Articles de revues : « Shock fatigue »

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Yamaguchi, Kenji, Itaru Matsumoto, Tsuyoshi Fujita, Yasuo Kondo, Satoshi Sakamoto et Mitsugu Yamaguchi. « Evaluation of the Thermal Shock Fatigue Resistance of Cutting Tools Using a CO₂ Pulse Laser Beam ». Key Engineering Materials 719 (novembre 2016) : 109–13. http://dx.doi.org/10.4028/www.scientific.net/kem.719.109.

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It is well-known that a series of cracks sometimes gets initiated perpendicular to the cutting edges on the rake faces of brittle cutting tools made of materials such as cemented carbide, ceramics, and cermet under high-speed intermittent cutting. The tools used in intermittent cutting processes are exposed to elevated temperatures during cutting and then cool quickly during the noncutting time. Previous studies have suggested that such repeated thermal shocks generate thermal stress in the tool and that the thermal cracks are then propagated by thermal fatigue. Recently, high-speed machining techniques have attracted the attention of researchers. To apply new cutting tool materials to this machining process, it is important to evaluate their thermal shock fatigue resistances. During high-speed intermittent cutting, the frequency of thermal shocks becomes high and the action area of the thermal shocks is limited to the rake face of the tool. Therefore, conventional thermal shock resistance evaluation methods are unsuitable for this case. Consequently, the authors have developed a new experimental evaluation method using a CO2 laser beam. In this study, we irradiated cemented carbide and TiN cermet cutting tools with the CO2 pulse laser beam and gauged the effectiveness of the proposed thermal shock fatigue resistance evaluation method. The results show a correlation between the thermal shock due to the CO2 pulse laser beam and those due to the intermittent cutting experiments.

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Sikhamov, Ruslan, Fedor Fomin, Benjamin Klusemann et Nikolai Kashaev. « The Influence of Laser Shock Peening on Fatigue Properties of AA2024-T3 Alloy with a Fastener Hole ». Metals 10, n^o 4 (9 avril 2020) : 495. http://dx.doi.org/10.3390/met10040495.

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The objective of the present study was to estimate the influence of laser shock peening on the fatigue properties of AA2024-T3 specimens with a fastener hole and to investigate the possibility to heal the initial cracks in such specimens. Fatigue cracks of different lengths were introduced in the specimens with a fastener hole before applying laser shock peening. Deep compressive residual stresses, characterized by the hole drilling method, were generated into the specimens by applying laser shock peening on both sides. Subsequently, the specimens were subjected to fatigue tests. The results show that laser shock peening has a positive effect regarding the fatigue life improvement in the specimens with a fastener hole. In addition, laser shock peening leads to a healing effect on fatigue cracks. The efficiency of this effect depends on the initial crack length. The effect of laser shock peening on the fatigue life periods was determined by using resonant frequency graphs.

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Czop, Piotr, et Damian Slawik. « Validation of Fatigue Model of a Hydraulic Shock Absorber Equipped with Shim Stack Valves ». Journal of Physics : Conference Series 2184, n^o 1 (1 mars 2022) : 012057. http://dx.doi.org/10.1088/1742-6596/2184/1/012057.

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Abstract The aim of the paper is to formulate and validate the fatigue model of a shock absorber equipped with shim-based clamped valves. The fatigue model has application potential in a virtual valve system pre-selection process during the shock absorber design and configuration stage. It allows the required testing capacity at shock absorber manufacturers to be significantly reduced, i.e. the number of long-term and expensive fatigue tests performed on servo-hydraulic load frame testers. The shock absorber fatigue model is a combination of the previously developed finite element model [1] and analytical routines using the experimentally derived Wöhler characteristics of shim materials [2]. The fatigue model validation process was conducted with a high-performance servo-hydraulic load frame tester. Six shock absorbers were subjected to the same long-cycle kinematic sine-load and tested until initial valve damage symptoms appeared. The paper reports the fatigue calculation process and validation results. The obtained model accuracy in the range of ±30% error of shock absorber life-time prediction. This result is accurate enough for the model to be recommended as a quick-and-dirty engineering tool saving shock absorber development costs.

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Pretorius, Jan G., Dawood A. Desai et Glen C. Snedden. « Effect of Laser Shock Peening on Fatigue Life at Stress Raiser Regions of a High-Speed Micro Gas Turbine Shaft : A Simulation Based Study ». International Journal of Engineering Research in Africa 45 (novembre 2019) : 15–27. http://dx.doi.org/10.4028/www.scientific.net/jera.45.15.

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Fatigue failure due to stress raiser regions on critical rotating components in gas turbine engines, such as the shaft, is a crucial aspect. Methods to reduce these stresses and improve fatigue life are a source of ongoing research. Laser shock peening is a method where compressive residual stresses are imparted on the stress raisers of such components. However, numerical based studies on multiple laser shock peening applied to stress raisers is under-researched. Hence, this study will attempt to predict the fatigue life at fillet radii step induced stress raiser regions on a high-speed gas turbine engine shaft by utilization of laser shock peening. The objective of this study was achieved by developing a more computational efficient finite element model to mimic the laser shock peening process on the fillet radii step induced stress raiser regions of a shaft. A modified laser shock peening simulation method for effective prediction of the residual stress field was introduced. Furthermore, the fatigue life improvement due to laser shock peening was predicted by employing Fe-safe fatigue software. From the results, the modified laser shock peening simulation method provided accurate prediction of the residual stress field with a reduced computational time of over 68% compared to conventional methods. The fatigue life revealed an improvement of 553% due to laser shock peening, which is comparable to similar findings in the literature. Hence, from the findings and results achieved, the developed finite element model can be an appropriate tool to assist in the fatigue life estimation of laser shock peening applied to stress raisers.

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Ren, Xu Dong, Yong Kang Zhang, Y. H. Li, W. Cheng et M. Zhuang. « Mechanism Influence on Fatigue Characters of Aerial Engine Blade by Laser Shock Processing ». Advanced Materials Research 24-25 (septembre 2007) : 371–75. http://dx.doi.org/10.4028/www.scientific.net/amr.24-25.371.

