Calculation Of Thermal Stresses Research Articles

Analytical modeling of part distortion in metal additive manufacturing

This work presents an analytical modeling methodology for the prediction of part distortion in powder bed metal additive manufacturing (PBMAM). The presented model consists of analytical thermal modeling, thermal stress modeling, residual stress modeling, and distortion modeling. It has promising short computational efficiency without resorting to finite element analysis or any iteration-based simulations. The temperature profile is calculated using a moving point heat source solution and heat sink solution with consideration of heat input from a moving laser and heat loss from boundary heat transfer. The thermal stress is calculated from the temperature calculation using a thermal stress model considering thermal load, surface tension, and hydrostatic pressure. The residual stress is calculated from the thermal stress calculation using an elastoplastic relaxation procedure. The residual stress–induced part distortion is finally calculated from the calculated residual stress and residual strain using a surface displacement model. The calculated part distortion was validated to experimental measurement on a twin-cantilever part produced by PBMAM of Ti6Al4V. Close agreements were observed. The computational time was recorded less than 10 s. The high predictive accuracy and high computational efficiency allow the process parameter planning for distortion control and elimination through inverse analysis.

Inverse analysis of the residual stress in laser-assisted milling

In laser-assisted milling, higher temperature in shear zone softens the material potentially resulting in a shift of mean residual stress, which significantly affects the damage tolerance and fatigue performance of product. In order to guide the selection of laser and cutting parameters based on the preferred mean residual stress, inverse analysis is conducted by predicting residual stress based on guessed process parameters, which is defined as the forward problem, and applying iterative gradient search to find process parameters for next iteration, which is defined as the inverse problem. An analytical inverse analysis is therefore proposed for the mean residual stress in laser-assisted milling. The forward problem is solved by analytical prediction of mean residual stress after laser-assisted milling. The residual stress profile is predicted through the calculation of thermal stress, by treating laser beam as heat source, and plastic stress by first assuming pure elastic stress in loading process, then obtaining true stress with kinematic hardening followed by the stress relaxation. The variance-based recursive method is applied to solve inverse problem by updating process parameters to match the measured mean residual stress. Three cutting parameters including depth of cut, feed per tooth, and cutting speed, and two laser parameters including laser-tool distance and laser power, are updated with respected to the minimization of resulting residual stress and measurement in each iteration. Experimental measurements are referred on the laser-assisted milling of Ti–6Al–4 V and Si3N4. The percentage difference between experiments and predictions is less than 5% for both materials, and the selection is completed within 50 loops.

Modeling of objects for reception and storage of spent nuclear fuel

Facilities for the storage of nuclear fuel are distinguished from other objects by high standards of safety in any operating conditions. A feature of these structures is the large thickness of the walls and floors. This feature should be taken into account in the calculations of seismic effects and thermal stresses caused by uneven temperature fields in concrete. In the work, calculations of joint effects on the building of thermal stresses and earthquakes are made. The calculations allowed us to distinguish the features of the deformation of concrete structures.

Thermal cracking prediction of frameless glazing exposed to radiant fluxes increasing with height

SummaryThe prediction of losing integrity of glazing elements exposed to compartment fires is important in building fire safety. Existing criterion is only appropriate for framed glazing but not frameless glazing due to omission of the flexing stress in the former. A robust and directly applicable expression to determine the location and time of thermal cracking of frameless glazing is lacking in the literature. In this work, thermal stress calculations including the effect of flexing stress were performed based on typical temperature distributions of glazing exposed to compartment fires, and then simple expressions of the maximum stress were derived. Besides, experiments of frameless glazing exposed to heat radiation were carried out to verify the applicability and accuracy of the obtained expressions, as well as to investigate the cracking behavior of frameless glazing. Results show that the proposed expression of maximum stress agrees well with the experimental cracking behavior. Cracks start from the bottom edge and the upper edge of the glazing when exposed to typical distribution of radiant fluxes from compartment fires. In addition, flexing stress has significant contribution to the total stress field.

Assessment of Thermal Stresses in Asphalt Mixtures at Low Temperatures Using the Tensile Creep Test and the Bending Beam Creep Test

Thermal stresses are leading factors that influence low-temperature cracking behavior of asphalt pavements. During winter, when the temperature drops to significantly low values, tensile thermal stresses develop as a result of pavement contraction. Creep test methods can be suitable for the assessment of low-temperature properties of asphalt mixtures. To evaluate the influence of creep test methods on the obtained low-temperature properties of asphalt mixtures, three point bending and uniaxial tensile creep tests were applied and the master curves of stiffness modulus were analyzed. On the basis of creep test results, rheological parameters describing elastic and viscous properties of the asphalt mixtures were determined. Thermal stresses were calculated and compared to the tensile strength of the material to obtain the failure temperature of the analyzed asphalt mixtures. It was noted that lower strain values of creep curves were obtained for the Tensile Creep Test (TCT) than for the Bending Beam Creep Test (BBCT), especially at lower temperatures. Results of thermal stress calculations indicated that higher reliability was obtained for the viscoelastic Monismith method based on the TCT results than for the simple quasi-elastic solution of Hills and Brien. The highest agreement with the TSRST results was also obtained for the Monismith method based on the TCT results. No clear relationships were noted between the predicted failure temperature and different methods of thermal stress calculations.

