Prediction on hot deformation behavior of spray-formed 7055 aluminum alloy via phenomenological models

Hot compression tests in the temperature range of 340-450 ℃ and strain rate range of 0.001-1 s^-1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological models including Johnson-Cook, modified Fields-Backofen and Arrhenius-type were introduced to predict the flow stresses during the compression process. And then, a comparative predictability of the phenomenological models was estimated in terms of the relative errors, correlation coefficient（R）, and average absolute relative error（AARE）. The results indicate that Johnson-Cook model and modified Fields-Backofen model cannot well predict the hot deformation behavior due to the large deviation in the process of line regression fitting. Arrhenius-type model obtains the best fit through combining the effect of strain rate and temperature.

Phenomenological Models of the Global Demographic Dynamics and Their Usage for Forecasting in 21st Century

A great discovery made by H. von Foerster, P. M. Mora and L. W. Amiot was published in a 1960 issue of “Science”. The authors showed that existing data for calculating the Earth’s population in the new era (from 1 to 1958) could be described with incredibly high proximity by a hyperbolic function with the point of singularity on 13 November 2026. Thus, empirical regularity of the rise of the human population was established, which was marked by explosive demographic growth in the 20th century when during only one century it almost quadrupled: from 1.656 billion in 1900 to 6.144 billion in 2000. Nowadays, the world population has already overcome 7.8 billion people. Immediately after 1960, an active search for phenomenological models began to explain the mechanism of the hyperbolic population growth and the following demographic transition designed to stabilize its population. A significant role in explaining the mechanism of the hyperbolic growth of the world population was played by S. Kuznets (1960) and E. Boserup (1965), who found out that the rates of technological progress historically increased in proportion to the Earth’s population. It meant that the growth of the population led to raising the level of life-supporting technologies, and the latter in its turn enlarged the carrying capacity of the Earth, making it possible for the world population to expand. Proceeding from the information imperative, we have developed the model of the demographic dynamics for the 21st century for the first time. The model shows that with the development and spread of Intelligent Machines (IM), the number of the world population reaching a certain maximum will then irreversibly decline. Human depopulation will largely touch upon the most developed countries, where IM is used intensively nowadays. Until a certain moment in time, this depopulation in developed countries will be compensated by the explosive growth of the population in African countries located south of the Sahara. Calculations in our model reveal that the peak of the human population of 8.52 billion people will be reached in 2050, then it will irreversibly go down to 7.9 billion people by 2100, if developed countries do not take timely effective measures to overcome the process of information depopulation.

A phenomenological model for plastic flow behavior of rotating band material with a large temperature range

The plastic flow behavior of the rotating band material is investigated in this paper. The rotating band material is processed from H96 brass alloy, which is hardened to a much higher yield strength compared to the annealed one. The dynamically uniaxial compression behavior of the material is tested using the split Hopkinson pressure bar(SHPB) with temperature and strain rate ranging from 297 to 1073 K and500 to 3000 s^(-1), respectively, and a phenomenological plastic flow stress model is developed to describe the mechanical behavior of the material. The material is found to present noticeable temperature sensitivity and weak strain-rate sensitivity. The construction of the plastic flow stress model has two steps. Firstly, three univariate stress functions, taking plastic strain, plastic strain rate and temperature as independent variable, respectively, are proposed by fixing the other two variables. Then, as the three univariate functions describe the special cases of flow stress behavior under various conditions, the principle of stress compatibility is adopted to obtain the complete flow stress function. The numerical results show that the proposed plastic flow stress model is more suitable for the rotating band material than the existing well-known models.

A comparative study of 85 hyperelastic constitutive models for both unfilled rubber and highly filled rubber nanocomposite material

Nonlinear finite element analysis is widely used for structural optimization of the design and the reliability analysis of complex elastomeric components.However,high-precision numerical results cannot be achieved without reliable strain energy functions(SEFs)of the rubber or rubber nanocomposite material.Although hyperelastic constitutive models have been studied for nearly 80 years,selecting one that accurately describes rubber's mechanical response is still a challenge.This work reviews 85 isotropic SEFs based on both the phenomenological theory and the micromechanical network theory proposed from the 1940s to 2019.A fitting algorithm which can realize the automatic fitting optimization and determination of the parameters of all SEFs reviewed is developed.The ability of each SEF to reproduce the experimental data of both the unfilled and highly filled rubber nanocomposite is quantitatively assessed based on a new proposed evaluation index.The top 30 SEFs for the unfilled rubber and the top 14 SEFs for the highly filled rubber nanocomposite are presented in the ranking lists.Finally,some suggestions on how to select an appropriate hyperelastic constitutive model are given,and the perspective on the future progress of constitutive models is summarized.