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In Laser Shock Processing when a material is irradiated with short laser pulses (ns)of very high densities(>GW/cm2), a high intensity shock wave is generated. This treatment can reduce the rate of fatigue cracking and stress corrosion cracking in structural metals or alloys needed for aerospace, nuclear power plants, and military applications. And laser shock processing has been shown to be a viable method of strengthen metallic components. Transformation on the characters of aerial engine blade by laser shock processing and influence on the fatigue life with these transformations were studied. And the relatively fatigue life experiment of aerial engine blade was done to validate the influence on the fatigue life of aerial engine by laser shock processing. It was found that laser shock processing could bring residual compressive stress and high-density dislocation on the surface of the blade. All these transformation greatly increase the fatigue life of aerial engine blade.

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Chiang, C. K., C. L. Yang, W. C. Chen, C. H. Chang, S. C. Huang et J. L. Wang. « Shock Attenuation of Intervertebral Disc Following Fatigue Loading ». Journal of Mechanics 27, n^o 1 (mars 2011) : 9–17. http://dx.doi.org/10.1017/jmech.2011.2.

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ABSTRACTShock absorption is one of the fundamental biomechanical functions of disc. The knowledge of the effect of fatigue loading, impact energy and contact period on the disc shock attenuation is important in clarifying the risk factors of back pain and evaluating the efficacy of novel disc prosthesis. The purpose of this study is to find the changes of shock attenuation of motion segment after fatigue loading, and the effect of impact energy and contact period on the disc shock attenuation pre and post fatigue loading.The 3-unit porcine spinal motion segment was used for testing. The impact test was applied pre and post fatigue loading. Impact energy and contact period were controlled in the experiment. Shock attenuation properties, including the acceleration attenuation (AA) of disc, force transmissibility (FT) and phase delay of force (PDF) of motion segment, were calculated from the acceleration and force responses.The results showed that the shock attenuation properties (acceleration attenuation and force transmissibility) decreased post fatigue. The disc acceleration attenuation was independent of impact energy and contact period. The disc acceleration attenuation was 0.78 (−1.06dB) pre fatigue and 1.04 (0.14dB) post fatigue. The force transmissibility of motion segment decreased post fatigue only during short contact period. The phase delay of force did not change significantly post fatigue.We found that the fatigue loading decreased the disc shock attenuation. The disc was at higher risk of injury following fatigue loading even at a mild impact loading. The disc acceleration attenuation was invariant of impact energy and contact period, but decreased post fatigue. The disc acceleration attenuation is a good index to evaluate the degree of fatigue injury.

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Ren, Xu Dong, Yong Zhuo Huangfu, Yong Kang Zhang, Da Wei Jiang et Tian Zhang. « Fatigue Crack Propagation Experiment and Simulation on 7050 Aluminum Alloy ». Key Engineering Materials 464 (janvier 2011) : 560–63. http://dx.doi.org/10.4028/www.scientific.net/kem.464.560.

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In this paper, an experiment of fatigue crack propagation in 7050 aluminum alloy was presented. Laser shock processing (LSP) is used to shock the crack surface. Compared with the specimen without LSP, the fatigue life after LSP increased greatly. The simulation of the fatigue crack growth in 7050 aluminum alloy is implemented in FRANC2D. Simulating result is in accordance with the result of the experiment well. Laser shock processing increases the fatigue life and reduce fatigue crack growth rate, it has good prospect on the study of crack arrestment.

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MAEKAWA, Ichiro, Hiroshi SHIBATA, Akira KOBAYASHI et Tsutomu WADA. « Thermal shock fatigue of Al2O3 ceramics. » Journal of the Society of Materials Science, Japan 38, n^o 429 (1989) : 658–62. http://dx.doi.org/10.2472/jsms.38.658.

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Wolfenden, A., JL Yuen et RJ Walter. « Thermal Shock and Thermal Fatigue Testing ». Journal of Testing and Evaluation 19, n^o 5 (1991) : 403. http://dx.doi.org/10.1520/jte12594j.

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Verbitsky, Oleg, Joseph Mizrahi, Arkady Voloshin, July Treiger et Eli Isakov. « Shock Transmission and Fatigue in Human Running ». Journal of Applied Biomechanics 14, n^o 3 (août 1998) : 300–311. http://dx.doi.org/10.1123/jab.14.3.300.

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The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO2pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike–induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.

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Benjamin, Daniel, Serge Odof, Boussad Abbès, François Fourchet, Benoit Christiaen et Redha Taïar. « Shock Response Spectrum Analysis of Fatigued Runners ». Sensors 22, n^o 6 (18 mars 2022) : 2350. http://dx.doi.org/10.3390/s22062350.

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The purpose of this study was to determine the effect of fatigue on impact shock wave attenuation and assess how human biomechanics relate to shock attenuation during running. In this paper, we propose a new methodology for the analysis of shock events occurring during the proposed experimental procedure. Our approach is based on the Shock Response Spectrum (SRS), which is a frequency-based function that is used to indicate the magnitude of vibration due to a shock or a transient event. Five high level CrossFit athletes who ran at least three times per week and who were free from musculoskeletal injury volunteered to take part in this study. Two Micromachined Microelectromechanical Systems (MEMS) accelerometers (RunScribe®, San Francisco, CA, USA) were used for this experiment. The two RunScribe pods were mounted on top of the foot in the shoelaces. All five athletes performed three maximum intensity runs: the 1st run was performed after a brief warmup with no prior exercise, then the 2nd and the 3rd run were performed in a fatigued state. Prior to the 2nd and the 3rd run, the athletes were asked to perform at maximum intensity for two minutes on an Assault AirBike to tire them. For all five athletes, there was a direct correlation between fatigue and an increase in the aggressiveness of the SRS. We noticed that for all five athletes for the 3rd run the average SRS peaks were significantly higher than for the 1st run and 2nd run (p < 0.01) at the same natural frequency of the athlete. This confirms our hypothesis that fatigue causes a decrease in the shock attenuation capacity of the musculoskeletal system thus potentially involving a higher risk of overuse injury.

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Thomas, J. A., et E. G. Noble. « Heat shock does not attenuate low-frequency fatigue ». Canadian Journal of Physiology and Pharmacology 77, n^o 1 (1 janvier 1999) : 64–70. http://dx.doi.org/10.1139/y99-011.

