Elastic Thermal Stress Research Articles

Thermal elastic and elasto-plastic analysis of the supporting cone shell of a waste heat boiler

In order to provide the basis for research on the cause of an explosion accident of a waste heat boiler, thermal elastic and elasto-plastic stress analysis of the structural component containing a supporting cone shell has been performed. In this paper, an iterative method is proposed for the solution of the reaction on the structure component. An elasto-plastic axisymmetric finite element program, which is suitable for use on a personal computer, has been developed and proved by a standard numerical example. The elasto-plastic stress analysis of the region of the thermal elastic stress peak has been implemented by application of the program. The result shows that high plastic stress exists in the weld joining the inner shell and the supporting cone shell. This proves that production of high creep rate and serious creep damage in the region is inevitable, which coincides with the appearance of the structure failure.

Effects of viscosity on the continuous growth of dendritic silicon crystal ribbon

This paper investigates the effects of viscosity on the thermal stresses developed in a silicon ribbon during its continuous growth. Kelvin models are used to study the viscous behavior of silicon. A specialization of the general three dimensional model for the plane stress conditions is presented. Results of the numerical studies, based on the assumed constants of the Kelvin models, indicate that the viscosity of silicon reduces peak elastic thermal stresses and does notcause any residual stress in the ribbon. The instability of the numerical solution process is also studied and various alternatives are proposed to avoid divergence of the numerical solution.

Theoretical Prediction of the Thermoelastic Properties and Thermal Stresses in Unidirectional Composites

A theoretical investigation is undertaken to predict the thermoelastic properties of com posites consisting of an isotropic matrix reinforced with either isotropic or transversely isotropic fibers. Both constituent materials are assumed to be elastic. The effects of the constituent material properties and fiber anisotropy on the elastic moduli and thermal ex pansion coefficients of unidirectional composites are evaluated for a square array model. The proposed expressions for the coefficients of thermal expansion are used in the analysis of unidirectional glass-epoxy and carbon-epoxy composites. The solutions for the thermo elastic properties and thermal stresses of the example problems considered in this study compare favorably with the existing results. The method of solution can be extended to ac count for the effect of inelastic strains.

Thermoelastic analysis of GaAs in lec growth configuration: II. Temporal evolution of the stress field

The temperature distribution in the growth system and the elastic thermal stress field in the growing crystal are calculated at three stages of the solidification process. Results indicate that at the early stages of growth excessive stresses are generated as the cone emerges from the encapsulant, and at later times the maximum stresses occur close to the solidification interface and the region where the crystal emerges from the encapsulant. Adjustment of heater power for reduction of stresses associated with excessive cooling of the crystal is found to be inadequate and result in enhanced convexity of the growth interface and generation of large stresses in that region.

Thermal elastic stresses in a notched bar constrained by hot surfaces. Application of the indirect fictitious boundary integral method to the thermal contact problem.

This paper describes the applicability of the indirect fictitious boundary integral method to the thermo-elastic contact problem. As an example, a notched bar constrained by two hot rigid surfaces in contact with both its end surface is treated. As a results, the isothermal line, the stress distribution etc., are shown.

Local elastic thermal stresses in a column (wall) with concave or convex surfaces.

Elastic thermal stresses in a column of wall, such as a boier wall, with concave or convex surfaces are analyzed by the indirect fictitious boundary integral method. As a example, we treat a wall, which has a cncavity (notch) or convexity (protrusion) on the one side of the wall and is heated on either side. As the results the temperature distributions and the thermal stresses were obtained and the influenced of shape parameters such as a depth of notch where observed. Also the availability of this method to this problem we shwon.

Grain-size dependence of fracture stress in anisotropic brittle solids

The stress concentrations that occur at grain boundaries due to thermal expansion anisotropy and elastic stress concentration are discussed, and the stress intensity factor that results from these stresses is estimated. The procedure for the stress intensity factor calculation is based on the model in which a spherical crystal (grain) is forced into a cavity of equal size possessing annular or radial cracks emanating from the boundary. The stress intensity factor equation thus obtained is extended to include the effect of elastic stress concentration due to the presence of a cavity, and is subsequently used to predict the grain-size dependence of strength in anisotropic brittle ceramics. In assessing the degradation of strength with increasing grain size in non-cubic ceramics, it is shown that, in addition to grain size, the effect of pre-existing crack size must also be considered. Cubic ceramics, on the other hand, are known to exhibit no thermal expansion anisotropy and, based on the present model, their strength is predicted to be governed by the pre-existing flaw size, rather than the grain size.

