SAE J 2749-2008 High Strain Rate Tensile Testing of Polymers《聚合物的高应变比率拉伸测试》.pdf

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4、Fax: 724-7760790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgJ2749 NOV2008 SURFACEVEHICLERECOMMENDEDPRACTICEIssued 2008-11High Strain Rate Tensile Testing of Polymers RATIONALENot applicable. 1. AIMS AND SCOPE 1.1 This recommended practice is a guideline for generating high strai

5、n rate tensile properties under defined conditions of unreinforced and reinforced plastics used in the automotive industry. Several types of test specimens are identified to suit different types of materials and test rates. 1.2 This document is intended for strain rates between 10-3/s and 103/s. Tes

6、t procedures for rates of 10-2/s and below; i.e., quasi-static conditions, are described in ASTM D 638 and ISO 527-1. The procedures in this document include quasi-static testing in order to provide a common test rate for both quasi-static and dynamic test programs. The general procedures listed in

7、ASTM D 638 and ISO 527-1 should be followed when appropriate. 1.3 The main purpose of this document is to determine the relative effects of increasing strain rate on the measured material properties. Data generated from these tests are comparative in nature. High rate tensile tests will not generate

8、 basic material properties as accurately as those generated by quasi-static tests. 1.4 The scope of this document covers Rigid and semi-rigid thermoplastic molding and extrusion materials, including filled and reinforced compounds in addition to unfilled types, and Rigid and semi-rigid thermoplastic

9、 sheets. Thermosetting materials, rigid cellular materials, and sandwich structures containing cellular material were not evaluated as part of this document. However, the test procedures may be used as a general guideline for these materials. This document is not recommended for materials whose inte

10、rnal structure is on the scale of the gage width and length of the selected specimen configuration. Fiber-filled polymers may require additional testing using an alternate sample geometry to establish the effect of strain rate on the measured properties. Copyright SAE International Provided by IHS u

11、nder license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2749 Issued NOV2008 - 2 -2. REFERENCES 2.1 Applicable Publications The following publications form a part of this specification to the extent specified herein. 2.1.1 ASTM Publications Availab

12、le from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, Tel: (610) 832-9585, www.astm.org.ASTM D 638 Standard Test Method for Tensile Properties of Plastics ASTM D 883 Standard Terminology Relating to Plastics ASTM D 1822 Standard Test Method for Tensile-I

13、mpact Energy to Break Plastics and Electrical Insulating Materials 2.1.2 ISO Publications Available from American National Standards Institute (ANSI), 25 West 43rd Street, New York, NY 10036-8002, Tel: 212-642-4900, www.ansi.org.ISO 294-1 PlasticsInjection moulding of test specimens of thermoplastic

14、 materialsPart 1: General principles, and moulding of multipurpose and bar test specimens ISO 527-1 PlasticsDetermination of tensile propertiesPart 1: General principles ISO 527-2 PlasticsDetermination of tensile propertiesPart 2: Test conditions for molding and extrusion plastics ISO 3167 PlasticsM

15、ultipurpose test specimens ISO 8256 PlasticsDetermination of tensile-impact strength 2.2 Related Publications The following publications are provided for information purposes and are not a required part of this document. 2.2.1 ASTM Publications Available from ASTM International, 100 Barr Harbor Driv

16、e, P.O. Box C700, West Conshohocken, PA 19428-2959, Tel: (610) 832-9585, www.astm.org.ASTM D 3641 Standard Practice for Injection Molding Test Specimens of Thermoplastic Molding and Extrusion Materials2.2.2 European Structural Integrity Society Publications Available from TC 5 Subcommittee on Dynami

17、c Testing at Intermediate Strain Rates, ESIS, Geesthacht, Germany, www.esisweb.org.Copies can be obtained from: Professor K-H Schwalbe, GKSS-Forschungszentrum Geesthacht, 21502 Geesthacht, Germany, schwalbegkss.de.ESIS P700 Procedure for Dynamic Tensile Tests Copyright SAE International Provided by

