Adhesion and Interfaces Involving Polymers, Studied by Electrical Resistance Measurement
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Adhesion and Interfaces Involving Polymers, Studied by Electrical Resistance Measurement Zhen Mei and D.D.L. Chung Composite Materials Research Laboratory, University at Buffalo State University of New York, Buffalo, NY 14260-4400, U.S.A. ABSTRACT The adhesion and interfaces involving polymers were studied by electrical resistance measurement. Adhesive bonding and bond degradation were monitored by measuring the resistance in real time during temperature or stress variation. The resistance measured was either the contact resistance of the joint interface or the apparent volume resistance of one of the two adjoining components in a direction in the plane of the joint interface. The polymers were in the form continuous carbon fiber thermoplastic-matrix composites, due to the importance of these composites for lightweight structures and due to the conductivity of carbon fibers and the necessity of conductivity for electrical resistance measurement. The technique was used for the case of both of the adjoining components being such composites, and for the case of one component being such a composite and the other component being concrete. The concrete case is relevant to the use of the composite to retrofit concrete structures. INTRODUCTION Joining is one of the key processes in manufacturing and repair. It can be achieved by welding, diffusion bonding (autohesion in the case of polymers), soldering, brazing, adhesion, fastening, or other methods. Joints can be evaluated destructively by mechanical testing which involves debonding. However, it is preferred to use nondestructive methods, such as modulus (dynamic mechanical), acoustic and electrical measurements. Electrical measurements are particularly attractive, due to the short response time and equipment simplicity. A requirement for the feasibility of electrical measurements for joint evaluation is that the components being joined are not electrical insulators. Thus, joints involving metals, cement (concrete) and conductor filled polymers are suitable. The method of electrical resistance measurement for joint evaluation commonly involves measurement of the contact electrical resistivity of the joint interface. The contact resistivity is the product of the contact resistance and the joint area; it is a quantity that is independent of the joint area. Degradation of the joint causes the contact resistivity to increase. A less common method involves measuring the apparent volume resistance of a component while the component (A) is joined to another component (B). When component B is less conducting than component A, but is not insulating, degradation of the joint causes the apparent volume resistance of component A to increase. Both of these methods are illustrated below. JOINTS INVOLVING COMPOSITE AND CONCRETE BY ADHESION Continuous fiber polymer-matrix composites are increasingly used to retrofit concrete structures, particularly columns [1-3]. The retrofit involves wrapping a fiber sheet around a concrete column or placing a sheet on the surface of a concret
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