Influence of curing processes on the development of fiber bridging during delamination in composite laminates

Fiber bridging can significantly influence the interlaminar toughness of laminated composites. However, very little is known about to what extent it depends on the processing conditions. In this paper, we performed a back-bonded double cantilever beam (BB-DCB) test to study the curing process influence on the development of fiber bridging for composite laminates with various thicknesses. The BB-DCB sample included a middle core plate and two backing adherends bonded to each side of the core plate. The total thickness of the BB-DCB samples was kept the same to guarantee the same structural effect due to beam curvature. Thus, only the core plate thickness effect was varied and studied. The experimental results showed that the core plate thickness significantly influences fiber bridging, as the samples with thicker core plates triggered more fiber bridging. Differential scanning calorimetry (DSC) was used to evaluate the degree of cure (DoC) for the different thicknesses, and a correlation was shown between the DoC and the fiber bridging extent. An embedded cell approach was also adopted to show that more fiber bridging was triggered with a larger variance of the fiber/matrix interface toughness and strength, which might have resulted from the change in the DoC with the plate thickness.