SIZE EFFECTS ON MATERIAL BEHAVIOR IN MICROFORMING

The development of cold metal forming processes for very small mechanical components by forging, coining, stamping, extrusion is limited by the understanding of geometric and material effects due to the size reduction of the components. In this study a set of experiments is performed on a copper alloy (CuZn10) where the diameter of the cylinder is scaled down from 5mm to 1mm, in order to evaluate the size effects on the flow stress. Compression tests were carried out by reducing the height of the cylinder by 80% at a constant rate of 0.03 mm/s and without lubricant. During these tests, the load-displacement curve can be plotted. For each specimen size the material behaviour is obtained. The material parameters were identified by an inverse method using the code LS-Dyna. Then, considering the results, a new model of the constitutive behaviour is proposed which takes into account size effects. This model is function of a semi-intrinsic parameter, the share of surface grains.