Mixed-Mode Delamination Failures of Quasi-Isotropic Quasi- Homogeneous Carbon/Epoxy Laminated Composite

Abstract

This chapter characterised the delamination behaviour of a quasi-isotropic quasi-homogeneous (QIQH) multidirectional carbon/epoxy-laminated composite. The delaminated surface constituted of 45 //0 layers. Specimens were tested using mode I double cantilever beam (DCB), mode II end-notched flexure (ENF) and mixed-mode I+II mixed-mode flexure (MMF) tests at constant crosshead speed of 1 mm/min. Results showed that the fracture toughness increased with the mode II component. Specifically, the mode I, mode II and mixed-mode I+II fracture toughness were 508.17, 1676.26 and 927.52 N/m, respectively. When the fracture toughness values were fitted using the Benzeggagh-Kenane (BK) criterion, it was found that the best-fit material parameter, η, was attained at 1.21. Furthermore, fibre bridging was observed in DCB specimens, where the steady-state fracture toughness was approximately 80% higher compared to the mode I fracture toughness. Finally, through scanning electron micrographs, it was found that there was resin-rich region at the crack tip of the specimens. In addition, fibre debonding of the 45 layer was found to be dominant in the DCB specimens. Significant shear cusps were noticed in the ENF specimens. As for the MMF specimens, matrix cracking and fibre debonding of the 0 layer were observed to be the major failure mechanisms.

Mode I and mode II delamination of a chopped strand mat E-glass reinforced vinyl ester composite

“…In addition, significant shear cusps were also noticed, which indicated shear mode of delamination. Similar observation was reported in [16,34]. Davidson et al [13] described the repeated pattern of shear cusps as hackles, which was common in mode II delamination of brittle matrix composites.…”

“…The maximum value of the R-curve was approximately 400 N/m −1 , which corresponded to 220% of augmentation. R-curve was about 80–100% in vacuum bagging fabricated and multidirectional (0//45) T600S/R368-1 carbon epoxy composite [16, 34]. Besides, it was about 25% only in the E-glass/bismaleimide composite that was immersed in sea water at 50°C [2].…”

“…Figure 9 (a) shows that matrix cracking, fibre debonding and fibre breakage were the major damage mechanisms during the delamination process. Fibre debonding was commonly observed in mode I delamination [31,34]. These damage mechanisms have contributed to the energy dissipation process, which contributed to G IC .…”

Interlaminar fracture toughness of a plain weave flax/epoxy composite

“…Table 2 compares the interlaminar fracture toughness of the flax/epoxy composite with some synthetic fibre composites reported in the literature [6, 22, 25, 26, 32-35]. Up to the authors’ knowledge, there was no mixed-mode delamination on flax/epoxy composites reported in the literature.…”

Displacement Rate Effects on the Mode II Shear Delamination Behavior of Carbon Fiber/Epoxy Composites

“…However, the complete damage ( D = 1) for all ten elements happens at the same time (around t = 210 s) immediately after the peak load is attained (at t = 209 s). The total damage ( D = 1) of the elements all occurring at the same instant leads to the sudden drop in the sustained load, implying an unstable crack propagation which is common in an ENF test [ 2 , 21 , 45 , 46 , 47 ]. This phenomenon is known as the crack jump [ 2 ].…”