Shear Moduli of Structural Composites from Torsion Tests JULIO F. DAVALOS Department of Civil and Environmental Engineering West Virginia University Morgantown, WV 26506-6103, USA PIZHONG QIAO* AND JIALAI WANG Department of Civil Engineering The University of Akron Akron, OH 44325-3905, USA HANI A. SALIM Department of Civil Engineering University of Missouri Columbia, MO 65211-2200, USA JEREMY SCHLUSSEL Department of Civil and Environmental Engineering West Virginia University Morgantown, WV 26506-6103, USA (Received August 10, 2000) (Revised November 9, 2000) ABSTRACT: A combined experimental/analytical approach for effective evaluation of in-plane and out-of-plane shear moduli of structural composite laminates from torsion is presented. The test samples are produced by pultrusion and consist of E-glass fiber systems and vinylester resin. Three types of rectangular samples are used: unidirectional samples cut from plates; angle-ply and angle/cross ply samples cut from wide-flange beams. The shear moduli are obtained from the experimental torsional stiffnesses (T/0) and data reduction techniques based on torsion solutions by Lekhnitskii and Whitney. The classical approach of using paired samples of different widths but same material orientation can grossly underestimate out-of- plane shear moduli. Thus, to overcome this problem, samples with material orientations normal to each other are used, and to obtain samples of larger dimensions than the available thicknesses of the material, the pultruded laminates are bonded flat-wise, from which transverse strips of different widths are cut. Consistent results are obtained by the two data reduction techniques, and the experimental values are compared to predictions by micro/macro-mechanics models. *Author to whom correspondence should be addressed. E-mail: Qiao@uakron.edu Journal of COMPOSITE MATERIALS, Vol. 36, No. 10/2002 1151 0021-9983/02/10 1151–23 $10.00/0 DOI: 10.1106/002199802023486 ß 2002 Sage Publications