Literatura académica sobre el tema "Transgranular Fractures"
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Artículos de revistas sobre el tema "Transgranular Fractures"
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Tatami, Junichi, Tomoko Ohbuchi, Katsutoshi Komeya y Takeshi Meguro. "Nanofractography of Alumina by Scanning Probe Microscopy". Key Engineering Materials 290 (julio de 2005): 70–77. http://dx.doi.org/10.4028/www.scientific.net/kem.290.70.
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Observation of fracture surfaces in ceramics is useful for improving their mechanical properties. In this study, fracture surfaces of polycrystalline alumina were observed using scanning-probe microscopy (SPM) on a nanoscale, also called “nano-fractography.” The average grain size of polycrystalline alumina specimen used in this study was 4.5µm, and the fracture toughness was 3.0MPa･m-1/2. The fracture mode was found to be a mixture of intergranular and transgranular fractures. The fracture surface of intergranular fractures consisted of smooth and rough areas composed of very small steps, whose detection was impossible using scanning electron microscopy. Cleavage and non-cleavage fractures were observed in transgranular fracture grains. The fracture surface of single-crystalline alumina, which is the typical model of the transgranular fracture, was also observed by SPM. The cleavage plane of alumina macroscopically exhibited a very smooth, glass-like surface. However, sub-nano meter steps can be observed on the cleavage fracture surface and appear to be formed by plastic deformation during crack propagation because the size of the step nears that of the Burgers vector.
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Liu, Guoping, Lianbo Zeng, Xiaojun Wang, Mehdi Ostadhassan, Zhenlin Wang, Zhe Mao y Qi Tie. "Natural fractures in deep tight gas sandstone reservoirs in the thrust belt of the southern Junggar Basin, northwestern China". Interpretation 8, n.º 4 (23 de julio de 2020): SP81—SP93. http://dx.doi.org/10.1190/int-2020-0051.1.
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The development of natural fractures is a significant characteristic of the Jurassic deep tight sandstone reservoirs in the thrust belt of the southern Junggar Basin, and these reservoirs have a great potential for natural gas resources. Based on the analyses of outcrops, cores, thin sections, and other laboratory data, natural fractures in these reservoirs are mainly tectonic ones, which appear in groups and vary in scale, dip angle, and density. We have classified fractures in thin sections into intragranular, grain boundary, and transgranular ones depending on their relationship with minerals grains. Almost 58% of the whole fracture population is opening-mode fractures, and calcite is the main filling mineral for the remaining ones. Fracture apertures vary based on their types, where transgranular fractures are the widest, followed by grain boundary and intragranular ones. Lithology, rock mechanical mechanics layers, and structures control the development of natural fractures. Fractures are more frequent in siltstone and fine sandstone. Sandstones with larger mineral grains are more likely to develop grain boundary and intragranular fractures. Intralayer fractures are the dominant ones, which intersect the rock mechanics interface at high angles or perpendicularly. The linear density of these fractures decreases when the thickness of the rock-mechanics layer increases. Furthermore, fractures have a higher degree of development in the hanging wall of the faults, with the degree decreasing when the distance from the fault plane increases. Additionally, the development degree of fractures in the damage zone is better than the adjacent rocks, and the width of damage zones is a function of the amount of fault displacement.
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Marchionni, M., Hellmuth Klingelhöffer, Hans Joachim Kühn, T. Ranucci y Kathrin Matzak. "Thermo-Mechanical Fatigue of the Nickel–Base Superalloy Nimonic 90". Key Engineering Materials 345-346 (agosto de 2007): 347–50. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.347.
