Evaluation of energy parameters of fracture during drop weight tear tests based on the analysis of the geometry of the specimens

摘要

An instrumented drop weight tear test allows one to obtain the work of fracture of the specimen. This work monotonously but nonlinearly increases with increasing the test temperature, that is, with increasing toughness of the specimen material. However, part of the work is spent on processes that are not directly related to the properties of the material (friction, etc.). In this work, the total energy expenditures for the deformation of specimens of pipe steel of strength class X80 were determined basing on experimentally measured geometry of the 3D images of specimens and tensile curves of the studied steel, adjusted for the strain rate. In the upper half of the specimen, where tensile deformation was preceded by compression, the total plastic deformation was calculated as the sum of compression and tension. The energy of elastic deformation in all cases was 1÷?5?% of the total energy of deformation (AD). An increase in the test temperature results to monotonous but nonlinear increases of AD from 7.5?kJ at ?67°С (brittle fracture) to 15 kJ at ?40°С (mixed fracture) and up to 17?kJ at +20°С (ductile fracture). Thus, AD is highly sensitive to the transition from brittle to mixed fracture and slowly sensitive to the transition from mixed to ductile fracture. The ratio of AD and the fracture work of the specimen is about 100?% for brittle fracture, >70?% for mixed fracture, and <70?% for ductile fracture. Thus, this ratio can be used as an indicator of the fracture type.