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Transactions of the Korean Society of Mechanical Engineers A
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Journal DOI :
The Korean Society of Mechanical Engineers
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Volume & Issues
Volume 24, Issue 12 - Dec 2000
Volume 24, Issue 11 - Nov 2000
Volume 24, Issue 10 - Oct 2000
Volume 24, Issue 9 - Sep 2000
Volume 24, Issue 8 - Aug 2000
Volume 24, Issue 7 - Jul 2000
Volume 24, Issue 6 - Jun 2000
Volume 24, Issue 5 - May 2000
Volume 24, Issue 4 - Apr 2000
Volume 24, Issue 3 - Mar 2000
Volume 24, Issue 2 - Feb 2000
Volume 24, Issue 1 - Jan 2000
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Residual Stress in U-Bending Deformations and Expansion Joints of Heat Exchanger Tubes
Jang, Jin-Seong ; Bae, Gang-Guk ; Kim, U-Gon ; Kim, Seon-Jae ; Guk, Il-Hyeon ; Kim, Seong-Cheong ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 279~289
DOI : 10.22634/KSME-A.2000.24.2.279
Residual stress induced in U-bending and tube-to-tubesheet joint processes of PWR's row-1 heat exchanger tube was measured by X-ray method and Hole-Drilling Method(HDM). Compressive residual stresses(-) at the extrados surface were induced in U-bending, and its maximum value reached -319 MPa in axial direction at the position of
. Tensile residual stresses(+) of
= 45 MPa and
= 25 MPa were introduced in the intrados surface at the position of
. Maximum tensile residual stress of 170 MPa was measured at the flank side at the position of
, i.e., at apex region. It was observed that higher stress gradient was generated at the irregular transition regions (ITR). The trend of residual stress induced by U bending process of the tubes was found to be related with the change of ovality. The residual stress induced by the explosive joint method was found to be lower than that by the mechanical roll method. The gradient of residual stress along the expanded tube was highest at the transition region (TR), and the residual stress in circumferential direction was found to be higher than the residual stress in axial direction.
State-Space Model Identification of Tandem Cold Mill Based on Subspace Method
Kim, In-Su ; Hwang, Lee-Cheol ; Lee, Man-Hyeong ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 290~302
DOI : 10.22634/KSME-A.2000.24.2.290
In this paper, we study on the identification of discrete-time state-space model for robust control of tandem cold mill, using a MOESP(MIMO output-error state-space model identification) algorithm based on subspace method. It is shown that the identified model is well adapted to input-output data sets, which are obtained from nonlinear mathematical equations of tandem cold mill. Furthermore, deterministic H
norm bounds on uncertainties including modeling errors and disturbances are quantitatively identified in the frequency domain. Finally, the results give a basic idea to determine weighting functions included in formulating some robust control problems of tandem cold mill
Evaluation of the Fracture Toughness Transition Characteristics of RPV Steels Based on the ASTM Master Curve Method Using Small Specimens
Yang, Won-Jon ; Heo, Mu-Yeong ; Kim, Ju-Hak ; Lee, Bong-Sang ; Hong, Jun-Hwa ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 303~310
DOI : 10.22634/KSME-A.2000.24.2.303
Fracture toughness of five different reactor pressure vessel steels was characterized in the transition temperature region by the ASTM E1921-97 standard method using Charpy-sized small specimens. T he predominant fracture mode of the tested steels was transgranular cleavage in the test conditions. A statistical analysis based on the Weibull distribution was applied to the interpretation of the scattered fracture toughness data. The size-dependence of the measured fracture toughness values was also well predicted by means of the Weibull probabilistic analysis. The measured fracture toughness transition curves followed the temperature-dependence of the ASTM master curve within the expected scatter bands. Therefore, the fracture toughness characteristics in the transition region could be described by a single parameter, so-called the reference temperature (T。), for a given steel. The determined reference temperatures of the tested materials could not be correlated with the conventional index temperatures from Charpy impact tests.
