Finite Correlation Research Articles

Thermomechanical finite element simulation and correlation analysis for orthogonal cutting of normalized AISI 9310 steels

A coupled thermomechanical finite element analysis is performed in order to simulate orthogonal cutting of normalized AISI 9310. Damage parameters are optimized to define the behavior of the material subjected to orthogonal cutting. AISI 1045, AISI 4140, and A2024-T351 are selected as precursors to validating the present finite element approach for orthogonal cutting of normalized AISI 9310. The numerical results obtained in this study include the average cutting force, residual stresses and strains, chip morphology, and tool temperature. These results are validated for each material with experimental results found in literature. The current study optimizes the Johnson–Cook damage parameters for steel materials in order to capture physical chip morphology. A correlation analysis is then performed using the validated finite element model for the AISI 9310 material to better understand the effect of specific input parameters such as the damage parameters, coefficient of friction, fracture energy, heat generation fractions and tool velocity on output results such as stresses and strains in the workpiece, chip thickness ratio and tool temperature. This analysis provides input-output relations for a physically reasonable range of input parameters and supports that the damage parameters, coefficient of friction, and fracture energy have a very strong influence on the residual stresses and strains, and the chip morphology. The coefficient of friction has a strong influence of tool temperature. Correlation analysis results can help manufacturers in understanding the nature of residual stresses and distortion, and in choosing optimized process parameters suitable for and applicable to the specific workpiece material. Tool wear that is observed in actual cutting of normalized AISI 9310 is also discussed. This study will benefit the manufacturing industry with the understanding of how specific cutting processing parameters will impact the distortions and residual stresses in the machined AISI 9310 parts.

Effects of turbulent environment and random noise on self-organized critical behavior: Universality versus nonuniversality.

Self-organized criticality in the Hwa-Kardar model of a "running sandpile" [Phys. Rev. Lett. 62, 1813 (1989)10.1103/PhysRevLett.62.1813; Phys. Rev. A 45, 7002 (1992)10.1103/PhysRevA.45.7002] with a turbulent motion of the environment taken into account is studied with the field theoretic renormalization group (RG). The turbulent flow is modeled by the synthetic d-dimensional generalization of the anisotropic Gaussian velocity ensemble with finite correlation time, introduced by Avellaneda and Majda [Commun. Math. Phys. 131, 381 (1990)10.1007/BF02161420; Commun. Math. Phys. 146, 139 (1992)10.1007/BF02099212]. The Hwa-Kardar model with time-independent (spatially quenched) random noise is considered alongside the original model with white noise. The aim of the present paper is to explore fixed points of the RG equations which determine the possible types of universality classes (regimes of critical behavior of the system) and critical dimensions of the measurable quantities. Our calculations demonstrate that influence of the type of random noise is extremely large: in contrast to the case of white noise where the system possesses three fixed points, the case of spatially quenched noise involves four fixed points with overlapping stability regions. This means that in the latter case the critical behavior of the system depends not only on the global parameters of the system, which is the usual case, but also on the initial values of the charges (coupling constants) of the system. These initial conditions determine the specific fixed point which will be reached by the RG flow. Since now the critical properties of the system are not defined strictly by its parameters, the situation may be interpreted as a universality violation. Such systems are not forbidden, but they are rather rare. It is especially interesting that the same model without turbulent motion of the environment does not predict this nonuniversal behavior and demonstrates the usual one with prescribed universality classes instead [J. Stat. Phys. 178, 392 (2020)10.1007/s10955-019-02436-8].

ХАЛДЕЙНОВСКИЕ ЦЕПОЧКИ

In a number of quasi-one-dimensional magnets, transition metal ions obeying the motives of the crystal lattice can form chains of integer spins that are distant from each other, named Haldane chains. This paper provides a brief overview of the magnetic properties of Haldane chains and considers some compounds containing such chains. The main features of the S=1 spin chain are that it has an unordered ground state with a finite correlation length and a spin gap in the magnetic excitation spectrum. In this paper, the manifestation of these properties is considered on the example of some compounds containing chains of Ni2+ ions (S=1). The disappearance of the spin gap and the establishment of antiferromagnetic ordering can lead to inter-chain interaction (as is the case in CsNiCl3), as well as an external magnetic field (in the case of Ni(C5H14N2)2N3(ClO4)), in which the Zeeman splitting of the Haldane triplet state occurs. To date, PbNi2V2O8 is the only known compound, in which the long-range magnetic order is induced by non-magnetic dilution of S=1 chains. In contrast to the above-listed compounds, Y2BaNiO5 remains disordered down to 0.1 K. When the non-magnetic Y3+ ion in Y2BaNiO5 is replaced by the rare earth ion R3+, a three-dimensional magnetic ordering occurs in the system. However, the Haldane gap in the spectrum of magnetic excitations of nickel is preserved both in the paramagnetic region and in the ordered state. In the ordered state, there is a paradoxical coexistence of the Haldane phase and spin waves, and the ordering occurs in the rare-earth subsystem, while the nickel subsystem remains internally disordered.

