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  • 1
    UID:
    kobvindex_GFZ107375
    Format: vi, 47 Seiten , Illustrationen
    Series Statement: CRREL Report 76-21
    Content: The effects of snow temperature and initial density on the stress vs density and stress vs deformation relationships were investigated for shallow compacted snow in the density range of 0.28 to 0.76 g/cu m, for stress range of 0.5 to 72 bars and a temperature range of -1 to -34 C at a deformation rate of 40 cm/s. A decrease in temperature increases the resistance to stress, the effect increasing with applied stress. For any stress, an increase in the initial density results in an increase in the resulting density, the effect decreasing with an increase in stress. The approximate yield envelopes, which define the stress required to initiate any deformation of snow of a particular density and temperature, were determined. Rapid compaction of snow results in extensive recrystallization, significantly different from that of naturally compacted snow. At a stress of 72 bars, transformation to ice occurs only at temperature above -10C.
    Note: MAB0014.001: ZSP-201-76/21 , CONTENTS Abstract Preface Nomenclature Introduction Description of study Sample preparation Test equipment and procedure Discussion of results Stress-density relationship Stress-deformation relationship Summary and conclusions Microstructural examination of artifically compacted snow Analytical techniques Results and discussion Conclusions Literature cited Appendix: Photographs of oscilloscope traces
    In: CRREL Report, 76-21
    Language: English
    Keywords: Forschungsbericht
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  • 2
    UID:
    kobvindex_GFZ122968
    Format: iv, 57 Seiten , Illustrations
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 336
    Content: CONTENTS: Abstract. - Preface. - Nomenclature. - Introduction. - Description of study. - Sample preparation. - Test equipment and procedure. - Discussion of results. - Stress-density relationship. - Effect of rate of deformation. - Effect of temperature. - Effect of initial snow density. - Stress-deformation relationship. - Summary and conclusions. - Microstructural analysis. - Introduction. - Analytical methods. - Results and discussion. - Conclusion. - Literature cited. - Anpendix: Test data.
    Content: The effects of snow temperature, rate of deformation, and initial density on the stress vs density and stress vs deformation relationships were investigated in the pressure range of 0.1 to 75 bars. The rate of deformation in the range of 0.027 to 27 cm sec^-1 does not have a significant effect. A decrease in temperature in the range of 0° to -40°C increases the resistance to stress and deformation, the temperature effect increasing with applied pressure and initial density. The effect of initial density is significant. For any stress, an increase in the initial density results in an increase in the resulting density, particularly at low stress levels and at temperatures near 0°C. The texture of artificially compacted snow is significantly different from that of naturally compacted snow of the same density because of the very short recrystallization time period.
    Note: MAB0014.001: ZSP-202-336 , Online frei verfügbar
    In: Research report
    Language: English
    Keywords: Forschungsbericht
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  • 3
    UID:
    kobvindex_GFZ105558
    Format: v, 26 Seiten , Illustrationen
    Series Statement: CRREL Report 79-2
    Content: The stress-density relaionships of snow-water mixtures were investigated and are shown as functions of water content, initial snow density, initial snow-water mixture density and rate of deformation. An increase in water content in snow at a particular density or a decrease in the rate of deformation (or strain rate) decreases the stress, but apparently not the specific energy required to reach a specific mixture density.
