Dynamic Recovery Model Research Articles

A new dynamic optimisation model for operational supply chain recovery

This paper focuses on the problem of dynamic supply chain (SC) recovery. We consider effectiveness and efficiency of various reactive measures to recover the SC with the minimum cost at the operational level. For this purpose, a new general model based on bounded optimal control theory is developed to determine the type, the extent, and the timing of reactive measures. We demonstrate its application using an example of a two-echelon poultry SC. The intention of the proposed model is to optimise both the recovery and its costs simultaneously. The developed model is solved exactly using the Pontryagin’s maximum principle. We performed a set of sensitivity analyses to illustrate the model's behaviour. The results obtained from applying the dynamic recovery model in the case study show that the proposed model can help SC managers to deal with disruptions by comparing alternative recovery options, based on two important criteria of the time and cost of SC's recovery. The findings of this research advocate the consideration of dynamic SC characteristics and the need for simultaneous attention to the effectiveness and efficiency of reactive measures in recovery planning.

A dislocation assisted self-consistent constitutive model for the high-temperature deformation of particulate metal-matrix composite

ABSTRACT A dislocation assisted self-consistent model based on Tandon and Weng approach and Bergstrom dynamic recovery model for particulate-reinforced composites has been extended to consider the matrix evolution during high-temperature deformation on flow stress. The impact of main influential processing parameters such as temperature, strain, and strain rate in addition to reinforcement characteristics, including particle size, and volume fraction, were successfully taken into account in the constitutive model. Moreover, the effect of particle fracture, diffusion relaxation around particles, dynamic recrystallization, and dynamic recovery of the matrix during deformation were precipitated as the softening factors in the presented model. It was found that the occurrence of particle stimulating nucleation mechanism can destroy the load transfer mechanism, which results in flow curve softening for a limited range of deformation conditions. It was shown that deformation mechanisms in single-phase alloy and metal matrix composite are the same, which are viscous glide and dislocation climb.

Dynamic Recovery from Depression Enables Rate Encoding in Inhibitory Synapses.

SummaryParvalbumin-expressing fast-spiking interneurons (PV-INs) control network firing and the gain of cortical response to sensory stimulation. Crucial for these functions, PV-INs can sustain high-frequency firing with no accommodation. However, PV-INs also exhibit short-term depression (STD) during sustained activation, largely due to the depletion of synaptic resources (vesicles). In most synapses the rate of replenishment of depleted vesicles is constant, determining an inverse relationship between depression levels and the activation rate, which theoretically, severely limits rate-coding capabilities. We examined STD of the PV-IN to pyramidal cell synapse in the mouse visual cortex and found that in these synapses the recovery from depression is not constant but increases linearly with the frequency of use. By combining modeling, dynamic clamp, and optogenetics, we demonstrated that this recovery enables PV-INs to reduce pyramidal cell firing in a linear manner, which theoretically is crucial for controlling the gain of cortical visual responses.

A Two-Stage Physical-Based Model for Predicting Flow Stress of As-cast TiAl Alloy Under Hot Deformation Conditions

The hot deformation behavior of Ti-30Al-4.2Mn-4.5Nb-0.2B alloy was investigated using the isothermal compression experiment at temperatures of 1020-1200 °C and strain rates of 0.001-1 s−1. The flow stress was sensitive to the deformation parameters like temperature and strain rate, which decreases with the increase in temperature and decrease in strain rates. Based on the true stress-true strain data, a two-stage physical-based model was proposed to describe the flow stress curve of as-cast TiAl alloy during hot deformation process. For establishing the model, at first, the flow curves of dynamic recovery (DRV) were modeled by employing stress-dislocation relation and adjusting dislocation annihilation coefficient Ω. Then, the flow curves of dynamic recrystallization (DRX) were modeled by considering the dynamic softening behavior into Avrami equation. Finally, the flow curves in the entire deformation stages could be described by embedding the predicted data of DRV model (i.e., flow stress before the critical strain) into the predicted data by DRX model (i.e., flow stress after the critical strain). The critical strain for initiation of DRX was determined by the double-differentiation method. To evaluate the applicability and effectiveness of DRX kinetics equation, the DRX curves were calculated and were consistent with the microstructure observation. Comparison between the experimental and predicted data shows that the proposed physical-based model can well forecast the flow stress under a wide working domain.