Phenomenological Anisotropic Study of Surface Finish in Pack Rolling

A phenomenological anisotropic model has been presented for the surface roughness modeling of pack rolling. The model is an assembly of grains in different orientations and sizes. The grain size is assumed to be in log-normal distribution. To model the macro anisotropic mechanical behavior of the grains induced by the slip deformation, the grains are assumed as isolated anisotropic units. The units have different mechanic behavior, and depend on the crystallographic orientations and the external loading as well as the interaction of the adjunctive grains. In the paper, the material properties of the grains are assumed as uniform distributions. The roughness of the contact surfaces depends on the distribution types and the scatters of the distributions. It is found that the initial roughness of the contact surfaces has a little influence on the surface roughness when the rolling deformation is large. The comparison between the phenomenological model and crystallographic model shows that the phenomenological model can also give out a reasonable result, while it only takes much less CPU time. The agreement between the single sheet model and the pack rolling model shows that in a certain degree the pack rolling model can be replaced by the single sheet model to decrease the CPU time.

Effect of curing, capillary action, and groundwater level increment on geotechnical properties of lime concrete: Experimental and prediction studies

Lime concrete and lime treatment are two attractive techniques for geotechnical engineers.However,researches have rarely been carried out to study the effects of moisture and capillary action due to increasing groundwater level on geotechnical properties of lime concrete.The aim of this study is to investigate the effects of curing time and degree of saturation on some of geotechnical properties of lime concrete such as unconfined compressive strength(UCS),secant modulus(ES),failure strain,brittleness index(IB),and deformability index(ID) using unconfined compression tests.First of all,geotechnical and chemical properties of used materials were determined.After curing times of 14 d,28 d,45 d,and 60 d in laboratory condition,the specimens were exposed to saturation levels ranging from 0 to 100%.The results showed that the moisture and curing time have significant effects on the properties of lime concrete.Based on the results of scanning electron micrograph(SEM) test,it was observed that the specimen was characterized by a rather well-structured matrix since both the filling of a large proportion of the coarse-grained soil voids by clay and the pozzolanic activity of lime led to retaining less pore water in the specimen,increasing the UCS and ES,and consequently resisting against swelling and shrinkage of the clay soil.Moreover,due to the pozzolanic reactions and reduction of water,by increasing the curing time and decreasing the degrees of saturation,UCS,ES,and IBincreased,and IDdecreased.Based on the experimental results,a phenomenological model was used to develop equations for predicting the properties in relation to the ratio of degree of saturation/curing time.The results showed that there was a good correlation(almost R2> 90%) between the measured parameters and the estimated ones given by the predicted equations.

Microstructure and mechanical properties of in-situ TiB_2/A356 composites and a prediction model of yield strength

The in-situ TiB2/A356 composites were successfully synthesized through the mixed salt reaction method. The advantage of this technique was that the particle sizes and morphology can be controlled by the melt reaction. Therefore, the technique can be designed to obtain expected properties, such as high strength at high and room temperatures, high damping capacity, high modulus and good fatigue life. Results showed that in the as-cast state of A356 alloy and TiB2/A356 composites, the eutectic Si phase is normally in the needle shape, and TiB2 particles are mostly in the cubic or near spherical shape, with the size ranging from 30 to 500 nm uniformly distributed in the grains. Also, TiB2 particle clusters are observed in composites. With an increase in TiB2 particles, the average grain size of composites decreases both in as-cast and T6 state. It is found that both the yield stength and ultimate tensile strength increase with an increase in the TiB2 volume fraction. On the contrary, the elongation reduces with the addition of TiB2 particles. Based on the experimental results and Clyne＇s report, a revised model related to particle strengthening mechanism was proposed to fairly predict yield strengths of TiBJA356 composites. The satisfactory agreement between the calculated values and experimental data reported in the literature was obtained.

