On the application of η-factor approach to determine compressive fracture toughness of fiber-reinforced composites under hydrostatic pressure environment

It was shown in the previous studies that the η-factor approach could be used to determine fracture toughness of fiber-reinforced composites in air environment. This work investigates the applicability of the η-factor approach to determine fracture toughness of thick graphite/epoxy composites in the hydrostatic pressure environment. The effects of hydrostatic pressure and stacking sequence on the elastic work factor were studied. The stacking sequences used were unidirectional, [0°]₈₈ and multi-directional, [0°/±45°/90°]_11s. The hydrostatic pressures applied for [0°]₈₈ case were 0.1, 70, 140, and 200 MPa. The hydrostatic pressures applied for [0°/±45°/90°]_11s case were 0.1, 100, 200, and 300 MPa. For each stacking sequence and hydrostatic pressure, the values of fracture toughness determined using the η-factor approach were compared with those determined from the compliance method. The results showed that the elastic work factor was not affected by the hydrostatic pressure and the stacking sequence. The elastic work factor decreased in a linear fashion with crack length. The results also showed that the values of fracture toughness determined from the η-factor approach are very comparable to those determined from the compliance method for each stacking sequence and hydrostatic pressure. Thus, fracture toughness of thick graphite/epoxy composites in the hydrostatic pressure environment can be determined from a single fracture test using the η-factor approach.