Static Relaxation Research Articles

Parameter Optimization for Laser Peen Forming on 6005A-T6 Aluminum Alloy Plates to Enhance the Constrained Deformation of Integral Stiffened Plates.

Multiscale parameter optimization for laser peen forming (LPF) on 6005A-T6 aluminum alloy plates was conducted through a combination of simulation and experimentation. By obtaining the optimal parameter, this study aims to explore the constrained deformation and forming laws of the integral stiffened plates. Detailed descriptions were provided regarding the dynamic response process and transient behavior of aluminum alloy plates under ultrahigh strain rates, along with an in-depth analysis of the stress evolution. The results reveal that laser beam diameter and laser beam energy can achieve large range forming, while the number of tracks facilitates the precise deformation adjustment. During the 12-track LPF process, there is an overall upward trend in deformation values accompanied by a dynamic increase in the bend curvature. After static relaxation, the deformation value recovers to 55.2% of the final bending curvature. The chord direction scanning of stiffened plates exhibits a larger bending curvature, indicating its greater forming capacity for large-sized single unfolding direction formation; whereas, the unfolding direction scanning of stiffened plates excels in achieving efficient integrated two-way forming.

Temperature-dependent dielectric relaxation studies of malononitrile from 10 MHz to 30 GHz using time domain reflectometry technique

Dielectric relaxation investigations of malononitrile have been carried out at different temperatures in the frequency range of 10 MHz–30 GHz using a time domain reflectometry technique. The static dielectric constant (ε0) and relaxation time (τ), and asymmetric distribution parameter (β) of liquid malononitrile at different temperatures have been determined using the Least Squares Fit method. The intermolecular hydrogen bonding in malononitrile has also been discussed with the use of the Kirkwood correlation factor and dielectric relaxation parameters.

Dielectric characterisation and intermolecular interactions in propionitrile-dimethyl sulphoxide mixtures using a time domain reflectometry

ABSTRACT Complex permittivity spectra of propionitrile (PN) – dimethyl sulphoxide (DMSO) mixtures in the 10 MHz–30 GHz frequency range were investigated using time-domain reflectometry (TDR). The Debye model was employed to fit the measured dielectric spectra, allowing for the calculation of dielectric parameters like the static dielectric constant (ε 0 ) and relaxation time (τ). Excess dielectric constant (ε 0 E ) and excess inverse relaxation time (1/τ) E were subsequently calculated from the measured ε 0 and τ. The observed variations in these excess parameters provide evidence for intermolecular interactions within the PN-DMSO mixtures. Theoretical estimates of the ε 0 were obtained using Luzar’s hydrogen-bonded model.

Molecular interaction between thiamine hydrochloride-DMSO binary mixture: a TDR spectroscopic approach

ABSTRACT The dielectric measurements of thiamine hydrochloride (vitamin B1 hydrochloride) and dimethyl sulphoxide (DMSO) binary mixtures have been carried out in the frequency range of 10 MHz to 50 GHz at 25°C, 20°C and 15°C using the TDR technique. The dielectric parameters such as complex dielectric permittivity ɛ*(ω), static dielectric permittivity (ɛs), relaxation time (τ), and asymmetric distribution parameter (β) are obtained by using Cole-Davidson model. These parameters are used to compute thermodynamic properties, Kirkwood correlation factor (geff), and excess molar volume (VE). The heteromolecular H-bonding existing in the binary mixture is explained.

H-bonding interaction study for binary mixtures of methyl cellosolve and ethanol: a dielectric, FTIR spectroscopic and volumetric approach

The dielectric measurement of neat ethylene glycol monomethyl ether (EGMME), neat ethanol and their binary mixtures have been carried out using time domain technique in frequency range of 10 MHz to 50 GHz at the temperature range from 10 °C to 25 °C with a difference of 5 °C. The frequency domain technique within the frequency range of 20 Hz to 2 MHz is used to obtain complex dielectric permittivity ε*(ω), electrical modulus M*(ω), complex electrical conductivity σ*(ω) and loss tangent (tan δ) at 25 °C. The dielectric spectra obtained using TDR technique are fitted in Cole-Davidson model to extract the dielectric parameters such as static dielectric permittivity (ε s), relaxation time (τ) and asymmetric distribution parameter (β). These relaxation parameter values are used to predict intermolecular hydrogen bonding between EGMME and ethanol molecules. Furthermore, the inter-molecular interactions through H-bonding between EGMME and ethanol molecules have been confirmed and discussed using Kirkwood correlation factor, excess permittivity, thermodynamic parameter, Bruggeman factor, excess molar volume, excess dielectric permittivity at high frequency and Fourier transform infrared (FTIR) spectra.

