Torsion Box Research Articles

Designing of Aircraft Reinforced Carbon- Composite Torsion Boxes

At the initial design stage, there is a problem of determining the thicknesses of the load-bearing elements of an aircraft structure made of composite materials. The paper presents the intelligent design of the composite caisson structural strength. Intelligent design is based on the finite element method. The task of optimization used the objective function of minimum mass and setting some constraints including no types of buckling al-lowed. In optimization, the parameter is the thickness of the element, which changes in the process of minimizing the objective function for elements made of PCM by an amount equal to the thickness of the package. The results show the strength margins of spar webs and rib webs of the caisson of vertical empennage torsion box satisfy the safety factor design.

Effect of the Torsion Box Dimensions on Local Stress Distribution and Fatigue Strength Assessment of a Container Ship

The aim of this paper is to estimate the influence of the dimensions of the torsion box (height and width), of a 2400 TEU feeder-class container ship, on local stress distribution and assessment of local fatigue strength by using a numerical approach based on the fatigue limit-state and ultimate limit-state in the midship region. In terms of the fatigue limit-state, the effect of the dimensions of the torsion box is obtained by geometrical modifications, in the connection between the side shell longitudinal stiffeners with the transverse web frame for nine structural details, referring to different arrangements of strengthening elements (brackets and flat bars). The process of comparing the different elements determines the most effective combination. This structural influence on the local stress distribution is assessed, along the longitudinal plates between ordinary stiffeners bounding the perimeter of the torsion box, by calculating the hull girder stresses, local buckling stresses and shear stress distribution induced by vertical and horizontal shear forces, Saint Venant and warping torques, and finally the shear stresses induced by a warping moment. Scantling criteria are obtained allowing for a better design of this very important region in container ships.

Numerical Analysis of the Impact of Geometric Parameters of the Outcuts in the Wing Torsion Box Wall on the Mechanical Properties of the Structure

Numerical Analysis of the Impact of Geometric Parameters of the Outcuts in the Wing Torsion Box Wall on the Mechanical Properties of the Structure

Normal stress flow evaluation in composite aircraft wing sections by strength of material models

The increasingly widespread use of composite materials in structural elements of commercial aircrafts (Airbus 350, Boeing 787), has led to consider the design of wings in composite material. Finite Element (FE) models have been used as a numerical tool for analysis and design, due to the geometrical complexity of these elements, together with the anisotropic nature of the composite material. However, the structural design of elements made of composite laminates using FE models is very expensive in terms of time needed for processing the results and for introducing modifications. The use of simpler Strength of Materials (SM) models has shown to be very efficient for the design of wind turbine blades.The objective of this work is to investigate the feasibility of using these SM models for composite layered aircraft wing design. To this end, a specific model that considers the geometric characteristics of these structural elements (multicellular sections and presence of longitudinal spars and transverse stiffeners) has been developed. The application of the SM model on a specific geometry of a wing torsion box under a given loading condition has allowed us to successfully compare the results, in terms of longitudinal stress flows, with those obtained by a numerical FE model for the same problem, using equivalent discretization.

Effect of Cut-Out Shape on the Stresses in Aircraft Wing Ribs under Aerodynamic Load

Ribs in aircraft wings maintain the airfoil shape of the wing under aerodynamic loads and also support the resulting bending and shear loads that act on the wing. Aircrafts are designed for least weight and hence the wings are made of hollow torsion box and the ribs are designed with cut-outs to reduce the weight of the aircraft structure. These cut-outs on the ribs will lead to higher stresses and stress concentration that can lead to failure of the aircraft structures. The stresses depend on the shape of the cut-outs in the ribs and thus in the present work, the commercial software ANSYS was used to evaluate the stresses on the ribs with different shapes of cut-outs. Four different shapes of cut-out were considered to study the effect of cut-out shape on the stresses in the ribs. It was found that the best shape for the cut-outs on the ribs of wings to reduce weight is elliptical.

