Thermal Shock Fracture Toughness Research Articles

High-performance concrete reinforced with fibres from waste

An experimental test programme was conducted to study the effectiveness of high-performance concrete (HPC) made with Algerian natural pozzolan (NP) and reinforced with steel fibres derived from electrical waste. For this purpose, Algerian NP was used as a filler and as a partial cement replacement in HPC. Fibres from electrical waste were employed to improve engineering properties such as flexural strength, thermal shock strength, fracture toughness and resistance under fatigue and impact. The laboratory programme was carried out to determine the isolated effect of NP (10, 15 and 20% by weight of cement) and the combined effect of NP/silica fume (SF = 8% and NP = 10, 15 and 20% by weight of cement) on the compressive and flexural strengths of HPC reinforced with 3% fibres derived from electrical waste.

Thermal Shock Tests and Thermal Shock Parameters for Ceramics

Thermal shock test methods and thermal shock parameters for ceramics were reviewed from the following viewpoints: (1) The test methods should be based on the precise estimation of both temperature and thermal stress distributions in a specimen taking into account the temperature-dependent thermo-mechanical properties; (2) The thermal shock parameters must be defined as a physical property of the materials and described as a function of temperature at the fracture point of the specimen; (3) The relation between the strength and fracture toughness of brittle ceramics under a thermal shock load must be the same as the relation under a mechanical load. In addition, appropriate thermal shock parameters should be defined by the thermal shock strength and thermal shock fracture toughness based on stress and energy criteria, respectively. A constant heat flux method is introduced as a testing technique suitable for estimating these thermal shock parameters directly from the electric power charged.

Estimation of thermal shock resistance of fine porous alumina by infrared radiation heating method

The thermal shock resistance of α-alumina porous capillary, the support material for hydrogen-permselective microporous ceramic membrane was studied. To study the effect of porosity on the thermal shock resistance systematically, porous alumina with different porosities was fabricated, and the thermal shock resistance of the fabricated samples as well as the porous capillary was estimated by the infrared radiation heating method. The mechanical and thermal properties concerned to the thermal shock resistance were also measured and the effect of the porosity on the properties was carefully examined. The fracture strength was not changed with temperature, but decreased with the porosity. The fracture toughness, Young's modulus and thermal conductivity were also decreased with porosity. Thermal shock resistance of porous alumina was estimated quantitively by the experimental thermal shock parameters, thermal shock strength, R1c and thermal shock fracture toughness, R2c. The thermal shock parameters of porous alumina were much lower than dense alumina, and decreased with porosity due to the decreasing of fracture strength and thermal conductivity. The experimental thermal shock strength was good accordance with that calculated from the material properties in this study. Thermal shock strength of porous alumina capillary at service temperature could be estimated by the comparison experimental and calculated thermal shock strength.

Estimation of Thermal Shock Resistance by Infrared Radiation Heating and Water Flow Cooling Techniques

Thermal shock is a mechanism often leading to failure of ceramic materials that may occur during rapid heating or cooling. These tests were performed in order to compare the thermal shock resistance of ceramic materials by cooling with that of the heating method and hence to evaluate parameters such as thermal shock strength (R1c) and thermal shock fracture toughness (R2c). During the present study, thermal shock resistance of alumina and mullite ceramics was estimated experimentally and theoretically using the thermal shock parameters. The critical thermal stress at the onset of thermal shock fracture was calculated using fracture time, which is measured by an acoustic emission. Results show that thermal shock parameters of alumina specimens decreased with increasing temperature of fracture point. This effect can be attributed to the temperature dependence of the thermal properties. The experimental values of thermal shock parameters evaluated by IRH and WFC techniques were in good agreement at the temperature of fracture point. The thermal shock parameters enabled the definition of a unified thermal shock resistance of ceramics, which is independent of the nature of the testing techniques.

