Comprehensive material constraints incorporation in coupled thermal-mechanical responses modelling for high-intensity pulsed ion beam processing of metals

Abstract

Thermodynamic numerical model is established for high-intensity pulsed ion beam (HIPIB) processing of metallic components. The HIPIB delivers a thermal energy input typically of several J/cm2 per pulse of 100 ns range. Incorporation of material constraints is emphasized in the modelling to predict residual surface stresses formation as a result of material loading, i.e. the coupled thermal-mechanical material responses of processed components. Taking tungsten as an example, five sets of material constraints were comparatively studied, including temperature-dependent thermophysical properties, Zerilli-Armstrong and Johnson-Cook constitutive equations, and simplified ones adopted in other studies by assuming constant specific heat Cp and/or thermal conductivity k, or ignoring the material yield strength, respectively. The highest surface temperature with the largest rising rate is observed at constant Cp due to the less thermal energy for the temperature increment, while the lowest surface temperature for constant k due to more thermal energy diffused. The transient temperature field evolutions induced large temperature gradients that simultaneously caused high thermal stresses. Residual surface stresses formed only if plastic strain occurred, where the model of ignoring yield strength predicted no residual stresses formation having the largest error among the five models. The models with comprehensively incorporated material constraints, particularly for incorporation of Z-A constitutive equation considering dislocation behaviors during plastic deformation, have a higher accuracy in residual surface stresses prediction. Comprehensive incorporation of material constraints in the thermodynamic model facilitates an accurate elucidation of coupled thermal-mechanical responses for resultant residual stresses under the processing load of thermal energy input.