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1
Zheng, Xiaomeng, Yongzhen Zhang, and Sanming Du. "Preliminary Research on Response of GCr15 Bearing Steel under Cyclic Compression." Materials 13, no. 16 (August 5, 2020): 3443. http://dx.doi.org/10.3390/ma13163443.
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During the bearing service, a series of microstructural evolutions will arise inside the material, such as the appearance of feature microstructures. The essential reason for the microstructural evolution is the cumulative effect of cyclic stress. The Hertz Contact formula is usually adopted to calculate the internal stress, and there is a correlation between the shape and distribution of the feature microstructure and the stress distribution. But it is insufficient to explain the relationship between the morphology of feature microstructures and the rolling direction, such as specific angles in butterfly and white etching bands. The rolling phenomenon will cause the asymmetry of stress distribution in the material, which is the source of the rolling friction coefficient. Moreover, slipping or microslip will produce additional stress components, which also cause the asymmetry of the stress field. However, there is no experimental or theoretical explanation for the relationship between the asymmetry of the stress field and the feature microstructure. According to the current theory, the appearance of feature microstructures is caused by stress with or without rolling. Therefore, it is of great significance to study the formation mechanism: whether feature microstructures will appear in the uniaxial cyclic compression stress field without rolling. In this paper, uniaxial cyclic compressive stress was loaded into a plate-ball system and a cylinder system. The characteristics of microstructural change of bearing steel (GCr15) were studied. It was found that the hardness of the material increased after the cyclic compressive load, and the inclusions interacted with the matrix material. In the local microregion a white etching area was found, although the scale is very small. No large-scale feature microstructures appeared. Other phenomena in the experiment are also described and analyzed. For example, the production of oil film in the contact area and the changing law of alternating load.
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Barboza, Luis, Enrique López, Hugo Guajardo, and Armando Salinas. "Effect of Initial Microstructure on the Temperature Dependence of the Flow Stress and Deformation Microstructure under Uniaxial Compression of Ti-407." Metals 14, no. 5 (April 26, 2024): 505. http://dx.doi.org/10.3390/met14050505.
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In this study, the influence of initial microstructure and deformation temperature on the flow stress behavior and microstructural evolution of TIMETAL®407 (Ti-407) alloy are investigated. For this purpose, compression cylinders were β-annealed at 940 °C and then cooled to room temperature using furnace cooling, static air, and water quenching to promote three initial microstructures with different α lath thicknesses. The annealed cylinders were compressed isothermally in the range of 750 °C to 910 °C at a constant crosshead speed of 0.05 mm/s up to an engineering strain of −0.8. The resulting stress–strain curves are discussed in terms of the morphology and distribution of the α and β phases. It was found that flow stress is inversely proportional to deformation temperature for all initial microstructures. At the lowest temperatures, compressive yield strength was higher in water-quenched and air-cooled samples than in furnace-cooled specimens, suggesting that the acicular α-phase morphology obtained by rapid cooling could enhance mechanical strength by hindering dislocation motion. Two high-temperature flow regimes were determined based on the shape of the flow stress curves, indicating microstructural changes occurring during deformation. At higher temperatures, the effect of the initial microstructure is negligible as the primary α phase is transformed to the β phase at around 850 °C irrespective of the initial α-lath thickness.
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Xi, Shangbin, and Yu Su. "Phase Field Study of the Microstructural Dynamic Evolution and Mechanical Response of NiTi Shape Memory Alloy under Mechanical Loading." Materials 14, no. 1 (January 2, 2021): 183. http://dx.doi.org/10.3390/ma14010183.
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For the purpose of investigating the microstructural evolution and the mechanical response under applied loads, a new phase field model based on the Ginzburg-Landau theory is developed by designing a free energy function with six potential wells that represent six martensite variants. Two-dimensional phase field simulations show that, in the process of a shape memory effect induced by temperature-stress, the reduction-disappearance of cubic austenite phase and nucleation-growth of monoclinic martensite multi-variants result in a poly-twined martensitic microstructure. The microstructure of martensitic de-twinning consists of different martensite multi-variants in the tension and compression, which reveals the microstructural asymmetry of nickel-titanium (NiTi) alloy in the tension and compression. Furthermore, in the process of super-elasticity induced by tensile or compressive stress, all martensite variants nucleate and expand as the applied stress gradually increases from zero. Whereas, when the applied stress reaches critical stress, only the martensite variants of applied stress-accommodating continue to expand and others fade gradually. Moreover, the twinned martensite microstructures formed in the tension and compression contain different martensite multi-variants. The study of the microstructural dynamic evolution in the phase transformation can provide a significant reference in improving properties of shape memory alloys that researchers have been exploring in recent years.
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Hanhan, Imad, and Michael D. Sangid. "Design of Low Cost Carbon Fiber Composites via Examining the Micromechanical Stress Distributions in A42 Bean-Shaped versus T650 Circular Fibers." Journal of Composites Science 5, no. 11 (November 7, 2021): 294. http://dx.doi.org/10.3390/jcs5110294.
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Recent advancements have led to new polyacrylonitrile carbon fiber precursors which reduce production costs, yet lead to bean-shaped cross-sections. While these bean-shaped fibers have comparable stiffness and ultimate strength values to typical carbon fibers, their unique morphology results in varying in-plane orientations and different microstructural stress distributions under loading, which are not well understood and can limit failure strength under complex loading scenarios. Therefore, this work used finite element simulations to compare longitudinal stress distributions in A42 (bean-shaped) and T650 (circular) carbon fiber composite microstructures. Specifically, a microscopy image of an A42/P6300 microstructure was processed to instantiate a 3D model, while a Monte Carlo approach (which accounts for size and in-plane orientation distributions) was used to create statistically equivalent A42/P6300 and T650/P6300 microstructures. First, the results showed that the measured in-plane orientations of the A42 carbon fibers for the analyzed specimen had an orderly distribution with peaks at |ϕ|=0∘,180∘. Additionally, the results showed that under 1.5% elongation, the A42/P6300 microstructure reached simulated failure at approximately 2108 MPa, while the T650/P6300 microstructure did not reach failure. A single fiber model showed that this was due to the curvature of A42 fibers which was 3.18 μm−1 higher at the inner corner, yielding a matrix stress that was 7 MPa higher compared to the T650/P6300 microstructure. Overall, this analysis is valuable to engineers designing new components using lower cost carbon fiber composites, based on the micromechanical stress distributions and unique packing abilities resulting from the A42 fiber morphologies.
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Chen, Haisheng, Fang Hao, Shixing Huang, Jing Yang, Shaoqiang Li, Kaixuan Wang, Yuxuan Du, Xianghong Liu, and Xiaotong Yu. "The Effects of Microstructure on the Dynamic Mechanical Response and Adiabatic Shearing Behaviors of a Near-α Ti-6Al-3Nb-2Zr-1Mo Alloy." Materials 16, no. 4 (February 7, 2023): 1406. http://dx.doi.org/10.3390/ma16041406.
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The formation and evolution of adiabatic shear behaviors, as well as the corresponding mechanical properties of a near-Ti-6Al-3Nb-2Zr-1Mo (Ti-6321) alloy during dynamic compression process, were systematically investigated by the split Hopkinson pressure bar (SHPB) compression tests in this paper. Ti-6321 samples containing three types of microstructures, i.e., equiaxed microstructure, duplex microstructure and Widmanstätten microstructure, were prepared to investigate the relationship between microstructures and dynamic mechanical behaviors under different strain rates in a range from 1000 s−1 to 3000 s−1. It was found by the dynamic strain–stress relation that the Ti-6321 alloys containing equiaxed microstructure, duplex microstructure and Widmanstätten microstructure all exhibited a strong strain-hardening effect. The samples containing equiaxed microstructure exhibited a larger flow stress than samples containing duplex microstructure and Widmanstätten microstructure. The adiabatic shearing behaviors in Ti-6321 alloy are significantly influenced by different types of microstructures. The formation of adiabatic shearing bands occurs in equiaxed microstructure when the strain rate is increased to 2000 s−1. The adiabatic shear bands are formed in duplex microstructure when the strain rate reaches 3000 s−1. However, the initiation of adiabatic shear bands is found in Widmanstätten microstructure under the strain rate of 1000 s−1. The Widmanstätten microstructure shows a larger sensitivity to adiabatic shearing than the equiaxed microstructure and duplex microstructure samples.
