Academia.edu no longer supports Internet Explorer.
To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to upgrade your browser.
2011, Acta Materialia
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.
2010, Journal of The Mechanics and Physics of Solids
2008, Acta Materialia
2015, Acta Materialia
2021
Because of its high content of polyphenolic compounds, dietary inclusion of grape pomace (GP) in ruminant diets can reduce reactive nitrogen (N) and methane emissions and enhance the shelf life and beneficial fatty acids content of meat. However, dietary inclusion of GP beyond a threshold that is still to be determined for feedlot cattle, can also compromise nutrient supply and, thus, growth performance. This study investigated the optimum proportion of GP in finishing cattle diets. Nutrient intake and apparent total tract digestion, ruminal pH and fermentation, estimated microbial protein synthesis, route of N excretion, and blood metabolites were measured. Six ruminally-fistulated crossbred beef heifers (mean initial BW ± SD, 714 ± 50.7 kg) were used in a replicated 3 × 3 Latin square with 21-d periods. Dietary treatments were 0, 15, and 30% of dietary dry matter (DM) as GP, with diets containing 84, 69, and 54% dry-rolled barley grain, respectively. There was a linear increase (P...
IJAER
This research work is an atomic theory of fracture and quantization of Kic Fracture toughness. Especially in ceramics. It shows the atomic level aspects of fracture process from the stress intensity factor or fracture toughness, KIc. The crystalline structure, the atomic positions and lattice points, and how nanomaterials show atomic level fracture process as well as nanoceramics exhibit Quantization of fracture toughness and other nanomaterials show higher stress intensity factor, KIc than microsize equivalents of those nanomaterials. This is a deep treatment of the fracture process with a survey of present status of fracture, the application of the fundamentals of fracture toughness for the atomic theory of fracture, the data evidence for confirmation of the theory and some extension for its applications in biomaterials, electronic materials and cutting tools for manufacturing. This is a rigorous and clear treatment of the atomic theory of fracture.
2009, Progress in Materials Science
2001, Jom
In this paper, the state-of-the-art progress in research on novel mechanical properties of nanocrystalline materials and carbon nanotubes is reviewed. There is evidence that the relation between the strength of nanocrystalline materials and grain size does not observe the classic Hall-Petch plot. Lowtemperature and high-strain rate superplasticity have been found in some nanocrystalline materials. Theoretical prediction and experimental data indicate
2018, Physical review letters
The recent observation of the reverse Hall-Petch relation in nanocrystalline ceramics offers a possible pathway to achieve enhanced ductility for traditional brittle ceramics via the nanosize effect, just as nanocrystalline metals and alloys. However, the underlying deformation mechanisms of nanocrystalline ceramics have not been well established. Here we combine reactive molecular dynamics (RMD) simulations and experimental transmission electron microscopy to determine the atomic level deformation mechanisms of nanocrystalline boron carbide (B_{4}C). We performed large-scale (up to ∼3 700 000 atoms) ReaxFF RMD simulations on finite shear deformation of three models of grain boundaries with grain sizes from 4.84 (135 050 atoms) to 14.64 nm (3 702 861 atoms). We found a reverse Hall-Petch relationship in nanocrystalline B_{4}C in which the deformation mechanism is dominated by the grain boundary (GB) sliding. This GB sliding leads to the amorphous band formation at predistorted icos...
2005, Physical Review B
2009, Progress in Materials Science
2011, Computational Materials Science
2013, Acta Materialia
2007, Acta Materialia
2018, Journal of the European Ceramic Society
Improving the mechanical performance of nanocrystalline functional oxides can have major implications for stability and resilience of battery cathodes, development of reliable nuclear oxide fuels, strong and durable catalytic supports. By combining Monte Carlo simulations, experimental thermodynamics, and in-situ transmission electron microscopy, we demonstrate a novel toughening mechanism based on interplay between the thermo-chemistry of the grain boundaries and crack propagation. By using zirconia as a model material, lan-thanum segregation to the grain boundaries was used to increase the toughness of individual boundaries and simultaneously promote a smoother energy landscape in which cracks experience multiple deflections through the grain boundary network, ultimately improving fracture toughness.
2014, Journal of the Mechanics and Physics of Solids
2010
2010, Physical Review Letters
2018, Ultramicroscopy
Twin boundary can both strengthen and soften nanocrystalline metals and has been an important path for improving the strength and ductility of nano materials. Here, using in-lab developed double-tilt tensile stage in the transmission electron microscope, the atomic scale twin boundary shearing process was in situ observed in a twin-structured nanocrystalline Pt. It was revealed that the twin boundary shear was resulted from partial dislocation emissions on the intersected {111} planes, which accommodate as large as 47% shear strain. It is uncovered that the partial dislocations nucleated and glided on the two intersecting {111} slip planes lead to a transition of the original <110> symmetric tilt ∑3/(111) coherent twin boundary into a <110> symmetric tilt ∑9/(114) high angle grain boundary. These results provide insight of twin boundary strengthening mechanisms for accommodating plasticity strains in nanocrystalline metals.
