Eric Paroissien

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-bars”. These models are robust, easy to use and provide the same results. They allow us 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.

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 one-dimensional 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 FE method using a formulation based on a four-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 three-dimensional (3D) models. Good agreements are shown.

An 1d-beam approach for both stress analysis and fatigue life prediction of bonded joints

An approach for both stress analysis and fatigue life prediction of bonded joints, based on a 1D-beam model, is presented. Only the adhesive is supposed to fail. The Goland and Reissner framework [1] is extended to unbalanced laminar or monolithic adherends under thermal loads. The J-integral is derived and employed in a modified Paris law, leading to fatigue lives, which are assessed w.r.t. published experimental results [2, 3].

Improving the Fatigue Life of Aeronautical Single-Lap Bolted Joints Thanks to the Hybrid (Bolted/Bonded) Joining Technology

It has been experimentally shown [1-5] the possibility to obtain with hybrid (bolted/bonded) joining technology higher static failure load and a longer fatigue life than the corresponding bolted or bonded joints by using a suitable adhesive. This paper aims at comprehensively showing, by both a simplified analytical approach and an accurate three-dimensional finite element analysis that the application of hybrid (bolted/bonded) joining technology instead of the classical bolted technology allows for a possible improvement of fatigue life. A simplified theoretical analysis is presented to understand the mechanical behaviour of such joints and to provide possible elastic mechanical properties of a suitable adhesive. Then, an accurate three-dimensional Finite Element model is developed to demonstrate the possible benefit on fatigue life.