Determination of metal material flow stress by the method of C-FEM

A common method used for the determination of material flow stress is the application of a compression test. At a low strain rate and deformation, the precise flow stress can be obtained in this method, but at a large level of deformation, the friction in the interface between the die and the specimen leads to inevitable bulging of the sample and thereby to inhomogeneous strain and stress. As a result, the flow-stress precision is affected because of the above-mentioned bulging. To reduce the error caused by inhomogeneous deformation, a new method combining compression tests with FEM simulation (C-FEM) is described in this paper. This method takes AISI 1006 and AISI 5140 as examples, and inputs their flow stress determined by compression tests into FEM programs. Then the flow stress is applied in the analysis of upsetting tests. On the basis of load–stroke curves determined by FEM simulation and compression tests, a target-function for evaluating flow-stress precision is set up. The flow stress direct from compression tests can be corrected by optimizing the target-function repeatedly, and as a result the precision of the material flow stress is improved.