ASTM D695-23

Standard Test Method for Compressive Properties of Rigid Plastics

SIGNIFICANCE AND USE
4.1 Compression tests provide information about the compressive properties of plastics when employed under conditions approximating those under which the tests are made.  
4.2 Compressive properties include modulus of elasticity, yield stress, deformation beyond yield point, and compressive strength (unless the material merely flattens but does not fracture). Materials possessing a low order of ductility may not exhibit a yield point. In the case of a material that fails in compression by a shattering fracture, the compressive strength has a very definite value. In the case of a material that does not fail in compression by a shattering fracture, the compressive strength is an arbitrary one depending upon the degree of distortion that is regarded as indicating complete failure of the material. Many plastic materials will continue to deform in compression until a flat disk is produced, the compressive stress (nominal) rising steadily in the process, without any well-defined fracture occurring. Compressive strength can have no real meaning in such cases.  
4.3 Compression tests provide a standard method of obtaining data for research and development, quality control, acceptance or rejection under specifications, and special purposes. The tests cannot be considered significant for engineering design in applications differing widely from the load-time scale of the standard test. Such applications require additional tests such as impact, creep, and fatigue.  
4.4 Before proceeding with this test method, reference should be made to the ASTM specification for the material being tested. Any test specimen preparation, conditioning, dimensions, and testing parameters covered in the materials specification shall take precedence over those mentioned in this test method. If there is no material specification, then the default conditions apply. Table 1 in Classification D4000 lists the ASTM materials standards that currently exist.
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. This procedure is applicable for a composite modulus up to and including 41,370 MPa (6,000,000 psi).  
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 D3410/D3410M or D6641/D6641M.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. A specific precautionary statement is given in 13.1.
Note 2: This standard is equivalent to ISO 604.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Jul-2023
• ICS: 83.080.01 - Plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.10 - Mechanical Properties

Relations

• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D6641/D6641M-23 - Standard Test Method for Compressive Properties of Polymer Matrix Composite Materials Using a Combined Loading Compression (CLC) Test Fixture
• Effective Date: 15-Nov-2023
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM D6641/D6641M-16 - Standard Test Method for Compressive Properties of Polymer Matrix Composite Materials Using a Combined Loading Compression (CLC) Test Fixture
• Effective Date: 01-Nov-2016
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014

Overview

ASTM D695-23 is the internationally recognized standard test method for determining the compressive properties of rigid plastics. Published by ASTM International, this standard outlines precise procedures for measuring key mechanical properties such as modulus of elasticity, compressive strength, yield stress, and deformation beyond the yield point in both unreinforced and reinforced rigid plastics. ASTM D695-23 is widely utilized in research, quality control, materials specification, and acceptance or rejection criteria, supporting consistent, reliable evaluation of plastics when subjected to compressive loads at uniform, relatively low rates. The scope includes plastics and high-modulus composites with moduli up to 41,370 MPa (6,000,000 psi), using specimens of standard shapes and sizes.

Key Topics

• Compressive Properties: This standard focuses on compressive strength, modulus of elasticity, yield strength, compressive deformation and strain, and related measurements for rigid plastics.
• Specimen Specification: Detailed requirements for preparing and sizing various specimen forms, including right cylinders, prisms, rods, tubes, and laminate sheets, are provided to ensure consistent, comparable results.
• Testing Procedure: The test requires a suitable testing machine and compressometer, standardized rate of loading, and precise alignment for specimen placement. Special jigs and handling methods are described for thin samples or high-strength reinforced plastics.
• Data Reporting: Comprehensive guidelines specify the information to be recorded and reported, including test conditions, material identification, specimen dimensions, compressive strength, yield values, modulus, and statistical analysis of results.
• Precision and Reproducibility: The standard includes recommendations for calculating and reporting repeatability (within-lab variation) and reproducibility (between-lab variation), enhancing confidence in data comparability.

Applications

ASTM D695-23 is essential for applications where knowledge of the compressive behavior of rigid plastics is critical, including:

• Material Research and Development: Provides a standardized method for benchmarking and comparing new plastic materials and formulations.
• Quality Control and Specification Compliance: Used by manufacturers and purchasers as an acceptance or rejection criterion for rigid plastic components and raw materials.
• Product Design and Engineering: While not a direct substitute for specialized design analyses, ASTM D695-23 supplies foundational compressive property data required for understanding material performance under load.
• Industry Sectors: Widely used in automotive, construction, electronics, aerospace, medical device manufacturing, and other industries where plastics are employed as structural elements.
• Interlaboratory and International Comparison: The methodology enables cross-laboratory and international comparison of compressive properties, supporting harmonized practices in global supply chains.