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Kim, K., B. Forest, and J. Geringer. "Two-dimensional finite element simulation of fracture and fatigue behaviours of alumina microstructures for hip prosthesis." Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 225, no. 12 (September 19, 2011): 1158–68. http://dx.doi.org/10.1177/0954411911422843.
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This paper describes a two-dimensional (2D) finite element simulation for fracture and fatigue behaviours of pure alumina microstructures such as those found at hip prostheses. Finite element models are developed using actual Al2O3 microstructures and a bilinear cohesive zone law. Simulation conditions are similar to those found at a slip zone in a dry contact between a femoral head and an acetabular cup of hip prosthesis. Contact stresses are imposed to generate cracks in the models. Magnitudes of imposed stresses are higher than those found at the microscopic scale. Effects of microstructures and contact stresses are investigated in terms of crack formation. In addition, fatigue behaviour of the microstructure is determined by performing simulations under cyclic loading conditions. It is shown that crack density observed in a microstructure increases with increasing magnitude of applied contact stress. Moreover, crack density increases linearly with respect to the number of fatigue cycles within a given contact stress range. Meanwhile, as applied contact stress increases, number of cycles to failure decreases gradually. Finally, this proposed finite element simulation offers an effective method for identifying fracture and fatigue behaviours of a microstructure provided that microstructure images are available.
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Ospina-Correa, Juan D., Daniel A. Olaya-Muñoz, Juan J. Toro-Castrillón, Alejandro Toro, Abelardo Ramírez-Hernández, and Juan P. Hernández-Ortíz. "Grain polydispersity and coherent crystal reorientations are features to foster stress hotspots in polycrystalline alloys under load." Science Advances 7, no. 15 (April 2021): eabe3890. http://dx.doi.org/10.1126/sciadv.abe3890.
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The mechanical properties of metallic alloys are controlled through the design of their polycrystalline structure via heat treatments. For single-phase microstructures, they aim to achieve a particular average grain diameter to leverage stress hardening or softening. The stochastic nature of the recrystallization process generates a grain size distribution, and the randomness of the crystallographic orientation determines the anisotropy of a mechanical response. We developed a multiscale computational formalism to capture the collective mechanical response of polycrystalline microstructures at unprecedented length scales. We found that for an averaged grain size, the mechanical response is highly dependent on the grain size distribution. The simulations reveal the topological conditions that promote coherent grain texturization and grain growth inhibition during stress relaxation. We identify the microstructural features that are responsible for the appearance of stress hotspots. Our results provide the elusive evidence of how stress hotspots are ideal precursors for plastic and creep failure.
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Barua, A., Y. Horie, and M. Zhou. "Microstructural level response of HMX–Estane polymer-bonded explosive under effects of transient stress waves." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, no. 2147 (August 15, 2012): 3725–44. http://dx.doi.org/10.1098/rspa.2012.0279.
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The effect of transient stress waves on the microstructure of HMX–Estane, a polymer-bonded explosive (PBX), is studied. Calculations carried out concern microstructures with HMX grain sizes on the order of 200 μm and grain volume fractions in the range of 0.50–0.82. The microstructural samples analysed have an aspect ratio of 5:1 (15×3 mm), allowing the transient wave propagation process resulting from normal impact to be resolved. Boundary loading is effected by the imposition of impact face velocities of 50–200 m s −1 . Different levels of grain–binder interface strength are considered. The analysis uses a recently developed cohesive finite element framework that accounts for coupled thermal–mechanical processes involving deformation, heat generation and conduction, failure in the forms of microcracks in both bulk constituents and along grain/matrix interfaces, and frictional heating along crack faces. Results show that the overall wave speed through the microstructures depends on both the grain volume fraction and interface bonding strength between the constituents and that the distance traversed by the stress wave before the initiation of frictional dissipation is independent of the grain volume fraction but increases with impact velocity. Energy dissipated per unit volume owing to fracture is highest near the impact surface and deceases to zero at the stress wavefront. On the other hand, the peak temperature rises are noted to occur approximately 2–3 mm from the impact surface. Scaling laws are developed for the maximum dissipation rate and the highest temperature rise as functions of impact velocity, grain volume fraction and grain–binder interfacial bonding strength.
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Miyazawa, Yuto, Fabien Briffod, Takayuki Shiraiwa, and Manabu Enoki. "Prediction of Cyclic Stress–Strain Property of Steels by Crystal Plasticity Simulations and Machine Learning." Materials 12, no. 22 (November 7, 2019): 3668. http://dx.doi.org/10.3390/ma12223668.
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In this study, a method for the prediction of cyclic stress–strain properties of ferrite-pearlite steels was proposed. At first, synthetic microstructures were generated based on an anisotropic tessellation from the results of electron backscatter diffraction (EBSD) analyses. Low-cycle fatigue experiments under strain-controlled conditions were conducted in order to calibrate material property parameters for both an anisotropic crystal plasticity and an isotropic J2 model. Numerical finite element simulations were conducted using these synthetic microstructures and material properties based on experimental results, and cyclic stress-strain properties were calculated. Then, two-point correlations of synthetic microstructures were calculated to quantify the microstructures. The microstructure-property dataset was obtained by associating a two-point correlation and calculated cyclic stress-strain property. Machine learning, such as a linear regression model and neural network, was conducted using the dataset. Finally, cyclic stress-strain properties were predicted from the result of EBSD analysis using the obtained machine learning model and were compared with the results of the low-cycle fatigue experiments.
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Koh, S. U., J. S. Kim, B. Y. Yang, and K. Y. Kim. "Effect of Line Pipe Steel Microstructure on Susceptibility to Sulfide Stress Cracking." Corrosion 60, no. 3 (March 1, 2004): 244–53. http://dx.doi.org/10.5006/1.3287728.
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Abstract The purpose of this experiment was to evaluate the effect of microstructure on sulfide stress cracking (SSC) properties of line pipe steel. Different kinds of microstructures, with chemical compositions identical to one steel heat, were produced by various thermomechanically controlled processes (TMCP). Coarse ferrite-pearlite, fine ferrite-pearlite, ferrite-acicular ferrite, and ferrite-bainite microstructures were investigated with respect to corrosion properties, hydrogen diffusion, and SSC behavior. SSC was evaluated using a constant elongation rate test (CERT) in a NACE TM0177 solution (5% sodium chloride [NaCl] + 0.5% acetic acid [CH3COOH], saturated with hydrogen sulfide [H2S]). The corrosion properties of steels were evaluated by potentiodynamic and linear polarization methods. Hydrogen diffusion through steel matrix was measured by an electrochemical method using a Devanathan-Stachurski cell. The effect of microstructure on cracking behavior also was investigated with respect to crack nucleation and propagation processes. Test results showed that ferrite-acicular ferrite microstructure had the highest resistance to SSC, whereas ferrite-bainitic and coarse ferritie-pearlitic microstructures had the lowest resistance. The high susceptibility to SSC inferritie-bainitic and coarse ferritic-pearlitic microstructures resulted from crack nucleation on hard phases such as grain boundary cementite in coarse ferritie-pearlitic microstructures and martensite/retained austenite (M/A) island in bainitic phases. Hard phase cementite at grain boundaries or M/A constituent in bainitic phases acted as crack nucleation sites and could be cracked easily under external stress; consequently, the susceptibility of steel to SSC increased. Metallurgical parameters including matrix structure and defects such as grain boundary carbides and inter-lath M/A constituents were more critical parameters for controlling SSC than the hydrogen diffusion rate.
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Allen, Robert M., and John E. Smugeresky. "Dynamic Compaction of Rapidly Solidified Al-6%Si Powder." Proceedings, annual meeting, Electron Microscopy Society of America 43 (August 1985): 36–37. http://dx.doi.org/10.1017/s0424820100117261.
