Inhomogeneous Evolution Research Articles

Microstructure and Magnetic Properties of Nanocrystalline Fe60-xCo25Ni15Six Alloy Elaborated by High-Energy Mechanical Milling.

In the present work, the effect of Si addition on the magnetic properties of Fe60−xCo25Ni15Six (x = 0, 5, 10, 20, and 30 at%) alloys prepared by mechanical alloying was analyzed by X-ray diffraction and magnetic vibrating sample magnetometry and SQUID. The crystallographic parameters of the bcc-solid solutions were calculated by Rietveld refinement of the X-ray diffraction patterns with Maud software. Scanning electron microscopy (SEM) was used to determine the morphology of the powdered alloys as a function of milling time. It was found that the Si addition has an important role in the increase of structural hardening and brittleness of the particles (favoring the more pronounced refinement of crystallites). The resulting nanostructure is highlighted in accordance with the concept of the structure of defects. Magnetic properties were related to the metalloid addition, formed phases, and chemical compositions. All processed samples showed a soft ferromagnetic behavior (Hc ≤ 100 Oe). The inhomogeneous evolution of the magnetization saturation as a function of milling time is explained by the magnetostriction effective anisotropy and stress induced during mechanical alloying.

Micromechanics-Based Low Cycle Fatigue Life Prediction Model of ECAPed Aluminum Alloy

Ultrafine-grained aluminum alloys (UFG AA) show great potential in the design of fatigue-resistant lightweight alloys, and the methodology to assess low-cycle fatigue (LCF) life remains to be studied. In this work, a micromechanics-based LCF life prediction model is presented by conducting crystal plasticity finite element simulation (CPFEM). The fatigue indicator parameter (FIP) of maximum accumulated equivalent plastic strain energy, modulated by triaxiality, is developed to assess the material damage in the microstructure. Particularly, a new multiaxial strain parameter is proposed by considering the combined influence of the mean strain and non-proportional cyclic additional hardening effect, and then directly embedding into the cyclic J-integral. Finally, the reformulated Manson-Coffin relationship is theoretically constructed by correlating the crack tip opening displacement to the crack propagation equation. The results show the scatter fatigue life of UFG AA6061 is not only related to the inhomogeneous evolution of plastic deformation but also to the local stress state. Since the proposed approach considers both the deformation mechanisms at the micro-scale and the corresponding macroscopic responses, it can predict the LCF life of UFG AA with reasonable accuracy.

Research on welding-induced inhomogeneous stress in thick plate EH40 butt joint considering phase transformation

In this work, the inhomogeneous residual stress distribution and evolution of thick plate in single-pass full penetration laser welding are systematically investigated using phase transformation model. The material constitutive model considering solid-state phase transformation according to the actual weld microstructure is proposed to predict the inhomogeneous stress distribution of the welded joint. The inhomogeneous stress distributions along the longitudinal, transverse and thickness direction surfaces of the welded joint are systematically analyzed and deeply discussed, respectively. The results show that there is an obvious inhomogeneous distribution of the temperature field between the start-welding, middle section and end-welding position of the weld. It is obviously observed that the top and bottom surfaces of welded joint produce remarkably high stress areas and high stress gradients. The maximum longitudinal and transverse stress gradient values in the top surface are up to 1240.1 MPa and 1175.7 MPa, respectively. It is found that martensitic transformation is the main reason for the inhomogeneous stress distribution including high stress areas and high stress gradients in thick plate welded joint. The current research is beneficial to reduce the detrimental effects of welding-induced inhomogeneous residual stress on thick plate welded joints.

Pore-scale study on Rayleigh-Bénard convection formed in the melting process of metal foam composite phase change material

Rayleigh-Bénard convection significantly affects the melting process of phase change material (PCM). It has been verified to exist in the model with bottom heating. Nevertheless, researchers rarely focus on the Rayleigh-Bénard convection in the metal foam composite PCMs (MFCPCMs). This paper took numerical investigations to study the melting behavior of the MFCPCMs when Rayleigh-Bénard convection was involved, and a visualized experiment was used to verify their accuracy. By analyzing the number of Bénard cells, dimensionless parameters of Rayleigh number and Nusselt number, we found three regimes, including the conductive regime, linear regime, and coarsening regime, forming in the models. The liquid fraction contour captured the evolution of the melting front, and the state of convective heat transfer was characterized by Bénard cells. Results show that the intensity of Rayleigh-Bénard convection in the MFCPCM is obviously weaker than that in the pure PCM. Moreover, the porosity of metal foam has a significant influence on the development of Rayleigh-Bénard convection. With the increase of the porosity, the suppression of liquid PCM flow is weakened, so the convection is more developed. The inhomogeneous evolution of the melting front is more pronounced. Besides, to study the effect of model size on the melting behavior, we built three groups of models with width-height ratios (γ) of 2, 1, and 0.5, respectively. Results show that the model with large γ has more significant inhibition on the development of Rayleigh-Bénard convection. The solid/liquid interface is flat or with a slight fluctuation. On the contrary, the model with small γ has more developed Rayleigh-Bénard convection. The interface of it has a violent fluctuation, which shows as a humped arch. This work interprets the internal heat-transfer characteristics of the MFCPCM model with Rayleigh-Bénard convection. It paves the way for the structural optimization of the metal skeleton to gain efficient heat storage.

