International Journal of Engineering
Volume:27 Issue: 3, Mar 2014

Fiber-metal laminates (FMLs) are new type of composite materials which could improve defects of traditional composites in ductility، formability، impact and damage tolerance. Drawing behavior of a thermoplastic based FML consisting of glass-fiber reinforced polypropylene laminate as the core and aluminum AA1200-O as skin layers was investigated. The effects of process variables consisting of blank-holder force، temperature، blank diameter and blank thickness on the forming behavior of the FML were studied. To reduce the number of experiments and investigate process variables on maximum drawing force and wrinkling of specimens، design of experiments was used. The experimental results were indicated that the general effects of blank-holder force on the failure mode in FMLs and the effects of blank diameter and blank thickness of a FML in deep drawing was similar to custom metals. Furthermore، results demonstrated that a high interaction between temperature and blank-holder force was required to remove the wrinkling. Engineering constants of GFRP were obtained using Timoshenko’s beam theory. Numerical simulations were performed by the finite element software، ABAQUS، and a good agreement was observed between the numerical and experimental data.

Pose estimation is one of the vital issues in mobile robot navigation. Odometry data can be fused with absolute position measurements to provide better and more reliable pose estimation. This paper deals with the determination of better relative localization of a two wheeled differential drive robot by means of odometry by considering the influence of parameters, namely weight, velocity, wheel perimeter and tyre width. Experiments have been conducted based on central composite rotatable design matrix. A mathematical model has been developed for the robot with the help of MINITAB software. An optimum range and condition for minimum odometry error were obtained by using Response Surface Methodology (RSM) and Excel (XL) Solver respectively.

In this paper, the conjugate gradient (CG) method is employed for identifying the parameters of crack in a functionally graded beam from natural frequency measurement. The crack is modeled as a massless rotational spring with sectional flexibility. Using the Euler-Bernoulli beam theory on two separate beams and applying the compatibility requirements of the crack, the characteristic equation can be obtained as a function of natural frequency and location and depth of crack. In direct problem, the natural frequency is computed using analytical analysis. Moreover, the location and depth of crack are determined by measuring the three natural frequencies of beam in inverse problem. In this study, the CG method is utilized in inverse problem to determine the location and depth of crack. The obtained results show the efficiency of CG algorithm in terms of accuracy and the convergence speed.

This paper deals with the effect of the intrinsic material length-scale parameter on the stability and natural frequency of a rectangular micro-plate for two different cases; fully clamped and fully simply supported. A variation formulation based on Hamilton’s principle and the modified couple stress theory is used to obtain the nonlinear governing equation of a micro-plate incorporating the stretching effect. In the static case, the nonlinear governing equation is solved using the step-by step linearization method (SSLM) and in the dynamic case, is integrated using fourth-ordered Runge-Kutta method. The static and dynamic pull-in parameters, limiting the stability regions of capacitive MEMS devices, are calculated and compared to those obtained by the classical theory. The numerical results reveal that the intrinsic size dependence of materials is more significant for smaller thicknesses and in this case, the stretching effect can be neglected.

In this paper, free vibration of an Euler-Bernoulli beam with variable cross-section resting on elastic foundation and under axial tensile force is considered. Beam’s constant height and exponentially varying width yields variable cross-section. The problem is handled for three different boundary conditions: clamped-clamped, simply supported-simply supported and clamp-free beams. First, the equation of motion that governs the free vibration is derived and then dimensionless frequencies are determined using differential transform method (DTM). DTM is a semi-analytical approach based on Taylor expansion series that is a powerful tool in solution ordinary and partial differential equations. The effects of axial force, elastic foundation coefficient and non-uniformity parameter on dimensionless frequencies are investigated. Wherever possible, comparisons are made with the studies in open literature. Results show, the DTM yields rapid convergence without any frequency missing although convergence rate depends on boundary conditions. Also, dimensionless frequencies are sensitive to axial force rather than other parameters.

Low weight and high load capacity are remarkable advantages of sandwich panels with corrugated core, which make them more considerable by engineering structure designers. It is important to consider the limitations such as yielding and buckling as design constraints for optimal design of these panels. In this paper, multi-objective optimization of sandwich panels with corrugated core is carried out by minimizing two supposed objective functions, the structure’s weight and deflection. The finite element model of structure is created using the commercial software ANSYS, which is employed to calculate the deflection of panel in different problem conditions. A NSGA-II code prepared in MATLAB, is used to perform the optimization process in a gradual evolution trend, which leads to obtain the Pareto front consisting a set of design vectors and optimal objective function vectors. Two conventional methods are then used to select the trade-off optimal point among the Pareto nondominant optimal set.

