Debonding of fibers

The fiber or whisker pull out has the potential for the greatest toughening effect and consists in a debonding of fiber from the adjacent matrix consuming large energy. This mechanism depends strongly on the aspect ratio of the second phase and is favored by weak interface bonds. 

After the interfacial debonding, fibers can either debond from the matrix or fracture in the crack plane, depending on the fiber aspect ratio. According to Hull and Clyne (1996), debonding of fibers occurs if the fiber aspect ratio, s ( = 1/d), is below a critical value. The critical value, ocrit, can be calculated using the following... 

Fig. 3 Refraction values of both (0°+ 90°) fiber directions with respect to impact energy per layer. The fiber/matrix debonding of CFRP laminates correlates significantly to the impact energy per volume (energy density).

Figure 18 shows a widely used test configuration where the matrix is a sphere of resin deposited as a liquid onto the fiber and allowed to solidify. The top end of the fiber is attached to a load-sensing device, and the matrix is contacted by load points affixed to the crosshcad of a load frame or another tensioning apparatus. When the load points are made to move downward, the interface experiences a shear stress that ultimately causes debonding of the fiber from the matrix. 

Sometimes the failure occurs by propagation of a crack that starts at the top and travels downward until the interface is completely debonded. In this case, the fracture mechanics analysis using the energy balance approach has been applied [92] in which P, relates to specimen dimensions, elastic constants of fiber and matrix, initial crack length, and interfacial work of fracture (W,). 

Kim, J.K., Baillic, C. and Mai, Y.W. (1992). Fnterfacial debonding and fiber pull-out stresses, part F. A critical comparison of existing theories with experiments. J. Mater. Sci. 27, 3143-3154. 

Fig. 4.6. Schematic drawing of a partially debonded single fiber composite model subject to external stress, (Ta, in the fiber fragmentation test.

Fig. 4.11. Plot of interface shear bond strength, ib, as a function of fiber length, 2L. showing the interface debond criteria, according to Eq. (4.71). After Kim et al. (1993b).

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

Hsueh C.H. and Becher, P.F. (1993). Some consideration of two-way debonding during fiber pull-out. J. Mater. Sci. Lett. 12, 1933-1936. 

Marshall, D.B. (1992), Analysis of fiber debonding and sliding experiments in brittle matrix composites. Acta Metall. Mater. 40. 427-442. 

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