This study analyzes the mechanical properties, including the attrition rate, of 50 μm size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grainboundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of 50 μm YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than BaTiO3 powder (Hv ~315).

PURPOSES: In this study, the effects of adding a superabsorbent polymer (SAP) to the concrete mixture on the strength of the concrete and abrasion resistance were analyzed, and whether the property of concrete can be improved by the internal curing effect of SAP was evaluated. METHODS: In this study, a total of eight different mixes were tested. The amounts of SAP added were 0%, 0.6%, 1.2% while that of silica fume were 0% and 6% based on the weight of the binder. The compressive test, rapid chloride penetration resistance test, and abrasion test were performed to verify the internal curing effects of SAP. RESULTS : The compressive test showed that SAP concrete had greater compressive strength than ordinary concrete. Comparison of the compressive strengths of dry and wet cured specimens of each mixture showed that SAP concrete had a smaller difference compared with ordinary concrete. The rapid chloride resistance test showed that SAP did not increase chloride penetration resistance. However, since this experiment only considered wet curing, further investigation of dry curing is necessary. The abrasion resistance test showed that for the case of concrete cured under dry conditions without spraying the curing compound, the abrasion resistance of the SAP concrete improved by approximately 49% at 14 days and 27% at 28 days of curing compared with ordinary concrete. CONCLUSIONS : The effect of SAP on the strength and abrasion resistance of concrete was analyzed. The results showed that the internal curing effect of SAP improved concrete strength and abrasion resistance. The internal curing effect maintains the overall internal humidity in concrete by supplying water held by the SAP to the dried cement paste.

PURPOSES : The purpose of this study is to analyze not only the strength but also the durability and abrasion resistance of concrete pavements as increasing the cases of domestic concrete pavement damage which do not meet the service years. METHODS: The bottom layer of a two-lift concrete pavement was paved with original Portland cement (OPC) with 20~23 cm thickness. On the other hand, the top-layer, which is directly exposed to the environment and vehicles, was paved with high-performance concrete (HPC) with 7~10 cm thickness. For the optimal mixed design of the top-layer material of a two-lift concrete pavement, silica fume and polymer powder were mixed. Furthermore, it analyzes abrasion resistance of concrete as follow‘ ASTM C 779’which is dressing wheel abrasion test method. RESULTS : As a result, abrasion resistance is improved with increasing the silica fume ratio. When the polymer powder is mixed, abrasion resistance of concrete is much improved. However, the effect of mixing ratio is not significant. It is very effective that adding both silica fume and polymer powder occur 20~40% of abrasion comparing with OPC variables. CONCLUSIONS : The concrete strength and durability increased with silica fume and polymer powder. In particular, it is significant increasing strength of polymer powder under the flexural strength. In the abrasion resistance side, it is also significant when the silica fume and polymer powder used together.

This study investigates the microstructure and wear properties of cermet (ceramic + metal) coating materials manufactured using high velocity oxygen fuel (HVOF) process. Three types of HVOF coating layers are formed by depositing WC-12Co, WC-20Cr-7Ni, and Cr3C2-20NiCr (wt.%) powders on S45C steel substrate. The porosities of the coating layers are 1 ± 0.5% for all three specimens. Microstructural analysis confirms the formation of second carbide phases of W2C, Co6W6C, and Cr7C3 owing to decarburizing of WC phases on WC-based coating layers. In the case of WC-12Co coating, which has a high ratio of W2C phase with high brittleness, the interface property between the carbide and the metal binder slightly decreases. In the Cr3C2-20CrNi coating layer, decarburizing almost does not occur, but fine cavities exist between the splats. The wear loss occurs in the descending order of Cr3C2-20NiCr, WC-12Co, and WC-20Cr-7Ni, where WC-20Cr-7Ni achieves the highest wear resistance property. It can be inferred that the ratio of the carbide and the binding properties between carbide–binder and binder–binder in a cermet coating material manufactured with HVOF as the primary factors determine the wear properties of the cermet coating material.

In this study, the amount of abrasive wear was predicted effectively by FE simulation and experiment regarding the material and shape of the abrasive. In order to calculate numerically the amount of wear using the Archard wear equation, the normal load between the abrasive and the polyurethane was calculated by FE simulation. The sliding distance can be calculated according to the working conditions, and the hardness of the polyurethane is a known value. The wear coefficient K was calculated inversely by experimental measurement of the wear amount according to the working conditions of the abrasive. In order to verify the proposed calculation method, the wear amount was calculated by using the Archard wear equation by applying the calculated wear coefficient K with regard to arbitrary working conditions. The deviation between the proposed calculation results and the experimental results was within 10%. When the wear coefficient K is calculated by using the proposed method, the wear amount can be estimated. In addition, it was found that the change of the vertical load value concerning penetration depth was the main factor for determining wear amount.

