Integration-point reformulation of an adiabatic shear band initiation criterion

An integration-point reformulation method is proposed for the adiabatic shear band (ASB) initiation criterion. The original criterion uses shear strain measured from a grid marked on the specimen surface. This strain cannot be used directly in finite-element integration-point calculations. The maximum plastic shear strain is calculated using Mohr’s circle for strain and the J2 associated flow rule. Its increment is used as the weight. The weighting is applied only to the stress-state history used to calculate the critical shear strain. An integration point meets the ASB initiation condition when the ratio of the maximum plastic shear strain to the weighted critical shear strain is not less than unity. The calculation procedure is implemented in LS-DYNA through a user-defined material subroutine. Shear-compression specimens with different notch angles are used for evaluation. The results show that the ASB initiation site generally shifts from the center of the shear zone toward a notch tip as the notch angle increases. This trend agrees with experimental observations. The increment-weighted scheme reduces the effect of early stress-state fluctuations on the critical shear strain. It also produces a more concentrated high-ratio region than the instantaneous and arithmetic-mean schemes. The potential initiation sites and orientations of the high-ratio regions remain generally consistent across different mesh sizes. The integration-point reformulation allows the critical shear strain variable derived from experimental measurements to be calculated directly at finite-element integration points. The resulting criterion provides a numerical method for identifying ASB initiation sites under complex loading.