Related Standards

For comprehensive material characterization and additional mechanical property requirements, consider referencing the following ASTM and ISO standards:

• ASTM D638 – Standard Test Method for Tensile Properties of Plastics
• ASTM D3410/D3410M – Test Method for Compressive Properties of Polymer Matrix Composite Materials
• ASTM D618 – Practice for Conditioning Plastics for Testing
• ASTM D4000 – Classification System for Specifying Plastic Materials
• ASTM D6641/D6641M – Test Method for Compressive Properties Using Combined Loading Compression Fixtures
• ASTM D883 – Terminology Relating to Plastics
• ISO 604 – Plastics - Determination of Compressive Properties (equivalent to ASTM D695)

By adhering to ASTM D695-23, laboratories and manufacturers ensure precise, repeatable measurement of the compressive properties of rigid plastics, which underpins informed decision-making throughout the plastics lifecycle. The standard helps maintain product reliability, supports regulatory compliance, and facilitates global trade in plastic materials and products.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D695 − 23
Standard Test Method for
Compressive Properties of Rigid Plastics
This standard is issued under the fixed designation D695; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* D883 Terminology Relating to Plastics
D3410/D3410M Test Method for Compressive Properties of
1.1 This test method covers the determination of the me-
Polymer Matrix Composite Materials with Unsupported
chanical properties of unreinforced and reinforced rigid
Gage Section by Shear Loading
plastics, including high-modulus composites, when loaded in
D4000 Classification System for Specifying Plastic Materi-
compression at relatively low uniform rates of straining or
als
loading. Test specimens of standard shape are employed. This
D5947 Test Methods for Physical Dimensions of Solid
procedure is applicable for a composite modulus up to and
Plastics Specimens
including 41,370 MPa (6,000,000 psi).
D6641/D6641M Test Method for Compressive Properties of
1.2 The values stated in SI units are to be regarded as the
Polymer Matrix Composite Materials Using a Combined
standard. The values in parentheses are for information only.
Loading Compression (CLC) Test Fixture
E4 Practices for Force Calibration and Verification of Test-
NOTE 1—For compressive properties of resin-matrix composites rein-
forced with oriented continuous, discontinuous, or cross-ply
ing Machines
reinforcements, tests may be made in accordance with Test Method
E83 Practice for Verification and Classification of Exten-
D3410/D3410M or D6641/D6641M.
someter Systems
1.3 This standard does not purport to address all of the
E456 Terminology Relating to Quality and Statistics
safety concerns, if any, associated with its use. It is the
E691 Practice for Conducting an Interlaboratory Study to
responsibility of the user of this standard to establish appro-
Determine the Precision of a Test Method
priate safety, health, and environmental practices and deter-
2.2 ISO Standard:
mine the applicability of regulatory limitations prior to use. A
ISO 604 Plastics—Determination of Compressive Properties
specific precautionary statement is given in 13.1.
3. Terminology
NOTE 2—This standard is equivalent to ISO 604.
3.1 Terms used in this standard are defined in accordance
1.4 This international standard was developed in accor-
with Terminology D883, unless otherwise specified. For terms
dance with internationally recognized principles on standard-
relating to precision and bias and associated issues, the terms
ization established in the Decision on Principles for the
used in this standard are defined in accordance with Terminol-
Development of International Standards, Guides and Recom-
ogy E456.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 3.2 Definitions:
3.2.1 compressive deformation—the decrease in length pro-
2. Referenced Documents duced in the gage length of the test specimen by a compressive
load. It is expressed in units of length.
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing 3.2.2 compressive strain—the ratio of compressive defor-
D638 Test Method for Tensile Properties of Plastics mation to the gage length of the test specimen, that is, the
change in length per unit of original length along the longitu-
dinal axis. It is expressed as a dimensionless ratio.
This test method is under the jurisdiction of ASTM Committee D20 on Plastics
3.2.3 compressive strength—the maximum compressive
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
stress (nominal) carried by a test specimen during a compres-
Current edition approved Aug. 1, 2023. Published August 2023. Originally
sion test. It may or may not be the compressive stress
approved in 1942. Last previous edition approved in 2015 as D695 - 15. DOI:
10.1520/D0695-23.
(nominal) carried by the specimen at the moment of rupture.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D695 − 23