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Whole-body hyperthermia or heat shock confers protection to myocardial contractility against reperfusion-induced injury. The purpose of this study was to determine whether heat shock could provide similar protection to skeletal muscle contractility against low-frequency fatigue. Male Sprague-Dawley rats (6 rats/group) were heat shocked at 41.5°C for 15 min either 24 h or 4 days prior to fatiguing stimulation to compare the contractile responses of the plantaris muscle with those of a nonheated group. Both 24 h and 4 days after heat shock, the 72-kDa heat shock protein (HSP72) was elevated above control levels. There were no differences between the heat-shocked and non-heat-shocked animals in measures of contractility prior to fatiguing contractions or in resistance to fatigue. Heat-shock preconditioning did not lead to improved postfatigue force recovery above control responses and, in fact, delayed the recovery of force. This study does not support the use of heat-shock therapy to improve skeletal muscle contractile performance under fatiguing conditions.Key words: heat shock proteins, rat, skeletal muscle, contractile properties, HSP72.

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Zhang, Hui, Yan Ruo Hong, Hong Xia Li et Yang Bin. « Thermal Fatigue Behavior of Ladle Purging Plug ». Advanced Materials Research 105-106 (avril 2010) : 158–61. http://dx.doi.org/10.4028/www.scientific.net/amr.105-106.158.

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The thermal fatigue behavior of alumina-magnesia based and alumina-chromia based purging plug materials are comparatively studied. By comparing thermal shock parameters, the changes of elastic modulus and hot modulus of rupture after thermal shock cycles, we come to a conclusion that microcracks emerge in the alumina-magnesia based material, which hinder the crack growth during thermal shock cycles. The fine-grained and network structure of alumina-magnesia based material are also helpful to improve thermal shock resistance. However, cracks are difficult to form in the alumina-chromia based material but it tends to fracture damage quickly once the cracks nucleation due to coarse-grained structure of alumina-chromia based material.

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Mészáros, István, et János Ginsztler. « Thermal Schock Fatigue Process Induced Magnetic Anisotropy ». Materials Science Forum 537-538 (février 2007) : 419–24. http://dx.doi.org/10.4028/www.scientific.net/msf.537-538.419.

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In this work the magnetic anisotropy of the 15Mo3 type steel was investigated which was induced by deterioration process caused by thermal shock fatigue. The applied thermal shock fatigue investigation can model the material degradation due to long term service in high temperature environment. The 15Mo3 steel is widely used as reheating pipeline base material of power plant boilers. Magnetisation curves were measured to characterise the induced magnetic anisotropy due to thermal shock fatigue process. A parallel motion vibrating sample magnetometer (PMVSM) which was designed at the Department of Materials Science and Engineering of BUTE was used for the magnetic measurements.

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Li, Song Bai, et Xiang Li. « Fatigue Property Test and Numerical Simulation Analysis of 2524 Aluminum Alloy by Laser Shock Process ». Key Engineering Materials 842 (mai 2020) : 265–71. http://dx.doi.org/10.4028/www.scientific.net/kem.842.265.

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Effects of laser shock peening on the fatigue properties of 2524 aluminum alloy were investigated by laser shock test, residual stress test and fatigue crack growth test respectively. The results show that the maximum residual stress is -220MPa at a distance of 1.1mm from the spot center after LSP (laser energy of 6.26J). The distribution of residual stress was simulated by Abaqus software, and the numerical simulation results were in good agreement with the experimental results. Compared with the untreated specimens, the fatigue life of the shocked specimens was increased by 32%. Fatigue fracture morphologies of the final rupture zone also show that more dimples of significantly larger depth and size occur. The fatigue life of 2524 aluminum alloy can be effectively extended by laser shock process (LSP).

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Smith, I. Christopher H., et Di J. Newham. « Fatigue and functional performance of human biceps muscle following concentric or eccentric contractions ». Journal of Applied Physiology 102, n^o 1 (janvier 2007) : 207–13. http://dx.doi.org/10.1152/japplphysiol.00571.2006.

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A long-lasting fatigue was measured in human biceps muscle, following 40 maximal isokinetic concentric or eccentric contractions of the forearm, as the response to single-shock stimuli every minute for 4 h. This protocol allowed new observations on the early time course of long-lasting fatigue. Concentric contractions induced a novel progressive decline to 30.2% (SE 7.8, n = 7) of control at 23 min with complete recovery by 120 min. Eccentric contractions lead initially to a smaller force reduction of similar time course followed by a slower decline to 40.0% (SE 5.1, n = 7) control at 120 min with recovery less than half complete at 4 h. A 50-Hz test stimuli overcame both fatigues, identifying low-frequency fatigue. EMG recordings from the biceps muscle showed moderate (<20%) changes during the fatigue. A visual-tracking task showed no decrement in performance at the time of maximal fatigue of the single-shock response. Because the eccentric contractions have a similar activation, a larger force, but much smaller metabolic usage than concentric contractions, it is concluded that the initial decline is related to the effects of metabolites, whereas the slower phase after eccentric contractions is associated with higher mechanical stress.

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Kluczyk, Marcin, Andrzej Grządziela, Michał Pająk, Łukasz Muślewski et Adam Szelezinski. « The Fatigue Wear Process of Rubber-Metal Shock Absorbers ». Polymers 14, n^o 6 (16 mars 2022) : 1186. http://dx.doi.org/10.3390/polym14061186.

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Rubber and rubber-metal vibration isolators are widely used vibration isolation systems in marine applications. For naval application, shock absorber mounting systems must fulfil two functions. The first one supports the suspended mass in the absence of waving or detonation while providing isolation from vibrations and shock impact. In the second case, during the machine operation, it reduces the force of movement to an acceptable value. Moreover, it returns the insulated mass to the position output without plastic deformation or residual buckling after removing shock stresses or harmonic vibrations. The environment in which marine vibration isolators are to be used strongly influences the selection of a shock absorber. The main environmental problem is the temperature range in marine power plants, which ranges from 20 °C to 55 °C. Temperature fluctuations may cause changes in the physical properties of typical vibration/shock insulators. Both rubbers and elastomers used for shock absorbers tend to stiffen, gain low-temperature damping, and soften and lose damping at elevated temperatures. Factors such as moisture, ozone and changes in atmospheric pressure are usually ignored in shipbuilding. The main environmental factors influencing the ageing of insulators are liquid saturated hydrocarbons, i.e., oils, fuels, coolants, etc., which may come into contact with the surface of the insulators. This work presents the results of the research carried out to determine the effect of overload and the impact of petroleum products on the materials of metal-rubber shock absorbers made of three different rubbers and one polyurethane mixture. For each of the materials, shock absorbers with three different degrees of hardness were tested.