Design methodology in transverse webs of the torsional box structure in an ultra large container ship

Container ships has a transverse section in the form of an open profile, making it very sensitive to torsion phenomena. To minimize this effect, a structure known as a torsion box exists, which is subject to high stresses influenced by the fatigue phenomenon and the existence of cut-outs, for the passage of the longitudinal stiffeners, acting as stress concentrators. The aim of this study is to propose a two-stage design methodology to aid designers in satisfying the structural requirements and contribute with to a better understanding of the considered structure. The transverse webs of a torsional box structure are examined by comparing different cut-out geometries from numerical models with different regular load conditions to obtain the variables of the fatigue safety factor through linear regression models. The most appropriate geometry of the torsion box is established in terms of minimum weight, from nonlinear multivariable optimization models.

The Impact of 3D Printing Parameters on the Post-Buckling Behavior of Thin-Walled Structures.

This study presents the results of experimental research and numerical calculations regarding models of a typical torsion box fragment, which is a common thin-walled load-bearing structure used in aviation technology. A fragment of this structure corresponding to the spar wall was made using 3D printing. The examined system was subjected to twisting and underwent post-critical deformation. The research was aimed at determining the influence of the printing direction of the structure’s individual layers on the system stiffness. The experimental phase was supplemented by nonlinear numerical analyses of the models of the studied systems, taking into account the details of the structure mapping using the laminate concept. The purpose of the calculations was to determine the usefulness of the adopted method for modeling the examined structures by assessing the compliance of numerical solutions with the results of the experiment.

Research on BOM multi-view mapping method orient to aircraft in-service data management

In order to establish the framework for aircraft life-cycle data management and ensure the efficient implementation of maintenance information management of in-service aircraft, the characteristics of maintenance information management of civil aircraft in service were analyzed. BOM views were classified, and a BOM multi-view model was constructed. By analyzing the main mapping forms of BOM multi-views, the node types of BOM multi-view were defined, the mapping rules of BOM multi-view model were proposed, and the mapping algorithm of BOM multi-view model was designed and implemented. Finally, method validation was performed by the BOM mapping of 48-section torsion box of a certain aircraft. The results show that, the mapping of EBOM to M-BOM is realized effectively, ensuring the full integration of the information management structure in the in-service maintenance phase and the development phase, and ensuring the consistency of the aircraft life-cycle data management framework.

Effects of high-amplitude low-frequency structural vibrations and machinery sound waves on ultrasonic guided wave propagation for health monitoring of composite aircraft primary structures

A reliable damage diagnostic by ultrasonic guided wave (GW) based structural health monitoring (SHM) can only be achieved if the physical interactions between wave propagation, the SHM system and environmental factors are fully understood. The purpose of this research was to gain knowledge about the effects of high-amplitude low-frequency structural vibrations (HA-LFV) and audible sound waves (SW) on ultrasonic GW propagation. Measurements were performed on a stiffened panel of a full-scale composite torsion box containing barely visible impact damage. Time-domain analysis of the filtered GW signals revealed that the main effect of HA-LFV was the presence of coherent noise. This was interpreted as the consequence of superposition of multiple dispersive wave groups produced by mode conversion at the moment of reflection on the corrugated panel surfaces during propagation. It was also observed that the coherent noise amplitude depends on the amplitude of the HA-LFV, and on the ratio between the HA-LFV frequency and the ultrasonic excitation frequency. These relationships can potentially be explored for the development of a HA-LFV compensation mechanism to enable in-service GW based damage diagnostics. In contrast, GW signals in the cases with audible SW present were almost unaffected. It was concluded that there is strong evidence supporting the hypothesis that ultrasonic GW propagation with HA-LFV effects can be analysed under the assumption of a permanently corrugated structure.

