• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1993년도 추계학술대회 논문집
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• pp.49-54
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• 1993

This paper discusses the reliability of solder joints of electronic devices on printed circuit board. Solder application is usually done by screen printing method for the bonding between outer leads of devices and thick film(Ag/Pd) pattern on Hybrid IC as wel1 as Cu lands on PCB. As result of thermal stresses generated at the solder joints due to the differences of thermal expansion coefficients between packge body and PCB, Micro cracking often occurs due to thermal fatigue failure at solder joints. The initiation and the propagate of solder joint crack depends on the environmental conditions, such as storage temperature and thermal cycling. The principal mechanisms of the cracking pheno- mana are the formation of kirkendal void caused by the differences in diffusion rate of materials, ant the thermal fatigue effect due to the differences of thermal expansion coefficient between package body and PCB. Finally, This paper experimentally shows a way to supress solder joints cracks by using low-${\alpha}$ PCB and the packages with thin lead frame, and investigates the phenomena of diffusion near the bonding interfaces.

• 한국정밀공학회지
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• 제13권5호
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• pp.164-172
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• 1996

In hard and brittle materials as advanced ceramics indented by a hard indenter, the indenter's transition radius, was defined as critical radius which distinguishes the occurrence of the first plastic deformation from the elastic cracking as the first damaging event, is analytically and experimentally investigated. The analytical result is shown that the critical load, which not enlarge pre-existing cracks as the form of median crack beneath a indenter, is constant, and is determined by the order of $k_{IC}$$^{4}$ $P_{Y}$$^{3}$(where, $K_{IC}$ , $P_{Y}$are the fracture toughness of materials and the applied pressure by indenting, respectively). And the size of transiton radii were experimentally obtained with the similar values to the analytical results.lts..

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.10-17
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• 2001

With the introduction of durability examination into design code of concrete structure, a prediction of early-age behavior of concrete and its cracking resistance becomes very important. But, the early-age behaviors such as hydration, micro-structure development, moisture transport and mechanical properties development is quite complicated and coupled each other, and thus those can not be solved independently. One way to analyze those is to model their behaviors analytically and solve those computationally within a unified framework. In this paper, we propose a finite element technique to predict the early-age behaviors of concrete within the unified framework. The technique is applied to evaluatio of cracking in a massive concrete structure and then the analysis results are discussed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.115-118
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• 2005

In this study, small scale model test was performed to verify the ultimate load capacity of spillway pier structure under static load. The 1/20 scale test specimen was made of specially designed micro-concrete and wire mesh. From the test result, the cracking load of specimen was 10 tonf and the ultimate was 19tonf. From the similarity rule, cracking and ultimate load of prototype pier structure were predicted 4000 tonf, 7600 ton, respectively.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 춘계학술대회 논문집
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• pp.124-124
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• 2015

Acoustic microscopy and scanning electron microscopy were applied to non-destructively evaluate the hydrogen-induced cracking of API X-80 steels and to find the initiation time of the crack. The API X-80 steel had the average grain size of about $4-10{\mu}m$. The hardness was reduced from 240 to 202 [Hv] after exposing in HIC environment for 2-days. Friction coefficient and wear loss were 0.745 and 0.392 mm, respectively. Empirical equation of corrosion potential and corrosion rate of the steel with HIC time in $5%NaCl-0.5%CH_3COOH$ at $25^{\circ}C$ were $Eh\;(up)=0.06^*t[day]+0.2951$, $Eh(down)=0.376^*t[day]+0.5938$, respectively. HIC grew with micro-size after 1-day exposure. The HIC tended to propagate on the surface with Al, Si, Ti, and Mn.

• Advances in nano research
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• 제15권6호
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• pp.495-511
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• 2023

In this research, the impact of micro-silica, nano-silica, and polypropylene fibers on the fracture energy of self-compacting concrete was thoroughly examined. Enhancing the fracture energy is very important to increase the crack propagation resistance. The study focused on evaluating the self-compacting properties of the concrete through various tests, including J-ring, V-funnel, slump flow, and T50 tests. Additionally, the mechanical properties of the concrete, such as compressive and tensile strengths, modulus of elasticity, and fracture parameters were investigated on hardened specimens after 28 days. The results demonstrated that the incorporation of micro-silica and nano-silica not only decreased the rheological aspects of self-compacting concrete but also significantly enhanced its mechanical properties, particularly the compressive strength. On the other hand, the inclusion of polypropylene fibers had a positive impact on fracture parameters, tensile strength, and flexural strength of the specimens. Utilizing the response surface method, the relationship between micro-silica, nano-silica, and fibers was established. The optimal combination for achieving the highest compressive strength was found to be 5% micro-silica, 0.75% nano-silica, and 0.1% fibers. Furthermore, for obtaining the best mixture with superior tensile strength, flexural strength, modulus of elasticity, and fracture energy, the ideal proportion was determined as 5% micro-silica, 0.75% nano-silica, and 0.15% fibers. Compared to the control mixture, the aforementioned parameters showed significant improvements of 26.3%, 30.3%, 34.3%, and 34.3%, respectively. In order to accurately model the tensile cracking of concrete, the authors used softening curves derived from an inverse algorithm proposed by them. This method allowed for a precise and detailed analysis of the concrete under tensile stress. This study explores the effects of micro-silica, nano-silica, and polypropylene fibers on self-compacting concrete and shows their influences on the fracture energy and various mechanical properties of the concrete. The results offer valuable insights for optimizing the concrete mix to achieve desired strength and performance characteristics.