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Mészáros, István, et János Ginsztler. « Magnetic Investigation of Thermal Shock Fatigue Process ». Key Engineering Materials 345-346 (août 2007) : 1283–86. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.1283.

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In the present paper we summarize some of our results obtained in the field of magnetic testing of thermal shock fatigue testing of power plant steels. In this work 15Mo3 type ferritic heat resistant steel was investigated. This steel and several similar grades are commonly used in power plants boilers as the material of reheating steam pipelines and pressure vessels. Their typical application temperature is about 500-550 °C. It is commonly accepted that a combined form of mechanical, thermal fatigue and the creep processes causes the long term deterioration of this structural steels. The applied thermal shock fatigue test can model the material degradation due to long term service in high temperature environment. A parallel motion vibrating sample magnetometer, an AC permeameter and a magnetic Barkhausen noise measuring device was used for testing the magnetic properties of the samples and several different magnetic properties were measured to characterize the microstructural processes of the deterioration.

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Kerezsi, B. B., A. G. Kotousov et J. W. H. Price. « Experimental apparatus for thermal shock fatigue investigations ». International Journal of Pressure Vessels and Piping 77, n^o 7 (juin 2000) : 425–34. http://dx.doi.org/10.1016/s0308-0161(00)00025-9.

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Fantozzi, Gilbert, C. Olagnon et Malika Saâdaoui. « Thermal Shock and Fatigue Behaviour of Ceramics ». Advanced Materials Research 1-2 (septembre 1994) : 35–46. http://dx.doi.org/10.4028/www.scientific.net/amr.1-2.35.

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Lanone, Sophie, Camille Taillé, Jorge Boczkowski et Michel Aubier. « Diaphragmatic fatigue during sepsis and septic shock ». Intensive Care Medicine 31, n^o 12 (28 septembre 2005) : 1611–17. http://dx.doi.org/10.1007/s00134-005-2748-4.

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Kang, Hong-Tae, et Sai Boorgu. « Fatigue Life Prediction of Self-Piercing Rivet Joints Between Magnesium and Aluminum Alloys ». MATEC Web of Conferences 165 (2018) : 10004. http://dx.doi.org/10.1051/matecconf/201816510004.

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Various light materials including aluminum alloys and magnesium alloys are being used to reduce the weight of vehicle structures. Joining of dissimilar materials is always a challenging task to construct a solid structure. Self-piercing rivet (SPR) joint is one of various joining methods for dissimilar materials. Front shock tower structures were constructed with magnesium alloy (AM60) joined to aluminum alloy (Al6082) by SPR joints. To evaluate the durability performance of the SPR joints in the structures, fatigue tests of the front shock tower structures were conducted with constant amplitude loadings. Furthermore, this study investigated fatigue life prediction method of SPR joints and compared the fatigue life prediction results with that of experimental results. For fatigue life prediction of the SPR joints in the front shock tower structures, lap-shear and cross-tension specimens of SPR joint were constructed and tested to characterize the fatigue properties of the SPR joint. Then, the SPR joint was represented with area contact method (ACM) in finite element (FE) models. The load-life curves of the lap-shear and cross-tension specimens were converted to a structural stress-life (S-N) curve of the SPR joints. The S-N curve was used to predict fatigue life of SPR joints in the front shock tower structures. The test results and the prediction results were well correlated.

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Liu, Li, Yao Nan Cheng, Jun Qian, Ya Nan Gong, Ming Yang Wu et Fu Gang Yan. « Analysis on Regularity of Fatigue Crack of Heavy Carbide Insert Under Dynamic Alternating Loading ». Key Engineering Materials 589-590 (octobre 2013) : 58–63. http://dx.doi.org/10.4028/www.scientific.net/kem.589-590.58.

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In the machining process of large parts, the dynamic alternating loading suffered by heavy carbide insert is very large, so the fatigue failure of the insert is serious. Through the analysis the effect of dynamic alternating force - thermal load on insert’s crack, and the fatigue crack experiment of inserts under dynamic alternating loading will be done, the formation conditions and distribution law of fatigue cracks can be researched under the effect of dynamic mechanical shock and thermal shock. And the fatigue crack will be theoretical analysis through the fatigue curve in the range of test cutting parameters. It can provide effective basis for the optimizing the heavy-duty cutting parameters and reducing the fatigue crack failure of heavy-duty cutting insert.

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Su, Chun, Jianzhong Zhou, Xiankai Meng et Jie Sheng. « Comparison of warm laser shock peening and laser shock peening techniques in lengthening the fatigue life of welded joints made of aluminum alloy ». International Journal of Modern Physics B 31, n^o 16-19 (26 juillet 2017) : 1744045. http://dx.doi.org/10.1142/s0217979217440453.

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Welded joints made of 6061-T6 Al alloy were studied to evaluate warm laser shock peening (WLSP) and laser shock peening (LSP) processes. The estimation model of laser-induced surface residual stress was examined by means of experiments and numerical analysis. The high-cycle fatigue lives of welded joint specimens treated with WLSP and LSP were estimated by conducting tensile fatigue tests. The fatigue fracture mechanisms of these specimens are studied by surface integrity and fracture surface tests. Experimental results and analysis indicated that the fatigue life of the specimens processed by WLSP was higher than that with LSP. The large increase in fatigue life appeared to be the result of the larger residual stress, more uniform microstructure refinement and the lower surface roughness of the WLSP specimens.

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Zhai, Jing Yu, Ying Yang et Qing Kai Han. « Fatigue Crack Propagation Simulation of Rubber Shock Absorbers ». Advanced Materials Research 415-417 (décembre 2011) : 2298–303. http://dx.doi.org/10.4028/www.scientific.net/amr.415-417.2298.

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Rubber shock absorbers are the key parts to isolate vibrations of the machinery and equipment. In this paper, a three dimensional finite element model of a rubber shock absorber is established; then the computation of three dimensional fatigue crack growth rates are discussed by using the nonlinear finite element method. The stress distribution which can determine the initial crack location and the possible risk surface under dynamic loads is obtained. The three dimensional crack growth is simulated by using finite element method and linear elastic fracture mechanics. A brittle fracture process of the rubber shock absorber along the dangerous surface is simulated by using the cohesive element of ABAQUS.

