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ANISOTROPY |
The condition of a particulate solid when its properties vary with direction. |
ANGLE OF EFFECTIVE YIELD LOCUS, 
|
The inclination of the effective yield locus (EYL) as specified by Jenike. |
ANGLE OF INTERNAL FRICTION, 
|
The angle between a tangent to the yield locus and the abscissa. |
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ANGLE OF REPOSE |
The maximum angle of a heap of particulate solid measured from the horizontal. This is not a unique property of a particulate solid. |
ANGLE OF WALL FRICTION, 
|
The angle of wall friction is defined as arctan of the ratio of the wall shear stress to the wall normal stress. |
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AXI-SYMMETRIC |
The term axi-symmetric is commonly used to describe the geometry of a silo or hopper. Axi-symmetric silos and hoppers have a circular or equilateral polygonal cross-section with respect to the vertical axis. A hopper of square cross-section is not axi-symmetric. |
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BIN |
Synonym for silo. This expression is sometimes used to refer to the parallel part of the silo only. |
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BULK DENSITY |
The mass of a quantity of particulate solid divided by its total volume. |
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BULK SOLID |
Synonym for a particulate solid. |
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BUNKER |
Synonym for silo, but sometimes understood as being a silo without any or only a small vertical part at the top of the hopper. |
COHESION, 
|
Shear stress at yield under zero normal stress, i.e. the intersection of the yield locus with the ordinate. |
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COMPACTION |
The process of volume reduction by application of stress. |
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COMPACTION, ISOSTATIC |
Compaction produced by the application of a stress which is the same in all directions. |
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COMPACTION, UNIAXIAL |
Compaction produced by the application of a stress applied in one direction. |
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CONSOLIDATED. CRITICAL |
A particulate solid is critically consolidated with respect to the state of stress applied, when it yields without change in bulk density at a constant state of stress. |
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CONSOLIDATED, OVER |
A particulate solid is overconsolidated with respect to the normal stress applied, when yield is accompanied by a decrease of bulk density and shear stress. |
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CONSOLIDATED, UNDER |
A particulate solid is underconsolidated with respect to the normal stress applied, when yield is accompanied by an increase of bulk density and shear stress. |
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CONSOLIDATION |
The process of increasing the strength of a particulate solid. |
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CONSOLIDATION LOCUS |
Locus representing the shear and normal stresses causing an underconsolidated particulate solid of a given initial bulk density to deform plastically. |
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CORE FLOW |
An alternative expression for funnel flow. |
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CRITICAL BULK DENSITY |
The bulk density of a particulate solid at critical state. |
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CRITICAL STATE |
A particulate solid is in critical state if it is critically consolidated with respect to the state of stress applied. |
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CRITICAL STATE LINE |
Line in the three-dimensional space of normal stress, shear stress and void ratio representing points of critical state of a particulate solid.
The critical state line (CSL) corresponds to the effective yield locus in the  ,  - plane. |
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CRITICAL VOID RATIO |
The void ratio of a particulate solid at critical state. |
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CRITICALLY CONSOLIDATED |
see consolidated, critical |
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DEFORMATION, ELASTIC |
A deformation which is entirely recoverable when the stress causing the deformation is removed. |
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DEFORMATION, PLASTIC |
The permanent deformation which remains after elastic deformation has been removed from the total deformation. Synonymous expressions in powder mechanics for plastic deformation are yield, failure and flow. Plastic deformation and yield are the more general expressions whereas the term incipient failure is associated with plastic deformation of an overconsolidated particulate solid and the term flow is used for steady state flow. |
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DILATION |
Increase in volume, or decrease in bulk density of a particulate solid subject to deformation. Dilation is the opposite to compaction. |
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EFFECTIVE ANGLE OF FRICTION,
|
Synonym for angle of effective yield locus. |
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EFFECTIVE YIELD LOCUS (EYL) |
Straight line passing through the origin of the ,  -plane and tangential to the steady state Mohr circle, corresponding to steady state flow conditions of a particulate solid of given bulk density. |
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ELEVATOR |
Synonym for silo, commonly used in grain industry. |
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FAILURE |
Plastic deformation of an overconsolidated particulate solid subject to shear, causing dilation and a decrease in strength. |
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FLOW, STEADY STATE |
Continuous plastic deformation of a particualte solid at critical state. |
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FLOW FACTOR, ff |
The ratio of the major consolidation stress  in a particulate solid flowing in a channel to the major principal stress,
 that would cause it to cease flowing. The value of the flow factor depends on the geometry of the hopper, especially on the slope of the channel walls, the angle of wall friction and the angle of internal friction as described by the angle of the effective yield locus. |
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FLOW FUNCTION, FF |
The plot of unconfined yield strength versus major consolidation stress for one specific particualte solid. |
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FLOW PATTERN |
The description of the type of flow in a hopper or silo. The type of flow may be differentiated into funnel flow and mass flow. |
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FUNNEL FLOW |
The flow pattern in a hopper of silo which is characterised by the fact that downward flow is confined to a central region above the outlet whilst the material adjacent to the walls remains stationary. This central zone is shaped like a funnel and extends either up to the top surface or intersects the walls of the bin somewhere above the hopper. |
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GRANULAR MATERIAL |
Synonym for particulate solid |
