Testing and Analysis of Hybrid Composite/Metal Connections and Hull Section for the MACH Project

Abstract

This report summarizes the development, testing and analysis of hybrid composite/metal connections and hybrid structural systems under the Modular Advanced Composite Hullform (MACH) project. The MACH project, funded by the Office of Naval Research, is part of a joint effort between the University of Maine, Navatek of Honolulu, HI, and Applied Thermal Sciences (ATS) of Sanford, Maine, and is performed in conjunction with the Naval Surface Warfare Center at Carderock, MD (NSWCCD). The primary motivation for the work summarized herein is to provide alternatives to conventional hull construction techniques and conventional hull forms by using modular hybrid construction methods. Included is a description of tests performed on sub-scale hybrid bolted connections, where the objective was to develop watertight connections for removable panels. An experimental study was conducted to quantify the performance of numerous hybrid joints with various geometries, loaded in flexure. The test results showed that for resisting bending loads, joints with doubler plates can be made stronger and rotationally stiffer than standard bolted joints, while also mitigating opening of the joint, thereby improving the ability to seal the connection for watertight integrity.The results of this study were used to select a connection geometry, which was incorporated into the hydrostatic testing of a full-scale four-panel assembly. Testing of the assembly is described in this report and shows that a linear response of the system was observed up to its design pressure load of 82.74 kPa. Damage initiated as stiffener delamination at 1.4 times the design load. After failure of several stiffeners, the hybrid assembly withstood up to 3 times its design load without leakage. Hence, the response of the hybrid joint employed was deemed successful.Numerical analysis of the connections and assembly are also presented. Simplified shell finite element models were developed at both local and global levels. These models were for estimation of the joint stiffness and good correlation with the test results was observed. Strength of the system was predicted using detailed plane strain contact models to capture the three-dimensional effects of the connection. ii ACKNOWLEDGMENTSThe authors gratefully acknowledge funding for this project through the Office of Naval