ASTM D6128-97
(Test Method)Standard Test Method for Shear Testing of Bulk Solids Using the Jenike Shear Cell
Standard Test Method for Shear Testing of Bulk Solids Using the Jenike Shear Cell
SCOPE
1.1 This method covers the apparatus and procedures for measuring the cohesive strength of bulk solids during both continuous flow and after storage at rest. In addition, measurements of internal friction, bulk density, and wall friction on various wall surfaces are included.
1.2 This standard is not applicable to testing bulk solids that do not reach the steady state requirement within the travel limit of the shear cell. It is impossible to classify ahead of time which bulk solids cannot be tested, but one example may be those consisting of highly elastic particles.
1.3 The values stated in SI units are to be regarded as standard.
1.4 The most common use of this information is in the design of storage bins and hoppers to prevent flow stoppages due to arching and ratholing, including the slope and smoothness of hopper walls to provide mass flow. Parameters for structural design of such equipment also may be derived from this data.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 6128 – 97
Standard Test Method for
Shear Testing of Bulk Solids Using the Jenike Shear Cell
This standard is issued under the fixed designation D 6128; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2.1.7 consolidation—the process of increasing the strength
of a bulk solid.
1.1 This method covers the apparatus and procedures for
2.1.8 effective angle of friction, d—the inclination of the
measuring the cohesive strength of bulk solids during both
effective yield locus (EYL) as defined by Jenike.
continuous flow and after storage at rest. In addition, measure-
2.1.9 effective yield locus (EYL)—straight line passing
ments of internal friction, bulk density, and wall friction on
through the origin of the s, t-plane and tangential to the steady
various wall surfaces are included.
state Mohr circle, corresponding to steady state flow conditions
1.2 The most common use of this information is in the
of a bulk solid of given bulk density.
design of storage bins and hoppers to prevent flow stoppages
2.1.10 elevator—synonym for bin, commonly used in the
due to arching and ratholing, including the slope and smooth-
grain industry.
ness of hopper walls to provide mass flow. Parameters for
2.1.11 failure (of a bulk solid)—plastic deformation of an
structural design of such equipment may also be derived from
overconsolidated bulk solid subject to shear, causing dilation
this data.
and a decrease in strength.
1.3 This standard does not purport to address all of the
2.1.12 flow, steady state—continuous plastic deformation of
safety concerns, if any, associated with its use. It is the
a bulk solid at critical state.
responsibility of the user of this standard to establish appro-
2.1.13 flow function, FF—the plot of unconfined yield
priate safety and health practices and determine the applica-
strength versus major consolidation stress for one specific bulk
bility of regulatory limitations prior to use.
solid.
2. Terminology
2.1.14 granular material—synonym for bulk solid.
2.1.15 hopper—the converging portion of a bin.
2.1 Definitions:
2.1.16 major consolidation stress, s —the major principal
2.1.1 angle of internal friction, f —the angle between the 1
i
stress given by the Mohr stress circle of steady state flow. This
tangent to the yield locus and the abscissa.
Mohr stress circle is tangential to the effective yield locus.
2.1.2 angle of wall friction, f8— the arctan of the ratio of
2.1.17 Mohr stress circle—the graphical representation of a
the wall shear stress to the wall normal stress.
state of stress in coordinates of normal and shear stress, that is,
2.1.3 bin—a container or vessel for holding a bulk solid,
in the s,t-plane.
frequently consisting of a vertical cylinder with a converging
2.1.18 normal stress, s—the stress acting normally to the
hopper. Sometimes referred to as silo, bunker, or elevator.
considered plane.
2.1.4 bulk density, r—the mass of a quantity of a bulk solid
2.1.19 particulate solid—synonym for bulk solid.
divided by its total volume
2.1.20 powder—synonym for bulk solid, particularly when
2.1.5 bulk solid—an assembly of solid particles handled in
the particles of the bulk solid are fine.
sufficient quantities that its characteristics can be described by
2.1.21 silo—synonym for bin.
the properties of the mass of particles rather than the charac-
2.1.22 shear stress, t—a stress acting parallel to the surface
teristics of each individual particle. May also be referred to as
of the plane being considered.
granular material, particulate solid, or powder. Examples are
2.1.23 shear test—an experiment to determine the flow
sugar, flour, ore, and coal.
properties of a bulk solid by applying different states of stress
2.1.6 bunker—synonym for bin, but sometimes understood
and strain to it.
as being a bin without any or only a small vertical part at the
2.1.24 shear tester—an apparatus for performing shear
top of the hopper.
tests.
