Connectors and Joints
The connection between two or more structural members is denoted a structural joint, and is very important for the strength, ductility and safety of the structure. The strength of each individual connector is well documented in the relevant structural standards, but this information is not sufficient for large scale simulations as their complete load-deformation characteristics are not given. By use of FEM, detailed 3D models can be established and used for studies of the local joint performance including failure. However, due to their computational expenses, such models cannot be directly used in large scale simulations and shell-based models have to be used. Such models have to produce robust and reliable results from the onset of loading until failure.
In this programme experimental methodologies and set-up will be developed to characterise the behaviour of connectors subjected to static and dynamic loading conditions. Furthermore, based on the experimental results models for large scale FE simulations using shell elements will be derived and validated.
During the last year this programme has mainly focused on behaviour and modelling of self-piercing riveted structures. Self-pierce riveting (SPR) is a method for joining two or more pieces of material. The process can be highly automated and is well suited for industrial purposes. It is attractive since the method can join different types of materials, such as aluminium sheet to a piece of plastic. SIMLab initiated an activity on self-piercing rivets (SPR) in 2000. We have gained considerable experience from research on connections consisting of two aluminium sheets joined by a SPR. Parameter studies have been done to study the influence of sheet thickness and material on the connector behaviour. Experimental facilities have been developed which allow for systematic studies of the riveting process and the final connector mechanical strength and ductility. The static connector capacity can be studied for a wide variety of loading conditions. We have also recently done experiments at the Ecole Normale Supérieure de Cachan/Laboratoire de Mécanique et Technologie (ENS/LMT)LMT Cachan, Paris, on the dynamic (impact) behaviour of SPR connections. Numerical models have been established and validated for riveting process simulation. Finally, we have suggested robust design formulas regarding strength and ductility for an SPR connection for shear and pull-out loading conditions.
New experimental test set-up was developed for testing of riveted connections of different materials. An extensive experimental programme was conducted to study the mechanical behaviour of SPR connections for novel material combinations. The selection of the new material was defined in collaboration with the industrial partners.
A new self-piercing riveting point connector model applicable for large-scale shell-based finite element simulations was developed. The new model was implemented in LS-DYNA and optimised/calibrated against the experimental database on aluminium-to-aluminium riveted connections.