ASTM D695-96
(Test Method)Standard Test Method for Compressive Properties of Rigid Plastics
Standard Test Method for Compressive Properties of Rigid Plastics
SCOPE
1.1 This test method covers the determination of the mechanical properties of unreinforced and reinforced rigid plastics, including high-modulus composites, when loaded in compression at relatively low uniform rates of straining or loading. Test specimens of standard shape are employed.
1.2 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
Note 1—For compressive properties of resin-matrix composites reinforced with oriented continuous, discontinuous, or cross-ply reinforcements, tests may be made in accordance with Test Method D 3410.
1.3 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. A specific precautionary statement is given in Note 11.
Note 2—This test method is technically equivalent to ISO 604.
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An American National Standard
Designation: D 695 – 96
Standard Test Method for
Compressive Properties of Rigid Plastics
This standard is issued under the fixed designation D 695; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope Determine the Precision of Test Method
1.1 This test method covers the determination of the me-
3. Terminology
chanical properties of unreinforced and reinforced rigid plas-
3.1 Definitions:
tics, including high-modulus composites, when loaded in
3.1.1 compressive deformation—the decrease in length pro-
compression at relatively low uniform rates of straining or
duced in the gage length of the test specimen by a compressive
loading. Test specimens of standard shape are employed.
load. It is expressed in units of length.
1.2 The values stated in SI units are to be regarded as the
3.1.2 compressive strain—the ratio of compressive defor-
standard. The values in parentheses are for information only.
mation to the gage length of the test specimen, that is, the
NOTE 1—For compressive properties of resin-matrix composites rein-
change in length per unit of original length along the longitu-
forced with oriented continuous, discontinuous, or cross-ply reinforce-
dinal axis. It is expressed as a dimensionless ratio.
ments, tests may be made in accordance with Test Method D 3410.
3.1.3 compressive strength—the maximum compressive
1.3 This standard does not purport to address all of the
stress (nominal) carried by a test specimen during a compres-
safety concerns, if any, associated with its use. It is the
sion test. It may or may not be the compressive stress
responsibility of the user of this standard to establish appro-
(nominal) carried by the specimen at the moment of rupture.
priate safety and health practices and determine the applica-
3.1.4 compressive strength at failure (nominal)—the com-
bility of regulatory limitations prior to use. A specific precau-
pressive stress (nominal) sustained at the moment of failure of
tionary statement is given in Note 11.
the test specimen if shattering occurs.
3.1.5 compressive stress (nominal)—the compressive load
NOTE 2—This test method is technically equivalent to ISO 604.
per unit area of minimum original cross section within the gage
2. Referenced Documents
boundaries, carried by the test specimen at any given moment.
It is expressed in force per unit area.
2.1 ASTM Standards:
3.1.5.1 Discussion—The expression of compressive proper-
D 618 Practice for Conditioning Plastics and Electrical
ties in terms of the minimum original cross section is almost
Insulating Materials for Testing
universally used. Under some circumstances the compressive
D 638 Test Method for Tensile Properties of Plastics
properties have been expressed per unit of prevailing cross
D 3410 Test Method for Compressive Properties of Unidi-
section. These properties are called “true” compressive prop-
rectional or Crossply Fiber-Resin Composites
erties.
D 4000 Classification System for Specifying Plastic Mate-
3.1.6 compressive stress-strain diagram—a diagram in
rials
which values of compressive stress are plotted as ordinates
D 4066 Specification for Nylon Injection and Extrusion
against corresponding values of compressive strain as abscis-
Materials
sas.
E 4 Practices for Load Verification of Testing Machines
3.1.7 compressive yield point—the first point on the stress-
E 83 Practice for Verification and Classification of Exten-
strain diagram at which an increase in strain occurs without an
someters
increase in stress.
E 691 Practice for Conducting an Interlaboratory Study to
3.1.8 compressive yield strength—normally the stress at the
yield point (see also section 3.113.1.11).
This test method is under the jurisdiction of ASTM Committee D-20 on Plastics
3.1.9 crushing load—the maximum compressive force ap-
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
plied to the specimen, under the conditions of testing, that
Current edition approved April 10, 1996. Published July 1996. Originally
published as D 695 – 42 T. Last previous edition D 695 – 91.
produces a designated degree of failure.
Annual Book of ASTM Standards, Vol 08.01.
3.1.10 modulus of elasticity—the ratio of stress (nominal) to
Annual Book of ASTM Standards, Vol 15.03.