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The thermo-mechanical fatigue (TMF) behaviour of the Nimonic 90 Nickel base superalloy has been investigated within two laboratories. In-phase-tests (IP) where the maximum mechanical strain occurs at the maximum temperature (850°C), and 180°-out-of-phase-tests (180° OP) where the maximum mechanical strain coincides with the minimum temperature (400°C) have been applied. All tests were carried out at varying mechanical strain ranges with a constant strain ratio of Rε = - 1. A temperature rate of 5 K/s was used throughout the whole cycle without any additional cooling system during decreasing temperature. The fatigue life of 180° OP tests is longer compared to identical IP tests. The stress / mechanical strain hysteresis loops are completely different and some characteristic values are compared to each other. The fracture surfaces observed show that fatigue crack (or cracks) starts on the external surface and propagates inwards. The fractures of 180° OP tests are transgranular showing the presence of fatigue striations, while the fractures of IP tests are mixed transgranular and intergranular with no fatigue striations.
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Traylor, L. B. y C. E. Price. "A Comparison of Hydrogen and Mercury Embrittlement in Monel at Room Temperature". Journal of Engineering Materials and Technology 108, n.º 1 (1 de enero de 1986): 31–36. http://dx.doi.org/10.1115/1.3225838.
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Slow strain rate tensile tests were performed on annealed and cold drawn Monel 400 and Monel R405 at room temperature in air, mercury, and electrolyte hydrogen. Hydrogen and mercury caused embrittlement with the fractures having the same specific features. Crack initiation was largely intergranular but an increasing proportion of transgranular cracking occurred subsequently, especially in the presence of hydrogen and for Monel R405. It is believed that the decreased cohesive strength and enhanced shear models of embrittlement apply to the intergranular and transgranular crack modes respectively.
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Wang, Shaojie, Yu Wang, Jing Han, Wei Zeng, Xuemei Zhang, Guangze Dai y Zhongxuan Xu. "Effect of pre-corrosion on the fatigue fracture behavior of ER8 wheel steel". Materials Express 11, n.º 5 (1 de mayo de 2021): 766–72. http://dx.doi.org/10.1166/mex.2021.1948.
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The salt spray pre-corrosion test was carried on the fatigue specimens of ER8 wheel steel, and then fatigue experiment with a stress ratio (R) of 0.1 was conducted. The fractures were characterized by field emission scanning electron microscopy. The results show that pre-corrosion significantly reduces the fatigue limit of the rim material, the main crack-induced fracture mechanism occurs under pre-corrosion conditions for 6 h at a lower stress, and the fracture mechanism of multi-crack interactions occurs at a higher stress after pre-corrosion for 48 h. For pre-corrosion fatigue test, cracks originate from pitting pits. Then, multiple fatigue crack nucleations expand from different orientations in the transgranular fracture mode, forming cleavage facets.
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Bartolomé, José F., Luis E. Fuentes-Cobas, Álvaro García, Alfredo Jacas y Lorena Pardo. "Cyclic Mechanical Fatigue Lifetime of Bi0.5Na0.5TiO3-Based Eco-Piezoceramics". Materials 14, n.º 15 (23 de julio de 2021): 4113. http://dx.doi.org/10.3390/ma14154113.
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The mechanical strength and cyclic fatigue behavior of PIC700 commercial eco-piezoceramic disks are investigated under biaxial loading on unpoled and poled samples. The bending strength of unpoled samples was higher than those of poled ones. Fatigue tests were conducted under a load ratio of 10 at a frequency of 20 Hz with a sinusoidal waveform. The curve fitting for the S-N fatigue diagram is used to predict the lifetime of these eco-piezoceramics and describe their fatigue behavior. It was also found that the unpoled samples exhibited higher fatigue resistance than the poled ones. The fatigue limit of maximum load for ten million cycles of unpoled and poled samples was estimated to be 160 and 135 MPa, respectively. The detailed observations of the fatigue fracture surfaces by scanning electron microscopy (SEM) indicated that a wavy surface with a mixture of transgranular and intergranular fractures occurred preferentially in the case of the poled material. On the other hand, transgranular fractures seem to be predominant in the unpoled samples. It appears that the poling process causes the change in failure characteristics due to domain orientation that leaves an anisotropic stress field in the material. The poled ceramics possess a local stress concentration created by the orientation under the electric poling field of the 90° ferroelectric–ferroelastic domains. Under this local stress concentration, a microstructural degeneration is induced by domain switching under the cyclic load that accelerates crack growth, thereby reducing fatigue lifetime.
