Elastic Thermal Stress Research Articles

Study on the ablative characteristics of steel target irradiated by nanosecond pulsed pseudo spark electron beams: Experiment and molecular dynamics simulation

A combination of simulation and experimentation is employed to explore the influence of the non-uniformity of energy distribution in nanosecond PSEB on the target ablation. Firstly, A spatiotemporally distributed heat source model is built using Monte Carlo computational method and an ablation phase transition model is established using molecular dynamics method. The results reveal the time evolution of multiple cavities in the sub-surface region, as well as the temperature and stress field distributions with electron beam irradiation. Phase explosion formation and lattice structure changes in the steel target during the ablation process is found for the first time. The PSEB modified AISI1045 steel samples is experimentally conducted. The characterization results show the changes in the crystal structure within AISI1045 steel, which is attributed to the formation of an amorphous layer resulting from grain refinement and structural defects, as well as the combined effects of thermal elastic stress waves, shock thermal stress waves and temperature gradient distribution. The experimentally obtained crystal phase changes are consistent with the simulation results, confirming the accuracy and validity of the modelling. The findings of this study provide a molecular-scale explanation for the formation of unique morphology and micro-structures during the PSEB ablated metal target.

Stresses in pipes subject to thermal fluctuations and linear temperature ramps

Closed-form exact expressions for local and linearized elastic thermal stresses in thick- and thin-walled circular pipes subject to steady-periodic sinusoidal temperature variations are presented. Fourier series are applied to obtain the corresponding response in the pipe wall to rectangular temperature fluctuations and linear temperature ramps. Universal diagrams of resulting temperatures and stress ranges in terms of dimensionless parameters are shown for various pipe cross sections, load frequencies and heat transfer coefficients for the three types of loads.

Effect of thermal barrier coatings and integrated cooling on the conjugate heat transfer and thermal stress distribution of nickel-based superalloy turbine vanes

Based on the comprehensive design of the thermal barrier coatings (TBCs) and advanced integrated cooling systems for the Ni-based superalloy turbine vanes. This study employs a multidisciplinary method to research the aerothermal performance and elastic thermal stress of the first stage Ni-based superalloy (DS GTD 111) turbine guide vane cooled by an integrated cooling system and TBC thickness of 0.5 mm. The results show that the highest temperature and average temperature on the substrate under TBC decreased by 126 K and 110 K, respectively. For the vanes without and with TBC, the thermal stresses are concentrated on the midchord region of the suction side, the upper edge of film holes outflow, and junction regions between the vane root, tip, and endwalls, which bear high-temperature gradient and high temperature. However, TBC reduces stress value by 50%∼95% in thermal stress concentration regions of the substrate, which significantly reduces the slip systems activated regions on the substrate. In addition, the activation of the dominant slip system (DSS) is a further optimization objective for cooling turbine vanes. This study provides macroscopic and microscopic perspectives for improving integrated cooling structures of actual vanes in the design process by comprehensively considering aerothermal and thermomechanical performance.

Logarithmic versus Andrade's transient creep: Role of elastic stress redistribution

Creep is defined as time-dependent deformation and rupture processes taking place within a material subjected to constant applied stress smaller than its athermal, time-independent strength. This time dependence is classically attributed to the thermal activation of local deformation events. The phenomenology of creep is characterized by several ubiquitous but empirical rheological and scaling laws. We focus here on primary creep following the onset of loading, for which a power law decay of the strain rate is observed, $\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\varepsilon}}\ensuremath{\sim}{t}^{\ensuremath{-}p}$, with the exponent $p$ varying between $\ensuremath{\simeq}0.4$ and 1, this upper bound defining the so-called logarithmic creep. Although this phenomenology is known for more than a century, the physical origin of Andrade-like $(p<1)$ creep remains unclear and debated. Here we show that $p<1$ values arise from the interplay between thermal activation and elastic stress redistribution. The latter stimulates creep dynamics from a shortening of waiting times between successive events, is associated to material damage and, possibly, at high temperature and/or stresses, gives rise to avalanches of deformation events.

Steady-periodic thermal stresses in an infinite hollow compound cylinder

Closed-form expressions for temperatures and elastic thermal stresses in an infinite hollow two-material compound cylinder subject to steady-periodic sinusoidal ambient temperatures are presented, taking finite heat transfer coefficients into account. The fluctuating temperatures and stresses in the cylinder are expressed in terms of complex-valued modified Bessel functions under the assumption of temperature-independent material properties. Transient thermal loads composed of linear temperature ramps are expressed as Fourier series, and studied by the presented method. In order to verify the analytic results, examples involving sinusoidal and linear loads are examined by finite element calculations.