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The production of alloy powders by processes involving rapid solidification can yield powder particles which exhibit highly-refined microstructures desireable from a mechanical properties standpoint. Unfortunately, traditional methods for compacting powders into parts often cause significant coarsening of the starting powder microstructure. Alternative methods such as dynamic compaction (the shock-loading of the powder under high stresses) are under study as means of preserving the fine-scale of the starting microstructure throughout the manufacturing of a fully-dense bulk part.The purpose of the present work was to examine the microstructures developed by the dynamic compaction of rapidly-solidified Al-6%Si alloy powders. The powder was prepared from cast alloy using an ultrasonic gas atomizer. Particles < 250 μm in diameter were sieved to produce uniform size splits for the compaction study. Dynamic compaction was carried out with a gas gun device which imposed a shock stress of ∼4 GPa on a powder sample, producing a fully-dense compact 30 mm in diameter and 5 to 6 mm thick. Microstructural characterization was carried out using a JEOL 35CF SEM and a 200CX STEM, both equipped with energy-dispersive x-ray spectrometry systems.
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Zeng, Qiu Lian, Zhong Guang Wang, and J. K. Shang. "Microstructural Effects on Low Cycle Fatigue of Sn-3.8Ag-0.7Cu Pb-Free Solder." Key Engineering Materials 345-346 (August 2007): 239–42. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.239.
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Low cycle fatigue behavior of Sn-3.8Ag-0.7Cu solder was investigated under fully reversed cyclic loading, with particular emphasis on microstructural effects. The LCF behavior of the solder with equiaxed microstructure was found to differ greatly from that of the solder with a dendrite microstructure. At a given total strain amplitude, the dendrite microstructure exhibited a much longer fatigue life than the equiaxed microstructure. Such a strong microstructural effect on fatigue life arose from the difference in cyclic deformation and fracture mechanisms between the two microstructures. A large number of microcracks along grain boundaries of the equiaxed structure solder developed with increasing cycling, while for the dendrite structure solder, cyclic deformation took place along the direction of the maximal shear stress during fatigue tests and microcracks initiated and propagated along shear deformation bands. Besides, the fatigue behavior of the dendritic microstructure was very sensitive to cyclic frequency whereas the fatigue behavior of the equiaxed microstructure showed less sensitivity to cyclic frequency.
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Lyu, Hao, and Annie Ruimi. "Understanding the Plastic Deformation of Gradient Interstitial Free (IF) Steel under Uniaxial Loading Using a Dislocation-Based Multiscale Approach." Crystals 12, no. 7 (June 23, 2022): 889. http://dx.doi.org/10.3390/cryst12070889.
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Gradient interstitial free (IF) steels have been shown to exhibit a superior combination of strength and ductility due to their multiscale microstructures. The novelty of the work resides in the implementation of a modified slip transmission and a back-stress quantity induced by a long-range dislocation interaction in the dislocation-based multiscale model. This is an improvement over the model we previously proposed. Simulations are performed on IF specimens with gradient structures and with homogeneous structures. The macroscopic behavior of the samples under tension and compression is studied. The evolution of the microstructure such as dislocations, geometrically necessary dislocations (GNDs), and the effects of grain orientation is analyzed. Results show that with our enhanced model, the simulations can successfully reproduce the stress-strain curves obtained experimentally on gradient nano IF steel specimens under tension. The simulations also capture the tension-compression asymmetry (TCA) in specimens with homogeneous and gradient microstructures. The initial texture is found to have a significant effect on the TCA of specimens with gradient microstructures.
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Snopiński, Przemysław, Tibor Donič, Tomasz Tański, Krzysztof Matus, Branislav Hadzima, and Ronald Bastovansky. "Ultrasound Effect on the Microstructure and Hardness of AlMg3 Alloy under Upsetting." Materials 14, no. 4 (February 20, 2021): 1010. http://dx.doi.org/10.3390/ma14041010.
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To date, numerous investigations have shown the beneficial effect of ultrasonic vibration-assisted forming technology due to its influence on the forming load, flow stress, friction condition reduction and the increase of the metal forming limit. Although the immediate occurring force and mean stress reduction are known phenomena, the underlying effects of ultrasonic-based material softening remain an object of current research. Therefore, in this article, we investigate the effect of upsetting with and without the ultrasonic vibrations (USV) on the evolution of the microstructure, stress relaxation and hardness of the AlMg3 aluminum alloy. To understand the process physics, after the UAC (ultrasonic assisted compression), the microstructures of the samples were analyzed by light and electron microscopy, including the orientation imaging via electron backscatter diffraction. According to the test result, it is found that ultrasonic vibration can reduce flow stress during the ultrasonic-assisted compression (UAC) process for the investigated aluminum–magnesium alloy due to the acoustic softening effect. By comparing the microstructures of samples compressed with and without simultaneous application of ultrasonic vibrations, the enhanced shear banding and grain rotation were found to be responsible for grain refinement enhancement. The coupled action of the ultrasonic vibrations and plastic deformation decreased the grains of AlMg3 alloy from ~270 μm to ~1.52 μm, which has resulted in a hardness enhancement of UAC processed sample to about 117 HV.
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Tang, Wei Neng, Rong Shi Chen, En Hou Han, and Wei Ke. "Flow Behavior and Microstructural Evolution of ZW61 Alloy during Hot Compressive Deformation." Materials Science Forum 686 (June 2011): 140–45. http://dx.doi.org/10.4028/www.scientific.net/msf.686.140.
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The flow behavior and microstructural evolution of the ZW61 (Mg-6Zn-0.6Y-0.5Zr ) alloy during uniaxial compressive deformation at temperatures of 250-400°C and strain rates of 0.5-0.001s-1.were investigated. The results indicated that the flow stress could be described with a power law equation related to the temperature and strain rate. Furthermore, the deformation microstructures at different strain rates and temperatures were different. Microstructural evolution deformed under 350 °C and 0.001s-1found that the twinning and different modes of slip systems were selectively activated during deformation, and that misorientation in some grains increased with lattice rotation during hot deformation, which resulted in the gradual formation of new grain boundaries. In addition, dynamic recrystallization (DRX) preferably took place nearby the boundaries of original grains/twinning/slipping bands and coarse particles, which resulted in an inhomogeneous deformation microstructure, i.e. necklace microstructure.
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Duan, J. Z. "Microstructure of chromium films grown on glass and silicon substrates." Proceedings, annual meeting, Electron Microscopy Society of America 47 (August 6, 1989): 474–75. http://dx.doi.org/10.1017/s0424820100154342.
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Thin metal films are widely used in microelectronics and this has stimulated a great deal of research about their microstructures and related properties. During the past two years, chromium microstructures and internal stresses generated during e-beam evaporation Cr film growth have been researched by us. Many relationships between Cr columnar microstructures and internal stresses have been discovered. In this paper, the results of studies of the dependance of Cr columnar microstructures on Si and glass substrates are reported. They have been found to be very useful for analyzing the internal stresses in Cr films and understanding the atomistic mechanism of their growth.It is well known that microstructures and properties are closely related to the processing conditions, so in our experiments, all experimental parameters are kept constant except for factor whose influence on on microstructure and internal stress is under study.
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Chen, Ming, Xiaodong Hu, Hongyang Zhao, and Dongying Ju. "Recrystallization Microstructure Prediction of a Hot-Rolled AZ31 Magnesium Alloy Sheet by Using the Cellular Automata Method." Mathematical Problems in Engineering 2019 (September 16, 2019): 1–15. http://dx.doi.org/10.1155/2019/1484098.
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A large reduction rolling process was used to obtain complete dynamic recrystallization (DRX) microstructures with fine recrystallization grains. Based on the hyperbolic sinusoidal equation that included an Arrhenius term, a constitutive model of flow stress was established for the unidirectional solidification sheet of AZ31 magnesium alloy. Furthermore, discretized by the cellular automata (CA) method, a real-time nucleation equation coupled flow stress was developed for the numerical simulation of the microstructural evolution during DRX. The stress and strain results of finite element analysis were inducted to CA simulation to bridge the macroscopic rolling process analysis with the microscopic DRX activities. Considering that the nucleation of recrystallization may occur at the grain and R-grain boundary, the DRX processes under different deformation conditions were simulated. The evolution of microstructure, percentages of DRX, and sizes of recrystallization grains were discussed in detail. Results of DRX simulation were compared with those from electron backscatter diffraction analysis, and the simulated microstructure was in good agreement with the actual pattern obtained using experiment analysis. The simulation technique provides a flexible way for predicting the morphological variations of DRX microstructure accompanied with plastic deformation on a hot-rolled sheet.