The Effects of Disk Surface Topography on Baseline Instability of MR Head
Jwa, Seong-Hun ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 311~318
DOI : 10.22634/KSME-A.2000.24.2.311
Several factors which influence baseline instability (BLI) phenomenon in MR drive were investigated experimentally. In particular, the role of surface topography on BLI was studied in detail. The r esults show that BLI is linearly proportional to the surface waviness with a spatial wavelength of 0.4 to 5.0 min. BLI becomes worse as the surface waviness increases. On the other hand, surface roughness which has a spatial wavelength below 25
m has no effect on BLI. The results further show that the effect of bias current on the BLI is amplified on the disk with worse surface waviness. The disk surface waviness is dependent on the manufacturing process and becomes an inherent surface property of media. The disk surface waviness. therefore, can not be overlooked when evaluating the media for a high-performance hard disk drive. In general, waviness is reduced mainly during grinding and polishing process during manufacturing.
A Design of an Automotive Wheel Bearing Unit for Long Life
Yun, Gi-Chan ; Choe, Dong-Hun ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 319~328
DOI : 10.22634/KSME-A.2000.24.2.319
This paper presents a new design method of the 1 generation wheel bearing unit using a numerical optimization technique in order to increase bearing fatigue life. For calculating the fatigue life, a method of load analysis is studied on the automotive wheel bearing system. The design variables selected are ball size, initial contact angle, number of balls, pitch diameter, pre-load, and distance between ball centers. The method of feasible directions in ADS (Automated Design Synthesis) is utilized to automatically find the optimum design variables. To validate the design method, a computer program is developed and applied to a practical passenger car model. The optimum design results demonstrated the effectiveness of the proposed design method showing that the system life of the optimally designed wheel bearing unit is enhanced in comparison with that of the initial ones within the given available design space.
Book Remodeling Analysis of Femur Using Hybrid Beam Theory
Kim, Seung-Jong ; Jeong, Jae-Yeon ; Ha, Seong-Gyu ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 329~337
DOI : 10.22634/KSME-A.2000.24.2.329
An investigation has been performed to develop an analysis tool based on a nonlinear beam theory, which can be used to predict the long-term behavior of an artificial hip joint. The nonlinear behav ior of the femur arise from the coupled dependence of the bone density and the mechanical properties on each other. The beam theory together with its numerical algorithm is developed to take into account the nonlinear bone remodeling process of the femur that is long enough to be assumed as a beam. A piecewise linear curve for the bone remodeling rate is used in the bone remodeling theory and the surface area density of bone is modeled as the third order polynomial function of bone density. At each section of the beam, a constant curvature is assumed and the longitudinal strains are also assumed to vary linearly across the section. The Newton-Rhapson iteration method is used to solve the nonlinear equations for each cross section of the bone and a backward method is used to march along the time. The density and the remodeling signal ar, calculated along with time for the various time steps, and the developed beam theory has been verified by comparing with the results of finite element analysis of a remodeling bone with an artificial hip joint of titanium prosthesis subjected to uni-axial loads and pure bending moment. It is concluded that the developed beam theory can be used to predict the long-term behavior of the femur and thus to design the artificial hip prosthesis.
Cut-off Grinding Characteristics of the Carbon Fiber Epoxy Composite Materials
Kim, Po-Jin ; Choe, Jin-Gyeong ; Lee, Dae-Gil ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 338~346
DOI : 10.22634/KSME-A.2000.24.2.338
Although the net-shape molding of composites is generally recommended, molded composites are frequently required cutting or grinding due to the dimensional inaccuracy for precision machine elements . During the composite machining operations such as cutting and grinding, the temperature at the cutting point may increase beyond the allowed limit due to the low thermal conductivity of composites, which might degrade the matrix of composite. Therefore, in this work, the temperature at the cutting point during cut-off grinding of carbon fiber epoxy composites was measured. The cutting force and surface roughness were also measured to investigate the cut-off grinding characteristics of the composites. The experiments were performed both under dry and wet grinding conditions with respect to cutting speed and feed rate. From the experimental investigation, the optimal conditions for the composite cut-off grinding were suggested.
