On the simulation of panel distortions due to hot curing adhesives

Hot curing one-part adhesives are often used to bond car body shells. The cure process of the adhesive, however, can lead to distortions, i.e. unwanted, visible deformations of the adherends. In case of outer car panels, these distortions are considered as visual defects, even though the structural integrity might not be affected. In order to avoid distortions by a proper control of the bonding process, a thorough understanding of the development of distortions is necessary. Finite element simulations can help to gain insight into this development. In this work, a simulation model is proposed and used to study the appearance of distortions in a steel sheet over different temperature cycles. The model takes chemical shrinkage and thermal deformation as well as gelation and stress relaxation into account. It was found that the heating rate can affect distortions. Lowering the cure temperature only lowers distortions for high temperature rates. Low heating rates can reduce distortions.