tp52
1. Preface:This method is derived from BS 4294 : 1968. It differs in respect to the load applied, number of specimens required and only residual extension after 1 minute is determined.
2. Scope:
This method is used to determine the performance of knitted fabrics. It indicates the ability for a knitted fabric to extend and then return after being mechanically stretched.
This method is applicable for knitted active wear, swimwear, underwear and corsetry fabrics as prescribed in TQM 41
3. Principles:
Applying a specified load stretches a specimen of standard dimensions.
The extension is recorded, the tension removed and resultant residual extension recorded
4. Apparatus:
4.1. Conditioning Facility:
Means of providing and maintaining the standard atmosphere in accordance with AS 2001.1 (Temperature 20 2 C and Relative Humidity 65 3%)
4.2. Stretching Equipment:
The test should be performed using a microprocessor controlled Constant Rate of Extension Tensile Tester.
This must be equipped with two clamps, each consisting of a pair of straight jaws not less than 75mm wide, capable of holding the test specimen uniformly across its width, without slippage.
The jaws shall be co-planar throughout testing.
It shall be possible to measure or record the distance between the inner edges of the two clamps with an error not exceeding 1mm.
It shall be possible to apply load of 60 0.5N to the specimen evenly and gently.
5. Test Specimen:
5.1. Dimensions
The width of the specimen shall be 75 1mm.
The length of the specimen shall be sufficient to allow a distance of 75mm between the inner edges of the clamps when the specimen has been inserted. This length is generally 175mm
5.2. Number of Specimens
A minimum of two specimens with their lengths parallel to the warp direction and two specimens with their lengths parallel to the weft direction.
5.3. Preparation of specimen :
Select specimens that are as representative as possible of the fabric under test. The specimens should exclude fabric from within 100mm of the selvedges.
In no case shall specimens parallel to the selvedge contain selvedge ends.
Place a pair of alignment marks on each specimen 75mm apart and equidistant from the ends.
6. Procedures:
6.1. Conditioning Fabrics
Fabrics shall be conditioned for a minimum of 4 hours prior to testing in a standard atmosphere
6.2. Test Speed
100mm/min
6.3. Load Conditions
Knit fabrics with elastane content 60 0.5N
6.4. Clamps
6.4.1. Ensure clamps are aligned and parallel.
6.4.2. Set clamps with their edges 75 1mm apart (L1)
6.4.3. Secure the specimen in the clamps (flat and unstrained) with the alignment marks level with the clamp edges.
6.4.4. Stretch the fabric with a cross head speed of 100mm/min until the load on the specimen is 60 0.5N or an extension of 300mm is obtained.
Maintain this extension for 10 2 seconds.
Record the cross head movement (the length of the specimen between the clamp faces). (L2)
Note: Most microprocessor controlled tensile testing machines can calculate % strain (extension %). If this function is available then record maximum %strain at 60N.
6.4.5. Return the crosshead to the initial gauge length and remove the specimen from the clamps. Place the specimen on a flat, smooth surface and measure the residual extension (distance between reference marks (L3).) after one minute.
7. Calculation and Expression of Results:
7.1. Calculate mean values from the three results L2 andL3 in each direction.
7.2. Calculate the mean extension percent (E) for the fabric in each direction from the following equation or record the maximum strain %.
E = 100 ( L2-L1)
L1
7.3. Calculate the mean residual extension percent after 1 minute (R1) for the fabric in each direction from the equation below:
R1 = 100 (L3-L1)
L1
8. Test Reports:
Record the extension results for both the warp and the weft (E) in Stretch Test TP52.If 300mm extension is reached before the prescribed load is reached then record load at 300mm extension.
Record the residual extension results for both the warp and the weft (R1)in the Recovery Test TP53.
9. Precision:
The mean value of E and R1 shall be quoted to the nearest 1%
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