数字散斑相关方法测量混凝土裂缝尖端演化过程

阐述了数字散斑相关方法的基本原理.采用爬山搜索法进行整像素搜索,基于梯度的搜索算法计算亚像素位移、位移场局部最小二乘拟合计算应变场.测量了混凝土三点弯曲梁裂缝尖端的演化过程,给出了试件加载过程的载荷-位移曲线以及裂缝扩展的过程.由DSCM分析结果,获得了试件在不同载荷下裂缝尖端的位移场与应变场.为深入研究含裂纹体材料和结构的断裂破坏提供了一个有效的实验方法.

基于数字图像相关方法的FGH96疲劳裂纹扩展分析

基于非接触全场高精度测量的数字图像相关(DIC)方法,对粉末镍基高温合金FGH96开展室温下的裂纹扩展试验。试验过程中,首先,利用DIC系统记录单边缺口试样循环载荷下的裂纹变化图像,由此获得裂纹扩展速率情况;其次,利用相关算法结合不同的计算策略,可获得裂纹尖端最大总应变场以及累计塑性应变场的演化规律;再次,基于最小二乘法对已有的位移场进行回归分析,可提取裂纹尖端应力强度因子获得裂纹扩展驱动力;最后,利用裂纹张开位移与载荷的关系,观察闭合现象并获得裂纹张开应力范围。

Transient near tip fields in crack dynamics

Transient effects of stress-strain fields in the vicinity of a stationary crack tip under high rate loads are discussed.Exact analytical solutions to near tip stresses are compared to fields prescribed by leading terms(one or several) of Williams asymptotic expansion.Influence of load application mode,time(or,which is the same,distance from a crack tip) and Poisson's ratio on this discrepancy is extensively examined.Some effects connected with crack tip propagation speed are also discussed.Significant inconsistencies between real(or received in numerical solutions of state equations-e.g.finite element computations) crack tip fields and stress intensity factor(SIF) singular field observed by numerous researchers are explained.The scope of problems where SIF field can be used for correct prediction of dynamic stress-strain fields in the crack tip region is established.Possibility to correctly approximate fields that are not SIF dominated,accounting additional terms of Williams expansion,is studied.