The thermal shock resistance of cement composites with hollow glass microspheres (HGM) is investigated. Cement composites containing various concentrations of HGM are prepared and their properties studied. The density, thermal conductivity, and coefficient of thermal expansion of the composites decrease with increasing HGM concentration. A thermal shock test is performed by cycling between -60 and 50oC. After the thermal shock test, the compressive strength of the cement composite without HGM decreases by 28.4%, whereas the compressive strength of the cement composite with 30 wt% HGM decreases by 5.7%. This confirms that the thermal shock resistance of cement is improved by the incorporation of HGM. This effect is attributed to the reduction of the thermal conductivity and coefficient of thermal expansion of the cement composite because of the incorporation of HGM, thereby reducing the occurrence of defects due to external temperature changes.

In order to improve the thermal shock and ablation resistance of high thermal conductivity carbon/carbon composites, carbon nanotubes (CNTs) were introduced by electrophoretic deposition. After modification, the flexural strength of the composites increases by 53.0% due to the greatly strengthened interfaces. During thermal shock between 1100 °C and room temperature for 30 times, the strength continues to increase, attributed to the weakened interfaces in favor of fiber and CNT pull-out. By introducing CNTs at interfaces, thermal conductivity of the composites along the fiber axial direction decreases and that along the fiber radial direction increases. As the thermal shock process prolongs, since the carbon structure integrity of CNT and matrix in the modified composites is improved, the conductivity increases whatever the orientation is, until the thermal stress causes too many defects. As for the anti-ablation performance, the mass ablation rates of the CNT-modified composites with fibers parallel to and vertical to the flame decrease by 69.6% and 43.9% respectively, and the difference in the mass ablation rate related with fiber orientations becomes much less. Such performance improvement could be ascribed to the reduced oxidative damage and the enhanced interfaces.

Heat shock proteins (HSPs) are highly conserved cellular proteins that contribute to adaptive responses of organisms to a variety of stressors. In response to stressors, cellular levels of HSPs are increased and play critical roles in protein stability, folding and molecular trafficking. The mRNA expression pattern of two well-known heat shock protein transcripts, HSP70 and HSP90 were studied in two tissues of nerve ganglia, cerebral ganglion and pleuropedal ganglion of Pacific abalone (Haliotis discus hannai). It was observed that both HSP70 and HSP90 transcripts were upregulated under heat stress in both ganglion tissues. Expression level of HSP70 was found higher than HSP90 in both ganglia whereas cerebral ganglion showed higher expression than pleuropedal ganglion. The HSP70 and HSP90 showed higher expression at Day-1 after exposed to heat stress, later decreased at Day-3 and Day-7 onwards. The present result suggested that HSP70 and HSP90 synthesize in nerve ganglion tissues and may provide efficient protection from stress.

Cordierite composed of an alumina-silica-magnesia compound has a low coefficient of thermal expansion(CTE) and excellent thermal shock resistance. It also has a low dielectric constant and high electrical insulation. However, due to low mechanical strength, it is limited for use in a ceramic heater. In this study, ZrO2 is added to an 80 wt% cordierite-20 wt% mullite composition, and the effect of ZrO2 addition on the mechanical strength and thermal shock resistance is investigated. With an increasing addition of ZrO2, cordierite-mullite formed ZrO2, ZrSiO4 and spinel phases. With sintering conducted at 1400 °C with the addition of 5 wt% ZrO2 to 80 wt% cordierite-20 wt% mullite, the most dense microstructure forms along with an excellent mechanical strength with a 3-point flexural strength of 238MPa. When this composition is quenched in water at ΔT = 400℃ , the 3-point flexural strength is maintained. Moreover, when this composition is cooled from 800℃ to air, the 3-point flexural strength is maintained even after 100 cycles. In addition, the CTE is measured as 3.00 × 10−6·K−1 at 1000℃ . Therefore, 80 wt% cordierite-20 wt% mullite with 5 wt% ZrO2 is considered to be appropriate as material for a ceramic heater.