• 에너지공학
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• 제8권2호
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• pp.248-255
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• 1999

미분형 고정층 반응기에서 고체산 촉매(HY 제올라이트, $\beta$-제올라이트, HZSM-5)를 이용하여 폐윤활유를 1차 열분해한 오일의 촉매분해 반응을 연구하였다. 촉매의 활성 검토에 사용된 원료물질은 폐윤활유를 반응온도 48$0^{\circ}C$, 반응시간($\tau$) 60분으로 진행되는 벤치규모의 연속공정에서 생산된 제품이다. HY제올라이트의 경우 탄소수 21개 이하의 경유 성분을 얻을 수 있는 최적 반응조건은 WHSV(weight hourly space velocity)=1, 반응온도는 375$^{\circ}C$임을 알 수 있었다. 암모니아 탈착법을 이용하여 전체의 산점 및 강산점 수를 측정한 결과 $\beta$-제올라이트가 가장 많은 것으로 나타났다. 탄소수 21개 이하 성분의 수율을 기준으로 촉매의 활성 순서를 평가할 때 HY제올라이트〉$\beta$-제올라이트〉HZSM-5 임을 알 수 있었다. 또한 코크의 생성량 역시 동일한 순서를 보였다. 이러한 결과를 보인점은 HY제올라이트의 경우 촉매내부 미세기공의 평균직경이 크므로. 반응물이 촉매내부로 쉽게 확산될 수 있어 내부의 산점에서 분해반응의 진행이 적절함으로 나타난 결과로 판단되었다. 이러한 점은 코크의 생성량으로도 확인할 수 있었다.

• Journal of Welding and Joining
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• 제18권2호
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• pp.86-94
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7N01 spot-welded by pulse Nd : YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed : center line crack({TEX}$C_{C}${/TEX}), diagonal crack({TEX}$C_{D}${/TEX}), and U shape crack({TEX}$C_{U}${/TEX}). Also, HAZ crack({TEX}$C_{H}${/TEX}) was observed in the HAZ region, furthermore, mixing crack({TEX}$C_{M}${/TEX}) consisting of diagonal crack and HAZ crack was observed. White film was formed at th hot crack region in the fractured surface after it was immersed to 10% NaOH water. In the case of A5083 alloy, white films in {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack region were composed of low melting phases, {TEX}$Fe_{2}SiAl_{8}${/TEX} and eutectic phases, $Mg_2$Al$_3$ and $Mg_2$Si. Such films observed $CuAl_2$, {TEX}$Mg_{32}(Al,Zn)_{3}${/TEX}, MgZn$_2$, $Al_2$CuMg and $Mg_2$Si were observed in the whitely etched films near {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Sim in the case of A7N01 alloy, respectively. The {TEX}$C_{C}${/TEX} and {TEX}$C_{D}${/TEX} cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of {TEX}$C_{M}${/TEX} crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The {TEX}$C_{U}${/TEX} crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.365-368
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• 2006

In this paper, the post cracking stress-crack width relationship of the composite is studied from a micromechanics points of view. Cook-Gordon debonding effect is studied by more refined method with considering of chemical friction of fiber interface. As a result, fiber with pre-debonding length retards stress development and shows more wide crack width for the same force level. longer pre-debonding length and lower pre-debonding bond strength results in lower full-debonding force, but same crack width.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.689-692
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• 2002

Composite materials, when damaged under thermal or mechanical loadings, show property changes. Among many mechanical properties of composite materials. the stiffness tend to be reduced due to micro-cracking, debonding, or delamination caused by external loadings. This research presents results regarding the detecting technique of internal damages within composite that experienced low-velocity impacts. Post-damage evaluations were made experimentally using flexural and compression loadings. Preliminary finite element analysis was made and compared with analytical solutions. The experimental results to determine the degree of damage will be compared with finite element results.