Standard Test Method for Stretch Properties of Knitted Fabrics Having Low Power
Fabric stretch and fabric growth are useful in selection of fabrics that are required to stretch, but also recover to their original shape.
5.1.1 In apparel, fabric stretch can be caused by a variety of factors. A momentary stress occurs when a fabric is required to accommodate movement, such as sportswear and other loose-fitting apparel (also known as comfort stretch apparel) or external stress such as grabbing and pulling. Additionally, comfort apparel can be subjected to prolonged stress, such as stretching to accommodate positions such as sitting. Another example of prolonged stress occurs when a fabric is required to stretch to accommodate fitting the form of the body, such as swimwear, anchored slacks, and other form-fitting apparel (also known as semi-support apparel).
5.1.2 Fabric growth can also be in response to a variety of stresses. This method evaluates fabric growth due to exposure to prolonged stresses. In form-fitting apparel, fabric growth can apply as garments are worn for a prolonged period of time or under long periods of stress such as sitting. Upon removal of garments or stress, its growth can be seen and evaluated.
5.2 This test method is not recommended for acceptance testing of commercial shipment because the between-laboratory precision is known to be poor.
5.2.1 If there are differences of practical significance between reported test results for two laboratories (or more), comparative tests should be performed to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, ensure the test samples to be used are as homogeneous as possible, are drawn from the material from which the disparate test results are obtained, and are assigned randomly in equal numbers to each laboratory for testing. The test results from the two laboratories should be compared using a statistical test for unpaired data, at a probability level chosen prior to the testing series. If a bias is found, either its cause must be found and corrected, or future test results for that material must be adjusted in consideration of the known bias.