Deformation of ice under low stresses

1983 ◽  
Vol 20 (4) ◽  
pp. 587-602 ◽  
Author(s):  
David C. Sego ◽  
Norbert R. Morgenstern
Keyword(s):  
Grain Size ◽  
Inflection Point ◽  
Stress Test ◽  
Constant Strain Rate ◽  
Constant Stress ◽  
Size Ratio ◽  
Ductile Material ◽  
Material Behaviour ◽  
Time Curve ◽  
Flow Law

This study confirms the existence of two flow laws for polycrystalline ice. One describes the behaviour of ice before the inflection point of a constant stress test, and one the behaviour well into the tertiary portion of the strain–time curve. Each flow law may be represented by a power law with an exponent of 3.0.The inflection point in constant stress experiments and the peak in constant strain rate experiments is shown to occur at about 1% strain in experiments conducted in the ductile material behaviour range. A Cottrell–Aytekin relationship has been used to fit the strain–time material behaviour up to the inflection point.The flow law of ice valid below 1% strain is shown to be dependent on the grain size ratio of the ice. The grain size ratio is a measure of the size effect of the sample tested. The temperature influence on the flow law is best described by using the inverse temperature relationship described by Voytkovskiy. Keywords: ice, creep deformation, long-term, failure strain.

Damage in Adhesive Joints During Low Cycle Fatigue

2010 ◽  
Author(s):  
Iva´n C. Ca´bulo-Pe´rez ◽  
Juan P. Casas-Rodri´guez
Keyword(s):  
Plastic Strain ◽  
Low Cycle Fatigue ◽  
Stress Test ◽  
Damage Model ◽  
Fatigue Tests ◽  
Constant Stress ◽  
Cycle Fatigue ◽  
Damage Behavior ◽  
Non Linear ◽  
Compressive Loads

The objective of this research is to study the damage behavior of bulk adhesive and single lap joint (SLJ) specimens during low cycle fatigue (LCF). Fatigue tests under constant stress amplitude were done and strain response was measured through cycles to failure using the bulk adhesive and SLJ data. A non linear damage model was used to fit experimental results. Identification of the damage parameters for bulk adhesive was obtained from the damage against accumulated plastic strain plot. It is shown that the plastic strain can be obtained from the constant stress test if the instantaneous elastic modulus, i.e. modulus affected by damage, is evaluated for each cycle. On the other hand, damage in SLJ was seen mainly in the adhesive for itself — no substrate failure — this fact is used to propose that fatigue response in the joint is due to continuum damage accumulation in the adhesive as the number of cycles increases. Damage behavior under compressive loads was not taken into account but good correlation of numerical and experimental data was obtained. It was found that damage evolution behaves in a non linear manner as the plastic deformation grows for each cycle: on fatigue onset an accelerated damage grow is observed, then a proportional evolution, and finally a rapid failure occurs; this characteristics were seen in both the SLJ and bulk adhesive specimen. So far, this research takes the damage model found in a standard adhesive specimen and assumes it is accurate enough to represent the damage behavior of the SLJ configuration.

scholarly journals The role of grain size evolution in the rheology of ice: implications for reconciling laboratory creep data and the Glen flow law

2021 ◽  
Vol 15 (9) ◽  
pp. 4589-4605
Author(s):  
Mark D. Behn ◽  
David L. Goldsby ◽  
Greg Hirth
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Stress Exponent ◽  
Ice Sheets ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Ice Flow ◽  
Size Evolution ◽  
Boundary Sliding ◽  
Flow Law

Abstract. Viscous flow in ice is often described by the Glen flow law – a non-Newtonian, power-law relationship between stress and strain rate with a stress exponent n ∼ 3. The Glen law is attributed to grain-size-insensitive dislocation creep; however, laboratory and field studies demonstrate that deformation in ice can be strongly dependent on grain size. This has led to the hypothesis that at sufficiently low stresses, ice flow is controlled by grain boundary sliding, which explicitly incorporates the grain size dependence of ice rheology. Experimental studies find that neither dislocation creep (n ∼ 4) nor grain boundary sliding (n ∼ 1.8) have stress exponents that match the value of n ∼ 3 in the Glen law. Thus, although the Glen law provides an approximate description of ice flow in glaciers and ice sheets, its functional form is not explained by a single deformation mechanism. Here we seek to understand the origin of the n ∼ 3 dependence of the Glen law by using the “wattmeter” to model grain size evolution in ice. The wattmeter posits that grain size is controlled by a balance between the mechanical work required for grain growth and dynamic grain size reduction. Using the wattmeter, we calculate grain size evolution in two end-member cases: (1) a 1-D shear zone and (2) as a function of depth within an ice sheet. Calculated grain sizes match both laboratory data and ice core observations for the interior of ice sheets. Finally, we show that variations in grain size with deformation conditions result in an effective stress exponent intermediate between grain boundary sliding and dislocation creep, which is consistent with a value of n = 3 ± 0.5 over the range of strain rates found in most natural systems.

