Effect of cold-working on corrosion induced damage in lug joints

Lug joints are preferred joineries for transferring heavy loads to parent components in aerospace vehicles.They experience corrosion due to environmental conditions,improper surface finishes and rubbing displacement between the pin and lug-hole.This causes damage of different sizes and shapes near the lug-hole.Stiffness degradation due to corrosion-induced damage is modelled as a through-pit at one of the identified critical locations through stress analysis.The effect of this pit on fatigue crack initiation life is estimated.Lug-hole is pre-stressed by cold-working and the benefits of inducing plastic wake on the intended performance of the lug joint during the damages due to corrosion are brought out and compared with non-cold-worked lug-hole.Numerical analysis is performed on this lug joint with pressfit.The results obtained highlight the benefits of cold-working and the methodology can be extended to damage growth and analyse the effect of surface treatments for better structural integrity of components of aerospace vehicles.

The Role of Particles in Fatigue Crack Propagation of Aluminum Matrix Composites and Casting Aluminum Alloys

Fatigue crack propagation （FCP） behaviors were studied to understand the role of SiC particles in 10 wt pct SiCp/A2024 composites and Si particles in casting aluminum alloy A356. The results show that a few particles appeared on the fracture surfaces in SiCp/Al composites even at high △K region, which indicates that cracks propagated predominantly within the matrix avoiding SiC particles due to the high strength of the particles and the strong particle/matrix interface. In casting aluminum alloy, Si particle debonding was more prominent.Compared with SiCp/Al composite, the casting aluminum alloy exhibited lower FCP rates, but had a slight steeper slope in the Paris region. Crack deflection and branching were found to be more remarkable in the casting aluminum alloy than that in the SiCp/Al composites, which may be contributed to higher FCP resistance in casting aluminum alloy.

Synthesize of AZ31/TiC magnesium matrix composites using friction stir processing

Friction stir processing(FSP)is a novel solid state technique to synthesize metal matrix composites.In the present work,an attempt has been made to synthesize AZ31/TiC magnesium matrix composites using FSP and to analyze the microstructure using scanning electron microscopy.A groove was prepared on 6 mm thick AZ31 magnesium alloy plates and compacted with TiC particles.The width of the groove was varied to result in four different volume fraction of TiC particles(0,6,12 and 18 vol.%).A single pass FSP was carried out using a tool rotational speed of 1200 rpm,traverse speed of 40 mm/min and an axial force of 10 kN.Scanning electron microscopy was employed to study the microstructure of the synthesized composites.The results indicated that TiC particles were distributed uniformly in the magnesium matrix without the formation of clusters.There was no interfacial reaction between the magnesium matrix and the TiC particle.TiC particles were properly bonded to the magnesium matrix.

Two-Dimensional Aerodynamic Models of Insect Flight for Robotic Flapping Wing Mechanisms of Maximum Efficiency

In the ＂modified quasi-steady＂ approach, two-dimensional （2D） aerodynamic models of flapping wing motions are analyzed with focus on different types of wing rotation and different positions of rotation axis to explain the force peak at the end of each half stroke. In this model, an additional velocity of the mid chord position due to rotation is superimposed on the translational relative velocity of air with respect to the wing. This modification produces augmented forces around the end of each stroke. For each case of the flapping wing motions with various combination of controlled translational and rotational velocities of the wing along inclined stroke planes with thin figure-of-eight trajectory, discussions focus on lift-drag evolution during one stroke cycle and efficiency of types of wing rotation. This ＂modified quasi-steady＂ approach provides a systematic analysis of various parameters and their effects on efficiency of flapping wing mechanism. Flapping mechanism with delayed rotation around quarter-chord axis is an efficient one and can be made simple by a passive rotation mechanism so that it can be useful for robotic application.

