Iosipescu Shear Properties of SMC Composite Materials

A shear test method introduced to ASTM in 1967 by Nicolae Iosipescu of Rumania for testing metals has been adapted by the University of Wyoming for testing many types of composite materials. These have included 3-D carbon-carbon, unidirectional glass/epoxy and graphite/epoxy, and five different types of sheet molding compounds (SMC). These SMC materials, all incorporating a polyester matrix, include random orientation chopped glass fiber composites (SMC-R25, SMC-R50, SMC-R65), unidirectional glass fiber plies combined with random, chopped fibers (SMC-C20/R30), and ±7½-deg angle-ply continuous glass fiber plies combined with random, chopped fibers (XMC-3). These various types of SMC materials are of particular interest in automotive applications at the present time. The Iosipescu test method and associated specimen configuration are briefly described, then detailed experimental results are presented for the five SMC materials described above, including both shear strength and stiffness data. It is demonstrated that the Iosipescu method is capable of testing composites in any one of the six shear loading modes. Short beam shear strengths for these same SMC materials were also determined, for comparison, demonstrating limitations of the short beam test for testing SMC materials, due to the predominance of bending rather than shear failure modes. Literature values of two-rail and three-rail shear tests of SMC materials are also compared with the Iosipescu shear data.