扫描云纹干涉法研究多孔NiTi形状记忆合金的微观形变特性

INVESTIGATION ON THE MICRO-DEFORMATION CHARACTERISTICS OF POROUS NiTi SHAPE MEMORY ALLOY USING SEM MOIR METHOD

利用扫描云纹技术研究了多孔NiTi形状记忆合金在压缩状态下的微观形变特征．通过压缩变形过程中云纹密度和方向的改变分析了多孔合金孔壁边缘和心部应变场的变化．结果表明:多孔NiTi形状记忆合金的失效是由孔隙边缘的应力集中所引起的．在外加压缩载荷的作用下,多孔NiTi合金的孔壁边缘和心部除承受压缩应力外,还承受较大的剪切应力作用．在孔隙的尖角区形成了应力集中,并逐步产生裂纹．裂纹沿着与加载方向成45°角的方向向孔壁中心扩展,最终产生断裂．多孔合金断裂后在孔壁边缘区域产生很大的应变,而孔壁心部的应变较小,几乎没有发生塑性变形．最后结合云纹干涉的结果分析了多孔NiTi形状记忆合金的压缩行为特征．

The micro-deformation characteristics of porous NiTi shape memory alloy under compression load have been investigated using SEM Moiré method. Strain field distribution, which was calculated from the changes of density and direction of moiré at the margin and the center of pore wall, indicated that the failure of porous NiTi alloy can be attributed to the stress concentration near the margin of pore wall. During loading, the margin and center of pore wall endured both shear stress and compressive stress. The stress concentration was formed at the sharp-angled area of pore and induced the crack propagation from the margin of pore wall to the center along 45°angle with the loading direction. Severe deformation occurred at the margin of pore wall after failure, however, the strains were slight at the center of pore wall. Based on the results of Moiré, the compressive behavior characteristics of porous NiTi alloy were analyzed.