数字图像相关法剪切带应变计算方法

Strain calculation method in shear band using digital image correlation

针对数字图像相关法在剪切带大变形测量中的问题,采用N-R方法直接计算得到的应变结果具有相对较高的测量精度及可信度。基于梯度塑性理论,通过仿射变换对散斑图施加了具有不同平均剪切应变的剪切大变形,利用不同计算方法对其应变进行计算。计算结果显示:当平均剪切应变分别为λP=π/12和λP=π/6时,不同方法计算结果均与理论值之间存在误差,但N-R方法在剪切带中心峰值的计算结果与理论值之间的最大误差仅为5. 64%,且计算结果相对稳定。中心差分法和基于位移场局部最小二乘拟合的方法由于受其计算参数的影响,计算精度和稳定性均明显低于N-R方法。同时,本文对粘接接头粘接面在拉伸荷载作用下的实际剪切变形进行了计算,对比分析结果显示N-R方法计算结果相对稳定可靠。

For the large deformation measurement of shear band using digital image correlation,this paper proposes using N-R method to calculate shear strain directly and the method achieves a relatively high measurement precision and credibility.Based on the theoretical solution of displacement in a shear band,which is based on gradient-dependent plasticity,shear bands with different averaged shear strains were generated using an affine transform.The calculation results showed that when the average shear strain areλP=π/12 andλP=π/6 respectively,there were divergence between three kinds of strain calculation results with theoretic values.But the maximum error between results of N-R method and the theoretical value was 564%at peak of shear band and the calculation results were relatively stable and reliable.Due to the influence of calculation parameters,stability and accuracy of central difference method and the method based on least-square fitting of local displacement calculation were significantly lower than that of N-R method.At the same time,the shear deformation of adhesive joint under load was calculated,results showed that calculation result of N-R method are more stable and reliable.