BS 4952 弹性织物试验方法（英文学习资料）

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弹性织物试验方法

Foreword
This British standard had been prepared under the direction of the Textiles and Clothing Standard Policy Committee. It supersedes BS 4952: 1973and BS 4294: 1968 which are withdrawn.
The principal changes introduced by this revision are this edition of BS 4952 USES A similar format to BS 5441 and lists properties which can be tested in accordance with existing British Standard. The test procedures have been brought up-to-date by deleting test variants that are no longer in use and the retain techniques have been refined. The standard also includes provisions for testing looped specimens in addition straight specimens.
Methods already published as British Standard have not been reproduced, but a list is given. in 1.6, of other test methods that can be of use in assessment of elastic fabrics.
Compliance with a British Standard dose not of itself confer immunity from legal obligations.   

Section 1. general
1.1         Scope
This British standard describes methods of test specific to both narrow and wide elastic fabrics. the test methods are applicable to woven and to warp knitted and weft knitted fabrics but certain test can also be applicable to stretch fabrics which are obtained by the use of elastomeric bulked yarns or by a process such as slack mercerization.
NOTE. The titles of the publication referred to in this standard are list on the inside back cover .
1.2         Definitions
For the purpose of this BRITISH standard the following definitions apply.
1.2. 1  elastic fabrics
fabrics, which incorporate elastomeric threads.
1.2.2  elastomer
A macromolecular material which returns rapidly to approximately its initial dimensions and shape after substantial deformation by a weak stress and release of stress.
1.2.3  modulus
The tensile force in the test specimen required to produce a specified elongation.
1.3        Apparatus
1.3.1        metal scale, graduated in millimeters
1.3.2        Autographic constant rate-of-extension stress/strain apparatus(unless otherwise indicated in the particular test procedure)capable of cycling between zero extension and either a predetermined force or a predetermined extension and capable of maintaining a specimen either under a constant tension or at a constant elongation.
The apparatus shall be provided with means for recording the extension of the test specimen and the corresponding force. It shall be equipped with either line contact clamps for straight specimen or loop assembly clamps
1.3.3   Clamps
1.3.3.1  General
The central point of the two clamps be in the line of pull and the testing device shall be calibrated with the clamps in position.
The clamps shall be capable of allowing the specimens to be maintained either at a constant elongation or under a constant force as appropriate for the test to be performed.
1.3.3.2  Line contact clamps
line contact clamps as shown in figure 1 shall consist of two jaws, one being a flat steel plate, the other having a convex 3 mm radius. The line of contact of the jaws shall be at right angles to the line of pull, and other clamping faces shall be in the same plane. The jaws shall be capable of holding the test specimen without allowing it to slip, shall be designed so that they do not cut or otherwise weaken the specimen and shall be not less than the width of the specimen.

1.3.3.3  Loop assembly clamps  
Loop assembly clamps shall be as shown in figure 2 and shall essentially comprise two removable steel bars of circular cross section and 4 mm in diameter, around which the specimen passes and by which it is extended as the bars move apart. The axes of pull and shall be in the same plane.

1.3.3.4  Gauge length and specimen length under extension
In the case of line contact clamps ,the gauge length and the length of the extended test specimen at any time is measured as the distance between the lines of contact of the two jaws.
Where specimen length is to be measured after removal of the specimen from the jaws, the gauge length marks shall be drawn on the specimen before it is inserted into the clamps.
NOTE: the method of marking should be such as to prevent damage to the specimen.
In the case of loop assembly jaws, the gauge length is measured as the circumference around the loop bars.
Take samples of fabric from which test specimens will be cut to represent the fabric under test.
Prepare the specimens according to whether machine direction or cross direction stretch of the fabric is to be tested. Where possible test at least five specimens in each direction.
1.4.2  Preparation of specimens
1.4.2.1   General
Prepare specimen in accordance with 1.4.2.2 to 1.4.2.5 as appropriate.
NOTE: Straight specimens and looped specimens do not necessarily give the same result.
1.4.2.2  Straight specimens
Fabrics 50 mm and below in width shall be tested full width in a lengthwise direction .For fabrics greater than 50 mm in width, specimens50 mm wide, excluding any fringe shall be prepared such that they are of sufficient length to provide a nominal gauge length of 100 mm.