The initiation and propagation of thermal shock cracks in graphite

Thermal shock resistance of a commercial grade of graphite was studied using an arc-discharge test. The thermal shock fracture initiation and crack propagation behaviour of the graphite disks at different input power levels were determined and analysed using fracture mechanics. The temperature gradient was measured experimentally and the profiles were force fitted with an even fourth-order polynomial. The thermal stresses were calculated from the force fits. A radial notch was introduced to the disk specimens to enable calculation of the thermal stress intensity factors. The crack mouth opening displacement was monitored using a special displacement transducer. The thermal stress and stress intensity factors were found to increase with increasing input current (and hence increasing thermal gradient). The thermal shock fracture toughness determined using the arc-discharge technique was found to increase from 0.8 to 1.4 MPa m 1/2 at temperatures from 220 to 420 °C. The longer the notch length, the shorter the time to crack, the smaller the crack mouth opening displacement jump and the shorter the unstable crack growth.

Thermal Shock Testing of Ceramics for Circuit Substrates

Thermal shock resistances of commercially available aluminum nitride and alumina ceramics as used for the circuit substrate were evaluated by infrared radiation heating (IRH) technique. Thermal shock fracture toughness, R2c of these materials was estimated experimentally and theoretically using IRH technique at various ambient temperatures. Temperature dependence of thermal properties of the materials was taken into account for the temperature and the thermal stress analysis. Experimental values of thermal shock fracture toughness were in good agreement with the calculated values. Thermal shock fracture toughness decreased with elevated ambient temperature in both ceramics.

Evaluation of thermal shock strengths for graphite materials using a laser irradiation method

Thermal shock is a physical phenomenon that occurs during the exposure to rapidly high temperature and pressure changes or during quenching of a material. The rocket nozzle throat is exposed to combustion gas of high temperature. Therefore, it is important to select suitable materials having the appropriate thermal shock resistance and to evaluate these materials for rocket nozzle design. The material of this study is ATJ graphite, which is the candidate material for rocket nozzle throat. This study presents an experimental method to evaluate the thermal shock resistance and thermal shock fracture toughness of ATJ graphite using laser irradiation. In particular, thermal shock resistance tests are conducted with changes of specimen thickness, with laser source irradiated at the center of the specimen. Temperature distributions on the specimen surface are detected using type K and C thermocouples. Scanning electron microscope (SEM) is used to observe the thermal cracks on specimen surface.

Evaluation of Thermal Shock Fracture Toughness for ATJ Graphite Using Laser Irradiation Method

Graphite has been developed as heat resistant material. To apply a reliable structural design using graphite, it is very important to investigate thermal shock characteristics. The common experimental methods of thermal shock fracture toughness are quenching and arc discharging heating methods. This paper describes experimental technique to evaluate the thermal shock fracture toughness using laser irradiation and proposes that a critical value of laser power can be a measurement to evaluate heat resistant materials. The laser source is CO2 laser having maximum power of 4.0kW. The range of laser beam is from 1.0 to 2.7 kW and the beam duration is fixed at 1sec. K and C type thermocouples were used to measure the temperature distribution of a thermal shock fracture toughness specimen. In this study, the temperature distribution of specimen surfaces and critical laser power was investigated. After test, the surface phenomenon of specimen is examined using radiography and SEM. It is concluded that the critical laser power causing fracture can be the major factor of thermal shock fracture toughness of ATJ graphite.

Evaluation of the integrity of divertor models of tungsten or SiC/SiC composites joined with copper

From viewpoints of thermal shock resistance, control of plasma particles, low activation, thermal efficiency and so on, it is planned to use heat-resisting metals and ceramic composites as plasma facing materials for the next experimental, demonstrative and commercial fusion reactors. In this study, a tungsten material and SiC/SiC composites were joined with oxygen free copper as a heat sink material using foils of titanium and copper, and a molybdenum plate was also inserted for the relaxation of residual thermal stresses in the case of a SiC/SiC-copper joint. The divertor model specimens using the joining materials were manufactured and heat load tests were carried out. Thermal cracks in the tungsten material and delaminating cracks at the joining boundary of SiC/SiC composites were observed during several heat load tests. Therefore, tungsten and SiC/SiC composites need to be improved further with respect to the thermal shock resistance, thermal conductivity and fracture toughness.

