Academic literature on the topic 'Varying grain sizes'
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Journal articles on the topic "Varying grain sizes"
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Kuronen, Mikko, and Lasse Leskelä. "Hard-Core Thinnings of Germ‒Grain Models with Power-Law Grain Sizes." Advances in Applied Probability 45, no. 03 (September 2013): 595–625. http://dx.doi.org/10.1017/s0001867800006509.
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Random sets with long-range dependence can be generated using a Boolean model with power-law grain sizes. We study thinnings of such Boolean models which have the hard-core property that no grains overlap in the resulting germ‒grain model. A fundamental question is whether long-range dependence is preserved under such thinnings. To answer this question, we study four natural thinnings of a Poisson germ‒grain model where the grains are spheres with a regularly varying size distribution. We show that a thinning which favors large grains preserves the slow correlation decay of the original model, whereas a thinning which favors small grains does not. Our most interesting finding concerns the case where only disjoint grains are retained, which corresponds to the well-known Matérn type-I thinning. In the resulting germ‒grain model, typical grains have exponentially small sizes, but rather surprisingly, the long-range dependence property is still present. As a byproduct, we obtain new mechanisms for generating homogeneous and isotropic random point configurations having a power-law correlation decay.
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Kuronen, Mikko, and Lasse Leskelä. "Hard-Core Thinnings of Germ‒Grain Models with Power-Law Grain Sizes." Advances in Applied Probability 45, no. 3 (September 2013): 595–625. http://dx.doi.org/10.1239/aap/1377868531.
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Random sets with long-range dependence can be generated using a Boolean model with power-law grain sizes. We study thinnings of such Boolean models which have the hard-core property that no grains overlap in the resulting germ‒grain model. A fundamental question is whether long-range dependence is preserved under such thinnings. To answer this question, we study four natural thinnings of a Poisson germ‒grain model where the grains are spheres with a regularly varying size distribution. We show that a thinning which favors large grains preserves the slow correlation decay of the original model, whereas a thinning which favors small grains does not. Our most interesting finding concerns the case where only disjoint grains are retained, which corresponds to the well-known Matérn type-I thinning. In the resulting germ‒grain model, typical grains have exponentially small sizes, but rather surprisingly, the long-range dependence property is still present. As a byproduct, we obtain new mechanisms for generating homogeneous and isotropic random point configurations having a power-law correlation decay.
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Dhami, Navdeep Kaur, M. Sudhakara Reddy, and Abhijit Mukherjee. "Significant indicators for biomineralisation in sand of varying grain sizes." Construction and Building Materials 104 (February 2016): 198–207. http://dx.doi.org/10.1016/j.conbuildmat.2015.12.023.
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Månsson, Marianne, and Mats Rudemo. "Random patterns of nonoverlapping convex grains." Advances in Applied Probability 34, no. 04 (December 2002): 718–38. http://dx.doi.org/10.1017/s0001867800011885.
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Generalizing Matérn's (1960) two hard-core processes, marked point processes are considered as models for systems of varying-sized, nonoverlapping convex grains. A Poisson point process is generated and grains are placed at the points. The grains are supposed to have varying sizes but the same shape as a fixed convex grain, with spheres as an important special case. The pattern is thinned so that no grains overlap. We consider the thinning probability of a ‘typical point’ under various thinning procedures, the volume fraction of the resulting system of grains, the relation between the intensity of the point processes before and after thinning, and the corresponding size distributions. The study is inspired by problems in material fatigue, where cracks are supposed to be initiated by large defects.
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Månsson, Marianne, and Mats Rudemo. "Random patterns of nonoverlapping convex grains." Advances in Applied Probability 34, no. 4 (December 2002): 718–38. http://dx.doi.org/10.1239/aap/1037990950.
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Generalizing Matérn's (1960) two hard-core processes, marked point processes are considered as models for systems of varying-sized, nonoverlapping convex grains. A Poisson point process is generated and grains are placed at the points. The grains are supposed to have varying sizes but the same shape as a fixed convex grain, with spheres as an important special case. The pattern is thinned so that no grains overlap. We consider the thinning probability of a ‘typical point’ under various thinning procedures, the volume fraction of the resulting system of grains, the relation between the intensity of the point processes before and after thinning, and the corresponding size distributions. The study is inspired by problems in material fatigue, where cracks are supposed to be initiated by large defects.
