The durability of adhesive joints: an engineering study

Water diffusion through the adhesive is the rate controlling factor for the durability of many metal-to-polymer bonds exposed to moist environments. A methodology is proposed, to relate the diffusion coefficient of water in polymers to temperature, strain and penetrant concentration. The approach used is based on well known free volume theories. In the rubbery state, it is assumed that the transport kinetics is governed by the constant redistribution of the free volume, caused by the segmental motions of the polymeric chains. An expression for the diffusion coefficient is inferred from the temperature, strain and penetrant concentration of the free volume. lt is shown that the free volume treatment can be extended to the glassy range by introducing a few additional features in the model. The stress dependence of solubility as well as the non-fickian driving forces contributing to mass transport are predicted from the Flory-Huggins theory. Experimental validation of the concentration dependence and temperature dependence of the diffusion coefficient is shown. The effect of mechanical strain on diffusivity and solubility in the glassy state is also investigated experimentally, using both the permeation and sorption techniques. Good agreement with theory is generally found. The coupling mechanisms between the diffusion process and the viscoelastic response of the adhesive are explained. A numerical scheme for fully coupled solutions is implemented in a two- dimensional finite element code. A few numerical solutions are shown. In the case of bonds undergoing unusually harsh environmental exposure however, alternative methods must be sought for durability characterization and prediction. This is illustrated with the case of rubber-to-steel joints exposed to a cathodic potential in seawater. The mechanical analysis of a durability specimen is presented and a procedure for debond prediction is suggested.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Materials Engineering Science

Department dc:contributor.department

Materials Engineering Science

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1988

Author dc:creator

• Lefebvre, Didier R.

Chairs dc:contributor.committeechair

• Brinson, H.F.
• Dillard, D.A.

Committee members dc:contributor.committeemember

• Ward, Thomas C.
• Wightman, James P.
• Reifsnider, Kenneth L.
• Grant, W.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/52325

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/52325