Fatigue crack propagation was investigated in polycarbonate and glass fibre reinforced polycarbonate and the effect of stress ratio and glass fibre content determined. The addition of glass fibre increases the tensile strength, but does not always contribute to an increase in fatigue crack propagation resistance. For polycarbonate the effect of stress ratio can be partly explained by using crack closure concepts as other researchers have suggested, but for glass fibre reinforced polycarbonate this was not possible. Fractography revealed a void growth process, which occurred by decohesion at the interface of the glass fibres and the base material, which was dependent on the maximum stress intensity factor. The process of linking the voids and the main crack growth behavior depended on the stress intensity factor range, AK. A proposed crack propagation model can explain the effect of stress ratio on crack propagation in fibre reinforced polycarbonate.
NOMENCLATUREda/dN =crack growth rate per cycle A , C, M , a, /i' = material constants AK = range of stress intensity factor AKeR = range of effective stress intensity factor K,,, = maximum stress intensity factor Kop = value of stress intensity factor corresponding to crack opening R = stress ratio
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