Effect Of Thermo-mechanical Stresses Research Articles

Combining synchrotron X-ray diffraction, mechanistic modeling and machine learning for in situ subsurface temperature quantification during laser melting.

Laser melting, such as that encountered during additive manufacturing, produces extreme gradients of temperature in both space and time, which in turn influence microstructural development in the material. Qualification and model validation of the process itself and the resulting material necessitate the ability to characterize these temperature fields. However, well established means to directly probe the material temperature below the surface of an alloy while it is being processed are limited. To address this gap in characterization capabilities, a novel means is presented to extract subsurface temperature-distribution metrics, with uncertainty, from in situ synchrotron X-ray diffraction measurements to provide quantitative temperature evolution data during laser melting. Temperature-distribution metrics are determined using Gaussian process regression supervised machine-learning surrogate models trained with a combination of mechanistic modeling (heat transfer and fluid flow) and X-ray diffraction simulation. The trained surrogate model uncertainties are found to range from 5 to 15% depending on the metric and current temperature. The surrogate models are then applied to experimental data to extract temperature metrics from an Inconel 625 nickel superalloy wall specimen during laser melting. The maximum temperatures of the solid phase in the diffraction volume through melting and cooling are found to reach the solidus temperature as expected, with the mean and minimum temperatures found to be several hundred degrees less. The extracted temperature metrics near melting are determined to be more accurate because of the lower relative levels of mechanical elastic strains. However, uncertainties for temperature metrics during cooling are increased due to the effects of thermomechanical stress.

MATHEMATICAL EQUATIONS FOR TEMPERATURE CONTROL IN THE CONTACT SURFACES OF DRILLING AND MAINTENANCE EQUIPMENT

The maintenance of equipment and tools used in the workover of oil and gas wells depends on keeping them in working condition, reliability, strength and temperature endurance of the tool. In order to restore wells in case of an accident and bring them back into operation, it is necessary to speed up the drilling and repair work by choosing the right repair equipment and following the existing rules and regulatory documents. The cutting elements of the tools working under high pressure and loads are deformed, a tense situation is created in the cutting – destruction zone, high temperatures (10000 - 12000) occur as a result of corrosion in the triboknots. The stress-deformation state in the cutting-destruction zone causes the formation of microcracks in the working area of the tool. Microcracks grow after a certain period of time. Cutting elements are quickly worn, in some cases broken and fail quickly. Such cases affect the structural composition of the cutting elements, the temperatures increase, as a result, riveting occurs. In order to keep the equipment and tools used in the repair in normal working condition, adjusting the mode parameters is one of the important requirements, in addition to taking special care of them. The high results obtained in repair and restoration works depend on the efficiency of the cutting-destructive tool, longevity, material selection, construction manufacturing technologies, tool that meet modern requirements, dimensions, weight and internal condition of the well being restored. It is necessary to keep the heat generated in the moving parts of the tool at the required level for the safe performance of restoration works. The thermal regime of cutting and rock-destroying tools depends on the physical-mechanical properties of the objects subjected to destruction and the effect of thermomechanical stresses generated on the contact surfaces of the tool and the amount of heat released from the working surface. Studying the problems related to heat issues will allow to ensure the temperature tolerance of not only the repair equipment, but also the equipment and tools used in other areas of the oil-field industry. Keywords: temperature, cutting and destructive tool, metal, rock.

Interfacial Delamination at Multilayer Thin Films in Semiconductor Devices.

With the evolution of semiconducting industries, thermomechanical failure induced in a multilayered structure with a high aspect ratio during manufacturing and operation has become one of the critical reliability issues. In this work, the effect of thermomechanical stress on the failure of multilayered thin films on Si substrates was studied using analytical calculations and various thermomechanical tests. The residual stress induced during material processing was calculated based on plate bending theory. The calculations enabled the prediction of the weakest region of failure in the thin films. To verify our prediction, additional thermomechanical stress was applied to induce cracking and interfacial delamination by various tests. We assumed that, when accumulated thermomechanical-residual and externally applied mechanical stress becomes larger than a critical value the thin-film cracking or interfacial delamination will occur. The test results agreed well with the prediction based on the analytical calculation in that the film with maximum tensile residual stress is the most vulnerable to failure. These results will provide useful analytical and experimental prediction tools for the failure of multilayered thin films in the device design stage.

