Aircraft Structural Components Research Articles

Rapid design generation and multifidelity analysis of aircraft structures

There is a huge demand for automation in geometry creation within aerospace industry for multidisciplinary design optimization. Currently, every model is being built independently for each discipline. Thus, any changes in design parameters require updates on all of the models, which is inefficient, time-consuming and prone to deficiencies. A parametric software called ‘Engineering Sketch Pad’ (ESP) is used to resolve this issue. It provides the user with the ability to generate new design concepts through modifying a text file. Another highly demanded feature is data transfer between different fidelity models automatically. The need to transfer loads and/or deformations data from one model to another in order to perform the multi-fidelity analysis. In this project, the load is transferred from the stick model to ribs of the wing to perform static optimization and deformation data from ribs and spars is transferred to stiffened panels to perform buckling optimization. This paper focuses on a novel concept of single click weight optimization of aircraft structural parts and components using a parametric design modeler (i.e., ESP) and the analysis solver (i.e., Nastran). The interface code has been done via a C-program.

TECHNICAL CONDITION EVALUATION OF CONSTRUCTION MATERIALS OF A TURBO-REFRIGERATION UNIT PARTS OF AN AIRCRAFT AIR CONDITIONING SYSTEM BY CHANGING THE LEVEL OF RESIDUAL STRESSES

One of the frequent causes of aviation incidents and accidents is the failure of technical equipment and the destruction of aircraft (AC) constructions resulting from unacceptable deformations and structural destruction of the parts operating under high mechanical loads. Operation of parts, assemblies and units of aeronautical equipment in the most typical cases does not allow their plastic strain. Thus, in accordance with the airworthiness standards, aeronautical equipment should not be used under the conditions leading to the occurrence of dangerous permanent yielding and fatigue damage to the material in its structures. The probability of these negative factors is determined by the stress condition of the aircraft structural component material during operation. An important factor that determines the stress condition as well as the technical condition of an object of technology is residual stresses, most often available in the material of the part. In particular, the summation of the residual stresses with the stresses of the operating load can lead to the exceedance of the critical values stress condition indicators, for example, the fatigue margin or the yield point of the material. In view of this, the development of new technologies that will provide information on the actual technical condition of the structure of each aircraft during its operation considering residual stresses is a critical task. The article describes a possible approach to evaluating and predicting the technical condition of the structural materials of assemblies and units operating under cyclic loading based on determining the change of residual stresses level on the surface of the parts during their operation. As a method for determining residual stresses, the X-ray diffractometric method was chosen, as it is characterized by high accuracy and reliability of the results obtained. The developed approach was tested on the components of the aircraft air conditioning system (turbo-refrigeration unit). The results of evaluating the technical condition of the parts conform to the facts of their operational damage. In these circumstances, although the proposed approach cannot currently be used directly on board an aircraft for continuous monitoring of the technical condition of aircraft structural materials, however, its development seems to the authors to be promising for these purposes.

The influence of flank lands of end mills on machined surface in milling in the context of chatter

Reliability and cost-effectiveness are the main requirements for aircraft materials and structure components used in manufacturing of aviation engines. This defines the requirements for them. The majority of components are thin-walled and made of hard-to-machine materials: nickel and titanium alloys, heat-resistant steels. The use of such materials places restrictions on the use of certain cutting modes. During rough milling and semi-finish milling with end-mill cutters chatter occur. The vibrations deteriorate the machined surface of engine parts, tool life decreases and machine units are worn out. Different process technologies and constructive features of tools are used to decrease the intensity of chatter. The use of end mills having lands has yielded mixed results. The influence of land usage on surface condition and decrease of chatter in up-milling and down milling has been studied. The mechanism of influence on machined surface and chatter in up-milling and down milling has been determined. At the experimental stand studies were carried out on its effect on changes in the laws of motion of detail during the cutting process. It has been shown that in up-milling and down milling, a land fl = 0.05 mm wide on the rear surface along the cutting tooth reduces the intensity of chatter has been shown. The results can be used to select the feed direction to reduce the intensity of chatter when milling thin-walled parts with end mills with a land on the rear surface along the cutting edges.

