Simulation of thermal shock cracking in ceramics using bond-based peridynamics and FEM

The effects of moderate intensity ‘hot’ or ‘cold’ shock in brittle solids have been extensively studied, while much less is known about thermal shock response during large temperature variations. In this study, a combined finite element – peridynamics numerical procedure is proposed for the simulation of cracking in ceramic materials, undergoing severe thermal shock. Initially, Finite Element nonlinear heat transfer analysis is conducted. The effects of surface convection and radiation heat exchange are also included. Subsequently, the interpolated temperature field is used to formulate a varying temperature induced action for a bond-based peridynamics model. The present model, which is weakly coupled, is found to reproduce accurately previous numerical and experimental results regarding the case of a ‘cold’ shock. Through several numerical experiments it is established that ‘cold’ and ‘hot’ shock conditions give rise to different failure modes and that large temperature variations lead to intensified damage evolution.     

纳米改性Ti(C,N)基金属陶瓷的力学性能及抗热震性能

真空烧结制备了Ti(C,N)基金属陶瓷,测试了不同金属黏结相成分的纳米TiN改性Ti(C,N)基金属陶瓷的力学性能及抗热震性能.力学实验结果表明:金属相含量越多,材料的强度和断裂韧性越高,而硬度则越低.金属相含量相同时,Ni能提供更高的强度与韧性,而Co能带来更高的硬度.热震试验结果表明:热循环温度较低时,40%TiC-10%TiN-15%WC-14%Mo-20%Ni-1%C.50%TiC-10%TiN-15%WC-4%Mo-10%Ni-10%Co-1%C和50%TiC-10%TiN-15%WC-4%Mo-20%Co-1%C(质量分数,下同)3组试样缺口处裂纹的形成均存在一定的孕育期,随着循环温度的升高,孕育期明显缩短,裂纹的扩展速率加快;与金属相为4%Mo-20%Co的金属陶瓷抗热震性能相比,4%Mo-10%Ni-10%Co的较好,14%Mo-20%Ni的最好.扫描电镜观察表明:微孔洞的连通形成裂纹,裂纹主要沿陶瓷相晶界及金属相扩展.     

High‐performance heat‐sink composites incorporating micron‐sized inorganic fillers and Sn/In metal particles

A novel thermal‐barrier composite system was developed by incorporating fusible metal particles in the epoxy matrix system. Using the latent heat of melting, the Sn/In metal particles having melting temperature at 125°C were imbedded in the polymer matrix to suppress the thermal shock and transient temperature variation. The high‐density metal particles were successfully dispersed in the polymer matrix without sinking by incorporating inorganic particles of aluminum nitride (AlN) and boron nitride (BN), which desirably facilitated the heat dissipation to give a high thermal conductivity at around 10 W/m‐K. Under the repeated melting and cooling cycles, the spherical shape of metal particles and the latent heat of melting were retained demonstrating the reversible thermal‐barrier capability of the developed composite system. Under the constant‐heating conditions, it was validated that the temperature rise was delayed by the endothermic melting of Sn/In particles. The developed composite system could find various applications since it could minimize damages caused by the repeated thermal fatigue and/or accidental thermal shock. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Impact of cathode loss on plasma characteristics,microstructures and properties of 7YSZ coatings in PS-PVD

The slight changes in geometry and mass of the cathode of O3CP plasma torch during service life caused the variety of arc motion between the cathode and anode. The voltage appeared to rise first and then fall. In this experiment, the impact of cathode loss on plasma characteristics, microstructures and properties of 7YSZ coatings was investigated. Optical emission spectroscopy (OES) was used to characterize the plasma jet characteristics such as plasma temperature and electron number density. It is found that vapor deposition is the main deposition mechanism, and the microstructures of the coatings are mainly affected by the supersaturation and subcooling of the vapor phase, which determine the nucleation and growth of crystals. At the middle of cathode service life, the plasma temperature and electron number density are the highest and the powder is completely evaporated. High crystal growth rates and surface diffusion lead to large columnar crystals with large grain size. The best thermal shock resistance. The thermal shock resistance is the best in this case. When the cathode is in the beginning and end of service life, there are columnar grains with small size produced and many solid particles in the gaps due to diffusion difficulties generated by low temperature. Shadowing enhances to manufacture fine grains and few branches. The presence of solid particles prevents the release of thermal stress and reduces thermal shock resistance of coatings. Fine grains prevent cracks propagation to improve the bonding strength of coatings.     

