Creep Stability of Thin-Walled Composite Structures

The studies on the long-term stability of composite plates and shells under limited creep carried out mainly by the research associates of the Institute of Polymer Mechanics are reviewed. The statement of the stability problems is discussed, according to which a viscoelastic structural member can be regarded as stable if a disturbance in the form of a small initial deflection asymptotically tends with time to a small constant value. In the case of stability, as evidenced by experiments, the increase in the axisymmetric components of the initial deflection, dominating in the early stage, die down with time. On the contrary, the amplitudes of nonaxisymmetric initial imperfections grow at an increasing velocity. Analytical investigations show that the initial imperfections, when expanded into Fourier series, have a spectrum of short- and long-term critical forces. The deflection components having a critical force exceeding the external load are damped out, whereas those having a smaller critical force increase infinitely. The accelerated growth in the deflection, after a time, leads to transient buckling of the shell into a new stable equilibrium form. The problems of optimization of the structure and geometry of thin-walled composite constructions, with constraints on their long-term stability and critical time, are discussed.