Issue 50

B. Benamar et alii, Frattura ed Integrità Strutturale, 50 (2019) 112-125; DOI: 10.3221/IGF-ESIS.50.11 113 I NTRODUCTION dhesive bonding is frequently used to manufacture complex-shaped structures and in the several fields of engineering; easy manufacturing and possibility to joint different materials [1]. However, the problem of the single lap joints is the concentrated stress at the edges. This concentration is usually due to the misalignment of the two applied forces . Many ideas have been proposed to reduce the stresses that occur at the end of the overlap. These ideas can be grouped into two categories: fracture parameter of adhesive and or geometric. Groth [2] used the finite element method for predicting breakage in single-cover joints with a spit net. A large number of predictive techniques is available for bonded joints, either analytical or numerical. Da Silva et al. [3] provide extensive reviews of these methods for analytical methods and X. He [4] for finite element based techniques. Analytical methods are easy to use, but they usually consider simplification assumptions [5]. For complex geometries and elaborate material models, a finite element analysis is preferable to obtain the stress distribution. Fracture mechanics based methods use the fracture toughness of materials as the leading parameter for fracture assessment [6]. Kaye and Heller [7] developed an optimal design of free form bonded and double lap joints, with the aim of achieving reduced peel stresses on the bond line region. Several parameters determine the quality of a bonded assembly. The strength of the adhesive and the elements to be assembled (brittle or ductile, strong or weak), as well as, the geometry of the joint and the assembled elements. We find the geometric shape of the single lap joint is the most studied in the behavior of assemblies. We find the experimental and numerical comparison work of Barbosa et al. [8] who conducted a study on the effect of lap length, in which they concluded that while tronger and more brittle adhesives are recommended for joint geometries. Banea et al. [9] also experimentally and numerically studied the strengths of joint adhesion. They concluded that failure is dominated by global adhesive yielding and the geometry influence. Luca Sorrentino et al. [10] have also studied the single-lap joint where they demonstrated the effect of surface treatments on the strength of assemblies. Other works such as Costanzo [11] and Banea et al. [12], include the thermal effect on the strength of the adhesive joints. The effect of the length and depth of a parallel slot on the stress distribution at the mid-bond line and in the adherend was investigated by Yan et al. [13] using the elastic finite element method. In the study of Gültekin et al. [14], mechanical properties of different single lap joint configurations with different adherend width values subjected to tensile loading were investigated experimentally and numerically. In the work of Pinto et al. [15], the Cohesive Zone Models (CZM) are widely used in delaminate on analysis. They not need an pre-existing of crack like (VCCT) Virtual Crack Closure Technique [16, 17]. Many different cohesive element (CZM) formulations have been proposed [18, 19]. However, two main difficulties concerning cohesive elements robustness and their application to large-scale structures still exist. Firstly, fine meshes are required to appropriate model, which leads to high, and sometimes unaffordable, computational requirements. Secondly, recent findings indicate that the mixed-mode crack propagation predicted by cohesive elements might be unreliable because of an improper estimation of the energy dissipated during the fracture process. The current paper addresses this last difficulty. Other technique implementation in ABAQUS® used without meshing again like the extended finite element modeling (XFEM) [20]. It has used also by Campilho et al. [21] for strength prediction of single and double-lap joints. The objective of this study is to evaluate by numerical simulation the effect of cohesive stiffness, cohesive strength and fracture energy of the adhesive in order to see their effect on the value of the failure load of the assembly type Aluminum / Aluminum under a compressive and tensile behavior. Four overlap lengths and geometrical parameters modification named tapered have been selected, in order to see also their effect on the failure load of the joint. We also put into consideration the effect of the percentile variation of mode I and mode II on the value of the failure load of the assembly, analyzing the numerical results show that the failure load increases as the adhesive have high strength especially in mode II. C OHESIVE INTERFACES AND INPUT PARAMETER he separation path using the CZM is entirely in the cohesive zone. The model is a linear tensile-separation law as represented in Fig. 1, defined by a surface of nodes in a mesh without interaction between the surfaces. This technique of selecting the interface with failure parameters is quite different from those already used before for similar studies. It consists of drawing the complete assembled system in a single geometry, no assembly between the different elements. Next, the orphan mesh existing in the ABAQUS calculation code is chosen and the mesh elements are A T