Crack Path Selection in Adhesively Bonded Joints

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dc.contributor.authorChen, Buoen
dc.contributor.committeechairDillard, David A.en
dc.contributor.committeememberDillard, John G.en
dc.contributor.committeememberLesko, John J.en
dc.contributor.committeememberGao, David Y.en
dc.contributor.committeememberLove, Brian J.en
dc.contributor.committeememberCase, Scott W.en
dc.contributor.departmentEngineering Mechanicsen
dc.date.accessioned2014-03-14T20:18:53Zen
dc.date.adate1999-11-23en
dc.date.available2014-03-14T20:18:53Zen
dc.date.issued1999-11-15en
dc.date.rdate2000-11-23en
dc.date.sdate1999-11-21en
dc.description.abstractThis dissertation is to obtain an overall understanding of the crack path selection in adhesively bonded joints. Using Dow Chemical epoxy resin DER 331® with various levels of rubber concentration as an adhesive, and aluminum 6061-T6 alloy with different surface pretreatments as the adherends, both symmetric and asymmetric double cantilever beam (DCB) specimens are prepared and tested under mixed mode fracture conditions in this study. Post-failure analyses conducted on the failure surfaces indicate that the failure tends to be more interfacial as the mode II component in the fracture increases whereas more advanced surface preparation techniques can prevent failure at the interface. Through mechanically stretching the DCB specimens uniaxially until the adherends are plastically deformed, various levels of T-stress are achieved in the specimens. Test results of the specimens with various T-stresses demonstrate that the directional stability of cracks in adhesive bonds depends on the T-stress level. Cracks tend to be directionally stable when the T-stress is compressive whereas directionally unstable when the T-stress is tensile. However, the direction of crack propagation is mostly stabilized when more than 3% mode II fracture component is present in the loading regardless of the T-stress levels in the specimens. Since the fracture sequences in adhesive bonds are closely related to the energy balance in the system, an energy balance model is developed to predict the directional stability of cracks and the results are consistent with the experimental observations. Using the finite element method, the T-stress is shown to be closely related to the specimen geometry, indicating a specimen geometry dependence of the directional stability of cracks. This prediction is verified through testing DCB specimens with various adherend and adhesives thicknesses. By testing the specimens under both quasi-static and low-speed impact conditions, and using a high-speed camera to monitor the fracture sequence, the influences of the debond rate on the locus of failure and the directional stability of cracks are investigated. Post-failure analyses suggest that the failure tends to be more interfacial when the debond rate is low and tends to be more cohesive when the debond rate is high. However, this rate dependence of the locus of failure is greatly reduced when more advanced surface preparation techniques are used in preparing the specimens. The post-failure analyses also reveal that cracks tend to be more directionally unstable as the debond rate increases. Finally, employing interface mechanics and extending the criteria for the direction of crack propagation to adhesively bonded joints, the crack trajectories for directionally unstable cracks are predicted and the results are consistent with the overall features of the crack paths observed experimentally.en
dc.description.degreePh. D.en
dc.identifier.otheretd-112199-224339en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-112199-224339/en
dc.identifier.urihttp://hdl.handle.net/10919/29709en
dc.language.isoenen
dc.publisherVirginia Techen
dc.relation.haspartch6.pdfen
dc.relation.haspartCh4-Figs.pdfen
dc.relation.haspartch5.pdfen
dc.relation.haspartch2.pdfen
dc.relation.haspartCh1-Figs.pdfen
dc.relation.haspartch4.pdfen
dc.relation.haspartCh2-Figs.pdfen
dc.relation.haspartch3.pdfen
dc.relation.haspartfront.pdfen
dc.relation.hasparttitle.pdfen
dc.relation.haspartCh5-Figs.pdfen
dc.relation.haspartBCVita.pdfen
dc.relation.haspartch1.pdfen
dc.relation.haspartCh3-Figs.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectT-stressen
dc.subjectadhesively bonded jointsen
dc.subjectcohesive failureen
dc.subjectdirection of crackingen
dc.subjectmixed mode fractureen
dc.subjectLocus of failureen
dc.subjectinterfacial failureen
dc.subjectalternating failureen
dc.subjectdirectional stability.en
dc.subjectsurface preparationen
dc.subjectfailure modeen
dc.subjectcrack path selectionen
dc.titleCrack Path Selection in Adhesively Bonded Jointsen
dc.typeDissertationen
thesis.degree.disciplineEngineering Mechanicsen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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