Beam shear

Compression/tension failure in the 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... 

Fig. 3.17. Effect of stress concentrations on short beam shear specimens (a) thin specimen (b) thick...

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... 

Fig. 3.19. Scanning electron microphotograph of buckling failure near the loading nose of a carbon fiber-epoxy matrix short beam shear specimen. After Whitney and Browning (1985).

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. 

Fig. 5.5. Normalized irKerfacial shear strength of unsized (bare) and sized E-glass fiber-epoxy matrix eomposites measured from the interfaeial testing system (ITS, equivalent to fiber push-out test), short beam shear (SBS) test, 0° flexural test and 90° flexural test. After Drown et al. (1991).

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 7. Normalized values for the interfacia] shear strength as measured by the ITS plotted against the short beam shear strength (SBS), 0° flexure strength, and 90° flexure strength for the bare and Epoxy-sized fibers.

A beam is really two cantilever beams joined baek to baek (Figure 10.5a) and then turned upside down (Figure 10.5b). Thus, the largest eompressive stress oeeurs on the concave surfaee of the beam at the mid-span, while the largest tensile stress occurs on the convex surface at the mid-point. Although it is obvious that tensile and compressive forees are generated within a beam when it is bent, it may not be self-evident that shear forees also exist. In a loaded beam, shear stresses aet in both the horizontal and vertieal directions. 

Beam shear Over large OPDs, or in critical applications, imperfections in the wavefronts convolved with misalignment of test and reference beams can introduce errors proportional to the wavefront shear. 

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