Fuselage Applications Research Articles

Mechanical and Metallurgical behaviour of Aluminum/graphene nanocomposites in Fuselage applications

Mechanical and Metallurgical behaviour of Aluminum/graphene nanocomposites in Fuselage applications

Hot Deformation Behavior of AA2024 with and without In Situ Titanium Diboride Dispersoids

AA2024 is known for its good combination of mechanical properties and is widely used in aircraft fuselage and other aerospace applications. However, because of its relatively lower yield strength, it has limited application in high-stress regions. In alloy AA2024, when titanium diboride particulates are embedded uniformly, it is expected to improve the strength of alloy by working as particulate dispersed composite. However, deformation of such metal matrix composite (MMC) is likely to be difficult and different from the base alloy. In this work, the deformation behavior of AA2024 alloy and its composite with titanium diboride particles developed in situ through salt-metal reaction have been studied. Hot deformation behavior was studied through hot isothermal compression tests over a temperature range of 300°C–450°C and strain rate from 0.01–10 s−1. The results show that there is an increase in flow stress with an increase in strain rate and a decrease in flow stress with an increase in temperature. Processing maps were generated based on the dynamic material model to identify the stable and unstable regions for hot working. The strain rate sensitivity of the composite has been compared to base alloy AA2024. Deformation parameters were calculated from the stress-strain data, and constitutive equations have been generated. Softening in alloy and in MMC is found to be caused by dynamic recrystallization. Microstructural modifications that are caused by titanium diboride reinforcement and its impact during hot deformation are reported. The safe zones for the hot working of both base alloy and MMC were found to be in the range of 380°C to 450°C in a strain rate of 0.001–10 s−1.

Some Examples of “Multi-Physical” Fatigue of Organic Matrix Composites for Aircraft Applications

This paper presents, discusses and review some recent results concerning the interaction between mechanics and the environment during fatigue tests carried out under accelerated environmental conditioning of laminated and woven Organic Matrix Composites (OMC) for high temperature aircraft parts, the synergy between electrical and mechanical fields during electro-mechanical fatigue of composite laminates for fuselage applications the damage behavior of 3D woven OMC under thermal cycling.For all case studies, the capabilities of the PPRIME Institute to perform such tests reproducing “multi-physical” fatigue environment and characterizing the phenomenology associated to multi-physics coupling at several scales will be highlighted. The main issues related to the development of “multi-physics” models for proper interpretation of test results are also reviewed.

Study of Crack Length Measurement and Crack Tip Plastic Zone Determination by Infrared Thermography

This paper reports a new way to conduct fracture mechanics experiments of welded thin-walled structure for aircraft fuselage applications made of the Al 6156 ally using lock-in infrared thermography. The heat wave, generated by both the themo-mechanical coupling and intrinsic energy dissipation was detected by an infrared camera. The crack growth rate measured by the lock-in infrared thermography is found to be consistent with that measured by conventional method. It is observed that the crack can either grow underneath the stiffener or grow into the stiffener web with the crack length measured at the same time. In addition, the crack tip plastic zone was observed before the specimen was about to be destroyed.

Crack Paths in a Friction Stir-Welded Pad-Up for Fuselage Applications

Crack paths in friction stir-welded 2198-T8 SE(T) plates with pad-up are investigated. Fatigue tests are performed with and without a friction stir weld in a range of samples, and crack paths and fatigue crack growth rates are compared. The effects of the weld on the damage tolerance of samples are studied. A hole is drilled through the specimen to study its effects on the crack trajectory. It is shown that the crack growth rate is slower with a weld than without a weld. The position of hole can change crack path and crack trajectories. A program is developed to input the residual stress distribution into an ABAQUS finite element model, and the crack paths are predicted to understand the effects of the weld. These predictions are compared with experimental data gathered on crack deviation behavior. The predictions agree well with the experimental findings.

