In this work a physical mechanism-based phase-field model for adiabatic shear bands (ASBs) in collapsing thick-walled cylinders (TWCs) is addressed within the framework of the unified phase-field theory for damage and fracture (Wu, 2017; Wu and Nguyen 2018). Owing to the properly constructed energetic degradation function and crack geometric function, this model is capable of characterizing the three-stage failure process typically for ASBs. After the theoretic aspect is introduced, the model is extensively verified by two representative benchmark tests of TWCs, i.e., a smaller specimen under electromagnetic loading and a larger one subjected to explosive loading. It is found that the proposed model reproduces the experimental results fairly well with calibrated model parameters. In particular, evolution of multiple shear bands and morphological characteristics unique to the failure of TWCs, e.g., intersections and counterchecks, etc., are well captured. Compared to previous works based on local damage models, the proposed model is objective with respect to mesh discretization -- a challenge issue been rarely achieved so far in the modeling of ASBs in TWCs. Moreover, the predicted shear band width is also consistent with analytical results, making it possible to calibrate the phase-field length scale provided test data are available.
