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1
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.
2
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.
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Liu, Wei Min, Jun Zhao y Yong Hui Zhou. "Effects of the Content of ZrO2 Nanoparticles on the Microstructure and Properties of Al2O3-TiC-ZrO2 Micro-Nano-Composites". Advanced Materials Research 652-654 (enero de 2013): 304–7. http://dx.doi.org/10.4028/www.scientific.net/amr.652-654.304.
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Al2O3-TiC-ZrO2 micro-nano-composites with addition of ZrO2 nanoparticles were fabricated by vaccum hot pressing with Mo and Ni powders as sintering aids. Results showed that the mechanical properties and relative density of the micro-nano-composites increased firstly and then decreased with the increase in the content of ZrO2 nanoparticles. Al2O3-TiC-ZrO2 micro-nano-composites containing about 4vol% ZrO2 nanoparticles have the highest synthetical properties, its flexural strength, Vicker's hardness, Fracture Toughness and relative density are 920MPa, 20.4GPa, 6.3MPa•m1/2 and 98.9%, respectively. The microstructural characterization revealed that adding proper ZrO2 nanoparticles to the matrix can greatly strengthen the grain boundaries, causing more transgranular fractures and consuming more fracture energy. The excessive amount of ZrO2 nanoparticles may bring about agglomeration effect, leading to the decrease of properties of the micro-nano-composites.
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Kim, Younghune y Woonbong Hwang. "High-Cycle, Low-Cycle, Extremely Low-Cycle Fatigue and Monotonic Fracture Behaviors of Low-Carbon Steel and Its Welded Joint". Materials 12, n.º 24 (9 de diciembre de 2019): 4111. http://dx.doi.org/10.3390/ma12244111.
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Low-carbon steels are commonly used in welded steel structures and are exposed to various fatigue conditions, depending on the application. We demonstrate that the various transitions in the fracture mode during fatigue testing can be distinguished by their different cyclic response curves and microstructural features after fracture. Fractography, surface damage micrographs, and microstructural evolution clearly indicated the transition of the fracture modes from high-cycle to low-cycle, extremely low-cycle fatigue, and monotonic behavior. The high-cycle fatigue mode showed initial cyclic softening, followed by cyclic stabilization, and showed inclusion-induced crack initiation at fish-eyes, while the low-cycle fatigue mode showed initial cyclic hardening followed by cyclic stabilization, where fractography images showed obvious striations. In addition, the extremely low-cycle fatigue mode showed no cyclic stabilization after initial cyclic hardening, which was characterized by quasi-cleavage fractures with a few micro-dimples and transgranular cracking, while the monotonic fracture mode predominantly showed micro-dimples.
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Zhong, Liqiong, Hao Hu, Yilong Liang y Chaowen Huang. "High Cycle Fatigue Performance of Inconel 718 Alloys with Different Strengths at Room Temperature". Metals 9, n.º 1 (21 de diciembre de 2018): 13. http://dx.doi.org/10.3390/met9010013.
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In this paper, the high cycle fatigue performance of solid solution state and aged Inconel 718 superalloys was studied at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the original structural features and fatigue deformation features of two kinds of alloys. SEM, laser scanning confocal microscopy, and electron backscatter diffraction (EBSD) were used to analyze the secondary fracture features of the fatigue fracture morphology and fatigue fracture profile. The results showed that the aging treatment significantly affected the strength and plasticity of the alloy, which in turn affected the fatigue performance of the alloy. After the aging treatment, the yield strength σs and the tensile strength σb of the Inconel 718 alloy increased by 152% and 65.9%, respectively, compared with those of the solid solution state, but the rate of elongation δ and rate of contraction in the cross-section area φ decreased by 63.7% and 52.3%, respectively. The fatigue limit of the aged state was lower than that of the solid solution state by 6.3%. The quadratic function relationship between the high cycle fatigue limit σ−1 and the tensile strength σb of the Inconel 718 superalloy at room temperature was σ−1 = σb · (0.869−3.67 × 10−4 · σb). An analysis of the fatigue fracture mechanism showed that the fatigue fractures before and after aging were all initiated in the grains oriented relatively unfavorably on the surface of the sample, with a mixture of intergranular and transgranular propagation after the transgranular propagation of several grains. The higher plasticity of the solid solution state Inconel 718 alloy resulted in a large number of slip deformation zones under high cycle fatigue loads, and the plastic deformation was relatively uniform. The lengths of the secondary fractures were as high as 120 μm, which formed the single-source plastic fatigue fracture that promoted an increase in the fatigue limit. After aging treatment, the higher strength of the Inconel 718 alloy made dislocation slip difficult under high cycle fatigue loads, and the plasticity compatible deformation capability was poor. When local dislocations slipped to the intragranular γ” phase, γ’ phase, or interfaces with nonmetallic compounds (NMCs), plugging occurred. The degree of stress concentration increased, causing the initiation of fatigue fracture; the secondary fracture was approximately 20 μm. Brittle cleavage due to multiple sources significantly reduced the fatigue limit.
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Qu, Feng, An, Bi, Du, Yang y Zheng. "Hydrogen-Assisted Crack Growth in the Heat-Affected Zone of X80 Steels during in Situ Hydrogen Charging". Materials 12, n.º 16 (12 de agosto de 2019): 2575. http://dx.doi.org/10.3390/ma12162575.
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Herein, the hydrogen embrittlement of a heat-affected zone (HAZ) was examined using slow strain rate tension in situ hydrogen charging. The influence of hydrogen on the crack path of the HAZ sample surfaces was determined using electron back scatter diffraction analysis. The hydrogen embrittlement susceptibility of the base metal and the HAZ samples increased with increasing current density. The HAZ samples have lower resistance to hydrogen embrittlement than the base metal samples in the same current density. Brittle circumferential cracks located at the HAZ sample surfaces were perpendicular to the loading direction, and the crack propagation path indicated that five or more cracks may join together to form a longer crack. The fracture morphologies were found to be a mixture of intergranular and transgranular fractures. Hydrogen blisters were observed on the HAZ sample surfaces after conducting tensile tests at a current density of 40 mA/cm2, leading to a fracture in the elastic deformation stage.
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Liu, Zhaoyi, Ligang Zhang, GR Liu, Wei Li, Shibin Li, Fengshan Wang, Yuanyuan Ma, Hao Li, Haijun Zhang y Lingling Han. "Material constituents and mechanical properties and macro-micro-failure modes of tight gas reservoirs". Energy Exploration & Exploitation 38, n.º 6 (30 de julio de 2020): 2631–48. http://dx.doi.org/10.1177/0144598720913069.