1.4.2.3  lopped specimens
Fabrics 75 mm and below in width shall be tested full width in a lengthwise direction .For fabrics greater than 75 mm in width, specimens 75 mm wide, excluding any fringe shall be prepared of length 250 mm. Mark a line 25 mm from each end, parallel to the short dimension .
Fold the specimens in half parallel to the short dimension and, starting in the center of the line, sew along the line to form the strip into a loop, turning at the edge without breaking the threads, returning along the same line to other edge and turning again to finish in the center.
The stitch, sewing thread and stitch density shall be such as to withstand the testing forces, i.e. to prevent the specimen opening on extending.
1.4.2.4  Specimens of woven fabric
For fabrics liable to fray  during testing , cut specimens 25 mm wide than the required testing width and fray them by removing excess threads in approximately equal numbers from each of the longer edges of the cut strip until the width of the specimen is as specified in 1.4.2.2 or 1.4.2.3.
1.4.2.5  Specimens of weft knitted fabrics
Prevent the cut edges of weft knitted test specimens from laddering by a method which will neither restrict the extension and retraction of the fabric, nor alter its stress /strain characteristics to any significant extent.
NOTE: In some cases it is possible to use an expandable seam, or alternatively the cut edges could be sealed with a light application of latex adhesive followed ,when the latex is dry, by a dusting of talc to prevent sticking.
1.5  Conditioning and testing
1.5.1  Atmosphere
Conditioning and testing shall be carried out in the standard temperate atmosphere for testing textiles as defined in BS 1051, i.e. a temperature of 20±2℃ and relative humidity of 65±2%.
1.5.2  conditioning of samples      
condition the samples from which the test specimens are to be taken for a period of not less than 16 h in a free , unrestrained state in the standard temperate atmosphere for testing textiles.
In case of dispute, precondition the test specimens for 4 h at a relative humidity not exceeding 10%at a temperate not greater than 52℃. An oven at 52℃under ordinary room conditions will give the required low humidity, Then expose the test specimens to the standard temperate atmosphere for testing textiles for at least 24 h before test in. and without removal from，this atmosphere.
1.6  Properties to be test in accordance with existing British Standards
A number of properties of elastic fabrics can be tested in accordance with other appropriate British Standards which include the follow.
BS 1006: E03 at an active chlorine concentration of 100 mg/L for determination of calourfastness to swimming-bath water.
BS 1930: for determination of width of woven or knitted fabrics when relaxed at zero tension.
BS 2471: for determination of mass per unit length and mass per unit area.
BS 2862: for determination of number of threads per unit length.
BS 4323: for determination of dimensional change of fabrics induced by free steam.
BS 5441: for determination of wales and courses per unit length in knitted fabrics.
BS 5807: for determination of dimensional change on domestic laundering.
Section 2. Test methods      
2.1  Determination of extension at a specified force
2.1.1  Apparatus
Use apparatus as described in 1.3.2 and 1.3.3
2.1.2  procedure
2.1.2.1   straight specimens
Set the clamps of the tensile testing machine to 100 mm apart. Clamp test specimen centrally in the stationary clamp so that its longitudinal axis passes through the center points of the front of the edges of the jaws.
Either:
  (a) apply a pre-tension of 2 N; or
  (b) slack-mount the specimen, with any extension that occurs prior to the force reaching the pre-tension level(as indicate on an autographic recording)being considered as part of the slack,ultimately to be added to the gauge length .
clamp the free end of the test specimen in the second clamp.
Set the rate gauge such that the circumference of the specimen to 500mm/min. Cycle the specimen twice between zero extension and the specified force. Record, from the force versus extension graph produced, the elongation at the specified force on the second cycle.
2.1.2.2  Looped specimens
Set the gauge length such that the circumference around the loop bars is 200 mm.
Slide the loop bars open in order to position the looped specimen ,after which , close The bars.
Adjust the position of the specimen around the bars so that the seam lies midway between the bars.