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Nian, Tao, Yanze Li, Tao Hou, Chengqian Tan y Chao Liu. "Natural fractures at depth in the Lower Cretaceous Kuqa Depression tight sandstones: identification and characteristics". Geological Magazine 157, n.º 8 (13 de enero de 2020): 1299–315. http://dx.doi.org/10.1017/s0016756819001444.
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AbstractThe Kuqa Depression in the northern Tarim Basin, NW China, is characterized by fault-controlled anticlines where natural fractures may influence production. Natural fractures in the Lower Cretaceous tight sandstones in the depression have been studied using seismic profiles, borehole images, cores and thin-sections. Results show that thrust faults, two types of opening-mode macrofractures and two types of microfractures are present. Thrust faults were generated during Cenozoic N–S-directed tectonic shortening and have hydraulically linked Jurassic source rocks and Cretaceous sandstones. Opening-mode fractures can be subdivided on the basis of sizes, filling characteristics and distribution patterns. Type 1 macrofractures are barren or mainly calcite-lined. They have straight traces with widths (opening displacements) that are of the order of magnitude of 10 μm, suggesting that their primary role is that of migration channels. Type 2 macrofractures are calcite-filled opening-mode fractures. They have an elliptical or tabular shape with sharply tapering tips. Transgranular microfractures are lens-shaped and open or filled mostly by calcite; maximum widths range between 0.01 mm and 0.1 mm. Intragranular microfractures are the most common microfracture type. They are filled by calcite, feldspar or quartz. The macrofractures and transgranular microfractures have regular distributions, while most intragranular microfractures are irregularly distributed owing to their inherited origin. The results imply that natural fractures in the tight sandstones were formed as tectonic, diagenetic and natural hydraulic origins. In situ stress and cementation analyses suggest that Type 1 macrofractures and their genesis-related microfractures have controlled the present flow system of the tight sandstones.
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Perek-Nowak, Małgorzata y Joanna Karwan-Baczewska. "Influence of Molybdenum and Boron Addition on Fracture of P/M Parts". Key Engineering Materials 682 (febrero de 2016): 265–69. http://dx.doi.org/10.4028/www.scientific.net/kem.682.265.
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Samples made of iron powder with addition of 1.5 and 2% of molybdenum and 0-0.6% of boron were compacted at 600 MPa and sintered at 1200°C for 60 minutes in hydrogen atmosphere after mixing in Turbula mixer. The samples were deformed in a tensile test till rupture. The effect of molybdenum and boron on topography of fracture is discussed. It is noted that the sintering mechanism changes upon addition of boron particles into Fe-Mo alloy. The fractures of the studied samples were observed by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The addition of Mo influences the change of fracture to ductile type. The type of fracture is brittle with Mo and borides segregating to grain boundaries. In the alloys with low concentrations of molybdenum boron induces brittle transgranular fracture.
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Islam, M. A. y Yo Tomota. "Fatigue Strength and Fracture Mechanisms of IF28 Steels". Advanced Materials Research 15-17 (febrero de 2006): 804–9. http://dx.doi.org/10.4028/www.scientific.net/amr.15-17.804.
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Interstitial free (IF) steels are widely used as thin sheet in the automobile industries because of their many favorable properties. Although, fatigue properties of IF steels do not have significant importance to auto body makers, however, they are very concerned about the tensile and fatigue strength of the steels used for structural purposes to ensure safety of passengers. So, fatigue results of this steel might help researchers to understand the behaviors of high strength steels. In this study cyclic and static properties have been studied at room temperature in the air. Initiative has also been taken to observe the fatigue fracture morphology of this steel. Experimental results show that the fatigue limit is corresponding to about 40% of tensile strength and 80% of the yield strength of this steel. Fractographic observations reveal a mixed type of fracture mode (intergranular and transgranular cracking) fractures.
