Wing Box Assembly Research Articles

Experimental and virtual testing of a composite-aluminium aircraft wingbox under thermal loading

Nowadays, carbon fibre composites are increasingly being used in aircraft which, in turn, has lead to carbon-metallic bolted assemblies. The large difference in the thermal expansion coefficient between these materials, and the considerable temperature excursions that occur during aircraft operations, lead to thermal stresses that may trigger different forms of local damage. This complex phenomenon can affect the integrity of large primary structural components such as an aircraft wingbox. In this work, we perform an experimental campaign and a finite element simulation of a full hybrid carbon-aluminium wingbox assembly. The structure contains two rib designs: a baseline rib and a new stiffer rib design with the objective of improving the structural behaviour. The wingbox was subjected to thermal loading. The numerical model is validated against the experimental data and employed to study additional phenomena in detail that cannot be analysed directly from the experiments. The model is able to reproduce reasonably well the experimental data, and demonstrates that thermal loading cannot be neglected since it leads to considerable stresses, particularly in the metallic ribs. Moreover, the stiffer rib design provides improved behaviour mainly at the bolted joints with the spar.

Progressive Failure Analysis of Composite/Aluminum Riveted Joints Subjected to Pull-Through Loading

Out-of-plane mechanical properties of the riveted joints restrict the performance of the wing box assembly of airplane. It is necessary to investigate the pull-through performance of the composite/metal riveted joints in order to guide the riveting design and ensure the safety of the wing box assembly. The progressive failure mechanism of composite/aluminum riveted joint subjected to pull-through loading was investigated by experiments and finite element method. A progressive damage model based on the Hashin-type criteria and zero-thickness cohesive zone method was developed by VUMAT subroutine, which was validated by both open-hole tensile test and three-point bending test. Predicted load-displacement response, failure modes and damage propagation were analysed and compared with the results of the pull-through tests. There are 4 obvious characteristic stages on the load-displacement curve of the pull-through test and that of the finite element model: first load take-up stage, damage stage, second load take-up stage and failure stage. Relative error of stiffness, first load peak and second load peak between finite element method and experiments were 8.1%, − 3.3% and 10.6%, respectively. It was found that the specimen was mainly broken by rivet-penetration fracture and delamination of plies of the composite laminate. And the material within the scope of the rivet head is more dangerous with more serious tensile damages than other regions, especially for 90° plies. This study proposes a numerical method for damage prediction and reveals the progressive failure mechanism of the hybrid material riveted joints subjected to the pull-through loading.

A pre-assembly analysis technology of aircraft components based on measured data

Compared with the traditional assembly simulation based on theoretical models, this paper proposes a new pre-assembly analysis method of aircraft components based on measured data. Specifically, before the actual assembly of the product, digital measurement methods are used to obtain the measured data of the target features of the manufactured parts. Subsequently, the measured data is processed and reconstructed to obtain the actual geometric shape of the part, based on which the product is pre-assembled and analyzed to evaluate the assembly quality in advance. Finally, according to the analysis results, the assembly process is adjusted in time to reduce assembly trial and error and improve assembly quality and efficiency. This article systematically introduces the implementation process of the method, which is illustrated through two cases study on aircraft wing box assembly process. Experimental results demonstrate the feasibility and effectiveness of this proposed method for assembly of large aircraft components.

Simulation and experimental testing of a bolted carbon-aluminium hybrid wingbox assembly under thermal loads

On the last decades, the aeronatical industry has increased the use of Carbon Fibre Reinforced Polymer matrix composites (CFRP), and at the same time, has kept the use of conventional metals. This has led to the presence of hybrid assemblies in the wingbox, fuselage, etc. Due to their high stiffness and strength, as well as the ease to dissasemble and repair, these assemblies are usually bolted. During its usage, an aircraft is subjected to large thermal jumps (the temperature difference between a landed aircraft and a flying one can reach 140 ºC). Because of the presence of hybrid bolted joints, the materials of the joint undergo different thermal expansion/contraction, which cause significant thermal stresses altering the mechanical behaviour of the joint. Framed in the aeronautical Clean Sky 2 project ‘INNOHYBOX’, this work studies the behaviour of hybrid bolted joints subjected to thermal loads, both numerically and experimentally, following a pyramidal approach. At the coupon level, a hybrid carbon-aluminium single-lap shear specimen with one bolt was used to comprehend and characterise its behaviour under thermal loads. At the substructural level, a subcomponent representative of a wingbox was tested under thermal conditions. Finally, a full wingbox was tested. Furthermore, a computationally efficient finite element model was developed to simulate the complex behaviour of these type of joints without comprimsing the computational cost. The numerical predictions correlate favourably against the experimental data.