Unsteady Reynolds-Averaged Navier-Stokes-Based Hybrid Methodologies for Rotor-Fuselage Interaction

L IFTING bodies produce wakes that interact with other bodies immersed in the same fluid. In particular for rotorcraft, the problem becomes significantly more complicated since the rotor wake remains near the vehicle in hover, descent, and low-speed forward flight. The proximity of the wake alters the inflow distribution at the rotor andmodifies the helicopter thrust.Moreover, since the main rotor wake may impinge on the fuselage, such interactions are an important consideration in modern rotorcraft design. For example, empennage impingement may result in undesirable handling qualities such as low-speed pitchup and tail buffet. Moreover, the wake can also generate unsteady impulsive loads on the fuselage, resulting in vibrations, thus negatively impacting the crew and passenger flight experience. Given the complexity of rotorcraft interactional aerodynamics problems, it is common for tail and empennage designs to be modified significantly after first flight [1]. Development of many aerospace technologies, not limited to helicopter rotor–fuselage applications, requires accurate resolution of both nearand far-field flow phenomena. Numerical prediction of wakes involve a tradeoff between accuracy, turnaround time, and computational expense [2]. Current grid-based computational fluid dynamics (CFD) codes can theoretically model the entire flowfield, but resolution and preservation of wake features become difficult since typical grid sizes used in industrial simulations are susceptible to numerical dissipation. The artificial diffusion of vorticity that results can be mitigated using grid adaptation techniques and higherorder methods [2–4], but this may not be practical for all applications since computational cost increases significantly. For this reason, computationally efficient hybrid methods may be more attractive, especially during design and for flight-test support. Traditional Lagrangian free-wake methods are inexpensive but become less accurate when vortex elements in the wake become distorted and tangled due to interactions with other vortices and solid bodies (i.e., rotor blades and the fuselage) [5]. These interactions typically occur in the rotor near field, which motivates coupling to a CFD solver to resolve the highly viscous and possibly compressible flow near the rotor. In such an approach, the CFD code does not have to resolve the entire wake region; thus, the size of the CFD domain can be greatly reduced and computational efficiency maximized. Additional challenges associated with surface interactions arise when modeling problems such as rotor–fuselage interactions. The ability of two approaches to hybridize a Reynolds-averaged Navier–Stokes (RANS) CFD solver and a free-wake method for the rotor–fuselage interaction problem is investigated. Predictions are compared with experimental data, as well as prior numerical predictions made with individual code simulations.

Methods to Increase the Fatigue Life of Friction Stir Lap Welds in No-load Transfer Coupons Using a Retractable Pin Tool

Abstract The purpose of this study was to obtain a better understanding of crack initiation at friction stir weld exit holes in no-load transfer coupons as a first-order approximation of the potential performance of friction stir welding (FSW) joints employed for aircraft fuselage applications. In order to meet this goal, the effects of weld exit location on fatigue life in discontinuous friction stir lap-welded panels were documented. Sheets of aluminum alloys 7075-T6 and 2024-T3 were chosen for the FSW lap welds. Constant amplitude fatigue tests were carried out in order to determine the effect of various welding scenarios on fatigue crack initiation. A number of weld exit strategies were investigated, as well as another FSW tool design called a retractable pin tool (RPT). This tool was shown to eliminate the exit hole and reduce the stress concentration around the weld exit location. Prior to this work, none of the attempted exit strategies was found to delay or eliminate the initiation of fatigue cracks at the exit holes of discontinuous FSW lap welds. Only by using the RPT, which is able to eliminate the exit hole completely, was it possible to produce fatigue life results in coupons with a tool extraction zone that were comparable to those in baseline coupons containing no extraction zone.

Damage Tolerance Properties of 2198-T8 Integral Fuselage Panel between Double Friction Stir Weld Joints

Al-Li alloy 2198-T8 was used in the fuselage application. Integral fuselage panels were joined by double friction stir welds. Fatigue tests were conducted in the R=0.1. Notch was made between two welds. Residual stresses were measured and analyzed in the test samples with double welds. Cracks grew from the centre of two welds and across the two welds were observed, and crack growth rates were measured and compared with parent material. It is shown that crack growth rates are lower between double welds, and it is close to parent material after cross the two welds. The virtual crack closure technique (VCCT) method was used to calculate stress intensity factor from residual stress (Kres) in aim to explain the experimental findings.

