Mitigation of Stress Corrosion Cracking, Cavitation Erosion & Forming Complex Shapes Using Laser Peening (2016-434)
- Hepburn and Sons, LLC
- Curtiss-Wright Surface Technologies
- Austal USA
- American Bureau of Shipping
- Detyens Shipyard
March 2016- November 2017
NSRP ASE INVESTMENT: $1,610K
INDUSTRY INVESTMENT: $511K
The objective of this project was to evaluate the benefits of using laser peening within the shipyard industry during new construction and repair phases with a focus on aluminum ship design, construction, and repair. The project team assessed aluminum structure fatigue strength and fatigue life improvements provided by laser peening while enabling weight reductions. The project team evaluated whether laser peen forming of complex geometries could improve fatigue strength, reduce weight, drag, and fuel consumption. Laser peening has was also shown to mitigate stress corrosion cracking (SCC) while enabling weld repairs in sensitized aluminum on ships. Cavitation erosion and electrolytic corrosion tests were performed to measure the benefits of laser peening in mitigating these challenges in the life cycle of ships.
This project has successfully accomplished its objectives in demonstrating that laser peening can slow the rate of material loss within heavy cavitation and corrosive environments and can slow the rate of sensitization and mitigate stress corrosion cracking (SCC) of sensitized aluminum. Cavitation erosion, electrolytic corrosion, and sensitization continue to plague our shipyards and in service ships, so understanding the benefits of laser peening is paramount for NSRP. In addition, Repair facilities currently have difficulty addressing stress corrosion cracking (SCC) and sensitization of aluminum deckhouses of “In Service” ships such as the US Navy cruisers, which use mostly AA5456-H116 in the deckhouse construction. SCC of aluminum alloys has been an ongoing issue for many years on cruisers. Austal USA, the shipyard responsible for constructing the Littoral Combat Ship (LCS) Independence Class primarily uses AA5083-H116. The observations and results of this project indicate a very promising mitigation to these three issues of cavitation erosion, electrolytic corrosion, and sensitization. Laser peening is shown to reduce mass loss rate by 30% of aluminum in accelerated cavitation erosion testing, slow the rate of electrolytic corrosion (physical observations), slow the rate of sensitization by 50%, and arrest and prevent SCC in sensitized material. In all cases, laser peening has been shown to improve the performance of the materials tested. Laser peening has been shown to slow the rate of sensitization of 5XXX aluminum alloys by 50% and prevent crack initiation on sensitized aluminums. This project sensitized new material (by heating in oven), verified the degree of sensitization, induced cracking through SCC tests, and evaluated laser peening effectiveness on mitigating SCC of aluminum alloys used on current in service ships. Both new construction and repair phases were emulated during this project. For example, new material was laser peened and then sensitized showing that the treatment can slow the rate of sensitization once the ship is put into service and exposed to long deployments in hot regions of the world. In addition, material was first sensitized, emulating the ship had been in service for many years and exposed to hot regions of the world, and then laser peened and tested for SCC. In both cases, laser peening shows significant promise to solving the sensitization challenge.
Request Final Report from NSRP– Limited distribution authorized to U.S. Shipbuilding and Repair Industry.
POINT OF CONTACT:
Dr. Daniel Georgiadis | Hepburn and Sons, LLC | firstname.lastname@example.org