Interlaminar fracture toughness and delamination fatigue under mode I and II loadings of unidirectional alumina fiber/epoxy laminates in air at room temperature

Abstract

Alumina fiber (ALF)/epoxy composites are possible candidates for the structural components of superconducting magnets because of their low thermal conductivity in addition to their higher specific strength and modulus. Since laminate structures are applied to the load support system for superconducting magnets, the evaluation of interlaminar strength both under static and fatigue loadings is essential from the view point of structural integrity. In the present study, mode I and II interlaminar fracture toughness and delamination fatigue crack growth behavior were investigated with unidirectional ALF/epoxy laminates using double cantilever beam specimens and end notched flexure specimens both with a special loading device. The fracture toughness values and the fatigue crack growth resistance of ALF/epoxy laminates were higher than those of CF/epoxy laminates with similar matrices. The analysis of the stress-ratio dependency showed that the contribution of the maximum stress was higher for ALF/epoxy than that for CF/epoxy laminates. The fractographic observation indicated that the interfacial fracture was dominant on the fracture surfaces of fatigue fracture, suggesting that the microscopic mechanism was different from that of CF/epoxy laminates.