The thermal shock resistance of solids (original) (raw)
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Crack channelling and spalling in a plate due to thermal shock loading
Journal of the Mechanics and Physics of Solids, 2000
The propagation of a pre-existing edge crack across a ®nite plate subjected to cold shock has been studied. The plate, initially at uniform temperature, is exposed to a cold shock on one surface whilst three dierent types of heat transfer boundary condition are separately considered for the opposing face: cold shock, thermal insulation and ®xed temperature. For all three boundary conditions, the plate experiences tensile stress near the cold-shocked surface and compressive stressing near the mid-plane. Consequently, a Mode I edge crack extending into the compressive region may grow in one of three dierent modes: continued extension in plane strain, channelling and spalling. The thermal shock conditions governing each failure mode are quanti®ed, with a focus on crack channelling and spalling. The dislocation method is employed to calculate the energy release rates for plane strain cracking and steady-state channelling. For steady-state spalling, the energy release rate is obtained by an energy analysis of elastic beams far ahead and far behind the crack tip. Analytical solutions are also obtained in the short crack limit in which the problem is reduced to an edge crack extending in a half space; and the parameter range over which the short crack solution is valid for a ®nite plate is determined. Failure maps for the various cracking patterns are constructed in terms of the critical temperature jump and Biot number, and merit indices are identi®ed for materials selection against failure by thermal shock.
Four different types of rock materials from Eastern Black Sea Region of Turkey were investigated to determine their change in porosity as well as the degree of cracking, fracturing, disintegration and strength loss under heating-cooling cycles with variations in temperatures up to 300 Co. Cooling time and thermal strains of the rock specimens were also determined in this study. Totally, sixty rock core samples were tested to evaluate their physico-mechanical and mechanical properties. Thermal cycling was found to lead for increase in the porosity of the rocks, making new cracks, particle disintegration for two types of tested rocks and considerable losses in uniaxial compressive strength values of all the rock materials tested in this study. The purpose of this study is to investigate immediate changes in temperature values rather than step by step heating up to a target temperature. For instance, rock samples were directly put in 250 oC stove from a -50 oC cabin in the last and fifth thermal cycling. After the heating process, specimens were cooled in water and air. This study aims to be a usable reference to establish a thermal change procedure and improve a new testing method for determination of thermal fatigue durability of rock materials.
Using the ASME and BSI codes to predict crack growth due to repeated thermal shock
This paper examines the use of the ASME and British Standard codes to estimate the growth of cracks driven mainly by thermal shocks. Thermal shock loading of operating pressure equipment is a common occurrence, particularly in thermal power stations. The tensile stresses that are produced at the surface of a heated component exposed to a rapid thermal down shock can be high, particularly in the presence of stress concentrations. Repeated application of the thermal shocks may lead to crack initiation and crack growth.
Prediction of Thermal-Shock Resistance During Heating at Very High Rates
Journal of the American Ceramic Society, 1972
A method of treating spalling failure during initial heat-up is presented. The assumptions include very high rates of convective heating, failure at hot surfaces from shear stresses, statistical failure, and failure defined by multiple crack intersection. On the basis of this and other work, it is concluded that scale-model tests are, in general, inappropriate.
Crack patterns corresponding to the residual strength plateau of ceramics subjected to thermal shock
Acta Mechanica Sinica, 2012
The formation mechanism of the residual strength plateau of ceramics subjected to thermal shock is addressed. A set of thermal shock experiments of 99Al2O3 are conducted, where the thin specimens of 1 mm×10 mm×50 mm exhibit parallel through edge cracks, and thus permit quantitative measurements of the crack patterns. The cracks evolve with the severity of thermal shock. It is found that there is a correlation between the length and density of the thermal shock cracks. The increase of crack length weakens the residual strength, whereas the increase of crack density improves it. In a considerably wide temperature range, the two contrary effects just counteract each other; consequently a plateau appears in the variation curve of the residual strength. A comparison between the numerical and experimental results of the residual strength is made, and they are found in good agreement. This work is helpful to a deep understanding of the thermal shock failure of ceramics.
