• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.38-45
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• 2000

In this research, MFL technique has been studied for the inspection of storage tank floor. The reference specimens having 20%, 40%, 60% and 80% slot's are fabricated using the carbon steel plates of a 6mm and 10mm thick. Powerful permanent magnets and Hall effect sensors are used to this application. It is shown that our system is able to detect metal loss like a slot. Also, it is possible that slot diameter is measured using transverse type of Hall generator. It is demonstrated that MFL can not differentiate between the response from top side and bottom side slot. Flux leakage response from a bottom side indication is significantly lower in amplitude than that from an equivalent top side slot. It is essential to know this sensor lift-off distance because the MFL signal also changes considerably with the sensor lift-off distance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1529-1534
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• 2012

In this study, tensile tests for 12-${\mu}m$-thick copper thin foils were performed by using the DIC method. The DIC method provided precise stress-strain curves for thin film materials, and a commercial inkjet printer can be simply and effectively used for printing speckle patterns on the specimen of Cu thin films whose surface contrast is too low to apply the DIC method. The mechanical properties of Cu thin foils obtained in this study are as follows: elastic modulus E = 89.2 GPa, 0.2% offset yield stress $S_{0.2%}$= 232.8 MPa, tensile strength $S_u$= 319.2 MPa, elongation at fracture ${\varepsilon}_f$=16.8 %, and Poisson's ratio ${\nu}$= 0.34.

• Composites Research
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• v.28 no.6
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• pp.356-360
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• 2015

In this paper, the carbon fiber reinforced plastic is processed as the double cantilever beam in order to estimate the fracture behavior of composite and is carried out with the static analysis as the mode I. The specimen sizes are 25 mm, 30 mm, 35 mm and 40 mm. And the material property is used with carbon. As the analysis result of mode I, the adhesive part is detached latest by the small force at the specimen thickness of 25 mm. The largest force is happened at the specimen thickness of 40 mm. The defection of the adhesive interface is shown slowest at the displacement of 9.75 mm at the specimen thickness of 25 mm. And the defection is shown quickest at the displacement of 7.82 mm at the specimen thickness of 40 mm. This defection is due to the fracture of specimen. The result of this study on the defection of the adhesive interface and the reaction force due to this defection is thought to be contributed to the safe structural design of the carbon fiber reinforced plastic.

• Journal of the Korean Wood Science and Technology
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• v.43 no.1
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• pp.60-67
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• 2015

In order to evaluate the bond performance of domestic larch glulam and the glass fiber reinforced plastic (GFRP) rod, the specimen with the GFRP rod bonded-in domestic larch glulam for pull-out test was produced. The test was carried out using various specimens with different gluing depth, width of glue-line and type of adhesive. The cantilever type rahmen structure specimen with bonded-in GFRP rods was produced based on the result of pull-out test, and its moment resistance performance was compared and examined with the moment resistance performance of slotted-in steel plate specimen. As a result of the pull-out test, the most excellent bond performance was found when the insertion depth of GFRP rods was 5 times larger than the diameter of GFRP rods. When the glue-line thickness was 1 mm, the bond performance improved by 17%~29% in comparison to the bond performance in the case of the glue-line thickness of 2 mm. Also, the bonded strength of the specimen used with poly-urethane adhesive was 2.9~4.0 times greater than the bonded strength of specimen used with resorcinol adhesive. The cantilever type rahmen structure specimen with bonded-in GFRP rods showed the moment resistance performance 0.82 times lower in comparison to the slotted-in steel plate specimen used with the drift pin, but the initial stiffness was similar as 0.93 times.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.471-478
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• 2010

Thin films play an important role in many technological applications including microelectronic devices, magnetic storage media, MEMS and surface coatings. It is well known that a thin film's material properties can be very different from the corresponding bulk properties and thus there has been a strong need for the development of a reliable test method to measure the mechanical properties of a thin film. We have developed an alternative and convenient test method to overcome the limitations of previous membrane deflection experiment and uniaxial tensile test by adopting a white light interferometer having sub-nanometer out-of-plane displacement resolution. The freestanding aluminium specimens are tested to verity the effectiveness of the test method developed and get the tensile properties. The specimens are 0.5 rum wide, $1{\mu}m$ thick and fabricated through MEMS processes including sputtering. 1 to 5 specimens are fabricated on Si dies. The membrane deflection experiments are carried out by using a homemade tester consisted of a motor-driven loading tip, a load cell, and 6 DOF alignment stages. The test system is compact enough to set it up beneath a commercial white light interferometric microscope. The white light fringes are utilized to align a specimen with the tester. The Young's modulus and yield point stress of the aluminium film are 62 GPa and 247 MPa, respectively.

• Journal of the Korean Wood Science and Technology
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• v.36 no.1
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• pp.36-44
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• 2008

It is necessary to assess wood quality and strength of the clear specimens from used members in old wooden structures for the reuse of old members on the same structure or a new structure. Wood species classification by microscope observation of each wood member that was used in truss cord and temple, and several physical and strength tests by the specification of present KS standards were conducted to compare with some references. From the comparison of strengths with references, Korean larch gives relatively better wood quality and mechanical properties than other wood species. No significant deterioration of cell wall was found by microscopic observation for the sound wood part that was selected visually. Tensile specimens with 3 mm in thickness on the middle span showed greater strength than 5 mm thick specimens, which explains that dimension of tensile specimen should be examined for evaluating precise tensile strength properties. Other tests, compression, shear, and bending, are adoptable for each strength properties. Test methods for the evaluation of basic strengths and fastener connections for old wood species should be further examined.

