Temperature Dependent Fracture Strength Model Research Articles

Stress-Induced Microcracking and Fracture Characterization for Ultra-High-Temperature Ceramic Matrix Composites at High Temperatures.

In this paper, we estimated the temperature-dependent critical inclusion size for microcracking under residual stress and applied stress for particulate-reinforced ultra-high-temperature ceramic matrix composites. The critical flaw size and applied stress for the stable growth of radial cracks under different temperatures were also estimated. It was found that under a lower applied stress, the critical inclusion size was sensitive to the temperature. Under higher applied stresses, the sensitivity became smaller. For ceramic materials with pre-existing microcracks, the crack resistance could be improved by increasing the service stress when the service stress was low. As the temperature increased, the critical flaw size of the materials decreased; the applied stress first increased and then decreased. Finally, a temperature-dependent fracture strength model of composites with a pre-existing critical flaw was proposed. A good agreement was obtained between the model prediction and the experimental data. In this work, we show a method for the characterization of the effects of temperature on the fracture behavior of ceramic-based composites.

Fracture Strength Behaviors of Ultra-High-Temperature Materials

Abstract Ultra-high-temperature materials have been widely used as key components in high-end equipment. However, the existing studies are mainly conducted at room and moderate temperatures. Besides, they are mainly carried out by experiments. Theories on the temperature dependence of fracture strength are rarely reported. In this work, experimental methods for the ultra-high-temperature tensile properties of advanced materials and the elastic–plastic properties of coatings are developed, respectively, based on induction heating and radiation furnace heating technologies. A temperature-dependent fracture strength model for ceramics is proposed in the view of energy. The experimental methods and theoretical model are verified on the 2D plain-weave carbon fiber reinforced silicon carbide thermal structure composite, yttria-stabilized zirconia thermal barrier coating, and Si3N4 ceramics. The study shows that the mechanical properties of materials decrease significantly at ultra-high temperatures. The results are useful for the applications of ultra-high-temperature materials in thermal structure engineering.

Modeling the effect of temperature on first matrix cracking stress and fracture strength of cross-ply fiber reinforced ceramic-matrix composites

In this work, we proposed a temperature-dependent first matrix cracking stress model for cross-ply fiber reinforced ceramic-matrix composites (FRCMCs) first. It takes into account of the effects of interfacial shear stress and residual thermal stress as well as their evolution with temperature. Moreover, in order to characterize the effect of temperature on fracture strength, we defined the critical strain energy density associated with composites fracture, by which and the force-heat equivalence energy density principle, the temperature-dependent fracture strength model for cross-ply FRCMCs was established. The models’ predictions of first matrix cracking stress and fracture strength at different temperatures are in good agreement with experimental results available. This study not only advances our in-depth understanding of the quantitative relationship between temperature and mechanical properties of cross-ply FRCMCs, but also offers a powerful tool to predict the temperature-dependent first matrix cracking stress and fracture strength.

Temperature and critical flaw size evolution dependence of fracture strength of the concretes

The fracture strength of concretes at elevated temperature has attracted increasing attention owing to the great risk of exposing them to elevated temperatures. However, there are few theoretical studies on high temperature fracture strength of the concretes. In this paper, a novel and simple temperature dependent fracture strength model for the concretes was developed by using the Griffith energy method and a concept of energy storage capacity. The effect of critical flaw size evolution is considered by this temperature dependent model based on primary and simple method. It should be noted that this model has no any fitting parameter and can be used simply just with some basic material parameters which have the clear physical meaning. Excellent agreement was achieved between model prediction and experimental measurement.

A novel and convenient temperature dependent fracture strength model for the laminated ultra-high temperature ceramic composites

At present, no suitable and convenient model has been developed to predict variation tendencies of fracture strength of laminated ceramic composites with temperature. In this paper, a novel and quite simple temperature dependent fracture strength model for the laminated ultra-high temperature ceramic composites was developed based on energy theories–the Griffith energy criterion and a concept of energy storage capacity. The complicated problems of characterization of combined effects of temperature, change in critical flaw size and laminated structure parameters on fracture strength are solved by using primary and simple method. The model prediction agreed well with the experimental value. The novel model can be used to determine both fracture strength and change in critical flaw size of laminated composite at elevated temperature. It should be noted that the model has no any fitting parameter, which is an easy-to-use method for the engineering.

A novel theoretical model to predict the temperature-dependent fracture strength of ceramic materials

A novel temperature-dependent fracture strength model for ceramic materials is developed, based on a critical fracture energy density associated with material fracture comprising strain energy, the corresponding equivalent potential energy, and kinetic energy of atoms per unit volume. It relates the fracture strength at high temperatures to that at the reference temperature, the temperature-dependent Young’s modulus, the temperature, and the melting point. The model is verified by comparison with experimental data of ceramic materials. The model predictions and the experimental data are in excellent agreement with each other. As the Young’s modulus can easily be obtained by experiments and the melting point can easily be obtained by materials handbook, the model can easily predict the fracture strength of ceramic materials at arbitrary temperatures.

