Thermal Shock by Radiation Heating

Thermal shock on heating by radiation is described. It is shown that for bodies at low initial temperature, the transient thermal-stress solution to a good approximation can be obtained by considering the bodies to be subjected to a constant heat flux. Expressions are derived for the maximum radiation temperature to which bodies of simple shape can be subjected without fracture. The emissivity of the material is shown to be as important as the thermal and mechanical properties usually considered in thermal-shock theory. Good agreement is found between theory and experiment.     

Shock Compression and Spalling of Cobalt at Normal and Elevated Temperatures

Searching for a possibility of registering polymorphic transformations in cobalt under rapid extension, we measured free-surface velocity profiles of high-purity cobalt samples subjected to shock-wave loading at temperatures of 20–400 °C. In this temperature range, the spalling strength of cobalt at rates of its extension of 10⁵ – 10⁶ sec^–1 was measured, and the relaxation properties of this material under compression in the shock-wave front were estimated. In the experiments, we failed to observe expected wave-profile anomalies due to possible high-temperature polymorphic transformation of cobalt under extension. Most probably, the volume change due to transformation is too small to exert notable influence on the wave-profile structure. Key words: high-purity cobalt, shock compression, phase transformations, spalling strength, temperature.     

Thermal Shock Testing

Practical experience has shown that thermal shock tests do not lead to generally useful test data. This is probably due to the fact that thermal shock failure is a complicated function of the external thermal shock conditions and of the temperature functions of five different material properties. These five material functions appear in a different combination in almost every thermal shock case and cannot be extracted from thermal shock test data. It is recommended that these five properties and their temperature dependence be determined by separate standard tests, not employing thermal shock. If the five property functions are known, thermal shock tests proper can be used to determine the maximum thermal shock stresses in any device.     

Modeling of Thermal Spalling During Electrical Discharge Machining of Titanium Diboride

Erosion in electrical discharge machining has been described as occurring by melting and flushing the liquid formed. Recently, however, thermal spalling was reported as the mechanism for machining refractory materials with low thermal conductivity and high thermal expansion. The process is described, here, by a model based on a ceramic surface exposed to a constant circular heating source which supplies a constant flux over the pulse duration. The calculations were based on TiB₂ mechanical properties along a and c directions. Theoretical predictions were verified by machining hexagonal TiB₂. Large flakes of TiB₂ with sizes close to grain size and maximum thickness close to the predicted values were collected, together with spherical particles of Cu and Zn eroded from cutting wire. The cutting surfaces consist of cleavage planes sometimes contaminated with Cu, Zn, and impurities from the dielectric fluid.     

浅谈平板显示器用玻璃基板的生产

介绍了平板显示器用玻璃基板的特点（简称“FPD”玻璃),如液晶显示器玻璃,等离子显示器玻璃等。重点探讨了组分及生产工艺,同时阐述了其应用前景。     

凝胶注模堇青石-莫来石复相材料的制备及其抗热震性能

采用凝胶注模方法制备堇青石-莫来石复相材料,研究了聚乙烯醇对浆料稳定性、固化时间和表面氧阻聚的影响,分析了堇青石-莫来石复相材料的抗热震性能。结果表明,聚乙烯醇可提高粗颗粒悬浮体系的稳定性,增大浆料黏度,延长固化时间。聚乙烯醇还可以起到消除表面起皮、开裂的作用。通过控制浆料固相含量调节堇青石-莫来石复相材料的气孔分布,从而影响其热震稳定性。当浆料中堇青石-莫来石固相体积分数为41%～44%时,堇青石-莫来石复相材料的热震稳定性最好。     

Improving Thermal Shock Test Reliability

The failure rate required of surface mount multilayer ceramic capacitors is so low that testing at use conditions will not detect important shifts in reliability performance. Multilayer ceramic capacitors manufactured from various dielectrics were tested at multiple temperatures to develop a sensitive test and to understand failure mechanisms occurring during wave solder. Test temperatures of the solder wave ranged from 240° to 450°C. Effects of preheat, flux type, and machine differences, as well as various termination and plating parameters, were also evaluated. Results from these production experiments were used to develop test conditions to screen commercial parts to 1 or 2 orders of magnitude lower failure rates and to study production processes and materials to further improve the reliability of ceramic chip capacitors. This paper documents the steps in developing an accelerated thermal shock test.     

