

PubMed

Morris, S; Li, Y; Smith, J A M; Dube', S; Burbridge, C; Symonds, T

2017-05-16

Fibromyalgia (FM), a disorder characterized by chronic widespread pain and tenderness, affects greater than five million individuals in the United States alone. Patients experience multiple symptoms in addition to pain, and among them, fatigue is one of the most bothersome and disabling. There is a growing body of literature suggesting that fatigue is a multidimensional concept. Currently, to our knowledge, no multidimensional Patient Reported Outcome (PRO) measure of FM-related fatigue meets Food and Drug Administration (FDA) requirements to support a product label claim. Therefore, the objective of this research was to evaluate qualitative and quantitative data previously gathered to inform the development of a comprehensive, multidimensional, PRO measure to assess FM-related fatigue in FM clinical trials. Existing qualitative and quantitative data from three previously conducted studies in patients with FM were reviewed to inform the initial development of a multidimensional PRO measure of FM-related fatigue: 1) a concept elicitation study involving in-depth, open-ended interviews with patients with FM in the United States (US) (N = 20), Germany (N = 10), and France (N = 10); 2) a cognitive debriefing and pilot study of a preliminary pool of 23 items (N = 20 US patients with FM); and 3) a methodology study that explored initial psychometrics of the item pool (N = 145 US patients with FM). Five domains were identified that intend to capture the broad experience of FM-related fatigue reported in the qualitative research: the Global Fatigue Experience, Cognitive Fatigue, Physical Fatigue, Motivation, and Impact on Function. Seventeen of the original pool of 23 items were selected to best capture these five dimensions. These 17 items formed the basis of a newly developed multidimensional PRO measure to assess FM-related fatigue in clinical trials: the Multidimensional Daily Diary of Fatigue-Fibromyalgia-17 (MDF-Fibro-17). Qualitative analysis, and preliminary quantitative item level data, confirmed that FM-related fatigue is multidimensional and provided strong support for the content validity of the MDF-Fibro-17. The next stage was to quantitatively evaluate the measure to confirm the factor structure, psychometric properties, sensitivity to change, and meaningful change. This has been conducted and is being reported separately.

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.

A possible genetic association with chronic fatigue in primary Sjögren's syndrome: a candidate gene study.

PubMed

Norheim, Katrine Brække; Le Hellard, Stephanie; Nordmark, Gunnel; Harboe, Erna; Gøransson, Lasse; Brun, Johan G; Wahren-Herlenius, Marie; Jonsson, Roland; Omdal, Roald

2014-02-01

Fatigue is prevalent and disabling in primary Sjögren's syndrome (pSS). Results from studies in chronic fatigue syndrome (CFS) indicate that genetic variation may influence fatigue. The aim of this study was to investigate single nucleotide polymorphism (SNP) variations in pSS patients with high and low fatigue. A panel of 85 SNPs in 12 genes was selected based on previous studies in CFS. A total of 207 pSS patients and 376 healthy controls were genotyped. One-hundred and ninety-three patients and 70 SNPs in 11 genes were available for analysis after quality control. Patients were dichotomized based on fatigue visual analogue scale (VAS) scores, with VAS <50 denominated "low fatigue" (n = 53) and VAS ≥50 denominated "high fatigue" (n = 140). We detected signals of association with pSS for one SNP in SLC25A40 (unadjusted p = 0.007) and two SNPs in PKN1 (both p = 0.03) in our pSS case versus control analysis. The association with SLC25A40 was stronger when only pSS high fatigue patients were analysed versus controls (p = 0.002). One SNP in PKN1 displayed an association in the case-only analysis of pSS high fatigue versus pSS low fatigue (p = 0.005). This candidate gene study in pSS did reveal a trend for associations between genetic variation in candidate genes and fatigue. The results will need to be replicated. More research on genetic associations with fatigue is warranted, and future trials should include larger cohorts and multicentre collaborations with sharing of genetic material to increase the statistical power.

Fatigue behavior of thin-walled grade 2 titanium samples processed by selective laser melting. Application to life prediction of porous titanium implants.

