• 제목/요약/키워드: Fracture Velocity

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텅스텐 중합금의 부피분율, 입자형상에 따른 단열전단밴드 형성 연구 (The Effects of Volume Ratio and Shape on the Formation of Adiabatic Shear Band in WHA)

  • 이승우;송흥섭;문갑태
    • 소성∙가공
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    • 제11권8호
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    • pp.682-690
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    • 2002
  • The formation of adiabatic shearband in tungsten heavy alloys(WHA) was studied in this investigation. Five prismatic specimens were loaded by high velocity impacts and treated as plane strain problems. To find out the effect of particle's volume ratio, specimens containing 81%, 93% and 97% volume percents of tungsten particles were used. Also the effects of particle's geometry and size on the formation of shearband were studied for 81% volume percent alloys by small size particle model, large size particle model and undulated particle models, and the results were discussed.be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, or incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

고속열차용 트리포드 축의 비틀림 해석 및 파단에 대한 실험적 연구 (Experimental Investigation on Torsional Analysis and Fracture of Tripod Shaft for High-speed Train)

  • 이주홍;김도식;남태연;이태영;조해용
    • 대한기계학회논문집A
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    • 제40권11호
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    • pp.979-986
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    • 2016
  • 등속조인트의 일종인 트리포드 축은 동력전달용으로 고속열차의 KTX와 KTX-산천에 모두 적용되고 있으며, 동력대차에서 모터 감속장치(MRU)와 차축 감속장치(ARU)를 연결해 고속회전동력을 전달하는 핵심 요소이다. 축 방향의 미끄럼 운동이 가능한 트리포드 축은 열차 구동을 위한 토크를 전달하며, 동력전달 시스템에 과토크 발생 시 축의 퓨즈부가 절단되어 동력을 차단한다. 본 연구에서는 리니어 액추에이터를 이용한 대용량 비틀림 시험장치의 개발과 이를 이용한 트리포드 축의 정적 비틀림 강도와 피로수명을 확인하고자 하였다. 또한 구조해석을 통해 축의 취약부를 파악하고 비틀림 피로해석 결과와 실제 피로시험의 결과를 비교분석하여 비틀림 성능 개선을 위한 설계안을 제시하고자 하였다. 한편 트리포드 축의 피로에 따른 열화를 파악하기 위해 히스테리시스 곡선을 이용하였으며, 히스테리시스 곡선의 기울기 변화를 통해 피로고장 시점을 확인하였다.

Weathering and Degradation Assessment of Rock Properties at the West Stone Pagoda, Gameunsaji Temple Site, Korea

  • Lee, Chan Hee;Lee, Myeong Seong;Kim, Jiyoung
    • Conservation and Restoration of Cultural Heritage
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    • 제1권1호
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    • pp.29-37
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    • 2012
  • The West Stone Pagoda at Gameunsaji Temple Site constructed in the 7th century is mainly composed of dark grey dacitic tuff bearing small numerous dioritic xenoliths. These xenoliths resulted in small holes due to differential weathering process from the host rocks. Physical strength of the pagoda was decreased due to weathering and damage caused by petrological, biological and coastal environmental factors. The southeastern part of the pagoda was extremely deteriorated that the rock surface showed exfoliation, fracture, open cavity, granular decomposition of minerals and salt crystallization by seawater spray from the eastern coast. The stone blocks were intersected by numerous cracks and contaminated by subsequent material such as cement mortar and iron plates. Also, the pagoda was colonized by algae, fungi, lichen and bryophytes on the roof rock surface and the gaps between the blocks. As a result of ultrasonic test, the rock materials fell under Highly Weathered Grade (HW) or Completely Weathered Grade (CW). Thus, conservational intervention is essentially required to prevent further weakening of the rock materials.