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Sob, P. Baonhe, A. Alfayo Alugongo, and T. Ba Bob Tengen. "Stochastic Effect of Grain Elongation on Nanocrystalline Materials Strain and Strain Rate Produced by Accumulative Roll-Bonding and Equal Channel Angular Pressing." Advances in Materials Science and Engineering 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/5418769.
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Severe plastic deformation techniques are acknowledged to produce elongated grains during fabrication of nanostructured materials. Previous models relating grain size to mechanical properties considered only equivalent radius, thus ignoring other approaches of measuring grain sizes such as semiminor axis, semimajor axis, and major axis radii that determine true grain shape. In this paper, stochastic models of nanomaterials mechanical properties that include the ignored parameters have been proposed. The proposed models are tested with data from nanocrystalline aluminum samples. The following facts were experimentally observed and also revealed by the models. Grain elongates to a maximum value and then decreases with further grain refinement due to grain breakages. Materials yield stress increases with elongation to a maximum and then decreases continuously. The varying approaches of measuring grain radius reveal a common trend of Hall-Petch and Reverse Hall-Petch Relationship but with different critical grain sizes. Materials with high curvature grains have more enhanced yield stress. Reducing strain rates leads to materials with more enhanced yield stress, with critical strain rates values beyond which further reductions do not lead to yield stress enhancement. It can be concluded that, by considering different approaches of measuring grain sizes, reasons for different yield stress for nanomaterials that were observed but could not be explained have been dealt with.
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Lan, Liangyun, Zhiyuan Chang, and Penghui Fan. "Exploring the Difference in Bainite Transformation with Varying the Prior Austenite Grain Size in Low Carbon Steel." Metals 8, no. 12 (November 24, 2018): 988. http://dx.doi.org/10.3390/met8120988.
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The simulation welding thermal cycle technique was employed to generate different sizes of prior austenite grains. Dilatometry tests, in situ laser scanning confocal microscopy, and transmission electron microscopy were used to investigate the role of prior austenite grain size on bainite transformation in low carbon steel. The bainite start transformation (Bs) temperature was reduced by fine austenite grains (lowered by about 30 °C under the experimental conditions). Through careful microstructural observation, it can be found that, besides the Hall–Petch strengthening effect, the carbon segregation at the fine austenite grain boundaries is probably another factor that decreases the Bs temperature as a result of the increase in interfacial energy of nucleation. At the early stage of the transformation, the bainite laths nucleate near to the grain boundaries and grow in a “side-by-side” mode in fine austenite grains, whereas in coarse austenite grains, the sympathetic nucleation at the broad side of the pre-existing laths causes the distribution of bainitic ferrite packets to be interlocked.
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Mattsson, L., J. P. U. Fynbo, and B. Villarroel. "Small-scale clustering of nano-dust grains in supersonic turbulence." Monthly Notices of the Royal Astronomical Society 490, no. 4 (October 24, 2019): 5788–97. http://dx.doi.org/10.1093/mnras/stz2957.
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ABSTRACT We investigate the clustering and dynamics of nano-sized particles (nano dust) in high-resolution (10243) simulations of compressible isothermal hydrodynamic turbulence. It is well established that large grains will decouple from a turbulent gas flow, while small grains will tend to trace the motion of the gas. We demonstrate that nano-sized grains may cluster in a turbulent flow (fractal small-scale clustering), which increases the local grain density by at least a factor of a few. In combination with the fact that nano-dust grains may be abundant in general, and the increased interaction rate due to turbulent motions, aggregation involving nano dust may have a rather high probability. Small-scale clustering will also affect extinction properties. As an example we present an extinction model based on silicates, graphite, and metallic iron, assuming strong clustering of grain sizes in the nanometre range, could explain the extreme and rapidly varying ultraviolet extinction in the host of GRB 140506A.
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Kamatar, Vishwanath S., Rajesh Yakkundimath, and Girish Saunshi. "Behavior of SVM based classification for varying sizes of heap-grain images." International Journal of Computer Sciences and Engineering 6, no. 12 (December 31, 2018): 32–42. http://dx.doi.org/10.26438/ijcse/v6i12.3242.
