The Experts below are selected from a list of 7335 Experts worldwide ranked by ideXlab platform
Detlev Stover - One of the best experts on this subject based on the ideXlab platform.
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atmospheric plasma sprayed thick thermal barrier coatings with high segmentation Crack Density
Surface & Coatings Technology, 2004Co-Authors: Robert Vasen, Detlev StoverAbstract:Atmospheric plasma sprayed thick thermal barrier coatings (TBCs), comprising of 1.5 mm thickness yttria stabilized zirconia (YSZ) coating, have been developed for increasing thermal protection of combustor applications. Different segmentation Crack densities of the YSZ coating were created by controlling the deposition conditions. It was found that the substrate temperature played a dominant role in determining the segmentation Crack Density. The Density was found to increase with the increase of substrate temperature and liquid splat temperature. High passage thickness, if achieved by low plasma gun speed, contributed to improve the segmentation Crack Density. The Density could not be effectively improved by increasing the powder feed rate, although a high passage thickness was obtained in this case. The pores, mainly consisting of delaminations with the radii range between 0.02 and 1 μm, prevent the segmentation Cracks from propagation. The coatings sprayed at high substrate temperature show an excellent intersplat bonding and often even continuous columnar grains through several splats. Additionally, horizontally branching Cracks were also formed together with the segmentation Cracks when a high lamellar thickness was used during the spraying. Thermal cycling tests showed that the coating with a segmentation Crack Density of approximately 3.6 mm−1 had a lifetime of more than 1700 cycles at 1238 °C (surface)/938 °C (bond coat), indicative of excellent thermal shock resistance. Failure of the TBCs occurred by chipping in the surface layer of YSZ coating, which is different from the traditional interface delamination failure occurred with thinner TBCs.
Y Wang - One of the best experts on this subject based on the ideXlab platform.
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what is the suitable segmentation Crack Density for atmospheric plasma sprayed thick thermal barrier coatings with the improved thermal shock resistance
Applied Surface Science, 2018Co-Authors: Liang Wang, X H Zhong, Feng Shao, Jinxing Ni, Junwei Yang, Y WangAbstract:Abstract The optimization and control of the segmentation Crack Density (Ds) for the thick thermal barrier coatings (TTBCs) with the improved thermal shock resistance has been performed via finite element modeling. The simulation results based on the current property parameters of each layer of the TTBCs fabricated by atmospheric plasma spraying (APS) are well consistent with the experimental results of thermal shock test. The investigation results indicate that too large or too low Ds will be not beneficial to the improvement of the thermal shock resistance of the TTBCs. The Ds must be located at a suitable range, and this paper has revealed the objective law quantitatively. Based on our simulation and experimental results, the appropriate segmentation Crack Density is in the range of 2.38–4.76 Cracks/mm which will be beneficial to improve the thermal shock resistance ability. It has been found that the as-sprayed TTBCs exhibited superior thermal shock resistance when the segmentation Crack Density is about 4 mm−1. The stress intensity factor (KI) and energy release rate (J integration) will increase with the increasing of segmentation Crack length. The existence of segmentation Crack will improve the strain tolerance of TTBCs. The strain tolerance has been characterized by Ds and segmentation Crack length quantitatively. The failure mechanism of APS-TTBCs can be attributed to the propagation of segmentation Crack at the top-coat of the TTBCs, formation and propagation of the horizontal Crack at the top-coat/TGO (thermally grown oxide) interface. The propagation rate of the main segmentation Crack has been calculated and the life prediction model of the TTBCs during thermal cycle has been established. The possible methods which can prolong the service life of the TTBCs have also been proposed.
Chunsheng Lu - One of the best experts on this subject based on the ideXlab platform.
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numerical study on interaction of surface Cracking and interfacial delamination in thermal barrier coatings under tension
Applied Surface Science, 2014Co-Authors: Liwen Yang, Yong Zhou, Chunsheng LuAbstract:Abstract The interaction of surface Cracking and interfacial delamination in thermal barrier coatings under tension is investigated by using a cohesive zone finite element model. It is found that the surface Crack Density has a significant effect on the initiation and propagation of interfacial delamination. The interfacial delamination length decreases with increase of the surface Crack Density. The influence of ceramic coating thickness and interfacial adhesion parameters on surface Cracking and interfacial delamination is discussed. It is shown that the saturated Crack densities decrease with increase of the ceramic coating thickness and interfacial delamination length, and the critical surface Crack Density without interfacial delamination decreases as the interfacial adhesion energy increases. The results imply that the larger the surface Crack Density and interfacial adhesion energy are, the less the probability of interfacial delamination.
