Delamination Growth and Thresholds in a Carbon/Epoxy Composite Under Fatigue Loading

A damage-based model for mixed-mode crack propagation in composite laminates

“…As already mentioned, when a crack propagates in a soft matrix layer between stiffer adherends, as in the case of inter-laminar and also tunnelling cracks, two main mechanisms can be observed at the micro-scale, depending whether the loading condition is Mode I or II dominated. As reported in [11,[16][17][18][19], the propagation of an inter-laminar crack under near mode I conditions occurs in a co-planar manner at the interface or within the matrix inter-layer, as shown in Figure 1a). In particular, if the interface is weaker than the matrix, a self-similar propagation will occur at the interface.…”

“…This region of damage ahead of the crack tip is commonly referred to as the process zone [18]. The same characteristics of the crack path have been reported in [16,17,19] for fatigue loading as well. Based on the reported damage mechanisms for interfacial cracks, Wang [20] proposed a quasi-static fracture criterion that uses the Mode I ERR and a Drucker-Prager type parameter for predicting the critical ERR in the near Mode I and Mode II conditions, respectively.…”

“…and Overgaard, L.C.T., "A damage-based model for mixed-mode crack propagation in composite laminates", Composites A, 107, 2018, 421-431. https://doi.org/10.1016/j.compositesa.2018.01.016 together with the macro-crack and result in a rough fracture surface with the presence of shear cusps [5], as shown in Figure 1b). As discussed in [11,17] and validated by FE analyses in [18], the evolution of this damage mode is controlled by the maximum principal stress within the matrix, ahead of the crack tip. This scenario was observed in [7] during the fatigue propagation of 45° off-axis cracks in a glass/epoxy laminate, where in a small region ahead of the crack tip (process zone) micro-cracks, inclined with respect to the fibres, initiated.…”

“…The series of events shown in Figure 1a) has been confirmed in [5], where the fracture surfaces of glass/epoxy tubes under Mode I dominated conditions showed both the presence of clean fibres and scarps and ribbons in the matrix, indicating that both the adhesive and the cohesive types of propagation could potentially occur for tunnelling cracks. A different damage scenario was observed for Mode II dominated loading conditions [11,[16][17][18][19] and is illustrated in Figure 1b). In this case the crack initially grows within the matrix layer along the Mode I dominated direction, which is at an inclined angle compared to the crack plane.…”

The fatigue of carbon fibre reinforced plastics - A review

“…They reported that fatigue damage was governed by cyclic creep due to the absence of 0 • -layers angle-ply laminates [232]. It is well-established that the stress ratio affects delamination and delamination growth [229,269,270,271,272]. Other causes of delamination may arise through machining and/or the cutting of FRP laminates, residual stresses from the manufacturing process (e.g.…”