Showing papers on "Deformation (meteorology) published in 2014"

Eastward expansion of the Tibetan Plateau by crustal flow and strain partitioning across faults

Abstract: The Tibetan Plateau is expanding eastwards, but the modes of deformation are poorly understood. High-resolution seismic images from the region identify localized zones of weak crustal rocks as well as deep faults, implying that deformation occurs through a combination of crustal flow and movement of rigid blocks of crust.

Dislocation interactions with grain boundaries

Abstract: Recent progress in understanding dislocation interactions with grain boundaries and interfaces in metallic systems via static and in situ dynamic experimental approaches is reviewed.

Improving InSAR geodesy using Global Atmospheric Models

Abstract: Spatial and temporal variations of pressure, temperature, and water vapor content in the atmosphere introduce significant confounding delays in interferometric synthetic aperture radar (InSAR) observations of ground deformation and bias estimates of regional strain rates. Producing robust estimates of tropospheric delays remains one of the key challenges in increasing the accuracy of ground deformation measurements using InSAR. Recent studies revealed the efficiency of global atmospheric reanalysis to mitigate the impact of tropospheric delays, motivating further exploration of their potential. Here we explore the effectiveness of these models in several geographic and tectonic settings on both single interferograms and time series analysis products. Both hydrostatic and wet contributions to the phase delay are important to account for. We validate these path delay corrections by comparing with estimates of vertically integrated atmospheric water vapor content derived from the passive multispectral imager Medium-Resolution Imaging Spectrometer, onboard the Envisat satellite. Generally, the performance of the prediction depends on the vigor of atmospheric turbulence. We discuss (1) how separating atmospheric and orbital contributions allows one to better measure long-wavelength deformation and (2) how atmospheric delays affect measurements of surface deformation following earthquakes, and (3) how such a method allows us to reduce biases in multiyear strain rate estimates by reducing the influence of unevenly sampled seasonal oscillations of the tropospheric delay.

Non-volatile organic memory with sub-millimetre bending radius

Abstract: Flexible organic electronics operated at extreme mechanical conditions are crucial for the next generation of smart foldable electronic applications. Kim et al. show non-volatile organic memory devices that are subject to sharp bending deformation without protection from a stress-release layer.

Integrability of the bi-Yang-Baxter sigma-model

Abstract: We construct a Lax pair with spectral parameter for a two-parameter doubly Poisson-Lie deformation of the principal chiral model.

How thermally activated deformation starts in metallic glass

Abstract: Understanding the atomic-scale processes by which deformation occurs in a metallic glass remains a challenge. Here, the authors apply atomic-scale simulations to study the mechanism by which thermally activated deformation initiates in a model binary metallic glass.

Mechanical Properties of Magnesium-Rare Earth Alloy Systems: A Review

Abstract: Magnesium-rare earth based alloys are increasingly being investigated due to the formation of highly stable strengthening phases, activation of additional deformation modes and improvement in mechanical properties. Several investigations have been done to study the effect of rare earths when they are alloyed to pure magnesium and other Mg alloys. In this review, the mechanical properties of the previously investigated different magnesium-rare earth based binary alloys, ternary alloys and other higher alloys with more than three alloying elements are presented.

Integrability of the Bi-Yang–Baxter σ-Model

Abstract: We construct a Lax pair with spectral parameter for a two-parameter doubly Poisson–Lie deformation of the principal chiral model.

Harnessing large deformation and instabilities of soft dielectrics: Theory, experiment, and application

Abstract: Widely used as insulators, capacitors, and transducers in daily life, soft dielectrics based on polymers and polymeric gels play important roles in modern electrified society. Owning to their mechanical compliance, soft dielectrics subject to voltages frequently undergo large deformation and mechanical instabilities. The deformation and instabilities can lead to detrimental failures in some applications of soft dielectrics such as polymer capacitors and insulating gels but can also be rationally harnessed to enable novel functions such as artificial muscle, dynamic surface patterning, and energy harvesting. According to mechanical constraints on soft dielectrics, we classify their deformation and instabilities into three generic modes: (i) thinning and pull-in, (ii) electro-creasing to cratering, and (iii) electro-cavitation. We then provide a systematic understanding of different modes of deformation and instabilities of soft dielectrics by integrating state-of-the-art experimental methods and observations, theoretical models, and applications. Based on the understanding, a systematic set of strategies to prevent or harness the deformation and instabilities of soft dielectrics for diverse applications are discussed. The review is concluded with perspectives on future directions of research in this rapidly evolving field.

