Short beam shear test

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 short beam shear test designated in ASTM D 2344 (1989) involves loading a beam fabricated from unidirectional laminate composites in three-point bending as 

This test has an inherent problem associated with the stress concentration and the non-linear plastic deformation induced by the loading nose of small diameter. This is schematically illustrated in Fig 3.17, where the effects of stress concentration in a thin specimen are compared with those in a thick specimen. Both specimens have the same span-to-depth ratio (SDR). The stress state is much more complex than the pure shear stress state predicted by the simple beam theory (Berg et al., 1972  

Sandorf, 1980 Whitney, 1985 Whitney and Browning, 1985). According to the classical beam theory, the shear stress distribution along the thickness of the specimen is a parabolic function that is symmetrical about the neutral axis where it is at its maximum and decreases toward zero at the compressive and tensile faces. In reality, however, the stress field is dominated by the stress concentration near the loading nose, which completely destroys the parabolic shear distribution used to calculate the apparent ILSS, as illustrated in Fig 3.18. The stress concentration is even more pronounced with a smaller radius of the loading nose (Cui and Wisnom, 1992) and for non-linear materials displaying substantial plastic deformation, such as Kevlar fiber-epoxy matrix composites (Davidovitz et al., 1984 Fisher et al., 1986), which require an elasto-plastic analysis (Fisher and Marom, 1984) to interpret the experimental results properly. 

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Compression/tension failure in the short beam shear test. 

Fig. 3.18. (a) Shear stress eontours and (b) shear stress distributions aeross the thickness of a three-point bending specimen in a short beam shear test. After Cui and Wisnom (1992). Reproduced by permission of... 

Sattar. S.A. and Kellogg, D.H. (1969). The effect of geometry on the mode of failure of composites in short beam shear test. In Composite Materials Testing and Design. ASTM STP 460, ASTM, Philadelphia, PA, pp. 62-71. 

Whitney, J.M. and Browning, C.E. (1985). On short-beam shear tests for composite materials, Exper. Mech. 42, 294-300. 

The degree of bonding analysis has been verified for both compression molding and online consolidation of thermoplastic composites. In these studies, composite test specimens were consolidated under controlled processing conditions. The most common types of tests performed to measure the interply bond strength were the interlaminar (short beam) shear test [21,25] or the lap shear test [12,21,26]. 

Two types of composite physical property tests were conducted to measure properties which are sensitive to the degree of adhesion and failure mode of the fiber-matrix interphase. Short beam shear tests (ASTM D2344-84) were conducted on 18 ply unidirectional laminates. The support span-to-thickness ratio... 

FIGURE 8. Short beam shear test to determine the yield shear strength (Tei of WHIPOX CMC (a) and cyclic fatigue test showing degradation if the toad exceeds (Tei (b). 

Figure 17.43 Short beam shear test showing test configuration. Source Reprinted from Course on Mechanicai Testing of Advanced Fibre Composites, University of London, imperiai Coiiege, Sep 1995.

Interlaminar shear strength (ILSS) depends primarily on the matrix properties and fiber-matrix interfacial adhesion rather than on the fiber properties [141]. The ILSS, measured by the short-beam shear test, can be enhanced by increasing the tensile strength and volume fraction of the matrix as well as by increasing the interfacial adhesion in the laminates. 

Table 10 summarizes the Inter Laminar Shear Strength obtained from Short Beam Shear tests on [0°]24 specimens and in Table 11 the moduli Eu and the strengths or found from tension tests on [0°] specimens are shown. 

Table 10 - Short Beam Shear Test Results Inter Laminar Shear Strengths...

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