Extensional Viscosity Of Highly Aligned Discontinuous Fiber Composites In Stretch Forming Processes
Date
2022-05
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
The demand for high quality materials in the aerospace industry has led to
continuous aligned fiber composites to be a popular choice in many applications.
However, these materials suffer from high costs and manufacturing restrictions. In
addressing these problems, aligned discontinuous fiber composites (ADFCs) are being
evaluated as an alternative. The relatively recent development of these composites has
resulted in a gap in literature regarding fiber direction deformation. The work herein
develops a model to predict the extensional deformation of ADFCs for a given
microstructure. From a selected matrix material, known fiber geometries, and a
desired fiber volume fraction, extensional viscosity is predicted as a function of
temperature and strain rate. Model validation was conducted with uniaxial stretch tests
on a single ply of thermoplastic matrix AFDC in the fiber direction. These tests
implemented digital image correlation techniques to accurately measure strain and
inform microstructural nonuniformity. Using this method, experimental extensional
viscosity was compared to the model for known input parameters. The model is
comprised of a piecewise Newtonian and shear thinning viscosity prediction. Relaxing
constituent material assumptions and improving the Newtonian and shear thinning
regimes for the polymer were considered to align observations with the model.
Implementing these methods was shown to successful bound extensional viscosity
data. Nevertheless, the start of the shear thinning regime was not accurately predicted
by the model. Further investigation of porosity and fiber reorientation is suggested to
explore possible explanations for early onset shear thinning.
Description
Keywords
Aerospace industry, Aligned discontinuous fiber composites, Viscosity