PubMed

Lipinski, P; Barbas, A; Bonnet, A-S

2013-12-01

Because of its biocompatibility and high mechanical properties, the commercially pure grade 2 titanium (CPG2Ti) is largely used for fabrication of patient specific implants or hard tissue substitutes with complex shape. To avoid the stress-shielding and help their colonization by bone, prostheses with a controlled porosity are designed. The selective laser melting (SLM) is well adapted to manufacture such geometrically complicated structures constituted by struts with rough surfaces and relatively small diameters. Few studies were dedicated to characterize the fatigue properties of SLM processed samples and bulk parts. They followed conventional or standard protocols. The fatigue behavior of standard samples is very different from the one of porous raw structures. In this study, the SLM made "as built" (AB) and "heat treated" (HT) tubular samples were tested in fatigue. Wöhler curves were determined in both cases. The obtained endurance limits were equal to σD(AB)=74.5MPa and σD(HT)=65.7MPa, respectively. The heat treatment worsened the endurance limit by relaxation of negative residual stresses measured on the external surface of the samples. Modified Goodman diagram was established for raw specimens. Porous samples, based on the pattern developed by Barbas et al. (2012), were manufactured by SLM. Fatigue tests and finite element simulations performed on these samples enabled the determination of a simple rule of fatigue assessment. The method based on the stress gradient appeared as the best approach to take into account the notch influence on the fatigue life of CPG2Ti structures with a controlled porosity. The direction dependent apparent fatigue strength was found. A criterion based on the effective, or global, nominal stress was proposed taking into account the anisotropy of the porous structures. Thanks to this criterion, the usual calculation methods can be used to design bone substitutes, without a precise modelling of their internal fine porosity. © 2013 Elsevier Ltd. All rights reserved.

Crack propagation modelling for high strength steel welded structural details

NASA Astrophysics Data System (ADS)

Mecséri, B. J.; Kövesdi, B.

2017-05-01

Nowadays the barrier of applying HSS (High Strength Steel) material in bridge structures is their low fatigue strength related to yield strength. This paper focuses on the fatigue behaviour of a structural details (a gusset plate connection) made from NSS and HSS material, which is frequently used in bridges in Hungary. An experimental research program is carried out at the Budapest University of Technology and Economics to investigate the fatigue lifetime of this structural detail type through the same test specimens made from S235 and S420 steel grades. The main aim of the experimental research program is to study the differences in the crack propagation and the fatigue lifetime between normal and high strength steel structures. Based on the observed fatigue crack pattern the main direction and velocity of the crack propagation is determined. In parallel to the tests finite element model (FEM) are also developed, which model can handle the crack propagation. Using the measured strain data in the tests and the calculated values from the FE model, the approximation of the material parameters of the Paris law are calculated step-by-step, and their calculated values are evaluated. The same material properties are determined for NSS and also for HSS specimens as well, and the differences are discussed. In the current paper, the results of the experiments, the calculation method of the material parameters and the calculated values are introduced.

The Piper Fatigue Scale-12 (PFS-12): psychometric findings and item reduction in a cohort of breast cancer survivors.

PubMed

Reeve, Bryce B; Stover, Angela M; Alfano, Catherine M; Smith, Ashley Wilder; Ballard-Barbash, Rachel; Bernstein, Leslie; McTiernan, Anne; Baumgartner, Kathy B; Piper, Barbara F

2012-11-01

Brief, valid measures of fatigue, a prevalent and distressing cancer symptom, are needed for use in research. This study's primary aim was to create a shortened version of the revised Piper Fatigue Scale (PFS-R) based on data from a diverse cohort of breast cancer survivors. A secondary aim was to determine whether the PFS captured multiple distinct aspects of fatigue (a multidimensional model) or a single overall fatigue factor (a unidimensional model). Breast cancer survivors (n = 799; stages in situ through IIIa; ages 29-86 years) were recruited through three SEER registries (New Mexico, Western Washington, and Los Angeles, CA) as part of the Health, Eating, Activity, and Lifestyle (HEAL) study. Fatigue was measured approximately 3 years post-diagnosis using the 22-item PFS-R that has four subscales (Behavior, Affect, Sensory, and Cognition). Confirmatory factor analysis was used to compare unidimensional and multidimensional models. Six criteria were used to make item selections to shorten the PFS-R: scale's content validity, items' relationship with fatigue, content redundancy, differential item functioning by race and/or education, scale reliability, and literacy demand. Factor analyses supported the original 4-factor structure. There was also evidence from the bi-factor model for a dominant underlying fatigue factor. Six items tested positive for differential item functioning between African-American and Caucasian survivors. Four additional items either showed poor association, local dependence, or content validity concerns. After removing these 10 items, the reliability of the PFS-12 subscales ranged from 0.87 to 0.89, compared to 0.90-0.94 prior to item removal. The newly developed PFS-12 can be used to assess fatigue in African-American and Caucasian breast cancer survivors and reduces response burden without compromising reliability or validity. This is the first study to determine PFS literacy demand and to compare PFS-R responses in African-Americans and Caucasian breast cancer survivors. Further testing in diverse populations is warranted.

