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ASTM D 5733 Tear (Trapezoid Procedure)

Standard:

ASTM

Method:

ASTM D 5733

Title:

Tearing Strength of Nonwoven Fabrics by the Trapezoid Procedure

Scope

ASTM D 5733 covers the measurement of the tearing strength of nonwoven fabrics by the trapezoid procedure using a recording constant-rate-of-extension (CRE) tensile testing machine.

The CRE-type tensile testing machine has become the preferred test apparatus for determining trapezoid tearing strength. It is recognized that some constant-rate-of-traverse (CRT) tensile testing machines continue to be used. As a consequence, these test instruments may be used when agreed upon between the purchaser and the supplier.

This test method applies to most nonwoven fabrics including those that are treated or untreated, heavily sized, coated, or resin-treated. This test method may not be useful for highloft nonwoven fabrics.

Trapezoid tear strength as measured in this test method is the maximum tearing force required to continue or propagate a tear started previously in the specimen. The reported value is not directly related to the force required to initiate or start a tear.

The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses may be approximate.

Summary of Test Method

An outline of an isosceles trapezoid is marked on a rectangular specimen cut for the determination of tearing strength.  The specimen is slit at the center of the smallest base of the trapezoid to start the tear.  The nonparallel sides of the trapezoid marked on the specimen are clamped in the parallel jaws of a tensile testing machine.  The separation of the jaws is continuously increased to apply a force to propagate the tear across the specimen.  At the same time, the force developed is recorded.  The maximum force to continue the tear is calculated from autographic chart recorders, or microprocessor data collection systems.

Significance and Use

This test method is used in the trade for acceptance testing of commercial shipments of nonwoven fabrics, however, caution is advised since information about between-laboratory precision is incomplete.  Comparative tests may be advised.

The trapezoid tear method is a test that produces tension along a reasonably defined course such that the tear propagates across the width of the specimen. It is useful for estimating the relative tear resistance of different fabrics or different directions in the same fabric.

For nonwoven fabrics, because the individual fibers are more or less randomly oriented and capable of some reorientation in the direction of the applied force, the maximum trapezoid tearing strength is reached when the resistance to further reorientation is greater than the force required to rupture one or more fibers or the fiber interlocking, simultaneously.  The tearing strength is determined primarily by the bonding or interlocking of fibers in the structure.

 

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