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Compaction is the process of bringing the individual fibre’s close to each other so they can transfer load to each other more effectively. Compaction plays another role of removing any trapped air that may cause voids or porosity in the laminate.

Compaction is very important because for the structure to perform as designed the individual fibre’s need to transfer the loads from one fibre to the next so the load can travel through the structure. The resin has strength and stiffness properties of about 1% of the fibre so it is important that the fibre can do the job it was intended to do. There is a misconception that compaction is only important to remove the excess “heavy” resin to reduce the weight of the part. This is false in that proper compaction provides not only a decrease in weight but an increase in strength and performance.

The overall laminate will have lower strength than a properly consolidated laminate having the optimal per ply thickness, and will generally require more plies to achieve the desired strength”.

The Boeing Company

Common problems associated with compaction are:

Resin voids – Pockets of trapped air in the resin.

Porosity – Areas of fine air bubbles in the resin. (Like a Violet Crumble)

Resin pooling – Areas of resin rich pockets, often associated with a geometry change.

Resin rich – Area of excess of resin in the part

Resin poor – Area of insufficient resin in the part.

Thickness variability – Areas outside the optimum laminate thickness.

With bicycle frames problems often occur when designers use shapes that aren’t optimum such as tight corners and also at areas of sudden thickness change such as molded in cable guides.

For all these production flaws Ultrasound is the preferred method of inspection because the thickness can be measured and because ultrasound scans are very sensitive to porosity and planar defects.