Time-lapse x-ray microtomographic imaging of compressive failure in carbon fibre-epoxy composites

The relatively low compressive strength of carbon fibre reinforced plastics (CFRPs) caused by kink bands has limited its use in primary load-bearing structures. In this paper, the evolution of kink bands has been captured in notched unidirectional (UD) T800 carbon fibre/epoxy composite under four-point bending (FPB) test. The sequence of damage mechanisms occurred in the three-dimensional (3-D) volume has been observed with time-lapse X-ray micro-tomography (µCT). The evolution of kink bands is significantly slowed down in the compressive region of the sample under FPB loading. The fibre buckling failure has been observed to propagate until the onset of fibre micro-buckling. The primary kink band, once formed, has been found to maintain its width and orientation under further loading. Multiple kink bands have been observed to originate from a primary narrow kink band. The sequential development of primary kink bands and conjugate kink bands has been found to realign the fibres in between along the original fibre direction. These experimental findings of the kink-band formation process could be used for the development of more reliable analytical and numerical models.