• Structural Engineering and Mechanics
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• v.72 no.5
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• pp.557-568
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• 2019

Accurate modeling of contact interface in bolted joints is crucial in predicting the dynamic behavior for bolted assemblies under external load. This paper presents a contact pressure distribution based non-uniform virtual material method to describe the joint interface of assembly structure, which is connected by sparsely distributed multi-bolts. Firstly, the contact pressure distribution of bolted joints is obtained by the nonlinear static analysis in the finite element software ANSYS. The contact surface around bolt hole is divided into several sub-layers, and contact pressure in each sub-layer is thought to be evenly. Then, considering multi-asperity contact at the micro perspective, the relationship between contact pressure and interfacial virtual material parameters for each sub-layer is established by using the fractal contact theory. Finally, an experimental platform for the dynamic characteristics testing of a beam lap structure with double-bolted joint is constructed to validate the efficiency of proposed method. It is found that the theoretical results are in good agreement with experimental results by impact response in both time- and frequency-domain, and the relative errors of the first four natural frequencies are less than 1%. Furthermore, the presented model is used to examine the effect of rough contact surface on dynamic characteristics of bolted joint.

• Tribology and Lubricants
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• v.39 no.4
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• pp.154-166
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• 2023

This study establishes a numerical analysis model of the finite element overhung rotor supported by a DTRB and describes the stiffness properties of the DTRB. The vibration characteristics and contact pressure of the RBR system are predicted according to the DTRB support characteristics such as the initial axial compression and roller profile. The stiffness of the DTRB significantly varies depending on the initial axial compression and external load owing to the occurrence of rollers under the no-load condition and increase in the Hertz contact force. The increase in the initial axial compression increases the rigidity of the DTRB, thereby reducing the displacement of the RBR system and simultaneously increasing the natural frequency. However, above a certain initial axial compression, the effect becomes insignificant, and an excessive increase in the initial axial compression increases the contact pressure. The roller crowning radius, which gives a curvature in the longitudinal direction of the roller, decreases the displacement of the RBR system and increases the natural frequency as the value increases. However, an increase in the crowning radius increases the edge stress, causing a negative effect in terms of the contact pressure. These results show that the DTRB support characteristics required for reducing the vibration and contact pressure of the RBR system supported by the DTRB can be designed.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.957-965
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• 2011

Recently, railway industry has been developed not only functional parts such as acceleration and high performance of the railway but also emotional parts such as improved ride comfort and blocking noise. However, some important components of railway such as wheel and rail always had exposed too much operation time, cyclic load and rolling contact directly. The variations of load, vibration and chemical compositions were caused of wheel and rail having a lot of different types of contact fatigue damages. Therefore, It is necessary to improve inspection and maintenance technology in order to ensure safety and reliability of railway. Many researchers have already been reported the technology. Magnetic camera, one of the non-destructive testing technique can be used to inspect and evaluate the changes of magnetic field in ferromagnetic and paramagnetic materials with cracks. When an electromagnetic is applied to a specimen, a magnetic field will be distorted around a crack on the specimen. In present paper, the distribution of magnetic property in wheel with cracks using magnetic camera had investigated. The crack can be detected and evaluated by distribution analysis of magnetic field. The magnetic camera technique can be detected and evaluated the crack by rolling contact fatigue.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.11 s.188
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• pp.42-49
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• 2006

In this paper error-compensating techniques in three-point weighing method to precisely measure unbalance properties such as center of gravity and unbalance moment. In the conventional static methods, 1) fixture-errors, 2) effects of the contact between the fixture and the load scales, and 3) side effect due to the lateral frictional forces acting on the contact points between the fixture and the load scales are the major factors that lead to measurement errors. The proposed error-compensating method perfectly eliminates both the fixture-error and the contact-error simultaneously by manipulating the three measured reaction forces at three different angular locations. Also the friction-error is calibrated by comparing the sum of three reactions with the actual mass of the specimen. A set of measurement is performed using the same measuring system as Lee's, and a comparison of the results from the convectional, Lee's, and the proposed method is provided. The results show that the proposed method effectively compensates the errors listed above.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.45-52
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• 2002

The tribological role of mass transfer layer was studied with silver coatings under various ranges of load and sliding speed. Silver coating was performed with a functionally gradient coating method. Tests were performed in dry sliding conditions, using a ball-on-disk contact configuration, at the load of 0.0196-17.64 N and the sliding speed of 20-1,000 mm/s in ambient air. Optical microscope and EPMA analyses showed that contact surfaces were covered with the mass transfer layers of agglomerated wear particles depending upon the contact conditions, and they greatly influenced the tribological characteristics of the surfaces. However, the formation of mass transfer layer was suppressed as the sliding speed increased, and above a critical sliding speed, no mass transfer layer was able to form. For building up a general framework of tribological behavior of the coated silver films, all test data were summarized on a map whose axes are contact pressure and sliding speed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.1
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• pp.99-106
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• 2011

