Dynamic fracture analysis of crack–defect interaction for mode I running crack using digital dynamic caustics method

•Investigated running crack crossing a round inclusion defect.•A Digital Dynamic Caustics System was used to capture the fracturing process of PMMA material.•The influence of the round inclusion on crack velocity and stress intensity factor was analyzed.•Both the size effect and the stiffness effect of inclusion on energy accumulation at crack–hole tip was investigated.•The relationship between dynamic stress intensity factor and crack velocity was discussed. The crack–defect interaction mechanism was studied both experimentally and numerically. Experimental results found that the presence of empty hole before crack results in both the velocity and stress intensity factor of crack decrease. More energy accumulated at crack–hole tip before second initiation. Dynamic stress intensity factor is qualitatively in accord with Crack velocity, but it oscillates strongly with hole size increasing. Numerical study shows that the stress concentration would be reduced significantly when the modulus radio between the inclusion and the matrix is more than 0.5. Results may shed lights on the interaction behavior between running crack and inclusion.