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    Snow rubbing squeal vibrations, and roaring cold snow
    (2013-06-26) Patitsas, Tom
    The objective of this study is the investigation of the mechanism responsible for the squeal vibrations excited when bodies with fairly rough surfaces are rubbed on a cold dry slightly compacted snow bed. To this end, signals were recorded and analyzed when the snow surface was rubbed by the ends of baseball bats, the ends of circular wood rods, and by the thick sole of a rubber boot. It is argued that the vibration modes are confined in the rubbing bodies and that the role of the snow bed is limited to providing the right conditions for the stick-slip effect to be applicable at the rubbing interface. An attempt is made to account for the reported very intense sound emission from a sheared very cold snow bed in terms of coherent snow granule column vibrations around the shearing body, as in the case of a sheared singing sand bed.
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    Singing sands, booming dune sands, and the stick-slip effect
    (2011-05-05T20:35:46Z) Patitsas, A. J.
    The origin of the acoustic and seismic emissions from impacted singing grains and from avalanching dune sand grains is sought in modes of vibration in discreet grain columns. It is postulated that when the grains in a column are pressed together, elastic shear bands are formed at the contact areas with distinct elastic properties. The central part of such contact shear bands, where the stress level is maximum, is more in a liquid-like rather than in a solid-like state, resulting in very low elastic moduli. In a given column, the elastic moduli would assume the lowest values just below the impacting pestle and higher values further below. The transfer of energy from the pestle to the modes of vibration of such columns is effected by the stick-slip effect. The concept of grain flowability is used to justify the great disparity between the acoustic emissions from impacted singing grains and from avalanching dune sand grains. The concept of grain columns is assumed to apply in the avalanching sand band, but with larger length to justify the lower frequencies. The concept of contact shear bands can be used to justify the variation of the emission frequency with blade speed and pile height when a grain pile is pushed by a blade. Finally, this approach can provide explanations as to why ordinary sands do not sing, and why singing sands do not boom and booming sands do not sing.
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    Squeal vibrations, glass sounds and the stick-slip effect
    (2010-07-19T13:26:20Z) Patitsas, A. J.
    The origin of the squeal acoustic emissions when a chalk is rubbed on a blackboard or better on a ceramic plate, and those when a wet finger is rubbed on a smooth surface, such as a glass surface, is sought in the stick-slip effect between the rubbing surfaces. The elastic agency is sought in a shear band between the two surfaces characterized by very low shear modulus. In the case of the squealing chalk, it can be argued that the shear band is a layer of chalk powder, about 0.3 mm thick, forced to slide over the ceramic plate surface. In the case of the wet finger on a glass surface, it can be argued that the shear band is the layer of soft tissue between the epidermis and the finger bone, and that the water layer simply facilitates the stick-slip effect.
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    Singing sands, musical grains and booming sand dunes
    (2008-07-14T10:00:40Z) Patitsas, A. J.
    The origin of the acoustic emissions from a bed of musical grains, impacted by a pestle, is sought in a boundary layer at the leading front of the pestle. The frequencies of the shear modes of vibration in such a layer are compared with the observed frequencies. It is assumed that such a layer is the result of the fluidization of the grain asperities due to the high stress level at the front end. Such a boundary layer can also account for the emissions from plates of sand sliding on a dune surface and from grains shaken in a jar.