Characterization of a cohesive zone model for adhesives with *MAT_240 and curve mapping method in LS-OPT

Kurzfassung

The importance of adhesives in automotive structures exposed to high crash loads has increased over the years. To improve the structural sizing, it is necessary to predict the behavior of bonded joints under dynamic impact and crash loads. Cohesive zone models have proven to be suitable for numerically representing adhesive behavior in Finite-Element simulations. However, the manual determination of the model parameters requires experience with the material model and a corresponding amount of time to derive the various parameters. The present work aims at developing an optimization scheme with LS-OPT for the effective and automated identification of input parameters for the material card *MAT_240 (*COHESIVE_MIXED_MODE_ELASTOPLASTIC_RATE) [1] which is used to represent the behavior of the adhesive layer. The present work focuses on a curve mapping process with LS-OPT. The investigated approach is based on the numerical simulation of the entire load-displacement curves of four different sample geometries. Of these, two sample types have nearly rigid joining partners. In the other two sample types the parts to be connected are made of sheet steel (which can be severely deformed during an experiment). The sample types were also chosen so that the adhesive layer in two sample types failed under peel load, while in the other two samples failure occurred under shear load. First, a parameter optimization scheme based on two fracture mechanical tests for mode I and mode III loading is implemented. As a basis for the optimization, a sensitivity analysis is previously performed to determine the decisive parameters in fitting the numerical to the experimental results and reduce the optimization space. In the next step, an optimization loop for the fracture mechanical tests will be investigated. Therefore, the least square method for the curve mapping process is used for the parameter optimization of with LS-OPT. The determined optimized parameters strength and fracture energy are being used to optimize the material cards on coupon level afterwards. The cohesive zone parameters are being calibrated to the experimental results and the parameter space can be minimized using the Sequential Response Surface Method (SRSM).