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Yun, Jong Guk, Xin Ming Cao, Yue Wang, Yan Kang y Xiao Wu Li. "Characterizations of Fatigue Deformation and Fracture Behavior of Commercially Pure Iron with Grain Boundary Micro-Voids". Applied Mechanics and Materials 66-68 (julio de 2011): 1942–47. http://dx.doi.org/10.4028/www.scientific.net/amm.66-68.1942.
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Fatigue deformation behavior of the commercially pure iron containing micro-voids at grain boundaries (GBs) were investigated under total strain amplitude control, and fatigue fractures were quantitatively characterized by fractal analyses. The cyclic response curves of the CP iron show an initial softening stage within early several cycles followed by a continuous cyclic hardening. No stress saturation phenomenon was found. Pre-existence of micro-voids at GBs spurs intergranular cracking to become a common damage mode besides transgranular cracking along slip bands. Quantitative analyses of fracture surface demonstrate that the value of fractal dimension D of the scanning profile in the crack growth zone is the largest as compared to those in the crack source zone and final rapid fracture area, almost regardless of the applied strain amplitude. This phenomenon was discussed in terms of the tortuosity of crack propagation path.
Tesis sobre el tema "Transgranular Fractures"
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Françon, Virginie. "Corrosion sous contrainte par l’iode des alliages de zirconium : étude des paramètres critiques pour l’amorçage intergranulaire et la transition inter/transgranulaire". Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0046.
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La corrosion sous contrainte par l’iode (CSC-I) est l’un des mécanismes de rupture potentiels des crayons combustibles en alliage de zirconium, pouvant intervenir au cours des transitoires de puissance des réacteurs nucléaires. La fissuration par CSC-I comporte trois étapes : amorçage de la fissure, développement intergranulaire puis propagation transgranulaire. Le but du travail est d’identifier des paramètres critiques gouvernant les transitions entre ces différentes étapes. En premier lieu, des essais sur des éprouvettes en Zircaloy présentant des finitions de surface et des états métallurgiques variés permettent de discriminer l’influence de différents paramètres sur l’amorçage des fissures. Nous mettons en évidence le rôle critique du niveau des contraintes résiduelles, de leur répartition en surface ainsi que de leur profil au sein du matériau. La sensibilité des alliages à l’amorçage des fissures n’est pas directement corrélée à la rugosité de la surface. Cependant, la dispersion des paramètres de rugosité traduit l’irrégularité du profil, l’hétérogénéité du niveau des contraintes résiduelles, et donc l’existence de zones où les contraintes résiduelles sont localement moins protectrices. Dans un second temps, des éprouvettes de Zircaloy-4 possédant différents états d’écrouissage sont sollicitées sous charge constante, en présence de méthanol iodé. Les modifications microstructurales induites par l’écrouissage favorisent l’apparition de la propagation transgranulaire des fissures de CSC-I. Des observations des faciès de rupture en MET révèlent que la transition inter/transgranulaire intervient dans des zones où les grains sont fortement désorientés les uns par rapport aux autres, suite à l’augmentation des contraintes locales résultant des incompatibilités de déformation grain à grainIodine-induced stress corrosion cracking (I-SCC) is one of the potential failure modes of zirconium alloy fuel claddings during power transients in nuclear reactors. I-SCC failures are usually described in three steps: initiation of cracks, intergranular development and transgranular propagation. The objective of this work is to identify critical parameters controlling transitions between crack propagation modes. First of all, experiments conducted on Zircaloy samples with various surface conditions and metallurgical states lead to discriminate the influence of several parameters responsible for cracks initiation. The critical role of residual stresses level, their distribution at the subsurface and their evolution in the bulk of the material is evidenced. Sensitivity to I-SSC is not directly correlated to surface roughness. However, dispersion in roughness parameters indicates the presence of surface irregularities, heterogeneities of residual stresses and the existence of surface areas where residual stresses are less protective. In a second step, Zircaloy-4 samples with various strain-hardening pre-treatments are submitted to constant load tests in an iodine methanol solution. Microstructural modifications induced by a strain-hardening pre-treatment enhance transgranular propagation of I-SCC cracks. TEM observations of fracture surfaces show that the intergranular to transgranular crack transition takes place preferentially where the relative crystallographic orientation is large between two adjacent grains, because of local stress concentrations resulting from strain incompatibilities between neighbouring grains
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Ayyildiz, Muhammed. "Scales Depencence of Fracture Density and Fabric in the Damage Zone of a Large Displacement Continental Transform Fault". Thesis, 2012. http://hdl.handle.net/1969.1/148095.
