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

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22 (β = 0 o ), positioning the outlet hole of the funnel along the sample axis of symmetry and not close to the mould wall as before. Every time the same quantity of grain filled the whole volume of the mould, therefore every time the same density of the medium was obtained. To estimate the degree of arrangement of the long axes of the grains, the samples prepared according to the method described above were flooded with polyester resin. Once the resin was set, the samples were cut along horizontal and vertical planes. The sections obtained were used to determine the measure of grain arrangement after [129], in accordance with the formula: preferred angle of inclination of long axes of grains with relation to chosen system of coordinates: ⎛ ⎜ 1 θ = arctg ⎜ 2 ⎜ ⎜ ⎝ n ∑ i=1 n ∑ i=1 ⎞ sin2θi ⎟ ⎟ , (3.3) ⎟ cos2θi ⎟ ⎠ intensity of parallel orientation of the long axes V ⋅ M = ⎛ ⎜ ⎝ n ∑ i=1 2 ⎞ ⎛ sin 2θi⎟ + ⎜ ⎠ ⎝ n ∑ i=1 2 ⎞ cos 2θi⎟ ⎠ 100 ⋅ , n (3.4) where: n – number of measurements, θ i – the angle of inclination of the long axis of a given grain with relation to the adopted system of reference. The value of the expression V·M varies within the range from 0 to 100%. The value of 0% corresponds to totally random orientation of the long axes of the grains, while 100% represents ideally parallel orientation of the long axes of the grains. For angle β = 20 o and for the vertical sample section, the measures had values of θ = 38 o , V·M = 65%, respectively, and therefore the sample was characterized by considerable anisotropy. The effect of spatial orientation of grains of three cereals and of rape on the angle of internal friction was examined with the triaxial compression method and with the direct shear method. The methods were chosen due to their popularity in experimental studies on the mechanics of granular materials. It was assumed that
23 comparison of the two methods would permit formulation of conclusions on their applicability in studies on agricultural materials. The procedure of sample preparation for the direct shear test was identical as in the case of the triaxial compression test. In the direct shear tests five levels of normal load σ were applied, equal to the values of stress σ 3 in the triaxial compression test. The speed of mutual displacement of two sample halves was 1.3 mm s -1 . Each variant of the experiment was repeated three times. A preliminary study of the effect of sample preparation, performed with the method of triaxial compression on rye seeds within an expanded range of the angle of sample inclination β = –40 o , –20 o , 0 o , 20 o and –40 o , permitted the conclusion that the manner of grain pouring into the mould had a significant effect on the mechanical characteristics obtained. The highest values of strength were obtained for grain samples poured into vertical mould. Those samples were also characterized by the highest uniformity of deformation. As a rule, no distinct plane of shear was observed. The sample swelled uniformly, assuming barrel shape. The behaviour of samples poured into mould tilted from the vertical by an angle β was totally different. Such samples lost the uniformity of deformation much sooner, and a clearly defined shear plane was formed. With increasing value of angle β, the maximum value of the ratio of main stresses decreased. A marked orientation of the shear plane occurred regularly in every experiment. On the basis of the obtained maximum values of principal stresses ratio σ 1 /σ 3 , the value of the angle of internal friction φ was calculated on the basis of the Coulomb-Mohr yield condition. Figure 3.5 presents the Angle of internal friction ϕ (deg) 25 23 21 19 17 -40 -20 0 +20 +40 Angle of sample inclination β (deg) Fig. 3.5. The values of the angle of internal friction ϕ of rye samples for various values of angle β of mould inclination from the vertical values of the angle of internal friction for various values of angle β of mould inclination from the vertical. The highest values of the angle of internal friction were obtained for the case of samples poured into vertical mould, and especially when
Page 2 and 3: EC Centre of Excellence AGROPHYSICS
Page 4 and 5: 4 9.3. Factors influencing the coef
Page 6 and 7: 6 BASIC NOTATION c - cohesion [kPa]
Page 8 and 9: 8 Numerous granular materials when
Page 10 and 11: 10 the tensor of plastic strain inc
Page 12 and 13: 12 Fig. 2.1. Yield curves with comp
Page 14 and 15: 14 Stable or unstable behaviour of
Page 16 and 17: 16 In turn, the model of Lade, also
Page 18 and 19: 18 same porosity need not have iden
Page 20 and 21: 20 where: A = ∫ E( β) sin βdβ
Page 24 and 25: 24 grain was poured into the mould
Page 26 and 27: 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
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72 galvanized steel received from d
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74 9.3.4. Velocity of sliding Becau
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76 1+ sinϕ k = . 1 − sinϕ (10.3
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78 N ϕ VLQϕ 3UHVVXUHUDWLRN
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80 10.4.1. Friction force mobilizat
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82 10.4.3. Moisture content With in
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84 Table 10.1. Measured (k s ) and
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86 conventional engineering analyse
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88 a, b - product-dependent coeffic
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90 also be performed as a function
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92 reliable processing and stable v
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94 unconfined yield strength to pow
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96 The Chute Index (CI) is recommen
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98 obtained the maximum deviation o
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100 efficient flow control using op
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102 In the field of experimental in
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104 22. Britton M.G., Moysey E.B.:
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106 69. Horabik J., Rusinek R.: Pre
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108 114. Morland L.W., Sawicki A.,
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110 158. 6WSQLHZVNL$ Influence of m
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112 16. APPENDIX - Physical Propert
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114 16.2. Density and porosity Tabl
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116 Table 16.7. Mean values (±St.
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126 Table 16.16. Cont. 1 2 3 4 Icin
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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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