Stress-Displacement Relations and Terrain-Vehicle Mechanics: A Critical Discussion
Current theoretical concepts of the soil-running gear interaction are based on empirical pressure-sinkage and shear stress-displacement relations. It was found that the tests from which these relations were obtained present a poor analogy, at best, to the soil-running gear interaction. In particular...
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| Format: | Text |
| Language: | English |
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1968
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| Online Access: | http://www.dtic.mil/docs/citations/ADA040177 http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA040177 |
| Summary: | Current theoretical concepts of the soil-running gear interaction are based on empirical pressure-sinkage and shear stress-displacement relations. It was found that the tests from which these relations were obtained present a poor analogy, at best, to the soil-running gear interaction. In particular, the use of the shear stress-displacement relation for an analytical evaluation of the shear stresses at the contact surface of rigid wheels on sand was found to be misleading, primarily because equations obtained by the bevameter or dragged plate tests describe the soil behavior in the intermediate state, which is a state between the elastic and plastic states. Recent publications point out that part of the soil in the immediate vicinity of a powered wheel is in a state of actual plastic flow and part is in a quasielastic state. Thus, the soil- bevameter interaction is of a fundamentally different nature than the soil-wheel interaction, which makes results of such tests unsuitable for predicting wheel performance. Sela's theory of the relation between a rigid wheel and dry sand is based exclusively on the shear stress-displacement concept, and thus provided an excellent means of checking the concept as a whole. Using a simple approximate relation between the M/RW ratio and the mean shear-to-normal stress ratio taken over the total contact surface, the theory was checked by means of constant-slip rigid wheel tests. The experimental findings strongly supported the conclusion that shear stress-displacement relations are irrelevant to soil-wheel mechanics. A new theory was developed to assess the variation of the shear-to-normal stress ratio along the soil-wheel interface, without referring to shear stress- displacement relations. Availability: Pub. in Jnl. of Terramechanics v5 n3 p67-85 1968. |
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