Limit load analysis of strength undermatched welded T‐joints under bending

ABSTRACTAn increasing amount of laser beam welded T‐joints (e.g. skin‐stringer) of aluminium alloys are now in use in advanced fuselage applications designed as ‘integral structures’ for weight and cost savings. It is known that weld joints generally show lower strength (undermatching) than base metal in both laser beam and friction stir welded joints of 6xxx series Al‐alloys. Damage tolerance considerations in terms of the residual strength of such joints require limit load solutions to be used in engineering fitness‐for‐service (FFS) analysis. The paper, therefore, provides an upper bound limit load solution in closed form for welded T‐joints (idealized) with strength undermatching and subject to a bending moment. In addition to the necessary requirements of the upper bound theorem, the kinematically admissible velocity field chosen leads to a stress field, which satisfies the equilibrium equations and some stress boundary conditions in the plastic zone. This is an advantage of the solution and, therefore, it is expected that the upper bound obtained is close to the exact limit load of such joints.

Advanced Aluminium and Hybrid Aerostructures for Future Aircraft

Alcoa has made a fundamental shift in its aerospace R&D program, broadening its scientific and engineering portfolio by creating an integrated, strategic, long-term initiative. The ultimate goal is to help re-define the future performance, cost and value of the metallic and hybrid aerostructures that the company feels will be required to meet the mission requirements of tomorrow’s aircraft. Having intensely studied various structural options, Alcoa believes Hybrid Structural Assembly optimized with a combination of Advanced Aluminum and Hybrid Components offer the best opportunities to maximize structural performance. Not only do the new alloys, notably 3rd Generation Al-Li alloys and high strength and high toughness 7xxx alloys provide structural performance enhancements, they also offer dramatic improvements in corrosion resistance. In this paper, several advanced alloys and structural concepts targeted for next generation wing and fuselage applications and large scale test article results supporting Alcoa’s optimism for Advanced Metallic and Hybrid Structures are reviewed.

Investigations on the long-term stability of 6013-T6 sheet

Sheet material of the Al–Mg–Si–Cu alloy 6013-T6 was additionally aged at 191 °C for up to 100 h and thermally exposed at temperatures ranging from 85 to 150 °C for time periods up to 3000 h. Microstructure, tensile properties and corrosion behaviour were investigated in the different heat treatment conditions using differential scanning calorimetry and transmission electron microscopy as well as performing tensile tests and various corrosion tests. Hardening precipitates present in the peak-aged microstructure were the metastable β″ and Q′ phases. Alloy 6013-T6 exhibited sensitivity to pitting and intergranular corrosion when immersed in chloride solutions, but was immune to intergranular stress corrosion cracking. Increasing aging at 191 °C resulted in progress in the precipitation sequence and coarsening of the precipitates. However, the degradation of tensile properties due to overaging was slight, and no change in corrosion behaviour was observed. Prolonged thermal exposure at temperatures between 85 and 120 °C did not cause significant alterations in microstructure, tensile properties, and corrosion performance of peak-aged 6013 sheet, indicating thermal stability of this alloy when used in fuselage applications.