Dislocation motion and multiplication during the growth of silicon ribbon

The production and motion of dislocations during the growth of silicon ribbon by the dentritic web process is treated. Thermal elastic stresses are calculated from a temperature distribution defined along the growth direction of the ribbon. Dislocation motion and multiplication in the ribbon due to thermal stresses are monitored taking the ribbon crystallography into consideration and employing the Hassen-Sumino deformation model. The dislocation density and distribution obtained from the crystallographic considerations are compared with experimental observations of the defect configuration in silicon ribbon and similar computational results obtained assuming isotropic deformation conditions.

Heat conduction vs crystal defects in GaSb ingots grown by the vertical Bridgman method

GaSb growths were performed in a vertical Bridgman arrangement to clarify the role of the radial heat loss, as the source of the radial component of thermal elastic stresses, in the formation of dislocations. Using identical ingot shapes, the variation of growth conditions — including a space experiment — has proved that correct isolation of the ampoule wall from the convection currents of the furnace can considerably decrease the dislocation density. It is concluded that the existence of radial stresses in the growing ingot has to be taken into account in both the theoretical calculations and the development of crystal growing methods.

The use of an electrode potential in the investigation of a single‐crystal semiconductor matrix (I). On the nature of structural sensitivity of an electrode potential

AbstractThe fields of application of electrode potential measurement technique for the evaluation of structural perfection of single‐crystal semiconductor matrix are considered. The dependence of the silicon stationary potential on the value of elastic stresses in etching electrolytes is investigated. The structural sensitivity of the technique is confirmed by the investigation of planar anisotropy of mechanical damages due to the treatment of silicon wafers with (111) orientation and by the investigation of distribution of thermal elastic stresses in silicon — silicon dioxide interface.

Grain‐Size Dependence of Fracture Energy in Ceramics

A simple model incorporating thermal elastic anisotropy stresses is used to calculate the microcrack zone size around cracks in Al2O3. It is found that the ratio of microcrack zone size to grain size is almost constant for notched beam tests, but increases with grain size for double cantilever beam data. It is suggested that notched‐beam ratios of fracture toughness are related to crack initiation, whereas double cantilever beam values are related to propagation and reflect R‐curve behavior of the material.

Elastic Thermal Stresses in Bimetallic Pipe Welds

The elastic thermal stresses in a welded transition between two pipes of the same size but different alloys are explored. A stress-free temperature is postulated and the stress due to a uniform change in temperature is characterized by the maximum stress intensity in the weld. A simple expression for predicting this maximum stress intensity is developed based on the results of finite element analysis.

Non-linear elastic thermal stress analysis with phase changes

The non-linear elastic, thermal stress analysis with temperature induced phase changes in the materials is presented. An infinite plate (or body) with a circular hole (or tunnel) is subjected to a thermal loading on its inner surface. The peak temperature around the hole reaches beyond the melting point of the material. The non-linear diffusion equation is solved numerically using the finite difference method. The material properties change rapidly at temperatures where the change of crystal structures and solid-liquid transition occur. The elastic stresses induced by the transient non-homogeneous temperature distribution are calculated. The stresses change remarkably when the phase changes occur and there are residual stresses remaining in the plate after one cycle of thermal loading.

Thermal stresses in anisotropic discs

A general solution is given for the elastic thermal stresses in a solid or hollow anisotropic disc of constant thickness when subjected to a temperature rise which varies symmetrically in an axial direction and arbitrarily with the radius. Graphs demonstrate the variations of stress distribution and maximum stresses with the degree of anisotropy and other parameters.

Stochastic thermal stress analysis of clad cylindrical fuel elements

After a review of deterministic elastic thermal stress analysis by means of the displacement method for a cylindrical system in which the temperature distribution is not only radially variable but azimuthally and axially variable also, a method is shown for the determination of the statistical moments of the stress components when (a) the outer boundary of the cladding is a stochastic quantity, and (b) the uncertainties in the elastic and thermal constants of the materials and in the magnitude of the heat generation term are taken into account. A typical model is proposed for describing the statistics of the outer radius of the cladding which is a stochastic variable owing to uncertainties produced by the extrusion process. The theory is illustrated by means of a simple example by examining a meaningful reliability index and the relative importance of each of the uncertainties.

Numerische berechnung eindimensionaler instationärer temperatur- und spannungsfelder

A method for numerical analysis of one-dimensional transient temperature fields and elastic thermal stress fields is outlined and a FORTRAN-program is described. Results of parametric studies are given in diagrams. The computer program listing is reproduced in the Appendix.