FORMATION OF TEMPERATURE FIELDS AND THERMAL STRESSES ARISING DURING SOLIDIFICATION OF CYLINDRICAL CONTINUOUSLY CAST STEEL BILLETS

The article presents investigation results of the effect of inhomogeneity of boundary conditions on the intensity of metal cooling in the process of continuous casting of cylindrical billets from corrosionresistant steels. It is assumed that the boundary conditions are nonuniform along the billet perimeter. In the longitudinal direction, the cooling intensity is assumed to be constant within the cooled sector of the billet. During the research it was believed that there are flows of thermal energy between the cooling sectors. A comparative analysis of temperature gradients and resulting thermal stresses in the solidified billet at different cooling intensities realized in the secondary cooling zone was carried out The values of thermal stresses are compared with the maximum permissible for each grade of steel in order to find those cooling conditions in which the thermal stresses do not exceed the permissible values. Based on the results obtained, conclusions are drawn about the effect of cooling intensity on the occurrence of external and internal defects in the resulting cylindrical continuous cast billets. The authors have also made the conclusions about the effect of inhomogeneity of the boundary conditions on the formation of temperature fields in a solidified cylindrical continuously cast billet. The results of the conducted studies are presented in a graphic form and their detailed analysis is carried out. To calculate the temperature fields in the solidifying billet, a specially developed mathematical model was used, based on the equation of nonstationary heat conductivity. For the calculation of thermal stresses, known mathematical formulas have been used that allow calculating the values of thermal stresses arising between cooling zones in the solidifying billet during the continuous casting of steel. The obtained data are of high practical importance, since they can be used to develop rational cooling regimes, in which excess permissible thermal stresses will not be observed. This, as a consequence, will reduce the number of internal and external defects arising in the solidifying continuously cast billet.

Application of dispersant to slow down physical hardening process in asphalt binder

Physical hardening in asphalt binder is recognized as one of the main factors leading to premature and excessive cracking in cold regions and high-altitude areas. To slow down the physical hardening process in asphalt binder, octyl aniline (OA), which is a commonly available non-ionic dispersant, was added to the asphalt binder. The effectiveness of OA in retarding the physical hardening process of the base asphalt binder was evaluated with an extended bending beam rheometer and critical-cracking temperature tests. Further, a thermal analysis was conducted to determine the glass transition temperature. The results showed that the one-step Laplace transformation method is an alternative to the asphalt binder thermal-stress calculation. Moreover, adding a sufficient amount of OA significantly decreased the magnitude of physical hardening in the base asphalt binder. The amphiphilic structure of OA can inhibit the aggregation of asphaltenes to a certain extent, which might be the main reason leading to a lower magnitude of physical hardening in the OA-modified asphalt binder.

Studying thermal stresses of a solar absorber in single and two-phase regimes and effects of various coatings on the absorber

In the solar parabolic trough collectors, functioning based on direct steam generation system, heat transfer system and appropriate thermal stress are indicated as two most important thermal parameters. High amount of the critical heat flux creates an extensive application range for the system so heat transfer systems can function without being subjected to high thermal stresses. In this regard, by using a coat on the external surface of the absorber thermal stresses can be reduces in single-phase, sub-cooled, boiling flow regimes and even at the critical heat flux point. In this study, by considering a numerical model of heat transfer, the input heat flux of the absorber which is considered to be a boundary condition for the absorber’s external surface is calculated. Energy conservation is assessed for three different zones of the fluid flow, single-phase, sub-cooled and boiling. Obtaining the temperature profile of the absorber’s surface from the beginning of the fluid flow to the critical heat flux point, leads to calculation of thermal stresses, which has been accomplished by finite element modeling of Misses and Tresca Model, and these two criteria have been compared. Mentioned analyses are performed and compared for coated and uncoated tubes. Three different coats (zinc, chromium and tungsten) are considered. It is shown that zinc is much more preferred than the two other coats, due to 39% and 83% reduction of thermal stress at the onset of critical thermal flux in both Mises and Tresca, respectively.