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quantitative assessment of the surface Crack Density in thermal barrier coatings
Acta Mechanica Sinica, 2014Co-Authors: Li Yang, Zhichun Zhong, Yichun Zhou, Chunsheng LuAbstract:In this paper, a modified shear-lag model is developed to calculate the surface Crack Density in thermal barrier coatings (TBCs). The mechanical properties of TBCs are also measured to quantitatively assess their surface Crack Density. Acoustic emission (AE) and digital image correlation methods are applied to monitor the surface Cracking in TBCs under tensile loading. The results show that the calculated surface Crack Density from the modified model is in agreement with that obtained from experiments. The surface Cracking process of TBCs can be discriminated by their AE characteristics and strain evolution. Based on the correlation of energy released from Cracking and its corresponding AE signals, a linear relationship is built up between the surface Crack Density and AE parameters, with the slope being dependent on the mechanical properties of TBCs.
Robert Vasen - One of the best experts on this subject based on the ideXlab platform.
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atmospheric plasma sprayed thick thermal barrier coatings with high segmentation Crack Density
Surface & Coatings Technology, 2004Co-Authors: Robert Vasen, Detlev StoverAbstract:Atmospheric plasma sprayed thick thermal barrier coatings (TBCs), comprising of 1.5 mm thickness yttria stabilized zirconia (YSZ) coating, have been developed for increasing thermal protection of combustor applications. Different segmentation Crack densities of the YSZ coating were created by controlling the deposition conditions. It was found that the substrate temperature played a dominant role in determining the segmentation Crack Density. The Density was found to increase with the increase of substrate temperature and liquid splat temperature. High passage thickness, if achieved by low plasma gun speed, contributed to improve the segmentation Crack Density. The Density could not be effectively improved by increasing the powder feed rate, although a high passage thickness was obtained in this case. The pores, mainly consisting of delaminations with the radii range between 0.02 and 1 μm, prevent the segmentation Cracks from propagation. The coatings sprayed at high substrate temperature show an excellent intersplat bonding and often even continuous columnar grains through several splats. Additionally, horizontally branching Cracks were also formed together with the segmentation Cracks when a high lamellar thickness was used during the spraying. Thermal cycling tests showed that the coating with a segmentation Crack Density of approximately 3.6 mm−1 had a lifetime of more than 1700 cycles at 1238 °C (surface)/938 °C (bond coat), indicative of excellent thermal shock resistance. Failure of the TBCs occurred by chipping in the surface layer of YSZ coating, which is different from the traditional interface delamination failure occurred with thinner TBCs.
Takato Takemura - One of the best experts on this subject based on the ideXlab platform.
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Microstructural based time-dependent failure mechanism and its relation to geological background
International Journal of Rock Mechanics and Mining Sciences, 2012Co-Authors: Takato Takemura, Hiroaki Kirai, Aliakbar GolshaniAbstract:Abstract The time-dependent hydro-mechanical behavior of rocks is important in assessing the long-term stability of deep underground excavation sites meant for long-term storage of radioactive waste. While evaluating the manner in which damage growth progresses at an excavation site, it is important to represent the failure criteria and microCrack evolution from the viewpoint of factors pertaining to microCrack geometry, such as the Crack Density. We performed creep tests on Inada granite samples to examine the effects of water, confining pressure, and weathering on time-dependent failure. The Crack Density of the samples, which was damaged at three characteristic stages of creep behavior (i.e., primary, secondary, and tertiary creep), was measured by means of a longitudinal wave velocity test; the microCrack evolution and failure criteria are discussed on the basis of the Crack tensor determined in the test. The following conclusions were reached from the test results. (1) The onset of tertiary creep corresponds to the peak stress under static loading conditions, and the tertiary creep stage corresponds to the post-failure region. (2) At the onset of tertiary creep, the Crack Density can be the failure criterion for time-dependent failure, and Crack Density can be estimated using the longitudinal wave velocity. (3) The time to failure for weathered granitic rock is approximately ten times faster than that for intact granitic rock. (4) The ratio of the mica group mineral in the granite may affect the time to failure, a fact that offers insight into the time-dependent stability of a rock mass on the field scale.
