Effect of the choice of creep instability criterion on the solution of the problem of optimizing rod-shaped structures

1992 ◽  
Vol 33 (4) ◽  
pp. 573-576
Author(s):  
M. N. Kirsanov
Keyword(s):  
Instability Criterion ◽  
Creep Instability

scholarly journals Prediction Models of Shear Parameters and Dynamic Creep Instability for Asphalt Mixture under Different High Temperatures

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2542
Author(s):  
Junxiu Lv ◽  
Xiaoyuan Zhang
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Stress Level ◽  
Prediction Models ◽  
Asphalt Mixture ◽  
Confining Pressure ◽  
Shear Strength Parameters ◽  
Dynamic Creep ◽  
Shear Stress Level ◽  
Creep Instability

This study mainly investigates the prediction models of shear parameters and dynamic creep instability for asphalt mixture under different high temperatures to reveal the instability mechanism of the rutting for asphalt pavement. Cohesive force c and internal friction angle φ in the shear strength parameters for asphalt mixture were obtained by the triaxial compressive strength test. Then, through analyzing the influence of different temperatures on parameters c and φ, the prediction models of shear strength parameters related to temperature were developed. Meanwhile, the corresponding forecast model related to confining pressure and shear strength parameters was obtained by simplifying the calculation method of shear stress level on the failure surface under cyclic loading. Thus, the relationship of shear stress level with temperature was established. Furthermore, the cyclic time FN of dynamic creep instability at 60 °C was obtained by the triaxial dynamic creep test, and the effects of confining pressure and shear stress level were considered. Results showed that FN decreases exponentially with the increase in stress levels under the same confining pressure and increases with the increase in confining pressure. The ratio between shear stress level and corresponding shear strength under the same confining pressure was introduced; thus, the relationship curve of FN with shear stress level can eliminate the effect of different confining pressures. The instability prediction model of FN for asphalt mixture was established using exponential model fitting analysis, and the rationality of the model was verified. Finally, the change rule of the parameters in the instability prediction model was investigated by further changing the temperature, and the instability forecast model in the range of high temperature for the same gradation mixture was established by the interpolation calculation.

New Experimental Data and Analysis for Two-Phase Flow-Induced Vibration of Tube Bundles: Preliminary Results

2003 ◽  
Author(s):  
Deepanjan Mitra ◽  
Vijay K. Dhir ◽  
Ivan Catton
Keyword(s):  
Two Phase Flow ◽  
Structural Parameters ◽  
Cross Flow ◽  
Instability Criterion ◽  
Phase Flow ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Void Fractions ◽  
Comparison Of The Results ◽  
Square Array

In the past, fluid-elastic instability in two-phase flow has been largely investigated with air-water flow. In this work, new experiments are conducted in air-water cross-flow with a fully flexible 5 × 3 normal square array having pitch-to-diameter ratio of 1.4. The tubes have a diameter of 0.016 m and a length of 0.21 m. The vibrations are measured using strain gages installed on piano wires used to suspend the tubes. Experiments are carried out for void fractions from 0%–30%. A comparison of the results of the current tests with previous experiments conducted in air-water cross-flow shows that instability occurs earlier in a fully flexible array as compared to a flexible tube surrounded by rigid tubes in an array. An attempt is made to separate out the effects of structural parameters of three different experimental datasets by replotting the instability criterion by incorporating the instability constant K, in the reduced velocity parameter.

Criterion of Mechanical Instability in Inhomogeneous Atomic System

2005 ◽  
Vol 482 ◽  
pp. 127-130 ◽  
Author(s):  
Yoshitaka Umeno ◽  
Takayuki Kitamura
Keyword(s):  
Mechanical Stability ◽  
Atomic System ◽  
Instability Criterion ◽  
Fundamental Issue ◽  
Mechanical Instability ◽  
Atomic Systems ◽  
Uniform Deformation ◽  
Atomic Structures ◽  
Homogeneous Structures ◽  
Deformation Modes

The mechanical stability of a material is a fundamental issue in strength of atomic systems. Although the criterion of the mechanical stability of homogeneous structures such as perfect crystals have been successfully investigated so far, the criterion has not been able to be precisely evaluated in the cases of non-uniform deformations or bodies of inhomogeneous atomic structures. Now we present an instability criterion of an arbitrary atomic structure based on the energy balance of the whole system. This method gives the mathematically rigorous condition for the onset of an unstable deformation in any inhomogeneous atomic system. Furthermore, the method can be applied to any type of potential field, which means that ab initio evaluations of the mechanical instability of inhomogeneous structure under non-uniform deformation will be possible. The validity of the method is clarified by the application to tension of a cracked body. The onsets of unstable deformations and their deformation modes are precisely evaluated by the method.