Enhanced Pose Adjustment System for Wing-Box Assembly in Large Aircraft Manufacturing

Abstract Strict quality requirements in aircraft manufacturing demand high-accuracy pose adjustment systems. However, the pose alignment process of a large complex structure is also affected by thermal and gravity deformations to a great extent. Even though the pose adjustment system passes accuracy verification, the pose of the large complex structure remains challenging to smoothly and efficiently converge to the desired pose. To solve this problem, we developed a pose adjustment system enhanced by integrating physical simulation for the wing-box assembly of a large aircraft. First, the development of the pose adjustment system, which is the base of the digital pose alignment of a large aircraft’s outer wing panel, is demonstrated. Then, pose alignment principles of duplex and multiple assembly objects based on the best-fit strategy are successively explored. After that, contribution analysis is conducted for nonideal pose alignment. Immediately following, influences of thermal and gravity deformations simultaneously coexisting for the pose alignment are discussed. Finally, a physical simulation-assisted pose alignment method is developed considering multisource errors, which uses the finite element analysis to integrate temperature fluctuation and gravity field effects. Compared with a conventional digital pose adjustment system driven by the classical best-fit, deviations of the key characteristic points significantly decreased despite the impacts of thermal and gravity deformations. The enhanced pose adjustment system has been applied to large aircraft wing-box assembly. It provides an improved understanding of the pose alignment of large-scale complex structures.

Pose and shape error control in automated machining of fastener holes for composite/metal wing-box assembly

Composite/metal wing-boxes are hard to drill by the conventional drilling method. In this paper, an automated machine-tool-based machining system equipped with a multifunctional end-effector is developed for helical milling, as well as circular and ellipsoidal dimple drilling of composite/metal wing-boxes. The system constitution, the control system, and the application software of the machining system are demonstrated. In aircraft manufacturing, the out-of-tolerance pose and shape of fastener holes deteriorate an aircraft’s strength and fatigue performances. Thus, a multi-sensor information fusion and integration architecture is built for enhanced pose and shape accuracy of machined fastener holes. The relative pose error of the end-effector and an aerostructure is analyzed. A coarse-to-fine control method by the touch probe and LDSs is applied for controlling the error. The fastener holes’ shape errors are controlled through the elaborate structure design and multi-sensor-based closed-loop motion control of the end-effector. Experiments performed on the machining system show that the positioning errors, hole diameter errors, dimple depth errors, and ellipsoidal dimple shape can fulfill the wing-box assembly requirements.

Static test of a variable stiffness thermoplastic composite wingbox under shear, bending and torsion

AbstractAutomated manufacturing of thermoplastic composites has found increased interest in aerospace applications over the past three decades because of its great potential in low-cost, high rate, repeatable production of high performance composite structures. Experimental validation is a key element in the development of structures made using this emerging technology. In this work, a $750\times640\times240$ mm variable-stiffness unitised integrated-stiffener out-of-autoclave thermoplastic composite wingbox is tested for a combined shear-bending-torsion induced buckling load. The wingbox is manufactured by in-situ consolidation using a laser-assisted automated tape placement technique. It is made and tested as a demonstrator section located at 85% of the wing semi-span of a B-737/A320 sized aircraft. A bespoke in-house test rig and two aluminium dummy wingboxes are also designed and manufactured for testing the wingbox assembly which spans more than 3m. Prior to testing, the wingbox assembly and the test rig were analysed using a high fidelity finite element method to minimise the failure risk due to the applied load case. The experimental test results of the wingbox are also compared with the predictions made by a numerical study performed by nonlinear finite element analysis showing less than 5% difference in load-displacement behaviour and buckling load and full agreement in predicting the buckling mode shape.