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Cheng, Hong, Chenchen Liu, Xueyong Zou, Jifeng Li, Jiajia He, Bo Liu, Yongqiu Wu, Liqiang Kang, and Yi Fang. "Aeolian creeping mass of different grain sizes over sand beds of varying length." Journal of Geophysical Research: Earth Surface 120, no. 7 (July 2015): 1404–17. http://dx.doi.org/10.1002/2014jf003367.
Full textDissertations / Theses on the topic "Varying grain sizes"
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Saadi, Yusron. "The influence of different time varying antecedent flows on the stability of mixed grain size deposits." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/12833/.
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The objective of this work was to examine the impact of unsteady flows on the erosion and movement of mixed grain size sediment. Time varying flows were examined as flowrates in natural rivers are rarely constant. There are very few reported studies on the movement of sediment in unsteady open channel flow and most of those used single sized sediment. River reach has its own sedimentological character and non-uniform beds exhibit very different behaviour from that of single sized material. Therefore it was thought important to examine the impact of time varying flow on the stability of water worked mixed grain size sediment beds. The thesis reports on a series of laboratory experiments in which a bimodal sediment bed was exposed to different flow hydrographs. The flow hydrographs consisted of constant flowrate with different duration and time varying flows with different rising and falling limb but had the same peak flowrate. Each experiment was followed by a stability test in which a standard "triangular shaped hydrograph" was used to assess the stability of each water worked deposit. The stability observation demonstrated that grain size fractions have different thresholds of motion when beds are formed by different antecedent flow patterns. The bed stability increased as the antecedent constant flow hydrograph progressed. The rising and falling limbs of the flowrate hydrographs were found to have a significant effect on the bed stabilisation process. It revealed that the shortest rising limb of flow hydrograph formed the weakest bed while the longest recession limb of flow hydro graph formed the most stable bed. It is believed that the short period of flowrate acceleration did not allow the coarse grains to stabilise with numerous exposed large grains spread on the bed. In a longer duration of recession limb of hydrograph, the coarse grains moved and eventually deposited over a length of time. As the flowrate declined the finer grains also rolled and then deposited forming a strong bond with the coarse grams. These experiments also provided important information on the flow structures and the changes in the bed topography as the tests progressed. There is strong evidence that only upward interactions (ejections) with high momentum magnitude were able to transport coarser grains. The lack of change in the distribution of downward looking-bed interactions (sweeps) in all tests indicated that these features are not important in determining transport. Changes in bed topography were also measured and characteristics of the distribution of bed surface elevation were linked to the observed changes in bed stability.
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Sob, Peter Baonhe. "Modelling stain rate sensitive nanomaterials' mechanical properties: the effects of varying definitions." Thesis, 2016. http://hdl.handle.net/10352/332.
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M. Tech. (Mechanical Engineering, Faculty of Engineering and Technology): Vaal University of TechnologyPresently there exist a lot of controversies about the mechanical properties of nanomaterials. Several convincing reasons and justifications have been put forward for the controversies. Some of the reasons are varying processing routes, varying ways of defining equations, varying grain sizes, varying internal constituent structures, varying techniques of imposing strain on the specimen etc. It is therefore necessary for scientists, engineers and technologists to come up with a clearer way of defining and dealing with nanomaterials’ mechanical properties. The parameters of the internal constituent structures of nanomaterials are random in nature with random spatial patterns. So they can best be studied using random processes, specifically as stochastic processes. In this dissertation the tools of stochastic processes have been used as they offer a better approach to understand and analyse random processes. This research adopts the approach of ascertaining the correct mathematical models to be used for experimentation and modelling. After a thorough literature survey it was observed that size and temperature are two important parameters that must be considered in selecting the relevant mathematical definitions for nanomaterials’ mechanical properties. Temperature has a vital role to play during grain refinement since all severe plastic deformation involves thermomechanical processes. The second task performed in this research is to develop the mathematical formulations based on the experimental observation of 2-D grains and 3-D grains deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing. The experimental observations revealed that grains deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing are elongated when observed from the rolling direction, and transverse direction, and equiaxed when observed from the normal direction. In this dissertation, the different experimental observations for the grain size variants during grain refinement were established