Thermal Shock Loading Research Articles

Thermal shock induced oxidation of beryllium

Beryllium has been chosen as a plasma facing material for the first wall of the experimental fusion reactor ITER, mainly because of its low atomic number and oxygen getter capabilities, which are favorable for a high plasma performance. While the steady state operational temperature of 250 °C has no deteriorating effect on the beryllium surface, transient plasma events can deposit power densities of up to 1 GW m−2 on the beryllium armor tiles. Previous research has shown that the oxidation of beryllium can occur under these thermal shock events. In the present study, S-65 grade beryllium specimens were exposed to 100 thermal shocks with an absorbed power density of 0.6 GW m−2 and a pulse duration of 1 ms, leading to a peak surface temperature of ∼800 °C. The induced surface morphology changes were compared to a steady state heated specimen at the same surface temperature with a holding time of 150 s. As a result, a pitting structure with an average pit diameter of ∼0.45 μm was observed on the thermal shock loaded surface, which was caused by beryllium oxide grain nucleation and subsequent erosion of the weakly bound beryllium oxide particles. In contrast, the steady state heated surface exhibited a more homogeneous beryllium oxide layer featuring small pits with diameters of tens of nm and showed the beryllium oxide grain nucleation in a beginning stage. The experiment demonstrated that thermal shock loading conditions can significantly accelerate the beryllium oxide grain nucleation. The resulting surface morphology change can potentially alter the fusion application relevant erosion, absorption, and retention characteristics of beryllium.

Применение методов атомно-силовой и растровой электронной микроскопии с целью визуальной диагностики состояния адгезивных соединений твердых тканей зуба и композиционных полимерных материлов при ударных циклических термонагрузках

Применение методов атомно-силовой и растровой электронной микроскопии с целью визуальной диагностики состояния адгезивных соединений твердых тканей зуба и композиционных полимерных материлов при ударных циклических термонагрузках

Investigation of W–B behavior during short transient events by laser irradiation

The study of thermal shock resistance during short transient events is crucial to the development of fusion devices. In the current study, reinforced tungsten–boron composites were produced through powder metallurgy and spark plasma sintering at 1700°C and 44.1MPa. The microstructure and properties of the consolidated composites were studied through field emission scanning electron microscopy and X-ray diffraction. Laser thermal shock test was performed to study melting behavior and crack formation under single thermal shock loading. Erosion and cracks were observed after thermal shock loading. Crack propagation path analysis involved the following three methods (a) analysis of crack propagation directly through particles, (b) analysis of crack propagation through the interface between particles and matrix, and (c) analysis of crack propagation directly through matrix. Thermal stress primarily influences this phenomenon.

Elastic and elastoplastic fracture analysis of a reactor pressure vessel under pressurized thermal shock loading

Abstract Due to the limitation of the manufacturing process and improper operation, there may be defects near the inlet nozzles of reactor pressure vessel (RPV). Under pressurized thermal shock (PTS), the crack region is subjected to a high tensile stress, and the material toughness is gradually decreased in the cooling process. So it is necessary to evaluate the integrity of RPV in the thermo-mechanical coupling field. The 3-D finite element model is established for the beltline region around the inlet nozzles of a RPV. According to the calculated nil-ductility reference temperature, the elastic constitutive relation is firstly established for the fracture analysis. The stress intensity factors along the crack tips are compared with the material toughness. Using the XFEM, the crack propagation path is obtained to verify the predicted results. At relatively low reference temperatures, the ductility characteristics of the nuclear material can be exhibited. In this case, the ultimate bearing capacity of the structure is demonstrated by the elastoplastic fracture analysis. Finally, the safe range of reference temperature is summed up to prevent the surface crack from running through the whole wall thickness of the vessel during the PTS transient.