Intra‐Island Coulomb Correlations in PEDOT:PSS Thin Films; Saturation of Spin Polarization Magnetoresistance

AbstractMagnetic field and temperature dependence of the magneto‐conductance (MC) of thin films made of self‐p‐doped poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) having room temperature conductivity of ≈200 S cm−1 in the range of fields B = 0–14 T and temperatures T = 1.8–300 K are reported. At B = 0 and for current parallel to the film surface, the conductance follows a variable range hopping mechanism in two dimensions. It is shown that the finite Coulomb correlations, U, within the nano‐crystalline PEDOT islands dominates MC at low temperatures and high fields. At T = 1.8 K, the intra‐island Coulomb correlation spin polarization mechanism is already saturated for B > 10 T establishing a finite minimum of ≈2 meV for U. This small value of U is in line with the delocalized nature of the holes within the PEDOT islands and the relatively high conductivity that makes it essential in organic opto‐electronics.

Mean-field dynamics of infinite-dimensional particle systems: global shear versus random local forcing

In infinite dimensions, many-body systems of pairwise interacting particles provide exact analytical benchmarks for the features of amorphous materials, such as the stress–strain curve of glasses under quasistatic shear. Here, instead of global shear, we consider an alternative driving protocol, as recently introduced by Morse et al 2020 (arXiv:2009.07706), which consists of randomly assigning a constant local displacement on each particle, with a finite spatial correlation length. We show that, in the infinite-dimensional limit, the mean-field dynamics under such a random forcing are strictly equivalent to those under global shear, upon a simple rescaling of the accumulated strain. Moreover, the scaling factor is essentially given by the variance of the relative local displacements of interacting pairs of particles, which encodes the presence of a finite spatial correlation. In this framework, global shear is simply a special case of a much broader family of local forcing, which can be explored by tuning its spatial correlations. We discuss the specific implications for the quasistatic driving of glasses—initially prepared at a replica-symmetric equilibrium—and how the corresponding ‘stress–strain’-like curves and elastic moduli can be rescaled onto their quasistatic-shear counterparts. These results hint at a unifying framework for establishing rigorous analogies, at the mean-field level, between different driven disordered systems.

Spectral Gaps and Incompressibility in a {varvec{nu }}\xa0=\xa01/3 Fractional Quantum Hall System

We study an effective Hamiltonian for the standard nu =1/3 fractional quantum Hall system in the thin cylinder regime. We give a complete description of its ground state space in terms of what we call Fragmented Matrix Product States, which are labeled by a certain family of tilings of the one-dimensional lattice. We then prove that the model has a spectral gap above the ground states for a range of coupling constants that includes physical values. As a consequence of the gap we establish the incompressibility of the fractional quantum Hall states. We also show that all the ground states labeled by a tiling have a finite correlation length, for which we give an upper bound. We demonstrate by example, however, that not all superpositions of tiling states have exponential decay of correlations.

Smart Beta Allocation and Macroeconomic Variables: The Impact of COVID-19

Smart beta strategies across economic regimes seek to address inefficiencies created by market-based indices, thereby enhancing portfolio returns above traditional benchmarks. Our goal is to develop a strategy for re-hedging smart beta portfolios that shows the connection between multi-factor strategies and macroeconomic variables. This is done, first, by analyzing finite correlations between the portfolio weights and macroeconomic variables and, more remarkably, by defining an investment tilting variable. The latter is analyzed with a discriminant analysis approach with a twofold application. The first is the selection of the crucial re-hedging thresholds which generate a strong connection between factors and macroeconomic variables. The second is forecasting portfolio dynamics (gain and loss). The capability of forecasting is even more evident in the COVID-19 period. Analysis is carried out on the iShares US exchange traded fund (ETF) market using monthly data in the period December 2013–May 2020, thereby highlighting the impact of COVID-19.