Annual Book of ASTM Standards, Vol 08.02.
Annual Book of ASTM Standards, Vol 03.01.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 695
corresponding strain below the proportional limit of a material. 5. Apparatus
It is expressed in force per unit area based on the average initial
5.1 Testing Machine—Any suitable testing machine capable
cross-sectional area.
of control of constant-rate-of-crosshead movement and com-
3.1.11 offset compressive yield strength—the stress at which
prising essentially the following:
the stress-strain curve departs from linearity by a specified
5.1.1 Drive Mechanism—A drive mechanism for imparting
percent of deformation (offset).
to the cross-head movable member, a uniform, controlled
3.1.12 percent compressive strain—the compressive defor-
velocity with respect to the base (fixed member), with this
mation of a test specimen expressed as a percent of the original
velocity to be regulated as specified in Section 9.
gage length.
5.1.2 Load Indicator—A load-indicating mechanism ca-
3.1.13 proportional limit—the greatest stress that a material
pable of showing the total compressive load carried by the test
is capable of sustaining without any deviation from propor-
specimen. The mechanism shall be essentially free from
tionality of stress to strain (Hooke’s law). It is expressed in
inertia-lag at the specified rate of testing and shall indicate the
force per unit area.
load with an accuracy of6 1 % of the maximum indicated
3.1.14 slenderness ratio—the ratio of the length of a col-
value of the test (load). The accuracy of the testing machine
umn of uniform cross section to its least radius of gyration. For
shall be verified at least once a year in accordance with
specimens of uniform rectangular cross section, the radius of
Practices E 4.
gyration is 0.289 times the smaller cross-sectional dimension.
5.2 Compressometer—A suitable instrument for determin-
For specimens of uniform circular cross section, the radius of
ing the distance between two fixed points on the test specimen
gyration is 0.250 times the diameter.
at any time during the test. It is desirable that this instrument
automatically record this distance (or any change in it) as a
4. Significance and Use
function of the load on the test specimen. The instrument shall
4.1 Compression tests provide information about the com-
be essentially free of inertia-lag at the specified rate of loading
pressive properties of plastics when employed under conditions
and shall conform to the requirements for a Class B-2
approximating those under which the tests are made. For many
extensometer as defined in Practice E 83.
materials, there may be a specification that requires the use of
NOTE 3—The requirements for extensometers cited herein apply to
this test method, but with some procedural modifications that
compressometers as well.
take precedence when adhering to the specification. Therefore,
it is advisable to refer to that material specification before using 5.3 Compression Tool—A compression tool for applying the
this test method. Table 1 in Classification D 4000 lists the load to the test specimen. This tool shall be so constructed that
ASTM materials standards that currently exist. loading is axial within 1:1000 and applied through surfaces that
4.2 Compressive properties include modulus of elasticity, are flat within 0.025 mm (0.001 in.) and parallel to each other
yield stress, deformation beyond yield point, and compressive in a plane normal to the vertical loading axis. Examples of
strength (unless the material merely flattens but does not
suitable compression tools are shown in Fig. 1 and Fig. 2.
fracture). Materials possessing a low order of ductility may not 5.4 Supporting Jig—A supporting jig for thin specimens is
exhibit a yield point. In the case of a material that fails in
shown in Fig. 3 and Fig. 4.
compression by a shattering fracture, the compressive strength 5.5 Micrometers—Suitable micrometers, reading to 0.01
has a very definite value. In the case of a material that does not
mm or 0.001 in. for measuring the width, thickness, and length
fail in compression by a shattering fracture, the compressive of the specimens.
strength is an arbitrary one depending upon the degree of
6. Test Specimens
distortion that is regarded as indicating complete failure of the
material. Many plastic materials will continue to deform in 6.1 Unless otherwise specified in the materials specifica-
compression until a flat disk is produced, the compressive tions, the specimens described in 6.2 and 6.7 shall be used.
stress (nominal) rising steadily in the process, without any These specimens may be prepared by machining operations
well-defined fracture occurring. Compressive strength can from materials in sheet, plate, rod, tube, or similar form, or
have no real meaning in such cases. they may be prepared by compression or injection molding of
4.3 Compression tests provide a standard method of obtain- the material to be tested. All machining operations shall be
ing data for research and development, quality control, accep- done carefully so that smooth surfaces result. Great care shall
be taken in machining the ends so that smooth, flat parallel
tance or rejection under specifications, and special purposes.
