ASTM D882-09B

Designation: D 882 – 09 Standard Test Method for Tensile Properties of Thin Plastic Sheeting1 This standard is issued under the fixed designation D 882; 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. These test methods have been approved for use by agencies of the Department of Defense to replace Method 1013 of Federal Test Method Standard 406. 1. Scope* 1.1 This test method covers the determination of tensile properties of plastics in the form of thin sheeting, including film (less than 1.0 mm (0.04 in.) in thickness). NOTE 1—Film has been arbitrarily defined as sheeting having nominal thickness not greater than 0.25 mm (0.010 in.). NOTE 2—Tensile properties of plastics 1.0 mm (0.04 in.) or greater in thickness shall be determined according to Test Method D 638. 1.2 This test method may be used to test all plastics within the thickness range described and the capacity of the machine employed. 1.2.1 Static Weighing, Constant-Rate-of-Grip Separation Test—This test method employs a constant rate of separation of the grips holding the ends of the test specimen. 1.3 Specimen extension may be measured in these test methods by grip separation, extension indicators, or displace- ment of gage marks. 1.4 A procedure for determining the tensile modulus of elasticity is included at one strain rate. NOTE 3—The modulus determination is generally based on the use of grip separation as a measure of extension; however, the desirability of using extensometers, as described in 5.2, is recognized and provision for the use of such instrumentation is incorporated in the procedure. 1.5 Test data obtained by this test method is relevant and appropriate for use in engineering design. 1.6 The values stated in SI units are to be regarded as the standard. The values in parentheses are provided for informa- tion only. 1.7 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 appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. NOTE 4—This test method is similar to ISO 527-3, but is not considered technically equivalent. ISO 527-3 allows for additional specimen configu- rations, specifies different test speeds, and requires an extensometer or gage marks on the specimen. 2. Referenced Documents 2.1 ASTM Standards:2 D 618 Practice for Conditioning Plastics for Testing D 638 Test Method for Tensile Properties of Plastics D 4000 Classification System for Specifying Plastic Mate- rials D 5947 Test Methods for Physical Dimensions of Solid Plastics Specimens D 6287 Practice for Cutting Film and Sheeting Test Speci- mens E 4 Practices for Force Verification of Testing Machines E 691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method 2.2 ISO Standard: ISO 527-3 Plastics—Determination of Tensile Properties— Part 3: Test Conditions for Films and Sheets3 3. Terminology 3.1 Definitions—Definitions of terms and symbols relating to tension testing of plastics appear in the Annex to Test Method D 638. 3.1.1 line grips—grips having faces designed to concentrate the entire gripping force along a single line perpendicular to the direction of testing stress. This is usually done by combining one standard flat face and an opposing face from which protrudes a half-round. 3.1.2 tear failure—a tensile failure characterized by fracture initiating at one edge of the specimen and progressing across the specimen at a rate slow enough to produce an anomalous load-deformation curve. 1 These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.19 on Film and Sheeting. Current edition approved Jan. 1, 2009. Published January 2009. Originally approved in 1946. Last previous edition approved in 2002 as D 882 - 02. 2 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. 3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org. 1 *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. 4. Significance and Use 4.1 Tensile properties determined by this test method are of value for the identification and characterization of materials for control and specification purposes. Tensile properties may vary with specimen thickness, method of preparation, speed of testing, type of grips used, and manner of measuring extension. Consequently, where precise comparative results are desired, these factors must be carefully controlled. This test method shall be used for referee purposes, unless otherwise indicated in particular material specifications. For many materials, there may be a specification that requires 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 D 4000 lists the ASTM materials standards that currently exist. 4.2 Tensile properties may be utilized to provide data for research and development and engineering design as well as quality control and specification. However, data from such tests cannot be considered significant for applications differing widely from the load-time scale of the test employed. 4.3 The tensile modulus of elasticity is an index of the stiffness of thin plastic sheeting. The reproducibility of test results is good when precise control is maintained over all test conditions. When different materials are being compared for stiffness, specimens of identical dimensions must be employed. 4.4 The tensile energy to break (TEB) is the total energy absorbed per unit volume of the specimen up to the point of rupture. In some texts this property has been referred to as toughness. It is used to evaluate materials that may be subjected to heavy abuse or that might stall web transport equipment in the event of a machine malfunction in end-use applications. However, the rate of strain, specimen parameters, and especially flaws may cause large variations in the results. In that sense, caution is advised in utilizing TEB test results for end-use design applications. 