5.1 The grab test procedure in this test method for the determination of breaking force and elongation is considered satisfactory for acceptance testing of commercial shipments of most woven or nonwoven textile fabrics, and the modified grab test procedure is considered satisfactory for acceptance testing of commercial shipments of most woven textile fabrics, since the procedures have been used extensively in the trade for acceptance testing.
5.1.1 In case of disagreement arising from differences in reported test values when using this test method for acceptance testing of commercial shipments, the purchaser and the supplier should conduct comparative tests to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a minimum, the two parties should take a group of test specimens which are as homogeneous as possible and which are from a lot of material of the type in question. The test specimens should then be randomly assigned in equal numbers to each laboratory for testing. The average results from the two laboratories should be compared using Student's t-test for unpaired data and an acceptable probability level chosen by the two parties before testing is begun. If a bias is found, either its cause must be found and corrected, or the purchaser and the supplier must agree to interpret future test results in light of the known bias.
5.3 Some modification of technique may be necessary for any fabric having a strength in excess of 200-N/cm (1140-lb/in.) width. Special precautionary measures are provided for use when necessary for strong fabrics.
5.5 Comparison of results from tensile testing machines operating on different principles is not recommended. When different types of machines are used for comparison testing, constant-time-to-break at 20 ± 3 s is the established way of producing data. Even then the data may differ significantly.
5.6 Although a constant-rate-of-extension is preferred in these procedures, in cases of dispute, unless there is agreement to the contrary between the purchaser and the supplier, a constant-time-to-break (20 ± 3 s) is to be used.
5.7 The grab test procedure is applicable to the determination of the effective strength of the fabric; that is, the strength of the yarns in a specific width together with the fabric assistance from the adjacent yarns. The breaking force determined by the grab procedure is not a reflection of the strength of the yarns actually gripped between clamps and cannot be used for direct comparison with yarn strength determinations. Grab test specimens require much less time to prepare although they require more fabric per specimen. There is no simple relationship between grab tests and strip tests since the amount of fabric assistance depends on the type of fabric and construction variables.
5.8 The modified grab test procedure is ap......
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