Current fatigue and fracture research in Portugal

This issue is a sample of current work in Portugal on diverse topics within the broad field of fatigue, fracture, structural integrity and related areas. The common feature of the papers included is the authorship by researchers of several Portuguese universities and other organizations, although in some cases the articles include co-authors from other countries such as France, Romania, the United Kingdom and the United States. The work presented in this issue covers composites and metals, involving experimental and numerical tools and concepts. It includes papers on topics such as biaxial fatigue, welded connections, pressure vessels, rolling contact, and aspects of the fatigue behaviour of aluminium alloys. Structural integrity studies of gas turbine discs, exhaust pipes of naval turbines, fighter aircraft, and cold worked cracked holes for fuselage applications are presented. As far as composites are concerned, studies on interlaminar fracture, intralaminar cracking and fracture of composite co-cured joints are included. Fatigue and fracture research in Portugal is the subject of regular Portuguese Conferences on Fracture organized by the Sociedade Portuguesa de Materiais (SPM). The 9th edition of this series, started in 1983, took place in Setúbal on 18–20 February 2004, and was included in the calendar of the European Structural Integrity Society (ESIS). In parallel with these national events, which usually attract a number of experts from other countries, several international meetings already took place in Portugal. To give just two examples, the ESIS 6th International Conference on Biaxial/Multiaxial Fatigue and Fracture, Lisbon, 25–28 June 2001, and the early 5th European Conference on Fracture, 17–21 September 1984, organized in the context of the European Group on Fracture (predecessor of ESIS), may be mentioned. Joint events with the Spanish researchers—the Iberian conferences—are occasionally organized, and these started with an event in Braga in 1987. The active community of researchers in the field, and the natural good conditions, make Portugal an interesting location for organizing these scientific meetings as indicated by the 1st International Conference on Engineering Failure Analysis ICEFA-1, Lisbon, 12–14 July 2004, or proposed future events in the context of the European Mechanics Society (EUROMECH). A relatively small country of approximately 10 million inhabitants, Portugal has seen a substantial increase in research and development activities since the 1970s. This is a result of several factors, among which should be mentioned a large concentrated effort of training academic staff in foreign universities started in the beginning of 1970s. In the areas of interest for this journal, that policy was translated into practice by Professor Luciano Faria in Lisbon (Instituto Superior Técnico of the Universidade Técnica de Lisboa— IST), and by Professor Vasco Sá in Porto (Faculdade de Engenharia da Universidade do Porto—FEUP). Among others, they led the selection and created conditions for the training of the first generations of experts in these fields, which took place principally in the United Kingdom and France. More recent decades witnessed the development of the research capacity in the country. In parallel there is an increasing internationalization of the activity, with frequent stays in Portuguese universities of post-doctoral researchers and visiting professors in the context of programmes such as the NATO post-doctoral scholarships or the U.S. Fulbright Commission, participation in European Union and other international R&D projects, and joint supervision of doctorates by Portuguese researchers in foreign universities, and by foreign researchers in Portuguese universities. The editors of Fatigue and Fracture of Engineering Materials and Structures (FFEMS) approved in 2002 a suggestion for the publication of a special issue concerning research in Portugal. The result, now in the hands of the readers of the journal, is a series of papers that went through the usual refereeing process of this journal. I would like to express my gratitude to the authors and referees. As Guest Editor of this issue, I am indebted to the editors of FFEMS, and to Professor Eann Patterson in particular, for encouragement and interest in this project.

Al-Li Alloy 1441 for Fuselage Applications

A cooperative investigation was conducted to evaluate Al-Cu-Mg-Li alloy 1441 for long service life fuselage applications. Alloy 1441 is currently being used for fuselage applications on the Russian Be-103 amphibious aircraft, and is expected to be used for fuselage skin on a new Tupolev business class aircraft. Alloy 1441 is cold-rollable and has several attributes that make it attractive for fuselage skin applications. These attributes include lower density and higher specific modulus with similar strength as compared to conventional Al-Cu-Mg alloys. Cold-rolled 1441 Al-Li sheet specimens were tested at NASA Langley Research Center (LaRC) and the All-Russia Institute of Aviation Materials (VIAM) in Russia to evaluate tensile properties, fracture toughness, impact resistance, fatigue life and fatigue crack growth rate. In addition, fuselage panels were fabricated by Tupolev Design Bureau (TDB) using 1441 skins and Al-Zn-Mg-Cu alloy stiffeners. The panels were subjected to cyclic pressurization fatigue tests at TDB and at LaRC to simulate fuselage pressurization/depressuirzation during aircraft service. This paper discussed the results from this investigation.

