Shear tearing test

With this test, it is possible to assess the quality of bonding. It can only be performed if a section of the composite material can be pulled in its own plane close to an edge lifted from the substrate. 

The apphcation passes the test if at least 80 % of the tests report a peak shear strain value no lower than a 24 kN. 

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The mechanical properties of a material describe how it responds to the application of either a force or a load. When this is compared to an area, it is called stress, another term for pressure. Three types of mechanical stress can affect a material tension (pulling), compression (pushing), and shear (tearing). Figure 15.27 shows the direction of the forces for these stresses. The mechanical tests consider each of these forces individually or in some combination. For example, tensile, compression, and shear tests only measure those individual forces. Flexural, impact, and hardness tests involve two or more forces simultaneously. 

There are three main configurations for the tear test. In the first two a tensile force is applied to the sample. In one configuration, the force is vertical to the plane of the sample, and in the second it is at right angles. In the third style, an element of shear is also introduced. Figure 9.3 shows the basic configuration of the tear test pieces. 

API Appendix SR 6 requires 40% minimum shear in a dropweight tear test on 50% of the heats for 20 in. (508 mm) diameter API X52 or stronger pipe ... 

Canadian Standards Association Z184 requires 50 to 75% shear average, 35% minimum in a dropweight tear test. 

Dr op weight tear testing on a 20 In. (50 a mm) dimeter and larger pipe shall be carried out at 32 F (oaC) in accordance with Appendix SR-6 of API 5L however, igg percent Of the heats shall exhibit 85 percent or more shear fracture area. 

Figure 5.2 DUferent types of tear test-pieee geometry (a) trouser, (b) pure shear, (c) angle and (d) split tear test-pieces.

In shear measurements, bimodal PDMS networks showed large upturns in the pure-shear modulus at high strains, similar to those reported for elongation and biaxial extension. Tear tests were carried out on bimodal PDMS elastomers, using the standard trouser-leg method. Tear... 

Using trouser tear tests, Gent and Tobias [21] showed that the Lake-Thomas model held reasonably well for a number of elastomers. In their analysis, they took the molecular mass of a strand as that extracted from the elastic modulus and thereby incorporated the effect of entanglements (Section 9.8.2). More recent results on poly(dimethyl siloxane) (PDMS) elastomers using simple shear tests [22,23] over a wide range of structure (extent of cross-links and trapped entanglements) indicate that the role of entanglements in elastomer fracture needs to be elucidated further. 

The specimens after tear test are shown in Figure 6. Various shear fractures were observed and they were categorized as follows ... 

TDI isomers, 210 Tear strength tests, 242-243 TEDA. See Triethylene diamine (TEDA) Telechelic oligomers, 456, 457 copolymerization of, 453-454 Telechelics, from polybutadiene, 456-459 TEM technique, 163-164 Temperature, polyamide shear modulus and, 138. See also /3-transition temperature (7)>) Brill temperature Deblocking temperatures //-transition temperature (Ty) Glass transition temperature (7) ) Heat deflection temperature (HDT) Heat distortion temperature (HDT) High-temperature entries Low-temperature entries Melting temperature (Fm) Modulu s - temperature relationship Thermal entries Tensile strength, 3, 242 TEOS. See Tetraethoxysilane (TEOS)... 

Tear strength is only applicable to flexible materials and is very little used to monitor ageing simply because tensile strength will serve perfectly well. There are circumstances where compression stress-strain properties would be relevant but the relatively bulky test pieces will be subject to the limitation of oxygen diffusion in any accelerated tests and changes can probably be estimated from tensile measurements. Similarly, shear stress-strain is very rarely used for monitoring ageing. 

Tests such as the tensile strength and tear strength tests evaluate polyurethanes to destruction. When polyurethanes are used in a practical situation, the aim is for them to have as long a life as needed in the application. Stress, strain, and shear are applied to the polyurethane at various frequencies and at different temperatures. There may also be dynamic variations on top of a static load, for example, vibrations on a loaded isolation pad. 

Pullout test is also a method, providing useful information about fabric tearing, its ability to absorb energy especially in ballistic applications, lllnishing efCbiency, bending, and shearing hysteresis of the fabric and Qially the frictional behavior of the fabric. 

The one limitation at this medial malleolus site of high shear pressure is an occasional (one in four of the test cases, DP-7T) splitting or tearing of the disk, with early signs for ulcer for-... 

Although lap-shear evaluations are more familiar, they do not necessarily evalnate the strength of adherent/adhesive interfaces. Cohesive failnre of the weaker component of an assembly can be a complicating factor, tearing of the PU layer being a possibility in certain of the present measurements. In principle, the detachment of the adhesive in the blister test is a pure interfacial event and one that can be quantified provided parameters... 

Table 13 gives an example which might be considered as a permanent label adhesive. The substrate in this example is Lusterkote label stock. The paper tear observed during the 180 peel test is an indication of the permanency one could expect from the formulation. The shear adhesion of this formulation is not extremely high, but it is as high as some commercial labels we have tested in the lab. 

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