Study the dynamic crack path in brittle material under thermal shock loading by phase field modeling

A thermal–mechanical coupled phase field fracture model is developed to study the complex dynamic crack propagation path in brittle material under thermal shock loading. By introducing a global continuum phase-field variable to describe the diffusive crack, the coupling between heat transfer, deformation and fracture is conveniently realized. A novel elastic energy density function is proposed to drive the evolution of phase-field variable in a more realistic way. The three-field coupling equations are efficiently solved by adopting a staggered time integration scheme. The coupled phase field fracture model is verified by comparing with three classical examples and is then applied to study the fracture of disk specimens under central thermal shock. The simulations reproduce the three different types of crack paths observed in experiments. It is found that the crack grows through the heating area straightly at lower heating body flux, while branches into two at higher heating body flux loading. The crack branching prefers to occur in the heating area with larger heating radius and prefers to occur outside the heating area with smaller heating radius. Interestingly, the crack branches when propagation speed is at its lowest point, and it always occurs close to the compression region. It is shown that the heterogeneous stress field induced by temperature inhomogeneity may have a strong influence on the crack branching under the thermal shock loading.

Shock-induced nonlocal coupled thermoelasticity analysis (with energy dissipation) in a MEMS/NEMS beam resonator based on Green–Naghdi theory: A meshless implementation considering small-scale effects

ABSTRACTIn this article, a meshless method based on the generalized finite difference (GFD) method is developed for coupled thermoelsaticity analysis (with energy dissipation) considering small-scale effects in a micro-electromechanical-systems/nano-electromechanical-systems beam resonator. The Green–Naghdi theory of the generalized coupled thermoelasticity and nonlocal Rayleigh beam theory are utilized for dynamic analysis of a micro/nanobeam resonator subjected to thermal shock loading. The small-scale effects and energy dissipation are considered to derive the governing equations for both displacement and temperature fields. The governing equations are discretized in the Laplace domain using GFD method. To find the dynamic and transient behaviors of fields’ variables in time domain, an inversion Laplace technique is utilized, which is called the Talbot method. The effects of some parameters such as small-scale parameter and height of the micro/nanobeam on the dynamic behaviors of temperature and lateral deflection are discussed in detail.

A generalized J-integral for thermal shock analyses of 3D surface cracks in spatially and temperature dependent materials

Thanks to their favorable mechanical properties and modern manufacturing technologies, functionally graded materials (FGM) and structures have gained increasing utilization in engineering. One major applications of functionally graded ceramics, refractories or heat protecting layers is to improve the resistance against thermal shock impact. Here, fracture mechanical methods are needed to evaluate the strength and durability of such structures exposed to transient thermomechanical loading. Despite a lot of theoretical work has been done for two-dimensional crack configurations in thermoelastic FGM, real defects and structural components are of three-dimensional (3D) nature. In most cases the real gradation of the thermoelastic material properties does not obey simple mathematical functions, but shows a complex physical dependency on location due to manufacturing. Moreover, the elastic and thermodynamic properties depend on temperature itself.In this paper, we present the derivation of the 3D J-integral for arbitrary location and temperature dependent anisotropic material behavior. The functionally varying material properties are implemented in the finite element method (FEM) by means of »graded elements«. The J-integral is calculated in post-processing using the equivalent domain integral technique. The method is applied to surface cracks in a functionally graded plate under mechanical and thermal shock loading. Hereby, the real measured variation of all thermal and mechanical properties with porosity and temperature is exploited for a CaAl ceramic. The influence of the material gradation on the fracture parameters J and KI is investigated in various examples in order to find optimal gradation functions. It could be shown that the temperature dependency of thermoelastic material properties has an important effect on the results and must not be neglected.

Coupled thermoelasticity of FGM annular plate under lateral thermal shock

This study deals with the response of an FGM annular plate under lateral thermal shock load. The equations of motion are obtained using the first order shear deformation plate theory. The governing equations are solved using the Laplace transformation and Galerkin finite element method. Finally, numerical inversion of the Laplace transform is carried out to obtain the results in real time domain. It is shown that coupling coefficient has a damping effect on the radial force resultant and deflection.