Rerformance Evaluation of ER Suspensions Under Field Test
Lee, Heon-Gyun ; Choe, Seung-Bok ; Han, Seung-Jik ; Jang, Yu-Jin ; Lee, Seong-Beom ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 347~354
DOI : 10.22634/KSME-A.2000.24.2.347
This paper presents performance characteristics of a semi-active suspension featuring continuously variable ER (electro-rheological) dampers. These are evaluated through the field test of a passeng er car. Four ER dampers (two for front and two for rear part) are manufactured and their field-dependent damping properties are experimentally investigated. The damping force responses to step input fields are also identified by employing small size of high voltage amplifiers which are made adaptable to the field test. A skyhook controller considering the vertical, pitch and roll motions is formulated and incorporated with a car to be tested. The field test is then undertaken in order to evaluate both comfortability and steering stability showing bump, dive and squat responses
Design and Application of Magnetic Damper for Reducing Rotor Vibration
Kim, Young-Bae ; Yi, Hyeong-Bok ; Lee, Bong-Ki ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 355~361
DOI : 10.22634/KSME-A.2000.24.2.355
In this study, active control magnetic actuator for reducing vibration of rotor system is performed. Identification, modeling, simulation, control system design, and evaluation of active magnetic damper system have been researched. Power amplifier modeling, connected magnetic actuator and augmented by system identification, is included to establish a magnetic damper simulation which provides close performance correspondence to the physical plant. A magnetic actuator, digital controller using DSP(Digital Signal Processor), and bipolar operational power supply/amplifiers are developed to show the effectiveness of reducing rotor vibration. Also the curve fitting procedure to obtain the transfer function of frequency dependent components is developed. Two kinds of test are executed as sliding and oil bearing. Results presented in this paper will provide a well-defined technical parameters in designing magnetic damper system for the proposed rotor.
The Geometrical Analysis of Vibration Modes and Frequency Responses of an Elastically Suspended Optical Disc Drive
Dan, Byeong-Ju ; Choe, Yong-Je ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 362~369
DOI : 10.22634/KSME-A.2000.24.2.362
Via screw theory, a vibration mode can be geometrically interpreted as a pure rotation about the vibration center in a plane and as a twisting motion on a screw in a three dimensional space. In thi s paper, applying the conditions that can be used to diagonalize the stiffness matrix by a parallel axis congruence transformation, the vibration modes and frequency response of an elastically suspended optical disc drive have been analyzed. It is first shown that the system has one plane of symmetry, which enables one to decouple the complicated vibration modes into two sets of modes independent of each other. Having obtained the analytical solutions for the axes of vibrations, the frequency response for a given applied input force has been demonstrated. Most importantly, it has been explained that this research result could be used in the synthesis process of a linear vibration system in order to improve the frequency response.
Performance Evaluation of a Mixed-Mode Type ER Engine Mount (I);Manufacturing and Test of Engine Mount
Choe, Yeong-Tae ; Choe, Seung-Bok ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 370~377
DOI : 10.22634/KSME-A.2000.24.2.370
This paper presents a mixed-mode type ER(electro-rheological) engine mount, and its vibration control performance for a passenger vehicle is presented. The field-dependent yield stress of a transfo rmer oil-based ER fluid is empirically distilled in both shear and flow modes. This is then incorporated with the governing equation of motion of the proposed mixed-mode(shear mode plus flow mode) type engine mount. The damping force is analyzed with respect to the intensity of the electric field and design parameters such as electrode gap. Subsequently, the ER engine mount which is equivalent to the conventional hydraulic engine mount in terms of the damping level is designed and manufactured. Both computer simulation and experimental test are undertaken in order to evaluate vibration isolation performance. In addition, this performance is compared with that of the conventional hydraulic engine mount.