Thermodynamics Properties of Amino Acid with Water Mixture using Time Domain Reflectometry Technique

In this paper we have reported the thermodynamics properties of the amino acids (L-alanine) in water solution were carried out using time domain reflectometry at 250C to -50C in the frequency range between 10 MHz to 30 GHz. The dielectric parameters i.e. static dielectric constant and relaxation time, were obtained from the complex permittivity spectra using a nonlinear least square fit method. From the values of the relaxation time, the thermodynamic parameters are determined. The dielectric relaxation parameters increase with an increase in concentration (mM) of amino acid due to the structure of hydrogen bond groups by the amino acid molecules in the aqueous solution. The relaxation peak shifted to lower frequency with an increase in molar concentration of amino acid.

Thermodynamic hydration behaviour of glycine below room conditions using time domain reflectometry

The present work reports the concentration-dependent hydrophobicity of glycine below room temperature. The dynamics of aqueous glycine have been studied by means of dielectric relaxation spectroscopy using Time Domain Reflectometry (TDR) technique in the frequency region of 10 MHz–30 GHz. Complex permittivity spectra are obtained using TDR that allowed evaluation of the static dielectric constant (ε0) and average relaxation time (τ). As dielectric relaxation spectroscopy provides information on the average relaxation time (τ) related to the mechanism of hydrogen bond (HB) formation and breaking, therefore the concentration-temperature dependence of τ was used to evaluate and study hydration behaviour through dielectric parameters such as dipole moment (μ), correlation factor (g), and the dynamics of irrationally bound water molecules (Zib). Aqueous glycine relaxes in two different relaxation modes in the broad microwave frequency region from MHz to GHz. The low-frequency relaxation process (l-process) observed is associated with glycine relaxation, while the detected peak in the high-frequency relaxation process (h-process) is attributed to water associated with glycine. We have attempted a concentration-temperature-dependent hydrogen bonding mechanism in both relaxation processes, and the results were corroborated with thermodynamical parameters such as molar entropy of activation (∆Sj), molar enthalpy of activation (∆Hj), and molar free energy of activation (∆Fj).

Dielectric relaxation and hydrogen bonding interactions study of aqueous D-sorbitol using time domain reflectometry

ABSTRACT Complex permittivity spectra for D-sorbitol-water mixtures in the frequency range 10 MHz to 30 GHz have been determined over the entire concentration range using a time domain reflectometry (TDR) method. The complex permittivity spectra have been fitted to the Cole-Davidson relaxation model. The static dielectric constant and relaxation time were calculated from the complex permittivity spectra using the nonlinear least square fit method. The Kirkwood correlation factors were calculated. The theoretical dielectric constant for the mixtures has been calculated using the hydrogen bonding model suggested by Alenka Luzar.

Meta-Dynamic Recrystallization in the Ni-Based Superalloy Haynes 282

Forging on an industrial scale often involves slow, size-limited cooling rates or high temperature hold times between, or after, deformation. This enables the dynamic recrystallization (DRX) initiated during forging to further progress under static conditions, a phenomenon called meta-dynamic recrystallization (mDRX). As mDRX will influence the final grain size, and thus properties, it is critical to understand and control it during processing. Here, we study the mDRX evolution in Ni-based superalloy Haynes 282 during post-deformation hold times of up to 120 s at 1080 °C after partial DRX. We find that mDRX is the dominating mechanisms responsible for the microstructure evolution the hold time. The very rapid mDRX kinetics in the initial stages suggest that quench delays (the time between the end of the deformation and the onset of the quenching intended to arrest the microstructure evolution) must be kept well below 1 s in order to allow reliable conclusions to be drawn from post-deformation microstructure investigations. A larger prior strain (larger DRX fraction) leads to faster mDRX kinetics and a larger final grain size. Larger strains leads to earlier impingement of the growing grains, which, in combination with smaller remaining deformed regions into which the grains can grow, limits the maximum size of the mDRX grains. We also note a close correlation between static recovery and stress relaxation during the hold time, whereas no such correlation between mDRX and stress relaxation can be observed.