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In this work, a series of intensive laboratory tests are conducted to measure the material constituents, mechanical properties, and to examine macro-micro-failure modes of various types of rocks from tight gas reservoirs in the Da Qing oilfield in China. A set of key parameters are experimentally determined, including porosity, mineralogical compositions, microstructure, Young’s modulus, Poisson’s ratio, triaxial compressive strength, as well as macro- and micro-morphology failure modes. The relationships of these parameters are systematically analyzed, and the effects of the material constituents and microstructure characteristics such as cementation type, porosity, and mineral composition on rock mechanical properties are revealed as well as the patterns of micro- and macro-failures in types of rocks are investigated. The result shows that the micro-failure mainly exhibits features of transgranular and intergranular porous polymer fracture, and the macro-failure modes are mainly three types: shear-dominated, mixed shear–tensile and mixed tensile–shear. The mixed tensile–shear failure has mainly tensile fractures with branch fractures crossing each other, which forms a complex system fracture network. These findings are of importance for “sweet pot” evaluations, wellbore stability analysis, and hydraulic fracturing design for oil and gas production in tight gas reservoirs.
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Desbois, Guillaume, Nadine Höhne, Janos L. Urai, Pierre Bésuelle y Gioacchino Viggiani. "Deformation in cemented mudrock (Callovo–Oxfordian Clay) by microcracking, granular flow and phyllosilicate plasticity: insights from triaxial deformation, broad ion beam polishing and scanning electron microscopy". Solid Earth 8, n.º 2 (9 de marzo de 2017): 291–305. http://dx.doi.org/10.5194/se-8-291-2017.
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Abstract. The macroscopic description of deformation and fluid flow in mudrocks can be improved by a better understanding of microphysical deformation mechanisms. Here we use a combination of scanning electron microscopy (SEM) and broad ion beam (BIB) polishing to study the evolution of microstructure in samples of triaxially deformed Callovo–Oxfordian Clay. Digital image correlation (DIC) was used to measure strain field in the samples and as a guide to select regions of interest in the sample for BIB–SEM analysis. Microstructures show evidence for dominantly cataclastic and minor crystal plastic mechanisms (intergranular, transgranular, intragranular cracking, grain rotation, clay particle bending) down to the nanometre scale. At low strain, the dilatant fabric contains individually recognisable open fractures, while at high strain the reworked clay gouge also contains broken non-clay grains and smaller pores than the undeformed material, resealing the initial fracture porosity.
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Ma, Tian Hao, Le Chang y Chang Yu Zhou. "Low Cycle Fatigue Behavior of CP-Ti at Different Temperatures". Key Engineering Materials 795 (marzo de 2019): 29–34. http://dx.doi.org/10.4028/www.scientific.net/kem.795.29.
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Low cycle fatigue (LCF) tests are performed on CP-Tiat different temperatures (293K,423K and 523K). It is found that the fatigue life of CP-Tidecreases with temperature. A short cycle hardening phenomenon occurs at the beginning of cyclic deformationat 293K and 423K, followed by cyclic softening untilfailure. At 523K, cycle hardening isexhibited throughout the entire cycle until thefracture. The fatigue-life curves obtained from the tests are constructed using Coffin-Manson-Basquin model. According to the relationship between the four parameters of Coffin-Manson-Basquin model and temperature, the temperature-based life prediction model is further proposed. Scanning electron microscopy observation of fatigue fractures showsthat the fatigue cracks of CP-Tiat 423K and 523K under different strain amplitudes initiate on the surface of fatigue specimens and extend to the fracture zone by the transgranular mode.
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Chen, Lin, Dong Han, Shu-Lin Bai, Feng Zhao y Jian-Kang Chen. "Study on the relation between microstructural change and compressive creep stress of a PBX substitute material". Science and Engineering of Composite Materials 25, n.º 4 (26 de julio de 2018): 731–37. http://dx.doi.org/10.1515/secm-2016-0261.
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Abstract A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an explosive material in which explosive powder is bound together in a matrix using small quantities (typically 5%–10% by weight) of a synthetic polymer. A PBX substitute material was made from sugar granules and polymer binder. Its compressive creep properties were investigated at room temperature. The creep deformation was found to depend strongly on the applied stress amplitude. Under an applied stress near the strength, creep deformation developed and reached the final rupture very quickly. A power law relationship, $\dot \varepsilon = 4.14 \times {10^{ - 8}}{\sigma ^{2.5}},$ was established between steady creep rate and applied stress. Microscopic observations show that the damage mechanism processes include mainly the intergranular and transgranular fractures, binder fracture, and peeling. Both porosity and granule size decrease almost linearly with increasing applied stress.
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Niculescu, Marius, Brandusa Ghiban, Alexandru Ghiban y Gheorghe Dan. "Titanium Implants Used in Traumatology Failed Sometime in Clinical Practice: Case Study". Key Engineering Materials 695 (mayo de 2016): 128–32. http://dx.doi.org/10.4028/www.scientific.net/kem.695.128.
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Tibial fractures were, still are and will be a challenge for the orthopedic surgeon. In this paper we conducted a case study on a system plate-screw made by titanium that was used in clinical practice for reduction and fixation of a tibial pilon fracture. After eight months the patient returns for the ablation of metallic implants. Clinical and strengthen the fracture callus is found radiologic hypertrophic and degradation plaque.On retrieved plate were made following investigations in order to establish the causes that lead to the failure: determining the chemical composition through spectral analysis, macrostructural analysis using stereomicroscopy, microstructure analysis using optical microscope metallographic, and fractographic analysis using scanning electron microscopy. Complex analysis of the fracture surfaces of the locking plate has led to the ultimate conclusion that the material has been made self-locking plate is inadequate chemical purity satisfactory embedding, which has led to breakage within an area of non-homogeneous structure. Breaking looks fragile behaviour by transgranular cleavage with sharp facets. There were also highlighted intergranular cracks between planes of cleavage sides.
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Zhao and, J., Y. Mutoh y T. Ogawa. "Effect of Stress Ratio on Fatigue Crack Growth in 95Pb-5Sn Solder". Journal of Electronic Packaging 123, n.º 3 (17 de marzo de 1999): 311–15. http://dx.doi.org/10.1115/1.1371780.