Strain-Hardening Model of Dual-Phase Steel With Geometrically Necessary Dislocations

The strain-hardening behavior of metal during the uniaxial tension can be treated as the competing result of generation and annihilation of statistically stored dislocations (SSDs). Geometrically necessary dislocations (GNDs) are generated to accommodate a lattice mismatch and maintain deformation compatibility in dual-phase (DP) steels because of the heterogeneous deformation of the microstructure. In this study, a dislocation-based strain-hardening model that encompasses GNDs was developed to describe the mechanical properties of dual-phase steel. The GNDs were obtained based on a cell model of uniaxial deformation and the SSDs were calculated using a dynamic recovery model. The strain of each phase is a nonlinear function of the overall material strain obtained by the point-interpolation method (PIM). The proposed strain-hardening model was verified by using commercially produced DP600 steel. The calculated results obtained with GNDs are able to predict more precisely the experimental data than that without. The effects of martensite volume fraction and grain size on the strain-hardening behaviors of individual phases and material were studied.

Analysis of Flow Behavior of an Nb-Ti Microalloyed Steel During Hot Deformation

The hot flow behavior of an Nb-Ti microalloyed steel is investigated through hot compression test at various strain rates and temperatures. By the combination of dynamic recovery (DRV) and dynamic recrystallization (DRX) models, a phenomenological constitutive model is developed to derive the flow stress. The predefined activation energy of Q = 270 kJ/mol and the exponent of n = 5 are successfully set to derive critical stress at the onset of DRX and saturation stress of DRV as functions of the Zener–Hollomon parameter by the classical hyperbolic sine equation. The remaining parameters of the constitutive model are determined by fitting them to the experiments. Through substitution of a normalized strain in the DRV model and considering the interconnections between dependent parameters, a new model is developed. It is shown that, despite its fewer parameters, this model is in good agreement with the experiments. Accurate analyses of flow data along with microstructural analyses indicate that the dissolution of NbC precipitates and its consequent solid solution strengthening and retardation of DRX are responsible for the distinguished behaviors in the two temperature ranges between T < 1100 °C and T ≥ 1100 °C. Nevertheless, it is shown that a single constitutive equation can still be employed for the present steel in the whole tested temperature ranges.

Did capital infusions enhance bank recovery from the great recession?

This paper investigates the long-run recovery experience of US banks that received capital infusions under the Capital Purchase Program (CPP), a part of the Troubled Asset Relief Program (TARP). Based on a dynamic recovery model, our results show that recovering CPP banks tended to be in better financial condition than other CPP banks. Long-run event study analyses of common stock prices reveal that, in the quarter after repayment of TARP funds, CPP banks experienced economically large and significant buy-and-hold wealth gains of 14%, equivalent to approximately $329billion. We conclude that TARP was successful in fostering bank financial and stock price recovery.

Hot deformation behavior and constitutive modeling of VCN200 low alloy steel

The hot working behavior of VCN200 medium carbon low alloy steel was analyzed by performing hot compression tests in temperature range of 850–1150°C and at strain rates of 0.001–1s−1. Flow curves were typical of dynamic recrystallization during hot working over temperature range of 900–1150°C and strain rates of 0.001–1s−1. However, at lower temperatures no indication of flow softening was observed. The constitutive analysis using the hyperbolic sine function was performed and the value of apparent activation energy for the hot deformation determined to be about 435kJ/mol. The flow curves up to the peak were successfully modeled using a dynamic recovery model. All the factors in this model were defined in terms of the Zener–Hollomon parameter. A modified form of Avrami equation was used to estimate the fractional softening due to the dynamic recrystallization for any given strain in flow curve. Using this model, the flow curves were successfully predicted and generalized to different deformation conditions.

High Temperature Deformation Behavior of 25Cr5MoA Nitriding Steel

The high temperature deformation law of nitriding steel 25Cr5MoA over the strain rate range 0.001S-1~20S-1and temperature range 850°C to 1150°C was studied in the thermal simulation testing machine Gleeble-1500. Under a certain strain rate and a certain deformation degree, the flow stress decreased with the increase of deformation temperature. Work hardening of nitriding steel 25Cr5MoA was strong when the true strain was less than 0.2, otherwise the flow stress increased slowly, even dropped. High temperature deformation flow stress of nitriding steel 25Cr5MoA was influenced by the deformation temperature and strain rate. When the strain rate was 0.1S-1, true stress-true strain curve exhibited a dynamic recrystallization model, and with the increase of deformation temperature, peak flow stress shift left. When deformation degree was 0.69, the strain rate was 1S-1, and when deformation temperature was in the region of 850°C~1050°C, true stress-true strain curve exhibited a dynamic recovery model. And when the deformation temperature was in the region of 1100°C~1150°C, it showed a dynamic recrystallization model. Dynamic recrystallization diagrams of nitriding steel 25Cr5MoA were also established.

