ASTM D76/D76M-21

Standard Specification for Tensile Testing Machines for Textiles

ABSTRACT
This specification covers operating characteristics of tensile testing machines for the determination of the force-elongation properties of textile materials. Types of tensile machine covered in this specification are constant-rate-of-extension, constant-rate-of-traverse, and constant-rate-of-loading. Testing machines calibration shall be verified using the methods indicated in this specification, especially when moved to different locations to make sure that they still meet the specified tolerances. Motor-driven machine is preferred over manually driven machine. Constant-rate-of-traverse type machines shall not be used for measuring forces below fifty times their resolution. Machines shall be equipped with a device for measuring force. Clamping or holding devices shall be prescribed in test methods. Maximum allowable error, indicated force, recorded elongation, nominal gage length, and moving clamp speed shall be within the tolerances prescribed in the individual standards. Verification methods for recorded clamp displacement, recorded elongation, and nominal gage length, shall conform to the procedures indicated in this specification.
SCOPE
1.1 This specification covers the operating characteristics of three types of tensile testing machines used for the determination of the force-elongation properties of textile materials. These types of tensile testing machines are:  
1.1.1 Constant-rate-of-extension, CRE.  
1.1.2 Constant-rate-of-traverse, CRT.  
1.1.3 Constant-rate-of-loading (force), CRL.  
1.2 Specifications for tensile testing machines to measure other tensile-related properties of textile materials not covered by this standard are given in the ASTM standards using those machines.  
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.4 The following safety hazards caveat pertains only to the test methods described in this specification: 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.  
1.5 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: 30-Jun-2021
• ICS: 59.080.30 - Textile fabrics
• Technical Committee: D13 - Textiles
• Drafting Committee: D13.58 - Yarns and Fibers

Relations

• Refers: ASTM D4849-13(2018) - Standard Terminology Related to Yarns and Fibers
• Effective Date: 01-Jul-2018
• Refers: ASTM D123-17 - Standard Terminology Relating to Textiles
• Effective Date: 01-Mar-2017
• Refers: ASTM D123-15b - Standard Terminology Relating to Textiles
• Effective Date: 15-Sep-2015
• Refers: ASTM D123-15a - Standard Terminology Relating to Textiles
• Effective Date: 01-Sep-2015
• Refers: ASTM D123-15 - Standard Terminology Relating to Textiles
• Effective Date: 01-Apr-2015
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM D4849-13e2 - Standard Terminology Related to Yarns and Fibers
• Effective Date: 01-Oct-2013
• Refers: ASTM D4849-13e1 - Standard Terminology Related to Yarns and Fibers
• Effective Date: 01-Oct-2013
• Refers: ASTM D4849-13 - Standard Terminology Related to Yarns and Fibers
• Effective Date: 01-Oct-2013
• Refers: ASTM D4849-13e3 - Standard Terminology Related to Yarns and Fibers
• Effective Date: 01-Oct-2013
• Refers: ASTM D123-13ae1 - Standard Terminology Relating to Textiles
• Effective Date: 15-Jun-2013
• Refers: ASTM D123-13a - Standard Terminology Relating to Textiles
• Effective Date: 15-Jun-2013
• Refers: ASTM D123-13 - Standard Terminology Relating to Textiles
• Effective Date: 15-May-2013
• Refers: ASTM E74-13a - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-May-2013
• Refers: ASTM E74-13 - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-Mar-2013

Overview

ASTM D76/D76M-21 is the internationally recognized standard specification for tensile testing machines used in determining the force-elongation properties of textile materials. Developed by ASTM International, this standard outlines the essential operational characteristics, required accuracy, calibration processes, and verification procedures for three primary types of tensile testing machines: constant-rate-of-extension (CRE), constant-rate-of-traverse (CRT), and constant-rate-of-loading (CRL). Adherence to this standard ensures consistency and reliability in the measurement of tensile properties across the textile industry.

