Determination of the dynamic stress intensity factor of a specimen under one-point bending from the measurement of the load-point displacement

Abstract
The use of dynamic one-point bending tests as an alternative to three-point bending tests allows fracture properties such as dynamic initiation fracture toughness to be obtained at high strain rate. To perform this kind of test, experimental devices based on modifications of the Hopkinson bar can be used. Several authors have been proposed simplified procedures to obtain the dynamic stress intensity factor, K_I(t), considering the specimen as a Timoshenko cracked beam subjected to a concentrated load at the central cross-section. The disadvantage of this procedure is that normally it is difficult to measure the force applied to the specimen in the above-mentioned tests. Here a simplified method is proposed for the calculation of K_I(t), based on an analysis of the behaviour of a Timoshenko cracked beam, knowing the displacement of the point of loading, which can be measured more accurately than the applied load. The results were compared with those of a finite element numerical simulation and good agreement was found.