Flow Stress Constitutive Equation of AZ31 Magnesium Alloy for Hot Compression

The AZ31 magnesium alloy flow stresses have been investigated in the strain rates of 0.03~3s-1and temperature range of 300~400°C. The result showed that dynamic recovery and dynamic recrystallization occurred obviously during the hot compression of AZ31 magnesium alloy. In order to represent the flow stress of plastic deformation accurately, the constitutive equation was built by using the dynamic recovery model and dynamic recrystallization model, and its parameters of the constitutive equation were determined by multivariate nonlinear regression analysis. The two-step constitutive equation not only expressed the variation of flow stress with strain rate, deformation temperature and strain, but also revealed the characteristic of dynamic recrystallization kinetics of AZ31 magnesium alloy. Its accuracy was higher than the flow stress of hyperbolic sine model, and the maximum relative errors of two constitutive equation models calculation values compared with experiment data were 5% and 6.5% respectively.

Modeling the initiation of dynamic recrystallization using a dynamic recovery model

Dynamic recrystallization flow curve was studied in AISI 410 martensitic stainless steel by performing hot compression tests in a temperature range of 900–1150 °C and at strain rates of 0.001–1 s −1. The Estrin and Mecking's equation for dynamic recovery was used to model the work hardening region of the flow curves. The critical strain and stress for the initiation of dynamic recrystallization were determined using the method developed by Poliak and Jonas. The critical dislocation density for starting dynamic recrystallization was estimated using the Estrin and Mecking's dynamic recovery model. A modified Arrhenius-type equation was used to relate the critical dislocation density to strain rate and temperature. The proposed model was also verified by the model proposed by Roberts and Ahlblom and developed to describe the variation of dislocation density and fractional softening due to dynamic recrystallization up to the peak of flow curve.

Did Capital Infusions Enhance Bank Recovery from the Great Recession?

This paper investigates the long-run recovery experience of U.S. banks that received capital infusions under the Capital Purchase Program (CPP), a part of the Troubled Asset Relief Program (TARP). Based on a dynamic recovery model, our results show that recovering CPP banks tended to be in better financial condition than other CPP banks. Long-run event study analyses of common stock prices reveal that, in the quarter after repayment of TARP funds, CPP banks experienced economically large and significant buy-and-hold wealth gains of 14 percent, equivalent to approximately $329 billion. We conclude that TARP was successful in fostering bank financial and stock price recovery.

A STUDY OF DYNAMIC RECRYSTALLIZATION IN TA15 TITANIUM ALLOY DURING HOT DEFORMATION BY CELLULAR AUTOMATA MODEL

The dynamic recrystallization (DRX) of TA 15 ( Ti -6 Al -2 Zr -1 Mo -1 V ) titanium alloy during the hot deformation process was studied by the Cellular Automata (CA) model which is base on the dislocation density theory. To build the CA model, the dislocation density model, dynamic recovery model, nucleation model and grain growth model were introduced and developed. The influences of strain rate on the microstructure evolution and flow stress character were investigated which shows that high strain rate leads to later DRX appearance, high flow stress peak value, small mean size of recrystallizing grains( R -grains) and low DRX percentage, but they have the similar Avrami curve. The characteristic of DRX process in a modeling non-uniform temperature filed (NTF) has been studied. All the simulation results show good agreement with the pioneer's work and experimental results.

Anomalous strain hardening behaviour of a supersaturated Al-Zn-Mg alloy

The work hardening behaviour and the evolution of resistivity were simultaneously followed during tensile tests at 300, 77 and 4.2 K, in an Al-Zn-Mg alloy in the as quenched state and in pure Aluminium. In pure Aluminium both the work hardening and the resistivity evolution can be interpreted in terms of dislocation storage and dynamic recovery models. In the alloy, both the work hardening rate and the resistivity evolution are anomalously high. These two effects can be interpreted in terms of dynamic precipitation of GP zones at low temperature during plastic flow.

A model of the high-temperature deformation of metallic materials with ellipsoidal second-phase particles

A micromechanics model developed in the previous work which incorporated the effect of dynamic recovery by diffusion of atoms was applied to the interpretation of the high-temperature deformation of metallic materials with ellipsoidal second-phase particles. A theoretical discussion based on this model was made on the effect of several factors including shape, particle size, orientation and elastic modulus of second phase on the work-hardening behaviour of the materials at high temperature. A good correlation was found between the result of the calculations and those of the experiments obtained by the present authors or other investigators of several kinds of metallic materials with ellipsoidal second-phase particles. The dynamic recovery model used in this study can be applied to the understanding of high-temperature deformation behaviour or to the prediction of the possible recovery mechanism of the materials.