Papers by Keyword: Fatigue Crack Growth (FCG)

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Authors: Alisa Boonyapookana, Yoshiharu Mutoh, Kohsoku Nagata
Abstract: In-situ observation of fatigue crack growth of epoxy resin composite reinforced with crushed silica particle was carried out. The test was performed under constant ΔK condition. Based on the results, the crack propagation mechanism was discussed. The in-situ observation revealed that in front of the main crack, a microcrack was nucleated at the interface of matrix/particle and then coalesced with the main crack. At the same time, new microcracking occurred ahead of the crack tip and the crack propagated by repeating these processes. Retardation of crack growth rate was found to result from crack bridging induced by microcracking at silica particles and crack deflection.
Authors: Fei Fang, Fang Cheng Zhang, Wei Yang
Abstract: In-situ observation of the fatigue crack growth and 90o domain switching was carried out for BaTiO3 ferroelectric single crystals under alternating electric field. It is shown that during the electric cycling, the crack propagates continuously. Parallel lines of 90o domain boundaries can be seen and they flip at each reversal of the alternating electric field. The width of the 90o domain switching zone grows with the number of cycles and its frontal always lies ahead of the crack tip. It is suggested that the cyclic stress field induced by the repeated 90o domain switching at the crack tip, as well as the stress field caused by the electrically activated material between the electrode and the material under the electrodes contribute to the observed fatigue crack growth.
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.
Authors: Nathan Klingbeil, Jeremy Daily, Craig Baudendistel
Abstract: This paper summarizes recent work on a new theory of fatigue crack growth in ductile solids based on the total plastic energy dissipation per cycle ahead of the crack. The fundamental hypothesis of the theory proposes a unified criterion for crack extension under monotonic and fatigue loading, so that the fatigue crack growth rate is given explicitly in terms of the total plastic dissipation per cycle and the monotonic fracture properties of the material. The total plastic dissipation per cycle is obtained by 2-D elastic-plastic finite element analysis of a stationary crack under constant amplitude loading, for both mode I (C(T)) and general mixed-mode I/II specimen geometries. Both elastic-perfectly plastic and bi-linear kinematic hardening constitutive behaviors are considered, and numerical results for a dimensionless plastic dissipation per cycle are presented over a wide range of relevant mechanical properties and mixed-mode loading conditions. Results are further extended to include fatigue delamination of layered material systems, where either discrete mismatches or a continuous grading of mechanical properties can exist across the interface.
Authors: Li Xiong Gu, Zhi Fang Liu, Zhong Yong Xu
Abstract: Almost all load bearing components usually experience variable amplitude loading (VAL) rather than constant amplitude loading (CAL) during their service lives. The present study aims at evaluating residual fatigue life under VAL by adopting a dynamical coefficient mechanics (DCM) model which we have reported. New formulas connecting the crack length with number of cycles and expressions for the FCG rate under VAL have been derived and were used to predict crack propagation. The ratios of predicted-to-experimental lives range from 1.00 to 1.04, which indicates that the results obtained from this DCM model are in good agreement with experimental data from published literatures and cover all stages of fatigue crack growth curve.
Authors: A.J. McEvily
Abstract: The behavior of short fatigue cracks is a matter of importance not only because much of the fatigue lifetime is spent in propagating these cracks, but also because the boundary between propagation and non-propagation separates the safe from the potentially unsafe fatigue regimes. The method of analysis is based upon the following equation:
Authors: Wyman Zhuang, Qian Chu Liu
Abstract: The fatigue critical structures of military aircraft are generally subjected to variable amplitude flight spectrum loading. Maintaining aircraft structural integrity to ensure safe operation of the fleet is critically dependent on accurate analysis and reliable prediction of fatigue crack growth in those structures under service operating conditions. To achieve this goal, laboratory experimental methods that can accurately measure and monitor fatigue crack growth under variable amplitude loading are required. This can be challenging as no test standard exists to guide the process of fatigue crack growth measurement under variable amplitude loading conditions to ensure the accuracy of the test results. This challenge was addressed by developing a modified compliance method as described in this paper. The results presented employed a modified compliance method complemented with a travelling microscope technique and marker band loads. The modified compliance method developed is able to measure in-situ, fatigue crack growth of standard compact-tension specimens under a fighter flight spectrum loading. The marker band loads and microscope readings were used to assist the post-test validation using quantitative fractography. The results from this study have demonstrated that the modified compliance method can produce consistent and accurate fatigue crack growth data under variable amplitude loading conditions.
Authors: Dang Hui Wang, Tian Han Xu
Abstract: Electrical parameters and low-frequency noise test were measured for N80 steel casing drilling, through extracting low-frequency parameters and combining with conventional fatigue crack growth characterization methods and analyzing their morphology. After fatigue crack growth, the results showed that: (1) Electrical parameters of N80 increase, and power spectral density of 1/f noise increases two orders of magnitude. (2) Values of γ and B are significantly increased, indicating that the process of fatigue produced more cracks, defects, and combination centers, from the mechanism of fatigue crack growth of N80, defects and cracks resulting from fatigue are the numbers of kind of fluctuations. In essence, low-frequency noise is a type of fluctuations, which show that low-frequency noise as the characterization of non-destructive., which can serve as a viable tool to study the defects and the characterization of defects.
Authors: Jan Ondráček, Aleš Materna, Vladislav Oliva
Abstract: A 2D elastic-plastic FEM simulation of growing fatigue crack under combined mode I and II loading was performed. An inclined fatigue crack propagated in a sheet of an Al-alloy D16CT1. The effect of increasing mode-mixity on cyclic zone size, shape and the amount of dissipated energy was investigated.
Authors: Md. Anowar Hossian, Man Bae Lim, Sun Chul Huh, Won Jo Park
Abstract: This study evaluated fatigue crack growth characteristics, Besides consider compressive residual stress effect and verified the most suitable shot peening velocity. Fatigue crack growth delay effect was compressive residual stress, but over peening did action projecting velocity that accelerate fatigue crack growth rate. X-ray diffraction technique according to crack length direction was applied to fatigue fractured surface. Fracture mechanics parameters could be estimated by the measurement of X-ray parameters, and the fractography observation was performed using a scanning electron microscope (SEM) for fatigue fracture surface. As the shot peening velocity increases, striation width increased. The changes in X-ray material parameters described above are directly related to the process of fatigue until the initiation of fatigue crack and X-ray diffraction pattern is thought that failure prediction with stress distribution is possible.
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