• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.3
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• pp.292-301
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• 2008

A linearized model for hysteretic acoustic nonlinearity of imperfectly joined interface is proposed and analyzed by using Coulomb damping to investigate the characteristics of the reflection and transmission coefficients for harmonic waves at the contact interface. Closed crack is modeled as non welded interface that has nonlinear discontinuity condition in displacement across its boundary. Based on the hysteretic contact stiffness of the contact interface, the reflected and transmitted waves are determined by deriving the tractions on both sides of the interface in terms of the discontinuous displacements across the interface. It is found that the amplitudes of the reflected and transmitted waves are dependent on the frequency and the hysteretic stiffness. As the frequency of the incident wave increases, the higher reflection and lower transmission are obtained. It also shows that the hysteresis of the interface increases the reflection coefficient, but reduces the transmission coefficient. A fatigue crack is also made in aluminum specimen to demonstrate these characteristics of the reflection and transmission of contact interfaces.

• Structural Engineering and Mechanics
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• v.12 no.1
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• pp.17-34
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• 2001

The frictionless contact problem for a layered composite which consists of two elastic layers having different elastic constants and heights resting on two simple supports is considered. The external load is applied to the layered composite through a rigid stamp. For values of the resultant compressive force P acting on the stamp vertically which are less than a critical value $P_{cr}$ and for small flexibility of the layered composite, the continuous contact along the layer - the layer and the stamp - the layered composite is maintained. However, if the flexibility of the layered composite increases and if tensile tractions are not allowed on the interface, for P > $P_{cr}$, a separation may be occurred between the stamp and the layered composite or two elastic layers interface along a certain finite region. The problem is formulated and solved for both cases by using Theory of Elasticity and Integral Transform Technique. Numerical results for $P_{cr}$, separation initiation distance, contact stresses, distances determining the separation area, and the vertical displacement in the separation zone between two elastic layers are given.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.1
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• pp.45-53
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• 2014

For the time integration solution of the impulsive dynamic contact problem of high-speed rotating disks formulated by the finite element technique, the velocity and acceleration contact constraints as well as the displacement contact constraint are imposed for the numerical stability without spurious oscillations. The solution of the present technique is checked by the numerical simulation using the concentric high-speed rotating disks with the clearance and impulsive loading. It is shown that the almost steady state solution agrees with the corresponding analytical solution of the elasticity and that the differentiated constraints are crucial for the numerical stability of such high-speed contact problems of the disks under impulsive loading.

• Composites Research
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• v.23 no.2
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• pp.24-30
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• 2010

Interfacial evaluation and hydrophobicity of Ni-nanopowder/epoxy composites were investigated for self-sensing and actuation. Contact resistance and resistivity were measured using gradient micro-specimens. The actuation of the composites in the electromagnetic field was studied with three wave functions, i.e., sine, triangle and square functions. Due tothe presence of hydrophobic domains on the heterogeneous surface, the static contact angle of Ni-nanopowder/epoxy nanocomposite wasabout $100^{\circ}$, which was rather lower than that for super-hydrophobicity. The dynamic contact angle showed the similar trend of static contact angle. Ni-nanopowder/epoxy composite was responded wellfor both self-sensing and actuation in electromagnetic field due to the intrinsic metal property of Ni-nanopowder. Displacement of the actuator of Ni-nanopowder/epoxy composite was evaluated to obtain the maximum and the optimum performance using laser displacement sensor as functions of the wave type, frequency, and voltage. Actuation of Ni-nanopowder/epoxy composites also increased as functions of applied frequency and voltage. Actuated strain increased more rapidly at sine wave with increasing voltage compared to those of triangle or rectangular waves.

• Steel and Composite Structures
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• v.26 no.6
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• pp.771-791
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• 2018

This paper deals with the low velocity impact response and dynamic stresses of composite sandwich truncated conical shells (STCS) with compressible or incompressible core. Impacts are assumed to occur normally over the top face-sheet and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The displacement fields of core and face sheets are considered by higher order and first order shear deformation theory (FSDT), respectively. Considering continuity boundary conditions between the layers, the motion equations are derived based on Hamilton's principal incorporating the curvature, in-plane stress of the core and the structural damping effects based on Kelvin-Voigt model. In order to obtain the contact force, the displacement histories and the dynamic stresses, the differential quadrature method (DQM) is used. The effects of different parameters such as number of the layers of the face sheets, boundary conditions, semi vertex angle of the cone, impact velocity of impactor, trapezoidal shape and in-plane stresses of the core are examined on the low velocity impact response of STCS. Comparison of the present results with those reported by other researchers, confirms the accuracy of the present method. Numerical results show that increasing the impact velocity of the impactor yields to increases in the maximum contact force and deflection, while the contact duration is decreased. In addition, the normal stresses induced in top layer are higher than bottom layer since the top layer is subjected to impact load. Furthermore, with considering structural damping, the contact force and dynamic deflection decrees.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.10
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• pp.1517-1522
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• 2015