Test Methodology Development for Experimental Structural Assessment of ASC Planar Spring Material for Long-Term Durability

NASA Technical Reports Server (NTRS)

Yun, Gunjin; Abdullah, A. B. M.; Binienda, Wieslaw; Krause, David L.; Kalluri, Sreeramesh

2014-01-01

A vibration-based testing methodology has been developed that will assess fatigue behavior of the metallic material of construction for the Advanced Stirling Convertor displacer (planar) spring component. To minimize the testing duration, the test setup is designed for base-excitation of a multiplespecimen arrangement, driven in a high-frequency resonant mode; this allows completion of fatigue testing in an accelerated period. A high performance electro-dynamic exciter (shaker) is used to generate harmonic oscillation of cantilever beam specimens, which are clasped on the shaker armature with specially-designed clamp fixtures. The shaker operates in closed-loop control with dynamic specimen response feedback provided by a scanning laser vibrometer. A test coordinator function synchronizes the shaker controller and the laser vibrometer to complete the closed-loop scheme. The test coordinator also monitors structural health of the test specimens throughout the test period, recognizing any change in specimen dynamic behavior. As this may be due to fatigue crack initiation, the test coordinator terminates test progression and then acquires test data in an orderly manner. Design of the specimen and fixture geometry was completed by finite element analysis such that peak stress does not occur at the clamping fixture attachment points. Experimental stress evaluation was conducted to verify the specimen stress predictions. A successful application of the experimental methodology was demonstrated by validation tests with carbon steel specimens subjected to fully-reversed bending stress; high-cycle fatigue failures were induced in such specimens using higher-than-prototypical stresses

Simulation of fatigue damage in ferroelectric polycrystals under mechanical/electrical loading

NASA Astrophysics Data System (ADS)

Kozinov, S.; Kuna, M.

2018-07-01

The reliability of smart-structures made of ferroelectric ceramics is essentially reduced by the formation of cracks under the action of external electrical and/or mechanical loading. In the current research a numerical model for low-cycle fatigue in ferroelectric mesostructures is proposed. In the finite element simulations a combination of two user element routines is utilized. The first one is used to model a micromechanical ferroelectric domain switching behavior inside the grains. The second one is used to simulate fatigue damage of grain boundaries by a cohesive zone model (EMCCZM) based on an electromechanical cyclic traction-separation law (TSL). For numerical simulations a scanning electron microscope image of the ceramic's grain structure was digitalized and meshed. The response of this mesostructure to cyclic electrical or mechanical loading is systematically analyzed. As a result of the simulations, the distribution of electric potential, field, displacement and polarization as well as mechanical stresses and deformations inside the grains are obtained. At the grain boundaries, the formation and evolution of damage are analyzed until final failure and induced degradation of electric permittivity. It is found that the proposed model correctly mimics polycrystalline behavior during poling processes and progressive damage under cyclic electromechanical loading. To the authors' knowledge, it is the first model and numerical analysis of ferroelectric polycrystals taking into account both domain reorientation and cohesive modeling of intergranular fracture. It can help to understand failure mechanisms taking place in ferroelectrics during fatigue processes.

Steel bridge fatigue crack detection with piezoelectric wafer active sensors

NASA Astrophysics Data System (ADS)