Efficient running-in of gears and improved prediction of the tooth flank load carrying capacity

PurposeThe purpose of this paper is to determine parameters for an efficient running-in of gears and an improved method for the prediction of the tooth flank load carrying capacity.Design/methodology/approachIn this contribution, a model for the calculation of the pitting life of involute spur gears is introduced, which is based on an extension of the life model according to Ioannides and Harris for rough surfaces. To achieve the most realistic thermal elastohydrodynamic lubrication simulation and stress calculation possible, measured real surfaces and elastic-plastic material properties of the area close to the surface are used. Special attention is paid to the compatibility of the fatigue life calculation for heterogeneous rough surfaces and their consistent consideration in the lifespan calculation.FindingsA non-destructive running-in for twin-disc pairings can be performed using suitable operating parameters, which subsequently can be transferred to tooth flank tests. Using the extended life model according to Ioannides and Harris, an enhanced prediction of the tooth flank load carrying capacity is possible.Originality/valueThe developed extended life model includes a new numerical approach for calculating the tooth flank load carrying capacity. It has the potential to reliably support and hence to accelerate the design process of gears.

Thermal Properties of a New Pavement Material for Using in Road Construction

Abstract The paper presents the results from a study of the thermo-physical properties of a new synthetic acrylic polymer used as material in road construction and as concrete on its basis. For the purposes of the study, the Modified Transient Plane Source Method (MTPS) was used. Data on the following thermal characteristics were obtained: thermal conductivity coefficient, thermal effusion, thermal diffusion and specific thermal capacity. A comparative analysis was made with the analogous indicators of conventional petroleum bitumen and asphalt concrete. The results of the study can be used for a more precise calculation and prognosis of temperature deformations and thermal stresses, as well as the crack propensity at low temperatures in asphalt concretes.

Heating and cooling induced stresses and displacements in heat exchanger piles in sand

Heating and cooling of heat exchanger piles causes changes in the axial stresses in the pile and vertical pile displacements. Changes in axial stress (thermal stresses) are more significant in the case of fixed head piles, while vertical displacements are more important in the case of free head piles. This paper presents a series of finite element analyses that was performed in order to investigate the effect of the heating or cooling duration, the surface thermal boundary condition, the mechanical and thermal parameters of the soil and the temperature change in the pile, on the thermal stresses that develop in fixed head piles and the thermal vertical displacements of free head piles in sand. The numerical modelling procedure is first validated through the simulation of a set of published centrifuge experiments of heat exchanger model piles in sand. The results of an extensive parametric numerical investigation are then presented and the effect of the abovementioned potentially influencing factors is presented and discussed. Based on the numerical results, the most important parameters that affect the mechanical response of heat exchanger piles to heating or cooling are identified. Finally, design charts are proposed for the calculation of the maximum thermal stresses that develop in fixed head piles and the pile head thermal vertical displacement of free head piles.

Thermal stress and damage risk in the stones of Al-Ziggurat in Al-Nimrud city, Iraq

Abstract The aim of this paper is to assess the risk of climate-induced damage to stone through the calculation of thermal stresses. The stone studied is white limestone, the building stone of the walls of Al-Ziggurat in Al-Nimrud city, Iraq. In order to assess the effect of climate on stone behavior, we measured the stone surface temperature and the extreme values of air temperature (i.e. actual stone dataset). As these parameters were measured for short period, they were completed with weather data recorded from Mosul station for three years (i.e. weather dataset). The actual stone data were used to estimate the statistical difference between stone surface temperature and air temperature. The weather data were treated with respect to actual stone data in order to estimate the thermal stress for a statistically relevant duration. The mechanical properties required for stress calculation are the elastic modulus, the Poisson's ratio and the thermal expansion coefficient. A simple mechanical model was applied to estimate the stress generated by restrained thermal strain. Results show that the risk of damage to the stone exposed to climate fluctuations can be significant. The damage risk is higher to the stone in the south wall orientation than in the north one. The combined use of both datasets proved to be usefull, since the damage risk is significantly higher with the resulting estimation compared to the exclusive use of actual stone data.

Thermal stress restrained specimen test on fiber enhanced asphalt concrete and thermal stress calculation models

Thermal stress restrained specimen test on fiber enhanced asphalt concrete and thermal stress calculation models

Numerical investigation of temperature gradient-induced thermal stress for steel–concrete composite bridge deck in suspension bridges

A 3D finite element model (FEM) with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system. First, a brief literature review indicates that traditional thermal stress calculation in suspension bridges is based on the 2D plane structure with simplified temperature profiles on bridges. Thus, a 3D FEM is proposed for accurate stress analysis. The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis. Following this, the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed 3D FEM model. Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure. Next, the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given. The calculation difference and their potential impact on the structure are shown in detail. Finally, some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.