In this study, the dynamic contact of a catenary system is analyzed by using the finite element method. We derive the equations of motion for the catenary system by taking into consideration tension on the catenaries. After establishing the weak form, they are spatially discretized with beam elements. Then, we analytically calculated the wave propagation speed for a string, bar, beam, and the catenaries subjected to tension. Further, finite element computer program for contact dynamic analyses is developed. Finally, we analyze the wave propagation response corresponding to the moving load to the contact line are calculated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.609-612
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• 2007

The HDD (hard disk drive) using Load/Unload (L/UL) technology includes the benefits which are increased areal density, reduced power consumption and improved shock resistance than those of contact-start-stop (CSS). Dynamic L/UL has been widely used in portable hard disk drive and will become the key technology for developing the small form factor hard disk drive. The main design objectives of the L/UL mechanisms are no slider-disk contact or no media damage even with contact during L/UL, and a smooth and short unloading process. In this paper, we focus on lift-off force, pitch static attitude (PSA), roll static attitude (RSA) and dimple point. The "lift-off" force, defined as the minimum air bearing force, is another very important indicator of unloading performance. A large amplitude of lift-off force increases the ramp force, the unloading time, the slider oscillation and contact-possibility. PSA and RSA are also very important parameters in L/UL system and stability of slider is mainly determined by PSA and RSA. Dimple point by PSA and RSA is also important indicator. Therefore we find the optimal dimple point of SFF HDD suspension for improving the unloading performance.

• Structural Engineering and Mechanics
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• v.30 no.1
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• pp.21-36
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• 2008

The static response of a finite beam resting on a tensionless Pasternak foundation and subjected to a concentrated vertical load is assessed in this study. The concentrated vertical load may be applied at the center of the beam, or it may be offset from the center. The tensionless character of the foundation results in the creation of lift-off regions between the beam and the foundation. An analytical/ numerical solution is obtained from the governing equations of the contact and lift-off regions to determine the extent of the contact region. Although there is no nonlinear term in the equations, the problem shows a nonlinear character since the contact region is not known in advance. Due to that nonlinearity, the essentials of the problem (the coordinates of the lift-off points) are calculated numerically using the Newton-Raphson technique. The numerical results are presented in figures to illustrate the behaviours of the free-free and pinned-pinned beams under symmetric or asymmetric loading. The figures illustrate the effects of the shear foundation parameter and the symmetric and asymmetric loading options on the variation of the contact lengths and the displacement of the beam.

• Transactions of Materials Processing
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• v.18 no.8
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• pp.607-616
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• 2009

There are three sub-processes associated with the assembly of the valve seat and cylinder head; heat fitting, cold fitting, and shrink fitting. In the heat fitting stage, the cylinder head is heated to a specified temperature and then squeezed toward the outer diameter of the valve seat. The cold fitting process cools the valve seat and safely squeezes it toward the inner diameter of cylinder head. However, these methods increased the installations & running cost and curtailed productivity. To address these problems, we analyzed the shrink fitting process using the contact pressure caused by fitting interference between the outer diameter of the valve seat and the inner diameter of the cylinder head. In this study, a closed form equation for predicting the contact pressure and fitting load is proposed. For quality control of the assembly line, principal factors of the shrink fitting process influenced in contact pressure were simulated by the FEM. Actual loads measured in the field showed good agreement with the results obtained by theoretical and finite element analysis.

• Journal of the Ergonomics Society of Korea
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• v.23 no.1
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• pp.39-48
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• 2004

In terms of women engaged in clerical job. working time of the workers who mainly keep standing with their high-heeled shoes on has been increasing. According]y. they are exposed to many kinds of foot deformation caused by loads of lower back and lower extremities due to high-heeled shoes. The type of heels they usually wear are diverse though the hight is same. In this study. we investigated most women's favorite styles of shoes concerned with heights. types and contact areas of the heels. Hence. we designed three kinds of shoes for an experiment: their contact areas with ground are 1 cm2. 2-4 cm2 and over 9 cm2 according to the heel heights. respectively. To investigate the biomechanical effects. analysis of motion and EMG were applied to the experiments. In addition. foot pressure distribution was measured for more detailed analysis. Six healthy young women were participated in this experiments. The result showed the heel becoming higher and narrower increased not only fluctuation of CBM(Center of Body Mass). but also the load of low back muscle and lower extremities. Accordingly. there was significant difference among types of the heel in terms of the role supporting load of the body. though the height is same. Especially. the difference among the pressures on a foot was most significant. In conclusion. we verified biomechanical effects are related with the contact area of a heel with ground as well as the hight.