Analytical parameter identification for a viscoplastic material model for structural adhesive bonds

Accurate parameter identification or calibration, respectively, is essential for material models used in finite element (FE) simulations, especially for nonlinear, inelastic, temperature- and/or rate-dependent models. This calibration normally relies on an inverse parameter identification scheme, combining numerical optimization and FE tools, which can be computationally intensive. This study presents an analytical identification method as an efficient and reliable alternative for determining material parameters for complex material models. The method is demonstrated for epoxy resin adhesives, whose loading rate- and temperature-dependent material behavior can be modeled with an extended Toughened Adhesive Polymer (TAPO) model. Our multi-stage analytical procedure allows the TAPO model to be calibrated directly using experimental data from thick adherend shear and butt joint tensile tests, eliminating the need for FE simulations. Both experiments have been conducted in a temperature range from −40 °C to 80 °C and at four different loading rates. The analytically derived temperature-dependent parameter sets are verified and validated against other experimental data and result in a very good agreement for all loading rates and most temperatures.