Whisker-matrix interface debonding

Fig. 2.1 Fracture surface of an alumina/20 vol.% SiC whisker composite showing microscopically rough surface. Presence of whiskers readily evident due to debonding along the matrix-whisker interface.

The interface between fiber (or whisker) and matrix is the key to the overall mechanical properties of a composite. A weak interface allows a propagating crack to be deflected, which increases the toughness of the composite. A strong interface allows transfer of the load from the matrix to the fiber and produces an increase in modulus and stiffness of the composite. In CMCs we are usually more interested in producing a weak interface so that debonding occurs, which often leads to fiber pull-out by frictional sliding and substantial absorption of energy. 

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. 

The chemistry ofthe whiskers is important since it affects many areas in fabrication and final composite properties. The bulk chemistry influences the stability ofthe whiskers at high temperatures and in reactive environments. The surface chemistry can change the interface properties between the whisker and the matrix and thereby change the debonding behavior... 

Debonding of tlie whisker from the matrix which absorbs energy in fracturing the interface. 

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