Simulations and Experiments of Hot Forging Design and Evaluation of the Aircraft Landing Gear Barrel Al Alloy Structure

In the present study, the hot forging design of a typical landing gear barrel was evolved using finite element simulations and validated with experiments. A DEFORM^3D software was used to evolve the forging steps to obtain the sound quality part free of defects with minimum press force requirements. The hot forging trial of a barrel structure was carried out in a 30 MN hydraulic press based on the simulation outputs. The tensile properties of the part were evaluated by taking samples from all three orientations (longitudinal, long transverse, short transverse). The hardness and microstructure of the part were also investigated. To study the soundness of the product, fluorescent penetrant inspection and ultrasonic testing were performed in order to identify any potential surface or internal defects in the part. From experiments, it was found that the part was formed successfully without any forging defects such as under filling, laps, or folds that validated the effectiveness of the process simulation. The tensile properties of the part were well above the specification limit (>10%) and the properties variation with respect to the orientation was less than 2.5%. The part has qualified the surface defects level of Mil Std 1907 Grade C and the internal defects level of AMS 2630 Class A (2 mm FBh). The microstructure shows mean grain length and width of 167 and 66 µm in the longitudinal direction. However, microstructure results revealed that the coarse grain structure was observed on the flat surface near the lug region due to the dead zone formation. An innovative and simple method of milling the surface layer after each pressing operation was applied to solve the problem of the surface coarse grain structure.     

Modelling and performance of distributed algorithm for scheduling dissimilar machines with set-up

Distributed arrival time control is a highly decentralized scheduling approach where each part entity autonomously controls its arrival time to meet the due-date in real time. This paper presents differential equation-based models for distributed arrival time control of parallel dissimilar machines including sequence-dependent set-up and flowshop scheduling. The main objective was to show that the behaviour of general systems under distributed arrival time control was predictable. Convergence properties of the resulting nonlinear systems were established using the theory of discontinuous differential equations. Geometry was used to gain insight into the behaviour of these nonlinear systems. An approximation model was proposed for mean arrival times when the dynamics resulted in a non-unique steady-state. The model was tested using numerical simulation and agreed well. Geometric insights were also used to investigate scheduling performance of distributed arrival time control. Simulation results indicated that distributed arrival time control could provide significant improvement, typically more than 20%, over commonly used dispatching rules for due-date-based measures. Improved predictability and favourable performance made distributed arrival time control an attractive approach for decentralized control of Just-In-Time production.     

Tensile and Fracture Properties of Aluminium Alloy AA2219-T87 Friction Stir Weld Joints for Aerospace Applications

Metallurgical and Materials Transactions A - The purpose of the present work is to study the mechanical behaviour of AA2219-T87 friction stir weld (FSW) joints at different temperatures (Room...     

Comparison of Hydrometallurgical Parameters of N,N‐Dialkylamides and of Tri‐n‐Butylphosphate

Straight‐chain N,N‐dihexyloctanamide (DHOA) and branched‐chain N,N‐di(2‐ethylhexyl)isobutyramide (D2EHIBA) have been identified as promising alternatives to tri‐n‐butylphosphate (TBP) for the reprocessing of spent uranium based fuels, and selective extraction of ²³³U from irradiated thorium fuels, respectively. The present work deals with the effects of different hydrodynamic parameters such as viscosity, density, and interfacial tension (IFT) on the phase‐separation time (PST) under uranium and thorium loading conditions. The IFT values have been determined under varying experimental conditions such as the aqueous nitric acid concentration, n‐dodecane purity, ligand concentration, and thorium/uranium loading conditions. These studies have suggested that the quality of n‐dodecane affects the IFT values of different solutions. The IFT values of D2EHIBA changed marginally (23.3 ± 0.9 mNm^?1) against THOREX feed solution for the wide range of D2EHIBA concentration (0.1–1.0 M). However, IFT, viscosity, and PST values increased with uranium loading of 1.1 M DHOA. These studies suggested that a lower phase‐disengagement rate with increased uranium loading was mainly due to the increased viscosity of the loaded 1.1 M DHOA solution.     

