Imaging of composites by helical x-ray computed tomography

Understanding the fatigue damage mechanisms of composite materials used in wind turbine rotor blades could potentially enhance the reliability and energy efficiency of wind turbines by improving the structure design. In this paper, the fatigue damage propagating mechanisms of unidirectional glass fibre composites was characterised by helical X-ray CT. The staining approach was used and it was effective to enhance the visibility of thin matrix cracks and partly closed fibre breaks instead of widely opened cracks. Fibre breaks in the centre UD bundle were found to occur locally, instead of being evenly distributed along the 0° fibre direction after 500,000 cycles. The locations of these damage sites were found to be correlated with intersecting points of +/-80° backing bundles. At higher number of cycles, edge effect becomes dominant with extensive fibre breaks in the edge UD bundles and matrix cracks in the resin-rich region.