Theoretical Research on Thermal Shock Resistance of Ultra-High Temperature Ceramics Focusing on the Adjustment of Stress Reduction Factor

Abstract

The thermal shock resistance of ceramics depends on not only the mechanical and thermal properties of materials, but also the external constraint and thermal condition. So, in order to study the actual situation in its service process, a temperature-dependent thermal shock resistance model for ultra-high temperature ceramics considering the effects of the thermal environment and external constraint was established based on the existing theory. The present work mainly focused on the adjustment of the stress reduction factor according to different thermal shock situations. The influences of external constraint on both critical rupture temperature difference and the second thermal shock resistance parameter in either case of rapid heating or cooling conditions had been studied based on this model. The results show the necessity of adjustment of the stress reduction factor in different thermal shock situations and the limitations of the applicable range of the second thermal shock resistance parameter. Furthermore, the model was validated by the finite element method.

The Effects of Constraint, Size and Aspect Ratio on Thermal Shock Resistance of ZNS Wave-Transparent Ceramic in its Actual Service

“…So R is the lower limit of the critical rupture temperature difference. In addition, although the second TSR parameter R' can reflect both mechanical properties and the thermal conductivity of materials, it still can't characterize the TSR correctly in many situations [18,28,29]. So the heat transfer condition and critical rupture temperature difference are used to characterize the TSR of ZnS plate in the calculation [24,25].…”

Zirconium-Doped Hybrid Composite Systems for Ultrahigh-Temperature Oxidation Applications: A Review

“…Zirconium-based ceramics belong to a different class of material called as ultrahigh-temperature ceramics (UHTCs), which have a melting point temperature more than 3000 °C. − In contradiction to their high melting temperature and impact strength, Feng et al, had reported that monolithic ultrahigh temperature ceramics are brittle materials with low values of fracture toughness and most of all have got poor thermal shock resistance (TSR) . TSR is an important parameter to be tested for the performance of high-temperature ceramics. − Many research groups have established that the TSR of a ceramics is sensitive to temperature and other external parameters, while Li et al, had reported that the TSR of UHTC also depends on mechanical and thermal properties and they fail at surfaces when the surface stress due to thermal shock exceed fracture strength. Also mathematical evaluation of mechanical properties have been undertaken for fracture at high time rate of thermal loads based on certain assumptions which state that the model (Figure ) is a two well-bonded plate, which does not consider the interface damage, there is no heat exchange between the UHTC plate and base plate, both the layers geometrically confirm with each other which make calculation easier, finally plate is continuous, isotropic, elastic, and is restricted in the domain of small deformation hypothesis.…”

“…The equations for the effective linear expansion in the ceramic layer then are given by eq : where Δ x 1 is the elongation in the ceramic plate without external restrictions and Δ x σ is the value of restricted elongation due to complementary compressive stress at the interface. From the above equation, it is evident that the net elongation of the system when assumed the changes in Young’s modulus ( Y c ) and Poisson’s ratio (μ c ) for ceramic material are devoid of temperature changes, could generate an internal stress σ in the ceramic plate plausibly at the interface, which was derived by Li et al, as shown in eq : Considering the above equation with the effects of temperature would be modified to eq .…”

“…The governing equation for CTDR by Wang et al, is as shown in eq where h is the heat-transfer coefficient, t S is the thickness of the ceramic plate, and R ′ is a constant parameter called as second thermal shock resistance parameter and is given by eq : Note that the physical properties of mechanical interest, such as the Young’s modulus and fracture stress, vary along with temperature as described by eq . where B 1 , B 2 , B 3 , and B o are material constants and Y o is Young’s modulus at ambient conditions. The fracture stress as a function of temperature is given according to Li et al, as in eq . In order to understand the dependence of the fracture stress with temperature, it has to be inferred from the function of Young’s modulus that it is dependent on temperature in a transcendental fashion and so does the fracture strength. It is mentioned that the term φ = 1 – belongs to a temperature-dependent fracture surface energy term and indicates that, as the operating temperature approaches the melting point, the ratio φ has a tendency to unity; as a result, the temperature-dependent fracture stress tends toward theoretical stress, leading to failure.…”

Improving the thermal shock resistance of ceramics by crack arrest blocks

“…However, the improvement of the thermal shock resistance always means the sacrifice of other material properties of the materials. The thermal shock resistance of the ceramics is not only related to their thermal properties, but also closely related to the interface structure of the ceramic materials [29][30][31][32][33][34]. Based on the microstructure of the wing membrane of dragonfly, Song et al [35] proposed a new method to pattern the surface of ceramics to a biomimetic nano-finned surface.…”