Thermal Shock Fracture Behavior Research Articles

Non-Fourier heat conduction induced thermal shock fracture behavior of multi-crack auxetic honeycomb structures

Non-Fourier heat conduction induced thermal shock fracture behavior of multi-crack auxetic honeycomb structures

Thermal shock fracture behavior of wave-transparent brittle materials in hypersonic vehicles under high thermal flux by digital image correlation.

During diving, high orbit maneuver, or target detection and positioning, a hypersonic vehicle will experience high thermal flux. Aerodynamic heating will cause intense thermal shock to the antenna window and radar dome, which are usually made of brittle materials that are transparent to electromagnetic waves and are critical to the mission of target positioning and hitting. Therefore, determination of the time to fracture of the brittle materials under high thermal flux is of great significance. In this study, thermal shock tests were performed on two brittle materials, i.e., SiO2 and Al2O3, using a quartz lamp radiator test system with a maximum thermal flux of 1.5MW/m2. The difference between the pre-set and actual thermal fluxes for the tests was smaller than 1.0%. The time to fracture was determined for the two brittle materials by employing the digital image correlation method to capture and analyze changes in speckle images of the specimen's surface. The speckle image analysis also revealed variations in the surface strain values (εx and εy) prior to fracture. The test results provide important input for the safety and reliability design of radar domes and other electromagnetic wave-transparent signal detection and positioning components of hypersonic vehicles when subjected to high thermal fluxes.

The numerical manifold method for crack modeling of two-dimensional functionally graded materials under thermal shocks

Profiting from its bi-cover systems, i.e., the mathematical cover and the physical cover, the numerical manifold method (NMM) is superior in crack modeling. In this work, the NMM is further extended to study thermal shock fracture behavior of two-dimensional functionally graded materials (FGMs). The discontinuity of temperature and displacement fields across crack surface is naturally represented by the NMM, while the singularity of the heat fluxes and stresses at the crack tip is captured through the use of associated asymptotic terms in the NMM local functions. The temperatures are firstly obtained through transient heat transfer simulation and then stepwisely imported into the thermoelastic counterpart to compute the mechanical quantities. The thermal stress intensity factors (TSIFs) are obtained through the domain-independent interaction integral. For verification, several numerical examples with increasing complexity are tested and the NMM results match well with the available published solutions. Moreover, the influences of the material gradation of the FGMs and the crack geometries on the TSIFs are also revealed.

Dual-phase-lag heat conduction and associate fracture mechanics of a ceramic fiber/matrix composite cylinder

This paper studies a ceramic fiber/matrix composite cylinder subjected to a fast heating shock on its surface, which may have its root application for future thermal protection system of space vehicles. Theoretical model of the thermoelasticity field is established under the framework of dual-phase-lag (DPL) heat conduction. It is found that the intensity of the thermal wave described by DPL model increases with the heating rate. However the classic Fourier model scarcely embodies the effect of the heating rate on the thermoelasticity response. In addition, a comparison of the thermal stresses is made when investigating the fiber/matrix composite cylinder and the monolithic matrix cylinder. The fiber increases the compression stress of the matrix and decreases the tension stress due to the high modulus of the fiber. And the tension stress in the fiber is much higher than that in the matrix. Thus the thermal shock fracture behavior of the fiber/matrix composite cylinder with a center crack is studied. There is an optimal volume content for the fiber/matrix composite cylinder so that the peak value of the thermal stress intensity factor is minimized. This study may be useful for designs of fiber reinforced composites under severe heating.

Surface thermal shock fracture and thermal crack growth behavior of thin plates based on dual-phase-lag heat conduction

This paper studies the thermoelastic problem of a surface cracked plate subjected to a suddenly cooling under the framework of dual-phase-lag heat conduction model. The thermally induced stress intensity factor is calculated based on the linear theory of thermoelasticity. The results demonstrated that the non-Fourier effect is significant in very small time scale which is comparable to the thermal flux lag of the material. The thermal stress intensity factor increases with the thermal flux lag and temperature gradient lag of the material. In addition, the dual-phase-lag heat conduction model predicts a faster cracking behavior than the hyperbolic single-phase-lag heat conduction model and Fourier model in the beginning of thermal shock. It is also found that the crack growth terminates at a critical crack length, which increases with the temperature gradient lag of the material.