Influence of cutting conditions in drilling of CFRP/Al stacked composites

Composite laminates are gorgeous for several applications such as aerospace and aircraft structural components due to their excellent properties. Typically, mechanical drilling has been important machining operation for components made of composite laminates. Nevertheless, laminated composites are considered as hard-to-machine material which results in low drilling efficiency and drilling-induced delamination which is undesirable. This paper reviews the experiments during drilling of CFRP/Al stacked and sandwich composites. The machinability facets of these material stacks has been generally used in aerospace applications, it has been studied based on impact of drill material, drill geometries, and drilling process parameters such as speed and feed. Composite material requires high spindle speed and low feed rate, whereas drilling aluminum requires stability between speedsto feed rate. The review reports essential results and gap in the collected literature for CFRP/Al stacked and sandwich composites. A compromise between several parameters is required during drilling of multi-material stacks. The problems and solutions allied to drilling of multi-material stacks are deliberated and the directions in which the research on drilling of multi-materials may be carried out are suggested in this paper. It is intended to assist readers to acquire a thorough view on mechanical drilling of laminated composite.

Comparison of Machine Learning Algorithms for Structure State Prediction in Operational Load Monitoring.

The aim of operational load monitoring is to make predictions about the remaining usability time of structures, which is extremely useful in aerospace industry where in-service life of aircraft structural components can be maximized, taking into account safety. In order to make such predictions, strain sensors are mounted to the structure, from which data are acquired during operational time. This allows to determine how many load cycles has the structure withstood so far. Continuous monitoring of the strain distribution of the whole structure can be complicated due to vicissitude nature of the loads. Sensors should be mounted in places where stress and strain accumulations occur, and due to experiencing variable loads, the number of required sensors may be high. In this work, different machine learning and artificial intelligence algorithms are implemented to predict the current safety factor of the structure in its most stressed point, based on relatively low number of strain measurements. Adaptive neuro-fuzzy inference systems (ANFIS), support-vector machines (SVM) and Gaussian processes for machine learning (GPML) are trained with simulation data, and their effectiveness is measured using data obtained from experiments. The proposed methods are compared to the earlier work where artificial neural networks (ANN) were proven to be efficiently used for reduction of the number of sensors in operational load monitoring processes. A numerical comparison of accuracy and computational time (taking into account possible real-time applications) between all considered methods is provided.

Covid-19 Pandemic: Need to Exercise Caution While Using Hypochlorite Sanitizer in Manufacturing Industries.

World is fighting Covid-19 pandemic since beginning of the year 2020. To prevent spread of Covid-19 disease, sanitization of workplaces using sodium hypochlorite (NaOCl) disinfectant is one of the several precautionary steps that are followed currently. In this letter, I share an experience wherein regular spraying of NaOCl solution in metal forming section of an organization led to development of corrosion damage and rejection of a large number of aircraft structural components made of Al-2024 alloy sheet material.

The influence of the process parameters on the surface integrity during peripheral milling of Ti-6Al-4V

Abstract The titanium alloy Ti-6Al-4V represents a significant metal portion of state-of-the-art aircraft structural and engine components. When critical structural components in the aerospace industry are manufactured with the objective to reach high reliability levels, surface integrity is one of the most relevant parameters used for evaluating the quality of machined surfaces. The residual stresses and the surface alteration induced by machining titanium alloys are critical due to safety and sustainability issues. In this paper, a series of end milling experiments was conducted to comprehensively characterize the surface integrity at various milling conditions. The experimental results have shown that the surface roughness value increases with the feed and the cutting velocity. However, the residual stress state in the surface layer zone is influenced by the variation of the process control variables. Here, compressive residual stresses occur both in cutting and in feed direction. In addition, a new type of sensory tool holder is presented, which should enable the indirect measurement of residual stresses during the milling process.

Comparative Study for Inspection Planning of Aircraft Structural Components

In the aircraft operation, the metallic airframes are usually exposed to the extreme loading conditions during the flights due to which the risk of failure should be assessed and held to an allowed level to prevent the associated loss. If the components are inspectable, the components should be inspected routinely so that the fatigue damage can be detected before failure, which usually requires non-destructive inspection (NDI) techniques to evaluate the damage growth during the maintenance action. There have been several methods to determine the inspection plan in the aircraft industry for this purpose. In this study, four methods: Aircraft Structural Integrity Program (ASIP), Reliability Centered Maintenance Analysis (RCMA), Modified RCMA and Stochastic Life APproach (SLAP), are selected to evaluate the performance in comparative manner for a couple of crack growth problems with the aim to help the maintenance planning engineers select their own inspection plan properly based on the performance of each method. The methods are briefly reviewed, implemented, and examined in comparison for the fatigue test data of the fastener hole specimen under an aircraft load spectrum.