2.1.25 time angle of internal friction, f —inclination of the
1 t
This testing method is under the jurisdiction of ASTM Committee D-18 on Soil
time yield locus of the tangency point with the Mohr stress
and Rock and is the direct responsibility of Subcommittee D18.24 on Character-
ization and Handling of Powders and Bulk Solids. circle passing through the origin.
Current edition approved May 10, 1997. Published October 1998.
2.1.26 time yield locus—the yield locus of a bulk solid
This method is based on the “Standard Shear Testing Technique for Particulate
which has remained at rest under a given normal stress for a
Solids Using the Jenike Shear Cell,” a report of the EFCE Working Party on the
certain time.
Mechanics of Particulate Solids. Copyright is held by The Institution of Chemical
Engineers and the European Federation of Chemical Engineering.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 6128
2.1.27 unconfined yield strength, f — the major principal
c
stress of the Mohr stress circle being tangential to the yield
locus with the minor principal stress being zero. A synonym for
compressive strength.
2.1.28 wall normal stress, s — the normal stress present at
w
a confining wall.
2.1.29 wall shear stress, t —the shear stress present at a
w
confining wall.
2.1.30 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.
2.1.31 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.
FIG. 2 Jenike Cell in Final Offset Position
3. Significance and Use
3.1 Reliable, controlled flow of bulk solids from bins and
hoppers is essential in almost every industrial facility. Unfor-
tunately, flow stoppages due to arching and ratholing are
common. Additional problems include uncontrolled flow
(flooding) of powders, segregation of particle mixtures, useable
capacity which is significantly less than design capacity, caking
and spoilage of bulk solids in stagnant zones, and structural
failures.
3.2 By measuring the flow properties of bulk solids, and
designing bins and hoppers based on these flow properties,
most flow problems can be prevented or eliminated.
3.3 For bulk solids with a significant percentage of particles
(typically, one third or more) finer than about 6 mm ( ⁄4 in.), the
cohesive strength is governed by the fines (-6-mm fraction).
For such bulk solids, cohesive strength and wall friction tests
may be performed on the fine fraction only.
4. Apparatus
4.1 The Jenike shear cell is shown in Figs. 1-3. It consists of
a base (1), shear ring (2), and shear lid (3), the latter having a
bracket (4) and pin (5). Before shear, the ring is placed in an
FIG. 3 Plan View of Jenike Cell Showing Offset
offset position as shown in Fig. 1, and a vertical force F is
v
applied to the lid and hence to the particulate solid within the
cell by means of a weight hanger (6) and weights (7). A
4.2 It is especially important that the shear force measuring
horizontal force is applied to the bracket by a mechanically
stem acts on the bracket in the shear plane (plane between base
driven measuring stem (8).
and shear ring) and not above or below this plane.
4.3 The dimensions of the Jenike shear cells supplied by
Jenike & Johanson, Inc. are given in the first two columns of
the table in Fig. 4. These dimensions have been derived from
English units. The standard size Jenike shear cell is made from
aluminum or stainless steel, and a smaller 63-mm diameter cell
made from stainless steel is also available. Since the actual
dimensions are not believed to be critical, the same results
could be obtained with a shear cell of the dimensions listed in
the third column of the table in Fig. 4. However, it is important
that the proportions of these dimensions be maintained ap-
proximately when using shear cells of different sizes. Besides
the shear cell, the complete shear tester includes a force
transducer which measures the shear force F , an amplifier and
s
a recorder, a motor driving the force measuring stem, a twisting
FIG. 1 Jenike Cell in Initial Offset Position wrench, a weight hanger, a time consolidation bench, an
D 6128
FIG. 4 Dimensions of the Jenike Cell
accessory for mounting wall material sample plates, and a
calibrating device. The force transducer should be capable of
measuring a force up to 500 N. The signal from the force
transducer is conditioned by an amplifier and shown on a
recorder. The motor driving the force measuring stem advances
the stem at a constant speed in the range from 1 to 3 mm/min.
The original Jenike shear tester has a speed of 2.72 mm/min
when the power supply is 60 Hz. As an alternative to the
twisting wrench, some shear testers are supplied with a
twisting device in which the twist is applied by means of a
shaft passing through bearings. In this way the likelihood of
off-axis forces or extra forces being generated during twisting
is minimized. Another alternative is to have the motor pull the
force measuring stem instead of pushing it. When using any
such alternative methods, it is essential that the user ensure that
no measurement deviations are introduced.
