BS 2782-3 Method 327A-1993 Methods of testing plastics - Mechanical properties - Determination of tensile strength and elongation at break of polytetrafluoroethylene (PTFE) product.pdf

1、BRITISH STANDARD BS2782-3: Method327A: 1993 Methods of testing Plastics Part 3: Mechanical properties Method327A: Determination of tensile strength and elongation at break of polytetrafluoroethylene (PTFE) products IMPORTANT NOTE. Before reading this method it is essential to read BS2782-0, Introduc

2、tion, issued separately.BS2782-3:Method 327A:1993 This British Standard, having been prepared under the directionof the Plastics and Rubber Standards Policy Committee, was published underthe authority of the Standards Board and comes intoeffect on 15 March1993 BSI06-1999 First published December1982

3、 Second edition March1993 The following BSI references relate to the work on this standard: Committee reference PRM/31 Draft for comment 91/48973 DC ISBN 0 580 21569 5 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber S

4、tandards Policy Committee (PRM/-) to Technical Committee PRM/31, upon which the following bodies were represented: British Fluoropolymers Processors Group British Plastics Federation Engineering Equipment and Materials Users Association Ministry of Defence Amendments issued since publication Amd. No

5、. Date CommentsBS2782-3:Method 327A:1993 BSI 06-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 Principle 1 5 Apparatus 1 6 Test specimens 2 7 Marking of test specimens 3 8 Conditioning 4 9 Procedure 4 10 Calculation and expressio

6、n of results 4 11 Test report 4 Figure 1 Turned dumb-bell test specimens 2 Figure 2 Punched dumb-bell test specimens (type A) 2 Figure 3 Test specimen/knife-edged die dimenions for use in the determination of tensile strength and elongation at break (type B) 3 Table 1 Dimensions of dumb-bell test sp

7、ecimens 3 List of references Inside back coverBS2782-3:Method 327A:1993 ii BSI 06-1999 Foreword This British Standard has been prepared under the direction of the Plastics andRubber Standards Policy Committee. It supersedes BS2782-3:Method327A:1982, which is withdrawn. This method is applicable to P

8、TFE rod, tube and tape, in addition to moulded basic shapes and sheet. Experience has shown that the variation of results to be expected from individual tests for determining tensile properties is considerably greater for PTFE than for most other plastics materials. For this reason, a testing machin

9、e conforming for accuracy to grade2 of BS1610-2:1985 is specified. WARNING NOTE 1. It is essential that tobacco products are kept well away from areas where they could be contaminated by PTFE dust. The smoking of tobacco products contaminated by PTFE can result in a temporary, flu-like condition, kn

10、own as polymer fume fever. This condition is the only adverse effect observed in humans to date. The symptoms do not ordinarily occur until several hours after inhalation of the fumes and pass off within36h to48h even in the absence of treatment. Observations indicate that these attacks have no last

11、ing effects and that the effects are not cumulative. When heated above260 C, PTFE begins to degrade and the rate of degradation increases with increasing temperature. The gases produced during degradation vary according to the temperature and other conditions but invariably contain toxic components,

12、 and good ventilation is therefore essential. It is strongly recommended that users of this standard refer to BFPG Publication No.254/1 Industrial health and safety for PTFE fluoroplastics and melt processable fluoroplastics 1 for further information. WARNING NOTE 2. This method does not necessarily

13、 detail all the precautions necessary to meet the requirements of the Health and Safety at Work etc. Act19742. Attention should be paid to any appropriate safety precautions and the test should be carried out only by trained personnel. A British Standard does not purport to include all the necessary

14、 provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4,

15、an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.BS2782-3:Method 327A:1993 BSI 06-1999 1 1 Scope This British Standard describes a method for the

16、 determination of the tensile strength and elongation at break of products manufactured from polytetrafluoroethylene (PTFE). It is applicable to products in the form of moulded basic shapes, rod, tube, sheet and tape. Five types of test specimen are described; the choice of test specimen depends on

17、the nature of the product to be tested. 2 References 2.1 Normative references This British Standard incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the i

18、nside back page. Subsequent amendments to, or revision of, any of these publications apply to this British Standard only when incorporated in it by updating or revision. 2.2 Informative references This British Standard refer to other publications that provide information or guidance. Editions of the

