Page 72 - Engineered Interfaces in Fiber Reinforced Composites

Chapter 3. Measurements of interfacelinterlaminar properties 55

0.05-01
mm
Fiber
\
. . . .;. :_.
:. :;. ..A,, J.

MicrodropCt
Thin strip of polymer film Polymer A
(a) film

1 Microvice

Fig. 3.9. Schematic presentation of (a) the procedure for forming thermoplastic resin microdrops and
(b) the microdebond test. After Gaur and Miller (1989).

strength values than in the fiber pull-out test. Mechanical properties of the matrix
microdroplet may also vary with size partly because of the variations of
concentration of the curing agent as determined by differential scanning calorimetry
(DSC), see Fig 3.10 (Rao et al., 1991). When compared with specimen geometry of
other single fiber composite tests, the microdebond test shows the least resemblance
to actual loading configuration of practical composite components.
In view of the fact that the above techniques examine single fibers embedded in a
matrix block, application of the experimental measurements to practical fiber
composites may be limited to those with small fiber volume fractions where any
effects of interactions between neighboring fibers can be completely neglected. To
relate the interface properties with the gross performance of real composites, the
effects of the fiber volume fraction have to be taken into account. To accommodate
this important issue, a modified version of the fiber pull-out test, the so-called
microbundle pull-out test, has been developed recently by Schwartz and coworkers
(Qui and Schwartz, 1991, 1993; Stumpf and Schwartz, 1993; Sastry et al., 1993). In