Dielectric relaxation and hydrogen bonding studies of chlorobutane-dioxane mixtures using a time domain technique

Complex permittivity spectra have been computed for the binary mixtures of Chlorobutane (CLB) with 1, 4-Dioxane (DX) using Time Domain Reflectometry (TDR) for different concentrations and temperatures in the frequency range from 10 MHz to 30 GHz. The static dielectric permittivity and relaxation time have been obtained by fitting complex permittivity spectra to the Debye relaxation using least squares fit method. The Kirkwood correlation factor have been determined at various concentrations of 1, 4-dioxane. The Bruggeman model for the non-linear case has been fitted to the dielectric data for the mixtures.

Static investigation of martensitic nucleation criticality in an atomistic model material

ABSTRACT This contribution investigates the nucleation of martensitic transformations in the bulk of austenitic single crystals. The transformation is associated with a decrease in the potential energy that is the driving force for the transformation. The coordinated atom displacements, which generate the martensite, produce large elastic strains in the material, which are associated with an elastic energy that opposes the transformation. A thermodynamic nucleation criterion for this type of transformations is derived. The criterion is evaluated by the method of static lattice relaxation for homogeneous nucleation in an atomistic 2D model material. The potential energy of martensitic clusters of different sizes and shapes, embedded in a stabilised austenitic matrix are calculated. The results exhibit non-monotonous progressions of the potential energy with the cluster size. This indicates that the elastic strain energy scales non-linearly with the size to allow the formation of local energy maxima at critical cluster sizes, interpreted as nucleation barriers. These barriers separate domains of stability from domains of instability in the configurations space, similar to Kelvin's classical theory of spherical fluid phase nucleation. The critical nuclei sizes are in the order of 100–150 unit cells, and their shapes are plate-like with long dimension parallel to the shear direction. The critical size of twinned clusters decreases with the twinning multiplicity.

Prominent β-relaxation and stress relaxation decoupling phenomenon in Gd-Ni-Al metallic glasses

GdxNi20Al80−x (x = 50, 60, 65, 70 at%) metallic glasses (MGs) with prominent β-relaxation were developed, which provide a new model system for studying some controversial issues concerning β-relaxation. The relaxation behavior and thermal stability of GdxNi20Al80−x MGs were probed by dynamic mechanical relaxation, static stress relaxation, and differential scanning calorimetry. In view of the temperature and frequency dependence of the dynamic mechanical relaxation spectrum, we investigated the β-relaxation and α-relaxation separation phenomena of Gd50Ni20Al30 and Gd60Ni20Al20 MGs. With increasing Gd/Al ratio, the activation energy of the β-relaxation decreased, which was conducive to the flow units and prominent β-relaxation. The Gd70Ni20Al10 alloy had the most significant β-relaxation phenomenon, although some nanocrystalline Gd3Ni phase was distributed in the amorphous matrix. The Gd50Ni20Al30 glass had a crystallization activation energy of 476 kJ/mol, corresponding to the highest thermal stability. At a constant strain, the static stress relaxation process of the Gd70Ni20Al10 alloy was analyzed over a wide time window and temperature range. A decoupling phenomenon of the relaxation into a two-step process occurred in the Gd70Ni20Al10 alloy, namely, a fast relaxation process and a slow relaxation process, at different time scales. Analysis of the relaxation dynamics and time scales of the relaxation confirmed that the fast relaxation process differed from the β-relaxation process. This study elucidates the β-relaxation behavior and stress relaxation decoupling phenomenon in Gd-Ni-Al MGs and should, therefore, help clarify the mechanical relaxation behavior and intrinsic characteristics of MGs in future work.

Molecular interactions studies of methyl cellulose-water solutions using dielectric spectroscopy

ABSTRACT Time Domain Reflectometry (TDR) and frequency domain techniques have been used for the dielectric measurement of methyl cellulose (MC) with water for different concentrations and frequency ranges from 20 Hz to 2 MHz and 10 MHz to 30 GHz at 25°C. The dielectric relaxation in these mixtures can be represented by the Debye relaxation behaviour. The dielectric parameters such as complex permittivity ε*(ω), complex electrical modulus M*(ω), complex electrical conductivity σ*(ω), loss tangent (tan δ), static dielectric constant (ε0) and relaxation time (τ) have been determined. The variation of dielectric parameters of methyl cellulose (MC) in water suggested that methyl cellulose (MC) bonds with water alter its structure and electric dipole moment.