2015, Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
The knowledge of the fracture of bulk metallic materials developed in the last 50 years is mostly based on materials having grain sizes, d, in the range of some micrometres up to several hundred micrometres regarding the possibilities of classical metallurgical methods. Nowadays, novel techniques provide access to much smaller grain sizes, where severe plastic deformation (SPD) is one of the most significant techniques. This opens the door to extend basic research in fracture mechanics to the nanocrystalline (NC) grain size regime. From the technological point of view, there is also the necessity to evaluate standard fracture mechanics data of these new materials, such as the fracture toughness, in order to allow their implementation in engineering applications. Here, an overview of recent results on the fracture behaviour of several different ultrafine-grained (d<1 μm) and NC (d<100 nm) metals and alloys covering examples of body- and face-centred cubic structures produced by...
2012, Nature Communications
2011, Acta Materialia
2021, Materials Research Letters
Heterostructured materials are an emerging class of materials with superior performances that are unattainable by their conventional homogeneous counterparts. They consist of heterogeneous zones with dramatic (>100%) variations in mechanical and/or physical properties. The interaction in these hetero-zones produces a synergistic effect where the integrated property exceeds the prediction by the rule-of-mixtures. The heterostructured materials field explores heterostructures to control defect distributions, long-range internal stresses, and nonlinear inter-zone interactions for unprecedented performances. This paper is aimed to provide perspectives on this novel field, describe the state-of-the-art of heterostructured materials, and identify and discuss key issues that deserve additional studies.
The review is devoted to a study of interface phenomena influencing advanced properties of nanoscale materials processed by means of severe plastic deformation, high-energy ball milling and their combinations. Interface phenomena include processes of interface defect structure relaxation from a highly nonequilibrium state to an equilibrium condition, grain boundary phase transformations and enhanced grain boundary and triple junction diffusivity. On the basis of an experimental investigation, a theoretical description of the key interfacial phenomena controlling the functional properties of advanced bulk nanoscale materials has been conducted. An interface defect structure investigation has been performed by transmission electron microscopy (TEM), high-resolution X-ray diffraction, atomic simulation and modeling. The problem of a transition from highly non-equilibrium state to an equilibrium one, which seems to be responsible for low thermostability of nanoscale materials, was studied. Also enhanced grain boundary diffusivity is addressed. Structure recovery and dislocation emission from grain boundaries in nanocrystalline materials have been investigated by analytical methods and modeling.
The review is devoted to a study of interface phenomena influencing advanced properties of nanoscale materiais processed by means of severe plastic deformation, high-energy ball milling and their combinations. Interface phenomena include processes of interface defect structure relaxation from a highly nonequilibrium state to an equilibrium condition, grain boundary phase transformations and enhanced grain boundary and triple junction diffusivity. On the basis of an experimental investigation, a theoretical description of the key interfacial phenomena controlling the functional properties of advanced bulk nanoscale materials has been conducted. An interface defect structure investigation has been performed by transmission electron microscopy (TEM), high-resolution X-ray diffraction, atomic simulation and modeling. The problem of a transition from highly non-equilibrium state to an equilibrium one, which seems to be responsible for low thermostability of nanoscale materials, was studi...
2004, Journal of Physics D: Applied Physics
Pristine monocrystalline graphene is claimed to be the strongest material known with remarkable mechanical and electrical properties. However, graphene made with scalable fabrication techniques is polycrystalline and contains inherent nanoscale line and point defects—grain boundaries and grain-boundary triple junctions—that lead to significant statistical fluctuations in toughness and strength. These fluctuations become particularly pronounced for nanocrystalline graphene where the density of defects is high. Here we use large-scale simulation and continuum modelling to show that the statistical variation in toughness and strength can be understood with 'weakest-link' statistics. We develop the first statistical theory of toughness in polycrystalline graphene, and elucidate the nanoscale origins of the grain-size dependence of its strength and toughness. Our results should lead to more reliable graphene device design, and provide a framework to interpret experimental results in a broad class of two-dimensional materials.
