Torsional shear test methods

In-Plane Shear Properties. The basic lamina in-plane shear stiffness and strength is characterized using a unidirectional hoop-wound (90°) 0.1 -m nominal internal diameter tube that is loaded in torsion. The test method has been standardized under the ASTM D5448 test method for in-plane shear properties of unidirectional fiber-resin composite cylinders. D5448 provides the specimen and hardware geometry necessary to conduct the test. The lamina in-plane shear curve is typically very nonlinear [51]. The test yields the lamina s in-plane shear strength, t12, in-plane shear strain at failure, y12, and in-plane chord shear modulus, G12. 

Damping can be determined using the half-power bandwidth method or from the logarithmic decrement by placing the sample in free vibration (ASTM 2007). This technique has been modified to allow cyclic torsional shear testing to strain levels above those typically achieved during a... 

ISO 11003-1 2001 Adhesives - Determination of shear behaviour of structural adhesives -Part 1 Torsion test method using butt-bonded hollow cylinders ISO 11003-2 2001 Adhesives - Determination of shear behaviour of structural adhesives -Part 2 Tensile test method using thick adherents ISO 13445 2003 Adhesives - Determination of shear strength of adhesive bonds between rigid substrates by the block-shear method... 

ISO 11003-1 2001 Adhesives - Determination of shear behaviour of structural adhesives -Part 1 Torsion test method using butt-bonded hollow cylinders... 

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

The same test method, although not standardized, can be used to characterize the laminate in-plane shear behavior. This is accomplished by winding a multiorientation (hoop/helical and/or helical only) tube. Other test methods that can be used to measure in-plane shear stiffhess/strength of filament wound composites are discussed by Tamopol skii and Kinds [45]. These methods include schemes for torsion of intact rings and split rings. Both of these ring test methods are used to evaluate the in-plane shear modulii G0r and G0z for a filament-wound laminate. 

Elastomers are cross-linked macromolecules above the glass transition temperature. The cross-link density is the fundamental engineering quantity which, for instance, determines the modulus of elasticity. Usually, it is measured during vulcanization of well-defined rubber samples in a vulcameter by the moment necessary to perform a given torsional shear of the test sample. Swelling experiments can be performed alternatively, but are problematic for filled elastomers. Such measurements are based on the assumption that the measured quantity does not vary over the sample volume. Inhomogeneous cross-link densities can be determined from the surface hardness, but volumetric resolution is achieved by conventional methods only after cutting the sample. 

A range of shear tests exists to satisfy all the requirements for in-plane and some throughthickness shear properties. Although torsion of tubes or rods is often recommended, it is rarely used in practice and has not been standardized. Equally, the rail shear test only appears as an ASTM guide [ASTM D 4255], It is not favored, since a large specimen is required and the test suffers from premature failure initiated at the bolt holes. Several other methods that have been standardized are discus.sed below. 

Two quantities can be measured to describe a material s resistance to crack propagation fracture toughness, IQ, and strain energy release rate, G. Different stress states can be applied, with the most common being the opening mode (Mode I). Materials can also be tested in inplane shear (Mode n) and in torsional shear (Mode III). Testing in these modes typically involves strain rates much lower than those associated with impact teste such as the Charpy and Izod methods. Other methods... 

Torsional Test n A test for determining shear properties of plastics, such as shear modulus, based on measuring the torques required to twist a specimen through a prescribed arc. See ASTM, www.astm.org, or standard test methods. 

E-0229. Test Method for Shear Strength and Shear Modulus of Structural Adhesives. This method employs torsional shear loading on a napkin ring specimen to determine the shear strength and shear modulus of structural adhesives in thin gluelines on high modulus adherends. 

There is a wide variety of shear tests. All the test methods described in this chapter do not show a systematic difference in the shear stress-strain curves. Torsion tests are the most accurate. However, torsion devices are not common in most laboratories. In case a torsion machine is not available, the TAST is probably the simplest and most reliable technique to use. 

Shear testing of polyethylene can follow one of two different regimes that measure different aspects of the material s properties. The shear strength of a sample is determined by punching a hole in it according to the procedure described in ASTM Method D 732. Shear modulus is determined from a test that applies torsion to a specimen, following a procedure described in ASTM Method D 1043. 

Of aU the test methods studied in this paper, the torsion test showed the highest apparent shear strength of 142.4 MPa. Torsion test has seen some development work recently and is deemed promising because of its true shear loading condition and its small specimen size. Less stress concentration near the joint is expected for torsion test compared to the other three tests... 

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