• Transactions of Materials Processing
• /
• v.26 no.6
• /
• pp.348-355
• /
• 2017

In recent years, dissimilar materials such as aluminum, magnesium, titanium, and advanced high strength steel are widely used in automotive body due to environment concerns and fuel consumption. Therefore, joining technology is important for assembling components made of dissimilar materials. In this study, friction stir hole clinching (FSHC) was proposed as a new mechanical joining method to join dissimilar materials. This process stirs and heats the upper sheet, forming mechanical interlocking with the lower sheet. The feasibility of this FSHC process was verified by comparing cross-section of joint in FSHC and hole clinching process under the same processing condition. Taguchi method was also applied to the FSHC process to estimate the effect of process parameters on joint strength and obtain optimal combination of process parameters. Joint strength of FSHC with optimal process condition was compared to that of FSHC with initial process condition as well as that of hole clinching with optimal process condition. Results showed that the FSHC process was useful for joining dissimilar materials, even if the formability of materials was low.

• Tribology and Lubricants
• /
• v.37 no.5
• /
• pp.195-202
• /
• 2021

This paper presents a numerical analysis of the lubrication characteristics of condensed water molecules on a solid surface by conducting molecular dynamics simulations. We examine two models consisting of a simple hexahedral substrate with and without water molecules to reveal the lubrication mechanism of mono-layered water molecules. We perform a sliding simulation by contacting and translating a single asperity on the substrate under various normal loads. During the simulation, we measure the friction coefficient and atomic stress. When water molecules were interleaved between solid surfaces, atomic stress exerted on individual atom and friction coefficient were smaller than those of model without water molecule. Particularly, at a low load, the efficacy of water molecules in the reduction of atomic stress and friction is remarkable. Conversely, at high loads, water molecules rarely lubricate solid surfaces and fail to effectively distribute the contact stress. We found a critical condition in which the lubrication regime changes and beyond the condition, significant plastic deformation was created. Consequently, we deduce that water molecules can distribute and reduce contact stress within a certain condition. The reduced contact stress prevents plastic deformation of the substrate and thus diminishes the mechanical interlocking between the asperity and the substrate.

• The Korean Journal of Ceramics
• /
• v.3 no.2
• /
• pp.129-133
• /
• 1997

Fine powder of $\alpha$-tricalcium phosphate, tetracalcium phosphate and dicalcium phosphate were mixed together to prepare self-setting cements which form hydroxyapatite, one of the well-known biocompatible materials, as the end of products of hydration. Hardening behaviour of the cements was examined at the temperature range of 37~$70^{\circ}C$ and 150~$250^{\circ}C$ under the normal and hydrothermal condition respectively. The conversion of cements into hydroxyapatite was significantly improved ast elevated temperature and the paste was strengtheed by interlocking of hydroxyapatite crystals, indicating that the strength is determined by microtexture rather the amount of conversion of cements into hydroxyapatite.

• Journal of the Korea Concrete Institute
• /
• v.12 no.2
• /
• pp.3-11
• /
• 2000

There is a possibility of poor-state concrete filling condition due to segregation and interlocking of aggregate and paste when a high performance concrete is used at reinforced concrete structure without compaction. This study was conducted to evaluate the flexural behavior of high performance concrete beams with design parameters such as c, t and different concrete filling conditions. Different concrete filling conditions were intentionally made such that the first type specimen was soundly cast to obtain the perfect concrete filling condition. Second type was cast in such a way that up to the longitudinal tensile reinforcement from the top, good concrete was filled while poor concrete was poured for the bottom part to simulate the poor strength, workability and unsatisfactory compaction. Third type was cast in such a was that up to the neutral axis of the beam section from the top, good concrete was filled while so did for the bottom part as the second type. The test results were analyzed in terms of load-displacement response, failure pattern, crack width and crack spacing. The test results indicate that have no effect of concrete filling conditions on the yielding strength of structures. But, have a grate influence on the stiffness and ductility of structures.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.11 no.6
• /
• pp.26-37
• /
• 2008

The purpose of the study was to evaluate the effect of pervious pavements on reducing the surface runoff caused by rainfall. The surface runoff from twelve steel experimental beds with different pavement had been recorded every minute from May to September 2008, by the measuring system of tipping buckets(0.1mm/count) and data aquisition systems(National Instrument's Labview and DAQ boards & Autonics PR12-4). The dimension of the experimental bed was $1.5m(W){\times}2.0m(L){\times}0.6m(D)$ and eleven different kinds of vegetational(grass, grass+cubic stone, grass+hole brick), modular(brick, cubic stone, small cubic stone, wood block, interlocking block, clay brick, granular clay brick) and granular(naked soil, gravel) paving materials and concrete were applied for the comparison. Six rain events with depth over 30mm were selected and compared. The maximum depth of the rainfall selected was 137.5mm for 28 hours, and the minimum 30mm for 5 hours. The maximum rainfall per hour was 23mm/hr and the minimum 11.4mm/hr. The major findings were as follows; 1. All pervious pavement applied reduced over 75% of the surface runoff compared with concrete pavement. The grassy and porous pavements were relatively efficient in reducing surface runoff. 2. The grass was the more efficient as intercepting average 69.5mm of initial surface runoff, and maximum 77.8mm at the condition of 13.5mm/hr rainfall. The next was gravel intercepting maximum 65.5mm at the condition of 13.5mm/hr and the 40.9mm at 19.1mm/hr, average 55.7mm. 3. The modular pavements common in urban area were not good in intercepting the runoff except the 'clay granular brick' compared with others. The 'clay granular brick' showed relatively efficient intercepting average 14.1mm, which was the bigger amount than the 'grass+hole brick'. 4. The 'naked soil' were more effective than the 'concrete', 'brick', and 'interlocking block' in reducing the surface runoff, but less efficient than other materials. The capacity of the 'naked soil' to intercept the initial rainfall was similar to the 'brick'. As summary, the more grassy and porous pavement shows more effective in reducing surface runoffs.

