Engineering Commons^™

The Impact Of Contact Geometry On Sea Ice Stress And Fracture At The Scale Of Ice Floes, Michael J. May

Dartmouth College Master’s Theses

Observations of stress and strain at the scale of ice floes are necessary to fill a gap in our understanding of sea ice mechanical behavior. Current climate and ice dynamics models represent ice mechanical properties using stress-strain relationships largely determined at laboratory-scale (<1m) or from regional-scale (10+km) deformation observations. The former scale does not include all mechanisms of deformation operating in the ice pack; the latter aggregates multiple modes of deformation into non-physical fluid analogies. The Sea Ice Dynamics Experiment (SIDEx) was run in Feb-Mar 2021 to fill this gap, observing stress and strain at the scale of sea ice failure processes. Here we present stress sensor observations. Stress gages (N=31) were deployed over a 4.5km² area in the southern Beaufort Sea to observe in-situ stress. These data were analyzed in the context of deformation observations from satellite imagery and local laser and radar interferometers to explain the drivers of sea ice stress variations before and after fracture. Three case studies between 14 March and 24 March, during which fractures propagated through …

A Foray Into Laboratory Scale Soil Incubations With Corn Stover And High Lignin Fermentation Byproduct, Michelle Wang

ENGS 88 Honors Thesis (AB Students)

As the production of biofuels increases to meet the demands of a growing low carbon economy, questions of sustainability surrounding its feedstock and waste streams have become increasingly relevant. In the biofuel production process, crop residues like corn stover are harvested from the field and converted to biofuels leaving generating a residue called high lignin fermentation byproduct (HLFB). From extensive process modelling in the literature, it is suggested that HLFB should be either combusted to fuel auxiliary conversion processes or returned to the soil in place of the crop residues that were harvested. Currently, there is little literature testing the …

Development Of An Rfid Tracking System For Coarse Sediment Transport In A Flume Setting, Peter Mahoney Jr.

ENGS 88 Honors Thesis (AB Students)

Development of an RFID Tracking System for Coarse Sediment Transport in a Flume Setting

Peter E. Mahoney

Professor Carl Renshaw

Understanding how sediment moves through a fluvial system has important implications for the study of river systems, sediment flux, and flood events. Over the past decade, RFID (radio frequency identification) technology has emerged as a useful method for tracking the movement and transport of coarse sediment clasts. This approach has been used to measure the transport of large clasts in mid-sized streams, ephemeral channels, and laboratory flume settings. However, this research utilized finite transport of sediment and focused on accurately …

The Role Of Damage And Recrystallization In The Elastic Properties Of Columnar Ice, Scott A. Snyder, Erland M. Schulson, Carl E. Renshaw

Dartmouth Scholarship

Effects of damage on elastic properties were studied in columnar-grained specimens of freshwater and saline ice, subjected, at −10°C, to varying levels of inelastic strain. The ice was compressed uniaxially at constant strain rates up to 0.20 strain, which caused localized recrystallization and imparted damage in the form of non-propagating cracks. Damage was quantified in terms of dimensionless crack density, which, along with recrystallized area fraction, was determined from thin sections. The change in porosity due to stress-induced cracks served as another indicator of damage. Elastic properties were derived using P-wave and S-wave ultrasonic transmission velocities measured in across-column directions …

Joint Diagonalization Applied To The Detection And Discrimination Of Unexploded Ordnance, Fridon Shubitidze, Juan Pablo Fernández, Irma Shamatava, Benjamin Barrowes, Kevin O’Neill

Dartmouth Scholarship

Efforts to discriminate buried unexploded ordnance from harmless surrounding clutter are often hampered by the uncertainty in the number of buried targets that produce a given detected signal. We present a technique that helps determine that number with no need for data inversion. The procedure is based on the joint diagonalization of a set of multistatic response (MSR) matrices measured at different time gates by a time-domain electromagnetic induction sensor. In particular, we consider the Naval Research Laboratory’s Time-Domain Electromagnetic Multisensor Towed Array Detection System (TEMTADS), which consists of a 5×5 square grid of concentric transmitter/receiver pairs. The diagonalization process …

Using Borehole Logging And Electron Backscatter Diffraction To Orient An Ice Core From Upper Fremont Glacier, Wyoming, Usa, R. W. Obbard, T. Cassano, K. Aho, G. Troderman, I. Baker

Dartmouth Scholarship

While glacier fabric reflects the accumulated strain, detailed azimuthal information is required to link the microstructure to the flow, and this is not easily gathered at depth. Borehole logging provides a way to obtain a log of azimuthal orientation of tilted stratigraphic features that can be used to orient the core with respect to glacier flow. We demonstrate this using acoustic borehole logs and the ice core from a 162 m borehole in Upper Fremont Glacier, Wind River Range, Wyoming, USA. We measured the dip of tilted dust and bubble layers in the actual ice core, identified them on the …

Do Loading Path And Specimen Thickness Affect The Brittle Compressive Failure Of Ice?, A. L. Fortt, E. M. Schulson

