Wplyw struktury zloza nasion na stan naprezenia

• Autorzy: Molenda M

Warianty tytułu

EN

Effect of structure of seeds bedding on stress state

• Języki publikacji: PL

Abstrakty

EN

The spatial arrangement of individual grains forming a bed of granular solids influences the mechanical behaviour of granular material. Several researchers reported reduction of the coordination number and an increase of the void fraction in the region near the wall of containers holding randomly packed beds of uniform spheres. The method of bin filling influences the pressure distribution on the wall as well as the flow pattern which develops at the onset of discharge. Anisotropic behaviour of grain medium was considered to be the reason for damage to silos built in compliance with current codes of practice. It was found that the filling method influences the magnitude of measured values of the stress ratio. The purpose of this study was to examine the influence of particle properties and bedding structure on transmission of stresses in the layer of seeds, A model bin 0.61 m in diameter and 0.62 m high was constructed. Its bottom was divided into five concentric rings. The apparatus allowed for the determination of vertical load on each of the floor rings, vertical wall load and horizontal load exerted by grain on the bin wall. Four methods of bin filling and two types of wall surface (rough and smooth) were tested. The seeds of five species of plants were used as bulk solids filling the bin. The filing method, and individual seed size and shape of the five test materials significantly influenced the radial distribution of vertical pressure on the silo bottom. From a practical point of view, the advantages of circumferential filling as compared to central filling are: lower pressure ratio, maximum of vertical pressure at the bottom centre and lower tangential stress in vertical direction. The characteristics of vertical pressure as the function of the radius was observed to be smooth for the ratio of bin radius to particle dimension higher than one hundred. The change in moisture content of wheat resulted in the change ofradial distribution of vertical pressure. The wall of the bin was loaded gravitationally and allowed to move down. The characteristics of shear stress as the function of the radius was found to be dependent on the seed size. The major part of shear stress change took place in the boundary layer along the wall, which thickness was less than ten seed equivalent diameters. The proposed method measures vertical normal pressure averaged over the cross sectional area and the horizontal normal pressure averaged over the perimeter. Simultaneously, it measures the coefficient of wall friction, thus the pressure ratio is determined in a manner consistent with the Janssen formula. The pressure ratio value was found affected by material type, filling method and load history. Analysis of radial variation of vertical pressure can be useful in the verification of assumptions concerning the location of regions of fully developed yield conditions inside the Janssen's differential slice which are frequently considered in the theoretical prediction of the stress ratio.

Słowa kluczowe

PL

agrofizyka; materialy biologiczne; materialy sypkie; ziarno; nasiona; silosy; wlasciwosci mechaniczne; napor; rozklad naporu; naprezenia styczne; naprezenia scinajace; tarcie; tarcie wewnetrzne; anizotropia

EN

agrophysics; biological material; granular material; grain; seed; silo; mechanical property; pressure; pressure distribution; tangential stress; shearing stress; friction; internal friction; anisotropy

• Wydawca: -
• Czasopismo: Acta Agrophysica
• Rocznik: 1998
• Tom: 12
• Opis fizyczny: ss.129,tab.,rys.,wykr.,bibliogr.

Twórcy

autor

Molenda M

Bibliografia

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