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HOPPER |
The converging part of a silo. |
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ISOSTATIC COMPACTION |
see Compaction, isostatic |
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ISOTROPIC |
The condition of a particulate solid when its properties are independent of direction. Antonym of anisotropic. |
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MAJOR CONSOLIDATION STRESS,
|
The major principal stress given by the Mohr stress circle of steady state flow. This Mohr stress circle is tangential to the effective yield locus. |
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MAJOR PRINCIPAL STRESS,
|
The greater normal stress represented by a Mohr stress circle. It is the greater value of the point of intersection of the Mohr circle with the normal stress axis. |
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MASS FLOW |
Mass flow is the flow pattern in a hopper or silo characterised by the fact that no stagnant zones are present, i.e. that all parts of the particualte solid including those adjacent to the wall, are moving when the hopper is discharged. |
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MEAN STRESS |
This expression is often used to denote the mean of the normal stresses on two mutually perpendicular planes. This stress is independent of the orientation of the planes and the mean stress as normally quoted is the mean of the corresponding principal stresses. The mean stress corresponds to the centre of a Mohr stress circle on the axis of normal stress. This value should not be confused with the intermediate principal stress which lies between the major and minor principal stresses and which includes those values. |
MINOR PRINCIPAL STRESS, 
|
The normal stress represented by the smaller value of the intersection of the Mohr stress circle with the normal stress axis. |
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MOHR STRESS CIRCLE |
The graphical representation of a state of stress in co-ordinates of normal and shear stress, i.e. in the ,
-plane |
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NORMAL STRESS,
|
The stress acting normally to the considered plane. |
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PARTICULATE SOLID |
An assembly of solid particles, the number of particles being sufficient for the statistical mean of any property to be independent of the number of particles present. In such a case a particulate solid may be considered as a continuum material. Particulate solids may also be called bulk solids, granular materials or powders although in certain contexts these terms may have different meanings from one another. |
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PLANE STRESS |
The term commonly used to describe one type of geometry of a silo or hopper. Plane strain silos or hoppers have an oblong cross-section. Deformation occurs only in one plane and is not influenced by the end walls. In order to achieve plane strain the length to width ratio has to be greater than or equal to 3. |
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PLASTIC DEFORMATION (or FLOW) |
Deformation that does not reverse on removal of stress. |
POROSITY, 
|
The volume of the voids within a quantity of particulate solid divided by the total volume, i.e. the volume of voids divided by the volume of voids plus the volume of solid present. Synonym for voidage. |
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POWDER |
Synonym for particulate solid, particularly when the particles of the solid are very fine |
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PRINCIPAL PLANE |
A plane within a material which experiences only normal stresses i.e. no shear stresses. In three dimensions there are three principal stress planes which are mutually perpendicular. For a given state of stress these planes are unique. The stresses on these planes are called the major, intermediate and minor principal stresses, in order of decreasing stress magnitude. |
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PRINCIPAL STRESS |
Normal stress acting on a plane on which no shear stress is acting. |
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PRINCIPAL STRESS RATIO |
The ratio of the minor principal stress to the major principal stress of a particulate solid. |
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SILO |
Container or vessel for storing particular solids usually consisting of a hopper and an upper cylinder. The words bin, bunker and elevator are often used as synonyms. |
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SHEAR STRESS,
|
A stress acting parallel to the surface of the plane being considered. |
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SHEAR TEST |
An experiment to determine the flow properties of a particulate solid by applying different states of stress and strain to it. |
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SHEAR TESTER |
An apparatus for performing shear tests. |
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STEADY STATE YIELD LOCUS |
The envelope of the Mohr stress circle at steady state flow, not necessarily passing through the origin of
the , -plane. |
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STRAIN |
Deformation or displacement of a particulate solid under shear. |
TENSILE STRENGTH, 
|
The uniaxial tensile principal stress acting on a particulate solid under tension causing failure. |
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TIME ANGLE OF INTERNAL FRICTION,
t |
Inclination of the time yield locus of the tangency point with the Mohr stress circle passing through the origin. |
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TIME YIELD LOCUS |
The yield locus of a particulate solid which has remained at rest under a given normal stress for a certain time. |
UNCONFINED YIELD STRENGTH, 
c |
The major principal stress of the Mohr stress circle being tangential to the yield locus with the minor principal stress being zero. A synonym for compressive strength. |
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UNDER CONSOLIDATED |
see Consolidated, under |
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UNIAXIAL COMPACTION |
see Compaction, uniaxial |
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VOIDAGE, e
|
Synonym for porosity. |
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VOID RATIO |
The ratio of the volume of voids in particulate solid to the volume of the solid component. |
WALL NORMAL STRESS, 
w |
The normal stress present at a confining wall. |
WALL SHEAR STRESS, 
|
The shear stress present at a confining wall. |
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WALL YIELD LOCUS |
A plot of the wall shear stress versus wall normal stress. The angle of wall friction is obtained from the wall yield locus as the arctan of
the ratio of the wall shear stress to wall normal stress. The wall yield locus is often a straight line in ,
-co-ordinates, resulting in a constant angle of wall friction. |
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YIELD |
Synonym for the plastic deformation of a particulate solid. |
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YIELD LOCUS |
Plot of shear stress versus normal stress at failure. The yield locus (YL) is sometimes called the instantaneous yield locus to differentiate it from the time yield locus. |