Thermal ageing effect on the mechanical properties of carbon fibre-reinforced epoxy laminates

Abstract

Thermostable matrix are extensively used in structural components because of their good mechanical properties [1]. The region of stability of these polymers is defined by the glass transition temperature (Tg) [2]. The typical service temperature of these materials should be lower than Tg but in some cases operating temperatures can exceed Tg which causes a variation in the properties of the polymer and consequently, modifies the mechanical properties of the composite material [3]. Therefore, it is important to understand the effect of temperature on the failure mechanisms that occur in the material in order to ensure stability and durability [4,5]. The objective of this work was to evaluate the effect of temperature and time of exposure on the mechanical properties of carbon/epoxy composites. For that purpose, samples were aged at different temperatures and periods of time and then, impact and flexural tests have been performed. It was observed that thermal ageing caused notable variations in the glass transition temperature of the epoxy resin. In consequence, two different effects were observed: in most cases, thermal ageing causes a reduction on the mechanical properties of the composites due to the thermo-oxidation of the epoxy resin and the loss of adhesion in the matrix/fibre interface, especially at higher temperatures; however, at temperatures below the Tg, there is an increase of the maximum strength because of a post-curing effect. [1] E. Selver, P. Potluri, C. Soutis, Impact damage tolerance of thermoset composites reinforced with hybrid commingled yarns, Compos. Part B 91 (2016) 522-538. [2] E. Ernault, E. Richaud and B. Fayolle, Origin of epoxies embrittlement during oxidative ageing, Polymer Testing 63 (2017) 448-454 [3] A. Mlyniec, J. Korta, R. Kudelski and T. Uhl, The influence of the laminate thickness, stacking sequence and thermal ageing on the static and dynamic behaviour of carbon/epoxy composites, Composite Structures 118 (2018) 208-216 [4] A. P. C. Barbosa, A. P. P. Fulco, E. S. S. Guerra, F. k. Arakaki, M. Tosatto, M. C. B. Costa and J. D. D. Melo, Accelerated ageing effect son carbon fibre/epoxy composites, Composites Part B, 110 (2017) 298-306 [5] S. Marouani, L. Curtil and P. Hamelin, Ageing of carbon/epoxy and carbon/vinylester composites used in the reinforcement and/or the repair of civil engineering structures, Composites Part B, 43 (2012) 2020-2030