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a b s t r a c tThe Saint-Venant torsional problem for homogeneous, monoclinic piezoelectric beams is formulated in terms of Prandtl's stress function and electric displacement potential function. The analytical approach presented in this paper generalizes the known formulation of Prandtl's solution which refers to homogeneous elastic beams. The Prandtl's stress function and electric displacement potential function satisfy the so called coupled Dirichlet problem (CDP) in the cross-sectional domain. A direct and a variational formulation are developed. Exact analytical solutions for solid elliptical cross-section and hollow circular cross-section and an approximate solution based on a variational formulation for thin-walled closed cross-section are presented.

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The paper examines the pure bending of a linearly elastic, isotropic, nonhomogeneous bar. The bending stress, elastic strain energy and the end cross-section rotations are determined for in-plane variation of the Young's modulus with small strains and displacements. It is shown that the governing formulae for elastic pure bending of nonhomogeneous bars have same forms as formulae for symmetrical bending (bending in the principal planes) of homogeneous bars. Two examples illustrate the application of the developed formulae. In the first, a composite beam is considered; the second deals with the determination of the maximum tensile and compressive stresses in a bent functionally graded elastic bar.

a b s t r a c tThe objective of the present paper is to analyse the static behaviour of elastic two-layer beams with interlayer slip. The Euler-Bernoulli hypothesis is assumed to hold for each layer separately, and a linear constitutive equation between the horizontal slip and the interlaminar shear force is considered. The applied loads act in the plane of symmetry of the composite beam, and the material and geometrical properties do not depend on the axial coordinate. Closed-form solutions for displacements and interlayer slips are developed. A second order differential equation is derived for the interlayer slip whose solution is used to determine the deflections and slopes. Examples illustrate the application of the method presented.