A modified Johnson-Cook material model with strain gradient plasticity consideration for numerical simulation of cold spray process

Abstract

Owing to the low processing temperatures and subsequent minimal thermal residual stresses, cold spray (CS) process has significant potential as a fabrication route for freeform components, thus making it a prospective additive manufacturing technology. Cold spray experiments have been accompanied by systematic computational modeling to optimize the coating deposition conditions and predict the coating properties and thereby their performance. One of the most widely used plasticity models for the prediction of material behavior at a high strain rate is the Johnson-Cook (JC) model. However, the model's shortcomings at the strain rates experienced during cold spray lead to inaccuracies in the predictions. Still, it is predominantly used owing to its simplicity and rich material parameters database. In this study, we have developed a modified form of the JC model to account for the viscous regimes experienced at high strain rates, which takes a simple mathematical form with less adjustable material parameters than previous modifications of the JC model. Subsequently, considering the inhomogeneous particle deformation in the presence of jetting, a strain gradient plasticity (SGP) consideration applicable to cold spray has been proposed. The predictions obtained from numerical simulations using the newly developed material model are found to be in good agreement with the cold spray experimental results. The new material model along with the SGP consideration developed in this study offers a critical new asset in numerical modeling of cold spray.