Effective reduction of stiffness at peak frequency in hydraulic engine mounts by using magneto-rheological fluids

Hydraulic engine mounts are generally used in aerospace and automotive applications for the purpose of cabin noise and vibration reduction. By careful selection of hydraulic mount design parameters, at a certain frequency, namely the notch frequency, the dynamic stiffness will be smaller than the static stiffness and cabin vibration and noise reduction is provided at that frequency. Literature review indicates that in all previous designs of hydraulic engine mounts the dynamic stiffness increases after the notch frequency. This phenomenon undesirable because of the increase in the force transmitted to the cabin. This paper proposes a new hydraulic engine mount that uses two working fluids. The new design has two notch frequencies and two peak frequencies. In this study, effective reduction of the peak frequencies has been demonstrated by using a controllable fluid as one of the working fluids and a non-controllable fluid as the second working fluid. As a result, one can obtain a hydraulic engine mount design with only one notch frequency but having no peak frequency. The new hydraulic engine mount design and its mathematical model are presented in detail and some discussions on the simulation results are provided

Self-Heating Measurements for a Dual-Phase Steel under Ultrasonic Fatigue Loading for stress amplitudes below the conventional fatigue limit

AbstractThe aim of the present research was to study the self-heating behavior of a dual-phase steel under ultrasonic fatigue loading for stress amplitudes lower than the conventional fatigue limit. The steel studied in this research was DP600 commercial dual phase steel. Fatigue tests were conducted for different values of stress amplitudes up to 107 cycles using an ultrasonic fatigue machine at a testing frequency of 20 kHz with flat specimens. An infrared camera was used to measure the mean temperature evolution during the tests. A specific form of heat diffusion equation was adopted in this work to calculate the intrinsic dissipation from temperature measurements. The variation of the dissipated energy versus stress amplitude under cyclic loading was also studied

On The Finite Element Modeling Of Turbo Machinery Rotors In Rotor Dynamic Analysis

In this study, a program based on finite element method is developed for rotor dynamic analysis of gas turbine rotors. In the FE model of the rotors, various minor and major parts of the rotor are modeled using the cylindrical and tapered Timoshenko beam elements and the lateral vibration behavior of the rotor is evaluated. In the paper, the lateral vibration behavior of a certain gas turbine rotor is analyzed using the developed finite element program and coupled lateral-torsional vibration behavior of the rotor is analyzed using 3D finite element model. A good agreement exists between the results obtained from two FE models. Two design models are used for the rotor one of which has 2 bearings and the other one has 4 bearings with specific locations. The effects of the number of the bearings on the critical speeds, operational deflection shapes and unbalance response of the rotor is investigated. It is found that the number of the bearings has significant effect on the first critical speed but slight effect on the second and third critical speeds. It is demonstrated that the number of the bearings can be used as one of the system design parameters

A finite element model for extension and shear modes of piezo-laminated beams based on von Karman's nonlinear displacement-strain relation

Piezoelectric actuators and sensors have been broadly used for design of smart structures over the last two decades. Different theoretical assumptions have been considered in order to model these structures by the researchers. In this paper, an enhanced piezolaminated sandwich beam finite element model is presented. The facing layers follow the Euler-Bernoulli assumption while the core layers are modeled with the third-order shear deformation theory (TSDT). To refine the model, the displacement-strain relationships are developed by using von Karman's nonlinear displacement-strain relation. It will be shown that this assumption generates some additional terms on the electric fields and also introduces some electromechanical potential and non-conservative work terms for the extension piezoelectric sub-layers. A variational formulation of the problem is presented. In order to develop an electromechanically coupled finite element model of the extension/shear piezolaminated beam, the electric DoFs as well as the mechanical DoFs are considered. For computing the natural frequencies, the governing equation is linearized around a static equilibrium position. Comparing natural frequencies, the effect of nonlinear terms is studied for some example

Correlation of the high and very high cycle fatigue response of ferrite based steels with strain rate-temperature conditions