Including relativistic and primordial non-Gaussianity contributions in cosmological simulations by modifying the initial conditions

We present a method to implement relativistic corrections to the evolution of dark matter structures in Newtonian simulations of a ΛCDM universe via the initial conditions. We take the nonlinear correspondence between the Lagrangian (Newtonian) evolution of dark matter inhomogeneities and the synchronous-comoving (relativistic) matter density description, and use it to promote the relativistic constraint as the initial condition for numerical simulations of structure formation. In this case, the incorporation of Primordial non-Gaussianity (PNG) contributions as initial conditions is straightforward. We implement the relativistic, f NL and g NL contributions as initial conditions for the L-PICOLA code, and compute the power spectrum and bispectrum of the evolved matter field. We focus specifically on the case of largest values of non-Gaussianity allowed at 1-σ by Planck observations (f NL = −4.2 and g NL = −7000). As a checkup, we show consistency with the one-loop perturbative prescription and with a fully relativistic simulation (GRAMSES) on the adequate scales. Our results confirm that both relativistic and PNG features are most prominent at very large scales and for squeezed triangulations. We discuss future prospects to probe these two contributions in the bispectrum of the matter density distribution.

Assessing the Influence of Input Magnetic Maps on Global Modeling of the Solar Wind and CME‐Driven Shock in the 2013 April 11 Event

AbstractIn the past decade, significant efforts have been made in developing physics‐based solar wind and coronal mass ejection (CME) models, which have been or are being transferred to national centers (e.g., SWPC, Community Coordinated Modeling Center) to enable space weather predictive capability. However, the input data coverage for space weather forecasting is extremely limited. One major limitation is the solar magnetic field measurements, which are used to specify the inner boundary conditions of the global magnetohydrodynamic (MHD) models. In this study, using the Alfvén wave solar model, we quantitatively assess the influence of the magnetic field map input (synoptic/diachronic vs. synchronic magnetic maps) on the global modeling of the solar wind and the CME‐driven shock in the 11 April 2013 solar energetic particle event. Our study shows that due to the inhomogeneous background solar wind and dynamical evolution of the CME, the CME‐driven shock parameters change significantly both spatially and temporally as the CME propagates through the heliosphere. The input magnetic map has a great impact on the shock connectivity and shock properties in the global MHD simulation. Therefore this study illustrates the importance of taking into account the model uncertainty due to the imperfect magnetic field measurements when using the model to provide space weather predictions.

Nature of field-induced antiferromagnetic order in Zn-doped CeCoIn5 and its connection to quantum criticality in the pure compound

Quantum criticality plays an important role in the unconventional nature of superconductivity in strongly correlated electron systems. However, the intrinsic antiferromagnetic (AFM) order parameter responsible for quantum criticality has been unidentified in the prototypical unconventional superconductor ${\mathrm{CeCoIn}}_{5}$. In this work, magnetization and specific-heat measurements for $\mathrm{CeCo}{({\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x})}_{5}$ with $x\ensuremath{\le}0.07$ demonstrate that the field-induced AFM order develops with Zn doping, along with a continuous increase in its critical field up to 10 T at $x=0.07$. The weak signals associated with the AFM phase transition strongly suggest spatially inhomogeneous evolution of the AFM phase, whose feature becomes pronounced with decreasing the Zn concentration. The temperature, magnetic field, and Zn concentration phase diagram is constructed from those experimental results. It is found that, in this diagram, extrapolating the $x$ dependence of the AFM critical field yields the value of $\ensuremath{\approx}5\phantom{\rule{4pt}{0ex}}\mathrm{T}$ for $x\ensuremath{\rightarrow}0$, which coincides with the location of the quantum critical point in ${\mathrm{CeCoIn}}_{5}$. The specific heat shows $\ensuremath{-}lnT$ diverging behavior characteristic of the non-Fermi-liquid state at the AFM critical fields for all of the $x$ range. The scaling analysis for the specific-heat data above critical fields leads to continuous variations of the scaling parameters as a function of $x$. These findings provide strong evidence that the quantum critical fluctuations in ${\mathrm{CeCoIn}}_{5}$ originate from the order parameter corresponding to the field-induced AFM state observed in Zn-doped systems.