The sweetpotato whitefly Bemisia tabaci is a serious pest and virus vector of many crops. To understand thermal tolerance of B. tabaci at molecular level, effects of rapid and acclimated thermal stress were analyzed by measuring mRNA levels of two heat shock proteins (hsp), hsp23 and hsp90, of B. tabaci using quantitative real-time RT-PCR. Mortality of adult whiteflies were 65.5% by 45°C for 1 h but 100% by 50°C for 1 h. However, mortality by subsequent exposures to 35°C for 1 h then 45°C for 1 h was 43.3%. Comparison between rapid and acclimated heat shock treatments showed that different patterns between hsp23 and hsp90 levels. At acclimated condition, hsp90 was higher but hsp23 was lower than rapid heat shock. The results suggest that the heat acclimation response is possibly advantageous to whiteflies that are often exposed to drastic temperature fluctuations.

This study investigates changes in the mechanical behaviors, especially hardness and indentation load-displacement curves, of thermal barrier coatings (TBCs) brought about by thermal shock. The TBCs on the Nickel-based bondcoat/superalloy was prepared with diameters of 25.4 mm and 600 μm thickness. The results of thermal shock cycling test from 1100 oC of the highest temperature indicate that the thermal shock do not influence on the mechanical behavior, but a continuous decrease in porosity and increase in hardness were observed after 1200 thermal shock cycles; these changes are believed to be due to sintering of thermal barrier coating materials. The results that no degradation in the indentation load-displacement curves indicate that the coating shows good thermal shock resistance up to 1200 cycles at 1100 oC in air.

This study investigates the thermal shock property of a polycrystalline diamond compact (PDC) produced by a high-pressure, high-temperature (HPHT) sintering process. Three kinds of PDCs are manufactured by the HPHT sintering process using different particle sizes of the initial diamond powders: 8-16 μm (D50 = 4.3 μm), 10-20 μm (D50 = 6.92 μm), and 12-22 μm (D50 = 8.94 μm). The microstructure observation results for the manufactured PDCs reveal that elemental Co and W are present along the interface of the diamond particles. The fractions of Co and WC in the PDC increase as the initial particle size decreases. The manufactured PDCs are subjected to thermal shock tests at two temperatures of 780oC and 830oC. The results reveal that the PDC with a smaller particle size of diamond easily produces microscale thermal cracks. This is mainly because of the abundant presence of Co and WC phases along the diamond interface and the easy formation of Co-based (CoO, Co3O4) and W-based (WO2) oxides in the PDC using smaller diamond particles. The microstructural factors for controlling the thermal shock property of PDC material are also discussed.

This study investigates the microstructure and thermal shock properties of polycrystalline diamond compact (PDC) produced by the high-temperature, high-pressure (HPHT) process. The diamond used for the investigation features a 12~22 μm- and 8~16 μm-sized main particles, and 1~2 μm-sized filler particles. The filler particle ratio is adjusted up to 5~31% to produce a mixed particle, and then the tap density is measured. The measurement finds that as the filler particle ratio increases, the tap density value continuously increases, but at 23% or greater, it reduces by a small margin. The mixed particle described above undergoes an HPHT sintering process. Observation of PDC microstructures reveals that the filler particle ratio with high tap density value increases direct bonding among diamond particles, Co distribution becomes even, and the Co and W fraction also decreases. The produced PDC undergoes thermal shock tests with two temperature conditions of 820 and 830, and the results reveals that PDC with smaller filler particle ratio and low tap density value easily produces cracks, while PDC with high tap density value that contributes in increased direct bonding along with the higher diamond content results in improved thermal shock properties.