scholarly journals Observations Within Cavities at the Bed of the Glacier Østerdalsisen, Norway

1979 ◽  
Vol 23 (89) ◽  
pp. 273-281 ◽  
Author(s):  
Wilfred H. Theakstone
Keyword(s):  
Grain Size ◽  
Stress Concentration ◽  
Creep Rate ◽  
Significant Influence ◽  
Ice Formation ◽  
Structural Anisotropy ◽  
Basal Ice ◽  
Anisotropic Structures ◽  
Sediment Particles ◽  
Flow Law

AbstractBasal ice at the glacier Østerdalsisen commonly deforms under stress within cavities at the glacier bed. Some ice subject to rapid strain, however, fails in a brittle manner. The creep-rate of basal ice is influenced by sediment particles within it, and by ice grain-size and structural anisotropy; a flow law for such ice has not been derived experimentally. Near the glacier bed, particles enclosed in ice may migrate as a result of stress concentration, bubbles may be flattened, and anisotropic structures may develop. Recrystallization leads to grain-size changes. Both regelation spicules and layers of regelation ice, generally thin, form within subglacial cavities but their occurrence is limited. Regelation-ice formation has a significant influence on the distribution of rock debris at the ceilings of subglacial cavities.

Development of Defect Interaction Criteria for Pipeline Girth Welds Subjected to Plastic Collapse Conditions

2006 ◽  
Author(s):  
Wim De Waele ◽  
Rudi Denys ◽  
Antoon Lefevre
Keyword(s):  
Large Scale ◽  
Specific Interaction ◽  
Ductile Failure ◽  
Elastic Interaction ◽  
Tensile Tests ◽  
Ductile Material ◽  
Plastic Collapse ◽  
Material Behaviour ◽  
Defect Interaction ◽  
Girth Welds

Multiple defects in welds, when detected, have to be assessed for interaction. Current defect interaction rules are largely based on linear elastic fracture mechanics principles (brittle material behaviour). Pipeline welding codes, however, specify toughness requirements to ensure ductile failure by plastic collapse. Therefore, the use of current (elastic) interaction rules for ductile girth welds can lead to unnecessary and possibly harmful weld repairs or cutouts. This paper reports on an assessment of the engineering significance of existing pipeline specific interaction criteria and on the development of new criteria. Rules for the interaction of coplanar surface breaking defects and ductile material behaviour have been developed on the basis of the performance requirement of remote yielding. The results of large-scale tensile tests illustrate that current interaction rules have a high degree of conservatism for plastic collapse conditions. The test data have been used to demonstrate that the developed procedure can be safely used for ductile girth welds.

Influence of Isothermal Forging Temperature on Microstructure and Tensile Properties of Ti-5.8Al-4.0Sn-4.0Zr-0.7Nb-0.4Si-1.5Ta Near-α Titanium Alloy

2010 ◽  
Vol 97-101 ◽  
pp. 153-157
Author(s):  
Tao Wang ◽  
Hong Zhen Guo ◽  
Jian Hua Zhang ◽  
Ze Kun Yao
Keyword(s):  
Grain Size ◽  
Tensile Strength ◽  
Titanium Alloy ◽  
Tensile Properties ◽  
Room Temperature ◽  
Volume Fraction ◽  
Constant Strain Rate ◽  
Isothermal Forging ◽  
Α Phase ◽  
Transus Temperature

The microstructures and room temperature and 600°C tensile properties of Ti-5.8Al-4.0Sn-4.0Zr-0.7Nb -0.4Si-1.5Ta alloy after isothermal forging have been studied. The forging temperature range was from 850°C to 1075°C, and the constant strain rate of 8×10-3/S-1 was adopted. With the increase of forging temperature, the volume fraction of primary α phase decreased and the lamellar α phase became thicker when the temperatures were in range of 850°C -1040°C; The grain size became uneven and the α phase had different forms when the forging temperature was 1040°C and 1075°C respectively; The tensile strength was not sensitive to the temperature and the most difference was within 20MPa. Tensile strength and yield strength attained to the maximum when temperature was 1020°C; the ductility decreased with the increase of forging temperature, and this trend became more obvious if forging temperature was above the β-transus temperature.

scholarly journals Statistical characteristics for the type and length of deformation-induced cracks in columnar-grain ice

1997 ◽  
Vol 43 (144) ◽  
pp. 311-320 ◽  
Author(s):  
Lorne W. Gold
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Strain Rate ◽  
Relative Proportion ◽  
Constant Strain Rate ◽  
Statistical Characteristics ◽  
Columnar Grain ◽  
Log Normal ◽  
Almost All ◽  
Log Normal Distribution

AbstractObservations are reported on cracks formed during compressive, unidirectional, constant-strain-rate deformation of columnar-grain ice. The axis of hexagonal crystallographic symmetry of each grain tended to be in the plane perpendicular to the long direction of the grains and to have a random orientation in that plane. For stress applied perpendicular to the long direction of the grains, the deformation was practically two-dimensional. It was found that the relative proportion of grain-boundary cracks increased with increasing strain rate, decreasing temperature and, for strain rate greater than 7 × 10−5 s−1, with decreasing grain-size. Almost all the grain-boundary cracks had at least one edge at a triple point. For each test, the grain-boundary and transcrystalline crack lengths tended to have a log-normal distribution. The logarithmic mean crack length (LMCL) decreased with increasing strain rate, decreasing grain-size and decreasing temperature and tended to a constant value of 0.75 mm at 10°C. For grain-size of 3 mm or greater, the LMCL had a maximum at a strain rate of 10−5 to 10−6 S−1 at −10°C. The LMCLs and the relative proportion of grain-boundary cracks tended to be normally distributed for given load conditions.

scholarly journals The role of grain-size ratio in the mobility of mixed granular beds

Geomorphology ◽  
2017 ◽  
Vol 278 ◽  
pp. 314-328 ◽  
Author(s):  
Franziska Staudt ◽  
Julia C. Mullarney ◽  
Conrad A. Pilditch ◽  
Katrin Huhn
Keyword(s):  
Grain Size ◽  
Size Ratio

scholarly journals Primary, secondary and tertiary creep of ice modelled as a viscoelastic fluid

2009 ◽  
Vol 55 (189) ◽  
pp. 170-178 ◽  
Author(s):  
L. W. Morland
Keyword(s):  
Strain Rate ◽  
Viscoelastic Fluid ◽  
Ice Sheet ◽  
Constant Strain Rate ◽  
Constant Stress ◽  
Constitutive Law ◽  
Asymptotic Limit ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Viscous Behaviour

AbstractAs an ice sheet evolves, there are ice elements near the surface only recently subjected to stress following deposition, and others that have been subjected to stress over many ranges of time. The constant stress and constant strain-rate responses of ice in uniaxial compressive stress exhibit non-viscous behaviour, that is, the strain rate is not fixed by the stress (and conversely) but both vary with time. At constant stress the initial primary strain rate decreases with time to a minimum, described as secondary creep. It then increases and approaches an asymptotic limit, described as tertiary creep. Analogously, at constant strain rate the initial stress increases to a maximum then decreases to an asymptotic limit. These responses are used to construct a simple viscoelastic fluid constitutive law of differential type. Such a time-dependent law, with timescales changing widely with temperature, can be expected to yield a flow field in an ice sheet that is very different from that obtained from the viscous law. Only comparison solutions for both constitutive laws can determine the differences and significance of the non-viscous behaviour, and the simple law constructed would be a candidate for such comparisons.

Creep Cavitation Enhanced by Glass Pocket Formation in a Tetragonal Zirconia Doped with 0.3 WT% Pure Silica

1998 ◽  
Vol 539 ◽  
Author(s):  
K. Morita ◽  
K. Hiraga ◽  
Y. Sakka
Keyword(s):  
Grain Size ◽  
Glass Phase ◽  
Tetragonal Zirconia ◽  
Constant Stress ◽  
Cavity Formation ◽  
Phase Precipitation ◽  
Pure Silica ◽  
Creep Cavitation ◽  
Pocket Formation ◽  
The Relationship

AbstractThe relationship between intergranular microstructures and cavitation is examined in a yttria-stabilized tetragonal zirconia doped with 0.2-0.4 wt% SiO2 under constant stress loading in tension. An increase in the initial grain size for a constant SiO2-addition or an increase in SiO2-addition for a constant grain size enhances the precipitation of a glass phase at the multiple grain junctions during deformation. Simultaneously with the enhanced glass phase precipitation, intergranular cavitation is also enhanced. This is because the precipitated glass phase act as the site of cavity formation.

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