Hydrothermal Aging of Glass Fiber Reinforced Benzoxazine Matrix Composites and Effect on the Mechanical Properties

Abstract

In this study, an E-glass fiber reinforced benzoxazine matrix composite material was subject to environmental conditioning and tested in both baseline (no conditioning) and conditioned (158°F and 85 relative humidity until near effective moisture equilibrium) variations to evaluate the effects of hydrothermal aging on the mechanical properties of the composite material. Diffusion properties of the material were evaluated in a water bath at 158°F and the moisture absorption of the mechanical testing specimens was tracked using a similar method as the alternative conditioning parameters. During the manufacturing phase, panels were manufactured via vacuum assisted resin transfer molding (VARTM) method. The laminate panels underwent quality assurance checks to verify that the composite specimens were manufactured to an acceptable standard. These checks included differential scanning calorimetry, ultrasonic nondestructive evaluation, and evaluation of the composite’s fiber weight fraction. The purpose of the testing phase was to measure, qualitatively and quantitatively, the effect of near-effective moisture equilibrium and elevated temperature on the mechanical properties of specimens conditioned in a hydrothermal chamber, under the same conditions previously mentioned. These specimens were tested by quasi-static tensile testing, modified Boeing open-hole compression, short beam shear, and unnotched compression testing. Results showed an average decrease in mechanical properties across tensile strength, short beam shear strength, unnotched compression strength, and open hole compression strength. The environmental conditioning method showed no significant effect on the tensile modulus of the material.