Improved Affordability for Composites Structures (2007-373)
- Northrop Grumman Ship Systems
- Naval Surface Warfare Center - Carderock (NSWCC)
January 2007 - March 2009
NSRP ASE Investment: $991K
Industry Investment: $991K
Develop and demonstrate a low cost joining capability for pultruded composite panels to be used in place of the Vacuum Assisted Resin Transfer Molding (VARTM) processed panels.
To realize the reduced maintenance cost and weight savings associated with composites, the project team demonstrated a low cost joining capability for pultruded composite panels to be used in place of the Vacuum Assisted Resin Transfer Molding (VARTM) processed panels. The use of composites in ship production is highly desirable due to its corrosion resistance, low maintenance cost, low life cycle cost, weight savings, low radar cross section and the ability to configure radar characteristics for specific applications. Future applications will provide even more incentive for the use of composites in naval structures. In spite of the performance advantages, composites currently have a high acquisition cost, which limits their use. The development of standard, low-cost composite manufacturing processes will benefit the Navy as well as the shipbuilding industry.
The technology to make long, 10-foot wide pultruded panels at a significantly lower cost has been demonstrated (initial estimates are 35-40% cost reduction), but a reliable, low-cost methodology for joining the pultruded panels is needed for making assemblies. The project began with a small scale version of the process to prototype the joining methodology and the assembly process. Once the small scale assembly was completed successfully, the approach was scaled up in order to demonstrate the assembly process on a production scale. The goal of this step was to assemble a 20’ x 40’ panel, using shipyard labor and equipment, from four pultruded panels, each 10’ wide by 20 feet long. The panel assembly fixture consisted of four tables mounted on rails. The tables could be rolled along the rails and pulled together by means of two 12 volt winches, one on each side.
An initial cost study on the production scale assembly revealed the potential for labor savings that far exceeded the project goal of 40% when comparing the new methodology to the current VARTM process. When preparing the test specimens for the pultruded composite panel, voids in the bond line became evident. An investigation concluded: 1) the adhesive did not bond well to the prepared pultruded surface and must be replaced with a better adhesive and 2) the panel joint had some warping along the length which must be accounted for in the assembly process. Using a new adhesive and a modified assembly process, the team conducted a successful production scale assembly in August 2008.
The final phase of the project was a test program conducted at the Naval Surface Warfare Center at Carderock to measure panel and joint strength and determine whether the joined pultruded panels perform as well as current VARTM panels. Results showed that joined, pultruded panels exhibited strength equal to or better than VARTM panels. Further testing and development of additional joint designs are being conducted as part of a follow-on effort.
Final Report – Approved for public release; distribution is unlimited
Point of Contact:
Mark Losset, Ingalls Shipbuilding