• Journal of the Korea Institute of Building Construction
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• v.11 no.2
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• pp.162-170
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• 2011

As the result of implementing a treated material test and durability test after quickly drying S.P.F. species, a type of softwood structural material, within a short period time, soaking it in liquid phosphate flame proof agent for an hour, microwave heating it, and compressing it from 3.8cm to 1cm, when setting the appropriate heating time of microwave heating at 7 minutes at 5kW, it is observed that it satisfies the target water content (4~5%). It is shown that in a water content measurement of the wood that is compressed after being softened by soaking in the flame proof agent, drying and heating at 3kW for 9 minutes, all specimens satisfied 12~14%, the appropriate water content for exterior wood. Also, it is shown that in terms of the flame performance obtained through a flame resistance treatment of the compressed wood and a treated material test, the specimen soaked in flame proof agent for 30 minutes was the most excellent, and that the performance test result of the compressed wood in all areas, such as nail withdrawal resistance, compression, bending strength, and shearing strength, were all improved in their mechanical features to twice to three times better performances.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.300-300
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• 2014

해양환경 하에서 대형 강구조물의 경우 장기간 부식손상을 방지하기 위해 아크 용사코팅 기술이 오래전부터 유용하게 이용되어 왔다. 아크 용사코팅 기술은 타 용사코팅 기술에 비해 경제성과 생산성이 뛰어나 대형 강구조물에 적용되고 있다. 용사재료로는 Al, Zn 또는 그 합금들이 주로 사용되어 강재에 대해 희생양극 방식효과를 나타낸다. 그러나 아크용사에 의해 적층된 코팅 층은 용사공정 중 불가피하게 수많은 기공과 산화물이 포함되어 내식성 및 내구성에 악영향을 미치게 된다. 따라서 본 연구에서는 알루미늄 합금의 용사코팅 층에 대하여 다양한 후처리를 통해 내식성과 더불어 내구성을 향상시키고자 하였다. 용사코팅은 알루미늄 합금 선재(1.6 ${\varnothing}$)를 사용하여 아크용사를 실시하였다. 용사 시 용사거리는 200 mm, 공기압력은 약 $7kg/cm^2$ 정도로 유지하면서 용사코팅을 실시하여 약 $200{\mu}m$ 두께로 코팅 층을 형성시켰다. 이후 용사코팅 층의 표면에 다양한 후처리재를 적용하였으며, 내구성을 평가하기 위하여 후처리 적용 전후 시험편에 대하여 캐비테이션 실험을 실시하였다. 캐비테이션 실험은 ASTM G32-92에 의거하여 주파수 20 kHz의 초음파 진동 장치(ultrasonic vibratory device)를 사용하였다. 그리고 시험편 표면과 발진 혼에 부착된 팁(tip)과의 거리는 1 mm로 일정하게 유지시킨 뒤, 캐비테이션 발생 시간을 변수로 하여 실험을 실시하였다. 손상된 용사코팅 층의 표면은 주사전자현미경과 광학현미경으로 관찰하였으며, 시험편 손상깊이는 3D 현미경으로 비교 분석하였다. 또한 캐비테이션 실험 전후의 무게를 측정하여 무게 감소량을 상호 비교하였다. 그리고 전기화학적 실험은 천연해수 속에서 자체 제작한 홀더(holder)를 이용하여 $0.33183cm^2$의 용사코팅 층만을 노출시켜 실시하였다. 그리고 기준전극은 은/염화은 전극을, 대극은 백금전극을 사용하였다. 분극실험을 통해 후처리 적용에 따른 용사코팅 층의 부식전위 및 부식전류밀도를 비교 평가하였다. 그 결과, 용사코팅 층에 의하여 강재에 대한 희생양극 방식전위가 확보되었으며, 후처리재가 적용된 용사코팅 층에서 내식성 및 캐비테이션 저항성이 향상되었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.63-69
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• 1992

Plane-strain fatigue crack growth behavior of 7075-76 aluminium alloy was investigated by using side-grooved through-thickness center cracked tension(CCT) specimens. The effect of side-groove on the stress intensity factor value was examined. The effective thickness expression of $B_{e}$= $B_{o}$-( $B_{o}$-( $B_{ o-B_{n}^{2}}$ $B_{o}$ is the most appropriate to evaluate the stress intensity factor of side-grooved CCT specimen for fatigue testing. Fatigue crack growth rates can be well described by the effective stress intensity factor range based on closure measurements, for both side-grooved and uniform thickness specimens. Provided that the thickness of specimen meets the requirements for valid plane-strain fracture toughness, uniform thickness specimen data may be assumed to approximately represent the plane strain through-thickness crack growth behavior.ehavior.r.

• Journal of Korean Society of Steel Construction
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• v.15 no.6 s.67
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• pp.629-637
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• 2003

This s paper presented the results of the three phases of fatigue tests to determine the fatigue strength of in-plane welded gusset joints, which are the most common details inevitably existing in the region of high stress range. A total of 57 fatigue specimens with varying thickness and strengths were made and tensile fatigue tests performed. One full-scale beam fatigue test was also performed. The validity of the fatigue strength of those details in the specification was confirmed, with the effects of thickness of flanges and welded attachments, length of attachments, and strength of applied steel examined. The characteristics of crack initiation and propagation were also observed. The test result was evaluated by comparing it with other test data and fatigue criteria of other countries. To determine the degree of stress concentration in the weld toe depending on geometric configuration such as attachment length and transition radius, analyses were performed. Compared to the present specification, analytical results indicate the need to revise and subdivide the detail categories.