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.     

Alumina/NiCu Laminate under Thermal Shock up to 1000°C: II, Prediction of the Laminate Behavior

In this investigation, a multilayered, multimaterial system with strong interface subjected to thermal shock loading was analyzed. The analysis was based on a one-dimensional spatio-temporal finite difference scheme of the temperature field, and the thermal residual stresses and zero misfit stress temperature were considered. Using a failure criterion based on crack initiation, the number of broken layers due to thermal shock and residual mechanical strength at room temperature could be predicted. Furthermore, the room temperature residual strength of the laminate as a function of thermal shock temperature was constructed, demonstrating steplike behavior. Using this model, the mechanical behavior of the alumina/NiCu laminate system subjected to thermal shock loading of up to 1000°C was predicted. The model revealed the superiority of this material system over monolithic ceramics under thermal shock conditions.     

Thermal shock resistance of porous ceramic foams with temperature-dependent material properties

The impact of temperature dependence of material properties on thermal shock resistance of porous ceramic foams is studied in this paper. Two cases of thermal shock are carried out: sudden heating and sudden cooling. Finite difference method and weight function method are employed to get the thermal stress field at crack tip. The effects of time dependence and temperature dependence of material properties on thermal shock behavior are analyzed. The thermal shock resistance is acquired based on two different criteria: fracture mechanics criterion and stress criterion. By comparison analysis, results show that taking temperature dependence of the material properties into account is crucial in the assessment of thermal shock resistance of ceramic foams. Cold shock fracture experiments of Al₂O₃ foams with different relative densities are also made, and the obtained results are in coincidence with theoretical results very well.     

Thermal Fracture Resistance of Ceramic Coatings Applied to Metal: I, Elastic Deformation

A study was made of the resistance to thermal fracture of four ceramic coatings of the cobalt-bearing ground-coat type applied to enameling-grade iron specimens. The study was made of coated-metal systems in the unsteady state, symmetrically cooled, and in the absence of viscous or plastic flow. Determinations were made of the elastic characteristics of the coating-metal composites, the effective coefficient of linear expansion, the temperature at which the coating and base metal were at dimensional equilibrium, and the temperature differential sufficient to induce coating fracture when water quenched. Coating-metal thickness ratios were correlated with the maximum specimen temperature withstood in water quenching without coating fracture. Studies indicated that ceramic coatings, after receiving a given thermal treatment, fracture when subjected to a thermal shock by a critical temperature differential. When no residual coating stress is present, thermal shock resistance is inversely related to the thermal expansion characteristics of the coating. The critical stress at which coating fracture occurs may be expressed as the sum of thermal and residual stresses developed in annealed systems in which viscous or plastic flow does not occur. Residual compressive stress in a coating is a major factor in improved thermal shock resistance. Increased thermal shock resistance is gained by decreased coating thickness.     

莫来石基复合材料研究进展

莫来石(3Al2O3· 2SiO2)陶瓷具有抗蠕变能力高、热膨胀系数和导热系数低、抗腐蚀性和抗热震性优异的特点,是一种很有前景的高温结构材料.它最显著的优势是强度和韧性随着温度升高不仅不会下降反而有所提高.然而,莫来石的室温力学性能较差,限制了它的广泛应用.针对如何提高莫来石的室温强度和韧性,目前的研究集中于利用第二相进行改性,取得了一定成果.本文介绍了非连续相(颗粒、晶须、短切纤维)和连续纤维增强莫来石基复合材料的研究现状,包括制备工艺、微观结构和主要性能,指出了存在的问题和今后的发展方向.     

