Aircraft Fuselage Section Research Articles

Framework of Physically Consistent Homogenization and Multiscale Modeling of Shell Structures**

A framework of physically consistent homogenization and multiscale modeling (PCHMM) for reduced-order analysis of plate/shell structures is developed in this paper. To address the inapplicability of conventional periodic boundary conditions and Hill’s condition involved in homogenization of shear-deformable shell structures, the paper proposes physically consistent boundary conditions and modified Hill’s condition for plate/shells. Unlike the PCHMM method for beams, considering the contradiction between high-order displacement fields induced by shear forces and low-order kinematic assumptions, additional constraints are applied to the plate/shell structure sectional strains during the solution of perturbation fields. The correctness and effectiveness of the proposed plate/shell PCHMM framework and method are verified by typical numerical examples. The proposed theory can also be conveniently embedded into commercial finite element software for homogenization and multiscale analysis of structures such as microscale metamaterials like lattice plates and large complex structures like aircraft fuselage sections.

Natural frequencies and modal shapes of folded sandwich plates made of porous core and FG-CNTRC coating layers resting on two parameters elastic foundation

Folded structures hold significant importance in aerospace technology due to their distinct design, effectively reconciling strength with a lightweight framework. Within aerospace applications, these structures fulfill diverse roles, serving as pivotal elements in aircraft wings, fuselage sections, and essential components of spacecraft and satellites. This study delves into the free vibration behavior of folded sandwich plates composed of a porous core and functionally graded carbon nanotube-reinforced composite (FG-CNTRC) coatings, resting on a two-parameter elastic foundation. Leveraging first-order shear deformation plate theory (FSDT), elasto-dynamic equations are established for each individual plate segment. Utilizing the two-dimensional generalized differential quadrature method (2D-GDQM), these equations are discretized. Subsequently, by applying boundary conditions to all six edges, including traditional clamped, simply supported, and free configurations, and incorporating continuity conditions for displacements, forces, and moments at the joint borders, natural frequencies and modal shapes are extracted for the folded plate structure. The validity of the proposed formulation and results is demonstrated by comparing them with numerical examples for both composite flat and folded plates. This comparison provides strong support for the accuracy and reliability of the present study. The study comprehensively examines the influence of various parameters on natural frequencies, including modal shape visualizations under different boundary configurations, plate thickness, crank angle, porosity parameter, core thickness, foundation stiffness, and CNTs distribution type.

Advances and Future Challenges in Aircraft Fuselage Section Crashworthiness: A Critical Review

Background: Crashworthiness studies the safety qualification of a vehicle (both airborne and road transports) to protect its occupants during an impact. Before an aircraft can receive transport certification, it must meet a number of crashworthiness requirements, such as the structure's deformation pattern, absorbed kinetic energy profile, and acceleration responses experienced by the components and human body models. Therefore, in recent times, crashworthiness has emerged as a crucial field of study during the early design stages of aircraft, along with other key parameters like weight reduction, load factor, fatigue life estimation, etc. Objective: The main objective of the present article is to undertake an in-depth analysis of the developments in crashworthiness related to the civil aircraft fuselage section. Furthermore, it aims to identify and address the future challenges that must be overcome to ensure the utmost safety of the occupants. Methods: Based on the research objectives, the available literature is categorized into three major groups: (i) finite element code validation; (ii) improvement of the crashworthiness criteria; and (iii) impact on different surface models. A methodology to solve fuselage section crashworthiness is briefly described. A review of the research articles discussing general purpose energy absorbers for crashworthy design without any implementation to the fuselage structure is out of the scope of this article. Results: Experimental testing of fuselage section crashworthiness is expensive and non-repeatable. Furthermore, the intricate structure of the fuselage, with its numerous components, makes it nearly impossible to devise crashworthy design solutions through classical hand calculations alone. As a result, commercial software codes play a crucial role in the development of fuselage section crashworthiness, offering valuable assistance in overcoming these limitations. Conclusion: Future challenges of crashworthy design involve exploring novel materials and devices to mitigate injury during controlled crash conditions. An intriguing area of study would be the analysis of lattice components, as they have the potential to enhance crashworthiness. Furthermore, as newly designed fuselage sections emerge, it will be crucial to investigate and establish the necessary requirements to ensure compliance with crashworthiness certification standards.

