Interfacial debonding

Shimizu, K. Nakahara, M. and Noguchi, K. (1992). Interfacial debonding strength between the edge surfaces of pyrolytic graphite and epoxy resins, J. Mater. Sci. 27, 6134-6140. 

The single fiber compression test has not been as popular as other microcomposite tests because of the problems associated with specimen preparation and visual detection of the onset of interfacial debonding. To be able to obtain accurate reproducible results, the fibers have to be accurately aligned. With time, this test method became obsolete, but it has provided a sound basis for further development of other testing techniques using similar single fiber microcomposite geometry. 

Lacroix, Th., Tilmans, B., Keunings, R., Desaeger, M. and Verpoest, F. (1992). Modelling of critical fiber length and interfacial debonding in the fragmentation testing of polymer composites. Composites Sci. Technol. 43, 379-387. 

Apart from the elastic stress transfer at the perfectly bonded interface, another important phenomenon that must be taken into account is the stress transfer by friction, which is governed by the Coulomb friction law after the interface bond fails. Furthermore, matrix yielding often takes place at the interface region in preference to interfacial debonding if the matrix shear yield strength, Xm is significantly smaller than the apparent interface bond strength, tb. It follows thus... 

Theoretical analyses of interfacial debonding and frictional pull-out in the fiber pull-out test were initially modeled for ductile matrices (e.g. tungsten wire-copper matrix (Kelly and Tyson, 1965, Kelly, 1966)) assuming a uniform IFSS. Based on the matrix yielding over the entire embedded fiber length, as a predominant failure mechanism at the interface region, a simple force balance shown in Fig. 4.19 gives the fiber pull-out stress, which varies directly proportionally to the cylindrical surface area of the fiber... 

There are many features in the analysis of the fiber push-out test which are similar to fiber pull-out. Typically, the conditions for interfacial debonding are formulated based on the two distinct approaches, i.e., the shear strength criterion and the fracture mechanics approach. The fiber push-out test can be analyzed in exactly the same way as the fiber pull-out test using the shear lag model with some modifications. These include the change in the sign of the IFSS and the increase in the interfacial radial stress, (o,z), which is positive in fiber push-out due to expansion of the fiber. These modifications are required as a result of the change in the direction of the external stress from tension in fiber pull-out to compression in fiber push-out. 

Bright, J.D., Shetty, D.K., Griffin, C.W. and Limaye, S.Y. (1989). Interfacial debonding and friction in SiC filament-reinforced ceramic and glass matrix composites. J. Am. Ceram. Soc. 72, 1891-1898. 

Hsueh. C.H. (1990a). Interfacial debonding and fiber pull-out stresses of fiber-reinforced composites. Mater. Sci. Eng. A 123, 1-11 bl-Ti. 

Kim, J.K., Zhou, L.M. and Mai, Y.W, (1993a), Interfacial debonding and pull-out stresses part 111, Interfacial properties of cement matrix composites. J. Mater. Sci. 28, 3923-3930. 

Marshall, D.B., Shaw, M.C. and Morris, W.L. (1992). measurement of interfacial debonding and sliding resistance in fiber reinforced inlermelallics. Acta Metall. Mater. 40, 443-454. 

Zhou, L.M., Kim, J.K. and Mai, Y.W. (1992b). A comparison of instability during interfacial debonding in fiber pull-out and fiber push-out. In Proc. Second Intern. Symp. on Composite Materials and Structures (ISCMS-2) (C.T. Sun and T.T. Loo, eds.), Peking University press, Beijing, pp. 284-289. 

Mai (1985) has also given a review of the fracture mechanisms in cementitious fiber composites. The total fracture toughness, / i, is given by the sum of the work dissipation due to fiber pull-out, fiber and matrix fraetures, fiber-matrix interfacial debonding and stress redistribution, i.e.. 

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...

In short fiber composites, energy absorption mechanisms, such as interfacial debonding and matrix cracking, most often occur at the fiber ends (Curtis et al., 1978). The damage model proposed by Bader et al. (1979) assumes that short fiber composites fail over a critical cross-section which has been weakened by the accumulation of cracks, since the short fibers bridging this critical zone are unable to carry the load. In fatigue loading, sudden fracture takes place as a direct result from the far-field effect of the composite, rather than due to the near field of the crack tip... 

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... 

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