Since electric railroad vehicle pass through repeatedly on the railroad bridge, the dynamic load that causes the change of tension of contact wire affect it constantly. In this paper, we measured the dynamic displacement of the railroad bridges to analyze the effect of tension in the catenary. A result of dynamic measurement of the longitudinal displacement, it's maximum value was 39.9mm which was lower than the primary management criteria 378mm. Also on the based of a maximum temperature, it shows a feature that the longitudinal displacement value increased as temperature rise from April to October. In terms of behavior characteristics of a tensioning device, it was confirmed to be the value of 50mm stroke movement when the temperature changes ±5℃.

• Smart Structures and Systems
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• v.12 no.3_4
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• pp.363-379
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• 2013

Dynamic displacement of structures is an important index for in-service structural condition and behavior assessment, but accurate measurement of structural displacement for large-scale civil structures such as long-span bridges still remains as a challenging task. In this paper, a vision-based dynamic displacement measurement system with the use of digital image processing technology is developed, which is featured by its distinctive characteristics in non-contact, long-distance, and high-precision structural displacement measurement. The hardware of this system is mainly composed of a high-resolution industrial CCD (charge-coupled-device) digital camera and an extended-range zoom lens. Through continuously tracing and identifying a target on the structure, the structural displacement is derived through cross-correlation analysis between the predefined pattern and the captured digital images with the aid of a pattern matching algorithm. To validate the developed system, MTS tests of sinusoidal motions under different vibration frequencies and amplitudes and shaking table tests with different excitations (the El-Centro earthquake wave and a sinusoidal motion) are carried out. Additionally, in-situ verification experiments are performed to measure the mid-span vertical displacement of the suspension Tsing Ma Bridge in the operational condition and the cable-stayed Stonecutters Bridge during loading tests. The obtained results show that the developed system exhibits an excellent capability in real-time measurement of structural displacement and can serve as a good complement to the traditional sensors.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2062-2072
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• 1994

This paper presents the development of a fuzzy controller for driving camera pan/tilt device so that the camera's viewing direction can automatically track a moving object. To achieve computational efficiency a non-contact type displacement follower is used as a feedback sensor instead of a vision camera. The displacement follower, however, is extremely sensitive to object's lighting condition and results in unstable response at high speed. To this end, a fuzzy controller is developed in such a way to provide stable tracking performance at high speed where the sensory signal is subjected to intermittant disturbances of large magnitude. The test result shows stable tracking response even for high speed and non-uniform lighting condition. The resulting camera autotracking system can be adopted as an effective tool for visual transfer in the context of teleoperation and autonomous robotics.

• Tribology and Lubricants
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• v.23 no.3
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• pp.89-94
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• 2007

The stress and displacement behavior analysis of an aluminum tube for an organic photo conductor drum has been presented using a finite element analysis technique by non-linear FEM program. The maximum displacement in the radial direction of OPC drum may directly affect to the quality of printed matter. Thus, the deformed profile of the aluminum tubes should be limited depending on the toner powder size and the contact rolling forces between an OPC drum and a paper. This paper recommends the critical loading of 400 Pa for the provided toner size, $8{\mu}m$ for excellent printed matters and long life of the toner cartridge.

• Tribology and Lubricants
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• v.24 no.1
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• pp.34-43
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• 2008

In this paper, an actively controlled aerostatic bearing is studied to overcome the defects of air bearing such as low stiffness and damping coefficients. The actively controlled aerostatic bearing is composed of aerostatic bearings, non-contact type of displacement sensors, piezoelectric actuators and controllers. The cylindrical capacitance sensor (CCS) is used as the displacement sensor. The reason for using CCS instead of the commercial gap sensor is that it can give us the pure error motion of the spindle because it removes the roundness error or the geometric errors in the spindle. The controller is designed by the state space equation and quadratic optimal control theory. The characteristic data of the actively controlled aerostatic bearing system in the frequency domain are presented and the stiffness and damping coefficients of the bearing are mentioned. This paper shows the possibility to reduce the motion error up to 6000 rpm.