Hydrostatic Pressure Effect on the Fracture Toughness of Unidirectional (0-deg) Graphite/Epoxy Laminated Composites

Abstract

Previous studies show that hydrostatic pressure affects elastic modulus, strength, and strain of fiber-reinforced composites. However, no work has been done to understand the compressive fracture behavior of laminated composites under hydrostatic pressure. This work is an experimental study of the hydrostatic pressure effects on the compressive fracture behavior of fiber-reinforced composites. Compressive fracture tests were conducted under various hydrostatic pressures from 0.1 MN/m2 (atmospheric pressure) to 200 MN/mi2 (2 Kbar). Test specimens used were unidirectional (0-deg) graphite/epoxy laminated composites with a single delamination at the center of specimen. First, compression load-displacement curves were determined as a function of hydrostatic pressure and delamination length. Second, the compressive fracture toughness was determined from the compliance method based on the load-displacement curves as a function of hydrostatic pressure. The results showed that compliance, fracture load, and fracture toughness were significantly influenced by hydrostatic pressure. The fracture load increases as hydrostatic pressure increases. The compliance decreases linearly with increasing pressure. Particularly, fracture toughness increased from 3.45 N-mm/mm2 to 4.53 N-mm/mm2 (32% increase) as hydrostatic pressure increased from 0.1 MN/mm2 to 200 MN/mm2. Apparently the increase of fracture toughness is due to the suppression of local delamination with increasing hydrostatic pressure.