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Modeling of Multi-Step Nonlinear Stress Relaxation in DGEBA/M-PDA Epoxy Resins



Gale A. Holmes, R C. Peterson, Donald L. Hunston


Multi-step stress relaxation data from a DGEBA/m-PDA epoxy resin is modeled using a nonseparable nonlinear constitutive equation. The form of the equation is based on nonlinear concepts and ideas developed in melt rheology. Although time-strain separability was found not to hold for the data analyzed, the nonseparable constitutive equation was developed empirically from a time-strain separable equation. To capture the change in the relaxation behavior of the epoxy resin with increasing strain, modified power law type expressions were used in the constitutive equation with the assumption that the change in relaxation behavior with strain could be approximated by a linear expression. A bi-exponential damping function of the class used by Osaki and Laun was used to capture the softening of the modulus with increasing strain. In addition, a strain dependent variable was incorporated into the constitutive equation to account for the effective strain rate dependence of multi-step stress relaxation tests. The resulting non-separable nonlinear constitutive equation was found to predict within 5% the multi-step relaxation behavior of the resin when the time between strain increments was increased from 10 minutes to 1 hour.
Proceedings Title
Proceedings of the 2nd International Conference
Conference Dates
March 1-4, 1998
Conference Location
Pasadena, CA
Conference Title
Mechanics of Time-Dependent Materials


Holmes, G. , Peterson, R. and Hunston, D. (1998), Modeling of Multi-Step Nonlinear Stress Relaxation in DGEBA/M-PDA Epoxy Resins, Proceedings of the 2nd International Conference, Pasadena, CA, [online], (Accessed April 13, 2024)
Created March 4, 1998, Updated June 2, 2021