April_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 0 1 7 F iber reinforced resinmatrix compos- ite materials are used in airplanes, wind generators, automobiles, and other applications where stiff, light-weight materials, or parts consolidation are ben- eficial. Most often, the fibers are made of carbon, glass, ceramic, or aramid, and the resin matrix is an organic thermosetting or thermoplastic material. These com- posites are generally semi-conductive or insulating to electric current. To protect against lightning damage, a manufactur- er often provides a low resistance path- way within the external skins to move the energy in a strike from one strike lo- cation to the other. Metallized materials havebeenusedon the exterior surfaces of composite parts to provide the necessary electrically conductive region. Typical metalized materials include metal woven fabric, random non-woven mat, solid foil, and foraminous (coveredwithholes)met- allized sheet. Thin conductive uniform and for- aminous foils are often placed with- in adhesive or surfacing films used on composite structures. These are used to protect from electromagnetic inter- ference (EMI), and high-intensity radi- ated field (HIRF) as well as providing current conduction, antenna ground planes, and energy reflection. Expand- ed metal foils have become beneficially adopted in these applications because they are not only highly conductive, but their foraminous nature allows them to be lighter weight and more conform- able than solid foils. These foils gener- ally have thicknesses in the range of 50 to 100 µm to accommodate the piercing and stretching processes used to cre- ate the expanded foil conductors. The expansion process generally results in holes of a marquise, or diamond shape, with dimensions that are limited by the stretching process, thus properties such as conductivity and stiffness are determined by the limited geometries of the process. Studies have been con- ducted to compare one expanded shape to another. Some studies have been prophetic, conducted by modeling only. Some have been conducted solely by experimentation [1-4] . Although every application is uni- que, it is generally desired to optimize • Add minimum weight to the air- frame Several of these objectives are ex- clusively or substantially controlled by the resin in the system. The resin-con- trolled objectives will not be addressed within this article. Although protecting the structure from strike damage is a key function of the conductor, the ob- jective of this work is to provide a neces- sary level of conduction for a minimum of weight. This objective is accom- plished by first designing a film with a pattern of perforations having the nec- essary conduction at the lowest weight using digital simulation software. Once designed, the foraminous film is fabri- cated and tested for conductance. FUNDAMENTAL TECHNOLOGY The process to analytically op- timize the foraminous conductor for damage resistance, conductivity, tear strength, conformability, weight and thermal expansion is clearly a problem involving multiple physics disciplines. For that reason, Comsol Multiphysics fi- nite element multi-physics analysis and simulation software [5] was chosen as a design tool. Use of a finite elementmod- eler required the geometry be available in digital format. The Solidworks [6] solid modeling computer-aided design (CAD) and computer-aided engineering (CAE) program from Dassault Systèmes was used to generate solid models, which were shared between the programs us- ing Comsol’s LiveLink interface [5] . the lightning protection conductor by maximizing conductivity, tear strength, and conformability while minimizing weight and thermal expansion. Nu- merous studies have been conducted on the benefits of one expanded foil shape/weight over another. This article considers what shape/weight of con- ductor is optimum if the shape of the perforations is unconstrained by the fabrication process. A foraminous foil conductor has been developed having the benefits of a thin foil without the constraints im- posed by the current pierce-and-stretch process. These engineered perforations are fabricated by one of several avail- able methods; including, plating direct- ly to shape, etching, ablation, punching, drilling and printing. Using one of these techniques, any perforation shape is possible, so this conductor can be de- signed to more efficiently manage the desired properties. The performance objectives of a good lightning protection surfacing sys- tem are: • Protect the structure from damage at the strike site • Conform to contoured surfaces • Maintain a barrier to prevent corro- sion of the conductor • Provide a smooth finish • Provide sufficient conduction to minimize indirect effects • Resist damaging effects from chem- icals