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Characterization of fractures in an arkosic sandstone from the western damage zone of the San Andreas Fault (SAF) at San Andreas Fault Observatory at Depth (SAFOD) was used to better understand the origin of damage and to determine the scale dependence of fracture fabric and fracture density. Samples for this study were acquired from core taken at approximately 2.6 km depth during Phase 1 drilling at SAFOD. Petrographic sections of samples were studied using an optical petrographic microscope equipped with a universal stage and digital imaging system, and a scanning electron microscope with cathodoluminescence (SEM-CL) imaging capability. Use of combined optical imaging and SEM-CL imaging was found to more successfully acquire true fracture density at the grain scale. Linear fracture density and fracture orientation were determined for transgranular fractures at the whole thin section scale, and intragranular fractures at the grain scale. The microscopic scale measurements were compared to measurements of mesoscopic scale fractures in the same core, as well as to published data from an ancient, exhumed trace of the SAF in southern California. Fracturing in the damage zone of the SAF fault follows simple scaling laws from the grain scale to the km scale. Fracture density distributions in the core from SAFOD are similar to distributions in damaged arkosic sandstone of the SAF along other traces. Transgranular fractures, which are dominantly shear fractures, indicate preferred orientation approximately parallel to the dominant sets of the mesoscale faults. Although additional work is necessary to confirm general applicability, the results of this work demonstrate that fracture density and orientation distribution over a broad range of scales can be determined from measurements at the mesoscopic scale using empirical scaling relations.
Capítulos de libros sobre el tema "Transgranular Fractures"
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Sieradzki, K. "Theory of Environmental Effects on Transgranular Fracture". En Chemistry and Physics of Fracture, 219–52. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3665-2_13.
Texto completoActas de conferencias sobre el tema "Transgranular Fractures"
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Li, Zhenlei, Duoqi Shi, Xiaoguang Yang y Nina Li. "Experimental Investigation on the Creep and Low Cycle Fatigue Behaviors of a Serviced Turbine Blade". En ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90717.
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Abstract This paper experimentally investigated the creep and fatigue behaviors of a low-pressure turbine (LPT) blade with 600 hours of service using a novel test system. Pure low cycle fatigue (LCF), pure creep and creep-fatigue interaction (CFI) experiments on the full-scale serviced blades were conducted respectively. Test results showed that the increasing of deformation amplitude was divided into three stages under both pure LCF and creep-fatigue loadings. The deformation of each blade increased rapidly until failure when the test cycle exceeded the 80% of their overall life under the pure LCF and CFI condition. The hold period in creep-fatigue tests shortens the first stage of whole life and has no influence on the proportion of crack initiation life to overall life. The fractures in pure LCF, pure creep and creep-fatigue tests emerged transgranular, intergranular and both transgranular and intergranular behaviors respectively. The crack initiated and propagated in a specific zone of the blade under all the experimental loadings, which limited its creep-fatigue resistance. At last, the remaining life of turbine blade was estimated conservatively by introducing the safety limit into a statistical method.
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Zheng, Guoxiong, Yifan Luo y Hideo Miura. "Degradation of the Strength of a Grain and a Grain Boundary due to the Accumulation of the Structural Defects of Crystal". En ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-87264.