Detailed FE aircraft fuselage sections for water impact simulations in the pre-design process chain

The automatic generation of representative fuselage section models with a detailed discretization for the application in computer-aided transient dynamic simulations in the aircraft pre-design process chains is described in this paper. The process consists of Python routines to select and reduce the section from the full fuselage and to refine the mesh and extrude cross-sections in arbitrary zones of the section. By this, different mesh qualities can be integrated in the model according to its individual application. These functionalities were integrated in the structural modelling and sizing framework PANDORA. A simple reinforced panel was used to investigate its structural behaviour with different discretization options under a bending loading condition. Also, a fuselage section model reinforced using either one of the discretization options was subjected to a quasi-static loading. The model was then simulated under crash conditions to investigate its non-linear structural behaviour. The focus of this paper lays on the application and the local structural analysis of the detailed fuselage section in water impact simulations.

Crashworthiness Study of a Newly Developed Civil Aircraft Fuselage Section with Auxiliary Fuel Tank Reinforced with Composite Foam

Over the past two decades, aircraft crashworthiness has seen major developments, mainly with modern computing systems and commercial finite element (FE) codes. The structure and the material have been designed to absorb more kinetic energy to ensure enough safety during a controlled crash condition. However, the fuselage section with an onboard auxiliary fuel tank requires special arrangements, since the inclined strut system with an efficient energy absorber is difficult to install under the cabin floor due to the space occupied by the fuel tank. To solve this shortcoming, a PVC composite foam along with an aluminum plate is introduced beneath the fuel tank to improve the crashworthiness metrics of the fuselage. Drop tests for both the conventional design and the proposed model are investigated by adopting the nonlinear explicit dynamics code Ansys Autodyn, with an impact velocity of 9.14 m/s. It was found that the kinetic energy absorption of the original fuselage section can be improved by 3.54% by reinforcing the foam and the plate. Moreover, they contribute to 20% of total internal energy dissipation. Numerical outcomes also suggest that the cabin floor surface experiences a 41% lower maximum stress, in addition to the mitigation of the maximum peak acceleration responses of the cabin floor at different measured locations from 6% to 36%.

Influence of Composite Skin on the Energy Absorption Characteristics of an Aircraft Fuselage

In aviation history, accidents during landing are more frequent compared to other phases of flight and in most cases the aircraft is forced to make an emergency belly landing when landing gear malfunctions. This study aims to analyse the energy absorption of a typical composite aircraft fuselage section under such crash belly landing. A finite element model of this composite fuselage section was created and analyzed using LS-Dyna finite element software and the effects of different composite materials on the energy absorption of fuselage section were studied. Four different composite materials that are commonly used in aerospace application were selected for the purpose of the present study namely glass/epoxy, graphite/epoxy, Kevlar/epoxy, and boron/epoxy. An impact velocity of 7 m/s against rigid ground was considered. Results showed that frames and skin contribute the most in energy absorption while the passenger floor and strut contribute the least. Moreover, it was found that fuselage skin made of glass/epoxy absorbed more energy compared to other materials and it had the highest specific energy absorption.