Error rates of DPSK systems with MIMO EGC diversity reception over Rayleigh fading channels

This paper analyzes the average bit error probability (BEP) of the differential binary and quaternary phase-shift keying (DBPSK and DQPSK respectively) with multiple-input multiple-output (MIMO) systems employing postdetection equal gain combining (MIMO EGC) diversity reception over Rayleigh fading channels. Finite closed-form expressions for the average BEP of DBPSK and DQPSK are presented. Two approaches are introduced to analyze the error rate of DQPSK. The proposed structure for the differential phase-shift keying (DPSK) with MIMO EGC provides a reduced-complexity and low-cost receiver for MIMO systems compared to the coherent phase-shift keying system (PSK) with MIMO employing maximal ratio combining (MIMO MRC) diversity reception. Finally, a useful procedure for computing the associated Legendre functions of the second kind with half-odd-integer order and arbitrarily degree is presented.     

Oxygen impurity in self-propagating high-temperature synthesis of NiAl

The technique of Self-propagating High-temperature Synthesis (SHS) was used to prepare NiAl from compacts using elemental powder mixtures in stoichiometric amounts under vacuum and argon atmosphere. Considerable changes in the oxygen contents of the specimen before and after the SH-synthesis were not observed. But, unusual occurrence of an impurity phase was noticed in the product as second phase precipitate. The sparsely distributed precipitates could be detected only in the Transmission Electron Microscope and was characterized to be an oxide of aluminium (-Al₂O₃) containing nickel oxide (NiO), whose solubility in -Al₂O₃ at room temperature has not been reported earlier. The occurrence of this phase could be traced to the oxygen on the surface of the reactant particles.     

A frictional Cosserat model for the flow of granular materials through a vertical channel

Summary A rigid-plastic Cosserat model has been used to study dense, fully developed flow of granular materials through a vertical channel. Frictional models based on the classical continuum do not predict the occurrence of shear layers, in contrast to experimental observations. This feature has been attributed to the absence of a material length scale in their constitutive equations. The present model incorporates such a material length scale by treating the granular material as a Cosserat continuum. Thus, localized couple stresses exist, and the stress tensor is asymmetric. The velocity profiles predicted by the model are in close agreement with available experimental data. The predicted dependence of the shear layer thickness on the width of the channel is in reasonable agreement with data. In the limit of small (ratio of the particle diameter to the half-width of the channel), the model predicts that the shear layer thickness scaled by the particle diameter grows as ^-1/3.     

Severe non-ketotic hyperosmolar coma--intensive care management

We prospectively studied 266 hands in 133 patients with carpal tunnel syndrome (CTS) in order to evaluate: the incidence of bilateral CTS symptoms; correlation between severity, duration of symptoms and bilateral occurrence of CTS; agreement of clinical and neurophysiological findings; and the neurophysiological findings in asymptomatic hands in unilateral CTS. The incidence of bilateral clinical CTS in our population was 87%. Neurophysiological impairment of median nerve was observed in about half of the asymptomatic hands. Follow-up of patients with unilateral CTS showed that contralateral symptoms developed in most cases. We found a significant positive correlation of bilateral CTS with the duration of symptoms, whereas there was no correlation with the severity of symptoms. Our data suggest that bilateral impairment of median nerve is the rule in patients with CTS and probably it has been underestimated in previous studies.     

Steady state and dynamic characteristics of partial journal bearings

The response of the lubricant film of a partial journal bearing to displacements and velocities of its journal for laminar Newtonian flow of the lubricant is presented. The bearing force coefficients (spring and damping coefficients) were evaluated experimentally on a sophisticated test rig, with control over all the essential variables. Test results are presented in non-dimensional form and are applicable to a bearing of 130° arc and with a length-to-diameter ratio of 0.8. Useful design data and a theoretical comparison are given.