A numerical study on the thermal expansion coefficients of fiber

CHAPTER SIX
RESULTS AND DISCUSSION
Carbon fiber reinforced composite material systems had axial fiber to matrix
stiffness ratios (E f1 /E m ) ranging from 6 to 140, and axial fiber to matrix coefficient of
thermal expansion (CTE) ratios (α f1 /α m ) ranging from −0.01 to −0.30. Besides, glass
fiber reinforced composite material had E f /E m of 20.6, and α f /α m of 10.5. Therefore,
this investigation has covered a wide range of fiber/matrix combinations.
CTE predictions from some of the analytical models presented in Chapter 3 were
compared with each other, with available experimental data and with finite element
results for all of the material systems. Predicted and measured values for the
longitudinal and transverse directions for all of the materials studied are given in
Tables 6.1 and 6.2 respectively. The comparisons of these model predictions with
experimental data show that for some material the agreement is very good, but for
others there is some discrepancy between the experimental results and model
predictions. The reason may be that the fiber-matrix interface bond which was
assumed to be perfect was not really so in the experimental materials. The interface
may either contain interfacial cracks or it might have elastic properties different from
those of matrix and fiber.
Figures 6.1 – 6.14 show a comparison of longitudinal and transverse CTEs as a
function of fiber volume fraction, predicted from the different methods for seven
different material systems: E-Glass/Epoxy, T300/934 (T300/5208), P75/934
(P75/930), P75/CE339, C6000/PMR15, HMS/Borosilcate, and P100/2024Al.
Experimental data are also shown on these figures.
The Shapery, Chamberlain (both hexagonal and square), Schneider, and Chamis
methods all used Equation (3.14) for predicting longitudinal CTEs. As shown in the
Table 6.1 and Figures 6.1, 6.3, 6.5, 6.7, 6.9, 6.11, and 6.13, the differences between
the Rosen-Hashin and finite element results were negligible and there were only
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