Designation: D 623 – 07

Standard Test Methods for

Rubber Property—Heat Generation and Flexing Fatigue In
Compression1
This standard is issued under the fixed designation D 623; 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 3. Summary of Test Method

1.1 These test methods may be used to compare the fatigue 3.1 The test consists of subjecting a specimen of rubber of
characteristics and rate of heat generation of different rubber definite size and shape to rapidly oscillating compressive
vulcanizates when they are subjected to dynamic compressive stresses under controlled conditions. Although heat is gener-
strains. ated by the imposed oscillating stress, the more convenient
1.2 The values stated in SI units are to be regarded as the parameter, the temperature rise, is measured. The measured
standard. The values given in parentheses are for information temperature rise is one of two types: (1) to an equilibrium
only. temperature or (2) the rise in a fixed time period. Additional
1.3 This standard does not purport to address all of the measured performance properties are the degree of permanent
safety concerns, if any, associated with its use. It is the set or other specimen dimensional changes, or both, and for
responsibility of the user of this standard to establish appro- certain test conditions, the time required for a fatigue failure by
priate safety and health practices and determine the applica- internal rupture or blow out.
bility of regulatory limitations prior to use. 3.2 Two test methods are covered, using the following
different types of apparatus:
2. Referenced Documents 3.2.1 Test Method A—Goodrich Flexometer.
2.1 ASTM Standards: 2 3.2.2 Test Method B—Firestone Flexometer.
D 395 Test Methods for Rubber Property—Compression
Set 4. Significance and Use
D 1349 Practice for Rubber—Standard Temperatures for 4.1 Because of wide variations in service conditions, no
Testing correlation between these accelerated tests and service perfor-
D 3182 Practice for Rubber—Materials, Equipment, and mance is given or implied. However, the test methods yield
Procedures for Mixing Standard Compounds and Prepar- data that can be used to estimate relative service quality of
ing Standard Vulcanized Sheets different compounds. They are often applicable to research and
D 4483 Practice for Evaluating Precision for Test Method development studies.
Standards in the Rubber and Carbon Black Manufacturing
Industries 5. Preparation of Sample
2.2 ASTM Adjuncts: 5.1 The sample may consist of any vulcanized rubber
Goodrich Flexometer Anvil Drawings3 compound except those generally classed as hard rubber,
provided it is of sufficient size to permit preparation of the test
specimen required for the test method to be employed. The
1
These test methods are under the jurisdiction of ASTM Committee D11 on sample may be prepared from a compound mixed experimen-
Rubber and are the direct responsibility of Subcommittee D11.15 on Degradation tally in the laboratory or taken from process during manufac-
Tests. ture, or it may be cut from a finished article of commerce.
Current edition approved May 1, 2007. Published May 2007. Originally
approved in 1941. Last previous edition approved in 1999 as D 623 – 99e1 . 5.2 If prepared in the laboratory, the procedure should
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or preferably be essentially as specified in Practice D 3182,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM except that when vulcanization is required, the sample should
Standards volume information, refer to the standard’s Document Summary page on
preferably be molded in block form of sufficient size to permit
the ASTM website.
3
Available from ASTM International Headquarters. Order Adjunct No. cutting of the required test specimens rather than in the form of
ADJD0623. Original adjunct produced in 1939. the standard test slab.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

1
 D 623 – 07
5.2.1 The direct molding of the specimen for Test Method A
is allowed (see 9.4) but may not yield results identical to
specimens cut from a molded block. Care must be taken in
preparation on the raw stock for direct molding of specimens.
5.3 Samples from commercial articles shall consist of a
piece slightly larger than the required test specimen and shall
subsequently be cut or buffed to size.
5.4 Comparison of results shall be made only between
specimens of identical size and shape.

TEST METHOD A—GOODRICH FLEXOMETER4

6. Nature of Test
1—Connection to eccentric which drives top anvil.
6.1 In this test method, which uses the Goodrich Flexom- 2—Top anvil.
eter, a definite compressive load is applied to a test specimen 3—Test specimen.
through a lever system having high inertia, while imposing on 4—Lower anvil.
5—Support for lower anvil.
the specimen an additional high-frequency cyclic compression 6—Lever through which load is applied.
of definite amplitude. The increase in temperature at the base of 7—Calibrated micrometer device.
the test specimen is measured with a thermocouple to provide 8—Bearing assembly or knife edge.
9—Supporting base.
a relative indication of the heat generated in flexing the 10—Test load.
specimen. Specimens may be tested under a constant applied 11—Inertia mass of 24 kg (53 lb).
load, or a constant initial compression. The change in height of 12—Pointer and reference mark for leveling of lever.