As product diversity increases and product life cycle gets shorter, lead time reduction and manufacturing cost saving of die & mold are getting important in machinery, automotive, and electronics industries. To develop a novel free-machining die & mold steel, we try to modify the chemical compositions of AISI P20 mold steel by adding boron, nitride, and sulfur. After making three types of mold steels which are base metal of AISI P20 mod., boron and nitrogen added, and boron, nitrogen, and sulfur added to the base metal. Milling tests are carried out using TiN, TiCN, and TiAlN coated WC end-mills under various cutting conditions. Boron and nitrogen added steel machined by TiN coated tool shows the most excellent tool wear and surface roughness characteristics. The results might come from BN inclusions in base metal acting as a stress concentration source and lowering strain resistance during cutting process. The relationship between tool wear and surface roughness are also discussed including feed rate effects.

Particle size reduction is an important step in many technological operations. The process itself is defined as the mechanical breakdown of solids into smaller particles to increase the surface area and induce defects in solids, which are needed for subsequent operations such as chemical reactions. To fabricate nano-sized particles, several tens to hundreds of micron size ceramic beads, formed through high energy milling process, are required. To minimize the contamination effects during highenergy milling, the mechanical properties of zirconia beads are very important. Generally, the mechanical properties of Y2O3 stabilized tetragonal zirconia beads are closely related to the mechanism of phase change from tetragonal to monoclinic phase via external mechanical forces. Therefore, Y2O3 distribution in the sintered zirconia beads must also be closely related with the mechanical properties of the beads. In this work, commercially available 100μm-size beads are analyzed from the point of view of microstructure, composition homogeneity (especially for Y2O3), mechanical properties, and attrition rate.

In order to expand the application of oxide dispersion-strengthened (ODS) steel, a composite material is manufactured by adding mechanically alloyed ODS steel powder to conventional steel and investigated in terms of microstructure and wear properties. For comparison, a commercial automobile part material is also tested. Initial microstructural observations confirm that the composite material with added ODS steel contains i) a pearlitic Fe matrix area and ii) an area with Cr-based carbides and ODS steel particles in the form of a Fe-Fe3C structure. In the commercial material, various hard Co-, Fe-Mo-, and Cr-based particles are present in a pearlitic Fe matrix. Wear testing using the VSR engine simulation wear test confirms that the seatface widths of the composite material with added ODS steel and the commercial material are increased by 24% and 47%, respectively, with wear depths of 0.05 mm and 0.1 mm, respectively. The ODS steel-added composite material shows better wear resistance. Post-wear-testing surface and cross-sectional observations show that particles in the commercial material easily fall off, while the ODS steel-added material has an even, smooth wear surface.

The friction characteristics of Al-Fe alloy powders are investigated in order to develop an eco-friendly friction material to replace Cu fiber, a constituent of brake-pad friction materials. Irregularly shaped Al-Fe alloy powders, prepared by gas atomization, are more uniformly dispersed than conventional Cu fiber on the brake pad matrix. The wear rate of the friction material using Al-8Fe alloy powder is lower than that of the Cu fiber material. The change in friction coefficient according to the friction lap times is 7.2% for the Cu fiber, but within 3.8% for the Al- Fe alloy material, which also shows excellent judder characteristics. The Al-Fe alloy powders are uniformly distributed in the brake pad matrix and oxide films of Al and Fe are homogeneously formed at the friction interface between the disc and pad, thus exhibiting excellent friction and lubrication characteristics. The brake pad containing Al-Fe powders avoids contamination by Cu dust, which is generated during braking, by replacing the Cu fiber while maintaining the friction and lubrication performance.

현재 국내 콘크리트 포장은 고속도로에서 약 40%, 일반 도로에서는 2% 정도를 차지하고 있다. 콘크리트 포장은 중차량에 대한 뛰어난 적용성과 20년 이상의 장기 공용연수를 가진다는 장점을 가지고 있다. 최근 국내 고속도로의 콘크리트는 장기간 사용으로 인해 노후화 되어있으며, 개통한지 오래되지 않은 콘크리트포장에서도 줄눈부 파손 및 표면박리, 표면마모 등으로 인한 보수비가 증가하고 있는 추세이다. 특히 표면마모의 경우 주행 중 소음발생을 증가시키고, 미끄럼저항성을 감소시켜 운전자의 피로도를 증가시키고 사고를 유발할 수 있다. 따라서 본 연구에서는 ASTM C 779(3중 마모휠 방법)을 사용하여 실리카퓸과 폴리머 분말을 사용한 포장용 콘크리트의 마모저항성을 분석하고자 한다. 기배합된 콘크리트에 실리카퓸과 폴리머 분말을 후 첨가하였으며, 혼화재료의 혼입으로 부족한 단위수량은 혼화재료 혼입 시 추가하여 W/C를 42%로 보정해주었다. 표 1은 실험에 사용한 배합표이다. 굳기 전 콘크리트의 공기량은 모든 변수에서 3∼5%로 목표 공기량을 만족하였으며, 슬럼프 시험결과 모든 변수가 슬럼프 40mm 이하를 만족하였지만, 실리카퓸 7% 혼입 변수에서 다른 변수에비해 다소 낮은 슬럼프를 보였다. 압축강도 시험결과 재령 28일에 모든 변수에서 30MPa 이상을 발도를 발현하였고, 실리카퓸 사용량이 증가할수록 강도가 증진되었지만 폴리머에 따른 영향은 거의 없는 것으로 나타났다. 마모시험결과 실리카퓸이 증가할수록 마모저항성이 증가하였고, 폴리머를 사용한 변수에서 큰 폭의 마모저항성 증가를 보였으나 혼입량에 따른 차이는 크지 않았다.

