Hybrid (bolted/bonded) joints applied to aeronautic parts : analytical one-dimensional models of a single-lap joint

The load transfer in hybrid (bolted/bonded) single-lap joint is complex due to the association of two different transfer modes (discrete and continuous) through elements with different stiffness. Analytical methods exist for these two different modes, when considered separately. In this paper two one-dimensional elastic analytical models are presented for the determination of the load transfer in single lap configuration. The first one is developed by using the integration of the local equilibrium equations. From this first method an elastic-plastic approach is presented. The second one uses the Finite Element Method, introducing a new element called “bonded-bar”. These models are robust, easy to use and provide the same results. They allow to analyze the load transfer and to evaluate different geometric and mechanical parameters’ influence. Thus they represent the first step for the design of a hybrid joint able to replace its bolted equivalent used on aircraft

Faisabilité d'assemblages mixtes boulonnés-collés en aéronautique

L'idée de l'assemblage hybride est de réduire le transfert aux fixations sous charge de fatigue, de manière à dépalcer le site critique en zone non trouée tout en garantissant la tenue aux charges extrêmes

Simulation of Single-Lap Bonded and Hybrid (Bolted/Bonded) Joints with Flexible Adhesive

Balanced single-lap bonded and hybrid (bolted/bonded) joints with flexible adhesives have been studied using finite element analysis. The two-dimensional plane strain and three-dimensional analyses have been carried out. Geometrical and material nonlinearities were taken into account. Flexible adhesives were modelled using hyperelastic Mooney–Rivlin potentials. Joint stiffness, as well as adhesive stress distribution, in the overlap has been investigated. The sensitivity of mechanical response to the compressibility of the adhesive material has been demonstrated. Numerical analyses of hybrid (bolted/bonded) joints showed their fatigue life is longer than corresponding bolted joints

Reprise Hydrique des Matériaux Composites Carbone Epoxy (IM7/977-2)

Reprise Hydrique des Matériaux Composites Carbone Epoxy (IM7/977-2)

Contribution aux assemblages hybrides boulonnés collés aéronautiques : modélisation analytique unidimensionnelle en simple cisaillement

Le calcul du transfert de charge dans les jonctions a été traité par des approches analytiques d’une part dans le cas des jonctions boulonnées et d’autre part dans celui des jonctions collées. Dans cet article, nous étudions le cas d’une jonction hybride boulonnée collée qui associe les deux modes de transfert (discret et continu) dans une configuration en simple cisaillement. Nous présentons une modélisation analytique monodimensionnelle qui prend en compte la rigidité des différents composants. Simple à mettre en oeuvre, elle permet d’analyser le transfert de charge et d’évaluer l’influence des différents paramètres géométriques et mécaniques. Son exploitation est intéressante dans le cadre du pré-dimensionnement d’une jonction hybride apte à remplacer son équivalent boulonné sur avion

Modélisation simplifiée des transferts d’effort dans les assemblages boulonnés et/ou collés

Le poste assemblage est le point critique de toutes les industries de construction mécanique. En effet, les assemblages structuraux sont garants de l’intégrité de la structure durant son utilisation en service. Il est donc crucial de dimensionner ces assemblages. Les travaux présentés dans ce mémoire visent alors à fournir aux concepteurs des méthodologies de calcul rapides et fiables pour la prédiction du comportement mécanique des assemblages par collage et/ou boulonnage. La modélisation par macro-élément (ME) est une approche attractive dans le sens où par nature elle permet dans le cadre d’une résolution macroscopique d’enrichir la modélisation en cohérence avec la réalité physique à l’échelle mésoscopique. Il est donc nécessaire d’identifier le niveau de complexité de modélisation à intégrer dans le ME pour représenter la physique. Ce besoin pose alors la question des méthodologies d’intégration de complexité croissante dans le ME mais aussi celles de l’identification des lois constitutives dans un contexte pluridisciplinaire. Une ouverture mêlant mécanique des structures et matériaux, physico-chimie des matériaux et interfaces et sciences de l’information est proposée. The joining stage is the critical stage of all the mechanical manufacturing industries. Indeed, the structural joints are driving the integrity of the structure in-service. It is of the highest significance to size these joints. The research works presented in this Thesis aim at providing to the designers fast and reliable methodologies for the prediction of the mechanical behavior of bolted and/or adhesively bonded joints. The macro-element (ME) modelling is an attractive approach since it offers a macroscopic resolution while enriching the modelling in relevance to the physical reality at the mesoscopic scale. The question is then to identify the level of modelling complexity to be integrated in the ME to be representative for the Physics. This question implies then to find methodologies for the integration of increasing complexity within the ME as well as to identify the constitutive law in a multidisciplinary context. A way forward involving Mechanics of Structures and Materials, Physics and Chemistry of Materials and Interfaces and Information Technology Sciences is suggested

