Characterization of interlaminar fracture modes I, II, and I-II of carbon/epoxy composites including in-service related bonding quality conditions. (August 2019)

• Record Type: Journal Article
• Authors: Fard, Masoud Yekani; Raji, Brian; Woodward, John; Chattopadhyay, Aditi
• Is Part Of: Polymer testing. Volume 77(2019)
• Publication Date: 2019-08
• Subjects: A. Polymer matrix composites (PMCs) -- B. Fracture -- C. Degradation -- D. Testing -- E. Heat -- F. Humidity; Polymers -- Testing -- Periodicals; Polymères -- Tests -- Périodiques; 620.1920287
• DOI: 10.1016/j.polymertesting.2019.05.010
• Languages: English
• ISSNs: 0142-9418

Abstract

Abstract: The effects of hot/wet environmental conditions for intervals of one and two years of exposure on fracture modes I, II, and I-II of biaxial carbon/epoxy composites were characterized. Tests were carried out on double cantilever beam, end-notched flexure, four-point end-notched flexure, and mixed mode bending specimens. For the purposes of this study, it was recognized that water absorption was governed by the Fickian mechanism. The effective crack method was used to analyze mode II and mode I-II with a high shear mode participation ratio. Hygrothermal effects degraded initiation toughness in all fracture modes, and extensive fiber bridging along with multiple damage modes within the mid-layers in specimens exposed to heat and humidity altered crack propagation behavior. Mixed mode fracture test results revealed a weak interaction between modes I and II for most parts of GI /GII, but the interaction was strongest when the fracture behavior changed from a pure mode to a mixed mode condition. Highlights: The effects of extreme environmental condition (hot and humidity) on the fracture modes I, II, and I-II in PMCs were studied. Exposure to heat and humidity up to 2 years were simulated and a convergence on the initiation energy release rate was obtained. The envelope function for mode I-II is used as a design guideline for composite structures exposed to extreme heat and humidity. Multimode damage is a characteristic feature of the exposed composite materials to extreme heat and humidity. The propagation energy release rate cannot be considered as a material property.