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Zhao, Zhan Yong, Ren Guo Guan, Fu Rong Cao, and Li Qing Chen. "Effects of Interfacial Friction on the Microstructures of Magnesium-Tin Alloy during Continuous Rheo-Forming Process." Materials Science Forum 675-677 (February 2011): 659–62. http://dx.doi.org/10.4028/www.scientific.net/msf.675-677.659.
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The influence of the interfacial friction on the continuous rheo-forming microstructures of magnesium alloy. The effects of interfacial friction on the microstructure evolution in magnesium alloy were investigated. It was shown that strong shear stress and internal friction occur inside the melt under the interfacial friction. In roller-shoe chamber, the growth direction of dendrites growing along the normal direction of the roller near the roller-shoe is changed under shear stress and melt resistance force. when the degree between dendrite and normal direction of roller is about 45 degree, the dendrites can be stablized and grow easily along this direction. Under an appropriate pouring temperature, with the increase of pouring temperature, there is enough room for the grains near the roller-shoe to grow, the grains are not easy to collide mutually, so the dendrites form. In roller-shoe chamber, coarse dendrites near the roller become gradually refined when they grow into the mushy region. Moreover, because dynamic friction force and shear stress of roller are stronger at the exit of the chamber, dendrites fracture and fracture layer or cracks appears. The microstructures consist of mainly rosette and spherical grains on the central position.
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Gao, Jie, Hao Li, Zhen Luo, Liang Gao, and Peigen Li. "Topology Optimization of Micro-Structured Materials Featured with the Specific Mechanical Properties." International Journal of Computational Methods 17, no. 03 (November 20, 2019): 1850144. http://dx.doi.org/10.1142/s021987621850144x.
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Micro-structured materials consisting of an array of microstructures are engineered to provide the specific material properties. This present work investigates the design of cellular materials under the framework of level set, so as to optimize the topologies and shapes of these porous material microstructures. Firstly, the energy-based homogenization method (EBHM) is applied to evaluate the material effective properties based on the topology of the material cell, where the effective elasticity property is evaluated by the average stress and strain theorems. Secondly, a parametric level set method (PLSM) is employed to optimize the microstructural topology until the specific mechanical properties can be achieved, including the maximum bulk modulus, the maximum shear modulus and their combinations, as well as the negative Poisson’s ratio (NPR). The complicated topological shape optimization of the material microstructure has been equivalent to evolve the sizes of the expansion coefficients in the interpolation of the level set function. Finally, several numerical examples are fully discussed to demonstrate the effectiveness of the developed method. A series of new and interesting material cells with the specific mechanical properties can be found.
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Walther, F., and Dietmar Eifler. "Fatigue Behaviour of Railway Wheel Steels under Constant and Variable Amplitude Loading." Materials Science Forum 537-538 (February 2007): 473–80. http://dx.doi.org/10.4028/www.scientific.net/msf.537-538.473.
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In this paper, the influence of the microstructure on the fatigue behaviour of specimens from defined rim positions of original railway wheels R7 (SAE 1050) and tyres B6 (SAE 1065) is characterised under constant and variable amplitude loading. Due to the industrial heat treatment and the component size, the ferrite fraction and the cementite lamellae spacing of the ferriticpearlitic microstructures increase with increasing tread distance. The microstructural gradients influence the fatigue behaviour in a characteristic manner. Mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed. Temperature and electrical resistance data represent the actual fatigue state in highly stressed volume parts and are not related to a gauge length. Furthermore the electrical resistance is qualified to detect a proceeding fatigue damage in load-free specimens and components. For variable amplitude loading a new testing procedure was applied, which combines any kind of near-service load spectrum with short single step measuring sequences. The plastic strain amplitude, the temperature and the electrical resistance data of each single step sequence are plotted in cyclic ‘deformation’ curves and represent the sum of microstructural changes caused by near-service loading. The substitution of the plastic strain amplitude by the changes of the temperature and the electrical resistance leads to modified Morrow and Manson-Coffin curves. Electron microscopic investigations allow to interpret the measured fatigue data on the basis of microstructural details.
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Zhou, Shujun, Wei Wu, Yilun Yang, and Xiao Huang. "Effect of Deposition Temperature on Long-Term Residual Stress Evolution of Au Films." Materials 16, no. 10 (May 10, 2023): 3645. http://dx.doi.org/10.3390/ma16103645.
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To increase the residual stress stability of Au films while reducing the residual stress level, the effect of deposition temperature on long-term residual stress evolution of Au films under different conditions were studied. Au films with a thickness of 360 nm were deposited using e-beam evaporation on fused silica under different temperatures. Observations and comparisons were made of the microstructures of Au films deposited under different temperatures. Results showed that by increasing the deposition temperature, a more compact microstructure of Au film was obtained, which was manifested in increased grain size and reduced grain-boundary voids. After deposition, a combined process consisting of natural placement and 80 °C thermal holding was conducted on the Au films, and the residual stresses were monitored using the curvature-based technique. Results showed that the initial tensile residual stress of the as-deposited film decreased with the deposition temperature. The Au films with higher deposition temperatures showed better residual stress stability, maintaining low stress levels in the subsequent long-term combination of natural placement and thermal holding. The mechanism was discussed based on the differences in microstructure. Comparisons were made between post-deposition annealing and increased deposition temperature.
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Wang, Hao, Yong-Yan Wang, Zhuo-Qun Yu, and Jian-Guang Li. "Experimental Study on the Effects of Stress-Induced Damage on the Microstructure and Mechanical Properties of Soft Rock." Advances in Civil Engineering 2021 (January 31, 2021): 1–11. http://dx.doi.org/10.1155/2021/6696614.
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After rocks are damaged under stress loading, the changes of their microstructural and mechanical properties are major factors that affect construction safety in geotechnical engineering projects. Studying the microstructures and mechanical behaviors of stress-damaged rocks can help better guide construction and reduce construction risks for geotechnical engineering projects. In this study, a sandstone was first artificially predamaged and then subsequently subjected to scanning electron microscopy (SEM) analysis, computed tomography (CT) scanning, and uniaxial compression testing. Afterwards, the rock microstructures were three-dimensionally (3D) reconstructed, and the pores were classified and characterized based on their diameters. Moreover, the microstructural and mechanical parameters of the rock were subjected to significance analysis. The results showed that as the stress-induced damage ( σ i ) increased, the uniaxial compressive strength ( σ c ) of the soft rock decreased by 13.7–31.8%; as σ i increased from 11.2 to 19.6 MPa, the elastic modulus (E) of the soft rock increased by up to 28.8%; and as σ i increased beyond 19.6 MPa, there was a significant (22.3%) decrease in E. Stress-induced damage significantly affected the spatial distribution of the pores’ structure of the soft rock. Changes in the spatial structure of the pores led to the formation of cracks. The microstructural parameters of the stress-damaged soft rock were correlated with its mechanical parameters.
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Shan, Wei Wei, Ju Fu Jiang, and Shou Jing Luo. "Microstructure and Stress Variation of Semi-Solid Magnesium Alloy during Isothermal Compression and Its Relationship to Thixotropy." Solid State Phenomena 116-117 (October 2006): 643–47. http://dx.doi.org/10.4028/www.scientific.net/ssp.116-117.643.
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Thixotropy is the most important characteristic of semi-solid materials, and it is decided by the variation of microstructure during action of handling. In this paper, for the sake of the industrial thixoforming and numerical simulation, microstructure and stress variation of semisolid magnesium alloys during isothermal compression is researched. Here, samples are heated to the desired temperature in the empty space with various holding times and compressed horizontally. Stress–strain curves during compression can be given directly by the experimental computer, and each of curves show a peak stress in a small strain and then decrease rapidly, which originally because of the thixotropy of semisolid materials. Moreover, thixotropy of semisolid magnesium alloys is clearer with the evolution of microstructures including agglomeration and deagglomeration of solid particles and the moving way of liquid at different places and strain under different conditions. Microstructures during isothermal compression show that the deagglomeration of solid particles increase with increasing the strain rate, therefore, the thixotropy of semisolid magnesium alloys increases. However, when solid volume fractions are lower, the agglomeration of solid particles doesn’t change obviously with increase or decrease factors, meaning that the thixotropy is smaller. Relationships between thixotropy and microstructure at other different conditions are also given according to the experiments and analysis.