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The stress ratio effect on the fatigue crack growth behavior of 95Pb-5Sn solder has been investigated. It is found that both ΔJ and ΔK can correlate fatigue crack growth data well, which means that the crack growth behavior of the 95Pb-5Sn solder under the frequency of 10 Hz was dominantly cyclic dependent. The da/dN-ΔJ relationship can be expressed as: da/dN=1.1×10−11s˙ΔJ1.45. Low level of crack closure was found only in the near-threshold region. Except in this region, no crack closure was observed in the present test conditions. Both transgranular and intergranular fractures were observed on fracture surfaces: the former was dominant in most test conditions and the latter was dominant at the high stress ratio of 0.7. Striations and striation-like features were also found. Many slip bands and cavities along the grain boundary were observed on the crack wake and ahead of the crack tip in the high crack growth rate region.
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Mostafa, Ahmad, Wail Adaileh, Alaa Awad y Adnan Kilani. "Mechanical Properties of Commercial Purity Aluminum Modified by Zirconium Micro-Additives". Crystals 11, n.º 3 (9 de marzo de 2021): 270. http://dx.doi.org/10.3390/cryst11030270.
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The mechanical properties and the fractured surfaces of commercial purity aluminum modified by zirconium micro-additives were investigated by means of experimental examination. A commercial purity Al specimen was used as a reference material and seven Al-Zr alloys in the 0.02–0.14 wt.% Zr composition range (with 0.02 wt.% Zr step) were prepared by microalloying methods. Optical microscopy was used to examine the microstructures and to calculate the grain sizes of the prepared specimens. The phase assemblage diagrams were plotted and the relative amounts of solid phases were calculated at room temperature using FactSage thermochemical software and databases. Proof stress, strength coefficient and strain hardening exponent were measured from the stress-strain curves obtained from tensile experiments and Charpy impact energy was calculated for all specimens. The experiments showed that the grain size of commercial purity Al was reduced by adding any Zr concentration in the investigated composition range, which could be due to the nucleation of new grains at Al3Zr particle sites. Accordingly, the microhardness number, tensile properties and Charpy impact energy were improved, owing to the large grain-boundary areas resulted from the refining effect of Zr, which can limit the movement of dislocations in the refined samples. The basic fracture mode in all specimens was ductile, because Al has an FCC structure and remains ductile even at low temperatures. The ductile fractures took place in a transgranular manner as could be concluded from the fractured surface features, which include voids, ridges and cavitation.
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Tsai, C.-H. y C.-J. Chen. "Formation of the breaking surface of alumina in laser cutting with a controlled fracture technique". Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 217, n.º 4 (1 de abril de 2003): 489–97. http://dx.doi.org/10.1243/095440503321628161.
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Laser cutting using the controlled fracture technique is based on the thermal breaking principle. The laser beam is applied to the surface of a ceramic substrate; the substrate is then controllably separated along the moving path of the laser beam. The fractography and cutting surface formation are studied in this work. It is found that the breaking surface can be divided into four regions. The first region is the laser evaporation region produced by the heat concentration. The second region is the columnar grain region produced by resolidification of the melted material. The third region is the intergranular fracture region produced by anisotropic thermal expansion. The fourth region is the transgranular fracture region characterized by unstable fractures. These experiments are conducted on alumina ceramics using a CO2 laser. The fracture mechanism is analysed using stress analysis and fractographic observation. The tensile stress generated on the surface due to the laser beam separates the material along its path. The effects of the cutting parameters such as the laser power, cutting speed, laser spot diameter and specimen geometry on the machining quality are obtained from the experimental analysis. It is concluded that the best cutting quality is obtained using a large laser spot size.
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Ii, S. "Identification of crack path of inter- and transgranular fractures in sintered silicon nitride by in situ TEM". Journal of Electron Microscopy 53, n.º 2 (1 de abril de 2004): 121–27. http://dx.doi.org/10.1093/jmicro/53.2.121.
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Soda, Yusuke, Taku Matsuda, Sachio Kobayashi, Motoo Ito, Yumiko Harigane y Takamoto Okudaira. "Reversely zoned plagioclase in lower crustal meta-anorthosites: An indicator of multistage fracturing and metamorphism in the lower crust". American Mineralogist 105, n.º 7 (1 de julio de 2020): 1002–13. http://dx.doi.org/10.2138/am-2020-7284.
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Abstract This paper describes the formation mechanism of reversely zoned plagioclase, which has been observed frequently in lower crustal shear zones and is indicative of multistage fracturing and meta-morphism in the lower crust, by studying the microstructural and chemical characteristics of plagioclase in sparsely fractured anorthosites and anorthositic mylonites from the Eidsfjord shear zone, Langøya, northern Norway. Based on the field relationship between sparsely fractured anorthosite and anorthositic mylonite, the fracturing of anorthosite occurred before the formation of mylonite. In sparsely fractured anorthosites, transgranular fractures are observed; hydration-reaction products, including Na-rich plagioclase, occur within cracks and fractures, suggesting that hydration reactions occurred during or after fracturing. The hydration reactions in sparsely fractured anorthosites are estimated to have occurred at higher-pressure (P) amphibolite-facies conditions (~0.9–1.0 GPa and ~550–700 °C). In anorthositic mylonites, which are considered to have initiated by fracturing and subsequent hydration metamorphism at lower-P amphibolite-facies conditions (~0.7 GPa and ~600 °C), recrystallized plagioclase grains often show compositional zoning with an Na-rich core and a Ca-rich rim. Because the compositions of metamorphic plagioclase grains in the sparsely fractured anorthosites and those of the Na-rich cores of the reversely zoned plagioclase in anorthositic mylonites are similar to each other, the Na-rich cores of the matrix plagioclase in the anorthositic mylonites have recrystallized under higher-P amphibolite-facies conditions and then been overgrown or replaced by the Ca-rich rims under lower-P conditions. Consequently, the reversely zoned plagioclase observed frequently in lower crustal shear zones is an indicator of multistage brittle fracturing and subsequent hydration metamorphism during exhumation, providing information relevant to understanding the deep rupture process caused by repeated seismicity alternating with aseismic creep below the seismogenic zone.
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Xie, Miaoxia, Xiangtao Shang, Yanxin Li, Zehui Zhang, Minghui Zhu y Jiangtao Xiong. "Rotary Friction Welding of Molybdenum without Upset Forging". Materials 13, n.º 8 (22 de abril de 2020): 1957. http://dx.doi.org/10.3390/ma13081957.