• Journal of the Korean Geosynthetics Society
• /
• v.19 no.3
• /
• pp.9-21
• /
• 2020

In this study, the design method of the combined sheet pile was considered in the coastal landfill where sandy and clayey soils are mixed, and the behavior in excavation was analyzed. It was confirmed from the elasto-plastic analysis that the predicted behavior of the temporary facilities of earth retaining differs according to the type of the combined sheet pile method (Built up, Interlocking, Welding) and the analysis method (soldier pile method, continuous wall method). In the case of sheet pile member force, the results of the continuous wall analysis method predicted the most conservative results. When the stress ratio (calculation/allowance) of each member was analyzed based on the maximum member force of the combined sheet pile method, the maximum value was obtained for bending moment in the side pile and combined stress in the case of the strut. As a result of finite element analysis, the member force of the side pile was the largest in the short-term effective stress analysis condition, while the compressive force of the strut was large in the consolidation analysis. When comparing the results of the elasto-plastic analysis and the finite element analysis, the shear force of the side pile and the axial force of the strut were greatly evaluated in the elasto-plastic analysis, and the bending moment of the side pile was the largest in the short-term effective stress condition of the finite element analysis. In addition, the displacement of the side pile was predicted to be greater in the finite element analysis than in the elasto-plastic analysis.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.8
• /
• pp.27-36
• /
• 2018

The collapse behavior of ground subsidence caused by continuous loss of particles depends on the saturated condition and density of the ground. In this study, types of ground subsidence were classified based on the saturated condition and each type was performed on the different relative density to analyze the influence factors on the collapse behavior by distinct element method. According to analysis results, the relatively small amount of settlement occurred on the dense ground and a cavity was created under dense-unsaturated ground. In contrast, loose ground showed the large amount of settlement and collapsed immediately without cavity formation even if the unsaturated ground was simulated. The results demonstrated that because the relative density has influence on the mechanical interlocking and saturated condition has influence on the inter-particle force, these are important factors to change the collapse behavior.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.26 no.3
• /
• pp.339-347
• /
• 2010

Enhancement of bond strength between new and old composite usually requires increasing the surface roughness to promote mechanical interlocking. This study evaluated the effect of different surface treatments on repair bond strength of resin composite after aging condition. Air abrasion with Al2O3, chairside silicacoating, and silanization provided higher resin-resin bond strength values compared to control group and HF group. Air abrasion is necessary to repair a resin restoration and additional application of silane seems to have good effects on bond strength.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.03a
• /
• pp.368-375
• /
• 2009

This paper describes field installation and load test results performed for three types of micropiles in the process of developing a new micropiling method. Field tests were performed for two conventional types(i.e., micropile reinforced with steel bar and gravity grouting, micropile reinforced with steel bar and steel casing and gravity grouting) and a proposed type(i.e., micropile reinforced with hollow steel pipe wrapped with geotextile-pack and pressurized grouting). The load test results subjected to axial compression and tension and lateral loading conditions are described in this paper. The micropiles were exposed in the air in order to verify the installation quality and curing condition of grouting material via ground excavation. Axial compression and tension test results indicate that the new micropile type provide at least 40% higher bearing capacity than that of conventional types. Based on the examination of exposed piles, it is induced that the proposed method, packed micropile, provides better interlocking between grouts and surrounding soils and increases higher frictional resistance comparing to conventional types.

• Korean Journal of Materials Research
• /
• v.17 no.4
• /
• pp.215-221
• /
• 2007

The effect of $CF_4$ plasma treatment condition on the interfacial adhesion energy of inkjet printed Ag/polyimide system is evaluated from $180^{\circ}$ peel test by calculating the plastic deformation energy of peeled metal films. Interfacial fracture energy between Ag and as-received polyimide was 5.5 g/mm. $CF_4$ plasma treatment on the polyimide surface enhanced the interfacial fracture energy up to 17.6 g/mm. This is caused by the increase in the surface roughness as well as the change in functional group of the polyimide film due to $CF_4$ plasma treatment on the polyimide surface. Therefore, both the mechanical interlocking effect and the chemical bonding effect are responsible for interfacial adhesion improvement in ink jet printed Ag/polyimide systems.