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

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26 axes of the ellipse characterizing granule packing tend towards a position coaxial with the directions of the principal stresses. 28 28 26 26 24 24 22 22 20 20 18 0 20 40 6 0 80 18 0 20 40 6 0 80 28 30 26 29 24 28 27 22 26 20 25 18 24 0 20 40 6 0 80 0 10 2 0 30 40 50 60 Fig. 3.8. Influence of the angle of slip plane inclination γ 1 and γ 2 on the angle of internal friction φ in direct shear test × and triaxial compression test ○ In the case of non-spherical grains, a different relation was observed between the angle of internal friction and the angle between the direction of granule long axis orientation and the direction of slip for the tests of triaxial compression and of direct
shearing. In the triaxial compression test, the angle φ increased with increasing values of angle γ 1 – of granule long axis inclination to the slip plane. The trend was observed for all the cereal species under study. The relation φ(γ 2 ) obtained in the direct shear test had an approximately parabolic form, with a minimum for the angle γ 2 ≈ 25 o . The divergence between the relations φ(γ 1 ) and φ(γ 2 ) results from differences in the mechanisms of sample deformation in the tests compared. In the triaxial compression test, the slip plane forms freely, conforming to the state of stress and to the structure of the material, while in the direct shear test the slip direction is forced. In the latter test, the process of shearing is additionally complicated by the non-uniform state of deformation and by the anisotropy of the material; the displacement and the rotation of individual grains are forced. Figure 3.7c presents schematically the two components of the shearing process under macroscopic observation. The minimum of the angle of friction φ obtained with the method of direct shearing should be interpreted as the result of optimum spatial distribution of grains under conditions of forces direction of sample shearing. The results of the experiments described above permit the formulation of several methodological remarks concerning the measurement techniques. Due to the relatively large dimensions of the grains, it is recommended to increase the size of samples with relation to those routinely used for soils. It appears that the sample dimensions used in the studies presented here (triaxial sample: D = 150 mm, H = 300 mm, direct shear test sample: D = 210 mm, H = 120 mm) are sufficient. Especially worthy of recommendation for measurement of the angle of internal friction is the triaxial compression method, though in the case of spherical granules the less complex direct shear test yields similar results. The recommendation of the triaxial compression method is also supported by the fact that the method has been frequently used for the determination of theoretical and empirical parameters of models describing the stress-strain relation. The method was used by Zhang et al. [173] and by Li et al. [94] for the determination of parameters of the elasto-plastic model adapted by the authors for the description of the stress-strain relation in wheat grain. In that model, formulated by Lade [92] for cohesionless sand, the total increase of strain caused by increase in stress equals the sum of three components: increase in elastic strain, increase in plastic strain caused by normal stress, and increase in plastic strain caused by stress deviator. The values of model parameters determined in the triaxial compression test permit an accurate description of the response of a medium to other loading conditions. For the description of anisotropy and hysteresis in the stress-strain relation in the case of multiple loading of wheat grain, Zhang et al. [173] used an elasto-plastic model that included the density and kinematic hardening of the medium. The determination of the values of the parameters of the model also involved the application of the triaxial compression test. Likewise, the method of triaxial compression was applied by Zhang and Jofriet 27
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 22 and 23: 22 (β = 0 o ), positioning the out
Page 24 and 25: 24 grain was poured into the mould
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
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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
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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
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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.:
Page 106 and 107:
106 69. Horabik J., Rusinek R.: Pre
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108 114. Morland L.W., Sawicki A.,
Page 110 and 111:
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
Page 116 and 117:
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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