Analytical solution of generalized coupled thermoelasticity problem in a rotating disk subjected to thermal and mechanical shock loads

ABSTRACTIn this article, a fully analytical solution of the generalized coupled thermoelasticity problem in a rotating disk subjected to thermal and mechanical shock loads, based on Lord–Shulman model, is presented. The general forms of axisymmetric thermal and mechanical boundary conditions as arbitrary time-dependent heat transfer and traction, respectively, are considered at the inner and outer radii of the disk. The governing equations are solved analytically using the principle of superposition and the Fourier–Bessel transform. The general closed form solutions are presented for temperature and displacement fields. To validate the solutions, the results of this study are compared with the numerical results available in the literature, which show good agreement. For the temperature, displacement and stresses, radial distributions, and time histories are plotted and discussed. The propagation of thermoelastic waves and their reflection from the boundary of the disk are clearly shown. Moreover, effects of relaxation time and angular velocity on temperature, displacement, and stress fields are investigated.

Effects of transient thermal shock loadings on the structure of zirconia ceramics

In this paper the influence of thermal shock loadings on the phase composition and microstructure of ZrO2(Y2O3) and ZrO2(MgO) ceramics was studied. It was found that thermal shock strains were no effect on phase composition of ZrO2(Y2O3) ceramics. Reducing the concentration of high-temperature tetragonal t-ZrO2 and cubic c-ZrO2 modifications and rising the content of low-temperature monoclinic m-ZrO2 crystal system with increasing the number of thermal shock strains were observed. The values of region coherent X-ray scattering of ZrO2(Y2O3) ceramics didn't changed, while the crystallite size of ZrO2(MgO) ceramics decreased. The formation of block structure in all studied ceramics was observed, the sizes of the blocks formed in the ZrO2(Y2O3) and ZrO2(MgO) ceramics were slightly different. The formation of the blocks in ZrO2(Y2O3) ceramics occurred on the grain boundaries, while the crystallites in ZrO2(MgO) ceramics were crushed due to phase transformation.

Elastic-plastic Fracture Mechanics Assessment of nozzle corners submitted to thermal shock loading

This paper focuses on the development of a simplified analytical scheme for the elastic-plastic Fracture Mechanics Assessment of large nozzle corners. Within that frame, following the specific numerical effort performed for the definition of a Stress Intensity Factor compendium, complementary elastic-plastic developments are proposed here for the consideration of the thermal shock loading in the elastic-plastic domain: this type of loading is a major loading for massive structures such as nozzle corners of large components. Thus, an important numerical was performed in order to extend the applicability domain of existing analytical schemes to those complex geometries. The final formulation is a simple one, applicable to a large variety of materials and geometrical configurations as long as the structure is large and the defect remains small in comparison to the internal radius of the nozzle.

Transient thermal fracture analysis of a penny-shaped magnetic and dielectric crack in a magnetoelectroelastic cylinder

ABSTRACTThe problem of penny-shaped magnetic and dielectric crack in a magnetoelectroelastic cylinder is investigated under thermal shock load. The problem is reduced to solve three coupled Fredholm integral equations. The field intensity factors are derived. Numerical results of crack opening displacement intensity factors are presented, and the effects of thermal shock time, crack configuration, and magnetoelectrical crack surface conditions on crack propagation and growth are evaluated. Among others, the larger cylinder's radius, the easier to propagate the crack is. For a fixed crack configuration, magnetoelectrical crack surface conditions have different effects on crack propagation as well.