Key Topics

• Machine Types
  • CRE (Constant-Rate-of-Extension): Pulling clamp moves at a uniform rate; considered the reference method for textile testing.
  • CRT (Constant-Rate-of-Traverse): Pulling clamp moves at a constant rate, but force application varies with sample characteristics.
  • CRL (Constant-Rate-of-Loading): Applies force at a uniform rate; elongation depends on the properties of the textile specimen.
• Calibration & Verification
  • Calibration of tensile testing machines must be verified-especially after relocation-to ensure compliance with specified tolerances.
  • Practices for calibration follow methods referenced in ASTM E4 and ASTM E74.
  • Full-system verification is advised after individual calibration of subsystems (force, extension, clamping).
• Machine Requirements
  • Machines must be equipped with accurate force and elongation measuring devices.
  • Clamping devices must maintain alignment and minimize specimen slippage or breakage.
  • Motor-driven machines are preferred for superior control and repeatability.
• Performance Tolerances
  • Force and elongation indications must stay within specified error margins.
  • Nominal gauge length and crosshead speed must maintain prescribed tolerances.

Applications

• Quality Assurance: Textile manufacturers use tensile testing machines conforming to ASTM D76/D76M-21 to verify the mechanical properties of fibers, yarns, and fabrics.
• Textile Research & Development: Laboratories leverage compliant testing machines to innovate and benchmark new materials.
• Product Certification: Regulatory bodies and certification agencies reference this standard to assure compliance with international and industry textile performance requirements.
• Equipment Validation: Machine manufacturers test and calibrate their devices to meet or exceed ASTM D76/D76M-21 specifications, ensuring suitability for textile industry customers.

Related Standards

• ASTM D123: Terminology Relating to Textiles - foundational definitions for textile testing.
• ASTM D2256: Test Method for Tensile Properties of Yarns by the Single-Strand Method - prescribes detailed apparatus and procedures for yarn testing.
• ASTM D4849: Terminology Related to Yarns and Fibers.
• ASTM E4: Practices for Force Verification of Testing Machines - referenced for machine calibration practices.
• ASTM E74: Practices for Calibration and Verification for Force-Measuring Instruments - used for verifying calibration devices.

Practical Value

Implementing ASTM D76/D76M-21 provides confidence in textile tensile testing results by reducing variability and increasing comparability across markets and laboratories. Relying on this standard helps organizations meet international trade requirements, improves product development accuracy, and ensures that testing equipment maintains consistent performance and reliability.

Keywords

Tensile testing machines, textiles, force-elongation, ASTM D76/D76M-21, CRE type, CRT type, CRL type, machine calibration, quality assurance, textile standards.