Investigation on the cutting responses of CFRP/Ti stacks: With special emphasis on the effects of drilling sequences

The compound CFRP/Ti stacks, as an advanced engineering structure, have been commonly applied in the manufacture of large aircraft structural components. However, their inhomogeneous characteristics and poor machinability have given rise to the great difficulty for the drilling process in one-shot time. Meanwhile, owing to their different mechanical and thermal performances of the involved CFRP and Ti phases, the cutting responses in the bi-material (i.e. CFRP-Ti interface) region are of great complexity. In comparison to the previous investigations, this paper was designed to specially address the effects of drilling sequences (i.e. CFRP → Ti and Ti → CFRP) on the machining outputs of CFRP/Ti stacks with more comprehensive aspects. The obtained results show that the drilling sequence does play an important role in determining the involved machining responses of CFRP/Ti stacks. When drilling the stacks from the CFRP layer, the maximum magnitudes of drilling forces and cutting temperatures show higher values than those when drilling from the Ti6Al4V layer. Meanwhile, the difference between the entry diameter of the CFRP layer and that of Ti6Al4V layer increases with the elevation of feed rate during drilling from CFRP layer while the diameter of Ti6Al4V is always larger than that of the CFRP layer by 0.02–0.03 mm and presents disparity to the drill diameter by 0.02 mm when drilling from Ti6Al4V layer. From the viewpoint of drilled hole accuracy, it is preferable to drill CFRP/Ti stacks from the Ti6Al4V layer while the drilling sequence of CFRP → Ti is mostly preferred in terms of reducing the delamination damages in practical engineering production.

Process selection charts based on economy and environment: subtractive or additive manufacturing to produce structural components of aircraft

Multi-criteria decision-making methods are commonly used to rank manufacturing processes based on weighted economic and environmental criteria. The weighting process can be challenging, especially at early design stages where costs and environmental data are not precisely defined. In addition, for weights resulting in equivalent alternatives, no conclusion can be drawn when costs and environmental impact data are scarce and heterogeneous. Therefore, new methodology and tools are needed to find trade-offs between economy and environment in selecting manufacturing processes. In this work, a new systematic methodology for manufacturing process selection using fuzzy logic is developed. Applied to neutral, environmentalist and economist modes of thinking, manufacturing process selection charts were generated for all cost and environmental impact values. These tools were used to compare machining and selective laser melting for the production of aluminum structural components of aircraft. Results show that selective laser melting is the best trade-off in the mindset of neutrals and environmentalists, while machining is preferred by economists. Moreover, the proposed methodology can be used in situations where costs and environmental impacts are defined as ranges rather than determined numerical values. This methodology ranks manufacturing processes when weighted-criteria methodologies are limited.

Reflection-Based Source Inversion for Sparse Imaging of Low-Loss Composite Panels

This article presents a bistatic reflection-based imaging technique for electromagnetic testing of conductor-backed composite panels, which is based on an inverse formulation of the numerical problem at hand, and technically extends a previously demonstrated transmission-based system. The technique exploits the a priori assumption of pixel-based sparsity and retrieves the final image using data from only a single measurement, thereby removing the necessity of a reference measurement to be conducted. To demonstrate the capability of the technique, retrieved images are presented for a synthetic proof-of-concept device under test and an industrially manufactured composite panel. The presented technique can be considered as the initial model in the development of more complex bistatic imaging systems and has been developed for the purpose of extending the opportunities to conduct reflection-based electromagnetic nondestructive testing on aircraft structural components.

Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 2: Analysis of carbon fibre reinforced epoxy composite

We have investigated the release of gases and volatile organic compounds (VOCs) from a carbon fibre reinforced epoxy composite matrix used in aircraft structural components. Analysis was performed at several temperatures both up to and above the recommended operating temperature (121 °C) for the material, to a maximum of 250 °C. Gas chromatography-mass spectrometry (GC-MS) combined with thermal desorption (TD-GC-MS) was used to identify and quantify VOCs, and in parallel real-time gas detection with commercial off-the-shelf (COTS) gas sensors. Under hydrocarbon free air, CO, SO2, NO, NO2 and VOCs (mainly aldehydes, ketones and a carboxylic acid) were detected as the gaseous products released during the thermal exposure of the material up to 250 °C, accompanied by increased relative humidity (4%). At temperatures up to 150 °C, gas and volatile emission was limited.