Characterization models for thermal shock resistance and fracture strength of ultra-high temperature ceramics at high temperatures

In this work, based on the traditional fracture mechanics theory and the fracture thought at high temperatures, the thermal shock resistance models for the ultra-high temperature ceramics (UHTCs) considering combined effects of temperature and microstructures are developed. The effects of microflaws including cracks and pores, grains and residual stress due to thermal expansion anisotropy on the thermal shock resistance and their evolution with increase of temperature are studied in detail. The study shows that there exists a dangerous zoon of temperature according to the much lower critical temperature difference of rupture of UHTCs. While introducing the micropores with suitable content and feature size into a UHTC significantly increases the thermal shock resistance of the material, and can eliminate the dangerous zone of temperature for thermal shock resistance. A temperature dependent fracture strength model for UHTCs is proposed. Excellent agreement is obtained between model predictions and experimental data. This work shows a method for quantitatively estimating effects of microstructures on the thermal shock resistance and fracture strength of UHTCs at high temperatures.

Temperature dependent fracture strength model for the laminated ZrB2 based composites

In this work, a new temperature dependent fracture strength model for the laminated ZrB2 based composites is developed by employing a temperature dependent fracture surface energy model and the classical fracture theories. The model unifies the effects of temperature, temperature dependent residual stresses owing to added reinforced particles and laminated structures, microstructures and laminated structures on the strength of laminated ZrB2 based composites into a single theory. Using the model, the effects of microstructures and laminated structure parameters on the strength of composites and their evolutions with temperature are studied in detail. The micro and laminated structure parameter optimizations for improvement of the material strength are discussed. The model is verified at different temperatures by comparison with experimental data of different laminated ZrB2 based composites. Excellent agreement is obtained between the model prediction and the experimental data.

The temperature-dependent fracture models for fiber-reinforced ceramic matrix composites

In this paper, based on a temperature-dependent fracture strength model and the theory of composite materials, two temperature-dependent fracture strength models for unidirectional and short random fiber reinforced ceramic matrix composites are developed. The effects of temperature, fiber content, fiber distribution, and matrix strength on the strength of fiber-reinforced ceramic matrix composites are included in the models. Furthermore, considering the effects of oxidation reaction for some kinds of fiber and size effect of unidirectional fiber on the strength of composites, a new temperature-dependent fracture strength model considering size effect and oxidation of reinforcing fiber is established. And good agreement between model predictions and experimental data indicates the applicability and rationality of our models. So the models can be used to predict the temperature-dependent fracture strength of fiber-reinforced ceramic matrix composites.

Effects of microstructures and flaw evolution on the fracture strength of ZrB2–MoSi2 composites under high temperatures

Based on the existing fracture theories and a temperature dependent fracture surface energy model, a temperature dependent fracture strength model for ZrB2–MoSi2 composites is established. The excellent agreement is obtained between the model predictions and experimental data. The model can be used for qualitative even quantitative analysis of the effect of SiO2 size on the strength of hot pressed composites under high temperatures, and to predict the temperature dependent critical flaw size of composites which thus can help us to discover the control mechanisms of material strength under different temperatures. The effects of microstructures and flaw evolution on the strength of ZrB2–MoSi2 under high temperatures are studied in detail using the model. The study shows that the critical flaw causing the failure of the hot pressed composites under high temperatures is related to the largest SiO2 grains. The fracture strength of materials is controlled by the combined effects of temperature, grains and flaws. Both with the increases of temperature and initial flaw size the sensitivities of fracture strength to grain size and flaw size decrease. During preparation of the composites reducing the initial flaw size should be firstly considered. Improving the starting powder purity and sintering method which could reduce the amount, sizes and their dispersion of dispersed phases present in the microstructure, MoSi2 grain size and initial flaw size would result in the greater strength of materials under high temperatures.

A new temperature dependent fracture strength model for the ZrB2–SiC composites

In this paper, based on a temperature dependent fracture surface energy model and the traditional Griffith fracture theories, a new temperature dependent fracture strength model for the ZrB2–SiC composites is developed. The combined effects of temperature, grain size, microflaw size and residual stress on the strength of ZrB2–SiC composites are included in the new model. According to the model, the temperature dependent fracture strength of materials can be easily predicted using some basic material parameters. The model is verified at different temperatures by comparison with experimental data of different ZrB2–SiC composites. Excellent agreement is obtained between predicted and experimental data of fracture strength of ZrB2–SiC composites.

The temperature-dependent fracture strength model for ultra-high temperature ceramics

Breaking down the entire structure of a material implies severing all the bonds between its atoms either by applying work or by heat transfer. Because bond-breaking is indifferent to either means, there is a kind of equivalence between heat energy and strain energy. Based on this equivalence, we assume the existence of a constant maximum storage of energy that includes both the strain energy and the corresponding equivalent heat energy. A temperature-dependent fracture strength model is then developed for ultra-high temperature ceramics (UHTCs). Model predictions for UHTCs, HfB2, TiC and ZrB2, are presented and compared with the experimental results. These predictions are found to be largely consistent with experimental results.