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A large instantaneous axial forging load is required to be applied for the final stage of rotary friction welding (RFW), which is usually conducive to obtaining clean, compact, and high-quality joints. However, for slender fuel claddings made of molybdenum (Mo) with low stiffness, the instantaneous axial forging load cannot be applied at the final stage of welding. This study carried out RFW tests without upset forging on Mo in the atmospheric environment and investigated the effects of welding time on joint morphology, axial shortening, microstructures, microhardness, tensile strength, and tensile fracture morphology. It found that the excessive and abrupt burning and a lot of smoke were generated around the weld zone during welding and spiral flashes were observed after welding. Under welding pressure of 80 MPa and spindle speed of 2000 r/min, the minimum average grain size and maximum tensile strength can be obtained in 4 s when the welding time is between 2–5 s. Scanning electron microscope (SEM) results show that there were morphologies of a large number of intergranular fractures and a small number of transgranular fractures in the fracture. The above results demonstrated that it is feasible to use RFW without upset forging to seal the last weld spot on upper end plugs of fuel claddings made of Mo in high-pressure inert gas, which would not only obtain reliable welding quality but also seal high-pressure inert gas in cladding tubes. The research results have a practical guiding significance of manufacturing accident-tolerant Mo nuclear fuel cladding.
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Atrens, Andrej, Qian Liu, Clotario Tapia-Bastidas, Evan Gray, Bartolomeus Irwanto, Jeff Venezuela y Qinglong Liu. "Influence of Hydrogen on Steel Components for Clean Energy". Corrosion and Materials Degradation 1, n.º 1 (13 de junio de 2018): 3–26. http://dx.doi.org/10.3390/cmd1010002.
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The influence of hydrogen on the mechanical properties of four, medium-strength, commercial, quenched-and-temped steels has been studied using the linearly increasing stress test (LIST) combined with cathodic hydrogen charging. The relationship was established between the equivalent hydrogen pressure and the hydrogen charging overpotential during cathodic hydrogen charging, though the use of electrochemical permeation experiments and thermal desorption spectroscopy. The cathodic hydrogen charging conditions were equivalent to testing in gaseous hydrogen at hydrogen fugacities of over a thousand bar. Under these hydrogen-charging conditions, there was no effect of hydrogen up to the yield stress. There was an influence of hydrogen on the final fracture, which occurred at the same stress as for the steels tested in air. The influence of hydrogen was on the details of the final fracture. In some cases, brittle fractures initiated by hydrogen, or DHF: Decohesive hydrogen fracture, initiated the final fracture of the specimen, which was largely by ductile micro-void coalescence (MVC), but did include some brittle fisheye fractures. Each fisheye was surrounded by MVC. This corresponds to MF: Mixed fracture, wherein a hydrogen microfracture mechanism (i.e., that producing the fisheyes) competed with the ductile MVC fracture. The fisheyes were associated with alumina oxide inclusion, which indicated that these features would be less for a cleaner steel. There was no subcritical crack growth. There was essentially no influence of hydrogen on ductility for the hydrogen conditions studied. At applied stress amplitudes above the threshold stress, fatigue initiation, for low cycle fatigue, occurred at a lower number of cycles with increasing hydrogen fugacity and increasing stress amplitude. This was caused by a decrease in the fatigue initiation period, and by an increase in the crack growth rate. In the presence of hydrogen, there was flat transgranular fracture with vague striations with some intergranular fracture at lower stresses. Mechanical overload occurred when the fatigue crack reached the critical length. There was no significant influence of hydrogen on the final fracture.
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Jiang, Hao, Zongyue Fan, Jian Lu y Bo Li. "Micromechanical Studies of Strain Rate Dependent Compressive Strength in Brittle Polycrystalline Materials". International Journal of Computational Methods 16, n.º 04 (13 de mayo de 2019): 1844011. http://dx.doi.org/10.1142/s0219876218440115.
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We propose a novel computational model for the high fidelity prediction of failure mechanisms in brittle polycrystalline materials. A three-dimensional finite element model of the polycrystalline structure is reconstructed to explicitly account for the micro-features such as grain sizes, grain orientations, and grain boundary misorientations. Grain boundaries are explicitly represented by a thin layer of elements with non-zero misorientation angles. In addition, the Eigen-fracture algorithm is employed to predict the crack nucleation and propagation in the grain structure. In the framework of variational fracture mechanics, an equivalent energy release rate is defined at each finite element to evaluate the local failure state by comparing to the critical energy release rate, which varies at the grain boundaries and the interior of grains. Moreover, constitutive models are considered as functions of the local microstructure features. As a result, a direct mesoscale simulation model is developed to resolve the anisotropic response, intergranular and transgranular fractures during the microstructure evolution of brittle materials under general loading conditions. A micromechanics-based interpretation for the rate dependent strength of brittle materials is derived and verified in examples of dynamic compression tests. In specific, the compressive dynamic response of hexagonal SiC with equiaxed grain structures is studied under different strain rates.
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Gobbi, Vagner, Silvio Gobbi, Danieli Reis, Jorge Ferreira, José Araújo y Cosme Moreira da Silva. "Creep Behaviour and Microstructural Characterization of VAT 36 and VAT 32 Superalloys". Metals 8, n.º 11 (27 de octubre de 2018): 877. http://dx.doi.org/10.3390/met8110877.
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Superalloys are used primarily for the aerospace, automotive, and petrochemical industries. These applications require materials with high creep resistance. In this work, evaluation of creep resistance and microstructural characterization were carried out at two new nickel intermediate content alloys for application in aerospace industry and in high performance valves for automotive applications (alloys VAT 32 and VAT 36). The alloys are based on a high nickel chromium austenitic matrix with dispersion of intermetallic L12 and phases containing different (Nb,Ti)C carbides. Creep tests were performed at constant load, in the temperature range of 675–750 °C and stress range of 500–600 MPa. Microstructural characterization and failure analysis of fractured surfaces of crept samples were carried out with optical and scanning electron microscopy with EDS. Phases were identified by Rietveld refinement. The results showed that the superalloy VAT 32 has higher creep resistance than the VAT 36. The superior creep resistance of the alloy VAT 32 is related to its higher fraction of carbides (Nb,Ti)C and intermetallic L12 provided by the amount of carbon, titanium, and niobium in its chemical composition and subsequent heat treatment. During creep deformation these precipitates produce anchoring effect of grain boundaries, hindering relative slide between grains and therefore inhibiting crack formation. These volume defects act also as obstacles to dislocation slip and climb, decreasing the creep rate. Failure analysis of surface fractures of crept samples showed intergranular failure mechanism at crack origin for both alloys VAT 36 and VAT 32. Intergranular fracture involves nucleation, growth, and subsequent binding of voids. The final fractured portion showed transgranular ductile failure, with dimples of different shapes, generated by the formation and coalescence of microcavities with dissimilar shape and sizes. The occurrence of a given creep mechanism depends on the test conditions. At creep tests of VAT 32 and VAT 36, for lower stresses and higher temperature, possible dislocation climb over carbides and precipitates would prevail. For higher stresses and intermediate temperatures shear mechanisms involving stacking faults presumably occur over a wide range of experimental conditions.
