Samples of unidirectional Kevlar 49/epoxy and S-glass/epoxy composites are subjected to elevated temperatures in an oven and the resulting thermal strains are measured by using strain gages oriented along the 1 and 2 directions, as shown in Figure 5.15. From the data in Figure 5.15, estimate the longitudinal thermal expansion coefficient \(\alpha_{1}\) and the transverse thermal expansion coefficient \(\alpha_{2}\) for both materials.

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FIGURE 5.15 Induced strain (%) 1.2 1.0 A, = Kevlar 49/epoxy o, = S-Glass/epoxy 0.8 [o] $ 0.6 0.4 0.2 0 -0.2 20 60 100 140 Temperature (C) 1 2 180 220