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

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78 N ϕ VLQϕ 3UHVVXUHUDWLRN R $FWLYHFDVH 3DVVLYHFDVH R R R R R Fig. 10.2. Pressure ratio as a function of the angle of internal friction and the angle of wall friction for yielding at the wall in the active and passive cases [68], w WKH SUHVVXUH UDWLR calculated according to equation 10.8 10.3. Experimental procedures The most popular method of experimental determination of the lateral to vertical pressure ratio is the uniaxial compression test [90, 110]. An experimental set for the uniaxial compression (fig. 10.3) described in the chapter 6 was built according to the general guideline of the Eurocode 1 standard [50,66]. The sample was poured into the test chamber through centrally located spout, without vibration or other compacting actions. The specimen was loaded to the reference vertical stress of 100 kPa using a universal loading frame at the constant displacement rate of 0.35 mm min -1 . The top plate was rotated backwards and forwards three times through an angle of 10 degrees to consolidate the sample. Next, the sample was reloaded to the reference vertical stress, and the slope of the lateral to the vertical pressure increase was determined. The pressure ratio k s appropriate for filling and storing was determined as [50, 135]: where k s =1.1k so , (10.9) k so =û 1 x /û 1 zm (10.10) at the reference vertical stress 1 zm =100 kPa, 1 zm =( 1 z + 1 zo )/2. Experiments were performed for samples of seeds of different size and shape and typical storage moisture content. Extended range of moisture content was applied for tests performed for cereal grain 10-20% (w.b.) and 6-15% (w.b.) for rape seeds. The angle of internal friction of tested seeds was measured using
79 Jenike shear tester of 210 mm in diameter according to the procedure recommended by Eurocode 1 [50] described in the chapter 7. ) /DWHUDOVWUHVVσ[ NVR ∆σ]P ∆σ[ 9HUWLFDOVWUHVVσ]P Fig. 10.3. Uniaxial compression tester and graph of the pressure ratio determination The second series of experiments was performed in the model silo 0.6 m in diameter and 0.6 m high. The experimental set-up allowed for determination of the mean lateral pressure 1 x , tangent wall stress, 1 t , and mean vertical pressure 1 z [110]. The coefficient of wall friction, * , was determined as the ratio of mean tangent wall stress 1 t to mean lateral pressure 1 x . The average value of the stress ratio, k, was calculated utilizing a numerical solution of Janssen’s equation for the mean vertical pressure on the bottom of the container. Layer of grain was loaded through flat, rigid top cover and a series of uniaxial compression tests were performed in the same way as in the uniaxial tester. The set-up was used to indicate the influence of filling method resulting in different structure of granular material on the pressure ratio. 10.4. Factors influencing the pressure ratio The recommended value of the lateral to vertical pressure ratio varies somewhat but the use of a value of approximately 0.4 is common. The pressure ratio depends on the type of grain, moisture content, bulk density and bedding structure of grain formed during the filling process. The angle of internal friction and the angle of friction on the wall material increase with an increase in the moisture content of grain, while the bulk density decreases or increases depending on the pressure level [100, 106, 107, 161]. The angle of friction at the interface of grain and the wall material depends strongly on the roughness of the wall surface. All those three properties of bulk of grain influence the pressure ratio.
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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
Page 28 and 29: 28 [176] for the determination of p
Page 30 and 31: 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 80 and 81: 80 10.4.1. Friction force mobilizat
Page 82 and 83: 82 10.4.3. Moisture content With in
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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128 Table 16.18. 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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