3.2.4 compressive strength at failure (nominal)—the com- 4. Significance and Use
pressive stress (nominal) sustained at the moment of failure of
4.1 Compression tests provide information about the com-
the test specimen if shattering occurs.
pressive properties of plastics when employed under conditions
approximating those under which the tests are made.
3.2.5 compressive stress (nominal)—the compressive load
per unit area of minimum original cross section within the gage
4.2 Compressive properties include modulus of elasticity,
boundaries, carried by the test specimen at any given moment.
yield stress, deformation beyond yield point, and compressive
It is expressed in force per unit area.
strength (unless the material merely flattens but does not
3.2.5.1 Discussion—The expression of compressive proper- fracture). Materials possessing a low order of ductility may not
exhibit a yield point. In the case of a material that fails in
ties in terms of the minimum original cross section is almost
universally used. Under some circumstances the compressive compression by a shattering fracture, the compressive strength
has a very definite value. In the case of a material that does not
properties have been expressed per unit of prevailing cross
fail in compression by a shattering fracture, the compressive
section. These properties are called “true” compressive prop-
strength is an arbitrary one depending upon the degree of
erties.
distortion that is regarded as indicating complete failure of the
3.2.6 compressive stress-strain diagram—a diagram in
material. Many plastic materials will continue to deform in
which values of compressive stress are plotted as ordinates
compression until a flat disk is produced, the compressive
against corresponding values of compressive strain as abscis-
stress (nominal) rising steadily in the process, without any
sas.
well-defined fracture occurring. Compressive strength can
have no real meaning in such cases.
3.2.7 compressive yield point—the first point on the stress-
strain diagram at which an increase in strain occurs without an
4.3 Compression tests provide a standard method of obtain-
increase in stress.
ing data for research and development, quality control, accep-
tance or rejection under specifications, and special purposes.
3.2.8 compressive yield strength—normally the stress at the
The tests cannot be considered significant for engineering
yield point (see also section 3.2.11).
design in applications differing widely from the load-time scale
3.2.9 crushing load—the maximum compressive force ap-
of the standard test. Such applications require additional tests
plied to the specimen, under the conditions of testing, that
such as impact, creep, and fatigue.
produces a designated degree of failure.
4.4 Before proceeding with this test method, reference
3.2.10 modulus of elasticity—the ratio of stress (nominal) to
should be made to the ASTM specification for the material
corresponding strain below the proportional limit of a material.
being tested. Any test specimen preparation, conditioning,
It is expressed in force per unit area based on the average initial
dimensions, and testing parameters covered in the materials
cross-sectional area.
specification shall take precedence over those mentioned in this
test method. If there is no material specification, then the
3.2.11 offset compressive yield strength—the stress at which
default conditions apply. Table 1 in Classification D4000 lists
the stress-strain curve departs from linearity by a specified
the ASTM materials standards that currently exist.
percent of deformation (offset).
5. Apparatus
3.2.12 percent compressive strain—the compressive defor-
mation of a test specimen expressed as a percent of the original
5.1 Testing Machine—Any suitable testing machine capable
gage length.
of control of constant-rate-of-crosshead movement and com-
prising essentially the following:
3.2.13 proportional limit—the greatest stress that a material
5.1.1 Drive Mechanism—A drive mechanism for imparting
is capable of sustaining without any deviation from propor-
to the movable cross-head member, a uniform, controlled
tionality of stress to strain (Hooke’s law). It is expressed in
velocity with respect to the base (fixed member), with this
force per unit area.
velocity to be regulated as specified in Section 9.
3.2.14 slenderness ratio—the ratio of the length of a column
5.1.2 Load Indicator—A load-indicating mechanism ca-
of uniform cross section to its least radius of gyration. For
pable of showing the total compressive load carried by the test
specimens of uniform rectangular cross section, the radius of
specimen. The mechanism shall be essentially free from
gyration is 0.289 times the smaller cross-sectional dimension.
inertia-lag at the specified rate of testing and shall indicate the
For specimens of uniform circular cross section, the radius of
load with an accuracy of 61 % of the maximum indicated