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Wang, Dong Sheng. "Effects of Feedstocks and Laser Remelting on Microstructural Characteristics of ZrO2-7wt.%Y2O3 Thermal Barrier Coatings Prepared by Plasma Spraying". Materials Science Forum 984 (abril de 2020): 23–30. http://dx.doi.org/10.4028/www.scientific.net/msf.984.23.
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Conventional and nanometer aggregate ZrO2-7wt.%Y2O3 ceramic powders taken as raw materials, plasma spraying and plasma spraying-laser remelting compound technology was used to prepare conventional and nanostructured thermal barrier coatings on the TiAl alloy surface. Effects of powder structure (feedstock) and laser remelting on organizational structure and phase of the coatings were analyzed using scanning electron microscope (SEM) and X-ray diffractometer (XRD). Results indicate that: conventional plasma sprayed ceramic coating presents typical lamellar stacking features; plasma sprayed nanostructured coating consists of fully melted region and partially melted region, presenting a two-phase structure. Under the comprehensive impacts of laser power, energy density, temperature field distribution in the laser action region, ceramic heat conductivity coefficient and coating thickness and other factors, the coating presents obvious lamellar structural features after laser remelting; the upper part is compact columnar crystal remelting region and the lower part is residual plasma spraying region. Due to toughening effect of residual nanoparticles in the remelting region of laser remelted nanostructured coating, grain-boundary strength is high and there are a considerable number of transgranular fractures, but the fractures in the remelting region of laser remelted conventional coating are basically intergranular fractures. Conventional plasma sprayed ceramic coating is mainly of tetragonal phase together with a small quantity of monoclinic phases, but nanometer plasma sprayed ceramic coating only has non-equilibrium tetragonal phases. After laser remelting, both conventional coating and nanometer coating mainly have non-equilibrium tetragonal phases with a small quantity of cubic phases.
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Guzman-Flores, Isidro, Benjamin Vargas-Arista, Juan Jose Gasca-Dominguez, Celso Eduardo Cruz-Gonzalez, Marco Antonio González-Albarrán y Joaquin del Prado-Villasana. "Effect of Torch Weaving on the Microstructure, Tensile and Impact Resistances, and Fracture of the HAZ and Weld Bead by Robotic GMAW Process on ASTM A36 Steel". Soldagem & Inspeção 22, n.º 1 (marzo de 2017): 72–86. http://dx.doi.org/10.1590/0104-9224/si2201.08.
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Abstract The effect of torch weaving on the microstructure, tensile strength, impact resistance and fracturing in robotic welded joints using varing welding speeds, voltages and currents was evaluated through fractography using scanning electron microscopy, tension, impact and micro-hardness tests and optic microscopy. Results indicated that linear, sinusoidal and circular weavings favored an increase of the width of the HAZ as well as a slight increase in yield resistance accompanied by hardening in comparison with a triangular weave. The latter favored larger impact energy in the HAZ with less width, containing coarse-grained ferrite due to lower tensile strength and Vickers hardness. A circular weave generated the highest level of hardening and the lowest energy absorbed in the HAZ as a consequence of an increase in yield strength related to the fine needles of acicular ferrite. A linear weave favored the greatest width of the HAZ compared with other weld weavings due to heat accumulation along the fusion line of the welded joint. Hardening and loss of toughness were evaluated through fractographic analysis showing mixed fractures mainly composed of brittle fracturing made by transgranular cleavages with facets containing well defined river patterns.
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Li, Yuqiang, Ning Tan, Zhishuai Xu, Zhiping Luo, Ke Han, Qijie Zhai y Hongxing Zheng. "Enhancement of Fatigue Endurance by Al-Si Coating in Hot-Stamping Boron Steel Sheet". Metals 9, n.º 7 (26 de junio de 2019): 722. http://dx.doi.org/10.3390/met9070722.
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Most structural components undertake cyclic loads in engineering and failures always cause catastrophic economic losses and casualties. In the present work, the phase evolution of Al-Si coating of high-strength boron steel during hot stamping was investigated. Two types of 1500 MPa grade boron steel sheets, one with Al-Si coating and the other without, were studied to reveal the effect on the high-cycle fatigue behavior. The as-received continuously hot-dip Al-Si coating was composed of α(Al), eutectic Al-Si and τ5. After hot stamping at 1193 K, three phases formed in this coating: β2, Fe(Al,Si)2 and α(Fe). The experimental results showed that the endurance limit of the coated steel sheet was 370 MPa under 107 fully reversed tension-compression loading cycles as opposed to 305 MPa in the uncoated sheet. Both the coated and the uncoated specimens showed surface-induced transgranular fatigue fractures. In the uncoated sheet, the fatigue cracks were generated from the decarburization surface, but the Al-Si coating effectively prevented the occurrence of near-surface decarburization during high-temperature hot stamping, and the only cracks in the coated steel sheet were initiated at wire-cutting surfaces.
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Li, Jielin, Liu Hong, Keping Zhou, Caichu Xia y Longyin Zhu. "Mechanical Characteristics and Mesostructural Damage of Saturated Limestone under Different Load and Unload Paths". Advances in Civil Engineering 2021 (15 de enero de 2021): 1–16. http://dx.doi.org/10.1155/2021/8831247.
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To study the evolutionary characteristics of mesostructural damage to saturated limestone under different loading and unloading paths, three types of loading and unloading tests involving three different loading rates and initial peak stresses were performed. Nuclear magnetic resonance technology and scanning electron microscopy were used to investigate the evolutionary characteristics of pore water during the loading and unloading of the limestone. The results indicated that, with an increase in the initial peak stress, the rock viscoplasticity gradually decreased, and the variation of pore radius and the reduction of bound water decreased. With an increasing loading rate, the mesostructure evolution law under disturbance-increasing amplitude (DIA) cycling was opposite to those under increasing amplitude (IA) and repeated-increasing amplitude (RIA) cycling. With the increasing loading stress level, the porosity decreased and then increased. Under increasing amplitude cycling, a larger initial porosity resulted in higher pore compaction and expansion limits. Reducing the initial peak stress inhibited the pore expansion, whereas it had the opposite effect under RIA and DIA cycling. During loading and unloading, bound water exists in pores of organic matter and mesopores, and free water exists in macropores of intergranular and transgranular fractures. These changes indicate certain laws under different loading and unloading paths. The results of this study indicate that the mesostructure characteristics of rock depend on the loading and unloading paths.
