Engineering Mechanics Institute Conference 2013

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A Multiscale-Multiphysics Model to Analyze Environmental Degradation of Thermoplastics

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Mahesh Bailakanavar
Columbia University
United States

Jacob Fish
Columbia University
United States

Venkat Aitharaju
General Motors
United States

William Rodgers
General Motors
United States

Abstract:
2013 Conference of the ASCE Engineering Mechanics Institute, August 4 – 7, 2013
Northwestern University, Evanston, IL
Abstract:
Semi crystalline thermoplastic materials like polyamides have attractive physical and mechanical properties that render them fir fort many industrial applications. However polyamides are hydrophilic which are known to absorb moisture in the amorphous due to the polymer–water affinity. The water molecules that attach to the polymer chain via hydrogen bonding, disrupt the inter-chain hydrogen bonding, inducing swelling, and plasticize the polymer causing reduction in the glass transition temperature, strength and stiffness.
In this study a coupled multiscale mechanical-diffusion model is developed to quantify the environmental degradation of short glass/carbon fiber filled thermoplastics. The multiscale-multiphysics model couples physical processes of moisture diffusion and deformation at multiple scales. The nonlinear diffusivity depends upon the polymer structure, moisture concentration, temperature, internal stress states and additional state variables. The time evolving diffusivity is formulated in terms of a residual-flux free formulation, by additively decomposing the concentration gradient into residual-flux free concentration gradient and eigen-concentration gradient. The mechanical material model effectively computes the reduction in the strength and stiffness of the fine scale phases due to moisture uptake and up-scales this to determine the coarse scale fields. The salient feature of the unified multiscale-multiphysics model is its computational efficiency accomplished through systematic model reduction which is carried out prior to nonlinear analysis. The model has been validated for glass and carbon fiber filled semi crystalline thermoplastics and the results are in good agreement with experiments.

 

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