Showing papers in "Journal of Mechanical Science and Technology in 2014"

Eigenvalue approach for an unbounded medium with a spherical cavity based upon two-temperature generalized thermoelastic theory

Abstract: The thermoelastic interaction in an unbounded medium with a spherical cavity is studied using two-temperature generalized thermoelasticity theory. The medium is assumed to be initially quiescent. The inner surface of the cavity is taken traction free and subjected to a thermal shock. By the Laplace transformation, the basic equations are expressed in the form of a vector-matrix differential equation, which is solved by an eigenvalue approach. Some comparison have been shown in figures to estimate the effect of the two-temperature parameter.

A hybrid Taguchi-artificial neural network approach to predict surface roughness during electric discharge machining of titanium alloys

Abstract: In the present study, electric discharge machining process was used for machining of titanium alloys. Eight process parameters were varied during the process. Experimental results showed that current and pulse-on-time significantly affected the performance characteristics. Artificial neural network coupled with Taguchi approach was applied for optimization and prediction of surface roughness. The experimental results and the predicted results showed good agreement. SEM was used to investigate the surface integrity. Analysis for migration of different chemical elements and formation of compounds on the surface was performed using EDS and XRD pattern. The results showed that high discharge energy caused surface defects such as cracks, craters, thick recast layer, micro pores, pin holes, residual stresses and debris. Also, migration of chemical elements both from electrode and dielectric media were observed during EDS analysis. Presence of carbon was seen on the machined surface. XRD results showed formation of titanium carbide compound which precipitated on the machined surface.

Optimization of machining parameters for EDM operations based on central composite design and desirability approach

Abstract: A novel aluminium metal matrix composite reinforced with SiC particles were prepared by liquid metallurgy route. Recent developments in composites are not only focused on the improvement of mechanical properties, but also on machinability for difficult-to-machine shapes. Electrical discharge machining (EDM) was employed to machine MMC with copper electrode. using EDM. Experiments were conducted using pulse current, gap voltage, pulse on time and pulse off time as typical process parameters. The experiment plan adopts face centered central composite design of response surface methodology. Analysis of variance was applied to investigate the influence of process parameters and their interactions viz., pulse current, gap voltage, pulse on time and pulse off time on material removal rate (MRR), electrode wear ratio (EWR) and surface roughness (SR). The objective was to identify the significant process parameters that affect the output characteristics. Further a mathematical model has been formulated by applying response surface method in order to estimate the machining characteristics such as MRR, EWR and SR.

Analytical solution for two-phase flow between two rotating cylinders filled with power law liquid and a micro layer of gas †

Abstract: This paper deals with the effects that a thin gas layer exerts on the hydrodynamic aspects of power law liquid in a radial Couette flow between two cylinders. Analytical solution is made to determine the velocity profile in the two-phase flow system occupied by the power law liquid and the micro layer of a gas. It is shown that the thin (micro) gas layer contributes in reducing torque to set the fluid in motion in most cases. However, by considering generalized power law liquids, this paper limits the credibility for the positive role of the gas layer on reducing the torque for lubrication. For instance, when n < 0.5 (n is the behavior index of the liquid), slight increment in the torque (about 6%) is reported. Finally, energy gradient method is used for stability analysis. It is shown that the stability nature may be changed based on behavior index of the liquid.

A machine learning approach for the condition monitoring of rotating machinery

Abstract: Rotating machinery breakdowns are most commonly caused by failures in bearing subsystems. Consequently, condition monitoring of such subsystems could increase reliability of machines that are carrying out field operations. Recently, research has focused on the implementation of vibration signals analysis for health status diagnosis in bearings systems considering the use of acceleration measurements. Informative features sensitive to specific bearing faults and fault locations were constructed by using advanced signal processing techniques which enable the accurate discrimination of faults based on their location. In this paper, the architecture of a diagnostic system for extended faults in bearings based on neural networks is presented. The multilayer perceptron (MLP) with Bayesian automatic relevance determination has been applied in the classification of accelerometer data. New features like the line integral and feature based sensor fusion are introduced which enhance the fault identification performance. Vibration feature selection based on Bayesian automatic relevance determination is introduced for finding better feature combinations.