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Altenberger, I., Yuji Sano, M. A. Cherif, Ivan Nikitin et Berthold Scholtes. « Residual Stress State and Fatigue Behaviour of Laser Shock Peened Titanium Alloys ». Materials Science Forum 524-525 (septembre 2006) : 129–34. http://dx.doi.org/10.4028/www.scientific.net/msf.524-525.129.

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Laser shock peening is a very effective mechanical surface treatment to enhance the fatigue behaviour of highly stressed components. In this work the effect of different laser shock peening conditions on the residual stress depth profile and fatigue behaviour without any sacrificial coating layer is investigated for two high strength titanium alloys, Ti-6Al-4V and Timetal LCB. The results show that the optimization of peening conditions is crucial to obtain excellent fatigue properties. Especially, power density, spot size and coverage severely influence the residual stress profile of laser shock peened Ti-6Al-4V and Timetal LCB specimens. For both alloys, subsurface as well as surface compressive residual stress peaks can be obtained by varying the peening conditions. In general, Timetal LCB exhibits steeper stress gradients than Ti-6Al-4V for identical peening conditions. The main parameters affecting the fatigue life are near-surface cold work and compressive residual stresses.

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Mészáros, István, et János Ginsztler. « Magnetic Testing of Power Plant Steel Deterioration ». Materials Science Forum 792 (août 2014) : 183–88. http://dx.doi.org/10.4028/www.scientific.net/msf.792.183.

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Nowadays, there is increasing importance of the remaining life time estimation of engineering structures. In this work the thermal shock fatigue process induced deterioration of the three different power plant steels was investigated. The tested steels are widely used as steam pipeline base material of power plants. The applied thermal shock fatigue test can model the material degradation due to long term service in high temperature environment. A special AC magnetometer was designed and used for the magnetic measurements at the Department of Materials Science and Engineering of BUTE. In this paper a new high sensitivity magnetic measurement is presented for controlling the thermal shock fatigue deterioration. This measurement technique was developed for non-destructive testing of pipelines and pressure vessels of steam power plants.

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Chen, Hongxia, Yunxia Chen et Yi Yang. « A fatigue and low-energy shock-based approach to predict fatigue life ». Journal of Mechanical Science and Technology 28, n^o 10 (octobre 2014) : 3977–84. http://dx.doi.org/10.1007/s12206-014-0909-5.

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Yang, Fei, Ping Liu, Liucheng Zhou, Weifeng He, Xinlei Pan et Zhibin An. « Review on Anti-Fatigue Performance of Gradient Microstructures in Metallic Components by Laser Shock Peening ». Metals 13, n^o 5 (18 mai 2023) : 979. http://dx.doi.org/10.3390/met13050979.

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Laser-shock-peening technology is an international research hotspot in the surface-strengthening field, which utilizes the mechanical effects of laser-induced plasma shock waves to effectively improve the fatigue performance of metallic components by introducing the gradient microstructures and compressive residual stress into the surface layer of processed materials. The fatigue failure caused by high-frequency vibrations in aeroengines during service is the most important threat to flight safety, and this case is more prominent for military aeroengines because their service situation is harsher. The present paper focuses on components such as high-temperature components, fan/compressor blade, and thin-walled weldments, and it systematically introduces the researching findings about surface nanocrystallization and compressive residual stress formation mechanism in typical aeronautical metallic materials treated by laser shock peening. The contents mainly involve the characteristics, formation process, fatigue resistance mechanism, thermal stability of residual compressive stress, and nanocrystallization generated by laser shock peening.

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Caruso, Henry, et Edward Szymkowiak. « A Clarification of the Shock/Vibration Equivalence in MIL-STD-810D/E ». Journal of the IEST 32, n^o 5 (1 septembre 1989) : 28–31. http://dx.doi.org/10.17764/jiet.1.32.5.t4r3xn43g37q8170.

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This paper presents a methodology for expanding the shock/vibration equivalence analysis defined in MIL-STD-810D/E, Method 516.3/516.4, Procedure I (Functional Shock), Paragraph I-3.3. Procedure I defines equivalence only for situations where the vibration response spectrum (VRS) exceeds the shock response spectrum (SRS) everywhere in the specified range of frequencies. This paper supplements the MIL-STD-810D/E methodology with an analytical procedure for evaluating possible equivalence when the SRS is greater than the VRS. Using Miner's Hypothesis, the fatigue damage potential of the vibration cycles above the 3-δ limit is compared with the fatigue damage potential of the shock pulses in each axis. An example is included.

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Jiang, Yin Fang, Xian Cong He, Yu Huang, Jian Wen Zhang et Zhi Fei Li. « Investigated on Fatigue Properties of Aluminum Ally 7050T7451 with Fastener Holes by Laser Shock Processing ». Advanced Materials Research 460 (février 2012) : 407–10. http://dx.doi.org/10.4028/www.scientific.net/amr.460.407.

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Based on the FEM code ABAQUS and MSC.Fatigue, the process of LSP before hole-drilling was adopted to study the residual stress field of aluminum alloy7050T7451 with Fastener Holes after Laser shock processing (LSP), and the fatigue life of the specimens by LSP was analyzed in this paper. The results indicate that multiple laser shock processing can improve the residual compressive stress and fatigue life to a certain degree, and with the increasing number of shot, the strengthening effect gradually decreases. The ratio of the fatigue life of specimens treated by LSP to the fatigue life of untreated specimens is gradually decreased as the mean stress σm increases, and when the σm is 67.3MPa, the fatigue life of specimens treated by LSP advances 719%, compared with that of untreated specimens.

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Wang, Zhi Ping. « Research on Fatigue Behaviors of Nodular Cast Iron QT800 by Laser Shock Processing ». Advanced Materials Research 136 (octobre 2010) : 260–63. http://dx.doi.org/10.4028/www.scientific.net/amr.136.260.

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The surface of nodular cast iron QT800 was processed with LSP, its micro-structures, residual stress and fatigue test were compared before and after LSP, and the rupture morphologies of fatigue test were analyzed, the effects of LSP on fatigue behavior of QT800 were discussed. The results shown that the compressive residual stress of QT800 by LSP is over 400MPa, and its fatigue life is increased 20% than that in primitive state; the fatigue resource or the sample by LSP is produced near the graphite, compressive residual stress and refined grain effectively delays cracks initiation of the fatigue source, the expansion speed of fatigue cracks is decreased, which increases fatigue life of QT800.

