Microstructural evolution and thermal fatigue damage mechanism of second-phase dispersion strengthened tungsten composites under repetitive thermal loads

In a fusion reactor,plasma-facing tungsten(W)materials inevitably suffer severe thermal shock,and the performance of W materials under repetitive high heat loads is one of the key concerns for long-term stable operation of the reactor.In this work,the microstructural evolution and thermal fatigue resistance of two representative W-0.5 wt.%ZrC(WZC)and W-1.0 wt.% Y_(2)O_(3)(WYO)composites were investigated under cyclic heat loads.Due to the intrinsic properties of ZrC and Y_(2)O_(3)particles such as coefficients of thermal expansion,particle size and distributions in W grains,the WZC composite exhibited a better thermal shock resistance than WYO.After thermal loads with the absorbed power density(APD)≥22 MW/m^(2),WYO showed obvious grain growth,Y_(2)O_(3)particles shedding and degradation of mechanical properties.While,in the case of WZC,these damage behaviors only occurred when APD≥25 MW/m^(2).Furthermore,an interesting crack mechanism in W composites was revealed due to interface debonding and progressive shedding of second-phase particles from the W matrix.The microstructures and tensile properties of the thermally loaded WZC and WYO specimens were also investigated and the correlations between the microstructure evolution and performance degradation are demonstrated.The results are useful for evaluating the thermal fatigue resistance of oxide/carbide dispersion strengthened W composites and their application in future fusion reactors.

A thermal stress loading technique for large-sized hot dry rock mechanical tests

Testing of large-sized specimens is becoming increasingly important in deep underground rock mechanics and engineering.In traditional mechanical loading,stresses on large-sized specimens are achieved by large host frames and hydraulic pumps,which could lead to great investment.Low-cost testing machines clearly always have great appeal.In this study,a new approach is proposed using thermal expansion stress to load rock specimens,which may be particularly suitable for tests of deep hot dry rock with high temperatures.This is a different technical route from traditional mechanical loading through hydraulic pressure.For the rock mechanics test system of hot dry rock that already has an investment in heating systems,this technology may reduce the cost of the loading subsystem by fully utilizing the temperature changes.This paper presents the basic principle and a typical design of this technical solution.Preliminary feasibility analysis is then conducted based on numerical simulations.Although some technical details still need to be resolved,the feasibility of this loading approach has been preliminarily confirmed.

Optimized scheduling of integrated energy systems for low carbon economy considering carbon transaction costs

With the introduction of the“dual carbon”goal and the continuous promotion of low-carbon development,the integrated energy system(IES)has gradually become an effective way to save energy and reduce emissions.This study proposes a low-carbon economic optimization scheduling model for an IES that considers carbon trading costs.With the goal of minimizing the total operating cost of the IES and considering the transferable and curtailable characteristics of the electric and thermal flexible loads,an optimal scheduling model of the IES that considers the cost of carbon trading and flexible loads on the user side was established.The role of flexible loads in improving the economy of an energy system was investigated using examples,and the rationality and effectiveness of the study were verified through a comparative analysis of different scenarios.The results showed that the total cost of the system in different scenarios was reduced by 18.04%,9.1%,3.35%,and 7.03%,respectively,whereas the total carbon emissions of the system were reduced by 65.28%,20.63%,3.85%,and 18.03%,respectively,when the carbon trading cost and demand-side flexible electric and thermal load responses were considered simultaneously.Flexible electrical and thermal loads did not have the same impact on the system performance.In the analyzed case,the total cost and carbon emissions of the system when only the flexible electrical load response was considered were lower than those when only the flexible thermal load response was taken into account.Photovoltaics have an excess of carbon trading credits and can profit from selling them,whereas other devices have an excess of carbon trading and need to buy carbon credits.

A Nonlinear Explicit Model of A Non-Circular Subsea Tunnel-Liner System with An FGM Inverted Arch Under Mechanical Loading and Fire Fields

This paper proposes an explicit scheme to analyze the failure of a subsea polyhedral tunnel-liner system with an inverted arch under mechanical loading and fire fields.The thin-walled liner is made of Functionally Graded Materials(FGMs),which may improve the stability behavior of the tunnel-liner system.Hydrostatic pressure is inevitable in the liner since underground water may penetrate the cracks of the tunnel,and reach the outer surface of the liner.In addition,an elevated temperature loading is taken into account,considering that fire may occur in the tunnel-liner system.Under the combination of mechanical loading and thermal loading,the liner deforms into a single-lobe shape,which is depicted by a trigonometric function.The total potential energy is expressed quantitatively after the energy approach and thin-walled shell theory are used.The minimum potential energy is obtained when the critical buckling occurs.The critical buckling pressure is calculated,which considers the effect of the thermal field.The present analytical prediction is subsequently compared precisely with other closed-form solutions.Finally,the effects of several parameters,such as the geometric shapes,temperature variations,and volume fraction indices,are discussed to further survey the buckling performance of the nonlinear buckling of an FGM polyhedral liner with an inverted arch.One may address a polyhedral liner with fewer polyhedral sides,and a lower volume fraction index is recommended to rehabilitate cracked tunnels in engineering applications.