熱による岩石の強度の変化あるいは破壊について

There has been a rapid increase of interest to unconventional methods of fracturing rocks.Particularly, mechanics of thermal fracture, either by the application of direct heat or electrothermal conversion, are most favourable for practice.In this paper, the authors reported their experiments to measure the strength changes of rocks heated to high temperatures and the thermal fracture.From the experiments, several fracturing mechanisms of rocks heated to high temperatures were found. Which are;a) Thermal elastic stresses induced in rock.b) Transformation of crystal form of the constituting minerals of rock.c) Decomposition of the constituting minerals.d) Melting.e) Thermal expansion of the constituting minerals.f) Others.Neverthless these mechanisms are all affecting to thermal fracturing of rock, one of them is a dominant factor to fracture a particular kind of rock by heat, for example b) to granite and c) to limestone.

Steady state thermal stresses in an elastic solid bounded by two cones

Es wird fur das Problem der Warmespannungen in einem kegelformig begrenzten elastischen Korper eine Ahnlichkeitstransformation entwickelt. Ist die Temperatur an der freien Oberflache als Potenz des Abstandes von der Spitze vorgeschrieben, so lasst sich ein Satz von Ahnlichkeitsvariablen angeben, welcher die thermoelastischen Beziehungen auf Legendre-Gleichungen reduziert und damit der Losung leicht zuganglich macht. Die Rechnung ist fur den Sonderfall konstant gehaltener Oberflachentemperatur im einzelnen durchgefuhrt.

Thermal Shock and Thermal Fatigue of Cast Iron

In recent years, the problem of thermal shock of metallic materials has been the subject of many studies, and several researchers have made fundamental works in this line. Surveying the previous works, it is found most of the studies on thermal shock are limited within the experiments on non-metallic materials, and so-called “thermal shock parameter” is defined as a criterion for thermal shock resistance. Thermal shock parameter is analysed from the concept based on maximum principal stress theory and elastic thermal stress therory. In the past study on nonmetallic materials such as ceramic, the thermal shock parameter is adopted as the measure of thermal shock resistance. However, this is true within the limited case of non-metallic materials. For the cases of most metallic materials, there are several questions as to criterion with which thermal shock resistance is evaluated. Furthermore, there is an open question as to the study on transition phenomenon from thermal shock fracture to thermal fatigue fracture. In this connection, it is necessary to establish the relation between thermal shock strength chracteristics and thermal fatigue strength characteristics.The authors, as well, have been interested in the problem concerned with thermal shock, and have done some works on the relation between tensile strength characteristics and thermal fatigue strength characteristics by employing heat-resisting metallic materials. In the present paper, the results of thermal shock tests for different heat-transfer conditions are presented, and the results are compared with those of thermal fatigue tests. Two types of tests of thermal shock and thermal fatigue are performed by solid cylindrical specimen of cast iron (3.79% C). Two sorts of heat-transfer conditions are realized by using air cooling and air mist cooling. Both tests are made by employing a conventional thermal fatigue test apparatus, and both ends of specimen are constrained at upper temperature level in thermal cycling. Maximum temperature level is chosen as 600°C.The results of the present study are summarized as follows:(1) Cast iron tested behaves transition phenomenon from thermal shock fracture to thermal fatigue fracture. Under air cooling condition (heat-transfer condition β=0.035), the material fractures at the begining of cooling path in the first cycling of temperature, when the upper temperature level is 500°C. If the upper level of temperature cycling is lower than 500°C cycle-dependent fracture occurs. On the other hand, under air-mist cooling condition (β=0.15), thermal shock fracture occurs for the case of the upper temperature level of 400°C. The parameter β is a non-dimensional heat-transfer coefficient and is denoted as β=r0h/k where r0 is outer radius of the specimen, h heat-transfer coefficient and k heat conductivity. The influence of heat-transfer condition on the temperature level under which such a transitional phenomenon occurs is related with the effect of increase in axial thermal stress at the outer surface of specimen due to multiaxial thermal stresses. In this case, the influence of strain rate on breaking strength of the material is not predominant.(2) From the results of thermal fatigue tests of which were carried out by taking the upper temperature level, the thermal strain amplitude and the thermal stress amplitude as variables, it is found that number of cycles to fracture is shorter in the case of air mist cooling condition than the case of air cooling condition. This trend is interpreted by taking account of plastic deformation produced in the material during a cycle of thermal strain cycling.(3) For the transition phenomenon of cast iron tested from thermal shock fracture to thermal fatigue fracture, simple maximum principal stress theory is applicable.

Symmetrical thermal bending of circular disks with power function profile

Steam- and gas-turbine disks are subjected to axial temperature gradients, especially when starting. A method is given in this paper for evaluating the resulting elastic thermal stresses when the thickness of the disk varies as any power function of the radius. The cases of a uniform disk and of one of composite form are also considered. The usual assumptions for thin disks are followed, and the elastic constants are assumed unaltered by thermal effects.