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Chen, G. H. y C. Chen. "Investigation of the heat-affected zone fracture in Ni3Al welds". Journal of Materials Research 7, n.º 5 (mayo de 1992): 1076–82. http://dx.doi.org/10.1557/jmr.1992.1076.
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Ternary Ni77Al23−yXy (X = Zr or Hf, y = 0.5 or 1) + 500 ppm boron compounds with various grain sizes were welded by a CO2 laser. Fractographic examinations of the heat-affected zone (HAZ) in the welds with or without postweld heat treatment (PWHT) were performed on the impact-fractured specimens. In laser welds, the fracture appearance of the HAZ was mixed transgranular/intergranular modes for fine-grained alloys and intergranular mode for coarse-grained materials. However, an entirely transgranular mode was observed in the base metal regardless of the grain size of the compounds. Boron desegregation at high temperatures during the thermal cycle of welding could be used to explain the fractographic change from originally ductile mode into less-ductile or even brittle fracture in the HAZ. Short-term PWHTs along with slow cooling provided sufficient time for boron segregation back to the grain boundary, resulting in a completely transgranular fracture mode in the fine-grained HAZ. Nevertheless, such a phenomenon was not observed in the HAZ of coarse-grained welds. Cracks in the HAZ of coarse-grained welds after long-term PWHT, if not so severe, could be healed by a sintering process.
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Kubošová, Andrea, Miroslav Karlík, Petr Haušild y J. Prahl. "Fracture Behaviour of Fe3Al and FeAl Type Iron Aluminides". Materials Science Forum 567-568 (diciembre de 2007): 349–52. http://dx.doi.org/10.4028/www.scientific.net/msf.567-568.349.
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Fracture behaviour of two intermetallic alloys based on FeAl and Fe3Al was studied. On the alloys Fe-40Al-1C (at%) and Fe-29.5Al-2.3Cr-0.63Zr-0.2C (at%) (FA06Z), a basic characterization, the fracture toughness tests and fractographic analysis were carried out. Tensile tests and fracture toughness tests were performed at 20, 200, 400 and 600°C. The fracture toughness values range from 26 MPa.m1/2 at 20°C to 42 MPa.m1/2 at 400°C. In addition, Jintegral dependence on a obtained by potential method was measured. The fractographic analysis showed that samples fractured at 20, 200 and 400°C in the tensile or fracture toughness tests exhibit transgranular cleavage fracture, while at 600°C the ductile dimple fracture predominates.
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Vargas-Arista, B., M. A. Gómez-Morales, E. Garfias-García y F. García-Vázquez. "Impact Behavior Characterization on Fractured Pins of AISI E52100 Steel". Materials Science Forum 793 (mayo de 2014): 1–10. http://dx.doi.org/10.4028/www.scientific.net/msf.793.1.
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Two fractured pins of impact wrench were evaluated by fractography using scanning electron microscopy. This pneumatic wrench is used to the fabrication of automotive components being characterized by its power and tightening capacity. The important part of the wrench is the pin clutch impact mechanism used to generate high torque. An original pin manufactured with AISI E52100 steel adjusted 2,580 nuts before fracture and a substitute pin of E52100 modified steel with S adjusted 7,095 nuts before failure. Fractographic analysis in both fracture surfaces indicated a ductile-brittle mixed fracture mode. Original pin surface exhibited a granular appearance while substitute pin surface showed fibrous and rough morphology. Precipitation of nearly rounded, elliptical and elongate second – phase particles containing Cr, C and Mn measured as intergranular and transgranular particle density was observed, promoting some brittle failure zones and ductile fracture measured as the volume fraction of grain boundaries and microvoids, respectively. A larger amount of intergranular medium precipitates was found on the original pin which favored the brittle failure among the grain boundaries compared to that of the substitute pin. The ductile fracture by larger transgranular fine particle density which acted as nucleation sites of higher volume fraction of microvoids was found in the substitute pin.
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Dlouhy, Ivo, Mita Tarafder y Hynek Hadraba. "Micromechanical Aspects of Transgranular and Intergranular Failure Competition". Key Engineering Materials 465 (enero de 2011): 399–402. http://dx.doi.org/10.4028/www.scientific.net/kem.465.399.
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Quantification of characteristics that govern intergranular fracture initiation and propagation of this fracture micromechanism in competition with cleavage one is main aim of the paper. A NiCr steel of commercial quality and the same steel with an increased content of impurity elements, Sn and Sb, were used. Step cooling ageing was applied in order to induce intergranular embrittlement. Standard and pre-cracked Charpy type specimens were both tested in three-point bending to determine fracture toughness characteristics. In order to characterise the quantitative differences in fracture surfaces roughness a fractal analysis was applied. A boundary level of fractal dimension has been determined to be 1.12: fracture surface roughness with a higher value reflects high level of intergranular embrittlement and thus fracture resistance degradation.
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Zhang, Yunlong, Yanbin Chen, Wang Tao, Zhenglong Lei, Zhaohui Yang y Tiantian Nan. "Influence of Post-Weld Heat Treatments on Microstructure and Mechanical Properties of Laser Beam Welded 2060-T3/2099-T3Al-Li T-Joints". Metals 9, n.º 12 (6 de diciembre de 2019): 1318. http://dx.doi.org/10.3390/met9121318.
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The durable structure and robustness of T-joints in the panel materials for civil aircraft are a crucial matter of importance. In this work, the impact of the post-weld heat treatments (PWHTs) on the microstructure and mechanical properties of laser beam welded T-joints of 2060-T3/2099-T3 Al-Li alloy was analyzed. Heat-treatment of the laser beam welded T-joints was carried out in two different ways, namely, solution treatment and artificial aging (STAA) at varied duration and only artificial aging (AA) at varied duration. The microstructure and mechanical properties of the heat-treated joints were investigated using metallographic and scanning electron microscopic images, micro-hardness test, and tensile test, respectively. The results showed that, in cases of STAA, the eutectic structures on the grain boundary were partially dissolved via solution treatment (ST), and increased dispersed precipitation of the second phase in matrix resulted in significant dispersion strengthening, as well as enhanced strength and plasticity. In contrast, in the AA process, alloy elements in the matrix continued to segregate towards the grain boundary, resulting in significant grain boundary strengthening, enhanced strength, and decreased plasticity. Additionally, joint fractures were micro-porous aggregation transgranular ones in the fusion zone (FZ). The joints treated by STAA exhibited excellent plasticity compared with those treated by AA. Furthermore, the micro-hardness of welded joints treated by AA was higher than that of those treated by STAA. Indeed, the tensile strength of joints treated by STAA and AA ranged from 405 to 475 MPa, which was 81–95% of the base metal 2060-T8, though the elongation of joints treated by STAA was superior to the counterpart AA.
