单峰过载对工业纯钛CT试样裂纹闭合效应的影响

Influence of Single Peak Overload on Crack Closure Effect of CT Specimens Using Commercial Pure Titanium

基于数字图像相关技术,使用非线性迭代法拟合工业纯钛CT试样表面位移场,获得了过载前、过载时、过载后循环的裂纹尖端位置随载荷的变化规律。使用数字图像相关技术获取裂纹张开位移,通过间接法测量裂纹张开力,进而研究过载对裂纹闭合效应的影响。对比过载前一循环与过载循环在卸载状态下裂纹尖端附近区域的应变场,结合裂纹尖端位置随载荷的变化规律及相对应循环的裂纹张开力,分析可知:过载在裂纹尖端附近区域产生较大塑性变形,即使卸载后仍在较大程度上得到保留,从而使裂纹闭合效应减弱,导致过载后裂纹尖端位置随载荷的变化规律与过载前明显不同,且力-位移曲线也未出现显著的转折点。

Based on the digital image correlation technology, a nonlinear iterative method is used to fit the surface displacement field of the industrial pure titanium CT sample, so as to obtain the law of the crack tip position changing with the load before, during, and after overload. The crack opening displacement is obtained using the digital image correlation technology, the crack opening force is measured by the indirect method, and then the influence of overload on crack closure effect is studied. Comparing the strain field near the crack tip in the unloaded state between the cycle before overload and the cycle during overload, combined with the variation of the crack tip position with load and the crack opening force corresponding to the cycle, the analysis shows that the overload causes a large plastic deformation in the region near the crack tip, which is remained to a large extent even after unloading, resulting the weakening of the crack closure effect. As a result, the change of the crack tip position with the load after the overload is obviously different from that before the overload, and there is no obvious turning point in the force-displacement curve.