19、se publications current at the time of issue of this standard are listed on the inside back page, but reference should be made to the latest editions. 3 Definitions For the purposes of this British Standard, the following definitions apply. 3.1 tensile stress the tensile force carried by the test pi

20、ece at any moment of time during the test, divided by the original cross-sectional area between the reference lines 3.2 tensile strength the maximum tensile stress which the test specimen is capable of supporting 3.3 percentage elongation at break the elongation at break produced in the gauge length

21、 of the test specimen expressed as a percentage of the original gauge length (distance between the reference lines) 4 Principle A test specimen is extended at a specified rate of grip separation. The elongation and corresponding force are recorded during the test, and the tensile stress and elongati

22、on at break are calculated. 5 Apparatus 5.1 Tensile testing machine, which shall be power driven and capable of maintaining a rate of grip separation of (50 5)mm/min. A continuous indication of the force applied to the test specimen shall be given. NOTEPreferably, the force applied should be recorde

23、d autographically with a permanent indication of the maximum force. The force scale shall be calibrated in accordance with BS1610-2:1985 to ensure that the error does not exceed the requirements for grade2 machines and proving devices. The machine shall be provided with a type of grip which maintain

24、s or increases grip pressure as the force applied to the test specimen increases. The test specimen shall be held in such a manner that slip relative to the grips is prevented as far as possible, and that the clamping system does not produce premature failure at the grips. 5.2 Micrometer, for measur

25、ing the thickness and width of test specimens (except for the width of test specimens prepared from thin or narrow tape). The micrometer shall conform to BS870:1950 and shall be accurate to within0.025mm. 5.3 Vernier callipers, for measuring the width of test specimens prepared from thin or narrow t

26、ape and for visual measurement of elongation, conforming to BS887:1982. 5.4 Extensometer (optional), which shall give a continuous indication of the elongation of the gauge length and a permanent indication of the maximum elongation. NOTEPreferably, the elongation should be recorded autographically

27、in the form of a force-elongation curve. When an extensometer is attached to the test specimen, care shall be taken to ensure that any distortion of, or damage to, the test specimen is minimal, and it is essential that no slippage occurs between the extensometer grips and the test specimen. The inst

28、rument shall be essentially free from inertia lag at the speed of testing.BS2782-3:Method 327A:1993 2 BSI 06-1999 6 Test specimens 6.1 General The appropriate type of test specimen shall be chosen from those given in6.2 to6.5 1) , as appropriate. At least three test specimens shall be prepared from

29、the sample and three specimens shall be tested. When testing extruded products, the test specimens shall be cut parallel to the axis of extrusion so that, as far as possible, each test specimen represents a different section along the axis and a different area of the cross section. When testing vene

30、ered tape, the test specimens shall be cut perpendicular to the direction in which the pressure was applied when moulding the billet from which the tape was veneered. If this direction is not known, two sets of test specimens shall be prepared and tested, the test specimens in one set being cut at90

31、 to those in the other set, and the mean results shall be calculated from the lower set of values (indicating the weaker direction). 6.2 Turned dumb-bell test specimens The test specimens shall be turned so that their dimensions are in the ratios given in Figure 1, with the shape shown. The value of

32、 the larger diameter (D) shall be (7 0.5)mm, (10 0.5)mm or(20 0.5)mm. 6.3 Small punched dumb-bell test specimens The sample shall be machined to produce a sheet or disc of thickness1.5mm to2.5mm, or turned to produce a rectangular sectioned ring which can be cut and flattened to give such a sheet. E

33、ither test specimens conforming to the shape shown in Figure 2 and the dimensions given in Table 1 for small dumb-bells (type A) or specimens conforming to the dimensions shown in Figure 3 (type B) shall be punched from sheet or disc using a single stroke press and the appropriate knife-edged dies.