Experimental analysis on cutting fluid dispersed with silver nano particles

Abstract: Cutting fluids play a significant role in machining operations, impact shop productivity, tool life and quality of work. The reduction in the consumption rate of the cutting fluid leads to the minimization of production cost and environmental hazards. This could be achieved by the enhancement of its thermal and tribological properties with the inclusion of suitable additives in the cutting fluid. In recent years various nanoparticles were used as additives in the conventional cutting fluid to enhance its properties. In the present work, silver nanoparticles was synthesized, characterized, dispersed in cutting fluid and experimented in a turning operation. Heat carrying capacities of the cutting fluid, cutting forces during machining process and surface finish of the work piece were assessed by suitable instruments for cutting fluids with and without silver nanoparticles under different machining conditions. From the experimental results, it was observed that inclusion of silver nanoparticles in cutting fluid showed a significant reduction in tool tip temperature, cutting force and surface roughness of the work piece.

Numerical study of blowing and suction slot geometry optimization on NACA 0012 airfoil

Abstract: The effects of jet width on blowing and suction flow control were evaluated for a NACA 0012 airfoil. RANS equations were employed in conjunction with a Menter’s shear stress turbulent model. Tangential and perpendicular blowing at the trailing edge and perpendicular suction at the leading edge were applied on the airfoil upper surface. The jet widths were varied from 1.5% to 4% of the chord length, and the jet velocity was 0.3 and 0.5 of the free-stream velocity. Results of this study demonstrated that when the blowing jet width increases, the lift-to-drag ratio rises continuously in tangential blowing and decreases quasi-linearly in perpendicular blowing. The jet widths of 3.5% and 4% of the chord length are the most effective amounts for tangential blowing, and smaller jet widths are more effective for perpendicular blowing. The lift-to-drag ratio improves when the suction jet width increases and reaches its maximum value at 2.5% of the chord length.

Fault diagnosis of rotating machine by thermography method on support vector machine

Abstract: Feature-based classification techniques consist of data acquisition, preprocessing, feature representation, feature calculation, feature selection, and classifiers They are useful for online, real-time condition monitoring and fault diagnosis / features, which are now available with the development of information technologies and various measurement techniques In this paper, an intelligent feature-based fault diagnosis is suggested, developed, and compared with vibration signals and thermal images Fault diagnosis is performed using thermal imaging along with support vector machine (SVM) classification to simulate machinery faults, resulting in an accuracy level comparable to vibration signals The observed results show that fault diagnosis using thermal images for rotating machines can be applied to industrial areas as a novel intelligent fault diagnostic method with plausible accuracy It can be also proposed as a unique non-contact method to analyze rotating systems in mass production lines within a short time

Modeling and simulation of joint clearance effects on mechanisms having rigid and flexible links

Abstract: In this study, kinematic and dynamic characteristics of a planar four-bar mechanism having joint clearance and link flexibility are investigated. Assuming that joint clearance as a virtual massless link, artificial clearances are developed at crank-coupler and coupler-follower joints. Contact model in joints with clearance is established using the nonlinear spring-damper model and the friction effect is considered using the Coulomb friction model. Then the simulation is implemented and the kinematic and dynamic characteristics of model mechanism are investigated. The computational methodology can predict the effects of clearance on planar mechanism having rigid and flexible links. The results are evaluated for the case of stationary phase, and naturally show that extreme values occur in output of the mechanism with clearances. Due primarily to the suspension effect of the flexible link, values of these peaks in the flexible mechanism decrease relative to that of the rigid mechanism. In addition, the flexibility has a significant effect on the vibration response of the mechanism with joint clearance.

