Strona 2_redak - Instytut Agrofizyki im. Bohdana DobrzaÅskiego ...

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82 10.4.3. Moisture content With increasing moisture content, the friction force and the cohesion between grains increase. As a result a smaller part of the vertical loading is transmitted into the lateral direction. Consequently, the lateral to vertical pressure ratio should decrease with an increase in moisture content. Tests performed for cereals grain confirm this relationship (fig. 10.6). Nearly a linear decrease of the pressure ratio with an increase in moisture content was obtained for corn, rye and rape seeds. Another course of changes was obtained for barley: the pressure ratio was almost constant in the range of moisture content up to 17.5% and then decreased. This indicates that the influence of some other factors still remains out of control. Fig. 10.6. Pressure ratio as influenced by moisture content of grain 10.4.4. Grain shape and surface roughness The shape, size and roughness of seeds were found to influence the pressure ratio. The influence of surface roughness can be determined in an indirect way by considering its influence on the angle of internal friction. The more rough the surface the higher the angle of internal friction and consequently the lower the pressure ratio. In practice it is difficult to separate the influence of the shape and roughness of grain. It is much easier to observe the combined effect of both factors: the smoother the surface and the closer the shape to a sphere, the higher the pressure ratio. The pressure ratio of the material composed of elongated grains, like cereal grain, is generally lower than the pressure ratio of material composed of spherical grains (Tab. 10.1 and
83 10.2). The spherical shape of soybeans as compared to the lenticular shape of lentil seeds results in different distribution of contact points in bedding of material. Almost vertical orientation of the shortest axes of lentil seeds obtained during filling the tester results in easier transmission of vertical load into the lateral direction than in the case of spherical (soybean) or irregularly shaped seeds (pea). 3UHVVXUHUDWLRN 3DVVLYHFDVH $FWLYHFDVH N ϕ VLQϕ %DUOH\ &RUQ 2DW :KHDW 5DSHVHHGV Fig. 10.7. Comparison of the experimental and theoretical values of the pressure ratio [69] 10.5. Concluding remarks The values of pressure ratio for tested seeds at all levels of moisture content were found to be significantly lower than recommended by Eurocode 1 for filling and storing of cereal grain, and lower than the values obtained from equation 10.8 (table 10.2). Experimental values of the pressure ratio are located near the lower limit of theoretical values obtained for yielding at the wall in the active stress case (i.e. for the wall friction angle 3 w approaching zero, fig. 10.7). Lower limit of the theoretical values of the pressure ratio (dashed line in fig. 10.7 indicated as 3 w0 = 0 o ) comprise the case of yielding at the centre of a silo in the active case when directions of the principal stresses are vertical and horizontal. This confirms the opinion that during uniaxial compression test the horizontal and vertical stresses are approximately principal stresses in the test sample, whereas they may not be in the silo [50].
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EC Centre of Excellence AGROPHYSICS
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4 9.3. Factors influencing the coef
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6 BASIC NOTATION c - cohesion [kPa]
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8 Numerous granular materials when
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10 the tensor of plastic strain inc
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12 Fig. 2.1. Yield curves with comp
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14 Stable or unstable behaviour of
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16 In turn, the model of Lade, also
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18 same porosity need not have iden
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20 where: A = ∫ E( β) sin βdβ
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22 (β = 0 o ), positioning the out
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24 grain was poured into the mould
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26 axes of the ellipse characterizi
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28 [176] for the determination of p
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30 A different approach to the desc
Page 32 and 33: 32 where: I - moment of inertia, k
Page 34 and 35: 34 a) b) f s f s m M f n f n Contac
Page 36 and 37: 36 The micropolar model yields resu
Page 38 and 39: 38 Fig. 3.17. Model of shear band f
Page 40 and 41: 40 In the case of agricultural mate
Page 42 and 43: 42 5.2. Density of consolidated mat
Page 44 and 45: 44 (cereal grain, sand, soil), the
Page 46 and 47: 46 Multiple wetting and drying of g
Page 48 and 49: 48 vertical pressure within the ran
Page 50 and 51: 50 of the curve defined by A, where
Page 52 and 53: 52 6. Vertical consolidation refere
Page 54 and 55: 54 poured into the box without vibr
Page 56 and 57: 56 7.2.2. Bulk density Stress-strai
Page 58 and 59: 58 near the box wall and lifted alo
Page 60 and 61: 60 and the upper boundary was 18.5
Page 62 and 63: 62 A -1 5 -1 0 -5 1 0 5 -5 5 1 0 1
Page 64 and 65: 64 Fig. 8.2. Yield locus and effect
Page 66 and 67: 66 in such a way that friction woul
Page 68 and 69: 68 a) b) µ = tg ϕw ϕ w c) d) e)
Page 70 and 71: 70 9.3. Factors influencing the coe
Page 72 and 73: 72 galvanized steel received from d
Page 74 and 75: 74 9.3.4. Velocity of sliding Becau
Page 76 and 77: 76 1+ sinϕ k = . 1 − sinϕ (10.3
Page 78 and 79: 78 N ϕ VLQϕ 3UHVVXUHUDWLRN
Page 80 and 81: 80 10.4.1. Friction force mobilizat
Page 84 and 85: 84 Table 10.1. Measured (k s ) and
Page 86 and 87: 86 conventional engineering analyse
Page 88 and 89: 88 a, b - product-dependent coeffic
Page 90 and 91: 90 also be performed as a function
Page 92 and 93: 92 reliable processing and stable v
Page 94 and 95: 94 unconfined yield strength to pow
Page 96 and 97: 96 The Chute Index (CI) is recommen
Page 98 and 99: 98 obtained the maximum deviation o
Page 100 and 101: 100 efficient flow control using op
Page 102 and 103: 102 In the field of experimental in
Page 104 and 105: 104 22. Britton M.G., Moysey E.B.:
Page 106 and 107: 106 69. Horabik J., Rusinek R.: Pre
Page 108 and 109: 108 114. Morland L.W., Sawicki A.,
Page 110 and 111: 110 158. 6WSQLHZVNL$ Influence of m
Page 112 and 113: 112 16. APPENDIX - Physical Propert
Page 114 and 115: 114 16.2. Density and porosity Tabl
Page 116 and 117: 116 Table 16.7. Mean values (±St.
Page 126 and 127: 126 Table 16.16. Cont. 1 2 3 4 Icin
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132 Table 16.22. Mean values (±St.
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136 Table 16.25. Cont. 1 2 3 4 Icin
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140 Table 16.29. Cont. Table sugar
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144 Table 16.35. Mean values (± St
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