Nair, Aravind R. (2006-08). Characterization of thermo-mechanical and long-term behaviors of multi-layered composite materials. Master's Thesis.
This study presents characterization of thermo-mechanical viscoelastic and long-term
behaviors of thick-section multi-layered fiber reinforced polymer composite materials.
The studied multi-layered systems belong to a class of thermo-rheologically complex
materials, in which both stress and temperature affect the time-dependent material
response. The multi-layered composites consist of alternating layers of unidirectional
fiber (roving) and randomly oriented continuous filament mat. Isothermal creep-recovery
tests at various stresses and temperatures are performed on E-glass/vinylester and Eglass/
polyester off-axis specimens. Analytical representation of a nonlinear single
integral equation is applied to model the thermo-mechanical viscoelastic responses for
each off-axis specimen. Long-term material behaviors are then obtained through vertical
and horizontal time shifting using analytical and graphical shifting procedures. Linear
extrapolation of transient creep compliance is used to extend the material responses for
longer times. The extended long-term creep strains of the uniaxial E-glass/vinylester
specimens are verified with the long-term experimental data of Scott and Zureick (1998).
A sensitivity analyses is then conducted to examine the impact of error in material
parameter characterizations to the overall long-term material behaviors. Finally, the
calibrated long-term material parameters are used to study the long-term behavior of
multi-layered composite structures. For this purpose, an integrated micromechanical
material and finite element structural analyses is employed. Previously developed
viscoelastic micromodels of multi-layered composites are used to generate the effective
nonlinear viscoelastic responses of the studied composite systems and then implemented
as a material subroutine in Abaqus finite element code. Several long-term composite
structures are analyzed, that is; I-shaped columns and flat panels under axial compression, and a sandwich beam under the point bending and transmission tower under
lateral forces. It is shown that the integrated micromechanical-finite element model is
capable of predicting the long-term behavior of the multilayered composite structures.