Design, analysis, and experimental investigation of a robust attachment system kit for naval sandwich panels

Composite sandwich panels have become an increasingly interesting alternative to steel and aluminum for applications in naval vessels and infrastructures due to high strength, stiffness, and thermal/acoustic insulation at low areal weights. The bending strength and rigidity of the panels is provided by facesheets bonded to a lightweight core material having appropriate shear and compressive properties. Currently, hard-point attachment methods are only possible during the manufacturing of the sandwich panels, whereas after-assembly hard-points may be necessary. Existing methods, including those developed for aerospace applications, are not attractive in naval and infrastructure applications due to requirements of large panel thickness, high load capacity, one-side installation, and minimal-damage failure modes. The purpose of this project is to explore the potential of a robust and efficient system for mounting medium- to heavy-weight equipment to thin-skin composite sandwich structures employed by the U.S. Navy.;The proposed attachment system consists of a metal insert supported by potting material in a cavity of optimally designed shape and size, excavated through an opening in the facesheet and into the core. The research and design includes the tailoring of materials and geometries to provide a balance between the strength and flexibility to manage the failure modes. The analysis and design for the potting and insert combinations require key strength information, including the toughness of the facesheet to core bond. Initial steps in the project include various bond and material component testing using both standard ASTM and novel testing procedures. These results are incorporated into a finite element approach for stress analysis using a damage initiation and propagation approach to characterize the failure progression. Pullout-, shear-, and oblique-load tests are performed on various prototype designs of the installation system for comparison with the numerical values and failure modes determined in the finite element analysis to develop a calibrated model The application of the calibrated finite element model can serve as an analytical design tool for research and development of a 'family' of varying load-rated, user-friendly attachment system kits. The testing approaches and finite element methods researched in this project will ultimately be extendable to alternative sandwich panel configurations and aid in the further development of mounting and other applications.