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James, R. D. "Microstructure of Shape-Memory and Magnetostrictive Materials." Applied Mechanics Reviews 43, no. 5S (May 1, 1990): S189—S193. http://dx.doi.org/10.1115/1.3120802.
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Recent advances in the analysis of microstructure is providing models and methods for treating the kinds of optimization problems that arise in the study of microstructure. The main advance has been the development of theory and methods for treating the case in which arbitrary microstructures compete for the minimum (or maximum). This contrasts for example with micromechanics in which the geometry of the microstructure is assumed, or assumed up to the choice of a few parameters, and then the optimization or stress analysis is carried out under severe geometric restrictions. Micromechanics is effective in dealing with a particular experimentally observed microstructure, but not for understanding microstructures that might be optimal in a certain sense. Much of this recent research has been fueled by critical discussions among engineering scientists, mathematicians and electron microscopists. The intent of this paper is first to summarize, in terms accessible to a broad audience, the nature of this research and then to describe applications to the improvement of shape-memory and magnetostrictive materials. The general part of the lecture will focus on three areas, effective properties of materials, optimal design of materials and phase transformation and active materials. A central role is played by the question “How does one meaningfully average a quantity whose values vary rapidly on a microstructural scale?” A second recurring theme is that the optimal microstructure is predicted to have fine structure. The latter is closely related to the failure of conditions of material stability.
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Ito, Yasumi, and Akira Shimamoto. "Effect of Microstructure on Fatigue Crack Growth Resistance of Magnesium Alloy under Biaxial Stress." Key Engineering Materials 297-300 (November 2005): 1559–64. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.1559.
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Fatigue crack propagation tests are conducted on magnesium alloy, cruciform specimens under biaxial and uniaxial loadings by using the biaxial fatigue tester which was developed by the authors. We investigate the effect of microstructures of specimens on fatigue crack growth resistance under biaxial stresses. From electron-microscope observations of a fatigue fracture and microstructure observations, it becomes clear that the mechanical properties of a magnesium-alloy, AZ31B, are greatly influenced by the diameter of crystal grains. We find that static tensile strength falls by heat-treating in the high temperature region where the diameter of crystal grains of an X-Y plane becomes large. We also find that the crack progress velocity under equal biaxial stresses gets faster by heat-treating in the high temperature region where the diameter of crystal grain of a Z-X plane becomes large.
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Sakurada, Koki, Mahmudul Kabir, Takuya Abe, and Masahiro Minowa. "Study on Fine Microstructures of ZnO Microvaristors under Over Current Stress." IEEJ Transactions on Fundamentals and Materials 140, no. 1 (January 1, 2020): 54–55. http://dx.doi.org/10.1541/ieejfms.140.54.
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Eres-Castellanos, Adriana, Vicente Perez-Aroca, Pedro Carrero-Santos, Francisca G. Caballero, and Carlos Garcia-Mateo. "Tuning Bainitic Microstructures by Complex Thermo-mechanical Treatments under Constant Stress." ISIJ International 64, no. 2 (January 30, 2024): 316–25. http://dx.doi.org/10.2355/isijinternational.isijint-2023-148.
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Nagai, Yuji, Takahiro Namazu, Nobuyuki Naka, Shinsuke Kashiwagi, Kunio Ohtsuki, and Shozo Inoue. "OS5-3-2 Raman Spectroscopic Analysis of Surface Stress Distribution on Single Crystal Silicon Microstructures under Uniaxial Tensile Loading." Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics 2007.6 (2007): _OS5–3–2–1—_OS5–3–2–4. http://dx.doi.org/10.1299/jsmeatem.2007.6._os5-3-2-1.
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Teel, Hunter, Joseph Steven Lopata, Taylor R. Garrick, Fengkun Wang, Yangbing Zeng, and Sirivatch Shimpalee. "Microstructure Model to Predict Mechanical Behavior of Lithium-Ion Battery Active Material Under Compressive Load." ECS Meeting Abstracts MA2023-01, no. 25 (August 28, 2023): 1658. http://dx.doi.org/10.1149/ma2023-01251658mtgabs.
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A three-dimensional microstructure-based modeling method (3DMS) is developed to predict the mechanical behaviors of porous electrode that includes both active material (AM) and binders inside lithium-ion battery during compression. The geometry of both AM and binder shown in Fig. 1a is generated stochastically to create microstructures by using a modified MATBOX opensource program with our in-house code. The advanced technique of volume element generation is also established to overcome the interfacial error due to complexity of binder distribution as illustrated in Fig. 1b. The Finite Element Analysis (FEA) based solid-stress model is applied to predict local mechanical activities including stress-strain relationship and microstructure evolution. The predictions of anisotropic behavior in the porous electrode under compressive loads will be presented and the insights into the microstructure deformation will be discussed. Further, the analysis results will be validated using experimental testing results acquired at various length scales. This work can be used for the model-based FEA platform to predict the impact of volume change under charge/discharge cycles, volume change of a jelly-roll during formation, and the response of the active material in typical pouch cells during battery module assembly. Figure 1
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Zeinali, Seyed Morteza, and Sherif L. Abdelaziz. "Identifying thermo-mechanical induced microstructural changes." E3S Web of Conferences 205 (2020): 09005. http://dx.doi.org/10.1051/e3sconf/202020509005.
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Robust engineering of geomaterials for energy applications requires a clear understanding of the impacts of temperatures and pressures applied to the soil on their microstructures. Such understandings will facilitate better designs of new geomaterials and technologies via ensuring accurate assessments of the performance of the existing ones. In this study, we assess the changes in the microstructure—specific surface area and pore size distribution—of a saturated clay subjected to stress and temperature cycle. Clay specimens were subjected to the desired mechanical stresses and thermal cycles in a triaxial system. Then, the specimens were swiftly extracted from the triaxial, flush frozen in liquid nitrogen, then freeze-dried to preserve their microstructure. The preserved specimens were then used for specific surface area and pore size distribution assessments using nitrogen (N2)-gas adsorption and mercury intrusion porosimetry. The results established qualitative explanations of the expected microstructural changes in geomaterials under operational conditions, which facilitate the development of new geomaterials that can overcome such alternations.
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Schouwenaars, Rafael, Víctor H. Jacobo, Sara M. Cerrud, and Armando Ortiz. "Finite Element Simulation of Microstresses in a Traditional FGM: The Case of Soft Tribo-Alloys." Materials Science Forum 492-493 (August 2005): 421–28. http://dx.doi.org/10.4028/www.scientific.net/msf.492-493.421.
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Journal bearings are graded systems with a metal-metal composite as the functional layer. Estimation of the microscale stress distributions is used to analyse the interaction between microstructure, material properties and damage mechanisms during wear. The analysis is executed by means of simple plane-strain finite element models mimicking experimentally observed microstructures. It is found that under realistic macrosstress conditions no tensile microstresses are induced in the triboalloy and that plastic flow is inhibited by the graded structure.
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Kim, Sang Joo, and Yun Jae Kim. "Domain Switching and Crack Tip Opening Stress Variation in Ferroelectric Ceramics." Key Engineering Materials 297-300 (November 2005): 2557–66. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2557.
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Evolution of switching zone near a crack tip in ferroelectric ceramics is calculated using the constitutive equations proposed in [1], with an assumption that switching-induced internal fields are minimized by fine domain microstructures and moving charges. A two-dimensional ferroelectric ceramic specimen that has an edge crack and that is poled perpendicular to the crack plane are subjected to external stress and electric fields. Diverse crack tip microstructures are obtained depending on both the history and the ratio of electric and stress loads. It is shown that opposite crack tip opening stresses under the same electric fields are due to opposite distributions of piezoelectric coefficients in the specimens with different crack tip microstructures.
