Multi-Scale FEM for Analyzing Flexible Waveguide Forming

A waveguide is a hollow metallic structure that is used to guide electromagnetic waves and is used to connect microwave transmitters and receivers to their antennas in satellite communications.  Flexible waveguide, in which the tube is corrugated, is often used where accurate positioning is not possible, or to allow for movement due to vibration or thermal expansion.  Material selection is driven by a trade between strength/ductility, electrical conductivity, and stability over life at high temperatures.  The resulting waveguide is typically comprised of a base material with several plating layers, where the total thickness of the plating is on the order of the thickness of the base material. 

The resulting waveguide geometry is complicated to analyze from a structural perspective, as the often ignored plating becomes a significant portion of both the strength and weight of the overall waveguide, and each material in the waveguide may plastically deform during final forming.  It is also difficult to determine how each of the material parameters (plating thickness & ductility, and base metal properties) affect the overall structure.

The following presentation will outline finite element modeling and material testing efforts of flex waveguide to determine the critical material properties required to avoid damage.  A serial multi-scale finite element modeling sequence was developed that captures the effects of localized details in successively higher order models.  From this method, it was possible to model the forming operation of the corrugated waveguide in different planes and include the effects of plating in a vibration response model of a large section of flex waveguide with multiple swept bends.  The results were used to locally determine stresses and strains in each plating layer and the base material.  These techniques can be generalized to any design where small details can affect global behaviors, and computational and/or time resources are limited.