Thermal-induced snap-through buckling of simply-supported functionally graded beams

The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal instability type of simply-supported FGM beams.First,based on the Euler-Bernoulli beam theory and von K′arm′an geometric nonlinearity,a nonlinear governing equation of simply-supported FGM beams under uniform thermal loads by Zhang’s two-variable method is formulated.Second,an approximate analytic solution to the nonlinear integro-differential boundary value problem under a thermal-induced inhomogeneous force boundary condition is obtained by using a semiinverse method when the coordinate axis is relocated to the bending axis(physical neutral plane),and then the analytical predictions are verified by the differential quadrature method(DQM).Finally,based on the free energy theorem,it is revealed that the symmetry breaking caused by the material inhomogeneity can make the simply-supported FGM beam under uniform thermal loads occur snap-through postbuckling only in odd modes;furthermore,the nonlinear critical load of thermal buckling varies non-monotonically with the functional gradient index due to the stretching-bending coupling effect.These results are expected to provide new ideas and references for the design and regulation of FGM structures.

Thermal-mechanical properties of short carbon fiber reinforced geopolymer matrix composites subjected to thermal load

Short carbon fiber preform reinforced geopolymer composites containing different contents of α-Al2O3 filler （Cr（a-Al2O3）/geopolymer composites） were fabricated, and the effects of heat treatment temperatures up to 1 200 ℃ on the thermal-mechanical properties were studied. The results show that the thermal shrinkage in the direction perpendicular to the lamination of the composites gradually increases with the increase of the heat treatment temperatures from room temperature （25 ℃ ） to 1000 ℃. However, the composites in the direction parallel to the lamination show an expansion behavior. Beyond 1 000℃, in the two directions the composites exhibit a larger degree of shrinkage due to the densification and crystallization. The mechanical properties of the composites show the minimum values in the temperature range from 600 to 800 ℃ as the hydration water of geopolymer matrix is lost. The addition of α-Al2O3 particle filler into the composites clearly increases the onset crystalline temperature of leucite （KAlSi2O6） from the amorphous geopolymer matrix. In addition, the addition of α-Al2O3 particles into the composites can not only help to keep volume stable at high temperatures but also effectively improve the mechanical properties of the composites subjected to thermal load to a certain extent. The main toughening mechanisms of the composites subjected to thermal load are attributed to fiber pulling-out.

Thermal Analysis of a Novel Oil Cooled Piston Using a Fluid-Solid Interaction Method

Thermal load has a vital influence on the normal operation and service life of diesel engines.In this study,the thermal load and oil-cooling effect on diesel engine pistons were investigated by means of computational fluid dynamics.In particular,the flow and heat transfer characteristics of the cooling gallery were determined during the oscillation of the piston.Moreover,the temperature field distribution of the piston with and without the cooling gallery were compared.The results revealed that the cooling gallery has a prominent effect on reducing the thermal load on the piston crown and piston lands.To fully understand the oscillating heat transfer effect related to the cooling gallery and verify the accuracy of the calculation,the numerical results were also compared with temperature values experimentally measured at key positions of the piston.The measurements were found to be consistent with the calculation results within an acceptable error range,which proves the rationality and accuracy of the mathematical and numerical models used.

Stability and local bifurcation of parameter-excited vibration of pipes conveying pulsating fluid under thermal loading

The parametric excited vibration of a pipe under thermal loading may occur because the fluid is often transported heatedly. The effects of thermal loading on the pipe stability and local bifurcations have rarely been studied. The stability and the local bifurcations of the lateral parametric resonance of the pipe induced by the pulsating fluid velocity and the thermal loading are studied. A mathematical model for a simply supported pipe is developed according to the Hamilton principle. Two partial differential equations describing the lateral and longitudinal vibration are obtained. The singularity theory is utilized to anMyze the stability and the bifurcation of the system solutions. The transition sets and the bifurcation diagrams are obtained both in the unfolding parameter space and the physical parameter space, which can reveal the relationship between the thermal field parameter and the dynamic behaviors of the pipe. The frequency response and the relationship between the critical thermal rate and the pulsating fluid velocity are obtained. The numerical results demonstrate the accuracy of the single-mode expansion of the solution and the stability and local bifurcation analyses. It also confirms the existence of the chaos. The presented work can provide valuable information for the design of the pipeline and the controllers to prevent the structural instability.

