Experimental determination of Through-Thickness Compression (TTC) enhancement factor for Mode II fracture energy

Abstract

Mode II fracture energy, GIIC, is a critical parameter for determining the propagation of delamination in composite laminates. Its value can be affected by Through-Thickness Compression (TTC) stress acting on the crack tip and here this effect has been studied using IM7/8552 carbon/epoxy laminates with cut central plies. External TTC loads were applied through bi-axial testing. Unidirectional (UD) cut-ply specimens were used to determine the TTC enhancement factor, ηG, for GIIC. A similar enhancement effect was also found in Quasi-isotropic (QI) specimens with 2 extra cut central 0° plies inserted into the layup. The TTC enhancement factor was implemented in a Finite Element Analysis (FEA) framework using cohesive interface elements, showing that the determined ηG can be successfully used to model the effect of TTC on delamination.

Delamination suppression in tapered unidirectional laminates with multiple ply drops using a tape scarfing technique

“…To gain ply-level stress distributions and a more fundamental understanding of how the scarfed ply drops change the stress distributions around the ply drop regions, numerical analyses were conducted based on a method previously demonstrated to accurately capture delamination type failures by multiple authors [18][19][20], which makes use of a custom written mesh generation code using the MATLAB software package.…”

An experimental and numerical investigation into damage mechanisms in tapered laminates under tensile loading

“…The fracture toughness pair ( IC and IIC ) follows Refs. [30,31]. There exists discrepancy in the literature regarding the cohesive strength pair [21,23,26,29,[32][33][34][35][36][37] and the TTC enhancement factor [28,38,39].…”

“…There exists discrepancy in the literature regarding the cohesive strength pair [21,23,26,29,[32][33][34][35][36][37] and the TTC enhancement factor [28,38,39]. The reason why [60 MPa, 90 MPa] is used here as the baseline cohesive strength pair is simply because that it has been proved to give satisfactory predictions for many of the previous IM7/8552 laminate models [21,23,26,31,40,41]. Effects of the strength pair and the TTC enhancement factor on the numerical predictions in these tapered cases will be discussed in Section 4.3.…”

“…An alternative model, defined in Eq. 9, is to assume the toughness enhancement as an independent definition to the strength enhancement [28,31]:…”

“…For Law A, the values suggested by Ref. [31], i.e. 0.3 and 0.064 for f and G were tested for these three tapered cases.…”