Non-linear viscoelastic and physical ageing characterisation of thermoset PR-500 epoxy resin

It is now well known that because of their polymeric matrices (and sometimes their use of viscoelastic fibres) structural polymer composites can exhibit creep or stress relaxation behaviour, leading to delayed failure long after the initial design and fabrication process. In addition, these time-dependent viscoelastic properties are significantly influenced by the sub-T-g physical ageing of these materials. Therefore any durability study of polymer composites for elevated use-temperature applications should address both the nonlinear viscoelastic response and the physical ageing effect of the constituents. The material nonlinearity in the resin has a 'softening' effect whereas physical ageing causes polymers to become stiffer and more brittle with age, increasing the likelihood of the more rapid progression of various damage states. Therefore, coupled material nonlinear and physical ageing conditions should be analysed to predict which effect would dominate under the applied loads and duration of loading. The primary objective of this paper is to present an experimental investigation of the nonlinear viscoelastic response of the PR500 resin at various stress levels. Also, the physical ageing characterisation results for a set of temperature and stress conditions are summarised. The properties summarised were successfully used in a multi-scale micro-mechanical methodology', to study the AS4/PR500 five-harness satin woven-fibre composite laminate. PR500 is the polymer matrix that was modelled using the data presented here.