TEMPERATURE INSENSITIVE CURVED BIMETAL ELEMENTS

Space structures are subjected to appreciable temperature variations w hen they enter and leave direct solar radiation zones. These variation s cause thermal strains and related structural distortions. Such defor mations are often a nuisance and much engineering effort, such as acti ve control methods, is currently being invested in reducing the deform ations and alleviating their effects. This paper will present a novel structural concept which can reduce thermal distortions and in many ca ses eliminate them. The idea hinges on curved bimetal elements where t he coefficient of thermal expansion of the outer layer is larger than the coefficient of the inner layer. When the element is heated the ele ment expands axially and the curvature increases due to the fact that the outer layer tends to elongate more than the inner one. The combine d action of these effects often cause reduced apparent expansivity and in some optimally designed cases the apparent expansivity can be redu ced to zero. The paper develops a general theory of bimaterial curved 3D elements under thermal loading. From here two cases are investigate d, a planar bimaterial curved element and a bimaterial helix. It is sh own that under a particular choice of the design parameters the chord- length of the 2D circular element is insensitive to a uniform temperat ure variation. In the case of 3D curved elements the paper shows that one can design bimaterial helices for which the axial distance of any two point on the helix is independent of temperature. The theory is il lustrated by numerical examples.