Characterization of Interlaminar Fracture Toughness of a Carbon/Epoxy Composite Material
Open Access
- Author:
- Zhu, Ye
- Graduate Program:
- Engineering Mechanics
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 15, 2008
- Committee Members:
- Charles E Bakis, Thesis Advisor/Co-Advisor
Charles E Bakis, Thesis Advisor/Co-Advisor - Keywords:
- FRP
interlaminar fracture toughness
IFT
carbon/epoxy composite - Abstract:
- The primary objective of this investigation is to characterize the Mode I, Mode II, and mixed Mode I/II interlaminar fracture of a proprietary carbon/epoxy composite material system. A state-of-the-art review of the literature on quasi-static and cyclic test methods for interlaminar fracture testing is given. The Mode I, Mode II, and mixed Mode I/II interlaminar fracture behavior of the carbon/epoxy laminated material in quasi-static and fatigue loadings was investigated using the double-cantilever-beam (DCB) specimen, the end-notched flexure (ENF) specimen, and the single leg bending (SLB) specimen, respectively. It was found that the Mode I interlaminar fracture toughness at crack onset (GIc) was low for the investigated material system in comparison to results reported in the literature for carbon/brittle epoxy material system. In addition, the Mode I fracture toughness increased by about 40% after 50 mm crack extension. The Mode II quasi-static tests were conducted with precracked and un-precracked specimens. Compared to results reported in the literature, the Mode II fracture toughnesses (GIIc) of the investigated material were in the common range for carbon fiber composites made with brittle epoxies. The GIIc value of an un-precracked specimen was 44% -60% higher than that of a precracked specimen. The mixed-mode fracture toughness (GTc) was found to be low in comparison to the results in the literature and it increased by 11 to 53% after 20 mm crack extension. For all fatigue tests, the modified Paris’ law was used to fit the experimentally determined crack growth rate per cycle (da/dN) versus the applied maximum strain energy release rate (SERR, Gmax). The delamination growth rate decreased rapidly with decreasing applied SERR, which gave rise to high exponents of the Modified Paris’ law for Mode I, Mode II, and mixed Mode I/II fatigue tests, with the highest in mixed Mode I/II. To assess the capability of commercial finite element software in solving delamination growth problems, a crack propagation analysis of the DCB specimen was carried out using the virtual crack closure technique (VCCT) for Abaqus and Abaqus/Standard V6.7. Preliminary results showed good agreement of load versus displacement behavior between the finite element analysis (FEA) and experimental results. However, the crack front shape predicted by FEA did not agree well with experimental results.