열응력, 내력 및 균열 경계하중을 고려한 2차원 균열문제의 에너지방출율 (The Energy Release Rate of the Two Dimensional Cracked Body Under Thermal Stresses, Body Forces and Crack-Face Tractions)

  • 이태원
    • 대한기계학회논문집
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    • 제17권9호
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    • pp.2172-2180
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    • 1993
  • Under general loadings, including body forces, crack-face tractions and thermal loading, the energy release rate equation for a two-dimensional cracked body is presented. Defining the virtual crack extension as the variation of the geometry, the equation is directly derived by a shape design sensitivity of the potential energy. Although the form of the derived energy release rate equation is different from other researchers's results, the three example show that the former is exactly the same as the latter. However, the final integral equation do not involve the derivative of the displacement on the crack surface and crack tip region, thereby improving the numerical accuracy in the computation of the energy relase rate. Moreover, as it was derived from the governing equation including non-linear elasticity without special assumptions, the energy release rate of a elasto-plastic fracture can be obtained and any numerical stress analysis method can be applied.

Wavelet 변환을 이용한 이방성 적층판의 판파 해석과 음원 위치 결정 (Wavelet Analysis of Plate Waves in Anisotropic Laminates and Acoustic Source Location)

  • 장영수;정현조
    • Composites Research
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    • 제13권1호
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    • pp.61-68
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    • 2000
  • 이방성 적층 복합재 판의 과도적인 파동 해석을 위한 새로운 방법을 제시하였다. Gabor wavelet을 사용하는 wavelet 변환을 분산성 굽힘파의 시간-주파수 해석에 적용하였다. 시간-주파수 영역에서 wavelet 변환의 크기의 최대값은 군속도의 도달시간을 나타냄을 보였다. 음향방출원으로서 연필심 파단을 사용하여 준등방성 판과 일방향 보강 적층판에서 실험을 수행하였다. 굽힘파의 분산 예측을 위하여 Mindlin 판이론을 사용하였으며,주파수의 함수로 몇 개의 방향에 대해 측정한 군속도 실험 결과와 잘 일치하였다. 굽힘파의 주파수 의존 도달 시간과 같은 파의군속도 방향의존성을 이용하여 이방성 판에서의 파손 위치를 결정하였으며, 그 결과를 제시하였다.

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직교 이방성체의 동적 응력확대계수에 관한 연구(I) (A Study on the Dynamic Stress Intensity Factor of Orthotropic Materials(I))

  • 이광호;황재석;최선호
    • 대한기계학회논문집
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    • 제17권2호
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    • pp.313-330
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    • 1993
  • The propagating crack problems under dynamic plane mode in orthotropic material is studied in this paper. To analyze the dynamic fracture problems in orthortropic material, it is important to know the dynamic stress components and dynamic displacement components around the crack tip. Therefore the dynamic stress components of dynamic stress field and dynamic displacement components of dynamic displacement field in the crack tip of orthotropic material under the dynamic load and the steady state in crack propagation were derived. When the crack propagation speed approachs to zero, the dynamic stress component and dynamic displacement components derived in this study are identical to the those of static state. In addition, the relationships between dynamic stress intensity factor and dynamic energy release rate are determinded by using the concept of crack closure closure energy with the dynamic stresses and represented according to physical properties of the orthotrophic material and crack speeds. The faster the crack velocity, the greater the stress value of stress components in crack tip. The stress value of the stress component of crack tip is greater when fiber direction coincides with the crack propagation than when fider direction is normal to the crack propagation.

빙해수조 모형빙판의 유효탄성계수 산출 (The Effective Young's Modulus of Model Ice Sheet in Ice Basin)

  • 이재환;최봉균;김태완;이춘주
    • 대한조선학회논문집
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    • 제52권4호
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    • pp.315-322
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    • 2015
  • In this paper, the theory of rectangular plate on the elastic foundation is used to get the relation equation between the effective Young’s modulus and the ice sheet deflection by applying the characteristic length concept, since the model ice sheet is rectangular shape in KRISO (Korea Research Institute for Ships and Ocean Engineering) ice basin. The obtained relation equation is equal to that of using the circular plate theory. A device is made and used to measure the deflection of ice plate using LVDT (Linear Variable Differential Transformer) for several loading cases and the procedure of experiments measuring the deflection used for getting the Young’s modulus is explained. In addition, the flexural strength value obtained through flexural strength experiments is compared with that of finite element analysis using the obtained effective Young’s modulus. Also, a nonlinear FEA (Finite Element Analysis) of cantilever ice beam is done with eroding effect and LS-DYNA result shows the fracture of brittle ice under 1 mm/s velocity load.

