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首页> 外文期刊>材料 >Stress Ratio Dependence of Fatigue Crack Initiation and Small Crack Growth in Cast Aluminium Alloy AC4CH
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Stress Ratio Dependence of Fatigue Crack Initiation and Small Crack Growth in Cast Aluminium Alloy AC4CH

机译：疲劳裂纹启动和小裂纹增长在铸铝合金AC4CH中的应力比依赖性

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摘要

This paper describes the stress ratio dependence of fatigue behaviour in a cast aluminium alloy, AC4CH. Axial fatigue tests have been conducted using smooth specimens at three different stress ratios, R, of -1, 0.05 and 0.4. Particular attention has been paid to crack initiation and small crack growth behaviour. The Goodman relationship gave fairly good or slightly conservative estimation of fatigue strength at 10~7 cycles. Cracks initiated from a casting porosity or Sb-segregated defect and the latter defect acted more predominantly as crack initiation site. Regardless of stress ratio, small cracks initially grew faster than the corresponding large cracks characterized in terms of the effective stress intensity factor range, DELTA K_(eff), then gradually approached the da/dN- DELTA K_(eff) relationship for large cracks and coincided with it at a DELTA K value of 2 approx 3MPa m~(1/2). Based on detailed fractographic analyses, shear-type growth region following the crack initiation was clearly discerned, the size of which showed remarkable stress ratio dependence, with increasing crack size with decreasing stress ratio, particularly very large at R = -1. This shear-type crack growth was responsible for the acceleration of small cracks because of a different growth mechanism from large cracks.
机译：本文描述了在铸造铝合金，AC4CH的疲劳行为应力比的依赖性。轴向疲劳试验已经使用光滑试样在三个不同应力比，R，-1，0.05和0.4进行。特别注意了裂纹萌生和小裂纹增长的行为。古德曼关系在10〜7个周期，得到的疲劳强度相当好的或稍微保守估计。从铸件气孔或Sb偏析缺陷和后者缺陷引发的裂纹作用更主要作为裂缝起始位点。不管应力比，小裂纹最初增长速度比其特征在于所述有效应力强度因子范围方面相应的大的裂纹更快，DELTA K_（EFF），然后逐渐接近DA为大的裂纹/ DN-DELTA K_（EFF）和关系与它正好在2约3MPa的米〜的DELTA K值（1/2）。根据详细的断口分析，以下裂纹萌生剪切式生长区域被清楚看到，其尺寸的显示出显着的应力比的依赖性，具有随应力比，特别是在R = -1非常大的增加裂纹尺寸。该剪切型裂纹生长负责的，因为从大的裂纹不同的生长机理的小裂纹的加速度。

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