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Dissertation
Interfacial micromechanics and environmental degradation in graphite/epoxy composites: a study using micro-Raman spectroscopy
Doctor of Philosophy (Ph.D.), Drexel University
Sep 1995
DOI:
https://doi.org/10.17918/00000450
Abstract
It is widely accepted that the mechanical performance of composite materials is controlled, to a large extent, by their interfacial properties. For three decades, interfacial micromechanics and environmental degradation of composites have been studied using measurement techniques that are based on invalid assumptions about the interfacial stress distribution and lack the required spatial resolution. As a result, a number of questions regarding the exact interfacial behavior are still unanswered, and the exact interfacial degradation mechanism is still unclear. In addition, the stress concentration phenomenon in multi-fiber composites which controls the composite fracture mechanism, can still be considered as a frontier due to the lack of experimental techniques. Micro-Raman spectroscopy (MRS) is able to measure strain in graphite fibers with a spatial resolution of 2 [mu]m. The technique is powerful for monitoring the interfacial behavior in the sense that it allows measuring the exact stress distributions and monitoring crack initiation and propagation at the interface. In this study, MRS was utilized to investigate interfacial micromechanics and environmental degradation in graphite/epoxy composites. Micromechanical behavior of the interface was found to depend on the presence of a brittle interphase, but the maximum interfacial shear stress (ISS) observed in both cases was 40 MPa. Results showed that the maximum ISS was limited by matrix plastic deformation in both cases. Exposure to distilled water at 100[degrees]C up to the saturation level, caused a 50% reduction in the ability of the interface to withstand shear stresses. The overall results demonstrated that the observed reduction in the ability of the interface to withstand shear stress was the result of interfacial bonds failure under the effect of tensile stresses created at the interface due to matrix swelling upon water absorption. These stresses were found to depend slightly on the composite fiber volume fraction. Results of investigating the stress concentration phenomenon demonstrated that the stress concentration factor depends strongly on the composite fiber volume fraction, and that the strain energy released upon fiber fracture plays a major role in controlling the stress concentration phenomenon.
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Details
- Title
- Interfacial micromechanics and environmental degradation in graphite/epoxy composites
- Creators
- Maher Sabri Amer
- Contributors
- Linda S. Schadler (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xv, 161 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991014970339404721