for 2-D and 3-D grains. This led to the development of a stochastic model of grain-elongation for 2-D and 3-D grains. The third task was experimentations and validation of proposed models. Accumulative Roll-Bonding, Equal Channel Angular Pressing and mechanical testing (tensile test) experiments were performed. The effect of size on elongation and material properties were studied to validate the developed models since size has a major effect on material’s properties. The fourth task was obtaining results and discussion of theoretical developed models and experimental results. The following facts were experimentally observed and also revealed by the models. Different approaches of measuring grain size reveal different strains that cannot be directly obtained from plots of the corresponding grain sizes. Grain elongation evolved as small values for larger grains, but became larger for smaller grains. Material properties increased with elongation reaching a maximum and started decreasing as is evident in the Hall-Petch to the Reverse Hall-Petch Relationship. This was alluded to the fact that extreme plastic straining led to distorted structures where grain boundaries and curvatures were in “non-equilibrium” states. Overall, this dissertation contributed new knowledge to the body of knowledge of nanomaterials’ mechanical properties in a number of ways. The major contributions to the body of knowledge by his study can be summarized as follows: (1) The study has contributed in developing a model of elongation for 2-D grain and 3-D grains. It has been generally reported by researchers that materials deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing are generally elongated but none of these researchers have developed a model of elongation. Elongation revealed more information about “size” during grain refinement. (2) The Transmission Electron Microscopy revealed the grain shape in three directions. The rolling direction or sliding direction, the normal direction and the transverse direction. Most developed models ignored the different approaches of measuring nanomaterials’ mechanical properties. Most existing models dealt only with the equivalent radius measurement during grain refinement. In this dissertation, the different approaches of measuring nanomaterials’ mechanical properties have been considered in the developed models. From this dissertation an accurate correlation can be made from microscopy results and theoretical results. (3) This research has shown that most of the published results on nanomaterials’ mechanical properties may be correct although controversies exist when comparing the different results. This research has also shown that researchers might have considered different approaches to measure nanomaterials’ mechanical properties. The reason for different results is due to different approaches of measuring nanomaterials’ mechanical properties as revealed in this research. Since different approaches of measuring nanomaterials’ mechanical properties led to different obtained results, this justify that most published results of nanomaterials’ mechanical properties may be correct. This dissertation revealed more properties of nanomaterials that are ignored by the models that considered only the equivalent length. (4) This research has contributed to the understanding of nanomaterials controversies when comparing results from different researchers.
Book chapters on the topic "Varying grain sizes"
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Zhang, Wei, Yanfei Gao, and Tai-Gang Nieh. "Competing Grain Boundary and Interior Deformation Mechanisms with Varying Sizes." In Handbook of Mechanics of Materials, 1239–54. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-10-6884-3_75.
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Zhang, Wei, Yanfei Gao, and Tai-Gang Nieh. "Competing Grain Boundary and Interior Deformation Mechanisms with Varying Sizes." In Handbook of Mechanics of Materials, 1–16. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-10-6855-3_75-1.
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Krishnan, Kannan M. "X-Ray Diffraction." In Principles of Materials Characterization and Metrology, 408–80. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198830252.003.0007.
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X-rays diffraction is fundamental to understanding the structure and crystallography of biological, geological, or technological materials. X-rays scatter predominantly by the electrons in solids, and have an elastic (coherent, Thompson) and an inelastic (incoherent, Compton) component. The atomic scattering factor is largest (= Z) for forward scattering, and decreases with increasing scattering angle and decreasing wavelength. The amplitude of the diffracted wave is the structure factor, F hkl, and its square gives the intensity. In practice, intensities are modified by temperature (Debye-Waller), absorption, Lorentz-polarization, and the multiplicity of the lattice planes involved in diffraction. Diffraction patterns reflect the symmetry (point group) of the crystal; however, they are centrosymmetric (Friedel law) even if the crystal is not. Systematic absences of reflections in diffraction result from glide planes and screw axes. In polycrystalline materials, the diffracted beam is affected by the lattice strain or grain size (Scherrer equation). Diffraction conditions (Bragg Law) for a given lattice spacing can be satisfied by varying θ or λ — for study of single crystals θ is fixed and λ is varied (Laue), or λ is fixed and θ varied to study powders (Debye-Scherrer), polycrystalline materials (diffractometry), and thin films (reflectivity). X-ray diffraction is widely applied.