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Zhou, Yu Mei, Feng Lin Zhang, Peng Cheng Li, Kun Bai y Shang Hua Wu. "Synthesis and Characterization of AlMgB14-Ni3Al Composites for Cutting Tool Materials". Advanced Materials Research 1136 (enero de 2016): 257–62. http://dx.doi.org/10.4028/www.scientific.net/amr.1136.257.
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AlMgB14 is a novel hard and brittle material which need be improved toughness for utilizing as cutting tool materials. In present study, intermetallic compound Ni3Al were attempted to dope the synthesised AlMgB14 materials. The microstructure of the AlMgB14-Ni3Al composites was analysized by scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX) and an X-ray diffractometer (XRD). The density, hardness and fracture toughness of AlMgB14-Ni3Al composites were also measured. The results showed that the major phases in AlMgB14-Ni3Al composites were AlMgB14, MgAl2O4 , Ni3Al and NiAl as well as W2B5. With the increasing of the amount of Ni3Al, more transgranular fractured features can be found in the fractured surface, the density of the AlMgB14-Ni3Al composites was increased, the hardness and fracture toughness of the AlMgB14-Ni3Al composites were decreased.
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Yang, Wein-Joe, Chang-Te Yu y Albert S. Kobayashi. "SEM Quantification of Transgranular vs Intergranular Fracture". Journal of the American Ceramic Society 74, n.º 2 (febrero de 1991): 290–95. http://dx.doi.org/10.1111/j.1151-2916.1991.tb06877.x.
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Cheng, Xu y Xiao Gang Wang. "Preparation and Properties of β/α SiC Composite Ceramics". Key Engineering Materials 727 (enero de 2017): 309–13. http://dx.doi.org/10.4028/www.scientific.net/kem.727.309.
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In this paper, the production of high-performance β/α SiC composite ceramics technology as the goal, by measuring density, we can optimize and determine the best technical ceramic formulations. Because a small amount of β-SiC in α-SiC,the sintered ceramic appeared long axis-like crystals, indicating fracture mode changes from the original transgranular fracture to transgranular fracture mainly and intergranular fracture supplement. The results show that, when added in an amount of 10% β-SiC, SiC ceramics having the best performance.
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Tang, Luyao, Jiangkun Fan, Hongchao Kou, Bin Tang y Jinshan Li. "Effect of Oxygen Variation on High Cycle Fatigue Behavior of Ti-6Al-4V Titanium Alloy". Materials 13, n.º 17 (1 de septiembre de 2020): 3858. http://dx.doi.org/10.3390/ma13173858.
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The element oxygen is expected to be a low-cost, strengthening element of titanium alloys due to its strong solid solution strengthening effect. High cycle fatigue behaviors of Ti-6Al-4V alloys with different oxygen contents (0.17%, 0.20%, 0.23% wt.%) were investigated in this paper. The results illustrated that Ti-6Al-4V-0.20O alloy possesses the highest fatigue strength and the lowest fatigue crack propagation rate. The fatigue fracture morphology verified that the fatigue cracks propagated transgranularly in both Ti-6Al-4V-0.17O and Ti-6Al-4V-0.20O alloys, and the fatigue cracks tended to extend intergranularly in the Ti-6Al-4V-0.23O alloy. The maximum nano-hardness varied from the <0001> direction to the <1¯21¯0> and <011¯0> directions with the increasing oxygen content, which suggested that the dominant slip system varied from prismatic slip to pyramidal slip. The number of the <c→+a→> type dislocations increased with the oxygen content, which indicated that the number of the first-order pyramidal and the second-order pyramidal <c→+a→> slip systems increased. The oxygen can significantly change the fatigue fracture mechanism of Ti-6Al-4V alloy: From transgranular fracture to intergranular fracture. These results are expected to provide valuable reference for the optimization of the composition and mechanical properties of titanium alloys.
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Hoff, H. A., A. A. Morrish, J. E. Butler y B. B. Rath. "Comparative fractography of chemical vapor and combustion deposited diamond films". Journal of Materials Research 5, n.º 11 (noviembre de 1990): 2572–88. http://dx.doi.org/10.1557/jmr.1990.2572.
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Polycrystalline diamond films of several thicknesses have been fractured by manual bending and examined by scanning electron microscopy. These films have been deposited in controlled environments at low pressures by chemical vapor deposition and in ambient atmosphere with an oxygen-acetylene torch. Fracture surfaces in the low pressure depositions exhibit cleavage steps across the grains. These surfaces, independent of thickness, are primarily transgranular, attesting to the inherent strength of the deposits. However, the ambient deposited diamond has primarily intergranular fracture indicative of weak grain boundaries. Internal defects, observed with transmission electron microscopy, such as twins, stacking faults, and dislocations, occur generally in both types of deposition with no apparent preference for location or type of deposition.
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Zhang, Yongjian, Weijun Hui, Xiaoli Zhao, Cunyu Wang y Han Dong. "Effects of Hot Stamping and Tempering on Hydrogen Embrittlement of a Low-Carbon Boron-Alloyed Steel". Materials 11, n.º 12 (10 de diciembre de 2018): 2507. http://dx.doi.org/10.3390/ma11122507.
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The effects of hot stamping (HS) and tempering on the hydrogen embrittlement (HE) behavior of a low-carbon boron-alloyed steel were studied by using slow strain rate tensile (SSRT) tests on notched sheet specimens. It was found that an additional significant hydrogen desorption peak at round 65–80 °C appeared after hydrogen-charging, the corresponding hydrogen concentration (CHr) of the HS specimen was higher than that of the directed quenched (DQ) specimen, and subsequent low-temperature tempering gave rise to a decrease of CHr. The DQ specimen exhibited a comparatively high HE susceptibility, while tempering treatment at 100 °C could notably alleviate it by a relative decrease of ~24% at no expanse of strength and ductility. The HS specimen demonstrated much lower HE susceptibility compared with the DQ specimen, and tempering at 200 °C could further alleviate its HE susceptibility. SEM analysis of fractured SSRT surfaces revealed that the DQ specimen showed a mixed transgranular-intergranular fracture, while the HS and low-temperature tempered specimens exhibited a predominant quasi-cleavage transgranular fracture. Based on the obtained results, we propose that a modified HS process coupled with low-temperature tempering treatment is a promising and feasible approach to ensure a low HE susceptibility for high-strength automobile parts made of this type of steel.