4.5 Materials that fail by tearing give anomalous data which cannot be compared with those from normal failure. 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—A set of grips for holding the test specimen between the fixed member and the movable member of the testing machine; grips can be either the fixed or self-aligning type. In either case, the gripping system must minimize both slippage and uneven stress distribution. 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, care must be taken 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 a 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 should be aligned as per- fectly 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. Grips lined with thin rubber, crocus-cloth, or pressure-sensitive tape as well as file-faced or serrated grips have been success- fully used for many materials. The choice of grip surface will depend on the material tested, thickness, etc. Line grips padded on the round face with 1.0 mm (40 mil) blotting paper or filter paper have been found superior. Air-actuated grips have been found advantageous, particularly in the case of materials that tend to “neck” into the grips, since pressure is maintained at all times. In cases where samples frequently fail at the edge of the grips, it may be advantageous to increase slightly the radius of curvature of the edges where the grips come in contact with the test area of the specimen. 5.1.4 Drive Mechanism—A drive mechanism for imparting to the movable member a uniform, controlled velocity with respect to the stationary member. The velocity shall be regu- lated as specified in Section 9. 5.1.5 Load Indicator—A suitable load-indicating mecha- nism capable of showing the total tensile load carried by the test specimen held by the grips. This mechanism shall be essentially free of inertial lag at the specified rate of testing (see Note 5). Unless a suitable extensometer is used (see 5.2), the motion of the weighing system shall not exceed 2 % of the specimen extension within the range being measured. The load indicator shall determine the tensile load applied to the specimen with an accuracy of 61 % of the indicated value, or better. The accuracy of the testing machine shall be verified in accordance with Practices E 4. 5.1.6 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 (see Note 5) and shall indicate the crosshead movement with an accuracy of 61 % of the indicated value, or better. 5.2 Extensometer (Optional)—A suitable instrument may, if desired, be used for determining the distance between two designated points on the test specimen as the specimen is stretched. This apparatus, if employed, shall be so designed as to minimize stress on the specimen at the contact points of the specimen and the instrument (see 8.3). It is desirable that this instrument automatically record the 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 only the latter is obtained, load-time data must also be taken. This instrument must be essentially free of inertial lag at the specified speed of testing (see Note 5). D 882 – 09 2 5.2.1 Modulus of Elasticity and Low-Extension Measurements—Extensometers used for modulus of elasticity and low-extension (less than 20 % elongation) measurements shall, at a minimum, be accurate to 61 % and comply with the requirements set forth in Practice E 83 for a Class C instru- ment. 5.2.2 High-Extension Measurements—Instrumentation and measuring techniques used for high-extension (20 % elonga- tion or greater) measurements shall be accurate to 610 % of the indicated value, or better. NOTE 5—A sufficiently high response speed in the indicating and recording system for the load and extension data is essential. The response speed required of the system will depend in part on the material tested (high or low elongation) and the rate of straining. 5.3 Thickness Gage—A dead-weight dial micrometer as prescribed in Method C of Test Methods D 5947, or an equivalent measuring device, reading to 0.0025 mm (0.0001 in.) or less. 5.4 Width-Measuring Devices—Suitable test scales or other width measuring devices capable of measuring 0.25 mm (0.010 in.) or less. 5.5 Specimen Cutter—For the apparatus and techniques for cutting film and sheeting used in this test method, refer to Practice D 6287. 5.5.1 Devices that use razor blades have proven especially suitable for materials having an elongation-at-fracture above 10 to 20 %. 5.5.2 The use of punch press or striking dies are not recommended because poor and inconsistent specimen edges may be produced. 6. Test Specimens 6.1 The test specimens shall consist of strips of uniform width and thickness at least 50 mm (2 in.) longer than the grip separation used. 6.2 The nominal width of the specimens shall be not less than 5.0 mm (0.20 in.) or greater than 25.4 mm (1.0 in.). 6.3 A width-thickness ratio of at least eight shall be used. Narrow specimens magnify effects of edge strains or flaws, or both. 6.4 The utmost care shall be exercised in cutting specimens to prevent nicks and tears which are likely to cause premature failures (Note 6). The edges shall be parallel to within 5 % of the width over the length of the specimen between the grips. NOTE 6—Microscopical examination of specimens may be used to detect flaws due to sample or specimen preparation. 6.5 Wherever possible, the test specimens shall be selected so that thickness is uniform to within 10 % of the thickness over the length of the specimen between the grips in the case of materials 0.25 mm (0.010 in.) or less in thickness and to within 5 % in the case of materials greater than 0.25 mm (0.010 in.) in thickness but less than 1.00 mm (0.040 in.) in thickness. NOTE 7—In cases where thickness variations are in excess of those recommended in 6.5, results may not be characteristic of the material under test. 6.6 If the material is suspected of being anisotropic, two sets of test specimens shall be prepared having their long axes respectively parallel with and normal to the suspected direction of anisotropy. 