Abstract
Experimental investigations were performed on unidirectional glass fibre reinfbrced/ epoxy laminates having fibre oriented at θ = 0°, ± 1.2° and ±2.4°, respectively, in mode II (forward shear) in the presence of a crack parallel to the neutral axis of the beam. An end-cracked beam was used. The stress-intensity factor at instability K 11R(INS) was obtained by the method developed by Giare. Engng Fract. Mech. 20, 11–21 (1984). The crack growth resistance at instability and the corresponding critical strain-energy release rate were independent of the initial crack in the range of the crack length investigated. Fracture toughness in mode II was found to increase considerably with fibre orientation for θ = ±1.2° and θ = ± 2.4°, as compared to fibre orientation at θ = 0°. Slight fibre orientation increased the crack propagating area, thus causing an increase in the fracture toughness of the composite in mode II. The path of crack propogation is shown in Figs 11–13. Slight fibre orientation had no effect on the longitudinal strength of the laminates. In composite materials, fibre-matrix interfacial shear stress plays an important role in the load transfer mechanism. Hence, if mode II fracture toughness is increased. then mode I fracture toughness may be improved.
Published Version
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