Discretization and material parameter characterization for a HAZ in direct-quenched armor steel

Studies conducted in recent years have shown that the ultimate load-bearing and deformation capacity of weldments manufactured from ultra-high-strength steel is often impacted by the heat-affected zone. Thus, to assess the strength properties of these welds, in addition to the base material properties and weld metal, the heat-affected zone's mechanical properties must be analyzed. In this study, a discretization and material parameter characterization are conducted for friction-welded joints in direct-quenched armor steel. The discretization is based on the microstructural analysis and hardness measurements conducted for the weld. After data analysis and considering the practical aspects, such as computational factors and other resources, a model with six different material parameter regions for the heat-affected zone was chosen. For all regions, the quasi-static part of the Johnson-Cook constitutive model was used. Three of the most distant zones measured from the weld interface were subcritically heated during the friction welding. The material parameters for these zones were identified using thermal simulations, tensile experiments, and numerical optimization, whereas the material parameters for the three remaining zones were identified using tensile experiments combined with numerical models and optimization routines. The generated model was successfully used in the fracture assessment of four friction-welded specimens with different degrees of metallurgical constraint. The effect of the subcritically-heated zones on the model's accuracy was studied. Neglecting the subcritical zone within the models caused an overestimation of the joint's tensile strength. Also, three alternative numerical models with different discretization's were generated and used in the fracture assessment. The validity of the generated models was tested by applying the HAZ model to models of tensile test specimens with different degrees of metallurgical constraint. The three alternative models could not correctly assess the fracture. In addition, the different models produced differing stress-strain curves.