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changes in Crack Density and wave velocity in association with Crack growth in triaxial tests of inada granite
International Journal of the JCRM, 2006Co-Authors: Takato TakemuraAbstract:A non-dimensional second rank tensor Fij, called the Crack tensor, has successfully been introduced to deal with geometrical aspects of microCracks (fabric) such as anisotropy and Crack Density. Unfortunately, however, its usage for practical purposes is rather limited because its determination involves tedious and time-consuming laboratory work. We seek the possibility of using the directional change of longitudinal wave velocities to conquer the difficulty associated with the determination of Crack tensors. A new second-rank tensor Vij is introduced, such that the directional change in the longitudinal wave velocities is represented in terms of the tensor, and the Crack tensor Fij is then given as a function of Vij. Based on the analyses of the Crack tensors for one intact and several damaged samples of Inada granite, we then discuss how microCracks grow through the whole inelastic process, terminating at brittle failure. The conclusions are summarized as follows: The second-rank symmetrical tensor Vij (or its inversion tensor Vij -1 ) can be determined experimentally, with sufficient accuracy from the directional change in the squared longitudinal wave velocity. It is found that the tensor changes markedly so as to reflect the fabric of the damaged Inada granite formed by open microCracks. The principal axes of Vij -1 are coaxial with the principal axes of Fij so that both tensors are correlated in terms of their principal values Fi and Vi -1 .
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changes in Crack Density and wave velocity in association with Crack growth in triaxial tests of inada granite
Journal of Geophysical Research, 2005Co-Authors: Takato TakemuraAbstract:[1] A nondimensional second-rank tensor Fij, called the Crack tensor, has successfully been introduced to deal with geometrical aspects of microCracks (fabric) such as anisotropy and Crack Density. Unfortunately, however, its usage for practical purposes is rather limited because its determination involves tedious and time-consuming laboratory work. We seek the possibility of using the directional change of longitudinal wave velocities to conquer the difficulty associated with the determination of Crack tensors. A new second-rank tensor Vij is introduced, such that the directional change in the longitudinal wave velocities is represented in terms of the tensor, and the Crack tensor Fij is then given as a function of Vij. On the basis of the analyses of the Crack tensors for one intact and several damaged samples of Inada granite, we then discuss how microCracks grow through the whole inelastic process, terminating at brittle failure. The conclusions are summarized as follows: The second-rank symmetrical tensor Vij (or its inversion tensor Vij−1) can be determined experimentally, with sufficient accuracy from the directional change in the squared longitudinal wave velocity. It is found that the tensor changes markedly so as to reflect the fabric of the damaged Inada granite formed by open microCracks. The principal axes of Vij−1 are coaxial with the principal axes of Fij so that both tensors are correlated in terms of their principal values Fi and Vi−1. Four successive stages can be distinguished in regard to the Crack growth as follows: In stage 1, the rock behaves like an elastic solid. In stage 2, microCracks start to grow so that inelastic volumetric strain is slowly accumulated, along with microCracking. However, Crack growth does not occur globally but rather is limited within some local zones (probably in each grain). In stage 3, microCracking is considerably accelerated, suggesting that the micromechanism leading to Crack growth changes substantially at the boundary stress between stages 2 and 3. In stage 4, the Crack Density, as well as the dilatancy, increases explosively in association with a drop of a few percent in the differential stress after the peak stress is reached. Interestingly, this explosive increase is always associated with the development of a few fault zones. Experimental evidence seems to support the postulate that Inada granite starts to collapse once the Crack Density, F0(f), the first invariant of Fij, attains a threshold value of 7–8, regardless of the applied confining pressure. This can be a failure criterion in terms of the Crack Density, and be an extended expression for the so-called “critical dilatancy” for creep failure suggested by Kranz and Scholz (1977).