Experimental estimation and optimization of process parameters under minimum quantity lubrication and dry turning of AISI-4340 with different carbide inserts

Abstract: An experimental study has been performed on AISI 4340 steel in this paper. The influence of approach angle, feed rate, cutting speed and depth of cut has been on cutting forces and tool tip temperature has been experimentally investigated. Before conducting experiments on the AISI 4340 steel work-piece, the chemical composition test, microstructure test were performed and hardness of the work-piece was improved by heat treatment. A total of 64 experiments each by two different coated carbide inserts (PVD and CVD-coated) were conducted on AISI-4340 steel under different environmental conditions (dry and MQL machining). During the experiments, approach angle, cutting speed, feed rate are varied to four levels and the depth of cut is kept constant to investigate the effect of the same on the three cutting forces component and the temperature variations on the tool-tip. It is observed that the main cutting force was largest among the three cutting force components in case of AISI 4340 steel turning and MQL machining show beneficial effects compared to dry machining.

Effects of pressure and carbon dioxide, hydrogen and nitrogen concentration on laminar burning velocities and NO formation of methane-air mixtures

Abstract: We studied the effects of increasing pressure and adding carbon dioxide, hydrogen and nitrogen to Methane-air mixture on premixed laminar burning velocity and NO formation in experimentally and numerically methods. Equivalence ratio was considered within 0.7 to 1.3 for initial pressure between 0.1 to 0.5 MPa and initial temperature was separately considered 298 K. Mole fractions of carbon dioxide, hydrogen and nitrogen were regarded in mixture from 0 to 0.2. Heat flux method was used for measurement of burning velocities of Methane-air mixtures diluted with CO2 and N2. Experimental results were compared to the calculations using a detailed chemical kinetic scheme (GRI-MECH 3.0). The results in atmosphere pressure for Methane-air mixture were calculated and compared with the results of literature. Results were in good agreement with published data in the literature. Then, by adding carbon dioxide and nitrogen to Methaneair mixture, we witnessed that laminar burning velocity was decreased, whereas by increasing hydrogen, the laminar burning velocity was increased. Finally, the results showed that by increasing the pressure, the premixed laminar burning velocity decreased for all mixtures, and NO formation indicates considerable increase, whereas the laminar flame thickness decreases.

Condition monitoring of engine timing system by using wavelet packet decomposition of a acoustic signal

Abstract: A change in the technical condition of mechanical components of internal combustion engines may not be detected by on-board diagnostic systems installed in vehicles. In similar cases, measurements and analyses of vibroacoustic signals being recorded prove useful. Since there are certain limitations to vibration measurements, including those related to the vibration transmission and the engine’s high temperature at measurement points, the authors of this paper have proposed that measurements and analyses of acoustic signals should be applied for the sake of assessment of the internal combustion engine technical condition. However, such an assessment requires new acoustic signal processing methods to be developed, and so this subject has been elaborated in the paper. The article provides a discussion on the option of applying a wavelet packet decomposition while filtering the internal combustion engine’s acoustic signal in order to diagnose an excessive valve clearance. The authors prepared an algorithm enabling selection of the chosen details and approximation of the wavelet analysis to low-frequency components, which constitute the noise, as well as high-frequency components comprising information on the possible enlarged engine valve clearance. Next, based on the selected high-frequency acoustic signal components, a method for automatic detection of enlarged clearance valves was developed, assuming that energy participations of the acoustic signal being emitted were to be determined while opening and closing individual valves. Under the study discussed, identification tests were conducted using two 4-cylinder internal combustion engines featuring valves of different clearances to consequently confirm the efficiency of the algorithm developed for the acoustic signal filtration and automatic detection of enlarged clearance valves.

Optimization of cryogenic cooled EDM process parameters using grey relational analysis

Abstract: This paper presents an experimental investigation on cryogenic cooling of liquid nitrogen (LN2) copper electrode in the electrical discharge machining (EDM) process. The optimization of the EDM process parameters, such as the electrode environment (conventional electrode and cryogenically cooled electrode in EDM), discharge current, pulse on time, gap voltage on material removal rate, electrode wear, and surface roughness on machining of AlSiCp metal matrix composite using multiple performance characteristics on grey relational analysis was investigated. The L18 orthogonal array was utilized to examine the process parameters, and the optimal levels of the process parameters were identified through grey relational analysis. Experimental data were analyzed through analysis of variance. Scanning electron microscopy analysis was conducted to study the characteristics of the machined surface.