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Čapek, Jiří, Karel Trojan, Jan Kec, Nikolaj Ganev, Ivo Černý, and Tomáš Mužík. "Residual Stresses and the Microstructure of Modeled Laser-Hardened Railway Axle Seats under Fatigue." Metals 14, no. 3 (February 29, 2024): 290. http://dx.doi.org/10.3390/met14030290.
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Railway wheels are usually attached to axles by press-fitting; therefore, the mechanical processes taking place during operation can result in failure, with fatal consequences for the axle seats. This manuscript describes the effect of laser hardening on the residual stress state, microstructural parameters (lattice defects—dislocations, crystallites, microstrains, etc.), and mechanical properties of laser-hardened EA1N steel railway axles under fatigue life conditions. Differences were found between ground, single-track, and multi-track hardened surfaces. Tensile residual stresses, low dislocation densities and hardnesses, and different microstructures (tempered cubic martensite) were found at the overlapped tracks and at the boundary of the heat-affected zone and bulk surface compared with the hardened zone. As a result, the surface treatment of axle seats by laser hardening improved the fatigue failure resistance compared with untreated seats. Optimal properties of the integrity of the axle seat surface were achieved, including fatigue resistance, which seems to be positively influenced mainly by sufficient hardness and the appropriate microstructure. The influence of the other investigated parameters was not evident, and was reduced by the presence of fretting corrosion and press-fitting.
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Rezvanian, O., M. A. Zikry, and A. M. Rajendran. "Statistically stored, geometrically necessary and grain boundary dislocation densities: microstructural representation and modelling." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2087 (August 14, 2007): 2833–53. http://dx.doi.org/10.1098/rspa.2007.0020.
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A unified physically based microstructural representation of f.c.c. crystalline materials has been developed and implemented to investigate the microstructural behaviour of f.c.c. crystalline aggregates under inelastic deformations. The proposed framework is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs) and grain boundary dislocations. This interrelated dislocation density formulation is then coupled to a specialized finite element framework to study the evolving heterogeneous microstructure and the localized phenomena that can contribute to failure initiation as a function of inelastic crystalline deformation. The GND densities are used to understand where crystallographic, non-crystallographic and cellular microstructures form and the nature of their dislocation composition. The SSD densities are formulated to represent dislocation cell microstructures to obtain predictions related to the inhomogeneous distribution of SSDs. The effects of the lattice misorientations at the grain boundaries (GBs) have been included by accounting for the densities of the misfit dislocations at the GBs that accommodate these misorientations. By directly accounting for the misfit dislocations, the strength of the boundary regions can be more accurately represented to account for phenomena associated with the effects of the GB strength on intergranular deformation heterogeneities, stress localization and the nucleation of failure surfaces at critical regions, such as triple junctions.
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Wang, Yu Tian, Wei Zhen Chen, and Fu Xiang Jiang. "Development and Evaluation for Microdamage of Concrete under Uniaxial Compressive Load." Applied Mechanics and Materials 507 (January 2014): 226–29. http://dx.doi.org/10.4028/www.scientific.net/amm.507.226.
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Development of microcracks and microstructures under uniaxial compressive load were studied by the measurement of axial residual strain and the calculation of specific crack area. Two opposite mechanisms could be distinguished for describing the development of microstructures, i.e. densification and micro-crack formation. Based on the experimental results, consistent tendency was found for the development of inside microcracks and overall deformation. Higher load level induced larger residual strain and residual specific crack area after unloading. Significant difference in the development of cracks was found for concrete specimens of different proportions. Specimen with higher water to binder ratio and lower strength developed earlier corresponds to lower initial stress-strength ratio for the beginning of crack propagation, and lower critical stress level for the beginning of unstable development. Effect of uniaxial compressive load on the durability of concrete specimen depends on the relative relationship between the two mechanisms.
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Qing, Hai, and Tianliang Liu. "Micromechanical Analysis of SiC/Al Metal Matrix Composites: Finite Element Modeling and Damage Simulation." International Journal of Applied Mechanics 07, no. 02 (April 2015): 1550023. http://dx.doi.org/10.1142/s1758825115500234.
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The influence of interface strengths and microstructures on the strength and damage of SiC particle reinforced aluminum Metal Matrix Composite (MMC) is investigated under uniaxial tensile, simple shear, biaxial tensile and combined tensile and shear loadings. An algorithm to generate automatically the microstructural models of MMCs with random distribution of particle shapes, dimensions, orientations and locations is proposed and implemented within Matlab. A damage model based on the stress triaxial indicator is developed to simulate the ductile failure of metal matrix, the other damage model based on the maximum principal stress criterion is developed to simulate the brittle failure of SiC particles, and 2D cohesive element is utilized to describe interface decohesion between matrix and particles. A series of numerical experiments are performed to study the macroscopic stress–strain relationships and microscale damage evolution in MMCs under different loading conditions.
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Correa, Sandro Rosa, Marcos Flavio de Campos, C. J. Marcelo, José Adilson de Castro, Maria Cindra Fonseca, T. C. Chuvas, M. A. Campos, and Linilsson Rodrigues Padovese. "Characterization of Residual Stresses and Microstructural by Technique of Magnetic Barkhausen Noise of API 5L X80 Steel Heat Treatment." Materials Science Forum 869 (August 2016): 556–61. http://dx.doi.org/10.4028/www.scientific.net/msf.869.556.
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Residual stresses typically are generated during the manufacturing process of mechanical components. The non-destructive techniques are quite sensitive to these residual stresses, and to microstructural changes resulting from thermal cycling. In this work, samples of API 5L X80 steel were exposed to several conditions of cooling, under water, air and oil, thus obtaining different microstructures and different levels of residual stresses. The residual stress measurements were made using the methods of Magnetic Barkhausen Noise and X-ray diffraction.
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MALARD, B., J. PILCH, P. SITTNER, V. GARTNEROVA, R. DELVILLE, D. SCHRYVERS, and C. CURFS. "MICROSTRUCTURE AND FUNCTIONAL PROPERTY CHANGES IN THIN Ni–Ti WIRES HEAT TREATED BY ELECTRIC CURRENT — HIGH ENERGY X-RAY AND TEM INVESTIGATIONS." Functional Materials Letters 02, no. 02 (June 2009): 45–54. http://dx.doi.org/10.1142/s1793604709000557.
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High energy synchrotron X-ray diffraction, transmission electron microscopy and mechanical testing were employed to investigate the evolution of microstructure, texture and functional superelastic properties of 0.1 mm thin as drawn Ni – Ti wires subjected to a nonconventional heat treatment by controlled electric current (FTMT-EC method). As drawn Ni – Ti wires were prestrained in tension and exposed to a sequence of short DC power pulses in the millisecond range. The annealing time in the FTMT-EC processing can be very short but the temperature and force could be very high compared to the conventional heat treatment of SMAs. It is shown that the heavily strained, partially amorphous microstructure of the as drawn Ni – Ti wire transforms under the effect of the DC pulse and tensile stress into a wide range of annealed nanosized microstructures depending on the pulse time. The functional superelastic properties and microstructures of the FTMT-EC treated Ni – Ti wire are comparable to those observed in straight annealed wires.
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Nzogang, Billy Clitton, Manuel Thieme, Alexandre Mussi, Sylvie Demouchy, and Patrick Cordier. "Characterization of recovery onset by subgrain and grain boundary migration in experimentally deformed polycrystalline olivine." European Journal of Mineralogy 32, no. 1 (January 15, 2020): 13–26. http://dx.doi.org/10.5194/ejm-32-13-2020.