Effect of Carbon Nanofibers on the Viscoelastic Response of Epoxy Resins.

Two epoxy resins with different viscosities were enhanced up to 1 wt.%, applying a simple method with carbon nanofibers (CNFs). These were characterized in terms of static bending stress, stress relaxation, and creep tests. In bending, the contents of 0.5 wt.% and 0.75 wt.% of CNFs on Ebalta and Sicomin epoxies, respectively, promote higher relative bending stress (above 11.5% for both) and elastic modulus (13.1% for Sicomin and 16.2% for Ebalta). This highest bending stress and modulus occurs for the lower viscosity resin (Ebalta) due to its interfacial strength and dispersibility of the fillers. Creep behaviour and stress relaxation for three stress levels (20, 50, and 80 MPa) show the benefits obtained with the addition of CNFs, which act as a network that contributes to the immobility of the polymer chains. A long-term experiment of up to 100 h was successfully applied to fit the Kohlrausch-Williams-Watts (KWW) and Findley models to stress relaxation and creep behaviour with very good accuracy.

Constructing Br-Doped Li 10 SnP 2 S 12 -Based All-Solid-State Batteries with Superior Performances

Ionic conductivity and electro/chemical compatibility of Li 10 SnP 2 S 12 electrolytes play crucial roles in achieving superior electrochemical performances of the corresponding solid-state batteries. However, the relatively low Li-ion conductivity and poor stability of Li 10 SnP 2 S 12 toward high-voltage layered oxide cathodes limit its applications. Here, a Br-substituted strategy has been applied to promote Li-ion conductivity. The optimal composition of Li 9.9 SnP 2 S 11.9 Br 0.1 delivers high conductivity up to 6.0 mS cm −1 . 7 Li static spin-lattice relaxation ( T 1 ) nuclear magnetic resonance (NMR) and density functional theory simulation are combined to unravel the improvement of Li-ion diffusion mechanism for the modified electrolytes. To mitigate the interfacial stability between the Li 9.9 SnP 2 S 11.9 Br 0.1 electrolyte and the bare LiNi 0.7 Co 0.1 Mn 0.2 O 2 cathode, introducing Li 2 ZrO 3 coating layer and Li 3 InCl 6 isolating layer strategies has been employed to fabricate all-solid-state lithium batteries with excellent electrochemical performances. The Li 3 InCl 6 -LiNi 0.7 Co 0.1 Mn 0.2 O 2 /Li 3 InCl 6 /Li 9.9 SnP 2 S 11.9 Br 0.1 /Li-In battery delivers much higher discharge capacities and fast capacity degradations at different charge/discharge C rates, while the Li 2 ZrO 3 @LiNi 0.7 Co 0.1 Mn 0.2 O 2 /Li 9.9 SnP 2 S 11.9 Br 0.1 /Li-In battery shows slightly lower discharge capacities at the same C rates and superior cycling performances. Multiple characterization methods are conducted to reveal the differences of battery performance. The poor electrochemical performance of the latter battery configuration is associated with the interfacial instability between the Li 3 InCl 6 electrolyte and the Li 9.9 SnP 2 S 11.9 Br 0.1 electrolyte. This work offers an effective strategy to constructing Li 10 SnP 2 S 12 -based all-solid-state lithium batteries with high capacities and superior cyclabilities.

Study of Dielectric Relaxation and Hydrogen Bonding Interaction of 1, 4-Butanediol-1, 4-Dioxane Mixture using TDR Technique

The complex permittivity spectra of 1, 4-butanediol -1, 4-dioxane binary mixtures have been measured in the frequency range from 10MHz to 30GHz using the time domain reflectometry (TDR) technique. The complex permittivity spectra show the Cole-Davidson type relaxation. The static dielectric constant and relaxation time at various temperatures have been obtained from complex permittivity spectra by using the nonlinear least squares fit method. The orientation of electric dipoles and solute-solvent interaction in the liquid mixture was confirmed from the excess, Bruggeman, Kirkwood correlation factor and thermodynamic parameters.

Dielectric Relaxation Studies of Cellulose-Water Mixtures Using Time and Frequency Domain Technique

The complex dielectric permittivity of hydroxypropyl methyl cellulose (HPMC)-water mixture was measured by using Time Domain Reflectometry (TDR) and Frequency Domain (LCR) Technique at 25 o C. The complex dielectric permittivity e*(w), complex electrical modulus M*(w), complex electrical conductivity s*(w), loss tangent (tan d), static dielectric constant (ε 0 ) and relaxation time (τ) have been determined for the cellulose-water system.

