A MODIFIED MODE II DYNAMIC FRACTURE TEST TECHNIQUE BASED ON SHTB

Dynamic fracture toughness under impact shear loading is an essential aspect in fracture behavior and mechanical property of material.Experiments have been done by several researchers using different specimens and test methods in order to measure mode II fracture toughness.But due to crack opening during loading process, the results obtained in these tests are not mode II but mixed mode I+II.Since crack opening are not be considered, dynamic shear fracture toughness of material can not be accurately detected.In view of this problem, a modified compact tension shear (MCTS) specimen based on split Hopkinson tension bar (SHTB) apparatus is proposed in this paper.The specimen was constrained with special designed clamp to prevent crack opening, so mode II fracture are ensured.Numerical analysis was carried out using experimental-numerical method.The incident pulse detected in test are introduced in ANSYS-LSDYNA as input pulse.Stress intensity factor at crack tip of MCTS specimen was calculated by relative displacement of corresponding nodes on crack surface in two directions.Simulation of compact tension shear (CTS) specimen was also done with same incident pulse as control.In addition, experimental study was also carried out using digital image correlation method based on SHTB apparatus to validate numerical results.Experimental results shows that during loading process, MCTS specimen ensures K_I\ll K_II and crack opening are not observed.However, for same incident pulse, the maximum mode I stress intensity factor of CTS specimen is even higher than mode II.Which indicates that dynamic shear fracture toughness of material can be measured effectively using MCTS specimen.This work provides an effective and convenient test technique for evaluating dynamic properties of a certain material.