Modeling the effect of intermolecular force on the size-dependent pull-in behavior of beam-type NEMS using modified couple stress theory

Abstract: Experimental observations reveal that the physical response of nanostructures is size-dependent. Herein, modified couple stress theory has been used to study the effect of intermolecular van der Waals force on the size dependent pull-in of nanobridges and nanocantilevers. Three approaches including using differential transformation method, applying numerical method and developing a simple lumped parameter model have been employed to solve the governing equation of the systems. The pull-in parameters i.e. critical tip deflection and instability voltage of the nanostructures have been determined. Effect of the van der Waals attraction and the size dependency and the importance of coupling between them on the pull-in performance have been discussed.

Bird strike analysis on a typical helicopter windshield with different lay-ups

Abstract: In the current paper, bird strike to a typical helicopter windshield is investigated using smoothed particles hydrodynamic (SPH) finite element method. Five types of lay-ups in a windshield (single layer stretch acrylic, single layer glass, two-wall cast acrylic, acrylic with Polyvinyl butyral (PVB) interlayer and glass with PVB interlayer) is considered and in each case the thickness which prevents the bird from perforating the windshield is calculated. Since helicopters can have lateral movement in addition to their longitudinal movement, the effect of incident angle on the integrity of windshield is also investigated. Simulations showed that among the five cases presented, glass with PVB interlayer can be the best choice for being used in windshield against bird strike. Another conclusion is that for the same initial velocity, the angled impact can cause more damage in the windshield than the direct impact.

Nonlinear adaptive robust backstepping force control of hydraulic load simulator: Theory and experiments

Abstract: High performance robust force control of hydraulic load simulator with constant but unknown hydraulic parameters is considered. In contrast to the linear control based on hydraulic linearization equations, hydraulic inherent nonlinear properties and uncertainties make the conventional feedback proportional-integral-derivative (PID) control not yield to high performance requirements. Furthermore, the hydraulic system may be subjected to non-smooth and discontinuous nonlinearities due to the directional change of valve opening. In this paper, based on a nonlinear system model of hydraulic load simulator, a discontinuous projection-based nonlinear adaptive robust back-stepping controller is developed with servo valve dynamics. The proposed controller constructs a novel stable adaptive controller and adaptation laws with additional pressure dynamic related unknown parameters, which can compensate for the system nonlinearities and uncertain parameters, meanwhile a well-designed robust controller is also synthesized to dominate the model uncertainties coming from both parametric uncertainties and uncertain nonlinearities including unmodeled and ignored system dynamics. The controller theoretically guarantee a prescribed transient performance and final tracking accuracy in presence of both parametric uncertainties and uncertain nonlinearities; while achieving asymptotic output tracking in the absence of unstructured uncertainties. The implementation issues are also discussed for controller simplification. Some comparative results are obtained to verify the high-performance nature of the proposed controller.

Effect of clearance and inclined angle on sheared edge and tool failure in trimming of DP980 sheet

Abstract: Ultra-high-strength steels are widely used in automotive industry for lightweight and high crash performance. In this study, the effects of process variables such as the clearance and the inclined angle of the die on the sheared edge characteristics of trimmed DP980 have been evaluated in detail. The maximum trimming load decreases with increasing clearance due to a large bending moment leading to a hydrostatic tensile stress in the sheared zone, and tensile typed burr occurs at a trimming clearance above 15.6%t. Also, a negative inclined angle improves the quality of sheared edge and decreases the trimming load. As a result of the trimming experiment, the burr height gradually increases with an increase in the number of strokes due to tool failure resulted from high contact pressure. Furthermore, the burr height significantly decreases as the localization zone is connected linearly from punch to die edge with the negative inclined angle.