Creep Instability of Thick Shell Structures

1976 ◽  
pp. 86-94
Author(s):  
F. A. Leckie ◽  
B. Hayman
Keyword(s):  
Shell Structures ◽  
Thick Shell ◽  
Creep Instability

scholarly journals The Investigation on Flow Behavior of Powder Metallurgy Ti-10V-2Fe-3Al Alloy Using the Prasad Stability Criterion

2019 ◽  
Vol 50 (11) ◽  
pp. 5314-5323 ◽  
Author(s):  
Krystian Zyguła ◽  
Marek Wojtaszek ◽  
Oleksandr Lypchanskyi ◽  
Tomasz Śleboda ◽  
Grzegorz Korpała ◽  
...  
Keyword(s):  
Powder Metallurgy ◽  
Power Dissipation ◽  
Hot Deformation ◽  
High Efficiency ◽  
Flow Instability ◽  
Flow Behavior ◽  
Material Model ◽  
Instability Criterion ◽  
Processing Maps ◽  
Compression Tests

Abstract The hot deformation behavior of Ti-10V-2Fe-3Al alloy obtained by the powder metallurgy (PM) method was investigated. Material for the research was produced by blending of elemental powders followed by uniaxial hot pressing. Thermomechanical tests of Ti-10V-2Fe-3Al compacts were carried out to determinate the stress-strain relationships at the temperature range of 800 °C to 1000 °C and strain rate between 0.01 and 10 s−1. Based on the dynamic material model (DMM) theory, processing maps at constant strain value were developed using data obtained from hot compression tests. The processing maps were elaborated for the final strain value, which was 0.9, and with flow instability criterion domains applied to it. Two critical regions associated with the flow behavior of the investigated material were revealed. Microstructural changes during hot deformation at various temperatures and strain rates were discussed. The correlation between calculated efficiency of power dissipation, flow instability criterion, and microstructure evolution was determined. The presence of defects was confirmed in regions predicted by the instability maps. The microstructure of the investigated alloy, corresponding to the high efficiency of power dissipation characterized by the occurrence of dynamic recrystallization (DRX) phenomena, was also shown. Additionally, average hardness values in relation to variable process parameters were designated. Based on the conducted studies and analysis, processing windows for Ti-10V-2Fe-3Al alloy compacts were proposed.

New Instability Criterion for Stability Analysis of Homogeneous Slopes

2020 ◽  
Vol 20 (5) ◽  
pp. 04020034 ◽  
Author(s):  
H. W. Fang ◽  
Y. Frank Chen ◽  
Y. X. Xu
Keyword(s):  
Stability Analysis ◽  
Instability Criterion

scholarly journals Processing Map for Hot Working of Powder Metallurgy 2124 AL - 20 VOL% SiCP Metal Matrix Composite

2000 ◽  
Vol 9 (2) ◽  
pp. 096369350000900
Author(s):  
S.V.S. Narayana Murty ◽  
B. Nageswara Rao ◽  
B.P. Kashyap
Keyword(s):  
Powder Metallurgy ◽  
Metal Matrix Composite ◽  
Matrix Composite ◽  
Metal Matrix ◽  
Processing Map ◽  
Hot Working ◽  
Flow Instabilities ◽  
Instability Criterion ◽  
Processing Maps ◽  
Instability Condition

A simple instability condition based on the Ziegler's instability criterion is found to be more appropriate in delineating the regimes of flow instabilities in the processing maps of 2124 Al-20 Vol% SiCp metal matrix composite. Applicability of the criterion is demonstrated using the reported microstructural observations in open literature.

scholarly journals Stability of lubricated viscous gravity currents. Part 1. Internal and frontal analyses and stabilisation by horizontal shear

2019 ◽  
Vol 871 ◽  
pp. 970-1006 ◽  
Author(s):  
Katarzyna N. Kowal ◽  
M. Grae Worster
Keyword(s):  
Viscous Fluid ◽  
Pressure Gradient ◽  
Dynamic Pressure ◽  
Jump Discontinuity ◽  
Local Analysis ◽  
Instability Criterion ◽  
Shear Stresses ◽  
Horizontal Shear ◽  
Dynamical Regimes ◽  
Inner Region

A novel viscous fingering instability, involving a less viscous fluid intruding underneath a current of more viscous fluid, was recently observed in the experiments of Kowal & Worster (J. Fluid Mech., vol. 766, 2015, pp. 626–655). We examine the origin of the instability by asking whether the instability is an internal instability, arising from internal dynamics, or a frontal instability, arising from viscous intrusion. We find it is the latter and characterise the instability criterion in terms of viscosity difference or, equivalently, the jump in hydrostatic pressure gradient at the intrusion front. The mechanism of this instability is similar to, but contrasts with, the Saffman–Taylor instability, which occurs as a result of a jump in dynamic pressure gradient across the intrusion front. We focus on the limit in which the two viscous fluids are of equal density, in which a frontal singularity, arising at the intrusion, or lubrication, front, becomes a jump discontinuity, and perform a local analysis in an inner region near the lubrication front, which we match asymptotically to the far field. We also investigate the large-wavenumber stabilisation by transverse shear stresses in two dynamical regimes: a regime in which the wavelength of the perturbations is much smaller than the thickness of both layers of fluid, in which case the flow of the perturbations is resisted dominantly by horizontal shear stresses; and an intermediate regime, in which both vertical and horizontal shear stresses are important.

The Simulation and Role of Discontinuous Yield Behaviors of Material

2010 ◽  
Vol 163-167 ◽  
pp. 4590-4594
Author(s):  
Shao Wei Hu
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Stress Rate ◽  
Instability Criterion ◽  
Stress Strain ◽  
Dynamic Behaviors ◽  
Jerky Flow ◽  
Thermal Origin

Discontinuous yield of material as Jerky flow was explained. Then, the strain rate sensitivity (SRS) and instability criterion was given out. Some tests were carried out at constant stress rate, so Jerky flow is manifested as a discontinuity in the stress-strain curves in form of strain bursts. Finally, the dynamic behaviors of specimens during instability of thermal origin were simulated with COLSYS software, whose results are good with test ones.

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