Analyses of the Decrease Phenomenon of Fracture Resistance Curve Under Tension-Compression Loading
Yun, Byeong-Gon ; Seok, Chang-Seong ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 378~385
DOI : 10.22634/KSME-A.2000.24.2.378
Fracture resistance (J-R) curves, which are used for elastic-plastic fracture mechanics analyses, decreased under tension-compression loading condition. This phenomenon was proved by several former researches, but the causes have not been clear yet. The objective of this paper is to investigate the cause of this phenomenon. On the basis of fracture resistance curve test results, strain hardening hypothesis, stress redistribution hypothesis and crack opening hypothesis were built. In this study, hardness tests, Automated Ball Indentation(ABI) tests, theoretical stress field analyses, and crack opening analyses were performed to prove the hypotheses. From this study, strain-hardening of material, generation of tensile residual stress at crack tip, and crack opening effects are proved as the causes of the decrease hypothesis.
Development of Mesh Generation Program for the Primary System of Nuclear Power Plant
Jang, Dong-Min ; Kim, Yeong-Jin ; Choe, Seong-Nam ; Seo, Myeong-Won ; Jang, Gi-Sang ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 386~393
DOI : 10.22634/KSME-A.2000.24.2.386
Fracture mechanics analysis (FMA) is an essential work for integrity evaluation of nuclear power plant. The flaws inspected by In-Service Inspection(ISI) should be confirmed by FMA for the decision of the operation status of stop or continuance. The basic data for FMA are the stress of the interested area. The purpose of this research is to develop a system which can obtain stress data efficiently based on various database. Mesh generation program generates mesh using MSC/PATRAN and provides input file for finite element analysis according to the databases (shape, dimension, transient and material). The stress data from the finite element analysis are stored to be stress database so that it can be applied to FMA. As an example, the system developed by this study is applied to pressurizer nozzle and confirmed to be a useful tool for efficient FMA.
Densification Behavior of Ti-6Al-4V Power Compacts by Hot Isostatic Pressing
Yang, Hun-Cheol ; Kim, Gi-Tae ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 394~402
DOI : 10.22634/KSME-A.2000.24.2.394
Densification behavior of titanium alloy powder was investigated under hot isostatic pressing at various pressures and temperatures. Uniaxial creep responses of a dense specimen were also obtained at high temperatures. The densification model of Abouaf and co-workers was implemented into a Finite element program (ABAQUS) to compare with experimental data for titanium alloy powder. The agreements between finite element calculations and experimental data for deformation and densification of titanium alloy powder were good during hot isostatic pressing,
Analysis for Residual Twisting Moment in a Steel Cord during Twisting Wires
Lee, Gyu-Nam ; Lee, Hyeong-Man ; Kim, Gi-Tae ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 403~410
DOI : 10.22634/KSME-A.2000.24.2.403
The effects of various factors were studied on the process of a steel cord by twisting wires. To remove residual twisting moment after the steel cord process, the twisting angles of residual elasti c twisting and overtwisting were measured and compared with finite element results. The agreement between experimental data and finite element calculations was good for the angles of residual elastic twisting and over-twisting. The stress distributions in a steel cord under complex loading conditions were also obtained by using the finite element analysis.
Multibody Dynamics Analysis for Contacting Rigid Bodies
Park, Jeong-Hun ; Hwang, Yo-Ha ; Yu, Hong-Hui ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 411~420
DOI : 10.22634/KSME-A.2000.24.2.411
This paper presents a new method for calculating contact position and contact force. The proposed method calculates accurate contact position by introducing intermediate parameters. Accurate contac t force can be obtained by solving reduced equations of motion iteratively. This method can be applied to calculate not only contact force on contact points but also contact force on kinematic joints such as a rotational joint and a translational joint. Four numerical examples are given to demonstrate the effectiveness of the proposed algorithm.
Ritz Analysis of Rectangular MEMS Structures (I);Formulation and Its Implementation
Kim, Eun-Seok ; Lee, Byeong-Chae ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 421~430
DOI : 10.22634/KSME-A.2000.24.2.421
We apply the Rayleigh Ritz method to analyze multi-layered plates with residual stresses. The method is very simple, straight forward, and easily programmable, but it should be applied to structure s only in simple shapes. We derive coupled variational equations based on the principle of virtual displacement, and investigate what kind of basis functions is desirable for the analysis of rectangular plates with various boundary conditions. We demonstrate the effectiveness and usefulness of the method through several examples. The analysis results obtained with the method are in good agreement with those available in literature. A multi-layered MEMS plate example shows that the coupling effect should not be ignored and that residual stresses do influence the stiffness of the structure very much.
