Hindustan Aeronautics Limited (India)

The present work deals with the identification of speed-dependent misalignment parameters in a multi-disk coupled rotor system supported on Tilting pad journal bearings (TPJB) and Active magnetic bearings (AMB). The stiffness matrix of misaligned coupling is modelled as the sum of static coupling stiffness (SCS) and additive coupling stiffness (ACS) matrices. The presence of parallel and/or angular misalignments gives rise to ACS matrix and its coefficients represent misalignment in/about a given direction. ACS coefficients are time dependent and a suitable mathematical function has been chosen to define the time varying nature of these coefficients. The global equations of motion (EOMs) are assembled and solved in time domain to obtain rotor vibration and AMB current data. This data is processed by full spectrum Fast Fourier Transform, and subsequently input to the identification algorithm. The stiffness and damping of TPJBs, stiffness of AMBs and ACS coefficients that correspond to misalignment are estimated at six different speeds along with speed-invariant disc unbalances, and SCS coefficients. The robustness of algorithm is tested against measurement noise and modelling bias. ACS coefficients have been identified within reasonable error margins. Finally, the method of application of the algorithm to real rotors is presented. The novelty of the work is the development of an inverse problem for the identification of parallel and angular misalignments in real rotors.

Abstract This study suggested the judicious application of the resin pre‐coating (RPC) technique during adhesive bonding. Electrochemical surface treatment (ECST) and ultrasonic chemical treatment (UCT) were done on the Al 7075 alloy. Subsequently heterogeneous adhesive bonding of the ECST‐processed and the UCT‐processed alloy with three different CFRPs, namely unidirectional (UD) CFRP, 4‐Harness Satin‐weaved (4HSW) CFRP, and plain‐weaved (PW) CFRP was investigated. ECST and UCT processes resulted in trench‐type surface structures and cavitation pits, respectively. After ECST, contact angles of deionized water and diiodomethane reduced drastically. The highest strengths for the adhesive joints with UD, 4HSW, and PW CFRPs were 28.50, 30.40, and 26.85 MPa, achieved respectively after 10 V ECST without RPC, 1 M UCT without RPC and 1 M UCT with RPC technique. Thin layer cohesive failure at the alloy interface (TLCF‐AI) respectively increased and decreased after application of the RPC technique on the ECST‐processed and the UCT‐processed alloy surface. RPC technique after ECST decreased the single lap shear strengths, whereas this after UCT increased the single lap shear strengths of the heterogeneous adhesive joints with all considered CFRPs. The effectiveness of the RPC technique depended on the combinations of adherend surface morphologies and adhesive properties.Highlights Judicious application of RPC technique during adhesive bonding was suggested. ECST or UCT was done on Al 7075 before joining with UD, 4HSW, and PW CFRP. ECST and UCT respectively caused trench‐type structures and cavitation pits. RPC after ECST decreased adhesive joint strength and increased TLCF‐AI. RPC after UCT increased adhesive joint strength and decreased TLCF‐AI.

Aircraft structures are frequently exposed to damage from environmental factors and operational wear, leading to the development of surface imperfections such as cracks. These imperfections can increase aerodynamic drag, a phenomenon known as excrescence drag. To mitigate these effects and quickly restore structural integrity, repair patches, often made from aluminium alloys and tailored to the damage, are applied following guidelines set out in the Aircraft Battle Damage Repair (ABDR) manuals. This paper investigates the aerodynamic performance impacts of applying such patches to two prominent airfoil models: the symmetric NACA 0012 and the cambered NACA 2412. Utilizing advanced computational tools including CATIA V5 for 3D modelling and CFD++ for fluid dynamics simulation, this study examines changes in aerodynamic characteristics such as lift, drag, and pressure distribution under various flow conditions. The research particularly focuses on quantifying the aerodynamic changes introduced by the patches through detailed analyses of lift curves, drag polars, and pressure coefficient (Cp) plots. Our findings aim to provide insights into the trade-offs involved in patch repairs, exploring how different patch configurations influence airfoil performance. This contributes to the development of optimized repair strategies that ensure minimal aerodynamic disruption while extending the operational lifespan of aircraft components.

In MANETs, nodes connect each other to share information. These nodes move from one place to other and co-operate with each other. Apart from the security, reliability is also one of the main concern in MANETs. Since, most of the devices in the MANET are mobile, mobility degrades the performance of routing protocol. We have proposed a Routing protocol for MANETs which takes mobility as a parameter and establishes a relative reliable path to the destination. our proposed routing protocol increased the throughput and packet Delivery ratio in mobility environment.

The purpose of this study is to investigate the influence of hybrid nanoparticle reinforcement with Al2O3 and ZrO2 on the mechanical and wear parameters of Al6061 alloy-based Nano composites. MMC’s (Metal Matrix Composite) specimens were produced using an ultrasonic-assisted stir casting method. Al6061 with varying weight percentages of Al2O3 (0.5%, 0.75%, 1% and 1.25%) and ZrO2 (0.5%, 0.75%, 1% and 1.25%) were used as reinforcement. The fabricated samples were made to undergo various tests as per ASTM standards to evaluate tensile strength, hardness and wear properties. Scanning Electron Microscopy was used to analyze the microstructure of the produced nano composite to ascertain the distribution of Al2O3 and ZrO2 nano particles and to analyze the fractured and wear characteristics. The results indicate that there is increase in tensile behavior for the composition of Al6061matrix alloy reinforced with 1wt. % Al2O3 and 1wt. % ZrO2 hybrid reinforcement. The maximum hardness achieved was 90.9 Hv with 1% ZrO2 and 1.25% Al2O3, representing a significant improvement over pure aluminum. The prepared specimens were subjected to a wear test utilizing a pin-on-disc machine and results reveal that highest wear resistance was obtained for the hybrid reinforcement of 1wt.% Al2O3 and 1wt.% ZrO2 with Al6061 alloy matrix.

The study of recrystallization and grain growth in annealed metals has been extensively investigated using various computational approaches, with Monte Carlo (MC) simulations proving particularly effective. This research highlights the application of the MC method in simulating microstructures that closely resemble experimentally observed ones. The experimental microstructures were obtained from a 50% cold-worked Al–4% Cu (Duralumin) alloy, annealed at different conditions. The Metropolis algorithm was employed to simulate the microstructures using a two-dimensional Potts model on a square lattice. The simulated results strongly correlate with the actual microstructures, validating the effectiveness of the MC method in exploring grain growth phenomena. This study underscores the potential of MC simulations as a robust tool for investigating recrystallization and grain evolution in annealed metals.

Diffusion welding is an advanced joining process that assures the feasibility of joining dissimilar metal alloys without producing metallurgical impurities at the joint interface. Two significant aerospace alloys, AA2219 and Ti-6Al-4V, are diffusion welded for the various holding times (30-120 minutes) by keeping the bonding temperature and pressure constant. The effect of holding time on the microstructure of the diffusion welded joints is evaluated using scanning electron microscopy (SEM), and the diffusion behaviour across the joint interface is ensued by the line scan energy dispersive spectroscopy (EDS). The obtained results show that the hardness across the joint interface is increased with increase in holding time. Furthermore, the maximum shear strength of 143.58 MPa is achieved for the joint formed at the holding time of 90 minutes and reduced thereafter. The formation of a thick intermetallic layer at a higher holding time strongly affects the shear strength. It is evident from the resulting fractured surfaces that the joints predominantly failed at the bonding interface, showcasing the brittle kind of failure. The X-ray diffraction (XRD) study on the fractured surfaces substantiates the formation of AlTi, Al2Ti and Al3Ti intermetallic compounds.