The imperfection sensitivity of cylindrical panels under compression loading is shown to be not only reduced but effectively eliminated using stiffness tailoring techniques. Shells are designed with variable angle-tow (VAT) laminae, giving their laminates variable-stiffness properties over the surface co-ordinates. By employing an asymptotic model of the non-linear shell behaviour and a genetic algorithm, the post-buckling stability was maximised with respect to the VAT design variables. Results for optimised straight-fibre and VAT shells are presented in comparison with quasi-isotropic designs. In the straight-fibre case, small improvements in the post-buckling stability are shown to be possible but at the expense of the buckling load. In the VAT case, on the other hand, considerable improvements in the post-buckling stability are obtained and drops in axial stiffness and load associated with buckling are reduced to negligible levels. The improvements are shown to be a result of a benign membrane stress distribution prior to buckling and a localisation of the buckling mode. The asymptotic results are compared with non-linear finite-element analyses and are found to be in good agreement. Potential future multi-objective optimisation studies are discussed.

In this paper, based on the viscoelastic theory, the creep buckling and post-buckling behaviors of a viscoelastic functionally graded material (FGM) cylindrical shell with initial deflection subjected to a uniform in-plane load are investigated. The material properties of the viscoelastic FGM cylindrical shell are assumed to vary through the structural thickness according to a power law distribution of the volume fraction of constituent materials and Poisson's ratio is assumed as a constant. Considering the transverse shear deformation and geometric nonlinearity, the constitutive relation of the viscoelastic FGM cylindrical shell is established. By means of the Newton-Newmark method and the Boltzmann superposition principle, the problem for the creep buckling and post-buckling of the FGM cylindrical shell is solved. The numerical results reveal that the transverse shear deformation, volume fraction and geometric parameters have significant effects on the creep buckling and post-buckling of the viscoelastic FGM cylindrical shell.

Dans certains procédés de mise en forme, tel que le laminage, l'apparition des contraintes résiduelles est inévitable et peut engendrer le flambage qui se traduit en défauts géométriques. Ceci exige la modélisation de ce phénomène d'instabilité mécanique afin de bien définir la forme et l'amplitude de ces défauts. Cela nécessite un modèle complet ayant des capacités pour le calcul du post-flambage. Dans le présent article, on présente un modèle de flambage possédant la faculté de détecter la charge critique de flambage et la forme post-flambée d'une plaque sous contraintes résiduelles. Des applications à des cas académiques et un cas de laminage seront aussi traités.

The work presented here concerns the design and manufacturing possibility of a polymodular autonomous microrobot moving like an earthworm. The study consists of the development of a new locomotion actuator based on shape memory alloys. This actuator is formed by a flexible frame forced in post-buckling by its assembly on a rigid skeleton cage. This mechanical structure, forming a knot in the microrobot chain, uses its two post-buckling equilibrium positions to achieve first the support and second the local lengthening enabling the movement of the microrobot. Initially, we present the technical solution designed for the locomotion actuator and the mechanical characterization of its malleable structure. Then, we present the instrumentation by educated SMA of a malleable structure and the capability of microrobot locomotion task in a vertical tube.