Experimental investigation on the compressive characteristics of multi-directional graphite/epoxy composites under hydrostatic pressure environment

The compressive behavior of thick graphite/epoxy composites under hydrostatic pressure environment was investigated in this work. The material system used was graphite/epoxy prepreg tapes (Hankuk Fiber, CU125NS) where the volume fraction of fiber was 64%. Compressive tests have been performed on [0°/90°]16s and [0°/±45°/90°]8s composite specimens under hydrostatic pressure environment. The pressures applied were 0.1 (atmospheric pressure), 100, 200, and 300 MPa. Compressive elastic modulus, strength, and strain were determined as a function of applied hydrostatic pressure for each composite. The results showed that for both composites, the stress–strain curves exhibited almost linear behavior followed by nonlinear behavior towards the end of curve at higher pressure. The compressive strength and strain increased with pressure in a linear fashion, while the compressive elastic modulus increased bilinearly with pressure with a discontinuity at 200 MPa. The results also showed that fracture occurred by end-crushing at all pressure levels for both specimens. Numerous delaminations in the transverse direction took place at multiple sites and propagated along the length of the specimens at low pressures (0.1 and 100 MPa) but they were reduced by 300 MPa pressure.