A new technique for tensile testing of engineering materials and composites at high strain rates

Abstract

A new test technique and bespoke apparatus to conduct high strain rate measurements of the tensile response of materials are presented. The new test method is applicable to brittle solids and composites as well as high-performance fibres, yarns and tapes used in composite construction. In this study, the dynamic response of monolithic poly(methyl methacrylate) and unidirectional composites based on Dyneema® tape, Dyneema® SK75 yarn and Kevlar® 49 yarn are explored. The technique allows early force equilibrium and yields valid tensile stress–strain curves, which include part of the elastic material response. The new method also enables investigation of size effects in tape and yarn materials, allowing testing of specimens of arbitrary length.

On the Development of New Test Techniques to Measure the Tensile Response of Materials at High and Ultra-high Strain Rates

“…Two different techniques will be analysed in this study. The first technique is the one presented in [16] and will be referred to as Test I. The second technique, which we will refer to as Test II, is an extension of Test I aimed at achieving ultra-high strain rates (which we define as rates higher than 1000 /s).…”

“…1b. This figure only shows the active part of the apparatus, and the rubber sleeve is idealised (and it will be modelled) as a thick-walled hollow circular cylinder (we refer the readers to [16] for drawings of the detailed geometry of such rubber sleeve). The SHPB is operated in the standard way: a compressive shockwave is generated following projectile impact and propagates down the input bar and piston, pressurizing the fluid and inducing hoop tension in the rubber sleeve and specimen.…”

“…We now write down four different equations relating the circumferential stress in the specimen to the other parameters, based on different sets of assumptions. In the following we will assume that the specimen is a monolithic ring with rectangular cross-section, however this assumption can be easily relaxed when focusing on testing of fibre bundles, as described in [16][17][18].…”

“…We have recently developed a new test technique for tensile testing of engineering solids at high strain rate [16], in which the test principle was the dynamic internal pressurisation of ring-shaped specimens, and we have shown [16][17][18] that this is suitable for high strain rate testing of brittle and strong materials, demonstrating this up to a strain rate of 323 /s and for a wide range of temperatures. This technique was shown to have several advantages over existing methods: the achievement of early force equilibrium, the elimination of gripping problems, the use of identical specimens in any test condition, and the suitability for studies of the effects of size, temperature and humidity on the measured response.…”

“…The technique is suitable for testing monolithic rings, composite rings, fibre bundles or yarns, and materials in the form of tape. Unlike any other existing technique, the method in [16] was shown to be able to capture part of the elastic material response at high strain rate.…”