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Jiao, Sheng Bo, Li Cheng, Quan Tong Li et Xiao Wei Li. « Study on Very-High-Cycle-Fatigue Property of Aero-Engine Blades Based on Subcomponent Specimen ». Key Engineering Materials 664 (septembre 2015) : 87–95. http://dx.doi.org/10.4028/www.scientific.net/kem.664.87.

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The cyclic load number of aero-engine blade during its service life is very likely beyond 107, which is regarded as the conventional fatigue limit. Moreover, surface strengthening is very often used in the manufacturing process of blade. The conventional testing method in the VHCF regime cannot exactly reflect the stress state of the blade, including the mechanism of crack initiation. To study the fatigue behavior and effects of laser shock peening, a kind of bending fatigue subcomponent specimen was designed and the laser shock peening model was established. Experiment about TC17 was accomplished by the Ulra-High Cycle bending fatigue system. It is found that the fatigue damage occurs beneath the surface and the S-N curve is continuously rather than multi-step declining in the VHCF regime. Process of surface strengthening has a significant effect on fatigue performance of TC17 titanium alloy.

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RAMAN, GANESH. « Screech tones from rectangular jets with spanwise oblique shock-cell structures ». Journal of Fluid Mechanics 330 (10 janvier 1997) : 141–68. http://dx.doi.org/10.1017/s0022112096003801.

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Understanding screech is especially important for the design of advanced aircraft because screech can cause sonic fatigue failure of aircraft structures. Although the connection between shock-cell spacing and screech frequency is well understood, the relation between non-uniformities in the shock-cell structures and the resulting amplitude, mode, and steadiness of screech have remained unexplored. This paper addresses the above issues by intentionally producing spanwise (larger nozzle dimension) variations in the shock-cell structures and studying the resulting spanwise screech mode. The spanwise-oblique shock-cell structures were produced using imperfectly expanded convergent–divergent rectangular nozzles (aspect ratio = 5) with non-uniform exit geometries. Three geometries were studied: (a) a nozzle with a spanwise uniform edge, (b) a nozzle with a spanwise oblique (single-bevelled) edge, and (c) a nozzle that had two spanwise oblique (double-bevelled) cuts to form an arrowhead-shaped nozzle. For all nozzles considered, the screech mode was antisymmetric in the transverse (smaller nozzle dimension) direction allowing focus on changes in the spanwise direction. Three types of spanwise modes were observed: symmetric (I), antisymmetric (II), and oblique (III). The following significant results emerged: (i) for all cases the screech mode corresponds with the spanwise shock-cell structure, (ii) when multiple screech modes are present, the technique presented here makes it possible to distinguish between coexisting and mutually exclusive modes, (iii) the strength of shocks 3 and 4 influences the screech source amplitude and determines whether screech is unsteady. The results presented here offer hope for a better understanding of screech and for tailoring shock-containing jets to minimize fatigue failure of aircraft components.

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Sun, Yaofei, Han Wu, Haifeng Du et Zhenqiang Yao. « Investigation of Strain Fatigue Behavior for Inconel 625 with Laser Shock Peening ». Materials 15, n^o 20 (18 octobre 2022) : 7269. http://dx.doi.org/10.3390/ma15207269.

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With excellent creep resistance, high-temperature thermal strength and high-temperature fatigue strength, Inconel 625 is widely applied to fabricate structural components in the aerospace field, where fatigue life is a key point. Laser shock peening (LSP) is considered to improve the fatigue strength and fatigue crack growth resistance of metal materials. The present work was conducted to investigate the influence of LSP on strain-controlled fatigue behavior of Inconel 625. The surface microstructures of specimens before and after LSP were observed by transmission electron microscope (TEM). The strain-controlled fatigue loading tests with different strain amplitudes ranging from 0.4% to 1.2% were carried out on the specimens, and the topography of fracture appearance was examined by scanning electron microscope (SEM). The investigations showed that the specimens with LSP presented fewer crack initiations, shorter fatigue striations space and smaller dimples or micropores, which account for the enhancement of the fatigue life for the LSP specimens. Furthermore, the plastic deformation, ultra-fine grains, twins and dislocations caused by LSP could prevent crack initiation, crack propagation and ultimate fracture, hence prolonging the fatigue life of the Inconel 625. In addition, it was revealed that the cyclic strain hardening as well as cyclic strain softening remains almost the same to Inconel 625 with or without LSP.

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Tang, Yang, MaoZhong Ge, Yongkang Zhang, Taiming Wang et Wen Zhou. « Improvement of Fatigue Life of GH3039 Superalloy by Laser Shock Peening ». Materials 13, n^o 17 (31 août 2020) : 3849. http://dx.doi.org/10.3390/ma13173849.

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In order to improve fatigue life of GH3039 superalloy, GH3039 superalloy sheets were treated by laser shock peening (LSP). The microstructure of GH3039 superalloy before and after LSP was characterized using an optical microscope, transmission electron microscope (TEM), and X-ray diffractometer. The fatigue life of the samples with and without LSP was investigated by fatigue experiments. Moreover, surface profile and residual stress were also examined. Experimental results indicated that the grains in the surface layer of the LSP sample were remarkably refined and reached the nanometer scale. The average surface roughness increased from 0.024 μm to 0.19 μm after LSP. The average fatigue life of the laser treated samples was 2.01 times larger than that of the untreated specimens. Additionally, mathematical statistical analysis confirms that LSP has a significant influence on the fatigue life of GH3039 superalloy. The improvement of fatigue life for the laser processed GH3039 superalloy was mainly attributed to compressive residual stress and grain refinement generated by LSP.

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Gupta, Pradeep, Pramod Kumar et Srisha M. V. Rao. « Low-frequency unsteadiness of recompression shock structures in the diffuser of supersonic ejectors ». Physics of Fluids 35, n^o 3 (mars 2023) : 036119. http://dx.doi.org/10.1063/5.0137051.

