• Journal of Mechanical Science and Technology
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• 제14권7호
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• pp.722-729
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• 2000

The goal of this paper is to describe an advanced method of a crack detection: a new way to localize position and to estimate depth of a crack on rotating shaft. As a first step, the shaft is physically modelled with a finite element method and the dynamic mathematical model is derived using the Hamilton principle; thus, the system is represented by various subsystems. The equations of motion of the shaft with a crack are established by adapting the local stiffness change through breathing and gaping from the crack to an undamaged shaft. This is the reference system for the given system. Based on a model for transient behavior induced from vibration measured at the bearings, a nonlinear state observer is designed to detect cracks on the shaft. This is the elementary NL-observer (Beo). Using the observer, an Estimator (Observer Bank) is established and arranged at the certain position on the shaft. When a crack position is localized, the procedure for estimating of the depth is engaged.

• 제어로봇시스템학회논문지
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• 제11권4호
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• pp.290-296
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• 2005

This paper presents the implementation of a crack tracking mobile robot. The crack tracking robot is built for tracking cracks on the pavement. To track cracks, crack must be detected by laser and camera sensors. Laser sensor projects laser on the pavement to detect the discontinuity on the surface and the camera captures the image to find the crack position. Then the robot is commanded to follow the crack. To detect crack position correctly, neural network is used to minimize the positional errors of the captured crack position obtained by transformation from 2 dimensional images to 3 dimensional images.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.28-32
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• 1995

This effective way for repairing a fatigue crack is making indetations around fatigue crack tip. In this paper, we performed fatigue test to investigate the optimal position of the indentations, and observed crack opening behavior at the same time. The indentation positions of specimens were on the crack tip, front and back of the crack tip. The results of the experiment showed taht it was veryeffective way to increase fatigue life that making indentations on the crack tip, and it was the optimal position that making indentations on the crack tip.

• Journal of Welding and Joining
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• 제19권1호
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• pp.112-117
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• 2001

The factor affecting on the fatigue strength of spot welded specimen have been studied. To analyze and predict crack initiation position and propagation directions on the spot welded area are very important for strength design of the automobile body structure. In fact, there are a various of loads in running automobile but, it is impossible to replay like an actual conditions in the laboratory. So, in this study tensile-shear type and in-plane bending type specimens were used in fatigue test and includes an analysis of fatigue crack initiation position and propagation directions about earth specimens. The results obtained in the present study are summarized as follows: 1. In tensile-shear type fatigue test, the region of fatigue crack initiation position was affected by out-of-plane bending deformation due to bending angle. 2 In in-plane bending type fatigue test, the behavior of fatigue crack initiation position and propagation derections due to angle between upper plate and lower plate was dominated by magnitude of in-plane bending moment.

• Transactions on Control, Automation and Systems Engineering
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• 제2권1호
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• pp.24-30
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• 2000

The aim of this paper is to describe an advanced method of the fault diagnosis using Control Theory with reference to a crack detection, a new way to localize the crack position under influence of the plant disturbance and white measurement noise on a rotating shaft. As the first step, the shaft is physically modelled with a finite element method as usual and the dynamic mathematical model is derived from it using the Hamilton-principle and in this way the system is modelled by various subsystems. The equations of motions with a crack are established by the adaption of the local stiffness change through breathing and gaping[1] from the crack to the equation of motion with an undamaged shaft. This is supposed to be regarded as a reference system for the given system. Based on the fictitious model of the time behaviour induced from vibration phenomena measured at the bearings, a nonlinear state observer is designed in order to detect the crack on the shaft. This is the elementary NL-observer(EOB). Using the elementary observer, an Estimator(Observer Bank) is established and arranged at the certain position on the shaft. In case, a crack is found and its position is known, the procedure, fro the estimation of the depth is going to begin.

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1115-1120
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• 2003

In this paper, we investigated the position dependent stress distribution of indium-tin-oxide (ITO) film on Polycarbonate (PC) substrate by external bending force. It was found that there are the maximum crack density at the center position and decreasing crack density as goes to the edge, In accordance with crack distribution, it was observed that the change of electrical resistivity of ITO islands is maximum at the center and decrease as goes to the edge. From the result that crack density is increasing at same island position as face plate distance (L) decreases, it is evident that the more stress is imposed on same island position as L decreases.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.856-860
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• 2002

The main objective of this study is to consider the effect of fatigue crack behavior on the variable depth of micro hole defects in SM20C at the symmetric position. The fatigue crack propagation test is performed by rotary bending fatigue test machine. The relationship between crack length(2a), cycles(N) and crack growth rate(da/dN) are investigated in this study. The result from the rotary bending fatigue test under the applied stress at 250MPa turned out that the fatigue life illustrated almost constant when the depth of symmetric micro hole deflects is both part A and B at the hope depth(h) = 0.5mm.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.64-69
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• 2002

The purpose of this paper was to investigate the welding characteristics and the fatigue crack propagation behavior of titanium commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the characteristics according to the notch position and compare with other materials. We compared and reviewed the fatigue crack propagation behavior of nontch base metal and welded specimens having different notch position to evaluate the fatigue crack propagation behavior by welding condition.

• 한국정밀공학회지
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• 제22권1호
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• pp.143-151
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• 2005

This paper study the effect of open cracks on the dynamic behavior of simply supported Timoshenko beam with a moving mass. The influences of the depth and the position of the crack in the beam have been studied on the dynamic behavior of the simply supported beam system by numerical method. Using Lagrange's equation derives the equation of motion. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modeled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces on the crack section and is derived by the applying fundamental fracture mechanics theory. As the depth of the crack is increased the mid-span deflection of the Timoshenko beam with the moving mass is increased. And the effects of depth and position of crack on dynamic behavior of simply supported beam with moving mass are discussed.

• 한국자동차공학회논문집
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• 제13권6호
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• pp.63-69
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• 2005

For the case that center crack is surrounded by four small cracks which are symmetrically distributed around center crack, the same values of normalized stress intensity factor of center crack according to the position of the tip of small cracks are located on the smooth curve. And the stress intensity factor according to any position of small cracks can be sufficiently obtained from this curve. The plastic zones between distributed cracks are also investigated by changing the positions of nearly small cracks. The occurrence of plastic zone due to the interaction between center crack and small cracks are analyzed by finite element method. The mechanical behavior at the vicinity of crack tips is investigated by plastic areas. The changes of plastic zones according to positions of distributed cracks are drawn schematically. The safety of materials is also analyzed.