Depth- and time-dependent vertical strain rates at Siple Dome, Antarctica

AbstractAs part of a project to investigate the flow of ice at low effective stress, two independent strain-gauge systems were used to measure vertical strain rate as a function of depth and time at Siple Dome, Antarctica. The measurements were made from January 1998 until January 2002 at the ice divide and a site 7km to the northeast on the flank. The strain-rate profiles place constraints on the rheology of ice at low stress, show the expected differences between divide and flank flow (with some structure due to firn compaction and probably ice stratigraphy), and suggest that the flow of the ice sheet has not changed much in the last 8.6 kyr. The strain rates show an unexpected time dependence on scales ranging from several months to hours, including discrete summer events at the divide. Time dependence in strain rate, water pressure, seismicity, velocity and possibly basal motion has been seen previously on the Siple Coast ice streams, but it is especially surprising on Siple Dome because the bed is cold.

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A 3 Year Record of Seasonal Variations in Surface Velocity, StorglaciÄren, Sweden

Journal of Glaciology ◽

10.3189/s0022143000004561 ◽

1989 ◽

Vol 35 (120) ◽

pp. 235-247 ◽

Cited By ~ 135

Author(s):

Roger LeB. Hooke ◽

Peter Calla ◽

Per Holmlund ◽

Mats Nilsson ◽

Arjen Stroeven

Keyword(s):

Strain Rate ◽

Shear Strain ◽

Seasonal Variations ◽

High Velocity ◽

Water Pressure ◽

Force Balance ◽

Surface Velocity ◽

Time Interval ◽

Strain Rates ◽

Lateral Shear

Abstract Between 3 June 1982 and 8 July 1985, a stake net consisting of up to 32 stakes covering the greater part of Storglaciären was surveyed 70 times, yielding roughly 2000 separate determinations of vertical and horizontal velocity. The time interval between surveys averaged about 1 week during the summer and 2 months during the winter. Horizontal velocities were normally highest during periods of high daily temperature or heavy rain early in the melt season. Comparable or sometimes higher temperatures or rainfalls later in the season usually had less effect, though minor velocity peaks were often present in August and early September. During periods for which bore-hole water-level measurements are available, velocity peaks generally coincided with periods of high basal water pressure, but not all periods of high water pressure resulted in velocity peaks. Despite increasing basal water pressures, velocity decreased gradually during the winter. Vertical velocities also vary seasonally. Beneath the upper part of the ablation area the glacier bed is overdeepened. Vertical velocities here are ˜3 mm/d higher during the summer. Down-glacier from the overdeepening, vertical velocities are ˜1 mm/d lower during the summer. These and other characteristics of the vertical velocity pattern are best explained by appealing to: (1) a decrease in strain-rate with depth, and (2) seasonal variations in this depth-dependence. Five periods of high velocity lasting from 3 to 11d were studied in detail. In an area where the bed is overdeepened, force-balance calculations suggest that basal drag decreased between 16 and 40% during these high-velocity events. This resulted in a decrease in compressive strain-rate at the up-glacier end of the overdeepening, an increase at the down-glacier end, and a slight increase in lateral shear strain-rates. Down-glacier from the overdeepening, basal drag increased during two events owing to an increased push from up-glacier and pull from down-glacier. Lateral shear strain-rates increased sharply here.

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Measurement of vertical strain and velocity at Siple Dome, Antarctica, with optical sensors

Journal of Glaciology ◽

10.3189/172756502781831421 ◽

2002 ◽

Vol 48 (161) ◽

pp. 217-225 ◽

Cited By ~ 15

Author(s):

Mark A. Zumberge ◽

Daniel H. Elsberg ◽

William D. Harrison ◽

Eric Husmann ◽

John L. Morack ◽

...

