Abstract: Single crystals of undoped and Au-doped MoS2 were grown by the chemical vapor transport method using iodine as a transporting agent. The doping effect of the Au was characterized by temperature-dependent piezoreflectance (PzR) spectroscopy measurements in broad range of temperatures from 25 to 300 K. The temperature dependent PzR spectra revealed prominent features in the vicinity of direct-band-edge excitons for both investigated samples. The energies and broadening parameters of the A and B excitons were determined via a detailed line shape fit of the PzR spectra. We observed that Au doping strongly reduces the splitting between A and B excitons as well as it causes the redshift of observed transitions in relation to the undoped MoS2. The origin of observed excitons was discussed.
Abstract: CNC turning is one among the metal cutting process in which quality of the finished product depends mainly upon the machining parameters such as feed, speed, depth of cut, type of coolant used, types of inserts used etc. Similarly the work piece material plays an important role in metal cutting process. This study involves in indentifying the optimized parameters in CNC turning of Brass. To identify and measure the formation of burrs in the turned samples, are examined under scanning electron microscope (SEM). The optimization techniques used in this study are Response surface methodology, and Genetic algorithm. Several comparisons were made between cutting parameters with surface roughness. These optimization techniques are very helpful in indentifying the optimized control factors with high level of accuracy.
Abstract: For numerical simulation of ship airwake by CFD, based on the use of an unstructured grid, the k-ε turbulence model and SIMPLE algorithm, the characteristic features of complex fluid flows eg recirculation zones and strong vortex fields in the aircarft operating region of a generic 3D frigate model was presented. The accuracy of the predication was checked by performing calculations on different grid sizes and comparing with wind-tunnel flow visualization data. A comparison of several typical spatial discretization schemes was performed. y+ values were also tested. The general features of the flow predicted in this paper compare reasonably well with experimental data. However, CFD simulation produced a higher velocity in the vicinity of vortex zone when compared to experimental data. Obvious differences exist between results by first-order upwind scheme (power law scheme) and second-order upwind scheme (QUICK scheme, third-order MUSCL scheme). Second-order upwind scheme (QUICK scheme, third-order MUSCL scheme) are recommended for the CFD simulation of ship airwakes with a modest increase in computational cost. y+ values from o (10) to o (1000) can all be accepted for the CFD simulation of ships (e.g., SFS1 ) with Reynolds number 108 or more.
Abstract: In order to study the influence of bend tube on firing accuracy due to gravity, a finite element model of sniper rifle, only considering the interaction between bullet and tube, was established based on nonlinear finite element method. The initial disturbance of bullet was taken as a measuring standard of firing accuracy. The model was used to simulate the launch process of sniper rifle under the condition of gravity static equilibrium in the method of the mixing calculation which had advantages of both dynamic explicit algorithm and static implicit algorithm. The simulation results show that vertical stiffness increases due to gravity and then the instantaneous velocity and attitude of bullet are largely influenced. Bending tube has a great influence on bullet motion.
Abstract: Ductile fracture of 2024-T3 aluminum alloy has been investigated under tensile and shear loading conditions. In order to predict rupture, a void–based meso–damage constitutive relationship which can deal with both tensile and shear problems is developed and implemented in commercial software ABAQUS. The tensile and shear fracture behaviors including the load–displacement response and crack propagation path, of 2024–T3 aluminum alloy are analyzed using the proposed approach and compared with experimental data. It is shown that the proposed approach can be used to predict the failure of ductile materials under complex loading conditions.
Abstract: Gear is one of the most important and commonly used components in machine system. Early detection of gear damage is crucial to prevent the machine system from malfunction. This paper proposes a method for detection of damaged tooth based on support vector machines. Statistical parameters of standard deviation, root mean square value, maximum value and mean value are extracted from the vibration signal as representative features of tooth conditions to be input to the support vector machine classifier. The validity of the presented method is confirmed by the application of detecting early damaged tooth during the cyclic fatigue test. The vibration acceleration on gear box is acquired as original data. Furthermore, the signal of each gear tooth is separately extracted from the signal for a further analysis.The experimental results demonstrate the effectiveness of the proposed method.
Abstract: This paper proposed a numerical approach called improved FE-BE (finite element-boundary element) method to solve the fluid-structure interaction problems of plate-like systems. In order to avoid the mesh of both faces of the thin plates, some dumb structures were added to make the plate systems closed. Thus the conventional FE-BE method can be adopted to solve this problem. The dynamic response equation of the inner region can be obtained by the FE method, and the acoustic added mass and damping coefficients of the exterior region can be obtained by the BE method. Then the final fluid-structure interaction equation can be easily solved. Numerical results of some examples are computed to demonstrate the validation of the present method. The comparison of numerical results and reference solutions shows that the proposed method is acceptable for solving the fluid-structure interaction of plates.
Abstract: In the paper a lift calculation of a two-dimensional airfoil with a plain flap and Krueger flap is investigated. Numerical-analytical method (NAM) is used to predict the flow field around this combination. In order to calculate the complex velocity in the flow field, the complex variable function theory is employed. NAM based on the joint application of conformal mapping and the discrete vortex method (DVM). The paper presents a brief description of the NAM and some results of the lift calculations of the airfoil with the plain flap and Kruger flap. Comparison of the calculation results with the theoretical data of other authors showed a good agreement.
Abstract: Vibratory transport and technological machines (VTTM) are widely used in the various spheres of the industry: for transportation of the friable and separate particles, their dosed supply, sorting and realization of various technological processes.One of the factors that has an influence on the process of vibratory transportation is elasticity of the working member bottom of a vibratory transportation and technologic machine.This problem is less studied in theory of vibratory transportation [1, 2].A system vibratory drive – rigid frame of the vibratory member – elastic bottom of the working member – friable load” is considered in the report and dynamical and mathematical models of their interaction are worked out.A systematic approach to the study of influence of the working member elastic bottom on the technologic process is used and some results of the research are presented.It has been established with the help of developed models that at coincidence of phases of vibrations of the working member frame and elastic bottom rigidly fastened to it a speed of transportation of the friable material (load) rises significantly. On the bases of the mentioned result a new construction is developed.
Abstract: Mastering the relationship between the final mechanical properties of carbon black reinforced rubber blends and their composition is a key advantage for an efficient design of the composition of the blend. In this work, some models to predict three relevant physical attributes of rubber blends — modulus at 100% deformation, Shore A hardness, and tensile strength — are built by machine learning methods and subsequently evaluated. Linear regression, artificial neural networks, support vector machine, and regression trees are used to generate the models. The number of used samples and the values for the input variables is determined by a Taguchi design of experiments, and prior to the modeling the uncertainty of the experimental data was analyzed.