Friction stir weld development and dynamic crash testing of bumper-beam / crash-box assemblies made from AA66082-T6 and AA6063-T6 extrusions
Advancements in friction stir welding (FSW) have enabled the development and testing of a lightweight automotive bumper-beam/crash-box assembly. Previously, a test fixture to dynamically (crash) test the functionality of advanced bumper assemblies fabricated by FSW was developed. This FSW development work included microstructural examination and static mechanical testing. Results from coupon-level development were compared against results from component-level testing of prototype articles using micrographs and an advanced electronic (signal/frequency analysis) non-destructive evaluation (e-NDE) technique in order to detect weld anomalies primarily in the form of voids. Due to the geometry of the welded part joint, conventional mechanical testing methods (tensile and peel test) were not applicable. Therefore, a wedge test was devised to test the relative toughness of the FSW joint. From recorded data, toughness plots were calculated to select the best joint from three weld tools, each having the same basic threaded probe and WiperTM shoulder designs, and differing only in probe features. In addition to the basic tool configuration, one tool had a set of partial CounterFlowTM grooves, and the other had a set of partial straight flats. Each also had a special geometrical feature added to the tip of the tool probe, referred to as a concentrating tip, to improve metal flow at the end of the probe in order to inhibit void formation. Traditional sled testing for low-speed bumper requirements was performed at the General Motors (GM) Research and Development (R&D) facility in Detroit, Michigan, and drop tower tests were performed using an FSW test fixture at the National Institute for Aviation Research (NIAR) at Wichita State University (WSU). These dynamic tests were performed on bumpers using both FSW and gas metal arc welding (GMAW). Finite element analysis (FEA) was used to compare the predicted damage to the actual damage sustained by the bumpers fabricated by GMAW and FSW, respectively.