• 반도체디스플레이기술학회지
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• 제5권3호
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• pp.5-10
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• 2006

This paper investigates cutting qualities after laser dicing and predicts the problems that can be generated by laser dicing. And through 3 point bending test, die strength is measured and the die strength after laser dicing is compared with the die strength after mechanical sawing. Laser dicing is chiefly considered as an alternative to overcome the defects of mechanical sawing such as chipping on the surface and crack on the back side. Laser micromachining is based on the thermal ablation and evaporation mechanism. As a result of laser dicing experiments, debris on the surface of wafer is observed. To eliminate the debris and protect the surface, an experiment is done using a water soluble coating material and ultrasonic. The consequence is that most of debris is removed. But there are some residues around the cutting line. Unlike mechanical sawing, chipping on the surface and crack on the back side is not observed. The cross section of cutting line by laser dicing is rough as compared with that by mechanical sawing. But micro crack can not be seen. Micro crack reduces die strength. To measure this, 3 point bending test is done. The die strength after laser dicing decreases to a half of the die strength after mechanical sawing. This means that die cracking during package assembly can occur.

• 대한기계학회논문집
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• 제13권5호
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• pp.921-927
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• 1989

본 연구에서는 피로 균열의 진전 특성 및 표면 균열과 같은 3차원 균열의 진전 특성에 나타나는 재질 열화의 영향, 열화와 피로 파괴 형태의 관계, 균열진전 속도의 분산(scattering)과 열화의 관계등에 주목해서 열화재와 회복재의 2종류의 재료를 사용해, 피로 시험에 의한 균열진전의 실험적 특성을 고찰하였다. 또한, 저자들의 종래 관통 균열 진전 특성에 대한 연구 결과를 응용해서 열화와 균열진전의 확률특성을 고려한 표면균열 진전에 대한 시뮬레이션(simulation)을 행해서 피로 수명 예측에 미치는 열화의 영향에 대해 검토해 보았다.

• 비파괴검사학회지
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• 제29권5호
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• pp.479-484
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• 2009

세라믹스의 비파괴평가 기술은 산업분야에 응용하기 위한 세라믹스 신뢰성 개발에 있어서 필수적인 기술이다. 본 연구는 초음파 C-Scan 방식을 이용하여 SiC 세라믹스의 표면균열을 탐상하기 위한 실험적 연구 결과를 제시하고자 한다. 이를 위해 SDS-win과 $\mu$-SDS 두 종류의 초음파 장치와 25, 50 및 125 MHz의 초음파센서를 이용하여 세라믹스의 표면균열 탐상 가능성에 대해 실험적인 연구를 수행하였다. 본 연구 결과, 세라믹스의 표면미소균열은 결국 25 및 50 MHz 센스로 정밀하게 검출할 수 없었으나, 125 MHz 센서에 의한 집속법 탐상 결과 희미한 형상 정도를 검출할 수 있었으며, 비집속법의 경우는 비커스 압입자의 형상 검출이 가능함을 알 수 있었다. 따라서 본 연구를 통하여, 초음파 C-Scan 집속 및 비집속 방법은 미세균열의 탐상방식으로 어느 정도 접근 가능함을 실험적으로 확인하였다

• 한국정밀공학회지
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• 제17권9호
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• pp.151-157
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• 2000

Stress intensity factors for the circumferential surface crack of a long composite cylinder under torsion is investigated. The problem is formulated as a singular integral equation of the first kind with a Cauchy type kernel using the integral transform technique. The mode III stress intensity factors at the crack tips are presented when (a) the inner crack tip is away from the interface and (b) the inner crack tip is at the interface.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1127-1134
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• 2002

The present paper provides an engineering J estimation equation for surface cracked plates under combined bending and tension. The proposed equation is based on the reference stress approach, and the most relevant normalising loads to define the reference stress for accurate J estimations are given for surface cracked plates under combined bending and tension. Comparisons with J results from extensive 3-D FE analyses, covering a wide range of crack geometry, plate geometry and loading combination, show overall good agreement not only at the deepest point but also at arbitrary points along the crack front. for pure tension, agreement between the estimated J and the FE results is excellent, even at the surface point. On the other hand, for pure bending and combined bending and tension, the estimated J values become less accurate for locations close to the surface point. Thus the results in this paper will be useful to assess short-term fracture or low cycle fatigue of surface defects in plates under combined bending and tension.

