Hyeon Gyu Beom

A Finite Element Analysis for Magnetostrictive Thin Film Structures and Its Experimental Verification

In this paper, a finite element code especially for micro-magnetostrictive actuators was developed. Two significant characteristics of the presented finite element code are: (1) the magnetostrictive hysteresis phenomenon is effectively taken into account; (2) intrinsic geometric feature of typical thin film structures of large length to thickness ratio, which makes it very difficult to construct finite element mesh in the region of the thin film, is considered reasonably in modeling micro-magneostrictive actuators. For verification purpose, magnetostrictive thin films were fabricated and tested in the form of a cantilevered actuator. The Tb-Fe film and Sm-Fe film are sputtered on the Si and Polyimide substrates individually. The magnetic and magnetostrictive properties of the sputtered magnetostrictive films are measured. The measured magnetostrictive coefficients are compared with the numerically calculated ones.

The Static and Dynamic Fracture Test of X70 Pipeline Steel

The Charpy V notch specimens of X70 pipeline steel with different notch orientation are tested under the static and dynamic conditions at different temperatures. By analyzing the load versus displacement curves and fracture appearances of specimens the relation of fracture behavior and loading rate is investigated. The maximum load increases and the displacement corresponding to maximum load reduces with test temperature decreasing. Both under the static conditions are larger than that under the dynamic conditions. The fracture sections of all test specimens are reduced in the thickness direction and quantity reduced depends on the load rate, notch orientation and test temperature. At the higher temperature, delamination cracks are found on the fracture surface both under the static and dynamic conditions, which are perpendicular to the thickness direction in T-L specimen and perpendicular to the main crack propagation direction in T-S specimen. Influence of loading rate on the delamination crack size and amount is obvious. The fracture initiation energy and total fracture energy increase with test temperature increasing. Influence of loading rate on the total fracture energy is unobvious at the higher temperature, but is obvious at the lower temperature. So the loading rate effects on total fracture energy are relevant to test temperature and notch orientation.

A Crack Emanating from a Wedge In Dissimilar Anisotropic Materials Under Antiplane Shear

A crack in a composite wedge consisting of two dissimilar anisotropic materials under concentrated antiplane loads is analyzed. The problem of a crack in an isotropic composite wedge is solved first by using the Mellin transform and the Wiener-Hopf method. Using a linear transformation of the original composite wedge into an isotropic composite wedge consisting of dissimilar isotropic materials, the antiplane displacement and stresses for the anisotropic composite wedge are obtained from the solution for the transformed wedge. The stress intensity factor for the crack in the original anisotropic composite wedge is obtained from the solution of the crack in the transformed wedge. Special attention is given to the asymptotic problem of a wedge crack in an anisotropic bimaterial. Numerical computations are carried out to obtain the energy release rate for various apex angles and anisotropic parameters as a function of crack angle.

Analysis of a Thin Electrode Layer between Two Dissimilar Piezoelectric Solids

A thin electrode layer at the interface between two dissimilar linear piezoelectric materials under electromechanical loading is investigated. The complex function theory is employed to obtain the exact solution to a finite thin conductive layer. Special consideration is devoted to the structure of singular stress and electric fields near the tip of the thin electrode between two dissimilar piezoelectric materials. The stress and electric field are found to have an inverse square root singularity. The electric field intensity factor characterizes uniquely the singular fields close to the edge of the conductive line sheet.

Study on Torque Analysis of Micro-Electromagnetic Clutch by Using the Finite Element Method

This study tries to analyze the torque generated in a micro-electromagnetic clutch by using FEM. For the purpose of design change and optimization of the micro-electromagnetic clutch, the torque prediction is very important. We employ a mathematical approach of the process based on electromagnetic principle. Then real material properties are substituted in the FEM model to obtain the analytical torque. For a test, the predicted torque is compared with the experimental one to discuss the rationality of torque analysis process. The analytical result agrees well with experimental data and hence explaining the validity of the mathematical process and the FEM model.

