Transverse Ply Cracking in Cross-Ply CFRP Laminates—Initiation or Propagation Controlled?

Abstract

The initiation and propagation stages of transverse ply cracking in crossply CFRP laminates under quasi-static loading have been studied using laminates with a range of transverse ply thicknesses. Specimens of two types have been tested-coupons with polished edges and coupons with defects (notches) introduced into the transverse ply prior to testing. Detailed observations of crack propagation across the transverse ply thickness and width have been made, along with measurements of crack density and residual properties. In laminates with thin transverse plies (less than 0.25 mm for the materials tested here), fully formed transverse cracks are observed at about the same strain in undamaged and notched laminates. In laminates with thicker transverse plies (greater than 0.25 mm), the notched laminates show fully formed transverse cracks at lower strains than the undamaged laminates. The experimental results have illustrated the situations (laminate properties, presence of flaws) in which fracture mechanics models for transverse cracking available in the literature can be applied. In particular, it is shown that the fracture mechanics models which assume implicitly the presence of initial defects spanning the thickness of the ply may underestimate the failure strain of laminates with thick transverse plies. The effect of composite intralaminar toughness is also discussed.

Numerical modeling of diffuse transverse cracks and induced delamination using cohesive elements

“…The crack spacing is not necessarily uniform and therefore, delamination length is not identical for all of matrix cracks. It was observed that delamination initiation and growth are the consequences of matrix cracking saturation and this is in agreement with many experimental findings as indicated in 5,8,14 . Similar to bisecting method, the critical crack density is decreased with increasing the number of 90 o layers.…”

Evaluation of toughness by finite fracture mechanics from crack onset strain of brittle coatings on polymers

“…the applied mechanical strain) of the h = 120 nm coating on 12 lm substrate amounted to e a = 1.3 ± 0.1% regardless of the temperature within 26-150°C range. Yanaka et al [37] interpreted this result as a proof of strength criterion for coating fracture; this criterion corresponds to the case of crack initiationcontrolled failure according to [38,39]. However, the COS data are amenable also to fracture mechanics, i.e.…”

Micromodel-based simulations for laminated composites

“…They occur relatively early in the case of transverse loading, but very late in the case of shear loading. They generally initiate at the edge of the samples, then propagate in a stable or unstable way towards the core [10] depending on the type of ply (the well-known thickness effect [11]) and on the loading (static or cyclic [12]). …”