Fe-Al/Al2O3复合材料与ZTA陶瓷的抗热震性研究

对Fe-Al／Al2O3复合材料的抗热震性进行了测定。通过与ZTA陶瓷的抗热震性对比，分析了该复合材料具有较好抗热震性的原因。试验发现：Fe-Al／Al2O3复合材料的残余硬度和抗压强度随AT的变化有明显差异。在热震温差很高时，Fe—Al相的高温热强性改善了Fe-Al／Al2O3复合材料的抗热震性。     

Thermal shock behavior of nano-sized ZrN particulate reinforced AlON composites

Aluminum oxynitride (AlON) has been considered as a potential ceramic material for high-performance structural and advanced refractory applications owing to its excellent stability and mechanical properties such as high rigidity and good chemical stability. Thermal shock resistance is a major concern and an important performance index of refractories and high-temperature ceramics. While zirconium nitride (ZrN) particles have been proven to improve mechanical properties of AlON ceramic, the thermal shock behavior has not been evaluated yet. The aim of this investigation was to identify the thermal shock resistance and underlying mechanisms of hot-pressed 2.7% ZrN–AlON composites by a water-quenching technique over a temperature range between 225 °C and 275 °C. The residual strength and Young's modulus after thermal shock decreased with increasing temperature range and thermal shock times due to large temperature gradients and thermal stresses caused by abrupt water-quenching. The presence of nano-sized ZrN particles exhibited a positive effect on the improvement of both residual strength and critical temperature difference of AlON ceramic due to the toughening effects, the higher thermal conductivity of ZrN, the refined grain size and the reduction of porosity. Different toughening mechanisms including crack deflection, crack bridging and crack branching were observed during thermal shock experiments, thus effectively enhancing the crack initiation and propagation resistance and leading to a considerable improvement in thermal shock resistance in the ZrN–AlON composites.     

Thermal Shock Failure in Thick Epoxy Coatings

In this paper we describe an apparatus for reproducibly measuring thermal shock resistance of thick polymer layers bonded to metals. The thermal shock behavior is discussed in terms of epoxy samples bonded to an aluminum substrate. It was found that both high resin toughness and low resin thermal expansion coefficient improved thermal shock resistance of thick coatings, but only a sample containing 60wt. % glass beads did not develop a failure crack. Effects of sample thickness, temperature gradient, and resin composition on thermal shock behavior are discussed.     

蜂窝陶瓷蓄热体的抗热震性研究进展

本文针对高风温燃烧技术和煤矿乏风瓦斯氧化技术的蜂窝陶瓷蓄热体,系统地综述了影响蓄热体抗热震性的因素,数值模拟分析了蓄热体在热冲击下的温度场和热应力场的分布特点,总结了蜂窝陶瓷蓄热体热震损伤机理等的研究进展情况,并提出今后的研究及发展方向。     

Study of the castable selection for blast furnace blowpipe

The contradictory properties required of castable refractories makes selecting castable refractories for industrial applications challenging. This paper seeks to describe the material selection for a blast furnace blowpipe application that is subjected to sudden temperature changes and must prevent heat loss. Three commercial high alumina castables containing andalusite or mullite from different manufacturers were characterized. Thermal shock damage resistance was evaluated using thermal shock damage resistance theory and experiments. The castables’ coefficient of thermal expansion was estimated using quantitative X-ray diffraction. Crack propagation resistance was measured using the work-of-fracture technique. Thermal shock damage was experimentally evaluated by measuring the modulus of elasticity and rupture prior to and after thermal cycles. Ultimately, the microstructure of the castables was related to the thermal shock damage behavior by estimating the aggregate size and the fracture toughening mechanisms using light optical and scanning electron microscopes. Heat loss was evaluated by calculating the blowpipe shell temperature using a one-dimensional steady-state heat conduction model. The best commercial castable refractory for blowpipe showed high thermal shock damage resistance and low thermal conductivity. The results in this study agreed with thermal shock damage resistance parameters and showed a correlation between coarse microstructure with large aggregate and higher thermal shock damage resistance.     

