Page 198 - Mechanics Analysis Composite Materials

Chapter 4. Mechanics of a composite layer 183

Fig. 4.52. Microstructure of a unidirectional two-matrix composite.

Table 4.3
Properties of glass+poxy unidirectional composites.
No. Material components Fiber volume Longitudinal Ultimate Density Specific strength
fraction strength 8: transverse p (g/cm3) 8:/p x lo3 (m)
(MP4 strain (%)
1 Composite fibers and 0.51 1420 3.0 1.83 77.6
deformable matrix
2 Composite fibers and 0.52 1430 0.3 1.88 76.1
high-stiffness matrix
3 Glass fibers and 0.67 1470 0.2 2.07 71.0
high-stiffness matrix
4 Glass fibers and 0.65 1100 1.2 2.02 54.4
deformable matrix

to increase transverse strains but results in 23% reduction in longitudinal specific
strength.
Thus, two-matrix glass-epoxy composites have practically the same longitudinal
strength as traditional materials but their transverse elongation is by an order
higher.
Comparison of a traditional cross-ply glass-epoxy layer and a two-matrix one is
presented in Fig. 4.53. Line 1 corresponds to a traditional material and has a typical
for this material kink corresponding to the matrix failure in transverse plies (see also
Fig. 4.37). Theoretical diagram was plotted using the procedure described above.
Line 2 corresponds to a two-matrix composite and was plotted with the aid of
Eqs. (4.60). As can be seen, there is no kink on the stress-strain diagram. To prove
that no cracks appear in the matrix of this material under loading, intensity of
acoustic emission was recorded during loading. The results are shown in Fig. 4.54.
Composite fibers of two-matrix materials can be also made from fine carbon
or aramid tows, while deformable thermosetting resin can be replaced with a
thermoplastic matrix (Vasiliev et al., 1998). The resulting hybrid thermoset-
thermoplastic unidirectional composite is characterized with high longitudinal
strength and transverse strain exceeding 1 YO. Having high strength composite fibers