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Uncertain eigenvalue problem of linear vibration is analyzed by means of the stochastic finite element method, the basis of which utilizes mean-centered second order perturbation technique. Attention is paid to the fluctuation of the stacking sequence, that is, fiber orientation and layer thickness of FRP laminated plates. The stacking sequence is expressed in terms of probabilistic variables. The eigenvalue problem is formulated based on the Kirchhoff-Love’s theory of thin plate, the stretching, coupled and bending stiffnesses of which are uncertain due to the stacking sequence. The numerical analyses deal with the vibration of simply-supported graphite/epoxy plates. The sensitivity of the input stacking sequence and the correlation coefficients of the probabilistic variables are evaluated quantitatively.

SUMMARYAn application of the finite element method to inelastic analysis of the Saint-Venant torsion problem, using a triangular element formulated on the basis of the hybrid stress approach, is described. The stress field in the element is defined by a stress function which is assumed to vary linearly within the element. The warping function on the element boundary is also dehed by a linear expression. Numerical results indicate that the method gives an accurate stress solution and is appropriate to the elastic-plastic analysis of bars of arbitrary cross-section which may include multiply connected regions. It is further shown that such phenomena as planar orthogonal plastic anisotropy, strain-hardening and unloading of relevant twisted bar can be treated in a unified manner.