On the investigation of the stress threshold from linear to nonlinear viscoelastic behaviour of polymer-matrix particulate composites

In the present work, the transition from linear to the nonlinear viscoelastic behaviour and the determination of the nonlinearity stress threshold of an epoxy resin as well as of its aluminium filler particulate composite are investigated. For the needs of the current study, an experimental program consisted of static and long term i.e. creep-recovery mechanical characterisation of the neat polymeric material and its certain composite was conducted. Through creep compliance and isochronal curves that occur from creep-recovery tests the nonlinearity threshold dependence on stress is presented. The parameters of nonlinearity are experimentally estimated and modelling of the stress dependence of these parameters is achieved using a well verified method and model respectively. The influence of the rigid filler on the creep recovery response of the composite is also studied. The reported results provide information that is critical when designing structures with particulate composites.