6.7 For tensile modulus of elasticity determinations, a specimen gage length of 250 mm (10 in.) shall be considered as standard. This length is used in order to minimize the effects of grip slippage on test results. When this length is not feasible, test sections as short as 100 mm (4 in.) may be used if it has been shown that results are not appreciably affected. However, the 250-mm gage length shall be used for referee purposes. The speed of testing of shorter specimens must be adjusted in order for the strain rate to be equivalent to that of the standard specimen. NOTE 8—Two round robin tests4 have shown that, for materials of less than 0.25-mm (10-mil) thickness, line grips padded on the round side with 1.0-mm (40-mil) blotting paper give the same results with a 100-mm test section as a 250-mm test section produces with flat-face grips. NOTE 9—Excessive jaw slippage becomes increasingly difficult to overcome in cases where high modulus materials are tested in thicknesses greater than 0.25 mm (0.010 in.). 7. Conditioning 7.1 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 D 618 unless otherwise specified by agreement or the relevant ASTM material specification. In cases of disagree- ment, the tolerances shall be 61°C (61.8°F) and 65 % relative humidity. 7.2 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 speci- fication. In cases of disagreement, the tolerances shall be 61°C (61.8°F) and 65 % relative humidity. 8. Number of Test Specimens 8.1 In the case of isotropic materials, at least five specimens shall be tested from each sample. 8.2 In the case of anisotropic materials, at least ten speci- mens, five normal and five parallel with the principal axis of anisotropy, shall be tested from each sample. 8.3 Specimens that fail at some obvious flaw or that fail outside the gage length shall be discarded and retests made, unless such flaws or conditions constitute a variable whose effect is being studied. However, jaw breaks (failures at the grip contact point) are acceptable if it has been shown that results from such tests are in essential agreement with values obtained from breaks occurring within the gage length. NOTE 10—In the case of some materials, examination of specimens, prior to and following testing, under crossed optical polarizers (polarizing films) provides a useful means of detecting flaws which may be, or are, responsible for premature failure. 4 Supporting data are available from ASTM Headquarters. Request RR: D20- 1058. D 882 – 09 3 9. Speed of Testing 9.1 The speed of testing is the rate of separation of the two members (or grips) of the testing machine when running idle (under no load). This rate of separation shall be maintained within 5 % of the no-load value when running under full- capacity load. 9.2 The speed of testing shall be calculated from the required initial strain rate as specified in Table 1. The rate of grip separation may be determined for the purpose of these test methods from the initial strain rate as follows: A 5 BC (1) where: A = rate of grip separation, mm (or in.)/min, B = initial distance between grips, mm (or in.), and C = initial strain rate, mm/mm·min (or in./in.·min). 9.3 The initial strain rate shall be as in Table 1 unless otherwise indicated by the specification for the material being tested. NOTE 11—Results obtained at different initial strain rates are not comparable; consequently, where direct comparisons between materials in various elongation classes are required, a single initial strain rate should be used. For some materials it may be advisable to select the strain rates on the basis of percent elongation at yield. 9.4 In cases where conflicting material classification, as determined by percent elongation at break values, results in a choice of strain rates, the lower rate shall be used. 9.5 If modulus values are being determined, separate speci- mens shall be used whenever strain rates and specimen dimensions are not the same as those employed in the test for other tensile properties. 10. Procedure 10.1 Select a load range such that specimen failure occurs within its upper two thirds. A few trial runs may be necessary to select a proper combination of load range and specimen width. 10.2 Measure the cross-sectional area of the specimen at several points along its length. Measure the width to an accuracy of 0.25 mm (0.010 in.) or better. Measure the thickness to an accuracy of 0.0025 mm (0.0001 in.) or better for films less than 0.25 mm (0.010 in.) in thickness and to an accuracy of 1 % or better for films greater than 0.25 mm (0.010 in.) but less than 1.0 mm (0.040 in.) in thickness. 10.3 Set the initial grip separation in accordance with Table 1. 10.4 Set the rate of grip separation to give the desired strain rate, based on the initial distance between the grips, in accordance with Table 1. Zero the calibrated load weighing system, extension indicator(s) and recording system. NOTE 12—Extensometers may be used for modulus of elasticity deter- minations with the expectation of obtaining more accurate values than may be obtained using grip separation as the effective gage length. Precautions should be taken to ensure that extensometer slippage and undue stressing of the specimen do not occur. Refer also to 6.7. 10.5 In cases where it is desired to measure a test section other than the total length between the grips, mark the ends of the desired test section with a soft, fi