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Griffeath, David, and Dean Hickerson. "A Two-Dimensional Cellular Automaton Crystal with Irrational Density." In New Constructions in Cellular Automata. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195137170.003.0007.
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We solve a problem posed recently by Gravner and Griffeath [4]: to find a finite seed A0 of 1s for a simple {0, l}-valued cellular automaton growth model on Z2 such that the occupied crystal An after n updates spreads with a two-dimensional asymptotic shape and a provably irrational density. Our solution exhibits an initial A0 of 2,392 cells for Conway’s Game Of Life from which An cover nT with asymptotic density (3 - √5/90, where T is the triangle with vertices (0,0), (-1/4,-1/4), and (1/6,0). In “Cellular Automaton Growth on Z2: Theorems, Examples, and Problems” [4], Gravner and Griffeath recently presented a mathematical framework for the study of Cellular Automata (CA) crystal growth and asymptotic shape, focusing on two-dimensional dynamics. For simplicity, at any discrete time n, each lattice site is assumed to be either empty (0) or occupied (1). Occupied sites after n updates grows linearly in each dimension, attaining an asymptotic density p within a limit shape L: . . . n-1 A → p • 1L • (1) . . . This phenomenology is developed rigorously in Gravner and Griffeath [4] for Threshold Growth, a class of monotone solidification automata (in which case p = 1), and for various nonmonotone CA which evolve recursively. The coarse-grain crystal geometry of models which do not fill the lattice completely is captured by their asymptotic density, as precisely formulated in Gravner and Griffeath [4]. It may happen that a varying “hydrodynamic” profile p(x) emerges over the normalized support L of the crystal. The most common scenario, however, would appear to be eq. (1), with some constant density p throughout L. All the asymptotic densities identified by Gravner and Griffeath are rational, corresponding to growth which is either exactly periodic in space and time, or nearly so. For instance, it is shown that Exactly 1 Solidification, in which an empty cell permanently joins the crystal if exactly one of its eight nearest (Moore) neighbors is occupied, fills the plane with density 4/9 starting from a singleton.
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Zimmerman, S. R. H., S. R. Hemming, and S. W. Starratt. "Holocene sedimentary architecture and paleoclimate variability at Mono Lake, California." In From Saline to Freshwater: The Diversity of Western Lakes in Space and Time. Geological Society of America, 2019. http://dx.doi.org/10.1130/2020.2536(19).
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ABSTRACT Mono Lake occupies an internally drained basin on the eastern flank of the Sierra Nevada, and it is sensitive to climatic changes affecting precipitation in the mountains (largely delivered in the form of snowpack). Efforts to recover cores from the lake have been impeded by coarse tephra erupted from the Mono Craters, and by disruption of the lake floor due to the uplift of Paoha Island ~300 yr ago. In this study, we describe the stratigraphy of cores from three recent campaigns, in 2007, 2009, and 2010, and the extents and depths of the tephras and disturbed sediments. In the most successful of these cores, BINGO-MONO10-4A-1N (BINGO/10-4A, 2.8 m water depth), we used core stratigraphy, geochemistry, radiocarbon dates, and tephrostratigraphy to show that the core records nearly all of the Holocene in varying proportions of detrital, volcanic, and authigenic sediment. Both the South Mono tephra of ca. 1350 cal yr B.P. (calibrated years before A.D. 1950) and the 600-yr-old North Mono–Inyo tephra are present in the BINGO/10-4A core, as are several older, as-yet-unidentified tephras. Laminated muds are inferred to indicate a relatively deep lake (³10 m over the core site) during the Early Holocene, similar to many records across the region during that period. The Middle and Late Holocene units are more coarsely bedded, and coarser grain size and greater and more variable amounts of authigenic carbonate detritus in this interval are taken to suggest lower lake levels, possibly due to lower effective wetness. A very low lake level, likely related to extreme drought, is inferred to have occurred sometime between 3500 and 2100 cal yr B.P. This interval likely corresponds to the previously documented Marina Low Stand and the regional Late Holocene Dry Period. The BINGO/10-4A core does not preserve a complete record of the period encompassing the Medieval Climate Anomaly, the Little Ice Age, and the historical period, probably due to erosion because of its nearshore position.