抗热震陶瓷材料的设计

随着高技术陶瓷的应用发展，迫切需要提高陶瓷材料的抗热震性，以适应各种恶劣的应用环境，本文讨论了各种抗热震性能优良的陶瓷，提出抗热震陶瓷的设计思想。     

Thermal Shock Behavior of Iron-Particle-Toughened Alumina

The thermal shock behavior of an alumina monolith and two alumina–iron ceramic-matrix composites has been investigated by superimposing the measured K _R-curves of the materials onto the theoretically generated curves of the thermally induced stress intensity factor. Predictions of the critical-temperature differentials and retained strengths after quenching are in good agreement with the experimental data. The inclusion of metallic particles into an alumina matrix improves the thermal shock resistance, although the increase in toughness is not solely responsible for this improvement. There is a decrease in thermal stress-intensity factor that is generated for the composites; this decrease is due to a reduction in the Young's modulus and/or Biot modulus. However, the increased toughness for large crack lengths may offer increased damage resistance for severe thermal shock treatments.     

莫来石-堇青石耐火材料的抗热震性

已经研究了在热震条件下，骨料尺寸对莫来石-堇青石样品强度减小的作用。被震样品的强度减小显示依赖于骨料的尺寸、被烧结样品的预震强度及堇青石的含量。热震后的残余强度在由细骨料制备的样品中有所增加，这是由于其较高的初始强度。这些样品含有较低量的堇青石，其结果是由于减小了骨料颗粒的尺寸而导致了堇青石分解的增加。     

Thermal Shock Resistance of Ladle Castables

High purity alumina-spinel( A-MA) and alumina-magnesia( A-M) castables are widely used in steel ladles due to their resistance against slag penetration and corrosion. With a calcium magnesium aluminate bond( CMA) excellent slag penetration resistance can be achieved which results in high wear resistance due to reduced structural spalling. This paper investigates the impact of matrix compositions and CMA-binder content of A-MA and A-M castables on thermal shock resistance( TSR). Standardized thermal shock tests have been applied with sample quenching from 950 ℃ down to room temperature. Results show that all castables are significantly damaged after 5 cycles despite their differences in microstructure. However,the mix with 12%CMA gave TSR that is at similar good level as the reference mix with 6% CAC( 70% alumina cement). While a similar strength level was achieved before and after the thermal cycling,the formulation with 12% CMA contains 0. 6% less total Ca O. The A-MA castables perform better on average than the A-M mixes with this test method. Within the group of A-M castables the mix with 18% CMA and 0. 5% SiO_2 gave superior TSR,similar good as castables of the A-MA group. The introduction of CMA in an A-M castable allows reduction of free Mg O and SiO_2-addition. The reduction of SiO_2 has been found beneficial for the TSR. This was also found during a thermal cycling trial at high temperature between 1 100 and 1 500 ℃. Here the A-M mix with18% CMA and 0. 5% SiO_2 performed better than the SiO_2-free A-MA castable.     

含碳耐火材料的抗热震性

由于抗热震性评估的综合过程所涉及的费用和时间，通常选用有良好导热性的含碳耐火材料。文中探讨了USIMINAS为确定浇注钢包用含碳耐火材料抗热震性所用的方法。所采用的检测方法涉及到根据裂纹开口位移和热震参数(R″″和Rst)测定断裂功。现已证实这种方法对选择和研究合适的显微结构借以延长耐火材料内衬寿命是有用的。     

Thermal Shock Resistance of Ceramic Foams

Thermal shock behavior of a variety of open-cell ceramic foams was evaluated using infrared heating and forced air cooling. The extent of damage after thermal shock was determined by a nondestructive, dynamic resonance technique. The damage in foams was found to be strongly dependent on cell size and weakly dependent on density. In zirconia-based foams, damage was found to increase with an increase in zirconia content. A thermal stress resistance parameter R '_f was derived to predict the effect of cell size and density on the damage incurred in foams. The experimental results were found to corroborate the predictions fairly well but a better approach was to compare the maximum applied thermal strains with the degree of damage.     

