THE INITIAL CREEP OF COLUMNAR-GRAINED ICE: PART I. OBSERVED BEHAVIOR

1965 ◽  
Vol 43 (8) ◽  
pp. 1414-1422 ◽  
Author(s):  
L. W. Gold
Keyword(s):  
Creep Rate ◽  
Creep Strain ◽  
Power Law ◽  
Creep Behavior ◽  
Small Angle ◽  
Transient Creep ◽  
Creep Stage ◽  
Resistance To Deformation ◽  
Creep Curves ◽  
Simple Compression

Previously undeformed columnar-grained ice exhibits a period of increasing or constant creep rate during the transient creep stage when loaded in simple compression perpendicular to the long axis of the columns. It is shown that this behavior is associated with the formation of small-angle boundaries and internal cracks. Creep strain beyond 0.25% for first load tends to a power-law dependence on time. On reload, specimens exhibit a normal transient creep behavior and have, initially, a lower resistance to deformation than for first load. With deformation, this resistance increases so that the reload creep curves cross the first load curves at about 0.2% creep. For reload, creep strain less than about 0.025% and greater than about 0.2% appears to have a power-law dependence on time with exponent about equal to that for first load.

scholarly journals THE INITIAL CREEP OF COLUMNAR-GRAINED ICE: PART II. ANALYSIS

1965 ◽  
Vol 43 (8) ◽  
pp. 1423-1434 ◽  
Author(s):  
L. W. Gold
Keyword(s):  
Creep Rate ◽  
Creep Strain ◽  
Power Law ◽  
Creep Behavior ◽  
Minimum Creep Rate ◽  
Transient Creep ◽  
Time Dependent ◽  
Secondary Creep ◽  
Stress Dependence ◽  
Deflection Rate

Observations on the initial creep behavior of columnar-grained ice are analyzed by assuming that the creep strain at a given time has a power-law dependence on the applied constant compressive stress. The exponent for the stress was time-dependent during transient creep. For first load it started at a low value, increased to a maximum of about 2.23 approximately 75 minutes after the application of the load, and decreased thereafter. For reload it started at a high value and decreased continuously to a constant value of 1.46 by 100 minutes after the application of the load. Creep rates at a given time, calculated from the observed power-law dependence of the creep strain on stress, also had a power-law dependence on stress for time greater than about 25 minutes after the application of the load. The observations are shown to be in agreement with observations by Krausz (1963) on the deflection rate of ice beams and by Steine-mann (1954) and Glen (1958) on the stress-dependence of the minimum creep rate during secondary creep. The observations indicate that the creep rate during secondary creep varies approximately as t−0.5.

INDENTATION SIZE EFFECT ON THE CREEP BEHAVIOR OF A SnAgCu SOLDER

2010 ◽  
Vol 24 (01n02) ◽  
pp. 267-275 ◽  
Author(s):  
Y. D. HAN ◽  
H. Y. JING ◽  
S. M. L. NAI ◽  
L. Y. XU ◽  
C. M. TAN ◽  
...  
Keyword(s):  
Creep Rate ◽  
Strain Rate ◽  
Creep Strain ◽  
Creep Behavior ◽  
Maximum Load ◽  
Creep Strain Rate ◽  
Lead Free ◽  
Lead Free Solder ◽  
Snagcu Solder ◽  
Free Solder

In the present study, nanoindentation studies of the 95.8 Sn -3.5 Ag -0.7 Cu lead-free solder were conducted over a range of maximum loads from 20 mN to 100 mN, under a constant ramp rate of 0.05 s-1. The indentation scale dependence of creep behavior was investigated. The results revealed that the creep rate, creep strain rate and indentation stress are all dependent on the indentation depth. As the maximum load increased, an increasing trend in the creep rate was observed, while a decreasing trend in creep strain rate and indentation stress were observed. On the contrary, for the case of stress exponent value, no trend was observed and the values were found to range from 6.16 to 7.38. Furthermore, the experimental results also showed that the creep mechanism of the lead-free solder is dominated by dislocation climb.