The standard design parameters of a compression ignition engine fail to give specified performance with strait vegetable oil (SVO) from different origins. This study is performed to find the effect of compression ratio on emission characteristics such as carbon monoxide (CO), carbon dioxide (CO2), hydrocarbon (HC), nitrogen oxides (NOx) and smoke opacity with all the tested fuels in a single cylinder, four stroke VCR engine fueled with neat Karanja oil blends (10 and 20%) with diesel (on volume basis) and Karanja oil methyl ester (KOME) blends (20, 40 and 60%) and compare the results with diesel. Experiments haves been conducted at compression ratios of 16:1, 17:1, 1: . At higher CR, minimum value of CO is recorded as being 0.04 for 20% blend of KOME (B20), while maximum CO2 is4.45%. Lowest HC and NOx emission recorded are 22 ppm and 552 ppm respectively for 40% blend of KOME (B40). Emissions are marginally higher for K10 and K20 than for diesel. Overall observation shows that B40 has the lowest emissions among other blends of KOME at higher compression ratios.

In the present work, the thermal conductivity coefficients of nanoparticle-oil suspensions for two types of carbon nanotubes, single-walled (SWNTs) and multi-walled (MWNTs) carbon nanotubes at 0.1, 0.2 and 0.3 wt.% were measured by a modified transient hot wire method (KD2-pro thermal property meter). Results showed that the thermal conductivity of suspension containing single walled carbon nanotubes is higher than that of suspension containing multi-walled carbon nanotubes. It was also observed that the thermal conductivity coefficients of both nanofluids increase with increasing temperature.

In this study the effect of input EDM parameters on the surface quality of 2312 hot worked steel parts has been modeled and optimized. The proposed approach is based on statistical analysis on the experimental data. The input parameters are peak current (I), pulse on time (Ton), pulse off time (Toff), duty factor (h) and voltage (V). The experimental data are gathered using Taguchi L36 design matrix. In order to establish the relations between input and output parameters, regression function has been fitted on the Signal to Noise ratios of the experimental data. The results of analysis of variance (ANOVA) revealed that pulse on time and peak currents significantly influence the surface quality. In the next stage, the developed model is embedded into a genetic algorithm to determine the optimal set of process parameters for any desired surface roughness (within feasible ranges). Using optimization results, a set of verification tests is performed to verify the accuracy of the optimization procedure in determining the optimal levels of machining parameters. Computational results indicate that the proposed modeling technique and genetic algorithm are quite efficient in modeling and optimization of EDM process parameters.

One of the surface defects that arise in sheet metal working is when the part is removed from the die. Since there are no external forces to make this defect, the origin of such fail is known as residual stress. Residual stress can develop in sheet metal forming due to non-uniform deformation. In this paper, the workpiece is carbon steel with different volume fractions and arrangements of ferrite and pearlite. Due to different stress-strain curves for each phase after cold rolling, one phase deforms elastically, whereas the other undergoes elastic-plastic deformation. On unloading to zero applied stress, this effect can produce residual stress. Therefore, in order to reduce the surface defects in sheet metal forming, an intelligent predictive code using a validated elastic-plastic finite element method is generated for a plain strain deformation of cold rolling process. Results show that in regular arrangement of ferrite and pearlite, workpiece microstructure has great influence on the residual stress distribution, and by decreasing the width of each strip, the fluctuation of residual stress is reduced. The purpose of this study is to develop the state of the art instructions for arrangement of phases after hot rolling process where the total residual stress produced after cold rolling and sheet metal working will be minimized.

In this paper, the modified couple stress theory is used to study vibration analysis of functionally graded rectangular micro-plates. Considering classical and first order plate theories, the couple governing equations of motion are obtained using the Hamilton’s principle. Using an assumed mode method, the accurate size dependent natural frequencies are established for simply supported functionally graded rectangular micro-plates. To show the accuracy of the formulations, present results in specific cases are compared with available results in literature and a good agreement is seen. It is found that the natural frequency parameter of micro-plates will decrease as thickness length ratio increases especially for lower length scale values. The effects of length scale, functionally graded parameter and plate theories on natural frequencies of functionally graded micro-plates are discussed in details.

In this study, a non-associated viscoplastic flow rule (NAVFR) with combining von Mises and Tresca loci in place of yield and plastic potential functions and vice verse is presented. It is shown that the proposed NAVFR can be adopted to forecast the experimental events more accurate than the conventional associated viscoplastic flow rules (AVFR). This outcome obtained with the aid of fully implicit time stepping scheme and discussing the other studies on plastic potential flow rules and also experimental results.

