3D characterisation of the tensile failure of CFRPS manufactured through tailored fibre placement

One of the promising automated fibre tow placement techniques for composite manufacturing is Tailored Fibre Placement (TFP) which provides flexibility for designing complex structures. The inherent anisotropic properties of carbon fibre reinforced plastic (CFRP) composites can be used during manufacturing through tailored placement of fibre tows to optimise lightweight and high performance simultaneously. In this study, the tensile response of a [0/60/−60]s TFP-manufactured CFRP composite was characterised through mechanical testing, carried out inside an X-ray microscope (XRM). Prior to loading a bespoke segmentation procedure was developed to clearly reveal the internal structure of the composite, including carbon fibre bundles and stitching threads. The sample was then progressively loaded with regular interruptions to scan the specimen and to characterise damage development. Results reveal the effect of stitching threads on both the morphology of carbon fibre bundles and the crack propagation process. The first crack initiated from the edge of the specimen and at mid-thickness. Further cracks appeared in the volume and in different plies as the load increased. A very fast propagation rate was recorded for these latter cracks which unloaded the first surface crack. This result emphasised the need for 3D observations to fully characterise the complex crack network eventually leading to failure of the specimen. Only a small amount of interlaminar delamination was observed, which was assumed to be prevented by the vertical stitching threads and no cracks were observed in the base material during the whole loading process.