Nonlinear Dynamic Mechanical Moduli for Polycarbonate and PMMA

Abstract

The multiple integral expansion of the Boltzmann superposition principle provides a good constitutive framework for the study of the nonlinear dynamic behavior of solid polymers. The material functions G3' and G3'', which describe the onset of nonlinear viscoelastic behavior in sinusoidal oscillations were measured over a wide temp. range for poly(Me methacrylate) (I) [9011-14-7] and bisphenol A-carbonic acid copolymer (II) [25037-45-0]. Below the glass transition temp. (Tg), G3' is neg. and G3'' is pos., which agrees with the concept that nonlinear response signals the onset of large-scale mol. motions, i.e. flow, and is in quant. agreement with other nonlinear data. Near Tg, both I and II become nonlinear. G3'' for I changes signs above Tg, again in agreement with data on polymer melts and solns. The nonlinear functions are useful for calcn. of strain limits for linear viscoelastic testing and predicting ultimate property response. [on SciFinder(R)]