Shimming design and optimal selection for non-uniform gaps in wing assembly

PurposeThis paper aims to provide a shimming method based on scanned data and finite element analysis (FEA) for a wing box assembly involving non-uniform gaps. The effort of the present work is to deal with gap compensation problem using hybrid shims composed of solid and liquid forms.Design/methodology/approachFirst, the assembly gaps of the mating components are calculated based on the scanned surfaces. The local gap region is extracted by the seed point and region growth algorithm from the scattered point cloud. Second, with the constraints of hole margin, gap space and shim specification, the optional shimming schemes are designed by the exhaustive searching method. Finally, the three-dimensional model of the real component is reconstructed based on the reverse engineering techniques, such as section lines and sweeping. Using FEA software ABAQUS, the stress distribution and damage status of the joints under tensile load are obtained for optimal scheme selection.FindingsWith the scanned mating surfaces, the non-uniform gaps are digitally evaluated with accurate measurement and good visualization. By filling the hybrid shims in the assembly gaps, the joint structures possess similar load capacity but stronger initial stiffness compared to the custom-shimmed structures.Practical implicationsThis method has been tested with the interface data of a wing tip, and the results have shown good efficiency and automation of the shimming process.Originality/valueThe proposed method can decrease the manufacturing cost of shims, shorten the shimming process cycle and improve the assembly efficiency.

Variation Analysis of Automated Wing Box Assembly

Manufacturing process variability is a major issue of concern in high value industries. Manufacturing small batches and in some cases batches of one is a very expensive process with specific requirements for manufacturing operations, tooling and fixturing and their level of automation and informatics provision. The automation targets cost reduction and a counterbalancing of the ever lower numbers of skilled shop floor workers. However, these small series typically are products that contain complex and compliant parts, and often also a high number of parts and components. The automation of this type of low-volume high-value production can be a daunting task.Each process has its own key parameters that are required to be within a certain tolerance band in order to ensure product quality, such as e.g. the dimensions and location of assembly mating features. Dimensional quality assurance is typically done with in-process measurement, or the measurement of certain key characteristics (KCs) in the current setup, but a special setup may have to be used in a measurement-only step in the manufacturing process. Each manufacturing stage introduces errors stemming from uncertainties in the fixturing, used processes etc. These errors will propagate in downstream stages and can even worsen errors introduced in the latter stages.The paper presents a new generic methodology for the use of stream of variation (SoV) analysis within a Smart Factory environment such as the Evolvable Assembly Systems (EAS) framework. The research is demonstrated using a simplified case study of one of EAS demonstrators for an aircraft wing box assembly. The wing box assembly and its KCs are described using formal representation. The SoV model is applied to model and simulate the assembly process. The simulation results are then analysed to predict, control and minimise the error propagation coming from uncertainties in process and equipment.

Automatic Temporary Fastener Installation System for Wingbox Assembly

Automatic Temporary Fastener Installation System for Wingbox Assembly

Tolerance simulation of composite wingbox assembly considering preloading-modified distribution

Purpose Tolerance simulation’s reliability depends on the concordance between the input probability distribution and the real variation. The prescribed clamp force introduced changes in parts’ variation, which should be reflected in the input probability distribution for the tolerance simulation. The paper aims to present a tolerance analysis process of the composite wingbox assembly considering the preloading-modified distribution and especially focuses on the spring-in deviation of the thin-walled C-section composite beam (TC2B). Design/methodology/approach Based on finite element analysis model of TC2B, the preloading-modified probability distribution function (PDF) of the spring-in deviation is obtained. Thickness variations of the TC2B are obtained from the data of the downscaled composite wingbox. These variations are input to the computer-aided tolerance tools, and the final assembly variations are obtained. The assembly of the downscaled wingbox illustrates the effect of preloading on the probability distribution of the spring-in deviation. Findings The results have shown that the final assembly variations estimated with the modified probability distribution is more reliable than the variation of the initial normal distribution. Originality/value The tolerance simulation work presented in the paper will enhance the understanding of the composite parts assembling with spring-in deviations, improve the chance to choose assembling processes that allow specifications to be met and help with tolerance allocation in composites assembly.

Development of Automated Flexible Tooling as Enabler in Wing Box Assembly

Flexible tooling has been a focal point of investigation for various industries with an emphasis on cost and time effectiveness. Previous research has shown that when combined with the general requirements of tooling such as rigidness and repeatability, the implementation of flexibility can be a very daunting task. Therefore, LOCOMACHS (Low Cost Manufacturing and Assembly of Composite and Hybrid Structures) project has dedicated a work package for the creation of an automated flexible tooling to meet the demands of future aerospace production. The work package focuses on a creation of a tooling technology that can facilitate the process requirements of an automated wing-assembly by using flexible tooling and intelligence support from a force sensor. Hence, this paper aims to present the framework for automated flexible tooling development and results on a hexapod fixture as a case study.