Keyword(s):

Optical Fibers ◽

Optical Sensors ◽

Ice Sheet ◽

Hot Water ◽

Constitutive Relationship ◽

Strain Rates ◽

Thin Wall ◽

Vertical Strain ◽

The North ◽

Siple Dome

AbstractAs part of a larger program to measure and model vertical strain around Siple Dome on the West Antarctic ice sheet, we developed a new sensor to accurately and stably record displacements. The sensors consist of optical fibers, encased in thin-wall stainless-steel tubes, frozen into holes drilled with hot water, and stretched from the surface to various depths (up to 985 m) in the ice sheet. An optical system, connected annually to the fibers, reads out their absolute lengths with a precision of about 2 mm. Two sets of five sensors were installed in the 1997/98 field season: one set is near the Siple Dome core hole (an ice divide), and a second set is on the flank 7 km to the north (the ice thickness at both sites is approximately 1000 m). The optical-fiber length observations taken in four field seasons spanning a 3 year interval reveal vertical strain rates ranging from −229 ± 4 ppm a−1 to −7 ± 9 ppm a−1. In addition to confirming a non-linear constitutive relationship for deep ice, our analysis of the strain rates indicates the ice sheet is thinning at the flank and is in steady state at the divide.

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Dating firn cores by vertical strain measurements

Journal of Glaciology ◽

10.3189/172756502781831250 ◽

2002 ◽

Vol 48 (162) ◽

pp. 401-406 ◽

Cited By ~ 12

Author(s):

Robert L. Hawley ◽

Edwin D. Waddington ◽

David L. Morse ◽

Nelia W. Dunbar ◽

Gregory A. Zielinski

Keyword(s):

Ice Core ◽

Video Camera ◽

Strain Rates ◽

West Antarctica ◽

Polar Ice ◽

Vertical Strain ◽

Ash Layer ◽

Siple Dome ◽

Polar Ice Sheets ◽

Rate Profile

AbstractWe have developed a system for measuring a vertical strain-rate profile in the firn on polar ice sheets using a readily available video camera to detect metal bands inserted in an air-filled hole. We used this system in 1995 and 1996 at Taylor Dome, Antarctica. We use density measurements combined with our strain rates to infer vertical velocities. From our velocities we calculate a steady-state depth–age scale for the firn at Taylor Dome. The age of a visible ash layer from 79.1 m is 675 ± 25 years; this ash can be correlated with ash found at 97.2 m in a recent ice core at Siple Dome, West Antarctica.

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Observations of a reversal in vertical and horizontal strain-rate regime during a motion event on Unteraargletscher, Bernese Alps, Switzerland

Journal of Glaciology ◽

10.3189/172756502781831043 ◽

2002 ◽

Vol 48 (163) ◽

pp. 566-574 ◽

Cited By ~ 18

Author(s):

G. Hilmar Gudmundsson

Keyword(s):

Strain Rate ◽

Global Positioning System ◽

Ice Thickness ◽

Strain Rates ◽

Mean Values ◽

Vertical Strain ◽

Motion Event ◽

Global Positioning ◽

Measuring Site ◽

Horizontal Strain

AbstractDuring a motion event on Unteraargletscher, Bernese Alps, Switzerland, in spring 1996, surface velocities were measured up to eight times a day at four different locations along the central flowline using global positioning system equipment. In addition, accumulated vertical strains over the uppermost 50 and 100 m were measured at a location where the total ice thickness is 260 m. The motion event was accompanied by high horizontal and vertical strain rates as compared to annual mean values. A reversal in strain regime was observed, with horizontal strain rates changing to extension while vertical strain rates became compressive. This strain-rate reversal coincided, within the temporal resolution of the data, with a maximum in vertical ice displacement at the surface.Within a day, variations in vertical strain from 0.04 a−1 to −0.06 a−1 were observed over the uppermost 100 m. Vertical stretching is estimated to have contributed to at least 20% of the anomalous vertical ice movement at the surface. There were significant differences between measured longitudinal strain, averaged over a distance corresponding to a few ice thicknesses, and measured vertical strain. In spring 1997 a similar, but more detailed, set of measurements was collected at the same measuring site, and vertical strain rates were found to vary non-uniformly with depth, with the largest values closest to the surface.

