Water lubrication mechanism of glacier surges

1969 ◽  
Vol 6 (4) ◽  
pp. 929-942 ◽  
Author(s):  
J. Weertman
Keyword(s):  
Power Law ◽  
Water Layer ◽  
Water Lubrication ◽  
Lubrication Mechanism ◽  
Stress Concentrations ◽  
Creep Equation ◽  
Glacier Surges ◽  
Power Law Creep

The author reviews and amplifies his theory of glacier surges. This theory is based on the premise that a glacier surge occurs when a water layer at the base of a glacier attains a thickness sufficient to drown the obstacles in the bed that offer the greatest hindrance to sliding. The following new result is presented: in the case of a glacier bed which is very smooth, the stress concentrations in the vicinity of obstacles in the bed are so high that the power-law creep equation is no longer valid. As a consequence, the size of the controlling obstacles is reduced and thus a surge is more likely to occur.

scholarly journals New Developments in Understanding Harper-Dorn, Five- power Law Creep and Power-law Breakdown

2020 ◽  
Author(s):  
michael kassner
Keyword(s):  
Stress Exponent ◽  
Power Law ◽  
Dislocation Network ◽  
Creep Equation ◽  
Self Diffusion ◽  
Wide Range ◽  
Recent Developments ◽  
Initial Dislocation Density ◽  
Power Law Creep ◽  
Edge Dislocations

This paper discusses recent developments in creep, over a wide range of temperature, that mqy change our understanding of creep. The five-power law creep exponent (3.5 to 7) has never been explained in fundamental terms. The best the scientific community has done is to develop a natural three power-law creep equation that falls short of rationalizing the higher stress exponents that are typically five. This inability has persisted for many decades. Computational work examining the stress-dependence of the climb rate of edge dislocations we may rationalize the phenomenological creep equations. Harper-Dorn creep, “discovered” over 60 years ago has been immersed in controversy. Some investigators have insisted that a stress exponent of one is reasonable. Others believe that the observation of a stress exponent of one is a consequence of dislocation network frustration. Others believe the stress exponent is artificial due to the inclusion of restoration mechanisms such as dynamic recrystallization or grain growth that is not of any consequence in the five power-law regime. Also, the experiments in the Harper-Dorn regime, which accumulate strain very slowly (sometimes over a year) may not have attained a true steady state. New theories suggest that absence or presence of Harper-Dorn may be a consequence of the initial dislocation density. Novel experimental work suggests that power-law breakdown may be a consequence of a supersaturation of vacancies which increase self-diffusion.

On the power-law creep equation

1980 ◽  
Vol 14 (12) ◽  
pp. 1297-1302 ◽  
Author(s):  
A.M. Brown ◽  
M.F. Ashby
Keyword(s):  
Power Law ◽  
Creep Equation ◽  
Power Law Creep

Calculation of Stress Relaxation Properties for 1CrMoV Bolt Material

2003 ◽  
Author(s):  
Fred V. Ellis ◽  
Sebastian Tordonato
Keyword(s):  
Stress Relaxation ◽  
Power Law ◽  
Uniaxial Stress ◽  
Flow Rule ◽  
Creep Equation ◽  
Relaxation Properties ◽  
Stress Levels ◽  
Long Time ◽  
Power Law Creep ◽  
Good Agreement

Analytical life prediction methods have been developed for high temperature turbine and valve bolts. For 1CrMoV steel bolt material, long time creep-rupture and stress relaxation tests were performed at 450°C, 500°C, and 550°C by the National Research Institute for Metals of Japan. Based on analysis of their data, the isothermal creep behavior can be described using a power law: ε=Kσn(t)m+1 where ε is the creep strain, t is the time, σ is the stress, K, n, and m are material constants. The time power is a primarily a function of temperature, but also depends slightly on stress. To obtain the value for the time power typical of low stress, the creep equation constants were found in two steps. The time power was found using the lower stress data and a heat-centered type regression approach with the stress levels taking the place of the heats in the analysis. The heat constants were then calculated at all stress levels and regression performed to obtain the stress dependence. For comparison with the measured uniaxial stress relaxation properties, the relaxed stress as a function of time was calculated using the power law creep equation and a strain hardening flow rule. The calculated stress versus time curves were in good agreement with the measured at initial strain levels of 0.10%, 0.15%, and 0.20% for all temperatures except 500°C. At 500°C, good agreement was found using the creep properties typical of a stronger (within heat variation) material.

Nano-Mechanical Creep Properties of Nanoclay/Epoxy Composite by Nanoindentation

2007 ◽  
Vol 334-335 ◽  
pp. 669-672 ◽  
Author(s):  
Chun Ki Lam ◽  
Alan Kin Tak Lau ◽  
Li Min Zhou
Keyword(s):  
Mechanical Properties ◽  
Power Law ◽  
Temperature Effects ◽  
Epoxy Composite ◽  
Epoxy Composites ◽  
Aircraft Industry ◽  
Creep Equation ◽  
Creep Properties ◽  
Mechanical Creep ◽  
Power Law Creep

Mechanical properties of nanoclay/epoxy composites (NC) have been studied by various experimental setups in bulk form recently. Creep mechanism of the NC is an important manufacturing criterion for the aircraft industry. In this paper, nanoindentation was employed to investigate the nano-mechanical creep effects on different wt. % of nanoclay contents in epoxy matrix. Creep behaviors of the nanoclay/epoxy composites with different wt. % of nanoclay contents were modeled by the power-law creep equation. Neglecting the temperature effects on creep, the stress exponents of tested composites were estimated.

scholarly journals New Developments in Understanding Harper–Dorn, Five-Power Law Creep and Power-Law Breakdown

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1284
Author(s):  
Michael E. Kassner
Keyword(s):  
Stress Exponent ◽  
Power Law ◽  
Dislocation Network ◽  
Creep Equation ◽  
Self Diffusion ◽  
Wide Range ◽  
Recent Developments ◽  
Initial Dislocation Density ◽  
Power Law Creep ◽  
Edge Dislocations

This paper discusses recent developments in creep, over a wide range of temperature, that may change our understanding of creep. The five-power law creep exponent (3.5–7) has never been explained in fundamental terms. The best the scientific community has done is to develop a natural three power-law creep equation that falls short of rationalizing the higher stress exponents that are typically five. This inability has persisted for many decades. Computational work examining the stress-dependence of the climb rate of edge dislocations may rationalize the phenomenological creep equations. Harper–Dorn creep, “discovered” over 60 years ago, has been immersed in controversy. Some investigators have insisted that a stress exponent of one is reasonable. Others believe that the observation of a stress exponent of one is a consequence of dislocation network frustration. Others believe the stress exponent is artificial due to the inclusion of restoration mechanisms, such as dynamic recrystallization or grain growth that is not of any consequence in the five power-law regime. Also, the experiments in the Harper–Dorn regime, which accumulate strain very slowly (sometimes over a year), may not have attained a true steady state. New theories suggest that the absence or presence of Harper–Dorn may be a consequence of the initial dislocation density. Novel experimental work suggests that power-law breakdown may be a consequence of a supersaturation of vacancies which increase self-diffusion.

scholarly journals Three Regions in the Power-Law Creep Regime of TiAl

1992 ◽  
Vol 33 (12) ◽  
pp. 1182-1184 ◽  
Author(s):  
Yukio Ishikawa ◽  
Kouichi Maruyama ◽  
Hiroshi Oikawa
Keyword(s):  
Power Law ◽  
Power Law Creep ◽  
Creep Regime
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