Application of Galerkin meshfree methods to nonlinear thermo-mechanical simulation of solids under extremely high pulsed loading

Beam facing elements of the International Fusion Materials Irradiation Facility (IFMIF) Linear Particle Accelerator prototype (LIPAc) must stop 5-40 MeV D+ ions with a peak current of 125 mA. The duty cycle of the beam loading varies from 0.1% to 100% (CW), depending on the device, with the ions being stopped in the first hundreds microns of the beam facing material. For intermediate duty cycles up to CW, the thermal load can be considered a heat flux load on the boundary, but this approximation gets too conservative as the duty cycle is reduced because the thermal diffusion becomes more important. Instant heat flux produced by the beam can reach up to 3 GW/m(2) in elements such as the beam dump and slits during short times of hundredths of microseconds. In these cases, the accuracy of the volumetric heat generation is critical for obtaining realistic results. Meshfree Galerkin methods discretize a continuum using scattered nodes. As opposed to FEM, no predefined connectivity is needed between the nodes, so C (infinitely differentiable) locally supported shape functions can be used to approximate both the trial and the test functions. This feature makes these type of methods well suited for those problems where the domain experiences very large deformations or has high gradients of the state variables. Radial basis (RBF) and moving least squares (MLS) functions have been applied to the simulation of complex nonlinear mechanical problems involving large strains and displacements (e.g. flexible multibody dynamics). When compared to Finite Element Method (FEM), they present higher robustness under large strains and a better precision for the same computer calculation time when dealing with rough discretizations. All these results have been previously shown in Pl. The experience gained with those applications and the reproductivity characteristics of the shape functions suggest that the number of degrees of freedom needed for a precise analysis of shallow volumetric heat loads can be drastically reduced from that of the usual FEM approach. We describe the development and implementation of a coupled nonlinear thermo-mechanical formulation which takes into account the particularities of the meshfree discretization. Numerical experiments of beam facing elements are presented and compared with FEM results. (C) 2013 Elsevier B.V. All rights reserved.