Transient Thermal Stress Field Research Articles

Mechanical properties and thermal shock resistance of TiB2‒B4C composite ceramic tool materials at microscopic scale

AbstractA finite model incorporating microstructure was developed to investigate the thermal shock resistance of TiB2‒B4C composite ceramic cutting tool materials. Numerical simulations were conducted to analyze changes in the transient temperature field and thermal stress field during the thermal shock process. TiB2‒B4C composite ceramic tool materials were fabricated using discharge plasma sintering technology. With different B4C contents, different sintering temperatures and holding times as study variables, optimization of the sintering process parameters and ceramic material components was achieved through testing the mechanical and microscopic morphology of the ceramics. Thermal shock water quenching experiments were performed, and the strength‐decay method was employed to assess the thermal shock resistance of TiB2‒B4C ceramics. The findings indicate that the optimal sintering conditions are temperature of 1700°C and holding time of 5 min. The TiB2‒B4C ceramic material containing 20 vol% B4C exhibits superior comprehensive mechanical properties and thermal shock resistance, and its relative density, fracture toughness, hardness, and flexural strength were 99.3%, 6.8 MPa m1/2, 22.8 GPa, and 598 MPa, respectively. The critical thermal shock temperature difference falls within the range of 400°C‒500°C.

Non-Fourier thermoelastic interaction of two collinear cracks in a functionally graded layer

Designed with a predetermined composition profile, functionally graded materials receive much attention in serving as the thermal barrier coating to resist severe thermal loading. By means of the dual-phase-lag theory, the non-Fourier effect is considered in establishing the theoretical thermoelastic model of the cracked layer under sudden thermal shocks. The novelty of the present work lies in revealing the interaction effects of two collinear Griffith cracks embedded in a functionally graded layer on the transient temperature and thermal stress fields under harsh conditions. Via employing the Fourier sine and cosine transforms, coupled with the Laplace transform, the dynamic mixed mode crack problem is transformed into a group of Cauchy-type singular integral equations. Numerical calculations are implemented to evaluate the transient temperature and stress intensity factors. The influences of the crack spacing, the nonhomogeneous parameters, and the thermal lags on the thermal and stress concentrations are explored. The results indicate that both mode I and II thermal stress intensity factors of the outer crack tips are noticeably higher than those of the inner crack tips, even up to 71% and 128%, respectively. A larger fracture risk may occur with the closer two adjacent cracks.

A methodology to predict thermal crack initiation region of tool for high-speed milling compacted graphite iron based on three-dimensional transient thermal stress field model

A methodology to predict thermal crack initiation region of tool for high-speed milling compacted graphite iron based on three-dimensional transient thermal stress field model

Numerical and Experimental Study on Thermal Damage Induced by Medium—Infrared Laser

We studied the laser-induced thermal damage on the surface of a single crystal silicon mirror illuminated by a mid-infrared intense laser. We used mid−infrared quasi-continuous wave lasers to irradiate the surface of the single−crystal silicon mirror. The power density of the irradiation process is 1 kW/cm2 to 17 kW/cm2, and the transient temperature field and thermal stress field under different laser fluxes were obtained. The simulation results show that we can calculate the thermal stress and temperature under laser irradiation. In addition, irradiance exceeding the corresponding breaking strength and melting point limit was obtained by the model. We can predict the irradiance that causes cracking and melting. There is little difference between experimental results and simulation results. On this basis, the thermal damage to the surface of the silicon wafer caused by continuous mid−infrared laser irradiation was studied.

Impacts of Startup, Shutdown and Load Variation on Transient Temperature and Thermal Stress Fields within Blades of Gas Turbines

Impacts of Startup, Shutdown and Load Variation on Transient Temperature and Thermal Stress Fields within Blades of Gas Turbines

Numerical investigation of thermo-mechanical properties for disc brake using light commercial vehicle

