Durability and thermo-oxidation behaviour of organic matrix composite materials at high temperatures

This paper introduces a review of the main activities carried out within the context of the ‘COMPTINN’ research program, for the activities focusing on the durability and thermo-oxidation behaviour of organic matrix composite materials at ‘high’ temperatures (120°C-180°C). The scientific aim of ‘COMPTINN’ research program was to better identify, with a multi-scale approach, the link between durability, accelerating ageing factors and physical mechanisms involved in thermo-oxidation phenomena, and to provide theoretical and numerical tools for predicting the mechanical behaviour of aged composite materials including damage onset and development. Work has been carried out on continuous carbon fibre composite with epoxy matrix. The influence of thermo oxidation on the mechanical behaviour of the matrix, the creep properties and durability of the composite, has been identified with ultra-micro indentation (UMI). Based on the evolution of the elastic indentation modulus of the resin in the thickness of a sample exposed to oxidative environment at 150°C for different durations, we have clearly validated that the thickness of the oxidised layer is linked with the exposed time. Another innovative experimental technique has also been used: a climbing drum peel test has been modified to investigate the influence of oxygen on mode I delamination propagation in a composite laminate. In this test, crack propagation is driven by oxidation under constant mechanical energy and the delamination propagation speed can be linked with the oxidation level. This enables one to identify the critical strain energy release rate associated with an oxidized interface and to predict the interaction between mechanical and environmental loadings. Thermo-oxidation is identified as the result of oxygen diffusion and oxygen reaction with the molecular structure of the resin. The predominance of chain scissions over crosslinking leads to a decrease in the glass transition temperature combined with an increase in the Young’s modulus at room temperature (called “antiplasticization” effect). This process is also at the origin of matrix shrinkage, weight loss and cracks initiation.