Estimation of Thermal Shock Properties for Silicon Nitride Having High Thermal Conductivity.

Thermal shock fracture test using an infrared radiation heating (IRH) method was performed on alumina and two kinds of silicon nitride that have high and normal thermal conductivity. The thermal shock strength, R1c, and thermal shock fracture toughness, R2c, of these materials were estimated experimentally and theoretically, where the experimentally obtained values, which were termed experimental R1c or R2c, were measured by the IRH technique, and the theoretical values were calculated using material properties, which were termed calculated R1c or R2c. The results revealed that the silicon nitride having high thermal conductivity showed three-fold higher R2c value than the silicon nitride with normal thermal conductivity. A technique for estimating the R1c value using the experimental R2c was also developed, because it is difficult to measure the thermal shock strength, R1c, for materials with high thermal shock resistance, using the IRH technique, due to insufficient heat flux.

The thermal shock resistance of a joining material of C/C composite and copper

Plasma facing materials for the next fusion reactor devices will have severe problems such as thermal shock fracture, surface erosion and injection of sputtering particles to plasma caused by charged particle fluxes and very high heat shocks. A joining material, in which a carbon fiber reinforced carbon composite was joined to oxygen-free copper by inserting a molybdenum plate and some metallic films in the joining layers, was developed for a solution of those problems. The thermal shock resistance and the thermal shock fracture toughness were evaluated by an eccentric local heating method of arc discharge. The joining material did not fracture during severe thermal shock tests such as plasma disruption, however, thermal and delamination cracks were observed at the joining parts by scanning electron microscope (SEM). These results can be useful in contributing to the development and the safety design of plasma facing components for fusion reactor devices.

Estimation of Thermal Shock Fracture Toughness of Si<sub>3</sub>N<sub>4</sub>

An infrared radiation heating method was proposed previously as a new technique for estimating thermal shock strength and thermal shock fracture toughness of ceramics using a thin-circular disk with or without an edge crack, heated by infrared rays at the center with a constant heat flux. In this paper, thermal shock fracture toughness was measured by the above method in four kinds of silicon nitride. Temperature distributions, thermal stresses and stress intensity factors for the specimens were also analyzed considering the temperature dependent thermal conductivity, thermal diffusivity and thermal expansion of the materials. The experimental results show that the highest value of thermal shock fracture toughness was observed in the material having the higher thermal conductivity, which was developed by growing the grains and decreasing the amount of the grain boundary phase.

Thermal Shock Resistances of a Joining Material of C/C Composite and Copper.

The purpose of this study is to contribute to the development and safety design of plasma facing components for fusion reactor devices. We evaluated the thermal shock resistance and the thermal shock fracture toughness of a joining material which was used to join a carbon fiber reinforced carbon composite(C/C composite) to oxygen-free copper. We also examined the microstructures of the joining layers using a scanning electron microscope before and after thermal shock tests. The joining material did not fracture during the thermal shock tests. However, thermal cracks and delamination cracks were observed in the joining layers.

Thermal Shock Parameters of Ceramics Evaluated by Infrared Radiation Heating.

An infrared radiation(IR) heating method was used to evaluate thermal shock parameters(thermal shock strength and thermal shock fracture toughness)of float glass and alumina. This technique makes it possible to evaluate the parameters directly from the electric power of the IR heater. In this paper we discuss how the pertinent thermal shock parameters should be estimated both as physical properties of a material and as a function of temperature. The stress intensity factors for a disk with an edge crack were analyzed numerically under a thermal shock loading. The thermal shock parameters in both ambient and elevated-temperature environments were measured by the IR heating technique and the results were compared with predicted values, which combined such emperature-dependent properties of the material as Young's modulus, thermal conductivity, linear thermal expansion, and tensile strength or fracture toughness.

