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An ex-situ state-based approach using rheological properties to measure and model cure in polymer composites

In this paper, studies of measurement and modeling of viscoelastic properties of two commercial prepregs, MTM45 and MTM45-1 manufactured by ACG, have been carried out using an encapsulated sample rheometer. The key variables of cure process directly correlated with the viscoelastic states of the material during the cure cycle. The viscoelastic properties (storage modulus, loss modulus, and tan δ) and glass transition temperature of the prepregs were measured using an oscillatory shear rheometry with different isothermal cure cycles below the final glass transition temperature (Tg∞ ). A semi-empirical curing model based on the viscoelastic properties of the prepreg was developed and compared with the experimental data collected at a constant frequency. The model can be used by a process engineer to monitor, control, and optimize a process and to aid in the curing of parts that have time and temperature history discrepancies. The model can be statistically correlated to critical composite properties and it can be validated with time and temperature feedback. Therefore, the primary in-situ sensor remains a temperature sensor and there is no need for additional material state sensors to be placed inside the autoclave or other process unit.