Friday, June 7, 2013

ASTM D5034 Fabric strength test method - Grab test

This is a tensile strength method,Which measure maximum strength of fabric & elongation of the fabric.This is a grab method, Which mean center part of specimen grip and apply load up to break & then measure maximum load & elongation at that point.

 This test method covers the grab and modified grab test procedures for determining the breaking strength and elongation of most textile fabrics.

 The grab test procedure is applicable to woven, non woven, and felted fabrics, while the modified grab test procedure is used primarily for woven fabrics

 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.

 This test method is not recommended for knitted fabrics because of their high stretch.
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.
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.
 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.

The modified grab test procedure is applicable to the determination of the breaking force of fabrics with constructions in which the application of tensile stress on raveled strip specimens produces further unraveling. This test method is particularly applicable to high-strength fabrics.

 This test method is not recommended for glass fabrics, or for knitted fabrics and other textile fabrics which have high stretch (more than 11 %).

Ultimate tensile strength (UTS), often shortened to tensile strength (TS) or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract. Tensile strength is the opposite of compressive strength and the values can be quite different.
The UTS is usually found by performing a tensile test and recording the stress versus strain; the highest point of the stress-strain curve is the UTS. It is an intensive property; therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material.
Tensile strengths are rarely used in the design of ductile members, but they are important in brittle members. They are tabulated for common materials such as alloys, composite materials, ceramics, plastics, and wood.
Tensile strength is defined as a stress, which is measured as force per unit area. For some non-homogeneous materials (or for assembled components) it can be reported just as a force or as a force per unit width. In the SI system, the unit is pascal (Pa) or, equivalently, newtons per square metre (N/m²). The customary unit is pounds-force per square inch (lbf/in² or psi), or kilo-pounds per square inch (ksi), which is equal to 1000 psi; kilo-pounds per square inch are commonly used for convenience when measuring tensile strengths

Tensile properties indicate how the material will react to forces being applied in tension. A tensile test is a fundamental mechanical test where a carefully prepared specimen is loaded in a very controlled manner while measuring the applied load and the elongation of the specimen over some distance. Tensile tests are used to determine the modulus of elasticity, elastic limit, elongation, proportional limit, reduction in area, tensile strength, yield point, yield strength and other tensile properties.

No comments:

Post a Comment