• 한국해양공학회지
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• 제3권2호
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• pp.125-137
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• 한국해양공학회지
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• 제3권2호
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• pp.625-625
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• Nuclear Engineering and Technology
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• 제28권2호
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• pp.185-196
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• 1996

이 연구의 목적은 원자력발전소 페라이트 배관에 존재하는 원주방향 표면균열을 평가하는데 사용되는 ASME Code Z-Factor를 수정하는데 있다. ASME Code Z-Factor는 소성하중을 탄소성하중으로 보정하는 하중 보정 계수로서, 현재 사용되는 ASME Code Z-Factor는 최대하중을 과소평가하는 문제점이 있다. 이 연구에서는 먼저 기존의 SC. TNP방법이 수정되었으며, 그 이유는 기존의 SC. TNP 방법으로 예측된 최대허용하중이 실험에서 측정된 방법보다 약간 큰 결과를 주는 문제가 있기 때문이다. 이 수정된 SC. TNP 방법을 사용하여 페라이트 배관에 대한 새로운 Z-Factor를 개발하였다. 수정된 SC. TNP 방법의 타당성 과 새로 개발된 Z-Factor의 타당성을 원주방향 표면균열을 갖는 배관에 대한 실험 결과를 통해 조사하였다. 평 가결과는 수정된 SC. TNP 방법은 페라이트 및 오스테나이트 배관의 원주 방향 표면균열의 거동을 잘 예측할 수 있음을 보여 주며, 또한 수정된 SC. TNP 방법으로 구한 새로운 Z-Factor는 페라이트 배관에 존재하는 원주방향 표면균열의 거동을 잘 예측할 수 있음을 보여준다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1988년도 학술세미나 강연집
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• pp.3-67
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• 1988

Model studies on the response of homgeneous earth embankment dams subjected to strike-slip fault movement have been penomed via centrifuge and finite element analysis. The centrifuge model tests have shown that crack development in earth embankment experiences two major patters: shear failure deep inside the embankment and tension failure near the surface. The shear rupture zone develops from the base level and propagates upward continuously in the transverse direction but allows no open leakage chnnel. The open tensile cracks develop near the surface of the embankment, but they disappear deep in the embankment. The functional relationship has been developed based on the results of the centrifuge model tests incorporating tile variables of amount of fault movement, embankment geometry, and crack propagation extent in earth des. This set of information can be used as a guide line to evaluate a "transient" safety of the duaged embankment subjected to strike-slip fault movement. The finite element analysis has supplemented the additional expluations on crack development behavior identified from the results of the centrifuge model tests. The bounding surface time-independent plasticity soil model was employed in the numerical analysis. Due to the assumption of continuum in the current version of the 3-D FEM code, the prediction of the soil structure response beyond the failure condition was not quantitatively accurate. However, the fundamental mechanism of crack development was qualitatively evaluated based on the stress analysis for the deformed soil elements of the damaged earth embankment. The tensile failure zone is identified when the minor principal stress of the deformed soil elements less than zero. The shear failure zone is identified when the stress state of the deformed soil elements is at the point where the critical state line intersects the bounding surface.g surface.

• 한국가구학회지
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• 제12권1호
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• pp.11-20
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• 2001

To investigate weathering and surface characteristics of coating film on lumbers coated with Hwangchil(varnish of Dendropanax morbifera), we carried out to investigate the resistance against discoloration, value of crack and surface characteristics of coating films on seven domestic lumbers and those of four introduced tropical lumbers. There was investigated to evaluate the properties of coating films by the varnish of Dendropanax morbifera. There was insignificant correlations between the hardness and moisture contents of each lumber treated by the varnish. There was no significant correlations between the thickness of coating film and the hardness, either. Although we investigated 11 wood species, we found only three species as resistance wood species against discoloration; Diospysos spp., Abies holophylla and Ulmus davidiana. The crack of coaing films was the largest on Zelkova serrata followed by Juglans sinensis, Cercidiphum japonicum, Tectona grands, Ulmus davidiana, Guibourtia tessmannii, Diospysos spp. and Dalbergia latifolia. However, there was no crack of coating films on the lumbers of Juniperus rigida, Prunus serrulata var. spontanea and Abies holophylla. The crack of coating film showed positive correlations with the thickness of coating film and hardness. The surface characteristics of the coating films evaluated on the basis of $R_{a}$ values indicated the lumbers of Ulmus davidiana($0.14{\;}{\mu}m$), Juniperus rigida($0.1 5{\;}{\mu}m$), Guibourtia tessmannii($0.19{\;}{\mu}m$), Dalvergia latifolia($0.20{\;}{\mu}m$) and Diospysos spp.($0.20{\;}{\mu}m$), Cercidiphum japonicum($0.24{\;}{\mu}m$) as good species while there was insignificant differences between softwoods and hardwoods. Tectona grands, Prunus serrulata var. spontanea and Abies holophylla showed rough surface with $1.53~2.63{\;}{\mu}m$ of $R_a$ values. The four kinds of rough indices($R_a,{\;}R_z,{\;}R_{max}{\;}and{\;}R_q$) showed very low correlations with moisture contents with the correlation coefficients. The $R_a{\;}and{\;}R_{max}$ also showed slight relationship with hardness.