Abstract
A model is derived for the viscoplastic behavior of polymers and polymer composites at finite strains. A polymer is treated as an equivalent network of strands bridged by permanent junctions. The elastic response of the network is attributed to deformation of strands, whereas its viscoplastic behavior is associated with sliding of junctions with respect to their reference positions. The rate of sliding is proportional to the rate of macro-deformation. Constitutive equations for the time-dependent response of an equivalent network are developed by using the laws of thermodynamics. The stress–strain relations are simplified for uniaxial tension and simple shear of an incompressible medium. The governing equations are determined by three material constants that are found by fitting experimental data in tensile and shear tests with constant strain rates on polycarbonate reinforced with short glass fibers. The effects of temperature, strain rate and filler content on the material constants are studied in detail.
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