1、BRITISH STANDARD BS 3424-21: 1993 Testing coated fabrics Part 21: Method 24. Method for determination of elongation and tension set IMPORTANT NOTE. It is recommended that this Part be read in conjunction with the information in Part 0 “Foreword and general introduction”.BS3424-21:1993 This British S
2、tandard, 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 June 1993 BSI 02-1999 First published October 1973 Second edition March 1987 Third edition June 1993 The followin
3、g BSI references relate to the work on this standard: Committee reference PRM/78 Draft for comment 91/43290 DC ISBN 0 580 21729 9 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to T
4、echnical Committee PRM/78, upon which the following bodies were represented: British Nonwovens Manufacturers Association British Plastics Federation British Railways Board British Resin Manufacturers Association British Rubber Manufacturers Association Ltd. British Textile Confederation British Text
5、ile Technology Group Department of Health Department of the Environment (Building Research Establishment) Electricity Industry in United Kingdom Furniture Industry Research Association Home Office Industrial Safety (Protective Equipment) Manufacturers Association London Regional Transport Made-Up Te
6、xtiles Association Ministry of Defence National Union of Dyers, Bleachers and Textile Workers (NUDBTW) RAPRA Technology Ltd. SATRA Footwear Technology Centre Society of Motor Manufacturers and Traders Ltd. The following body was also represented in the draft of the standard, through subcommittees an
7、d panels: Ministry of Defence Amendments issued since publication Amd. No. Date CommentsBS3424-21:1993 BSI 02-1999 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 Preparation of test specimens 2 7 Conditioni
8、ng 2 8 Procedure 2 9 Calculation and expression of results 5 10 Test report 6 Figure 1 Preparation of right hand and left hand bias test samples 3 Figure 2 Dimensions, marking and mounting of a single bias direction specimen 4 Figure 3 Example of determination of yield stress from an autographic str
9、ess-strain curve 5 List of references Inside back coverBS3424-21:1993 ii BSI 02-1999 Foreword This revision has been prepared under the direction of the Plastics and Rubber Standards Policy Committee. The response of many textiles, including coated fabrics, to stresses in the bias direction is parti
10、cularly important, and this is especially so when one considers that the integrity of a structure depends upon its weakest link. When the tensile properties of textile materials are examined or specified with a particular end-use in mind, their bias direction performance is quite often overlooked. T
11、ension set, sometimes referred to as permanent set, is defined in various ways depending upon the discipline concerned. The general descriptions of tension set or permanent set, however, invariably agree; it is only the means by which it is derived that differs. In order to avoid any misunderstandin
12、g, therefore, a definition of tension set as applied to coated fabrics has been prepared. The factors affecting the determination of tension set are: a) the rate at which the specimen is extended; b) the temperature and relative humidity prior to and during testing; c) the period or elapse of time b
13、etween the extension of the specimen and the release of the load or strain.; d) the period allowed for recovery; e) the previous mechanical history of the specimen. This last factor can be of particular importance, as specimens can be mechanically conditioned by repeated loadings followed by periods
14、 of relative recovery in which some strain is maintained or periods of recovery in which the specimen is under zero strain. Generally, however, the point of interest in conducting the test is to discover the extent to which the coated fabric will suffer permanent deformation after it has been strain
15、ed beyond a given point. The extent of the permanent deformation is the value referred to as tension or permanent set. Because of all these variables and as the designers of coated fabrics for airships, sails and inflated structures will have different interests than designers of coated fabrics for
16、upholstery and clothing applications for example, a method of test has been developed which caters for all these interests and at the same time permits direct comparisons to be made between materials of different types. For methods related to creep and creep recovery, reference should be made to BS3
17、424-0:1982. This edition supersedes BS 3424-21:1987 which is withdrawn. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer im
18、munity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 6, 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 th
