• 한국철도학회논문집
• /
• 제8권5호
• /
• pp.444-453
• /
• 2005

The safety evaluations of railway wheelsets make use of the static fracture toughness obtained in ingot materials. The static fracture toughness of wheelset materials has been extensively studied by experiments, but the dynamic fracture toughness with respect to wheelset materials has not been studied enough yet. It is necessary to evaluate the characteristics of the fracture mechanics depending on each location for a full-scale wheelset for high-speed trains, because the load state for each location of the wheelset while running is different the contact load between the wheel and rail, cyclic stress in the wheel plate, etc. This paper deals with the fracture toughness depend on load rates. The fracture toughness depending on load rate data shows that once the downward curve from quasi-static values was reached, subsequent values showed a slow increase with respect to the impact velocity. This means that dynamic fracture toughness should be considered in the design code of the wheelset material.

• 터널과지하공간
• /
• 제19권4호
• /
• pp.366-372
• /
• 2009

최근, 암반발파에서 평활한 파단면과 굴착손상영역을 제어하기 위한 목적으로 전자지발뇌관 및 노치장약공 등을 이용한 제어발파기술들이 개발되어 오고 있다. 본 연구에서는 날개형 노치 장약공을 이용한 SB발파에서 암반 내 파괴과정을 모사하여 파단면과 암반손상제어에 미치는 영향인자에 대하여 고찰하였다. 최종적으로 장약공 노치의 파단면 제어효과에 관한 수치해석적 고찰을 날개형 노치장약공과 전자뇌관을 이용한 새로운 SB발파법으로, ED-Notch SB발파법(Elerectronic Detonator Notched Charge Hole Smooth Blasting Method)을 제안하였다.

• Structural Engineering and Mechanics
• /
• 제48권1호
• /
• pp.17-39
• /
• 2013

In the present paper, a coaxial rotating smeared crack model is proposed for mass concrete in three-dimensional space. The model is capable of applying both the constant and variable shear transfer coefficients in the cracking process. The model considers an advanced yield function for concrete failure under both static and dynamic loadings and calculates cracking or crushing of concrete taking into account the fracture energy effects. The model was utilized on Koyna Dam using finite element technique. Dam-water and dam-foundation interactions were considered in dynamic analysis. The behavior of dam was studied for different shear transfer coefficients considering/neglecting fracture energy effects. The results were extracted at crest displacement and crack profile within the dam body. The results show the importance of both shear transfer coefficient and the fracture energy in seismic analysis of concrete dams under high hydrostatic pressure.

• 대한기계학회논문집
• /
• 제13권5호
• /
• pp.947-951
• /
• 1989

본 연구에서는 디지틀식 균열속도 측정장치를 보완, 확장시켜 몇몇 고분자 (polymer)재료에 있어서의 동적 균열전파속도를 측정하였으며, 다른 연구자들의 실험 데이터와 비교하였다.

• 대한기계학회논문집
• /
• 제14권1호
• /
• pp.112-118
• /
• 1990

본 연구에서는 ASTM-E24.01.06에서 제안하고 있는 실험방법을 응용하여 균열 정지 파괴인성값을 측정하였다.즉 쐐기와 분리형 부싱(wedge and split bushing)으 로 압축하중을 가함으로 균열선 웨지하중 시편[crack line wedge loaded specimen(CL- WL시편)]에 인장력을 발생시켜서 균열정지 응력확대계수( $K_{1a}$)를 결정하였다. 그리고 균열개시 응력확대계수가 균열정지 응력확대계수에 미치는 영향들을 여러가지 재료들에 대하여 체계적으로 검토하였다.다.

• Structural Engineering and Mechanics
• /
• 제58권1호
• /
• pp.103-119
• /
• 2016

Multi-storey frame structures are frequently exposed to static and dynamic forces. Therefore analyses of static (buckling) and dynamic stability come into prominence for these structures. In this study, the effects of number of storey, static and dynamic load parameters, crack depth and crack location on the in-plane static and dynamic stability of cracked multi-storey frame structures subjected to periodic loading have been investigated numerically by using the Finite Element Method. A crack element based on the Euler beam theory is developed by using the principles of fracture mechanics. The equation of motion for the cracked multi-storey frame subjected to periodic loading is achieved by Lagrange's equation. The results obtained from the stability analysis are presented in three dimensional graphs and tables.

