Rheologic behavior of epoxy resins in the transition region

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Abstract
Master curves of log Q(t/K) against log (t/K) were constructed from experimental data on creep compliance, relaxation modulus, stress‐optical and strain‐optical coefficients of two types of epoxy resins at a series of temperatures in the transition region. The characteristic creep or relaxation time K for each temperature was defined and tabulated. The master curves were fitted to the reduced equation of the Gauss error integral form and the following characteristic parameters were calculated: Q1, the glassy‐state parameters (creep compliance, relaxation modulus, stress‐optical or strain‐optical coefficients); Q2, the rubbery‐state parameters; Td, the distinctive temperature; Kd, the characteristic creep or relaxation time at Td; and the parameters ht and hg of the steepness of master curves at the transition and glassy regions, respectively. The investigation was extended to the determination of the distribution functions of mechanical and optical retardation and relaxation times L (log τ) and H (log τ), respectively, representing the differential contribution to instantaneous compliance, stress‐optical or strain‐optical coefficients associated with retardation times and instantaneous modulus, stress‐optical or strain‐optical coefficients associated with relaxation times.