Micro-scale shear testing for localized constitutive characterization of Al-Steel resistance spot weld under large deformation

This study presents a methodology for characterizing local constitutive properties in Al-Steel resistance spot weld through micro-scale shear testing, focusing on capturing localized mechanical behavior under large deformation. Although conventional methods such as hardness testing and nano-indentation can capture these gradients to some extent, they are limited in directly measuring the full local stress–strain response, especially under large deformation. While micro-scale tensile testing has been used for localized property evaluation, strain localization severely limits the measurable deformation range, restricting its applicability in characterizing hardening behavior at large strains. To overcome these limitations, micro-scale shear tests combined with micro-Digital Image Correlation (μDIC) were employed, enabling stress-strain characterization at significantly larger deformations. Due to the highly localized nature of the analysis, strain field irregularities arise from the limited number of grains within the region of interest. This study introduces a μDIC data processing method to mitigate these effects for constitutive modeling. Furthermore, shear testing provides access to strain regimes beyond the limits of tensile tests, reducing uncertainties in hardening modeling under large deformations. The results reveal distinct hardening behaviors across different weld regions that could not be captured only by tensile testing.