ASTM D1938-19

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: D1938 − 14 D1938 − 19
Standard Test Method for
Tear-Propagation Resistance (Trouser Tear) of Plastic Film
and Thin Sheeting by a Single-Tear Method
This standard is issued under the fixed designation D1938; 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 test method covers the determination of the force necessary to propagate a tear in plastic film and thin sheeting
(thickness of 1 mm (0.04 in.) or less) by a single-tear method. The method is not applicable for film or sheeting material where
brittle failures occur during testing.
NOTE 1—Film has been arbitrarily defined as sheeting having nominal thickness not greater than 0.25 mm (0.010 in.).
1.2 Constant-Rate-of-Grip Separation Test—This test method employs a constant rate of separation of the grips holding the test
specimen.
1.2.1 Specimen extension may be measured in this test method by grip separation.
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information
only.
1.4 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.
NOTE 2—This standard is similar to ISO 6383-1, but is not considered technically equivalent. The specimen size for ISO 6383-1 is larger, and the
method specifies different test speeds.
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:
D618 Practice for Conditioning Plastics for Testing
D882 Test Method for Tensile Properties of Thin Plastic Sheeting
D883 Terminology Relating to Plastics
D4000 Classification System for Specifying Plastic Materials
D5947 Test Methods for Physical Dimensions of Solid Plastics Specimens
D6988 Guide for Determination of Thickness of Plastic Film Test Specimens
E4 Practices for Force Verification of Testing Machines
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 ISO Standard:
ISO 6383-1 Film and Sheeting—Determination of Tear Resistance Part 1 Trouser Tear Method
3. Terminology
3.1 Definitions: Definitions—For definitions of terms used in this test method, refer to Terminology D883.
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.19 on Film, Sheeting, and Molded
Products.
Current edition approved Dec. 1, 2014April 1, 2019. Published December 2014May 2019. Originally approved in 1962. Last previous edition approved in 20082014 as
D1938 – 08.14. DOI: 10.1520/D1938-14.10.1520/D1938-19.
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.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 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
D1938 − 19
FIG. 1 Load-Time Chart for Low-Extensible Film
4. Summary of Test Method
4.1 The force to propagate a tear across a film or sheeting specimen is measured using a constant-rate-of-grip separation
machine as described in Test Methods D882 and is calculated from the load-time chart.
5. Significance and Use
5.1 This test method is of value in rating the tear-propagation resistance of various plastic films and thin sheeting of comparable
thickness. For highly extensible film or sheeting the deformation energy of the specimen legs is significantly greater than the
tearing energy. The tear-propagation resistance in slightly extensible or non-extensible film or sheeting is distinguished from the
tear-propagation resistance in highly extensible film or sheeting by the load-time or load-displacement data, (Fig. 1 and Fig. 2).
The tear-propagation force for slightly extensible or non-extensible material is determined from the average tear force versus the
initial and peak force for a highly extensible material.
5.2 This test method shall be used for specification acceptance testing only after it has been demonstrated that the data for the
particular material are acceptably reproducible.
5.3 The data obtained by this test method furnish information for ranking the tear-propagation resistance of plastic films and
sheeting of similar composition. Actual use performance may not necessarily correlate with data from this test method. Sets of data
from specimens of dissimilar thickness are usually not comparable.
5.4 Before proceeding with this test method, reference should be made to the specification of the material being tested. Any test
specimen preparation, conditioning, dimensions, or testing parameters, or combination thereof, covered in the relevant ASTM
material specification shall take precedence over those mentioned in this test method. If there are no relevant ASTM material
specifications, then the default conditions apply. Table 1 of Classification Systems D4000 lists the ASTM materials standards that
currently exist.
6. Apparatus
6.1 Testing Machine—A testing machine of the constant rate-of crosshead-movement type and comprising essentially the
following:
6.1.1 Fixed Member—A fixed or essentially stationary member carrying one grip.
6.1.2 Movable Member—A movable member carrying a second grip.
6.1.3 Grips—Preferably, a set of self-aligning grips for holding the test specimen between the fixed member and the movable
member of the testing machine. The grips should minimize both slippage and uneven stress distribution.
