• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.132-138
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• 2010

Vibro-contact of cantilever tip is studied with respect to contact mechanics and an elastic characteristic of nanoscale surface is imaged. The contact resonance frequency is calculated theoretically using the spring-mass and Herzian models, and the variation of resonance frequency of cantilever was analyzed when the cantilever was free and contact. The elasticity imaging was also achieved successfully using phase and amplitude signals obtained from the spheroidized steel specimens by prototype ultrasonic AFM.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.2
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• pp.174-180
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• 2011

Nondestructive surface imaging of elastic characteristic and mechanical property has been studied on nanoscale surface with ultrasonic AFM. Resonance frequency variation of cantilever is theoretically analyzed with respect to contact mechanics as well as experimentally measured. The contact resonance frequency is calculated theoretically using the spring-mass and Herzian model in accordance with the resonance frequency of UAFM cantilever measured experimentally. Consequently, the topography and amplitude images could be obtained successfully and the elastic characteristic at the nanoscale surface was evaluated qualitatively by amplitude signals.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.78-85
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• 2020

The scaffolding system, which is a construction workbench of the cargo containment for a membrane LNG carrier, is a large truss structure composed of various members. To shorten the installation period and process of the scaffolding system, it is effective to enlarge the mounting unit from the existing two stages to eight stages. Owing to the increase in lifting load according to the large size of the module, the stresses around the pin and hole will be increased significantly. In this study, a tensile strength test and contact stress analysis were performed to confirm the structural safety. The relatively large hole deformation was observed visually near the average load generated in the vertical pipe at the top through tensile strength tests. A contact stress calculation confirmed the stress distribution around the hole. The contact problem was dealt with in terms of the Herzian contact stress. The possibility of 8-stage loading was examined by comparing the yield strength and contact stresses of failure critical locations. As a result, the 8-stage loading method of the existing scaffolding material was inadequate, and a new loading method with proper safety is proposed.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.92-97
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• 2000

Low-velocity impact damage of a thick pressure vessel by composite materials was studied using the modified Herzian contact radius theory. Impactors of various masses and various tup shapes were dropped freely in the range of 20m to 200mm height. With acceleration gage and strain gage installed on the impactor, impact force and acceleration and Contact radius were measured. After a test, the samples were radiographed to scan the state of damage. Compared with hemispherical tup of 12.7mm diameter, the contact radius of hemispherical tup of 25.4mm diameter was bigger. And the experimental data and the theoretical data was different due to the mechanical properties difference. The acceleration value was changed linearly according to the height.

• Tribology and Lubricants
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• v.16 no.1
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• pp.9-14
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• 2000

It has been cleared in previous author's paper that the fatigue life before the pitting on the rolling contact surface with lubricant are influenced by the wear amount. In this study, the wear type has been clarified when wear amount is extremely large such as the case without lubricant. The test of rolling contact fatigue has been conducted under two different of herzian pressures and three different of slide ratios without lubricant. In addition, residual stress and half-value breadth using X-ray diffraction on worn surface have been measured as well as the wear amount. The results show that the pitting type wear by rolling contact fatigue has not been occurred when the wear amount is considerably large. Thus this type of wear has been deduced by the fatigue wear depending on delamination theory.

• Korean Journal of Materials Research
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• v.7 no.3
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• pp.224-228
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• 1997

Rolling contact fatigue tests were performed for two types silicon nitrides using disk- type specimens. Materials showed a fatigue behaviour similar to that typically found in metallic materials From the fractographic and metallographic observations, it has been found that the crack initation in the silicon nitrides subjected to rolling contact fatigue is to be induced by cyclic subsurface shear stress, as is known in steel bearing. On the mid-sections of the specimens, many subsurface cracks which lay parallel to the contact surface can be found at a depth where fluctuation of the Herzian shear stress was the maximum.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.8
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• pp.863-869
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• 2006

A new CVT, the inner spherical traction CVT (ISCVT) is introduced. Transmission of the most scooters is the self-controlled variable pulley-belt type of CVT having some disadvantages in the fuel consumption and the limitation of the transmittable power due to the slippage between the belt and pulley. Unlike this, ISCVT controlled directly by driver is more efficient and the contact mechanism having the same line of contact normal of the spherical rotors of different radii on common center causes that the power density and torque capacity are remarkably improved. The prototype with the specifications of 50cc scooter is designed and tested.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1343-1350
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• 1998

A study is made of mechanical properties of unglazed matrix as a funtion of sintering temperature and crack patterns in layer structur pottery consisting of glaze and substrate and in matrix which is sintered at 120$0^{\circ}C$ and 130$0^{\circ}C$ respectively. The mechanical properties of matrix are increased due to density and vitrification to 130$0^{\circ}C$ The interface of glazed bilayer reveals the reactive intermediate layer. Herzian indentation testing is used to investigate the evolution of damage modes as a function of load. In the materials sintered at 120$0^{\circ}C$ quasi-plastic deformation is developed at the matrix and the cone-like cracks initiate at the glazing top surface and additionally upward-extending transverse cracks initiate at the internal in-just initiate at the glazing top surface which pass through the interface with increasing of indentation load. Finally the dominant damage mode shifts from substrate quasi-plasticity to coating fracture with increasing sintering temperature.

• Journal of the Korean Ceramic Society
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• v.56 no.3
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• pp.211-232
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• 2019

Porous ceramics are promising materials for a number of functional and structural applications that include thermal insulation, filters, bio-scaffolds for tissue engineering, and preforms for composite fabrication. These applications take advantage of the special characteristics of porous ceramics, such as low thermal mass, low thermal conductivity, high surface area, controlled permeability, and low density. In this review, we emphasize the direct foaming method, a simple and versatile approach that allows the fabrication of porous ceramics with tailored microstructure, along with distinctive properties. The wet foam stability is achieved under the controlled addition of amphiphiles to the colloidal suspension, which induce in situ hydrophobization, allowing the wet foam to resist coarsening and Ostwald ripening upon drying and sintering. Different components, like contact angle, adsorption free energy, air content, bubble size, and Laplace pressure, play vital roles in the stabilization of the particle stabilized wet foam to the porous ceramics. The mechanical behavior of the load-displacements curves of sintered samples was investigated using Herzian indentations testes. From the collected results, we found that microporous structures with pore sizes from 30 ㎛ to 570 ㎛ and the porosity within the range from 70% to 85%.

• Journal of Korean Society of Steel Construction
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• v.19 no.4
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• pp.345-355
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• 2007

During winter, the CWR (continuous welded rail) may be broken when a temperature drop below the neutral level changes the axial force, causing tensile fracture and creating a rail gap. The passage of a train on a rail with an open gap may lead to very costly derailments. In this paper, the use of a track-and-train-coupled model whose rail has an open gap is proposed for dynamic interaction analysis. Linear track and train systems were coupled in this study by a nonlinear Herzian contact spring, and the complete system matrices of the total track-train system were constructed. Moreover, the interaction phenomenon considering the presence of an open gap in the rail was toughly defined by assigning the irregularity functions between the two sides of the gap. Time history analysis, which has an iteration scheme such as the Newmark-$\beta$ method (based on the Modified Newton-Raphson methods), was conducted to solve the nonlinear equation. .Finally, numerical studies were conducted to assess the effect of the various parameters of the system when applied to various speeds, open-gap sizes, and support stiffnesses of the rail.