gyration is 0.250 times the diameter. For specimens of tubular
value of the test (load). The accuracy of the testing machine
cross section, the radius of gyration is calculated as follows:
shall be verified at least once a year in accordance with
Practices E4.
2 2
=D 1d
R 5 (1)
g
4 5.2 Compressometer—A suitable instrument for determin-
ing the distance between two fixed points on the test specimen
where:
at any time during the test. It is desirable that this instrument
R = radius of gyration,
g
automatically record this distance (or any change in it) as a
D = outside diameter, and
function of the load on the test specimen. The instrument shall
d = inside diameter.
be essentially free of inertia-lag at the specified rate of loading
D695 − 23
FIG. 2 Compression Tool
NOTE 1—Devices similar to the one illustrated have been successfully
used in a number of different laboratories. Details of the device developed
at the National Institute for Standards and Technology are given in the
paper by Aitchinson, C. S., and Miller, J. A., “A Subpress for Compressive
Tests,” National Advisory Committee for Aeronautics, Technical Note No.
912, 1943.
FIG. 1 Subpress for Compression Tests
and shall conform to the requirements for a Class B-2
extensometer as defined in Practice E83.
NOTE 3—The requirements for extensometers cited herein apply to
compressometers as well.
FIG. 3 Support Jig for Thin Specimen
5.3 Compression Tool—A compression tool for applying the
load to the test specimen. This tool shall be so constructed that
loading is axial within 1:1000 and applied through surfaces that
6.2 The standard test specimen for strength measurements,
are flat within 0.025 mm (0.001 in.) and parallel to each other
except as indicated in 6.3 – 6.8, shall be in the form of a right
in a plane normal to the vertical loading axis. Examples of
cylinder or prism whose length is twice its principal width or
suitable compression tools are shown in Fig. 1 and Fig. 2.
diameter. Preferred specimen sizes are 12.7 by 12.7 by 25.4
5.4 Supporting Jig—A supporting jig for thin specimens is
mm (0.50 by 0.50 by 1 in.) (prism), or 12.7 mm in diameter by
shown in Fig. 3 and Fig. 4.
25.4 mm (cylinder). The standard test specimen for modulus or
offset yield measurements shall be of such dimensions that the
5.5 Micrometers—Suitable micrometers, reading to 0.01
slenderness ratio is in the range from 11 to 16:1. In this case,
mm or 0.001 in. for measuring the width, thickness, diameter,
preferred specimen sizes are 12.7 by 12.7 by 50.8 mm (0.50 by
and length of the specimens.
0.50 by 2 in.) (prism), or 12.7 mm in diameter by 50.8 mm
6. Test Specimens (cylinder).
6.2.1 When the standard specimens (right cylinders or
6.1 Unless otherwise specified in the materials
prisms) cannot be obtained due to the thinness of the material
specifications, the specimens described in 6.2 through 6.8 shall
(typically less than 6.4 mm (0.25 in.)), alternative specimens
be used. These specimens may be prepared by machining
outlined in 6.7.1 and 6.7.2 shall be used.
operations from materials in sheet, plate, rod, tube, or similar
form, or they may be prepared by compression or injection 6.3 For rod, the test specimen for strength measurements
molding of the material to be tested. All machining operations shall have a diameter equal to the diameter of the rod and a
shall be done carefully so that smooth surfaces result. Great length twice the diameter of the rod. The test specimen for
care shall be taken in machining the ends so that smooth, flat modulus or offset yield measurements shall have a diameter
parallel surfaces and sharp, clean edges, to within 0.025 mm equal to the diameter of the rod and a length such that
(0.001 in.) perpendicular to the long axis of the specimen, slenderness ratio is in the range from 11 to 16:1. If the diameter
result. of the rod is too large to obtain failure due to limitations of the
D695 − 23
NOTE 1—Cold rolled steel.
NOTE 2—Furnished four steel machine screws and nuts, round head, slotted, length 31.75 mm (1 ⁄4 in.).
NOTE 3—Grind surfaces denoted “Gr.”
FIG. 4 Support Jig, Details
test equipment, specimens outlined in 6.2 shall be machined prism having a cross section of 12.7 mm (0.5 in.) by the
from the center of the rod. thickness of the material and a length of 12.7 mm (0.5 in).
(Specimen length may be shortened if buckling is observed).
6.4 For tubes, the test specimen for strength measurements
For material greater than 6.4 mm (0.25 in.) in thickness,
shall have a diameter equal to the diameter of the tube and a
specimens outlined in 6.2 shall be used. The test specimen for
length of 25.4 mm (1 in.). This specimen shall be used for tubes
modulus or offset yield measurements shall be of such dimen-
with a wall thickness of 1 mm (0.039 in.) or over, to inside
sions that slenderness ratio is in the range from 11 to 16:1
diameters of 6.4 mm (0.25 in.) or over, and to outside
(Note 4).