Dynamics of a Vibrating Micro Three-Axis Ring Gyroscope

This paper presents electro-mechanical characteristics of a micro-machined vibrating silicon ring gyroscope which can measure angular velocity components about three orthogonal axes. The ring gyroscope has a ring connected to the gyroscope main body by support ligaments that are arranged with cyclic symmetry. The natural modes of its vibration can be distinguished into the in-plane motion and the out-of-motion that are coupled by the gyro-effect due to the rotation of the gyroscope main body. The motions of the ring are electro-statically driven, sensed and balanced by electrodes. The equations of motion are formulated with considering the electrostatic effects of electrodes. The measuring method of angular velocities of the gyroscope main body by force-torebalance is proposed. The dynamic characteristics of the ring gyroscope are discussed.

Atomistic simulations on intergranular fracture toughness of copper bicrystals with symmetric tilt grain boundaries

The intergranular fracture toughness of Cu bicrystals with symmetric tilt grain boundaries was investigated using atomistic simulations. Mode I fracture of Cu bicrystals with an intergranular crack was considered. The boundary conditions were specified by the near-tip displacement fields obtained based on linear elastic fracture mechanics (LEFM). Based on the energy interpretation of the energy release rate, a two-specimen method was adopted to determine the fracture toughness. The simulation results of the fracture toughness matched well with those determined using LEFM. In contrast to the toughness obtained using the Griffith energy criterion, the atomistic simulation results for the same bicrystal were not constants, but dependent on the crack-tip circumstances. This behavior was mainly associated with the different local stress conditions and fracture patterns observed for the different models.

Semi-analytical Annular Mindlin Plate Element for Out-of-plane Vibration Analysis of Thick Disks

This paper presents a new semi-analytical annular Mindlin plate element with which out-of-plane natural vibration of thick disks can be analyzed simply, efficiently, and accurately through FEM by including effects of rotary inertia and transverse shear deformation. Using static deformation modes which are exact solutions of equilibrium equations of annular Mindlin plate, the element interpolation functions, stiffness and mass matrices corresponding to each number of nodal diameters are derived. The element is capable of representing out-of-plane rigid-body motions exactly and free from shear locking. Natural frequencies of uniform and multi-step disks with or without concentric ring support are analyzed by applying the presented element. Such results are compared with theoretical predictions of previous works or FEA results obtained by using two-dimensional shell element to investigate the convergence and accuracy of the presented element.

Different Delamination Cracks during Fracture and Their Influences on the Fracture of X70 Pipeline Steel

Single or multiple of delaminations have been found frequently on the fracture surface of X70 pipeline steel. In this study, the delamination cracks and their influence on the fracture of pipeline are investigated by both experiment and three-dimensional fracture analyses. It is shown that the three-dimensional stress state is prerequisite for delamination crack and the strength distribution of material influences the form and direction of delamination crack. The delamination cracks are produced on the weak interfaces among the material by the tensile stress perpendicular to them before the fracture passes. The direction of delamination crack depends on the three-dimensional stress fields and strength distribution of material near the crack tip or notch root. The delamination cracks of the fracture through thickness of pipe wall make the effective thickness decrease and the delamination cracks of surface crack are perpendicular to the direction of fracture propagation direction. The delamination cracks reduce the stress triaxiality near crack tip and in turn, improve the fracture toughness of X70 pipeline steel.

Evaluation of Cracked Beam-to-Column Connection from Brittle Failure Using Finite Element Method

The bolted end-plate composite beam-CCSHRC column connection was validated to be ductile and offered an alternative to pre-Northridge connection. This study aims at the beam lower flange fracture in the connection test, and applies the J-integral criteria to examine the connection’s nonlinear fracture behavior. Advanced 3-D connection models containing initial crack in the high stress zone at lower flange are created, and the J values at the crack tip are calculated with considering the influences of certain parameters. The results demonstrate that the J values are strongly affected by the initial crack length and interstory drift. For 0.94, 1.35, 1.86 and 2.50 mm long crack, the J values sharply increase during loading history. The crack with a length of 2.50 mm propagates at a 66 mm drift, while the 1.35 mm long crack grows at a 120 mm drift. For 0.94 or 0.61 mm long crack, it keeps stable without growing upon loading. Besides, the J values exhibit a weak sensitivity to the beam concrete strength and tensile reinforcement ratio for beam. Under the same drift, the J-integral increases by about 3.5% when concrete strength changes from 15 to 24 MPa, and the J values at 0.6% tensile reinforcement ratio for beam are 1.5% larger than those at 0.3% or 1% reinforcement ratio.