Novel method in the modeling of adiabatic shear bands in ballistic impact: An application on Inconel 718 alloy

Abstract

The failure mechanism for thick metal plates ballistically impacted by blunt projectiles is known as an Adiabatic Shear Band (ASB), which results in a catastrophic failure due to concentrated shear deformation. ASBs are generally considered to be a material or structural instability and as such are not controllable. ASBs are also a thermodynamic phenomenon occurring at high strain rates and are characterized by large deformations, localized in a narrow band consisting of highly sheared material. Due to the extreme localization of the shear band, it is difficult to model ASBs using the Finite Element Method, because the mesh size needed to capture it is often not practical for real applications.Validated numerical two-dimensional simulations revealed that the tabulated Johnson-Cook (J-C) material model is successful in predicting this mode of failure only using meshes composed of elements with a size that is of the same magnitude order of the ASB width. Because the ASB width of some high-performance metal alloys such as Inconel 718 is on the order of 1 µm, this material model cannot be used in practical applications to predict ASB.This paper describes the enhancements made to the tabulated J-C material model that allow simulations of Adiabatic Shear Band development, under the correct loading conditions, in meshes with element size of practical use in current engineering applications. Full scale impact tests were used to validate the accuracy of the enhanced material model by comparing the ballistic limit, projectile residual velocity, and failure morphology. It is shown that this approach provides a robust and efficient method for simulating Inconel 718 structures under impact, with meshes composed of element of size compatible with modern commonly available computational resources even when the failure mode is an ASB.