Influence of Thermal Load on Mechanical Property of Cemented Carbide Material and Heavy Cemented Carbide Inserts Life

A large amount of cutting heat is produced during the heavy cutting process,and insert life is restricted by the effect of thermal load.The thermal load experiment of cemented carbide SCS,WF and YT15 is carried out,and the results show that the bending strength and fracture toughness of cemented carbide material decrease obviously under cyclic thermal load,while in the cooling process,the material mechanical property changes worse suddenly.The high-temperature mechanical property of SCS is the most stable,and that of YT15 is the worst.Further,a relation model among cutting temperature,cutting parameters and insert life is established.Finally,the measures to improve heavy cemented carbide inserts life are summarized from the aspects of cutting parameters selection,insert optimization design and TiCN,Al2O3,TiN complex insert coating.The research results are expected to provide support and reference for heavy cutting technology and insert technology.

A Study on the Relationship between Anodic Oxidation and the Thermal Load on the Aluminum Alloy Piston of a Gasoline Engine

In order to analyze the influence of the anodizing process on the thermal load of an aluminum alloy piston,dedicated temperature tests have been carried out using the Hardness Plug method and the results for the anodized piston have been compared with those obtained separately for an original aluminum piston.In addition,numerical simulations have been conducted to analyze the temperature field and thermal stress distribution.Simulations and experiments show that the maximum temperature of the anodized piston is 16.36%and 5.4%smaller than that of the original piston under the condition of maximum torque and maximum power,respectively.The thermal stress of the temperature field of both pistons is within 50 Mpa,which meets the strength requirements of the material at high temperature.However,the area with significant thermal stress of the anodized piston is significantly smaller than that of the original piston.Combined with the fatigue analysis data,it can be seen that the safety factor of the anodized piston greater than 1.8 is 99.13%.Therefore,adopting the anodizing process not only reduces the piston thermal load,but also helps to extend its life and improve its reliability.

The thermal effect in diode-end-pumped continuous-wave 914-nm Nd:YVO_4 laser

The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd：YVO4 lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd：YVO4 laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd：YVO4 quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd：YVO4 quasi-three-level laser is calculated by matching the experimental and the simulated end deformations.

Transverse Vibration and Stability Analysis of Circular Plate Subjected to Follower Force and Thermal Load

Transverse vibration and stability analysis of circular plate subjected to follower force and thermal load are analyzed.Based on the thin plate theory in involving the variable temperature,the differential equation of transverse vibration for the axisymmetric circular plate subjected to follower force and thermal load is established.Then,the differential equation of vibration and corresponding boundary conditions are discretized by the differential quadrature method.Meanwhile,the generalized eigenvalue under three different boundary conditions are calculated.In this case,the change curve of the first order dimensionless complex frequency of the circular plate subjected to the follower force in the different conditions with the variable temperature coefficient and temperature load is analyzed.The stability and corresponding critical loads of the circular plate subjected to follower force and thermal load with simply supported edge,clamped edge and free edge are discussed.The results provide theoretical basis for improving the dynamic stability of the circular plate.

Experimental Measurements of the Sensitivity of Fiber-optic Bragg Grating Sensors with a Soft Polymeric Coating under Mechanical Loading,Thermal and Magnetic under Cryogenic Conditions

The strain and temperature sensing performance of fiber-optic Bragg gratings （FBGs） with soft polymeric coating, which can be used to sense internal strain in superconducting coils, are evaluated under variable cryogenic field and magnetic field. The response to a temperature and strain change of coated-soft polymeric FBGs is tested by comparing with those of coated-metal FBGs. The results indicate that the coated-soft polymeric FBGs can freely detect temperature and thermal strain, their At variable magnetic field, the tested results indicate accuracy and repeatability are also discussed in detail. that the cross-coupling effects of FBGs with different matrixes are not negligible to measure electromagnetic strain during fast excitation. The present results are expected to be able to provide basis measurements on the strain of pulsed superconducting magnet/cable （cable- around-conduit conductors, cable-in-conduit conductors）, independently or utilized together with other strain measurement methods.

Effect of Thermal Cycling under Load on Martensite Transformation and Two-way Shape Memory Effect in a TiNi Alloy

The effect of thermal cycling under loading on martensitic transformation and two-way shape memory effect was investigated for Ti-49.8 at, pet Ni alloy. It is shown that M(s), and M(f) temperature increase with increasing the number of cycles, while A(s) and A(f) temperature decrease during thermal cycling. The total strain at and permanent strain epsilon (p) increase with increasing applied stress and number of cycles. The two-way shape memory effect can be improved by proper thermal cycling training under loading, while excessively high applied stress results in the deterioration of TWSME. The reason for the changes in martensitic transformation characteristics and two-way shape memory effect during thermal cycling under loading is discussed based on the analysis of microstructure by TEM observations.

