Page 90 - Engineered Interfaces in Fiber Reinforced Composites

Chapter 3. Measurements of interfacelinterlaminar properties 73

-

2.54 to 6.60 6.4
1 4 k363 -

7 to 1,65 -Ib
1,02

Fig. 3.25. Schematic drawings of specimen and loading jig for in-plane shear test. After ASTM D 3846
(1985).

~ also be estimated in the same way as for the ILSS b
transverse strength, r ~ can ,
considering a brittle matrix with cylindrical pores, i.e, oI = om[l - (4J4/n) I/? ]
(Greszczuk, 1967). For a good interface bond, the transverse strength will increase
accordingly due to the constraints of the matrix material between the reinforcing
fibers.
There is renewed evidence that shows the sensitivity of this test to interface
properties. For example, recent transverse tensile and flexural tests on carbon fiber-
epoxy matrix composites with several different levels of fiber surface treatments
(Madhukar and Drzal, 1991; Drzal and Madhukar 1993) show that while there is
little effect of the IFSS on the transverse tensile modulus, the transverse tensile
strength and the maximum strain increase approximately in the same ratio as the
increase in the IFSS (Fig 3.27). However, since the transverse tensile strength is
governed not only by the interface bond strength, but also by the mechanical
properties of the fiber and matrix and by the presence and distribution of voids and
foreign objects, etc. (Chamis, 1974), the test results may sometimes be misleading
unless care is taken in interpretation. In particular, the mode of failure in this test
may relate only indirectly to the interfacial bond. Therefore, it can be rationalized
that the significance of this test method is to provide some measure of the relative
bond strength of different fiber-matrix composite systems.