基于背景值及数字图像相关方法的土样剪切带宽度测量

Measurement of shear band widths of clay specimen based on background value method and digital image correlation method

【目的】建立剪切带宽度的准确测量方法,为正确揭示材料的渐进破坏过程提供支持。【方法】根据仿射变换和梯度塑性理论制作了水平虚拟剪切带,检验了高斯拟合方法的剪切带宽度测量精度,同时提出了测量剪切带宽度的背景值方法,并测量了单轴压缩条件下土的剪切带宽度。【结果】利用高斯拟合方法能准确测量常应变剪切带宽度,而对于含应变梯度的剪切带,测量误差很大。利用背景值方法测量的剪切带宽度较为可信;随着纵向应变的增加,剪切带宽度的演变主要有增加、减小、基本不变及不确定4种趋势;剪切带宽度为15～38像素(1.35～3.42mm)。【结论】对于常应变剪切带,可以利用高斯拟合方法准确测量剪切带宽度,而对于含应变梯度的剪切带,建议利用背景值方法测量。

[Objective] An accurate method for measurement of shear band width was proposed to pro vide basis for revealing the deformation and fallure processes of materials. [Method] Horizontal shear bands were generated based on the gradient plasticity theory and affine transformation to check the accura cy of the Gaussian fitting method for measurement of shear band widths. A background value method was also proposed to measure shear band widths, and was used to measure widths of shear bands in clay in uni axial compression. [Result] The Gaussian curve fitting method was applicable for accurate measurement of shear bands widths with constant strains, but not for shear bands widths with strain gradients. Four cate gories of the evolution of shear band widths of clay were increasing, decreasing, invariant and uncertain. The range of shear band widths was 15 38 pixels （1.35- 3.42 mm）. [Conclusion] The Gaussian fitting method can be used to accurately measure widths of shear bands with constant strains, while the back ground value method was suggested for shear bands with strain gradients.