• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.321-322
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• 2006

Nano-structured ceramics, which consist of structural elements with nanometer-size crystallites, are expected to show various unusual properties. We developed the novel nano-structured ceramics which consists of $Si_3N_4$ and TiN and a self-lubricant material. The ceramics was fabricated by powder metallurgy process using mechano-chemical grinding process and short-time sintering process. Each grain size of matrix and the self-lubricant particle was under about 50 nm and a few namometer. It showed high wear resistance and low friction coefficient by controlling of microstructure.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.342-349
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• 2018

Polystyrene (PS) was coated on carbonyl iron (CI) particles via dispersion polymerization to produce core-shell structured CI/PS particles and adopted as magnetorheological (MR) material. Two MR fluids were prepared by dispersing CI/PS and CI particles in silicone oil. Their MR and tribological properties were investigated using a rheometer and a reciprocating friction and wear tester, respectively. Experimental data showed that tribological properties of MR fluid based on CI/PS particles are significantly enhanced compared to those of CI based MR fluid. Sedimentation problem of CI/PS MR fluid was also expected to be improved due to relatively lower density of CI/PS particles.

• Geomechanics and Engineering
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• v.28 no.1
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• pp.35-48
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• 2022

The effect of discrete polypropylene fibre reinforcement on shear strength parameters, tensile properties and isotropic index of stabilized compacted residual subgrade was investigated. Composites of compacted subgrade were developed from polypropylene fibre dosage of 0%, 1%, 2.5% and 4% and 3% cement binder. Saturated compacted soil benefited from incremental fibre dosage, the mobilized friction coefficient increased to a maximum at 2.5% fibre dosage from 0.41 to 0.58 and the contribution due to further increase in fibre dosage was marginal. Binder stabilization increased the degree of isotropy for unreinforced soil at lower fibre dosage of 1% and then decreased with higher fibre dosage. Saturation of 3% binder stabilized soil decreased the soil friction angle and the degree of isotropy for both unstabilized and binder stabilized soil increased with fibre dosage. The maximum tensile stress of 3% binder stabilized fibre reinforced residual soil was 3-fold that of 3% binder stabilized unreinforced soil. The difference in computed and measured maximum tensile and tangential stress decreased with increase in fibre dosage and degree of stabilization and polypropylene fibre reinforced soil met local and international criteria for road construction subgrade.

• Journal of Welding and Joining
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• v.30 no.6
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• pp.98-105
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• 2012

The focus of this investigation is to evaluate the effect of joining parameter on the microstructure and mechanical properties of welds produced by friction stir lap welding. The dissimilar Al alloys, KS5J32 and AA6K31, were joined by friction stir lap welding technique under several welding conditions, and KS5J32 alloy was placed on the top of AA6K31 alloy. The tool rotation speeds were 1000, 1250, and 1500rpm, and the welding speeds were 100, 300, 500, 700mm/min, respectively. The results showed that two shapes of nugget, such as onion ring and irregular vortex type, were observed with various revolutionary pitch. In all welding conditions, fracture occurred at the soften region of bottom sheet(AA6K31) and the strengths were 64~78% of those of base metal. Fractured positions were classified into three types : HAZ, triple point, void depending on the revolutionary pitch. The actual thickness of specimen at the fractured location was decreased with decreasing heat input. A linear relationship exists between the effective thickness of fractured position and peak load.

• Journal of Adhesion and Interface
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• v.16 no.3
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• pp.95-100
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• 2015

In this work, we observed the effect of silica, zinc oxide, zinc ion coated silica on carboxylic acid modified styrenic thermoplastic elastomer (m-TPS) film for friction-induced surface fracture. m-TPS film added general silica showed poor mechanical properties, anti-abrasion and friction-induced surface fracture, caused by strong filler-filler interaction of silica. In case of m-TPS films added zinc oxide or zinc ion coated silica, mechanical properties, anti-abrasion and friction-induced surface fracture were improved due to forming ionic cluster between carboxylic acid group of m-TPS and zinc ion. Ionic cluster were confirmed by FT-IR analysis that observed zinc carboxylated group stretch peak at $1550{\sim}1650cm^{-1}$.

• Geomechanics and Engineering
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• v.23 no.1
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• pp.39-50
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• 2020

In order to understand the shear mechanical properties of the interface between clay and structure and better serve the practical engineering projects, it is critical to conduct shear tests on the clay-structure interface. In this work, the direct shear test of clay-concrete slab with different joint roughness coefficient (JRC) of the interface and different normal stress is performed in the laboratory. Our experimental results show that (1) shear strength of the interface between clay and structure is greatly affected by the change of normal stress under the same condition of JRC and shear stress of the interface gradually increases with increasing normal stress; (2) there is a critical value JRC_cr in the roughness coefficient of the interface; (3) the relationship between shear strength and normal stress can be described by the Mohr Coulomb failure criterion, and the cohesion and friction angle of the interface under different roughness conditions can be calculated accordingly. We find that there also exists a critical value JRC_cr for cohesion and the cohesion of the interface increases first and then decreases as JRC increases. Moreover, the friction angle of the interface fluctuates with the change of JRC and it is always smaller than the internal friction angle of clay used in this experiment; (4) the failure type of the interface of the clay-concrete slab is type I sliding failure and does not change with varying JRC when the normal stress is small enough. When the normal stress increases to a certain extent, the failure type of the interface will gradually change from shear failure to type II sliding failure with the increment of JRC.