Simplified stress analysis of multilayered bonded structure under 1D-bar kinematics

Many current materials and structural systems are layered. The structural performances of these multilayered systems are dependent on interfaces, the presence of which is inherent to them. A methodology for the simplified stress analysis of such structures under 1D-bar kinematics is presented. The macro-element technique is used to solve the set of ordinary differential equations involved. A dedicated macro-element is formulated through the approximation of displacements fields by Taylor expansion power series. The predictions of the simplified stress analysis are in close agreements with those obtained by FE analyses. Finally, the influence of adhesive thickness and of the overlap length on the adhesive stress peaks is presented

On the potential static strength of hybrid (bolted/bonded) lap joints with functionally graded adhesives

In this paper, the potential static strength of hybrid (bolted/bonded) – termed HBB – joints with functionally graded adhesives (FGA) is theoretically investigated, in reference to the pure bolted joint, the pure bonded joint and the HBB joint with homogeneous adhesive (HA). The investigation is performed on a particular in-plane tensile loaded single-lap joint made of identical aluminum adherends with two lines of fasteners and three various adhesive symmetrical graduation laws. The stress analysis is performed using the macro-element (ME) technique within 1D-bar framework. Moreover, closed-form expressions for the bolt load transfer rates and maximal adhesive stresses of balanced single-lap HBB joint with two identical fasteners are derived. It is shown that the FGAs allows fort a better load sharing between the adhesive and the fasteners than the HA. Moreover, the use of FGAs instead of HA could lead to a potential static strength benefit for the adhesive layer part rather than for the fastening part

A direct method for the assessment of cohesive zone models for thin adhesive layers loaded in mode I, mode II, and mixed-mode I/II

In the context of increasing the strength-to-mass ratio of lightweight structures, the adhesively bonded joining technology appears to be an attractive solution. Nevertheless, this attractiveness of the adhesive bonding is effective only when the structural integrity of joints is ensured. In the literature, the cohesive zone models (CZMs) are shown to be able to predict both the static and fatigue strengths of adhesively bonded joints. The strength prediction is dependent on material laws and associated material parameters, characterizing the bondline behaviour mainly under pure mode I, mode II and mixed-mode I/II. The characterization methods are thus crucial. This paper aims at assessing the capabilities to identify the parameters of a particular CZM for both the inverse method, based on the energy balance associated with the path independent J-integral, and of a direct method described in this present work. The particular CZM has a classical shape based on the definition of a bilinear law for each of both pure modes, associated with pure mode interaction energy laws for initiation and propagation under mixed-mode I/II. The methodology used in this paper is based on a numerical test campaign only, involving the macro-element (ME) technique. A new approach for the fast formulation and implementation of ME modelling of two bonded beams is described

Elasto-Plastic Analysis of Bonded Joints with Macro-Elements

The Finite Element (FE) method could be able to address the stress analysis of bonded joints. Nevertheless, analyses based on FE models are mainly computationally cost expensive and it would be profitable to develop simplified approaches, enabling extensive parametric studies. Firstly, a 1D-bar and 1D-beam simplified models for the bonded joint stress analysis, assuming a linear elastic adhesive material, are presented. These models derive from an approach, inspired by the finite element (FE) method using a formulation based on a 4-node macro-element, which is able to simulate an entire bonded overlap. Moreover, a linear shear stress variation in the adherend thickness is included in the formulation. Secondly, a numerical procedure is then presented to introduce into both models an elasto-plastic adhesive material behavior, while keeping the previous linear elastic formulation. Finally, assuming an elastic perfectly plastic adhesive material behavior, the results produced by simplified models are compared with the results predicted by FE using 1D-bar, plane stress and 3D models. Good agreements are shown