Dimensional precision controlling on out-of-plane welding distortion of major structures in fabrication of ultra large container ship with 20000TEU

Ultra large container ship as an essential role during international trade, is required for precision fabrication due to highly efficient TEU loading and unloading. In this study, two major structures, so called watertight transverse bulkhead structure and torsion box structure of ultra large container with 20000TEU were examined for out-of-plane welding distortion prediction and mitigation with measurement and computational analysis. Based on the welding inherent deformation theory, typical welded joints of two major structures were systematically classified with the different material, thickness, welding condition and joining form; and the relationships between welding heat input and inherent deformations were also presented. Elastic FE analysis with shell elements model and welding inherent deformation as input loading was employed for welding distortion prediction. Not only the distributions but also the magnitudes of predicted out-of-plane welding distortions of considered major structures have a good agreement comparing to the measurements. Furthermore, welding sequence influence was considered for dimensional precision controlling during the watertight transverse bulkhead structure fabrication, and welding groove optimization of thick plate was examined for out-of-plane welding distortion mitigation during the torsion box structure fabrication. Computational results show that welding distortions of both ship block structures can be significantly reduced for requirement of fabrication precision.

The structural optimum design of laminated slender beam section with arbitrary material distribution using a genetic algorithm

In this paper, a study on optimum design methodology of a section structure of a composite material rotor blade using genetic algorithm is conducted, in order to calculate repetitive optimum design, analysis of strength, fatigue and vibration on blade section. In the analysis, the minimum mass of the rotor blade was defined as objective function; stress damage index, center of mass on blade section and fatigue life of blade were set as constraints. By applying genetic algorithm, laminate angle and thickness of skin, thickness, location and width of torsion box were established as design variables; the optimum design methodology on section structure of the composite material rotor blade was validated. The integrated design program of the section structure of the composite material rotor blade based on this study deals with designing the optimal rotor blade section which meets the design load and constraints given by the random position of rotor blade. By using blade’s section design variables derived from this, it can be facilitated for basic information on detailed design of rotor blade.

Educational Software for Stress Analysis of Idealized Closed Thin Walled Sections

Aerospace structures are typically semi-monocoque structures that are made up of thin-walled closed section reinforced with stiffeners. Stress analysis of such closed thin-walled structures which are statically indeterminate is tedious and time consuming. An educational software which can aid students in carrying out stress analysis of such idealized thin-walled closed sections has been developed. The software enables students to select different types of wing torsion box sections with stiffeners, which may be subjected to bending, shear or torsional loads and evaluate the resulting stresses on it. The software allows the student to idealize a selected twin spar unsymmetrical wing section with multiple booms under multiple loads. Results from this software have been validated against the results in the literature. The software has been developed using MATLAB with graphical user interface (GUI) which is very user friendly.

A level-set-based strategy for thickness optimization of blended composite structures

An approach is presented for the thickness optimization of stiffened composite skins, which guarantees the continuity (blending) of plies over all individual panels. To fulfill design guidelines with respect to symmetry, covering ply, disorientation, percentage rule, balance, and contiguity of the layup, first a stacking sequence table is generated. Next, a level-set gradient-based method is introduced for the global optimization of the location of ply drops. The method aims at turning the discrete optimization associated with the integer number of plies into a continuous problem. It gives the optimum thickness distribution over the structure in relation to a specific stacking sequence table. The developed method is verified by application to the well-known 18-panel Horseshoe Problem. Subsequently, the proposed method is applied to the optimization of a composite stiffened skin of a wing torsion box. The problem objective is mass minimization and the constraint is local buckling.

An End-To-End Airframe Structural System Design

Design of aerospace reusable launch vehicle (RLV) structures offers diverse challenges due to stringent specifications in geometry, structural mass, integrity for thermal protection system and interfaces with propulsion, avionics and power systems. Airframe structures for RLVs should cater to the specified strength, stiffness and stability, and meet the functional and integration requirements of aerospace vehicles. To address these challenges, an integrated design cycle comprising load estimation, layout design, torsion box analysis and sizing of structural components is devised and presented. Verification of structural design is done by structural and thermo-structural analyses of the integrated airframe. Qualification of the airframe by integrated airframe test, thermo-structural test and acoustic test is also discussed.

Sensitivity Algorithm as a Solution of an Inverse Strength Problem Applied to Thin-Walled Structures

The problem of identifying rigidities in stiffeners of a four-stiffener torsion box operating in tension–compression under the action of an external load is considered. An iterative approach is proposed using a sensitivity function and a sensitivity matrix.