Experimental Study on Hardness and Wear Characteristics of Welded Rails
Kim, Chung-Kyun ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 431~437
DOI : 10.22634/KSME-A.2000.24.2.431
In this paper, thermite and gas pressure weldings have been used to join rails in-track and analyzed as functions of hardness and wear characteristics. The wear rate of thermite welded rail is low compared with that of gas pressure welded rail, which is tested in a pin-on-disk wear tester. The hardness of thermite welded materials is relatively high and narrowly distributed between three zones; welded part, thermally affected zone, and base matrix. Wear of a welded rail may be a major factor in railroad maintenance costs and failures at the rail-rail huh joint.
An Experimental Study on the Strength Evaluation of Mechanical Press Joint
Park, Yeong-Geun ; Jeong, Jin-Seong ; Kim, Ho-Gyeong ; Lee, Yong-Bok ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 438~448
DOI : 10.22634/KSME-A.2000.24.2.438
Mechanical press joining technique has been used in sheet metal joining processes because of its simple process and possibility of joining dissimiliar metals, such as steel and aluminum. The static and cyclic behavior of single overlap AI-alloy and steel(SPCC) joints has been investigate. Relationships were developed to estimate the strength of the joint taking into consideration base metal strength properties and the geometry of the joint. Fatigue test results have shown that fatigue resistance of the SPCC mechanical press joints is almost equal to that of the spot weld at the life of
cycles. Also, the dissimilar material jointed specimen with upper SPCC plate and button diameter corresponding to the nugget diameter of the spot welded specimen has almost same strength as the same material jointed specimen and as the spot welded specimen.
Tribology Characteristics on the Atmospheric Pressure of Alumina Ceramics with Different Purity
Jin, Dong-Gyu ; Park, Heung-Sik ; Seo, Yeong-Baek ; Ok, Cheol-Ho ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 448~454
DOI : 10.22634/KSME-A.2000.24.2.448
This study was undertaken to investigate tribological characteristics with atmospheric pressure for three alumina ceramics of different purity, such as, 85 %, 95 % and 99.7 %. The wear test was carried out using the wear test device which was designed for this study in air,
Torr. The friction coefficient depends entirely on atmospheric pressure and alumina with lower purity than higher purity has been much affected by heat accumulation. The friction surface of ceramics have been protected in the air by the influence of the oxides transferred from STB2. However, the protective layer can not be formed due to the decrease of oxygen in vacuum.
Estimation of Creep Cavities Using Neural Network and Progressive Damage Modeling
Jo, Seok-Je ; Jeong, Hyeon-Jo ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 455~463
DOI : 10.22634/KSME-A.2000.24.2.455
In order to develop nondestructive techniques for the quantitative estimation of creep damage a series of crept copper samples were prepared and their ultrasonic velocities were measured. Velocities measured in three directions with respect to the loading axis decreased nonlinearly and their anisotropy increased as a function of creep-induced porosity. A progressive damage model was described to explain the void-velocity relationship, including the anisotropy. The comparison of modeling study showed that the creep voids evolved from sphere toward flat oblate spheroid with its minor axis aligned along the stress direction. This model allowed us to determine the average aspect ratio of voids for a given porosity content. A novel technique, the back propagation neural network (BPNN), was applied for estimating the porosity content due to the creep damage. The measured velocities were used to train the BP classifier, and its accuracy was tested on another set of creep samples containing 0 to 0.7 % void content. When the void aspect ratio was used as input parameter together with the velocity data, the NN algorithm provided much better estimation of void content.
