scholarly journals ANALYSIS OF THE PARAMETERS OF DYNAMIC SUPERPLASTICITY THE INDUSTRIAL ALUMINUM ALLOYS

2021 ◽  
pp. 49-54
Author(s):  
G. Amanbaeva ◽  
Ch. Ismailova
Keyword(s):  
Diffusion Coefficient ◽  
Aluminum Alloys ◽  
Grain Boundary ◽  
Diffusion Processes ◽  
Planck Equation ◽  
Metastable States ◽  
Velocity Range ◽  
Boundary Slippage ◽  
Velocity Interval ◽  
Drift Coefficient

The problem of determining the features of the development of blurred phase transitions observed under conditions of dynamic superplasticity of aluminum alloys is solved using the specific heat capacity function. Within the framework of the developed model representations, the deformation mechanisms characteristic of superplasticity and boundary metastable states are analyzed using the Fokker-Planck equation. Using a macrokinetic model, an explicit expression is obtained for the function that characterizes the mechanism of grain boundary slippage (the “drift " coefficient) that prevails in superplasticity. By integrating the differential equations resulting from the model, the solution of which establishes the type of functions responsible for the implementation of the mechanisms of grain boundary slippage and diffusion processes. It is proposed that the diffusion coefficient is responsible for the accumulation of irreversible deformations outside the velocity range of superplasticity. The function responsible for the effects of grain boundary slippage (the "drift" coefficient) is particularly active towards the middle of the superplasticity velocity interval. It is confirmed that outside the velocity range of superplasticity, there is a redistribution of mass transfer forms, the responsibility for which is assigned to the diffusion coefficient. It is shown that the diffusion function shows a tendency to decrease when approaching the range of superplasticity rates. Metastable states are characterized by the competition of diffusion mechanisms and grain boundary slippage.

Diffusion of Water in Composite Filling Materials

1976 ◽  
Vol 55 (5) ◽  
pp. 730-732 ◽  
Author(s):  
M. Braden ◽  
E.E. Causton ◽  
R.L. Clarke
Keyword(s):  
Diffusion Coefficient ◽  
Composite Materials ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Resin Phase ◽  
Filling Materials ◽  
Irreversible Breakdown

The absorption and desorption of water by seven composite materials are diffusion processes, with the diffusion coefficient decreasing with concentration. The magnitude of the diffusion coefficients were consistent with diffusion occurring in the resin phase. Although most materials showed reversible behavior during repeated sorption-desorption cycles, one material showed irreversible breakdown.

Quantification of Model-Form Uncertainty in Drift-Diffusion Simulation Using Fractional Derivatives

2015 ◽  
Author(s):  
Yan Wang
Keyword(s):  
Diffusion Processes ◽  
Planck Equation ◽  
Optimization Procedure ◽  
Physical World ◽  
Drift Diffusion ◽  
Long Range Correlations ◽  
Modeling Process ◽  
Model Form ◽  
Generic Description ◽  
Non Gaussian

In modeling and simulation, model-form uncertainty arises from the lack of knowledge and simplification during modeling process and numerical treatment for ease of computation. Traditional uncertainty quantification approaches are based on assumptions of stochasticity in real, reciprocal, or functional spaces to make them computationally tractable. This makes the prediction of important quantities of interest such as rare events difficult. In this paper, a new approach to capture model-form uncertainty is proposed. It is based on fractional calculus, and its flexibility allows us to model a family of non-Gaussian processes, which provides a more generic description of the physical world. A generalized fractional Fokker-Planck equation (fFPE) is proposed to describe the drift-diffusion processes under long-range correlations and memory effects. A new model calibration approach based on the maximum accumulative mutual information is also proposed to reduce model-form uncertainty, where an optimization procedure is taken.

scholarly journals Optimization of the Accelerated Degradation Test Plan for Electrical Connector Contact Pairs Based on a Nonlinear Wiener Process

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Ping Qian ◽  
Lei Hong ◽  
Wenhua Chen ◽  
Yongwang Qian ◽  
Zhe Wang ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Wiener Process ◽  
Stress Level ◽  
Test Plan ◽  
Accelerated Degradation ◽  
Stress Levels ◽  
Degradation Test ◽  
Accelerated Degradation Test ◽  
Stress Dependent ◽  
Drift Coefficient

Accelerated degradation test is an effective method to evaluate the reliability of products with long life and high reliability. The performance of most products fluctuates randomly in the degradation process, so it is suitable to use Wiener process. At present, the diffusion coefficient is regarded as constant in Wiener process, while the drift coefficient is related to stress. However, in practice, the amplitude of product performance fluctuation increases with the increase of stress level, which is not constant. Therefore, for the nonlinear Wiener case where both the drift coefficient and the diffusion coefficient are stress dependent, this paper studies the constant-stress accelerated degradation test theories and methods. Taking the contact pairs of electrical connectors as the research object, the minimum variance of reliable life estimate under normal stress is taken as the target. After determining the censored time at each stress level, the test stress level, the sample distribution ratio at each stress level, and the test interval at the one-third power scale of time are taken as design variables. The test plan under 3, 4, and 5 stress levels is optimized and compared with the general test plan. The influence of the difference between high and low stress levels on the evaluation accuracy is analyzed. Finally, the sensitivity analysis of parameters shows that the optimization plan has good robustness, and the change of stress quantity has little influence on the robustness of the plan.

Grain boundary ductile fracture in precipitation hardened aluminum alloys

1987 ◽  
Vol 35 (6) ◽  
pp. 1193-1219 ◽  
Author(s):  
A.K. Vasudévan ◽  
R.D. Doherty
Keyword(s):  
Aluminum Alloys ◽  
Grain Boundary ◽  
Ductile Fracture

Intergranular Coupling and Grain Isolation of Thin Co Films

1998 ◽  
Vol 517 ◽  
Author(s):  
Heng Gong ◽  
Wei Yang ◽  
David N. Lambeth ◽  
David E. Laughlin
Keyword(s):  
Grain Boundary ◽  
Thermal Instability ◽  
Boundary Diffusion ◽  
Oxidation Process ◽  
Diffusion Processes ◽  
Narrow Range ◽  
Grain Boundary Diffusion ◽  
Temperature Dependent ◽  
In Situ Diffusion

AbstractThe effects of rapid oxidation and overcoat diffusion processes on the intergranular coupling and grain isolation in thin Co films were studied. The oxidation process was found to be strongly temperature dependent. The optimal coercivities can only be achieved within a narrow range of temperatures, while further increasing the temperature incurs significant thermal instability. CrMn underlayers were confirmed to be more effective in enhancing the grain isolation by the grain boundary diffusion during the oxidation process. The oxidation process does not change the Co anisotropy, and hence the coercivity increase is appears to be a result of better grain isolation. The in-situ diffusion of Ag and Cr overcoats were also found to have siginificant effects on the grain isolation in Co and CoCr films.

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