Strain measurement utilizing micro-indentation in upset forgeability evaluation

An alternative method for determining the surface strains from a micro-indentation specimen is proposed for cold forgeability evaluation. The cylinder upset test is the most simple and popular approach to evaluate the forgeability of the materials. The forgeability is limited by the occurrence of ductile fracture, which initially occurs at the equatorial surface of the specimen because of the inhomogeneous barreling effect. Thus surface strain measurement is an indispensable experimental procedure to establish the strain paths and limit strains in the forgeability test. To obtain the local strains at the equatorial surface of specimen, experimental approaches using types of micro-indentation tests are investigated. In addition, variations of pattern size deviation and position accuracy in micro-indentation are studied to find the most adaptive strain-measuring conditions. Finally, the local strains at the equator of specimens, which construct strain paths and limit strains, are obtained. The experimental results show that Vickers micro-indentation, a proposed strain measurement method, can be applied with good accuracy and fine resolution for forgeability evaluation in the cylinder upset test.