Influence of voids on damage mechanisms in carbon/epoxy composites determined via high resolution computed tomography

A multi-scale computed tomography (CT) technique has been used to determine the material structure and damage mechanisms in hydrostatically loaded composite circumferential structures. Acoustic emission sensing was used to locate macroscopically regions of high damage under load to inform the computed tomography. The resultant images allow direct three-dimensional analysis of voids, fibre breaks and cracking, for which a high level of confidence can be placed in the results when compared to other indirect and/or surface-based methods.Ex situ analysis of loaded samples revealed matrix cracking in the longitudinally wound plies, whilst fibre breaks were observed in the circumferentially wound plies. The matrix cracking within the longitudinally wound plies is shown to interact directly with intralaminar voids. The correlation of voids with fibre breaks in the circumferentially wound plies is less distinct. A three-dimensional tessellation technique was used to analyse the spatial distribution of the voids and to compare with single fibre break locations. Whilst there was no first order correlation between fibre break densities and void volume fractions or void dimensions, a distinct correlation was found between voids and nearest neighbouring fibre breaks, where 2.6–5 times more fibre breaks occurred immediately adjacent to a void than would be expected for randomly distributed breaks.