Fracture and Wear Behavior of Dental Composite Resins Containing Prepolymerized Particle Fillers
Kim, Yeong-Bin ; Kim, Gyo-Han ; Kim, Seok-Sam ; Im, Jeong-Il ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 464~471
DOI : 10.22634/KSME-A.2000.24.2.464
The fracture and wear behavior of dental composite resins containing prepolymerized particle fillers were investigated. Composite resins such as Metafil, Silux Plus, Heliomolar and Palfique Estelite were selected as specimens and contents of filler in specimens in order to evaluate the effect of prepolymerized particle fillers in fracture and wear characteristics. Ball on flat wear tester was used for the wear test at room temperature. The friction coefficient of Metafil was quite high relatively, and the wear resistances of Silux Plus and Palfique Estelite were better than those of Metafil and Heliomolar at the same experimental condition. It was found that the main wear mechanism was abrasive wear containing of plastic deformation of dental material.
A Constitutive Law for Porous Solids with Pressure-Sensitive Matrices and a Void Nucleation Model
Jeong, Hyeon-Yong ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 472~480
DOI : 10.22634/KSME-A.2000.24.2.472
A macroscopic yield criterion for porous solids with pressure-sensitive matrices modeled by Coulomb's yield criterion was obtained by generalizing Gurson's yield criterion with consideration of the hydrostatic yield stresses for a spherical thick-walled shell and by fitting the finite element results of a voided cube. The macroscopic yield criterion is valid for negative mean normal stresses as well as for positive mean normal stresses. From the yield criterion, a plastic potential function for the porous solids was derived either for plastic normality flow or for plastic non-normality flow of pressure- sensitive matrices. In addition, the elastic relation, an evolution equation of the plastic flow stress of the matrices and an evolution equation of the void volume fraction were presented to complete a set of constitutive relations. The set of constitutive relations was implemented into a finite element code ABAQUS to analyze the material behavior of rubber-toughened epoxies. The cavitation and the deformation behavior were analyzed around a crack tip under three-point bending and around notch tips under four-point bending. In the numerical analyses, the cavitation of rubber particles was considered via a stress-controlled nucleation model. The numerical results indicate that a reasonable cavitation zone can be obtained with void nucleation controlled by the macroscopic mean normal stress, and a plastic zone is smaller around a notch tip under compression than under tension. These numerical results agree well with corresponding experimental results on the cavitation and plastic zones.
A Passive Gravity-Compensation System for Articulated Robots
Lee, Yong-Ho ; Sin, Yong-Su ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 481~488
DOI : 10.22634/KSME-A.2000.24.2.481
This paper presents a new passive gravity -compensating system for articulated robot manipulators. The system, which consists of linear zero- free -length springs, achieves exact counterbalancing o f the gravitational loads throughout the entire range of the manipulator workspace, A basic concept is to design springs such that the total potential energy of the system including the manipulator and the springs should be maintained constant. A prototype has been developed for a direct-drive five-bar manipulator and its performances have been investigated. Results show that the gravity-induced motor torques have been reduced to less than 5% of those of uncompensated robots. Also, the gravity-compensating system simplifies the position control algorithm while maintaining the trajectory-tracking errors in a satisfactory level. In conclusion, the proposed system efficiently improves the manipulator performances by reducing the driving motor size and the energy consumption as well as by simplifying the control systems.
Matrix and Dyadic Representation of Stress and Strain
Kim, Chan-Jung ; Jo, Jong-Du ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 489~495
DOI : 10.22634/KSME-A.2000.24.2.489
Stress and strain in continuum mechanics have a mathematical form of the second order tensor. it is well-known that the usefulness of tensor components could be explained in a relation with coordin ates system transformation and Mohr's circle could be easily used to make a coordinate system transformation of tensors. However, Mohr's circle is applied mainly to plane problems and its use to three dimensional cases is limitedly employed. In this paper, we propose a matrix and dyadic representation of stress and strain tensors which could equivalently replace the graphical representation of second order tensors. The use of the proposed representation might provide a valuable means for the educational respects as well as research view point.
