An Extension of MAT_240 to Consider the Failure of Structural Adhesive Joints in Crash Simulations

MAT COHESIVE MIXED MODE ELASTOPLASTIC RATE, or in short MAT 240, is a cohesive zone model, which has been recently developed to consider the failure behaviour of structural joints in crash simulations. The model is applicable to different kinds of structural joints as adhesively bonded or spot/seam welded joints, but its development focused on the efficient crash simulation of structural adhesive joints of small layer thickness. However, tolerances in the manufacturing process may lead to a larger adhesive layer thickness. In the present work, MAT 240 has been extended via a user-defined subroutine to consider the dependency of the critical energy release rates GIc and GIIc , which are model parameters of MAT 240, on the thickness of an adhesive layer. While the fracture energy GIc under Mode I loading is evaluated in Tapered Double Cantilever Beam (TDCB) tests, the End-Loaded Shear Joint (ELSJ) test is used to analyze the Mode II fracture behaviour. Five adhesive layer thicknesses, ranging from 0.25 to 4.0 mm, were investigated for both fracture modes. All tests have been performed at quasi-static test conditions. The experimentally detected correlations between the critical energy release rates and the adhesive layer thickness are implemented into the user-defined cohesive zone model, which is based on MAT 240. Simulations of asymmetric tapered double cantilever beam (ATDCB) tests, which exhibit an adhesive layer loaded in mixed-mode, give a first validation of the model extension. Finally, simulations of quasi-static crash box tests are compared to experimental data.

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