Modeling Inelastic, Nonequilibrium Behavior of Polymers

Our group has strong interests in developing nonlinear constitutive theories for the nonequilibrium, viscoelastic, and viscoplastic behavior of polymers and polymer composites.

Amorphous Polymers
droppedImageAmorphous polymers have a wide-range of complex time-dependent and temperature-dependent behavior. At high temperatures, amorphous polymers exhibit an elastomeric, viscoelastic solid, or viscoelastic fluid-like  behavior.  At low temperatures, below the glass transition temperature, the materials are stiff and exhibit rate-dependent and temperature-dependent yielding, strain softening, and orientation hardening.  Our group aims to develop coupled continuum thermomechanical theories that can capture the full extent of the nonequilibrium behaviors of polymers.  We are also developing innovative experiments to measure the time-dependent evolution  of physical properties of amorphous polymers and to validate the model predictions.  Our current work focuses on applying the effective temperature concept to describe the glass transition, physical aging, and mechanical rejuvenation.

Current and former students and postdoctoral fellows

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Ultrahigh Molecular Weight Polyethylene Fibers

PE1UHMWP fibers have a heterogenous microstructure that includes oriented fibrillar crystalline domains, folded lamellar crystalline domains, and entangled  amorphous domains. The fibers are also populated by defects, such as voids.  We propose to develop experimentally validated micromechanical models for the rate-dependent and temperature-dependent inelastic behavior  to study how these morphological features determine the strength and toughness of polymer fibers at different deformation rates and temperatures.  This will guide the development of constitutive models for the inelastic behavior of the fibers.   We are developing computational micromechanical models that integrate data from fiber-level experimental efforts and lower scale atomistic modeling efforts to determine the fiber morphology and mechanical properties of the constituent domains.

Current and former students and postdoctoral fellows

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Anisotropic Inelastic Behavior of Fiber-Reinforced Polymers

Soft fiber-reinforced composites describes polymeric fibers dispersed in a soft polymeric matrix. The class of materials describe most connective tissues, and also engineering materials such as filled woven fabrics for impact protection and reinforced elastomers for  automotive tires and hoses.  We have developed nonlinear constitutive theories for the anistropic viscoelastic and viscoplastic behavior. The models assume affine deformation of the fibers and matrix, but the fibers and matrix can exhibit different inelastic deformation.

aniso1 aniso2
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