Ensemble Machine‐Learning‐Based Analysis for In Situ Electron Diffraction

AbstractIn situ transmission electron microscopy is an important characterization approach for exploring the structural dynamics of materials. However, the recorded high resolution in situ videos normally have tremendous amount of data, which is challenging for quantitative analysis. In case of in situ electron diffraction (ED), the classical analysis method only tracks changes of the integral profile and ignores important information of position, intensity, and distribution angle due to the lack of a proper data processing tool. In this work, an ensemble machine‐learning‐based framework which enables the fore‐and‐after tracking of all diffraction spots of an in situ ED video is established. As demonstrated in the case of the lithiation of the Co3O4 nanoparticles, the method precisely quantifies the changes of lattice parameters and then unveils the inhomogeneous structural evolution induced by the insertion of lithium ions. This method is generally applicable to analyze in situ ED data derived from any dynamical processes, enlarging the capability to grasp the key information from massive in situ data.

Inhomogeneous Deformation and Texture Evolution of 30SiMn2MoVA Steel Gun Barrel Processed by Radial Forging Based on Cross-scale Crystal Plasticity Finite Element Method

There is anisotropy in 30SiMn2MoVA steel gun barrel processed by radial forging which results in the low service life of the gun barrel. While the texture is the main reason for the anisotropy. The crystal plasticity finite element (CPFE) method is usually used to simulate the microstructure and the texture of the metal. In the present work, a two-dimensional polycrystalline finite element model based on electron back-scattered diffraction (EBSD) experiment data is developed to represent virtual grain structures of polycrystalline 30SiMn2MoVA steel. The displacement of nodes in the macro radial forging process finite element model is used as the cross-scale boundary condition in the CPFE model which realizes cross-scale simulation. The texture evolution and inhomogeneous deformation of 30SiMn2MoVA steel in the radial forging processing under three different forging ratios were simulated. The simulated texture results are consistent with the experimental results. The inhomogeneous deformation of grains is obvious and will intensify with the increase of the forging ratio. The distributions of stress and equivalent plastic strain in polycrystals are statistically Gaussian. With the increase of deformation, the further refinement of grains is due to the large shear strain in large grains.

Laboratory characterisation of anisotropic and heterogeneous damage of rock sample using acoustic emission and ultrasonic monitoring technologies

Rock damage characterisation of Gosford sandstone samples under triaxial loading was achieved using an integrated approach, combing passive acoustic emission (AE) and active ultrasonic wave monitoring. The location of AE events is firstly obtained using isotropic wave velocity field measured by continuous ultrasonic wave. Then, passive AE tomography is conducted to progressively-update the anisotropy and heterogenous P-wave velocity field of rock samples. According to the variance in P-wave velocity, damage induced anisotropy and heterogeneity can be identified. The results suggest that the inhomogeneous damage evolution highly dependent on the loading stages and can well reflect the microcrack behaviour. Anisotropic damage variable along the whole loading process is also analysed, by a second order damage tensor with a transversely anisotropy assumption. It is observed that the lateral component of damage is much higher than the axial component. This is mainly due to the dilation behaviour of rock sample. This paper will cast more light on anisotropic and heterogenous damage characterisation using acoustic/ultrasonic lab experiments.

Effect of inhomogeneous microstructure evolution on the mechanical properties and corrosion behavior of rotary friction welded AA2024 joints

The intrinsic flaws of radial gradient heat generation and uneven deformation during rotary friction welding process will damage the structural integrity of the resultant joint but almost no attention has been paid before. The relationship between radial inhomogeneous microstructure, mechanical properties and corrosion behavior of rotary friction welded 2024 aluminum alloy joint was thus systematically investigated to reveal the impact. The results showed that the highest and lowest tensile strength appeared in 0.25R and 0.75R positions along radius, respectively. And the texture evolution in 0.25R and 0.75R positions can be summarized as: Copper {112}<111> → S{123}<634> → Brass {011}<211>(strong) → Brass {011}<211> (weak), Copper {112}<111> → S{123}<634> → Rotated Goss {110}<110> → Brass {011}<211> (weak), respectively. The corrosion resistance of rotary friction welded joint is gradually weakened along radius, caused by the different distribution of grain size, second phase particles and residual stress. The heat affected zone (HAZ), thermo-mechanically affected zone (TMAZ) adjacent to HAZ and dynamic recrystallization zone (DRZ) exhibited high corrosion susceptibility and occurred severe exfoliation corrosion. But the TMAZ adjacent to DRZ and base metal acquired the good corrosion resistance due to the dispersive distribution of GPB zones. Furthermore, the qualitative relationship between microhardness and corrosion susceptibility was revealed. The regions with low microhardness exhibited high corrosion susceptibility while the regions with high microhardness (except DRZ) presented good corrosion resistance. • Microstructure and mechanical properties of joints unevenly distributed along radius. • Texture evolution in 0.25R and 0.75R position was systematically investigated. • The corrosion resistance in TMAZ adjacent to DRZ is the highest. • Qualitative relation between microhardness and corrosion susceptibility was revealed.

