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Compared with single-phase ceramics, the thermal shock crack propagation mechanism of multiphase layered ceramics is more complex. There is no experimental method and theoretical framework that can fully reveal the thermal shock damage mechanism of ceramic materials. Therefore, a multiphase phase-field fracture model including the temperature dependence of material for thermal shock-induced fracture of multilayer ceramics is established. In this study, the effects of residual stress on the crack propagation of ATZ (Al2O3-5%tZrO2)/AMZ (Al2O3-30%mZrO2) layered ceramics with different layer thickness ratios, layers, and initial temperatures under bending and thermal shock were investigated. Simulation results of the fracture phase field under four-point bending are in good agreement with the experimental results, and the crack propagation shows a step shape, which verifies the effectiveness of the proposed method. With constant thickness, high-strength compressive stress positively changes with the layer thickness ratio, which contributes to crack deflection. The cracks of the ceramic material under thermal shock have hierarchy and regularity. When the layer thickness ratio is constant, the compressive residual stress decreases with the increase in the layer number, and the degree of thermal shock crack deflection decreases. [ABSTRACT FROM AUTHOR]

Abstract The constitutive relation of micro-cracked ultra-high temperature ceramics deduced by energy method and the temperature-dependent critical energy release rate of ceramics were demonstrated in this paper. Taking advantage of the constitutive relation and temperature-dependent critical energy release rate, the thermal shock behavior of Al 2 O 3 had been simulated firstly with finite element method. Results showed that the crack patterns of simulation approximated in the experiments. That confirmed the accuracy of our model. The ZrB 2 -based ceramic was then used as an example to study the effects of the temperature dependence of crack propagation criterion on the evaluation of thermal shock resistance of ultra-high temperature ceramics. In addition, given that the cracks forming during thermal shock lead to discontinuities in the ceramic material and influence thermal conduction. The interaction between thermal shock cracks evolution and thermal conduction, and the corresponding effects on the thermal shock behavior of ultra-high temperature ceramics were studied for the first time. Results indicated that the thermal shock crack patterns and temperature fields were significantly different while the thermal conductivities at the cracks were different for identical thermal shock conditions. Therefore, in order to improve the accuracy of simulation and the evaluation of thermal shock resistance of ultra-high temperature ceramics, the temperature dependence of the crack propagation criterion and the interaction between the cracks evolution and thermal conduction must be taken into consideration. Graphical abstract Image 1 Highlights • A temperature-dependent constitutive relation of micro-cracked ultra-high temperature ceramics. • Temperature-dependent critical energy release rate. • The interaction between thermal shock cracks evolution and thermal conduction. [ABSTRACT FROM AUTHOR]

Alumina ceramic specimens that suffered a specific water quench thermal shock were used for three-point bending test at different temperatures to investigate the effect of thermal shock damage on flexure strength for the first time. Results indicate that the sensitivity of the alumina flexure strength to thermal shock damage decreased with increasing temperature. When evaluating the thermal shock resistance of alumina by using critical thermal shock temperature difference, which determined by thermal shock residual strength at room temperature, will result in one-sided conclusion for the thermal shock resistance of ceramics. The mechanism of sensitivity of alumina ceramic strength to the thermal shock damage at elevated temperature was analyzed by the microstructure of the facture surface with SEM images. Therefore, this study can provide references for engineering application of alumina materials and improve the understanding of thermal shock resistance for ceramic materials. [ABSTRACT FROM AUTHOR]

The effects of water entry postures on thermal shock behavior during quench tests were investigated for the first time using alumina ceramic. The differences in the crack patterns and residual strength for specimens with different water entry postures after the quench tests were shown. At the initial thermal shock temperature of 310°C, the average residual strength of the lateral posture specimens is 330.4 MPa, but the longitudinal ones' is 118.4 MPa. The results showed that water entry posture strongly affects the quenching thermal shock behavior; to better experimentally characterize the thermal shock resistance, the unified water entry posture during testing must be considered. [ABSTRACT FROM AUTHOR]

• Proposed a thermo-mechanical phase-field model with a temperature-dependent energy threshold. • The model eliminates the unexpected damage evolution at the intact places in experiments. • The 3D phase-field modeling results show strong agreement with the experimental results. Current theoretical and experimental methods cannot fully reveal the mechanisms of the rapid and complex thermal shock-induced crack initiation and propagation processes in ceramic materials. Herein, a three-dimensional (3D) coupled thermo-mechanical phase-field model (PFM) is developed for thermal shock-induced fracture with the consideration of the temperature dependence of material properties. Compared with other PFMs, the present model can eliminate the unexpected damage evolution at the initially intact area of materials by introducing a temperature-dependent fracture energy threshold. Both the two-dimensional (2D) and 3D phase-field modeling results of thermal shock-induced fracture show strong agreement with the experimental results. The net-like topologies of thermal shock-induced cracks on the specimen surfaces are captured. Specifically, the crack topologies on the bottom surface (i.e., the first part submerged in water) are significantly different from those on the top surface in 3D cases. These essential findings reveal the mechanism that the tensile part of the strain energy mainly dominates the thermal shock-induced cracking in ceramics. [ABSTRACT FROM AUTHOR]