Comparative laboratory investigation for the effect of thermo-mechanical stresses on mandibular denture base deformation for 3d printed and conventional dentures

Comparative laboratory investigation for the effect of thermo-mechanical stresses on mandibular denture base deformation for 3d printed and conventional dentures

Влияние термомеханической нагрузки на старение изоляции тяговых электродвигателей тепловозов

Purpose: To consider the problem of increasing the reliability of traction electric machines. To assess the effect of thermomechanical stresses on the service lifetime of insulating material of traction electric motors. Methods: Finite element method, implemented in SolidWorks 2005 software package, was chosen as the main method for studying and calculating temperature fields. Results: The results show that thermomechanical stresses play a significant role during dynamic thermal aging of stator winding insulation system. With dynamic temperature changes, an insulation system experiences repeated thermomechanical stresses since the coefficients of thermal expansion of insulating materials and copper conductors are different. Practical importance: The need for further study of the actual thermal state of electrical machines has been identified which will allow to a rise temperature definition accuracy, to give a warning for possible overheating in operation by that extending traction motor lifetime and reducing sudden failure likelihood. The developed methods for determining electrical machine thermal state are recommended for practical use.

Thermomechanical voltages in the insulation of traction electric machines of locomotive

In recent years, the production of locomotives in our country has increased significantly. At the same time, a lot of efforts are made to increase the power, reliability and efficiency of their work. One of the key components of any locomotive is electric traction machines, which are usually designed to the limit in order to obtain maximum torque and power density in the limited space of the rolling stock. Previously, this problem was solved by increasing the electromagnetic properties of materials, thermal conductivity of insulating materials. However, this path has exhausted the possibilities for increasing the efficiency of traction electric machines. As the design of traction electric machines improves, their level of functionality, reliability and durability increases, electric traction systems become more relevant and important for reducing the cost of materials, maintenance and ensuring traffic safety. The insulation state of the windings of traction electric machines mainly determines their reliability and performance, affects the service life and the cost of maintenance. Therefore, when designing a traction electric machine, it is important to take into account all operational factors that determine the optimal service life of a locomotive. The article discusses the effect of thermomechanical stresses in the insulation of traction electric machines on their reliability and durability.

Residual lifetime assessment of thermal power plant superheater header

Abstract The safe operation of thermal power plants (TPPs) is largely determined by the reliability of main components of steam systems of power units, to which belong the headers of boiler superheaters. The aim of this study is to estimate the residual lifetime of superheater header starting from the initial defect size and up to the maximum allowable one. The above-mentioned lifetime is affected by the fluctuations of temperature under steady mode of operation of TPP superheater header. Superheaters headers operate in a steamy environment under the pressure of 15.5 MPa at temperature of 545 °С. The header is a thick-walled cylinder made of 12Cr1MoV steel with a length of 2314 mm, outer diameter of 325 mm and thickness of 50 mm. To estimate the residual lifetime of the header, the steam temperature in header was measured and digitized. The temperature range of the header under quasi-stable operational mode was divided into three classes: (1) Δt Δt Δt > 30 °C. The local minima and maxima were determined based on the obtained steam temperature history. The residual durability was evaluated taking into account the effect of thermo-mechanical stresses and also the stresses caused by internal steam pressure. The stress intensity factors (SIFs) at the crack tip in the ligament between the holes of superheater collector were estimated by FEM. The SIF of mode I (K I ) were determined along the fronts of modelled semi-elliptical cracks. The SIF correction function at the midpoint of the semi-elliptical crack front in the ligament between holes of the superheater header versus the crack depth and the temperature difference between the external and internal surfaces under a constant internal pressure of steam was obtained. Based on the analysis of header defects, the proposed front shape was taken in the form of the semi-ellipse. The crack growth at 500 °C was modelled by Paris and NASGRO equations. With the increase of temperature difference between the external and internal header surfaces from 10 °С to 50 °С, the number of cycles, that is necessary for the crack to reach 35 mm in depth, decreases approximately in 25 times. It was calculated, that the average value of temperature fluctuations is 15 °С for the Class 1, and is 46.2 °С for the Class 2. The lifetime of header can be extended due to the decrease of fluctuations of temperature range and their frequency.