Multi-objective multi-laminate design and optimization of a Carbon Fibre Composite wing torsion box using evolutionary algorithm

The present study aims to minimize the weight of multi-laminate aerospace structures by a classical Genetic Algorithm (GA) interfaced with a CAE solver. The structural weight minimization is a multi-objective optimization problem subjected to fulfilling of strength and stiffness design requirements as well. The desired fitness function connects the multi-objective design requirements to form a single-objective function by using carefully chosen scaling factors and a weight vector to get a near optimal solution. The scaling factors normalize and the weight vector prioritizes the objective functions. The weight vector selection was based on a posteriori articulation, after obtaining a series of Pareto fronts by 3D hull plot of strength, stiffness and assembly weight data points. During the optimization, the algorithm does an intelligent laminate selection based on static strength and alters the ply orientations and thickness of laminae for faster convergence. The study further brings out the influence of mutation percentage on convergence. The optimization procedure on a transport aircraft wing torsion box has showed 29% weight reduction compared to an initial quasi-isotropic laminated structure and 54% with respect to the metallic structure.

NiTi SMA Wires Coupled with Kevlar Fabric: a Real Application of an Innovative Aircraft LE Slat System in SMAHC Material

This paper investigates experimentally and numerically the response of a smart hybrid thermoplastic aircraft slat system subjected to a short-duration and high-frequency event like a birdstrike. The focus of the paper is to exploit the ability that superelastic shape memory alloys have to absorb and dissipate energy compared to conventional composite structures. The final objective of the work is to develop an innovative thermoplastic wing leading edge slat able to resist to an impact of 4-lb (1.8 kg) bird at speed of 350 kts (132 m/s), as requested by the aeronautical requirements. Aircraft leading edges must be certified for a proven level of bird impact resistance. In particular, the main structural requirement is to protect the torsion box and control devices from any significant damage caused by birdstrike in order to allow the aircraft to land safely. A clear increase of the composites toughness and higher absorbed energy levels before failure were also observed. This is due to the fact that SMA wires can absorb kinetic energy during the impact due to their remarkably large failure and recoverable strain and to their superelastic and hysteretic behaviour. The activities have been performed within the European Project COALESCE “Cost Efficient Advanced Leading Edge Structure”, funded by the Seventh Framework Program Theme 7 Transport (incl. Aeronautics).

Study of cross-correlation signals in a data-driven approach for damage classification in aircraft wings

This paper discusses, experimental results of classifying several mass adding in a wing aircraft structure, using cross-correlated piezoelectric signals, represented by principal components. Piezoelectric signals are applied and recorded at specific points of the structure under analysis. Then, statistical features are obtained by means of principal component analysis to the correlation between excitation and response signals. Unsupervised learning is implemented to the reduced feature space, in order to identify clusters of damaged cases. The main result of this paper is the advantage resulting from using cross-correlated signals, evaluated through the performance of clustering indexes. Experimental data are collected from two test structures: i.) A turbine blade of a commercial aircraft and ii.) The skin panel of the torsion box of a wing. Damages are induced adding masses at different locations of the wing section surface. The results obtained show the effectiveness of the methodology to distinguish between different damage cases.

A technique of computer-aided synthesizing a finite element model of wing center section and outer wing torsion box joint for a transport aircraft

A technique of synthesizing the finite element model of the flange joint of the outer wing torsion box with the wing center section for a transport aircraft is presented. The technique is based on the functional decomposition principle, in which the general model of wing torsion box is synthesized from the separate substructure models including the flange joint. It has been shown that the manual input is significantly reduced, when the computer-aided synthesis is applied. This made it possible to cut time of synthesis and decrease the probability of error occurrence.

복합재 로터 블레이드 단면 이산최적설계

In this paper, the optimal design of composite rotor blade cross-section is performed using a genetic algorithm. Skin thickness, torsion box thickness and skin lay-up angle are adopted as discrete design variables. The position and width of a torsion box are considered as continuous variables. An object function of optimal design is to minimize the mass of a rotor blade, and constraints are failure index, center mass, natural frequency and blade minimum mass per unit length. Finally, design variables such as the thickness and lay-up angles of a skin, and the thickness, position and width of a torsion box are determined by using an in-house program developed for the optimal design of rotor blade cross-section.