6.1.3.1 Fixed grips are rigidly attached to the fixed and movable members of the testing machine. Fixed grips are to be used
only if alignment can be verified when 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.
6.1.3.2 Self-aligning grips are attached to the fixed and movable member 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. The specimens shall be aligned with the direction of pull so that
no rotary motion that may induce slippage will occur in the grips.
NOTE 3—Grips lined with thin rubber have successfully been used. Grips may be of the self-tightening type. In cases where specimens frequently fail
at the edge of the grips, the radius of curvature of the edges of the grips may be increased slightly at the point where they come in contact with the
specimen.
6.1.4 Drive Mechanism—A drive mechanism capable of separating the movable member (grip) from the stationary member
(grip) at a controlled velocity of 250 mm (10 in.) 6 5 % ⁄min.
6.1.5 Load Indicator—A suitable load-indicating mechanism capable of showing the total tensile load carried by the test
specimen held by the grips. The testing machine shall be essentially free from inertia lag at the specified rate of testing and shall
indicate the load with an accuracy of 61 %. The accuracy of the testing machine shall be verified in accordance with Practices
E4.
D1938 − 19
FIG. 2 Load-Time Chart for Highly Extensible Film
6.1.6 Crosshead Extension Indicator—A suitable extension-indicating mechanism capable of showing the amount of change in
the separation of the grips (crosshead movement).
6.2 Thickness—A micrometer as prescribed in Test Methods D5947 and D6988, or an equivalent measuring device, reading to
0.0025 mm (0.0001 in.) or less. The pressure exerted by the gage on the specimen being measured shall not distort or deform the
specimen. For thin films, ≤0.025 mm (0.001 in.), or films which exhibit visual deformation during measurement, a maximum
pressure of 70 kPa (10 psi) is recommended. For thicker or stiffer films and thin sheeting, the pressure shall be between 160 and
185 kPa (23 and 27 psi).
6.3 Die—A die having the dimensions shown in Fig. 3 shall be used to cut all specimens. The cutting edge of the die shall have
a 5° negative rake, and shall be kept sharp and free from nicks to avoid leaving ragged edges on the specimen. The sample shall
rest on a smooth, slightly yielding surface that will not injure the die blade. Care shall be taken that the cut edges of the specimen
are parallel and perpendicular to the samples longitudinal and transverse directions.
7. Test Specimens
7.1 The specimens shall conform to the dimensions shown in Fig. 3 and shall not vary by more than 0.5 % from these
dimensions.
NOTE 4—The thickness of the test specimens shall be uniform to within 5 % of the thickness over the length of the unslit portion of the specimen.
7.2 Measure the thickness of the specimen below the slit (see Fig. 3) in several places and record it in millimetres to the nearest
0.0025 mm (0.0001 in.).
7.3 Cut enough specimens to provide a minimum of five tear-propagation force determinations each in the machine direction
and in the transverse direction of the material being tested.
NOTE 5—This is required because the properties of anisotropic specimens vary with direction.
8. Conditioning
8.1 Conditioning—Condition the test specimens at 23 6 2°C (73.4 6 3.6°F) and 50 6 10 % relative humidity for not less than
40 h prior to test in accordance with Procedure A of Practice D618 unless otherwise specified by agreement or the relevant ASTM
material specification. In cases of disagreement, the tolerances shall be 61°C (61.8°F) and 65 % relative humidity.
8.2 Test Conditions—Conduct the tests at 23 6 2°C (73.4 6 3.6°F) and 50 6 10 % relative humidity unless otherwise specified
by agreement or the relevant ASTM material specification. In cases of disagreement, the tolerances shall be 61°C (61.8°F) and
6 5 % relative humidity.
9. Procedure
9.1 Secure Tongue A (see Fig. 3) in one grip and Tongue B in the other grip of the constant-rate-of-grip separation-tes
...