The isochronous stress–strain curves for an epoxy material at different times are shown in Figure 8.28. This material is used as the matrix in a unidirectional E-glass–epoxy composite having a fiber...

The isochronous stress–strain curves for an epoxy material at different times are shown in Figure 8.28. This material is used as the matrix in a unidirectional E-glass–epoxy composite having a fiber volume fraction of 0.6. Using micromechanics and the Elastic–Viscoelastic Correspondence Principle, determine the longitudinal relaxation modulus E₁(t) for the composite at t = 1 h and t = 10,000 h. Note that the strain in Figure 8.28 is given in percent

strain (e.g., a percent strain value of 1.5 corresponds to a strain of 0.015). Elastic properties of fibers are given in Table 1.1.