Strength prediction of single- and double-lap joints by standard and extended finite element modelling

Abstract

The structural integrity of multi-component structures is usually determined by the strength and durability of their unions. Adhesive bonding is often chosen over welding, riveting and bolting, due to the reduction of stress concentrations, reduced weight penalty and easy manufacturing, amongst other issues. In the past decades, the Finite Element Method (FEM) has been used for the simulation and strength prediction of bonded structures, by strength of materials or fracture mechanics-based criteria. Cohesive-zone models (CZMs) have already proved to be an effective tool in modelling damage growth, surpassing a few limitations of the aforementioned techniques. Despite this fact, they still suffer from the restriction of damage growth only at predefined growth paths. The eXtended Finite Element Method (XFEM) is a recent improvement of the FEM, developed to allow the growth of discontinuities within bulk solids along an arbitrary path, by enriching degrees of freedom with special displacement functions, thus overcoming the main restriction of CZMs. These two techniques were tested to simulate adhesively bonded single-and double-lap joints. The comparative evaluation of the two methods showed their capabilities and/or limitations for this specific purpose.

Modelling Damage and Failure in Adhesive Joints Using A Combined XFEM-Cohesive Element Methodology

“…If XFEM was used for crack propagation in the adhesive layer as well as in the fillet, the crack initiating in the fillet would grow towards the adherend based on the principal stress / strain direction. Since the crack cannot continue in the adherend, it would continue to grow at the interface [44]. This would not be representative of the experimental failure in the single lap adhesive joints where cohesive failure occurs in the adhesive layer.…”

“…A relatively recent enhancement to the finite element method is the extended finite element method (XFEM) [44,45]. XFEM can be used to predict fracture in a material without prior consideration of the crack path in the finite element mesh.…”

Modelling adhesive joints with cohesive zone models: effect of the cohesive law shape of the adhesive layer

“…In contrast, triangular CZM are efficient for brittle materials that do not plasticize by a significant amount after yielding [27], and also for the intralaminar fracture of composite adherends in bonded structures, due to their intrinsic brittleness [28]. For adhesives that exhibit a relatively brittle behaviour in tension while showing large plastic flow in shear, the proper selection of the CZM parameters and also the minimisation of the constant stress (plastic flow) region in the tensile law result on a good representation of the adhesive behaviour.…”

Effect of hole drilling at the overlap on the strength of single-lap joints

“…The adherends were fabricated from the high strength aluminium alloy AW6082 T651, showing a manufacturer specified strength of 340 MPa achieved by artificial ageing at approximately 180 1C. This aluminium alloy was previously characterized [26] using dogbone specimens. The stress-strain (s-e) plots, obtained through tensile testing following the principles specified in the standard ASTM-E8M-04 [27], showed a nearly elastic-perfectly plastic law with the following mechanical properties: E of 70.07 7 0.83 GPa, tensile yield stress (sy) of 261.67 7 7.65 MPa, tensile failure strength (sf) of 324 7 0.16 MPa and tensile failure strain (ef) of 21.70 7 4.24%.…”