In-Soo Son

Free vibration analysis of Euler-Bernoulli beam with double cracks

In this paper, the influence of two open cracks on the dynamic behavior of a double cracked simply supported beam is investigated both analytically and experimentally. The equation of motion is derived by using the Hamilton’s principle and analyzed by numerical method. The simply supported beam is modeled by the Euler-Bemoulli beam theory. The crack sections are represented by a local flexibility matrix connecting three undamaged beam segments. The influences of the crack depth and the position of each crack on the vibration mode and the natural frequencies of a simply supported beam are analytically clarified for the single and double cracked simply supported beam. The theoretical results are also validated by a comparison with experimental measurements.

Influence of tip mass on dynamic behavior of cracked cantilever pipe conveying fluid with moving mass

In this paper, we studied about the effect of the open crack and a tip mass on the dynamic behavior of a cantilever pipe conveying fluid with a moving mass. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method. The cantilever pipe is modelled by the Euler-Bernoulli beam theory. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influences of the crack, the moving mass, the tip mass and its moment of inertia, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the tip-displacement of the cantilever pipe are analytically clarified.

Dynamic Behavior of Cracked Pipe Conveying Fluid with Moving Mass Based on Timoshenko Beam Theory

In this paper we studied about the effect of the open crack and the moving mass on the dynamic behavior of simply supported pipe conveying fluid. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments i.e. the crack is modeled as a rotational spring. The influences of the crack severity, the position of the crack, the moving mass and its velocity, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the mid-span displacement of the simply supported pipe are depicted.

A Study on Dynamic Behavior of Simply Supported Fluid Flow Pipe with Crack and Moving Mass

In this paper, studied about the effect of open crack and the moving mass on the dynamic behavior of simply supported pipe conveying fluid. The equation of motion is derived by using Lagrange`s equation. The influences of the velocity of moving mass, the velocity of fluid flow and a crack have been studied on the dynamic behavior of a simply supported pipe system by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. Therefore, the crack is modelled as a rotational spring. Totally, as the velocity of fluid flow is increased, the mid-span deflection of simply supported pipe conveying fluid is increased. The position of the crack is located in the middle point of the pipe, the mid-span deflection of simply supported pipe presents maximum deflection.

Effects of Attached Mass on Stability of Pipe Conveying Fluid with Crack

In this paper, the dynamic stability of a cracked simply supported pipe conveying fluid with an attached mass is investigated. Also, the effect of attached mass on the dynamic stability of a simply supported pipe conveying fluid is presented for the different positions and depth of the crack. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by the energy expressions using extended Hamilton`s principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of a fracture and to be always opened during the vibrations. Finally, the critical flow velocities and stability maps of the pipe conveying fluid are obtained by changing the attached mass and crack severity.

Dynamic Behavior of Rotating Cantilever Beam with Crack

In this paper, we studied about the dynamic behavior of a cracked rotating cantilever beam. The influences of a rotating angular velocity, the crack depth and the crack position on the dynamic behavior of a cracked cantilever beam have been studied by the numerical method. The equation of motion is derived by using the Lagrange`s equation. The cracked cantilever beam is modeled by the Euler-Bernoulli beam theory. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The lateral tip-displacement and the axial tip-deflection of a rotating cantilever beam is more sensitive to the rotating angular velocity than the depth and position of crack. Totally, as the crack depth is increased, the natural frequency of a rotating cantilever beam is decreased in the first and second mode of vibration. When the crack depth is constant, the natural frequencies of a rotating cantilever beam are proportional to the rotating angular velocity in the each direction.

Effect of highly pressurized hydrogen gas charging on the hydrogen embrittlement of API X70 steel

During the use of API X70 steel as a pipeline structural material for the transportation of natural gas, hydrogen embrittlement can occur due to the hydrogen contained in natural gas. The aim of this study is to investigate the effects of the hydrogen content under high-pressure hydrogen gas conditions on the hydrogen embrittlement of air-cooled API X70 steel. The air-cooled API X70 steel was manufactured by hot rolling and was then air-cooled to room temperature. Tensile test specimens were held for 0 h, 1000 h, and 2000 h within a pressure vessel filled with 100% hydrogen gas at a gas pressure of 10 MPa, with the tensile tests then performed at room temperature. The microstructure of the API X70 steel consists of coarse polygonal ferrite, coarse pearlite, and fine acicular ferrite. The yield and tensile strength increased and elongation decreased considerably after a holding time of 2000 h compared to those of 0 h and 1000 h within the pressure vessel. The morphology of the fracture surface changed from ductile to brittle upon hydrogen gas charging. Secondary cracks were observed in both of the hydrogen-gas-charged specimens. No external cracks were formed on the surface of the tensile-tested specimen with a 0 h holding time; however, many external cracks were observed on the specimen surface subjected to hydrogen gas charging.