Navigation of autonomous mobile robot using adaptive network based fuzzy inference system

Abstract: Intelligent soft computing techniques such as fuzzy inference system (FIS), artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) are proven to be efficient and suitable when applied to a variety of engineering systems. The hallmark of this paper investigates the application of an adaptive neuro-fuzzy inference system (ANFIS) to path generation and obstacle avoidance for an autonomous mobile robot in a real world environment. ANFIS has also taken the advantages of both learning capability of artificial neural network and reasoning ability of fuzzy inference system. In this present design model different sensor based information such as front obstacle distance (FOD), right obstacle distance (ROD), left obstacle distance (LOD) and target angle (TA) are given input to the adaptive fuzzy controller and output from the controller is steering angle (SA) for mobile robot. Using ANFIS tool box, the obtained mean of squared error (MSE) for training data set in the current paper is 0.031. The real time experimental results also verified with simulation results, showing that ANFIS consistently perform better results to navigate the mobile robot safely in a terrain populated by variety obstacles.

Unsteady cavitation characteristics and alleviation of pressure fluctuations around marine propellers with different skew angles

Abstract: Cavitating flow around two marine propellers with different skew angles, a conventional propeller (CP) and a highly skewed propeller (HSP), operating in the non-uniform wake was simulated using a mass transfer cavitation model and the k-omega SST turbulence model. The numerical model reasonably predicted experimental data for the unsteady cavitation patterns as well as the oscillation amplitudes of the dominant pressure components. The results indicate that the effect of skew angle is very important on the cavitation characteristics as well as the pressure fluctuations and that the amplitudes of pressure fluctuations for the HSP are 50∼70% less than that for the CP. Therefore, the skewed propeller will reduce noise and vibration compared to the conventional propeller. Furthermore, the numerical model verified the relation between the hull pressures and changing cavitation patterns as the blades sweep through the high wake region. The results demonstrate that volumetric acceleration of entire cavity around a propeller blade is the main reason for the pressure fluctuations, which agrees with previous experiments.

Effects of surface coating on weld growth of resistance spot-welded hot-stamped boron steels

Abstract: Aluminum-silicon-based and zinc-based metallic coatings have been widely used for hot-stamped boron steel in automotive applications. In this study, resistance spot weldability was explored by investigating the effects of the properties of metallic coating layers on heat development and nugget growth during resistance spot welding. In the case of the aluminum-silicon-coated hot-stamped boron steel, the intermetallic coating transformed into a liquid film that covered the faying interface. A wide, weldable current range was obtained with slow heat development because of low contact resistance and large current passage. In the case of the zinc-coated hot-stamped boron steel, a buildup of liquid and vapor formation under large vapor pressure was observed at the faying interface because of the high contact resistance and low vaporization temperature of the intermetallic layers. With rapid heat development, the current passage was narrow because of the limited continuous layer at the faying interface. A more significant change in nugget growth was observed in the zinccoated hot-stamped boron steel than in the aluminum-silicon-coated hot-stamped boron steel.

Improvement of surface conditions of 36 Cr Ni Mo 6 steel by ball burnishing process

Abstract: Ball burnishing, a mechanical surface treatment, is becoming more popular as a finishing process. As results ball burnishing is noticed as a very simple way of surface mirror finishing and surface work-hardening. Applying the optimal input parameters, a pre-machined surface roughness Ra about of 3.01 μm can be finished to approximately 0.30 μm, whereas an initial hardness HRA about 66.35 can be increased to 71.33. A metallographic observation and some measurement of micro-hardness show that the depth of penetration strengthened by plastic surface deformation (PSD) reaches 100 μm. Results analysis show that burnishing force, burnishing ball radius and number of ball burnishing tool passes have the most significant effects on both surface responses (Ra and HRA). For the generating of high surface qualities and strengthening superficial layers, an alternative to chip-forming process and heat treatments can be given by ball PSD process.

