engleski

Durability modeling and analysis of composite structures exposed to the marine environment

The experimental part of this research was devised, based on samples of epoxy/glass and polyester/glass composites in form of standardized coupons, with various fiber orientation layout configurations submerged under the sea for prolonged periods (6, 12 and 24 months) in order to enable the assessment of the influence of the prolonged exposure to the sea on the mechanical properties of the material. Numerical finite element analysis (FEA) tensile test and three-point bending simulations on the coupons geometry indicated that the ultimate uniaxial tensile strength (UTS) is the most important parameter for the characterization of the structural mechanical behavior of the material. This parameter value variations were measured experimentally after each time period of exposure to the sea and compared to the values obtained numerically. The research results have shown that all submerged specimens have exhibited mass increase due to water absorption and growth of attached algae and sea microorganisms. Furthermore, various levels of reduction in ultimate tensile strength (UTS), depending on the fiber layout configurations, were observed. Significant changes in the matrix material structure were noticed in the areas of marine organisms and microorganisms’ attachment and imbedding, effectively producing “voids” in the matrix material. Numerical analysis and simulations were conducted during the “wet” coupons’ submersion periods, yielding in a predictive model for the long-term behavior of composites in real marine environment. The model was then verified by comparison with the results of experimental tensile tests. Additionally, the usage of composites as a repair material in process equipment and structural elements made from different materials, was verified. The research showed the importance of environmental degradation of the mechanical properties of composite materials in the real marine environment. The findings of this research could improve the technical regulations of classification societies for composite marine structures exposed to the marine environment in their lifetime and expand their application in this industry sector. The design process of such structures can be further optimized by incorporating the material degradation prediction model proposed here.

FRP composites ; marine environment ; material degradation ; fatigue life ; durability of composite marine structures

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