An in-depth study on the time-temperature behavior of epoxy based continuous and elastic fiber reinforced composite materials and the feasibility of using the time-temperature analogy as an accelerated characterization method to predict the long-term behavior are presented. This is a two-pronged investigation as the material investigated (graphite/epoxy) is essentially quasi-elastic at room temperature and viscoelastic at elevated temperatures. Correlations between analysis and experiments are presented whenever possible.
At elevated temperatures, master curves of matrix dominated unidirectional laminates are obtained using the time-temperature superposition principle. Using the principal properties (E₁₁, E₂₂(t), G₁₂(t) and v₁₂), master curves of other off-axis laminates reduced at any arbitrary ambient temperature are predicted. The results obtained from the short-term (16-minute) tests, medium term (25-hour) tests and predictions are shown to correlate reasonably well. In addition, the delayed failure prediction and experimental results are shown to correlate reasonably well. Both the experimental and predicted delayed failure results indicate that the creep strength master curves are dependent on the in-plane stress states and that failure modes vary from ductile to aquasi-brittle depending on the duration of the tests.
At room temperature, a summary of the unnotched and notched behavior is presented. In the unnotched case, total stress-strain responses of general symmetric laminates are predicted with a non-linear analysis and compared with experimental results. The analysis is used to validate intralamina shear test methods. In the notched case, test results for specimens containing variations in notch geometries and anisotropy are given. These results are correlated to three two-parameter and one one-parameter analytical fracture models. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/37611 |
| Date | 13 April 2010 |
| Creators | Yeow, Yew Thye |
| Contributors | Engineering Mechanics |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xii, 139 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 40341760, LD5655.V856_1978.Y45.pdf |
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