Dartmouth Scholarship

Compressive experiments were performed on square (160 mm × 160 mm) prismatic specimens of columnar-grained, S2 freshwater ice, biaxially loaded across the columns at −10°C. The work focused on brittle behavior, achieved by deforming the specimens at an applied strain rate of 4.5 ± 1.2 × 10 3s 1 in the direction of shortening. The results show that the specimen thickness (25–150 mm) has no detectable effect on the terminal failure strength of the ice. Likewise, the strength of the ice when loaded under proportional loading, where the minor stress varies during the test, was similar to that when loaded …

The Effect Of Particles On Dynamic Recrystallization And Fabric Development Of Granular Ice During Creep, Min Song, Ian Baker, David M. Cole

Dartmouth Scholarship

The mechanical behavior and microstructural evolution of laboratory-prepared, particle-free fresh-water ice and ice with 1 wt.% (~0.43 vol.%) silt-sized particles were investigated under creep with a stress level of 1.45 MPa at −10°C. The particles were present both within the grains and along the grain boundaries. The creep rates of specimens with particles were always higher than those of particle-free ice. Dynamic recrystallization occurred for both sets of specimens, with new grains nucleating along grain boundaries in the early stages of creep. The ice with particles showed a higher nucleation rate. This resulted in a smaller average grain-size for the …

On The Strain-Rate Sensitivity Of Columnar Ice, M. E. Manley, E. M. Schulson

Dartmouth Scholarship

A power law relation between stress and strain rate of the form σ ∝ ε̇1/n was used to describe the response to strain rate of S1 ice loaded across the columns at -10°C. The rate exponent, n, decreased with increasing strain from about 4.6 at an observed peak on the load displacement curve to approximately 2.6 at a shortening of 2%. Analysis of these results and of the results of other authors on different forms of ice deformed at the same temperature suggests that the power law exponent, n, is proportional to Fc/Fg. The parameter Fc/Fg is the far-field basal …

Across-Column Cracks And Axial Splits In S2 Saline Ice Under Compression, E. M. Schulson, S. Qi, J. S. Melton, E. T. Gratz

Dartmouth Scholarship

Experiments on plate-like specimens have established that across-column cracks from within S2 (columnar) salt-water ice when compressed uniaxially along a direction inclined to the long axis of the grains. Wing cracks initiate from the across-column cracks and lengthen into axial splits when the ice is rapidly deformed; correspondingly; the macroscopic behavior changes from ductile to brittle. The across-column cracking is attributed to grain-boundary sliding, and the splitting to the suppression of crack-tip creep.

Brittle Compressive Failure Of Salt-Water Columnar Ice Under Biaxial Loading, T. R. Smith, E. M. Schulson

Dartmouth Scholarship

The brittle failure of saline columnar ice was investigated under biaxial compression at and −10° and −40°C over the range 0 ≤ R A < 1 where R A is the ratio of the intermediate to major principal compressive stress. The major principal stress and the intermediate (confining) stress were orthogonal to the columnar axes (type-A confinement); both stresses and the c-axes of the grains were co-planar. The results confirm earlier work by Hausier (1981) and Timco and Frederking (1983, 1986) on saline ice and follow similar behavior to fresh-water columnar ice found by Smith and Schulson (1993) and Frederking (1977). Failure stress and failure mode are sensitive to the confinement and two regimes of behavior are found: the failure stress first rapidly increases with R A in the range 0 ≤ R A < R T and then tends to decrease for R A > R t. The transition stress ratio, R t changes from ≈0.2 at −10°C to ≈0.1 at −40°C. The failure mode changes from axial splitting to shear faulting in the loading plane for 0 < R A < R t. Above R t failure changes to a combined mode of splitting across the columns and shear faulting out of the loading plane. The failure-stress envelope is of a truncated Coulomb-type. Damage studies show wing cracks and local fragmentation of grains involving the brine pockets. The results are explained in terms of Coulombic sliding and Hertzian crack mechanics.

The Fracture Of Ice On Scales Large And Small: Arctic Leads And Wing Cracks, E. M. Schulson, W. D. Hibler

Dartmouth Scholarship

From observations and calculations of crack patterns in ice, it is suggested that a similar mechanism may account for cracking over a wide range of scales.

The Effect Of The Specimen–Platen Interface On Internal Cracking And Brittle Fracture Of Ice Under Compression: High-Speed Photography, E. M. Schulson, M. C. Gies, G. J. Lasonde, W. A. Nixon

Dartmouth Scholarship

Uniaxial compression experiments at –10°C at 10−3s−1 on fresh-water, granular ice have established through the use of high-speed photography that internal cracks nucleate preferentially away from the ice/platen (i/p) interface under conditions of i/p contraint, but near the interface under conditions of i/p expansion. Under conditions of little i/p interaction, cracks nucleate more or less randomly throughout the specimen. Correspondingly, the brittle-fracture strength decreases as the i/p interaction changes from compressive to tensile. These effects are explained in terms of the spatial variation of the maximum shear stress and the crack density.

A Procedure For Testing Cored Ice Under Uniaxial Tension, Russell W. Lee

Dartmouth Scholarship

A procedure is described for testing cored ice specimens under uniaxial tension. The procedure incorporates an end-capping system described by Cole and others (1985), two carpeted Synthane end caps, and extensometers mounted directly on the ice. Use of the procedure has resulted in a successful test rate of 75%