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Various brittle fractures have been found to occur at grain boundaries in polycrystalline materials. In thin film interconnections used for semiconductor devices, open failures caused by electro- and strain-induced migrations have been found to be dominated by porous random grain boundaries that consist of a lot of defects. Therefore, it is very important to explicate the dominant factors of the strength of a grain boundary in polycrystalline materials for assuring the safe and reliable operation of various products. In this study, both electron back-scatter diffraction (EBSD) analysis and a micro tensile test in a scanning electron microscope was applied to copper thin film which is used for interconnection of semiconductor devices in order to clarify the relationship between the strength and the crystallinity of a grain and a grain boundary quantitatively. Image quality (IQ) value obtained from the EBSD analysis, which indicates the average sharpness of the diffraction pattern (Kikuchi pattern) was applied to the crystallinity analysis. This IQ value indicates the total density of defects such as vacancies, dislocations, impurities, and local strain, in other words, the order of atom arrangement in the observed area in nano-scale. In the micro tensile test system, stress-strain curves of a single crystal specimen and a bicrystal specimen was measured quantitatively. Both transgranular and intergranular fracture modes were observed in the tested specimens with different IQ values. Based to the results of these experiments, it was found that there is the critical IQ value at which the fracture mode of the bicrystal specimen changes from brittle intergranular fracture at a grain boundary to ductile transgranular fracture in a grain. The strength of a grain boundary increases monotonically with IQ value because of the increase in the total number of rigid atomic bonding. On the other hand, the strength of a grain decreases monotonically with the increase of IQ value because the increase in the order of atom arrangement accelerates the movement of dislocations. Finally, it was clarified that the strength of a grain boundary and a grain changes drastically as a strong function of their crystallinity.
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Ellis, Fred V. "Fatigue and Corrosion Fatigue Failures". En ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71051.
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A metallurgical failure analysis was performed for a hanger rod and a waterwall tube sample. The hanger is a rigid type and supports a long vertical run of piping. The fracture is in one of the threaded ends and the fracture surface consists of three regions. The outermost portion adjacent to the thread root has ratchet marks that are an indication of fatigue crack initiation. The center portion has concentric, oval shaped beachmarks. The oval shape is consistent with an applied loading due to two bending moments. The inner portion is the final fracture and is approximately 1/4 of the thread root area indicating relatively low remote stresses. The failure mechanism is fatigue based on the beachmarks on the fracture surface and the transgranular cracking. The lower slope waterwall tube failure had a window opening fracture appearance. The axial fractures forming the window are located at the edge of the membrane welds on the cold or backside. There are shallow toe cracks at the membrane weld on the tube outside surface. The fracture surface had multiple, thumbnail-shaped fatigue cracks connected to the inside surface. These fatigue cracks are due to the corrosion fatigue mechanism based on two factors: (1) the stress responsible for their growth is related to the unit thermal cycling and the welded panel geometry near the corner of the boiler, and (2) they are oxidized indicating a corrosion contribution.
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Kim, Dal Sun, Sia Nemat-Nasser y Yun Seon Kim. "Preliminary Study of Alternative Material Development of Ballistic Attributes". En ISTFA 1998. ASM International, 1998. http://dx.doi.org/10.31399/asm.cp.istfa1998p0093.
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Abstract The purpose of this research is to examine the performance of tungsten heavy alloy (WHA) susceptible to adiabatic shear failures and to identify the microscopic findings of shear band and its effect on the engineering behavior. Experimental results show that the binder-phase (Fe-Ni) and tungsten particles (W) have the high work-hardening rate at low-strain-rate compression (10-3 /sec). Thermal softening behavior is dominant at high-strain-rate (> 103 /sec), and this material is relatively insensitive to strain rate in the range of 3000 - 5000 /sec. The microscopic analysis by SEM reveals that most fractures in the shear band are intergranular where the Fe-Ni matrix has the least resistance to fracture. Transgranular fracture is also observed, but not significantly. With the constant strain rate, no shear band was observed under 30% compressive strain, whereas the extensive shear band was formed at the 50% strain with significant crack formation along the shear band zone and extends through the specimen thickness forming a cone shape inclined at an angle 40° to 50° to the loading direction. The measured surface temperature of the 40%-strained specimen is approximately 250 °C using high speed infrared temperature technique. A significant decrease in the ultrasonic velocities is measured with extension of the shear band.
