Abstract
Adhesive joints get a growing part of assembly solutions in various industrial applications and are considered as an alternative to soldering and welding. Their small thickness to length or aspect ratio and the importance of the interface with the assembled parts increase the difficulties for measuring their characteristic mechanical properties such as constitutive law, endurance limit, etc… Several testing configurations and methods have been proposed in the literature without a clear emergence of an optimal configuration. This paper proposes a critical review of four different methods taken from the literature and industrial standards: the single lap joint shear test, the thick adherent shear test, the ARCAN test and napkin ring test. In order to contribute to the emergence and to help the experimentalist find an optimal specimen design, the heterogeneities of stress and strain field distributions are here discussed. The test specimens and configurations under scrutiny are compared using both closed-form expressions and Finite-Element computations and considering two different criteria: the spatial distribution of shear stress and the triaxiality ratio between normal and shear stresses in the joint. This study highlights both advantages and limits of each method for mechanical behavior and fatigue characterization. As a final consequence of the remarks an optimal specimen configuration is proposed.
Highlights
In the last decades, adhesive joints obtained a growing share of the bonding and assembly solutions in various industries
For the SLJ, Thick Adherent Shear Test (TAST) and ARCAN configurations, the joint under scrutiny is modeled with a rectangular shape (see Figure 5 (a)): the joint length is aligned with the direction, the joint thickness corresponds to the direction and the joint width is taken in the last direction, where, and denote the unit coordinate vectors of a Cartesian coordinate system
Verifying that the substrate material is much stiffer than the tested joint is not sufficient, one has to take into account the structural stiffness of the whole assembly to ensure substrate rigidity compared to the adhesive joint
Summary
Adhesive joints ( denoted as “adhesive layer”) obtained a growing share of the bonding and assembly solutions in various industries. The dimensions of the adhesive joint are characterized by a small thickness when compared with the two in-plane directions This geometric feature adds further difficulties when measuring the properties or proposing models to characterize their behavior. The small thickness will increase the importance of the interfaces in the global behavior of the assembly and the need to characterize it These two properties often lead to microscopic homogenization studies and macroscopic model reduction. In the case of a rate-dependent (viscoelastic) behavior characterization, the strain gradient inside the joint implies a non-uniform strain rate, resulting in a more complex identification procedure. This method will not be discussed in detail in this paper. As a final consequence of the discussion, a “hybrid” specimen geometry for the test is proposed
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