A Preliminary Numerical Investigation of Airborne Droplet Dispersion in Aircraft Cabins

The emergence of the novel coronavirus has led to a global pandemic which has led to the airline industry facing severe losses. For air travel to recover, airlines need to ensure safe air travel. In this paper, the authors have modeled droplet dispersion after a single breath from an index patient. Computational Fluid Dynamics (CFD) simulations are conducted using the k-ωSST turbulence model in ANSYS Fluent. The authors have taken into consideration several parameters such as the size of the mouth opening, the velocity of the cabin air as well as the number of droplets being exhaled by the index patient to ensure a realistic simulation. Preliminary results indicate that after a duration of 20 s, droplets from the index patient disperse within a 10 m2 cabin area. About 75% of the droplets are found disperse for up to 2 m axially behind the index patient. This could possess an enhanced risk to passengers sitting behind the index patient. Ultimately, this paper provides an insight into the potential of CFD to visualise droplet dispersal and give impetus to ensure that necessary mitigating measures can be taken to reduce the risk of infection through droplet dispersal.

CHT/CFD Analysis of Thermal Sensitivity of a Transonic Film-Cooled Guide Vane

Thermal parameters are important variables that have great influence on life time of turbine vanes.Therefore,accurate prediction of the thermal parameters is essential.In this study,a numerical approach for conjugate heat transfer(CHT)and computational fluid dynamics(CFD)is used to investigate thermal sensitivity of a transonic guide vane which is fully film-cooled by 199 film holes.Thermal barrier coating(TBC),i.e.,the typical TBC and a new one as the candidate TBC,and turbulence intensity(Tu),i.e.,Tu=3.3%,10%and 20%,are two variables used for the present study.At first the external surface temperatures of the vane material are compared.Next,the TBC surface temperatures are considered.Results show the major role of the lower thermal conductivity of TBC which results in the lower and more uniform temperature on the external surface of the vane substrate.Finally,the thermal sensitivity is presented in terms of the percentage reduction of the external surface temperatures of the vane material and the structural temperatures of the vane material at midspan,including the variations of average and maximum vane temperatures.Results show that TBC and Tu have significant effects on the external surface and structural temperatures of the vane substrate.The lower thermal conductivity of TBC leads to the higher difference between the thermal conductivity of the vane substrate and TBC,the reduction of heat transfer and the more uniform temperature within the vane structure.The results also show more effective protection for the average vane temperature from the two TBCs at higher Tus.However,Tu does not significantly affect the reduction of the maximum vane temperature even though the new TBC,which has the very low thermal conductivity,is used.

FPGA Implementation of Elliptic-Curve Diffie Hellman Protocol

This paper presents an efficient crypto processor architecture for key agreement using ECDH(Elliptic-curve Diffie Hellman)protocol over GF2163.The composition of our key-agreement architecture is expressed in consisting of the following:(i)Elliptic-curve Point Multiplication architecture for public key generation(DESIGN-I)and(ii)integration of DESIGN-I with two additional routing multiplexers and a controller for shared key generation(DESIGN-II).The arithmetic operators used in DESIGN-I and DESIGNII contain an adder,squarer,a multiplier and inversion.A simple shift and add multiplication method is employed to retain lower hardware resources.Moreover,an essential inversion operation is operated using the Itoh-Tsujii algorithm with similar hardware resources of used squarer and multiplier units.The proposed architecture is implemented in a Verilog HDL.The implementation results are given on a Xilinx Virtex-7 FPGA(field-programmable gate array)device.For DESIGN-I and DESIGN-II over GF2163,(i)the utilized Slices are 3983 and 4037,(ii)the time to compute one public key and a shared secret is 553.7μs and 1170.7μs and(iii)the consumed power is 29μW and 57μW.Consequently,the achieved area optimized and power reduced results show that the proposed ECDH architecture is a suitable alternative(to generate a shared secret)for the applications that require low hardware resources and power consumption.

STUDY OF NUMERICAL AND PHYSICAL FRACTURE WITH SPH METHOD

Two kinds of fractures can be observed in the SPH （smoothed particle hydrodynamics） simulations, which are the physical fracture and the numerical fracture. The physical one exists in reality, while the numerical one is fictitious. This paper presents the effects of both fractures and proposes a simple adding particle technique to avoid the numerical fracture. The real physical fracture is then figured out by using an applicable fracture criterion. Firstly, the effect of the numerical fracture on the computational accuracy is investigated by introducing the artificial fracture in a model of wave propagation. Secondly, a simple adding particle technique is proposed and validated by a three dimensional bending test. Finally, the experiments of penetration on the skin of aircrafts are simulated by both the initial SPH method and the improved method with the adding particle technique. The results show that the improved SPH method can describe the physical fracture very well with better accuracy.