diameters of 50.8 mm (2.0 in.) or less. If the diameter of the
6.7.2 For materials under 3.2 mm (0.125 in.) thick, or where
tube is too large to obtain failure due to limitations of the test
elastic modulus testing is required and the slenderness ratio
equipment,
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D695 − 15 D695 − 23
Standard Test Method for
Compressive Properties of Rigid Plastics
This standard is issued under the fixed designation D695; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. 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. This procedure is applicable for a composite modulus up to and including 41,370 MPa (6,000,000
psi).
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 D3410/D3410M or D6641/D6641M.
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 healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use. A specific precautionary statement is given in 13.1.
NOTE 2—This standard is equivalent to ISO 604.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D638 Test Method for Tensile Properties of Plastics
D883 Terminology Relating to Plastics
D3410/D3410M Test Method for Compressive Properties of Polymer Matrix Composite Materials with Unsupported Gage
Section by Shear Loading
D4000 Classification System for Specifying Plastic Materials
D5947 Test Methods for Physical Dimensions of Solid Plastics Specimens
D6641/D6641M Test Method for Compressive Properties of Polymer Matrix Composite Materials Using a Combined Loading
Compression (CLC) Test Fixture
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
Current edition approved Sept. 1, 2015Aug. 1, 2023. Published September 2015August 2023. Originally approved in 1942. Last previous edition approved in 20102015
as D695 - 10.D695 - 15. DOI: 10.1520/D0695-15.10.1520/D0695-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D695 − 23
E4 Practices for Force Calibration and Verification of Testing Machines
E83 Practice for Verification and Classification of Extensometer Systems
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 ISO Standard:
ISO 604 Plastics—Determination of Compressive Properties
3. Terminology
3.1 General—The definitions of plastics Terms used in this test method are standard are defined in accordance with Terminology
D883 unless otherwise indicated., unless otherwise specified. For terms relating to precision and bias and associated issues, the
terms used in this standard are defined in accordance with Terminology E456.
3.2 Definitions:
3.2.1 compressive deformation—the decrease in length produced in the gage length of the test specimen by a compressive load.
It is expressed in units of length.
3.2.2 compressive strain—the ratio of compressive deformation to the gage length of the test specimen, that is, the change in length
per unit of original length along the longitudinal axis. It is expressed as a dimensionless ratio.
3.2.3 compressive strength—the maximum compressive stress (nominal) carried by a test specimen during a compression test. It
may or may not be the compressive stress (nominal) carried by the specimen at the moment of rupture.
3.2.4 compressive strength at failure (nominal)—the compressive stress (nominal) sustained at the moment of failure of the test
specimen if shattering occurs.
3.2.5 compressive stress (nominal)—the compressive load per unit area of minimum original cross section within the gage
boundaries, carried by the test specimen at any given moment. It is expressed in force per unit area.
3.2.5.1 Discussion—
The expression of compressive properties in terms of the minimum original cross section is almost universally used. Under some
circumstances the compressive properties have been expressed per unit of prevailing cross section. These properties are called
“true” compressive properties.
3.2.6 compressive stress-strain diagram—a diagram in which values of compressive stress are plotted as ordinates against
corresponding values of compressive strain as abscissas.
3.2.7 compressive yield point—the first point on the stress-strain diagram at which an increase in strain occurs without an increase
in stress.
3.2.8 compressive yield strength—normally the stress at the yield point (see also section 3.2.11).
3.2.9 crushing load—the maximum compressive force applied to the specimen, under the conditions of testing, that produces a
designated degree of failure.
3.2.10 modulus of elasticity—the ratio of stress (nominal) to corresponding strain below the proportional limit of a material. It is
expressed in force per unit area based on the average initial cross-sectional area.
3.2.11 offset compressive yield strength—the stress at which the stress-strain curve departs from linearity by a specified percent
of deformation (offset).
3.2.12 percent compressive strain—the compressive deformation of a test specimen expressed as a percent of the original gage
length.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D695 − 23
