• Journal of the Korean Ceramic Society
• /
• v.32 no.4
• /
• pp.436-440
• /
• 1995

Effects of microstructure of two Mg-ferrite specimens with the same starting composition and relative density but with different grain size on B-H hysteresis loop, natural resonance frequency, and ferromagnetic resonance line width are reported. Such properties as B-H hysteresis loop, saturation magnetization, natural resonance frequency, and ferromagnetic resonance line width were influenced by the microstructure development during sintering. Large grain size specimen showed high saturation magnetization, low coercive force, low natural resonance frequency, and low ferromagnetic resonance line width compared with the specimen of small grain size. The main reason for the changes in properties can be explained by the variation in anisotropic characteristics due to Fe+2 content generated during sintering process.

• Journal of the Korean Ceramic Society
• /
• v.21 no.3
• /
• pp.209-216
• /
• 1984

The influence of the particle size of quartz and the change of cooling rate to the strength of conventional triaxial porcelain was studied, . The results indicate that 1. The residual quartz content was increased by particle size increasing. And the strength was increased by increas-ing residual quartz content which increased the total stress in the specimen. But the influence of residual quartz was lessened by the extent of crack between quartz particle and glass matrix 2. In order to increase the strength of the body fast cooling is suitable to small quartz particle and slow cooling is suitable to large quartz particle.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.6
• /
• pp.867-876
• /
• 1987

Corrosion fatigue fracture with change in the grain size of M.E.F. dual phase steel is investigated in 3.5% NaCI aqueous solution at pH 2, 4, 6, 9, and 11. Generally speaking, decrease in corrosion fatigue life is strongly dependent on decrease in pH and slightly on the grain size. For the B material with the big grain size, the fatigue life is small due to its large reduction ratio of corrosion fatigue life. The influence of grain size on the reduction ratio of corrosion fatigue life is large at pH 11-6. Whi9le at pH 4-2 the reduction ratio of corrosion fatigue life only depends on the corrosion effect. The larger grain size and the lass pH result in the greater influence on corrosion fatigue crack propagation rate. As pH decreases, the plateau portion in the crack propagation rate curves of the B material are distinct. Crack propagation rate curves become slow down at high .DELTA.K range because crack closure effect by minute corrosion products inside crack causes the oxidation corrosion action less effective for a certain period of time. In A material with small grain size, fatigue life is increased in proportion with increase of martensite intergranular which brings forth restraining the crack propagation decreases crack propagation rate. Corrosion pit which is created in the surface of specimen is found at pH 6,4 and 2 which is noticeable and the unevenness of the surface of the specimen becomes severe as pH decreases. The unevenness of corrosion fatigue fracture surface is severe as the effect of pH increases i.e. as pH decreases. In proportion with increase in the grain size and decrease in pH, the aspect of brittle fracture becomes evident.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.2
• /
• pp.451-462
• /
• 1995

Single overload tests performed to examine the crack retardation behavior for the specimen thickness and overload ratios. Delayed crack length was tend to increase in small thickness and big overload ratio but was difference between delayed crack length and plastic zone size that expected in specimen thickness. So retardation behavior that estimated in plastic zone size, was not sufficient. Crack tip branching and striation distribution, secondary mechanisms that effected in retardation behavior, was examined by experiment and finite element analysis. Crack tip branching was affected by micro structure, and appeared the more complicatedly according to increasing damage by overload and decreasing crack driving force in base line stress level. And crack tip branching the branching angle decreased crack driving force in the crack tip. And a characteristic of the fractography on retardation zone was that striation distribution did not appear due to decreased crack driving force.

• Journal of the Korean Geotechnical Society
• /
• v.29 no.7
• /
• pp.37-46
• /
• 2013

Various sizes of gravels are included in the most field soils that are utilized for civil constructions. Especially, the small amounts of gravel are often included in selected soils for backfill materials, earth dams, and subbase ground. In such cases, the small amounts of mixed gravel and its shape may influence the determination of dry density of soils, which results in an inaccurate degree of compaction for soils in the field. In this study, a dry density of sand with various gravel contents (0, 10, 17, 23, 29 and 33%) and three different sizes (2.0-2.36, 3.35-4.75, 5.6-10.0 mm) was experimentally investigated for compacted or loosely packed conditions. The loosely packed sand with gravels was simulated by pouring sand into compaction mould and its density was determined. When a 33% of gravel content was mixed with sand, its dry density increased up to 15-20% for compacted specimen and 20-23% for loosely packed specimen. When a gravel content and size were the same, a dry density of compacted specimen was $0.1-0.16g/cm^3$ higher than that of loosely packed specimen. Even though the same gravel content was used, a dry density of sand with big gravels was $0.04-0.08g/cm^3$ higher than that of sand with small gravels for compacted specimen and $0.03-0.05g/cm^3$ for loosely packed specimen.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.07a
• /
• pp.881-884
• /
• 2000

