Length-scale-insensitive phase-field material point method for spall fracture and adiabatic shear bands in ductile metals
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Thick-walled metallic cylinders may exhibit complex failure modes under impact loads, including spall fracture and adiabatic shear bands (ASBs), making their accurate modeling and prediction a challenging problem in explosion and impact engineering. This study presents an explicit phase-field material point method (PF-MPM) equipped with convected particle domain interpolation (CPDI) for modeling impact-induced fragmentation of thick-walled metallic cylinders. Within a unified phase-field formulation, we develop a length-scale-insensitive model to mitigate the well-known sensitivity of conventional phase-field approaches to the intrinsic regularization length. To capture both spall fracture and ASBs, a stress decomposition strategy consistent with a volumetric-deviatoric split is derived and implemented, enabling a mixed-mode fracture describing within the same framework. An explicit time integration scheme combined with a staggered update of the displacement and phase fields is then developed to efficiently solve the coupled governing equations. Furthermore, the CPDI is employed to reduce grid-crossing noise and improving robustness under large deformations. The proposed PF-MPM framework is validated against several representative benchmarks, and its capability in capturing complex failure patterns and fragmentation responses of thick-walled metallic cylinders under different impact scenarios are demonstrated.