18、IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2749 Issued NOV2008 - 3 -Available from ISO Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical Properties ISO/FDIS 18872 2006(E) Final Draft PlasticsDetermination of

19、tensile properties at high strain rates 3. INTERFERENCE 3.1 Specimens may be molded or machined to final dimensions, or cut or punched from finished and semi-finished products such as moldings and extruded or cast sheet. The specimen preparation methods may affect the test results1, and guidance on

20、preparation may be found in appropriate material specifications. The procedures specify preferred test specimen dimensions based on the maximum test rate. Tests that are carried out on specimens of different dimensions may produce results that are not directly comparable, especially with regard to p

21、lastic deformation behavior. 3.2 Specimens must be properly conditioned after molding or extrusion to allow the material to come to thermal equilibrium with the environment and allow materials to go through stages of secondary crystallization or amorphous densification. Failure to properly condition

22、 the material may influence final test results. Guidance on conditioning may be found in appropriate material specifications. 3.3 Other factors, such as the load application, strain measuring device, equipment response, etc., can also influence results. Consequently, these factors must be carefully

23、controlled and recorded. 4. TERMINOLOGY The terms and abbreviations used in this document are listed in Table 1. Additional terms and definitions are described in ASTM D 638, ASTM D 883, and ISO 527-1. 5. SIGNIFICANCE AND USE 5.1 Stress waves of varying amplitudes are present in the gage section dur

24、ing a high rate test and a homogeneous stress state does not exist. The goal in high strain rate tests is to introduce enough stress waves in the gage area to produce an approximate equilibrium relatively quickly after load is introduced into the specimen. Thus, a “quasi-homogeneous“ stress and stra

25、in field will exist and the nominal stress and strain states can be defined. 1ASTM 638-01 Section 6.1.4 Notes 6 and 11, ISO 294-1:1996 Introduction.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE

26、 J2749 Issued NOV2008 - 4 -TABLE 1 - TERMINOLOGY AND SYMBOLS Symbol Unit Term d m Displacement E Pa Elastic modulus calcCalculated strain noms-1Nominal plastic strain rate s-1Strain rate elass-1Elastic strain rate plass-1Plastic strain rate yYield strain lsm Length of narrow parallel-sided portion o

27、f specimen Lfixtm Length of fixturing from grip end closest to load-measuring device and load-measuring device.Ldbgm Distance between grip locations on specimen LVDT Linear variable differential transformer NgageNumber of reflected waves in gage length kg/m3Densitym/s Displacement rate (Velocity of

28、crosshead or actuator) r Repeatability RReproducibility xsMPa Standard deviation of cell averages rsMPa Repeatability standard deviation rSMPa Reproducibility standard deviation twaves Travel time for a single wave tyields Time to yield vfixtm/s Wave propagation speed in fixturing vmm/s Wave propaga

29、tion speed through material x MPa Cell average High rate tests dictate the use of a small specimen in order to maximize the number of reflected stress waves along the gage length. Use of a small specimen may violate the spirit of some static test methods. However, if it is assumed that specimen geom

30、etry will bias the results equally over the range of strain rates used, the strain rate dependency of the material properties can be determined. 5.2 Many properties of polymeric materials vary with logarithmic changes in strain rate. Therefore, it is often necessary to test across at least four orde

31、rs of magnitude in strain rate to properly determine the effects of strain rate on the measured material properties. The same specimen geometry and test procedures should be used across all tested rates.6. SPECIMEN CONFIGURATION 6.1 The recommended specimen configuration will depend on the maximum d

32、esired strain rate, material stiffness, material density, yield strain, stroke displacement rate (crosshead or actuator speed), and equipment resonant frequency. The same specimen geometry should be used across all tested rates so that specimen geometry will not be a source for variability in the da

33、ta. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2749 Issued NOV2008 - 5 -It is difficult to predict the relative response at high rates. Appendix A describes how to select an initial specime