Dynamic Characterization of Thermal Shock Fracture Behavior in Alumina Ceramics under Unbalanced Thermal Stress State

Dynamic Characterization of Thermal Shock Fracture Behavior in Alumina Ceramics under Unbalanced Thermal Stress State

Effect of temperature-dependency of material properties on thermal shock fracture of solids associated with non-Fourier heat conduction

This paper investigates the thermal shock fracture behavior of a cracked semi-infinite medium with temperature-dependent material properties. The medium is subjected to a sudden temperature drop at its surface and all material properties are the functions of temperature. The temperature field and associated thermal stress in the medium without cracking are obtained by using the Laplace transform method and the numerical technology of Laplace inversion. The thermal stress intensity factors at the crack tip are obtained by using the weight function method. The thermal stress intensity factor and crack growth behavior are analyzed numerically by comparing the temperature-dependent model with temperature-independent model. The studies indicate the significance of temperature-dependent material properties on the thermal shock fracture and crack growth behavior of solids for high-temperature applications.

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.

Micromechanics-based Study on Thermo-mechanical Behavior of ZrO2/Ti Functionally Graded Materials

The aim of this study is to investigate thermo-mechanical response of ZrO 2 /Ti functionally graded materials (FGMs) fabricated by spark plasma sintering (SPS) based on a mean-field micromechanics model, which takes account of micro-stress relaxation due to interfacial diffusion between ceramic and metal phases as well as creep of both phases. A resistance to cyclic thermal shock loadings of FGMs with different compositional gradation patterns including Ti-rich, linear and ZrO 2 -rich gradation patterns has been investigated. The results demonstrate that Ti-rich FGMs show superior properties among the tested FGM samples. Mean-field micromechanics-based examinationsreveal that the range and ratio of thermal stresses in ZrO 2 surface layers in FGMs can affect cyclic thermal shock fracture behaviour but not mean thermal stresses. Creep of ZrO 2 have a large influence on dependence of the range and ratio of thermal stresses in ZrO 2 surface layers on compositional gradation patterns in the FGMs.

Analysis of Fracture Behavior of Metal/Ceramic Functionally Graded Materials under Thermal Stress

In this presented work, a coupled thermo-mechanical model is employed to analyze the thermo-mechanical behavior of ceramic functionally graded materials (FGMs) and the crack formation and propagation process of ceramic coating was simulated step in step and step by step using the RFPA (Realistic Failure Process Analysis) 2D-Thermo code. The thermal shock fracture behavior is discussed based on the basis of the simulated crack morphology and elucidated the mechanism of crack deformation and crack propagation. The state change from compression to tension whose magnitude is large enough to exceed the tension strength of ceramic causes the vertical crack. The numerical results agreed well with the experimental results in the previous literature.

Dynamic Characterization of Thermal Shock Fracture Behavior in Toughened Ceramics.

Dynamic Characterization of Thermal Shock Fracture Behavior in Toughened Ceramics.

Thermal fracture behavior of metal/ceramic functionally graded materials

Thermal fracture behavior of metal/ceramic functionally graded materials (FGMs) was evaluated by a well controlled burner heating method using a H 2/O 2 combustion flame, which simulated real environment. Partially stabilized zirconia (PSZ)/IN100 FGMs having finely mixed microstructures and PSZ/Inco718 FGMs having rather coarse microstructures were prepared by a slurry dipping and HIP sintering process. Also, three types of functionally graded thermal barrier coatings (TBCs) as well as duplex coatings, each designed to have the same thermal resistance, were fabricated by an air plasma spraying process. The fracture mechanism has been discussed on the basis of the crack morphology, the analysis of acoustic emissions and the variation of effective thermal conductivity. The thermal shock fracture behavior is discussed on PSZ/In100 FGMs and PSZ/Inco718 FGMs, while the cyclic fracture behavior is discussed on plasma sprayed coatings. The cyclic fracture behavior is found to be: orthogonal crack formation on the top surface during cooling, then transverse crack formation in the graded layer during heating, and subsequent growth of transverse cracks and their coalescence which eventually causes the ceramic coat to spall. Compared to duplex coatings, it has been revealed that functionally graded TBCs possess the desirable effect for improvement of spallation life under cyclic thermal loads. The dependence of spallation life on composition profile in functionally graded coatings has been discussed.

Thermal Shock Fracture Behavior of Alumina Ceramics Containing Pores.

Thermal shock fracture behavior of alumina ceramics containing pores was studied by measuring strength after water-quenching. The thermal shock fracture behavior was evaluated by a critical temperature difference (ΔTc) and a survival strength (σr) after water-quenching test. The critical temperature difference increased with increasing porosity. On the other hand, an influence of pore size could not be recognized. From the comparison between measured and estimated values, it was suggested that an increase in critical temperature difference was originated from the adiabatic effect by air bubbles generating at surface pores. The survival strength after water-quenching test increased with increasing pore size, but increase became smaller in pore sizes over 10μm. The reciprocal of squared survival strength could be related with the elastic strain energy stored up to fracture.

