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Onsite Structural Restoration Methods for Aircraft Components

Description:

 
 

TECHNOLOGY AREA(S): Electronics, Materials/Processes

ACQUISITION PROGRAM: PMA-276, H-1 USMC Light/Attack Helicopters

OBJECTIVE: Develop an innovative repair process that restores dimensional and structural capability of damaged Ti-6AI-4V aircraft components.

DESCRIPTION: There is an ongoing need for precise and effective methods for full dimensional and strength restoration of aircraft components to enhance the logistics and maintenance of Navy aircraft. There are many instances where Navy fleet aircraft components are damaged while in service before they reach their life limit. Causes of these damages are either maintenance induced, during component install/removal/handling/inspection, or service induced, due to foreign object debris (FOD). Typical damage includes nicks, dings, and dents. Current Navy aircraft components that are damaged in the fleet need to be sent back to a Navy depot for disposition and repair. Repairs generally include blending away the damages until the surface is smooth to reduce stress risers that may cause fatigue cracking. By blending, repaired components are left with a lower thickness in the repair location which reduces the ability for future repair capability.

For all components, design tolerances exist. Damages that exceed those tolerances generally cause the component to be scrapped, costing the Navy hundreds of thousands of dollars each year. There are ongoing efforts to produce damage limits and tolerances (DL&T’s) to increase the usability of aircraft components, but those too have limits which, when exceeded inevitably lead to scrapped components. The result is an increase in downtime for the fleet as the aircrafts age and as the number of spare parts goes down.

There has been considerable research leading to innovations in equipment and repair processes which can guide toward solutions of dimensional restoration on aircraft components. The Friction stir process [3] can be employed to refine the grain structure and remove porosity produced by other manufacturing processes, but it is yet to be proven as a viable deposition or repair option on its own. The cold spray process [1] has repeatability and uniformity of material deposition, while negating thermal residual stresses by being a solid state process. The main benefit of cold spray is the reduced thermal input, but porosity is common and its success is also limited with materials having poor malleability and high hardness. The metallic melt deposition process [2,4] is a highly versatile process that can produce fully dense structures from diverse materials. It is capable of producing uniform and repeatable deposition, while cooling rate control can lead to highly customizable and refined grain structures. Owing to the potential of metallic melt deposition to deposit free-form objects, it can be employed as a low volume quality production/repair process.

An innovative aircraft component damage restoration method is necessary to restore dimensional and structural capability and reduce the process time for the disposition and repair of Ti-6Al-4V aircraft components. The restoration method should result in a component with the same strength capability as an original non-damaged component. In addition, the resulting restoration method should be environmentally friendly, not require the use of hazardous materials, and should not generate or require the disposal of hazardous wastes, such as chromate containing primers and coatings.

PHASE I: Develop an innovative metallic melt deposition approach for the restoration of damaged Ti-6Al-4V aircraft components. Demonstrate feasibility of the developed approach by performing limited testing and characterization of the deposited material, substrate, and interface at a coupon level.

PHASE II: Fully develop the restoration process that can be applicable to an array of aircraft component geometries. Demonstrate the restoration technique on a demonstration article that is representative of basic geometries seen on aircraft components such as radii, edges, curvatures, etc. The demonstration article may be fabricated or purchased, damage induced, and then the repair process demonstrated. Fully characterize the resulting mechanical and microstructural properties achieved through the process through the use of coupon level testing.

PHASE III DUAL USE APPLICATIONS: Fully qualify the repair process and perform structural certification for the repair of specific military Ti-6Al-4V aircraft components. Transition the technology to military air platforms, as well as civilian cargo, passenger aircraft components, and other industrial applications. Private Sector Commercial Potential: The technology can be used for the restoration of aircraft components in both military and commercial sectors since Ti-6Al-4V components are widely used.

REFERENCES:

  • Champagne, V., & Helfritch, D., (2015). Critical Assessment 11: Structural Repairs By Cold Spray. Materials Science and Technology (United Kingdom), 31(6), pp. 627-634. http://dx.doi.org/10.1179/1743284714Y.0000000723
  • Hong, C., Gu, D., Dai, D., Gasser, A., Weisheit, A., Kelbassa, I., Zhong, M., & Poprawe, R., (2013). Laser Metal Deposition Of Tic/Inconel 718 Composites With Tailored Interfacial Microstructures. Optics and Laser Technology, 54, pp. 98-109. http://www.sciencedirect.com/science/article/pii/S003039921300176X
  • Ma, Z. Y., (2008). Friction stir processing technology: A review. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 39 A(3), pp. 642-658. http://link.springer.com/article/10.1007%2Fs11661-007-9459-0
  • Pinkerton, A. J., Wang, W., Wee, M. & Li, L., (2008). Component Repair Using Laser Direct Metal Deposition. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 222(7), pp. 827-836. http://link.springer.com/chapter/10.1007%2F978-1-84628-988-0_78

KEYWORDS: Quality; Onsite Repair; Bonding; Process Robustness; Dimensional Restoration, Ti-6Al-4V Repair

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