• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.11a
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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.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.63-66
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• 2000

This research addresses study on thermal residual stress of a composite patch repair of the edge cracked aluminium panel of aging aircraft. Composite patch repair is an efficient and economical technique to improve the damage tolerance of cracked metallic structures. These are thermal residual stresses due to the mismatch of coefficient of thermal expansion, and these are affected by the curing cycle of patch specimen. In this study, three curing cycles were selected for F.E. analysis. This study features the effect on composite patch and aluminum by thermal residual stress during crack propagation in aluminum plate.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.3
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• pp.202-210
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• 2006

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can be occurred due to coolant leaking in the check valve. The thermal stratification produces excessive thormal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, when the turbulence penetration occurs in the branch pipe, the maximum temperature differences of fluid at the pipe cross-sections of the T-branch with thermal stratification are examine.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.413-416
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• 2006

This paper presents the analytical results on the heat of hydration and induced thermal cracking of the wall elements in LiNAC that is a radioactive shield concrete structure. This wall elements measuring 1.2 m in thickness and 32 m in length tend to exhibit thermal cracking due to heat of hydration and high constraint effects caused by slab element located in the lower part of structure. In this analysis, four different construction stages were considered to find out the most effective concrete casting method in terms of thermal stress. Among the construction methods adopted in this analysis, the method of installation of construction connection measuring 1.2 m at the both side of wall elements was very effective way to control the thermal stress, resulting in increase thermal cracking index of wall elements in LiNAC structure. Finally, the wall elements in LiNAC structure was cast successfully according to the proposed construction method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2139-2157
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• 1994

In order to understand the delamination between leadframe and epoxy molding compound in an electronic packaging of surface mounting type, the stress intensity factor, T-stress and J-integral in fracture mechanics are obtained. The effects of geometry, material properties and molding process temperature on the delamination are investigated taking into account the temperature dependence of the material properties, which simulates as more realistic condition. As the crack length increases the J-integral increases, which suggest that the crack propagates if it starts growing from the small size. The effects of the material properties and molding process temperature on stress intensity factor, T-stress is and J-integral are less significant than the chip size for the practical cases considered here. The T-stress is negative in all eases, which is in agreement with observation that interfacial crack is not kinked until the crack approaches the edge of the leadframe.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.508-515
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• 2011

Bovine incisor was investigated using active infrared thermography(IRT) to visualize crack on bovine teeth. An artificial crack was carefully created in bovine incisor sample by compression load of universal tensile machine. While applying a sinusoidal heat wave to the cracked bovine incisor through halogen lamp, consecutive digital infrared images was captured from the sample surface at a frequency synchronized with heat excitation. Phase information of thermal image was calculated by four-point correlation method and processed to produce the phase image of bovine incisor. This phase image showed clearly the crack on the incisor, which was hardly detected in traditional passive thermography.

• Journal of Power System Engineering
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• v.13 no.5
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• pp.52-58
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• 2009

A gas turbine consists of an upstream compressor and a downstream turbine with a combustion chamber, and also the compressor and the turbine are generally coupled using a single shaft. Many casing bolts are used to assemble two horizontally separated casings, the gas turbine casing and the compressor casing, in both of axial and vertical directions. Because drilled holes for casing bolts in vertical direction are often too close to drilled holes for casing bolts in axial direction, one can observe cracks in the area frequently during operations of a gas turbine. In this study of the root cause analysis for the cracking initiating from the drilled holes of the casings of a gas turbine, the finite element analysis(FEA) was applied to evaluate the thermal and mechanical characteristics of the casings. By applying the field operation data recorded from combined cycle power plants for FEA, thermal and thermo-mechanical characteristics of a gas turbine are analyzed. The crack is initiated at the geometrical weak point, but it is found that the maximum stress is relieved when the same type of cracks is introduced on purpose during FEA. So, it is verified that the local fracture could be delayed by machining the same type of defects near the hole for casing flange bolts of the gas turbine, where the crack is initiated.

• International Journal of Highway Engineering
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• v.16 no.6
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• pp.59-67
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• 2014

PURPOSES : The purpose of this study is to analyse the longitudinal steel strain and stress of continuously reinforced concrete pavement(CRCP) with longitudinal and transverse direction at early age using stress dependent strain analysis method. METHODS : To measure the longitudinal steel strain, 9-electrical resistance and self-temperature compensation gauges were installed to CRCP test section (thickness = 250mm, steel ratio = 0.7%) and continuously measured 10min. intervals during 30days. In order to properly analyze the steel stress first, temperature compensation process has been conducted. Secondly, measured steel strains were divided into stress dependent strain (elastic strain) and stress independent strain (thermal strain) and then stress dependent strain was applied to stress calculation of longitudinal steels. RESULTS : Steel strains were successfully measured during 30days. To verify the accuracy of temperature compensation process, measured coefficient of thermal expansion(COTE,$11.46{\times}10^{-6}m/m/^{\circ}C$) of longitudinal steel before paving was compared with that of unrestrained steel. Max. steel stress in the transverse direction shows about 266MPa at 23days after placement. CONCLUSIONS : Steel stresses in the longitudinal and transverse direction have been evaluated. In longitudinal direction, steel stress from the crack was rapidly reduced from 183MPa at crack to 18MPa from 600mm apart the crack. From this observation, stress effective length can be identified as within 600mm apart from the crack. In transverse direction, max. stress point was located near the center of pavement width and stress level(266MPa) is about 66% of yield stress of steel.

• Elastomers and Composites
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• v.41 no.2
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• pp.79-87
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• 2006

This study are conducted for the purpose of developing rubber material with noise and crack resistance. Cure characteristics, physical properties, thermal resistance, fuel resistance, abrasion resistance, crack resistance and noise resistance of NBR compounds with the various amounts of oleamide and aramid chip were investigated. From the measurements of cure characteristics and Mooney viscosities, cure characteristics of uncured rubber showed that a torque was decreased as the amount of oleamide increased. Hardness, modulus and elongation of rubber specimens tended to be reduced gradually, however, tensile strength remained unchanged as the amount of the oleamide increased. As a testing results of heat resistance for 70 hours at $120^{\circ}C$ and oil resistance far 70 hours at $40^{\circ}C$, tensile strength and elongation were all reduced. From the TGA/DSC analysis, there was no such a change observed in thermal characteristics of rubber materials. As a result of testing basic physical properties, abrasion resistance, noise resistance and crack resistance, the optimum ratio of oleamide to NBR was found to be 3 phr, while that of aramid to NBR 227001 was 1 phr.

• Elastomers and Composites
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• v.37 no.2
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• pp.86-98
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• 2002

The application of silica/carbon black dual phase fillers to natural rubber(NR) compound was investigated. When the amounts of filler content were restricted to 60phr, the optimum ratio of dual phase fillers were 25phr/35phr of silica/carbon black. It was found that these new fillers give better overall performance in comparison with carbon black in tear strength, crack resistance, and cutting resistance. Also the thermal degradation resistance of NR vulcanizates which were filled with dual phase fillers was better than that of the carbon black. Dual phase fillers filled NR vulcanizates showed better viscoelastic properties, like tan${\delta}$, for the wet skid resistance and rolling resistance of motor vehicle tires.