Thermal Shock Resistances of a Bonding Material of C/C Composite and Copper.

The purpose of this study is to contribute to the development and the safety design of plasma facing components for fusion reactor devices. We evaluated the thermal shock resistance and the thermal shock fracture toughness of a bonding material which was jointed a carbon-fiber-reinforced carbon composite (C/C composite) to oxygen-free copper. We also examined the microstructures of the bonding layers using a scanning electron microscope before and after thermal shock tests. The bonding material did not fracture during thermal shock tests. However, thermal cracks and delamination cracks were observed in the bonding layers.

サーメットの耐熱衝撃性評価ヘの赤外線放射加熱法の適用

Thermal shock resistance of cermets was tried to evaluate by the infrared radiation heating method that a thin circular disk is heated and fractured by infrared ray concentrated on the central area with a constant heat flux. Thermal shock fracture toughness R2c could be measured for specimens with an edge notch, while thermal shock strength R1c could not for the specimens without the notch. It was thought, however, that R2c might depend on radius of curvature of the edge notch. Using the data of R2c, thermal shock strength R1c was calculated from the consideration of stress concentration. As a result, it was considered that thermal shock strength R1c could be applied to evaluation of thermal shock resistance of cermet and thermal shock resistance of Ti(C, N)-Mo2C-Ni cermets increased with an increase in the content of nitrogen and Ni.

Thermal Shock Fracture Toughness by Infrared Radiation Heating Technique.

Thermal Shock Fracture Toughness by Infrared Radiation Heating Technique.

Thermal Shock Fracture Testing for Float Glass by Infrared Radiation Technique

An infrared radiation heating method was proposed previously as a new technique for estimating thermal shock resistance of ceramics, and a concept of thermal shock fracture toughness and stress intensity factors for a disk-shaped specimen with an edge crack was expressed. The method uses a thin circular disk which is heated by infrared ray at the central area with a constant heat flux. The technique makes it possible to evaluate the thermal shock strength, R1c, and thermal shock fracture toughness, R2c, directly from the electric power charged and the time to fracture, despite the fact that R1c and R2c consist of the thermal properties of the material tested. In this report, the thermal shock strength and the thermal shock fracture toughness for float glass at room and high temperature are evaluated by the infrared radiation heating technique, and shown as a function of temperature when the specimen failures. The thermal shock parameters obtained experimentally are also compared with the estimated values which are calculated by combining the temperature-dependent mechanical properties of float glass.

A New Testing Method for Thermal Shock.

Thermal shock testing should aim at determining a definite value for the thermal shock properties of materials, and the thermal shock properties should be characterized by two parameters : (1) thermal shock strength, which represents a material's resistance to fracture, and (2) thermal shock fracture toughness, which denotes a material's resistance to crack propagation. For effectual thermal shock testing, it is essential that these parameters should be evaluated directly from thermal loading. The arc-discharge heating method reported in a previous work enables an evaluation of these parameters directly from the electrical power charge. An infrared radiation heating technique proposed here will also make it possible to estimate these parameters directly from the charged electric power. This method can be applied to a wide range of ceramics.

Effect of cooling configuration on thermal shock fracture toughness of SiC

Experiments were carried out to establish a test method for thermal shock fracture toughness and to generate the experimental data for silicon carbide. A 20mm wide, 50 mm long, and 6 mm thick specimen having an edge crack in the central section was heated up to a given temperature and quenched in such a way that the crack mouth side of the specimen was sunk to a depth of 1 mm from the water surface. The thermal shock fracture toughness of SiC was greater than the fracture toughness obtained using a three-point bending specimen at the corresponding temperature. This was well explained from the fact that the normal stress component parallel to the crack line is greater than the perpendicular stress component near the crack tip in the thermal shock specimen. Time histories of the stress intensity factors for various values of a/W and two cooling methods were analysed by using the finite element method and appropriate conditions were determined.