Conference papers on the topic "Varying grain sizes"
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Bouchey, Stephanie N. Q., and Jeromy T. Hollenshead. "Mesoscale modeling and debris generation in hypervelocity impacts." In 2019 15th Hypervelocity Impact Symposium. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/hvis2019-017.
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Abstract Material fragmentation after a hypervelocity impact is of interest to predictive electro-optical and infrared (EO/IR) modeling. Successful comparisons with data require that submicron fragments are generated in such impacts; however, experimental data has so far been unable to produce fragments of this scale [e.g., 1-3]. This effort investigated the generation of predicted debris from hypervelocity impact of a sphere on a flat, semi-infinite plate. It is hypothesized that explicit modeling of grains, especially in the presence of void and varying grain properties, may lead to differences in predicted strain rates (locally higher) associated with the grain boundaries. Such an effect may lead to smaller predicted fragments sizes than when using the traditional bulk modeling approach and may provide improved understanding of fragmentation modeling in hypervelocity impacts. Comparisons of predicted strain rates at failure (a proxy for fragment size) and material temperature were made between simulations run using a bulk modeling approach and a mesoscale grain modeling approach.
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Pan, Liming, Ben Dawson, Jacqueline Krim, Colin Baker, James Pearson, Mohammed Zikry, and Andrey Vovoedin. "Nanoscale Design of Adaptive Tribological Coatings." In STLE/ASME 2008 International Joint Tribology Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/ijtc2008-71196.
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We report a joint theoretical and experimental study of the tribological properties of gold-yttrium stabilized zirconia (YSZ) based nanocomposite coatings, with a focus on the role of nanocrystalline grain size. Nanocomposites hold great promise for space and ambient applications, on account of their ability to adapt to and exhibit low friction and wear rates in constantly varying environmental conditions. Their internal structure has been the topic of prior literature, but the impact of grain size on tribological performance has heretofore not been considered, and the surface topology has not been reported. As such, we have performed both experimental and theoretical studies, to model the impact of grain size on film stress and wear attributes, and to document surface region grain size distributions through scanning tunneling microscopy (STM) measurements of self-affine fractal scaling properties. Nanocrystalline gold crystal sizes, as determined from STM and x-ray diffraction (XRD) data are consistent with those inferred from high resolution transmission electron microscopy (HRTEM) measurements. Our modeling results associate smaller grain sizes with lower wear rates, consistent with experiments. The findings show promise for nanoscale customization of coatings so as to tailor them at the nanoscale in an application specific manner.
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Fono-Tamo, R. S., and Jen Tien-Chien. "Effect of Ingredient Particle Sizes on Surface Roughness Characteristics of PKS Brake Lining." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-70659.
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Besides pad failure due to thermal damage, brake pads can also experience mechanical damage when they are exposed to a corrosive environment. A typical solid surface like a brake pad has a complex structure and complex properties depending on the nature of the solids, the method of surface preparation, and the interaction between the surface and the environment. The surface roughness of a novel friction linings prepared using varying palm kernel shell (PKS) powder particle sizes (0.300 mm, 0.425 mm and 0.850 mm) as reinforcements were investigated. The investigation was conducted via a profilometer dotted with a diamond stylus at a speed of 0.2 m/s. The determined surface roughness parameters values were in ascending order with S0.300 having the least values (Ra = 6.13 μm, Rz = 24.04 μm and Rmax = 37.3 μm) and S0.850 having the highest values (Ra = 9.87 μm, Rz = 37.28 μm and Rmax = 53.8 μm). This was an indication that the roughness characteristics of the reinforced composite were associated to the presence of pulverised PKS particles. It was further shown by scanning electron microscope images that pulverised PKS grain sizes by nature have rough surfaces and this could have contributed to the overall roughness behaviour of the reinforced composite since PKS was the only ingredient with grain size variation in the experiment.
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Goods, Steve, Samuel Graham, and James Kelly. "The Effects of Grain-Refinement and Heat Treatment on the Properties of Ni-Alloys for LIGA Microsystems." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-42090.
