Post-debond Friction

Ac can be approximated to Cf if Cm is neglected in brittle matrix composites (Harris, 1980). It is shown that Rd( contributes substantially to the total fracture toughness of glass fiber-polymer matrix composites (Harris et al, 1975 Kirk et al., 1978 Beaumont and Anstice, 1980 Munro and Lai, 1988). 

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Fig. 6.12. Toughness maps depicting contours of predicted fracture toughness (solid lines in kJ/m ) for (a) glass-epoxy composites as a function of fiber strength, Uf, and frictional shear stress, tf and (b) Kevlar-cpoxy composites as a function of at and clastic modulus of fiber, Ef. The dashed line and arrows in (a) indicate a change in dominant failure mechanisms from post-debonding friction, Rif, to interfacial debonding, Sj, and the effect of moisture on the changes of Of and Tf, respectively. Bundle debond length...

Lhymn and Schultz, 1983). This observation is analogous to the fracture process in the outer process zone which is termed the dissipation zone as distinct from the inner process zone ahead of crack tip (Lauke and Schultrich, 1986b Lauke and Pompe, 1988). In the dissipation zone, intensive energy dissipation by fiber-matrix interfacial debonding and post-debonding friction is concentrated mainly at the fiber... 

Similarly, the initial debond stress, oq, is obtained for the infinitesimal debond length, the maximum debond stress, debond length becomes = L - Zmax and the post-debond initial friction pull-out stress, [Pg.153]

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