• Title/Summary/Keyword: Static friction

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The Analysis of Draw-bead Process According to the Effect of the Drawbead Shape by Using Static-explicit Finite Element Method (정적 외연적 유한요소법을 이용한 드로우비드 형상에 따른 비드공정 해석)

  • 정동원
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.10a
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    • pp.275-281
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    • 2001
  • In the sheet metal forming process, the drawbead is used to control the flow of material during the forming process. The drawbead provides proper restraining force to the material and prevents defects such as wrinkling or breakage. For these reasons, many studies for designing the effective drawbead have been conducted. In this paper, the effect of the drawbead shape will be introduced. For the analysis, the numerical method called the static-explicit finite element method was used. The finite element analysis code for this method has been developed and applied to the drawbead process problems. In result, convergence problem and computation time due to large non-linearity in the existing numerical analysis methods were no longer a critial Problem. Futhermore, this approach could treat the contact friction problem easily by applying very small time intervals. It is expected that various results from the numerical analysis will give very useful information for the design of tools in sheet metal forming process.

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Occurrence of Sand Liquefaction on Static and Cyclic Loading (정적 및 동적 하중에서 모래의 액상화 발생)

  • 양재혁
    • Journal of the Korean Geotechnical Society
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    • v.17 no.6
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    • pp.235-244
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    • 2001
  • Liquefaction may be caused by sudden decrease in the soil strength under undrained conditions. This loss of soil strength is related to the development of excess pore pressures. During this study, fines content affects the maximum and minimum void ratios are investigated. The results of static and cyclic triaxial test on silty saturated sands are presented. These tests are performed to evaluate liquefaction strength and static and cyclic behavior characteristics. The samples are obtained from Saemangeum and drying on air. The main results are summarized as follows : 1) The maximum and minimum void ratio lines follow similar trends. 2) Maximum and minimum void ratios are established at 20~30% fines content. 3) As confining pressures and overconsolidation ratio are increased, the resistance to liquefaction are increased. 4) Instability friction angles are increased with increasing initial relative density. 5) The resistance to liquefaction are decreased with increasing effective stress ratio.

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Mechanical Strength Experiment of Carbon/Carbon Composite for Aircraft Brake Disk (탄소/탄소 브레이크 디스크의 기계적 강도 시험에 관한 연구)

  • 유재석;오세희;김천곤;홍창선;윤병일;김광수
    • Composites Research
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    • v.13 no.6
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    • pp.55-62
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    • 2000
  • The strength test was done for the Carbon/Carbon rotor disk which is the critical part of a carbon/carbon brake system in an operating time. The loading fixture was designed for the static strength test of a single carbon/carbon brake disk using finite element analysis. To simulate the real dynamic system in a static condition, the friction surface of the rotor disk was fixed and static load was applied to the rotor slot in the circumferential direction. The described failure mechanism of the brake disk can be described as matrix cracking occurred first at the contact surface of the rotor slot, subsequent delamination from the cracked contact surface, and the final fracture at the notch of the rotor.

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Mesoscale modelling of concrete for static and dynamic response analysis -Part 2: numerical investigations

  • Lu, Yong;Tu, Zhenguo
    • Structural Engineering and Mechanics
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    • v.37 no.2
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    • pp.215-231
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    • 2011
  • As a brittle and heterogeneous material, concrete behaves differently under different stress conditions and its bulk strength is loading rate dependent. To a large extent, the varying behavioural properties of concrete can be explained by the mechanical failure processes at a mesoscopic level. The development of a computational mesoscale model in a general finite element environment, as presented in the preceding companion paper (Part 1), makes it possible to investigate into the underlying mechanisms governing the bulk-scale behaviour of concrete under a variety of loading conditions and to characterise the variation in quantitative terms. In this paper, we first present a series of parametric studies on the behaviour of concrete material under quasi-static compression and tension conditions. The loading-face friction effect, the possible influences of the non-homogeneity within the mortar and ITZ phases, and the effect of randomness of coarse aggregates are examined. The mesoscale model is then applied to analyze the dynamic behaviour of concrete under high rate loading conditions. The potential contribution of the mesoscopic heterogeneity towards the generally recognized rate enhancement of the material compressive strength is discussed.

Effect of Annealing Conditions on Microstructure and Damping Capacity in AZ61 Magnesium Alloy (열처리조건에 따른 AZ61 마그네슘 합금의 미세조직과 감쇠능에 미치는 영향)

  • Ahn, Jae-Hyeon;Kim, Kwon-Hoo
    • Journal of the Korean Society for Heat Treatment
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    • v.31 no.2
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    • pp.56-62
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    • 2018
  • Many researchers have studied on the precipitation control after solution treatment to improve the damping capacity without decreasing the strength. However, studies on the damping capacity and microstructure changes after deformation in the solid solution strengthening alloys were inadequate, such as the Al-Zn series magnesium alloys. Therefore, in order to investigate the effect of annealing condition on microstructure change and damping a capacity of AZ61 magnesium alloy. In this study, it was confirmed that the microstructure changes affect the damping capacity and hardness when annealed AZ61 alloy. AZ61 magnesium alloy was rolled at $400^{\circ}C$ with rolling reduction of 30%. These specimens were annealed at $350^{\circ}C$ to $450^{\circ}C$ for 30-180 minutes. After annealing, microstructure was observed by using optical microscopy, and damping capacity was measured by using internal friction measurement machine. Hardness was measured by Vickers hardness tester under a condition of 0.3 N. In this study, static recrystallization was observed regardless of the annealing conditions. In addition, uniform equiaxed grain structure was developed by annealing treatment. Hardness is decreased with increasing grain size. This is associated with Hall-Petch equation and static recrystallization. In case of damping capacity, bigger grain size show the larger damping capacity.

