Polymeric composites exhibit time-dependent behavior, which raises a concern
about their long term durability and leads to a viscoelastic study of these materials.
Linear viscoelastic analysis has been found to be inadequate because many polymers
exhibit nonlinear viscoelastic behavior. Classical laminate theory is commonly used in
the study of laminated composites, but due to the plane stress/strain assumption its
application has been limited to solving two dimensional, simple plate problems. A
three dimensional analysis is necessary for the study of interlaminar stress and for
problems involving complex geometry where certain local effects are important.
The objective of this research is to develop a fully three-dimensional, nonlinear
viscoelastic analysis that can be used to model the time-dependent behavior of
laminated composites. To achieve this goal, a three-dimensional finite element
computer program has been developed. In this program, 20-node isoparametric solid
elements are used to model the individual plies. The three-dimensional constitutive
equations developed for numerical calculations are based on the Lou-Schapery one-dimensional
nonlinear viscoelasticity model for the uniaxial stress case. The transient
creep compliance in the viscoelastic model is represented as an exponential series plus
a steady-flow term, which allows for a simplification of the numerical procedure for
handling hereditary effects. A cumulative damage law for three dimensional analysis
was developed based on the Brinson-Dillard two-dimensional model to predict failure
initiation.
Calculations were performed using this program in order to evaluate its
performance in applications involving complex structural response. IM7/5260-H
Graphite/Bismaleimide and T300/5208 Graphite/Epoxy were the materials selected for
modeling the time-dependent behavior. The cases studied include: 1) Tensile loading
of unnotched laminates; 2) bending of a thick laminated plate; and 3) tensile loading
of notched laminates. The analysis emphasized the study of the traction-free edge-effect
of laminated composites, stress distribution around a circular hole, and stress
redistribution and transformation in the layers. The results indicate that the stress
redistributions over time are complicated and could have a significant effect on the
long-term durability of the structure. / Graduation date: 1994
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35709 |
| Date | 01 June 1993 |
| Creators | Wang, Min |
| Contributors | Kennedy, Timothy C. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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