NDTnet 1998 Aug, Vol.3 No.8

Abstract

The aim of this investigation is the verification of the quality and the strength of the adhesion of two materials with synthetic adhesives by means of the method of ultrasounds. The method consists of making two Plexiglas short beam test pieces which are tested by three point bending load. The test pieces are bonded together by varling composition of epoxy resins and are stressed in a way that the failure to be done in the bonded surfaces, the interface, by bending loading and with shear stresses. At this point the velocity and attenuation measurements of the longitudinal waves are checked as well as the failure load of the bended double short beam.
Some of the test pieces are bonded with adhesives, which are very good degassed in a vacuum chamber for 20min to remove all bubbles and others without any degas. Also adhesives of varling composition and strength are used by epoxy resins adhesives in which different quantities of plasticizer has been used. In this way adhesions with differend degree of ductility between brittle and ductile adhesives are produced.

By this proceeding derives the following useful conclusions:For instance, the adhesion strength by synthetic adhesives is increased when the ductility of the adhesive is increased.The degas of the adhesive does not bettering the strength of the adhision, but on the contrary minimise its strength, although was expected that the absence of the air bubbles increases its strength.

This difference is greater as more brittle is the adhesive while as more ductile is, this difference is minimized and tends to be reversed for greater values of ductility. Therefore, when the adhesions are made by brittle adhesives the degas does not affect the strength of adhesion but only their edge shape. But when they are ductile the degas of the epoxy adhesilon affects its strength.

The critical comprehensiveness in plasticizer of the epoxy adhesive which creates the greater strength of the adhesion, is 40% for not degassed adhisions and 80% for degassed adhisions. All these informations arise according to known procedures, using the NDT method of ultrasounds and are in agreement with known conclusions, Refs [1-2].

References:
1. Wang, T. T., Ryan, F. W., and Schonhorn, H., Effect of Bonding Defects on Shear Strength in Tension of Lap Joints Having Brittle Adhesives, J. Appl. Polym. Sci., Vol. 16, pp. 1901-1909, 1972.
2. Prassianakis l.N., Correlation of Mechanical and Acoustical Properties of Plasticized Epoxy Polymers, J.of Applied Polymer Science, Vol.39, pp.2031-2041, 1990.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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