Parallel Crack with Constant Velocity in Two Bonded Anisotropic Strip Under Anti-Plane Deformation
Park, Jae-Wan ; Kim, Nam-Hun ; Choe, Seong-Ryeol ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 496~505
DOI : 10.22634/KSME-A.2000.24.2.496
A semi-infinite parallel crack propagated with constant velocity in two bonded anisotropic strip under anti-plane clamped displacement is analyzed. Using Fourier integral transform a Wiener-Hopf equation is derived. By solving this equation the asymptotic stress and displacement fields near the crack tip are determined, where the results give the more general expression applicable to the extent of the anisotropic material having one plane of elastic symmetry for the parallel crack. The dynamic stress intensity factor and energy release rate are also obtained as a closed form, which are the results applicable to the problem both of dynamic and static crack under the same geometry as this study. The stress intensity factor approaches zero at the critical crack velocity which is less than the shear wave velocity, but in typical case of isotropic or orthotropic material agrees with the velocity of shear wave. Also a circular shear stress around crack tip is considered, from which the stress is shown to be approximately symmetric about the horizontal axis. Referring to the maximum stress criteria, it could be shown that a brenched crack is formed by crack growth as crack velocity increases.
A Study on the Correction Factor of Flow Angel by using the One Dimentional Performance Model of Torque Converter
Im, Won-Sik ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 506~517
DOI : 10.22634/KSME-A.2000.24.2.506
One dimensional performance model has been used for the design of torque converter. The model is based on the concept of constant mean flow path and constant flow angle. These constant-assumed para meters make the design procedure to be simple. In practice, some parameters are usually replaced with geometric raw data and, the constant experiential correction factors have been used to minimize the design error. These factors have no definite physical meaning and so they cannot be applied confidently to the other design condition. In this study, the detail dynamic model of torque converter is presented to establish the theoretical background of correction factors. To verify the validity of theoretical model, steady state performance test was carried out on the several input speed. The oil temperature effect on the performance is analysed and adjusted. The constant equivalent flow angles are determined at a part of performance region by comparing the theoretical model and the test data. The sensitivity of correction factors to the input speeds are studied and the change of torus flow is presented.
Damage Detection in a Beam by the Wavelet Transform
Kim, Eung-Hun ; Kim, Yun-Yeong ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 518~525
DOI : 10.22634/KSME-A.2000.24.2.518
This paper presents a new wavelet-based structural diagnostic technique. A continuous Gabor wavelet transform is shown to a very effective method in detecting damage in a beam. The beam is excited by a broad-band excitation force. For satisfactory results, the selection of an optimal wavelet is very important though the wavelet transform outperforms existing techniques such as the Wigner-Ville distribution. A specific example is given in a solid circular cylinder with a small defect
Near-Net-Shape Forming and Finite Element Analysis for Ceramic Powder Under Cold Combination Pressing and Pressureless Sintering
Kim, Hong-Gi ; Lee, Hyeong-Man ; Kim, Gi-Tae ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 526~534
DOI : 10.22634/KSME-A.2000.24.2.526
Near-net-shape forming of zirconia powder was investigated under the combination of cold die and isostatic pressing and pressureless sintering. A novel combination pressing technique, i.e., die com paction under cold isostatic pressing, allowed to produce a complex shaped ceramic powder compact with the controlled dimensions and relatively uniform density distributions. The constitutive models proposed by Kim and co-workers for densification of ceramic powder under cold compaction and high temperature were implemented into a finite element program (ABAQUS). Experimental data for relative density distributions and deformations of zirconia powder compacts produced by cold combination pressing and pressureless sintering were compared with finite element results. Finite element results agreed well with experimental data.
Dynamic Analysis of Constrained Multibody Systems Undergoing Collision
Park, Jeong-Hun ; Yu, Hong-Hui ; Yang, Hyeon-Ik ; Hwang, Yo-Ha ;
Transactions of the Korean Society of Mechanical Engineers A, volume 24, issue 2, 2000, Pages 535~542
DOI : 10.22634/KSME-A.2000.24.2.535
This paper presents a method for the dynamic analysis of constrained multibody systems undergoing abrupt collision. The proposed method uses a longer time interval to check collision than that of c onventional method. This reduces the computational effort significantly. To calculate collision points on two colliding rigid bodies, one may introduce constraints of contact. However, this causes reduction of degree of freedom and difficulty of numerical analysis. The proposed method can calculate collision points without above mentioned problems. Three numerical examples are given to demonstrate the computational efficiency and the usefulness of the proposed method