Thermal shock resistance property has recently been considered to be one of the most important basic properties, in the same way that the transverse-rupture property is important for sintered hard materials such as ceramics, cemented carbides, and cermets. Attempts were made to evaluate the thermal shock resistance property of 10 vol% TaC added Ti(C,N)-Ni cermets using the infrared radiation heating method. The method uses a thin circular disk that is heated by infrared rays in the central area with a constant heat flux. The technique makes it possible to evaluate the thermal shock strength (Tss) and thermal shock fracture toughness (Tsf) directly from the electric powder charge and the time of fracture, despite the fact that Tss and Tsf consist of the thermal properties of the material tested. Tsf can be measured for a specimen with an edge notch, while Tss cannot be measured for specimens without such a notch. It was thought, however, that Tsf might depend on the radius of curvature of the edge notch. Using the Tsf data, Tss was calculated using a consideration of the stress concentration. The thermal shock resistance property of 10 vol% TaC added Ti(C,N)-Ni cermet increased with increases in the content of nitrogen and Ni. As a result, it was considered that Tss could be applied to an evaluation of the thermal shock resistance of cermets.

This paper presents a method for the assesment of thermal and vibration fatigues in integral exhaust manifold/turbine housing system. Most of failures on turbine housing are observed by thermal cyclic loads. In order to predict thermal failures by finite element analysis, we considered the temperature-dependent inelastic materials and transient temperature histories based on the thermal shock test. The results showed that the plastic strains of localized critical regions such as valve seat coincided well with crack locations from an endurance test. But, some failures around neck areas of turbine housing could not predict from thermal stress analysis. These cracks were originated due to the vibration excitations near resonance frequencies within engine operating ranges. The stress results of neck areas, which divided by temperature dependent yield stresses, from harmonic analysis showd a good agreement with experimental results.

This paper was studied on the characteristics of acid resistance and thermal shock for epoxy coatings in the strong acidic environment. The exhaust gas system, such as a air preheater, desulfurization equipment, for industrial boiler is damaged by dew point corrosion. To protect the acid corrosion, the coating using nonmetal was applied. The electrochemical polarization test, acid resistance and thermal shock test for epoxy coatings were carried out. And the acid resistance and thermal shock characteristics, aspect, and electrochemical anti-corrosion characteristics for epoxy coatings in the strong acidic environment were considered. The main results are as followings: As the epoxy glass flake coating by acidic thermal shock was damaged to the crack, blistering and elution etc., the current density of epoxy glass flake coating is high. But the damage of epoxy metal complex coating by acidic thermal shock was not occurred. Therefore the characteristics of acid resistance and thermal shock for epoxy metal complex coating is better than those for epoxy glass flake coating.

The microstructure and mechanical properties of nanocomposites synthesized by chemical processing were investigated. The nanocomposites containing 15 vol% hexagonal BN (h-BN) were fabricated by hot-pressing powders covered with turbostratic BN (t-BN). The t-BN coating on particles was prepared by heating particles covered with a mixture of boric acid and urea in hydrogen gas. TEM observations of this nanocomposite revealed that nano-sized h-BN particles were homogeneously dispersed within grains as well as at grain boundaries. The strength and thermal shock resistance were significantly improved in comparison with the microcomposites.

자동차, 항공기 및 기타 산업에서 복합재료의 사용은 증가되어 왔고 활발한 연구가 진행되고 있다. 이러한 복합재료중의 하나인 carbon-epoxy 복합재료의 열 특성에 관하여 알아보았다. 반복적인 냉각과 가열이 부가된 후 복합재료의 탄성계수의 변화를 관찰하여 봄으로써 복합재료가 가지고 있는 여러 열 특성에 관하여 여러 열 특성에 관하여 연구하였다. 이 연구에서는 G(sub)13값은 약한 감소하기는 하였으나 별다른 변화를 보이지 않았으며 열충격의 경우가 열피로의 경우보다 변화량이 작았다. E1값은 가해진 온도와 가열 횟수에 따라하여 조금씩 증가하였고, E2, G(sub)23값은 열피로의 경우 처음에는 어느 정도 그 값이 감소하나 가해진 횟수에는 큰 영향을 받지 않았으며 열충격의 경우에는 온도에 따라 다른 현상을 보였다.