The tests cannot be considered significant for engineering surfaces and sharp, clean edges, to within 0.025 mm (0.001 in.)
perpendicular to the long axis of the specimen, result.
design in applications differing widely from the load-time scale
of the standard test. Such applications require additional tests 6.2 The standard test specimen, except as indicated in
such as impact, creep, and fatigue. 6.3-6.7, shall be in the form of a right cylinder or prism whose
4.4 Before proceeding with this test method, reference length is twice its principal width or diameter. Preferred
should be made to the specification of the material being tested. specimen sizes are 12.7 by 12.7 by 25.4 mm (0.50 by 0.50 by
Any test specimen preparation, conditioning, dimensions, and 1 in.) (prism), or 12.7 mm in diameter by 25.4 mm (cylinder).
testing parameters covered in the materials specification shall Where elastic modulus and offset yield-stress data are desired,
take precedence over those mentioned in this test method. If the test specimen shall be of such dimensions that the slender-
there is no material specification, then the default conditions ness ratio is in the range from 11 to 16:1. In this case, preferred
apply. specimen sizes are 12.7 by 12.7 by 50.8 mm (0.50 by 0.50 by
D 695
FIG. 3 Support Jig for This Specimen
1 mm (0.039 in.) or over, to inside diameters of 6.4 mm (0.25 in.) or over,
and to outside diameters of 50.8 mm (2.0 in.) or less.
6.5 Where it is desired to test conventional high-pressure
laminates in the form of sheets, the thickness of which is less
than 25.4 mm (1 in.), a pile-up of sheets 25.4 mm square, with
a sufficient number of layers to produce a height of at least 25.4
NOTE 1—Devices similar to the one illustrated have been successfully
mm, may be used.
used in a number of different laboratories. Details of the device developed
6.6 When testing material that may be suspected of anisot-
at the National Institute for Standards and Technology are given in the
ropy, duplicate sets of test specimens shall be prepared having
paper by Aitchinson, C. S., and Miller, J. A., “A Subpress for Compressive
their long axis respectively parallel with and normal to the
Tests,” National Advisory Committee for Aeronautics, Technical Note No.
suspected direction of anisotropy.
912, 1943.
6.7 Reinforced Plastics, Including High-Strength Compos-
FIG. 1 Subpress for Compression Tests
ites and High-Strength Composites and Highly Orthotropic
Laminates—The following specimens shall be used for rein-
forced materials, or for other materials when necessary to
comply with the slenderness ratio requirements or to permit
attachment of a deformation-measuring device.
6.7.1 For materials 3.2 mm ( ⁄8 in.) and over in thickness, a
specimen shall consist of a prism having a cross section of 12.7
mm ( ⁄2 in.) by the thickness of the material and a length such
that the slenderness ratio is in the range from 11 to 16:1 (Note
5).
6.7.2 For materials under 3.2 mm ( ⁄8 in.) thick, or where
elastic modulus testing is required and the slenderness ratio
does not provide for enough length for attachment of a
compressometer or similar device, a specimen conforming to
that shown in Fig. 5 shall be used. The supporting jig shown in
Fig. 3 and Fig. 4 shall be used to support the specimen during
testing (Note 6).
NOTE 5—If failure for materials in the thickness range of 3.2 mm ( ⁄8
in.) is by delamination rather than by the desirable shear plane fracture, the
material may be tested in accordance with 6.7.2.
FIG. 2 Compression Tool
NOTE 6—Round-robin tests have established that relatively satisfactory
2 in.) (prism), or 12.7 mm in diameter by 50.8 mm (cylinder).
measurements of modulus of elasticity may be obtained by applying a
6.3 For rod material, the test specimen shall have a diameter
compressometer to the edges of the jig-supported specimen.
equal to the diameter of the rod and a sufficient length to allow
6.8 When testing syntactic foam, the standard test specimen
a specimen slenderness ratio in the range from 11 to 16:1.
shall be in the form of a right cylinder 25.4 mm (1 in.) in
6.4 When testing tubes, the test specimen shall have a
diameter by 50.8 mm (2 in.) in length.
diameter equal to the diameter of the tube and a length of 25.4
mm (1 in.) (Note 4). For crushing-load determinations (at right
7. Conditioning
angles to the longitudinal axis), the specimen size shall be the
7.1 Conditioning—Condition the test specimens at 23 6
same, with the diameter becoming the height.
2°C (73.4 6 3.6°F) and 50 6 5 % relative humidity for not less
NOTE 4—This specimen can be used for tubes with a wall thickness of than 40 h prior to testing in accordance with Procedure A of
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