白光散斑相关法多尺度分析Portevin-Le Chatelier剪切带变形

在适当的温度、应变率或预变形下,合金材料的拉伸试验中,将会出现伴随雪崩式剪切变形带的锯齿形塑性失稳、即PLC(Portevin-Le Chatelier)效应。本文利用图像相关求位移场的方法,对恒定加载应变率下(10-4/s),拉伸铝合金(A2017)试件时出现的PLC效应从宏观剪切带变形到微观晶粒变形等多尺度进行了观察和定量化的分析。通过对PLC效应发生时采集的试件表面的白光散斑图进行相关运算,得到试件表面剪切变形区域各点的精细位移,并在此基础上计算出剪切带区域的应变分布及剪切带的宽度。实验结果显示,当PLC效应发生时,剪切带区域的应变曲线呈台阶型,带的前后边缘应变梯度较大,中间近似呈平台状,带外区域应变值接近零,塑性拉伸变形主要集中在带内。

White-Light Digital Speckle Image Correlation Analysis of the Portevin-Le Chatelier Shearing Band in Multiscale

In a certain range of temperatures,strain rates and appropriate predeformation,the PLC(Portevin-Le Chatelier) effect will occur during plastic deformation for many alloy materials.As a typical plastic instability in alloy materials,PLC effect has been researched for many years.In our experiments,white light digital speckle image correlation method was used to study the PLC effect of aluminum alloy samples in tensile test under constant tensile strain rate.Through an optical microscope,the images of the macro shearing band and the grains were recorded respectively when PLC effect happened.By calculating these images with the correlation method,the displacement field of the shearing region was measured quantitatively.Based on the displacement field,the distribution of strain and the width of the shearing band were calculated.The results show that when PLC effect happened the strain field around the shearing band is like a trapezoid,the strain gradient of the front and back edge of the band is much larger than that in the inner area of the band and out of the band the strain is nearly zero.the plastic deformation is concentrated in the band region.