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: D76/D76M −21
Standard Specification for
Tensile Testing Machines for Textiles
This standard is issued under the fixed designation D76/D76M; 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.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 Thisspecificationcoverstheoperatingcharacteristicsof
D123Terminology Relating to Textiles
three types of tensile testing machines used for the determina-
D2256Test Method for Tensile Properties of Yarns by the
tion of the force-elongation properties of textile materials.
Single-Strand Method
These types of tensile testing machines are:
D4849Terminology Related to Yarns and Fibers
1.1.1 Constant-rate-of-extension, CRE.
E4Practices for Force Verification of Testing Machines
1.1.2 Constant-rate-of-traverse, CRT.
E74Practices for Calibration and Verification for Force-
1.1.3 Constant-rate-of-loading (force), CRL.
Measuring Instruments
1.2 Specifications for tensile testing machines to measure
3. Terminology
other tensile-related properties of textile materials not covered
by this standard are given in the ASTM standards using those 3.1 For terminology related to tensile testing, see Terminol-
ogy D4849.
machines.
3.1.1 The following terms are relevant for this standard:
1.3 The values stated in either SI units or inch-pound units
bench marks, calibrate, capacity, clamp, constant-rate-of ex-
are to be regarded separately as standard. The values stated in
tension type tensile testing machine (CRE), constant-rate-of-
each system are not necessarily exact equivalents; therefore, to
load tensile testing machine (CRL), constant-rate-of-traverse
ensure conformance with the standard, each system shall be
tensile testing machine (CRT), effective carriage mass, effec-
used independently of the other, and values from the two
tive gauge length, grip, jaw face, jaw liner, jaws, least count,
systems shall not be combined.
nominal gauge length, response time, sensitivity, in electronic
1.4 The following safety hazards caveat pertains only to the systems, sensitivity, stress, tensile testing machine, test skein,
testmethodsdescribedinthisspecification: This standard does time-to-break, true gauge length.
not purport to address all of the safety concerns, if any, 3.1.2 For all other terminology related to textiles, see
associated with its use. It is the responsibility of the user of this Terminology D123.
standard to establish appropriate safety, health, and environ-
4. Performance Requirements
mental practices and determine the applicability of regulatory
limitations prior to use.
4.1 Individual ASTM methods for tensile testing of textile
1.5 This international standard was developed in accor-
materials that prescribe apparatus which conforms to this
dance with internationally recognized principles on standard- specification shall also include such other detailed specifica-
ization established in the Decision on Principles for the
tions as may be necessary to describe the testing machine and
Development of International Standards, Guides and Recom- its operation completely.
mendations issued by the World Trade Organization Technical
4.1.1 This specification shall not be construed as being
Barriers to Trade (TBT) Committee.
intended to preclude the evolution of improved methods of
testing or testing apparatus, which is recognized as being vital
in an advancing technology.
This specification is under the jurisdiction of ASTM Committee D13 on
Textiles and is the direct responsibility of Subcommittee D13.58 on Yarns and
Fibers. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2021. Published August 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1920. Last previous edition approved in 2016 as D76–11(2016). DOI: Standardsvolume information, refer to the standard’s Document Summary page on
10.1520/D0076_D0076M-21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D76/D76M − 21
4.2 Comparison of results from tensile testing machines 5.2 Measuring Devices—Machinesshallbeequippedwitha
operating on different principles is not recommended. When suitable device for measuring the force and, when needed, a
these machines are used for comparison testing however, device to measure extension. Preferably, the data must be
constant time-to-break at 20 6 3 s is the established way of electronicallystoredusingadata-acquisitionsystem,oratleast
producing data, but even then the data may differ significantly. the curve shall be recorded graphically, or the force and
4.2.1 Comparison of test data from machines of the same extension data may be indicated on appropriate scales or
type, especially two or more CRT-type or two or more displays.
CRL-type machines, requires consideration of the effect of 5.2.1 Most testing machines record only force-extension
individual machine characteristics; for example, inertia effects,
data. When the capacity of a testing machine is adjusted to fit
capacity, sensitivity, type of loadcell, etc., which may cause the predetermined linear density or cross-sectional area of the
significant differences in results even though uniform proce- specimen, instead of force the stress will be recorded. When
dures are employed. Data from different CRE-type testing the machine is adjusted to record extension in terms of unit