Estimation of equivalent stresses and equivalents of the fatigue test programs of airframe composite elements

It is known that for metal components of aircraft structures, stress is one of the most important parameters used to assess the fatigue damage resistance of a structural element for a given program of its fatigue tests. The method and the procedure for estimating the values of this parameter for metal elements of aircraft structures are presented It is noted that for aircraft structural elements made of polymer composite materials, neither the concept of the stress parameter nor the methods for calculating estimates of the values of this parameter are currently defined in domestic and foreign studies of the fatigue strength of such elements. In order to achieve particular progress in the considered area, the definition of the stress parameter of fatigue test programs for composite aircraft structural elements is proposed. For the case of uniaxial tension-compression load of laminates from layered composites representing the upper and lower panels of composite wings of transport category aircraft, a method for calculating the estimation of this parameter is proposed. It is shown that using the stress parameter, the following main tasks can be solved: assessment of the damage resistance of a structural element with a given program of its fatigue tests; comparison of damages resistance of various programs, calculation of equivalents between the programs; calculation of fatigue life of layered composites samples and elements using the fatigue curve under regular load. It is noted that the fundamental meaning of the proposed method for calculating the equivalent stresses and equivalents of fatigue test programs is the use of a special hypothesis of a fatigue damage accumulation rule. An example of calculating the equivalent stresses and equivalents of various modifications of the quasi-random program for CFRP T300/5208 [45/0/-45/90] 2s samples of fiber-carbon composite with the open hole is presented. The fatigue life of these samples under load with the considered modifications was calculated using the obtained values of equivalent stresses and equivalents. Good agreement between the calculated results and experimental data is shown.

Design and prototyping of a novel composite architecture for a widebody landing gear bay

Composite materials may reduce the final weight of the aircraft structural components, in addition to improve fatigue performance and corrosion resistance. In order to achieve the optimization of air transport systems, making them increasingly sustainable, the structural design must be surely reviewed, starting to follow the “composite thinking” philosophy. The present research provides some relevant outcomes concerning the design of a composite sample for the main landing gear bay of a large commercial airplane (EASA CS25 category), within ITEMB (InTEgrated Full Composite Main landing gear Bay Concept) project, a program of Clean Sky 2 EU research framework. The most ambitious goal is to develop a new generation of Lower Center Fuselage (LCF) with an innovative integrated landing system in the fuselage, which is considered the next frontier in the development of landing systems for medium-haul aircraft, such as the Airbus A320 aircraft family. The development of a different architecture, with the landing gear integrated within the related fuselage bay, could lead to a simplification of the whole sub-assembly with potential advantage in terms of construction and assembly times. Final target of the project is the manufacturing of an innovative monolithic composite structure that will replace the actual configuration (a mixed structure of metal and composite sub-assemblies) reducing or actually removing all the cost of assembly and increasing the production rate. This paper presents the main results of the work, introducing the main processing steps and prototype results; in the last part of the work, also some experimental test on significant element are introduced as first assessment of the technology readiness level that has been achieved.

Predicting the relative magnitude of interlaminar stresses due to edge effects in thin angle-ply laminates using macroscopic finite element modeling

Carbon-epoxy and other composite materials are widely used in the design of aircraft and other structural components, but can be susceptible to delamination at free edges due to the presence of out-of-plane stresses. Finite element (FE) modeling can be used to predict the magnitude and location of these edge stresses, but the often used macroscopic approach to representing laminates can result in predictions that vary considerably due to the numerical singularities that are created. In this study, two macroscopic FE approaches are tested for thin angle-ply laminates in tension, and recommendations are made for the most effective method for evaluating the edge-effect phenomenon early in the design process. It has been determined that perfect interface models cannot be used for predicting maximum interlaminar stresses at free edges. Perfect interface models can effectively predict the relative magnitude of the interlaminar shear stress, τxz but resin interface models must be used for the interlaminar normal stress, σz.

