Papers by Author: Hyeon Chang Choi

Paper TitlePage

Authors: Hyeon Chang Choi, Hyeon Ki Choi
Abstract: The relationship between fatigue crack growth behavior and cyclic crack tip opening displacement is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the growth behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. We investigate the relationship between the reversed plastic zone size and the changes of the cyclic crack tip opening displacement along the crack growth. The cyclic crack tip opening displacement is related to fatigue crack opening behavior.
1051
Authors: Hyeon Chang Choi
Abstract: A relationship between fatigue crack opening behavior and the reversed plastic zone size is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the opening behavior of fatigue crack. The contact elements in this analysis are adopted in the mesh of the crack tip area. The smaller element size than reversed plastic zone size is used for evaluating the distribution of reversed plastic zone. In the author’s previous results, the FEA could predict the crack opening level, which the size of crack tip elements was in proportion to the theoretical reversed plastic zone size. It is found that the calculated reversed plastic zone size is related to the theoretical reversed plastic zone size and crack opening level. The calculated reversed plastic zone sizes are almost equal to the reversed plastic zone size considering crack opening level obtained by experimental results. It is possible to predict the crack opening level from the reversed plastic zone size calculated by the FEA. We find that the experimental crack opening levels correspond with the opening values of crack tip contact nodes on the calculated reversed plastic zone.
66
Authors: Hyeon Ki Choi, Si Yeol Kim, Hyeon Chang Choi
Abstract: In this study we presented kinematic and kinetic data of foot joints by using passive elastic characteristics of joints during gait. During the calculation process we used approximate equations and partial plantar pressures. The maximum angular displacements of each tarsometatarsal joint ranged from 4o to 7o and the maximum moments were from 200N⋅cm to 1500N⋅cm. It was relatively wide distribution. Foot kinematic data calculated from the approximated equations, which were represented by the correlation between moment and angular displacement, and the data from motion analysis were very similar. We found that the movements of foot joints were mainly decided by the passive characteristics of the joints when ground reaction force acts. The kinematic and kinetic analysis using approximated equations which is presented in this study can be usefully applied to describing the movements of foot joints during gait.
2231
Authors: Jun Hyub Park, Sung Il Chu, Hyeon Chang Choi
Abstract: This paper represents the development of 3-axises loadcell for measuring the side-force of the suspension module of MPV (Multi Purposed Vehicle). The side force causes the failure of damper, such as leakage. The loadcell was developed using strain gauges, and the Wheastone bridge circuit to compensate for the cross-talk between each axises and the measurement error by temperature. Structure analysis of loadcell was accomplished with FEM (Finite Element Method) to optimize the location of strain gages. The design optimization for the important factors that have effects on performance of loadcell was accomplished by using DOE (Design of Experiment). Loadcell was produced and successfully tested, showing good sensitivity and low cross-talk. The cross-talk of the developed loadcell is below 2%. The measured history using the manufactured load cell will be utilized in the vibration, and fatigue analysis in the future.
2802
Authors: Hyeon Ki Choi, Jae Hoon Jeong, Sung Ho Hwang, Hyeon Chang Choi, Won Hak Cho
Abstract: We recognized EMG signal patterns of lower limb muscles by using neural networks and performed feature evaluation during the recovery of postural balance of human body. Surface electrodes were attached to lower limb and EMG signals were collected during the balance recovery process from a perturbation without permitting compensatory stepping. A waist pulling system was used to apply transient perturbations in five horizontal directions. The EMG signals of fifty repetitions of five motions were analyzed for ten subjects. Twenty features were extracted from EMG signals of one event. Feature evaluation was also performed by using DB (Davies-Bouldin) index. By using neural networks, EMG signals were classified into five categories, such as forward perturbation, backward perturbation, lateral perturbation and two oblique perturbations. As results, motions were recognized with mean success rates of 75 percent. With the neural networks classifier of this study, the EMG patterns of lower limb muscles during the recovery of postural balance can be classified with high accuracy of recognition.
867
Authors: Hyeon Ki Choi, Min Jwa Seo, Ja Choon Koo, Hyeon Chang Choi, Won Hak Cho
Abstract: We assessed the effects of muscle forces on ankle joint kinetics during postural balance control of human boy. Nine male subjects (mean age of 25.8 yrs) participated in the experiment. An ankle joint model assumed ball and socket joint was used, which was capable of three dimensional rotations. A six-camera VICON system was used for motion analysis. Waist pulling system and force platform were adopted for forward sway and GRF (ground reaction force) measurement. We used linear optimization programs to calculate the variation of muscle forces and angular displacements of shank and foot segments. With the experimental data and linear programs, we could calculate joint reaction forces, and bone-on-bone forces. The results presented in this study give us the insights to understand the roles of lower limb muscles during postural balance control and ankle injury mechanism.
871
Authors: Hyeon Chang Choi, Hyeon Ki Choi, Jun Hyub Park
Abstract: The cyclic crack tip opening displacement is well related to fatigue crack opening behavior. In this paper, we investigate the effect of the maximum stress intensity factor, Kmax, when predicting fatigue crack opening behavior using the cyclic crack tip opening displacement obtained from FEA. The commercial finite element code, ANSYS, for fatigue crack closure analysis in this study is used. We derive the prediction formula of crack opening behavior when using the cyclic crack tip displacement obtained from the FEA. The numerical prediction shows the good results regardless of stress ratios. It is confirmed that the crack opening behavior depends upon the maximum stress intensity factor Kmax.
1106
Authors: Hyeon Chang Choi
Abstract: An elastic-plastic finite element analysis (FEA) is performed to examine the opening behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. The relationship between fatigue crack opening behavior and cyclic crack tip opening displacement was studied in the previous study. In this paper, we investigate the effect of the element size when predict fatigue crack opening behavior using the cyclic crack tip opening displacement obtained from FEA. The cyclic crack tip opening displacement is well related to fatigue crack opening behavior.
295
Showing 1 to 8 of 8 Paper Titles