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Specific Properties of Nanoparticles
Published in Ko Higashitani, Hisao Makino, Shuji Matsusaka, Powder Technology Handbook, 2019
Wolfgang Peukert, Johannes Walter
So far, the mechanical properties of nanostructured materials, which exhibit at least one relevant length scale below 100 nm (in most cases “nanostructured” refers to the grain size), have mainly been studied.42, 43 Reported synthesis routes for nanostructured materials include the top-down routes mechanical alloying, nanomilling and severe plastic deformation or bottom-up routes like inert gas condensation, plasma synthesis and spark erosion. For nanostructured materials, a significant portion of all atoms is in grain boundaries, which gives rise to special mechanical properties: For metals a decrease of the Young’s modulus has been reported. An increase of the yield strength approximately scales with the grain size d according to the well-known Hall-Petch relation (~d−n, 0.3 ≤ n ≤ 0.7), also improved toughness and reduced elastic modulus and ductility have been reported for such materials.44 Often defects mask intrinsic material properties: in most cases there is still a widespread disagreement and contradicting data is often reported. One striking example is the so-called inverse Hall-Petch effect. Both the existence and possible physical mechanisms of a deviation from the well-known Hall-Petch mechanism below a critical grain size (in the order of 10 nm) is still a matter of debate.45 In the field of nanoscale ceramics, the systems ZrO2, TiO2, BaTiO3 and SiC have been extensively studied. Especially superplasticity of ceramics has seen scientific attention. At elevated temperatures (T/Tm > 0.5) and small strain rates (as compared to deformation of metals) nanoscaled ceramics can be deformed to large extents without breakage. Grain boundary “sliding” (i.e. translation and rotation of individual grains) is generally accepted as the deformation mechanism. However, the physical mechanisms of grain motion are still unknown.
Material Characterization and Microstructural Assessment: Fatigue Curve S-N Development Using Fracture Mechanics
Published in Frank Abdi, Mohit Garg, Characterization of Nanocomposites, 2017
In principle, all properties of all materials and phenomena are describable by quantum mechanics.The fundamental deformation mechanisms in solids are dilatational and distortion, which are governed by the microstructure of the material and environmental factors, including load and geometry.It is not all about material properties. It is more about material behavior.Application of both applied mechanics and materials science is needed in advanced design to properly understand and assess the critical failure mechanisms as part of the design process.As we progress from global to micro-mechanism behavior, we will identify and implement the related unique parameters for an optimum design.Ultralight and durable materials with high strength and stiffness are desirable for aerospace and aircraft parts. This can be accomplished through the multiscale modeling and simulation technique.Through multiscale modeling and simulation technique, it is possible to predict material allowables (including DaDT) without conducting significant tests. With this technique, Boeing can significantly reduce the cost and time of testing.The fatigue S-N virtual testing proposed is very significant and extremely useful for life assessment of aircraft and space structures. With the implementation of the proposed analytical method, considerable cost can be saved by eliminating the laboratory testing at the expense of analysis.The implementation of the techniques proposed including advanced composites can save significant cost and schedule improvements on programs.
Mechanistic model for stresses in the oxide layer formed on zirconium alloys
Published in Journal of Thermal Stresses, 2019
Isha Gupta, J. R. Barber, M. D. Thouless, Wei Lu
Platt et al. [6] assumed the Coble-creep law proposed by Choksi et al. [17] for stabilized-tetragonal zirconia, and showed that this mechanism had negligible impact on the oxide stresses. However, the possibility of other creep mechanisms was not considered. In particular, it should be noted that the high compressive stresses that occur in an oxide film suppress brittle fracture. This permits deformation mechanisms associated with dislocation motion to occur, such as dislocation glide and power-law creep. Indeed, experimental studies [18] have indicated that such plastic deformation occurs both in the oxide films formed on zirconium alloys and in pure monoclinic zirconia.
Experimental study of thermomechanical behaviour of Gum Metal during cyclic tensile loadings: the quantitative contribution of IRT and DIC
Published in Quantitative InfraRed Thermography Journal, 2023
Karol M. Golasiński, Michał Maj, Leszek Urbański, Maria Staszczak, Arkadiusz Gradys, Elżbieta A. Pieczyska
The deformation of a solid is a macroscopic manifestation of the activity of deformation mechanisms occurring at the microscale (e.g. reversible phase transition, motion of dislocations, etc.). Therefore, analyses of local and global values of temperature of solids under deformation can contribute to better understand their thermomechanical behaviour related to the activity of specific deformation mechanisms [11–15].
Modelling the rate and temperature-dependent behaviour and texture evolution of the Mg AZ31B alloy TRC sheets
Published in Philosophical Magazine, 2018
G. Ayoub, A. K. Rodrigez, M. Shehadeh, G. Kridli, J. P. Young, H. Zbib
HCP metals exhibit strong plastic anisotropy, leading to large variations in the critical resolved shear stress (CRSS) needed to activate the available slip systems via dislocation glide or twinning. This anisotropic behaviour is mainly attributed to the dislocations’ core structure resulting in low, intermediate and large values of Peierls stress on the basal, prismatic and pyramidal planes, respectively. Furthermore, the CRSS required to activate dislocation slip is found to be sensitive to temperature [3, 4, 7, 10, 41, 44]. Moreover, it is well established that in single crystalline metals, the high-strain-rate or low-temperature deformation is accommodated not only by dislocation slip, but also by deformation twinning [4, 49–55]. However, the CRSS of twin systems is reported to be insensitive to temperature and strain rate [45]. In polycrystalline materials such as Magnesium alloys, additional plasticity mechanisms can be active such as grain boundary sliding (inter-granular deformation mechanisms active at high temperature) [3] and grain fragmentation. The relative activity of inter-granular and intra-granular deformation mechanisms depends on the loading conditions, temperature, texture and grain size. While magnesium alloys at relatively low temperatures exhibit limited plasticity and ductility, which is mainly induced by the activation of crystallographic slip and deformation twinning, the improved ductility of magnesium at elevated temperature may be attributed to the presence of inter-granular deformation mechanisms such as grain boundary sliding (GBS). GBS is one of the most important high-temperature deformation mechanisms when the deformation temperatures exceed one-third of the absolute melting temperature [3, 42, 46]. Furthermore, dynamic recrystallization (DRX) is another important mechanism accommodated by the plastic deformation of Mg alloys. DRX leads to the formation of new grain structures in a deformed material through the development and migration of high-angle grain boundaries. DRX could be associated with twinning, GBS, grain fragmentation and rotation. The literature and data available on the DRX of superplastic Mg alloy sheets are limited [16, 47–49].