A gauge invariant order parameter for monopole condensation in QCD vacuum

In this paper we improve the existing order parameter for monopole condensation in gauge theory vacuum, making it gauge-invariant from scratch and free of the spurious infrared problems which plagued the old one. Computing the new parameter on the lattice will unambiguously detect weather dual superconductivity is the mechanism for color confinement.As a byproduct we relate confinement to the existence of a finite correlation length in the gauge-invariant correlator of chromo-electric field strengths.

Non-Markovian dynamics of a two-level system in a bosonic bath and a Gaussian fluctuating environment with finite correlation time

The character of evolution of an open quantum system is often encoded in the correlation function of the environment or, equivalently, in the spectral density function of the interaction. When the environment is heterogeneous, e.g. consists of several independent subenvironments with different spectral functions, one of the subenvironments can be considered auxiliary and used to control decoherence of the open quantum system in the remaining part of the environment. The control can be realized, for example, by adjusting the character of interaction with the subenvironment via suitable parameters of its spectral density. We investigate non-Markovian evolution of a two-level system (qubit) under influence of three independent decoherence channels, two of them have classical nature and originate from interaction with a stochastic field, and the third is a quantum channel formed by interaction with a bosonic bath. By modifying spectral densities of the channels, we study their impact on steady states of the two-level system, evolution of its density matrix and the equilibrium emission spectrums. Additionally, we investigate the impact of the rotation-wave approximation applied to the bath channel on accuracy of the results.

Theoretical studies of dense hydrogen-like plasmas with the unified description of linear screening

A unified framework for describing dense plasma screenings from warm dense matter to hot dense matter, including gradient correction and exchange-correlation, has been recently proposed by Stanton and Murillo [Phys. Rev. E 91,033104 (2015)]. With this unified description of linear screening, the energy levels, absorption oscillator strengths, and radiative transition probabilities of hydrogen-like plasmas are reported for a wide range of critical screening parameters (plasma temperatures and densities), where the bound level nl merges into continuum. The importance of both finite temperature gradient correction and exchange correlation increases with the increasing plasma coupling strength or the Coulomb coupling parameter Γ, and the effect of exchange correlation is generally greater than that of finite temperature gradient correction. Further results from the weakly coupled and strongly coupled limits or Debye plasmas and dense quantum plasmas also show consistency with those from the unified framework, respectively.

Ultrabosonic behavior in photoexcited one-dimensional Mott insulators in the region of weak intersite Coulomb interaction

This paper reports a unique behavior expected for the optical excitations in one-dimensional Mott insulators. When the intersite Coulombic attraction does not work between two elementary charge excitations, i.e., a doublon and a holon, the lowest optical excitations are described as an unbound pair of them, still having finite mutual correlation due to the forbidden double occupancy on the same site. We find that, in such a situation, the pairs obey a particle statistics that exceeds that of ordinary bosons. This feature appears most directly in the enhancement factor of the matrix element for the pair photocreation. We discuss the possible mechanism for this ultrabosonic behavior and also demonstrate that this behavior is maintained even if we include a small amount of interiste Coulomibic interaction. Lastly, this enhancement factor almost coincides with that for ordinary bosons when the degree of the intersite interaction exceeds a certain value that switches on the formation of a bound doublon-holon pair.

Spin polarization recovery and Hanle effect for charge carriers interacting with nuclear spins in semiconductors

We report on theoretical and experimental study of the spin polarization recovery and Hanle effect for the charge carriers interacting with the fluctuating nuclear spins in the semiconductor structures. We start the theoretical description from the simplest model of static and isotropic nuclear spin fluctuations. Then we describe the modification of the polarization recovery and Hanle curves due to the anisotropy of the hyperfine interaction, finite nuclear spin correlation time, and the strong pulsed spin excitation. For the latter case, we describe the resonance spin amplification effect in the Faraday geometry and discuss the manifestations of the quantum Zeno effect. The set of the experimental results for various structures and experimental conditions is chosen to highlight the specific effects predicted theoretically. We show that the spin polarization recovery is a very valuable tool for addressing carrier spin dynamics in semiconductors and their nanostructures.

