• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.11
• /
• pp.171-179
• /
• 1997

This paper describes a nesting system of a computer-aided design of blanking and piercing for irregularly shaped sheet metal products. An approach to the system is based on knowledge-based rules. A nesting system is designed by considering several factors, such as utilization ratio which minimises the scrab for single or pairwise operation, bridge width, grain orientation and design requirements which maximise the strength of the part when subsequent bending is involve. Therefore this system which was implemented blank layout and strip layout module can carry out a nesting with a best utilization and a process planning for irregular shaped sheet metal products in single or pairwise operation and generate the blank layout and strip layout in graphic forms. Knowledges for a nesting and a process planning are extracted from plasticity theories, relevant references and empirical know-hows of experts in blanking industries. This provides its efficiency and effectiveness for nesting irregularly shaped sheet metal products.

• Korean Journal of Materials Research
• /
• v.33 no.6
• /
• pp.251-256
• /
• 2023

This study aims to examine the correlation between microstructures and the mechanical properties of two high-strength API X70 linepipe steels with different specimen directions and Moaddition. The microstructure of the Mo-added steel has an irregularly shaped AF, GB matrix with pearlite because of the relatively large deformation in the non-recrystallization temperature region, while that of the Mo-free steel shows a PF matrix with bainitic microstructure. In the Mo-added steel, the M/A (martensite-austenite) in granular bainite (GB) and pearlite act as crack initiation sites with decreased upper shelf energy and an increased ductile to brittle transition temperature (DBTT). Regardless of Mo addition, all of the steels demonstrate higher strength and lower elongation in the T direction than in the L direction because of the short dislocation glide path and ease of pile-up at grain boundaries. In addition, the impact test specimens with T-L direction had a lower impact absorbed energy and higher DBTT than those with the L-T direction because the former exhibit shorter unit crack path compared to the latter.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.4 no.3
• /
• pp.238-244
• /
• 1994

We investigated solution growth of silicon on borosilicate and quartz glass substrates in the temperature range of $800^{\circ}C~520^{\circ}C$. A thin Al-Si layer evaporated onto the substrate serves to improve the wetting between the substrate and the Al/Ga solvent. Nucleation takes place by a reaction of Al with $SiO_2$ from the substrate. We obtained silicon deposits with a grain size up to a few 100 $\mu\textrm{m}$. There was a perferential (111) orientation for the case of quartz glass substrates while there is a strong contribution of other orientations for the deposition of Si on borosilicate glass substrates.

• Archives of Metallurgy and Materials
• /
• v.64 no.2
• /
• pp.623-626
• /
• 2019

Rare earth Nd-Fe-B, a widely used magnet composition, was synthesized in a shape of powders using gas atomization, a rapid solidification based process. The microstructure and properties were investigated in accordance with solidification rate and densification. Detailed microstructural characterization was performed by using scanning electron microscope (SEM) and the structural properties were measured by using X-ray diffraction. Iron in the form of α-Fe phase was observed in powder of about 30 ㎛. It was expected that fraction of Nd₂Fe₁₄B phase increased rapidly with decrease in powder size, on the other hand that of α-Fe phase was decreased. Nd-rich phase diffused from grain boundary to particle boundary after hot deformation due to capillary action. The coercivity of the alloy decreased with increase in powder size. After hot deformation, Nd₂Fe₁₄B phase tend to align to c-axis.

• The Journal of Engineering Geology
• /
• v.7 no.2
• /
• pp.151-159
• /
• 1997

Since healed microcracks in quartz grain of grantic rocks within the same mass have identical preferred orientations, the oreintations of granitic cores may be determined if the distinctive feature of healed microcracks can be used.In this study, the possibility of determining orientations of granitic cores using healed microcrack orientations were examined using samples from the borehole drilled to 200 m in depth at the Hongcheon. Eight sections whose core recoveries are 100% were selected. Two to six samples were collected in each section and orientations of healed microcracks in each sample were measured. Healed microcracks in samples from each section show almost identical orientations. The error range for sections with only one preferred orientations is within $\pm$5$^{\circ}$, indicating that correct orientations of core can be determined. However, orientations of cores in sections which have 2 or more healed microcrack orientations should be determined using orientations as well as distribution of peaks of orientations. The error range for this case is lager than former one and is within $\pm$15$^{\circ}$. The orientations of joint which is very impontant factor for designing tunnel and slope stability can be determined using healed microcrack orientation in cores.

• Nuclear Engineering and Technology
• /
• v.24 no.1
• /
• pp.75-85
• /
• 1992

The texture changes and their effect on the 0.2% yield strength of Zircaloy-4 sheet were examined after quenched from the ($\alpha$+$\beta$) phase temperature. When the prior ($\alpha$+$\beta$) gram size was slightly larger than that of the $\alpha$-annealed, the observed texture was similar to the $\alpha$-annealed texture having an ideal orientation of the (0001) basal pole at 30$^{\circ}$away from the normal direction toward the transverse direction. When the prior ($\alpha$+$\beta$) grain size was twice as large as that of the $\alpha$-annealed, the location of maximum basal pole intensity was distributed between the transverse and the rolling direction making an angle 15$^{\circ}$from the normal direction, and the observed texture became isotropic. It was found that the Kearns texture parameter, fr, in the rolling direction increased steadily, and fr in the transverse direction increased slightly, while fr in the the normal direction decreased with increasing heat treatment time. With a small increase in fr, the 0.2% yield strength increased drastically. The influence of texture was analyzed by deriving the Schmid orientation factors and the resolved shear stresses for the deformation systems. It was found that the large increase in the 0.2% yield strength was attributed mainly to the microstructural changes and partly to the texture changes by the ($\alpha$+$\beta$) heat treatment.

