Influence of moisture absorption on mechanical properties and damage mechanisms of three-dimensional six-directional braided composites under hydrostatic pressure

Abstract

Fibre-reinforced composites have shown a growing interest in pressure-resistant materials for deep-sea use due to their excellent properties. This paper presents the influence of the moisture absorption on the mechanical properties and damage mechanisms of three-dimensional six-directional (3D6D) braided composites under hydrostatic pressure. The bisphenol A epoxy resin, bisphenol F epoxy resin, and hydrogenated bisphenol A epoxy resin, are chosen. SEM and X-ray Micro-CT are employed to investigate the moisture absorption, tensile and compressive damage before and after subjecting to the hydrostatic pressure. Results show that the bisphenol F carbon/epoxy composite has the lowest porosity at 0.082% among the three composite materials. The average moisture absorption was the lowest at 0.3755%. Furthermore, moisture is mainly transported along micro cracks in the matrix and the fiber-matrix interface under hydrostatic pressure. After the composites absorb moisture, the average tensile strength retention rates of bisphenol A carbon/epoxy composite, bisphenol F carbon/epoxy composite, and hydrogenated bisphenol A carbon/epoxy composites drop to 88.282%, 76.34%, and 66.43%, respectively. Moreover, their average compressive strength retention rates drop to 53.15%, 74.26%, and 83.45%, respectively. The tensile and compressive strengths of the 3D6D braided composites decreased significantly after moisture absorption, mainly due to fiber-matrix debonding and matrix cracking.