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Plasma treatment for bonding of aerospace components

TWI has launched a research project to explore the potential of using plasma treatment on the surface of composite aerospace components before they are adhesively bonded.

The project will use plasma to treat the surface of composite coupons before they are bonded in single-lap shear configuration. It will consider different joining conditions, and samples will undergo testing to establish the joints’ lap shear strength. These values will be compared with others obtained using the conventional methods used in the aerospace industry.

Background

Aircraft are highly complex structures that require extensive maintenance. A major portion of this maintenance effort relates to health and usage monitoring; another is repair and replacement.

Adhesively bonded composite patches are a superior solution for repair and lifetime extension of airframes, primarily due to reduced stress concentrations compared with mechanically fastened repairs. Such repairs reduce aircraft downtime, reduce maintenance and labour costs, and increase the life of the aircraft.

One of the key factors in the adhesive bonding process is the surface preparation of the substrates to be joined. Current methods in the aerospace industry consume considerable amounts of time and require special training.

This research will evaluate plasma treatment (Figure 1) as an alternative energetic technique. This method sidesteps many of the disadvantages of current pre-treatments, such as debris, environmental issues and health and safety concerns.

Benchmarking

The aim of this project is to compare one of the most popular surface treatments in the aerospace industry (abrasion) against the plasma method. Different joining conditions will be used in order to define the processing window.

Figure 1 Plasma treatment equipment
Figure 1 Plasma treatment equipment

Variables and testing

The following parameters will be considered in this study:

  • treatment distance
  • dwell time (by changing speed)
  • number of passes
  • gas flow rate

The speed of the process and the number of passes will be changed, while the other parameters are kept constant. Three different treatments will be investigated:

  • Treatment one: abrasion.
  • Treatment two: grit blasting.
  • Treatment three: plasma.

Around 200 joints will be manufactured and tested as shown in the test matrix in Figure 2.

Future Developments

Testing will identify the best treatment conditions to be selected for the next phase. Specimens will be bonded and tested through mechanical test (BS ISO 4587 ‘Determination of tensile lap-shear strength of rigid-to-rigid bonded assemblies’)

For more information about this project, please email contactus@twi.co.uk.

Figure 2 Panel manufacturing and specimens
Figure 2 Panel manufacturing and specimens
Avatar Berta Navarro Senior Project Leader – Adhesives, Composites and Sealants

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