Mixed mode fracture study of PMMA using digital gradient sensing method

•We calculate mix mode stress intensity factors first using DGS method.•Nonlinear least squares was proposed to fitting angular deflections (stress gradient).•Rigid-body motion was eliminated.

The optical method of digital gradient sensing is used to the study of fracture characteristics. Fracture experiments are performed on PMMA specimens with different offset crack under three-point-bending, which is appropriate for mixed-mode fracture analysis. The full-field displacements around the crack-tip are used to study the fracture characteristics such as evaluation of deformation field, crack tip stress gradients, and crack initiation. Mixed-mode stress intensity factors and crack tip location are calculated simultaneously from DGS data by fitting the analytically angular deflections (or in-plane gradients of stresses) field using the method of nonlinear least-squares and are in good agreement with finite element results.