A brake is a device using which frictional resistance is applied for stopping a moving vehicle. In disc brakes, the component on which the pads are squeezed when the brake pedal is applied. Disc brakes are subjected to both mechanical and thermal stresses. The cyclic thermal stress is more significant than mechanical stress. In this study, three-disc brakes with different profiles are selected to investigate the thermo-mechanical behavior analytically and numerically. This analysis develops a three-dimensional (3D) thermo-structural coupling model, implements transient thermal Analysis and transient structural Analysis of disc brake profiles with a frictional heat. The thermo-structural problem is solved by the finite element method to get the transient temperature and thermal stress fields of the disc brake under emergency braking. Comparison between the three profiles has been made using different parameters, including the maximum temperature on the surface, equivalent thermal stress (Von-Mises), and thermal deformation. The result has shown that the having grooved profile on its surface exhibited 34Mpa of equivalent stress, whereas the solid type and the drilled type have shown 80Mpa and 57Mpa. It also shows that the grooved type brake is efficient by far more magnitude than the other two profiles. In general, the thermal stress developed and thermal deformation on the would significantly decrease when it has a profile that allows for better heat dissipation to the surrounding.

Thermal shock resistance behavior of auxetic ceramic honeycombs with a central crack or an edge crack

In this paper, the thermal shock resistance of an auxetic ceramic honeycomb plate is studied based on the fracture mechanics concept for the cases of a central crack or an edge crack. The transient temperature field and transient thermal stress field are obtained for both auxetic and non-auxetic structures. The relationship between the thermal stress intensity factor (TSIF) and the internal cell angle, crack length and time is determined and the critical temperature for the initiation of crack propagation is predicted. Results show that compared with the non-auxetic ceramic honeycombs which are at an internal cell angle of 30°, the critical temperature of the auxetic ceramic honeycombs whose cell are orientated at an angle of −30° increases by 78.5% and the TSIF at the crack tip decreases by 40%, respectively. Hence, the auxetic structures have better thermal shock resistance. This study indicates that auxetic ceramic honeycombs have significant potential applications in harsh temperature environments.

Analytical solution to thermal stresses of high speed PM rotor considering thermal load and heat convection

Aiming at the high speed permanent magnet (PM) rotor with the heat source, this work investigates the analytic solution to the transient temperature field and thermal stress field of the rotor, considering the influence of the forced air cooling of rotor surface on the stress field. Firstly, dimensionless formulation of the transient heat conduction equation including interior heat source is derived, where the axially non-uniform heat convection coefficient and the temperature of main flow region are equivalent to their mean values. Secondly, the Fourier integral transform method is used to solve the dimensionless heat conduction equation. Then, the obtained temperature field is loaded into the analytical solution of strength, in which three types of stress sources such as interference fit, centrifugal force and temperature gradient are included. Finally, examples are carried out to verify the analytical solutions and relative results are discussed.

Study of Crack Interaction Effects Under Thermal Loading by Digital Photoelasticity and Finite Elements

The effect of an interacting internal crack on the edge crack in a transient thermal stress field is evaluated using digital photothermoelastic experiments and finite element (FE) analysis. Initially, a transient thermal stress field is simulated using FE analysis for which the thermal boundary conditions are set based on the experimental isochromatic fringes. In this simulated thermal stress field, single edge crack with and without an internal short crack interacting at different configurations are modeled and the non-dimensional Stress Intensity Factor (SIF) values are evaluated at different time intervals. It is observed that the asymmetric and collinear configurations tend to increase the SIF of the edge crack whereas a parallel crack tends to decrease the SIF of the edge crack. For experimental evaluation, specimens with a single edge crack and asymmetric configuration of interacting cracks are considered and the non-dimensional SIF values are evaluated under a thermal stress field generated by edge heating and cooling. The results are compared with those obtained using the FE analysis.

Thermal shock resistance of ceramic foam sandwich structures: Theoretical calculation and finite element simulation

In this paper, the thermal shock resistance of a ceramic foam sandwich (CFS) slab is studied. Two typical thermal shock conditions are considered, i.e., the hot shock and the cold shock. Variations of transient temperature and thermal stress fields with thermal shock time and position are derived. The transient thermal stress intensity factor (SIF) of the thermally induced embedded and edge crack are detected by the developed theoretical model. Simultaneously, the corresponding thermal shock simulation of CFS slab is performed based on finite element (FE) analysis. The results between the presented theoretical model and FE analysis exhibit excellent agreement. Furthermore, the effects of the faceplate thickness and the relative density of the foam core on the thermal shock resistance of CFS slab under hot shock are discussed. Constructive suggestions for the structural optimization design of CFS structures are provided. The study demonstrates the asymmetric fracture behavior under the asymmetric hot shock, and determines the position of the danger zone. Notably, the variations of the influence degree of foam core density on the thermal shock resistance of the CFS slab under cold shock are indicated. The Crack propagation behaviors are investigated and the corresponding crack growth trajectories are provided from the fracture mechanics criterion.

