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Title: The long-term durability of adhesive joints
Author: Court, R. S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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Hot-wet ageing was performed on three different adhesive joint systems for over 10,000 hours. Joint strengths were found to decrease with ageing time and failure was near-interfacial in the adhesive. There was no evidence of an adhesion type failure mechanism. A novel video imaging system was developed for one of the joint systems which was transparent, and this gave new, in-situ information on damage initiation and propagation in joints. The material properties of the acrylic and epoxy adhesives used for the joints were needed as input for the theoretical studies. Tensile properties were determined for adhesive samples that had been hot-wet aged and which had a range of water contents. Increased water content caused significant reductions in tensile strength and failure strain for both acrylic and epoxy. The reduction in modulus was only significant for the acrylic. A new shear test procedure using a bonded tube-plate sample was developed for adhesives with high failure strains. Accurate and reliable shear properties were measured for the acrylic adhesive. A thickness effect was observed with thin adhesive layers being stronger than thick layers. An analysis was derived, using observations from video images of the fracture process during the shear tests, that helped explain the observed thickness-strength relationship. The theoretical model for adhesive joint durability was developed based on changes to the mechanical properties of the adhesive due to water up-take. The adhesive joints were modelled using crack-bridging concepts not previously applied to this type of problem. The crack-bridging model uses large-scale bridging (LSB) conditions, which requires the material behaviour to be coupled to the component geometry, and this was implemented in a finite element model. The LSB model was found to give accurate results and to give useful predictions of joint performance in response to ageing. The LSB model was able to simulate damage development occurring in joints under load. Failure surfaces for the three joint types were developed and the most appropriate was found to be related to the shear-normal stress ratio in the adhesive.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available