Page 73 - Engineered Interfaces in Fiber Reinforced Composites

56 Engineered interfaces in fiber reinforced composites

0.1 : 1 I I I
0 200 400 600 800 11
Approximate droplet size (pm)

Fig. 3.10. Effect of curing cycle on the fraction of amine curing agent estimated to have diffused out of
droplets as a function of their size. After Rao et al. (1991).

this test, a central fiber is pulled out of a seven-fiber microcomposite as shown in Fig
3.11. Great difficulties are encountered in constructing the specimens since accurate
control of the geometry determines the embedded fiber length. No clear correlations
exist between the IFSS and the fiber volume fraction. This indicates that the actual
failure mechanisms during fiber pull-out are matrix dominated (Qiu and Schwartz,
1993).

3.2.5. Microindentation (or jiber push-out) test

The microindentation technique (or ‘push-out’ test as opposed to the ‘pull-out’ test)
is a single fiber test capable of examining fibers embedded in the actual composite. The

Surrounding fiber (six) Centy fiber

/ \

PET fiber knot Epoxy bonded part

Fig. 3.1 1. Schematic presentation of a multi-fiber pull-out specimen