Mixed-Mode Delamination of Multidirectional Carbon Fiber/Epoxy Laminates

Abstract

SUMMARYScanning electron microscopy was used to identify fractographic features that are characteristic of different modes of interlaminar fracture. The cusp angle and the amount of fibre pull-out on the fracture surface can be used to characterise the different loading modes.A large amount of fibre pull-out is the dominant feature of a mode I fracture whilst in mode II large cusp angles and many cusps are the main characteristics. The amount of fibre pullout, and subsequently broken fibres, per unit area was investigated and found to vary in proportion to the degree of mode I loading. Such methods can be used to analyse failure and the propagation of delamination in structural components. The energy associated with cusp formation constitutes a large proportion of the mode II fracture toughness component whilst the amount of fibre pull-out and fracture has a considerable influence on the mode I fracture component. The cusp angle was seen to provide a quantitative measure of the fracture surface roughness. A failure criterion which takes the fracture surface appearance into account was evaluated. The cusp angle was subsequently used to modify this failure criterion. As a consequence, this provided an improved agreement with the experimental data.2

Mixed-mode fracture toughness of co-cured and secondary bonded composite joints

“…It has been shown that the fracture toughness of some adhesively bonded systems is independent of mode-mixity [6]. It may also be the case that an increase in the mode I component of the mixed-mode fracture toughness can occur as percentage mode II increases, particularly during interlaminar fracture [7,8]. The scrim cloth used in numerous film adhesives (e.g.…”

Designing the energy absorption capacity of functionally graded foam materials

“…However, the inter-laminar stresses within laminated materials are localised at interfaces due to the strong discreteness in the material properties. This localisation of stress can lead to delamination and crack propagation [4][5][6]. To eliminate the stress localisation, a proper continuous gradient is required to smooth the property transition 3 through the thickness.…”

Fracture and fatigue performance of textile commingled yarn composites

“…The cusps in the different fracture modes also stood more upright (i.e. the cups angle was larger) than the cusps previously observed in epoxy matrices [21,25].…”

“…8. The formation of cusps has been attributed to a brittle failure of the matrix [17][18][19][20][21] and can be described as the coalescence of brittle microcracks which form perpendicular to the resolved principal stresses just ahead of the crack tip, as shown schematically in Fig. 9.…”