On the development of new test techniques to measure the tensile response of materials at high and ultra-high strain rates

Abstract

Background: There is a lack of reliable methods to obtain valid measurements of the tensile response of high performance materials such as fibre composites, ceramics and textile products at high rates of strain. Objective: We propose and assess two new test techniques aimed at measuring valid tensile stress versus strain curves at high and ultra-high strain rates. Methods: We conduct detailed, non-linear explicit Finite Element (FE) simulations of the transient response of the test apparatus and specimen during the tests and we develop simple analytical models to interpret the test measurements. We consider two test techniques: one based on the split Hopkinson bar apparatus, and suitable for strain rates of up to 1000 /s, and a second technique relying on ballistic impact and aimed at measurements at strain rates higher than 1000 /s. Results: The simulations are successfully validated using test data at strain rates of order 200 /s and then used to predict the test performance at strain rates up to approximately 5500 /s. We find that both techniques can give valid stress versus strain curves across a wide range of strain rates. Conclusions: We identify the limits of both techniques and recommend optimal measurement strategies for dynamic testing of materials with different ductility.