본 연구에서는 국내에서 가장 취약할 것으로 예상되는 원자력 발전소에 가압열충격 사고를 유발할 수 있는 주증기관 파단사고를 가정하여 열수력 해석과 파괴역학 해석을 수행하였다. 원전수명관리연구의 일환으로 계통열수력 해석 및 혼합열유동 해석에 의하여 구한 냉각제의 온도와 압력의 이력 및 용기의 재질성분으로부터 용기의 응력확대계수와 파괴인성치를 계산하고 이들을 비교하여 균열의 진전여부를 판단하여 형상계수가 1/6인 표면균열이 견딜 수 있는 최대 기준무연성천이온도를 결정하였다.

We have evaluated the role of Ag additions on the strength, fracture toughness, elastic modulus and resistance to thermal shock of (YBCO) superconductor. Addition of 10 vol.% Ag improved strength and fracture toughness, whereas, decreased elastic modulus of YBCO. In addition, YBCO-Ag composites improved resistance to thermal shock probably due to enhanced strength, fracture toughness and thermal conductivity as a result of Ag addition. It is to be noted that YBCO-Ag made by mixing with solution showed slightly higher strength, fracture toughness and resistance to thermal shock, compared to that made by mixing with metallic Ag powder. These improvements are believed to be due to the microstructure of more finely and uniformly distributed Ag particles.

본 연구에서는 가압열충격 사고로 소형 냉각재 상실사고를 가정하여 냉각재의 온도와 압력의 이력으로 부터 용기 벽의 온도분포를 구하고, 이로 부터 열응력과 압응력을 해석적으로 구하였다. 또 균열 선단에서의 응력강도계수와 파괴인성치를 ASME코드의 방법을 이용하여 구하였고, 이들을 시간에 따라 비교하여 균열의 진전여부를 평가하였다. 원자로 용기 벽에 존재하는 여러 형태의 균열이 견딜 수 있는 최대 기준무연성천이온도를 결정하였으며 평가 결과에 대하여 고찰하였다.

본 논문에서는 가압열충격의 파괴역학적 해석에 필요한 이론을 조사하였고 원자로용기의 구조건전성을 평가하기 위하여 해석과정을 전산화하였다. 우선 사고 transient에 대하여 원자로용기내의 압력과 주입되는 냉각재의 온도변화가 주어지면 이들로 부터 시간에 따른 용기에서의 온도와 응력분포를 구하고, 중성자 조사량과 용기 재질의 화학성분으로 부터 기준무연성천이온도의 분포가 구해지며 이로부터 파괴인성치 KIA와 KIC의 분포가 얻어진다. 또한 응력분포로 부터 균열의 크기 및 형상에 따라 응력확대계수 KI이 구해지므로 이를 KIA및 KIC와 비교함으로써 균열의 성장거동을 예측할 수 있다. 지금까지 보고된 가압열충격을 유발할 수 있는 대표적인 사고 transient가 국내 발전소에 발생할 경우를 가정하여 해석을 수행하였고 그 결과에 대하여 검토하였다.

PAN계 탄소섬유와 페놀수지를 이용하여 rod를 인발성형 한 후, 다른 섬유분율을 갖는 두종류의 hexagonal type 4D 프리폼을 제작하였다. 석탄계 핏치를 가압함침 탄화공정을 통하여 함침한 후 탄화와 고온열처리를 하였다. 이와 같은 공정을 반복하여 고밀도화된 4D CRFC를 제조하였다. 열충결 시험 후 새로운 크랙이 생성되었을 뿐만 아니라 기존의 크랙이 확장되었으며 이와 같은 크랙들은 공기와의 접촉면을 제공하여 중량감소를 보였다. 공기 산화 저항성을 고온열처리 공정을 거친 것이 약 20% 우수하게 나타났다. 4D CFRC의 밀도와 섬유의 분율이 높을 수록 삭마 저항성이 커지고, 삭마량은 시간에 따라 선형적으로 증가하였으며 type II가 type I보다 삭마저항성이 우수하였다. 삭마 메카니즘을 관찰한 결과 1차적으 기질의탈리가 먼저 일어난 다음 섬유가 삭마되었다.