Numerical Study of an Interrupted Pulse Electromagnetic Expanding Ring Test

Light weighting of vehicle structures will play an important part in the efforts to reduce fuel consumption and enable alternatively powered vehicles. The use of aluminum alloys and advanced high strength steels is one potential way of achieving significant weight reductions in the short to medium term. One of the main challenges posed by these materials is their relatively poor formability when compared with traditional automotive steel alloys. High speed forming has been studied as a way of increasing the formability of these alloys, with promising results. The lack of accurate constitutive data and models for these materials at the strain rates encountered in high speed forming, which can exceed 1,000 s -1 , presents a significant challenge to their implementation. Expanding ring tests have been used to measure the stress strain response at materials at high strain rates. In principle, these tests generate a uniaxial tensile stress state within the ring. If the driving force is known and the acceleration of the sample can be measured, then the stress and strain response of the material can be obtained. Significant challenges need to be overcome to obtain stress-strain data from this test, namely understanding the induced forces, Joule heating and the actual stress distribution in the ring. An interrupted pulse electromagnetic expanding ring test is being developed at the University of Waterloo to study the high rate behaviour of sheet metals. The test minimizes the induced forces generated on the sample and can produce free flight conditions. Given the complex nature of the phenomena and the speed at which they occur, numerical simulations play a critical role in analyzing the test. This paper presents the results of a multi-physics numerical analysis of the test based on a 3-D simulations using LS-DYNA ® . This analysis has been done to determine the effect of Joule heating and the driving force on the data generated by the test.