Adaptive state estimation of groundwater contaminant boundary input flux in a 2-dimensional aquifer

In many circumstances involving heat and mass transfer issues,it is considered impractical to measure the input flux and the resulting state distribution in the domain.Therefore,the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative.Adaptive state estimator(ASE)is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique,thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters.The ASE is particularly designed for a system that encompasses independent unknowns and/or random switching of input and measurement biases.The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE,which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10%in 2-dimensional problems.Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios.Results also show that ASE enjoys a better estimation performance than its competitor,Recursive Least Square Estimator(RLSE)due to its larger error tolerance in greater process noise regimes.ASE's inherent deficiency of being slower than the RLSE,resulting from the complexity of algorithm,was also noticed.The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location.

Fatigue Behaviour of Silicon Carbide and Fly Ash Dispersion Strengthened High Performance Hybrid Al 5083 Metal Matrix Composites

Fatigue is a major issue concerning the use of aluminium composites in structural applications. Fatigue leads to weakening of material majorly due to the strain bands formed in the material when it is subjected to repeated loading;the damage that occurs due to fatigue is a progressive and localized one. The fatigue may occur at a stress limit much lesser than the ultimate stress limit of the composite specimen. Henceforth in the current work, fatigue behaviour of silicon carbide and fly ash dispersion strengthened high performance hybrid Al 5083 metal matrix composites are evaluated. The main purpose of fatigue characterisation is to distinctly evaluate the life cycle of components that are fabricated from metal matrix composites and eventually develop a framework model for the significant study of fatigue strength of the structure with persistent striations all along the interstitials of aluminium- silicon carbide-fly ash interfaces. Fatigue is a stochastic process rather than a deterministic one that gives a considerable scatter, even among samples of similar composition with the tests carried out in some of the critically controlled environments. Hence there is a need for statistical validation of the results to authenticate the data collected. Thus in the current work, analysis of variance is carried out to establish the authenticity of the results and validate them. The results and plots are presented with suitable rationale and inferences.

The Influence of Demoiselle Aircraft on Light and General Aviation Design

In 1907, aviation pioneer Santos-Dumont had the idea of building a very light airplane. He designed and built the SD 19, the Demoiselle, an aircraft with a 6 meter wing span and a 24 HP engine of his own design. The Demoiselle was very successful in flying and, became very popular and its development continued as SD20, SD21 and SD22 （his last airplane）. The influence of the Demoiselle on design principles of light aircraft and general aviation were studied in this work, using statistical entropy, The designs number 20 and 22 may be considered dominant and influenced the design principles of light aircraft and general aviation.

Studies on the Internal Ballistics of Composite Solid Rocket Propellants Incorporating Nano-Structured Catalysts

This paper deals with the analysis of burn rate using various catalysts of Iron Oxide and determining which gives the higher burn rate with low pressure variation. The Ammonium Perchlorate (AP) was obtained and ground into fine powder with the particle size ranging from 63 to 125 μm. The propellant strands were prepared with proportions by mixing AP with the binder (Hydroxyl Terminated Polybutadiene), the catalyst (Iron Oxide), curing agent (Isophorone diisocyanate) and the plasticizer (Dioctyladipate). The prepared propellant mixture was cured at around 63 deg C to get various propellant strands. The first strand was prepared with the absence of a catalyst to set an initial base of comparison with other Iron Oxide catalysts, namely, Flower Shaped, Micro and Nano, based on the size of the particles. The combustion process was carried out in a strand burner, which was in turn connected to a data acquisition system. The obtained output was analysed in the form of graphs. The burn rate was achieved by calculating the slope of the graph i.e . by calculating the difference between the highest and the lowest peak of the graph and dividing the total time by the answer. The experiment was repeated with the different catalyst types, as mentioned above, at different pressures. It was observed that the Nano shaped Iron Oxide exhibits better burning characteristics when compared to the rest with the pressure index of 0.792. In this paper, the various experiments carried out along with their procedures are explained in detail. The results obtained and the techniques used are also elaborately described in this paper.