• Journal of Welding and Joining
• /
• 제11권1호
• /
• pp.42-51
• /
• 1993

In this study, investigations were conducted in calculating parameters of elastic-plastic fracture mechanics using single specimen. The validity of these testing methods was judged by the confirmation of multiple specimen method of stop block test. The results were as follows: In order to measure a fracture toughness using the instrumented impact test, two general requirement must be considered; One, setting up proper impact velocity considered the effect of loading and the other, the necessity of low blow test for obtaining true energy by the compliance correction. It was possible to detect a crack initiation point by calculating the compliance changing rate from a load-defection curve. Criterion of a stable crack growth, $T_{mat}$ could be estimated by using key-curve method for a base metal. and combining Kaiser's rebound compliance with Paris-Hutchison's $T_{appl}$ equation for the brittled zone of welding heat affected.at affected.d.

• Journal of Mechanical Science and Technology
• /
• 제16권2호
• /
• pp.165-174
• /
• 2002

In the present study, interfacial cracks between an isotropic and orthotropic material, subjected to static far field tensile loading are analyzed using the technique of photoelasticity. The fracture parameters are extracted from the full-field isochromatic data and the same are compared with that obtained using boundary collocation method. Dynamic photoelasticity combined with high-speed digital photography is employed for capturing the isochromatics in the case of propagating interfacial cracks. The normalized stress intensity factors for static cracks are greate. when ${\alpha}$: 90$^{\circ}$(fibers perpendicular to the interface) than when ${\alpha}$=0$^{\circ}$(fibers parallel to the interface), and those when ${\alpha}$=90$^{\circ}$are similar to ones of isotropic material. The dynamic stress intensity factors for interfacial propagating cracks are greater when ${\alpha}$=0$^{\circ}$ than ${\alpha}$=90$^{\circ}$. For the velocity ranges (0.1 < C/C$\sub$s1/<0.7) observed in this study, the complex dynamic stress intensity factor │K$\sub$D/│increases with crack speed c, however, the rate of increase of │K$\sub$D/│with crack speed is not as drastic as that reported for homogeneous materials.

• Computers and Concrete
• /
• 제25권1호
• /
• pp.15-27
• /
• 2020

During the past decades, the application of acoustic emission techniques (AET) through the diagnosis and monitoring of the fracture process in materials has been attracting considerable attention. AET proved to be operative among the other non-destructive testing methods for various reasons including their practicality and cost-effectiveness. Concrete and rock structures often demand thorough and real-time assessment to predict and prevent their damage nucleation and evolution. This paper presents an overview of the work carried out on the use of AE as a monitoring technique to form a comprehensive insight into its potential application in brittle materials. Reported properties in this study are crack growth behavior, localization, damage evolution, dynamic character and structures monitoring. This literature review provides practicing engineers and researchers with the main AE procedures to follow when examining the possibility of failure in civil/resource structures that rely on brittle materials.

• 전산구조공학
• /
• 제11권4호
• /
• pp.383-390
• /
• 1998

0.93m/sec의 평균속도는 변위제어 삼점휨 실험된 콘크리트 보의 하중-변위 측정결과를 선형탄성파괴역학모델과 가상균열모델에 기초한 유한요소법으로 분석하였다. 두 모델 모두 실험결과와 잘 일치하며, 균열성장길이가 약 60∼70㎜가 될 때까지 안전된 균열성장을 보이다 불안정한 균열성장에 의해 파손되었다. 선형탄성파괴역학모델에 의한 수치해석 결과 에너지해방률은 균열성장길이에 비례해서 증가하였으며, 최대값(202N/m)에 이르게 되면 일정한 값을 유지하였다. 가상균열모델에 기초한 수치해석결과 이 연구에 사용된 하중속도와 시험편의 크기에 대해 70㎜의 완전한 파괴진행대가 평성되었으며, 이는 기존의 정적 실험결과에 대한 수치해석 결과보다 상당히 작은 값이었다.