The dependence of the transverse (through-the-thickness) diffusivity of unidirectional AS/3501-5 graphite/epoxy composite on temperature is given in Figure 5.11. For a temperature of \(77^{\circ} \mathrm{C}\) and a thickness of \(2.54 \mathrm{~mm}\), use the results from Figure 5.11 and Problem 5.2 to estimate the time required for this material to reach \(99.9 \%\) of its fully saturated equilibrium moisture content from an initially dry condition. Compare your estimate with the experimental data in Figure 5.12. Does the estimate seem to be reasonable?

Problem 5.2

Using Equation 5.6 for moisture diffusion, derive an equation for the time required for an initially dry material to reach \(99.9 \%\) of its fully saturated equilibrium moisture content. The series in Equation 5.6 converges rapidly, so for the purposes of this problem, it is necessary only to consider the first term. The answer should be expressed in terms of the thickness, \(h\), and the diffusivity, \(D_{z}\).

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FIGURE 5.11 Diffusivity, D (mm2/s) 10-6 400 Temperature, T (K) 350 300 Dave = 6.51 exp 10-7 10-8 Present data Delasi and Whiteside (1978) Whitney and Browning (1978) P(-5722) T 1 2.4 2.6 2.8 3.0 3.2 3.4 3.6 1/Tx 103 (1/K)