Influence of Metal Material Properties on Heat and Mass Transfer into Thermal Protection Surface with Phenomenological Catalytic Model

Surface heterogeneous catalysis in a high-enthalpy dissociated environment leads to a remarkable enhancement of aerodynamic heating into the thermal protection surface of hypersonic aircraft.To more accurately predict this catalytic heating,a kinetic catalytic model was constructed.This model involved four elementary reactions,the rates of which were determined on mean-field approximation and surface steady-state reaction assumption.By coupling this model into the viscous wall boundary condition of computational fluid dynamics(CFD)solver,the influences of metal material catalytic properties on heat and mass transfer into thermal protection materials were numerically investigated.Numerical results showed that atomic oxygen recombination catalyzed by surface material accounts for a major contribution to aerodynamic heating and thus variation in recombination rates from different materials leads to the significant difference in surface heat fluxes.From a comparative analysis of various materials,the catalytic activity increases from the inert platinum(Pt)to nickel(Ni)and finally to the active copper(Cu).As a result,the catalytic heating on Cu surface was more than twice of that on Pt surface.Further parametrical research revealed that the proper layout of inert material at the nose of aircraft could prevent stagnation catalytic heating from thermal damage by carrying near-wall dissociated atoms from the stagnation zone downstream.The material-relied heterogeneous catalysis mechanism in this study provides some technical support for the thermal protection system design of hypersonic aircraft.

CHEMORHEOLOGY OF MODIFIED BISMALEINIDE RESIN SYSTEM

The chemorheology of bismaleimide (BMI) resin system comprised of 4,4'-bismaleimidodiphenyl-methane, 4,4'-diaminodiphenyl-methane, phenoltype epoxy resin, and carboxyl-terminated butadiene-acrylonitrile rubber was investigated. Thermal analysis techniques were employed to obtain Kinetic and network parameters which is necessary for the development of a phenomenological viscosity model based on a modified version of the Wiliams-Landel-Ferry (WLF) equation. The model predictions agreed well with experimental value of viscosity.

A minimal model for the auxetic response of liquid crystal elastomers

We develop a minimal phenomenological model to describe the auxetic response recently observed in liquid crystal elastomers, and further determine by theoretical calculation the critical condition required for the auxetic response to occur.

Phenomenological Based Soft Sensor for Online Estimation of Slurry Rheological Properties

This work proposes a soft sensor based on a phenomenological model for online estimation of the density and viscosity of a slurry flowing through a pipe-and-fittings assembly(PFA). The model is developed considering the conservation principle applied to mass and momentum transfer and considering frictional energy losses to include the variables directly affecting slurry properties. A reported proposal for state observers with unknown inputs is used to develop the first block of the observer structure. The second block is constructed with two options for evaluating slurry viscosity, generating two possible estimator structures, which are tested using real data. A comparison between them indicates different uses and capabilities according to available process information.

A novel phenomenological model using a sine function for finite-element simulation of large-strain hot deformation

In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.

Phenomenological model for torsional galloping of an elastic flat plate due to hydrodynamic loads

This study investigates the torsional galloping phenomenon, an instability type flow-induced oscillation, in an elastic stru-cture due to hydrodynamic loads into the water current. The structure applied here is a rectangular flat plate with an elastic axis in its mid-chord length. The elasticity is provided by torsion spring. The flat plate has only one degree of freedom which is rotation in pure yaw about its axis. It is observed that as the current speed is higher than a critical velocity, the flat plate becomes unstable. The instability leads to torsional galloping occurrence, as a result of which the flat plate begins to yaw about the elastic axis. By testing two different chord lengths each with several torsion spring rates, the flat plate behavior is investigated and three different responses are recognized. Then, a phenomenological model is developed with the original kernel in the form of the van der Pol-Duffing equa-tion. The model explains these three responses observed experimentally.

Theoretical Characterization of Indentation Depth-Dependent Creep Behavior of CoCrFeNiAl_(0.3) High-Entropy Alloy

The effects of indentation loading depth and dynamic pre-compression on the creep behavior of CoCrFeNiAl_(0.3) high-entropy alloy(HEA)were studied through a series of indentation creep tests.Results show that the creep displacement,creep stress exponent and creep strain rate are all sensitive to loading depth.A phenomenological model based on the holding time and loading depth was established by studying the characteristic relation between the loading depth and the creep displacement of CoCrFeNiAl_(0.3) HEA.The phenomenological model was used to analyze the creep behavior of the alloy under dynamic pre-compression(i.e.,dynamic compressive deformation caused by Hopkinson bar impact).