machines, however, should not be significantly different. specimen length, the chart can be read directly in percent
4.2.2 In any case, all types of tensile testing machines must elongation or strain. When these conditions do not exist, the
satisfy the accuracy requirements as given in Section 7. force-extension curve must be converted to obtain stress-strain
characteristics.
4.3 While changes in humidity affect the tensile properties
5.2.2 Theforce-indicatingandforce-recordingdevicesshall
ofmanytextilematerials,changesinhumiditynormallydonot
be in conformance with the requirements of this specification
affect the testing machines themselves.
as to accuracy, sensitivity, and response time, and shall permit
4.4 When machines are moved to different locations, their
calibration or verification by appropriate methods described or
calibrationshallbeverifiedtomakesurethattheystillmeetthe
referenced herein.
specified tolerances.
5.3 Clamping or Holding Devices—Specimen clamping or
4.5 When each of the sub-systems (force, extension, clamp-
holding devices shall be prescribed in the individual test
ing) has been individually calibrated, verified, or checked, it is
methods in sufficient detail for all users to employ the same or
recommendedthatthetotalsystembeverifiedusingastandard
comparable devices.
materialappropriateforthetypetestingtobecarriedout. This
5.3.1 The prescribed specimen clamping or holding devices
testing of the total system is the established way of ensuring
shall be designed to ensure that the pulling axis of the testing
that the clamping system is operating properly.
machine and the central axis of a properly mounted specimen
coincide.
5. Apparatus
5.3.2 The clamping or holding device may be designed for
5.1 Tensile Testing Machines—Tensile testing machines for
manual or automatic mounting of specimens.
textile materials are classified according to their operating
5.3.3 The required clamping force can be obtained with the
principle as follows:
clamping or holding devices by any suitable mechanism; for
Type Principle of Operation
example, screw, cam action, pneumatic, or toggle.
CRE Constant rate-of-extension
5.3.4 Clamping surfaces in contact with a test specimen
CRT Constant rate-of-traverse (pendulum type)
CRL Constant rate-of-load (inclined plane type)
shall be of any suitable material and configuration which
provides the required restraint, preclude slippage, and mini-
5.1.1 CRE-Type—A testing machine in which the pulling
mize specimen failure in the clamped areas. Clamp liners may
clamp moves at a uniform rate, and when loaded at the
be used, provided the above conditions are met.
maximum allowable force, the force-measuring mechanism
5.3.5 When the flat-faced type clamp proves unsatisfactory
(load cell) moves a negligible distance of less than 0.2 mm
because of slippage or excessive breakage in the clamp,
[0.008 in.].
snubbing type devices (capstan, drum, split-drum, etc.) may be
5.1.2 CRT-Type—A testing machine in which the pulling
used.
clamp moves at a uniform rate and the force is applied through
the other clamp, which moves appreciably to actuate a force-
5.4 Calibrating Devices—Calibrating weights or other cali-
measuring mechanism, producing a rate of increase of force or
brating devices conforming to Practice E74 are required for
extensionwhichisusuallynotconstantandisdependentonthe
verificationofcalibration.Calipers,asteelrulethatcanberead
extension characteristics of the specimen.
to 0.25 mm [0.01 in.], or a suitable cathetometer, and a stop
5.1.3 CRL-Type—A testing machine in which the rate of
watch are required for verification of recorded elongation, and
increase of the force is uniform with time after the first3sand
crosshead and chart speed.
the specimen is free to elongate, this elongation being depen-
dent upon the extension characteristics of the specimen at any
6. Machine Operational Design
applied force.
6.1 The use of motor-driven machines is preferred over
5.1.4 Multiple-Purpose Type—Machines capable of being
manually driven machines because of improved control of
operated as both a CRE-type and a CRL-type may be used.
testing.
6.2 Testing machines of the CRT-type shall not be used for
Two styles of standard break fabrics obtained from Testfabrics, Inc., P.O.
measuring forces below fifty times their resolution. For
Drawer O, Middlesex, NJ 08846 have been found satisfactory for this purpose. See
also A1.3 of this specification. example, if the minimum force that can be read is 0.5 cN [0.5
D76/D76M − 21
gf], the testing machine may not be used for materials which
test at 25.0 cN [25 gf] or less.
6.2.1 Choose the full scale force such that the expected
maximum force falls within:
6.2.1.1 10 to 90% full scale for the CRE-type testing
machines,
6.2.1.2 15 to 85% full scale for the CRT-type testing
machines,
6.2.1.3 15 to 85% full scale for the CRL-type testing
machines,
6.3 Machines shall operate at a uniform rate of pulling
clamp (CRE), and (CRT), or loading (CRL) as specified in6.4,
6.5, and 6.6.
6.3.1 Machinesmaybebuiltforoperatingatvariousratesof
operation or at a single constant rate.
6.3.2 When machines are intended for operation at a speci-
fiedorrequiredaveragetimetobreakasspecifiedinindividual
FIG. 1 Limitations on Response Speed of Recorder Pen
standards(forexample,20stobreakasinTestMethodD2256)
then their rate of operation must be adjustable.The adjustment
