ASTM D638-22
(Test Method)Standard Test Method for Tensile Properties of Plastics
Standard Test Method for Tensile Properties of Plastics
SIGNIFICANCE AND USE
4.1 This test method is designed to produce tensile property data for the control and specification of plastic materials. These data are also useful for qualitative characterization and for research and development.
4.2 Some material specifications that require the use of this test method, but with some procedural modifications that take precedence when adhering to the specification. Therefore, it is advisable to refer to that material specification before using this test method. Table 1 in Classification D4000 lists the ASTM materials standards that currently exist.
4.3 Tensile properties are known to vary with specimen preparation and with speed and environment of testing. Consequently, where precise comparative results are desired, these factors must be carefully controlled.
4.4 It is realized that a material cannot be tested without also testing the method of preparation of that material. Hence, when comparative tests of materials per se are desired, exercise great care to ensure that all samples are prepared in exactly the same way, unless the test is to include the effects of sample preparation. Similarly, for referee purposes or comparisons within any given series of specimens, care shall be taken to secure the maximum degree of uniformity in details of preparation, treatment, and handling.
4.5 Tensile properties provide useful data for plastics engineering design purposes. However, because of the high degree of sensitivity exhibited by many plastics to rate of straining and environmental conditions, data obtained by this test method cannot be considered valid for applications involving load-time scales or environments widely different from those of this test method. In cases of such dissimilarity, no reliable estimation of the limit of usefulness can be made for most plastics. This sensitivity to rate of straining and environment necessitates testing over a broad load-time scale (including impact and creep) and range of environmental conditions i...
SCOPE
1.1 This test method covers the determination of the tensile properties of unreinforced and reinforced plastics in the form of standard dumbbell-shaped test specimens when tested under defined conditions of pretreatment, temperature, humidity, and testing machine speed.
1.2 This test method is applicable for testing materials of any thickness up to 14 mm (0.55 in.). However, for testing specimens in the form of thin sheeting, including film less than 1.0 mm (0.04 in.) in thickness, ASTM standard D882 is the preferred test method. Materials with a thickness greater than 14 mm (0.55 in.) shall be reduced by machining.
1.3 This test method includes the option of determining Poisson's ratio at room temperature.
Note 1: This standard and ISO 527-1 address the same subject matter, but differ in technical content.
Note 2: This test method is not intended to cover precise physical procedures. It is recognized that the constant rate of crosshead movement type of test leaves much to be desired from a theoretical standpoint, that wide differences may exist between rate of crosshead movement and rate of strain between gage marks on the specimen, and that the testing speeds specified disguise important effects characteristic of materials in the plastic state. Further, it is realized that variations in the thicknesses of test specimens, which are permitted by these procedures, produce variations in the surface-volume ratios of such specimens, and that these variations may influence the test results. Hence, where directly comparable results are desired, all samples should be of equal thickness. Special additional tests should be used where more precise physical data are needed.
Note 3: This test method may be used for testing phenolic molded resin or laminated materials. However, where these materials are used as electrical insulation, such materials should be tested in accordance with Test Methods D229 and Test Method D651...
General Information
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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: D638 − 22
Standard Test Method for
Tensile Properties of Plastics
This standard is issued under the fixed designation D638; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber 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* consider the precautions and limitations of this method found
in Note 2 and Section 4 before considering these data for
1.1 This test method covers the determination of the tensile
engineering design.
properties of unreinforced and reinforced plastics in the form
1.5 The values stated in SI units are to be regarded as
ofstandarddumbbell-shapedtestspecimenswhentestedunder
standard. The values given in parentheses are for information
defined conditions of pretreatment, temperature, humidity, and
only.
testing machine speed.
1.6 This standard does not purport to address all of the
1.2 This test method is applicable for testing materials of
safety concerns, if any, associated with its use. It is the
any thickness up to 14 mm (0.55 in.). However, for testing
responsibility of the user of this standard to establish appro-
specimensintheformofthinsheeting,includingfilmlessthan
priate safety, health, and environmental practices and deter-
1.0 mm (0.04 in.) in thickness, ASTM standard D882 is the
mine the applicability of regulatory limitations prior to use.
preferred test method. Materials with a thickness greater than
1.7 This international standard was developed in accor-
14 mm (0.55 in.) shall be reduced by machining.
dance with internationally recognized principles on standard-
1.3 This test method includes the option of determining
ization established in the Decision on Principles for the
Poisson’s ratio at room temperature.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
NOTE 1—This standard and ISO 527-1 address the same subject matter,
but differ in technical content.
