Prediction of strain rate sensitivity of polymers by integral transform of DMA data

Interest in designing lightweight structures has resulted in the adoption of polymers and particulate composites in numerous structural applications. Weight saving is extremely beneficial both in terms of increased payload and reduced fuel consumption in transportation sector. Major challenges to the adoption of composite materials for such applications include unavailability of predictive models for high strain rate response and creep life. Dynamic mechanical analysis (DMA) is a widely used technique in polymer science for determining transition temperatures and activation energies. However, DMA results are not directly applicable to the design of structures because only frequency-domain properties are reported from those measurements. This work develops a transformation method for converting the DMA data from frequency to the time domain by appropriate integral relations from viscoelasticity theory. The material relaxation function can then be determined in order to predict the response over varying strain rates and loading conditions. The procedure is demonstrated for three material systems: vinyl ester, polycarbonate and high density polyethylene/fly ash composites. Close matching between the DMA predictions and the results of separate tensile tests and literature data is observed at a wide range of strain rates.