• Journal of the KSME
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• v.51 no.12
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• pp.37-41
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• 2011

이 글에서는 원전배관의 안전설계 개념인 양단순간파단(DEGB: Double Ended Guillotine Break) 및 파단전누설(LBB: Leak Before Break)에 대해 설명하고, 파단전누설 설계를 위한 다양한 실배관 파과저항시험 방법 및 실배관 파괴저항시험의 필요성에 대해 소개하고자 한다.

• Journal of Welding and Joining
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• v.4 no.3
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• pp.26-31
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• 1986

(1) Implant 용접저온귀열시험은 용접 열cycle에 따른 금속조직의 경향과 구속상태의 경향을 분 리하여 평가할 수 있는 사용한 시험법이다. (2) 한계파단응력(.sfgma.$_{cr}$ .)은 재료의 탄소다량( $C_{eq}$ .) 및 융접부 광산성수소량 ( $H_{D}$)과 밀접한 관계를 가지며 $C_{eq}$ . 및 $H_{D}$가 작을수록 .sfgma.$_{cr}$ .가 높다. (3) 시험편의 notch형상이 circular이든 spiral이든 한계파단응력은 동일하다. (4) 시험편의 파단은 notch로 부터 발생하기 시작하여 그 부분에서는 수소포화 의벽개파면은 나타낸다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1054-1064
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• 2009

In this work, we predict a true fracture strain using load-displacement curves from tensile test and finite element analysis (FEA), and suggest a method for acquiring true stress-strain (SS) curves by predicted fracture strain. We first derived the true SS curve up to necking point from load-displacement curve. As the beginning, the posterior necking part of true SS curve is linearly extrapolated with the slope at necking point. The whole SS curve is then adopted for FE simulation of tensile test. The Bridgman factor or suitable plate correction factors are applied to pre and post FEA. In the load-true strain curve from FEA, the true fracture strain is determined as the matching point to test fracture load. The determined true strain is validated by comparing with test fracture strain. Finally, we complete the true SS curve by combining the prior necking part and linear part, the latter of which connects necking and predicted fracture points.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.575-584
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• 1993

The effects of atmosphere on the creep rupture properties of Ni-base superalloy Ren6 80 were investigated. Creep rupture tests were performed at $760^{\circ}C$, 657MPa and 982%, 157MPa under Ar gas atmospheres. Creep rupture mode and rupture properties (rupture life and elongation) were similar in two different atmospheres under the condition of $760^{\circ}C$, 657MPa. However, the results at $982^{\circ}C$, 157MPa showed different creep rupture mode and life between air and Ar gas atmospheres. In air, it was shown that creep cracks were initiated at surface-exposed grain boundaries and propagated along grain boundaries. In Ar gas atmosphere, the cracks were initiated at inner grain boundaries and coalesced to surface cracks which cause cup-and-cone type fracture. Due to protective oxide layer formation, air test showed longer rupture life than Ar test.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1172-1182
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• 1993

In orthogonal machining a quantitative model for burr formation process and fracture when tool exits workpiece is proposed. When no fracture during burr formation burr formation process is divided by three parts; Initiation, Development and Final burr formation. According to the properties of workpiece fracture will happen or not after initiation of burr formation. Considering the fact that fracture depends on the ductility of workpiece, the fracture strain obtained from ductile fracture criterion is used for prediction. It is verified that the fracture strain from tension test can be used as fracture criterion in burr formation without large error. For detailed observation of burr formation an experimental stage for micro orthogonal cutting inside SEM (Scanning Electron Microscope) is built. Through the comparison between model prediction and experimental result from orthogonal machining in milling machine the model is verified.

• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.17-24
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• 2018

The pullout test, a nondestructive testing(NDT), for pre-installed inserts is perhaps the most widely used technique to estimate the in-situ compressive strength of concrete. It measures the force needed to pullout a standardized metal insert embedded into concrete members. The pullout test was certified by the American Society for Testing and Materials(ASTM) and Canadian Standards Association(CSA) as a reliable method for determining the strength of concrete in concrete structures under construction. To easily estimate the strength of ultra-high-strength concrete, a simplified pullout tester, primarily composed of a standard 12mm bolt with a groove on the shaft as a break-off bolt, an insert nut, and a hydraulic oil pump without a load cell, was proposed. Four wall and two slab specimens were tested for two levels of concrete strength, 80MPa and 100MPa, using a simplified pullout tester with a load cell to verify the advantages of the pullout test and simplified pullout test. The compressive strength of concrete, pullout load, and the rupture of the break-off bolt were measured 11 times, day 1 to 7, 14, 21, 28, and 90. The correlation of the pullout load and the compressive strength of each specimen show a higher degree of reliability. Therefore, a simplified pullout test can be used to evaluate the in-place strength of ultra-high-strength concrete in structures. The prediction equation for the groove diameter of the break-off bolt(y) with the concrete strength(x) was proposed as y=0.0184x+5.4. The results described in this research confirm the simplified pullout's utility and potential for low cost, simplicity, and convenience.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.450-450
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• 2009