크랙을 가진 단순지지 보의 동특성에 미치는 이동질량의 영향 (Influence of Serial Moving Masses on Dynamic Behavior of Simply Supported Beam with Crack)

  • 윤한익;김영수;손인수
    • 한국소음진동공학회논문집
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    • 제13권7호
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    • pp.555-561
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    • 2003
  • An iterative modal analysis approach is developed to determine the effect of transverse open cracks on the dynamic behavior of simply supported Euler-Bernoulli beams with the moving masses. The influences of the velocities of moving masses, the distance between the moving masses and a crack have been studied on the dynamic behavior of a simply supported beam system by numerical method. The Presence of crack results In large deflection of beam. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section and is derived by applying fundamental fracture mechanics theory. Totally, as the velocity of the moving masses and the distance between the moving masses are increased, the mid-span deflection of simply supported beam with the crack is decreased.

Simulation of material failure behavior under different loading rates using molecular dynamics

  • Kim, Kunhwi;Lim, Jihoon;Kim, Juwhan;Lim, Yun Mook
    • Structural Engineering and Mechanics
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    • 제30권2호
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    • pp.177-190
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    • 2008
  • Material failure behavior is generally dependent on loading rate. Especially in brittle and quasi-brittle materials, rate dependent material behavior can be significant. Empirical formulations are often used to predict the rate dependency, but such methods depend on extensive experimental works and are limited by practical constraints of physical testing. Numerical simulation can be an effective means for extracting knowledge about rate dependent behavior and for complementing the results obtained by testing. In this paper, the failure behavior of a brittle material under different loading rates is simulated by molecular dynamics analysis. A notched specimen is modeled by sub-million particles with a normalization scheme. Lennard-Jones potential is used to describe the interparticle force. Numerical simulations are performed with six different loading rates in a direct tensile test, where the loading velocity is normalized to the ratio of the pseudo-sonic speed. As a consequence, dynamic features are achieved from the numerical experiments. Remarkable failure characteristics, such as crack surface interaction/crack arrest, branching, and void nucleation, vary in case of the six loading cases. These characteristics are interpreted by the energy concept approach. This study provides insight into the change in dynamic failure mechanism under different loading rates.

Si, Mn, V이 첨가된 비조질강의 미세조직 및 기계적 성질에 미치는 냉각속도의 영향 (Effect of Cooling Velocity on the Microstructures and Mechanical Properties of Si, Mn, V added HSLA Steels)

  • 박연서;최창수;정인상
    • 열처리공학회지
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    • 제14권5호
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    • pp.267-274
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    • 2001
  • Microalloyed steels, which substituted by conventional quenched and tempered steels, have been used in a wide variety of structural and engineering application. The main driving force for preference of MA steels is a cost reduction which can be achieved by an omission of heat treatment. In this study, low carbon martensitic MA steels in 0.18C-0.30(0.60)Si-2.00(1.80)Mn-0.05S-1.5Cr-0.05(0.10)V-0.015Ti(wt%) were investigated to know the effects of cooling method on the mechanical properties and microstructures of Si, Mn, V added microalloyed steel at different reheating temperature. Microstructure of oil quenched steels which were comprised lath martensite, auto-tempered martensite and retained austenite, had more various structure than that of air cooled steel made of mainly bainite. Therefore, oil quenched steels, which had more various microstructure, had better strength-toughness balance compare to air cooled steels. In the impact test, fracture mode of oil quenched steels, which showed good mechanical properties, were dimple, but that of air cooled steels were cleavage.

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