On the parameters of dynamic deformation and damage models of aluminum alloy 6008-T4 used for high-speed railway vehicles

Abstract

High-speed railway vehicles are subjected to complex stress and environmental conditions in service. Aluminum alloy extrusions are widely used in energy absorption structures of high-speed trains, due to their excellent mechanical and processing properties. The crashworthiness of the aluminum alloy extrusions is critical to the safe and steady operations of the railway vehicles. In this study, a variety of mechanical tests were conducted on a novel aluminum alloy used for vehicles, i.e., aluminum alloy 6008-T4, including quasi-static and dynamic tension/compression tests, quasi-static tension tests at a wide range of temperatures, fracture tests along different stress paths, etc. The results show that the yield stress of the 6008-T4 aluminum alloy increases by about 15% while the fracture strain increases by about 25% when the strain rate varies from 0.001 s−1 to 2500 s−1. The aluminum alloy 6008-T4 exhibits significant temperature softening in strength: the yield stress decreases by about 60% when the temperature rises from 25 ℃ to 300 ℃. However, the fracture strain at 300 ℃ shows an 80% increase compared to the ambient (25 ℃) result. With the increase of stress triaxiality from 0.1 to 0.6, the fracture strain of the aluminum alloy 6008-T4 decreases by about 40%, and the decreasing trend conforms well to the theoretical prediction by the Johnson-Cook (J-C) model. Then the parameters of the J-C constitutive and damage models were calibrated according to the experimental results. In particular, the local fracture strains are critical for deriving the parameters of the damage model parameters. Therefore, the finite element simulations were combined with the force-displacement curves obtained in the tests to calculate the local fracture strains of the specimens. Compared to the direct measurements, the combined method of the experiments and simulation is more simple and accurate. The experimental curves at different strain rates and temperatures were compared with those predicted by the J-C model. The compariosn shows that they agree well at high temperatures. Finally, the impact penetration test was adopted to verify the acquired parameters. The simulation and experimental results, regarding the projectile positions and the fracture patterns of the target, are consistent, indicating that the parameters and calibration methods presented in this paper are reliable and effective.