Ductile-Brittle Transition Behaviors with Two Striker Geometries in the Instrumented Charpy Impact Test

Abstract

Instrumented Charpy impact test method is possible to obtain various dynamic fracture characteristics from the load-deflection or load-time curve. Recently, instrumented Charpy impact test method is widely used for the evaluation of toughness of various specimens of different materials with different sizes. It is important to record an accurate impact load in order to improve the reliability of this test method. In some standards of instrumented Charpy impact test method such as ISO and ASTM, they haven.t clearly standardized striker geometry which seem to directly influence the obtained impact load. There are some differences between standards, although standard procedures are well defined. Therefore, instrumented Charpy impact test method has a problem that measurement value is different depending on each standard. In the present study, the effect of striking edge geometries, which are difference between ISO and ASTM, on load-deflection curve and absorbed energy were investigated. According to ISO and ASTM, two types of striker having different radius were machined. There was no difference between the two different striking edge geometries for values of absorbed energy per unit ligament area less than 0.75J/mm2. However, striking edge geometry according to ASTM is not propriety for Charpy impact test method because of four, instead of three, point bending on process of fracture at high level of absorbed energy. The effect of brinelling deformation, which was considered as an advantage of striking edge geometry according to ASTM, is very small on instrumented Charpy impact test. Consequently, there seem to be not an advantage of striking edge geometry according to ASTM. Therefore, standards should be unified in the striking edge geometry according to ISO.