• Journal of the Korean GEO-environmental Society
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• v.11 no.3
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• pp.23-32
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• 2010

In this study, Generally sandbag was used to reinforce slope or restore levee by using the in-situ material. To increase shear strength of sandbag, the Velcro system was effective for geosynthetic interface and make up for the weakness of shear strength between sandbag to sandbag. In this study, shear properties of geosynthetic-geosynthetic and geosynthetic-soil were evaluated from large scale direct shear tests. The cohesion and the angle of internal friction of each interface was evaluated. And laboratory model tests were performed to compare strength of reinforcement with strength of none reinforcement. As a result of this study, the cohesion and the angle of internal friction of each interface was increased, especially the cohesion was increased more than the angle of internal friction. Also according to the result of model test, the bearing capacity was increased by 20%.

• Journal of Biosystems Engineering
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• v.32 no.4
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• pp.215-222
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• 2007

In the study, the cone index, the cohesion and the internal friction angle of soil were measured before and after tillage in order to suggest relative improvement in soil properties by comparing the two measured values before and after tillage. The tillage methods tested in the study were five combinations of plowing and rotovating; one plow tillage operation, one plow followed by one rotary, one plow followed by two rotary, one rotary without plow and two rotary without plow. The experiments were performed in a soil bin in Sunggyunkwan Univ. and in four selected test fields in Yeoju, Seodun-Dong, Suwon (especially, two different fields) and Chungju. In general, the internal friction angle and cohesion of soil increased with the increase of soil compaction. After applying the tillage operations, the internal friction angle reduced by 14 degree and the cohesion decreased up to about $2.2N/cm^2$ on the soil bin in comparison with those before tillage. The two values, however, reduced by 9 degree and up to about $1.0N/cm^2$ on the tested fields. The CIs for all the tillage operations on the soil bin and on 4 different test fields were decreased by 800 kPa in comparison with those before tillage. The best combination of tillage operations for decreasing the CIs of soil was one plow operation followed by one rotary. The CIs for one plow operation followed by two rotary were slightly higher than that for one plow operation followed by one rotary because one plow operation followed by two rotary crushed down the soil excessively, so that the porosity of soil decreased.

• Journal of the Korean institute of surface engineering
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• v.39 no.4
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• pp.160-165
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• 2006

Ni-SiC composite coating layers were prepared by electroplating method and their deposition rate, codeposition of SiC, morphology, surface roughness, hardness, wear and friction properties were investigated. It was found that the deposition rate and the codeposition of SiC in the composite coating layer increased with increasing concentration of SiC in the solution only at the early stage. Both of them reached certain maxima and then decreased with increasing concentration of SiC. Rough surface was obtained with increasing codeposition of SiC, which is probably due to the agglomeration of the SiC particle in the vicinity of surface. Vickers hardness increased with increasing codeposition of SiC and heat treatment at $300^{\circ}C$ in air for 1 hour. Wear volume decreased with increasing codeposition of SiC and friction coefficient increased with increasing codeposition of SiC at the early stage, and it became almost constant. Such wear and friction behaviors are desirable for the practical application.

• KSTLE International Journal
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• v.6 no.2
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• pp.33-38
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• 2005

Submicron-scale patterns made of polymethyl methacrylate (PMMA) were fabricated on silicon-wafer using a capillarity-directed soft lithographic technique. Polyurethane acrylate (PUA) stamps (Master molds) were used to fabricate the patterns. Patterns with three different aspect ratios were fabricated by varying the holding time. The patterns fabricated were the negative replica of the master mold. The patterns so obtained were investigated for their adhesion and friction properties at nano-scale using AFM. Friction tests were conducted in the range of 0-80 nN. Glass (Borosilicate) balls of diameter 1.25 mm mounted on cantilever (Contact Mode type NPS) were used as tips. Further, micro-friction tests were performed using a ball-on-flat type micro-tribe tester, under reciprocating motion, using a soda lime ball (1 mm diameter) under a normal load of 3,000 mN. All experiments were conducted at ambient temperature ($24{\pm}1^{\circ}C$) and relative humidity ($45{\pm}5\%$). Results showed that the patterned samples exhibited superior tribological properties when compared to the silicon wafer and non-patterned sample (PMMA thin film) both at the nano and micro-scales, owing to their increased hydrophobicity and reduced real area of contact. In the case of patterns it was observed that their morphology (shape factor and size factor) was decisive in defining the real area of contact.