Cross-linked polyelectrolyte reinforced SnO_(2)electron transport layer for robust flexible perovskite solar cells

SnO_(2)electron transport layer(ETL)is a vital component in perovskite solar cells(PSCs),due to its excellent photoelectric properties and facile fabrication process.In this study,we synthesized a water-soluble and adhesive polyelectrolyte with ethanolamine(EA)and poly-acrylic acid(PAA).The linear PAA was crosslinked by EA,forming a 3D network that stabilized the SnO_(2)nanoparticle dispersion.An organic–inorganic hybrid ETL is developed by introducing the cross-linked PAA-EA into SnO_(2)ETL,which prevents nano particle agglomeration and facilitates uniform SnO_(2)film formation with fewer defects.Additionally,the PAA-EA-modified SnO_(2)facilitated a uniform and compact perovskite film,enhancing the interface contact and carrier transport.Consequently,the PAA-EA-modified PSCs exhibited excellent PCE of 24.34%and 22.88%with high reproducibility for areas of 0.045 and 1.00 cm~2,respectively.Notably,owing to structure reinforce effect of PAA-EA in SnO_(2)ETL,flexible device demonstrated an impressive PCE of 23.34%while maintaining 90.1%of the initial PCE after 10,000 bending cycles with a bending radius of 5 mm.This successful approach of polyelectrolyte reinforced hybrid organic–inorganic ETL displays great potential for flexible,large-area PSCs application.

A survey on future research about electron beam welding for aerospace applications

Electron beam welding plays an important role in the aerospace industry where components like sensors,gears,actuators and air frames used in aircraft and rocket engines were welded using this technique.Welding is normally performed in a vacuum to avoid the scatter of electron due to the presence of gas molecules in the atmosphere and hence electron beam welding process provides the greater results.But still joining of dissimilar metals is challenging.This paper represents review of process,generation and distribution of heat source various input parameters,materials,microstructure,mechanical strength and the possibilities of joining dissimilar metals using electron beam welding.

Computational Simulation to Predict the Syngas Composition Produced during Charcoal Gasification

Charcoal gasification could mitigate the energetic problems in the rural zones since these regions have considerable amounts of wood, which is the base of such a fuel available. This paper presents some CFD （computational fluid dynamic） predictions of the experimental results obtained from the fixed bed gasification of charcoal made in a pilot-scale downdraft reactor using air, which was designed and built by the Research Group in Clean Development Mechanisms and Energy Management, from the National University of Colombia. The quality of the syngas obtained from the process was evaluated through the CO and CO2 percentages measured in its composition. The performance at various air flow rates （measured at the system entrance, through an analog flow meter） is evaluated with the help of 11 thermocouples, which give the information to create a temperature profile, and three load cells to measure the solid fuel conversion rate. To simulate the process, the information from temperature profile, charcoal proximate analysis, air flow meter and load cells were taken as inputs and the syngas composition was obtained as the result from the calculation. The domain was defined as 2D with an axis-symmetric description, using quads as mesh elements. The calculation and results were performed in a CFD commercial code widely used for this type of simulations： ANSYS FLUENT. The predictions made by the software were validated with the experimental results obtained in the laboratory.

A numerical optimization of high altitude testing facility for wind tunnel experiments

Abstract High altitude test facilities are required to test the high area ratio nozzles operating at the upper stages of rocket in the nozzle full flow conditions. It is typically achieved by creating the ambient pressure equal or less than the nozzle exit pressure. On average, air/GN2 is used as active gas for ejector system that is stored in the high pressure cylinders. The wind tunnel facilities are used for conducting aerodynamic simulation experiments at/under various flow velocities and operating conditions. However, constructing both of these facilities require more laboratory space and expensive instruments. Because of this demerit, a novel scheme is implemented for conducting wind tunnel experiments by using the existing infrastructure available in the high altitude testing （HAT） facility. This article presents the details about the methods implemented for suitably modifying the sub-scale HAT facility to conduct wind tunnel experiments. Hence, the design of nozzle for required area ratio A/A＊, realization of test section and the optimized configuration are focused in the present analysis. Specific insights into various rocket models including high thrust cryogenic engines and their holding mechanisms to conduct wind tunnel experiments in the HAT facility are analyzed. A detailed CFD analysis is done to propose this conversion without affecting the existing functional requirements of the HAT facility.