Set the rate of extension and retraction of the specimen to 500 mm/min. Cycle the specimen twice between zero extension and the specified force. Record, from the force versus extension graph produced, the elongation at the specified force on the second cycle.
2.1.3  Test report  
The follow shall be reported:
(a)        specified force used;
(b)        percentage elongation for each specimen and their arithmetic mean
(c)        direction of test of the fabric, i. e. either machine direction or cross direction;
(d)        specimen type, i. e. whether straight or looped.
(e)        specimen width.
2.2  Determination of modulus
2.2.1  Apparatus
Use apparatus as described in 1.3.2 and 1.3.3
2.2.2  procedure
Read from the force versus extension curves as described in 2.1, the force on the extension and/or recovery curves on the second cycle, at intervals of elongation as arranged between the interested parties.
2.2.3  Test report  
The follow shall be reported:
  (a) modulus, i. e. force (in N) at each value of elongation where reading have been taken, the value of each elongation at which modulus reading has been taken and whether these were from the extension or retraction portion of the  cycle, and their arithmetic mean;
(b) direction of test of the fabric, i. e. either machine direction or cross direction;
(c) specimen type, i. e. whether straight or looped.
(d) specimen width

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2.3  Determination of tension decay
2.3.1  Principle
The test specimen is stretched to a specified elongation and the tension recorded. The elongation is maintained for 5 min during which the decay of tension over this period is determined
2.3.2  Apparatus
Use Apparatus described in 1.3.2 and 1.3.3.2
2.3.3  Test specimens
straight specimens as described in 1.4.2.2shall be used.
2.3.4  procedure
The rate of extension and retraction shall be 500 mm/min. Set the separation of the clamps to give a specimen gauge length L1 of 100 mm. Mount the test specimen in such a way that it is straight and untensioned. Set the cycling controls to cycle between zero extension and a force either 5.0N/cm or 10.0N/cm as agreed between interested parties. After cycling twice to this force, and without a pause , extend the specimen at the specified rate, to the specified elongation and record the maximum force. Maintain the specimen at this elongation for 5 min after which time again record the force.
The tension decay, expressed as a percentage of the maximum force, is calculate from the equation:
  Tension decay =100(F0-Ft)F0
Where
  F0  is the maximum force (in N) at the specified elongation; and
Ft    is the force(in N) after 5 min.
2.3.5  Test report   
the follow shall be reported:
(a)    cycling force
(b)    specified elongation to which the specimens have been subjected and the resulting (maximum) in the specimen;
(c)    percentage elongation for each specimen and their arithmetic mean
(d)    direction of test of the fabric, i. e. either machine direction or cross direction
(e)    specimen width
2.4  Determination of residual extension
2.4.1  Apparatus
Use apparatus as described in 1.3.2 and 1.3.3
2.4.2  Test specimens
straight specimens as described in 1.4.2.2shall be used.
2.4.3  Procedure
Carry out the test as described in 2.1, except on the second cycle maintain the specified force for 10±2s. Return the clamps to their original position such that the force is gradually reduced to zero within a period of 7.5±2.5 s.
Remove the specimen from the clamps, immediately place it on a flat, smooth surface and, after a period of 1±0.1 min from the time when the clamps were returned to their original position, measure the distance between the outside edges of the gauge marks(L2) .
If the determination of residual extension after a longer period of relaxation is required, the distance between the gauge marks shall be measured after total relaxation time of 30±1 min(L3).
L2and L3shall be measured to the nearest 1 mm.
NOTE: when tests are made at right angles to the wale direction of weft knitted fabrics, the results are invalid if laddering occurs. When elastomeric threads are laid-in , precautions should be taken to prevent slippage of these threads through the fabric.
2.4.4  calculate and expression of results
2.4.4.1  calculate the arithmetic mean values of L2 and of L3 in each direction separately for the five specimens. These are denoted by L2ˉand L3ˉ respectively.
2.4.4.2  Calculate the mean residual extension, expressed as a percentage, after 1 min (R1) for the fabric in each direction from the equation:
  R1=100(L2ˉ-L1)/L1  
Where L1 is the initial gauge length (in mm)
2.4.4.3  If required, calculate the mean residual extension, expressed as a percentage, after 30 min (R30) for the fabric in each direction from the equation:
  R30=100(L3ˉ-L1)/ L1   
2.4.4.4  The mean values of R1 and R30 shall be quoted to the nearest 1%.
2.4.4.5  Calculate the arithmetic mean of the maximum values of the force applied in each direction separately for the five specimens.
