Radial expansion of metal tubes: Static testing and simulation correlation

Railway passive safety regulation states that numerical models of areas of large deformation, such as crumple zones, must be validated by appropriate physical testing. The radial expansion of tubes is used as an energy absorption mechanism in the event of crashes in railway vehicles. Here we present the physical test and finite element analysis correlation activity of scaled radial expanding tubes. Dimensionally scaled tubes were tested under quasi-static conditions. Four different dies, with expansion ratio (the ratio of die outer diameter to tube inner diameter) R = 1.10 and R = 1.25 and die conical semi-angle A = 15° and A = 30°, were used to crush the expanding tubes. Numerical simulation models were constructed to predict the behaviour of the tubes. Correlation between simulation and static test was achieved by matching the deformed shape and energy absorption of the specimens. The friction coefficient was inferred by adjusting its value in the numerical model until the simulation matched the test results. The friction coefficient (u) was predicted to be on the range 0.07-0.11, depending on the expansion ratio and semi-angle of the crushing dies. These values are slightly larger than the value frequently quoted in the literature of u = 0.05.