Bond-Alternation-Induced Topological Quantum Gaussian Transition and Topological Quantum Crossover in Ising Chains with the Dzyaloshinskii-Moriya Interaction

Non-local orders, entanglement entropy, and quantum fidelity are investigated in an infinite-size bond-alternating Ising chain with the Dzyaloshinskii-Moriya interaction by employing the infinite matrix product state representation with the infinite time evolving block decimation method. Directly computing two distinct types of finite string correlations for very large lattice distances, in contrast to an extrapolated extreme value for finite size chains, reveals two topologically ordered phases. As the bond alternation varies, a topological quantum phase transition with continuously variable critical exponents along the phase boundary occurs between the two Haldane phases for a Dzyaloshinskii-Moriya interaction stronger than the Ising interaction while a topological quantum crossover between them happens through an intermediate antiferromagentic phase demonstrated with the quantum fidelity for a Dzyaloshinskii-Moriya interaction weaker than the Ising interaction. The critical exponents of the order parameters and the central charges from the entanglement entropy quantify the universality classes of the phase transition points. Anisotropic Heisenberg types of spin chains with bond alternations are finally discussed to share the same criticality.

Assessment of Notch Effect Based on Finite Element Analysis and Digital Image Correlation Technique

Triaxial state of stress experienced by structural components due to complex geometry, discontinuities, or type of loading can be studied by tensile testing of notched specimens. Herein, assessment of tensile deformation of 316LN austenitic stainless under the uniaxial and triaxial stresses is presented based on finite element (FE) analysis and digital image correlation (DIC). To study their effects, notches of different root radii are incorporated in flat smooth specimens. The strength of the material increases in the presence of notch. Among the various constitutive expressions, the Swift equation provides a better representation of the tensile response for the smooth specimen. The analysis is further extended by incorporating Swift equation parameters as the deformation model in the FE analysis for notched specimens. The tensile response of the notched specimens is predicted well using the FE analysis. The in‐house algorithm is developed for DIC and used to estimate the strain in smooth and notched specimens by speckle‐pattern image analysis. The total displacement of smooth and notched specimens obtained from the FE analysis and DIC technique is comparable to the experimental results. Both the techniques complemented each other in understanding the deformation behavior of the steel.

Lightning Interferometry Uncertainty, Beam Steering Interferometry, and Evidence of Lightning Being Ignited by a Cosmic Ray Shower

AbstractWe present an uncertainty analysis on correlation‐based time delay estimate, the basis for broadband lightning interferometry. A normal interferometry would yield much higher uncertainties than the theoretically predicted lower bound due to finite correlation window lengths. However, if the signals are aligned in time, the uncertainties approach the lower bound and can be used to indicate the interferometric uncertainties. Based on this, we introduce a beam steering interferometry technique. It first estimates a direction centroid for the lightning sources with a normal interferometry and computes the time delays among the signals. It then shifts the raw data with the time delays to align the signals roughly in time and reprocess the aligned signals. It finally pushes the reprocessed results to their correct positions, based on the time delays estimated in the first step. We apply this technique on a fast positive breakdown (FPB) process that started a normal intracloud lightning. The FPB process is shown to have a much more complex structure and development than a normal interferometry would provide. More importantly, from both interferometric and polarization analyses, the FPB appears to be ignited by a cosmic ray shower (CRS). We estimate the radio frequency strength and frequency content related to a presumed CRS in a thunderstorm electric field and find that they are in agreement with the observations. We examine the electric field effect of the CRS front and find that it could raise the field above the threshold for positive breakdown and is capable of igniting the FPB (and the lightning).

Spatio-temporal dynamics of jerky flow in high-entropy alloy at extremely low temperature

ABSTRACT Despite a large body of literature, mechanisms contributing to low temperature jerky flow remain controversial. Here, we report a cross-over from a smooth at room and liquid nitrogen temperatures to serrated plastic flow at 4.2 K in high-entropy CrMnFeCoNi alloy. Several complimentary investigations have been carried out to get a coherent physical picture of low temperature jerky flow in these alloys. Microstructural characterisations at 77 K and 4.2 K show that the number of Lomer-Cottrell (L-C) locks at 4.2 K is much higher than that at 77 K, inducing stronger barriers for dislocation glide at 4.2 K. A stability analysis shows that the jerky flow results from an interaction between dislocation inertial motion with L-C locks. The instability results from a competition between inertial and viscous time scales characterised by a Deborah number. A detailed nonlinear time series analysis of experimental serrated stress signals shows that jerky flow is chaotic characterised by the existence of a finite correlation dimension and a positive Lyapunov exponent. Further, the minimum degree of freedom required for the chaotic dynamics turns out to be four, consistent with four collective modes degrees of freedom used in our model equations. These results highlight the crucial ingredients for jerky flow at liquid helium temperatures.