2.4.5  test report
(a)    mean value of the maximum force applied  
(b)    value of the mean extension of the fabric in each direction .
(c)    value of the mean residual extension of the fabric in each direction after 1 min relaxation.
(d)    If required, value of the mean residual extension after 1 min relaxation.
(e)    Direction of test of the fabric, i. e. either machine direction or cross direction  
(f)    specimen width
2.5  Method for fatiguing specimens
2.5.1  Principle
This method is designed to standardize the procedure for fatiguing specimens of elastic fabric. Specimen are subjected to an agreed number of cycles of elongation and retraction, so that appropriate properties can be and compared with the corresponding properties of the unfatigued specimens. For certain properties, e. g. elongation and modulus ，appropriate gauge marks shall be made on the specimens to be fatigued and these same marks used in subsequent testing, irrespective of any change in length during the fatigue procedure.
2.5.2  Apparatus
2.5.2.1  fatiguing apparatus, consisting of one or more pairs of clamps,
for moving one clamp (reciprocating clamp) at a rate of 60±1 cycles per minute with means for recording the number of cycles.
Each pair of clamps shall be set so that the specimens are alternately stretched and relaxed. The movement of the reciprocating clamp shall be adjustable between 50 mm and 250 mm. The position of the stationary clamp shall be adjustable to give an effective length to be fatigued of 125 mm, irrespective of amplitude of reciprocation.
2.5.3  Test specimens
straight specimens as described in 1.4.2.2 shall be used except that specimens shall be cut parallel to the general direction of the elastomeric threads and that the length shall be such that the effective length to be fatigued is 125 mm. Make gauge marks centrally 100 mm apart on each specimens
The number of specimens to be subjected to the fatigue test shall be appropriate to the tests subsequently intended to be applied.
2.5.4  Procedure  
Adjust the reciprocating clamp to give a fatigue-cycle elongation equal to 80% of the mean elongation as determined by using the procedure described in 2.1. Adjust the stationary clamp to give a length between the clamps of 125 mm. Mount each specimen so that it is at zero tension not slack in the clamps. Fatiguing each specimen at the specified rate. The number of fatiguing cycles shall be agreed between the interested parties.
NOTE. It is recommended that the number of fatiguing cycles be in multiples of 5000.
Remove the specimens from the apparatus and allow them to relax for 30±1 min before remeasuring the relevant properties as required after fatiguing.
2.5.5  Test report
In addition to reporting the results of the relevant tests on fatigued specimens, the number of fatiguing cycles used and the fatigue cycling elongation shall be stated.
2.6  Determination of fatigue set
2.6.1  Apparatus
Use apparatus as described in 1.3.1 and 2.5.2.
2.6.2  Test specimens
Prepare the test specimens as described in 2.5.3.
2.6.3  Procedure
Mount each test specimen with the gauge marks positioned centrally between the clamps. Subject each specimen to the fatiguing procedure described in 2.5.4 for the agreed number of cycles, after which remove the specimen from the clamps and lie it on a smooth flat surface. Allow it to relax for 30±1 min. Measure the distance between the gauge marks to the nearest millimeter. Calculate the percentage increase in length to the nearest 1%.
2.6.4  Test report            
The following shall be report
(a)    number of fatiguing cycles ;
(b)    number of specimens tested;
(c)    fatigue extension;
(d)    fatigue set as the mean percentage increase in length;
(e)    specimen width where less
2.7  Determination of elastomeric thread breaks
2.7.1  apparatus
Use apparatus as described in 2.5.2.
2.7.2  Test specimens
Prepare the test specimens as described in 2.5.3.
2.7.3  procedure
Subject each specimens to the fatiguing procedure described in 2.5.4 for the agreed number of cycles. Remove the  specimen from the clamps and count the number of elastomeric thread breaks if any, within the area of fabric between the gauge marks.
