Finite element assisted prediction of ductile fracture in sheet bulging of magnesium alloys
Hunt, David (2008) Finite element assisted prediction of ductile fracture in sheet bulging of magnesium alloys. Master of Engineering thesis, Dublin City University.
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There is currently a growing demand for energy efficiency, particularly in reducing the rate of oil consumption. One solution in this area is for the aerospace and automotive industries to produce lighter vehicles that are more fuel efficient. Magnesium alloys provide that solution as they have a high strength to weight ratio and can contribute to reducing the overall weight of the vehicle. Over the past few years many researchers have tried shaping these alloys using various forming techniques. These studies have shown however, that the formability of these alloys is very difficult to predict. The material properties of magnesium alloys would suggest that they are ideal for sheet metal forming, yet their formability is still inferior to many other alloys used in sheet metal forming. In order to overcome this unpredictability in shaping Mg alloys it is necessary to introduce a range of failure that will predict fracture over a range of draw depths rather than a single depth. It is difficult to make the leap from a process that is unpredictable to pinpointing the exact point of failure. It is more logical to firstly determine a range of formability where failure can occur. In this study a Finite Element Model of a sheet bulging process was built and validated with results obtained from physical testing. The FEA model uses Oyane’s ductile fracture criterion to predict whether fracture has occurred in the material and also to predict the location of fracture if it occurs. This validated FEA model implements a failure range where failure is predicted over a range of draw depths, and sensitivity analysis provides a confidence level in this range by varying some of the material properties and examining the effects on the prediction of fracture.
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