Abstract

Digital image correlation has been used, in conjunction with Mode I and Mode II fracture mechanics tests under static and dynamic loading conditions, to determine the position of the crack front during interlaminar testing. A MATLAB code has been developed to post process the digital image correlation analysis to determine the experimentally measured crack position and these results have been compared to compliance-based predictions of crack position which do not use a physical measure of the crack length. Results have shown that the digital image correlation analysis has successfully tracked the crack position providing a physical measure of the crack front during static and dynamic testing for the calculation of fracture toughness values. This methodology, incorporating digital image correlation for crack position monitoring, was then expanded to analyses for fatigue tests showing that the physical crack length has a varied growth rate in comparison to the steady change in specimen compliance.

Highlights

  • Composite materials have gained widespread acceptance in aerospace and automotive industries since their initial introduction in the early 1950s

  • Tests have been conducted to identify the static fracture toughness and confirm the viability of the defined methodology, and this has been expanded to crack measurements in dynamic tests with results compared to traditional compliance-based methods to highlight the benefits of adopting digital image correlation techniques (DIC) techniques in standardised test methods

  • Static test results were compared between the physically measured crack position and the compliance-based measurement techniques

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Summary

Introduction

Composite materials have gained widespread acceptance in aerospace and automotive industries since their initial introduction in the early 1950s. They are especially susceptible to low velocity impacts, with delamination being the most commonly observed failure mechanism within the laminate structure [1,2,3]. Proceedings 2018, 2, 389 FOR PEER REVIEW To this end, fracture mechanics testing of carbon fibre epoxy composites has been conducted under static and fatigue loading conditions for Mode I and Mode II analyses using the double cantilever beam test (DCB) and the end load split test (ELS) in conjunction with digital image correlation techniques (DIC) for automated crack growth monitoring and subsequent fracture toughness measurements. DIC is a non-destructive optical measurement technique that provides an analysis of the displacements and strain fields on the surface of a sample under an applied loading [4,5]

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