2.7.4  Test report
The following shall be reported
(a)    number of breaks for each individual specimen;
(b)    number of fatiguing cycles;
(c)    specimen width where less than 50 mm.
2.8  Determination of runback
2.8.1  Apparatus
Use apparatus as described in 2.5.2.
2.8.2  Test specimens
Prepare the test specimens as described in 2.5.3.At a position midway between the gauge marks, entirely cut through three elastomeric threads.
With certain fabrics it could be necessary to cut the associated covering and/or structural threads also. This is permissible provided that the cutting through of these threads dose not result in laddering or fraying. The three elastomeric threads shall be uniformly spaced across the fabric at intervals of 12.5 mm.
NOTE: For fabrics less than 50 mm in width, the number of elastomeric threads to be cut througth in any one specimens will depend on the width of fabrics and the total number of elastomeric threads it contains. Not more than approximately 10% of the  elastomeric threads should be cut through.
2.8.3  Procedure
Mount each specimen with the gauge marks centrally between the clamps. Subject each specimen to the fatiguing procedure described in 2.5.4 for 5000 cycles. Remove the specimens from the clamps and lay them on a smooth flat surface. Allow them to relax for 30 min. Measure the distance between the two cut ends of each elastomeric thread to the nearest millimeter. This is the runback distance.
2.8.4  Test report
The following shall be reported:
(a)    mean runback distance in millimeters;
(b)    number of threads cut;
(c)    number of specimens tested;
(d)    specimen width where less than 50 mm.
2.9  Method for ageing specimens
2.9.1  principle
This ageing procedure is designed to accelerate the oxidative deterioration of elastic fabrics which occurs with the passage of time. Specimens are aged by a prescribed heating treatment in air and are afterwards submitted to any of the preceding tests to determine the effect on their properties.
NOTE. Accelerated ageing tests do not truly reproduce under all circumstances the changes produced by natural ageing.
2.9.2  Apparatus
2.9.2.1  Ventilated oven, in which there is slow circulation of air, providing not less than three, nor more than 10, air changes per hour.
The incoming air shall be within ±2℃ of the temperature specified before coming into contact with the test specimens. No copper or copper alloy shall be within the ageing chamber of the oven. The total volume of the test specimens shall not exceed 10% of the free air space of the oven. Means shall be provided for suspending the test specimens within the oven such that they are not within 10 mm of each other nor within 50 mm of the inner surfaces of the oven. Means shall be provided for maintaining an atmosphere within the oven at a temperature of 70±1℃. Any direct heat and/or light radiation on to the test specimens shall be avoided. Means shall be provided for the introduction of temperature-measuring instruments, at a suitable point, for measuring the operating conditions.
2.9.3  Test specimens
2.9.3.1  Dimensions
The dimensions of the test specimens shall be chosen so that they are suitable for any subsequent tests to be conducted.
2.9.3.2  Quantity
The number of test specimens selected shall be as required by the particular physical test intended to be carried out after the ageing procedure.
NOTE. It is recommended that in any event the number of test specimens chosen for post ageing comparisons should be not less than five.
2.9.4  Procedure
Preheat the oven to the operating temperature of 70±1℃. Suspend the test specimens in the ageing chamber, ensuring that the volume of the specimens dose not exceed 10% of the air space of the oven and that the air circulates freely on both sides of each specimen.
Allow the specimens to remain under these conditions for a period agreed between the interested
Parties.
NOTE 1. It is recommended that specimens be aged for 1,3,7 and 10 days and thereafter in multiples of 7 days from the start of the test.
NOTE 2.the test period used should be such that deterioration of the test specimens will not be so great as to prevent determination of the final values of the relevant physical property after ageing.
NOTE 3. The rate of change in physical characteristics of materials such as those considered in this British Standard has been found to approximately double with each 10℃ rise in temperature, e.g. 1 day at 70 ℃ is approximately equal to 32 days at 120 ℃.
After removing the test specimens from the oven, condition them as specified in 1.5 for not less than 16 h or more than 24 h.
2.9.5  Test report
In addition to reporting the results of the appropriate tests on aged specimens, the number of days for which the specimens have been aged shall be tested.