3.2.13 proportional limit—the greatest stress that a material is capable of sustaining without any deviation from proportionality
of stress to strain (Hooke’s law). It is expressed in force per unit area.
3.2.14 slenderness ratio—the ratio of the length of a column of uniform cross section to its least radius of gyration. For specimens
of uniform rectangular cross section, the radius of gyration is 0.289 times the smaller cross-sectional dimension. For specimens
of uniform circular cross section, the radius of gyration is 0.250 times the diameter. For specimens of tubular cross section, the
radius of gyration is calculated as follows:
2 2
=D 1d
R 5 (1)
g
where:
R = radius of gyration,
g
D = outside diameter, and
d = inside diameter.
4. Significance and Use
4.1 Compression tests provide information about the compressive properties of plastics when employed under conditions
approximating those under which the tests are made.
4.2 Compressive properties include modulus of elasticity, yield stress, deformation beyond yield point, and compressive strength
(unless the material merely flattens but does not fracture). Materials possessing a low order of ductility may not exhibit a yield
point. In the case of a material that fails in compression by a shattering fracture, the compressive strength has a very definite value.
In the case of a material that does not fail in compression by a shattering fracture, the compressive strength is an arbitrary one
depending upon the degree of distortion that is regarded as indicating complete failure of the material. Many plastic materials will
continue to deform in compression until a flat disk is produced, the compressive stress (nominal) rising steadily in the process,
without any well-defined fracture occurring. Compressive strength can have no real meaning in such cases.
4.3 Compression tests provide a standard method of obtaining data for research and development, quality control, acceptance or
rejection under specifications, and special purposes. The tests cannot be considered significant for engineering design in
applications differing widely from the load-time scale of the standard test. Such applications require additional tests such as impact,
creep, and fatigue.
4.4 Before proceeding with this test method, reference should be made to the ASTM specification for the material being tested.
Any test specimen preparation, conditioning, dimensions, and testing parameters covered in the materials specification shall take
precedence over those mentioned in this test method. If there is no material specification, then the default conditions apply. Table
1 in Classification D4000 lists the ASTM materials standards that currently exist.
5. Apparatus
5.1 Testing Machine—Any suitable testing machine capable of control of constant-rate-of-crosshead movement and comprising
essentially the following:
5.1.1 Drive Mechanism—A drive mechanism for imparting to the movable cross-head member, a uniform, controlled velocity with
respect to the base (fixed member), with this velocity to be regulated as specified in Section 9.
5.1.2 Load Indicator—A load-indicating mechanism capable of showing the total compressive load carried by the test specimen.
The mechanism shall be essentially free from inertia-lag at the specified rate of testing and shall indicate the load with an accuracy
of 61 % of the maximum indicated value of the test (load). The accuracy of the testing machine shall be verified at least once a
year in accordance with Practices E4.
5.2 Compressometer—A suitable instrument for determining the distance between two fixed points on the test specimen at any
time during the test. It is desirable that this instrument automatically record this distance (or any change in it) as a function of the
load on the test specimen. The instrument shall be essentially free of inertia-lag at the specified rate of loading and shall conform
to the requirements for a Class B-2 extensometer as defined in Practice E83.
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NOTE 1—Devices similar to the one illustrated have been successfully used in a number of different laboratories. Details of the device developed at
the National Institute for Standards and Technology are given in the paper by Aitchinson, C. S., and Miller, J. A., “A Subpress for Compressive Tests,”
National Advisory Committee for Aeronautics, Technical Note No. 912, 1943.
FIG. 1 Subpress for Compression Tests
NOTE 3—The requirements for extensometers cited herein apply to compressometers as well.
5.3 Compression Tool—A compression tool for applying the load to the test specimen. This tool shall be so constructed that
loading is axial within 1:1000 and applied through surfaces that are flat within 0.025 mm (0.001 in.) and parallel to each other in
a plane normal to the vertical loading axis. Examples of suitable compression tools are shown in Fig. 1 and Fig. 2.
5.4 Supporting Jig—A supporting jig for thin specimens is shown in Fig. 3 and Fig. 4.