Design concepts of an aircraft wing： composite and morphing airfoil with auxetic structures

This paper is categorized into two parts. （1） A frame work to design the aircraft wing structure and （2） analysis ofa morphing airfoil with auxetic structure. The developed design frame work in the first part is used to arrive at the sizes of the various components of an aircraft wing structure. The strength based design is adopted, where the design loads are extracted from the aerodynamic loads. The aerodynamic loads acting on a wing structure are converted to equivalent distributed loads, which are further converted point loads to arrive at the shear forces, bending and twisting moments along the wing span. Based on the estimated shear forces, bending and twisting moments, the strength based design is employed to estimate the sizes of various sections of a composite wing structure. A three dimensional numerical model of the composite wing structure has been developed and analyzed for the extreme load conditions. Glass fiber reinforced plastic material is used in the numerical analysis. The estimated natural frequencies are observed to be in the acceptable limits. Furthermore, the discussed design principles in the first part are extended to the design of a morphing airfoil with auxetic structure. The advantages of the morphing airfoil with auxetic structure are （i） larger displacement with limited straining of the components and （ii） unique deformation characteristics, which produce a theoretical in-plane Poisson＇s ratio of -1. Aluminum Alloy AL6061-T651 is considered in the design of all the structural elements. The compliance characteristics of the airfoil are investigated through a numerical model. The numerical results are observed to be in close agreement with the experimental results in the literature.

Minimum Control Energy of Spatial Beam with Assumed Attitude Adjustment Target

The dynamic analysis on the ultra-large spatial structure can be simplified drastically by ignoring the flexibility and damping of the structure.However,these simplifications will result in the erroneous estimate on the dynamic behaviors of the ultra-large spatial structure.Taking the spatial beam as an example,the minimum control energy defined by the difference between the initial total energy and the final total energy in the assumed stable attitude state of the beam is investigated by the structure-preserving method proposed in our previous studies in two cases:the spatial beam considering the flexibility as well as the damping effect,and the spatial beam ignoring both the flexibility and the damping effect.In the numerical experiments,the assumed simulation interval of three months is evaluated on whether or not it is long enough for the spatial flexible damping beam to arrive at the assumed stable attitude state.And then,taking the initial attitude angle and the initial attitude angle velocity as the independent variables,respectively,the minimum control energies of the mentioned two cases are investigated in detail.From the numerical results,the following conclusions can be obtained.With the fixed initial attitude angle velocity,the minimum control energy of the spatial flexible damping beam is higher than that of the spatial rigid beam when the initial attitude angle is close to or far away from the stable attitude state.With the fixed initial attitude angle,ignoring the flexibility and the damping effect will underestimate the minimum control energy of the spatial beam.

Impact analysis of compressor rotor blades of an aircraft engine

Frequent failures due to foreign particle impacts are observed in compressor blades of the interceptor fighter MIG-23 aircraft engines in the Ethiopian air force,supplied by the Dejen Aviation Industry.In this paper,we made an attempt to identify the causes of failure and hence recommend the suitable materials to withstand the foreign particle impacts.Modal and stress analysis of one of the recently failed MIG-23 gas turbine compressor blades made up of the following Aluminum based alloys:6061-T6,7075-T6,and 2024-T4,has been performed,apart from the impact analysis of the rotor blades hit by a granite stone.The numerical results are correlated to the practical observations.Based on the modal,stress and impact analysis and the material properties of the three considered alloys,alloy 7075-T6 has been recommended as the blade material.

Highly efficient computation method for hazard quantification of uncontained rotor failure

Uncontained Engine Rotor Failure(UERF)can cause a catastrophic failure of an aircraft,and the quantitative assessment of the hazards related to UERF is a very important part of safety analysis.However,the procedure for hazard quantification of UERF recommended by the Federal Aviation Administration in advisory circular AC20-128A is cumbersome,as it involves building auxiliary lines and curve projections.To improve the efficiency and general applicability of the risk angle calculation,a boundary discretization method is developed that involves discretizing the geometry of the target part/structure into node points and calculating the risk angles numerically by iterating a particular algorithm over each node point.The improved efficiency and excellent accuracy for the developed algorithm was validated through a comparison with manual solutions for the hazard quantification of the engine nacelle structures of a passenger aircraft using the guidance in AC20-128A.To further demonstrate the applicability of the boundary discretization method,the proposed algorithm was used to examine the influence of the target size and the distance between the target and rotor on the hazard probability.