Ultra-fast time-lapse synchrotron radiographic imaging of compressive failure in CFRP

In this study, the compressive failure of unidirectional (UD) carbon fibre/epoxy composite rods is studied using time-lapse synchrotron X-ray imaging. Ultra-fast two-dimensional (2D) radiography (0.1 ms per frame) and three-dimensional (3D) X-ray computed tomography (CT) (0.46 s per tomograph) were used to follow the catastrophic damage evolution under axial compression loading. Radiographs demonstrate the sequence of events leading to the formation of multiple kink bands. Fibre buckling occurs in accompany with splitting, and excessive fibre bending results in fibre failure and the formation of kink bands. Multiple splits at maximum fibre bending points are opened with large matrix shear deformation. The initiation and full propagation of a kink band (across the specimen) is found to occur in less than 1.2 ms. Tomographs just before failure reveal that fibre micro-buckling/kinking due to fibre misalignment proves to be the incipient damage mechanism, the extent of which is small until the sudden formation of a kink band.