Comparison of the Thermal Stress Behavior of AlN Single Crystal Growth on AlN and SiC Seeds via the Physical Vapor Transport Method through Three-Dimensional Numerical Modeling and Simulation

We extend a thermal-elastic stress model by the finite element method to evaluate anisotropic three-dimensional thermal stress in AlN bulk crystals grown on on-axis 2H-AlN and 6H-SiC seeds. The dis...

3D modelling of the effect of thermal-elastic stress on grain-boundary opening in quartz grain aggregates

During the exhumation of rocks and the associated temperature and pressure decrease, the anisotropic thermoelastic properties of minerals lead to internal stresses on the grain scale, which in turn cause fracturing and opening of grain and phase boundaries. To gain deeper insight into the onset of grain-boundary cracking and the subsequent evolution of grain-boundary fracture networks after crack initiation, 3D grain-scale numerical modelling has been performed. In detail, the fracturing and opening of quartz grain boundaries during exhumation of quartzite with millimeter-scale grains and randomly oriented crystallographic axes, accompanied by cooling from 300 to 25°C and decompression from 300 to 22MPa, have been modelled with contact mechanics and the finite-element method. Model grains have an anisotropic linear-elastic rheology and an anisotropic thermal-expansion tensor. Grain boundaries are modelled as contact surfaces with a non-linear strain-softening rheology in tension and a Mohr-Coulomb rheology in shear. Grain-boundary fractures nucleate at grain vertices and triple lines, in agreement with observations in nature and experiment. Comparison with grain-boundary opening data from natural quartzite indicates that the tensile yield strength (σy) of quartz grain boundaries has an upper bound of 75MPa, with best-fit results for σy=25MPa. Moreover, the best-fit model implies that quartz grain-boundary opening initiates after a temperature and pressure decrease of around 80°C and 80MPa.

Optimization of total resolved shear stress in AlN single crystals homoepitaxially grown by physical vapor transport method

We investigate the distribution and evolution of the total resolved shear stress (TRSS) in AlN single crystals homoepitaxially grown by the physical vapor transport method based on an in-house three-dimensional thermal-elastic stress code. The thermal stresses of three primary slip systems in 2H-AlN crystals are modeled. The simulation results show that the magnitude of the TRSS increases tremendously after the crystal reaches its critical thickness δc at 6 mm under our specific hotzone and growth conditions. The location of the maximum TRSS transitions from the bottom surface of the crystal to the peripheral region beneath the seed crystal during the growing process. The influences of the power ratio between two resistant heaters on the TRSS and the growth rate are also investigated. The results suggest that a high growth rate could be maintained until the crystal thickness reaches δc and that the temperature gradient inside the growth chamber should be decreased during the later stages by adjusting the power ratio to reduce the overall TRSS and defect propagation. The TRSS could be reduced by 93.31% by rapidly decreasing the temperature differences in AlN crystals immediately after the growth process.

Anisotropic Three-Dimensional Thermal Stress Modeling and Simulation of Homoepitaxial AlN Single Crystal Growth by the Physical Vapor Transport Method

We develop a thermal-elastic stress model using the finite element method to predict three-dimensional anisotropic stress in AlN single crystals homoepitaxially grown by the physical vapor transport process; we also perform numerical experiments for a 1-in. AlN crystal surrounded by different cone-tube designs and grown along various orientations. The influences of the cone-tube shape and the growth orientation on the stresses inside the AlN crystal are investigated in detail. The simulation results show that the von Mises stress exceeds 1.11 GPa under all specified growth conditions, while the anisotropy is negligible. The resolved shear stresses are strongly dependent on the thermal gradient inside the growing crystal and the growth orientation. Strong anisotropy of the resolved shear stress is observed upon tilting of the growth orientation. The resolved shear stress along {0001}⟨112̅0⟩ primary slip system reveals that the c-axis growing crystal is under tensile stress along all three primary slip directions. Nevertheless, an inversion of the resolved shear stress from tensile to compressive along the −a3 slip direction is observed when changing the growth orientation. The total resolved shear stress shows 6-fold symmetry, reflection symmetry and 2-fold symmetry along [001], [10√3], and [100] growth orientations, respectively.

