Determining the Parameters of Adhesives

Methods for Determining the Parameters

Describing an adhesive material by way of comprehensive parameters is the foundation for realistic results in the calculation of glued forms of construction. The scope of the determination of the parameters depends on the material to be described and the mechanical modeling. Two experimental options for deter­mining parameters have proved worthwhile for the phenomenological descrip­tion of the material: studies of material specimens and in situ specimens. The material specimens consist merely of pure adhesive material. Parameters spe­cific to the material, e. g., elastic modulus and Poisson’s ratio, can be determined with the help of such specimens. The in situ specimens consist of the compo­nents that are joined together by the adhesive [36-38].

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Uniaxial Tensile Test

ISO 527-1 [39] describes the procedure for determining the tensile properties of plastics by means of material specimens (Fig. 7). These are stretched along their longest principal axis at a constant rate until failure occurs or until the stress or strain has reached a predetermined value. Load and deformation are recorded during the test. So-called dumbbell specimens are preferred for this test: the wider ends of these specimens ensure that they are properly clamped in the test­ing machine, and the transition between the wide and narrow parts of the speci­men ensures that the force introduced is concentrated in the narrow central section; thus generating a uniform stress distribution. Different types of dumbbell specimens are recommended depending on the material to be investi­gated and the manufacturing process. The standard form is type 1 according to ISO 527-2 [40].

FIG. 7—Dumbbell specimen in the testing machine (left). Stress-strain diagram for a 2-part epoxy resin adhesive at different testing temperatures (right).

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