In the present study, a computational fluid dynamics (CFD) method has been utilized to investigate the effects of exhaust gas recirculation (EGR) and initial charge pressure using a supercharger on the emissions and performance of a SI engine. This engine is fueled separately by gasoline and two potential alternative fuels, hydrogen and ethanol. The results of simulation are compared to the experimental data. There is a good agreement among the results. The calculations are carried out for EGR ratios between 0% and 20% and four cases of initial pressure have been mentioned: Pin= 1, 1.2, 1.4, 1.6 bar. The effect of EGR on NOx emission of hydrogen is more than others while its effect on IMEP of hydrogen is less than others. From the viewpoints of emission and power, 10% of EGR seems to be the most desirable amount. The most noticeable effect of supercharging is on gasoline unlike hydrogen that seems to be affected the least. The comparison of results shows that hydrogen due to its high heating value and burning without producing any carbon-based compounds such as HC, CO and CO2 is an ideal alternative fuel compared to other fuels.

The performance of an existing heating system of a residential building incorporated with an array of solar thermal collectors was studied. For this purpose, transient systems simulation program model was assembled to estimate the hour-by-hour performance of the existing and the system equipped with the solar thermal collectors in terms of the provided space air conditions and energy consumption. In the modified heating system, the capability of the three standard types of solar collectors, namely, unglazed, glazed painted absorber, and evacuated tube liquid flat-plate solar collectors for providing required heating energy into the space was examined to determine the most appropriate configuration. Based on the simulation results, the system incorporated with the solar thermal collectors was capable of providing the desired indoor air conditions for four and five months of the year. However, the energy performance of the plants indicated that the existing system incorporated with the glazed painted absorber solar collectors (Plant B) has the priority in terms of the energy savings while it could provide the desired indoor air conditions for five months of the year and it is recommended to be implemented in the existing central heating system.

This paper presents a new method to control rehabilitation robots. An intelligent algorithm called Brain Emotional Learning Based Intelligent Controller (BELBIC) is participating to develop an admittance control scheme. This control system modifies the reference trajectory based on reactions of patient during therapy. Three main reactions has been identified and included in reference trajectory: small variations, force shocks in a single moment and variable level of participation. This reference trajectory can facilitate all patient-cooperative rehabilitation systems with an evaluation factor. Tracking performance of BELBIC on a 2-DOF exoskeleton was compared to PID with simulations and better results were observed especially when controller encountered a force shock.

In this paper, considering an adhesively bonded composite single-lap joint, a novel approach is presented to predict the peel and shear stress distributions of the adhesive layer for an ASTM standard test sample. In the current method, the equilibrium equations are derived using the energy method and based on the Timoshenko’s beam theory. Two solution procedures then are discussed; one of them represents a solution approach based on the direct variational method allied with use of the Ritz approximation; while the second one is based on a linear estimating function. Unlike previous methods, in which the variation of stress through the thickness of adhesive is neglected or is assumed to be linear and they cannot be used to analyze the joints with thick adhesive layers; considering the effects of adhesive thickness makes it possible to employ present method to analyze the joints with thick adhesive layers as well as thin ones.

This paper addresses the static and dynamic stabilities of a parametrically excited torsional microactuator. The system is composed of a rectangular micro-mirror symmetrically suspended between two electrodes and acted upon by a steady (dc) while simultaneously superimposed to an (ac) voltage. First, the stability of the system subjected to a quasi-statically applied (dc) voltage is investigated, where the pull-in instability, equilibrium positions, and bifurcation points of the system are determined. Then by superimposing an (ac) voltage and extracting a Mathieu type governing equation the effects of (ac) component on the stability of the system is investigated. By varying excitation parameters (steady (dc) voltage and time-dependent amplitude of (ac) excitation), transition curves and the stability margins of the micro-mirror are demonstrated. Theoretically obtained margins are checked by means of numerical simulations. The results show that superimposing the harmonic (ac) component could have a stabilizing effect and allow an increase of the steady (dc) component beyond the pull-in value. These results could be used in design of micro-actuators.

In vibratory systems, linear and nonlinear vibration absorbers can be used to suppress primary and super-harmonic resonance responses. In this paper, the behavior of a nonlinear system with a nonlinear absorber, under the primary and super-harmonic resonances is investigated. Comparison of the effects of attached nonlinear absorber on a nonlinear system with that of a linear one, under the resonance cases is performed. The stiffness of the main system and the absorber are considered to be cubically nonlinear, whereas the behavior of the dampers is supposed to be linear. Using multiple time scales (MTS) method, approximate solution of the nonlinear equations of motion is obtained. It is concluded that at primary resonance, a linear absorber can suppress the peak amplitude of the system better than a non-linear one, but under super-harmonic resonance, effective reduction in the vibration amplitude can be achieved using a nonlinear absorber.