The Off-Axis IBII Test for Composites

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RESEARCH PAPER

The Off‑Axis IBII Test for Composites S. Parry1 · L. Fletcher1 · F. Pierron1 Received: 11 May 2020 / Accepted: 3 September 2020 © The Author(s) 2020

Abstract Composite components regularly experience dynamic loads in service. Despite this, it is still difficult to obtain accurate mechanical properties of composite materials under high strain rate conditions. In this study, a new application of the Image-Based Inertial Impact (IBII) test methodology was developed, to generate an accurate in-plane transverse and shear moduli dataset from unidirectional (UD) off-axis composite specimens. The obtained dataset was consistent across different sample configurations, where results from the UD45◦ off-axis specimens agreed well with the UD90◦ values. Validation of the shear modulus identification was also undertaken by comparing the results from the UD90◦ and UD45◦ specimens with a multi-directional (MD) configuration. Here, it was found that MD±45◦ specimen shear modulus values where marginally lower than that from the UD specimens, in accordance with the lower fibre volume fraction of the MD laminate. Low strain rate sensitivities in the 0.5 − 2×103 s−1 regime evidenced in this work suggest previously published data (often from splitHopkinson bar tests) may include both a material and system i.e. testing apparatus response. Keywords  High-speed imaging · Composites · High strain rate · Full-field measurements · Virtual fields method · IBII test

Introduction There are many examples of composite components being subjected to dynamic loads. In the aerospace industry, aircraft nose caps, wings and rear stabilisers can be impacted by a range of objects such as birds, hail or ice and runway debris. Design engineers regularly use a combination of experiments and finite element simulations in order to predict the response of these structures under impact conditions. The simulation’s ability to predict a realistic structural response hinges largely on the accuracy of the data used in the individual material models specified for the component. This is especially true for fibre reinforced polymer composite materials, where the resin dominant (i.e. transverse and shear) properties are generally considered rate sensitive [1].

* S. Parry [email protected] L. Fletcher [email protected] F. Pierron [email protected] 1



Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, Hampshire SO17 1BJ, UK

One problem for simulation engineers utilising high strain rate material data is that there is significant scatter in published values. For example, in-plane transverse modulus strain rate sensitivities of Carbon Fibre Reinforced Polymer (CFRP) composites reported in literature are presented in Fig. 1a. Here, up to 20% variation in the reported values can be seen at strain rates below 102 s−1 . However, beyond 102 s−1 the scatter is anywhere between – 20 and 40%. Scatter can also be seen in the reported shear modulus values from unidirectional (UD) samples, where at strain rates o