Barriers to Trade (TBT) Committee.
NOTE 2—This test method is not intended to cover precise physical
procedures. It is recognized that the constant rate of crosshead movement
2. Referenced Documents
type of test leaves much to be desired from a theoretical standpoint, that
2.1 ASTM Standards:
wide differences may exist between rate of crosshead movement and rate
of strain between gage marks on the specimen, and that the testing speeds D229Test Methods for Rigid Sheet and Plate Materials
specified disguise important effects characteristic of materials in the
Used for Electrical Insulation
plastic state. Further, it is realized that variations in the thicknesses of test
D412TestMethodsforVulcanizedRubberandThermoplas-
specimens,whicharepermittedbytheseprocedures,producevariationsin
tic Elastomers—Tension
thesurface-volumeratiosofsuchspecimens,andthatthesevariationsmay
D618Practice for Conditioning Plastics for Testing
influence the test results. Hence, where directly comparable results are
desired, all samples should be of equal thickness. Special additional tests
D651Test Method for Test for Tensile Strength of Molded
should be used where more precise physical data are needed.
Electrical Insulating Materials (Withdrawn 1989)
NOTE 3—This test method may be used for testing phenolic molded
D882Test Method for Tensile Properties of Thin Plastic
resin or laminated materials. However, where these materials are used as
Sheeting
electrical insulation, such materials should be tested in accordance with
D883Terminology Relating to Plastics
Test Methods D229 and Test Method D651.
NOTE 4—For tensile properties of resin-matrix composites reinforced D1822Test Method for Determining the Tensile-Impact
with oriented continuous or discontinuous high modulus >20-GPa
Resistance of Plastics
(>3.0×10 -psi) fibers, tests shall be made in accordance with Test
D3039/D3039MTest Method forTensile Properties of Poly-
Method D3039/D3039M.
mer Matrix Composite Materials
1.4 Test data obtained by this test method have been found
D4000Classification System for Specifying Plastic Materi-
to be useful in engineering design. However, it is important to
als
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction ofASTM Committee D20 on Plastics contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties. Standards volume information, refer to the standard’s Document Summary page on
CurrenteditionapprovedJuly1,2022.PublishedJuly2022.Originallyapproved the ASTM website.
in 1941. Last previous edition approved in 2014 as D638-14. DOI: 10.1520/ The last approved version of this historical standard is referenced on
D0638-22. www.astm.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
D638 − 22
D4066Classification System for Nylon Injection and Extru- the limit of usefulness can be made for most plastics. This
sion Materials (PA) sensitivity to rate of straining and environment necessitates
D5947Test Methods for Physical Dimensions of Solid testing over a broad load-time scale (including impact and
Plastics Specimens creep) and range of environmental conditions if tensile prop-
E4Practices for Force Calibration and Verification of Test- erties are to suffice for engineering design purposes.
ing Machines
NOTE 5—Since the existence of a true elastic limit in plastics (as in
E83Practice for Verification and Classification of Exten-
many other organic materials and in many metals) is debatable, the
someter Systems
propriety of applying the term “elastic modulus” in its quoted, generally
E132Test Method for Poisson’s Ratio at RoomTemperature
accepted definition to describe the “stiffness” or “rigidity” of a plastic has
beenseriouslyquestioned.Theexactstress-straincharacteristicsofplastic
E456Terminology Relating to Quality and Statistics
materials are highly dependent on such factors as rate of application of
E691Practice for Conducting an Interlaboratory Study to
stress, temperature, previous history of specimen, etc. However, stress-
Determine the Precision of a Test Method
strain curves for plastics, determined as described in this test method,
E2935Practice for Evaluating Equivalence of Two Testing
almost always show a linear region at low stresses, and a straight line
Processes drawn tangent to this portion of the curve permits calculation of an elastic
modulus of the usually defined type. Such a constant is useful if its
2.2 ISO Standard:
arbitrary nature and dependence on time, temperature, and similar factors
ISO 527-1Determination of Tensile Properties
are realized.
