Relation between interfacial shear strength and compressive strength of carbon fiber/epoxy resin composite strands

The mechanism with which the fiber-matrix interfacial strength exerts its i nfluence on the compressive strength of fiber reinforced composites has bee n studied by measuring the axial compressive strength of carbon fiber/epoxy resin unidirectional composite strands having different levels of interfac ial shear strength. The composite strands are used for experiments in order to investigate the compressive strength which is not affected by the delam ination taking place at a weak interlayer of the laminated composites. The interfacial strength is varied by applying various degrees of liquid-phase surface treatment to the fibers. The efficiency of the compressive strength of the fibers utilized in the strength of the composite strands is estimat ed by measuring the compressive strength of the single carbon filaments wit h a micro-compression test. The compressive strength of the composite stran ds does not increase monotonically with increasing interfacial shear streng th but showes lower values at higher interfacial shear strengths. With incr easing interfacial shear strength, the suppression of the interfacial failu re in the misaligned fiber region increases the compressive strength, while at higher interfacial shear strengths, the enhancement of the crack sensit ivity decreases the compressive strength.