Friction Stir Blind Riveting of Dissimilar Materials.

Date
2017-05
Authors
Wang, Wei-Ming
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Mechanical Engineering
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oining of dissimilar materials receives great attentions to broaden the implementation of lightweight components for vehicle applications. Friction stir blind riveting (FSBR), as a newly developed method, shows potentials in joining dissimilar metals and thermoplastic composites for complex structures. In this process, a rotating blind rivet is applied to soften and penetrate two workpieces with frictional heat. The rotation stops after the head of blind rivet contacts the top surface of workpiece, and then the mandrel is pulled up and breaks off at the setting force. Finite element is one of the best technique to observe material flow and temperature during a friction stir process; nevertheless, the main issue to simulate FSBR process is the large deformation of work materials. Therefore, FEM coupled with smoothed particle hydrodynamics (SPH) was utilized to simulate FSBR process for joining magnesium and aluminum alloys. To validate the model, plunge force and torque were compared to experimental measurements. The history of temperature, von Mises stress, and material flow of workpieces are available in this SPH-FEM model. To broaden the application of FSBR, the knowledge of mechanical properties and failure mechanisms of FSBR joints is required. Three optimal configurations of FSBR lap joints, including aluminum, magnesium, and a carbon-fiber reinforced polymeric composite (CFRP), were studied in this dissertation. In situ nondestructive testing method, acoustic emission (AE), was applied to identify the deformation zone and failure mode of FSBR lap joints under uniaxial tensile loading. Scanning electron microscopy (SEM) was also performed to analyze the fractured microstructures. Post-corrosion mechanical behavior of dissimilar material joints is a primary consideration for their applications subjected to a corrosive environment. In this study, it was found that for CFRP constituent exposed joints, the dominated failure mode was tension failure and there was no loss in strength observed under current corrosion condition; however, exposed Mg/Al joints depicted a complex failure mechanism where failure was caused by bearing force and secondary bending during tensile tests, and degradation in strength was observed.
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