The effect of mode mixty on fatigue crack growth behavior from delamination was investigated with UD laminates (made of unidirectional laminates) and C laminates (made of unidirectional laminates and cloth laminates) of high strength glass fiber reinforced plastics (GFRP).Fatigue crack growth tests were carried out by mixed mode bending specimens at a stress ratio of
R=0.1. In UD and C laminates, the crack propagation rate da/dN decreased as mixed mode ratio
GI max/
GT maxdecreased when compared at the same total maximum energy release rate
GT max (=
GI max+
GII max). At a constant crack propagation rate under mixed mode loading, the driving force is expressed in terms of a linear combination of the pure mode I
GI maxand the pure mode II
GII max. The
G T max in C laminates approached the
GT maxin UD laminates as
GI max/
GT maxincreased at the same crack propagation rate. In UD and C laminates, fiber bridging took place at
GI max/
GT max=0.70 and the crack propagation rate was expressed by a power function of the maximum value,
GT tip max, of the energy release rate at the crack tip. Fractographic observation UD and C laminates showed that the crack propagation path was on the surface of fibers at
GI max/
GT max≤0.41 and some resin facture was observed at
GI max/
GT max=0.70.
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