ID-1081 INTERLAMINAR SHEAR TEST FOR LAMINATED TEXTILE FABRIC COMPOSITES Kunigal Shivakumar, Adrian Pora and Felix Abali Center for Composite Materials Research North Carolina A&T State University Greensboro, NC 27411 Phone (336) 334-7411 Ext. 2112 and Email: kunigal@ncat.edu SUMMARY : Modified short beam shear (MSBS) test was used to measure interlaminar shear strength (ILSS) of nine different textile fabric composites. This includes carbon and glass fibers from unidirectional to 8-harness satin weaves and engineered layered fabrics with through-the-thickness interlocks. The resin system varied from brittle 5208 epoxy to marine grade vinyl ester, toughened SC-15 epoxy and carbon matrix. Test results from MSBS were very consistent with failure modes and small data scatter (standard deviation <3%) compared to standard and 4-point short beam shear tests. Therefore MSBS is simple and accurate test to measure ILSS of laminated composites. A detailed nonlinear finite element stress analysis of the test specimen with different composites having different transverse shear to flexural moduli showed that the beam theory shear stress equation requires a correction. The correction factor κ is 1 for isotropic and relatively high G xz /E x whereas it is 0.95 for shear flexible composites (G xz /E x >10) carbon/epoxy. KEYWORDS: Laminated Composites, Interlaminar Shear Strength, and Modified Short Beam Shear Test INTRODUCTION Interlaminar Shear Strength (ILSS) is an important material property for design of laminated composite structures subjected to transverse loads. American Society for Testing and Materials (ASTM) [1] proposes two test standards: short beam shear (D2344) and double - notched shear (D3846-99) to measure ILSS of laminated polymeric composites. The four- point short beam shear test (ASTM D790) was also used in the literature. Both standard short beam shear (SBS) and 4-point shear (4P-SBS) tests have limitations. A number of analytical and experimental studies [2-6] have been conducted to determine the validity of these tests. The analytical studies include classical anisotropic beam and laminate analyses [2,6], and linear and non-linear finite element analyses [3-5]. A review of these studies conclude that SBS test, at best, gives a qualitative value of ILSS, and many times failure was not interlaminar shear, instead by indentation and/or flexure. A major problem of this test is the indentation deformation and concentration of compressive and transverse shear stresses at the loading head. Furthermore, in textile fabric composites the waviness of fiber reduces the compression strength [7] and causes the compression failure on the loading side. The brittle matrix composites, like carbon/carbon composites are crushed under the loading head. Although, the 4P-SBS is a better test for ILSS measurements, loading heads restricts the specimen size. Thin specimens cannot be tested by the standard (1/4" dia.) loading heads. Smaller diameter loading heads will aggravate the indentation failure. Therefore, a larger diameter loading head [4] and tabbed (sandwich) specimen [8] are the alternate methods suggested in the literature. Recently, Abali et al. [9] suggested a modification to SBS test to alleviate the problems mentioned above. In this modified short beam shear test (MSBS), the central point loading is