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Messer, Barry, Shahab Soltaninia y Ted Hamre. "Susceptibility of Carbon Steel Pipe, Fittings and Flanges to Brittle Fracture". En ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65825.
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Brittle fractures in parent material carbon steel pipe, fittings, and flanges are surfacing in recent ASME B31.3 refinery and gas plant construction and facility start-ups with unexpected low toughness of 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at −10°C (14°F) to −29°C (−20°F). The issue is becoming wide-spread globally, affecting up to 30 percent of materials tested, although many manufacturers are not experiencing this issue. The issue creates a new brittle fracture risk that needs to be addressed as the uncertainty of not knowing suitability for service at temperatures down to −29°C (−20°F) is concerning for reliability and safety. These components are considered by ASME VIII Div I and ASME B31.3 Code as being inherently ductile, and brittle fracture resistant without any Charpy impact testing requirements. Testing showed brittle transgranular cleavage cracks. The components were deemed to be unsuitable and not safe for use at low temperatures even though they complied with the applicable ASME Codes [1, 2] and ASTM material standards. Low toughness can result in brittle fracture of the material during hydrostatic tests, cold start-ups, or upset conditions that result in low temperature operations. Additionally, some ASTM A350 LF2 CL1 [3] forged flanges certified to −46°C (−50°F) exhibited the same 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at −46°C (−50°F). This paper discusses historical literature, metallurgical investigations, findings, and factors that contribute to susceptibility to brittle fracture including chemistry, grain size, heat treatment and forming techniques and also issues of ductile to brittle temperature transition shift, and fracture mechanical assumptions. This paper provides guidance to ensure the components are suitable for service and proposes options in addition to the current minimum Codes requirements to mitigate risks of in-service brittle fracture.
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Ozawa, Yuji, Tatsuya Ishikawa y Yoichi Takeda. "Characterization of Crack Tip Damage Zone Formation on Alloy 625 During Fatigue Crack Growth at 750°C by Transmission EBSD Method". En ASME 2017 Power Conference Joint With ICOPE-17 collocated with the ASME 2017 11th International Conference on Energy Sustainability, the ASME 2017 15th International Conference on Fuel Cell Science, Engineering and Technology, and the ASME 2017 Nuclear Forum. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/power-icope2017-3458.
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In order to clarify the mechanism of fatigue crack growth in alloy 625, which is a candidate material for use in advanced ultra supercritical power plants, the crack tip damage zone formation after a crack growth test conducted in high temperature steam was investigated. It was observed that the oxide thickness at the crack tip tended to increase with decreasing cyclic loading frequency. The crack path was a mix of transgranular and intergranular fractures. According to the grain reference orientation deviation (GROD) maps, it was revealed that the density of geometrically necessary dislocations (GNDs) in the matrix along the crack path and ahead of crack tip increased with an increase in the fatigue crack growth rate (FCGR) due to environmental effects. It was observed that (1) mobile dislocations at the crack surface were blocked due to the thick oxide layer, resulting in an increase in the density of GNDs, and (2) an increase in the density of GNDs might induce stress concentration at the crack tip, deformation twinning, and the acceleration of FCGRs.
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Li, Yan y Min Zhou. "Effect of Competing Mechanisms on Fracture Toughness of Polycrystalline Metals". En ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-52896.
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Fracture toughness in ductile materials is the combined effect of the plastic dissipation and the energy spent in creating new surfaces. The design of polycrystalline metals with improved fracture toughness requires in-depth understanding of two levels of competitions: the competition between plastic deformation and crack formation as well as the competition between transgranular and intergranular fracture. Currently, no systematic approach exists to address the two competitions. The fundamental challenges lie in the difficulty in separating the two energy dissipations and inadequate knowledge about the correlation between fracture mechanisms and material fracture toughness. In this paper, a Cohesive Finite Element Method (CFEM) based multiscale framework is introduced to quantify the two levels of competitions. The fracture toughness of ductile materials is predicted by calculating the J-integral at the macroscale. The fracture surface energy for different type of failure mechanisms is evaluated through explicit simulation of crack propagation at the microstructure level. The calculations carried out here concern AZ31 Mg alloy. Results indicate that the mixed transgranular and intergranular failure can lead to optimized fracture toughness. Microstructures with refined grain size and grain boundary bonding strength can best promote the favorable failure mechanisms.