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NAGAI, Masayuki y Sachio SHIMADA. "Transgranular Fracture Mechanism of Zirconium in Iodine Environment". Journal of Nuclear Science and Technology 25, n.º 2 (febrero de 1988): 153–57. http://dx.doi.org/10.1080/18811248.1988.9733570.
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Verhoosel, C. V. y M. A. Gutiérrez. "Modelling inter- and transgranular fracture in piezoelectric polycrystals". Engineering Fracture Mechanics 76, n.º 6 (abril de 2009): 742–60. http://dx.doi.org/10.1016/j.engfracmech.2008.07.004.
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Ford, I. J. "Transgranular fracture of Fast Reactor irradiated stainless steel". Journal of Nuclear Materials 182 (mayo de 1991): 52–59. http://dx.doi.org/10.1016/0022-3115(91)90414-3.
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Shimanuki, Hiroto, Hiroyuki Yamada, Tsuyoshi Kami, Yoshihiro Yamasaki, Hiroshi Ikaida, Toru Kamita, Hiroaki Amakawa, Miki Nishimoto y Hidetoshi Kobayashi. "Impact Tensile Properties of Notched Titanium Alloy Bolt for Fairing Separation of Launch Vehicle". EPJ Web of Conferences 183 (2018): 04006. http://dx.doi.org/10.1051/epjconf/201818304006.
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The payload fairing in Japan is fixed by a lot of notched bolts. These notched bolts were fractured by axial impact tensile using the explosive devices to separate the fairing. In this case, the stress waves and the oscillations propagate, which may seriously damage the satellites. In this study, the impact deformation and the fracture behavior of notched titanium alloy bolt was investigated using a split Hopkinson pressure bar method. The notched bolt specimen was made of commercial Ti-6Al-4V alloy. The maximum load value was increased with increasing the displacement rate. It can be said that the strain rate dependence of strength for Ti-6Al-4V alloy appeared. From the observation of fracture surface using a scanning electron microscope, compared with the quasi-static test, it was clear that the irregularities of the fractured surface at the impact tensile test became rough. Therefore, it was found that the brittle fracture was mainly observed due to the increase in displacement rate, which may mean that the mode of fracture changes from the transgranular to the intergranular. It was surmised that this change of fracture mode was caused by the high strain rate due to stress concentration of the notched part.
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Min, Guang Hui, Li Xia Yang, Hua Shun Yu y Jiande Han. "Mechanical Properties of CaB6 Sintered Body". Key Engineering Materials 297-300 (noviembre de 2005): 2707–12. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2707.
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In this paper, CaB6 sintered body was fabricated by hot-pressed sintering with/without nickel as a sintering aid. The microstructure and fracture morphology were observed by means of SEM. CaB6 polycrystalline hot-pressed at 2123K showed insufficient densification. Fracture surface revealed that the existence of pores and the poor grain boundaries made the occurrence of intergranular fracture. When 28wt% nickel was added, nearly full density was obtained, although the sintering temperature is 200K lower. Hardness, Bending strength and fracture toughness of polycrystalline CaB6 were measured. By adding the Ni in CaB6 matrix, the flexural strength and the fracture toughness were enhanced, and the ratio of transgranular to intergranular fracture type was increased notably. The fracture surface showed a transgranular fracture. The crack bridging, micro-cracking and crack deflecting were deemed as the contribution to the improved fracture toughness.
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Ding, Wen Jiang, Peng Huai Fu, Li Ming Peng, Hai Yan Jiang y Xiao Qin Zeng. "Study on the Microstructure and Mechanical Property of High Strength Mg-Nd-Zn-Zr Alloy". Materials Science Forum 546-549 (mayo de 2007): 433–36. http://dx.doi.org/10.4028/www.scientific.net/msf.546-549.433.
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The microstructure and mechanical properties of Mg-3wt％Nd-0.2wt％Zn-0.4wt％Zr alloy in as-cast, solution-treated and solution-treated + peak-aged were investigated. The alloy had a cast structure with large intergranular Mg12Nd phase between the α-Mg matrix. After solution-treated, the intergranular Mg12Nd phase disappeared and lots of small Zr-containing particles distributed inside the grains. Small plate-like phases precipitated inside the grains strengthened the alloy to a high level after peak-aged at 200°C for 16 hours: the ultimate strength of the alloy up to 305 MPa, with considerable elongation rate 11%, and yield strength 140 MPa. The peak-aged samples also had good creep resistance, with strain rate less than 0.2% after 120 hours creep test under the condition of 110 MPa at 200°C. The minimum creep rate was about 4.64×10-9. The alloy had different fracture pattern in different states: as-cast state, intergranular fracture was the key pattern to failure; after solution-treated, the fracture pattern turned to cleavage transgranular fracture; after peak-aged, the alloy had a mixed fracture pattern of transgranular and intergranular, in which transgranular was the main style.
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Peng, Wen Wen, Wei Dong Zeng, Qing Jiang Wang y Yan Chun Zhu. "The Study on Fracture Behavior in Hot Compression of As-Cast Ti60 Titanium Alloy". Advanced Materials Research 750-752 (agosto de 2013): 725–29. http://dx.doi.org/10.4028/www.scientific.net/amr.750-752.725.
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Hot compression testing of as-cast Ti60 alloy was carried out 970-1120 °C, 0.01-10 s1 and 30-75%. The fracture behavior of the alloy was investigated by light optical microscope, scanning electron microscope. The result shows that, at high strain rate and large height reduction, 45° transgranular fracture and longitudinal intergranular fracture are observed, which are confirmed to be transgranular cleavage brittle fracture and ductile fracture respectively. Moreover, the cracking degree increases with the increasing height reduction. Besides, the alloy deformed at high temperature exhibits a good ductility, whereas lots of longitudinal cracks occurs on its surface due to the brittle alpha-case formation. Consequently, the systematic analysis on the fracture mechanism for as-cast Ti60 alloy is vitally necessary for the optimization of processing parameters in its cogging process.