3. Terminology
5. Apparatus
3.1 Terms used in this standard are defined in accordance
5.1 Testing Machine—A testing machine of the constant-
with Terminology D883, and Annex A2. For terms relating to
rate-of-crosshead-movement type and comprising essentially
precision and bias and associated issues, the terms used in this
the following:
standard are defined in accordance with Terminology E456.
5.1.1 Fixed Member—A fixed or essentially stationary
4. Significance and Use
member carrying one grip.
4.1 This test method is designed to produce tensile property 5.1.2 Movable Member—A movable member carrying a
dataforthecontrolandspecificationofplasticmaterials.These
second grip.
data are also useful for qualitative characterization and for
5.1.3 Grips—Grips for holding the test specimen between
research and development.
the fixed member and the movable member of the testing
machine can be either the fixed or self-aligning type.
4.2 Some material specifications that require the use of this
test method, but with some procedural modifications that take 5.1.3.1 Fixed grips are rigidly attached to the fixed and
precedence when adhering to the specification. Therefore, it is movable members of the testing machine. When this type of
advisabletorefertothatmaterialspecificationbeforeusingthis grip is used take extreme care to ensure that the test specimen
test method. Table 1 in Classification D4000 lists the ASTM is inserted and clamped so that the long axis of the test
materials standards that currently exist. specimen coincides with the direction of pull through the
center line of the grip assembly.
4.3 Tensile properties are known to vary with specimen
5.1.3.2 Self-aligning grips are attached to the fixed and
preparation and with speed and environment of testing.
movablemembersofthetestingmachineinsuchamannerthat
Consequently, where precise comparative results are desired,
they will move freely into alignment as soon as any load is
these factors must be carefully controlled.
applied so that the long axis of the test specimen will coincide
4.4 Itisrealizedthatamaterialcannotbetestedwithoutalso
with the direction of the applied pull through the center line of
testingthemethodofpreparationofthatmaterial.Hence,when
the grip assembly.Align the specimens as perfectly as possible
comparativetestsofmaterialspersearedesired,exercisegreat
with the direction of pull so that no rotary motion that may
caretoensurethatallsamplesarepreparedinexactlythesame
induce slippage will occur in the grips; there is a limit to the
way, unless the test is to include the effects of sample
amountofmisalignmentself-aligninggripswillaccommodate.
preparation. Similarly, for referee purposes or comparisons
5.1.3.3 The test specimen shall be held in such a way that
within any given series of specimens, care shall be taken to
slippage relative to the grips is prevented insofar as possible.
secure the maximum degree of uniformity in details of
Grip surfaces that are deeply scored or serrated with a pattern
preparation, treatment, and handling.
similar to those of a coarse single-cut file, serrations about 2.4
4.5 Tensile properties provide useful data for plastics engi-
mm (0.09 in.) apart and about 1.6 mm (0.06 in.) deep, have
neering design purposes. However, because of the high degree
been found satisfactory for most thermoplastics. Finer serra-
ofsensitivityexhibitedbymanyplasticstorateofstrainingand
tions have been found to be more satisfactory for harder
environmental conditions, data obtained by this test method
plastics,suchasthethermosettingmaterials.Itisimportantthat
cannotbeconsideredvalidforapplicationsinvolvingload-time
the serrations be kept clean and sharp. Should breaking in the
scales or environments widely different from those of this test
grips occur, even when deep serrations or abraded specimen
method.Incasesofsuchdissimilarity,noreliableestimationof
surfaces are used, other techniques shall be used. Other
techniques that have been found useful, particularly with
smooth-faced grips, are abrading that portion of the surface of
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. the specimen that will be in the grips, and interposing thin
D638 − 22
pieces of abrasive cloth, abrasive paper, or plastic, or rubber- classification within the range of use for modulus measure-
coated fabric, commonly called hospital sheeting, between the ments meets this requirement.
specimen and the grip surface. No. 80 double-sided abrasive 5.2.2 Low-Extension Measurements—For elongation-at-
paper has been found effective in many cases. An open-mesh yield and low-extension measurements (nominally 20% or
fabric, in which the threads are coated with abrasive, has also less), the same above extensometer, attenuated to 20 %
been effective. Reducing the cross-sectional area of the speci- extension, is acceptable. In any case, the extensometer system
men may also be effective. The use of special types of grips is must meet at least Class C (Practice E83) requirements, which
sometimes necessary to eliminate slippage and breakage in the include a fixed strain error of 0.001 strain or 61.0% of the
grips. indicated strain, whichever is greater.