Influence of surface morphology and microstructure on performance of CVD tungsten coating under fusion transient thermal loads

Thick tungsten coatings have been deposited by chemical vapor deposition (CVD) at a rapid growth rate. A series of tungsten coatings with different thickness and surface morphology were prepared. The surface morphology, microstructure and preferred orientation of the CVD tungsten coatings were investigated. Thermal shock analyses were performed by using an electron beam facility to study the influence of the surface morphology and the microstructure on the thermal shock resistance of the CVD tungsten coatings. Repetitive (100 pulses) ELMs-like thermal shock loads were applied at various temperatures between room temperature and 600°C with pulse duration of 1ms and an absorbed power density of up to 1GW/m2. The results of the tests demonstrated that the specific surface morphology and columnar crystal structure of the CVD tungsten have significant influence on the surface cracking threshold and crack propagation of the materials. The CVD tungsten coatings with a polished surface show superior thermal shock resistance as compared with that of the as-deposited coatings with a rough surface.

An investigation of the destabilizing behaviors of cemented carbide tools during the interrupted cutting process and its formation mechanisms

The premature failure of cemented carbide cutting tools is one of the main technical challenges in interrupted cutting. During the interrupted cutting process, the cutting edges of cemented carbide cutting tools are more susceptible to early fracture and failure than in the continuous process. This paper presents the results of an experimental study on the cutting performances of cemented carbide cutting tools without coatings, in interrupted cutting. Analysis is performed on the relevant destabilizing features and the fracture formation mechanism. Special workpieces were carried out in the cutting experiments, and relevant working states were monitored by a high-speed camera. The 3D force analyzer and thermal imaging instruments were combined, and the mechanical and thermal shock loads were collected, showing the evolution process of tool failure behaviors and further revealing the regularity of the destabilizing behaviors of the cemented carbide cutting tools. Laser confocal scanning microscopy and scanning electron microscopy were performed to observe tool cracks and micro-morphologies of the fracture surface of the cutting tools, which further demonstrated the failure mechanisms at different cutting stages. The cutting speeds and feed rates corresponding to different failure modes are regionally divided using statistical analysis, and the parameter area for safe cutting for cemented carbide tools is obtained. This study provides methods, data, and theoretical reference for the design of cemented carbide tools and the choice of cutting parameters.

A novel method to evaluate the thermal shock behavior of ZrB2-SiC-graphite composites under alternating complex thermal stress environments

The thermal shock behavior of ZrB2-SiC-graphite (ZSG) composites was investigated in this study using a novel method of simulating complex thermal stress states that involved electric resistance heating followed by dynamic water cooling. The ZSG composites were heated and cooled to 1020–2020°C at a constant heating rate of ~134°C/s and a constant cooling rate of ~536°C/s. The residual strength of the composites decreased at temperature difference of 1000–1400°C. This weakening in strength was attributed to the multiple microcracks and flaws that were created by the two-dimensional thermal stresses and by the expanding and shrinking in the volume of the composites, attributed to chemical/physical reactions. Next, it was found that the residual strength of the composites increased at temperature difference of 1400–1700°C, due to the formation of a liquid SiO2 glass and the increase in the quantity of oxides both of which were favorable to healing the flaws and cracks. Finally, the residual strength decreased slowly at temperature difference above 1700°C, which was attributed to the ZrO2-induced crack healing. It was found that the thermal shock behavior of the ZSG composites depended on both the temperature difference and the mode of the thermal shock loading. The material was particular sensitivity to the regime of alternating heating and cooling, which would be similar to actual flight conditions.

Integrity analysis of a reactor pressure vessel subjected to a realistic pressurized thermal shock considering the cooling plume and constraint effects

The fracture mechanic analysis of a reactor pressure vessel subjected to Pressurized Thermal Shock (PTS) loading is one of the most important issues for the assessment of life time extension of a nuclear power plant. The most severe scenario occurs during cold water injection in the cold leg due to a Loss-Of-Coolant Accident (LOCA). Two hypothetical LOCAs are assumed for an adopted reference design of a two-loop pressurized water reactor. Boundary conditions obtained from the RELAP5 code are used as input for three-dimensional computational fluid dynamics which provides the accurate description of the transient including the plume cooling effect. The safety assessment considers the comparison of the stress intensity factor for the deepest point of a surface crack front with the fracture toughness of the material. However, the fracture toughness of the materials is influenced by crack constraints determined by the T-stress. Therefore, safety margin of the reactor pressure vessel should be based on the K-T instead of on the K approach. The existence of a cooling plume affects the stress intensity factor and T-stress. Even if the cooling plume affects the T-stress, it is not translated into an increase of the safety margin. Therefore, in a PTS event with pronounced plume cooling a detailed model of the plume has to be considered in the structural analysis.