The discrepancies observed between conventional and ultrasonic fatigue testing are assessed through the mechanisms of dislocation mobility in BCC metals. The existence of a transition condition between thermally-activated and athermal regimes for screw dislocation mobility is studied under fatigue loading based on infrared thermography and microstructural characterization, here in the case of DP600 dual-phase steel. Evidence is obtained regarding the microstructural sources of crack initiation, which is found to be consistent with the existence of a transition in the modes of deformation. From the analysis of the experimental data gathered in this work, guidelines are given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. The inevitable temperature increases under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a BCC structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue

Thermal response of DP600 dual-phase steel under ultrasonic fatigue loading

The present work employed in situ infrared thermography to investigate the thermal response and dissipative mechanisms of a dual-phase steel under ultrasonic tension-compression fatigue testing. A classical thermal response occurred for stress amplitudes below 247 MPa but an abnormal thermal response was observed for stress amplitudes above 247 MPa, in that the temperature stabilized after a steep increase of up to 350 °C. The mean dissipated energy per cycle was estimated based on temperature measurements using the heat diffusion equation. The relationship between the mean dissipated energy per cycle and the stress amplitude was studied, and mechanisms related to the observed thermal response were discussed

Calorimetric Studies and Self-Heating Measurements for a Dual-Phase Steel Under Ultrasonic Fatigue Loading

The objective of the present research is to study the self-heating behavior of a dual-phase (DP) steel under ultrasonic fatigue loading and to investigate the effect of frequency on intrinsic heat dissipation of the material. The steel studied in this work is DP600 commercial DP steel. Fatigue tests were conducted using an ultrasonic fatigue machine at a testing frequency of 20 kHz with flat specimens. An infrared camera was used to measure the mean temperature evolution during the tests. A specific form of heat diffusion equation was adopted in this work to calculate the heat dissipation per cycle from temperature measurements. The variation of this dissipation versus stress amplitude in cyclic loading was also studied

Numerical study of hydrodynamic flow of a Casson nanomaterial past an inclined sheet under porous medium

The main aim of the current paper is to investigate the mass and heat transportation of a Casson nanomaterial generated by the inclination of the surface. The magnetic field effect along with suction or injection are considered. The working nanomaterial is taken into consideration based on the concept of the Buongiorno nanofluid theory, which explores the thermal efficiencies of liquid flows under movement of Brownian and thermophoretic phenomena. The emergent system of differential expressions is converted to dimensionless form with the help of the appropriate transformations. This system is numerically executed by the implementation of Keller–Box and Newton's schemes. A good agreement of results can be found with the previous data in a limiting approach. The behavior of the physical quantities under concern, including energy exchange, Sherwood number, and wall shear stress are portrayed through graphs and in tabular form. The Nusselt number and Sherwood number are found to diminish against the altered magnitudes of Brownian motion and the inclination parameter. Moreover, the velocity profile decreases with the growth of the inclination effect. In the same vein, the buoyancy force and solutal buoyancy effects show a direct relation with the velocity field. The outcomes have promising technological uses in liquid-based systems related to stretchable constituents

Elastic behavior of carbon nanocoils: A molecular dynamics study

Elastic behavior of carbon nanocoils is investigated through molecular dynamics simulations. In particular, spring constants of various nanocoils are derived. To do so, first a geometric model is prepared with the aid of finite element mesh generator. Then applying AIREBO potential, the model is simulated under tensile loading. Using the obtained deformation data, the spring constant is calculated. In order to study the effect of structural parameters, change of elastic properties with helix diameter as well as tube diameter is examined. The results are compared to those obtained via other methods reported in literature

Dynamic behavior of Jeffcott rotors with an arbitrary slant crack orientation on the shaft

Dynamic behaviour of a Jeffcott rotor system with a slant crack under arbitrary crack orientations is investigated. Using concepts of fracture mechanics, flexibility matrix and stiffness matrix of the system are calculated. The system equations motion is obtained in four directions, two transversal, one torsional and one longitudinal, and then solved using numerical method. In this paper a symmetric relation for global stiffness matrix is presented and proved; whereas there are some literatures that reported nonsymmetrical form for this matrix. The influence of crack orientations on the flexibility coefficients and the steady-state response of the system are also investigated. The results indicate that some of the flexibility coefficients are greatly varied by increasing the crack angle from 30◦ to 90◦ (transverse crack). It is also shown that some of the flexibility coefficients take their maximum values at (approximately) 60◦ crack orientation