Temperature effects on the time dependent viscoelastic behaviour of carbon/epoxy composite materials: Application to T700GC/M21

• Medium strain rates testing of laminated composite.
• Low temperature dependency of laminated composite.
• Dynamic Mechanical Analysis of the constitutive epoxy resin.
• Influence of matrix sub-Tg transition on the temperature dependency.
• Strain-rate dependency analysis with the time–temperature superposition principle.

In this study, strain rate and low temperature dependencies of the viscoelastic behaviour of the T700GC/M21 composite material are characterised and analysed. Dynamic tests for various environmental temperatures are performed on hydraulic jack equipped with an environmental chamber. Three speeds, between 8.33 · 10−4 m s−1 and 0.5 m s−1, at three temperatures (20 °C, −40 °C and −100 °C) are tested. The increase of the shear modulus with the decrease of the temperature is more pronounced between −40 °C and −100 °C than between 20 °C and −40 °C. Complementary DMA (Dynamic Mechanical Analysis) tests are performed on the M21 epoxy resin to characterise the viscoelastic behaviour of the matrix which contributes to the viscoelastic behaviour of the laminate. DMA tests highlight a low temperature transition called β transition (−67 °C for the 1 Hz test) which is responsible of the larger increase of the storage modulus, for the epoxy matrix, between −40 °C and −100 °C. Consequently the β transition could also be at the origin, for the composite, of the observed larger increase of the shear modulus with respect to the strain rate, for strain rates higher than 10 s−1.