Torsion Test

In order to achieve a state of stress that is as uniform as possible, in situ speci­mens are prepared according to DIN EN 14869-1 [41] from butt-bonded hollow cylinders with a complete ring of adhesive (Fig. 8). Two cylinders made from the relevant material are connected with the adhesive to be investigated and subsequently subjected to torsion or tension. This means the details of the ten­sile stress-strain relationship and the shear stress-shear strain relationship are possible with a single specimen geometry. Combinations of loading are also possible. This type of specimen was further developed for glass-metal joints within the scope of the work by Vogt [37].

Test Method with Butt-Jointed Specimens

In the course of research work concerning glass-metal joints, Tasche [42] devel­oped specimens that allow the tensile and shear strengths of thin adhesive joints

FIG. 8—Butt-bonded hollow cylinder in the testing maschine (left). Shear stress-shear strain diagram fora 2-part epoxy resin adhesive at different testing temperatures (right).

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to be determined using small-scale in situ specimens. These specimens allow an adhesive joint with the brittle material glass to be loaded in tension or shear. They enable the adhesive layer within the composite construction to be investi­gated and therefore take into account the influences of the materials being con­nected. Furthermore, tests on these specimens allow statements to be made regarding the mechanical behavior of the joint. For instance, in order to evalu­ate the adhesive behavior of various adhesives for bonded fittings, tensile tests were carried out on these specimens. The determination of the adhesive behav­ior was carried out at different temperatures. As the temperature rises, so the strength of the adhesive joint decreases for all the adhesives investigated (Fig. 9). Embrittlement is frequently apparent at low temperatures.

In many cases the adhesion depends on the surface of the annealed glass to which the adhesive is applied. Owing to the production process, the surface characteristics of the tin and air sides are different. The influences of both sides of the annealed glass on the adhesive behavior were therefore investigated. However, it is not possible to derive a generally applicable statement for all the adhesives investigated.