Optimization of process parameters for friction stir lap welding of carbon fibre reinforced thermoplastic composites by Taguchi method

Abstract: Friction stir welding process parameters such as welding speed, rotational speed and tilt angle affect the strength of the weld joint For maximizing the weld strength, these process parameters must therefore be properly selected and optimized This study presents an application of Taguchi method to optimize process parameters like welding speed, rotational speed and tilt angle to maximize lap weld tensile-shear strength in 4 mm thick polypropylene composite sheets with 20 wt% carbon fiber To this end, a L9 orthogonal array of Taguchi method using three factors at three levels was used Analysis of variance and confirmation tests were conducted The results indicated that welding speed, rotational speed and tilt angle are respectively the significant parameters affecting the lap weld strength Optimization results also showed that tensile-shear strength of 606 MPa was obtained when welding speed, rotational speed and tilt angle were 25 mm/min, 1250 rpm and 1 degree, respectively

An improved surface roughness prediction model using Box-Cox transformation with RSM in end milling of EN 353

Abstract: In the present work, an attempt has been made to use Box-Cox transformation with response surface methodology to develop improve surface roughness prediction model in end milling of EN 353 steel using carbide inserts. The analysis has been carried out in two stages. In the first stage quadratic model has been developed in terms of feed, speed, depth of cut and nose radius using response surface methodology (RSM) based on center composite rotatable design (CCRD). The quadratic model, thus developed predicts the surface roughness with 92% accuracy. In the second stage, the improved quadratic model has been developed using Box-Cox transformation with RSM based on CCRD. The prediction ability of this develop model has been found more accurate (mean absolute error 4.7%) than previous one. An attempt has also been made to investigate the influence of cutting parameters on surface roughness. The result shows that the machining speed is the main influencing factor on the surface roughness while the depth of cut has no significant influence.

Combined rotor fault diagnosis in rotating machinery using empirical mode decomposition

Abstract: Unbalance, misalignment, partial rub, looseness and bent rotor are one of the most commonly observed faults in rotating machines. These faults cause breakdowns in rotating machinery and create undesired vibrations while operating. In this study, an approach to detect combined fault of unbalance and bent rotors for advance detection of the features of the fault rotors diagnosis is proposed. Empirical mode decomposition (EMD) is used efficiently to decompose the complex vibration signals of rotating machinery into a known number of intrinsic mode functions so that the fault characteristics of the unbalanced and bowed shaft can be examined in the time-frequency Hilbert spectrum. A test bench of Spectra-Quest has been used for performing experiments to illustrate the unbalance and the bent rotor conditions as well as the healthy rotor condition. Analysis of the results shows the usefulness of proposed approach in diagnosing the unbalance and bowed fault of the shaft in rotating machinery.

Experimental and finite element analysis of residual stress and distortion in GTA welding of modified 9Cr-1Mo steel

Abstract: In this paper, investigation of residual stress and distortion induced in 3 mm thick Modified 9Cr-1Mo steel plates during GTA welding is carried out. SYSWELD software is used for the thermo-mechanical analysis. A 3D meshed model is created for the simulation and double ellipsoidal heat source distribution is used for the thermal analysis. Thermal cycles predicted near the fusion zone are compared with experimentally measured thermal cycles using thermocouples. Predicted residual stress profile across the fusion zone is compared with the measured profile using X-ray diffraction method. There is a good agreement between measured and predicted thermal cycles and residual stress profile. Distortion of the weld joint is measured using vertical electronic height gauge. Finite element analysis of distortion of the weld joint is carried out by applying both large and small distortion theories. Comparison of experimental and numerical results showed better accuracy if large distortion theory is applied.

Fault diagnosis of rotating machinery based on kernel density estimation and Kullback-Leibler divergence †

Abstract: Based on kernel density estimation (KDE) and Kullback-Leibler divergence (KLID), a new data-driven fault diagnosis method is proposed from a statistical perspective. The ensemble empirical mode decomposition (EEMD) together with the Hilbert transform is employed to extract 95 time- and frequency-domain features from raw and processed signals. The distance-based evaluation approach is used to select a subset of fault-sensitive features by removing the irrelevant features. By utilizing the KDE, the statistical distribution of selected features can be readily estimated without assuming any parametric family of distributions; whereas the KLID is able to quantify the discrepancy between two probability distributions of a selected feature before and after adding a testing sample. An integrated Kullback- Leibler divergence, which aggregates the KLID of all the selected features, is introduced to discriminate various fault modes/damage levels. The effectiveness of the proposed method is demonstrated via the case studies of fault diagnosis for bevel gears and rolling element bearings, respectively. The observations from the case studies show that the proposed method outperforms the support vector machine (SVM)-based and neural network-based fault diagnosis methods in terms of classification accuracy. Additionally, the influences of the number of selected features and the training sample size on the classification performance are examined by a set of comparative studies.

