The Use of Nanonindentation to Determine Composite Interfacial Shear Strength and the Effects of Environmental Aging

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dc.contributor.authorHaeberle, David Claibourneen
dc.contributor.committeechairLesko, John J.en
dc.contributor.committeememberRiffle, Judy S.en
dc.contributor.committeememberCase, Scott W.en
dc.contributor.departmentEngineering Science and Mechanicsen
dc.date.accessioned2014-03-14T20:40:17Zen
dc.date.adate2001-06-25en
dc.date.available2014-03-14T20:40:17Zen
dc.date.issued2001-06-08en
dc.date.rdate2002-06-25en
dc.date.sdate2001-06-21en
dc.description.abstractFiber sizings are used to improve the performance of fiber-reinforced polymer composites made from low-cost fiber and matrix materials. Evaluation of three sizings, poly(vinylpyrrolidone) (PVP), a carboxyl modified polyhydroxyether (PHE), and a standard industrial sizing (G'), have revealed tremendous improvements in static mechanical and enviro-mechanical properties. The focus of this work is to determine if these improvements in performance can be ascertained from a micromechanical test for interfacial shear strength (IFSS) on as-processed materials. The accomplishment of this goal would create more information with fewer experiments and a need for less experimental materials. In this study, a nanoindenter uniquely outfitted with a blunt tip is effectively used to obtain microindentation results where the debond load is extracted directly from the experimental load-deflection curve. Shear lag and finite element analyses are used to evaluate the mechanics of the system, but both methods show limitations with regard to determining interfacial stresses in an experimental system. In the results obtained, the PHE and Gâ materials outperform the PVP in IFSS, but the bulk properties for PVP and PHE outperform the Gâ material, suggesting the presence of another dominant mechanism. Despite better retention of bulk properties after hygrothermal exposure, PHE experiences degradation in IFSS that PVP does not. The PHE loses 10% of its original IFSS after 576 hours of 65ºC moisture exposure, while PVP improves by 25%. The tensile strengths for PHE and PVP decrease 7% and 10% respectively at 576 hours exposure. Finite element modeling shows that matrix swelling due to moisture absorption increases interfacial shear stresses, a finding supported by a comparison of wet and dry specimens subjected to equivalent aging times. Matrix swelling is not, however, responsible for the increase in IFSS of the PVP material. The relationship between tensile strength and IFSS proves to be small as predicted by a tensile strength model, but processing defects and other failure processes that are not included in the tensile strength model appear to have strong influences over the experimental results. IFSS is important in composite materials, but in the case of the G', PHE and PVP materials, other factors dominate fiber direction tensile performance. Therefore, this one simple micromechanical test provides significant insight into the composite material behavior, but it does not provide the same magnitude of information as from bulk composite experiments.en
dc.description.degreeMaster of Scienceen
dc.identifier.otheretd-06212001-134023en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-06212001-134023/en
dc.identifier.urihttp://hdl.handle.net/10919/33668en
dc.publisherVirginia Techen
dc.relation.haspartthesis.PDFen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectinterfacial shear strengthen
dc.subjectcomposite strengthen
dc.subjectfiber-reinforced polymer compositesen
dc.subjectmicroindentationen
dc.subjectnanoindentationen
dc.titleThe Use of Nanonindentation to Determine Composite Interfacial Shear Strength and the Effects of Environmental Agingen
dc.typeThesisen
thesis.degree.disciplineEngineering Science and Mechanicsen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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