19、e amendment table on theinside front cover.BS3424-21:1993 BSI 02-1999 1 1 Scope This Part of BS 3424 describes a method of test for determining the elongation and tension set of coated fabrics. 2 References 2.1 Normative references This Part of BS3424 incorporates, by reference, provisions from spec
20、ific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside back page. Subsequent amendments to, or revisions of, any of these publications apply to this Part of BS 3424 only when incorporated in it by
21、updating or revision. 2.2 Informative reference This Part of BS 3424 refers to another publication that provides information. The edition of this publication current at the time of issue of this standard is given on the inside back page but reference should be made to the latest edition. 3 Definitio
22、ns For the purposes of this Part of BS3424 the following definitions apply. 3.1 stress the force applied to the test specimen NOTEBecause of the difficulty of accurately measuring the cross-sectional area of textiles and consequently coated fabrics, cross-sectional area is ignored. Mass per unit are
23、a is self cancelling and can be ignored for these purposes. 3.2 strain the ratio of elongation to original length, i.e the difference between the elongated length of the test specimen and the original length divided by the original length 3.3 tension set the extension remaining after a test specimen
24、 has been stretched and allowed to retract in a specified manner, expressed as a percentage of the original test length or test strain NOTEThis is sometimes referred to as permanent set. 3.4 set the deformation remaining after complete release of the force producing the deformation 3.5 yield stress
25、(S y ) the tensile stress at which occurs the first marked inflection of the stress-strain curve when extended either under the condition described in BS 3424-4:1982 or under the conditions described in this Part of BS3424 where any increase in strain occurs without any increase in stress, this poin
26、t is taken as the yield stress 3.6 percentage elongation at yield (E y ) the percentage elongation produced in the gauge length of the test specimen at the yield stress 3.7 percentage elongation the difference between the elongated length of the test specimen and the original gauge length, expressed
27、, as a percentage of the original gauge length 4 Principle A strip of pre-conditioned coated fabric is extended at a specified rate either until a predetermined percentage elongation or until a predetermined load on the test specimen is attained. This deformation or load is maintained for a specifie
28、d duration, after which the load is released at a specified rate. The test specimen is then allowed to relax under zero load for a specified duration. The amount of unrecovered deformation is measured. 5 Apparatus 5.1 Measuring device, suitable for measuring the distance between the gauge marks (see
29、 6.3) of the test specimen to the nearest 0.1 mm. 5.2 Constant rate of traverse tensile testing machine, having a recording system for measuring the variation in applied force and conforming to grade 1 of BS EN 10002-2:1992 or conforming to grade B of BS 5214-1:1975.BS3424-21:1993 2 BSI 02-1999 The
30、central points of the two jaws of the machine shall be in the line of pull, the front edges of the jaws shall be at right angles to the line of pull, and their clamping faces shall be in the same plane. The jaws shall be capable of holding the test specimen without allowing it to slip; designed so t
31、hat they do not cut or otherwise weaken the test specimen; and their width shall be not less than the width of the test specimen. The faces of the jaws shall be smooth and flat, except that when, even with packing, the test specimen cannot be held satisfactorily with flat faced jaws engraved or corr
32、ugated jaws shall be used. One jaw is nominally fixed and one jaw is capable of moving at a nominal rate of 5 mm/min or as specified in the relevant product specification. NOTESuitable packing materials for use with either smooth or corrugated jaws include paper, felt, leather, plastics or rubber sh
33、eet. 6 Preparation of test specimens 6.1 Longitudinal and transverse specimens Avoiding the selvedges, cut three specimens in the longitudinal direction of the roll and three specimens in the transverse direction of the roll. Each test specimen shall be 50 mm wide and of a length sufficient to allow
34、 a distance of 200 mm between the edges of the pairs of clamping jaws. 6.2 Bias direction specimens Unless otherwise stated in the relevant product specification, cut three samples across the transverse direction of the roll, avoiding the selvedge. Each test sample shall be not less than200 mm in th
