Influence of relative humidity and loading frequency on the PA6.6 cyclic thermomechanical behavior: Part I. mechanical and thermal aspects

Using quantitative infrared techniques, this study investigated the influence of relative humidity (RH) and loading rate on the mechanical and thermal responses of PA6.6 matrix specimens. The specimens were subjected to tensile and oligocyclic tensile-tensile tests at 3 different RHs. For tensile experiments, the studied samples were loaded at 4 displacement rates. For oligocyclic tensile-tensile fatigue tests, they were subjected to 2 distinct loading frequencies with a 0.1 stress ratio. The overall aim of this study was to analyze the mechanical and thermal responses for each cyclic loading case. The influence of the loading frequency on the hysteresis loops and self-heating was particularly highlighted. The plasticizing role of water and its influence on the glass transition temperature were also discussed relative to the nature of temperature variations accompanying the deformation processes. These thermal responses were associated with dissipation, standard and/or entropic thermoelastic coupling sources. These different heat sources and the complete energy rate balances will be analyzed in the second part of this paper.