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Characterization of Time Dependent Behavior of Polymeric Composites
Objective and Background
Storage Modulus vs. Frequency - PolycarbonatePolymeric composites are extensively used industrially due to their high strength to weight ratios. Unlike their metallic counterparts, polymeric materials exhibit a material response that is both time and frequency dependant. Fortunately or unfortunately, this material response time-temperature behavior is often on the order of typical industrial applications and it therefore must be fully characterized. Time-Tempearture-Superposition (TTS) is a process in which to obtain a Master Curve of a polymeric material that characterics the structural response of a material, such as the storage modulus, overMaster Curve - 155 degC - Polycarbonate a span of multiple decades. TTS provides a way to measure the properties of a material over a short time span (such as that shown in the figure in the upper right) and then using the appropriate shift factor shift each data set to compile the complete master curve (shown to the left for the master curve generated for polycarbonate at 155 degC).

While the shift factor computed from the classical WLF equation is very accurate when compared to data found experimentally for temperatures above Tg, the shift factor for each temperature should not be calculated by the WLF equation alone. To get an accurate shift factor for all temperatures a best fit line is created using the WLF data points only from temperatures above  Tg.

Current studies are focusing on extending to polymeric systems with carbon and/or fiberglass. It is well understood that the incorporation of an additional phase to the polymeric system will reduce the glass transition temperature, it is uncertain a-priori how the inclusion of the carbon or fiberglass for enhanced stiffness will alter the master curve of the composite system.
Baylor University School of Engineering and Computer Science Department of Mechanical Engineering Sic'Em - Scientific Innovations in Composites and Engineering Materials