5.5 Micrometers—Suitable micrometers, reading to 0.01 mm or 0.001 in. for measuring the width, thickness, diameter, and length
of the specimens.
6. Test Specimens
6.1 Unless otherwise specified in the materials specifications, the specimens described in 6.2 through 6.8 shall be used. These
specimens may be prepared by machining operations from materials in sheet, plate, rod, tube, or similar form, or they may be
prepared by compression or injection molding of the material to be tested. All machining operations shall be done carefully so that
smooth surfaces result. Great care shall be taken in machining the ends so that smooth, flat parallel surfaces and sharp, clean edges,
to within 0.025 mm (0.001 in.) perpendicular to the long axis of the specimen, result.
6.2 The standard test specimen for strength measurements, except as indicated in 6.3 – 6.8, shall be in the form of a right cylinder
or prism whose length is twice its principal width or diameter. Preferred specimen sizes are 12.7 by 12.7 by 25.4 mm (0.50 by 0.50
by 1 in.) (prism), or 12.7 mm in diameter by 25.4 mm (cylinder). The standard test specimen for modulus or offset yield
measurements shall be of such dimensions that the slenderness ratio is in the range from 11 to 16:1. In this case, preferred specimen
sizes are 12.7 by 12.7 by 50.8 mm (0.50 by 0.50 by 2 in.) (prism), or 12.7 mm in diameter by 50.8 mm (cylinder).
6.2.1 When the standard specimens (right cylinders or prisms) cannot be obtained due to the thinness of the material (typically
less than 6.4 mm (0.25 in.)), alternative specimens outlined in 6.7.1 and 6.7.2 shall be used.
6.3 For rod, the test specimen for strength measurements shall have a diameter equal to the diameter of the rod and a length twice
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FIG. 2 Compression Tool
FIG. 3 Support Jig for Thin Specimen
the diameter of the rod. The test specimen for modulus or offset yield measurements shall have a diameter equal to the diameter
of the rod and a length such that slenderness ratio is in the range from 11 to 16:1. If the diameter of the rod is too large to obtain
failure due to limitations of the test equipment, specimens outlined in 6.2 shall be machined from the center of the rod.
6.4 For tubes, the test specimen for strength measurements shall have a diameter equal to the diameter of the tube and a length
of 25.4 mm (1 in.). This specimen shall be used for tubes with a wall thickness of 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. If the diameter of the tube is too large to obtain
failure due to limitations of the test equipment, specimens outlined in 6.2 shall be machined from the wall of the tube. For
crushing-load determinations (at right angles to the longitudinal axis), the specimen size shall be the same, with the diameter
becoming the height. The test specimen for modulus or offset yield measurements shall have a diameter equal to the diameter of
the tube and a length such that the slenderness ratio is in the range from 11 to 16:1.
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 12.7 mm square, with a sufficient number of layers to produce a height of approximately 25.4 mm
(actual height achievable will be dependent upon individual layer thickness), shall be used for strength measurements. The test
specimen for modulus or offset yield measurements shall consist of a pile-up of 12.7 mm square sheets to produce a height such
that slenderness ratio is in the range from 11 to 16:1.
6.6 When testing material that may be suspected of anisotropy, duplicate sets of test specimens shall be prepared having their long
axis respectively parallel with and normal to the suspected direction of anisotropy.
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NOTE 1—Cold rolled steel.
NOTE 2—Furnished four steel machine screws and nuts, round head, slotted, length 31.75 mm (1 ⁄4 in.).
NOTE 3—Grind surfaces denoted “Gr.”
FIG. 4 Support Jig, Details
6.7 Reinforced Plastics, including High-Strength Composites and Highly Orthotropic Laminates—The following specimens shall
be used for reinforced materials.
6.7.1 For materials 3.2 mm to 6.4 mm (0.125 in. to 0.25 in.), the specimen used for strength measurements shall consist of a prism
having a cross section of 12.7 mm (0.5 in.) by the thickness of the material and a length of 12.7 mm (0.5 in). (Specimen length
may be shortened if buckling is observed). For material greater than 6.4 mm (0.25 in.) in thickness, specimens outlined in 6.2 shall
be used. The test specimen for modulus or offset yield measurements shall be of such dimensions that slenderness ratio is in the
range from 11 to 16:1 (Note 4).
6.7.2 For materials under 3.2 mm (0.125 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 5).
NOTE 4—If failure for specimens utilized in 6.7.1 is by delamination rather than by the desirable shear pl
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