CREEP ANALYSIS FOR A WIDE STRESS RANGE BASED ON STRESS RELAXATION EXPERIMENTS

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5413-5418 ◽  
Author(s):  
HOLM ALTENBACH ◽  
KONSTANTIN NAUMENKO ◽  
YEVGEN GORASH
Keyword(s):  
Experimental Data ◽  
Creep Rate ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Power Law ◽  
Creep Behavior ◽  
Minimum Creep Rate ◽  
High Stress ◽  
Stress Range ◽  
Power Law Creep

Many materials exhibit a stress range dependent creep behavior. The power-law creep observed for a certain stress range changes to the viscous type creep if the stress value decreases. Recently published experimental data for advanced heat resistant steels indicates that the high creep exponent (in the range 5-12 for the power-law behavior) may decrease to the low value of approximately 1 within the stress range relevant for engineering structures. The aim of this paper is to confirm the stress range dependence of creep behavior based on the experimental data of stress relaxation. An extended constitutive model for the minimum creep rate is introduced to consider both the linear and the power law creep ranges. To take into account the primary creep behavior a strain hardening function is introduced. The material constants are identified for published experimental data of creep and relaxation tests for a 12% Cr steel bolting material at 500°C. The data for the minimum creep rate are well-defined only for moderate and high stress levels. To reconstruct creep rates for the low stress range the data of the stress relaxation test are applied. The results show a gradual decrease of the creep exponent with the decreasing stress level. Furthermore, they illustrate that the proposed constitutive model well describes the creep rates for a wide stress range.

High-temperature deformation of mullite and analysis of creep curves

2003 ◽  
Vol 18 (8) ◽  
pp. 1771-1776 ◽  
Author(s):  
H. Rhanim ◽  
C. Olagnon ◽  
G. Fantozzi ◽  
A. Azim
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Behavior ◽  
Slow Crack Growth ◽  
Steady State Creep ◽  
The Other ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Steady State Creep Rate ◽  
Creep Curves

The creep behavior of mullite was studied under different stresses and in the temperature range 1200–1450 °C, and an analysis of creep curves was proposed. The study of creep behavior of mullite at high temperatures clearly indicates that this material exhibits concurrent creep and slow crack growth. An effective transition stress exists at each temperature. The analysis takes account of the total creep curve; in particular, the primary and stationary stages. It is now possible to determine by extrapolation the steady-state creep rate for specimens that break in the transient domain during tests. Thus, one can verify the influence of the stress on the steady-state creep rate over a wide stress range. On the other hand, this analysis clearly indicates the existence of two values of the activation energy around 1300 °C; this suggests a change of creep mechanism at this temperature.

Creep Testing and Visco-Elastic Behaviour Reseach on Carbon Cathodes during Aluminum Electrolysis

2011 ◽  
Vol 314-316 ◽  
pp. 1430-1434
Author(s):  
Qing Sheng Liu ◽  
Hai Feng Tang ◽  
Hui Fang
Keyword(s):  
Creep Rate ◽  
Constitutive Model ◽  
Creep Strain ◽  
Creep Behavior ◽  
Aluminum Electrolysis ◽  
Creep Testing ◽  
Elastic Behaviour ◽  
Testing Data ◽  
Short Time ◽  
Stress Dependency

An apparatus to measure compressive creep in carbon cathode materials has been developed. Short-time creep were measured at 30°C，965°C and during aluminum electrolysis at 965°C. The creep strain increases with stress, indicating that the creep behavior is of the stress dependency. The ranking from low to high creep was at 30°C<965°C<during aluminum electrolysis at 965°C. The integral creep conctitutive mdoel were estalished based on the relevant rheological mdoel. The results indicate the proposed rheological model can discribe the creep rate at the first stage and the stady-state stage on the creep strain curves. Simultaneously, the viscous coefficents denoting the viscous behavior in visco-elastic constitutive model were determined by taking use of the creep testing data.