Proposal of new damage model for thermal shock based on dynamic fracture on the brittle materials
Journal of Non-Crystalline Solids, 2005
In the current paper, we propose that the mechanical resistance of the brittle materials under dynamic loading can be used to predict the thermal shock damage resistance via a new proposed damage criterion. The increase of the mechanical resistance based on high loading rate has been investigated by experimental methods for ÔLead Crystal GlassÕ including the static and dynamic loadings by universal ÔINSTRONÕ and Ôsplit Hopkinson pressure bars (SHPB)Õ. The relationship between the measured static and dynamic strengths of materials has been compared and developed via Tuler and ButcherÕs dynamic criterion. ÔModified Brazilian disk (MBD)Õ specimens are used to obtain indirect tensile stress concentration at notch tip. The fracture process under various loading rates has been observed by optical and scanning electronic microscope (SEM) to study the fracture phenomenon according to the high loading rate effect for Lead Crystal Glass. The dynamic stress due to high loading rates can be considered as the thermal stress during thermal shock phenomenon with high heat convection coefficient values which leads to high gradient temperature, low duration time and intrinsic damage feature like cracks and flakes for concerned material. The transient thermal stress analysis has been carried out by numerical method for MBD specimen subjected to rapid cooling condition. The numerical results and experimental dynamic resistance of selected material are utilized to develop a new semi-empirical damage criterion based on the continuum damage mechanics (CDM) including dynamic material resistance, critical thermal shock time which corresponds to maximum transient thermo-mechanical stress and heat convection coefficient evolution according to the thermal shock severity.
Thermal shock resistance of functionally graded materials
Acta Materialia, 2004
Transient temperature field and associated thermal stresses in functionally graded materials (FGMs) are determined by a finite element/finite difference (FE/FD) method. Temperature-dependent material properties are taken into consideration. Explicit expressions for one-dimensional transient thermal conduction in some common elements, such as plate, shell and sphere, are given. These expressions are useful for material engineers and scientists to determine the thermal stresses and strength distributions in FGMs for high temperature applications. Thermal shock fracture of a FGM plate is analyzed when the plate is suddenly exposed to an environmental medium of a different temperature. The admissible temperature jump that the materials can sustain is studied using stress-based and fracture-toughness-based failure criteria. The critical parameters governing the level of the transient thermal stress in the medium are identified. The thermal shock resistance of the FGMs is analyzed using both maximum local tensile stress and maximum stress intensity factor criteria.
INCAS BULLETIN, 2013
Protective layers of "hot parts" of the turbo engines as well as co-generative systems of energy industry are exposed to a combination of wear factors which may act together at high values. The main goal of the paper is the behavior of some advanced layers, duplex and triplex, multifunctional, ceramics in relation to the most complex wear factor and disturbing as well, the quick thermal shock. The quick thermal shock test installation designed and constructed by the INCAS covers the domain of some high gradients of heating/cooling and is currently integrated in a network of European infrastructure that evaluates the properties of functional layers for turbo engines. Micro-structure inter-and intra-facial changes gradually induced in ceramic structures are highlighted and on this basis their ranking and selection for application on physical parts are established.
Comparative analysis of three thermal fatigue experiments
Fatigue & Fracture of Engineering Materials & Structures, 2008
A B S T R A C T This paper presents an analysis of the ability of different criteria to predict fatigue crack initiation under thermal loading. More precisely the predictions of the number of cycles to crack initiation are compared with experimental results obtained using five different fatigue criteria in three types of thermal fatigue tests (namely the FAT3D, JRC and SPLASH test campaigns). This analysis has revealed that:
Experimental analysis on physical and mechanical properties of thermal shock d.PDF
The purpose of this study was to explore the changes of mechanical and physical properties of granite under different thermal loading effects. Uniaxial compression experiments studying the rules of the influence of temperature load on mechanical properties of granite were carried out. After high-temperature heating at above 600 °C, granite tended to have stronger ductility and plasticity as well as declined peak stress and compressive strength. Thermogravimetry -differential scanning calorimetry (TG-DSC) analysis results showed that, thermal load at different temperatures induced reactions such as water loss, oxidation and crystallization in the microstructure of granite, which led to physical changes of granite. Hence it is concluded that, heating can significantly weaken the mechanical performance of granite, which provides an important support for the optimization of heating assisted processing of granite. It also reveals that, heating assisted cutting technique can effectively lower energy consumption and improve processing efficiency.