Brazed Carbon Nanotube Arrays: Decoupling Thermal Conductance and Mechanical Rigidity

Bonding two solids at their interface is the most effective way to achieve a mechanically robust and thermally conducting interface. However, for high‐temperature applications, bonded interfaces between dissimilar materials experience high thermomechanical stress that degrades their performance in terms of cyclic stability (under thermal load) and lifetime. The present study shows that integrating a carbon nanotube (CNT) array as a stress‐relief element to a traditional braze joint mitigates the adverse effects of thermomechanical stress while preserving mechanical robustness and excellent heat transfer characteristic at the interface. A substantial reduction in total thermal interface resistance is achieved (from 41 mm2 K W−1 for bare CNT array to less than 3 mm2 K W−1 for a CNT array integrated with braze alloy). A brazed metal/insulator interface (between Cu and quartz) with a CNT array between them exhibits low thermal interface resistance even after extreme thermal cycling whereas the same interface delaminates readily when brazed without a CNT array. The reported technique provides a promising route for substantially improving the problematic high‐temperature interface, a major hindrance in achieving stable and efficient operation for systems such as thermoelectric generators that operate at elevated temperatures (above 400 °C).

Experimental evaluation of thermo-mechanical performances of candidate rocks for use in high temperature thermal storage

Packed-bed of rocks using air as heat transfer fluid (HTF) are identified as a promising alternative and cost effective solution for thermal energy storage (TES) in concentrating solar power plants (CSP). Desert sands, igneous and other rocks are being intensively tested for heat storage at high temperature. This paper focuses on the study of several candidate rocks for heat storage. Thirteen samples are collected from diverse places in Morocco and thermally cycled between 20°C and 650°C. The chemical and thermo-physical properties influencing the lifetime of rocks are identified. Vickers hardness test has been used to evaluate the compressive strength of the samples and the effect of thermo-mechanical stress during thermal cycling. The obtained results show that quartz and calcite are the principal minerals controlling rock physical properties. Limestone, marble and granite have not withstood thermal cycling. Their hardness decreases after each cycle. Rhyolite and quartzitic sandstone show excellent ability during thermal cycling. When comparing their principal characteristics, rhyolite seems to be the most promising candidate for high temperature TES.

Lifetime estimation of superheater header

The safe operation of thermal power plants (TPPs) is largely determined by the reliability of main components of steam systems of power units, to which belong the headers of boiler superheaters.The aim of the study is to estimate the residual lifetime of superheater header starting from the initial defect size and up to the maximum allowable one. The above-mentioned lifetime is affected by the fluctuations of temperature under steady mode of operation of TPP superheater header. Superheaters headers operate in a steamy environment under the pressure of 15.5 MPa at temperature of 545 ºС. The header is a thick-walled cylinder made of 12Cr1MoV steel with a length of 2314 mm, outer diameter of 325 mm and thickness of 50 mm.To estimate the residual lifetime of header, the registered operational data of steam temperature in header were used. The temperature range of header under quasi-stable operational mode was divided into three classes: the temperature range (1) T < 10 °C; (2) 10 °C < T < 30 °C; (3) T > 30 °C. The local minima and maxima were determined using the obtained steam temperature history. The stresses in the wall of header for the given temperature fluctuations were calculated by finite element method (FEM).The residual durability was evaluated taking into account the effect of thermo-mechanical stresses and also the stresses caused by internal steam pressure. The stress intensity factors at the crack tip in the ligament between the holes of superheater collector were estimated by FEM. Based on the analysis of header defects, the proposed front shape was taken in the form of semi-ellipse. The crack growth at 500 ° C was modelled by Paris equation.With the increase of temperature difference between the external and internal header surfaces from 10 °С to 50 °С, the number of cycles, that is necessary for the crack to reach 35 mm in depth, decreases approximately in 25 times. It was calculated, that the average value of temperature fluctuations is 15°С for the Class 1, and is 46.2 °С for the Class 2. The lifetime of header can be extended due to the decrease of fluctuations of temperature range and their frequency.

