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Abstract:There is currently a need for an efficient numerical optimization strategy for the quality of friction stir welded (FSW) joints. However, due to the computational complexity of the multi-physics problem, process parameter optimization has been a goal that is out of reach of the current state-of-the-art simulation codes. In this work, we describe an advanced meshfree computational framework that can be used to determine numerically optimized process parameters while minimizing defects in the friction stir weld zone. The simulation code, SPHriction-3D, uses an innovative parallelization strategy on the graphics processing unit (GPU). This approach allows determination of optimal parameters faster than is possible with costly laboratory testing. The meshfree strategy is firstly outlined. Then, a novel metric is proposed that automatically evaluates the presence and severity of defects in the weld zone. Next, the code is validated against a set of experimental results for 1 /2" AA6061-T6 butt joint FSW joints. Finally, the code is used to determine the optimal advancing speed and rpm while minimizing defect volume based on the proposed defect metric.

In this chapter, we describe the development of a new approach to simulate the friction stir-welding FSW process using a solid-mechanics formulation of a mesh-free Lagrangian method called smoothed particle hydrodynamics SPH . "lthough this type of a numerical model typically requires long calculation times, we have developed a very efficient parallelization strategy on the graphics processing unit GPU . This simulation approach allows the determination of temperature evolution, elastic and plastic deformation, defect formation, residual stresses, and material flow all within the same model. More importantly, the large plastic deformation and material mixing common to FSW are well captured by the mesh-free method. The parallel strategy on the GPU provides a means to obtain meaningful simulation results within hours as opposed to many days or even weeks with conventional FSW simulation codes.

This study investigates the influence of laser cladding parameters on the geometry and composition of metal-matrix composite (MMC) coatings. Composite coatings are made of a Ni-Cr-B-Si metallic matrix and of WC reinforcement with a volume fraction of 50 %. Optical microscopy is used to characterize the coating geometry (height, width and penetration depth) and to determine the real volumetric content ofWC. Laser cladding on low carbon steel substrate is carried out using a cw Nd:YAG laser, a coaxial powder injection system and a combination of Taguchi and E.M. methods to design the experiments. This combination explores efficiently the multidimensional volume of laser cladding parameters. The results, which express the interrelationship between laser cladding parameters and the characteristics of the clad produced, can be used to find optimum laser parameters, to predict the responses and to improve the understanding of laser cladding process.