the test specimen can be measured continuously during flexure. FIG. 1 Goodrich Flexometer
By comparing this change in height with the observed perma-
nent set after test, the degree of stiffening (or softening) of the
test specimen may be estimated. Anisotropic specimens may be 8. Adjustment
tested in different directions producing measurable differences 8.1 Locate the machine on a firm foundation. Adjust the
in temperature rise due to the anisotropy. leveling screws in the base to bring the machine into a level
position in all directions at a point just to the rear of the
7. Apparatus fulcrum of the loading lever. With the loading lever locked in
place with the pin, place a level on the lever bar and verify the
7.1 The essential parts of the apparatus are shown in Fig. 1.
level setting.
The test specimen is placed between anvils faced with inserts
8.2 Adjust the eccentric to give a stroke of 4.45 6 0.03 mm
of a black NEMA Grade XX Paper-Phenolic, for heat-
(0.175 6 0.001 in.) (Note 1). This is best accomplished by
insulation purposes. The top anvil or hammer is connected to
means of a dial micrometer resting on either the cross bar of the
an adjustable eccentric usually driven at 30 6 0.2 Hz (1800
upper anvil or by means of adapters attached to the loading arm
rpm). The static load is applied by means of a lever having a
of the eccentric.
fulcrum point consisting of a low friction bearing cartridge
block or resting on a knife edge. The moment of inertia of the NOTE 1—The 4.45-mm (0.175-in.) stroke is selected as the standard for
lever system is increased, and its natural frequency reduced, by calibration purposes. When strokes other than 4.45 mm (0.175 in.) are to
be used, the displacement of the lower anvil should be maintained within
suspending masses of approximately 24 kg (53 lb) at each end
the tolerance specified for its height above the loading lever. The tolerance
of the lever system. The lower anvil may be raised or lowered for all stroke settings shall be 60.03 mm (60.001 in.).
relative to the lever by means of a calibrated micrometer
device. This device permits the lever system to be maintained 8.3 Raise the top anvil as far as the eccentric will permit by
in a horizontal position during the test as determined by a its rotation. Place a calibrating block (Note 2) 25.40 6 0.01
pointer and a reference mark on the end of the bar or a gear mm (1.000 6 0.0005 in.) in height on the lower anvil. Raise the
motor mounted to the end of the lever system to automatically anvil by means of the micrometer until the bottom side of the
drive the micrometer device based on sensors indicating the metal cup holding the thermocouple is 67 6 3 mm (2.625 6
level position of the system. The increase in temperature at the 0.125 in.) above the top of the loading lever. The loading lever
base of the specimen is determined by means of a thermo- is to be in the locked position. Adjust the cross bar of the upper
couple placed at the center of the bottom anvil. anvil, maintaining a parallel setting with the lower anvil and a
firm contact with the calibrating block. The micrometer should
7.2 The machine may be equipped with a well-insulated,
now be set at zero. This may require disengagement of the gear
temperature-controlled oven to permit testing at elevated
train nearest the vernier scale of the micrometer. Remove the
temperatures.
calibrating block and recheck the stroke for a 4.45-mm
(0.175-in.) setting. Set the pointer on the mark on the end of the
lever bar to mark the level position. If equipped with a
4
Lessig, E. T., Industrial and Engineering Chemistry, IENAA, Analytical computer system, follow the calibration procedure provided in
Edition, Vol 9, 1937, pp 582-588. the software.

2
 D 623 – 07
TABLE 1 Recommended Load on Specimen
NOTE—For calculation of masses, the long arm is 288.3 mm (11.35 in.) and the shorter arm 127.0 mm (5.0 in.).
Load on Beam Load on Specimen Unit Load on Specimen
N lbf N lbf kPa psi
70.5 6 0.2 15.86 6 0.03 160 36 644 93.54
108.0 6 0.2 24.23 6 0.03 245 55 990 142.91
216.0 6 0.2 48.46 6 0.03 489 110 1970 285.83

