The effect of matrix toughness and loading rate on the mode-II interlaminar fracture toughness of glass-fibre/vinyl-ester composites

• Published in: Composites science and technology 2001-01, Vol.61 (2), p.321-333
• Main Authors: Compston, P., Jar, P.-Y.B., Burchill, P.J., Takahashi, K.
• Format: Article
• Language: English
• Subjects: A. Polymer-matrix composites; Applied sciences; B. Fracture toughness; C. Deformation; C. Delamination; Exact sciences and technology; Forms of application and semi-finished materials; Laminates; Mode II; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0266-3538; 1879-1050
• DOI: 10.1016/S0266-3538(00)00226-8

Glass-fibre-reinforced composites are increasingly used for structural applications. However, like high-performance carbon-fibre composites, they are susceptible to mode-II-dominated delamination. In response to this problem, this paper investigates the effect of matrix toughness and loading rate on the mode-II interlaminar fracture toughness ( G IIc) of unidirectional glass-fibre composites with brittle and rubber-toughened vinyl ester matrices. Mode II tests were conducted σn end-notch-flexure (ENF) specimens at test rates ranging from 1 mm/min to 3 m/s. The G IIc results were compared to the order of matrix G Ic. There was no significant effect of loading rate or matrix toughness on G IIc. The absence of a loading rate effect is consistent with the bulk of the experimental data in the literature, but the absence of a matrix effect is not. Microscopic examination of fracture surfaces shows similar matrix deformation in each composite. The through-thickness matrix deformation zone size is also similar. These observations suggest similar energy absorption in each composite and hence support the G IIc test results. It is concluded that failure is interface controlled, whereby unstable fracture is initiated after a similarly short period of crack growth in each composite, and before an increase in G IIc as a result of increased matrix toughness becomes apparent. The G IIc results indicate that the use of rubber-toughened vinyl ester matrices in glass-fibre composites will not improve resistance to impact-induced mode II-delamination. However, through-thickness impact damage in composite structures is likely to result from mixed-mode (I/II) loading. Therefore, suggestions for future work include investigation of the matrix effect on mixed-mode (I/II) interlaminar fracture toughness, and on delamination resistance of plate structures subjected to transverse low-velocity impact.