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Electrodeposited Ni and Ni-alloys are being considered for use in a number of microelectromechanical systems (MEMS) applications employing LIGA processing technology. For these materials, research has shown that various organic and metallic alloying additives, often in combination with pulse plating techniques allows the development of microstructures with nanocrystalline to microcrystalline grain sizes [1–10]. This range of grain sizes yields widely varying material properties that may, at times, be exploited to tailor the performance of LIGA microsystems. In order to make use of this potential, a better understanding of the effect of processing on material properties such as elastic modules, yield strength, and electrical conductivity is required. In addition to analyzing the effects that material processing may have on initial properties of the nanostructured materials, it is also imperative to understand how exposures to thermal environments which may be seen in post-processing or service life may induce changes in these properties.
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Bhatt, Chinmay P., and Stephen T. McClain. "Assessment of Uncertainty in Equivalent Sand-Grain Roughness Methods." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-42105.
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The equivalent sand-grain roughness model is an empirical model initiated by Schlichting for predicting skin friction and heat transfer for turbulent flows over rough surfaces. For the equivalent sand-grain roughness model, rough surfaces with various features are compared to data from Nikuradse concerning flow in pipes with varying sizes of sieved sand glued to the wetted surface. Rough surfaces are assigned a value of equivalent sand-grain roughness height based on comparisons with Nikuradse’s fully rough data. Recent literature on the equivalent sand-grain roughness method has involved seeking correlations for equivalent sand-grain roughness height based on roughness metrics such as height, shape, and density. The Sigal-Danberg parameter has demonstrated the most promise for correlating the available equivalent roughness height data to geometric surface information. The Sigal-Danberg parameter was recently modified to include the mean surface elevation as an important parameter. While the modified Sigal-Danberg parameter provides a unified correlation for the equivalent sand-grain roughness height, the new formulation does not improve the scatter of the experimental data around the correlation. An uncertainty analysis is presented to evaluate the uncertainty of equivalent sand-grain roughness height predictions using the unified correlation. The analysis begins by estimating the uncertainties in the experimental measurements of Schlichting, and the uncertainty propagation is evaluated through each step of the equivalent sand-grain method development. The uncertainty associated with using empirical equations and conceptual uncertainties not associated with experimental measurements are also discussed. The result is an improved understanding of and uncertainty quantification for skin friction and heat transfer predictions made using equivalent sand-grain roughness methods.
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Heberlein, J., N. P. Rao, A. Neuman, J. Blum, N. Tymiak, P. H. McMurry, and S. L. Girshick. "Thermal Spraying of Nanostructured Coatings by Hypersonic Plasma Particle Deposition." In ITSC 1997, edited by C. C. Berndt. ASM International, 1997. http://dx.doi.org/10.31399/asm.cp.itsc1997p0329.
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Abstract A novel plasma spray process for producing nanostructured coatings, hypersonic plasma particle deposition (HPPD), has been experimentally investigated. In HPPD, vapor phase precursors are injected into a plasma stream generated by a DC arc. The plasma is quenched by supersonic expansion through a nozzle into a vacuum (~ 2 torr) deposition chamber. Ultrafine particles nucleated in the nozzle are accelerated in the hypersonic free jet downstream of the nozzle and inertially deposited onto a substrate. The short transit times between the nozzle and the substrate (< 50 μs) prevent inflight agglomeration, while the high particle deposition velocities result in the formation of a consolidated coating. We have investigated the production of silicon and silicon carbide coatings using SiCl4 and CH4 precursors. Silicon deposits analyzed by transmission electron microscopy were found to have nanostructured regions with grain sizes varying from 5-20 nm. Corresponding particle size distributions measured before deposition using an extractive aerosol probe peaked around 15 nm, suggesting negligible grain growth occurred in the samples studied. Silicon carbide particle size distributions measured at various deposition chamber pressures verify that the low residence time characteristic of the HPPD process minimizes in-flight agglomeration.
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Martin, Steven A., Kumar V. Jata, Richard W. Martin, Shamachary Sathish, Donald O. Thompson, and Dale E. Chimenti. "MODELING OF ACOUSTIC WAVE PROPAGATION THROUGH VARYING GRAIN SIZE STRUCTURE." In REVIEW OF PROGRESS IN QUANTITATIVE NONDESTRUCTIVE EVALUATION: 34th Annual Review of Progress in Quantitative Nondestructive Evaluation. AIP, 2008. http://dx.doi.org/10.1063/1.2902560.
