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This document is developed in accordance with the rules given in GB/T 1.1-2020 Directives for standardization — Part 1: Rules for the structure and drafting of standardizing documents.
This document replaces FZ/T 7006-2004 Stretch and recovery testing method for knits. The following main technical changes have been made with respect to FZ/T 7006-2004:
——The definition of pre-tension has been added (see 3.5);
——The principles of constant rate of elongation method and delayed load stretching method have been added (see 4.1 and 4.2);
——The test speed requirements for the constant rate of elongation method have been modified (see 6.1.2 herein; and 5.1.2 of 2004 edition);
——The equipment requirements for delayed load stretching method have been added (see 6.2);
——The sampling requirements for delayed load stretching method have been added (see 7.5);
——The pre-tension of constant rate of elongation method has been modified (see 8.1.1.2 herein; 8.2.1, 8.2.2, 8.3.1 and 8.3.2 in 2004 edition);
——The determination method of the stretch and recovery rate of once tension under constant elongation of delayed load stretching method has been added has been added (see 8.3.2);
——The determination method of the stretch and recovery rate of once constant tension of delayed load stretching method has been added has been added (see 8.3.4).
This document was proposed by the China National Textile and Apparel Council.
This document is under the jurisdiction of National Technical Committee on Textiles of Standardization Administration of China (SAC/TC 209/SC 6).
The previous editions of this document are as follows:
——ZB W60 001 was issued for the first time in 1989.
——FZ/T 70006 was issued for the first time in1999, its first revision was issued in 2004, and this is the second revision.
Stretch and recovery testing method for knitted fabrics
1 Scope
This document specifies the test methods for the determination of tensile elastic deformation and plastic deformation of knitted fabrics by using tension under constant elongation and constant tension.
This document is applicable to all kinds of knitted fabrics, and others may be implemented by reference.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute indispensable provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T 6529 Textiles—Standard atmospheres for conditioning and testing
GB/T 8170 Rules of rounding off for numerical values & expression and judgement of limiting values
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
elasticity deformation
recoverable deformation of test piece after removing external, for knitted fabric, which is expressed by stretch and recovery rate
3.2
plastic deformation
deformation of test piece that cannot be recovered after removing the external force under the specified conditions and express in terms of plastic deformation rate
3.3
tension under constant elongation
corresponding force when the test piece is stretched to the specified elongation
3.4
elongation under constant tension
elongation of the test piece under the specified tensile force
3.5
pre-tension
force applied to the test piece to straighten it before stretching but without causing it to be elongated
4 Principle
4.1 Constant rate of elongation method: The test piece is stretched at a constant speed by using special instruments and equipment to deform its length, and the stretch and recovery rate and plastic deformation rate are calculated according to its deformation size after the release of the load.
4.2 Delayed load stretching method: Use special instruments and equipment to stretch the test piece, so that its length can be deformed and the deformation state may be maintained for a long time. After the release of the load, the stretch and recovery rate can be calculated according to its deformation size.
5 Standard atmosphere for conditioning and test
5.1 Standard atmosphere for conditioning and test shall meet the requirements of GB/T 6529.
5.2 After pre-conditioning, the sample should be placed in the atmosphere for conditioning to reach moisture equilibrium, and the conditioning of cotton and blended fabrics should be 24 h, and that of pure chemical fiber fabrics should be 4 h.
6 Instruments and tools
6.1 The testing instrument of constant rate of elongation method shall meet the following requirements (CRE tensile tester is adopted):
a) Clamp distance: 100 mm ± 1 mm;
b) The instrument shall be able to set the stretch speed within the range of 50 mm/min ~ 300 mm/min, with an accuracy of ± 2%;
c) The maximum error of strength indication value is not greater than 1%, and the maximum error of elongation indication value is not greater than 1%;
d) The instrument shall be able to set pre-tension;
e) The center point of the two clamps of the instrument shall be on the tension axis, the jaw line of the clamp shall be perpendicular to the tension line, and the clamping surface shall be on the same plane; the clamping surface shall be able to hold the sample without slipping, shearing or destroying the test piece, and the length of the clamping surface shall be at least 60 mm;
f) The instrument shall have a constant tension retention function.
6.2 The testing instruments for delayed load stretching method shall meet the following requirements:
a) Appropriate bracket: It is used to support the hanger assembly and the tension applied during the test, as shown in Figure 1;
b) Hanger assemblies: Including a hanger, a hanger rod and a hanger chain, as shown in Figure 2; the length of the hanger rod shall not be less than 125 mm, and there shall be no deformation and other changes affecting the results during the test;
c) Weight: It can be connected to the bottom of the hanger assembly and may apply the required tension on the test piece;
d) Screw buckle or equivalent tool: It can fix weight or hanger chain.
6.3 Timer: The timing unit is seconds.
6.4 Equipment for sewing the specified seams.
6.5 One pair of scissors and a steel ruler (accurate to 1 mm).
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Standard atmosphere for conditioning and test
6 Instruments and tools
7 Sample and test piece
8 Procedure
9 Test report
Annex A (Nominative) Example diagram of test piece cutting
Annex B (Informative) Tension under constant elongation, constant tension, repeated stretching times and relaxation residence time by constant rate of elongation method
