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Effect of elasto-plastic compatibility of grains on void-initiation criteria in low-carbon steel
No full textThe present study provides evidence for the role of ferrite-grain-size distributions on the occurrence of void initiation in a low-carbon steel. Various thermomechanical treatments were undertaken to create ultrafine, bimodal and coarse distributions of ferrite grain sizes. A two-parameter characterisation of probable void initiation sites is proposed, namely an elastic modulus difference and a difference in Schmid factor of the grains surrounding the void. All microstructures were categorised based on the ability to facilitate or resist void nucleation. For coarse grains, the elastic modulus and the Schmid factor differences are the highest, while they are intermediate for ultrafine grains and the lowest for the bimodal microstructure
Laser material interaction parameter: New tool for developing property diagrams for welds
No full textDetailed processing-property correlation studies have been attempted on laser beam welded AA 5024 (Al-Mg-Sc) alloys. These alloys are mostly used for integrally stiffened panels for aerospace applications. Different combinations of laser power, weld speed, beam diameter, and beam shape were chosen, and an optimized yield stress and uniform elongation map has been obtained. A comparative assessment of weld quality was done for the solid-state laser and the CO2 laser with two heat transfer modes, i.e., deep penetration (keyhole) and partial penetration (conduction) modes used for various aforementioned parameters. The weld parameters are ranked thereafter according to their merits and demerits encountered in this work. It has been seen that flexibility in terms of power, speed, and energy of a solid-state laser is more compared to the CO2 laser. Fundamental laser material interaction parameters have been studied, and an optimization strategy was formulated based on specific point energy of beam material interaction. The weld pool geometry has also been studied and correlated with interaction parameters. Weld size, shape, geometry, and evidence of solidification cracking have been studied from weld cross section macrographs. Variations of weld yield strength and elongation with welding energy input have been investigated thoroughly. Based on the above examinations, exaction of the optimal processing window is achieved
Superior Strength with Enhanced Fracture Resistance of Al-Mg-Sc Alloy Through Two-Step Cryo Cross Rolling
No full textThe evolution of microstructure and the preferred orientation during the two-step cross rolling at room (RT) and cryogenic temperatures (CTs) on Al-Mg-Sc alloy were investigated and compared with the unidirectional rolled Al-Mg-Sc alloy in this study. In addition, the effects of two-step cross rolling on tensile, forming and void coalescence behavior were analyzed. After the solution heat treatment, the two-step cross rolling was executed with an initial 25 pct reduction in the unidirectional path and the final 25 pct reduction in the transverse direction. The two-step cross-rolled (TSCR) Al-Mg-Sc alloy at CT showed a higher fraction of sub-micron grains. The TSCR Al-Mg-Sc alloy exhibited brass and copper and a strong S texture. The texture indices and in-plane anisotropy values indicated the highly anisotropic nature of the TSCR Al-Mg-Sc alloy. During tensile deformation, the TSCR Al-Mg-Sc alloy at CT exhibited a strength value of 423 MPa, whereas the TSCR Al-Mg-Sc alloy at RT revealed only 378 MPa. The TSCR Al-Mg-Sc alloy at CT exhibited inferior formability compared with the TSCR Al-Mg-Sc alloy at RT and the solution heat-treated base alloy. The formability of the TSCR Al-Mg-Sc alloy was evaluated through the combined forming and fracture limit diagram (CFFLD). The presence of higher Goss-oriented grains enhanced the fracture resistance of the TSCR Al-Mg-Sc alloy at CT. Furthermore, consistency was found between the evaluated void coalescence parameters and the CFFLD
Flight Envelope Protection for a Fighter Aircraft
No full textAn automatic scheme for the flight envelope protection of fighter aircraft is developed to prevent departure due to loss of control. The scheme involves taking control away from the pilot some time prior to an impending departure. The automatic recovery system then puts the aircraft into a safe attitude for recovery. The stability of the recovery trajectory is analysed within the flight envelope of the aircraft. The analysis demonstrates that the phugoid mode become critical for the recovery from low speed. The specific energy is demonstrating to be a much simple way of handling low speed recovery problems compare to existing solutions available.In addition,a unique command path design has been incorporated to assist automatic low speed recovery. The scheme is illustrated using the database of a high performance fighter aircraft with multiple redundant controls
Arrhythmia classification with single beat ECG evaluation and support vector machine
No full textAbnormal electrical activity of the human heart
indicates cardiac dysfunction. The Electrocardiogram (ECG) is one of the non-invasive diagnostic techniques to detect cardiac abnormalities. Irregularity and non-stationarity in the ECG signal impose difficulties to clinicians for accurate diagnosis of heart diseases only by visual inspection. Automatic recognition of
abnormal ECG beats aids in early detection of heart diseases. This paper explores the ECG single beat analysis to identify the cardiac abnormality. In this work, seven classes of arrhythmia are considered as recommended by AAMI(Association for the Advancement of Medical Instrumentation) standard. Beat feature database is generated from 44 recordings of the MIT-BIH
