Modelling the influence of temperature and relative humidity on the time-dependent mechanical behaviour of a short glass fibre reinforced polyamide

Polymer matrix composites, and especially short glass fibre reinforced polyamides, are widely used in the automotive industry. Their application on structural components requires a confident mechanical design taking into account the sensitivity of the mechanical response to both temperature T   and relative humidity HH. In this paper, the constitutive model already developed by the authors (Launay et al., 2011) is applied to describe the non-linear time-dependent behaviour of a PA66-GF35 under various hygrothermal conditions. The extensive experimental database involves testing conditions under and above the glass transition temperature TgTg. An equivalence principle between temperature and relative humidity is applied and validated, since the non-linear mechanical response is shown to depend only on the temperature gap T-Tg(H)T-Tg(H).

► A constitutive model for the cyclic behaviour of SGFR thermoplastics is used.
► The model is suitable for hygrothermal conditions below or above the glass transition.
► A temperature–humidity equivalence principle is proposed from experimental results.
► The equivalence principle regards both viscoelastic and nonlinear properties.