A finite element stress analysis of aircraft bolted joints loaded in tension

Abstract

Mechanically fastened joints are the most common method of connecting structural components in aerospace structures. The skinto-spar/rib connections in a wing structure and the wing-to-fuselage connection are typical examples of bolted joints in aircraft primary structures. It is well-recognised that bolt fasteners can clamp joint parts together well and show a good load carrying capability. In this respect, a number of authors (1)(2)(3)(4) have detailed the design methods for bolted joints mostly under static loading conditions. However, drilling fastener holes in members inherently introduces a stress concentration near the hole and reduces the load carrying cross sectional area. A drilling process may also cause a rough surface finish in the bore of the fastener hole which is prone to fatigue crack initiations under cyclic loads.Aircraft structures are primarily constructed from high strength light alloys and composites as their low density provides optimum strength-to-weight ratio aerospace materials. Since safety is of paramount importance in aerospace vehicles, several investigations have been conducted with the aim to optimise the design of structural bolted joints (metallic and composites) so that catastrophic failure during the flight can be prevented (5)(6)(7)(8)(9)(10)(11) .A bolted joint is most commonly preloaded through an initial torque. When the torque is applied to the nut, the bolt is axially ABSTRACT Accurate stress and strain analysis in bolted joints is of considerable interest in order to design more efficient and safer aerospace structural elements. In this paper, a finite element modelling of aluminium alloy 7075-T6 bolted plates, which are extensively used in aircraft structures, is discussed. The ANSYS Finite Element (FE) package was used for modelling the joint and estimating the stresses and strains created in the joint due to initial clamping forces and subsequent longitudinal tensile loadings. A double-lap bolted joint with a single bolt and nut was considered in the study. A three-dimensional (3D) finite element model of the joint was generated, and then subjected to three different simulated clamping forces followed by different levels of longitudinal tensile load. 3D surface-to-surface contact elements were employed to model the contact between the various components of the bolted joint. Friction effects were considered in the numerical analysis; and moreover, the clearance between the bolt and the plates was simulated in the model. FE results revealed beneficial compressive stresses near the hole edge as a result of applying the clamping. It was found that a higher clamping force can significantly decrease the magnitude of the resultant tensile stress at the hole edge and also bearing stress in the joint when subjected to the longitudinal tensile load.

Improving fretting fatigue behaviour of Al 7075-T6 bolted plates using electroless Ni–P coatings

“…A review of the literature generally confirms that the bolt clamping force can significantly increase the fatigue life of the joints [7][8][9]. Preliminary work showed the presence of longitudinal compressive stresses around Al 7075-T6 bolt-filled holes with localised maximum magnitudes at the critical edge of the hole as a result of the bolt clamping force [10,11]. The compressive stress in the plate clearly reduced the net effect of the damaging cyclic longitudinal tensile stress which causes fatigue crack initiations and propagation due to the applied loads.…”

A new approach for evaluating fatigue lives of multi-fastener mechanical joints based on a nominal stress concept and minimal datasets

“…With aid of Equation (15) or (18) and the level and number of the above load cycles, the level and number of nominal stress cycle for the first row of rivet hole are evaluated as:…”

“…Local stress/strain state around the fastener holes can be determined by using the strain-gauge measurement [7,13] . FE analysis [7,14,15] is also important for understanding fatigue characteristics and failure mechanism of mechanically fastened joints. However, due to the interaction between friction, contact force and secondary bending of joined members, it is difficult to accurately obtain local stress/strain fields around the fastener holes.…”

Partially open crack model for leakage pressure analysis of bolted metal-to-metal flange

“…Some of these studies have focused on the tightening process [36] and the bolt-up sequence of a flanged connection [37,53]. The stiffness of bolted joints was investigated in [54][55][56][57][58] and the bolt self-loosening was examined in [59][60][61]. Recent analyses of flanged joints have proposed FE simulations to investigate the contact pressure distributions between the two flange mating surfaces [2,10,62].…”