Metallurgical Design of Alloys for Aerospace Structures

New aluminum alloys for aircraft structures have been introduced recently. These new alloys are designed in such a way as to improve the weight efficiency of the structure. A good understanding of the loading of the different airframe parts is needed for this purpose. The present paper focuses on the micro-mechanical models which are used, or will be used, to find the optimum property balance. These models are based on microstructural features, which can be measured on the material or modeled by physical metallurgy equations. Examples are given for the typical rolled products used for the fabrication of an aircraft: thin sheets for fuselage application and plates for spars and ribs.

Damage tolerance and failure analysis of a composite geodesically stiffened compression panel

A geodesically stiffened continuous-filament composite structural concept has been designed for a transport aircraft fuselage application and fabricated using an automated manufacturing process. Both large panels and element specimens derived from these panels have been experimentally and analytically investigated when subjected to axial compression to understand their buckling, postbuckling, and failure responses. The primary failure mode for this structural concept is skin-stiffene r separation in the skin postbuckling load range. The large panels are subjected to low-speed impact damage and tested to failure in axial compression to evaluate the damage tolerance of this structural concept. These results suggest that damage to the stiffener and a stiffener intersection point from the skin side do not influence the failure load or failure mode of this structural concept. Nonlinear finite element analysis using a detailed element specimen model indicates that failure of this specimen may have initiated at the skin-stiffener flange region close to the stiffener intersection. When the skin is in the postbuckling range at four times its initial buckling load, the interlaminar shear stress concentrations at a region where the stiffener makes a 20-deg turn away from the stiffener intersection seem to initiate panel failure.

Effect of stiffness characteristics on the response of composite grid-stiffened structures

A study of the effect of stiffness discontinuities and structural parameters on the response of continuousfilament grid-stiffened flat panels is presented. The buckling load degradation due to manufacturing-introduced stiffener discontinuities associated with a filament cut-and-add approach at the stiffener intersections is investigated. For practical discontinuity sizes, the reduction in buckling load is negligible. The degradation of buckling resistance in isogrid flat panels subjected to uniaxial compression, combined axial compression, shear loading conditions, and induced damage, is quantified using finite element analysis. The combined loading case is the most critical one. The benefit of utilizing nonsolid stiffener cross sections is evaluated. Nonsolid stiffener cross sections, such as a foam-filled blade or hat with a 0-deg dominant cap, result in grid-stiffened structures that are structurally very efficient for wing and fuselage applications. The results of a study of the ability of gridstiffened structural concepts to enhance the effective Poisson's ratio of a panel is presented. Grid-stiffened concepts create a high effective Poisson's ratio which can produce large camber deformations for certain elastic tailoring applications.

A Flying Finish

GOOD looks and long life are prime interests of any aircraft user, especially airline operators. Finishing products, particularly paints and anti‐corrosive treatments, play a vital role in manufacture, operation and maintenance. The special demands of aviation, including the abrasive conditions of high speed flight, place a premium on highly durable finishes, whether designed for exterior fuselage application or internal protection of essential components. In fact, every part of the structure should be protected by an anti‐corrosion coating.

The Utilisation of Reinforced Plastics in the Wessex Helicopter to Prevent Corrosion

MAGNESIUM metal with its low density high strength and stiffness properties is a material which is used extensively in the Wessex helicopter for castings, forgings, and in sheet form in the skin stringer constructed fuselage. Extensive utilisation of these aircraft has shown that a corrosion hazard is present with this material in the fuselage application. Accidental damage, mis‐use and normal wear and tear removes the carefully applied organic protection permitting moisture to come into contact with the non‐protected metal, with the result that corrosive conditions are generated and it is found that in the non‐accessible areas, intensive corrosion damage occurs and it is not discovered in time for remedial action and the efficiency of the structure and airframe is impaired.