Thermal Shock Behavior of Duplex Ceramics

The thermal-stress fracture behavior of duplex ceramics is investigated by quenching in water and in oil. Comparison with the matrix materials shows that the critical quenching temperature difference, Δ T _c , is not or is only slightly reduced, even for duplex ceramics of significantly reduced strength. In sintered composites, thermal-stress-induced microcracking within pressure zones and crack initiation at pressure zone–matrix interfacial defects develop before Δ T _c is reached. The effects are accompanied by a gradual reduction in strength. At Δ T _c , critical crack propagation occurs. The retained strength after thermal shock of duplex ceramics is significantly improved compared with the respective matrix materials. This behavior can be related reasonably well with the K ^R -curve behavior.     

低水泥耐热浇注料抗热震性的研究

研究了5批以粘土熟料作骨料的低水泥耐热浇注料的抗热震性。查明了含有5%～16%二氧化硅细粉时对浇注料抗热震性的影响。分析了当一次加热至1300℃时对浇注料抵抗冷热交替能力的影响。受冷热交替作用之后,浇注料试样表面形成裂纹的观察结果与在浇注料试样中超声波脉冲传播速度及其抗热震性的数据是有相互关系的。     

Indentation Thermal Shock Test for Ceramics

This paper presents an indentation-quench method to determine the resistance of ceramics to thermal cycling. The method defines a critical quench temperature difference, Δ T _c, based on a criterion which includes a minimum amount of crack growth and a minimum fraction of growing cracks. The method is applied to three different materials, which are ranked according to the individual values of Δ T _c. The variation of ΔT_c with different indentation loads and indentation positions is investigated. This technique uses a small number of specimens, avoids subsequent mechanical testing, and provides information about the ΔT C of the materials. The effect of repeated cycling on crack extension is also discussed.     

保温陶瓷的抗热震性研究与探讨

闭孔发泡陶瓷保温装饰产品属于战略性新兴产业,它作为绿色陶瓷的代表性产品,近年来从无到有,再到进入国家绿色建材产品序列,许多科技工作者为之付出了努力。由于生产者和建设者对于建筑耐久年限的误解,导致许多研究者、生产者和销售者产生诸多困惑,如我国建筑平均寿命只有30年,保温陶瓷产品定价高,市场状况如何?保温陶瓷产品的耐久年限有没有必要设计为100年,又该如何设计?笔者从建筑设计年限、标准方法设计、保温陶瓷循环疲劳影响因素、循环疲劳研究价值几个角度作一陈述并与大家共同探讨。     

烧结的抗热震性赛隆材料

利用含有赛隆微米级细粉并加入CaO和Y2O3及Y2O3-Al2O3-MgO系共晶体制成了烧结试样。研究了材料的抗热震性、强度及热导率与加入剂种类和烧结条件的关系。     

基于盲孔法的ABS热焊板件残余应力测量

采用盲孔法对4种丙烯腈–丁二烯–苯乙烯塑料(ABS)热焊板进行了残余应力的测量,获得了这4种热焊板焊趾区的残余应力数据,结果发现,ABS经过热焊成型后容易在焊趾区形成较高的残余应力,随着测量时间的延长,热焊板焊趾区的残余应力逐渐增大,在测量7 min后释放完全。为了验证盲孔法应用于塑料热焊板残余应力检测的可行性,对ABS热焊板母材区和焊趾区以及热处理前后焊趾区的残余应力进行了测量,同时测试了4种热焊板的焊接强度,发现母材区的残余应力低于焊趾区,80℃热处理后焊趾区的残余应力比热处理前的低,残余应力较低的热焊板具有较高的焊接强度,这些结果均表明盲孔法对塑料热焊板件残余应力测量结果具有一定的参考价值。