Long-term durability of polymer composites

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Polymer composites are increasingly used in structural applications in both aerospace and non-aerospace applications. The forthcoming Boeing 787 Dreamliner, with polymer composites making-up more than 50% of its structural weight, is the latest highlight of this trend. Other examples are composite turbine blades, composite bridge decks, etc. Owing to the viscoelasticity of the polymer matrix, time-dependent degradation of modulus (creep) and strength (creep rupture) of the composite occurs during service. Additional contribution comes from damage that develops within a lamina / laminate with time. A good understanding of this degradation and ability to quantify this degradation are required for reliable design and application of polymer composites in load bearing structural applications. While past research has advanced the knowledge in this area significantly, additional fundamental work is needed. Hence, the overall objective of this research program is to fill the critical knowledge gaps in this area and develop a comprehensive model to quantify this degradation. The proposed research will develop a model for time-dependent evolution of various damage modes and its effect on modulus and strength of polymer composite laminates. This model will be validated using experimental results from a number of laminate types. A user will be able to use this model with properties of a lamina, the basic builiding block of a laminate, to predict the degree of degradation during the service life of a structural composite structure. The novelty of this research program is in new fundamental knowledge (such as delayed fracture criteria, interactive influence of various service parameters on creep, creep rupture, and time-dependent damage evolution, interactive influence among various damage modes, creep - fatigue interaction) and the comprehensive predictive model. The anticipated impact is enrichment of the focus area (long term durability of composites) with a comprehensive understanding and contribution towards reliable design and application of load bearing composite structures. This is envisaged to benefit aerospace (both OEM and MRO) and composite industries of Canada.