Papers by Keyword: Crack Closure

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Authors: Xue Ping Zhang, C.H. Wang, Jia Cai Li, Yiu Wing Mai, Lin Ye
Authors: Chow Shing Shin, Shi Wei Lin
Abstract: There are situations where baseline fatigue crack propagation (FCP) data are needed but the available material for its evaluation is far from enough to fabricate full sized standard specimens. Miniature specimen testing techniques have been proposed but published data seems to be slightly but consistently slower under the same stress intensity than that from standard specimen results. In this work, an aluminum alloy and a steel, which have vastly different mechanical behaviors, are used to generate different stress states and premature crack closure to allow the validity of miniature specimen FCP data to be critically examined.
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: Hong Cai Zhang, K.Z. Huang, J.H. Cheng
Abstract: A new model for predicting the small-crack growth rates is proposed under the constant amplitude loading. With the use of two important parameters, the transition crack length a0 and the barrier characteristic parameter d*, the new model can reflect the abnormal feature of small-crack growth. The effect of crack closure is considered in the model as well. The model is shown to provide a better correlation to the experimental results for the Ti-6Al-4V alloy under various stress levels at a stress ratio of R = 0.4.
Authors: Masahiro Endo, A.J. McEvily
Abstract: A modified linear-elastic fracture mechanics approach proposed by McEvily has been applied to predict the effects of small defects on the fatigue limit and the threshold level. In the analysis, three modifications were taken into account (1) the effect of elastic-plastic behavior of small cracks, (2) the Kitagawa effect where in the very small crack regime the required stress for propagation is controlled by the fatigue limit of a smooth specimen rather than by the long-crack threshold condition, and (3) the effect of crack closure development from zero up to the macroscopic level as a newly formed crack extends. Three steels, a brass and an Al alloy were investigated. Good agreement between predicted and experimental results has been obtained and a rational basis for the area parameter model was shown.
Authors: Ya Zhi Li, Jing He, Zi Peng Zhang
Abstract: The behavior of plasticity induced fatigue crack closure (PICC) in middle tension specimen was analyzed by the elastic-plastic finite element method. For the constant-K (CK) loading cases, the opening stress intensity factor are independent of crack length. The level of increases with the maximal applied stress intensity factor for given load ratio and increases with for fixed . The in plane strain state is much smaller than that in plane stress state. The results under CK loadings can be deduced to constant amplitude cyclic loading case during which the load ratio, maximal load level, crack length and specimen thickness are all the factors affecting the crack closure effect. The phenomena revealed in the analysis are beneficial in understanding the driving force mechanism of the fatigue crack growth.
Authors: Ivo Černý, Václav Linhart
Abstract: The paper contains results of an experimental programme aimed at an evaluation of fatigue crack growth rate and threshold conditions in a reactor pressure vessel steel. Though the main target of the work was to gain a data basis for possible future needs of defect and risk assessment, an emphasis was put on an evaluation of crack growth mechanisms, too. It was shown that despite some recent works infirming crack closure phenomenon itself or methods of its evaluation, crack closure explained near-threshold fatigue crack behaviour in the specific case of the reactor steel in air conditions and was in a direct consistency with results of fractographical analyses. A fairly recent model of partial crack closure was very suitable for an explanation of an unexpected fatigue crack growth behaviour in water environment, when fatigue crack growth rates were rather irregular and significantly lower that in air.
Authors: Xiang Yang Huang, M. Lang, Xue Ren Wu, H. Döker
Authors: Aaron Alejandro Aguilar Espinosa, Neil Fellows, Oscar Portillo
Abstract: The numerical simulation of crack closure is employed to assist on the prediction of crack growth rate. Under fatigue load, the stress-strain response of metals is altered due to cyclic loading. For this reason, the material properties characterization is of prime concern as an input parameter to obtain reliable results. From numerical simulations, it was observed that simple material models do not provide accurate data for long crack lengths. In this paper, the effect that different hardening models have on the opening response of a cracked component when it is subject to variable amplitude loading is analyzed. The interaction effects (crack arrest/acceleration) for long crack length simulation are specially highlighted. For this purpose, a 6082-T6 aluminium alloy was analyzed experimentally and numerically in order to measure crack closure, and then, those data were used to predict fatigue crack growth rate under different patterns of overload. The Paris equation and the Elber crack closure concept were employed. The results showed that small variations in the opening stresses obtained from different material models produce high overestimated simulations of crack growth rate. Also, it was proved that the crack closure mechanism is able to take into account interaction effects due to variable amplitude loading.
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