Yu, Lingyu; Giurgiutiu, Victor; Ziehl, Paul; Ozevin, Didem; Pollock, Patrick

2010-04-01

Piezoelectric wafer active sensors (PWAS) are well known for its dual capabilities in structural health monitoring, acting as either actuators or sensors. Due to the variety of deterioration sources and locations of bridge defects, there is currently no single method that can detect and address the potential sources globally. In our research, our use of the PWAS based sensing has the novelty of implementing both passive (as acoustic emission) and active (as ultrasonic transducers) sensing with a single PWAS network. The combined schematic is using acoustic emission to detect the presence of fatigue cracks in steel bridges in their early stage since methods such as ultrasonics are unable to quantify the initial condition of crack growth since most of the fatigue life for these details is consumed while the fatigue crack is too small to be detected. Hence, combing acoustic emission with ultrasonic active sensing will strengthen the damage detection process. The integration of passive acoustic emission detection with active sensing will be a technological leap forward from the current practice of periodic and subjective visual inspection, and bridge management based primarily on history of past performance. In this study, extensive laboratory investigation is performed supported by theoretical modeling analysis. A demonstration system will be presented to show how piezoelectric wafer active sensor is used for acoustic emission. Specimens representing complex structures are tested. The results will also be compared with traditional acoustic emission transducers to identify the application barriers.

Efficacy of Ginseng Supplements on Fatigue and Physical Performance: a Meta-analysis

PubMed Central

2016-01-01

We conducted a meta-analysis to investigate the efficacy of ginseng supplements on fatigue reduction and physical performance enhancement as reported by randomized controlled trials (RCTs). RCTs that investigated the efficacy of ginseng supplements on fatigue reduction and physical performance enhancement compared with placebos were included. The main outcome measures were fatigue reduction and physical performance enhancement. Out of 155 articles meeting initial criteria, 12 RCTs involving 630 participants (311 participants in the intervention group and 319 participants in the placebo group) were included in the final analysis. In the fixed-effect meta-analysis of four RCTs, there was a statistically significant efficacy of ginseng supplements on fatigue reduction (standardized mean difference, SMD = 0.34; 95% confidence interval [CI] = 0.16 to 0.52). However, ginseng supplements were not associated with physical performance enhancement in the fixed-effect meta-analysis of eight RCTs (SMD = −0.01; 95% CI = −0.29 to 0.27). We found that there was insufficient clinical evidence to support the use of ginseng supplements on reducing fatigue and enhancing physical performance because only few RCTs with a small sample size have been published so far. Further lager RCTs are required to confirm the efficacy of ginseng supplements on fatigue reduction. PMID:27822924

Three Dimensional Numerical Simulation and Characterization of Crack Growth in the Weld Region of a Friction Stir Welded Structure

NASA Technical Reports Server (NTRS)

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

2013-01-01

Friction stir welding (FSW) fabrication technology is being adopted in aerospace applications. The use of this technology can reduce production cost, lead-times, reduce structural weight and need for fasteners and lap joints, which are typically the primary locations of crack initiation and multi-site fatigue damage in aerospace structures. FSW is a solid state welding process that is well-suited for joining aluminum alloy components; however, the process introduces residual stresses (both tensile and compressive) in joined components. The propagation of fatigue cracks in a residual stress field and the resulting redistribution of the residual stress field and its effect on crack closure have to be estimated. To insure the safe insertion of complex integral structures, an accurate understanding of the fatigue crack growth behavior and the complex crack path process must be understood. A life prediction methodology for fatigue crack growth through the weld under the influence of residual stresses in aluminum alloy structures fabricated using FSW will be detailed. The effects and significance of the magnitude of residual stress at a crack tip on the estimated crack tip driving force are highlighted. The location of the crack tip relative to the FSW and the effect of microstructure on fatigue crack growth are considered. A damage tolerant life prediction methodology accounting for microstructural variation in the weld zone and residual stress field will lead to the design of lighter and more reliable aerospace structures

The Effect of Ultrasonic Peening on Service Life of the Butt-Welded High-Temperature Steel Pipes

NASA Astrophysics Data System (ADS)

Daavari, Morteza; Vanini, Seyed Ali Sadough

2015-09-01

Residual stresses introduced by manufacturing processes such as casting, forming, machining, and welding have harmful effects on the mechanical behavior of the structures. In addition to the residual stresses, weld toe stress concentration can play a determining effect. There are several methods to improve the mechanical properties such as fatigue behavior of the welded structures. In this paper, the effects of ultrasonic peening on the fatigue life of the high-temperature seamless steel pipes, used in the petrochemical environment, have been investigated. These welded pipes are fatigued due to thermal and mechanical loads caused by the cycle of cooling, heating, and internal pressure fluctuations. Residual stress measurements, weld geometry estimation, electrochemical evaluations, and metallography investigations were done as supplementary examinations. Results showed that application of ultrasonic impact treatment has led to increased fatigue life, fatigue strength, and corrosion resistance of A106-B welded steel pipes in petrochemical corrosive environment.

