Calibration and Validation of Epoxy Adhesive Joints: Evaluation of LAW36 and LAW59 in Radioss

This work presents a comparative study of adhesive material models LAW36 and LAW59, in Radioss, with the objective of assessing their predictive capabilities for epoxy-based structural adhesives. The investigation focuses on simulating stress distributions, fracture energies, and failure mechanisms in joints of varying adhesive thicknesses (0.1, 0.2, and 0.5 mm). A comprehensive experimental program supports numerical analysis, including bulk tensile, Thick adherend shear test, and Mode I fracture toughness tests, based on ISO 527-2, ISO 11003-2, and EN 6033 standards, respectively. An additional validation test replicating multi-mode loading conditions is incorporated to establish transferability of the calibrated models to realistic applications. Numerical models employ solid elements for adhesive layers and shell elements for metallic adherends, with mesh refinement in adhesive regions to resolve local stress gradients. Displacement-controlled loading is applied to reproduce tensile and shear conditions, enabling extraction of stress-strain responses, fracture energies, and failure patterns. Model calibration is performed against experimental data using fracture toughness, failure strain, and maximum stress as reference parameters. Comparative evaluation is conducted with quantitative error metrics to assess accuracy and computational cost. The results aim to identify the most reliable adhesive law for joint-level simulations, providing guidance for model selection in structural applications.