基于标点法的土体局部应变数字图像量测

Digital Image Measurement for Local Strain of Soil Based on Target Marks

提出一种基于标点法的土体局部应变数字图像量测方法来测量加载过程中土样中部区域的应变。精度分析表明,利用该方法测得轴向应变和横向应变量测精度可达±0.007%,剪切应变量测精度可达±9.0×10-5;通过刚体平移试验分析了镜头畸变引起的系统误差分布规律,在保持目标区域尽量居中的前提下,系统误差可以控制在0.02%以内。给出了一个无侧限压缩试验的应用实例,在加载的各个阶段利用数码相机拍摄照片,借助数字图像处理技术得到各阶段节点位移进而求得标记区域内4个高斯点处的应变值,并对试样中部区域和试样整体的变形过程进行对比。结果表明,该方法可以真实详细地反映土样局部区域的变形演化过程。

A digital image measurement method based on target marks was proposed to measure the strains of middle area of soil samples during loading process.Precision was analyzed for this method,the results demonstrated that the precision of the measurement of axial strain and transverse strain was ±0.007%,shear strain was ±9.0×10-5,respectively.The systematic error distribution was analyzed through rigid body translation test,systematic error could be controlled under 0.02% if the target area was exactly constrained in the middle of viewing field.An unconfined compression test was carried out using this method and photos were taken with the digital camera at each step during the loading process.The strains at four Gaussian points were calculated based on the nodal displacements obtained by image processing technology.Additionally,the deformation processes of the middle area and the whole sample were compared.The deformation evolution process within the local area of soil could be faithfully reflected by this method.