• Transactions of Materials Processing
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• v.33 no.4
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• pp.248-254
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• 2024

The triply periodic minimal surface (TPMS) structure is characterized by a high surface-to-volume (S/V) ratio and the separated internal structure for flow. Combining the different TPMS structures can provide unique flow and strength characteristics. This paper investigates the effects of dimension, density and arrangement of the unit cell of the TPMS on contact and flow areas of combined TPMS structures. Several representative TPMS structures, including primitive, gyroid and diamond structures, are adopted to design gradient and heterogeneous types TPMS structures. The estimation method of contact and flow areas using an image processing technique is proposed. Python software is used to predict contact and flow area. The influence of the combination method of TPMS on contact and flow areas in the contact surface of combined TPMS structures with different shapes is investigated. Based on the results of the investigation, an appropriate combination method of TPMS structures is discussed.

• Communications of the Korean Mathematical Society
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• v.33 no.1
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• pp.325-335
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• 2018

We prove every oriented compact cyclic 3-orbifold has a contact structure. There is another proof in the web by Daniel Herr in his uploaded thesis which depends on open book decompositions, ours is independent of that. We define overtwisted contact structures, tight contact structures and Lutz twist on oriented compact cyclic 3-orbifolds. We show that every contact structure in an oriented compact cyclic 3-orbifold contactified by our method is homotopic to an overtwisted structure with the overtwisted disc intersecting the singular locus of the orbifolds. In course of proving the above results we prove a classification result for compact oriented cyclic-3 orbifolds which has not been seen by us in literature before.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.2
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• pp.73-79
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• 1999

Most of mechanical structures are combined of substructures such as beams and/or plates. There are few systems with unibody structures but are many systems with united body structures. Generally the dynamic a nalysis of whole structures is performed under alternation load. In the structure design, the analysis of each bolted joint is more important than others for zero severity. This paper presents the analysis method of contact stress distribution factor in the bolted joint with variable fastening torque on joints in the structure. At first, a static vibration test was performed to find out a nominal stress of bolt jointed plates from the relationship between natural frequency and nominal stress. Then a contact stress was computed at contact point between bolt and plate in the structure. It is believed that the proposed method has promisiong implications for safer design with index of contact stress distribution factor and has merits for cost-down and saving time at the beginning of vehicle development.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.129-132
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• 2005

This study analyzes the behavior of adhesion and friction according to the pore size of nanohoneycomb structures in atomic force microscope (AFM). Anodic aluminum oxide (AAO) films are fabricated as nanohoneycomb structures. According to the pore diameters of the nanohoneycomb structures, the adhesive forces and the frictional coefficients arc obtained in AFM, and the behaviors are analyzed in the view of the contact area between the sphere particle and nanohoneycomb substrate. The effective Young's moduli of the nanohoneycomb structures are measured from the nanoindentation tests, and the contact areas at zero applied load are calculated by combining the porosity of the nanohoneycomb structures and the contact radius determined from JKR and DMT theory.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.3
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• pp.282-289
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• 2010

Most nondestructive testing techniques require good contact between the sensor and tested concrete surface to obtain reliable data. But the surface preparation is often very time and labor consuming due to the rough surface or limited access of concrete structures. One approach to speed up the data collection process is to eliminate the need for physical contact between the sensor and tested structure. Non-contact air-coupled sensing technique can be a good solution to this problem. An obvious advantage of the non-contact air-coupled sensing technique is which can greatly speed up the data collection in field and thus the damage detection process can be completed very rapidly. In this article, recent developments in non-contact air-coupled sensing technique for rapid detection of damages in concrete structures are summarized to evoke interest, discussion and further developments on this technique to a NDT research community in Korea. It is worth noting that the works in this article have been published in the types of thesis, proceedings, and journals. All published sources are cited in the text and listed in reference.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.5
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• pp.424-429
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• 2008

Surface wettability in terms of the size of the micro nano structures has been examined. To evaluate the influence of the nano structures on the contact angles, we fabricated two different kinds of structures: squarepillar-type microstructure with nano-protrusions and without nano-protrusions. Microstructure and nanostructure arrays were fabricated by deep reactive ion etching (DRIE) and reactive ion etching (RIE) processes, respectively. And plasma polymerized fluorocarbon (PPFC) was finally deposited onto the fabricated structures. Average value of the measured contact angles from microstructures with nanoprotrusions was $6.37^{\circ}$ higher than that from microstructures without nano-protrusions. This result indicates that the nano-protrusions give a crucial effect to increase the contact angle.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3185-3194
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• 1994

In this study, an impact model and impact response analysis method was suggested for the impacts between arbitrary shaped bodies. Unlike the impacts between geometrically simple structures, there is no rules to analyze the impacts between general elastic structures First of all, it has been attempted to explain the impoot between arbitrary elastic structures as the elastic deformation of a virtual contact spring in the vicinity of contact points. The contact stiffness and the exponent are determined from the Hertz's contact theory and F. E. analysis. In order to evaluate the validities and limitations of the proposed methods, an impact tester and the miniature of container, missile and isolators have been provided and tested experimentally. All the experiments were performed with various impact conditions. The results obtained by the proposed methods were directly compared with the measured values in terms of maximum contract force, contact duration, the shape of contact force and the structure responses. The computed contact force and responses, using this proposed methods, were very close to the measured results, unless any plastic deformations were presented.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.2989-2998
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• 2022

Line contact structures, such as the contact between graphite brick and graphite tenon, widely exist in high-temperature gas-cooled reactors. Due to the stress concentration effect, the line contact area is one of the dangerous positions prone to failure in the nuclear reactor core. In this paper, the failure mechanism of line contact structures composed of IG11 nuclear graphite column and brick were investigated by means of experiment and finite element simulation. It was found that the failure process mainly includes three stages: firstly, the damage accumulation in nuclear graphite material led to the characteristic yielding of the line contact structure, but no macroscopic failure can be observed at this stage; secondly, the stresses near the contact area met Mohr failure criterion, and a crack initiated and propagated laterally in the contact zone, that is, local macroscopic failure occurred at this stage; finally, a second crack initiated in the contact area and developed in to a Y-shape, resulting in the final failure of the structure. This study lays a foundation for the structural design and safety assessment of high-temperature gas-cooled reactors.

• Interaction and multiscale mechanics
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• v.1 no.4
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• pp.411-422
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• 2008

Atomistic simulation of nanoindentation with spherical indenters was carried out to study dislocation structures, mean contact pressure, and nanohardness of Au and Al thin films. Slip vectors and atomic stresses were used to characterize the dislocation processes. Two different characteristics were found in the induced dislocation structures: wide-spread slip activities in Al, and confined and intact structures in Au. For both samples, the mean contact pressure varied significantly during the early stages of indentation but reached a steady value soon after the first apparent load drop. This indicates that the nanohardness of Al and Au is not affected by the indentation depth for spherical indenters, even at the atomistic scale.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.383-388
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• 2008

A modeling method for the impact analysis of plate structures employing Hertzian contact theory is presented in this paper. Since local deformation as well as bending deflection of the plate occurs due to the collision, it has to be considered for the impact analysis. When the coefficient of restitution is employed for the impact analysis, the local deformation is not considered. For more accurate and reliable impact analysis, however, the local deformation should be considered. The effects of the location of collision and the collision mass on the impact duration time and the contact force magnitude are investigated through numerical studies employing Hertzian contact theory.