Test procedures, bonded joints shear tests

Secondly, the layered structure causes interlaminar shear stresses at each layer interface together with other in-plane shear stresses. Therefore, it should also be verified that the allowable in-plane shear stress of the adherend is not exceeded. This is not included, however, in the conditions above, as the interlaminar shear failure is typically preceded by a throughthickness tensile failure. The required value of the interlaminar shear strength is also seldom available, and there are no standardised test procedures to determine such a value. As a result, bonded joint induced interlaminar shear stresses are not calculated in the design procedures presented. 

There have, for decades, now, been reliable analytical tools available for the design and analysis of adhesively bonded joints. Even so, there is still far too much reKance on the oversimplified model whereby the bond strength is assumed to be the product of some fictitious uniform adhesive allowable shear stress and the bond area. If more joint strength were needed, all one had to do, according to this procedure, was to increase the bonded area. Bonded joints do not obey such rules. Such a formula is valid today only in the context of short-overlap test coupons in which the goal is to create as closely as possible a uniform state of... 

Many adhesive suppliers indicate certification authority approval for marine use in their product data sheets. O Table 48.1 shows typical requirements. It is important to note that these tests are performed on adhesively bonded joints, usually in the form of lap shear specimens, and not bulk adhesives. The approval is therefore specified for particular substrates, and includes their surface preparation and the joint manufacturing procedure. 

Automatic Bonding Evaluation System (ABES) The ABES consists of a small press and a tiny testing machine in a single unit. It enables bonds to be formed under highly controlled conditions the joints that contain the bonds which are to be measured are pressed against heated blocks for a certain time, cooled within a few seconds, and pulled immediately thereafter in shear mode. Repetition of this procedure at different curing times and temperatures yields the points (a point for each specimen) of a near-isothermal strength development curve. 96,97... 

In this procedure, the specimens were stressed weekly to 50% of initial shear strength and then returned to the exposure conditions, providing no bond failure occurred. After 52 weeks of testing, the joints were deliberately failed for quantitative determination of the actual bond strength as shown. 

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