The torsional response of a composite laminate of rectangular cross-section was analyzed by the Mindlin-Reissner theory. The analysis takes into account separately the shear properties of each layer. A general closed-form relationship was derived between torque and angle of twist in terms of the geometric parameters and shear properties of the laminae. In the case of unidirectional laminates, relations can be expressed involving the three principal shear moduli, G12, G13, and G23. An experimental method was also developed for determining these moduli by measuring surface and edge strains with strain gages. Results for a typical graphite/epoxy composite show the validity of the usual assumption of transverse isotropy.

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