Modeling of fuel in crashworthiness study of aircraft with auxiliary fuel tank

Numerical techniques have become very practical and effective in dynamic simulation for large systems. However, till date, computational modelling of fuel in auxiliary fuel tank during aircraft fuselage section crashworthiness remains a challenge to solve. Previously, four different fluid modelling techniques, namely, Lagrange, Euler, Arbitrary Lagrange Euler (ALE) and Smoothed hydrodynamics particle (SPH) have been investigated to represent fluid in different applications ranging from marine science to rotorcraft fuel tank crashworthiness. However, for a full-scale aircraft fuselage section with auxiliary fuel tank, fluid modelling has not been yet reported. Therefore, in this current research, a commercial explicit dynamic code Autodyn is adopted to solve Fluid-structure interaction (FSI) problems numerically on a standalone civil aircraft type fuel tank with four different fluid models, respectively, i.e. Lagrange, Euler, Arbitrary Lagrange Euler and Smoothed Hydrodynamics Particle. Virtual drop tests are conducted with a vertical impact velocity of 7 m/s to investigate the most suitable fluid model, which can be further utilized to represent fuel inside an auxiliary fuel tank in a fuselage section to study the crashworthiness. After studying the structural deformation, von Mises stress, equivalent plastic strain, absorbed internal energy, fluid sloshing events and computational time duration due to the adoption of different fluid models, it is found that Lagrange fluid model with the node erosion algorithm setup suits best to the fuel. In the second part of the research, crashworthiness of a full-scale fuselage section with auxiliary fuel tank considering fluid as Lagrange model and fluid as distributed mass is investigated. Results are compared with the available experimental and numerical outcomes and it is found that, modeling the fluid inside of an auxiliary fuel tank is crucial to capture the appropriate plastic deformation of the fuselage section; however, presence of fluid does not affect the acceleration responses of the cabin floor.

A novel 3D impact energy absorption structure with negative Poisson’s ratio and its application in aircraft crashworthiness

The negative Poisson's ratio (NPR) structures exhibit some unusual but highly useful mechanical properties. In comparison to two-dimensional (2D) NPR structures, less attention has been paid to the studies on three-dimensional structures due to the complex manufacturing process. In this paper, based on the two-dimensional nonconvex hexagonal cell, a novel three-dimensional (3D) NPR energy-absorbing structure is proposed. According to the beam theory, the equivalent Young's modulus and Poisson's ratio are deduced. Subsequently, numerous finite element (FE) simulations and compression tests were performed and a good agreement was observed among the theoretical results, the numerical simulations, and the experimental results. Moreover, a typical fuselage section of aircraft during a crash landing was considered and the fuselage section with the 3D NPR structure presented in this work showed better energy absorption capacity than the one without the 3D NPR structure.

Impact test and numerical simulation of typical sub-cargo fuselage section of civil aircraft

This paper deals with impact test and numerical investigations on the crashworthiness of the typical sub-cargo fuselage section of a civil aircraft. The sub-cargo fuselage section with three-frame and two-span is designed and manufactured, and the 3.95 m/s impact test is conducted to research the failure modes and impact response characteristics for the upside-down sub-cargo fuselage section. The impact process is simulated by using the LS-DYNA finite element code. The impact velocity, displacement, and acceleration response are compared, and a good agreement between test results and numerical simulation results is observed. The energy absorption characteristics and impact load transfer path are further studied based on the verified finite element model (FEM). The results show that the impact phases are characterized by the bending and twisting of fuselage frames, the bending of middle stanchions and C-channel stanchions, the pull-off failure and shear failure of rivets, and the two plastic hinges formed at the joints of C-channel stanchions and fuselage frames. The fuselage frames and middle stanchions are the main energy absorption components. The impact load is transmitted along with the fuselage frames, middle stanchions, and C-channel stanchions to the cargo cross beams, and the area of middle stanchions is the most important energy absorption design area.

A Statistical Energy Analysis (SEA) model of a fuselage section for the prediction of the internal Sound Pressure Level (SPL) at cruise flight conditions

Comfort plays an increasingly important role in the interior design of airplanes. In general, comfort is defined as ‘freedom from pain, well-being’; in scientific literature, indeed, it is defined as a pleasant state of physiological, psychological and physical harmony between a human being and the environment or a sense of subjective well-being. Cabin noise in passenger aircraft is one of the comfort parameter, which creates straightaway discomfort when exceeding personal thresholds. In general the cabin noise varies by the seat position and changes with flight condition. It is driven by several source types, which are transmitted through different transfer paths into the cabin. In the forward area the noise is mainly dominated by the turbulent boundary layer described by pressure vortexes traveling along the fuselage surface.In this paper evaluation of the Sound Pressure level, for the medium-high frequency range, of an aircraft fuselage section at different stations and locations inside the cabin has been performed numerically by using Statistical Energy Analysis (SEA) method. Different configurations have been considered for the analysis: from the “naked” cabin (only primary structure) up to “fully furnished” (primary structure with interiors and noise control treatments) one. These results are essential to understand which are the main parameters affecting the noise insulation. Furthermore the Power Inputs evaluation has been determined to see the contribution of each considered aeronautic component on the acoustic insulation. Finally, the effect of a viscoelastic damping layer embedded in the glass window has been evaluated.