An Assembly Simulation Optimization Method Based on View Transformation

In order to improve showing effect of the aircraft assembly simulation, a new assembly process simulation optimization method was proposed with combining evaluation of viewpoints with view transformation. First, viewpoints evaluation principle was put forward according to assembly simulation features; then a new view coordinate system was calculated based on the view coordinate system transformation matrix by integrating the direction of assembly paths with the viewpoints evaluation principle; finally, entire optimized process of assembly simulation was analyzed. Efficiency of this method was verified by comparing the result of the optimized wing box assembly simulation with the one which had not been optimized.

Modelling and analysis of Airbus wingbox assembly

The production of aircraft involves the assembly of large, complex, and deformable components using mechanical fasteners. Assembly problems associated with dimensional variations consistently occur during part-to-part assembly. An investigation of the prediction of the geometric deformation on the next joining location with respect to the present joining location is presented. The direct influence of bolt tightening on the next assembly point is studied using the finite element method (FEM). A case study of the displacement between each foot from the rib of the wingbox with actual data gathered at the Airbus assembly factory is conducted using the FEM and validated on an experimental research test rig. General results obtained from the study indicate that displacement of the next rib foot does occur when assembly of the current rib foot is performed. However, bolt tightening does not significantly contribute to the overall displacement of the rib feet.

Prediction of geometrical variations in Airbus wingbox assembly

PurposeThis paper aims to present a method for predicting dimensional variation in assembly processes of a wingbox structure concentrating on the assembly of skin panels to rib feet.Design/methodology/approachFinite element modelling and experimental tests are conducted on the rib structure based on the site measurement gathered from the Airbus assembly factory.FindingsThe results have shown that the simulated model has the capability of predicting to an acceptable degree of accuracy the overall geometrical variations of the ribs and skin panels, as well as the positional variations of each individual rib foot.Originality/valueThe authors believe that no previous research has offered a similar prediction method for large aerostructures.

Design search and optimization in aerospace engineering

In this paper, we take a design-led perspective on the use of computational tools in the aerospace sector. We briefly review the current state-of-the-art in design search and optimization (DSO) as applied to problems from aerospace engineering, focusing on those problems that make heavy use of computational fluid dynamics (CFD). This ranges over issues of representation, optimization problem formulation and computational modelling. We then follow this with a multi-objective, multi-disciplinary example of DSO applied to civil aircraft wing design, an area where this kind of approach is becoming essential for companies to maintain their competitive edge. Our example considers the structure and weight of a transonic civil transport wing, its aerodynamic performance at cruise speed and its manufacturing costs. The goals are low drag and cost while holding weight and structural performance at acceptable levels. The constraints and performance metrics are modelled by a linked series of analysis codes, the most expensive of which is a CFD analysis of the aerodynamics using an Euler code with coupled boundary layer model. Structural strength and weight are assessed using semi-empirical schemes based on typical airframe company practice. Costing is carried out using a newly developed generative approach based on a hierarchical decomposition of the key structural elements of a typical machined and bolted wing-box assembly. To carry out the DSO process in the face of multiple competing goals, a recently developed multi-objective probability of improvement formulation is invoked along with stochastic process response surface models (Krigs). This approach both mitigates the significant run times involved in CFD computation and also provides an elegant way of balancing competing goals while still allowing the deployment of the whole range of single objective optimizers commonly available to design teams.

Automatic wing box assembly developments

A demonstrator cell has been developed at Airbus UK for building large aircraft wing box assemblies by a partnership of six companies partly funded under the UK government’s civil aviation research and demonstration (CARAD) programme. The cell has shown the feasibility of assembling the three principle components of a wing box automatically using robotic technology. It includes handling 6m high ribs and placing them between the leading and trailing edge spars and skin wrapping and fastening. Two robot systems were developed for external and internal work, employing a combination of standard robot arms and specials fitted with vision sensing and drilling and fastening tooling. Software tools were used to plan, simulate and programme the cell and also to develop a full scaled‐up version of the cell for studying the potential of the systems employed for future applications in production.