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.

We have had quite a few bikes come in for assessment after crashing recently. Some have had the usual cracking/delamination type damage, however a number of front fork steerer tubes have had significant damage that would render them unsafe.

The concern has been that this damage cannot be found visually as it is usually a "interlaminar" shear type failure within the carbon laminate. This damage shows up very well with the ultrasound scan and the integrity of this vital structural part on the bike can be assessed.

This damage is common if you have crashed where the front wheel has been twisted or knocked sideways or other front impacts.

If you have crashed and are concerned about your bike contact us for an assessment.

One answer is cost however it is a little more complex than that.

To get set up with Ultrasound scanning equipment is expensive with a basic unit costing about $10 000. The prices go up from there with fully automated robotic systems costing up to $5 million. For aerospace repairs we use a portable unit with a typical cost of about $15 000 including the probes which cost about $1500 each. So as you can see from the numbers not many repair shops could afford such specialist equipment.

The main answer to this question however is the level of training and experience required.

The training required to use this equipment is very time consuming and expensive. It takes a typical aerospace technician many years of training to be certified in this inspection method. Experience is everything in this field, and that takes time to acquire, experience working with carbon composite and knowing the engineering involved with the part that is being inspected.

Most people are familiar with medical ultrasound scans, these differ significantly from the type of scans typically used on a carbon bike. Just like you go to a specialist medical technician if you need a scan on your body, you should go to a specialist carbon composite technician for your bike scan.

So as you can imagine it is not a simple process of buying a cheap unit and scanning parts, it takes years of training and specific knowledge to understand what the output signal is indicating.

Because we have this experience and equipment we are able to find damage that would not be found by any other methods, we can find the "undetectable" damage that others repairers don't know even exists. It isn't possible to repair damage when you don't know where it is!

This puts us at a significant advantage when it comes to accurately assessing if your bike is safe to ride or not.

Here is a video showing how useful Ultrasound scans are for evaluating damage on carbon bikes and parts.

In this example apart from the small paint damage there is very little indication of any damage to the head tube. However as you will see on the video there is a disbond between the Aluminium headset insert and the carbon head tube.

This is where specialist methods make all the difference, we can find damage that the others can't. It is difficult to repair something  they don't know is there!!