최근 전세계적으로 태양전지의 대량보급에 따라 실리콘 원료의 공급에 차질이 생겨 원자재 값이 상승하는 추세에 있다. 결정질 실리콘 태양전지의 제조비용중 실리콘 재료 및 웨이퍼가 차지하는 비율은 약 50~60%정도로 높기 때문에 실리콘 웨이퍼의 두께를 감소시키는 것이 비용절감을 위한 효과적인 방법으로 기대되고 있다. 그러나 실리콘 웨이퍼의 두께가 앓아질수록 제조공정중 균열이나 파손이 발생할 가능성이 높아지기 때문에 이에 따른 실리콘 웨이퍼의 기계적 물성에 대한 연구가 필수적이라 할 수 있다. 본 연구에서는 현재 상용으로 사용되고 있는 크기가 5 인치인 $200{\mu}m$ 두께의 실리콘웨이퍼 (As-saw)를 약 80여개의 시편으로 절단한 후 각각의 파단강도를 부위별로 측정하였다. 또한 표면절단결함을 제거하는 saw damage etching(SDE) 시간을 제어하여 두께가 $150{\mu}m$, $130{\mu}m$인 웨이퍼를 준비하였다. 이들 시험편에 대해서도 부위별 파단강도를 측정하여 as-saw상태의 시험편과 비교하였다. 파단강도 측정은 4 접 굽힘시험을 통하여 측정하였으며 파단면은 주사전자현미경을 통하여 관찰하였다. 또한 실리콘 웨이퍼의 미세균열을 비파괴적으로 검출하기 위하여 100MHz 고주파수를 이용하는 초음파현미경(SAM, scanning acoustic microscope)을 이용하여 균열의 분포를 영상화하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.6
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• pp.471-478
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• 2018

Static tests of the composite wing structure were performed to verify damage tolerance design. Both 5 cases of DLLT and 3 cases of DULT were completed to meet requirements for static strength. After inducing BVID and open hole damages on the critical areas of the composite wing based on associated regulations, the DULT and fracture test were performed. In major wing parts, the measured strains and displacements agreed well with those of structural analysis. The initial structural fracture occurred at the area having minimum margin of safety as expected by analysis. As a result, it was confirmed that results from analytic model and strength evaluation were similar to behaviors of the composite wing structure.

• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.63-77
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• 1994

The objective of this work is to investigate fluid mixing phenomena related to pressurized thermal shock(PTS) in a pressurized water reactor(PWR) vessel downcomer during transient cooldown with direct vessel injection(DVI) using test models. The test model designs were based on ABB Combustion Engineering(C-E) System 80＋ reactor geometry. A cold leg small break loss-of-coolant accident(LOCA) md a main steam line teak were selected as the potential PTS events for the C-E System 80＋. This work consist of two parts. The first part provides the visualization tests of the fluid mixing between DVI fluid and existing coolant in the downcomer region, and the second part is to compare the results of thermal mixing tests with DVI in the other test model. Row visualization tests with DVI have clarified the physical interaction between DVI fluid and primary coolant during transient cooldown. A significant temperature drop was observed in the downcomer during the tests of a small break LOCA Measured transient temperature profiles agree well with the predictions by the REMIX code for a small break LOCA and with the calculations by the COMMIX-1B code for a steam line break event.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.81-85
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• 2006

Through-the-thickness properties of thick-walled cylindrical composites are required to determine structural performances because interlaminar tensile stress is primarily responsible for structural failure of the composites during their curing process. It is necessary for evaluating the tensile properties to find individual test methods to find appropriate methods because there are no recognised international standards(test methods and test specifications) available for generating reliable tensile properties in the direction. This paper has performed an experimental Study to measure that properties of carbon fabric/phenolic composites are produced by domestic company. Several test methods using an aluminum specimen were compared and evaluated. The best method, found out, was adopted to measure transverse through-the-thickness properties of composite materials. The results show that strain trends on four faces of composite specimen are the same.