Progress in the Application of Rare Light Metal Beryllium

As a special functional and structural material, the rare metal beryllium has been widely applied in many key areas due to its excellent nuclear properties, optical properties and physical properties such as low density, high specific stiffness, high specific strength, and excellent thermal properties. This article systematically reviews application of beryllium in strategic nuclear energy, high-energy physics, inertial navigation systems, aircraft structural components, optical systems and commercial fields. The paper also examines how beryllium promoted technological advances and improved the facilities performance in its applications fields. Beryllium plays an important role in the development of nuclear technology, defense, and aerospace, which make beryllium become a strategic and critical engineering material. The paper provides a reference for scientists and technicians to employ beryllium in more fields.

Weight optimization of metal T stiffened panel of a transport aircraft wing using CAE tools

Skin stiffened constructions are common in aircraft structural components that are subjected to compressive loads. The skin is so thin that it provides very little resistance to buckling against in-plane compressive loads. The objective of the design optimization is to obtain the minimum structural weight of the stiffened panel. The MSC/NASTRAN is used for design optimization. Von Misses failure criteria, Panel Buckling criteria (Metal) and Eigen value criteria are incorporated in an automatic way by exploiting the secondary response constraint feature of the design optimizer. The optimizer allows calculating the secondary response quantities at any stage of design optimization, using the primary response quantities like stress values and design variables values as input; and the secondary response constraint is used in defining the design constraints. Therefore, this study reveals that 125 mm stinger spacing is the optimum spacing and this configuration provides a reduction in weight by 22.14%

In-situ measurement of the β to α phase transformation kinetics in a Ti-5553 alloy using laser ultrasonics

Ti-5553 alloy (Ti-5Al-5Mo-5V-3Cr wt.%) is one of the newest high strength metastable β-titanium alloys to be used in large section components of aircraft structures. Like other Ti-alloys, Ti-5553 can be strengthened by precipitation of the α-phase during aging heat treatments. In the present study, we explored the potential of laser ultrasonics for metallurgy (LUMet) as an in-situ tool to measure the α precipitation kinetics during high temperature isothermal aging in a Ti-5553 alloy. The observed change in longitudinal ultrasound velocity was seen to be linearly correlated with the α-phase fraction measured via post-mortem electron microscopy. The results are promising for a wider use of LUMet to design optimized heat treatment schedules for commercial Tialloys. Laser ultrasonics offers the potential for real-time monitoring of microstructure evolution in industrial production lines.

Fabrication and characterization of stir cast Al2024/SiCp metal matrix composite

The arising issues concerning to requirement of high strength, light weight and energy conservation among automobile, aircraft and marine applications has significantly increased the demand for advanced materials having enhanced capabilities to sustain and perform efficiently at elevated temperature. Aluminum alloys have been selected as ultimate choice for the fabrication of structural components for aircraft and marine ships. These alloys are being reinforced with different kind of reinforcements to yield desired properties like high fatigue strength, heat and wear resistance combined with improved mechanical properties. The ongoing developments among these materials have allowed the product designer to select variety of materials to minimize cost, increase effectiveness with optimal utilization of resources. The aim of this study is to fabricate Al2024/SiCp metal matrix composite through stir casting route with variation in proportion of SiC reinforcement. The objective of study is to investigate the effect of variation in proportion of SiC in matrix on the mechanical properties of processed composite. SiC reinforcement of 400 Mesh has been used to produce the samples with 2, 4, 6, and 8 wt% using stir casting technique. After the fabrication of composite tests were conducted to assess the mechanical properties such as impact strength, hardness, and tensile strength. It has been observed that overall tensile strength decreases with increase in proportion of SiC whereas overall hardness and impact strength increases with increase in proportion of SiC.

Axial stress monitoring strategy in arbitrary cross-section based on acoustoelastic guided waves using PZT sensors

Axial stress monitoring in arbitrary cross sections is a challenging task. Stringers are the main axial load carrying components of aircraft skin structures and have typical complex cross sections. This paper investigates the strategy of axial stress monitoring in an arbitrary cross section based on acoustoelastic guided waves using piezoelectric lead zirconate titanate (PZT) sensors. To select appropriate guided wave frequencies and modes sensitive for axial stress monitoring in an arbitrary cross section, the feature guided waves are investigated using acoustoelastic theory combined with the semianalytical finite element method. The mode shapes are derived, which show that these longitudinal-like modes are more sensitive to axial stress. A PZT transducer array is also considered to maximize desired modes. Piezoelectric sensors are used to excite and detect the guided waves in the experiments. Results from acoustoelastic measurements on a T-type stringer are presented, showing the feasibility of this method for axial stress monitoring.