of the reading for CRE-type machines and 61.0% for CRT-
may be continuous or in steps not exceeding 125:100. Ma-
and CRL-type machines (see Section 8).
chineswithacontinuouslyadjustablerateofoperationshallbe
equipped with a device indicating the rate of operation.
7.2 Themaximumallowableerrorinrecordedgripdisplace-
6.3.3 The machine rate of operation shall be within the
ment shall be 61% of the recorded values for CRE-type
tolerances prescribed in the individual standards.
machines and 62.5 mm [0.5 in.] for CRT- and CRL-type
machines (see Section 9 for CRE-type machines and Section
6.4 CRE-Type:
10 for CRT- and CRL-type machines).
6.4.1 Machines shall be designed for operation at such
uniform rates of pulling clamp as are specified in individual
7.3 The maximum allowable variation in nominal gauge
standards.
lengthonrepeatedreturnoftheclampstotheirstartingposition
6.4.2 Using a data-acquisition system, the sampling rate
shall be less than 0.25 mm [0.01 in.].
should be set to approximately 500/(time-to-break). Using a
7.4 Themaximumallowablevariationofcrossheadspeedof
graphical recording system, the force-measuring system, in-
the CRE-type tester or moving clamp of the CRT-type tester
cluding the recording mechanism, shall have a full-scale pen
from the required testing speed shall be less than 4%.
response time less than2sin either direction. In addition, the
7.5 The maximum allowable variation of the loading rate
responsetimeforpendeflectionsoflessthanfullscaleshallbe
for the CRL-type of tester from the required rate shall be less
proportional to the fraction of full-scale time represented by
than 5 %.
those deflections within a tolerance of 610 % of the nominal
full-scale response time.
8. Verification of Indicated Force
NOTE 1—The response time of the recording mechanism is the limiting
8.1 This section provides a general procedure for the veri-
factor affecting the choice of a rate for testing. The rate chosen shall give
fication of the force calibration of tensile testing machines for
the maximum slope of the recorded curve which does not exceed one half
textiles. No attempt is made to give detailed instructions
of the slope of the maximum pen speed. See Fig. 1.
applicable to any particular case. The verification should be
6.5 CRT-Type—Machines shall be designed for operation of
performed or supervised by a qualified person competent to
the pulling clamp at a uniform rate as specified in individual
exercise scientific judgment in matters not covered herein.
standards.
Detailed instructions are given in Annex A1 covering verifi-
6.6 CRL-Type—Machines shall be designed to apply forces
cation of one variety of testing machine of the CRL-type.
at a uniform rate, or at a uniform rate of loading per unit of
8.2 Verify tensile testing machines as directed in the appli-
specimen linear density, as specified in individual standards.
cable procedure and at the suggested time intervals listed in
6.7 Machines may be built for either manual or automatic
Practices E4, except as otherwise provided in the following
mounting of the specimen into the clamp or holding devices.
paragraphs.
8.3 Verify the machine in the condition under which it is
7. Tolerance on Indicated Force, Recorded Elongation,
used, with all attachments and recording mechanisms in
Nominal Gauge Length, and Speed of Moving Clamp
operation if they are to be used in actual testing; but with any
7.1 On instruments where the capacity of the force measur- pawlsorotherdetentdeviceintheforce-measuringmechanism
ing mechanism (load cell) is used for digital analysis without rendered inoperative. Following the application of each test
regard to the full scale force displayed on the recorder, the force, eliminate the effect of friction by gently oscillating the
maximum allowable error in force indication shall be 60.5% force-measuring mechanism or by tapping the machine to
D76/D76M − 21
theloadcellinCRE-typetestingmachinesshallnotexceed0.2mm[0.008
ensure that the applied force is in equilibrium with the force
in.]forforceswithintheratedcapacityofthemachine.Thedeflectionmay
registered by the measuring mechanism.
be measured with a cathetometer or other similar equipment having a
8.4 Examine the measuring, indicating, and recording
precision of 0.03 mm [0.001 in.]. Testing at short gauge lengths of high
modulus materials may require corrections or stiffer measuring systems.
mechanismsforfrictionorslack.Estimate,intermsoftheunits
in which the machine is calibrated, the magnitude of such
10. Verification of Recorded Elongation for CRT- and
factors and, if excessive, reduce the error at the source to
CRL-Type Machines
conform to the tolerance as stated in 7.1.
10.1 Bringtheclampsofthetestingmachinetotheirnormal
8.5 Ifotherthanverticaltestforcesmustbeapplied,suitable
positions for the start of a test. Place a chart in the holder and
apparatus must be devised subject to the general requirements
adjust its position with the pen at the zero force and zero
for accuracy of calibration devices prescribed in Practice E74.
elongation points. (On machines having a specific location for
If cords and pulleys are used, any errors due to axle friction,
the chart as determined by supports, adjust the pen to record
pulley eccentricities, cord friction, and uncertainty of cord
zero force and zero elongation.) Measure the dis
...