34、In any one test specimen, the thickness of the narrow parallel portion shall nowhere deviate by more than2% from the mean. The sheet shall be supported, while the test specimens are punched from it, on a slightly yielding material having a smooth surface (e.g.leather, rubber or high quality cardboar

35、d) on a flat rigid base. The cutting edge of the die shall be sharp and free from notches. Figure 1 Turned dumb-bell test specimens 1) Test specimens prepared from moulded basic shapes, rod or tube and conforming to6.2 are likely to give similar results to test specimens prepared from the same produ

36、ct but conforming to6.3. Figure 2 Punched dumb-bell test specimens(type A)BS2782-3:Method 327A:1993 BSI 06-1999 3 In the case of thin sheet or veneered tape of thickness1.0mm to2.5mm, the test specimens shall be punched from the materialas received. Table 1 Dimensions of dumb-bell test specimens 6.4

37、 Test specimens prepared from thin or narrow tape When testing tape of less than1.0mm in thickness, either the test specimens shall be parallel sided strips25mm wide and of an appropriate length to suit the testing machine and grips to be used, or alternatively, test specimens conforming to the shap

38、e shown in Figure 2 and the dimensions given in Table 1 for large dumb-bells shall be punched from the tape, by the method described in6.3. In any one test specimen, the thickness of the narrow parallel portion shall nowhere deviate by more than2% from the mean. In the case of tape of less than25mm

39、in width, the full width shall be tested. 6.5 Test specimen prepared from small diameter rod When testing rod of not more than7mm in diameter, the test specimens shall consist of100mm lengths cut from the rod either “as received”, or with a reduction in diameter of up to15%over a test length of25mm

40、to30mm to facilitate gripping in the testing machine without breakage occurring within the grips. 7 Marking of test specimens If measurements of elongation are made visually the gauge length shall be marked on the test specimens. Before marking test specimens of the types specified in6.2, 6.3 or6.5,

41、 remove any machining or punch marks by lightly sanding with a medium or fine abrasive paper. Dimension Small dumb-bells a mm Large dumb-bells b mm A overall length, minimum 75 115 B width at ends 12.5 1.0 25 1 C length of narrow parallel portion 25 1 33 2 D width of narrow parallel portion 4 0.1 E

42、small radius 8 0.5 14 1 F large radius 12.5 1.0 25 2 a Corresponds to the type2 test specimen specified in BS903-A2:1989. b Corresponds to the type1 test specimen specified in BS903-A2:1989 and the test specimen specified in method320A of BS2782:Methods320A to320F:1976. 6 +0.4 0 Figure 3 Test specim

43、en/knife-edged die dimensions for use in the determination of tensile strength and elongation at break (typeB)BS2782-3:Method 327A:1993 4 BSI 06-1999 Mark each test specimen with two reference marks,10mm to25mm apart(15mm to20mm apart for a small dumb-bell test specimen) and approximately equidistan

44、t from the midpoint, taking care to avoid damaging the test specimen. Ensure that the marking medium has no detrimental effect on the material being tested and that the marks are as narrow as possible. Do not scratch, punch or impress the lines upon the test specimen. 8 Conditioning Condition the te

45、st specimens at a temperature of(23 2) C for at least4h before testing and carry out the tests at the same temperature. If the material has been exposed to temperatures below20 C in the24h prior to conditioning, the conditioning period shall be at least24h. 9 Procedure Determine the mean cross-secti

46、onal area of the test specimens at several points along the gauge length as follows: a) for test specimens conforming to6.4, measure the width to an accuracy of 0.1mm and the thickness to an accuracy of 0.025mm; b) for all other test specimens, measure either the thickness and the width or the diame

47、ter to an accuracy of 0.025mm. Insert the ends of the test specimen in the grips and mount it in the tensile testing machine in axial alignment with the direction of pull. For test specimens conforming to6.4 and6.5, ensure that the distance between the jaws of the testing machine is at least twice t

48、he gauge length of10mm to25mm. Adjust the extensometer, if used, to the gauge length to an accuracy of 0.5mm and set it so that it is positioned approximately in the middle along the test specimen length. If elongation is to be measured visually, measure the initial distance between the reference li

49、nes to an accuracy of 0.5mm. Apply a tensile force to the test specimen, by separating the grips at a rate of traverse of(50 5)mm/min, and continually measure the gauge length to an accuracy of 1mm, until the test specimen breaks. If a test specimen breaks within the area held by one of the grips, disregard the results for that test specimen and test a further test specimen. 10 Calculation and expression of results Calculate the tensile strength of each test specimen by dividing the maximum force (in newtons) recorded during the