Determination of relaxation modulus of polymers and composites

The feasibility of three point bending testing for determination of relaxation modulus of polymers and composites was demonstrated. A test frame was manufactured, and the fully cured resin and composite specimens were used to measure the relaxation modulus at various temperatures. Coefficients of thermal expansion (CTE) were measured in order to account for cross sectional dimension changes of the samples at different temperatures. Electrical resistance strain gages as well as extrinsic Fabry-Perot fiber optic gages were employed for the CTE measurements from room temperature to one above the glass transition temperature. Strong relaxation phenomena in the range above the glass transition temperature were found, which rendered the CTE measurement impractical. Master curves and shift functions of the resin and the composite were obtained by the time-temperature equivalence principle. The results showed successful application of the test system and that the critical parameters, such as shift functions and relaxation spectrum patterns of the resin and the composite were found to be identical.