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: D76/D76M − 11 (Reapproved 2016) D76/D76M − 21
Standard Specification for
Tensile Testing Machines for Textiles
This standard is issued under the fixed designation D76/D76M; 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.
1. Scope
1.1 This specification covers the operating characteristics of three types of tensile testing machines used for the determination of
the force-elongation properties of textile materials. These types of tensile testing machines are:
1.1.1 Constant-rate-of-extension, CRE.
1.1.2 Constant-rate-of-traverse, CRT.
1.1.3 Constant-rate-of-loading (force), CRL.
1.2 Specifications for tensile testing machines to measure other tensile-related properties of textile materials not covered by this
standard are given in the ASTM standards using those machines.
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system mayare not benecessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used
independently of the other. Combiningother, and values from the two systems may result in non-conformance with the
standard.shall not be combined.
1.4 The following safety hazards caveat pertains only to the test methods described in this specification: 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.
1.5 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:
D123 Terminology Relating to Textiles
D2256 Test Method for Tensile Properties of Yarns by the Single-Strand Method
D4849 Terminology Related to Yarns and Fibers
E4 Practices for Force Verification of Testing Machines
This specification is under the jurisdiction of ASTM Committee D13 on Textiles and is the direct responsibility of Subcommittee D13.58 on Yarns and Fibers.
Current edition approved July 1, 2016July 1, 2021. Published July 2016August 2021. Originally approved in 1920 .1920. Last previous edition approved in 20112016 as
D76 – 11.D76 – 11(2016). DOI: 10.1520/D0076_D0076M-11R16.10.1520/D0076_D0076M-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standardsvolume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D76/D76M − 21
E74 Practices for Calibration and Verification for Force-Measuring Instruments
3. Terminology
3.1 For terminology related to tensile testing, see Terminology D4849.
3.1.1 The following terms are relevant for this standard: bench marks, calibrate, capacity, clamp, constant-rate-of extension type
tensile testing machine (CRE), constant-rate-of-load tensile testing machine (CRL), constant-rate-of-traverse tensile testing
machine (CRT), effective carriage mass, effective gauge length, grip, jaw face, jaw liner, jaws, least count, nominal gauge length,
response time, sensitivity, in electronic systems, sensitivity, stress, tensile testing machine, test skein, time-to-break, true gauge
length.
3.1.2 For all other terminology related to textiles, see Terminology D123.
4. Performance Requirements
4.1 Individual ASTM methods for tensile testing of textile materials that prescribe apparatus which conforms to this specification
shall also include such other detailed specifications as may be necessary to describe the testing machine and its operation
completely.
4.1.1 This specification shall not be construed as being intended to preclude the evolution of improved methods of testing or
testing apparatus, which is recognized as being vital in an advancing technology.
4.2 Comparison of results from tensile testing machines operating on different principles is not recommended. When these
machines are used for comparison testing however, constant time-to-break at 20 6 3 s is the established way of producing data,
but even then the data may differ significantly.
4.2.1 Comparison of test data from machines of the same type, especially two or more CRT-type or two or more CRL-type
machines, requires consideration of the effect of individual machine characteristics; for example, inertia effects, capacity,
sensitivity, type of loadcell, etc., which may cause significant differences in results even though uniform procedures are employed.
Data from different CRE-type testing machines, however, should not be significantly different.
4.2.2 In any case, all types of tensile testing machines must satisfy the accuracy requirements as given in Section 7.
4.3 While changes in humidity affect the tensile properties of many textile materials, changes in humidity normally do not affect
the testing machines themselves.
4.4 When machines are moved to different locations, their calibration shall be verified to make sure that they still meet the
specified tolerances.
4.5 When each of the sub-systems (force, extension, clamping) has been individually calibrated, verified, or checked, it is
recommended that the total system be verified using a standard material appropriate for the type testing to be carried out. This
testing of the total system is the established way of ensuring that the clamping system is operating properly.
5. Apparatus
5.1 Tensile Testing Machines—Tensile testing machines for textile materials are classified according to their operating principle
as follows:
Type Principle of Operation
CRE Constant rate-of-extension
CRT Constant rate-of-traverse (pendulum type)
CRL Constant rate-of-load (inclined plane type)