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Supersonic ejectors are passive gasdynamic devices that compress a low-pressure fluid by utilizing the kinetic energy of a high-pressure fluid in a variable area duct. The ejector consists of a primary supersonic nozzle in a mixing duct where the secondary flow is entrained and mixed. The mixed flow can undergo a series of recompression shocks resulting in a subsonic flow in the diverging portion to aid pressure recovery. Recompression shocks usually lead to unsteady shock boundary layer interactions. The performance of the ejector is influenced by shear layers, shock and expansion waves, and their mutual interactions. While existing literature has extensively dealt with mixing of the primary and secondary flows, the unsteadiness in flow resulting from recompression shocks has been seldom investigated. Fluctuations in pressure due to the unsteadiness of the shock often lead structural fatigue issues. This paper reports a detailed investigation on low-frequency unsteadiness of recompression shock using high-speed schlieren images and dynamic pressure measurements. Modal analyses using proper orthogonal decomposition and dynamic mode decomposition techniques are used to determine the dominant spatial modes and associated frequencies. Multimodal frequencies ranging between 80 and 300 Hz are observed. These findings are further corroborated by Fourier and wavelet transformations of the experimentally measured wall static pressure signals. Subsequently, scaling parameter is established for the dominant frequencies based on flow velocities upstream of the shock and the distance between two consecutive shocks. This results in a unique scaling frequency of 4.58% ± 18%, for the recompression shock independent of operating conditions.

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Shao, Jiang, Hongjian Zhang et Bo Chen. « Experimental Study on the Reliability of PBGA Electronic Packaging under Shock Loading ». Electronics 8, n^o 3 (2 mars 2019) : 279. http://dx.doi.org/10.3390/electronics8030279.

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Plastic Ball Grid Array (PBGA) one of the most important electronic packaging methods, is widely used in aeronautical industry field. According to the JEDEC standard, shock tests of PBGA assemblies are conducted under different loading conditions. Several important parameters, such as the fatigue life of PBGA assemblies, the relationship between solder joint positions and fatigue life, the relationship between strain energy density and fatigue life, are analyzed based on experiment results. The failure modes of PBGA assemblies are studied by optical microscope (OM). The results show that during the shock tests, the strains of the solder joints near the center of the specimen are larger than other positions, and these solder joints are prone to form micro cracks. With the increase of the shock times, these micro cracks extend rapidly which will eventually cause the failure of the PBGA electronic packaging.

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Mahendra, Afrizal Yose, Aditya Rio Prabowo et Triyono Triyono. « Failure analysis of motorcycle shock breakers ». Open Engineering 11, n^o 1 (1 janvier 2021) : 1150–59. http://dx.doi.org/10.1515/eng-2021-0109.

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Abstract The shock breaker is one of the most important parts of a motorcycle, which functions as a vibration damper. This study aims to analyze the causes of motorcycle shock breaker failure. The research method used is comprised of visual observation, chemical composition testing, Vickers hardness testing, scanning electron microscopy-energy dispersive X-ray spectroscopy analysis, and tensile testing of a damaged shock breaker. From visual observation, it is found that the damage can be classified as a fatigue fracture, forming a damage pattern at 45°. The chemical composition testing results of the shock breaker fractures show that the material includes low-carbon alloy steel (of ST42 series) with a carbon content of 0.162%. The average hardness value of the damaged part of the shock breaker was increased to 204.87 HV, compared with 171.02 HV in areas far from the damage. The difference in hardness in the shock breaker was caused by the high stress acting on the shock breaker and the consequent strain hardening. The results of this study indicate that the failure mechanism of the motorcycle shock breaker was a functional failure due to errors in the shock breaker manufacturing process and fatigue.

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Jin, Jia, De Guang Shang, Xiao Dong Liu, Li Hong Zhang, Yu Bo Guo et Tao Chen. « Multiple Healing Fatigue Damage by Laser Shock Peening for Copper Thin Film ». Advanced Materials Research 760-762 (septembre 2013) : 413–16. http://dx.doi.org/10.4028/www.scientific.net/amr.760-762.413.

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Multiple healing fatigue damage for polycrystal copper film was investigated by laser shock peening (LSP). The damaged specimens were healed several times under the optimal laser parameters. The relationship among the fatigue life, healing times and the damage degree were investigated. The experimental results showed that the multiple heal based on LSP can maximize fatigue life of the damaged specimens under the definite optimal condition with the obtained at damage degree of 0.4 and healing times of 3, in which nearly 4.6 times increase in residual fatigue life for the damaged specimens, and 7.8 times increase in the accumulated fatigue life.

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SAKAI, Noboru, et Kazuhiro DATE. « Assessment of thermal shock fatigue tests in rocks. » Journal of the Japan Society of Engineering Geology 28, n^o 3 (1987) : 126–40. http://dx.doi.org/10.5110/jjseg.28.126.

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Panda, P. K., T. S. Kannan, J. Dubois, C. Olagnon et G. Fantozzi. « Thermal shock and thermal fatigue study of alumina ». Journal of the European Ceramic Society 22, n^o 13 (décembre 2002) : 2187–96. http://dx.doi.org/10.1016/s0955-2219(02)00022-5.

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Roussos, Charis. « Diaphragmatic fatigue and blood flow distribution in shock ». Canadian Anaesthetists’ Society Journal 33, S1 (mai 1986) : S61—S64. http://dx.doi.org/10.1007/bf03019158.

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Zhang, Yongkang, Shuyi Zhang, Chengye Yu, Yaxin Tang, Hong Zhang, Hongxing Wu, Dahao Guo et al. « Laser shock-processing for fatigue and fracture resistance ». Science in China Series E : Technological Sciences 40, n^o 2 (avril 1997) : 170–77. http://dx.doi.org/10.1007/bf02916949.

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Zichil, Valentin, Adrian Judele, Aurelian Albut, Carol Schnakovszky, Alexandre Sava et Petru Lozovanu. « Internal Energy Use in Calculating the Lifetime of 2P Armor Steel ». Applied Mechanics and Materials 809-810 (novembre 2015) : 537–42. http://dx.doi.org/10.4028/www.scientific.net/amm.809-810.537.

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Armored steel sheets have various uses in civil and military industry. For the last one, especially in aeronautics, a better determination of the lifetime for the fatigue and shock loaded parts, is a major challenge. Several methods for fatigue calculus are known: safe-life, fail-safe, crack propagation method. All of this methods are not considering in any way the shocks that can accidentally occur, so in the calculation of lifetime, the role of impact multiplier is null. The authors propose a corrected formula for the calculus of the lifetime for 2P armor steel, based on the internal energy developed into the test specimens, through the impact multiplier.

