Investigation of damage initiation in carbon fibre reinforced polymer composites using synchrotron radiation computed tomography and digital volume correlation

Abstract

Despite the vast interest in this critical research area, the complicated, interacting early stage damage mechanisms in cross ply Carbon Fibre Reinforced Polymers (CFRP) are poorly understood. The two‐dimensional nature of the techniques commonly used to date in the analysis of these mechanisms is insufficient to adequately explain the three-dimensional nature of damage initiation. The work conducted in this research makes use of synchrotron radiation computed tomography (SRCT) in an effort to develop our understanding of the physical micromechanics associated with the earliest stages of damage initiation. Complementary techniques such as Digital Volume Correlation (DVC) and image segmentation have been used to analyse the strains associated with crack initiation in cross ply laminates loaded and imaged in 3D in situ. (The use of these techniques, to investigate damage initiation in CFRP is limited to the best of the author’s knowledge). The use of SRCT and DVC has been evaluated to determine the techniques ability to track displacements in an anisotropic & heterogeneous material, the results of which show that reasonable levels of confidence may be achieved in measuring strain heterogeneity perpendicular to the fibres within a ply. The formation of transverse ply cracks is shown to correlate with an extended region of elevated tensile strain, which exists at lower loads than that at which the transverse ply crack formed. The study shows the usefulness of the SRCT technique in determining where damage initiates and the local strain state at initiation, which is potential significant for accurate and physically based initialization and validation of micromechanical models.

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