INFLUENCE OF TEMPERATURE-DEPENDENT PROPERTIES ON TEMPERATURE RESPONSE AND OPTIMUM DESIGN OF C/M FGMS UNDER THERMAL CYCLIC LOADING

The influence of temperature-dependent properties on temperature response and optimum design of newly developed ceramic-metal functionally graded materials under cyclic thermal loading and high temperature gradient environment is studied. The thermal conductivity of the material is considered to be dependent on the temperature. In this paper, the temperature response of the material is calculated using a nonlinear finite element method. Emphasis is placed on the influence of temperatue-dependent properties on the thermal response and insulation property of the material render the different graded compositional distributions and different heat flux magnitudes. Through the analysis, it is suggested that the influence of temperature-dependent properties can not be neglected in the temperature response analysis and the optimum design process of the material must be based on the temperature-dependent temperature analysis theory.

THERMAL CONSOLIDATION OF LAYERED POROUS HALF-SPACE TO VARIABLE THERMAL LOADING

An analytical method was derived for the thermal consolidation of layered, saturated porous half-space to variable thermal loading with time. In the coupled governing equations of linear thermoelastic media, the influences of thermo-osmosis effect and thermal filtration effect were introduced. Solutions in Laplace transform space were first obtained and then numerically inverted. The responses of a double-layered porous space subjected to exponential decaying thermal loading were studied. The influences of the differences between the properties of the two layers （e.g., the coefficient of thermal consolidation, elastic modulus） on thermal consolidation were discussed. The studies show that the coupling effects of displacement and stress fields on temperature field can be completely neglected, however, the the thermal responses. effect has an obvious influence on

INFLUENCE OF TEMPERATURE-DEPENDENT PROPERTIES ON THERMAL STRESSES RESPONSE AND OPTIMUM DESIGN OF C/M FGMS UNDER THERMAL CYCLIC LOADING

The influence of temperature-dependent properties on thermal stresses response and optimum design of newly developed ceramic-metal functionally graded materials under cyclic thermal loaning and high temperature gradient environment is studied. The thermal conductivity of material is considered to be dependent on the temperature. In this paper, the thermal stresses response of the material is calculated rising a nonlinear finite element method. Emphasis is placed on the influence of temperature-dependent properties on the thermal stresses response characteristics, the thermal stresses relaxation property and the thermal stresses history under the different graded compositional distributions and different heat flux magnitudes. Through tile analysis. it is suggested that the influence of temperature-dependent properties can not be neglected In the thermal stresses response analysis and the optimum design process of the material must be based on the temperature-dependent thermo-elastic-plastic theory.

Three-Dimensional Thermal-Stress Analysis of Semi-infinite Transversely Isotropic Composites

By making use of the direct integration method,an exact analysis of the general three-dimensional thermoelasticity problem is performed for the case of a transversely isotropic homogeneous half-space subject to local thermal and force loadings.The material plane of isotropy is assumed to be parallel to the limiting surface of the halfspace.By reducing the original thermoelasticity equations to the governing ones for individual stress-tensor components,the effect of material anisotropy in the stress field is analyzed with regard to the feasibility requirement,i.e.,the finiteness of the stress field at a distance from the disturbed area.As a result,the solution is constructed in the form of explicit analytical dependencies on the force and thermal loadings for various kinds of transversely isotropic materials and agrees with the basic principles of the continua mechanics.The solution can be efficiently used as a benchmark one for the direct computation of temperature and thermal stresses in transversely isotropic semi-infinite domains,as well as for the verification of solutions constructed by different means.

Numerical modeling of thermally-induced fractures in a large rock salt mass

Numerical modeling of thermally-induced fractures is a concern for many geo-structures including deep underground energy storage caverns. In this paper, we present the numerical simulation of a large-scale cooling experiment performed in an underground rock salt mine. The theory of fracture mechanics was embedded in the extended finite element code used. The results provide reliable information on fracture location and fracture geometry. Moreover, the timing of the fracture onset, as well as the stress redis- tribution due to fracture propagation, is highlighted. The conclusions of this numerical approach can be used to improve the design of rock salt caverns in order to guarantee their integrity in terms of both their tightness and stability.

A Theoretical Analysis of Functionally Graded Beam under Thermal Loading

Modeling of the behavior for Functionally Graded Beam (FGB) under thermal loading is introduced in the present work. The material properties are assumed to vary according to power function along the thickness of the beam. The effects of several parameters such as thermal expansion parameter, thermal conductivity and modulus of elasticity on the resultant axial stress of the FG beam have been studied. For thermal loading the steady state of heat conduction with power and exponentially variations through the thickness of FGB, is considered. The results obtained show that temperature distribution plays very important parameter controlling thermal resultant distribution of stresses and strains.