5.2.3 High-Extension Measurements—Formakingmeasure-
5.1.4 Drive Mechanism—A drive mechanism for imparting
ments at elongations greater than 20%, measuring techniques
a uniform, controlled velocity to the movable member with
with error no greater than 610% of the measured value are
respect to the stationary member. This velocity is to be
acceptable.
regulated as specified in Section 8.
5.1.5 Load Indicator—A suitable load-indicating mecha-
5.3 Micrometers—Apparatus for measuring the width and
nism capable of showing the total tensile load carried by the
thickness of the test specimen shall comply with the require-
testspecimenwhenheldbythegrips.Thismechanismshallbe
ments of Test Method D5947.
essentially free of inertia lag at the specified rate of testing and
shall indicate the load with an accuracy of 61% of the
6. Test Specimens
indicated value, or better. The accuracy of the testing machine
6.1 Sheet, Plate, and Molded Plastics:
shall be verified in accordance with Practices E4.
6.1.1 Rigid and Semirigid Plastics—The test specimen shall
NOTE 6—Experience has shown that many testing machines now in use conform to the dimensions shown in Fig. 1. The Type I
are incapable of maintaining accuracy for as long as the periods between
specimen is the preferred specimen and shall be used where
inspection recommended in Practices E4. Hence, it is recommended that
sufficientmaterialhavingathicknessof7mm(0.28in.)orless
each machine be studied individually and verified as often as may be
is available. The Type II specimen is recommended when a
found necessary. It frequently will be necessary to perform this function
materialdoesnotbreakinthenarrowsectionwiththepreferred
daily.
Type I specimen. The Type V specimen shall be used where
5.1.6 The fixed member, movable member, drive
only limited material having a thickness of 4 mm (0.16 in.) or
mechanism, and grips shall be constructed of such materials
less is available for evaluation, or where a large number of
and in such proportions that the total elastic longitudinal strain
specimens are to be exposed in a limited space (thermal and
ofthesystemconstitutedbythesepartsdoesnotexceed1%of
environmental stability tests, etc.). The Type IV specimen is
thetotallongitudinalstrainbetweenthetwogagemarksonthe
generally used when direct comparison
...
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: D638 − 14 D638 − 22
Standard Test Method for
Tensile Properties of Plastics
This standard is issued under the fixed designation D638; 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 tensile properties of unreinforced and reinforced plastics in the form of
standard dumbbell-shaped test specimens when tested under defined conditions of pretreatment, temperature, humidity, and testing
machine speed.
1.2 This test method is applicable for testing materials of any thickness up to 14 mm (0.55 in.). However, for testing specimens
in the form of thin sheeting, including film less than 1.0 mm (0.04 in.) in thickness, ASTM standard D882 is the preferred test
method. Materials with a thickness greater than 14 mm (0.55 in.) shall be reduced by machining.
1.3 This test method includes the option of determining Poisson’s ratio at room temperature.
NOTE 1—This standard and ISO 527-1 address the same subject matter, but differ in technical content.
NOTE 2—This test method is not intended to cover precise physical procedures. It is recognized that the constant rate of crosshead movement type of test
leaves much to be desired from a theoretical standpoint, that wide differences may exist between rate of crosshead movement and rate of strain between
gage marks on the specimen, and that the testing speeds specified disguise important effects characteristic of materials in the plastic state. Further, it is
realized that variations in the thicknesses of test specimens, which are permitted by these procedures, produce variations in the surface-volume ratios of
such specimens, and that these variations may influence the test results. Hence, where directly comparable results are desired, all samples should be of
equal thickness. Special additional tests should be used where more precise physical data are needed.
NOTE 3—This test method may be used for testing phenolic molded resin or laminated materials. However, where these materials are used as electrical
insulation, such materials should be tested in accordance with Test Methods D229 and Test Method D651.