Study of the mechanical properties of Ti2AlC after thermal shock

The ternary carbides and nitrides, known as MAX phases combine the attractive properties of both ceramics and metals; for example the Ti2AlC ceramics examined in this work have attracted attention for aerospace applications. In the current work Ti2AlC ceramics were subjected to high level thermal shock (ΔT=1100°C) from a temperature of 1200°C with a cooling rate of more than 90°C/sec. After the thermal shock process the mechanical properties and the microstructure were investigated. Combined thermal shock and mechanical loading with an applied stress of 0, 50, 100 and 150MPa was examined and in all cases the samples maintained their microstructure without any micro-cracks or phase change as observed. Compression testing of all samples to failure indicated that their mechanical properties did not show any deterioration in the testing range examined. Such ceramic materials therefore show potential for high temperature and high load applications.

Evolution and interaction of surface cracks under thermal shock load

Thermal cracks would be easily formed on the surface of material under thermal shock. To investigate the thermal crack evolution behavior, the cyclic thermal shock test is applied and the finite element simulation is proposed to study the thermal stress field and the interactions between thermal cracks. Test results show that the thermal cracks nucleate on the specimen surface largely and finally form in stable thermal crack network. The length of the cracks could reach several millimeters, however, their depth is only about hundreds of microns. Simulation results show that large temperature and thermal stress gradient would occur in the cooling process, and the higher the cooling speed the higher the maximal thermal stress. Parallel and coplanar cracks both reflect weak interactions in crack shielding and enhancing effect, respectively. And the influence factors are also modeled in different crack distributions. All the simulation results agrees well with the experiment. DOI: http://dx.doi.org/10.5755/j01.mech.22.2.12671

Non-Fourier effect and inertia effect analysis of a strip with an induced crack under thermal shock loading

In this paper, the transient temperature fields and the dynamic stress intensity factors of a thermo-elastic strip containing an inner crack parallel to the heated surface under thermal shock are studied. The Biot number of the crack gap, hyperbolic heat conduction theory and equation of motion are considered to investigate the behavior of the temperature fields around the crack and the stress intensity factors. Fourier transform and Laplace transform are used to reduce this mixed boundary value problem. Numerical methods are used to solved the singular integrate equations. Finally, the numerical results are presented illustrating the influence of Biot number, non-Fourier effect and inertia effect on temperature field and stress intensity factors. It is found that the Biot number strongly affect the uniformity of the temperature field and the magnitude of the stress intensity factors. The stress intensity factors have higher amplitude and an oscillating feature comparing to those obtained under conventional Fourier thermal conduction condition and quasi-static hypothesis, which can help to better understand the crack behaviors of advanced materials under thermal impact loading.

Stress intensity factor calculation in sharp and beveled edge nozzle corners

This paper presents the work performed for the development of Stress Intensity Factor compendia for defects in nozzle corners. For that purpose, a large set Finite Element modeling were performed in order to cover the geometries, the defect sizes, the loading situations … encountered by large nuclear components. Then, based on that set of Finite Element modeling, an approximate solution relying on a fit of the stress field along the bisector line of the nozzle corner is proposed. This solution allows determining accurately the mean and maximum Stress Intensity Factor along the crack front for pressure loading and at the maximum of cold thermal shock loading. It is validated through a comparison to existing solutions or Finite Element modeling results.