Fatigue of Nitinol: The state-of-the-art and ongoing challenges.

PubMed

Mahtabi, M J; Shamsaei, Nima; Mitchell, M R

2015-10-01

Nitinol, a nearly equiatomic alloy of nickel and titanium, has been considered for a wide range of applications including medical and dental devices and implants as well as aerospace and automotive components and structures. The realistic loading condition in many of these applications is cyclic; therefore, fatigue is often the main failure mode for such components and structures. The fatigue behavior of Nitinol involves many more complexities compared with traditional metal alloys arising from its uniqueness in material properties such as superelasticity and shape memory effects. In this paper, a review of the present state-of-the-art on the fatigue behavior of superelastic Nitinol is presented. Various aspects of fatigue of Nitinol are discussed and microstructural effects are explained. Effects of material preparation and testing conditions are also reviewed. Finally, several conclusions are made and recommendations for future works are offered. Copyright © 2015 Elsevier Ltd. All rights reserved.

A model of rotationally-sampled wind turbulence for predicting fatigue loads in wind turbines

NASA Technical Reports Server (NTRS)

Spera, David A.

1995-01-01

Empirical equations are presented with which to model rotationally-sampled (R-S) turbulence for input to structural-dynamic computer codes and the calculation of wind turbine fatigue loads. These equations are derived from R-S turbulence data which were measured at the vertical-plane array in Clayton, New Mexico. For validation, the equations are applied to the calculation of cyclic flapwise blade loads for the NASA/DOE Mod-2 2.5-MW experimental HAWT's (horizontal-axis wind turbines), and the results compared to measured cyclic loads. Good correlation is achieved, indicating that the R-S turbulence model developed in this study contains the characteristics of the wind which produce many of the fatigue loads sustained by wind turbines. Empirical factors are included which permit the prediction of load levels at specified percentiles of occurrence, which is required for the generation of fatigue load spectra and the prediction of the fatigue lifetime of structures.

Fully Coupled Micro/Macro Deformation, Damage, and Failure Prediction for SiC/Ti-15-3 Laminates

NASA Technical Reports Server (NTRS)

Bednarcyk, Brett A.; Arnold, Steven M.; Lerch, Brad A.

2001-01-01

The deformation, failure, and low cycle fatigue life of SCS-6/Ti-15-3 composites are predicted using a coupled deformation and damage approach in the context of the analytical generalized method of cells (GMC) micromechanics model. The local effects of inelastic deformation, fiber breakage, fiber-matrix interfacial debonding, and fatigue damage are included as sub-models that operate on the micro scale for the individual composite phases. For the laminate analysis, lamination theory is employed as the global or structural scale model, while GMC is embedded to operate on the meso scale to simulate the behavior of the composite material within each laminate layer. While the analysis approach is quite complex and multifaceted, it is shown, through comparison with experimental data, to be quite accurate and realistic while remaining extremely efficient.

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.

Fatigue Crack Prognostics by Optical Quantification of Defect Frequency

NASA Astrophysics Data System (ADS)

Chan, K. S.; Buckner, B. D.; Earthman, J. C.

2018-01-01

Defect frequency, a fatigue crack prognostics indicator, is defined as the number of microcracks per second detected using a laser beam that is scanned across a surface at a constant predetermined frequency. In the present article, a mechanistic approach was taken to develop a methodology for deducing crack length and crack growth information from defect frequency data generated from laser scanning measurements made on fatigued surfaces. The method was developed by considering a defect frequency vs fatigue cycle curve that comprised three regions: (i) a crack initiation regime of rising defect frequency, (ii) a plateau region of a relatively constant defect frequency, and (iii) a region of rapid rising defect frequency due to crack growth. Relations between defect frequency and fatigue cycle were developed for each of these three regions and utilized to deduce crack depth information from laser scanning data of 7075-T6 notched specimens. The proposed method was validated using experimental data of crack density and crack length data from the literature for a structural steel. The proposed approach was successful in predicting the length or depth of small fatigue cracks in notched 7075-T6 specimens and in smooth fatigue specimens of a structural steel.

Analyses of Fatigue and Fatigue-Crack Growth under Constant- and Variable-Amplitude Loading

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1999-01-01

Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily crack growth from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using small-crack theory under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta K(sub eff)) under constant-amplitude loading. Modifications to the delta K(sub eff)-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.

