数字散斑法在局域剪切带三维变形研究中的应用

在适当的温度、应变率和预变形下,合金材料的拉伸试验中,将会出现伴随应力锯齿形跌落的雪崩式剪切变形带,即波特文-勒夏特利埃(Portevin-Le Chatelier,PLC)效应。利用高速数字摄像系统(分辨力1000 frames/s)并结合数字散斑干涉法(Digital speckle pattern interferometry,DSPI)和数字散斑相关法设计了一套光学变形测量系统,实现了拉伸试验中对试件表面三维变形的实时、精确测量。利用该光学系统对铝铜合金试件在拉伸试验中产生的跳跃传播的局域剪切带瞬态成核过程进行捕捉。通过结合数字散斑相关法得到的面内变形定量结果和数字散斑干涉法得到的表现离面变形的条纹图,再现了剪切变形带成核和传播瞬间的三维变形过程。

Investigation on the Three-Dimensional Deformation of Local Shearing Band by Digital Speckle Metrology Technique

The Portevin-Le Chatelier(PLC) effect associated with avalanching shearing deformation,will occur during a tensile test for many alloy materials.With the aid of the digital speckle metrology technique including digital speckle pattern interferometry(DSPI) and digital speckle correlation(DSC),an optical system was set up to measure the three-dimensional deformation on the specimen in real time during tensile test.The nucleation process of a shearing band in Al-Cu polycrystal was captured by using a high-speed digital photography(1000 frame/s).The quantitative results of the displacement field and axial strain field on the front and lateral surface are obtained by digital speckle correlation method and the propagation of the out-plane deformation of the band is vividly visualized by correlation fringes.By combining the in-plane and out-plane deformation results,a report of three-dimensional nucleation process for the shearing band is presented here.