An efficient strategy for coupling thermal and mechanical computations. Application to the analysis of a multibody system

Full text: This paper deals with the modeling of a coupled tool-workpiece system during the forming process. The initial software is based on the finite element method to solve the deformation of the part which can be viscoplastic or elastoviscoplastic. Interaction with the rigid tool are performed through a penalization algorithm for contact, coupled with a friction and a thermal dissipation term. A MINRES method is used to solve the systems and the program is fully parallel. The multi-body algorithm is based on a master slave algorithm with a node to face approach. The nodes of the tool are related to the surface triangle (creating a fictitious tetrahedron) of the part to express the contact and friction term in the mechanical system and the conduction in the thermal one. The fully coupled system is solved with an iterative method. If the thermal coupled problem requires an acceptable computation time, the mechanical coupled problem is 11 times more expensive than the single domain one if the number of nodes of the coupled system is 5 times higher. The parallel algorithm for the multi-body system is based on the domain decomposition of the standard program. The main issue being to partition the whole domains in order to give equivalent computation work to each processor. The simplest is to assign a domain to each processor, leads to unbalanced tasks if the rheologies are of same type and the number of nodes very different. The selected procedure is to assign to each processor one fraction of each domain. The contact analysis is then performed for each processor and the fictitious elements are local to the processor. An optimization would be to re-partition after the definition of these elements to improve the communication. Remeshing step is also to be considered. Another way to improve the computation time of multi-body systems is to alternate multi-body and single-body computations for the mechanical problem. The deformation of the tool can be neglected except for few time steps. This simplification can be done if the contact pressure is still precise enough because this parameter is necessary to further developments as computation of the tools' wear. Comparisons of parallel and sequential computations will be provided and the analysis of this simplified mechanical assumption on these result will be done on several cases. Refs. 2 (author)