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Hashida, Toshiyuki, Yohei Takeyama y Kazuhisa Sato. "The Effects of Oxygen Vacancy Concentration on the Mechanical Properties of Zirconia and Ceria-Based Electrolytes for SOFCs". En ASME 2009 7th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2009. http://dx.doi.org/10.1115/fuelcell2009-85241.
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In this paper, we discuss the effects of different oxygen partial pressures on the deformation property and fracture characteristics of representative constituent materials for solid oxide fuel cells (SOFCs). The elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC) treated under different oxygen partial pressures were evaluated using the small-punch testing method in this study. The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 °C under an oxygen partial pressure in the range of 0.21 to 10−22 atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10−15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ. The elastic modulus and fracture strength of 10GDC for the treatment under 10−22 atm was reduced down to 10–20% of those treated under the atmospheric pressure. SEM observations revealed that the fracture surface of the 10GDC specimens was changed from transgranular mode to intergranular mode when the oxygen partial pressure was reduced, whereas the fracture surface of the 8YSZ specimens was transgranular regardless of the different oxygen partial pressures.
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Alexandreanu, Bogdan, Yiren Chen, Ken Natesan y Bill Shack. "Cyclic and SCC Behavior of Alloy 152 Weld in a PWR Environment". En ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57463.
Texto completoResumen
Alloys 600 and 182 are used as structural materials in pressurized water reactors (PWRs) and have been found to undergo stress corrosion cracking (SCC). Alloys 690 and 152 are the replacement materials of choice for Alloys 600 and 182, respectively. The objective of this work is to determine the crack growth rates (CGRs) in a simulated PWR water environment for Alloy 152. In order to meet the objective, specimens made from a laboratory-prepared Alloy 152 double-J weld in the as-welded condition were tested. For the SCC CGR measurements, the specimens were pre-cracked under cyclic loading in a primary water environment, and the cyclic CGRs were monitored to determine the transition from the fatigue transgranular fracture mode to the intergranular SCC fracture mode. The environmental enhancement of cyclic CGRs for Alloy 152 was minimal; nevertheless, the transition from transgranular to intergranular cracking was successful. Weld samples tested from the single heat of Alloy 152 exhibited SCC CGR rates of 10−11 m/s in the simulated PWR environment at 320°C, which is only about an order of magnitude lower than typical for Alloy 182.
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Naoki, Tashiro, Yoshiharu Kariya y Yoshihiko Kanda. "Fatigue Life and Fracture Behavior of Micro Size Sn-Ag-Cu Solder Joint". En ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems. ASMEDC, 2011. http://dx.doi.org/10.1115/ipack2011-52104.
Texto completoResumen
The influence of the joint size on low cycle fatigue characteristic of Sn-Ag-Cu has been investigated by a micro size joint specimen fabricated using solder balls. Although the effect of joint size on crack initiation life is not obvious at 298K, the reduction of the joint size changes the cyclic strain hardening nature and the fracture behavior that induces the life reduction at 398K. With a decrease in size, the failure mechanism transforms from a transgranular fracture to an intergranular fracture at the high energy grain boundary that is formed by high angle boundary formation following dynamic recovery in whole of joint. Therefore, the failure life is greatly reduced as a complete failure occurs simultaneously with the crack initiation at the grain boundaries. This is more remarkable at higher temperatures.
Informes sobre el tema "Transgranular Fractures"
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Mohammed, I., M. A. Zikry y S. Ziaei. Microstructural Modeling of Dynamic Intergranular and Transgranular Fracture Modes in Zircaloys. Office of Scientific and Technical Information (OSTI), abril de 2017. http://dx.doi.org/10.2172/1409268.
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