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The effects of strain and strain rate on residual microstructures in copper

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100143687 ◽

1986 ◽

Vol 44 ◽

pp. 420-421

Author(s):

M. F. Stevens ◽

P. S. Follansbee

Keyword(s):

Strain Rate ◽

Applied Stress ◽

Threshold Stress ◽

Rate Sensitivity ◽

Viscous Drag ◽

Strain Rates ◽

Strain And Strain Rate ◽

Threshold Strength ◽

Mechanism Transition ◽

Intrinsic Strength

The strain rate sensitivity of a variety of materials is known to increase rapidly at strain rates exceeding ∼103 sec-1. This transition has most often in the past been attributed to a transition from thermally activated guide to viscous drag control. An important condition for imposition of dislocation drag effects is that the applied stress, σ, must be on the order of or greater than the threshold stress, which is the flow stress at OK. From Fig. 1, it can be seen for OFE Cu that the ratio of the applied stress to threshold stress remains constant even at strain rates as high as 104 sec-1 suggesting that there is not a mechanism transition but that the intrinsic strength is increasing, since the threshold strength is a mechanical measure of intrinsic strength. These measurements were made at constant strain levels of 0.2, wnich is not a guarantee of constant microstructure. The increase in threshold stress at higher strain rates is a strong indication that the microstructural evolution is a function of strain rate and that the dependence becomes stronger at high strain rates.

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A Review on Mechanical Properties of Natural Fibre Reinforced Polymer Composites under Various Strain Rates

Journal of Composites Science ◽

10.3390/jcs5050130 ◽

2021 ◽

Vol 5 (5) ◽

pp. 130

Author(s):

Tan Ke Khieng ◽

Sujan Debnath ◽

Ernest Ting Chaw Liang ◽

Mahmood Anwar ◽

Alokesh Pramanik ◽

...

Keyword(s):

Mechanical Properties ◽

Strain Rate ◽

Polymer Composites ◽

Stress Transfer ◽

Natural Fibre ◽

Transfer Efficiency ◽

Strain Rates ◽

Reinforced Polymer ◽

Fibre Reinforced Polymer ◽

Fibre Matrix

With the lightning speed of technological evolution, the demand for high performance yet sustainable natural fibres reinforced polymer composites (NFPCs) are rising. Especially a mechanically competent NFPCs under various loading conditions are growing day by day. However, the polymers mechanical properties are strain-rate dependent due to their viscoelastic nature. Especially for natural fibre reinforced polymer composites (NFPCs) which the involvement of filler has caused rather complex failure mechanisms under different strain rates. Moreover, some uneven micro-sized natural fibres such as bagasse, coir and wood were found often resulting in micro-cracks and voids formation in composites. This paper provides an overview of recent research on the mechanical properties of NFPCs under various loading conditions-different form (tensile, compression, bending) and different strain rates. The literature on characterisation techniques toward different strain rates, composite failure behaviours and current challenges are summarised which have led to the notion of future study trend. The strength of NFPCs is generally found grow proportionally with the strain rate up to a certain degree depending on the fibre-matrix stress-transfer efficiency. The failure modes such as embrittlement and fibre-matrix debonding were often encountered at higher strain rates. The natural filler properties, amount, sizes and polymer matrix types are found to be few key factors affecting the performances of composites under various strain rates whereby optimally adjust these factors could maximise the fibre-matrix stress-transfer efficiency and led to performance increases under various loading strain rates.

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Experimental Study on Biaxial Dynamic Compressive Properties of ECC

Materials ◽

10.3390/ma14051257 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1257

Author(s):

Shuling Gao ◽

Guanhua Hu

Keyword(s):

Strain Rate ◽

Lateral Pressure ◽

Deformation Modulus ◽

Strain Curve ◽

Peak Stress ◽

Pressure Level ◽

Strain Rates ◽

Peak Strain ◽

Stress Strain Curve ◽

Toughness Index

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10−4, 10−3 and 10−2 s−1. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete.

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Using Artificial Neural Networks to Predict Influences of Heterogeneity on Rock Strength at Different Strain Rates

Materials ◽

10.3390/ma14113042 ◽

2021 ◽

Vol 14 (11) ◽

pp. 3042

Author(s):

Sheng Jiang ◽

Mansour Sharafisafa ◽

Luming Shen

Keyword(s):