Thermal Challenges in 3D Stacks

Thermal Management of high performance 3D SiP Modules is gaining momentum in telecommunication and networking applications. With increasing need for bandwidth and reduced real estate on boards, there is an acute need for 3D SiP modules. At the same time, the stacked modules come with a host of new challenges in terms of thermal management, packaging, thermo-mechanical stresses etc. This study looks at one such module with stacked dies for memories along with another high performance silicon all under a single lid. The study focuses on the effect of underfill materials on thermal performance, effect of through silicon vias, effect of non-uniform heat source on hot spots on the die etc. It will also focus on thermal management of a single module as well as a series of modules in a networking application. The effect of thermo-mechanical stresses will also be investigated and conclusions drawn on the effect of each of these parameters.

Wetting and adhesion of Si on Si 3N 4 and BN substrates

Wetting, adhesion and reactivity are the principal factors determining the capability of a solid to be used as mould material. In this work wetting of silicon and boron nitrides by molten silicon is studied in neutral gas atmosphere by the sessile drop technique at temperatures close to the silicon melting point. Adhesion is qualified by the behaviour of solidified droplets under the effect of thermo-mechanical stresses generated during cooling at room temperature. The reactivity at silicon/nitride interfaces is studied by scanning electron microscopy and EDX-microanalysis.

Effect of thermo-mechanical stress during quench on nb sn cable performance

Several high field magnets using Nb{sub 3}Sn superconductor are under development for future particle accelerators. The high levels of stored energy in these magnets can cause high peak temperatures during a quench. The thermomechanical stress generated in the winding during the fast temperature rise can result in a permanent damage of the brittle Nb{sub 3}Sn. Although there are several studies of the critical current degradation of Nb{sub 3}Sn strands due to strain, little is known about how to apply the strain limitations to define a maximum acceptable temperature in the coils during a quench. Therefore, an experimental program was launched, aimed at improving the understanding of the effect of thermo-mechanical stress in coils made from brittle Nb{sub 3}Sn. A first experiment, reported here, was performed on cables. The experimental results were compared to analytical and finite element models. The next step in the experimental program will be to repeat similar measurements in small racetrack coils and later in full size magnets.

Effect of thermo-mechanical stress during quench on Nb/sub 3/Sn cable performance

Several high field magnets using Nb/sub 3/Sn superconductor are under development for future particle accelerators. The high levels of stored energy in these magnets can cause high peak temperatures during a quench. The thermo-mechanical stress generated in the winding during the fast temperature rise can result in a permanent damage of the brittle Nb/sub 3/Sn. Although there are several studies of the critical current degradation of Nb/sub 3/Sn strands due to strain, little is known about how to apply the strain limitations to define a maximum acceptable temperature in the coils during a quench. Therefore, an experimental program was launched, aimed at improving the understanding of the effect of thermo-mechanical stress in coils made from brittle Nb/sub 3/Sn. A first experiment, reported here, was performed on cables. The experimental results were compared to analytical and finite element models. The next step in our experimental program will be to repeat similar measurements in small racetrack coils and later in full size magnets.

The Interplay of Thermo-Mechanical Properties in the Growth and Processing of III-V Materials

AbstractThe thermo-mechanical properties of III-V semiconductors, in general, and of GaAs and InP in particular, are reviewed. They play an important role in many aspects of semiconductor device fabrication starting from the growth of bulk crystals. Dislocation generation in GaAs and InP are discussed with the emphasis on the theoretical and experimental aspects of reducing the dislocation density in these materials. Such mechanical properties as glide systems, critical resolved shear stress and impurity hardening are covered. The effects of dislocations on device performance are illustrated with examples from photonic and electronic devices. Finally, the effect of thermomechanical stresses in the degradation and reliability of GaAs/AlGaAs and InP/InGaAsP based opto-electronic devices is considered.

Effect of thermomechanical stresses on the strength of enameled glass plates

Effect of thermomechanical stresses on the strength of enameled glass plates