34、n geometry. The specimen geometries listed in Appendix A are general guidelines. Analysis of the test results should be the final guide as to whether changes in specimen geometry or equipment are needed. 6.2 Data obtained from samples that fail outside the narrow test section, such as in the grip ar

35、ea or in the radius region, should be eliminated from the data set.2Figure 1 defines the gage, grip and radius region of the test specimen. If a significant fraction of the failures in a sample population are unacceptable, the method of loading, specimen geometry/preparation, and/or material being t

36、ested should be reexamined for suitability to this method of high strain rate testing. FIGURE 1 - IDENTIFICATION OF THE GRIP, GAGE AND RADIUS REGION OF A TEST SAMPLE 7. APPARATUS 7.1 Ideally, the test machine will provide a constant displacement rate from the onset of load application through the po

37、int of necking/instability. This document allows a tolerance in the displacement rate of 15%, excluding the region at the onset of loading. The displacement rate should be constant by the time the specimen is loaded to a level equivalent to 25% of its yield load. Deviations from these percentages sh

38、ould be reported and potential causes and potential effects on the results should be included. The effect of a changing crosshead rate during a test is dependent on the material. If the material is not strain-rate sensitive, then larger changes in crosshead rate (e.g. 15%) should not affect the mate

39、rial properties. If a material is strain-rate sensitive, then a 15% tolerance band on the rate may not be tight enough. 7.2 Damping at the onset of loading is recommended for strain rates above 10/s. The damping method should have a minimal effect on the initial material response to the load applica

40、tion. Any damping-related effects should be gone by the time the applied load is at 25% of yield. 7.3 Grips should be lightweight to minimize inertial effects. 7.4 Load can be measured with standard devices for strain rates less than 1/s if the 0.5 dB frequency of the complete measuring equipment ch

41、ain is at least 250 Hz. Rates above 1/s require proportionally higher frequency responses. A test system with a resonant frequency response of at least 4 kHz is needed when testing above 200/s. A lower system resonant frequency may result in unacceptably high amplitude stress waves in the response.

42、Appendix A provides more details. 7.5 The displacement signal of a LVDT or comparable device should be used with caution to determine strain. The displacement data reflect the global behavior of the load train and normally do not have the resolution to record the transition from elastic to plastic d

43、eformation or to determine the modulus of elasticity. In addition, the displacement measurement may not accurately reflect the post-yield strain, especially if a localized reduction in the cross-section occurs, i.e. necking. 2ASTM 63801 Section 7.3 and ISO 527-1:1993 Section 7.2.Copyright SAE Intern

44、ational Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2749 Issued NOV2008 - 6 -Strain along the gage length may be measured with various techniques, such as strain gages, low inertia extensometers, clip-on extensometers,

45、 and non-contact extensometers. Care should be taken that the measurement techniques do not affect the test results, as mentioned in Appendix B. The practical upper test rate to use attached extensometers will depend on the weight and durability of the extensometer. Inertial effects may be a signifi

46、cant factor at strain rates as low as 1/s. 7.6 It is necessary to determine whether the equipment is capable of accurately recording the test. The maximum test rate for a given test system will depend on the frequency response of the transducers, signal conditioners, signal amplifiers, and recorders

47、. Further, each component of the test system, as well as the whole system, may have a characteristic resonant frequency. It is necessary to determine the combined effect of all of the system components in order to identify the maximum test rate. Details are provided in Appendix A. 7.7 The potential

48、for system resonance; i.e. ringing, increases with the test rate. Discreet waves can occur in the elastic or plastic portion of the response, as described in Appendix A and shown in Figure 2. The relative wave amplitude may be significant, especially in the pre-yield response. Ringing can be minimized by: Use of a damping method for strain rates above 10/s. Use of lightweight grips to minimize inertial effects. Minimizing the length of the load train. Measuring load with a high frequency response device. Selecting a specimen that has a small enough