SAINT-VENANT END EFFECTS IN COMPOSITE STRUCTURES

Thin-walled structures, such as rifle barrels, rocket casings, helicop ter blades and containment vessels, are often constructed of layers of anisotropic, filament or fiber-reinforced materials which must be des igned to remain elastic. A proper assessment of end or edge effects in such structures is of fundamental technological importance. The exten t to which local stresses, such as those produced by fasteners and at joints, can penetrate girders, beams, plates and shells must be unders tood by the designer. Thus a distinction must be made between global s tructural elements (where Strength of Materials or other approximate t heories may be used) and local elements which require more detailed (a nd more costly) analyses based on exact elasticity. Moreover, it must be recognized that it is impossible, in general, to refine global appr oximate theories (such as various so-called higher-order plate and she ll theories) without a simultaneous consideration of local effects. Th e neglect of end effects is usually justified by appeals to some form of Saint-Venant's principle, and years of experience with homogeneous isotropic elastic structures have served to establish this standard pr ocedure. Saint-Venant's principle also is the fundamental basis for st atic mechanical tests of material properties. Thus property measuremen ts are made in a suitable gage section where uniform stress and strain states are induced and local effects due to clamping of the specimen are neglected by an appeal to Saint-Venant's principle. Such tradition al applications of Saint-Venant's principle require major modification s when strongly anisotropic and composite materials are of concern. Fo r such materials, local stress effects persist over distances far grea ter than are typical for isotropic materials. In this paper, we descri be some problems of static and dynamic elasticity where anisotropy ind uces such extended Saint-Venant end zones. The paper is a review and a comprehensive list of references is given to original work where deta ils of the analysis may be found. The consideration of such extended e nd zones due to anisotropy is essential in the proper analysis and des ign of structures using advanced composite materials.