Master trends in the elasto-viscoplastic behaviour of highly cross-linked epoxy resins

Highly cross-linked epoxy resins are ubiquitous in high-performance structural applications, particularly when used as matrices for fibre-reinforced composites. The optimisation of composites requires a quantitative and predictive description of the mechanical behaviour of the matrix. To explore master trends in the mechanical response as well as to guide first-order modelling, the complete stress-strain response of six epoxies is characterised under uniaxial compression up to large strain and fracture. A number of characteristic properties are analysed and rationalised mainly through establishing partly physical and partly empirical relationships with the ratio T / T g T / Tg of test over glass transition temperature. Among others, an enhanced Eyring-type model is identified for the yield stress and found valid for a wide range of temperatures and strain rates below T g Tg . The yield stress of all six epoxies is related to T g Tg within 10% error without any other adjustment of parameters. A similar relationship for the modulus with T / T g T / Tg also accounts for strain rate. Lastly, the failure stress and strain are found to also correlate to T / T g T / Tg in subgroups of resins with similar molecular structure, while the re-hardening modulus does not.