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Hao, Huibing, et Chunping Li. « Reliability Modeling and Evaluation for Complex Systems Subject to New Dependent Competing Failure Process ». Mathematical Problems in Engineering 2022 (10 août 2022) : 1–17. http://dx.doi.org/10.1155/2022/5432809.

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The objective of this study is to construct some system-level reliability models subject to new dependent competing failure process of the soft failure process and hard failure process. In those complex system-level models, the soft failure caused by continuous degradation and sudden degradation increases by random shocks and hard failure due to the same shock process; in addition, the bidirectional effects between natural degradation and random shock are considered in this study; in other words, the random shock can bring additional degradation, and the natural degradation may also impact the shock process. Therefore, the soft failure process and hard failure process are dependent. By using the cumulative shock model and Gaussian stochastic degradation process with line mean value and line standard deviation, five types of reliability models were established: (1) single component model; (2) series system model; (3) parallel system model; (4) series-parallel system model; and (5) parallel-series system model. Finally, an example of fatigue crack growth dataset is taken to verify the effectiveness of the established model and method, and some sensitivity analyses are given. The results show that the bidirectional effects can significantly accelerate the system failure, and the impact of natural degradation process to random shocks should not be ignored. In addition, the results also show that random shock and failure threshold have significant effects on the different complex systems.

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Morrison, J. B., S. H. Martin, D. G. Robinson, G. Roddan, J. J. Nicol, M. J.-N. Springer, B. J. Cameron et J. P. Albano. « Development of a Comprehensive Method of Health Hazard Assessment for Exposure to Repeated Mechanical Shocks ». Journal of Low Frequency Noise, Vibration and Active Control 16, n^o 4 (décembre 1997) : 245–56. http://dx.doi.org/10.1177/026309239701600403.

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This study describes a Health Hazard Assessment (HHA) method for evaluating exposures to repeated shocks in tactical ground vehicles (TGV). This method will predict the risk of injury to the crew of a TGV given its acceleration signature. The HHA will identify both acute and chronic health risks resulting from either a single shock, or prolonged exposure due to travel over rough terrain. The HHA is based partly on existing models, human response and injury data, as well as partly on experimental data obtained from volunteers exposed to a range of shock profiles and to prolonged repeated shock exposures. The HHA consists of three components: dynamic response models which predict seat-to-spine transmission of acceleration; a dose-recovery model for exposure to repeated shocks based on fatigue failure theory and subjective tolerance data; and an injury risk model based on the cumulative probability of failure. A biomechanical model was also developed which analyses spinal compression in response to shock. This model does not form part of the HHA model, but will provide an independent evaluation of the HHA using the experimental data from this study. The components of the HHA are outlined and some test results presented.

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Yaxin, Tang, Zhang Yongkang, Zhang Hong et Yu Chengye. « Effect of Laser Shock Processing (LSP) on the Fatigue Resistance of an Aluminum Alloy ». Journal of Engineering Materials and Technology 122, n^o 1 (10 mars 1999) : 104–7. http://dx.doi.org/10.1115/1.482773.

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The laser shock induced stress wave is described and measured with a polyvinylidene fluoride (PVDF) transducer. A principle for selecting laser parameters is proposed. A small sized laser with a high power is used for Laser Shock Processing (LSP). The fatigue life of the aluminum alloy 2024T62 is greatly improved after LSP. With 95% confidence, the mean fatigue life of LSP specimens is 4.5–9.8 times that of unshocked ones. The fatigue and fracture resistance mechanisms of LSP such as the variation of the surface hardness, the microstructure and the fracture section of specimens before and after LSP are analyzed. [S0094-4289(00)01601-7]

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Chen, Rui Fang, Hui Jiang, Yin Qun Hua, Yu Xiao Chen et Zhen Grong Cai. « Effect of Laser Shock Processing on Fatigue Performance of 7075-T651 Aluminum Alloy ». Advanced Materials Research 139-141 (octobre 2010) : 430–33. http://dx.doi.org/10.4028/www.scientific.net/amr.139-141.430.

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The effect of laser shock processing (LSP) on bending fatigue performance of 7075-T651 aluminum alloy was studied. LSP was performed on fatigue testing specimens with optimized parameters. Stress-life fatigue data were generated for both shocked and as-machined conditions. The fatigue improvements of LSP were discussed accounting for the effect of residual stress. The results show that shocked specimens exhibited significantly improved fatigue performance, with as-machined specimens having a factor of 1.6-4.4 improvement in fatigue life (depending on fatigue stress level). The stability of the residual stress induced by LSP under cyclic load was particularly investigated by means of X-ray diffraction measurements. Residual stress relaxation was observed. And the higher the cyclic load, the higher the relaxation rate. Due to the cyclic creep effect, the residual stress decreases linearly with the logarithm of the number of cycles.

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Encarnación-Martínez, Alberto, Antonio García-Gallart, Roberto Sanchis-Sanchis et Pedro Pérez-Soriano. « Effects of Central and Peripheral Fatigue on Impact Characteristics during Running ». Sensors 22, n^o 10 (16 mai 2022) : 3786. http://dx.doi.org/10.3390/s22103786.

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Fatigue and impact can represent an injury risk factor during running. The objective of this study was to compare the impact transmission along the locomotor system between the central and peripheral fatigued states during running. Tibial and head acceleration as well as shock attenuation in the time- and frequency-domain were analyzed during 2-min of treadmill running in the pre- and post-fatigue state in eighteen male popular runners (N = 18). The impact transmission was measured before and after a 30-min central fatigue protocol on the treadmill or a peripheral fatigue protocol in the quadricep and hamstring muscles using an isokinetic dynamometer. The time-domain acceleration variables were not modified either by peripheral or central fatigue (p > 0.05). Nevertheless, central fatigue increased the maximum (p = 0.006) and total (p = 0.007) signal power magnitude in the high-frequency range in the tibia, and the attenuation variable in the low- (p = 0.048) and high-frequency area (p = 0.000), while peripheral fatigue did not cause any modifications in the frequency-domain variables (p > 0.05). Furthermore, the attenuation in the low (p = 0.000)- and high-frequency area was higher with central fatigue than peripheral fatigue (p = 0.003). The results demonstrate that central fatigue increases the severity of impact during running as well as the attenuation of low and high components.

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