Module 6: Failure and Damage
  Lecture 20: Damage Mechanisms in Unidirectional Composites
 


Defects in Composites

The following are the types of defects that generally occur in a composite:

1) Fibre-matrix debonding     8) Matrix cracking and crazing
2) Fibre misalignment  9) Density variation (due to resin distribution)
3) Cut or broken fibres     10) Improper curing of resin
4) Delamination   11) Impact damage (tool drop)
5) Inclusions    12) Abrasion and scratches
6) Voids and blisters 13) Machining problems
7) Wrinkles  

Sources of Defects and Damages in Composite:

There are two main sources which can introduce defects and/or damage in a composite. These two sources are:

  1. Fabrication or processing defects and

  2. In-field or service defects

The defects in these two categories are listed below.

1) Fabrication or Processing Defects:

The defects that can occur during fabrication or processing are listed below:

  1. Abrasions, scratches, dents and punctures

  2. Cut fibres

  3. Knots and kinks in fibres

  4. Improper splicing (joining) of layers

  5. Voids (due to poor processing, high humidity)

  6. Inferior quality of the materials used

  7. Improper curing of resin

  8. Resin rich or resin lean areas due to improper distribution of resin

  9. Inclusions and contamination

  10. Mandrel removal problem

  11. Machining problems

  12. Improper tooling

  13. Tool drop causing low energy impact which results in impact damage

2) In-field or Service Defects:

The defects that can occur during in-field or service are listed below:

  1. Shock

  2. Environmental cycle of temperature and humidity

  3. Exposure to hazardous chemicals

  4. Exposure to radiations

  5. Bacterial degradation

  6. Vibrations

  7. Improper handling and storage

  8. Tool drop

  9. Abrasions, dents and punctures

  10. Corrosion

  11. Erosion due to sand and dust

  12. Improper maintenance or repair