PSI - Issue 28

I.J. Sánchez-Arce et al. / Procedia Structural Integrity 28 (2020) 1084–1093 Sánchez-Arce et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction Most of the objects used in our daily life are composed of several components, regardless of their size, joint together. Throughout the years, several mechanical ways to joint materials have been developed and perfected (e.g., riveting, bolting, welding, brazing). Although adhesives have been used in human life for thousands of years [1,2], they have become more ubiquitous in recent years with applications to the aerospace, automotive, energy, and construction fields, to name a few [3,4]. The single-lap joint (SLJ) is the most used type for analysis and experimental testing being followed by the double-lap joint (DLJ) [1]. SLJs are more used because of their easiness to manufacture. However, the SLJ has a disadvantage, the load acts eccentrically because of the lap. Conversely, in DLJs, the load acts concentrically, but it is more complex to be executed for repair work. The strength ( P max ) of an adhesively bonded SLJ can be influenced by several variables such as adherend and adhesive mechanical properties, adherend thickness, overlap length ( L O ), adhesive layer thickness, surface preparation, and adhesive curing time [5]. Although analytical models provide an insight into the stresses in an adhesive joint, the continuous development of numerical and computational technologies had proven to provide better means to analyze stress and strains in the joints [1]. Analytical models were developed for joints with certain characteristics, both geometrical and physical (i.e., materials) while the numerical techniques do not possess such constraints [1]. The most known and used technique is the finite element method (FEM) in which any geometry is represented by a set of small elements. Moreover, the FEM allows investigating the effect of geometrical changes in the adhesive and adherends to reduce stress concentration at the joint ends [6–8]. Although adhesive joints as the SLJ are three-dimensional cases, the use of two-dimensional models to numerically analyze them has been demonstrated to be a good alternative, which also reduces computational time [6,9]. Meshless methods (MM) have been evolving throughout the years. There are two main classifications for such methods, those using approximation functions and those using interpolation. Interpolating MM possess Kronecker’s delta property, as the FEM. The Kronecker’s delta property allows to directly impose the essential and natural boundary conditions. In the FEM, nodes are connected by elements that should obey shaped polygons. Under large deformation cases, the elements can be heavily distorted causing convergence issues. Conversely, MM and NNRPIM in particular do not have those restrictions, which makes them more suitable to large deformation analyses [10–14]. In the adhesively bonded joints case, their P max is determined by deforming the joint until failure; this process causes a large-deformation state to the adhesive. MM have been successfully applied to adhesive joints. The Element Free Galerkin Method (EFGM) was applied to layer-composed plates and cantilever beams; afterward, the results were compared with FEM solutions for the same cases [15]. The double cantilever beam (DCB) test was analyzed using the ‘symmetric smoothed particle hydrodynamics’ (SSPH) and cohesive zone models; the results were compared with both experimental and numerical data [16]. Later, a combination of cases SLJ, bonded, bolted, and bonded-bolted were modeled using a ‘radial point interpolation method’ (RPIM) being the first work including non-linear material behavior, and the bolt to adherends contact was also considered [17]. This paper aims to evaluate the NNRPIM method for the elastic analysis of adhesive joints. P max was predicted and stress distributions along the adhesive layer were obtained, both with FEM and NNRPIM. The suitability of the NNRPIM was evaluated form the comparison of its predictions against those from the FEM. This evaluation could be the basis for further analyses of adhesive joints such as elastic-plastic and joint geometries with industrial applications. 2. Experimental work 2.1. Materials The adherends were manufactured from an aluminum AW6082-T651 plate cut to the desired size in a shear brake. The mechanical properties of this aluminum alloy were determined following the guidelines and dimensions from the ASTM-E8M-04 standard [18], and it was performed in a previous work [19]; having the following properties: Young’s modulus E=70.07±0.83 GPa, yield strength  y =261.67±7.65 MPa, ultimate strength  f =324.00±0.16 MPa, and a failure strain ε f =21.70±4.24% [19].