Crashworthiness analysis of an aircraft fuselage section with an auxiliary fuel tank using a hybrid multibody/plastic hinge approach

The drop test of a Boeing-737 fuselage section is modelled using a multibody (MB) with spatial plastic hinge method. The test is simulated in MADYMO to evaluate the structural interaction of the cabin with a stiff auxiliary fuel tank underneath the floor, in a severe but survivable impact condition. The fuselage ribs, cargo door frame, cargo door, and passenger floor with spar webs are modelled using a large number of bodies and universal joints with directional properties to allow for appropriate torsional and bending deformations. The contacts for the fuselage section are modelled using a Hertzian-based contact force model with dissipative damping. The simulation results from the MB approach show reasonably good agreement with those from the experimental test and from a detailed finite element (FE) model. This MB approach then could be a viable tool in modelling occupant and structural deformations for aircraft crashworthiness problems.

Occupants’ Injury during a Drop Test of an Advanced Composite Fuselage Section

The emergency landing is an important design criteria in airworthiness certification. It is associated to the cabin safety and consequently to the risk of serious injury for the occupant. The loads transmitted to the passengers during a hard landing can be fatal both in terms of intensity and duration time, and the energy absorbing systems play a fundamental role to dissipate the energies unleashed during the impacts. A barrel section was studied by the Finite Element Method to simulate the drop test consequences for the fuselage section of a wide body aircraft, and a medium velocity impact was applied to design devices and substructures able to dissipate the biggest amount of kinetic energy. A validation process was obtained following three different steps: firstly, investigating the materials, layups and material characteristics changing with load’s velocity, secondly different tests were performed on the demonstrators in order to verify the installation parameter of the devices devoted to absorb the energies, and finally the experimental results were extended on the lower lobe of the sub-cargo compartment tested at low velocity impact. These experimental results and the correlation with the numerical models allowed to extend the results on the barrel section and to evaluate the accelerations transmitted during the drop to the occupants. The satisfactory results estimated by the numerical solvers are able to aid the design and to reduce the experimental testing for the identification and the choice of different candidate solutions.

Computational modelling and experimental verification of the vibro-acoustic behavior of aircraft fuselage sections

The aerodynamics of an aircraft impose significant stresses upon its structure. The turbulent boundary layer (TBL) is a highly turbulent layer that forms along the fuselage skin inducing localized pressure fluctuations resulting its vibration, and in turn, the generation of noise inside the passenger cabin. During flight, the noise generated by the TBL dominates the sound field between 100 Hz and 5 kHz, to be regarded as the frequency range of interest. While the audible range is between 20 Hz and 20 kHz, human hearing and speech intelligibility is most sensitive between 250 Hz and 2 kHz. This investigation considers a BEM-FEM-BEM modelling technique to predict the vibro-acoustic response of the fuselage and an experimental methodology to verify the results (following ASTM and ANSI testing standards) by imitating the frequency profile of the TBL using an acoustic source. The research incited construction of an atypical acoustic testing facility, the development of DAQ software and post-processing techniques of test data. The principal quantity of interest is transmission loss. Four panels (0.04 in., 0.063 in. (milled pockets to 0.043 in.), 0.063 in., and 0.09 in. in thickness) were simulated and tested between 20 Hz and 20 kHz. Analysis of the results sought to determine the limitations of the computational methodology by observing divergence of the predictions from the results. Divergence was defined as a difference exceeding 10% (approximately 4 dB), which was observed beyond 8 kHz. The comparisons show the frequency-averaged errors between the proposed methodologies to be within 5 dB between 20 Hz and 20 kHz, and 3 dB between 100 Hz and 5 kHz. Variability in reproducibility of experimental results (same test specimen and between test specimens) is a significant challenge when determining transmission loss values. The experimental methodology proved successful in differentiating between the panels with confidence using at least six tests over a period of three years. The computational methodology was accurate in estimating the transmission loss and the general (frequency-dependent) response.