35、e longitudinal direction and not less than 400 mm in the transverse direction. Bisect each individual 200 mm 400 mm test sample by a line AB to yield two adjacent 200 mm 200 mm test specimens (see Figure 1). Draw a line from the bottom left hand corner of the 200 mm 400 mm test sample to the top of
36、the bisecting line and from this point down to the bottom right hand corner of the 200 mm 400 mm test sample. This yields “lefthand” and “right hand” bias test specimens (seeFigure 1). Mark each bias specimen with individual identification as shown in Figure 1 and then cut along the bisecting line A
37、B. Mark each bias specimen in accordance with Figure 2. 6.3 Gauge marking of test specimens Across the centre of each test specimen draw gauge marks 100 mm apart at right angles to the length of the test specimens as shown in Figure 2. 7 Conditioning Condition the test specimens in accordance with B
38、S3424-2:1992. 8 Procedure 8.1 Standard atmospheres Conduct the test in the standard atmosphere for conditioning and testing specified in BS 3424-2:1992. 8.2 Clamping and marking 8.2.1 Clamping Set the jaws of the machine 200 mm 1 mm apart. Clamp a test specimen centrally in the stationary jaw so tha
39、t its longitudinal centre line passes through the centre points of the front edges of the jaws. 8.2.2 Marking Make a small mark across the test specimen at each of the jaw/specimen interfaces with a suitably coloured crayon, so that any slippage of the specimen in the jaws can be ascertained. 8.3 Op
40、eration 8.3.1 General When a bias sample is being evaluated, each single test consists of a left hand and right hand bias test specimen from one original test sample. There are two basic modes of operation, either: a) mode 1, in which the test specimen is strained to a given percentage elongation; o
41、r b) mode 2, in which the test specimen is stressed up to a given load. 8.3.2 Mode 1 operation Engage the device for recording the stress (load) and extension of the test specimen. Put the moving jaw in motion and extend the test specimen at the nominal rate of 5 mm/min, or some other rate specified
42、 in the relevant product specification, until the required percentage elongation is obtained, or, if not specified, until the percentage elongation at the yield point is exceeded (see 3.5 and 3.6 and Figure 3). 8.3.3 Mode 2 operation Engage the device for recording the stress (load) and extension of
43、 the test specimen. Put the moving jaw in motion and extend the test specimen at the nominal rate of 5 mm/min, or some other rate specified in the relevant product specification, until the required stress, or, if not specified, until the yield stress is obtained (see 3.5 and 9.5 and Figure 3).BS3424
44、-21:1993 BSI 02-1999 3 NOTEAll dimensions are in millimetres. Figure 1 Preparation of right hand and left hand bias test samplesBS3424-21:1993 4 BSI 02-1999 NOTEAll dimensions are in millimetres. Figure 2 Dimensions, marking and mounting of a single bias direction specimenBS3424-21:1993 BSI 02-1999
45、5 8.3.4 Duration of test Unless otherwise stated in the relevant product specification, maintain the desired extension or loading of the test specimen for 1 h, this period commencing immediately the desired extension or loading is obtained. NOTEIn order to compensate for any stress decay during the
46、period of applied load, it may be necessary to employ a closed-loop correction to the application of the actual load, in order to maintain the stress at a nominally constant value. This would not be necessary for mode 1 operations. 8.3.5 Measurement of set After the appropriate duration of deformati
47、on, release the strain at a speed of 5 mm/min, remove the test specimen from the jaws of the machine and lay it free of stress on a flat horizontal surface. Immediately measure and record the distance (L 2 ) to the nearest millimetre between the central gauge marks on the test specimen (see 6.3). 8.
48、3.6 Measurement of tension set After a period corresponding to the duration of strain (see 8.3.4), measure and record the distance (L R ) to the nearest millimetre between the central gauge marks on the test specimen (see 6.3). 9 Calculation and expression of results 9.1 Bias tests In calculating th
49、e result for a bias sample, the mean result from the test on adjacent left hand and right hand test specimens shall be recorded. 9.2 Percentage elongation Calculate the percentage elongation, E, where necessary, from the equation: where 9.3 Set Calculate the percentage set, S, from the equation: where 9.4 Tension set Calculate the percentage tension set, T, from the equation: where Figure 3 Example of determination of yield stress from an autographic stress-strain curve L 0 is the original gauge length (in mm); L 1 is the elongated gauge length (in m
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