采用Ａ５３７钢单边缺口试样，研究了以不同方式叠加在主载荷△Ｐ上的小幅载荷在疲劳裂纹扩展过程中的作用，并采用激光散斑技术测量了循环加载过程中的裂纹闭合效应。结果表明：３０％△Ｐ以下的小幅载荷叠加在主载荷底部时，对由主载荷引起的裂纹扩展速率ｄａ／ｄＮ几乎没有影响，３０％△Ｐ以上的小幅载荷可使裂纹扩展速率增加。叠加在主载荷顶部的各小幅载荷均可使裂纹扩展速率加大。通过对加载条件下裂纹闭合效应的测量，并结合裂尖的应力应变状态的变化进行分析认为：小幅载荷对裂纹扩展速率的影响受裂纹闭合程度的制约，其损伤作用只体现在裂尖材料产生不可逆塑性形变的外加载荷范围内。
The influence of small loads superposed upon principal cyclic load △P on the fatigue crack growth rate da/ dN has been studied for the single edge notched plate specimens of A537 steel, and the crack closure behaviour has been investgated by measurement of crack opening displacement with speckle interferometry(SPI) technique. The results showed that the small loads with amplitude below 30% △P had little influence on da/ dN caused by the principal load when they superposed on the bottom of △P; whereas the small loads with amplitude above 30% △P enhanced the crack growth in the same condition. All small loads superposed on the top of △P made the da / dN increased. It could be proved by the analysis of measured crack closure effect that the influence of small loads on da / dN is determined by crack closure, and the damage of crack tip material caused by the superposed small loads comes from the irreversible plastic deformation which only appears in a certain range of applied load.
参考文献
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