Determination of energy-notch depth relationship using force-displacement diagrams in instrumented Charpy impact testing of API X65 steel

In this paper, dynamic behavior of API X65 steel under impact loading was studied using an instrumented Charpy machine of 450J capacity. The fracture energy can be measured using this testing machine in two different ways. In the first method, the difference in potential energy before and after impact test is reported via machine dial. In the second method, the output voltage from load-cell (mounted on the machine tup) gives load-displacement data from which energy is calculated via curve integration. Using instrumented data, the initiation energy, propagation energy and total fracture energy for eight series of specimens made from tested steel were measured and found to have exponential behavior versus initial notch depth. Furthermore, the characteristic forces used for the design of dynamically loaded structures (namely general yielding, Fgy, and maximum force, Fm) were determined from the force-displacement diagram. The important innovation of this research is presentation of eight new correction factors for different notch depth of specimens. These new correction factors and their mean value were compared with a similar data from a previous research work for conventional fracture models of energy transportation steel pipelines which showed good agreement.