4.4 The consolidation bench consists of several stations for
time consolidation tests. One station is shown in Fig. 5. The
station is equipped with a weight carrier (14) on which the
weights may be placed and a flexible cover (15) to constrain
FIG. 5 Consolidating Bench Station
the test cell and prevent any influence from environmental
D 6128
effects such as evaporation or humidification during time place the hanger (6) on the twisting lid with weights (7) of
consolidation. mass m being hung from the hanger. See Fig. 1. Lower the
Wtw
4.5 The arrangement for wall friction tests is shown in Fig. lid, hanger, and weights as slowly as possible to minimize
6. For these tests it is convenient to have a special shear lid aerated material being ejected from the cell.
with a longer pin and bracket to permit a longer shear distance.
NOTE 1—During this operation the material is compressed. With fine
4.6 A device for calibrating the force transducer is shown in
particulate solids it is necessary to wait until the vertical movement stops.
Fig. 7. It consists of a pivot (1) around which levers of equal
5.2.2 Remove the weights, hanger, and twisting lid. Fill and
length, (2) and (3) rotate. With counterweight (4) the device is
level the space above the compressed material as during filling.
balanced to have its neutral position as shown in the figure. The
lever (2) exerts a force to the force measuring stem correspond-
NOTE 2—As will be mentioned later, this refilling procedure may not be
ing to the weights (5) which are hung on the lever (3). The necessary at all or may need to be performed several times, depending on
the compressibility of the powder being tested. This operation determines
calibration curve is used to convert the recorder reading to the
what height of compacted material will have to be scraped off the ring
applied shear force.
after twisting.
4.7 The laboratory used for powder testing should be free of
vibrations caused by traffic or heavy machinery. Ideally the 5.3 Twisting:
5.3.1 Place the twisting lid (12) with a smooth bottom
room should be temperature and humidity controlled, or, if this
surface on the leveled surface of material in the mould after
is not possible, it should be maintained at its nearly constant
filling or refilling. Place the hanger with weights of m on the
ambient conditions. Direct sunlight, especially on the time
Wtw
twisting lid. The weights on the hanger should correspond to a
consolidation bench, is to be avoided.
pressure of s , approximately equal to s .
tw p
5. Specimen Preparation
NOTE 3—If the surface of material in the cell is seen to be not level,
5.1 Filling the Cell (Fig. 8):
then the filling procedure was not satisfactory and the filling operation will
5.1.1 Place the shear ring on the base in the offset position
have to be repeated.
shown in Fig. 1 and gently press the ring with the fingers
5.3.2 Having filled the cell, the twisting lid is usually
against the locating screws (10) as shown in Fig. 3 and Fig. 9.
twisted through 20 cycles by means of the twisting wrench
Set these screws to give an overlap of approximately 3 mm for
(spanner) (13) or twisting device. Each twist consists of a 90°
standard cell sizes and to ensure that the axis of the cell is
rotation of the lid which is then reversed. Care must be taken
aligned with the force measuring stem. Then place the mould
not to apply vertical forces to the lid during twisting. While
ring (11) on the shear ring.
twisting, press the ring against the locating screws with the
5.1.2 Fill the assembled cell uniformly in small horizontal
fingers to prevent it from sliding from its original offset
layers by a spoon or spatula without applying force to the
position.
surface of the material until the material is somewhat over the
NOTE 4—The mould and ring should be allowed to rotate freely and
top of the mould ring. The filling should be conducted in such
independently of each other. The rotation of the ring may be small but has
a way as to ensure that there are no voids within the cell,
an influence on the consolidation.
particularly at “a” (Fig. 8) where the ring and the base overlap.
Remove excess material in small quantities by scraping off 5.3.3 If the shear apparatus is not fitted with a special
with a blade (1). The blade should be scraped across the ring in twisting device, the twisting is performed by holding the
a zig-zag motion. Take care not to disturb the position of the wrench in one hand and using the thumb and forefinger of the
ring on the base. For scraping, a rigid sharp straight blade other to maintain the ring in the offset position against the
should be used, and, during scraping, the blade should be tilted locating screws (2) shown in Fig. 8. The twisting operation
as shown in Fig. 8. should be smooth and continuous, without jerks, and at the rate
5.2 Preconsolidation: of about one twist per second. It is useful to mark the shear cell
5.2.1 Place the twisting or consolidation lid (12) shown in or twisting device to ensure a 90° rotation. After twisting,
Fig. 9 on the leveled surface of the material in the mould, then carefully
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