SUPERSONIC FLUTTER OF COMPOSITE SKIN PANELS OF REPEATED-SUBLAMINATE LAYUP

In high-speed aerospace vehicles, supersonic flutter is a well-known p henomenon of dynamic instability to which external skin panels are pro ne. In theory, the instability stage is expressed by the 'flutter crit ical parameter' Q(crit), which is a function of the stiffness-, and dy namic pressure parameters. For a composite skin panel, Q(crit) can be maximised by lay-up optimisation. Repeated-sublaminate lay-up schemes possess good potential for economical lay-up optimisation because the corresponding effort is limited to a family of sublaminates of few lay ers only. When Q(crit) is obtained for all sublaminates of a family, a nd the sublaminates ranked accordingly, the resulting ranking reveals not only the optimum lay-up, but also the near-optimum lay-ups, which are useful design alternatives, and the inferior lay-ups which should be avoided. In this paper, we examine sublaminate-ranking characterist ics for a composite panel prone to supersonic flutter. In particular, we consider a simple supported midplane-symmetrical rectangular panel of typical aspect ratio alpha and flow angle psi, and for four-layered sublaminates, obtain the Q(crit)-based rankings for a wide range of t he number of repeats, r. From the rankings, we find that an optimum la y-up can exist for which the outermost layer is oriented wide of, rath er than along, the flow. Furthermore, for many lay-ups other than the optimum and the inferior, we see that as r increases, Q(crit) undergoe s significant change in the course of converging. To reconcile these f indings, eigenvalue-coalescence characteristics are discussed in detai l for specific cases. (C) 1998 Elsevier Science Ltd. All rights reserv ed.