arrhythmia database to support the arrhythmia classification. Classification is implemented with Multiclass Support Vector Machine (SVM) for non-linearly separable data effectively. Classification accuracy up to 93% is achieved for the selected input feature sets. This work assesses the suitability of the ECG input features for multi-class classification of arrhythmia
Health management of a typical small aircraft fuel system using an adaptive technique
No full textFaults in the aircraft fuel system will degrade its performance and may lead to the complete system failure. In commercial aircraft system, efficient diagnosis can optimize the time to return the aircraft to service, thus allowing less disruption to passenger travel. In this work, an adaptive fault diagnosis technique is developed for a typical small aircraft fuel system, which facilitates efficient learning procedure to forecast the system parameters for non-linear situations. This adaptive technique represents the integration of the Fuzzy Logic and Support Vector Machine (SVM) algorithms in the field of fault diagnosis. Using this adaptive technique health monitoring of aircraft fuel system is discussed. In an aircraft fuel tank, the fault is effectively located by assessing and contrasting the actual parameters and set point parameters related to the system for various time-frames. The fuzzy logic controller is configured with the logical rules as per the required target output. It relies on the aircraft fuel system parameters like the fuel flow rate, level of fuel in the tank, fuel temperature, and fuel pressure. From the logical rules, the control signals related to the aircraft fuel system are derived by the SVM technique. The efficiency in execution of this fault diagnosis tool-based aircraft fuel system gets authenticated in the MATLab/Simulink platform. The simulation is carried by assuming normal operating conditions of aircraft in the laboratory environment
Effect of hygrothermal aging on the interlaminar shear strength of a carbon fibre composite
No full textCarbon Fibre Reinforced Plastic (CFRP) composites are used many applications in
aerospace structures due to their high specif ic strength and stiffness. Composite aircraft structures are usually exposed to a range of environmental conditions such as hygroth ermal, UVradiation, chemical environments, biological condition etc., in their service life and may degrade. Moisture absorption at different hygrotherma l conditions and its effects on properties of CFRP composites is a useful parameter to designers and application engineers. In this study, UD carbon fiber/epoxy composite laminates were fabricated (HexPly® M21E/34%/UD/194/IMA) from prepreg using standard autoclave process. Inter Laminar Shear Strength (ILSS) test specimens were cut and prepared from theses laminates. Hot-wet specimens were aged at two different conditions; 75 0C/ 85% RH, 55 0C/ 100% RH until attaining moisture absorption saturation. Three-point bend tests were conducted as per ASTM test standard specifications using a 25 KN servo-hydraulic test machine to determine ILSS properties for aged and unaged material. Respective hot -wet conditions were maintained even during the mechanical tests. Tests results show that moisture absorption rate increases gradually and attains saturation at about 1 wt. % under both conditions. Inter laminar shear strength reduced significantly by about 33% due to presence of moisture. Microscopic observation of failed samples also investigated to study the fracture behavior and reported in this paper
Enhanced microwave absorption properties of PMMA modified MnFe2O4-polyaniline nanocomposites
No full textA manganese based spinel ferrite, chemically modified with polymethyl methacrylate (PMMA) and polyaniline (PANI) are synthesized and their composites are used as electromagnetic interference (EMI) shielding materials. X-ray diffraction studies show that the as-prepared manganese ferrite crystallizes in a cubic spinel structure. The particles are highly agglomerated and nanocrystalline as indicated by transmission electron microscopy. Manganese exists in +2 and +4 oxidation states and Fe in +2 and +3 oxidation states. Modified manganese ferrite and polyaniline composites in different weight ratios are evaluated for their EMI shielding properties. It is observed that composites containing the PMMA modified ferrite show enhanced total shielding effectiveness (SET) compared to those containing the unmodified ferrite in the X band frequency range (8-12 GHz). The optimized ratio of the PMMA modified ferrite and PANI demonstrates SET values as high as 44 dB in the X band frequency range
Electro-Hydraulic Actuation Systems Design, Testing, Identification and Validation
No full textThis brief highlights the importance and the necessity of carrying out system identification in the context of electro-hydraulic actuation system for flight control applications
Cyclostationarity analysis of GPS signals for spoofing detection
No full textAnalysis of cyclostationarity property in GPS signals for spoofing detection is presented in a software-defined GPS receiver framework. GPS spoofing is an attempt to mislead GPS
receivers by sending false GPS signals. For the analysis of spoofed GPS signals, cyclic autocorrelation function (CAF) and spectral correlation density (SCD) graphs are considered. For the validation of the proposed method, a set of recorded GPS spoofed data known as Texas Spoofing Test Battery (TEXBAT), which is an evolving standard test for evaluating GPS spoofing countermeasures, is used. When CAF and SCD of a GPS signal with and without spoofing are calculated, results showed that the fundamental cyclic frequency of GPS signal changes due to spoofing