The Effects of Fracture Origin Size on Fatigue Properties of Ductile Cast Iron with Small Chill Structures

NASA Astrophysics Data System (ADS)

Sameshima, Daigo; Nakamura, Takashi; Horikawa, Noritaka; Oguma, Hiroyuki; Endo, Takeshi

Reducing the weight of a machine structure is an increasingly important consideration both for the conservation of resources during production and for the energy saving during operation. With these objectives in mind, thin-walled ductile cast iron has recently been developed. Because rapid cooling could result in brittle microstructure of cementite (chill) in this cast iron, it is necessary to investigate the effect of cementite on the fatigue properties. Therefore, fatigue tests were carried out on a ductile cast iron of block castings which contained a relatively small amount of cementite. Fracture surface observation indicated that the fracture origins were located at graphite clusters and cast shrinkage porosity, not at cementite. It appears that when the size of the cementite is smaller than that of the graphite, the cementite does not affect the fatigue properties of ductile cast iron. Not surprisingly, the fatigue lives were found to increase with decrease in the size of the fatigue fracture origin. The threshold initial stress intensity factor range ΔKini,th for fatigue failure was found to be about 3-4MPa√m, independent of microstructure.

Ae Behavior of Smart Stress Memory Patch after Variable Amplitude Loading

NASA Astrophysics Data System (ADS)

Fujino, Y.; Nambu, S.; Enoki, M.

Recently, the structural health monitoring becomes increasingly great important to assure the ease and safety of our life, and it is required significantly to develop non-destructive evaluation for structures such as bridges and tunnels. Some sacrificed specimens have been developed to evaluate the fatigue damage of structures such as fatigue cycles and residual lifetime, but it can be applied only when the stress history is known beforehand. These fatigue sensors need no cable and can be used at low cost in contrast to strain gage. In previous study, a smart stress memory patch was developed as a new fatigue sensor. The patch can measure simultaneously the maximum stress, stress amplitude and the number of fatigue cycles by crack length measurement and Kaiser effect of Acoustic Emission (AE). The crack growth behavior under constant amplitude (CA) loading has been investigated, and AE behavior also has been evaluated only after CA loading. However, AE characteristics after variable amplitude (VA) loading in service are extremely important. Moreover, it is very important to control AE behavior of the smart patch in order to evaluate the applied stress using Kaiser effect. In this study, fatigue test with single overload was investigated to evaluate its influence. Moreover, effect of crack length and heat treatment on AE behavior was also investigated. Finally, AE behavior of the patch was evaluated after fatigue CA loading with overload or VA loading with log-normal distribution and overload.

Power spectral density analysis of the electromyogram from a work task performed in a full pressure suit. Ph.D. Thesis - Houston Univ.; [for determining muscular fatigue

NASA Technical Reports Server (NTRS)

Lafevers, E. V.

1974-01-01

Surface electromyograms (EMG) taken from three upper torso muscles during a push-pull task were analyzed by a power spectral density technique to determine the utility of the spectral analysis for identifying changes in the EMG caused by muscular fatigue. The results confirmed the value of the frequency analysis for identifying fatigue producing muscular performance. Data revealed reliable differences between muscles in fatigue induced responses to various locations in the reach envelope at which the subjects were required to perform the push-pull exercise, and the differential sensitivity of individual muscles to the various reach positions; i.e., certain reach positions imposed more fatigue related shifts in EMG power than did others. It was found that a pressurized space suit changed the pattern of normal shirtsleeve muscle fatigue responses in all three of the muscles.

Real-time sensing of fatigue crack damage for information-based decision and control

NASA Astrophysics Data System (ADS)

