Fiber orientation effects on heat source distribution in reinforced polyamide 6.6 subjected to low cycle fatigue

The present study was aimed at gaining further insight into the behavior of short fiber-reinforced semicrystalline-polymeric (SFRSP) composites conditioned at atmospheric pressure with air containing 50 % relative humidity and subjected to repetitive loadings. The experimental approach was based on synchronized full-field temperature and strain data to investigate and characterize the thermomechanical response of these heterogeneous materials throughout tensile-tensile oligocyclic loading tests. The overarching aim was to determine the thermomechanical constitutive properties of SFRSP composites over a range of fiber orientation angles, for example, , , and . The thermomechanical behavior of a dry polyamide 6.6 matrix was also analyzed in a previous study using the same experimental approach. This approach involved digital image correlation (DIC) and infrared thermography (IRT). The first was used to track random surface pattern movements to monitor displacement or deformation, while the second recorded in-plane temperature changes from which the amount of heat sources involved during the material deformation was derived. Noticeable in-plane heterogeneities and the effects of fiber orientation on heat-source patterns, for example, intrinsic dissipation and thermoelasticity ranges, were highlighted and examined using these imaging techniques. The energy content of hysteresis loops was identified, and no elastic or plastic shakedown was noted, so there was no real cyclic adaptation. The heat conversion factor, i.e., Taylor-Quinney coefficient, was also calculated to quantify the relative contribution of stored and dissipated energies in the energy balances of the SFRSP composites.