Mechanism investigation of friction-related effects in single point incremental forming using a developed oblique roller-ball tool

Abstract: Single point incremental forming (SPIF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. In the SPIF process, a ball nose tool moves along a predefined tool path to form the sheet to desired shapes. Due to its unique ability in local deformation of sheet metal, the friction condition between the tool and sheet plays a significant role in material deformation. The effects of friction on surface finish, forming load, material deformation and formability are studied using a newly developed oblique roller ball (ORB) tool. Four grades of aluminum sheet including AA1100, AA2024, AA5052 and AA6111 are employed in the experiments. The material deformation under both the ORB tool and conventional rigid tool are studied by drilling a small hole in the sheet. The experimental results suggest that by reducing the friction resistance using the ORB tool, better surface quality, reduced forming load, smaller through-the-thickness-shear and higher formability can be achieved. To obtain a better understanding of the frictional effect, an analytical model is developed based on the analysis of the stress state in the SPIF deformation zone. Using the developed model, an explicit relationship between the stress state and forming parameters is established. The experimental observations are in good agreement with the developed model. The model can also be used to explain two contrary effects of friction and corresponding through-the-thickness-shear: increase of friction would potentially enhance the forming stability and suppress the necking; however, increase of friction would also increase the stress triaxiality and decrease the formability. The final role of the friction effect depends on the significance of each effect in SPIF process.

An Integrable Deformation of the AdS5 x S5 Superstring

Abstract: The S-matrix on the world-sheet theory of the string in AdS5 x S5 has previously been shown to admit a deformation where the symmetry algebra is replaced by the associated quantum group. The case where q is real has been identified as a particular deformation of the Green-Schwarz sigma model. An interpretation of the case with q a root of unity has, until now, been lacking. We show that the Green-Schwarz sigma model admits a discrete deformation which can be viewed as a rather simple deformation of the F/F_V gauged WZW model, where F=PSU(2,2|4). The deformation parameter q is then a k-th root of unity where k is the level. The deformed theory has the same equations-of-motion as the Green-Schwarz sigma model but has a different symplectic structure. We show that the resulting theory is integrable and has just the right amount of kappa-symmetries that appear as a remnant of the fermionic part of the original gauge symmetry. This points to the existence of a fully consistent deformed string background.

Mechanical and microscopic properties of the reversible plastic regime in a 2D jammed material.

Abstract: At the microscopic level, plastic flow of a jammed, disordered material consists of a series of particle rearrangements that cannot be reversed by subsequent deformation. An infinitesimal deformation of the same material has no rearrangements. Yet between these limits, there may be a self-organized plastic regime with rearrangements, but with no net change upon reversing a deformation. We measure the oscillatory response of a jammed interfacial material, and directly observe rearrangements that couple to bulk stress and dissipate energy, but do not always give rise to global irreversibility.

Effects of Current Frequency on Electromagnetic Sheet Metal Forming Process

Abstract: In the paper, the effects of current frequency on the electromagnetic sheet metal forming process are investigated using an efficient finite element model, which couples analysis of circuit, electromagnetic, and mechanical equations. Based on the initial electrical and structural parameters of the system, the model calculates the pulsed current flowing through the coil, the consequent magnetic force acting on the metal sheet, and finally the generated sheet deformation. The effects of current frequency on the maximum displacement in axial direction of the sheet are analyzed for two sheets by changing the capacitance of capacitor bank, while keeping the stored energy constant. The results show that there exist two optimum frequencies that produce relatively large sheet deformation and the optimum frequencies are related with the thickness of the sheet.

A Phase-Field Model Coupled with Large Elasto-Plastic Deformation: Application to Lithiated Silicon Electrodes

Abstract: aDepartment of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA bWoodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA cDepartment of Engineering, Pennsylvania State University, The Altoona College, Altoona, Pennsylvania 16601, USA dDepartment of Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania 16802, USA

Effects of Principal Stress Rotation on the Cumulative Deformation of Normally Consolidated Soft Clay under Subway Traffic Loading

Abstract: The authors investigated the effects of principal stress rotation (PSR) on the traffic load–induced settlement of subways in soft subsoil. Here, a series of hollow cylinder tests on normally consolidated, medium-plasticity soft clay with and without principal stress rotation were performed along with finite-element modeling and simulation. The results show significant increases in both excess pore-water pressure and cumulative deformation of the normally consolidated soft clay when PSR is present and simulated, and the effects become more pronounced as the maximum effective principal stress ratio or load frequency increases. Under the actual traffic load–induced stress in subsoil below the subway tunnel, the presence of PSR increases the cumulative deformation of soft clay by 9–23% compared with that without PSR. As an approximation, the cumulative deformation of soft clay with the effect of PSR can be estimated by multiplying the deformation derived from the repeated triaxial testing without PSR ...

On the visual deformation servoing of compliant objects: Uncalibrated control methods and experiments

Abstract: In this paper, we address the active deformation control of compliant objects by robot manipulators. The control of deformations is needed to automate several important tasks, for example, the manipulation of soft tissues, shaping of food materials, or needle insertion. Note that in many of these applications, the object's deformation properties are not known. To cope with this issue, in this paper we present two new visual servoing approaches to explicitly servo-control elastic deformations. The novelty of our kinematic controllers lies in its uncalibrated behavior; our adaptive methods do not require the prior identification of the object's deformation model and the camera's intrinsic/extrinsic parameters. This feature provides a way to automatically control deformations in a model-free manner. The experimental results that we report validate the feasibility of our controllers.