• Journal of the Korean Magnetics Society
• /
• v.14 no.5
• /
• pp.196-200
• /
• 2004

In order to improve dendritic formation of Nd$_2$Fe$\_$14/B phase in the strip-cast Nd-Fe-B alloys that are frequently used for production of high energy sintered magnets, effect of small substitutional additives such as Cu (0.3～1.0 at. %) and Co (0.5～1.5 at.%) on the phase formation and microstructures of the strip-cast alloys based on Nd$\_$14/Fe$\_$80/B$\_$6/ were investigated. As the amount of Cu addition increased, formation of Nd$_2$Fe$\_$14/B dendrites along the direction normal to the strip surface was suppressed with the reduction of the strip thickness mainly due to the increase of fluidity of the melt. However, both the dendrites and their <001> preferred orientation along the direction normal to the strip surface were improved with the increase of the strip thickness as the amount of Co addition increased. The dendrites became finer after small amount of Cu or Co was added. While small copper additions tended to stabilize the formation of primary Fe, small cobalt additions suppressed it. When small amount of Zr was added, however, the dendrite structures were totally collapsed with excessive grain growth of Nd$_2$Fe$\_$14/B.

• Journal of the Korean Ceramic Society
• /
• v.36 no.1
• /
• pp.43-49
• /
• 1999

Gas pressure sintered silicon nitride based composites with 0~5wt% $\beta$-Si3N4 whiskers were prepared. The whiskers were unidirectionally oriented by a modified tape casting technqiue and green bodies with various microstructure were formed by changing stacking sequences of sheets cut from the tape. Orientations of the large elongated grains of the sample after gas pressure sintering were the same as the those of the whiskers of green body, and the sintering shrinkage and mechanical properties of sintered sample were consistent with the microstructural characteristics. In case of unidirectional samples, the sintering shrinkage normal to whisker alignment direction was larger than that parallel to the direction. The shrinkage difference inceaed as the whiskercontent increaed. As whisker content increaed, the crack length normal to and parallel to tape casting direction became shorter and larger, respectively. Although the grain size increased by th whisker addition, the flexural strength of unidirectional samples was not lower than that of smaple without the whisker. In case of crossplied and 45$^{\circ}$rotated samples, the anisotropy of mechanical preoperties disappeared.

• Journal of the Korean Ceramic Society
• /
• v.39 no.9
• /
• pp.829-834
• /
• 2002

Ferroelectric properties of $ErMnO_3$ thin films deposited on Si(100) substrate using Sol-gel process with metal salts were investigated. $ErMnO_3$ thin films with a (001) preferred orientation were crystallized at 800$^{\circ}C$. The $ErMnO_3$ thin film post-annealed at 800$^{\circ}C$ for 1 h showed the dielectric constant(k) of 26 and the dielectric loss(tan ${\delta}$) of 0.032 at the frequency range from 1 to 100 KHz. The grain size of $ErMnO_3$ thin film post-annealed at 800 for 1 h was 10∼30 nm. The remanent polarization($P_r$) of the $ErMnO_3$ thin films increased with increasing (001) preferred orientation. The $ErMnO_3$ thin films post-annealed at 800$^{\circ}C$ for 1 h showed the remanent polarization($P_r$) of 400 nC/$cm^2$, with the increase of post-annealing time at 800$^{\circ}C$, the coercive field($E_c$) of thin films was lowered because the dense and homogeneous thin films were obtained.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.16 no.2
• /
• pp.59-65
• /
• 2006

Al-doped and F-doped ZnO (ZnO : Al & ZnO : F) thin films were coated onto glass substrate by sol-gel method. These films showed c-axis orientation in common, but different I(002)/[I(002) + I(101)] and FWHM (full width at half-maximum). In particular, the grain size of the ZnO : Al films decreased with the increase in the Al-doping concentration, while for the ZnO : F films the grain siae increased up to F 3 at% and then decreased. For the electrical properties, Hall effect measurement was used. The resistivity of the ZnO : Al films and the ZnO : F films were, respectively, $2.9{\times}10^{-2}{\Omega}cm$ at Al 1 at% and $3.3{\times}10^{-1}{\Omega}cm$ at F 3 at%. Moreover compared with ZnO:Al films, ZnO:F films have lower carrier concentration (ZnO : Al $4.8{\times}10^{18}cm^{-3}$, ZnO : F $3.9{\times}10^{16}cm^{-3}$) and higher mobility (ZnO : Al $45cm^2/Vs$, ZnO : F $495cm^2/Vs$). For average optical transmittances, ZnO : Al thin films have $86{\sim}90%$ and ZnO : F films have $77{\sim}85%$ comparatively low.