Delamination characteristics of multi‐directional carbon fiber/epoxy composites under high pressure

Abstract

AbstractIt was shown in a previous study that for unidirectional (0‐deg) graphite/epoxy composites, the fracture toughness under hydrostatic pressure increased 38% as hydrostatic pressure increased from 0.1 MPa to 200 MPa. This work investigates the compressive delamination behavior of multi‐directional graphite/epoxy laminated composites subjected to various hydrostatic pressures. Compressive delamination tests were performed under four hydrostatic pressure levels: 0.1, 100, 200, and 300 MPa Eighty‐eight‐ply dog‐bone type specimens with a single delamination at the center of the specimen were used. The stacking sequence applied was [0°/±45°/90°]lls. The compliance and fracture load were determined from load‐displacement curves as a function of hydrostatic pressure.The results show that the compliance decreases with increasing pressure while fracture load increases with increasing pressure. The compressive delamination toughness, Gc, was determined from the compliance method as a function of applied hydrostatic pressure. The results also show that Gc is significantly affected by hydrostatic pressure and increases from 2.11 kJ/m2 to 3.04 kJ/m2 (44% increase) as hydrostatic pressure increased from 0.1 MPa to 300 MPa. Visual examination of the fractured surface revealed that the increase of Gc is due to the suppression of micro‐cracks With increasing pressure. It was also found from SEM examination of delaminated surface that the Gc increase is due to more epoxy adhering to the fibers and more plastic deformation of epoxy material as applied hydrostatic pressure increases.