• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.197-204
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• 2006

The purpose of this study is to evaluate the AE characteristics for the basemetal, PWHT (post-weld heat treatment) and weldment specimens of SA-516 steel during fracture testing. Four-point bending and AE tests were conducted simultaneously. AE signals were emitted in the process of plastic deformation. AE signal strength and amplitude of the weldment was the strongest, followed by PWHT specimen and basemetal. More AE signals were emitted from the weldment samples because of the oxides, and discontinuous mechanical properties. AE signal strength and amplitude for the basemetal or PWHT specimen decreased remarkably compared to the weldment because of lower strength. Pre-cracked specimens emitted even lower event counts than the corresponding blunt notched specimens. Dimple fracture from void coalescence mechanism is associated with low-level AE signal strength for the basemetal or PWHT. Tearing mode and dimple formation were shown on the fracture surfaces of the weldment, but only a small fraction produced detectable AE.

• 동력기계공학회지
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• 제13권4호
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• pp.43-48
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• 2009

The purpose of this study is to show how to eliminate the noises and to obtain the data related with the relationship between AE signal characteristics and mechanical behaviors for the pressure vessel steel. Various kinds of noises are introduced into the AE data in the course of experiments. Accordingly, real AE data have to be obtained after tests. AE test was carried out under four point bending load. Among AE signals, counts and signal strength are used to find out the differences of AE characteristics between the basemetal and weldment. After tests, this paper shows the procedures of filtering the noises against basemetal of the pressure vessel steel to obtain the real data around crack tip. Relationships between plastic zone size and cumulative AE counts are shown also. AE signals were absent within an elastic region, regardless of the specimens. Most of AE signals are produced in the process of plastic deformation. The deformation and fracture modes of basemetal and weldment are quiet different.

• 자원환경지질
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• 제25권4호
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• pp.379-395
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• 1992

The gold ore deposits of Nakcheon, Gongyeong and Dongmyeong mine in the Imgye district are E-W trending fissure filling veins emplaced in Precambrian Jungbongsan granite and sedimentary rocks of Cambrian Yangdeog group. The K-Ar age for vein alteration sericite and vein laced muscovite are 73 and 93 Ma, respectively. Vein structure and mineralogy indicate the three distinct depositional stages: I) basemetal sulfides and tin minerals, II) gold-basemeatl sulfides, III) gold-silver-basemetal sulfides. Major gold and silver ore minerals are electrum, native silver, pyrargyrite and argentite. Fluid inclusion data indicate that filling temperatures were from $350^{\circ}C$ to $190^{\circ}C$ through stage I, II and III. Salinities were in the range of 0.0~9.5 NaCl eq.wt.% and do not reveal any systematic trend. Intermittent boiling of ore fluid during stage I is indicated by fluid inclusions in quartz. Fluid pressure during stage I which is estimated from fluid inclusions showing boiling evidence range from 50 to 100 bars. Gold ore deposits of the Imgye district were formed under higher temperatures and lower sulfur fugacities compared with the Eunchi silver ore deposits about 8 Km apart from the Imgye district.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.282-285
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• 2009

Selective laser sintering (SLS) is a fast growing process of rapid production fur metallic based parts. To restore damaged mold surface using SLS, single layer experiments of $20{\mu}m$ Fe-Cr powder was performed under various heat input. Process window of $20{\mu}m$ Fe-Cr powder provided feasible process parameters for the smooth regular surface. To estimate coherence between melted powder and basematal, tendency of hardness distribution has been observed. Hardness of melted zone and remelted zone was diversified from 5GPa to 6.5GPa. It is over 2 times compared of hardness of basemetal. Average surface roughness of each direction on surface of melted powder was measured. Experimental results show that the mold restoring process using SLS can be successfully applied in the mold repair industry.

• Journal of Welding and Joining
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• 제30권6호
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• pp.56-61
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• 2012

Magnesium alloy sheet which is commercially available in the market presently is AZ31B, a Mg-Al-Zn three elements alloy. AZ31B is used by being classified into AZ31B-H24 and AZ31B-O depending on temper designation. In this study, AZ31B-H24 and AZ31B-O alloy sheets with 1.25mm thickness were butt-welded using CW Nd:YAG laser. And the effect of materials on mechanical properties was investigated by tensile and hardness tests. As a result of this study, regardless of materials, the butt-welded joint did not show a significant difference in tensile strength and hardness values. However, compared with the basemetal, the AZ31B-O showed more outstanding mechanical properties than AZ31B-H24, and that is because H24 material lost the effect of work hardening during welding.

• 대한기계학회논문집A
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• 제33권7호
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• pp.681-686
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• 2009

Direct laser metal forming technology was applied to restore the damaged mold surface. In order to estimate melting characteristics of the $20{\mu}m$ Fe-Cr-Ni powder, single layer experiments were performed at various levels of heat input. The process window of the $20{\mu}m$ Fe-Cr-Ni powder provided feasible process parameters for the smooth regular surface. The cross hatching scanning strategy on the multiple layer experiment was performed to reduce the thickness non-uniformity of edge portions compared with the one direction scanning. To estimate the coherence between the melted powder and the basematal, the tendency of hardness distribution has been observed. The hardness of the melted and the remelted zone was distributed from 400HV to 600HV. It is over 2 times compared of the hardness of the basemetal. Experimental results show that the mold restoring process using direct laser metal forming can be successfully applied in the mold repair industry.