An approach for the assessment of the statistical aspects of the SEA coupling loss factors and the vibrational energy transmission in complex aircraft structures: Experimental investigation and methods benchmark

In the application of Statistical Energy Analysis “SEA” to complex assembled structures, a purely predictive model often exhibits errors. These errors are mainly due to a lack of accurate modelling of the power transmission mechanism described through the Coupling Loss Factors (CLF). Experimental SEA (ESEA) is practically used by the automotive and aerospace industry to verify and update the model or to derive the CLFs for use in an SEA predictive model when analytical estimates cannot be made. This work is particularly motivated by the lack of procedures that allow an estimate to be made of the variance and confidence intervals of the statistical quantities when using the ESEA technique.The aim of this paper is to introduce procedures enabling a statistical description of measured power input, vibration energies and the derived SEA parameters. Particular emphasis is placed on the identification of structural CLFs of complex built-up structures comparing different methods. By adopting a Stochastic Energy Model (SEM), the ensemble average in ESEA is also addressed. For this purpose, expressions are obtained to randomly perturb the energy matrix elements and generate individual samples for the Monte Carlo (MC) technique applied to derive the ensemble averaged CLF. From results of ESEA tests conducted on an aircraft fuselage section, the SEM approach provides a better performance of estimated CLFs compared to classical matrix inversion methods. The expected range of CLF values and the synthesized energy are used as quality criteria of the matrix inversion, allowing to assess critical SEA subsystems, which might require a more refined statistical description of the excitation and the response fields. Moreover, the impact of the variance of the normalized vibration energy on uncertainty of the derived CLFs is outlined.

A crack propagation study on T-joints of AA6013-T4 aluminum alloy welded by an Yb:fiber laser

A fundamental aspect of the replacement of the riveted to welded aluminum aircraft fuselage sections is the fatigue behavior. In this work, a fiber laser was used to produce different types of T-joint coupons in order to evaluate their crack propagation procedure during standard C(T) tests. Some defects such as cracks and pores had been observed and directly influenced the lifetime during testing. The cracks observed in high-speed regimes were associated with the hot cracking phenomena, and those coupons were not considered for crack propagation tests. These tests were carried out with the stringer parallel or perpendicular to the crack tip. The stringer has a positive effect on the fatigue crack propagation results, but the appearance of defects dramatically decreases the fatigue lives. The better results were those where the stringer was placed perpendicular to the crack, because of a retardation of the crack growth, in particular, 4 mm before reaching the joint.

Evaluate the crashworthiness response of an aircraft fuselage section with luggage contained in the cargo hold

ABSTRACTThis article investigates the effect of luggage on the crashworthiness of fuselage section with under-floor cargo compartment. Detailed nonlinear finite element models of an aircraft fuselage section with and without luggage were developed for crash simulations which were subjected to the velocity of 9.14 m/s. The overall deformation of the fuselage, the acceleration time histories at selected locations on the fuselage and the energy absorption of key structural components were studied. It was determined that the under-floor luggage and the fuselage frame play the most important roles in energy absorption during impact which account for 45.62% and 19.42%, respectively, and that the luggage markedly affects the deformation of the entire structure. Without luggage, the cabin structure would be damaged heavily, while with luggage loaded, the integrity of the cabin structure can be maintained. Besides, the luggage model had lower peak acceleration values and shorter pulse durations when compared with the absence of luggage model results. Furthermore, the effects of luggage stiffness, viscosity and the worst-case scenario on crashworthiness were also examined. It was shown that the strength and stiffer luggage could evoke the inherent ability of cargo floor structure to absorb more energy during impact.

