Characterization and control of the fiber-matrix interface in ceramic ...

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throughout the composite sample. The metal apparently reacted to form
volatile species and hindered the matrix-deposition process, result-ing in
poor densification. It is obvious that the interlayer must be relatively
inactive with respect to the composite components and fabrication
procedures.
11.3 Interfacial Frictional Stress Measurement
11.3.1 Indentation
The indentation method for determining interfacial frictional stress
is relatively simple and is easily implemented. The test provides a
quantitative value for the degree of bonding and friction at the
interface of a completed composite sample. The method is applied to
finished specimens; thus, no speculation is necessary to account for
unseen effects. The procedure also employs a standard hardness
instrument to apply loads to the fibers and an indentor, which is a
common item in most materials laboratories.
The technique has a few disadvantages. The results are a measure of
the load necessary to break the fiber-matrix bond combined with the load
required to overcome the frictional stresses and push the fiber a small
distance. There are two distinct stresses at work at the interface,
bonding and friction (154). Both phenomena contribute to the mechanical
behavior of a composite; thus, both must be characterized to relate
composite properties to interfaces, A number of in situ techniques that
measure both bonding and friction are currently being developed.
These
methods will benefit from the recent advances in indentor instruments,
such as instruments that simultaneously record load and displacement
(155-157). These range from standerd dash-pot indentors equipped with
load cells and displacement gages to the Nanoindentors (157) that utilize