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Abstract. To apprehend plate tectonics and the dynamics of the lithosphere–asthenosphere boundary, composed principally of olivine, we need to understand the mechanisms that control plastic deformation of olivine in the relevant temperature domain. After more than 50 years of laboratory studies and investigations on natural rocks, the interplay of several key parameters (e.g. temperature, pressure, vacancy concentration, dislocation densities, grain size, strain rate) controlling polycrystalline olivine plasticity remains difficult to assess. Here, we study four olivine polycrystals, which have been deformed in axial compression under a confining pressure of 300 MPa, at 1273 or 1473 K. Despite significant differences in mechanical properties (stress–strain curves), previous characterization by scanning (SEM) and transmission electron microscopy (TEM) did not reveal significant differences in dislocation microstructures which could explain these contrasted behaviours. We have undertaken automatic crystallographic orientation mapping (ACOM) analyses in TEM to increase the spatial resolution of characterization compared to previously obtained electron backscatter diffraction maps to further decipher the microstructures at nanoscale. With this novel technique applied to olivine, a noticeable difference in the onset of microstructural recovery has been identified between specimens deformed at 1273 and 1473 K. The microstructures of the olivine polycrystals deformed at 1473 K exhibit numerous curved grain and subgrain boundaries, advocating for recovery by boundary migration. In contrast, the microstructures of the olivine polycrystals deformed at 1273 K have significantly fewer subgrain boundaries and show more straight boundaries (i.e. closer to an equilibrium microstructure) than in the specimen deformed at 1473 K. Characterization by ACOM-TEM has permitted the identification of the onset of recovery, which is led by boundary migration even for very low macroscopic finite strains.
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Lin, Chen, Yijun Chai, and Yueming Li. "Oxidation Simulation of Thermal Barrier Coatings with Actual Microstructures Considering Strength Difference Property and Creep-Plastic Behavior." Coatings 8, no. 10 (September 25, 2018): 338. http://dx.doi.org/10.3390/coatings8100338.
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A scanning electron microscope (SEM) image based direct finite element (FE) mesh reconstruction method is employed to reflect microstructure features of thermal barrier coatings (TBC). The creep-plastic assumption of thermally grown oxide (TGO) scale and metallic bond coat (BC) as well as the strength difference (SD) property of ceramic top coat (TC) are considered to simulate the mechanical behavior. A diffusion oxidation model considering oxygen consumption is proposed to characterize TGO growth. The oxidation simulation of TBC is carried out under the consideration of actual microstructure features. The results revealed that the interface defects increase the surface-area-to-volume ratio of BC exposed to oxygen anion. This leads to the non-uniform TGO growth, which has also been observed in experimental studies. The microstructures and mechanical behavior strongly affect stress evolution in TBC. The consideration of actual microstructure features and reasonable mechanical behaviors, including the creep-plastic behavior and SD property, is helpful for the accurate evaluation of interface stress.
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Dönges, Benjamin, Claus Peter Fritzen, and Hans Jürgen Christ. "Experimental Investigation and Simulation of the Fatigue Mechanisms of a Duplex Stainless Steel under HCF and VHCF Loading Conditions." Key Engineering Materials 664 (September 2015): 267–74. http://dx.doi.org/10.4028/www.scientific.net/kem.664.267.
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High frequency push-pull fatigue experiments on the austenitic-ferritic duplex stainless steel X2CrNiMoN22-5-3 (318LN) revealed that crack nucleation and crack propagation through the first grain determine significantly the lifetime of the material. Only in very few cases it was observed that fatigue samples which endured one billion load cycles without failure (run-out samples) contain microcracks which reached or overcame the first microstructural barrier (phase or grain boundary). This leads to the conclusion that in most cases the highest macroscopic stress or strain amplitude which does not lead to fatigue crack propagation through the entire first grain can be considered as the fatigue limit of the material. The present study documents that the experimentally identified fatigue mechanisms can be represented in mesoscopic finite element simulations by taking into account the effects of anisotropic elasticity, crystal plasticity, macro and micro residual stresses, plastic strain concentration in form of slip bands, crack nucleation and short crack propagation through the first grain. The current investigation shows that such simulations enable the determination of the fatigue limit of both real and synthetic microstructures. By means of real microstructures, containing slip traces and microcracks, the calculations can be verified and the required microstructural parameters can be determined.
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Zhang, W., M. L. Sui, Y. Z. Zhou, J. D. Guo, G. H. He, and D. X. Li. "Evolution of microstructure in TiC/NiCr cermet induced by electropulsing." Journal of Materials Research 18, no. 7 (July 2003): 1543–50. http://dx.doi.org/10.1557/jmr.2003.0213.
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Microstructures of a TiC/Ni80Cr20 cermet, subjected to single high-current-density electropulsing, were characterized by x-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. Under the electropulsing, the shift of NiCr peaks versus the reverse change of TiC counterparts illustrates that the treatment gives rise to strong thermal stress impacting on the cermet. The stress, accompanied by the transient rise of temperature, led to microstructural evolutions of the cermet. Some nanostructured TiC grains, consisting of many nanocrystallites with small-angle grain boundaries, developed during electropulsing. Also, many regions teemed with coexisting nanosized TiC and NiCr crystallites, which possessed good bonding. Within the NiCr regions, large amounts of deformation twins were produced by the electropulsing.
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Shimizu, Ichiko, and Katsuyoshi Michibayashi. "Steady-State Microstructures of Quartz Revisited: Evaluation of Stress States in Deformation Experiments Using a Solid-Medium Apparatus." Minerals 12, no. 3 (March 6, 2022): 329. http://dx.doi.org/10.3390/min12030329.
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Dynamically recrystallizing quartz is believed to approach a steady-state microstructure, which reflects flow stress in dislocation creep. In a classic experimental study performed by Masuda and Fujimura in 1981 using a solid-medium deformation apparatus, two types of steady-state microstructures of quartz, denoted as S and P, were found under varying temperature and strain rate conditions. However, the differential stresses did not systematically change with the deformation conditions, and unexpectedly high flow stresses (over 700 MPa) were recorded on some experimental runs compared with the applied confining pressure (400 MPa). Internal friction in the sample assembly is a possible cause of reported high differential stresses. Using a pyrophyllite assembly similar to that used in the previous work and setting up paired load cells above and below the sample assembly, we quantified the frictional stress acting on the sample and corrected the axial stress. The internal friction changed in a complicated manner during pressurization, heating, and axial deformation at a constant strain rate. Our results suggest that Masuda and Fujimura overestimated the differential stress by about 200 MPa in their 800 °C runs. Crystallographic fabrics in the previous experimental sample indicated that the development of elongated quartz grains, which are characteristics of Type-S microstructures, was associated with preferential growth of unfavorably oriented grains during dynamic recrystallization.
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Seo, Seongji, and Jiyong Park. "Annealing Heat Treatment for Homogenizing the Microstructure and Mechanical Properties of Electron-Beam-Welded Thick Plate of Ti-6Al-4V Alloy." Materials 16, no. 23 (November 29, 2023): 7423. http://dx.doi.org/10.3390/ma16237423.
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In the application of Ti-6Al-4V to aerospace structural components, when welding thick plates similar of the thickness of the components, microstructure and hardness gradients emerge between the base material (BM) and the joint. This leads to the issue of significant stress concentration in the BM under tensile stress. To address this problem through post-welding heat treatment, this study conducted heat treatments at temperatures both below (mill annealing, MA) and above the beta-transus temperature (beta annealing, BA) on electron-beam weldments of 18 mm thickness Ti-6Al-4V plates. Subsequently, microstructures and hardness were analyzed at different depths from the upper surface and areas (fusion zone (FZ), heat-affected zone (HAZ), and BM), and tensile properties were measured at various depths. The results indicated that α′ observed in FZ and HAZ was resolved through both MA and BA. Particularly after BA, the microstructural gradient that persisted even after MA completely disappeared, resulting in the homogenization of widmanstätten α + β. Consequently, after BA, the hardness gradient in each zone also disappeared, and the tensile strength was higher than in just-welded and MA heat-treated plates.
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Fujii, Toshiyuki, Shizuma Uju, Chihiro Watanabe, Susumu Onaka, and Masaharu Kato. "Cyclic Deformation of Al-Mg Single Crystals with a Single Slip Orientation." Materials Science Forum 561-565 (October 2007): 2213–16. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2213.