Effect of thermal shock cycling on the quasi-static and dynamic flexural properties of flax fabric-epoxy matrix laminates

The aim of the present work is to investigate the influence of thermal shock cycling on the quasi-static and dynamic flexural properties of epoxy matrix composites reinforced with natural flax fibers fabric. Polymer composite laminates reinforced with four plies of natural flax fiber fabric have been manufactured. The samples have been exposed to different number of thermal shock cycles (0, 50, 100, 200, 300, 400), at a temperature range from −40 °C to +28 °C. Dynamic mechanical analysis (DMA) tests were performed on both pristine and thermally shocked specimens in order to determine their viscoelastic response. Due to the thermal shock cycling and after 100 thermal shock cycles, a maximum decrease in storage and loss modulus on the order of 50% was observed. After 100 thermal shock cycles, no further degradation of dynamic properties was observed. On the contrary, damping factor and glass transition temperature values showed a minor variation as number of thermal shock cycles increased. In addition, the time–temperature superposition principle (TTSP) was successfully applied, confirming the fact that the flax fiber fabric-epoxy laminate is a thermo-rheologically simple material. Likewise, quasi-static three-point bending tests were executed and a maximum decrease of 20% in flexural strength was observed after 400 thermal shock cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48529.     

Thermal Shock Resistance of Zirconia with 15 Mole % Titanium

The thermal shock resistance of zirconia with 15 mole % titanium prepared either by cold-pressing and vacuum-sintering or by vacuum hot-pressing was determined by radially quenching disks with thermally insulated faces under various conditions of heat transfer. The thermal shock resistance of calcia-stabilized zirconia disks was determined for comparison. For quenches from below the transformation temperature range of zirconia, the thermal shock resistance of zirconia with 15 mole % titanium was much better than that of calcia-stabilized zirconia, but for quenches from above the transformation range it was slightly inferior. The thermal shock resistance of zirconia with 15 mole % titanium is fairly insensitive to the methods of manufacture used in this investigation. In an attempt to identify the physical properties responsible for the improved thermal shock resistance of zirconia with 15 mole % titanium, the heat capacity, thermal expansion, modulus of rupture, modulus of elasticity, and thermal conductivity as functions of temperature were determined.     

The Thermal Shock Resistance Analysis of Ceramic Foams

This article studies the thermal shock resistance behavior of ceramic foams under sudden thermal load induced by a sudden temperature variation. Two types of thermal shock loading conditions are considered: cold shock and hot shock. Variations of the stress and stress intensity factor with thermal shock time, location, crack size, medium thickness, and relative density of the ceramic foam are given. Crack growth behavior is studied and crack growth velocity is explained from energy equilibrium consideration. The thermal shock resistances of ceramic foams are established from the view points of energy criterion and fracture mechanics concept.     

SOME EFFECTS OF THERMAL SHOCK IN CAUSING CRAZING OF GLAZED CERAMIC WARE1

The characteristics of glazes are too frequently regarded as the only important factor governing the resistance of glazed ware to thermal shock crazing. In this investigation it was found that thermal shock crazing was caused, in some cases, by craze-like cracks which developed in the bodies. The importance of selecting suitable bodies, as a means of controlling crazing, became evident at once when it was found that bodies with a high resistance to thermal shock were not so liable to craze when glazed and subjected to sudden temperature changes as those with a low resistance to thermal shock. In general, glazed ware on which the glazes are under fairly high compression are more resistant to thermal shock crazing than those on which the glaze is under either low compression or tension. Glazed ware which is susceptible to thermal shock crazing may be resistant to moisture crazing and vice versa.     

Thermal Shock Damage Assessment in Ceramics Using Ultrasonic Waves

Structural ceramics are susceptible to microcrack damage by thermal shock. There is a critical temperature for thermal shock damage initiation with damage severity increasing at greater shock temperatures. In this work the applicability of an ultrasonic method to determine the critical temperature and the accumulated damage is demonstrated in alumina. Information is obtained via velocity and attenuation measurements using surface and obliquely incident bulk ultrasonic waves. The elastic anisotropy effect due to preferred crack orientation has been estimated. The critical temperature for the alumina is about 200°C. The damage increases steeply from 200° to 400°C and grows significantly above 400°C. Changes of up to 17% from the original values in the effective shear moduli and up to 45% in the longitudinal effective modulus in the direction transverse to crack orientation are measured at high thermal shock temperatures.