COMPOSITE REPAIR

What is Composite?

Composites are one of the most advanced and adaptable engineering materials known to men. Progresses in the field of materials science and technology have given birth to these fascinating and wonderful materials. Composites are heterogeneous in nature, created by the assembly of two or more components with fillers or reinforcing fibers and a compactable matrix .The matrix may be metallic, ceramic or polymeric in origin. The primary advantages of composite materials are their high strength, relatively low weight, and corrosion resistance.

Why Composite Repair

Even though composite materials poses excellent mechanical, thermal, corrosion resistance and environmental resistance properties, they are also subject manufacturing and in-service failures. Sources of manufacturing defects include:

• Improper cure or processing

• Improper machining

• Mishandling

• Improper drilling

• Tool drops

• Contamination

• Improper sanding

• Substandard material

• Inadequate tooling

• Misalocation of holes or details.

In-service defects include:

• Environmental degradation

• Impact damage

• Fatigue

• Cracks from local overload

• Debonding

• Delamination

• Fiber fracturing

• Erosion

Defect Detection in Composites

Defects in composites can be detected by:

Nondestructive Inspection (NDI) such as

Visual Inspection Audible Sonic Testing (Coin Tapping) Automated Tap Test Ultrasonic Inspection Through Transmission Ultrasonic Inspection Pulse Echo Ultrasonic Inspection Radiography Thermography

Composite Repair

The need for repairs can be categorized into three types of damage or defect; negligible or acceptable damage, repairable or correctable damage and non-repairable.

Types of Repair

Easy Repair Complex Repair

Easy Repair

Usually small and does not affect a part’s structural integrity. These repairs are made to protect the surface of the component and do not require reinforcing materials.

Complex Repair

Complex repairs are required when the damage interferes with the structural performance of the composite. It is sometimes necessary to make temporary repairs to the composite to keep severe mechanical problems at bay until it is possible to perform a complete repair.

Types of Complex Repair

Fill Injection Bolted or Bonded

Fill Repair: Simple fill repairs are conducted with paste adhesives to repair non-structural damage such as minor scratches, gouges, nicks and dings.

Injection: Injection repairs use low-viscosity adhesives that are injected into composite delaminations or adhesive unbonds.

Bolted or Bonded: Bolted repairs are usually done on thick highly loaded composite laminates while bonded repairs are often required for thin skin honeycomb assemblies.