Experimental characterization of the viscoelastic behavior of a curing epoxy matrix composite from pre-gelation to full cure

Process models have been used to predict the flow and stress development during manufacturing of composite structures for over 20 years. To date, these models have been treated separately, and the required material property models (viscosity and modulus) have also been treated separately. The latest breakthrough in process modeling of composite structures is an integrated stress-flow model. However, a consistent viscosity and viscoelastic material model required by the integrated stress-flow model has not been developed. Presented in this thesis is a consistent material model that predicts the viscoelastic liquid and viscoelastic solid behavior of a commercially available thermoset polymer, namely MTM45-1 epoxy. The goal here is to show that a single material model can predict the viscosity and viscoelastic modulus for all temperature, degree of cure and time scales encountered in composite manufacturing. The model was generated by fitting a generalized Maxwell model to test results from both dynamic mechanical analysis and rheological tests. Both resin and prepreg samples were examined. Thermo-rheological complex behavior was captured by applying linear temperature dependence to the un-relaxed modulus. The effect of cure was accounted for by applying a degree of cure dependent shift function. The relaxed modulus was predicted using the cross-link concentration and the theory of rubber. Excellent agreement was found when comparing predictions from the model to experimental data ranging from temperatures of -50°C to 245°C, degree of cure of 0.01 to 1.0 and frequencies of 0.01Hz to 10Hz.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat