Indentation and Penetration of Edge-Loaded Freshwater Ice Sheets in the Brittle Range

1987 ◽  
Vol 109 (3) ◽  
pp. 287-294 ◽  
Author(s):  
G. W. Timco
Keyword(s):  
Aspect Ratio ◽  
Ice Sheets ◽  
Ice Thickness ◽  
Test Results ◽  
Tabular Form ◽  
Test Procedures ◽  
Freshwater Ice ◽  
Edge Loading ◽  
Ice Failure ◽  
Penetration Tests

A series of indentation and penetration tests have been performed by edge loading of a vertical indentor into a floating sheet of columnar S2 freshwater ice. The load on the indentor was measured as a function of interaction speed (v = 0.1 – 60 cm-s−1), indentor width (D = 2.54 – 12.7 cm), ice thickness (h = 0.6 – 3.3 cm), strain rate (ε˙ = v/2D = 10−2 – 101 s−1) and aspect ratio (D/h = 0.5 − 22). In total, 66 tests were performed. In this paper, a description of the test procedures is given along with the full results in both graphical and tabular form. Five different ice fracture modes are identified and described. From the test results, an ice-failure mode map is derived which indicates the conditions in which each ice fracture mode predominates.

Performance Estimation of Axial Flow Turbines

1970 ◽  
Vol 185 (1) ◽  
pp. 407-424 ◽  
Author(s):  
H. R. M. Craig ◽  
H. J. A. Cox
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Gas Turbines ◽  
Three Dimensional ◽  
Axial Flow ◽  
Performance Estimation ◽  
Speed Ratio ◽  
Test Results ◽  
Wide Range ◽  
Relevant Variables

A comprehensive method of estimating the performance of axial flow steam and gas turbines is presented, based on analysis of linear cascade tests on blading, on a number of turbine test results, and on air tests of model casings. The validity of the use of such data is briefly considered. Data are presented to allow performance estimation of actual machines over a wide range of Reynolds number, Mach number, aspect ratio and other relevant variables. The use of the method in connection with three-dimensional methods of flow estimation is considered, and data presented showing encouraging agreement between estimates and available test results. Finally ‘carpets’ are presented showing the trends in efficiencies that are attainable in turbines designed over a wide range of loading, axial velocity/blade speed ratio, Reynolds number and aspect ratio.

scholarly journals The Effect of Probe Geometry on Rind Puncture Resistance Testing of Maize Stalks

2020 ◽  
Author(s):  
Douglas D. Cook ◽  
Kyler Meehan ◽  
Levan Asatiani ◽  
Daniel J Robertson
Keyword(s):  
Meta Analysis ◽  
Resistance Testing ◽  
Test Results ◽  
Lodging Resistance ◽  
Puncture Resistance ◽  
Analysis Of Results ◽  
Stalk Lodging ◽  
Penetration Tests ◽  
Shape And Size ◽  
Probe Geometry

Abstract Background: Stalk lodging (breaking of plant stems prior to harvest) is a major impediment to increasing agricultural yields of grain crops. Rind puncture resistance is commonly used to predict the lodging resistance of several crop species. However, there exist no standard operating procedures or suggested protocols for conducting rind penetration experiments. In addition, experimental details of rind penetration tests such as the shape and size of the penetrating probe are rarely reported in the literature. This has prevented meta-analysis of results and has likewise prevented key findings of past studies from being replicated. As a first step towards establishing an agreed upon measurement standard for rind puncture resistance this study investigates the effect of the puncturing probe’s geometry on test results.Results: Results demonstrate that probe geometry has a significant impact on test results. In particular, results showed that a 2mm diameter chamfered probe produced stronger correlations with stalk bending strength than a 1.5mm diameter pointed probe. The chamfered probe was also more strongly correlated with geometric features of the stalk that are known to influence stalk lodging resistance (e.g., rind thickness, diameter and section modulus). In addition, several alternative rind penetration metrics were investigated, and some were found to be superior to the most common rind penetration metric of maximum load. Conclusions:There is a need in the agricultural and plant science community to create agreed-upon operating procedures and testing standards related to mechanical traits of plant stems. In particular, a standardized probe geometry and insertion rate for rind penetration studies are needed to enable greater interoperability and meta-analysis of results. Probe shape and size should be reported in any study conducting rind penetration tests as these factors significantly impact test results.

scholarly journals Elastic properties of floating sea ice from air-coupled flexural waves

2021 ◽  
Author(s):  
Rowan Romeyn ◽  
Alfred Hanssen ◽  
Bent Ole Ruud ◽  
Tor Arne Johansen
Keyword(s):  
Sea Ice ◽  
Elastic Properties ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Flexural Wave ◽  
Ice Thickness ◽  
Linear Filter ◽  
Flexural Stiffness ◽  
Flexural Waves ◽  
Impulsive Source

Abstract. Air-coupled flexural waves appear as wave trains of constant frequency that arrive in advance of the direct air-wave from an impulsive source travelling over a floating ice sheet. The frequency of these waves varies with the flexural stiffness of the ice sheet, which is controlled by a combination of thickness and elastic properties. We develop a theoretical framework to understand these waves, utilizing modern numerical and Fourier methods to give a simpler and more accessible description than the pioneering, yet unwieldly analytical efforts of the 1950's. Our favoured dynamical model can be understood in terms of linear filter theory and is closely related to models used to describe the flexural waves produced by moving vehicles on floating plates. We find that air-coupled flexural waves are a robust feature of floating ice-sheets excited by impulsive sources over a large range of thicknesses, and we present a simple closed-form estimator for the ice thickness. Our study is focussed on first-year sea ice of ~20–80 cm thickness in Van Mijenfjorden, Svalbard, that was investigated through active source seismic experiments over four field campaigns in 2013, 2016, 2017 and 2018. The air-coupled flexural frequencies for sea-ice in this thickness range are ~60–240 Hz. While air-coupled flexural waves for thick sea-ice have received little attention, the higher frequencies associated with thin ice on fresh water lakes and rivers are well known to the ice-skating community and have been reported in popular media. Estimation of ice physical properties, following the approach we present, may allow improved surface wave modelling and wavefield subtraction in reflection seismic studies where flexural wave noise is undesirable. On the other hand, air-coupled flexural waves may also permit non-destructive continuous monitoring of ice thickness and flexural stiffness using simple, relatively inexpensive microphones located in the vicinity of the desired measurement location, either above the ice-sheet or along the shoreline. In this case, naturally forming cracks in the ice may be an appropriate impulsive source capable of exciting flexural waves in floating ice sheets in a passive monitoring context.

Experimental characterization of composites to support an orthotropic plasticity material model

2017 ◽  
Vol 52 (14) ◽  
pp. 1847-1872 ◽  
Author(s):  
Bilal Khaled ◽  
Loukham Shyamsunder ◽  
Canio Hoffarth ◽  
Subramaniam D Rajan ◽  
Robert K Goldberg ◽  
...  
Keyword(s):  
Material Model ◽  
Unidirectional Composite ◽  
Deformation Model ◽  
Test Results ◽  
Dynamic Impact ◽  
Test Procedures ◽  
Stress Strain ◽  
Damage And Failure ◽  
Orthotropic Behavior

Test procedures for characterizing the orthotropic behavior of a unidirectional composite at room temperature and quasi-static loading conditions are developed and discussed. The resulting data consisting of 12 stress–strain curves and associated material parameters are used in a newly developed material model—an orthotropic elasto-plastic constitutive model that is driven by tabulated stress–strain curves and other material properties that allow for the elastic and inelastic deformation model to be combined with damage and failure models. A unidirectional composite—T800/F3900, commonly used in the aerospace industry, is used to illustrate how the experimental procedures are developed and used. The generated data are then used to model a dynamic impact test. Results show that the developed framework implemented into a special version of LS-DYNA yields reasonably accurate predictions of the structural behavior.

On the Flexural Failure of Thick Ice Against Sloping Structures

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Fwu Chyi Teo ◽  
Leong Hien Poh ◽  
Sze Dai Pang
Keyword(s):  
Reference Model ◽  
Ice Sheets ◽  
Axial Loading ◽  
Breaking Load ◽  
Ice Thickness ◽  
Design Code ◽  
Modified Model ◽  
Flexural Failure ◽  
Bending Effect ◽  
Loading Eccentricity

This paper investigates the breaking load of ice sheets up to 6 m thick, against a sloping structure. The reference model by Croasdale, which the design code is based on, neglects the edge moment arising from the loading eccentricity, as well as a second-order bending effect induced by the axial loading in its formulation. In this paper, the model is reformulated to incorporate these effects into the governing equation, as well as to account for the occurrence of local crushing at the point of contact between the ice sheet and sloping structure. For thin ice, predictions from the modified model resemble closely those by Croasdale's model. As the ice thickness increases, however, significant deviations from the reference model can be observed. For thick ice, the terms omitted for brevity in the reference model have a significant influence, without which the breaking load is under-estimated. It is furthermore demonstrated that against sloping structures, the dominant failure mode is that of flexural, except in very limiting cases where it switches to crushing.

scholarly journals Indentation of an S2 Floating Ice Sheet in the Brittle Range

1983 ◽  
Vol 4 ◽  
pp. 180-187 ◽  
Author(s):  
B. Michel ◽  
D. Blanchet
Keyword(s):  
Aspect Ratio ◽  
Research Work ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Theory Of Elasticity ◽  
Maximum Pressure ◽  
Shear Cracks ◽  
Aspect Ratios ◽  
Two Parameters ◽  
The Impact

The problem of a floating ice sheet hitting a structure with a vertical face appears to be a simple one but, in fact, has only been solved for a limited number of cases. Research work on this question usually reports on an indentation coefficient which relates the average pressure on the indenter to the uniaxial crushing strength of the ice. Very few tests have been made in the brittle range of ice failure. In this particular area of study, this paper reports on 27 tests that were conducted in a cold-room water basin where controlled S2floating ice sheets were produced with a surface area of 4 × 4 m, three sides being fully restrained and the other, freely float! no, being submitted to the impact of the moving indenter. All tests were carried out at computed indentation rates varying from 0.017 to 0.34 s-1. In this range this ice would normally be considered to act as a brittle material. The thickness of the ice sheets varied from 1.2 to 9.0 cm and the indenter width from 5 cm to 1 m. Overall, the aspect ratio relating these two parameters could be varied from 0.5 to 83.Results have shown that for aspect ratios <5, there was an important oscillatory effect which caused the formation of pi asti fi ed triangles in front of the indenter, increasing its resistance as it would under ductile conditions. Because of this plastification, an extrusion effect appeared in front of the indenter as the broken ice crystals were blown up and down in front of the fast-moving indenter. The theory of plasticity which gives an indentation coefficient of 2.97 seems to apply in this case. Another mode of failure which occurred with aspect ratios 5 was cleavage in the plane of the ice sheet which also gives a higher indentation coefficient for S2ice, but of the same order of magnitude as previously.For intermediate values of the aspect ratio, between 5 and 20, the theory of elasticity used by Michel (1978) seems to apply well. Shear cracks are first formed on both sides of the square indenter and control the maximum pressure when they propagate inside forming big triangles in front of it.Finally, for aspect ratios ~>20, buckling of the ice occurs, either after or at the same time as the formation of wedges, together with a reduction in the indentation coefficient to a value close to that given by the theory of buckling of a truncated 45° wedge with a hinged edge.

scholarly journals Upper and lower limits on the stability of calving glaciers from the yield strength envelope of ice

2011 ◽  
Vol 468 (2140) ◽  
pp. 913-931 ◽  
Author(s):  
J. N. Bassis ◽  
C. C. Walker
Keyword(s):  
Yield Strength ◽  
Water Depth ◽  
Shear Failure ◽  
Ice Sheets ◽  
Direct Consequence ◽  
Ice Thickness ◽  
Tightly Coupled ◽  
The Stability ◽  
Induced Changes ◽  
Lower Limits

Observations indicate that substantial changes in the dynamics of marine-terminating ice sheets and glaciers are tightly coupled to calving-induced changes in the terminus position. However, the calving process itself remains poorly understood and is not well parametrized in current numerical ice sheet models. In this study, we address this uncertainty by deriving plausible upper and lower limits for the maximum stable ice thickness at the calving face of marine-terminating glaciers, using two complementary models. The first model assumes that a combination of tensile and shear failure can render the ice cliff near the terminus unstable and/or enable pre-existing crevasses to intersect. A direct consequence of this model is that thick glaciers must terminate in deep water to stabilize the calving front, yielding a predicted maximum ice cliff height that increases with increasing water depth, consistent with observations culled from glaciers in West Greenland, Antarctica, Svalbard and Alaska. The second model considers an analogous lower limit derived by assuming that the ice is already fractured and fractures are lubricated by pore pressure. In this model, a floating ice tongue can only form when the ice entering the terminus region is relatively intact with few pre-existing, deeply penetrating crevasses.

Experimental Study on Deep Four-Pile Caps with Different Reinforcement Layouts Based on 3D Strut-and-Tie Analogy

2008 ◽  
Vol 400-402 ◽  
pp. 917-922 ◽  
Author(s):  
Qian Gu ◽  
Cheng Fang Sun ◽  
Shao Min Peng
Keyword(s):  
Load Capacity ◽  
Longitudinal Reinforcement ◽  
Test Results ◽  
Test Procedures ◽  
Strut And Tie ◽  
Pile Cap ◽  
Scale Ratio ◽  
Pile Caps ◽  
Strut And Tie Model ◽  
Distributed Reinforcement

Based on 3D strut-and-tie analogy developed for analyzing the load-transferring mechanism of deep pile cap, this paper focuses on the effect of different longitudinal reinforcement layouts at the lower part of cap on the mechanical behaviors of deep four-pile cap. Besides a common layout of uniformly distributed reinforcement by the flexural theory, three different layouts of concentrated reinforcement over piles were designed by 3D strut-and-tie analogy. All specimens were limited in same reinforcement percentages, dimensions, materials and test procedures. Four specimens with the scale ratio of 1/5 were tested under the statically incremental gravity loading. The load capacity, deflection, strain of longitudinal reinforcement of specimens were measured, and the failure mode, crack propagation, deformation of specimens and stress distribution of reinforcement were analyzed. Through comparisons of the test results among all specimens, it was found that deep pile cap failed in shear and corner-pile punching whether with concentrated or uniform reinforcement, and the reinforcement concentrated over each two adjacent piles, similar to the tension bars in the strut-and-tie model, had considerable advantages than common uniform reinforcement layout. The ultimate strength of deep pile cap with concentrated reinforcement was significantly increased, while the improvement of deformation resistance and brittleness of deep pile cap was limited. According to above findings, the appropriate reinforcement layouts for deep pile cap were suggested in this paper.

scholarly journals High-Altitude Radar Measurements of Ice Thickness Over the Antarctic and Greenland Ice Sheets as a Part of Operation IceBridge

2013 ◽  
Vol 51 (2) ◽  
pp. 742-754 ◽  
Author(s):  
Jilu Li ◽  
John Paden ◽  
Carl Leuschen ◽  
Fernando Rodriguez-Morales ◽  
Richard D. Hale ◽  
...  
Keyword(s):  
High Altitude ◽  
Ice Sheets ◽  
Ice Thickness ◽  
Radar Measurements ◽  
The Antarctic

Shoulder Ice Barrier Ice Tank Testing—Part II: Estimation of Breaking Length and Block Size Using Image Analysis

2009 ◽  
Author(s):  
Ada H. V. Repetto-Llamazares ◽  
Ove T. Gudmestad ◽  
Arne Gu¨rtner ◽  
Knut V. Ho̸yland
Keyword(s):  
Image Analysis ◽  
Linear Trend ◽  
Phase 1 ◽  
Block Size ◽  
Model Tests ◽  
Characteristic Change ◽  
Ice Thickness ◽  
Breaking Length ◽  
Ice Failure ◽  
Block Sizes

When studying ice interaction on sloped structures, a key parameter that is usually reported after experiments and observations either in Full Scale or Model Scale is the breaking length associated with the ice failure. Moreover, either for numerical modeling or load calculations the size of the blocks generated during ice-structure interaction that accumulates rubble is of importance. In this paper, the technique of image analysis has been used to obtain values of the breaking length and the ice block sizes generated during model tests of a Shoulder Ice Barrier (SIB)-ice interaction. The model tests were performed in the Hamburg Ship Model Basin (HSVA) during July 2007. Since the SIB represents a new concept in ice barrier structures, model tests were intended to evaluate its general performance. A brief description of the model tests and the image analysis technique used to analyze the data is done. A total of five experiments where ice thickness, ice flexural strength and shoulder inclination were varied, are analyzed. Results of the breaking length analysis show that there is a characteristic change in the breaking length associated with the transition from ice interactions on the bare structure (Phase 1) and interaction onto accumulated rubble (Phase 2). Average values of the breaking length of both phases for each experiment are presented. Since the information regarding breaking length in structures that accumulate rubble is sparse, the experimental results of Phase 1, where the rubble accumulation is still small, are compared with the predictions from three different models presented in the literature for sloped structures, under similar ice conditions, that do not accumulate rubble. The comparison allows concluding that the breaking phenomenon is being reasonably well modeled in the experiments. The block sizes of the upper layer of the accumulated rubble were analyzed and the block length and width distributions were found for each experiment. A linear trend was found between block size and ice thickness. A linear fitting of the data was performed in order to obtain simple equations which give an upper limit of the length and width of the ice blocks generated during the SIB-ice interaction as function of the ice thickness. The results may apply for ice interaction on sloped structures in general as well.

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