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Hazra, Sougata, Yashvi Singh, Mehdi Asheghi, and Kenneth Goodson. "Characterization and Prevention of Metal Overflow in Ultra-Thin Au-Sn Eutectic Chip Bonding for Packaging and Integration of Extreme Heat Flux Micro-Coolers." In ASME 2020 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ipack2020-2533.
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Abstract In this study, a detailed characterization of Au-Sn eutectic ultra-thin metal stack (∼ 1 μm) bonding has been performed between Pyrex and silicon substrates using a commercial flip-chip bonder. A thorough recipe characterization and development was performed on three different bond sizes of 9, 49 and 100 mm2 by varying bonding temperature between 320 and 380°C with pressure ranging between 2 to 10 MPa. Results indicate that better bond quality was observed at higher temperatures but was relatively unaffected by the bond pressure magnitude. It was also found that flatness of contact is one of the most important parameters that determine the bond uniformity and thus the quality, which is especially important for ultra-thin metal bonding. In addition, this study puts special emphasis on observing the bond uniformity and metal overflow through the transparent Pyrex top substrate. The mean overflow width increased with increasing temperature, reaching as high as 300 μm at 380°C, but was not significantly affected by the bond pressure applied. Simultaneously, the ultra-thin bond layer made it possible for us to observe several different types of microstructures forming within the bond zone, which provided crucial information about sample cool down rate, grain size and intermetallic composition in the eutectic alloy. For a specific case, Kirkendall voids were observed under the optical microscope at the interface between Pyrex and bonded metal because of dissimilar rates of migration of Au and Sn during the eutectic reaction. We believe that this is the first successful observation of voids in bond alloy using non-destructive optical imaging techniques. Following successful characterization of metal reflow from the bond site, a simple method to control this overflow has been demonstrated by precisely controlled misalignment of the two complementary chips. This fundamental study on eutectic bonding aims to further the understanding of eutectic bonding process as well as facilitate development of effective ultra-thin layer, high strength bonding recipes between chips for versatile applications in the electronic packaging industry.
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Mondal, Debabrata, Abdullah Fahim, KM Rafidh Hassan, Jeffrey C. Suhling, and Pradeep Lall. "Deformation Behavior of SAC305 Solder Joints With Multiple Grains." In ASME 2020 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ipack2020-2694.
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Abstract Lead-free solder joints are the most widely used interconnects in electronic packaging industries. Usually solder joints in most of the electronic devices are exposed to an environment where variation of temperature exists, which indicates cyclic thermal loading to be a very common type of external loading. Moreover, due to difference in the coefficient of thermal expansion (CTE) among dissimilar contact materials, shear stress develops in junctions under thermal loading, which significantly deteriorates the overall reliability. Hence, characterization of lead-free solder materials under thermal loading is essential to predict the performance and deformation behavior of joints in practical applications. A significant portion of the studies in this field are concerned with thermal loading of lead-free solder interconnects, each of which has a very small diameter, in sub-millimeter range. Although the solder balls have very small dimensions, most of the analyses considered them as a bulk material with homogeneous and isotropic properties. However, with the decrease of specimen dimensions, size effects and material directionality play a significant role in deformation mechanisms. Since a very few grains exist in a small specimen, individual grain properties play a vital role on overall material response. Therefore, modeling from the grain structure and orientation point of view could be an effective and more accurate way to predict solder joint deformation behavior under thermal loading. In this study, the effect of grain size and orientation of SAC305 is investigated for predicting anisotropic behavior of solder joints under thermal load. A simplified three-dimensional model of beach-ball configuration solder joint was generated and simulated using ABAQUS finite element (FE) software. Experimentally obtained directional properties such as elastic modulus and CTE were assigned to the computational geometry to create material anisotropy. The effects of material anisotropy were studied for varying grain size specimens, as well as for specimens with varying grain orientation.
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Krawczynska, Agnieszka. "STEM observations of irradiation induced defects in molybdenum mirrors varying in grain size." In European Microscopy Congress 2020. Royal Microscopical Society, 2021. http://dx.doi.org/10.22443/rms.emc2020.1061.
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