Abstract

SUAREZ, J.C.; MIGUEL, S.; LOPEZ, F.  and  HERREROS, M.A.. Leyes cohesivas en uniones adhesivas: ensayo de desgarro/pelado para la caracterización de películas adhesivas delgadas. C.Tecn. Mat. [online]. 2010, vol.22, n.3-4, pp.12-18. ISSN 0870-8312.

To be able to predict the strength of adhesive joints accurately, correct material data of adhesives are essential. Hence, it is critical to develop reliable testing methods to obtain the constitutive behaviour of adhesive layers. In use, adhesives are constrained to thin layers. Thus, an adhesive constrained into a layer is expected to behave differently compared to the adhesive as a bulk material. Under loading, the size of the Failure Process Zone (FPZ) in the adhesive layer is often much larger than the thickness of the layer. Thus, the small scale FPZ condition is not fulfilled and the traditional Linear Elastic Fracture Mechanics (LEFM) can not be applied. At the same time, experiments show that test specimens are prone to produce unstable crack propagation and combined adhesive/cohesive fracture patterns appear frequently, especially when mixed mode loading (peel and shear) is involved. Cohesive law should be taken as the basic fracture property for adhesives characterization; cohesive laws must be determined experimentally. The effects of loading rate and adhesive layer thickness on the cohesive law shape have to be investigated experimentally. The coupling of elasticity, adhesion and fracture make difficult interpretation of test results, especially if the adhesive is an elastomer, which has a failure strain of several hundred percents. A new test has been proposed, combining tearing of the adhesive layer and debonding from the substrate in a controlled way and using a simplified geometry. Results are closely related to the stiffness, work of fracture and adhesive energy of the adhesive system, all of them plying simultaneously an active role during the very same test.

Keywords : Adhesive; Tearing; Debonding; Cohesive law.

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