Abstract
The design of sample geometries and the measurement of small strains are considered the main challenges when testing composite materials at high strain rates using the split Hopkinson bar technique. The aim of this paper is to assess two types of tensile sample geometries, namely dog-bone and straight strip, in order to study the tensile behaviour of basalt fibre reinforced composites at high strain rates using the split Hopkinson bar technique. 2D Digital image correlation technique was used to study the distribution of the strain fields within the gauge section at quasi-static and dynamic strain rates. Results showed that for the current experiments and the proposed clamping techniques, both sample geometries fulfilled the requirements of a valid split Hopkinson test, and achieved uniform strain fields within the gauge section. However, classical Hopkinson analysis tends to overestimate the actual strains in the gauge section for both geometries. It is, therefore, important to use a local deformation measurement when using these 2 geometries with the proposed clamping technique.
Highlights
Composite materials have been increasingly used in many applications which can be subjected to impact loads, such as automotive and aeronautical applications
The design of the tensile composite sample, has to achieve the following main requirements: (a) the specimen has to be short enough to achieve the required quasi-static stress equilibrium and to increase the achievable maximum strain rate, (b) a state of uniform stress and strain has to be achieved in the gauge section, (c) the design of the specimen has to promote failure within the gauge section, (d) the geometry has to be representative of the material constituents
In order to study the uniformity of the strain fields within the gauge section, average strain fields were extracted for a gauge area of 5x4 mm and compared to that of area 8x4 mm
Summary
Composite materials have been increasingly used in many applications which can be subjected to impact loads, such as automotive and aeronautical applications. Split Hopkinson bar setups have been typically used for that purpose, where high strain rates up to 8000 s-1 can be achieved [1]. Specimen design has been a critical element in high strain rate testing of composite materials with the split Hopkinson bar tensile technique, since its introduction by Kawata et al [2]. The design of the tensile composite sample, has to achieve the following main requirements: (a) the specimen has to be short enough to achieve the required quasi-static stress equilibrium and to increase the achievable maximum strain rate, (b) a state of uniform stress and strain has to be achieved, (c) the design of the specimen has to promote failure within the gauge section, (d) the geometry has to be representative of the material constituents The design of the tensile composite sample, has to achieve the following main requirements: (a) the specimen has to be short enough to achieve the required quasi-static stress equilibrium and to increase the achievable maximum strain rate, (b) a state of uniform stress and strain has to be achieved in the gauge section, (c) the design of the specimen has to promote failure within the gauge section, (d) the geometry has to be representative of the material constituents
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