Recently mobile communication fields need piezoelectric ceramic resonators and filters as possible as small. The length-extensional vibration mode of a rectangular piezoelectric cesamic plate has the advantage of the small size, but the mode has not been studied sufficiently because it was not used extensively until now. In this paper, PZT + x[wt%l $Cr_20_3$ ceramics with rhombohedra1 phase were fabricated. And temperature stability for the mode of the ceramic specimen was investigated. Contrary to our expectations, addition of the stabilizer, $Cr_20_3$ did not promote the temperature stability for the mode in the PZT ceramic specimen with rhombohedra1 phase.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.11a
• /
• pp.232-233
• /
• 2005

Stainless steel has been stably used closed by passivity oxidation films($Cr_2O_3$) is made by neutral atmospheric environment. However, passivity oxidation films of the surface of stainless steel occasionally comes to be destroyed in seawater which is influenced by an environment having halogen ion like $Cl^-$, then, localization corrosion comes to occur. Stainless steel 304 for shaft system material of the small-size FRP fishing boat on seawater environments made an experiment on simulation of sacrifical anode(Al, Zn). Through these experiment and study, following results have been obtained ; According to the field inspection and corrosion simulation, the corrosion on the 2nd class stainless steel shaft(STS 304) in FRP fishing boat has been verified to occur by crevice corrosion and galvanic corrosion etc.. According to the comparison and analysis of Stainless steel 304 shaft materials after simulation leaving unprotected and applying cathodic protection, unprotected shaft specimen of stainless steel 304 was severely corroded, but, protected shaft specimen was not totally corroded. This result is assumed to be made by the facts that anodic reaction, $Fe{\rightarrow}Fe^{2+}$ + $2e^-$, has been restricted by the cathodic protection current of sacrificial anode material.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2014.10a
• /
• pp.1-1
• /
• 2014

Side scuttle in the shipboard windows is used in a smaller size in order to prevent damage to the glass. This shipboard windows should have high sound insulation performance (More than $R_w$ 53 dB) according to norsok standards. However, side scuttle having a small size and high sound insulation material is difficult to measure exact result without a suitable filler wall. In this study, the test was conducted according to the number of changes in the small window. As a result, before starting the test should be conducted to the selection of the suitable filler wall or secure a specimen area.

• Journal of the Korean Society of Mechanical Technology
• /
• v.13 no.2
• /
• pp.115-121
• /
• 2011

The size of hydrogen molecule is not so small as to invade into the lattice of material, and therefore, hydrogen invades into the material as atom. Hydrogen movement is done by diffusion or dislocation movement in the near crack tip or plastic deformation. Hydrogen appeared to have many effects on the mechanical properties of the Cr-Mo steel alloys. The materials for this study are 1.25Cr-0.5Mo and 2.25Cr-1Mo steels used at high temperature and pressure. The hydrogen amount obtained by theoretical calculation was almost same with the result solved by finite element analysis. The distribution of hydrogen concentration and average concentration was calculated for a flat specimen. Also, finite element analysis was employed to simulate the redistribution of hydrogen due to stress gradient. The calculation of hydrogen concentration diffused into the material by finite element method will provide the basis for the prediction of delayed fracture of notched specimen. The distribution of hydrogen concentration invaded into the smooth and notched specimen was obtained by finite element analysis. The hydrogen amount is much in smooth specimen and tends to concentrate in the vicinity of surface. Hydrogen embrittlement susceptibility of notched specimen after hydrogen charging is more remarkable than that of smooth specimen.

• International Journal of Concrete Structures and Materials
• /
• v.5 no.1
• /
• pp.49-55
• /
• 2011

The main objective of this investigation is to study size effect on compressive strength of CFRP confined concrete cylinders subjected to axial compressive loading. In total 24 concrete cylinders with different sizes were tested, small specimens with a diameter of 100 mm and a height of 200 mm, medium specimens with a diameter of 200 mm and a height of 400 mm, and big specimens with a diameter of 300 mm and a height of 600 mm. The lateral confining pressure of each specimen is the same and from that hypothesis the small specimens were confined with one layer of CFRP, medium and big specimens were performed by two and three layers of CFRP respectively. Test results indicate a significant enhancement in compressive strength for all confined specimens, and moreover, the compressive strengths of small and medium specimens are almost the same while a bit lower for big specimens. These results permit to conclude that there is no size effect on compressive strength of confined specimens regardless of cylinder dimension.