Calculation and verification of thermal stress in InSb focal plane arrays detector

Both the InSb chip fracture and the local delamination appearing in the negative electrode region of InSb infrared focal plane arrays (IRFPAs) detectors in liquid nitrogen shock tests are the major failure patterns of the InSb IRFPAs. To analyze the inducements to these typical failure patterns, it is imperative to obtain both the thermal mismatch stresses values and their distributions in the InSb IRFPAs. In this paper, the analytical model developed by C. H. Hsueh is firstly employed to calculate the in-plane normal stresses in the center region of the InSb IRFPAs, the in-plane shear forces per unit width outside the center region of the InSb IRFPA, and the peeling moments per unit width outside the center region of the InSb IRFPA. Secondly, the structural model of the InSb IRFPAs created by us with ANSYS software is also employed to extract the distributions of the in-plane normal stresses, the distributions of the interfacial shear stresses, and the distributions of the out-of-plane normal stresses. After that comparing both the calculated in-plane normal stresses and the interfacial shear forces with the corresponding simulated results, we think that the calculating accuracy of the analytical model is comparable to the simulating accuracy of the ANSYS model of the InSb IRFPAs, and the relative errors are smaller than 10%. All these findings provide the technical means in guiding both the structural design and the structural optimization of the InSb IRFPAs assembly in the future.

Thermal stress analysis on 2D C/SiC composites of thin-walled structure of anti-heat head cone

The thermal protection performance of C/SiC composites can be improved by coating the thermal barrier coating on the surface of C/SiC composites.The wall heat flux density distribution of the 2D C/SiC composite thermal insulation structure at the front end of the hyper-sonic vehicle was calculated by steady state heat transfer at different Mach numbers in the atmosphere. In the thermal stress calculation, an effective finite element numerical model is established by the method of partitioning and based on the flexible gradient density method. The model was treated as heterogeneous materials which consists of C/SiC composite region, the coating zone and transition zone, and the results show that the maximum thermal stress appears near the end of the head cone.

Development of an Effective Method for Calculations related to Creep

An effective method combining the retardation spectrum method from Bažant and derived recursive equations based on generalized Kelvin model is proposed for calculations of creep in this paper. The retardation spectrum method can convert most compliance functions into Dirichlet series, and recursive equations are derived from Kelvin element and then expanded to fit the generalized Kelvin model. With recursive equations, the storage of stress history can be avoided during creep calculations. The ACI 209R-92 model is taken as the converted model throughout the presented research. The usefulness of recursive equations is proved by comparisons with the original formulas. Moreover, comparisons between this method and an existing method are conducted, and it is found that the new method presented in this paper is more accurate, especially for aging materials. A creep test is simulated using this method embedded in FEM, and the computed results show that this method is effective in numerical methods. A complete case of early-age thermal stress of a concrete structure is conducted at last, and the results reveal that this method is feasible and stable, and as an important behavior of concrete, creep should not be neglected in calculations of thermal stress of concrete.

Numerical analysis of the influence of carbon content on the initial shell of continuous casting slab

ABSTRACTA numerical model for calculation of temperature and thermal stress in initial steel shell in plate and grooved slab continuous casting moulds was established to predict the influence of steel carbon content on the temperature and stress fields. The calculated results show that the temperature non-uniformity and surface stress of the initial shell increase as the steel temperature decreases. Among the steel grades with carbon contents of 0.06, 0.17, 0.45 and 0.80 wt-%, the initial shell surface stress of steel with 0.17 wt-% (peritectic steel) is the highest. In the grooved mould the temperature non-uniformity and surface stress of the initial shell are significantly lower than those in the plate mould. At 1.7 s after initial shell formation, the non-uniformity of shell surface temperature and stress in the grooved mould are four to nine times and three to nine times, respectively, lower than those in the plate mould.

22pA6 シリコン単結晶の高温でのヤング率の測定と熱応力計算(バルク成長シンポジウム)

22pA6 シリコン単結晶の高温でのヤング率の測定と熱応力計算(バルク成長シンポジウム)

Reducing the thermal stress in a heterogeneous material stack for large-area hybrid optical silicon-lithium niobate waveguide micro-chips

The bonding of silicon-on-insulator (SOI) to lithium niobate-on-insulator (LNOI) is becoming important for a new category of linear and nonlinear micro-photonic optical devices. In studying the bonding of SOI to LNOI through benzocyclobutene (BCB), a popular interlayer bonding dielectric used in hybrid silicon photonic devices, we use thermal stress calculations to suggest that BCB thickness does not affect thermal stress in this type of structure, and instead, thermal stress can be mitigated satisfactorily by matching the handles of the SOI and LNOI. We bond LNOI with a silicon handle to a silicon chip, remove the handle on the LNOI side, and thermally cycle the bonded stack repeatedly from room temperature up to 300°C and back down without incurring thermal stress cracks, which do appear when using LNOI with a lithium niobate handle, regardless of the BCB thickness. We show that this process can be used to create many hybrid silicon-lithium niobate waveguiding structures on a single patterned SOI chip bonded to a large-area (16 mm × 4.2 mm) lithium niobate film.