NOTE 4—For tensile properties of resin-matrix composites reinforced with oriented continuous or discontinuous high modulus >20-GPa (>3.0 × 10 -psi)
fibers, tests shall be made in accordance with Test Method D3039/D3039M.
1.4 Test data obtained by this test method have been found to be useful in engineering design. However, it is important to consider
the precautions and limitations of this method found in Note 2 and Section 4 before considering these data for engineering design.
1.5 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.6 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
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 Dec. 15, 2014July 1, 2022. Published March 2015July 2022. Originally approved in 1941. Last previous edition approved in 20102014 as
D638 - 10.D638 - 14. DOI: 10.1520/D0638-14.10.1520/D0638-22.
*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
D638 − 22
1.7 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:
D229 Test Methods for Rigid Sheet and Plate Materials Used for Electrical Insulation
D412 Test Methods for Vulcanized Rubber and Thermoplastic Elastomers—Tension
D618 Practice for Conditioning Plastics for Testing
D651 Test Method for Test for Tensile Strength of Molded Electrical Insulating Materials (Withdrawn 1989)
D882 Test Method for Tensile Properties of Thin Plastic Sheeting
D883 Terminology Relating to Plastics
D1822 Test Method for Determining the Tensile-Impact Resistance of Plastics
D3039/D3039M Test Method for Tensile Properties of Polymer Matrix Composite Materials
D4000 Classification System for Specifying Plastic Materials
D4066 Classification System for Nylon Injection and Extrusion Materials (PA)
D5947 Test Methods for Physical Dimensions of Solid Plastics Specimens
E4 Practices for Force Calibration and Verification of Testing Machines
E83 Practice for Verification and Classification of Extensometer Systems
E132 Test Method for Poisson’s Ratio at Room Temperature
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E2935 Practice for Evaluating Equivalence of Two Testing Processes
2.2 ISO Standard:
ISO 527-1 Determination of Tensile Properties
3. Terminology
3.1 Definitions—Definitions of terms applying to this test method appear in Terms used in this standard are defined in accordance
with Terminology D883, and Annex A2. For terms relating to precision and bias and associated issues, the terms used in this
standard are defined in accordance with Terminology E456.
4. Significance and Use
4.1 This test method is designed to produce tensile property data for the control and specification of plastic materials. These data
are also useful for qualitative characterization and for research and development.
4.2 Some material specifications that require the use of this test method, but with some procedural modifications that take
precedence when adhering to the specification. Therefore, it is advisable to refer to that material specification before using this test
method. Table 1 in Classification D4000 lists the ASTM materials standards that currently exist.
4.3 Tensile properties are known to vary with specimen preparation and with speed and environment of testing. Consequently,
where precise comparative results are desired, these factors must be carefully controlled.
4.4 It is realized that a material cannot be tested without also testing the method of preparation of that material. Hence, when
comparative tests of materials per se are desired, exercise great care to ensure that all samples are prepared in exactly the same
way, unless the test is to include the effects of sample preparation. Similarly, for referee purposes or comparisons within any given
series of specimens, care shall be taken to secure the maximum degree of uniformity in details of preparation, treatment, and
handling.
4.5 Tensile properties provide useful data for plastics engineering design purposes. However, because of the high degree of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D638 − 22
sensitivity exhibited by many plastics to rate of straining and environmental conditions, data obtained by this test method cannot
be considered valid for applications involving load-time scales or environments widely different from those of this test method.
In cases of such dissimilarity, no reliable estimation of the limit of usefulness can be made for most plastics. This sensitivity to
rate of straining and environment necessitates testing over a broad load-time scale (including impact and creep) and range of
environmental conditions if tensile properties are to suffice for engineering design purposes.
NOTE 5—Since the existence of a true elastic limit in plastics (as in many other organic materials and in many metals) is debatable, the propriety of
applying the term “elastic modulus” in its quoted, generally accepted definition to describe the “stiffness” or “rigidity” of a plastic has been seriously
questioned. The exact stress-strain characteristics of plastic materials are highly dependent on such factors as rate of application of stress, temperature,
previous history of specimen, etc. However, stress-strain curves for plastics, determined as described in this test method, almost always show a linear
region at low stresses, and a straight line drawn tangent to this portion of the curve permits calculation of an elastic modulus of the usually defined type.
