Page 329 - Engineered Interfaces in Fiber Reinforced Composites

310 Engineered interfaces in fiber reinforced composites
Table 7.4 (Contd.)

Matrices CTEs (x IO-' K-')
Polymers
Epoxies 55-90
Polyester 50- IO0
Phenolfomaldehyde 26-60
High density polyethylene (HDPE) 150-300
Polypropylene (PP) 100-300
Polytetrafluoroethylene (PTFE) 70-100
Polymethylmethacrylate (PMMA) 54-72
Polyamide (PA, Nylon 6,h) 80-95
Polysulfone (PS) 56
Polyethersulfone (PES) 55
Polyetherimide 62
Polyamideimide 63
Polyphenylenesulfide 54
Polyetherketone 47
Liquid crystal polymer (Vectra) -5-75
Metals
Steels (0.9% C) 12
Copper 17
Nickel 13
Aluminum and alloys 22-24
Titanium and alloys 8-9
Ceramics
A1203 8.5
Sic 4.3
Borosilicate glass 4.0
Soda glass 8.5
Si3N4 3.2
ZrA 8.0

(i.e. aCL < ~1,~) because fibers in general have lower CTEs than matrix materials. At
a low fiber volume fraction, the CTEs of unidirectional fiber composites in the
transverse direction, aC~, tend to be even greater than the CTEs of bulk matrix
materials, a,. This is due to the fact that the long stiff fibers prevent the matrix from
expanding in the fiber axial direction, forcing the matrix to expand more in the
transverse direction.
Three-dimensional distributions of the micro-residual stresses are very compli-
cated, and are affected by the elastic properties, local geometry and distribution of
the composite constituents within a ply. Many analytical (Daniel and Durelli, 1962;
Schapery, 1968; Harris, 1978; Chapman et al., 1990; Bowles and Griffin, 1991a, b;
Sideridis, 1994) and experimental (Marloff and Daniel, 1969; Koufopoulos and
Theocaris, 1969; Barnes et al., 1991; Barnes and Byerly, 1994) studies have been
performed on residual thermal stresses. A two-dimensional photoelastic study
identified that the sign and level of the residual stresses are not uniform within the
composite, but are largely dependent on the location (Koufopoulos and Theocaris,