CHEVRON CRACK PREDICTION USING THE EXTREMELY LOW STRESS TRIAXIALITY TEST

Abstract

Forward extrusion is typical way of mass-production of cold formed bars or rods with constant cross section. This process is used for production of engine alternator shafts and it is based on reducing the diameter of semi-product without removing material in several reductions. However, there is a potential danger of the chevron cracking. Chevron cracks are inside the material and therefore invisible on the surface of the semi-product. Using computational methods, the potential cracking can be predicted in advance, therefore it may lead to considerable savings. Three various phenomenological ductile fracture criteria were calibrated and then applied to forward extrusion process. As there are specific stress states in this process, new extremely low stress triaxiality fracture test were designed and used in the criteria calibration process. The test is based on the compression of the cylinder with a specific recess. Then, the criteria prediction ability and reliability is discussed.

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