Abstract
It is necessary to consider the influence of moisture damage on the interlaminar fracture toughness for composite structures that are used for outdoor applications. However, the studies on the progressive variation of the fracture toughness as a function of moisture content M (%) is rather limited. In this regard, this study focuses on the characterization of mode II delamination of carbon/epoxy composites conditioned at 70 °C/85% relative humidity (RH). End-notched flexure test is conducted for specimens aged at various moisture absorption levels. Experimental results reveal that mode II fracture toughness degrades with the moisture content, with a maximum of 23% decrement. A residual property model is used to predict the variation of the fracture toughness with the moisture content. Through numerical simulations, it is found that the approaches used to estimate the lamina and cohesive properties are suitable to obtain reliable simulation results. In addition, the damage initiation is noticed during the early loading stage; however, the complete damage is only observed when the numerical peak load is achieved. Results from the present research could serve as guidelines to predict the residual properties and simulate the mode II delamination behavior under moisture attack.
Highlights
Carbon/epoxy composites are increasingly used in aircraft industry [1,2]
LeBlanc and LaPlante [8] reported that upon distilled water immersion at aging temperature of 70 ◦ C for around 11 months, the mode II fracture toughness GIIC of the carbon/epoxy composites has decreased by 37.5% when compared to the unaged specimens
As for eight-harness satin-weave glass/epoxy composites immersed in distilled water at aging temperature of 72 ◦ C, GIIC has dropped by 55% and 40% in warp and weft directions respectively after around 4 months of immersion [10]
Summary
Carbon/epoxy composites are increasingly used in aircraft industry [1,2]. aircraft structures are exposed to different environmental conditions throughout their service lifetime. LeBlanc and LaPlante [8] reported that upon distilled water immersion at aging temperature of 70 ◦ C for around 11 months, the mode II fracture toughness GIIC of the carbon/epoxy composites has decreased by 37.5% when compared to the unaged specimens. As for eight-harness satin-weave glass/epoxy composites immersed in distilled water at aging temperature of 72 ◦ C, GIIC has dropped by 55% and 40% in warp and weft directions respectively after around 4 months of immersion [10]. Nash et al [12] immersed non-crimp carbon fabric/benzoxazine composites in deionized water at aging temperature of 80 ◦ C for nearly 4 months. For non-precracked specimens, the authors discovered GIIC increased by 153% and 34% for BZ9120 and BZ9130 resins, respectively. Moisture effects on the mode II delamination of unidirectional carbon/epoxy composites were studied. This was followed by the numerical analyses of the mode II delamination behavior using cohesive zone modeling
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