Two styles of standard break fabrics obtained from Testfabrics, Inc., P.O. Drawer O, Middlesex, NJ 08846 have been found satisfactory for this purpose. See also A1.3
of this specification.
D76/D76M − 21
5.1.1 CRE-Type—A testing machine in which the pulling clamp moves at a uniform rate, and when loaded at the maximum
allowable force, the force-measuring mechanism (load cell) moves a negligible distance of less than 0.130.2 mm [0.005[0.008 in.].
5.1.2 CRT-Type—A testing machine in which the pulling clamp moves at a uniform rate and the force is applied through the other
clamp, which moves appreciably to actuate a force-measuring mechanism, producing a rate of increase of force or extension which
is usually not constant and is dependent on the extension characteristics of the specimen.
5.1.3 CRL-Type—A testing machine in which the rate of increase of the force is uniform with time after the first 3 s and the
specimen is free to elongate, this elongation being dependent upon the extension characteristics of the specimen at any applied
force.
5.1.4 Multiple-Purpose Type—Machines capable of being operated as both a CRE-type and a CRL-type may be used.
5.2 Measuring Devices—Machines shall be equipped with a suitable device for measuring the force and, when needed, a device
to measure extension. Preferably, the data must be electronically stored using a data-acquisition system, or at least the curve shall
be recorded graphically, or the force and extension data may be indicated on appropriate scales or displays.
5.2.1 Most testing machines record only force-extension data. When the capacity of a testing machine is adjusted to fit the
predetermined linear density or cross-sectional area of the specimen, instead of force the stress will be recorded. When the machine
is adjusted to record extension in terms of unit specimen length, the chart can be read directly in percent elongation or strain. When
these conditions do not exist, the force-extension curve must be converted to obtain stress-strain characteristics.
5.2.2 The force-indicating and force-recording devices shall be in conformance with the requirements of this specification as to
accuracy, sensitivity, and response time, and shall permit calibration or verification by appropriate methods described or referenced
herein.
5.3 Clamping or Holding Devices—Specimen clamping or holding devices shall be prescribed in the individual test methods in
sufficient detail for all users to employ the same or comparable devices.
5.3.1 The prescribed specimen clamping or holding devices shall be designed to ensure that the pulling axis of the testing machine
and the central axis of a properly mounted specimen coincide.
5.3.2 The clamping or holding device may be designed for manual or automatic mounting of specimens.
5.3.3 The required clamping force can be obtained with the clamping or holding devices by any suitable mechanism; for example,
screw, cam action, pneumatic, or toggle.
5.3.4 Clamping surfaces in contact with a test specimen shall be of any suitable material and configuration which provides the
required restraint, preclude slippage, and minimize specimen failure in the clamped areas. Clamp liners may be used, provided the
above conditions are met.
5.3.5 When the flat-faced type clamp proves unsatisfactory because of slippage or excessive breakage in the clamp, snubbing type
devices (capstan, drum, split-drum, etc.) may be used.
5.4 Calibrating Devices—Calibrating weights or other calibrating devices conforming to Practice E74 are required for verification
of calibration. Calipers, a steel rule that can be read to 0.25 mm [0.01 in.], or a suitable cathetometer, and a stop watch are required
for verification of recorded elongation, and crosshead and chart speed.
6. Machine Operational Design
6.1 The use of motor-driven machines is preferred over manually driven machines because of improved control of testing.
6.2 Testing machines of the CRT-type shall not be used for measuring forces below fifty times their resolution. For example, if
the minimum force that can be read is 0.5 cN [0.5 gf], the testing machine may not be used for materials which test at 25.0 cN
[25 gf] or less.
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6.2.1 Choose the full scale force such that the expected maximum force falls within:
6.2.1.1 10 to 90% full scale for the CRE-type testing machines,
6.2.1.2 15 to 85% full scale for the CRT-type testing machines,
6.2.1.3 15 to 85% full scale for the CRL-type testing machines,
6.3 Machines shall operate at a uniform rate of pulling clamp (CRE), and (CRT), or loading (CRL) as specified in 6.4, 6.5, and
6.6.
6.3.1 Machines may be built for operating at various rates of operation or at a single constant rate.
6.3.2 When machines are intended for operation at a specified or required average time to break as specified in individual
standards (for example, 20 s to break as in Test Method D2256 and Test Methods D1682) then their rate of operation must be
adjustable. The adjustment may be continuous or in steps not exceeding 125:100. Machines with a continuously adjustable rate
of operation shall be equipped with a device indicating the rate of operation.
6.3.3 The machine rate of operation shall be within the tolerances prescribed in the individual standards.