Combined Hybrid Finite Element Method Applied in Elastic Thermal Stress Problem

In view of combinative stability, combinative variational principle based on domain decomposition for elastic thermal stress problem is constructed with the merits of avoiding Lax–Babuska–Brezzi (LBB) conditions. Compared with the principle of elasticity problem, new load items from thermal are involved. In addition, combined hybrid finite element is proposed to discretize the new principle and to formulate element stiffness matrix. Energy compatibility is introduced not only to simplify the variational principle and the corresponding element stiffness matrix but also to reduce the error of finite element solutions. On cuboid element, the energy compatible stress mode is given explicitly. The numerical results indicate that combined hybrid element with eight nodes can give almost the same computing accuracy of displacement and better computing accuracy of stress compared with cuboid element with 20 nodes, is not sensitive to mesh distortion and can circumvent Poisson-locking phenomenon.

Thermal transport study across interface “nanostructured solid surface / fluid” by photoacoustic technique

In the paper the experimental study of heat transport across the interface “porous silicon/liquid” by photoacoustic technique is reported. Two cases with and without liquid covering of porous silicon surface were considered. Thermal perturbations were excited at the surface of porous silicon as a result of absorption of the light with modulated intensity. The resulting thermal-elastic stresses arising in the system were registered with piezoelectric transducer. The amplitude-frequency dependencies of the voltage on the piezoelectric electrodes were measured. The presence of the liquid film leads to decreasing of the amplitude of photoacoustic signal as a result of the thermal energy evacuation from the porous silicon into the liquid. The experimental dependencies were fitted with the results of simulation that takes into account heat fluxes separation at the porous silicon/liquid interface. With the presented method one can precisely measure heat fluxes transferred from the solid into contacting fluid. Moreover, the presented approach can be easily adopted for the thermal conductivity study of the different nanofluids as well as thermal resistance at the interface nanostructured solid/fluid.

Thermal stress analysis of PCM containers for temperature smoothing of waste gas

This article develops an analytical and numerical approach to evaluate thermal stress in a phase change material (PCM) system, used for temperature smoothing of waste gas of Electric Arc Furnace, in which the PCM is encapsulated in a cylindrical steel container. Thermal analysis shows that temperature distribution in the PCM system can be considered as uniform at any time instant according to the lumped capacitance method; the thermal behaviour of PCM system is thus simulated as a sequence of steady state analyses. Mechanical analysis adopts an axialsymmetric plane analytical model to compare elastic thermal stress distribution for different stainless steels and to identify AISI 316 as the most suitable material for the PCM container. A simple two-bars model and a stress index are also used to allow a physical understanding and a satisfactory interpretation of the PCM system response. Mechanical analysis shows that thermal stresses exceed the yield point of both stainless steels used in the container. A finite element elastic-plastic model is then developed to estimate the extension of the plastic zone. Finally, an alternative PCM system geometry based on concentric pipes is designed to keep the maximum stresses in the PCM container below the yielding point. A sensitivity analysis shows that the most relevant design parameters of the alternative geometry are the diameter of inner pipe and thickness of the external pipe.

Elastic-Plastic Thermal and Residual Stress Analysis of Adhesively Bonded Single Lap Joint

In this work, an elastic-plastic thermal and residual stress analysis were performed for adhesively bonded single lap joint. For this purpose, thermoplastic composite adherents were bonded to each other with epoxy adhesive. Thermoplastic composite material was reinforced by steel-fibres, unidirectionally. Finite element method (FEM) was preferred to obtain thermal elastic and elastic-plastic stress distributions on single lap joint. Accordingly, modelling and solution processes were achieved using ANSYS software. So as to determine effects of uniform temperature loadings on thermal and residual stresses, different values of it were loaded on the joint, uniformly. Briefly, both thermal and residual thermal stresses were calculated under uniform temperature loading which was selected from 40 °C to 80 °C. According to obtained results different thermal expansion coefficients of composite adherents and adhesive layer caused thermal and residual stresses on adhesively bonded single lap joint due to applied uniform temperature loadings. Thermal stress values for x and y-directions are very different from each other owing to orthotropic material properties of thermoplastic composite. The magnitudes of elastic analyses results are higher than elastic-plastic analysis results. Contrary to elastic analysis results, elastic-plastic analysis results were nonlinear. Thermal and residual stresses are increased by increasing uniform temperature values, so the highest values were calculated when 80 °C. The plastic yielding was firstly come into being for 50 °C loading and it is expanded related to raising thermal loadings as nonlinear.

