Yulong Cai

The Mechanism of Critical Strain of Serrated Yielding in Strain Rate Domain

The mechanism of the critical strain of serrated yielding is studied via tension tests at various strain rates. Before the critical strain, it is deduced that dislocations are not pinned at high strain rates, and dislocations at low strain rates are pinned but cannot escape. The critical strain depends on the first pinning process at high strain rates and on the first unpinning process at low strain rates. The calculated results based on the two criteria are in good consistency with the experiment.

Digital image correlation using energy minimization in full-field displacement and strain measurement

Digital image correlation (DIC) method is an effective way for full-field strain measurement. Optical flow estimation methods combined with a global searching strategy for displacement field measurement are introduced in this paper. Compared with the conventional DIC method, this strategy can lessen possible mismatching between the reference image and warped image. By minimization the energy function of displacement field, displacement continuity and displacement gradients continuity among calculation points are achieved. For detecting large displacements, a coarse-tofine strategy is also employed. More importantly, the architecture parallelization of optical flow estimation and searching strategy can decrease the running time of this method for time-critical conditions. This proposed method is universally applicable to the images with shadows, rotation, and large deformation. Several pairs of simulated digital speckle images were used to evaluate the performance of this novel DIC method, and the experimental results clearly demonstrate its robustness and effectiveness.