Crashworthiness Study of Composite Fuselage Section

Crashworthiness is one of the requirements for design of aircraft to ensure the safety of passengers on aircraft. With increasing applications of advanced composite in aircraft structures, study on the crashworthiness of composite fuselage is desirable and important. For this purpose, this paper investigates the influence of composites on crashworthiness of fuselage section. Firstly, model of fuselage section of aircraft is established. Skin, frame, stringer and stiffener are made of the composite T800/QY8911 or GLARE. Then, the crash responses subjected to vertical impact velocity of 9.14m/s are analyzed. The acceleration history is recorded for assessment of the crashworthiness. In addition, the deformation process and failure mode of composite fuselage section are analyzed. Results indicate that the frame made of brittle composite may fracture in the crash process, which leads to serious damage to the fuselage. While the frame with good toughness can maintain the integrity of fuselage, thereby protecting passengers.

Crashworthiness Analysis and Evaluation of Fuselage Section with Sub-floor Composite Sinusoidal Specimens

Crashworthiness is one of the main concerns in civil aviation safety particularly with regard to the increasing ratio of carbon fiber reinforced plastic (CFRP) in aircraft primary structures. In order to generate dates for model validations, the mechanical properties of T700/3234 were obtained by material performance tests, and energy-absorbing results were gained by quasi-static crushing tests of composite sinusoidal specimens. The correctness of composite material model and single-layer finite element model of composite sinusoidal specimens were verified based on the simulation results and test results that were in good agreement. A typical civil aircraft fuselage section with composite sinusoidal specimens under cargo floor was suggested. The crashworthiness of finite element model of fuselage section was assessed by simulating the vertical drop test subjected to 7 m/s impact velocity, and the influences of different thickness of sub-floor composite sinusoidal specimens on crashworthiness of fuselage section were also analyzed. The simulation results show that the established finite element model can accurately simulate the crushing process of composite sinusoidal specimens; the failure process of fuselage section is more stable, and the safety of occupants can be effectively improved because of the smaller peak accelerations that was limited to human tolerance, a critical thickness of sub-floor composite sinusoidal specimens can restrict the magnitude of acceleration peaks, which has certain reference values for enhancing crashworthiness capabilities of fuselage section and improving the survivability of passengers.

Crash simulations of aircraft fuselage section in water impact and comparison with solid surface impact

Aircraft water landing emergency provisions 14 CFR 25.801 demand requirement of ditching provision if requested in certification. This requires evaluation of the dynamic behaviour and response of aircraft in water impact to analyse the immediate injury to occupants. A correlated finite element model of a narrow-body Boeing-737 fuselage section and smoothed-particle hydrodynamics model of a body of water are coupled and utilised to investigate the structural response of the aircraft fuselage section when subjected to vertical drop test. The vertical drop of the fuselage section onto a body of water is simulated at an impact speed of 9.14 m/s, and also at higher impact speeds of 10.67 and 12.19 m/s. The vertical drop simulations are modelled using the non-linear explicit code, LS-DYNA, to predict the deformation of the fuselage section and acceleration pulses of the cabin floor, as well as the energy absorbed by the fuselage structure. The acceleration pulses from the cabin floor are then utilised as input for the occupant simulation performed using the mathematical code, MADYMO 7.5. The occupant model consists of a MADYMO FAA Hybrid-III 50th percentile dummy, a 2-point lap belt and a rigid seat. The lumbar loads experienced by the occupants in relation to both types of impacts are also presented. The dynamic simulation results from this study suggest that the fuselage section in water impact may be less severe than solid surface impact.

Crashworthiness study of a civil aircraft fuselage section

This paper studies the crashworthiness characteristics of a fuselage section and its improvement. A full-scale three-dimensional finite element model of the fuselage section is developed using a nonlinear finite element code, PAM-CRASH. The simulation is implemented to determine the structural deformation and impact response in terms of peak loads and acceleration peaks at the floor-level, deformation mode, energy absorption, and structural integrity, and then to assess the crashworthiness of the fuselage section. By partitioning the total energy dissipated, it is shown that the frames and the supports of the cargo floor play important roles in the process of energy dissipation. Based on the results, an effective approach to improve the crashworthiness of the fuselage section is presented. The paper also provides an in-depth analysis in the deformation mechanism of the fuselage section under a vertical crash, which will be helpful to effectively prevent the cabin floor from heavily damage and maintain the integrity of the fuselage section.