INVESTIGATION OF THE TENSILE STRENGTH BEHAVIOR OF E-GLASS/VINYL-ESTER COMPOSITE UNDER SYNERGISTIC HYGROTHERMAL EXPOSURE AND SUSTAINED STRAIN

摘要

The aim of the present research is to provide insights into the degradation mechanisms of a unidirectional pultruded E-glass/vinyl ester composite subjected to synergistic hygrothermal exposure (ambient atmosphere and deionized water at 22°C, 40°C and 60°C) and sustained load (three levels of constant bending strains), by investigating changes in the composite mechanical and physico-chemical properties. First, moisture sorption profiles will be compared to the widely accepted Fickian diffusion model and to the alternate Langmuir diffusion model, believed to be more accurate. Retention strength results are presented in the wet state as well as after redrying in order to assess any recovery in tensile strength due to water desorption. Scanning Electron micrographs will be used to correlate the appearance of microscopic damage in the form of interfacial debonding, fiber pitting and fiber cracking to the change in tensile properties. Attempts will be also made to dissociate the effect of matrix plasticization with other irreversible damage on the tensile strength loss. Finally, changes in the glass transition temperature as determined by Dynamic Mechanical Thermal Analysis, which can be correlated to physical and chemical changes within the polymer structure, will be presented.