Bonded nutplates are utilized extensively in advanced aircraft assembly as a strong, lightweight alternative to riveted fasteners. Surface preparation prior to nutplate installation is critical to bond strength and affects aircraft maintainability. The current best practice for preparing composite substrates is a labor-intensive hand sanding, wiping, and cleaning process which can produce variable bond quality. A single nutplate disbond due to insufficient surface preparation can create hundreds of hours of rework, or worse, become Foreign Object Debris (FOD) and cause catastrophic damage to the aircraft and loss of life.
There is a need for a process that eliminates the inherent variability in the manual sanding process to consistently provide a properly prepared faying surface and strong resultant bond. A plasma activation process, including optimized parameters such as offset distance, exposure time, flow rate, and power level, was developed specifically for nutplate installation with aircraft composites and adhesives. The performance of this plasma process was studied using techniques such as water contact angle measurement, push-off and torque-out destructive testing, X-ray Photoelectron Spectroscopy (XPS), as well as a heat cycling and contamination testing. The proposed plasma process will increase bond reliability, decrease touch labor, reduce scrap/rework/repair (SRR), and improve customer confidence.
- Describe the current best practices for nutplate installation, the challenges with relying on manual sanding, and the benefits of chemical bonding over mechanical interlocking
- Understand the relationship between surface activation, water contact angle, and bond strength, and the methods used to measure each
- Explain the testing techniques used to validate bond strength, possible contamination scenarios, and the design/manufacturing process of a production tool
Why Is It Important?
Plasma surface activation has been studied as a bond preparation method for many years, but this research program is the first to investigate this technique for use with aircraft substrates, adhesives, and fasteners. The outcomes of this program could eliminate the industry standard “sand and wipe” process for composite surface preparation.