摘要
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PLC(Portevin-Le Chatelier)效应。本文利用高速(1000 fps)数字散斑干涉法(DSPI),对不同加载应变率下,铝合金(LY10)试件中出现的连续(A-type)、间断(B-type)传播和随机(C-type)出现的三种PLC剪切带的瞬态成核与演化过程进行捕捉,通过对捕捉的试件表面系列散斑干涉图进行顺序相减处理,得到试件表面变形过程中位移的分布和演化系列条纹图。实验结果显示,对应于三种类型的剪切带,有两种主要的成核演化形式:1.A型剪切带的主要成核形式为先形成一个在观察平面上与拉伸轴方向成60°角并且横跨试件宽度的窄带,伴随着应力下落,剪切带开始沿自身宽度方向高速扩展达到最终宽度;2.对应于B、C型剪切带,先在观察平面上试件的一侧形成沿与拉伸轴方向呈60°角、长度约为最终长度一半的窄带。随着应力下落,带的前沿开始向试件的另一侧面沿自身长度方向传播,在传播过程中带逐渐沿自身宽度方向膨胀。带的前沿贯穿试件后,带开始高速膨胀,导致雪崩式剪切变形发生。
The Portevin-Le Chatelier （PLC） effect associated with avalanching shear deformation will occur during a tensile test for many alloy materials. A technique based on a high-speed （1000 fps） digital speckle pattern interferometry （DSPI） was used for investigating the nucleation of Portevin-Le Chatelier （PLC） deformation bands. With the help of this method, the digital images of the instant nucleation process were captured successfully. Analyzing these images by sequential method, the deformation distribution of the specimen surface was acquired. The results show that there are two main nucleation formats which associated with three different types of PLC deformation bands： （i） at the observation plane, the type-A band initiates as a sample-scale narrow band at an angle of 60°with respect to the tensile axis, then with the drop of the stress, the narrow band begins to expand in its width direction and reachs its final width; （ii） at the observation plane, the type-B and type-C bands initiate at a lateral specimen surface as a narrow band at an angle of 60° with respect to the tensile axis, and this narrow band has half of its final length. Subsequently the band front begins to propagate to the other lateral specimen surface along its length direction and expands in its width direction accompanying with the drop of the stress. When the front of the band reaches the other lateral surface, the band begins to expand in its width direction instantly and avalanching shear deformation happens.
出处
《实验力学》
CSCD
北大核心
2006年第4期411-417,共7页
Journal of Experimental Mechanics
基金
国家自然科学基金项目(编号:10232030
10372098)