Nanoindentation of polysilicon and single crystal silicon: Molecular dynamics simulation and experimental validation

Abstract: This paper presents novel advances in the deformation behaviour of polycrystalline and single crystal silicon using molecular dynamics (MD) simulation and validation of the same via nanoindentation experiments. In order to unravel the mechanism of deformation, four simulations were performed: indentation of a polycrystalline silicon substrate with a (i) Berkovich pyramidal and a (ii) spherical (arc) indenter, and (iii and iv) indentation of a single crystal silicon substrate with these two indenters. The simulation results reveal that high pressure phase transformation (HPPT) in silicon (Si-I to Si-II phase transformation) occurred in all cases; however, its extent and the manner in which it occurred differed significantly between polycrystalline silicon and single crystal silicon, and was the main driver of differences in the nanoindentation deformation behaviour between these two types of silicon. Interestingly, in polycrystalline silicon, the HPPT was observed to occur more preferentially along the grain boundaries than across the grain boundaries. An automated dislocation extraction algorithm (DXA) revealed no dislocations in the deformation zone, suggesting that HPPT is the primary mechanism in inducing plasticity in silicon.

Hot deformation behavior of AA7085 aluminum alloy during isothermal compression at elevated temperature

Abstract: The isothermal deformation compression tests of AA7085 aluminum alloy were performed on Gleeble-1500 system in the temperature range from 250 °C to 450 °C and at strain rate range from 0.01 s −1 to 10 s −1 . The microstructure of samples was observed using optical microscopy (OM) and transmission electron microscopy (TEM) techniques. The results show that the peak stress levels decreased with the increase of deformation temperatures or the decrease of strain rate, which can be represented by the Zener–Hollomon parameter in the exponent-type equation with the hot deformation activation energy of 249.11 KJ/mol. Dynamic recrystallization more obviously occurred in the sample with higher Z value than in the sample with lower Z value. Dynamic recrystallization is sensitively dependent on the deformation temperature.

A Framework for Three-Dimensional Mesoscale Modeling of Anisotropic Swelling and Mechanical Deformation in Lithium-Ion Electrodes

Abstract: Lithium-ion battery electrodes rely on a percolated network of solid particles and binder that must maintain a high electronic conductivity in order to function. Coupled mechanical and electrochemical simulations may be able to elucidate the mechanisms for capacity fade. We present a framework for coupled simulations of electrode mechanics that includes swelling, deformation, and stress generation driven by lithium intercalation. These simulations are performed at the mesoscale, which requires 3D reconstruction of the electrode microstructure from experimental imaging or particle size distributions. We present a novel approach for utilizing these complex reconstructions within a finite element code. A mechanical model that involves anisotropic swelling in response to lithium intercalation drives the deformation. Stresses arise from small-scale particle features and lithium concentration gradients. However, we demonstrate, for the first time, that the largest stresses arise from particle-to-particle contacts, making it important to accurately represent the electrode microstructure on the multi-particle scale. Including anisotropy in the swelling mechanics adds considerably more complexity to the stresses and can significantly enhance peak particle stresses. Shear forces arise at contacts due to the misorientation of the lattice structure. These simulations will be used to study mechanical degradation of the electrode structure through charge/discharge cycles. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0081411jes] All rights reserved.

Characterization of hot deformation behavior of as-homogenized Al–Cu–Li–Sc–Zr alloy using processing maps

Abstract: The hot deformation behavior of Al–Cu–Li–Sc–Zr alloy and its microstructure evolution were investigated by isothermal compression tests under various deformation conditions. The tests were carried out in the deformation temperature range between 380 and 500 °C and at strain rates between 0.001 and 10 s −1 . The constitutive model based on the hyperbolic-sine equation was established to characterize the dependence of flow stress on strain, strain rate and deformation temperature. Based on the experimental data and dynamic materials model, the processing maps at strain of 0.4 and 0.6 were generated to demonstrate the hot workability of the alloy. The results show that the flow stress decreases with increasing deformation temperature, and increases with increasing strain rate. The main softening mechanism is dynamic recovery at 440 °C/0.1 s −1 ; the dynamic recrystallization of the alloy can be easily observed at 470 °C/0.001 s −1 , with peak efficiency of power dissipation of around 57%. With increasing deformation temperature, the volume fraction of dynamic recrystallization increases. At strains of 0.4 and 0.6, the flow instability domain is found at higher strain rates (>0.3 s −1 ), which mainly locates at the upper part of processing maps. On the basis of processing maps and microstructure evolution, the optimum hot working parameters are in deformation temperature range from 460 to 500 °C and at strain rate range from 0.001 to 0.1 s −1 with higher power efficiency of around 42–60%.