In order to use PUR/CuO Composites as the sealing materials for ships equipment, this research has been performed. PUR/CuO composites are produced by using ultrasonic waves. The increase of CuO leads to increase in the tensile strength and shore hardness. The cumulative wear volume shows a tendency to increase in proportional to sliding distance. As the CuO particles of these composites indicated, the friction coefficient was slightly increased. The major failure mechanisms were lapping layers, deformation of matrix, plowing, debonding of particles and microcracking by scanning electric microscopy photograph of the wear tested surface.

Carbon fiber reinforced plastics are typical examples of carbon fiber, which retain high strength and high strength at high temperatures. Also, it is applied to various fields, such as the structure of the aircraft, automobile, and the core industries. CFRP machining methods include machining tools such as cutting machining and laser machining. In this thesis, a tool dynamometer and tool microscope were used to measure the cutting characteristics of various cutting conditions and tool wear and tool wear. As a result, the cutting force of the new shape drill (lower shape drill) was measured higher than other tools, the amount of tool wear was the lowest, and it was found that a good machined surface was obtained.

WC-CrC-Ni coatings were prepared by nine processes of the Taguchi program with three levels for the four spray parameters: spray distance, flow rates of hydrogen and oxygen, and powder feed rate. The optimal coating process (OCP) was oxygen flow rate of 38 FMR, hydrogen flow rate of 53 FMR, powder feed rate of 25 g/min, and spray distance of 7 inches. Hardness of 1150 Hv and porosity of 1.2 %, were obtained by OCP; these are better results compared with the highest 1033 Hv and the lowest 1.5% porosity obtained by nine processes of the Taguchi program. Friction coefficient of the WC-CrC-Ni coating decreased from 0.36 ± 0.07 at 25 oC to 0.23 ± 0.07 at 450 oC. These values were smaller than those of the EHC (electrolytic hard chrome) plating at both temperatures due to lubrication from the oxide debris. The wear trace and wear depth of the coating are smaller than those of the EHC at both temperatures. Pitting was not found in the WC-CrC-Ni coating sample, while it did appear in the EHC sample.

In this study, SCM440 alloys are investigated to research the effect of wear resistance. For this purpose, three wear factors which are friction force, wear loss and coefficient of friction applied to test wear-resistance. For the wear test, ball-on-disk was used to assess the variation of wear characteristics. Lastly, the coefficient of wear was calculated by using the Archard's wear equation in SCM440 alloys. The applied normal load was fixed at 30N in all test. The test results showed that SCM440 alloy's Vickers hardness average value is near 671.4Hv, the friction force is 4.11N through the Ball-on-disk test, the coefficient of friction and the wear loss are 0.431 and 0.080 respectively. Finally, Archard’s wear value of SCM440 alloys could be shown approximately 0.1514.

Railroad ballast materials tend to degrade due to the increase of ballast abrasion and fracture that results in decreasing the capability of shock absorption, interlocking friction, and the resistance to track irregularity. Therefore, it is necessary to establish a methodology to improve or maintain the structural condition of ballast materials which is in the middle of fouling. This study aimed to investigate the effect of reinforcement on the fouled ballast using ballast stabilizer. Field experimental program was conducted to compare the lateral ballast resistance in case of before and after application of ballast stabilizer. A series of laboratory repetitive load triaxial compression test was then performed to compare the accumulated plastic strain in case of before and after application of ballast stabilizer to the ballast materials having a different level of Fouling Index(FI). In the event of application of ballast stabilizer, the accumulated plastic strain decreased by 41.8 and 28.8 percent, respectively, when the FI was 14 and 21, which appears to indicate the ballast stabilizer is effective for the moderate level fouled ballast materials.

Metal matrix composites(MMC) can obtain mechanical characteristics of application purposes that a single material is difficult to obtain. Al2 O3/AC8A composites were fabricated by low pressure infiltration process. The purpose is establishing the optimal casting conditions for composite preparation under low pressure. It is known the inorganic binder help infiltration. Therefore Al2O3 fiber preform's optimum sinter temperature is 1160℃, added inorganic binder is mixed binder(SiO2 sol:Al2O3 sol=5:2). And three fibers have been compared (Al2O3 80%/SiO2 20%, Al2O3 80%/SiO2 10% and Al2O3 97%/SiO2 3%). Al2O3/AC8A composites was made by each melting temperatures(650℃, 700℃, 750℃) and wear test was performed about effect of temperatures, kind of fiber, matrix and composites, aging time. Wear test is Ball on disk wear test. The resistance increased with the low melting temperature and Al2O3 80%/SiO2 20% fiber.