Investigation of Instabilities in Granular Media and Their Numerical Simulation

The inception of instabilities in sand across different “length-scales,” viz., continuum, discrete, and laboratory element tests, has been highlighted in this study. With instability onset, the material behavior no longer remains “single element” in the sense of continuum mechanics, and due care is required while calibrating different constitutive relationships for use in various numerical simulations. A laboratory “element” test can instead be viewed as a boundary value problem at the instability onset. The post-instability response of a soil specimen represents the “system-response” with the evolution of inhomogeneities being primarily influenced by the boundary conditions among various other factors. Instability onset in drained and undrained biaxial tests has been explored by adopting the bifurcation framework with the aid of a generalized nonassociative elastoplastic material model. For the locally drained globally undrained scenario within a continuum numerical framework, instability onset is found to be influenced by the refinement of mesh discretization. Signatures of rate-dependent localized behavior of sand specimens are also commented on from numerical simulations of drained biaxial tests. To address the “pathological mesh dependence” of classical continuum modeling, we resort to a micromechanical discrete granular framework that considers the actual particle morphology. The numerical predictions match reasonably well with the flexible boundary plane strain experiments. The inherent grain fabric arrangement is found to be the triggering mechanism behind the localized strain accumulation at multiple zones. The influence of loading boundary conditions and various signatures of local nonuniformities is also explored with the aid of image analysis in plane strain and triaxial tests.

Investigation of Deformation Inhomogeneity and Low-Cycle Fatigue of a Polycrystalline Material

Considering the relationship between inhomogeneous plastic deformation and fatigue damage, deformation inhomogeneity evolution and fatigue failure of superalloy GH4169 under temperature 500 °C and macro tension compression cyclic loading are studied, by using crystal plasticity calculation associated with polycrystalline representative Voronoi volume element (RVE). Different statistical standard deviation and differential entropy of meso strain are used to measure the inhomogeneity of deformation, and the relationship between the inhomogeneity and strain cycle is explored by cyclic numerical simulation. It is found from the research that the standard deviations of each component of the strain tensor at the cyclic peak increase monotonically with the cyclic loading, and they are similar to each other. The differential entropy of each component of the strain tensor also increases with the number of cycles, and the law is similar. On this basis, the critical values determined by statistical standard deviations of the strain components and the equivalent strain, and that by differential entropy of strain components, are, respectively, used as fatigue criteria, then predict the fatigue–life curves of the material. The predictions are verified with reference to the measured results, and their deviations are proved to be in a reasonable range.

Generation of wave packets and breathers by oscillating kinks in the sine-Gordon system

Evolution of the nonequilibrium inhomogeneities and topological defects is studied in terms of complex kink solutions of the sine–Gordon equation. The weakly damped oscillation of the sine–Gordon kink, named as the kink quasimode, is described explicitly. It is shown that the oscillatory kink behavior and the wave packet generation depend significantly on the initial nonequilibrium kink profile. In order to specify conditions of the generation of wobbling kinks with a multibreather structure we reformulate the direct scattering problem associated with the sine-Gordon equation as the spectral problem of the Schrödinger operator. We obtain the dependence of the radiation energy, which is emitted during formation of the multi-frequency wobbling kink, on the effective dimension of its initial profile.

All-Optically Reconfigurable Plasmonic Metagrating for Ultrafast Diffraction Management.

Hot-electron dynamics taking place in nanostructured materials upon irradiation with fs-laser pulses has been the subject of intensive research, leading to the emerging field of ultrafast nanophotonics. However, the most common description of nonlinear interaction with ultrashort laser pulses assumes a homogeneous spatial distribution for the photogenerated carriers. Here we theoretically show that the inhomogeneous evolution of the hot carriers at the nanoscale can disclose unprecedented opportunities for ultrafast diffraction management. In particular, we design a highly symmetric plasmonic metagrating capable of a transient symmetry breaking driven by hot electrons. The subsequent power imbalance between symmetrical diffraction orders is calculated to exceed 20% under moderate (∼2 mJ/cm2) laser fluence. Our theoretical investigation also indicates that the recovery time of the symmetric configuration can be controlled by tuning the geometry of the metaatom, and can be as fast as 2 ps for electrically connected configurations.