Real-time forecasts of the COVID-19 epidemic in China from February 5th to February 24th,2020

The initial cluster of severe pneumonia cases that triggered the COVID-19 epidemic was identified inWuhan,China in December 2019.While early cases of the disease were linked to a wet market,human-to-human transmission has driven the rapid spread of the virus throughout China.The Chinese government has implemented containment strategies of city-wide lockdowns,screening at airports and train stations,and isolation of suspected patients;however,the cumulative case count keeps growing every day.The ongoing outbreak presents a challenge for modelers,as limited data are available on the early growth trajectory,and the epidemiological characteristics of the novel coronavirus are yet to be fully elucidated.We use phenomenological models that have been validated during previous outbreaks to generate and assess short-term forecasts of the cumulative number of confirmed reported cases in Hubei province,the epicenter of the epidemic,and for the overall trajectory in China,excluding the province of Hubei.We collect daily reported cumulative confirmed cases for the 2019-nCoV outbreak for each Chinese province from the National Health Commission of China.Here,we provide 5,10,and 15 day forecasts for five consecutive days,February 5th through February 9th,with quantified uncertainty based on a generalized logistic growth model,the Richards growth model,and a sub-epidemic wave model.Our most recent forecasts reported here,based on data up until February 9,2020,largely agree across the three models presented and suggest an average range of 7409e7496 additional confirmed cases in Hubei and 1128e1929 additional cases in other provinces within the next five days.Models also predict an average total cumulative case count between 37,415 and 38,028 in Hubei and 11,588e13,499 in other provinces by February 24,2020.Mean estimates and uncertainty bounds for both Hubei and other provinces have remained relatively stable in the last three reporting dates(February 7th e 9th).We also observe that each of the models predicts that the epidemic has reached saturation in both Hubei and other provinces.Our findings suggest that the containment strategies implemented in China are successfully reducing transmission and that the epidemic growth has slowed in recent days.

Estimating epidemic exponential growth rate and basic reproduction number

The initial exponential growth rate of an epidemic is an important measure of the severeness of the epidemic,and is also closely related to the basic reproduction number.Estimating the growth rate from the epidemic curve can be a challenge,because of its decays with time.For fast epidemics,the estimation is subject to over-fitting due to the limited number of data points available,which also limits our choice of models for the epidemic curve.We discuss the estimation of the growth rate using maximum likelihood method and simple models.

A data-driven approach to π^0,η and η＇ single and double Dalitz decays

The dilepton invariant mass spectra and integrated branching ratios of the single and double Dalitz decays P→l^＋l^-γ and P→l^＋l^-l^＋l^-（P=π^0,η,η＇;l=e or μ） are predicted by means of a data-driven approach based on the use of rational approximants applied to π^0,η and η＇ transition form factor experimental data in the space-like region.

Pair Production of the Doubly Charged Leptons Associated with a Gauge Boson γ or Z in e^+e^-and γγ Collisions at Future Linear Colliders

In this paper,we investigate the production of a pair of doubly charged leptons associated with a gauge boson V(γ or Z) at future linear colliders via e^+e^-and γγ collisions.The numerical results show that the possible signals of the doubly charged leptons may be detected via the processes e^+e~→VX^(++)X^(--)and γγ→VX^(++)X^(--)at future ILC or CLIC experiments.

Helium-3 global optical model potential with energies below 250 MeV

A new set of global phenomenological optical model potential parameters has been obtained for helium-3 projectile, by simultaneously fitting the experimental data of helium-3 total reaction cross sections and elastic scattering angular distributions in the mass range of target nuclei 20〈〈A〈209 at incident energies below 250 MeV. A comparison has been made between the extracted helium-3 global optical model potential parameters and the existing ones. The calculated results of total reaction cross sections and elastic scattering angular distributions are also agreement. compared with experimental data with their satisfactory

Physics of ferroelectric differential capacitance based upon free energy, and implications for use in electronic devices

In this paper,it is shown that for stable,steady state operation of devices typical of microwave and millimeter wave electronics,no negative differential capacitance is possible with conventional thinking.However,it may be possible,with strain engineering of materials,to obtain some if not all elements of the differential capacitance tensor which are negative.Rigorous derivations are provided based upon analyzing the physics using thermodynamic phenomenological free energy.It should be emphasized that,even with strain engineering,and possible discovery of some negative capacitive elements,stable operation will not be obtained because the thermodynamics precludes it.