Papers by Keyword: Fatigue Crack Initiation

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Authors: Dale L. Ball, Mark A. James, Robert J. Bucci, John D. Watton, Adrian T. DeWald, Michael R. Hill, Carl F. Popelar, R. Craig McClung
Abstract: The fully effective utilization of large aluminum forgings in aerospace structures has been hampered in the past by inadequate understanding of, and sometimes inaccurate representation of, bulk residual stresses and their impact on both design mechanical properties and structural performance. In recent years, significant advances in both computational and experimental methods have led to vastly improved characterization of residual stresses. As a result, new design approaches which require the extraction of residual stress effects from material property data and the formal inclusion of residual stresses in the design analysis, have been enabled. In particular, the impact of residual stresses on durability and damage tolerance can now be assessed, and more importantly, accounted for at the beginning of the design cycle.
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Authors: Kyung Su Kim, Sung Chan Kim, Chun S. Shim, Hyung M. Cho, Sung Won Lee
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Authors: Jiří Man, Miroslav Valtr, Ivo Kuběna, Martin Petrenec, Karel Obrtlík, Jaroslav Polák
Abstract: Atomic force microscopy (AFM) and focused ion beam technique (FIB) were adopted to study the early stages of surface relief evolution in 316L steel and polycrystalline copper fatigued with constant plastic strain amplitudes at different temperatures (316L steel at 93, 173 and 573 K; copper at 83, 173 and 295 K). Qualitative and quantitative data on the morphology and shape of persistent slip markings (PSMs), occurrence of extrusions and intrusions and the kinetics of extrusion growth are reported. They are discussed in relation with recent physically based theories of surface relief formation leading to fatigue crack initiation.
524
Authors: Wen Li Wang, Wei Lian Qu, Jie He
Abstract: This paper proposes a new method for assessing the degree of the cumulative fatigue crack initiation damage of the joint welds at the guyed mast earplate. Based on the multi-scale wind-induced stress analysis of the guyed mast earplate joint, and considering the welding residual stress in earplate joint, the critical plane approach is used for the calculation of cumulative strain fatigue damage due to the combined actions of the welding residual stress and the wind load.
776
Authors: Karel Slámečka, Karel Němec, Ladislav Čelko, Marta Kianicová, Jana Horníková, Jaroslav Pokluda, Jiří Švejcar
Abstract: Room temperature fatigue behaviour of two variants of diffusion aluminide coatings and conventional air plasma sprayed CoNiCrAlY + ZrO2-Y2O3 thermal barrier system, which were deposited on a cast nickel-based supperalloy substrate, was studied under symmetrical bending loading regime. The study elucidates the differences in a fatigue crack initiation micromechanism with respect to applied stress level and its impact on the fatigue performance of studied coating systems.
716
Authors: Guo Cai Chai, Robert Lillbacka
Abstract: Two phase metals during cyclic loading can suffer from non-uniform load or strain sharing between the phases due to elastic/plastic anisotropy. This can strongly influence the fatigue damage and crack initiation behavior. In this study, the fatigue damage and crack initiation behavior of an austenitic-ferritic duplex stainless steel with anneal/quenched and aged conditions has been studied by both experimental investigations and simulation using multi-scale material modeling. It was found, both experimentally and via simulations, that the material damage and crack initiation start in the ferrite phase in the material with the anneal/quenched condition and in either the ferrite or austenite phase in the material with the aged condition, mainly in the weakest phase if the deformation hardening is considered.
1117
Authors: Yun Wang, Hidehiko Kimura, Yoshiaki Akiniwa, Keisuke Tanaka
Abstract: Both EBSD and AFM methods were used to investigate the active slip systems and fatigue crack initiation behavior in face-centered cubic polycrystalline metal, austenitic stainless steel, SUS316NG, under cyclic torsional loading. Most active slip planes are the primary slip planes having the largest Schmid factor. Grains with slip band cracks or transcrystalline cracks have larger Taylor's factors. On the basis of EBSD and AFM observations, h, the depth of intrusion vertical to the surface, S, and the component of the slip displacement perpendicular to the surface trace, SB, showed a sharp increase at the onset of crack initiation. The critical value of SB at crack initiation was 170 nm.
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Authors: You Shi Hong, Gui An Qian
Abstract: In this paper, rotary bending fatigue tests for a structural steel were performed in laboratory air, fresh water and 3.5% NaCl aqueous solution, respectively, thus to investigate the influence of environmental media on the fatigue propensity of the steel, especially in high cycle and very-high-cycle fatigue regimes. The results show that the fatigue strength of the steel in water is remarkably degraded compared with the case tested in air, and that the fatigue strength in 3.5% NaCl solution is even lower than that tested in water. The fracture surfaces were examined to reveal fatigue crack initiation and propagation characteristics in air and aqueous environments.
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Authors: Y. Iino
Abstract: Notched compact tension specimen of 304 stainless steel (0.8CT, notch tip radius of 1mm, thickness of 6mm) was low-cycle-fatigued at room temperature at stress ratio of -1 in 99.9999% H2 and in pure air at 1 and 0.1 Hz at apparent stress intensity factor of 34.4MPa . The H2 acceleration of both crack initiation and growth at notch is significant: 3-4 times faster than pure air. The accumulated plastic zone was analyzed by the recrystallization technique. It is shown that the accumulated plastic zone in H2 is smaller than in pure air.
285
Authors: Ryuichiro Ebara, A.J. McEvily
Abstract: The fatigue lifetime of the aluminum alloy 7075-6 depends upon the cyclic stress amplitude and the environment. At an R value of 0.05, and a maximum stress of 400 MPa the lifetime in vacuum is an order of magnitude greater than that in air, but interestingly at a maximum stress of 275 MPa, the lifetime in vacuum is only three times that in air. It was noted that well defined striations were observed in air, whereas striations were absent in vacuum, instead indications of ductile rupture were observed. The mechanism of fatigue crack initiation and propagation behavior as influenced by the environment is discussed.
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