单峰过载对裂尖塑性区晶内损伤分布的影响

Effect of single peak overload on intragranular damage distribution in plastic zone of crack tip

为探究金属材料受到变幅疲劳载荷时的晶内损伤状况,采用宏观Chaboche与细观晶体塑性有限元相结合的方法,建立了裂尖多晶模型,模拟的应力-应变曲线与实验基本一致。以修正的Fatemi-Socie准则为疲劳指示因子,筛出裂尖损伤最大的晶粒,统计了晶内总滑移变形量分布,并结合晶内纵向应力分布和广义施密特因子GSF分布情况来对其形成原因进行分析。结果表明,相较于恒幅循环,过载瞬间晶内的纵向应力及GSF最大值与均值的增大导致晶内易滑移的区域扩大和已滑移区域的滑动趋势增加,进而导致晶内总滑移变形量瞬间增大且滑移不均匀性增加。过载会导致后续循环拉伸峰值时刻纵向应力减小及GSF区间的扩大,提高滑移分布不均匀性,且卸载峰值时刻纵向拉应力的减小和压应力的增大会抑制晶内原有滑移增长速率。

To explore the intragranular damages of metal materials under fatigue load with variable amplitudes,the polycrystalline model of the crack tip was established by the combination method of macro Chaboche and meso crystal plastic finite element.The simulated stress-strain curves were basically consistent with the experiment.Taking the modified Fatemi-Society criterion as the fatigue indicator factor,the grain with the largest damage at the crack tip was screened out,the distribution of total slip deformation in the grain was counted,and its formation reason was analyzed combining with the distribution of longitudinal stress in the grain and the distribution of generalized Schmidt factor GSF.The results show that compared with the constant amplitude cycle,the increase of the longitudinal stress and the maximum value and average value of GSF at the moment of overload leads to the expansion of the region easy to slip and the increase of sliding trend of the slip region,which further leads to the instantaneous increase of the total slip deformation in grain and the increase of the non-uniformity of slip.Overload can lead to the decrease of longitudinal stress at the peak moment of subsequent cyclic tension and the expansion of GSF interval,improve the non-uniformity of slip distribution,and the decrease of longitudinal tensile stress and the increase of compressive stress at the peak of over-load can inhibit the original slip growth rate in the grain.