Extrapolation of Creep Curve and Creep Rate by Strain Acceleration Parameter in Al-Mg Solid Solution Alloys

2014 ◽  
Vol 794-796 ◽  
pp. 307-312
Author(s):  
Hiroyuki Sato ◽  
Kosuke Omote ◽  
Akira Sato
Keyword(s):  
Solid Solution ◽  
Steady State ◽  
Creep Rate ◽  
Creep Curve ◽  
Creep Behavior ◽  
Minimum Creep Rate ◽  
Strain Rate Change ◽  
Acceleration Parameter ◽  
Creep Characteristics ◽  
Creep Curves

It has been widely accepted that the creep characteristics at high temperatures are mainly evaluated by a minimum creep rate. Although, a shape of creep curve may vary depending on deformation conditions, the apparent steady state or minimum creep rates be the same. Thus,for detailed analysis and prediction of creep behavior, other values which reflect the shape of each creep curve should be considered. For the purpose, authors have proposed Sato’s strain- acceleration-parameter (Strain Acceleration and Transition Objective index, SATO-index) which reflects strain rate change during creep deformation. Based on the concept of SATO-index, the whole creep curve can be represented by a set of small number of numerical parameters, and can be extrapolated from a part of creep curve. In this paper, application of the concept of SATO-index to the creep curves of aluminum-magnesium solid solutions that the creep behavior of the alloys are well investigated and analyzed. The creep curve can be extrapolated by the concept from transient part of creep curve, and the extrapolated creep rates at the minimum creep rate agree well with experiment. Efficiency of the concept of SATO-index to creep experiments is pronounced.

Microstructures and Creep of AM50-Sb-Gd Alloys

2005 ◽  
Vol 488-489 ◽  
pp. 749-752 ◽  
Author(s):  
Su Gui Tian ◽  
Keun Yong Sohn ◽  
Hyun Gap Cho ◽  
Kyung Hyun Kim
Keyword(s):  
Activation Energy ◽  
Creep Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Deformation Mechanism ◽  
Creep Resistance ◽  
Fine Particles ◽  
Dislocation Climb ◽  
The Matrix

Creep behavior of AM50-0.4% Sb-0.9%Gd alloy has been studied at temperatures ranging from 150 to 200°C and at stresses ranging from 40 to 90 MPa. Results show that the creep rate of AM50-0.4%Sb-0.9%Gd alloy was mainly controlled by dislocation climb at low stresses under 50 MPa. The activation energy for the creep was 131.2 ± 10 kJ/mol and the stress exponent was in the range from 4 to 9 depending on the applied stress. More than one deformation-mechanism were involved during the creep of this alloy. Microstructures of the alloy consist of a–Mg matrix and fine particles, distinguished as Mg17Al12, Sb2Mg3, and Mg2Gd or Al7GdMn5 that were homogeneously distributed in the matrix of the alloy, which effectively reduced the movement of dislocations, enhancing the creep resistance. Many dislocations were identified to be present on non-basal planes after creep deformation.

Creep Behavior and Microstructural Stability of Lamellar γ-T1AI (Cr, Mo, Si, B) with Extremely Fine Lamellar Spacing

2000 ◽  
Vol 646 ◽  
Author(s):  
Wolfram Schillinger ◽  
Dezhi Zhang ◽  
Gerhard Dehm ◽  
Arno Bartels ◽  
Helmut Clemens
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Primary Creep ◽  
Vacuum Arc ◽  
Internal Stresses ◽  
Microstructural Stability ◽  
Thermodynamical Equilibrium ◽  
Creep Tests

ABSTRACTγ-T1AI (Cr, Mo, Si, B) specimens with two different fine lamellar microstructures were produced by vacuum arc melting followed by a two-stage heat treatment. The average lamellar spacing was determined to be 200 nm and 25–50 nm, respectively. Creep tests at 700°C showed a very strong primary creep for both samples. After annealing for 24 hours at 1000 °C the primary creep for both materials is significantly decreased. The steady-state creep for the specimens with the wider lamellar spacing appears to be similar to the creep behavior prior to annealing while the creep rate of the material with the previously smaller lamellar spacing is significantly higher. Optical microscopy and TEM-studies show that the microstructure of the specimens with the wider lamellar specing is nearly unchanged, whereas the previously finer material was completely recrystallized to a globular microstructure with a low creep resistance. The dissolution of the fine lamellar microstructure was also observed during creep tests at 800 °C as manifested in an acceleration of the creep rate. It is concluded that extremely fine lamellar microstructures come along with a very high dislocation density and internal stresses which causes the observed high primary creep. The microstructure has a composition far away from the thermodynamical equilibrium which leads to a dissolution of the structure even at relatively low temperatures close to the intended operating temperature of γ-T1AI structural parts. As a consequence this limits the benefit of fine lamellar microstructures on the creep behavior.

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