6.4 CRE-Type:
6.4.1 Machines shall be designed for operation at such uniform rates of pulling clamp as are specified in individual standards.
6.4.2 Using a data-acquisition system, the sampling rate should be set to approximately 500/(time-to-break). Using a graphical
recording system, the force-measuring system, including the recording mechanism, shall have a full-scale pen response time less
than 2 s in either direction. In addition, the response time for pen deflections of less than full scale shall be proportional to the
fraction of full-scale time represented by those deflections within a tolerance of 610 % of the nominal full-scale response time.
NOTE 1—The response time of the recording mechanism is the limiting factor affecting the choice of a rate for testing. The rate chosen shall give the
maximum slope of the recorded curve which does not exceed one half of the slope of the maximum pen speed. See Fig. 1.
6.5 CRT-Type—Machines shall be designed for operation of the pulling clamp at a uniform rate as specified in individual
standards.
6.6 CRL-Type—Machines shall be designed to apply forces at a uniform rate, or at a uniform rate of loading per unit of specimen
linear density, as specified in individual standards.
FIG. 1 Limitations on Response Speed of Recorder Pen
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6.7 Machines may be built for either manual or automatic mounting of the specimen into the clamp or holding devices.
7. Tolerance on Indicated Force, Recorded Elongation, Nominal Gauge Length, and Speed of Moving Clamp
7.1 On instruments where the capacity of the force measuring mechanism (load cell) is used for digital analysis without regard
to the full scale force displayed on the recorder, the maximum allowable error in force indication shall be 60.5 % of the reading
for CRE-type machines and 61.0 % for CRT- and CRL-type machines (see Section 8).
7.2 The maximum allowable error in recorded grip displacement shall be 61% of the recorded values for CRE-type machines and
62.5 mm [0.5 in.] for CRT- and CRL-type machines (see Section 9 for CRE-type machines and Section 10 for CRT- and CRL-type
machines).
7.3 The maximum allowable variation in nominal gauge length on repeated return of the clamps to their starting position shall be
less than 0.25 mm [0.01 in.].
7.4 The maximum allowable variation of crosshead speed of the CRE-type tester or moving clamp of the CRT-type tester from
the required testing speed shall be less than 4%.
7.5 The maximum allowable variation of the loading rate for the CRL-type of tester from the required rate shall be less than 5
%.
8. Verification of Indicated Force
8.1 This section provides a general procedure for the verification of the force calibration of tensile testing machines for textiles.
No attempt is made to give detailed instructions applicable to any particular case. The verification should be performed or
supervised by a qualified person competent to exercise scientific judgment in matters not covered herein. Detailed instructions are
given in Annex A1 covering verification of one variety of testing machine of the CRL-type.
8.2 Verify tensile testing machines as directed in the applicable procedure and at the suggested time intervals listed in Practices
E4, except as otherwise provided in the following paragraphs.
8.3 Verify the machine in the condition under which it is used, with all attachments and recording mechanisms in operation if they
are to be used in actual testing; but with any pawls or other detent device in the force-measuring mechanism rendered inoperative.
Following the application of each test force, eliminate the effect of friction by gently oscillating the force-measuring mechanism
or by tapping the machine to ensure that the applied force is in equilibrium with the force registered by the measuring mechanism.
8.4 Examine the measuring, indicating, and recording mechanisms for friction or slack. Estimate, in terms of the units in which
the machine is calibrated, the magnitude of such factors and, if excessive, reduce the error at the source to conform to the tolerance
as stated in 7.1.
8.5 If other than vertical test forces must be applied, suitable apparatus must be devised subject to the general requirements for
accuracy of calibration devices prescribed in Practice E74. If cords and pulleys are used, any errors due to axle friction, pulley
eccentricities, cord friction, and uncertainty of cord center line shall be within the required limits of Practice E74. If an elastic
calibration device is used, take due account of possible variations in its readings resulting from its inclined or horizontal position.
9. Verification of Recorded Clamp Displacement of CRE-Type Machines
9.1 This procedure is applicable to machines with synchronous drives between the crosshead and the chart, and to machines with
independent crosshead and independent chart drives.
9.2 Bring the clamps to their normal position for the start of the test. Measure the distance between the clamps from nip to nip
to the nearest 0.25 mm [0.01 in.]. Designate this distance as the nominal gauge length.
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9.3 Set the speed of the crossh
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