Dynamic Characterization of Thermal Shock Fracture Behavior in Oxide Ceramics

Dynamic Characterization of Thermal Shock Fracture Behavior in Oxide Ceramics

236 Experimental Characterization of Thermal Shock Fracture Behavior in Ceramic Materials

236 Experimental Characterization of Thermal Shock Fracture Behavior in Ceramic Materials

242 セラミック材料における熱衝撃破壊挙動のディスクオンロッド試験による動的評価(OS6-9 AE法)(OS6 実験力学の新展開)

New experimental technique (Disk-on-Rod Test) for the evaluation of thermal shock fracture behavior of ceramics was developed. The disk specimen with 20mm radius was heated to high temperature and quenched by means of contacting with the cool metal rod. The transient temperature on the disk specimen was measured by IR camera and thermal stress was calculated by finite element method. AE signals during thermal shock fracture were detected using an AE sensor attached on the bottom of the metal rod. It was understood that the maincrack was initiated at the center of the disc specimen and it was propagated with the deflection, arrested and re-propagated after several seconds. This behavior showed good agreement with the result of the thermal stress field and AE analysis. The critical stress for maincrack formation was determined by AE analysis. Consequently, the microfracture process during thermal shock fracture was well understood.

307 セラミックスにおける熱衝撃破壊過程のディスクオンロッド試験による動的評価(OS セラミックス,CMC及びMMC)

New experimental technique(Disk-on-Rod Test) for the evaluation of thermal shock fracture behavior of ceramics was developed. The disk specimen with 20mm radius was heated to high temperature and quenched by means of contacting with the cool metal rod. The transient temperature on the disk specimen was measured by IR camera and thermal stress was calculated by finite element method. AE signals during thermal shock fracture were detected using an AE sensor attached on the bottom of the metal rod. The maincrack was initiated at the center of the disc specimen and was propagated with the deflection, arrested and re-propagated after several seconds. This behavior showed good agreement with the result of the thermal stress field and AE analysis.

Grain Size Dependence of Thermal Shock Resistance in KZr<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> Ceramic

Thermal shock fracture behavior of KZr2(PO4)3 ceramic, which has a near-zero thermal expansion coefficient, was evaluated by the water-quenching test. The specimens having almost the same density, strength, Young's modulus, and thermal expansion coefficient, but different grain sizes, were prepared by adjusting the sintering conditions. The maximum temperature difference (ΔTmax), to which the specimens were subjected without failure in the thermal quench test, increased with decreasing grain size. KZr2(PO4)3 ceramic composed of fine grains<3μm withstood the test without lowering of strength even when quenching from 1300°C into water was repeated 20 times. The grain size dependence of ΔTmax has been attributed to residual stress caused by the thermal expansion anisotropy. As a result, grain size and thermal expansion anisotropy were incorporated into the equation for the thermal shock resistance.

Grain‐Size Dependence of Thermal‐Shock Resistance of Yttria‐Doped Tetragonal Zirconia Polycrystals

Thermal‐shock fracture behavior of yttria‐doped tetragonal zirconia polycrystals (Y‐TZP) of various grain sizes was evaluated by the quenching method using water as the quenching solvent. The tetragonal‐to‐monoclinic phase transformation behavior of Y‐TZP around cracks introduced by thermal stress was investigated by using Raman microprobe spectroscopy. The critical quenching temperature difference (ΔTc) of Y‐TZP ceramics increased from 250° to 425°C with increasing grain size of zirconia from 0.4 to 3.0 μm, while the fracture strength decreased from 900 to 680 MPa. The improvement of ΔTc of Y‐TZP with increasing grain size of zirconia corresponded with the quantity of tetragonal‐to‐monoclinic phase transformation around cracks introduced by thermal stress.

Microstructure and Mechanical Properties of Mullite Ceramics

Microstructural effects on the mechanical and thermomechancical properties of mullite ceramics have been investigated. The mullite ceramics were fabricated by reaction-sintering of mixture of kaolin and Al2O3(M-1) and by pressureless-sintering of a powder prepered from Al2O3 and SiO2 sols (M-2) and Al2O3 sol-ethylsilicate (M-3) system from the sol-gel method. Transmission electron microscopic observation revealed that samples M-1 and M-2 contained foreign phases, but that they were much less in M-2. These showed different temperature dependence in mechanical properties such as hardness, Young's modules, fracture toughness and strength. These differences were explained by the amount of grain boundary impurity phases. Thermal shock fracture behavior was also discussed.