Carbonation resistance study and inhomogeneity evolution of recycled aggregate concretes under loading effects

Carbonation-load coupling effects can aggravate the inhomogeneity of recycled aggregate concrete (RAC) which contains old attached mortar (OAM) and new added mortar (NAM). In this study, these mortars are first distinguished using an iron oxide. Afterwards, accelerated carbonation coupled with four-point bending effects are applied on the RAC samples, and the carbonation depths in compressive, load-free and tensile zones are compared. The loading rate equals to 40% RAC flexural strength. The microstructures of the mortars in different zones are then compared. Moreover, a computing method for the steel corrosion zone widths of the RACs is proposed after the figures determined using the OAMs and NAMs in different zones as samples are compared. The results show that the carbonation depths of RACs present a significant difference which is more remarkable compared with natural aggregate concrete. Besides, the load shows significant impacts on the mortar microstructure and steel corrosion zone width. Specifically, the effect of tensile stress on OAMs is more obvious than that on NAMs, but there is no such difference in compressive zone. Furthermore, using the OAMs in tensile zone as the samples concludes the highest steel corrosion zone width which is suggested to be used to evaluate the carbonation service life of RAC structures for avoiding the overestimation of structure safety.

Mechanics of cucumber tendril:

The helical coiling of plant tendrils has fascinated scientists for centuries, yet the formation process of the inverted helical structure is still unclear and further investigation is required. In this study, we investigate the formation mechanism of the helical structure from experiments and finite element analysis. First, we measured the geometry of the tendrils using photogrammetry technique. This analysis yields a distribution of curvature and torsion from a least square fitting of a space curve to the point cloud data. The formation process is then estimated from inhomogeneous evolution of the curvature and torsion. We also conducted finite element analysis on a Riemannian manifold. This analysis reveals that the formation of helical structure is explained by development of internal curvature.

Changes in the Defective Structure of the Surface of a Fe77Ni1Si9B13 Metal Glass Ribbon under the Influence of Hydrostatic Pressure and Isothermal Annealing

The features and generality of the effect of hydrostatic pressure and annealing on the surface relief of the contact and non-contact side of the Fe77Ni1Si9B13 metal glass ribbon are revealed. The relationship between transformation of the ribbon surface inhomogeneities under these effects and possible formation of nanocrystalline regions are analyzed. We found that the evolution of the surface inhomogeneities at the contact side of the ribbon after annealing procedure leads to appearing of discrete-sized fractions in these regions.

Spurious gauge-invariance of higher-order contributions to the spectral energy density of the relic gravitons

In the same way as the energy density associated with the tensor modes of the geometry modifies the evolution of the curvature perturbations, the scalar modes may also indirectly affect the cosmic backgrounds of relic gravitons by inducing higher-order corrections that are only superficially gauge-invariant. This spurious gauge-invariance gets manifest when the effective anisotropic stresses, computed in different coordinate systems, are preliminarily expressed in a form that only depends on the curvature inhomogeneities defined on comoving orthogonal hypersurfaces and on their corresponding time derivatives. Using this observation we demonstrate in general terms that the higher-order contributions derived in diverse coordinate systems coincide when the wavelengths are smaller than the sound horizon defining the evolution of the curvature inhomogeneities but they lead to sharply different results in the opposite limit. A similar drawback arises when the energy density of the relic gravitons is derived from competing energy–momentum pseudotensors and should be consistently taken into account in the related phenomenological discussions.

Three-Step Description of Single-Pulse Formation of Laser-Induced Periodic Surface Structures on Metals.

Two different scenarios are usually invoked in the formation of femtosecond Laser-Induced Periodic Surface Structures (LIPSS), either “self-organization” mechanisms or a purely “plasmonic” approach. In this paper, a three-step model of formation of single-laser-shot LIPSS is summarized. It is based on the periodic perturbation of the electronic temperature followed by an amplification, for given spatial periods, of the modulation in the lattice temperature and a final possible relocation by hydrodynamic instabilities. An analytical theory of the evolution of the temperature inhomogeneities is reported and supported by numerical calculations on the examples of three different metals: Al, Au, and Mo. The criteria of the possibility of hydrodynamic instabilities are also discussed.