To overcome the limitations of widely used criteria, maximum principal stress and maximum tension stress, in simulating and evaluating thermal shock resistance of ceramics for 3-dimension (3D) problems, a temperature-dependent critical fracture energy density criterion was proposed based on the force-heat equivalence energy density principle for the 3D thermal shock fracture problems of ceramic materials in this paper. Taking advantage of the criterion and finite element method, the thermal shock behavior of water quenching of cuboid Al 2 O 3 specimens with different temperature differences were simulated. The crack patterns of the simulation results were shown to be approximated in the experiments. Especially the essential features, the longitudinal main crack and crack branches, are embodied well in the simulation results. However, the thermal shock cracks obtained by using the criteria, maximum principal stress and maximum tension stress, failed to meet the experiments. The effects of water entry posture on thermal shock crack features revealed in the results confirm the efficiency of the criterion in 3D conditions of thermal shock fracture in this paper. Finally, the maximum temperature gradient, not maximum temperature difference, was found to be the main controlling factor which caused the fracture energy density to reach a critical value to produce thermal shock crack. • A temperature-dependent critical fracture energy density criterion was propose. • Thermal shock cracking behaviors of simulation agreed well with experiments. • The effect of water entry posture of the specimen was uncover by the criterion. [ABSTRACT FROM AUTHOR]

In this paper, the thermo-elastic fracture problems of functionally graded materials (FGMs) are thoroughly investigated based on a modified phase field model. In this model, the material constants and fracture toughness vary along a specified direction, the thermal conductivity and stiffness constants in the damaged regions are degraded by the phase-field variable, and the crack evolution is driven by the variation of elastic energy induced by the thermo-mechanical loading. Therefore, the temperature, mechanical and damage fields are coupled with each other. The validation of the present approach has been checked by comparing the present results with the analytical, numerical, and experimental results in literature. The examples of thermo-elastic tensile fracture and thermal shock cracking of FGMs are performed to investigate the influence of material heterogeneity and external thermal loading. Furthermore, the experimental phenomenon of crack deflection in FGMs has been captured by the present simulations. The present study provides a guidance for understanding the fracture mechanism, material design and safety assessment of FGM structures in engineering practice. • The thermo-elastic fracture of FGMs is studied based on a phase-field model. • Both the tensile fracture and thermal shock cracking of FGMs can be simulated. • Effects of material heterogeneity and heat load on fracture behavior are studied. • The present study guides the structural design of FGMs in engineering practice. [ABSTRACT FROM AUTHOR]

The ascending thermal shock resistance of ceramics is studied using a new, simple and efficient test method. The results show that our testing succeeds in developing internal cracks in the shocked specimen that are cause by tensile stresses, while there is no visible change in the surface morphology. This coincides with the failure mechanism of ascending thermal shock, and this has not been reported before. Considering there is no proper experimental characterization parameter for evaluating the ascending thermal shock resistance, we propose an experimental evaluation index called the critical temperature difference of rupture, which is defined as the temperature difference after which a sharp decrease of retained strength appears until fracture. The value of the critical temperature difference of rupture is determined by the microstructures and material properties. A method for modelling the critical temperature difference of rupture of a rectangular specimen is proposed. [ABSTRACT FROM AUTHOR]

The research for the thermal shock resistance of ceramic materials during the ascending thermal shock has great significance. In this paper, a simple test method for the thermal shock testing of ceramic materials during heating is developed by refitting the quenching furnace. The method can control the target temperature of thermal shock and temperature distribution in the surface of materials better compared to the existing commonly used testing methods. During the testing, the specimen is designed to fall into a furnace chamber with a desired thermal shock temperature accurately and momentarily. The retained flexural strength of the specimen after thermal shocking is obtained. The results show that the thermal shock resistance of ceramic materials is very sensitive to the thermal shock temperature. The retained flexural strength of specimen without optical cracks on the surface can degrade seriously owing to the emergence of cracks in the interior of materials. The microstructure evolution in the interior of materials such as the phase transition has great effect on the thermal shock resistance of ceramic materials. This study will provide the technical reserves and theoretical bases for the research of the thermal shock resistance of ceramic materials under heating. [ABSTRACT FROM AUTHOR]

The thermal shock behavior of ceramics with the cooling medium temperatures in the range 5 °C to 100 °C has been studied in detail by measuring the retained flexural strength after water quenching. The test materials is ZrO 2 (3Y). Results show that the thermal shock resistance of ceramics is very sensitive to the cooling medium temperature, even which is very low. When characterizing the thermal shock resistance of ceramics the effect of cooling medium temperature should be taken into account. A higher water-bath temperature may not correspond to a greater thermal shock resistance of ceramic materials owing to the effect of thermal shock initial temperature on the material properties. When the temperature difference in thermal shock is close to the critical temperature difference of rupture, a little change of which can cause a great change in the retained strength of materials. As the retained strength of materials is too sensitive to the temperature difference close to the critical temperature difference of rupture, it is unsuitable to use the critical temperature difference of rupture to characterize the thermal shock resistance of ceramic materials. This study shows some innegligible problems in the evaluation system for the thermal shock resistance of ceramic materials. [ABSTRACT FROM AUTHOR]