Keller, Eric Evans

Information-based decision and control for structures that are subject to failure by fatigue cracking is based on the following notion: Maintenance, usage scheduling, and control parameter tuning can be optimized through real time knowledge of the current state of fatigue crack damage. Additionally, if the material properties of a mechanical structure can be identified within a smaller range, then the remaining life prediction of that structure will be substantially more accurate. Information-based decision systems can rely one physical models, estimation of material properties, exact knowledge of usage history, and sensor data to synthesize an accurate snapshot of the current state of damage and the likely remaining life of a structure under given assumed loading. The work outlined in this thesis is structured to enhance the development of information-based decision and control systems. This is achieved by constructing a test facility for laboratory experiments on real-time damage sensing. This test facility makes use of a methodology that has been formulated for fatigue crack model parameter estimation and significantly improves the quality of predictions of remaining life. Specifically, the thesis focuses on development of an on-line fatigue crack damage sensing and life prediction system that is built upon the disciplines of Systems Sciences and Mechanics of Materials. A major part of the research effort has been expended to design and fabricate a test apparatus which allows: (i) measurement and recording of statistical data for fatigue crack growth in metallic materials via different sensing techniques; and (ii) identification of stochastic model parameters for prediction of fatigue crack damage. To this end, this thesis describes the test apparatus and the associated instrumentation based on four different sensing techniques, namely, traveling optical microscopy, ultrasonic flaw detection, Alternating Current Potential Drop (ACPD), and fiber-optic extensometry-based compliance, for crack length measurements.

Low-cycle thermal fatigue

NASA Technical Reports Server (NTRS)

Halford, G. R.

1986-01-01

A state-of-the-art review is presented of the field of thermal fatigue. Following a brief historical review, the concept is developed that thermal fatigue can be viewed as processes of unbalanced deformation and cracking. The unbalances refer to dissimilar mechanisms occurring in opposing halves of thermal fatigue loading and unloading cycles. Extensive data summaries are presented and results are interpreted in terms of the unbalanced processes involved. Both crack initiation and crack propagation results are summarized. Testing techniques are reviewed, and considerable discussion is given to a technique for thermal fatigue simulation, known as the bithermal fatigue test. Attention is given to the use of isothermal life prediction methods for the prediction of thermal fatigue lives. Shortcomings of isothermally-based life prediction methods are pointed out. Several examples of analyses and thermal fatigue life predictions of high technology structural components are presented. Finally, numerous dos and don'ts relative to design against thermal fatigue are presented.

Slow Crack Growth and Fatigue Life Prediction of Ceramic Components Subjected to Variable Load History

NASA Technical Reports Server (NTRS)

Jadaan, Osama

2001-01-01

Present capabilities of the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time-dependent reliability of ceramic structures subjected to simple time-dependent loading. For example, in slow crack growth (SCG) type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time-dependent loads, while for cyclic fatigue applications various types of repetitive constant amplitude loads can be accounted for. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as, for example, engine start up, shut down, and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time-dependent reliability of components subjected to transient thermomechanical loads that takes into account the change in material response with time. In this paper, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code, which has also been modified to have the ability of interfacing with commercially available FEA codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.

Design and Evaluation of Glass/epoxy Composite Blade and Composite Tower Applied to Wind Turbine

NASA Astrophysics Data System (ADS)

Park, Hyunbum

2018-02-01

In the study, the analysis and manufacturing of small class wind turbine blade was performed. In the structural design, firstly the loading conditions are defined through the load case analysis. The proposed structural configuration of blade has a sandwich type composite structure with the E-glass/Epoxy face sheets and the Urethane foam core for lightness, structural stability, low manufacturing cost and easy manufacturing process. And also, this work proposes a design procedure and results of tower for the small scale wind turbine systems. Structural analysis of blade including load cases, stress, deformation, buckling, vibration and fatigue life was performed using the finite element method, the load spectrum analysis and the Miner rule. Moreover, investigation on structural safety of tower was verified through structural analysis by FEM. The manufacturing of blade and tower was performed based on structural design. In order to investigate the designed structure, the structural tests were conducted and its results were compared with the calculated results. It is confirmed that the final proposed blade and tower meet the design requirements.

77 FR 50576 - Fatigue Tolerance Evaluation of Metallic Structures; OMB Approval of Information Collection

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-22

...-0413; Amdt. No. 29-55] RIN 2120-AJ51 Fatigue Tolerance Evaluation of Metallic Structures; OMB Approval of Information Collection AGENCY: Federal Aviation Administration, DOT. ACTION: Final rule; OMB approval of information collection. SUMMARY: This document notifies the public of the Office of Management...

Small, Self-Contained Aircraft Fatigue Data Recorder.

DTIC Science & Technology

1986-08-01

need to monitor structural fatigue damage on military aircraft has become critical. It is particularly important to be able to study the dynamic...serve to heighten concerns over the accumulation of fatigue damage . Accordingly, there is a requirement for a fatigue data recorder readily installed...report is to apprise the sponsor of the progress to date and to solicit comments from the sponsor on the report content and the direction the design is