Transient temperature fields and thermal stress fields in glazing of different thicknesses exposed to heat radiation

Thermal performance analysis and cracking prediction of glazing elements are essential for fire safety evaluation of a building. This work investigated the transient temperature fields and the corresponding stress fields in glazing of different thicknesses with one side exposed to heat radiation. Based on the results of investigation, the criterion of critical temperature difference in cracking prediction was formulated. Glass samples of different thicknesses were tested under the same radiation exposure. Besides, a transient two-dimensional heat transfer model was presented to obtain the transient temperature fields in the glass samples. In addition, the temperature fields were loaded to ANSYS to obtain the thermal stress fields. It is found that in the initial heating period, the maximum stress was mainly caused by the temperature gradient component across thickness and the stress value was larger for thicker glazing; as time evolved, the maximum stress was gradually dominated by the temperature gradient component along the planar direction. Thus, for thick glazing under strong heat, thermal bending stress caused by temperature gradient across thickness should be calculated first to evaluate the cracking time, and the criterion of critical temperature difference is appropriate only if the thermal bending stress cannot reach the breaking value. For other conditions, cracks will result from the stress caused by the temperature gradient along the planar direction, and the criterion of critical temperature difference is applicable for cracking prediction of glazing in any thickness.

Effects of substrate thickness and heat transfer scheme on edge cracking of a brittle coating due to thermal transients

Brittle coatings may suffer edge cracking due to thermal transients. The thermal stress intensity factor (TSIF) is used here to characterize the driving force for such damage modes. The purpose of this paper is to investigate the effect of substrate thickness and heat transfer scheme on the edge cracking behavior. The transient temperature and thermal stress field of the un-cracked system are first obtained in closed forms. The weight functions suitable for thermal loading are then developed for the edge-cracked coating. The TSIF at the crack tip is finally obtained based on the principle of superposition, with the equal thermal stresses utilized as the crack surface tractions. The dependence of the normalized TSIF is examined on different thermal boundary condition, normalized time, and relative crack depth as well as substrate/coating thickness ratio. It is found the thicker substrate leads to much higher driving force for the edge cracking. The heat transfer schemes on the lower surface of the substrate, however, have insignificant effect on it. The findings of this study may assist in the integrity analysis of coatings due to rapidly changing thermal environments.

Simulations in multipass welds using low transformation temperature filler material

Transient thermal and residual stress fields in flux-cored arc welds were examined using a finite element (FE) model. Experimental multipass welds were produced using both conventional and low transformation temperature (LTT) filler metals. Temperature-dependent material properties and both convective and radiant heat loss boundary condition have been considered in the FE model. The effects of the transformation temperature and interpass intervals on residual stresses were examined. It was found that compressive longitudinal residual stresses were developed at the weld centreline in the LTT filler metal. A short-time interpass interval causes the weld fusion zone to be above the martensite start temperature allowing the optimal use of the phase transformation effect. The FE model is sensitive to alteration in welding parameters and can satisfactorily predict the residual stress distribution in welded parts.

Optimization on start-up process of high-pressure rotor for large power steam turbine

This paper combines thermal-structure coupling technique and pattern search optimization algorithm to establish an optimization system for the start-up process of a turbine unit. Firstly, a finite element model for thermal-structure coupling calculation is established to accurately analyze the transient temperature field and thermal stress field, which can obtain the thermal stress distribution during start-up process. Afterwards, a program of optimization on rotor start-up process is exploited to improve the time allocation in each operating stage of start-up process, which minimizes the maximum equivalent stress of rotor. The maximum equivalent stress has reduced 25.7% after the optimization, which reveals obvious effect.

