High resolution damage detection of loaded carbon/epoxy laminates using synchrotron radiation computed tomography

Scott, A.E., Hepples, W., Kalantzis, N., Wright, P., Mavrogordato, M.N., Sinclair, I. and Spearing, S.M. (2011) High resolution damage detection of loaded carbon/epoxy laminates using synchrotron radiation computed tomography. 18th International Conference on Composite Materials (ICCM-18), Cheju, Korea, Republic of. 20 - 25 Aug 2011.

Abstract

The inherent anisotropy and heterogeneity of polymer matrix composites leads to complex macro and micro-mechanical material behaviour. Many micro-mechanical theories exist to predict the failure of unidirectional composites, for example the strength distribution and stress transfer models of Rosen, Batdorf and Hedgepeth. However experimental analysis to confirm the underpinning assumptions made in these theories is limited and hence the validity of the work has not yet been fully determined.

Conventional micromechnical assessment methods however are limited, typically having one or more of the following constraints; destructive, time consuming, low spatial resolution or mechanistic ambiguity. Contemporary computed tomography (CT) methods have great potential to overcome these problems, providing resolutions (to sub-micron levels) at sample scales that may allow multiple damage mechanisms to be quantified in three dimensions.

In the present work, high-resolution synchrotron radiation computed tomography (SRCT) results have been obtained for a commercial grade carbon/epoxy composite laminate under load that is widely used in engineering applications. The double edge notched [90/0]s laminate plates were loaded in-situ to failure and scanned in the preloaded state, and then at incrementally increasing stress levels to the point of final failure.

The imaging techniques enable major damage mechanisms to be identified and quantified, with the present work particularly focused on individual fibres breaks. To the authors' knowledge it provides the first detailed quantification of the accumulation of broken fibres in a carbon/epoxy laminate up to a near-failure condition. It can be seen that failure of fibres is the dominant damage mechanism controlling tensile fracture stress. The incidence of fibre break clusters evidences the role of load sharing in the build up of a failure. No correlation was found between the location of matrix cracks in the 90° plies and fibre breaks in the 0°ply. At present the image analysis has shown no obvious correlation between the location of fibre breaks and other micro-structural features, i.e. presence of voids and resin rich regions. However the data obtained in this experiment gives scope for further quantification.

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Contributors

Author: S.M. Spearing

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