Such a constant is useful if its arbitrary nature and dependence on time, temperature, and similar factors are realized.
5. Apparatus
5.1 Testing Machine—A testing machine of the constant-rate-of-crosshead-movement type and comprising essentially the
following:
5.1.1 Fixed Member—A fixed or essentially stationary member carrying one grip.
5.1.2 Movable Member—A movable member carrying a second grip.
5.1.3 Grips—Grips for holding the test specimen between the fixed member and the movable member of the testing machine can
be either the fixed or self-aligning type.
5.1.3.1 Fixed grips are rigidly attached to the fixed and movable members of the testing machine. When this type of grip is used
take extreme care to ensure that the test specimen is inserted and clamped so that the long axis of the test specimen coincides with
the direction of pull through the center line of the grip assembly.
5.1.3.2 Self-aligning grips are attached to the fixed and movable members of the testing machine in such a manner that they will
move freely into alignment as soon as any load is applied so that the long axis of the test specimen will coincide with the direction
of the applied pull through the center line of the grip assembly. Align the specimens as perfectly as possible with the direction of
pull so that no rotary motion that may induce slippage will occur in the grips; there is a limit to the amount of misalignment
self-aligning grips will accommodate.
5.1.3.3 The test specimen shall be held in such a way that slippage relative to the grips is prevented insofar as possible. Grip
surfaces that are deeply scored or serrated with a pattern similar to those of a coarse single-cut file, serrations about 2.4 mm (0.09
in.) apart and about 1.6 mm (0.06 in.) deep, have been found satisfactory for most thermoplastics. Finer serrations have been found
to be more satisfactory for harder plastics, such as the thermosetting materials. It is important that the serrations be kept clean and
sharp. Should breaking in the grips occur, even when deep serrations or abraded specimen surfaces are used, other techniques shall
be used. Other techniques that have been found useful, particularly with smooth-faced grips, are abrading that portion of the surface
of the specimen that will be in the grips, and interposing thin pieces of abrasive cloth, abrasive paper, or plastic, or rubber-coated
fabric, commonly called hospital sheeting, between the specimen and the grip surface. No. 80 double-sided abrasive paper has been
found effective in many cases. An open-mesh fabric, in which the threads are coated with abrasive, has also been effective.
Reducing the cross-sectional area of the specimen may also be effective. The use of special types of grips is sometimes necessary
to eliminate slippage and breakage in the grips.
5.1.4 Drive Mechanism—A drive mechanism for imparting a uniform, controlled velocity to the movable member with respect to
the stationary member. This velocity is to be regulated as specified in Section 8.
5.1.5 Load Indicator—A suitable load-indicating mechanism capable of showing the total tensile load carried by the test specimen
when held by the grips. This mechanism shall be essentially free of inertia lag at the specified rate of testing and shall indicate
the load with an accuracy of 61 % of the indicated value, or better. The accuracy of the testing machine shall be verified in
accordance with Practices E4.
NOTE 6—Experience has shown that many testing machines now in use are incapable of maintaining accuracy for as long as the periods between
inspection recommended in Practices E4. Hence, it is recommended that each machine be studied individually and verified as often as may be found
necessary. It frequently will be necessary to perform this function daily.
D638 − 22
5.1.6 The fixed member, movable member, drive mechanism, and grips shall be constructed of such materials and in such
proportions that the total elastic longitudinal strain of the system constituted by these parts does not exceed 1 % of the total
longitudinal strain between the two gage marks on the test specimen at any time during the test and at any load up to the rated
capacity of the machine.
5.1.7 Crosshead Extension Indicator—A suitable extension indicating mechanism capable of showing the amount of change in the
separation of the grips, that is, crosshead movement. This mechanism shall be essentially free of inertial lag at the specified rate
of testing and shall indicate the crosshead movement with an accuracy of 610 % of the indicated value.
5.2 Extension Indicator (extensometer)—A suitable instrument shall be used for determining the distance between two designated
points within the gauge length of the test specimen as the specimen is stretched. For referee purposes, the extensometer must be
set at the full gage length of the specimen, as shown in Fig. 1. It is desirable, but not essential, that this instrument automatically
record this distance, or any change in it, as a function of the load on the test specimen or of the elapsed time from the start of the
test, or both. If
...
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