Elastic modulus and thermal stress in coating during heat cycling with different substrate shapes

The elastic modulus of a deposit (E d) can be obtained by monitoring the temperature (ΔT) and curvature (Δk) of a one-side coated long plate, namely, a onedimensional (1D) deformation model. The aim of this research is to design an experimental setup that proves whether a 1D deformation model can be scaled for complex geometries. The setup includes a laser displacement sensor mounted on a robotic arm capable of scanning a specimen surface and measuring its deformation. The reproducibility of the results is verified by comparing the present results with Stony Brook University Laboratory’s results. The Δk-ΔT slope error is less than 8%, and the E d estimation error is close to 2%. These values reveal the repeatability of the experiments. Several samples fabricated with aluminum as the substrate and 100MXC nanowire (Fe and Cr alloy) as the deposit are analyzed and compared with those in finite element (FE) simulations. The linear elastic behavior of 1D (flat long plate) and 2D (squared plate) specimens during heating/cooling cycles is demonstrated by the high linearity of all Δk-ΔT curves (over 97%). The E d values are approximately equal for 1D and 2D analyses, with a median of 96 GPa and standard deviation of 2 GPa. The correspondence between the experimental and simulated results for the 1D and 2D specimens reveals that deformation and thermal stress in coated specimens can be predicted regardless of specimen geometry through FE modeling and by using the experimental value of E d. An example of a turbine-bladeshaped substrate is presented to validate the approach.

Application of Study on Liquid Ablation in Laser Propulsion

It was found that evaporation and thermal elastic stress wave and cavity were dominant phenomenon in laser-induced ablation propulsion with liquid propellant according to our perceptual knowledge established in relative experiment and by analysis of physical mechanism of laser-induced ablation of liquid. The research result of the above phenomenon was introduced in this paper in order to give some elicitations to the researchers who were interested in the mechanism of laser propulsion with liquid ablation.

Thermal Elastic Stress Analysis of Steel Fiber Reinforced Aluminum Composites

Thermal Elastic Stress Analysis of Steel Fiber Reinforced Aluminum Composites

Elastic thermal stresses in a hollow circular overlay/substrate system

This paper investigates the thermal elastic fields in the hollow circular overlay fully bonded to a rigid substrate, which is subjected to a temperature change. Following our previous work for a solid circular overlay/substrate system (Yuan and Yin, Mech. Res. Commun. 38, 283–287, 2011), this paper presents a closed form approximate solution to the axisymmetric boundary value problem using the plane assumption, whose accuracy is verified by the finite element models. When the inner radius is reduced to zero, the present solution recovers the previous solution. When the outer radius approaches infinite, the solution provides the elastic fields for a tiny hole in the overlay. The effects of thickness and width of the overlay are investigated and discussed. When a circular crack initiates in a solid circular overlay, the fracture energy release rate is investigated. This solution is useful for thermal stress analysis of hollow circular thin film/substrate systems and for fracture analysis of spiral cracking in the similar structures.

Temperature-Graded Ferroelectric Thin Films under Two Boundary Conditions

In the framework of the mean field approximation, a transverse Ising model (TIM) was adopted to analyze the polarization properties of temperature-graded ferroelectric films under two boundary conditions, free boundary condition (FBC) and clamped boundary condition (CBC). Due to the ferroelectric distortion aroused by temperature gradient across the film, the elastic thermal stress increased. A distribution function was introduced to characterize the different boundary conditions. The results show that boundary conditions have very important influence on film properties. Polarizations under FBC are larger than that under CBC, polarization variations aroused by changed film thickness and temperature gradient under FBC are not as obvious as that under CBC, and films under different boundary conditions present obviously different physical behavior.

The Stress Calculating and Analysis of the Second HP Turbine Disc of a Certain Type of Aeroengine

This paper takes the 2nd HP turbine disc of an aeroengine as research object, construct its finite element model in software-Patran. According to the work environment of 2nd HP turbine disc, the boundary conditions of stress field analysis and temperature field analysis are confirmed. Based on the finite element theory of thermal analysis and structure analysis, we use finite element software-Nastran to analyze centrifugal stress and thermal stress. Numerical calculation method was used to fit the data and finally we got the thermal elastic stress field. According to the computed results, the life assessment points of disc were confirmed. The static strength of 2nd HP turbine disc was tested based on the EGD-3 criterion. All the work established the foundation for subsequent life analysis.

The Thermal Stress between the Interfaces of Different Materials of the Axis Symmetric Structural

In researching the thermal transmit and elastic thermal stress properties between the interfaces of different materials, such as the bricks and the fire – resistant soil in the annual structural of the blast furnace. This paper presents a axis symmetric model to calculate the temperature, the elastic deformation and the stress. This model has the advantages of high accuracy, simple in structure and easy in calculation. The research of the thermal stress by the interfaces mechanics has never been reported before.