Modeling and analysis of thin-walled Al/steel explosion welded transition joints for shipbuilding applications

The study presents an analysis of S355J2+N steel and AA5083 aluminum alloy welded structural joints using explosion welded transition joints of reduced thickness. The transition joint thickness reduction significantly hinders the welding of the joints due to the risk of damage to the Al/steel interface as a result of the high temperatures during welding. Numerical modeling of the welding process is performed to determine safe welding parameters for the transition joint. The numerical analysis is supported by measurements of the temperature areas by a thermographic method. Welded structural joints are analyzed to determine the welding influence on the mechanical properties and microstructure of the transition joints. On this basis, a number of tests are carried out, including microhardness distribution measurements, strength tests of joints in two welding configurations and strength tests of the microspecimens of transition joints. Moreover, an experimental and numerical analysis of strain and stress distributions is carried out in combination with the use of the finite element method and digital image correlation, which allow us to identify the critical areas of the joints with regards to their strength. The results of the microstructural and strength tests carried out using macro- and microspecimens show softening of the aluminum alloy layers. However, the AA5083 and AA1050 layer softening as a result of welding did not reduce the load capacity of the transition joints, which could determine the strength of the dissimilar Al/steel welded structural joints.

Comparison of femur strain under different loading scenarios: Experimental testing.

Bone fracture, formation and adaptation are related to mechanical strains in bone. Assessing bone stiffness and strain distribution under different loading conditions may help predict diseases and improve surgical results by determining the best conditions for long-term functioning of bone-implant systems. In this study, an experimentally wide range of loading conditions (56) was used to cover the directional range spanned by the hip joint force. Loads for different stance configurations were applied to composite femurs and assessed in a material testing machine. The experimental analysis provides a better understanding of the influence of the bone inclination angle in the frontal and sagittal planes on strain distribution and stiffness. The results show that the surface strain magnitude and stiffness vary significantly under different loading conditions. For the axial compression, maximal bending is observed at the mid-shaft, and bone stiffness is also maximal. The increased inclination leads to decreased stiffness and increased magnitude of maximum strain at the distal end of the femur. For comparative analysis of results, a three-dimensional, finite element model of the femur was used. To validate the finite element model, strain gauges and digital image correlation system were employed. During validation of the model, regression analysis indicated robust agreement between the measured and predicted strains, with high correlation coefficient and low root-mean-square error of the estimate. The results of stiffnesses obtained from multi-loading conditions experiments were qualitatively compared with results obtained from a finite element analysis of the validated model of femur with the same multi-loading conditions. When the obtained numerical results are qualitatively compared with experimental ones, similarities can be noted. The developed finite element model of femur may be used as a promising tool to estimate proximal femur strength and identify the best conditions for long-term functioning of the bone-implant system in future study.

29‐4: Edge Strength Measurement of Free‐form Displays

The Edge Strength Measurement System (ESMS) is proposed as method for measuring the edge strength of free‐form displays. Its feasibility on free‐form monolithic glass samples with varying radius of curvatures is demonstrated. Finite element modeling and digital image correlation are performed to determine the load‐to‐stress correlation and understand the measurement sensitivity. ESMS can provide full edge testing which can help detect weak flaws and improve product reliability of free‐form displays.

Bioinspired multilayered cellular composites with enhanced energy absorption and shape recovery

Inspired by the multiscale configuration of the microstructure of cork, the paper describes the design, 3D printing, and evaluation of a new type of multilayered cellular composite (MCC) structure composed of hard brittle and soft flexible phases. The mechanical behavior of 3D printed MCC structures have been investigated both experimentally and numerically. The experiments show that the MCC structure absorbs four times the amount of energy of a conventional cellular configuration under compressive strains up to 70 %. Finite element simulations and 2D digital image correlation (DIC) also show that the multilayered architecture provides a more uniform strain distribution and higher stress transfer efficiency, with a resulting progressive failure mode rather than a catastrophic one. Cyclic loading tests demonstrate that the MCC structure also possesses exceptional shape recoverability under compressive deformations up to 40 %. These remarkable performance characteristics result from synergies between the properties of the two constituent materials and the chosen multilayered cellular microstructure. The soft phase, in particular, plays a pivotal role in absorbing elastic energy during loading and then releasing the stored energy while unloading. The volume fraction of the soft phase is also essential to control energy absorption and the transition of failure modes. The deformation mechanisms demonstrated here are robust and applicable to other architected cellular materials across multiple length scales and suggest new ways to design lightweight and high-resilience structural materials.