熱応力比の異なるセラミックスの熱衝撃破壊挙動の評価

The thermal shock fracture behavior of alumina ceramics was characterized by Disc-on-Rod test, which was developed by the authors. Thin disc specimen was uniformly heated to high temperature and the center region of specimen was quenched by means of contacting with the cool metal rod. Then, the center of disc specimen was subjected to the biaxial tensile stress. The temperature distribution of specimen was measured by a high speed infrared camera and used for the determination of transient thermal stress field by the finite element analysis. Furthermore, microfracture process was characterized by AE measurement. In order to obtain various thermal stress ratio, elliptical specimens, as well as circular specimens, were prepared. Consequently, experimental technique for evaluating thermal shock behavior under various stress ratio has been developed.

Mechanisms for the millisecond laser-induced functional damage to silicon charge-coupled imaging sensors

A three-dimensional model was established to simulate the process of a millisecond Nd:YAG laser irradiating the CCD, based on its array and multilayer structure. The transient temperature and thermal stress field of the CCD were calculated by using the finite element method. The temperature dependence of material parameters was taken into consideration in the calculation. The results indicated that coupling of the heat damage and thermal stress damage was the main reason for the millisecond laser damage CCD. Softening of the PMMA microlens or rupture of the silica microlens reduced the fill factor of the CCD. Plastic deformation of the silicon substrate increased a great deal of dark current. The leakage current was introduced due to the peeled Al shield. Most importantly, the melting through of the Al-shield layer and the fracture of the silica insulating layer are the two critical factors for functional damage to the CCD. Meanwhile, the influence of the material and fill factor of the microlens was also considered. The results showed that plastic damage of the silicon substrate was more dramatic than the PMMA microlens CCD. And the damage threshold decreased along with the increasing fill factor.

Thermal Stress Distribution Simulation Analysis for Disc Brake of Heavy Vehicles

Aiming at the phenomenon that a large amount of friction heat produced during braking process has important influence on the contact surface of heavy vehicle, according to the actual size of the friction plate and the static slice, a three-dimensional transient thermal stress field calculation model has established, using multi-physics coupled method of ANSYS in Workbench, after the numerical simulation of disk brake, the transient thermal stress field distribution has revealed in the process of braking friction piece, the results showed that the stress field and temperature field has a significant influence on each other, indicated that between them there is a clear relationship between the couple.

Parameter Analysis of Fluid-Solid Coupling for Wet Brake Disc

Due to the poor conditions of wet brake cooling and the high temperature of the working characteristics, this paper intended to introduce the oil film vadose between the brake linings, considered the variation of volume of grooves on the friction plate, and then proposes the three-dimensional transient dynamic response of fluid-solid coupling mathematical model. By parameter analysis of the disc transient thermal stress field distribution on the friction plate, and according to the real dimension of the brake disc, the distribution of the temperature and the stress of the wet brake disc during the braking are analyzed, the variation of temperature field and stress field in friction plate are obtained. The data curves shown the temperature and the stress are coupled. Finally, the results shows that the mathematical model is effective and feasible.

Parameter Analysis of Fluid-Solid Coupling for Wet Brake Disc

Due to the poor conditions of wet brake cooling and the high temperature of the working characteristics, this paper intended to introduce the oil film vadose between the brake linings, considered the variation of volume of grooves on the friction plate, and then proposes the three-dimensional transient dynamic response of fluid-solid coupling mathematical model. By parameter analysis of the disc transient thermal stress field distribution on the friction plate, and according to the real dimension of the brake disc, the distribution of the temperature and the stress of the wet brake disc during the braking are analyzed, the variation of temperature field and stress field in friction plate are obtained. The data curves shown the temperature and the stress are coupled. Finally, the results shows that the mathematical model is effective and feasible.

Numerical Simulation on Stress Field in Inside-Beam Laser Cladding

In the process of deposition, the moving high energy heat source effect on the metal entity, and form the molten pool and the temperature field of directional conduction. Powder is accumulated in the substrate point by point, molten powder instantly solidify into a solid which is combined with substrate (or sediment) to reach metallurgical combination, from the perspective of the thermodynamic, the temperature field produced by coupling ring of heat source is regarded as a moving load to the base plate and the sedimentary section, and transient thermal stress field is generated, the load and boundary conditions (temperature field) of thermal stress field change over time, at the same time, the solution domain of thermal stress field change over time as a result. Therefore, through the life and death unit technology (ANSYS finite element analysis software of advanced analysis techniques) combined with the circulation order, the simulation of point to add deposition process is realized.