    Note: MAB0014.001: ZSP-201-79/2 , CONTENTS Abstract Preface Nomenclature Introduction Description of study Sample preparation Test equipment and procedure Test sample characteristics Discussion of results Data presentation format Effect of water content and mixture density Effect of water content and initial snow density Effect of deformation rate Effect of water content and rate of deformation on specific energy Summary Literature cited Appendix A. Derivation of equations Appendix B. Load-deformation traces
    In: CRREL Report, 79-2
    Language: English
    Keywords: Forschungsbericht
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  • 4
    UID:
    kobvindex_GFZ20191029150202
    Format: vii, 15 Seiten , Illustrationen
    Series Statement: CRREL Report 76-45
    Content: The maneuverability of air cushion vehicles can become a serious operational problem when the vehicle's travel route is restricted by obstacles, slopes or cross-wind conditions, or when close-quarter turns are required. While improvement and perfection of aerodynamic methods may be a more desirable approach, there is a practical limit to these methods, and the use of ground contact devices requires consideration for providing more positive directional control. Wheels deserve special attention, and therefore are analyzed in more detail because of their obvious application on a variety of land terrains. Brake rods and harrows are more suitable on water, ice and snow. The saucer-shaped ground contact device would cause the least ecological impact on fragile organic terrains such as tundra. Relative directional stability is evaluated in terms of the total yawing moments produced by wheel arrangements (single, dual, tandem), location on the vehicle, and operational modes (free-rolling, braked, or a combination of the two). The available moments are plotted against the yaw angle of the vehicle to determine the most effective operational mode with a particular wheel arrangement for any yaw condition. The analysis is limited to retractable devices which act as moment producing brakes or rollers and do not serve as either propulsion or load support aids. Controlled ground contract with skirt sections having special wearing surfaces may provide a suitable control method and would require the least significant change to the basic design of the vehicle or its components. The concept involves the use of an air flow control mechanism for deflating specific skirt sections.
    Note: CONTENTS Abstract Preface Nomenclature Conversion factors: U.S. customary to metric (SI) units of measurement Section I: Use of auxiliary devices for ACV control Introduction Discussion of wheels as a control device Dual wheels Single wheel Tandem wheels Application to existing ACV’s Other control devices Turning force Conclusions Section II: Use of flexible skirts for ACV control Introduction The flexible skirt as a control device Model tests Conclusions Literature cited
    In: CRREL Report, 76-45
    Language: English
    Keywords: Forschungsbericht
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  • 5
    UID:
    kobvindex_GFZ123542
    Format: iv, 67 Seiten , Illustrationen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 273
    Content: CONTENTS: Introduction. - Background. - Physical characteristics of snow. - Mechanical behavior of snow. - Failure mechanism of snow. - Description of experimental work. - Method. - Preparation of test samples. - Test apparatus and equipment. - Procedure. - Results and discussion. - Mechanical properties of test samples. - Experimental results. - Summary, conclusions, and recommendations. - Literature cited. - Selected bibliography. - Appendix A. Development of theoretical equations. - Appendix B. Test data and calculations. - Appendix C. Selected, representative photographs. - Appendix D. Schedule of tests performed. - Abstract.
    Content: This report presents the results of a study performed on the behavior, particularly the deformation, of snow under a load applied to a rigid plate at a constant rate of penetration. The results will eventually be used in the development of design criteria for snow roads, runways, and foundations in the polar regions. The tests were conducted on snow samples having a high width/length ratio, simulating a two-dimensional case. The effect of snow density, plate size, and pressure on the deformation of snow below the load was investigated. The pressure-sinkage relationships and the bearing strength as functions of density were also investigated. It was determined that density, in the range 0.3 to 0.6 g/cm^3, can be used as a reasonably reliable index for predicting deformation and behavior of snow under load. In general, the critical pressure (bearing strength) increased as a power function of density, and critical sinkage decreased as a power function of density. It was also observed that the deformation bulb resembled the typical Boussinesq stress bulb. The experimental pressure-sinkage relationships agreed closely with recently developed theoretical values. For the range of plate sizes used, the test data did not provide conclusive evidence of the effect of plate size on deformation and bearing capacity of snow. The possibility of using the Moire fringe method for determing deformation patterns in snow and soils under various loading conditions should be investigated.
    Note: MAB0014.001: ZSP-202-273 , Online frei verfügbar
    In: Research report
    Language: English
    Keywords: Forschungsbericht
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  • 6
    UID:
    kobvindex_GFZ107306
    Format: iv, 14 S. : Ill., graph. Darst.
    Series Statement: CRREL Technical Report 85
    Note: MAB0014.001: ZSP-204-85
    In: CRREL Technical Report
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