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Repair

  • Thursday, 24th January 2019
  • 0 comments
  • Reading time: about 2 minutes

Introduction

Damaged composite structures are definitely repairable, shown clearly in the before and after images below.

However, there are challenges:

  • Hidden damage issues, including manufacturing defects. (for example, a low velocity impact, which normally wouldn’t cause much damage may cause a sandwich structure to disbond between the skin and core due to poor adhesion during manufacture. If this disbond is the only damage, there may be no visible trace of it from the surface.)
  • Unexpected damage sources. (for example, an aircraft vertical tail part may be designed to withstand hailstone impact but not able to resist damage from being dropped during shipping or removal for inspection)
  • “Best” repair techniques are heavily dependent on details of the structure. In other words, because composites excel at being tailored to meet very specific needs, there are few “universal” materials and methods that can be used to achieve successful results. Composite repair specifics really have to be determined on a case-by-case basis.

Basic Repair Process

The very basic fundamentals of composite repair include the following steps:

  • Inspect to assess damage (extent and degree)
  • Remove damaged material
  • Treat contaminated material
  • Prepare repair area
  • Complete composite repair
  • Inspect repair for quality assurance (e.g. delaminations, inclusions, proper cure, etc.)
  • Restore surface finish

Published courtesy of Abaris Training Resources, Inc

http://www.abaris.com


Damage Assessment

Impact energy affects the visibility, as well as the severity, of damage in composite structures.

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Damage Removal

Explains the steps involved.

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Contamination

Damaged composite structures may be contaminated by fuel, oil, hydraulic fluid, etc.

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Repair Design

Considerations, practicalities and parameters of composite repair.

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Types of Repair

Covers some of the basic types of composite repair.

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Bolted or Bonded

Which is better?

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Scarfing

Scarfing, or taper sanding, is usually achieved using a compressed-air powered high-speed grinder.

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The Repair Patch

The repair patch attempts to replace the damaged area in the composite laminate.

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Scarfed Repair

Provides a general outline for the steps involved in a scarfed repair.

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Portable Repairs

Gives a brief explanation of portable repair systems or "hot bonders".

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Heating Methods

Describes the best solutions for even distribution of heating.

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Cure Temperature

Covers the four common choices and asks, which is best?

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Thermocouples

Describes proper thermocouple placement.

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Repair Tooling

Descibes caul plates and repair tooling.

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Vacuum Bagging

Explains the three main purposes for vacuum bagging.

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Vacuum Bag Terms

Defines various terms commonly used.

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Repair Summary

Provides a précis of repair methods used.

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