Study on Detection of Crack and Damage for Cantilever Beams Using Vibration Characteristics

ABSTRACT In this paper, the purpose is to investigate the natural frequency of a cracked Timoshenko cantilever beams by FEM(finite element method) and experiment. In addition, a method for detection of crack in a cantilever beams is presented based on natural frequency measurements. The governing differential equations of a Timoshenko beam are derived via Hamiltons principle. The two coupled governing differential equations are reduced to one fourth order ordinary differential equation in terms of the flexural displacement. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The detection method of a crack location in a beam based on the frequency measurements is extended here to Timoshenko beams, taking the effects of both the shear deformation and the rotational inertia into account. The differences between the actual and predicted crack positions and sizes are less than 6 % and 23 % respectively. * 1. 서 론 결함을 가진 기계나 건축 등의 구조물은 동일한 하중이 작용하더라도 구조물의 자체 탄성에 의한 변형에너지 이외에 크랙에 의해서 추가로 변형에너지가 존재하게 되며, 이 부가되어진 에너지만큼 변형이 더 발생한다. 또 일반적으로 크랙을 갖는 구조물에 어떤 하중이나 외력이 작용하게 되면 일정 한계 이상으로 힘을 받지 못하고 크랙을 기점으로 해서 급격히 균열이 전파되어 파괴된다. 따라서 구조물에 존재하는 결함을 파악하는 것은 매우 중요하다 할 수 있다. 이 같이 구조물의 파괴 원인이 되는 †교신저자; 정회원, 동의대학교 기계공학과E-mail : isson92@deu.ac.krTel : (051)890-2239, Fax : (051)890-2232* 정회원, 동의대학교 기계공학과결함을 진단하기 위하여 구조물에 손상을 주지 않고 결함의 탐지가 가능하고, 경제적으로나 편의성 측면에서 매우 효과적인 비파괴 검사법이 널리 사용되고 있다. 일반적인 비파괴 검사법으로는 초음파 탐상법, 방사선 투과법, 그리고 음향방출법 등이 수행되고 있으나, 비교적 길이가 긴 요소들은 비용과 시간이 많이 소비된다. 특히 각각의 검사 방법에 따라 검출 가능한 요소들이 제한되거나 적용대상이 한정된다는 문제점들을 갖고 있다. 이러한 비파괴적인 방법 중의 하나가 구조물이나 시스템의 고유진동특성 변화를 측정하여 크랙의 존재, 위치 및 크기를 탐지하는 것이다.크랙이 구조물의 동특성에 미치는 영향을 연구하기 위하여 초기에는 구조물에서 단지 크랙이 존재하는 부분의 강성을 줄이는 방법

Dynamic Stability of Elastically Restrained Cantilever Pipe Conveying Fluid with Crack

The dynamic stability of elastically restrained cantilever pipe conveying fluid with crack is investigated in this paper. The pipe, which is fixed at one end, is assumed to rest on an intermediate spring support. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by the energy expressions using extended Hamilton`s Principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influence of a crack severity and position, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe by the numerical method are studied. Also, the critical flow velocity for the flutter and divergence due to variation in the support location and the stiffness of the spring support is presented. The stability maps of the pipe system are obtained as a function of mass ratios and effect of crack.

Effects of Crack on Stability of Timoshenko Beams Subjected to Subtangential Follower Force

In this paper, the purpose is to investigate the stability of cracked Timoshenko cantilever beams subjected to subtangential follower force. In addition, an analysis of the instability(critical follower force of flutter and divergence) of a cracked beam as slenderness ratio and subtangential coefficient is investigated. The governing differential equations of a Timoshenko beam subjected to an end tangential follower force is derived via Hamilton`s principle. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The results of this study will contribute to the safety test and stability estimation of structures of a cracked beam subjected to subtangential follower force.