Temperature Dependent Dielectric Relaxation Studies of 2-Nitrotoluene-DMSO mixture using Time Domain Relectometry from 10MHz to 50GHz

The dielectric relaxation properties of 2-Nitrotoluene (2-NT) with DMSO for 11 different concentrations has been studied in the frequency range from 10 MHz to 50 GHz using time domain reflectometry (TDR) method. In this frequency range Dielectric relaxation spectra of 2-NT-DMSO mixtures shows Debye type behavior. The temperature dependent static dielectric constant and relaxation time have been determined from 20oC to 5oC. Effective Kirkwood correlation factor is calculated to determine the effect of strong directional forces such as microwaves on heterogeneous molecules under different temperatures. The excess permittivity and excess inverse excess relaxation time is found to be negative for 2-NT-DMSO system with weak molecular interactions. The activation enthalpy have been calculated to find the energy required to rotate the molecules

Two-step Mott transition in Ni(S,Se)2 : μSR studies and charge-spin percolation model

A pyrite system ${\mathrm{NiS}}_{2\ensuremath{-}x}{\mathrm{Se}}_{x}$ exhibits a bandwidth controlled Mott transition via (S,Se) substitutions in a two-step process: the antiferromagnetic insulator (AFI) to antiferromagnetic metal (AFM) transition at $x\ensuremath{\sim}0.45$ followed by the AFM to paramagnetic metal (PMM) transition at $x\ensuremath{\sim}1.0$. Among a few other Mott systems which exhibit similar two-step transitions, $\mathrm{Ni}{(\mathrm{S},\mathrm{Se})}_{2}$ is of particular interest because a large intermediate AFM region in the phase diagram would provide unique opportunities to study the interplay between the spin and charge order. Muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$) measurements on ${\mathrm{NiS}}_{2\ensuremath{-}x}{\mathrm{Se}}_{x}$ have been carried out on seven different Se concentrations from $x=0$ to 1.0. The results on quantum evolution demonstrate significantly random spin correlations in the AFM region associated with a rapid reduction of the average local static Ni moment size with increasing $x$, yet without signatures of macroscopic phase separation as confirmed by nearly full volume fraction participating in the static muon relaxation process up to $x\ensuremath{\sim}$ 0.9 at low temperatures. The observed time spectra in the AFM region indicate Lorentzian distribution of static internal field expected for a spatially dilute spin structure. No signature of dynamic critical behavior was observed in thermal phase transitions. The previous neutron scattering studies found sharp magnetic Bragg peaks with a slower reduction of the average ordered moment size in the AFM region. By comparing and combining the muon and neutron results, here we propose a picture where the spin order is maintained by the percolation of ``nonmetallic'' localized and dangling Ni moments surrounded by S, while the charge transition from AFI to AFM is caused by the percolation of the conducting paths generated by the Ni-Se-Ni bonds. This model of interpenetrating charge and spin percolation captures the behavior of experimental results on (a) Se concentration for the insulator to metal transition, (b) Se concentration for the AFM to PMM transition, (c) variation of Hall effect in the AFM region due to conducting Ni charges on the backbone of the percolating charge network, (d) evolution of the neutron Bragg intensity, (e) evolution of the muon static local fields, and (f) spatial variation of the local conductance observed by STM.

Formation and relaxation of K-2 and K-2V double-core-hole states in n-butane.

Using a magnetic bottle multi-electron time-of-flight spectrometer in combination with synchrotron radiation, double-core-hole pre-edge and continuum states involving the K-shell of the carbon atoms in n-butane (n-C4H10) have been identified, where the ejected core electron(s) and the emitted Auger electrons from the decay of such states have been detected in coincidence. An assignment of the main observed spectral features is based on the results of multi-configurational self-consistent field (MCSCF) calculations for the excitation energies and static exchange (STEX) calculations for energies and intensities. MCSCF results have been analyzed in terms of static and dynamic electron relaxation as well as electron correlation contributions to double-core-hole state ionization potentials. The analysis of applicability of the STEX method, which implements the one-particle picture toward the complete basis set limit, is motivated by the fact that it scales well toward large species. We find that combining the MCSCF and STEX techniques is a viable approach to analyze double-core-hole spectra.