S. S. Akhtar

Parametric models for helicopter identification using ANN

An artificial neural network (ANN) based helicopter identification system is proposed. The feature vectors are based on both the tonal and the broadband spectrum of the helicopter signal, ANN pattern classifiers are trained using various parametric spectral representation techniques. Specifically, linear prediction, reflection coefficients, cepstrum, and line spectral frequencies (LSF) are compared in terms of recognition accuracy and robustness against additive noise. Finally, an 8-helicopter ANN classifier is evaluated. It is also shown that the classifier performance is dramatically improved if it is trained using both clean data and data corrupted with additive noise.

Characterization of Nanoreinforcement Dispersion in Inorganic Nanocomposites: A Review

Metal and ceramic matrix composites have been developed to enhance the stiffness and strength of metals and alloys, and improve the toughness of monolithic ceramics, respectively. It is possible to further improve their properties by using nanoreinforcement, which led to the development of metal and ceramic matrix nanocomposites, in which case, the dimension of the reinforcement is on the order of nanometer, typically less than 100 nm. However, in many cases, the properties measured experimentally remain far from those estimated theoretically. This is mainly due to the fact that the properties of nanocomposites depend not only on the properties of the individual constituents, i.e., the matrix and reinforcement as well as the interface between them, but also on the extent of nanoreinforcement dispersion. Therefore, obtaining a uniform dispersion of the nanoreinforcement in the matrix remains a key issue in the development of nanocomposites with the desired properties. The issue of nanoreinforcement dispersion was not fully addressed in review papers dedicated to processing, characterization, and properties of inorganic nanocomposites. In addition, characterization of nanoparticles dispersion, reported in literature, remains largely qualitative. The objective of this review is to provide a comprehensive description of characterization techniques used to evaluate the extent of nanoreinforcement dispersion in inorganic nanocomposites and critically review published work. Moreover, methodologies and techniques used to characterize reinforcement dispersion in conventional composites, which may be used for quantitative characterization of nanoreinforcement dispersion in nanocomposites, is also presented.

Laser gas assisted melting of preprepared alumina surface including TiC particles at surface

Abstract Laser gas assisted remelting of prepared alumina surface is carried out. In the prepreparation cycle, carbon film containing TiC particles of 50 μm thickness is formed at the alumina surface. Laser controlled melting is carried out on the preprepared alumina surface at high pressure nitrogen environment. The microstructural and morphological changes in the laser treated section are examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction (XRD). The microhardness of the resulting surface is measured, and the residual stress developed in the surface is determined from the XRD technique. ABAQUS code is used to predict the temperature and stress fields in the laser treated region. It is found that a dense structure containing undissolved TiC particles is formed in the surface region of the laser treated layer. The nitride compounds of AlN and Al(C, N) are formed at the surface during the laser treatment process. The columnar structure is formed beneath the dense structure. The predictions of residual stress agree with the results obtained from the XRD technique.

Laser Remelting of Zirconia Surface: Investigation into Stress Field and Microstructures

Investigation into the laser remelting of zirconia surfaces in a nitrogen gas environment is carried out. The thermal stress fields during and after the laser treatment process are predicted numerically. The microstructural and morphological changes in the laser-treated region are examined using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The residual stresses are determined using the XRD technique. It is found that the residual stress predicted remains high along a depth of 50 µm below the laser-treated surface. The predictions of residual stress agree well with the XRD data. A fine dendritic structure is formed in the vicinity of the surface, which contributes to the surface hardness. In addition, transformation of t-ZrO2 to c-ZrO2 at high temperature is accompanied by the formation of ZrN in the surface vicinity.

Laser forming and welding processes

Introduction to Laser Forming and Welding Processes.- Analytical Treatment of Laser Forming and Welding Processes.- Numerical Analysis for Laser Forming and Welding.- Experimental Analysis for Laser Forming and Welding.- Concluding Remarks.

Detection of helicopters using neural nets

Artificial neural networks (ANNs), in combination with parametric spectral representation techniques, are applied for the detection of helicopter sound. Training of the ANN detectors was based on simulated helicopter sound from four helicopters and a variety of nonhelicopter sounds. Coding techniques based on linear prediction coefficients (LPCs) have been applied to obtain spectral estimates of the acoustic signals. Other forms of the LPC parameters such as reflection coefficients, cepstrum coefficients, and line spectral pairs (LSPs) have also been used as feature vectors for the training and testing of the ANN detectors. We have also investigated the use of wavelet transform for signal de-noising prior to feature extraction. The performance of various feature extraction techniques is evaluated in terms of their detection accuracy.

Laser Cutting of Thin Aluminum and Silicon Alloy: Influence of Laser Power on Kerf Width

Laser cutting of aluminum-silicon sheet is carried out. The influence of laser output power on the kerf width is examined in details. The lump parameter analysis is introduced to predict the kerf width size. The percentage of kerf width size variation due to different laser output power levels is formulated. It is found that the kerf width size predicted agrees well with the experimental data. The influence of laser output power on the kerf width size is more pronounced for power levels 350 W. Keywords: laser cutting, aluminum-silicon, kerf width

Laser Cutting of Alloy Steel: Three-Dimensional Modeling of Temperature and Stress Fields

Laser cutting of alloy steel is of wide interest in metal industry due to precision of operation. In the present study, laser cutting of alloy steel, Haynes 188, is carried out. Temperature and stress fields in the cutting section are modeled using ABAQUS code in the line with the experimental conditions. In the model study, three-dimensional heating and thermal stress formation are incorporated. The resulting cut surfaces are examined using scanning electron microscope (SEM) and X-ray diffraction (XRD). The predictions of the residual stress formed around the edges are compared with the experimental data obtained from the XRD technique. It is found that the residual stress predicted agrees with the experimental data. High stresses are formed in the region, where the temperature gradients are high, while temperature is less than the melting temperature of the substrate material.

Microstructure and Thermal Stress Distributions in Laser Carbonitriding Treatment of Ti–6Al–4V Alloy

The results of experiments into laser assisted gas carbonitriding of a Ti-6Al-4V alloy are reported. The temperature and thermal stress fields were simulated using finite element analysis. Microstructural changes in the laser treated region were examined using scanning electron microscopy, energy dispersive X-ray, and X-ray diffraction. In the process, a carbon film was formed at the workpiece surface prior to laser processing and the laser scanning speed was kept constant during the process. It was found that the laser treated layer extended uniformly along the surface; the depth of the layer was about 55 μm. The formation of TiC x N 1-x , TiN, and TiC in the surface region enhances the hardness significantly.

Laser Cutting of Small Diameter Holes Into Alumina Tiles: Thermal Stress Analysis

Laser cutting of small diameter holes in alumina tiles is carried out. Temperature and stress fields are predicted numerically using the A B AQUS finite element code. The cut sections are examined by incorporating scanning electron microscope and optical microscope. The residual stress developed in the cutting section is determined using the X-ray diffraction technique. It is found that high residual stresses are formed in the cutting section, and predictions agree well with the experimental results. The laser cut edges are found to be free from the large cracks. However, interconnected shallow cracks are observed at the hole cut surface.