Volume 35, Issue 3 (May 2007)
Short-Beam-Shear Testing of Composite Rings With Variable Cross Section as Representative for Full-scale Delamination
Carbon fiber reinforced/epoxy (CFR-E) rings are used as radial reinforcement for polymer bearing elements with diameter 249 mm, functioning under 150-MPa contact pressure. Full-scale loading revealed shear failure caused by a critical radial-axial shear stress. This stress, acting in a section of the CFR-E ring under nonhydrostatic conditions, should be representatively simulated on small-scale short-beam-shear tests. Finite element analysis will be used for verification of a small-scale stress failure criterion. A standard sample geometry could not be applied as the reinforcing ring contains machined edges leading to stress concentrations. A nonhydrostatic stress condition similar to full-scale tests should be simulated in the center of the small-scale beam. Therefore, the effects of various loading conditions and testing parameters such as cross-sectional geometry, beam support and span, beam curvature, and convex/concave loading are investigated. It is concluded that curved beams are preferred over flat geometries and convex loading is preferred above concave loading since it induces a nonhydrostatic stress situation identical to full-scale tests. During small-scale testing of nonrectangular ring sections, an asymmetric stress distribution near the machined edge is representatively simulated. Experimental short-beam-shear tests confirm the influence of the test geometry and a 27-kN equivalent normal load is required for avoiding fulls-cale fracture.