2003, Acta Materialia
2019, Progress in Materials Science
High-entropy alloys (HEAs), also known as multi-principal element alloys or multi-component alloys, have been the subject of numerous investigations since they were first described in 2004. One of the earliest HEAs was the equiatomic CrMnFeCoNi “Cantor” alloy, which has been one of the most studied, but HEAs now encompass a broad class of metallic and ceramic systems based on the same design principle. The original concept, of utilizing the high entropy of mixing to develop stable multi-element alloys, has produced extraordinary mechanical properties in specific HEAs, mainly CrCoNi-based alloys, associated with their continuous work-hardening rate that is sustained to large plastic strains. The enhanced work-hardening ability in these face-centered cubic HEAs, which is maintained up to tensile strains of ~0.5 and at low temperatures, in combination with the high frictional forces on dislocations and a propensity for twinning, leads to outstandingly high fracture toughness values and resistance to localization of deformation and shear-band formation under dynamic loading. The fracture toughness of some of the CoCrNi-based alloys is on the order of, and can even exceed, 200 MPa.m1/2, with yield strengths that range from 200 MPa to close to 1000 MPa, depending on a number of intrinsic parameters including grain size. The critical shear strain for the onset of adiabatic shear band formation is ~7 for the Cantor alloy. This is much higher than that for conventional alloys and suggests superior ballistic properties. The slower diffusion rates resulting from the multi-element environment contribute to the excellent intermediate-temperature performance. We review the principal mechanical properties of these alloys with emphasis on the CrCoNi-based systems and their nano-/micro-structural features. We also discuss high-entropy ceramics and more complex systems having more than one phase. Due to the very favorable mechanical properties of some of these HEAs, and to the fact that most can be processed by conventional means, we anticipate that they will find extensive utilization in many future structural applications.
2009, Journal of Materials Research
Decreasing scales effectively increase nearly all important mechanical properties of at least some “brittle” materials below 100 nm. With an emphasis on silicon nanopillars, nanowires, and nanospheres, it is shown that strength, ductility, and toughness all increase roughly with the inverse radius of the appropriate dimension. This is shown experimentally as well as on a mechanistic basis using a proposed dislocation shielding model. Theoretically, this collects a reasonable array of semiconductors and ceramics onto the same field using fundamental physical parameters. This gives proportionality between fracture toughness and the other mechanical properties. Additionally, this leads to a fundamental concept of work per unit fracture area, which predicts the critical event for brittle fracture. In semibrittle materials such as silicon, this can occur at room temperature when the scale is sufficiently small. When the local stress associated with dislocation nucleation increases to tha...
Materials Science and Engineering A
2013, Materials Science and Engineering: A
2004, Composites Part B: Engineering
2013, Journal of the Mechanics and Physics of Solids
2009, Journal of Applied Physics
Severe plastic deformation is nowadays used to produce sizable amounts of bulk nanocrystalline materials, which render them suitable for innovative applications ranging from biomedical implants to off-shore or aerospace structures, owing to favorable combinations of high mechanical strength and enhanced ductility they offer. Enhanced atom diffusion along internal interfaces is largely responsible for the resulting property combinations. Severe plastic deformation processing of metals is demonstrated to create bulk nanostructured materials with a hierarchy of internal interfaces. On top of that, specific diffusion channels providing pathways for ultrafast transport of atoms have been identified. The defects that represent the constituents of the fast diffusion network were visualized by means of the focused ion beam technique. Nonequilibrium grain boundaries, nonequilibrium triple junctions, and microvoids/microcracks compose the percolating network of ultrafast diffusion channels, which represent an important and newly recognized feature of severely deformed materials.
2009, International Journal of Plasticity
The mechanical response of engineering materials evaluated through continuum fracture mechanics typically assumes that a crack or void initially exists, but it does not provide information about the nucleation of such flaws in an otherwise flawless microstructure. How such flaws originate, particularly at grain (or phase) boundaries is less clear. Experimentally, “good” vs. “bad” grain boundaries are often invoked as the reasons for critical damage nucleation, but without any quantification. The state of knowledge about deformation at or near grain boundaries, including slip transfer and heterogeneous deformation, is reviewed to show that little work has been done to examine how slip interactions can lead to damage nucleation. A fracture initiation parameter developed recently for a low ductility model material with limited slip systems provides a new definition of grain boundary character based upon operating slip and twin systems (rather than an interfacial energy based definition). This provides a way to predict damage nucleation density on a physical and local (rather than a statistical) basis. The parameter assesses the way that highly activated twin systems are aligned with principal stresses and slip system Burgers vectors. A crystal plasticity-finite element method (CP-FEM) based model of an extensively characterized microstructural region has been used to determine if the stress–strain history provides any additional insights about the relationship between shear and damage nucleation. This analysis shows that a combination of a CP-FEM model augmented with the fracture initiation parameter shows promise for becoming a predictive tool for identifying damage-prone boundaries.