A Method for In-Process Failure Prediction in Cold Upset Forging

Abstract

This paper addresses the prediction of plastic tensile instability and ductile fracture of a specimen undergoing a compression test (simple upsetting). The method used to predict failure is based primarily on Thomason’s approach for predicting tensile plastic instability in compression tests. However, to apply this method to in-process prediction, a means for calculating the flow stress-strain properties from in-process measurements is needed. A method is introduced that is derived from Bridgman’s correction factor for effective stress after necking occurs in the tensile test, but with a different approach that is suitable for compression specimens. The new correction factor enables one to correct the effective stress after barreling occurs, which eliminates the need for an ideal test (without barreling) to find the effective stress of a specimen. The results were in agreement with those derived from an ideal compression test. Stress data found using this correction factor was then used to predict failure using Thomason’s method.