Analysis of Cylindrical Hydrostatic Bearing (진원형 정수압 베어링의 해석)

  • 문호지;한동철
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1989.11a
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    • pp.94-99
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    • 1989
  • This paper analyzes file stiffness, damping coefficient, friction force and flow coefficient of externally pressurized oil journal beating, including the effect of journal rotation according to the Sommerfeld number. This paper assumed that the oil in the whole pocket has constant pressure, and that the oil in the whole bearing region has constant viscosity, temperature and density. Reynolds equation is derived from Nuvier - Stokes equation and continuity equation. And solved bearing pressure by ADI method for whole bearing region and fitted with out flow rate of pocket region. The model for numerical simulation is hydro - static oil journal bearing for high-speed, high-accuracy lathe spindle.

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다축 공작기계의 위치정밀도 향상을 위한 추적제어기 설계

  • 서정환;양호석;이천환;이승욱;이건복
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1992.10a
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    • pp.192-197
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    • 1992
  • The position error in multi-axis machine tools are due to many elements, such as the static friction, servo lag, a nonlinear disturbance, the gain mismatch between multi-axis controllers. In the work, modeling for the plant was carried out through the velocity response by the step input signal. Digital PI controllers, LQ optimal controllers and feedforward controllers are designed for a high tracking performance based on the model. The results of experimentation showed that the controllers worked properly.

볼스크류를 이용한 유정압테이블의 고정밀위치 결정

  • 황주호;박천흥;이후상
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.288-292
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    • 1997
  • Positioning accuracy largely depends on the variation of friction force in guide table, geometric accuracy of feed unit like as ballscrew and controllable accrecy of servo unit, in general. This paper deals with improvement of microstep resolution about hydrostatic table. Torque control mode have a advantage in microstep test, and more stable than velocity control mode in low velocity motion. Hydro static table have the elastic behavior within several .mu.m, so different character exist between the elastic motion and rolling motion. Integral gain is dominant than other gain in elastic motion. In order to improve response time in elastic motion,increasing gain is suggested within the stable region.

A Study on Teachers' Knowledge of Mathematics -With Respect to the Concept of Function- (교사의 수학적 지식에 대한 연구 -함수 개념과 관련하여-)

  • 김원경;김용대
    • The Mathematical Education
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    • v.41 no.1
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    • pp.101-108
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    • 2002
  • The purpose of this study is to estimate teachers' knowledge of mathematics via the concept of function. For the purpose, a survey was done to measure their knowledge of mathematics. The result obtained from the survey was as follows With respect to the knowledge on concept of friction, they understood the function as ordered pairs and graph rather than as relation and expression. This study reached the following conclusions from the result : They have the more static cognition than the dynamic one on the concept of unction.

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Measurement of Mechanical and Physical Properties of Pepper for Particle Behavior Analysis

  • Nam, Ju-Seok;Byun, Jun-Hee;Kim, Tae-Hyeong;Kim, Myoung-Ho;Kim, Dae-Cheol
    • Journal of Biosystems Engineering
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    • v.43 no.3
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    • pp.173-184
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    • 2018
  • Purpose: This study was conducted to investigate the mechanical and physical properties of a Korean red pepper variety for particle behavior analysis. Methods: Poisson's ratio, modulus of elasticity, shear modulus, density, coefficient of restitution, and coefficient of friction were derived for "AR Legend," which is a domestic pepper variety. The modulus of elasticity and Poisson's ratio were measured through a compression test using a texture analyzer. The shear modulus was calculated from the modulus of elasticity and Poisson's ratio. The density was measured using a water pycnometer method. The coefficient of restitution was measured using a collision test, and the static and dynamic friction coefficients were measured using a inclined plane test. Each test was repeated 3-5 times except for density measurement, and the results were analyzed using mean values. Results: Poisson's ratios for the pepper fruit and pepper stem were 0.295 and 0.291, respectively. Elastic moduli of the pepper fruit and pepper stem were $1.152{\times}10^7Pa$ and $3.295{\times}10^7Pa$, respectively, and the shear moduli of the pepper fruit and pepper stem were $4.624{\times}10^6Pa$ and $1.276{\times}10^7Pa$, respectively. The density of the pepper fruit and the pepper stem were $601.8kg/m^3$ and $980.4kg/m^3$, respectively. The restitution coefficients between pepper fruits, pepper stems, a pepper fruit and a pepper stem, a pepper fruit and plastic, and a pepper stem and plastic were 0.383, 0.218, 0.277, 0.399, and 0.148, respectively. The coefficients of static friction between pepper fruits, pepper stems, a pepper fruit and a pepper stem, a pepper fruit and plastic, and a pepper stem and plastic were 0.455, 0.332, 0.306, 0.364, and 0.404, respectively. The coefficients of dynamic friction between a pepper fruit and plastic and a pepper stem and plastic were 0.043 and 0.034, respectively.