The Fabric Extensometer measures the exact change in the length using tensile of knitted and woven testing material. Thus, it is useful for woven and warp-knitted fabrics. It can also be useful to test Lycra materials.
They are particularly applicable to stretch fabrics. Usually made using elastomeric fibres or bulked yarns, or by a process such as slack mercerisation.
The Fabric Extensometer determines the stretching capacity of a testing specimen. It does this with help of a specific weight load. The machine records the extension of the fabric. And finally, the tension can be removed. To check the results, observe the length of outstretched sample after recovery.
Testing Elastic Fabrics Procedure
The Testing Stnadard BS 4952: 1992 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 tests 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.
The central points of the two clamps shall 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. Specimens of woven fabric
- For fabrics liable to fray during testing, cut specimens 25 mm wider than the required testing width and fray them down 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.
2. 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.
Terms related to testing elastic textiles
- Elastic fabrics: fabrics, which incorporate elastomeric threads
- 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
- Modulus: the tensile force in the test specimen required to produce a specified elongation
The following shall be reported:
a) modulus, i.e. force (in N) at each value of elongation where readings 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, whether straight or looped;
d) specimen width.