Constitutive equation for Ti–6Al–4V at high temperatures measured using the SHPB technique

Abstract

A high temperature split Hopkinson pressure bar (SHPB) test system is used to investigate the effects of temperature as well as those of strain and strain-rate. Effects of temperature for the titanium alloy (Ti–6Al–4V) are investigated by developing a high temperature SHPB test system. In this work, high temperatures greater than 1000°C are attained in the SHPB test specimens by using two ellipsoidal radiant heating reflectors with two halogen lamps. The thermal gradients in the specimens are observed as they are heated. Methods for solving problems related to conduction between the specimens and elastic bars and techniques for measuring the temperature of the specimens are suggested. When testing with the high-temperature SHPB apparatus, care is required to prevent oxidation of the surface of the specimen, and to prevent an inhomogeneous temperature distribution from developing in the specimen. To determine the true flow stress–true strain relationship, specimens are tested from room temperature to 1000°C at intervals of 200°C and at a strain-rate of 1400 s −1 . The parameters for a Johnson–Cook constitutive equation and a modified Johnson–Cook constitutive equation are determined from the test results. The modified Johnson–Cook constitutive equation is more suitable for expressing the dynamic behavior of the Ti–6Al–4V titanium alloy in the vicinity of the recrystallization temperature.