NOTE 2—A suitable block may be made from brass having a diameter 9. Test Specimen
of 17.8 mm (0.7 in.). The end to be placed on the lower anvil should be
counterbored for clearance of the thermocouple disk.
9.1 The test specimen as prepared from vulcanized rubber
shall be cylindrical in shape, having a diameter of 17.8 6 0.1
8.4 During the initial setup of the Flexometer, remove the mm (0.700 6 0.005 in.) and a height of 25 6 0.15 mm (1.000
locking pin from the loading lever and gently oscillate the lever 6 0.010 in.).
system to determine the point of rest. If the bar does not come 9.2 The standard test specimen shall be cut from a labora-
to rest in approximately the level position, slowly return it to its tory slab, prepared in accordance with Practice D 3182. The
level position and release. If the movement from the level cured thickness shall be such that buffing is not required. See
position is observed, add or remove a slight amount of weight 5.2. A cured block approximately 76.2 by 50.8 by 25.4 mm (3
to the required inertia weight to obtain a balance. by 2 by 1 in.) has been found satisfactory.
8.5 The rate of cyclic compression, usually 30 6 0.2 Hz 9.3 The circular die used for cutting the specimen shall have
(1800 6 10 rpm) is maintained by means of the adjustable an inside diameter of 17.78 6 0.03 mm (0.700 6 0.001 in.). In
shive or shives for the V-belt drive. Many systems use an cutting the specimen the die shall be suitably rotated in a drill
electronically controlled direct drive motor. press or similar device and lubricated by means of a soap
8.6 A Type J (IC) thermocouple using 0.40 mm (0.0159 in.) solution. A minimum distance of 13 mm (1⁄2 in.) shall be
wire is centered in the face of the lower anvil. The black maintained between the cutting edge of the die and the edge of
NEMA Grade XX Paper-Phenolic face is backed up with a the slab. The cutting pressure shall be as light as possible to
hard rubber disk. The thermocouple may be connected to a minimize cupping or taper in the diameter of the specimen.
recording device. A minimum of 100 mm (4 in.) of wire shall 9.4 An optional method of preparing the test specimen may
be retained in the oven when used at elevated temperatures. be the direct molding of the cylinder.
8.7 A suitable oven for measurements at elevated tempera- NOTE 3—It should be recognized that an equal time and temperature if
tures may be purchased with the machine or constructed. The used for both the slab and molded specimen will not produce an equivalent
inside dimensions should be approximately 100 mm (4 in.) in state of cure in the two types of specimen. A “tighter” cure will be
width, 130 mm (5 in.) in depth, and 230 mm (9 in.) high. The obtained in the molded specimen. Adjustments, preferably in the time of
top of the floor of the oven shall be 25.4 6 2.5 mm (1.0 6 0.1 cure, must be taken into consideration if comparisons between the two
types of specimen are to be considered valid.5
in.) above the loading lever.
NOTE 4—It is suggested, for purposes of uniformity and closer toler-
8.8 The air circulation is to be maintained by a squirrel-cage ances in the molded specimen, that the dimensions of the mold be
type blower 75 mm (3 in.) in diameter. The air intake should specified and shrinkage compensated for. A plate cavity 25.78 6 0.05 mm
have a diameter of approximately 59 mm (2.313 in.). The scroll (1.015 6 0.002 in.) in thickness and 18.00 6 0.05 mm (0.709 6 0.002 in.)
opening for the air discharge shall be 38 by 44 mm (1.5 by 1.75 in diameter, with overflow cavities both top and bottom when combined
in.). A motor capable of maintaining a constant rpm under load with two end plates will provide one type of a suitable mold.
between 25.8 and 28.3 Hz (1550 and 1700 rpm) shall be used 9.5 Samples from a manufactured article shall consist of a
for the blower. A platform shall be provided in the base of the piece slightly larger than the required test specimen and shall
oven on which the specimens may be placed for conditioning. subsequently be cut or buffed to size.
Such a platform can suitably be obtained from 6-mm (0.25-in.)
wire screen netting supported at least 9 mm (0.375 in.) above 10. Recommended Test Conditions
the floor of the oven. 10.1 Recommended load on the specimen is given in Table
8.9 A thermocouple of a matching type as that used in the 1.
lower anvil shall be used for measuring the ambient air 10.2 The stroke may be varied to provide a satisfactory test
temperature. It shall be located approximately 6 to 9 mm (0.25 condition in respect to the load. The recommended strokes are
to 0.375 in.) to the rear of the upper and lower anvils and 4.45 mm (0.175 in.), 5.71 mm (0.225 in.), and 6.35 mm (0.250
slightly right of center. The sensing point should be at a point in.).
about midway between the anvils. A minimum 100 mm (4 in.)
of wire should be retained within the oven. 5
Conant, F. S., Svetlik, J. F., Juve, A. E., “Equivalent Cures in Specimens of
8.10 A thermostatic control shall be capable of main-taining Various Shapes” Rubber World, RUBWA, March, 1958; Rubber Age, RUAGA,
a ambient air within 61.1°C (2°F) of the set point. March, 1958; Rubber Chemistry and Technology, RCTEA, July-Sept. 1958.