Tear resistance test methods

This test was developed to determine the tear resistance of foam. The tear-resistance test, also known as the block method, uses the block specimen described in Figure 14-7. The block specimen is mounted by spreading the block so that each tab is held in the jaw of the tensile testing machine. The load is applied by separating the jaws at a specified speed. The force required to rupture the specimen is recorded. The tear resistance is calculated from the maximum load recorded and the average thickness of the specimen. The tear resistance is reported in newtons per meter. 

Tables 4—6 Ust ASTM methods used for the characterization of PB and PMP. A number of specialized methods were developed for testing particular articles manufactured from polyolefins several of these determine the performance of PB and PMP film, including the measurement of the film s dart impact strength and tear strength. Dart impact strength is measured by dropping a heavy dart with a round tip on a stretched film. Tear resistance, which reflects the film s resistance to tear propagation, is measured with the Ehnendorf tear tester. Two values for the tear strength are usually reported, one in the machine dkection of the film and the other in the transverse dkection. Pipes manufactured from PB are tested by pressurizing them internally with water the time-to-burst failure is determined at various temperatures (46). The standard test method for haze and luminous transmittance (ASTM D1003) is used for the measurement of PMP optical characteristics.

For both the tongue and Elmendorf test methods, it is important to observe the behavior of the specimen as the tear is propagated. In cases where the yams in the test direction are much stronger than the perpendicular yams, it is sometimes difficult or impossible to propagate the tear in the desired direction. In this case, a crosswise tear results. Tear resistance is primarily a function of fabric constmction. Loose, open weaves such as cheesecloth tend to resist tear, whereas tight weaves tend to tear easily. In the open weave, the concentrated force field at the point of tear is dissipated by the compliance of the fabric stmcture to accommodate the stress field, thereby distributing the force over a greater number of yams. 

Testing. Various test methods are provided by ASTM (16). These iaclude pigment tests of importance such as chemical analysis, presence of oversize particles, oil absorption, particle size distribution, degree of dispersion, presence of soluble components, etc. Numerous tests are also given by ASTM for the properties of filled and unfilled polymers. These iaclude, for example, such properties as impact resistance, stiffness, viscosity, tear resistance, hardness, color, and electrical resistivity. 

The trapezoid test method (ASTM Dll 17) is recommended for determining the tear resistance of nonwoven fabrics. An outline of a trapezoid is marked on a 7.5 x 15 — cm specimen, and the nonparallel sides are clamped in the jaws of the tensile-testing machine. The load is applied to the specimen in such a way that the tear propagates across the specimen width. The value of the breaking load is obtained from the load—elongation curve and is determined primarily by the bonding or interlocking of the fibers of the composite structure. 

ASTM D 624-86 Standard Test Method for Rubber Property — Tear Resistance, 5 pp (DOD Adopted) (FSC 9320) (MR) (Comm D-11)... 

Russian State Standard 14236-81. Polymer Films. Tensile Testing Method. ISO 6383-1 1983. Plastics - Film and Sheeting - Determination of Tear Resistance - Part 1 Trouser Tear Method. 

ASTMD 1922-03. Standard Test Method for Propagation Tear Resistance of Plastic Film and Thin Sheeting by Pendulum Method. 

FIGURE 3.72 Test for tear propagation resistance of plastic film and thin sheeting. Tear resistance (gf/cm/mil) = force required to tear sample (gf/cm)/thickness offilm (mil). Standard test methods ASTM D1922, BS 2782 method 308B. 

Propagation Tear Resistance of Plastic Film and Thin Sheeting by Pendulum Method, Elmendorf Tear. Primary Film Test Method ASTM D1922. Tear strength is the force necessary to eontinue tearing a sample after a nick has been made it is reported in grams. 

There are two European standards that spedly a method of testing cut resistance of a fabric against sharp objects. These are BS EN 388 2003 and BS EN ISO 13997 1997. - BS EN 388 2003 was developed specifically for gloves and it details the test methods for measuring abrasion resistance, blade cut resistance, tear resistance, and puncture resistance. BS EN ISO 13997 1997 was developed for any protective clothing and specifies the test method for the determination of resistance of a fabric to cutting by sharp objects. 

This test method, invented by Armin Eknendorf (47) is of value in ranking the relative tearing resistance of various plastic films and thin sheeting of comparable thickness (48,49). 

Standard test method for propagation tear resistance of plastic film and thin sheeting by pendulum method, ASTM Standard D1922-09, ASTM International, West Gonshohocken, PA, 2011. DOL10.1520/ D1922-09. 

D 1790 Test method for Brittleness Temperature of Plastic Film by Impact D 1938 Test method for Tear Propagation Resistance of Plastic Film and Thin Sheeting by a Single-Tear Method D 2240 Test Method for Rubber Property - Durometer Hardness D 2702 Standard Practice for Rubber Chemicals - Determination of Infrared Absorption Characteristics... 

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