Neural Network ◽

Artificial Neural Network ◽

Strain Rate ◽

Network Model ◽

Neural Network Model ◽

Artificial Neural Network Model ◽

Rock Strength ◽

Strain Rates ◽

Filling Material ◽

Artificial Neural

Pre-existing cracks and associated filling materials cause the significant heterogeneity of natural rocks and rock masses. The induced heterogeneity changes the rock properties. This paper targets the gap in the existing literature regarding the adopting of artificial neural network approaches to efficiently and accurately predict the influences of heterogeneity on the strength of 3D-printed rocks at different strain rates. Herein, rock heterogeneity is reflected by different pre-existing crack and filling material configurations, quantitatively defined by the crack number, initial crack orientation with loading axis, crack tip distance, and crack offset distance. The artificial neural network model can be trained, validated, and tested by finite 42 quasi-static and 42 dynamic Brazilian disc experimental tests to establish the relationship between the rock strength and heterogeneous parameters at different strain rates. The artificial neural network architecture, including the hidden layer number and transfer functions, is optimized by the corresponding parametric study. Once trained, the proposed artificial neural network model generates an excellent prediction accuracy for influences of high dimensional heterogeneous parameters and strain rate on rock strength. The sensitivity analysis indicates that strain rate is the most important physical quantity affecting the strength of heterogeneous rock.

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Static Mechanical Properties of Expanded Polypropylene Crushable Foam

Materials ◽

10.3390/ma14020249 ◽

2021 ◽

Vol 14 (2) ◽

pp. 249

Author(s):

Przemysław Rumianek ◽

Tomasz Dobosz ◽

Radosław Nowak ◽

Piotr Dziewit ◽

Andrzej Aromiński

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Strain Rate ◽

Energy Absorption ◽

Experimental Tests ◽

Absorption Capacity ◽

Strain Rates ◽

Foam Density ◽

Energy Absorption Capacity ◽

Closed Cell

Closed-cell expanded polypropylene (EPP) foam is commonly used in car bumpers for the purpose of absorbing energy impacts. Characterization of the foam’s mechanical properties at varying strain rates is essential for selecting the proper material used as a protective structure in dynamic loading application. The aim of the study was to investigate the influence of loading strain rate, material density, and microstructure on compressive strength and energy absorption capacity for closed-cell polymeric foams. We performed quasi-static compressive strength tests with strain rates in the range of 0.2 to 25 mm/s, using a hydraulically controlled material testing system (MTS) for different foam densities in the range 20 g/dm3 to 220 g/dm3. The above tests were carried out as numerical simulation using ABAQUS software. The verification of the properties was carried out on the basis of experimental tests and simulations performed using the finite element method. The method of modelling the structure of the tested sample has an impact on the stress values. Experimental tests were performed for various loads and at various initial temperatures of the tested sample. We found that increasing both the strain rate of loading and foam density raised the compressive strength and energy absorption capacity. Increasing the ambient and tested sample temperature caused a decrease in compressive strength and energy absorption capacity. For the same foam density, differences in foam microstructures were causing differences in strength and energy absorption capacity when testing at the same loading strain rate. To sum up, tuning the microstructure of foams could be used to acquire desired global materials properties. Precise material description extends the possibility of using EPP foams in various applications.

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Comparison in Deformation Behavior, Microstructure, and Failure Mechanism of Nickel Base Alloy 625 under Two Strain Rates

Materials ◽

10.3390/ma14102652 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2652

Author(s):

Meng Liu ◽

Quanyi Wang ◽

Yifan Cai ◽

Dong Lu ◽

Tianjian Wang ◽

...

Keyword(s):

Strain Rate ◽

Deformation Behavior ◽

Tensile Deformation ◽

Base Alloy ◽

Inconel 625 ◽

Tensile Fracture ◽

Nickel Base Superalloy ◽

Strain Rates ◽

Tensile Fracture Surface ◽

Nickel Base

Tensile deformation behavior and microstructure of nickel-base superalloy Inconel 625 are investigated under different strain rates of 5 × 10−4 s−1 and 5 × 10−5 s−1. According to the experimental results, yield strength and ultimate tensile strength of the alloy increase with the increase in strain rate in room temperature. Microstructure results indicate that the size of dimples is smaller in the tensile fracture surface at low strain rate than the high strain rate, and the number of dimples is also related to the strain rates and twins appear earlier in the specimens with higher strain rates. Apart from Hollomon and Ludwik functions, a new formula considering the variation trend of strength in different deformation stages is deduced and introduced, which fit closer to the tensile curves of the 625 alloy used in the present work at both strain rates. Furthermore, the Schmid factors of tensile samples under two strain rates are calculated and discussed. In the end, typical work hardening behavior resulting from the dislocations slip behavior under different strain rates is observed, and a shearing phenomenon of slip lines cross through the δ precipitates due to the movement of dislocations is also be note.

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