Progressive Failure Analysis of Adhesively Bonded Joints in Crash Simulations

The phenomenological description for the mechanical behaviour of ductile, toughened polymers is currently an active field of research in interfacial mechanics, since the recently developed crashmodified adhesives are well suited to bond structural components of automotive bodies reliably. Therefore, constitutive models for the inelastic behaviour of adhesives and substitute elements for the effective modelling of thin layers are needed for the crashworthiness analysis of bonded car structures. The transition is shown from solid elements with three-dimensional constitutive models to interface elements for the analysis of thin adhesive layers in this contribution. Two different material models for the rate-dependent, ductile mechanical behaviour of toughened adhesives are briefly discussed. The first approach is based on a three-dimensional elastic-plastic continuum model with a rate-dependent yield stress and a failure criterion. The second approach makes use of an interface element with a traction-separation model for ductile materials. A reliable estimate for the size of the critical step length is provided, if the equations of motion for the substitute element of the adhesive layer are numerically integrated in time by means of explicit methods. An adequate experimental setup for testing the inelastic behaviour of a thin layer of crash-modified adhesives up to fracture is analyzed with the finite element method by making use of the substitute element for the bonding. The numerical investigations comprise various modes of failure of the adhesive layer under pure and combined loading in normal and shear direction. The results of the simulation are compared to the corresponding data form experimental tests.