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Fully reversed tension-compression fatigue tests were performed on solid-solutioned Al-0.7mass%Mg single crystals with a single slip orientation under constant plastic-strain amplitudes. Dislocation microstructures were quantitatively examined by transmission electron microscopy. The cyclic stress–strain curve (CSSC) exhibited three distinct regions with a short plateau region in the intermediate plastic-strain amplitude range, and the plateau stress was 26MPa. Characteristic microstructures were developed corresponding to the three regions in the CSSC. Vein structure was observed at the low strain-amplitude region. In the plateau regime, the persistent slip bands (PSBs) were observed. Labyrinth structure was also observed at the higher strain-amplitude region. The plateau stress, the cyclic flow stress of PSBs, can be explained by considering not only the Orowan bowing stress and the dipole passing stress of screw dislocations but also solid-solution hardening by Mg atoms.
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Zhao, Hongbao, Tao Wang, Huan Zhang, and Ziqiang Wei. "Comparison of Local Load Influence on Crack Evolution of Coal and Briquette Coal Samples." Advances in Civil Engineering 2018 (September 4, 2018): 1–12. http://dx.doi.org/10.1155/2018/1790785.
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Taking raw coal and briquette coal samples with preset center holes as research objects, this paper makes a systematic analysis and research of crack evolution laws of the two different coal samples under the local load. The results show that the raw coal and briquette coal samples are different mainly in number, dimension, and complexity of the internal microstructures, so it is not right to replace raw coal with briquette coal when performing observational study of the crack evolution of microstructures; under the effect of local load, local property, randomness of crack initiation position, and crack initiation stress of raw coal samples are greater than those of briquette coal samples; law of instantaneous maximum effective cut-through rate of raw coal samples is more complex than that of briquette coals; under the effect of uniformly distributed load, end effect factor Fe, sample microstructure influencing factor Fs, and preset center hole factor Fh are the major factors influencing crack growth, among which the amplified end effect factor Fe and sample microstructure influencing factor Fs are dominant factors; under the effect of local load, local load influencing factor Fp, end effect factor Fe, sample microstructure influencing factor Fs, and preset center hole factor Fs are the major factors influencing crack growth, among which the local load influencing factor Fp, end effect factor Fe, and sample microstructure influencing factor Fs are dominant factors. Compared with briquette coal samples, raw coal samples are more sensitive to influencing factors, such as local load influencing factor Fp, end effect factor Fe, sample microstructure influencing factor Fs, and preset center hole factor Fh, and can aggravate the influence of these factors on the crack growth; the paper also puts forward a method for describing local load based on a coupling mechanical model of uniaxial compression and local shear.
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Horníková, Jana, Pavel Šandera, and Jaroslav Pokluda. "Computation of Effective Fatigue Thresholds Based on a New Concept of Crack Closure." Key Engineering Materials 324-325 (November 2006): 803–6. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.803.
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A new theoretical concept of crack closure under plain strain was applied to assess the effective fatigue threshold under various loading condition for selected aluminium and titanium alloys of different microstructures. The concept is based on the long-range effect of geometrically necessary dislocations remaining in the wake of propagating fatigue cracks. Calculated threshold values FKeff,th for 7475 aluminium alloy are about 1.9 MPa.m1/2 (in vacuum) and 1 MPa.m1/2 (in air), and about 2.5 MPa.m1/2 and 3.3 MPa.m1/2 for c-titanium and Ti-2.5%Cu, respectively. All calculated values are nearly independent on both the microstructure and the applied stress ratio and they are in a good agreement with experimental data.
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Sugahara, Tarcila, Danieli A. P. Reis, Carlos de Moura Neto, M. J. R. Barboza, E. A. C. Perez, Francisco Piorino Neto, and Ana Coh O. Hirschmann. "The Effect of Widmanstätten and Equiaxed Microstructures of Ti-6Al-4V on the Oxidation Rate and Creep Behavior." Materials Science Forum 636-637 (January 2010): 657–62. http://dx.doi.org/10.4028/www.scientific.net/msf.636-637.657.
Full textAbstract:
Ti-6Al-4V is currently used in aeronautic and aerospace industry mainly for applications that require resistance at high temperature such as, blades for aircraft turbines and steam turbine blades. The titanium affinity by oxygen is one of main factors that limit the application of their alloys as structural materials at high temperatures. Notable advances have been observed in the development of titanium alloys with the objective of improving the creep properties. Increased oxygen levels are associated with increased microhardness and decreased ductility in titanium. In spite of this, Ti-6Al-4V containing an (+) structure continues to be the workhorse of the titanium industry due to their high specific strength, corrosion resistance, excellent high temperature properties and metallurgical stability. The objective of this work was to study the influence of equiaxed and Widmanstätten microstructures on oxidation rates and creep behavior of the Ti-6Al-4V alloy. The samples were exposed to different conditions of time and temperature to evaluate the oxidation rates. This influence on the oxidation rates was evaluated in terms of weight gain, -case depth and microhardness profile at 500 and 600 °C. Preliminary results indicated that the equiaxed microstructure with average grain size of 10 m exhibits faster oxygen diffusion. Short-term creep tests were performed under constant load in a stress range from 291 to 472 MPa at 500 °C and in a stress range from 97 to 291 MPa at 600 °C. The stress exponents obtained lie in the range from 4.0 to 11.3. The apparent activation energies for steady-state creep determined in the present work were estimated to be 316 and 415 kJ/mol at 291 MPa for the equiaxed and Widmanstätten microstructures, respectively. On the basis, the creep of Ti-6Al-4V is consistent with the lattice diffusion-controlled dislocation climb process in -Ti, for both microstructures. The creep rates of Widmanstätten microstructure were two orders of magnitude lower than of equiaxed microstructure in both temperatures. Apparently, the higher creep resistance with a Widmanstätten microstructure can be attributed to / interfaces acting as obstacles to dislocation motion and to the average grain size of 395 m, which reduces the grain boundary sliding, dislocations sources and the rate of oxygen diffusion along grain boundaries.
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Talib, R. J., A. A. Mahaidin, S. A. Manaf, and M. A. Selamat. "Mechanical Properties and Microstructures of WC-Co Cutting Tool Inserts with Addition of VC." Advanced Materials Research 879 (January 2014): 213–17. http://dx.doi.org/10.4028/www.scientific.net/amr.879.213.
Full textAbstract:
The mechanical properties and microstructures of WC-Co are highly dependent on its cobalt content, grain size of the WC particles and sintering temperature. In this work, the effect of addition of VC powder on the mechanical properties and microstructures during the consolidation of process will be investigated. The WC-Co and WC-Co-VC cutting tool inserts were fabricated using powder metallurgy route. The powders were wet mixed with heptane in turbula mixer for three hours, dried and then granulated. The mixed powders were uniaxially pressed at a pressure of 625 MPa and cold-isostatic pressed at a pressure of 200 MPa. The compacted samples were sintered in the temperature range of 1350 1450°C under nitrogen-based atmosphere. The mechanical properties of the samples are analyzed using Vickers microhardness tester, universal tensile machine and the microstructures of the sintered sample were observed using field emission scanning electron microscope. Microstructural examinations showed that VC particle is good as grain growth inhibitor as a result of good precipitation of VC in WC grain boundaries. However the addition of VC in WC-Co hardmetal resulted in the reduction of hardness and transverse rupture stress due to increase of pores in the microstructures of sintered samples.
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Sumitani, Takahiro, Katsushi Tanaka, and Haruyuki Inui. "Microstructural evolution of monocrystalline Co–Al–W-based superalloys by high-temperature creep deformation." MRS Proceedings 1516 (2012): 221–26. http://dx.doi.org/10.1557/opl.2012.1683.
Full textAbstract:
ABSTRACTCreep tests of monocrystalline Co–Al–W-based alloys with a tensile stress of 137 MPa at 1000 °C were carried out. The microstructures of the crept specimens were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The γ′ phase in the specimens was not only elongated along the stress direction as expected by the sign of the lattice misfit but also elongated in one of the <100> directions perpendicular to the stress direction. As a result, the shape of the γ′ phase is not a rod but a plate. In the TEM images, it was observed that many SISFs are induced in the γ′ phase by creep. A similar microstructure is also observed in Ni-based superalloys, but the microstructure was formed under relatively lower temperatures and higher applied stresses. The observation of numerous stacking faults in the γ′ phase is a clear indication that the γ′ phase precipitated in the present alloy is weaker than that in many modern Ni-based superalloys.