Reliable materials performance data from impact testing

Swinburne University of Technology has a wide range of facilities for measuring the mechanical properties of materials under impact and high speed loads. The facilities include a drop‐weight test machine, three sets of split Hopkinson pressure bar (SHPB), a gas gun and an INSTRON test machine, which are capable of conducting experiments in the strain rate range of 10-3 to 103 s-1. It is difficult to conduct reliable experiments in the strain rate range of 102 to 103 s-1, which is vital, for instance, to the development of crash‐worthy vehicles and the high-speed machining of aerospace metals. The SHPB has been commonly used for the dynamic characterisation of materials for over a century. The high strain rate testing capabilities and simplicity of the technique are reasons for its popularity. This technique can be used for the dynamic characterisation of various materials such as brittle, ductile and soft materials. This technique can also be applied in several load directions such as compression, tension, torsion, shearing and triaxial tests. It also can be used for conducting impact bending to determine the dynamic fracture toughness of materials. Despite its longevity, the Hopkinson bar technique has not been standardised yet. The standardised SHPB technique is necessary in order to provide guidelines for determining the intrinsic material properties. This thesis fills a gap covering materials that has not been discussed yet in previous researches. This research examines the reliability of the compressive SHPB on the metal testing by experimental work, in parallel with the numerical simulation. The main outcomes of this thesis include the quality of bar production, standardisation of the pressure bar, specimen design criteria, consistency of the testing results, identification of measurement uncertainties, effect of paper layer as pulse shaper, and detailed data processing and analysis. It was found that if a greater care and preparation of apparatus and the specimen were taken, and then followed by a standardised data processing and analysis, the SHPB technique produced quite consistent results (within an acceptable error of less than 5%). This consistency was confirmed by the apparatus itself (repeated test) and inter-equipment (compared with the quasistatic and round-robin tests). Based on those results, the author believes that the SHPB technique could and should be standardised in the future.