Optimal design of Magneto-Rheological damper comparing different configurations by finite element analysis

Abstract: Magnetorheological (MR) damper is one of the most advanced applications of semi active damper in controlling vibration. Due to its continuous controllability in both on and off state its practice is increasing day by day in the vehicle suspension system. MR damper’s damping force can be controlled by changing the viscosity of its internal magnetorheological fluids (MRF). But still there are some problems with this damper such as MR fluid’s sedimentation, optimal design configuration considering all components of the damper. In this paper both 2-D Axisymmetric and 3-D model of MR Damper is built and finite element analysis is done for design optimization. Different configurations of MR damper piston, MR fluid gap, air gap and Dampers housing are simulated for comparing the Dampers performance variation. From the analytical results it is observed that among different configurations single coil MR damper with linear plastic air gap, top and bottom chamfered piston end and medium MR fluid gap shows better performance than other configurations by maintaining the same input current and piston velocity. Further an experimental analysis is performed by using RD-8041-1 MR Damper. These results are compared with the optimized MR Damper’s simulation results, which are clearly validating the simulated results.

Optimization of weld characteristics of friction welded AA 6061-AA 6351 joints using grey-principal component analysis (G-PCA)

Abstract: Friction welding is a solid state joining process in which the quality of welded joint is influenced by the input parameter setting. The objective of the present study is to conduct experimental investigation of the bond strength and hardness of the friction welded joints involving AA 6061 and AA 6351 alloys by conducting experiments designed by Taguchi’s L9 orthogonal matrix array. A systematic approach becomes essential to find the optimal setting of friction welding parameters. Hence a new approach named grey-principal component analysis (G-PCA) is presented in which the principal component analysis (PCA) is used to generate weights for the grey relational coefficients obtained in the grey relational analysis (GRA). The results of the confirmation experiment conducted with the optimal setting predicted by the G-PCA have shown improvements in the performance characteristics. Hence G-PCA can be used for experimental welding optimization.

An experimental study on the performance and emission characteristics of a CI engine fuelled with Jatropha biodiesel and its blends with diesel

Abstract: The performance and emission characteristics of a compression ignition engine using mixture of jatropha biodiesel and mineral diesel have been experimentally investigated. It is observed that brake specific fuel consumption increases with higher percentage of biodiesel in the blends. Brake thermal efficiency decreases with the increased percentage of biodiesel in the blends. The maximum efficiency is found to be 29.6% with pure diesel and 21.2% with pure biodiesel. Carbon mono-oxide and hydrocarbon emissions are improved with the addition of biodiesel to diesel. NOx emission is found to be increased with pure biodiesel by 24% compared to mineral diesel.

Static and dynamic pull-in instability of multi-walled carbon nanotube probes by He’s iteration perturbation method

Abstract: A continuum model is utilized to extract the nonlinear governing equation for Carbon nanotube (CNT) probes near graphite sheets. The van der Waals (vdW) intermolecular force and electrostatic actuation are included in the equation of motion. Static and dynamic pull-in behavior of the system is investigated in this paper. To this end, a new asymptotic procedure is presented to predict the pull-in instability of electrically actuated CNTs by employing an analytic approach namely He’s iteration perturbation method (IPM). The effects of basic non-dimensional parameters such as initial amplitude, intermolecular force, geometrical parameter and actuation voltage on the pull-in instability as well as the fundamental frequency are studied. The obtained results from numerical simulations by employing three mode assumptions verify the strength of the analytical procedure. The qualitative analysis of the system dynamics shows that the equilibrium points of the autonomous system include stable center points and unstable saddle nodes. The phase portraits of the carbon nanotube actuator exhibit periodic and homoclinic orbits.