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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!!

 

Here is a video showing the advantages of having Ultrasound scan equipment.

This fork showed no visual signs of any damage, however as you will see on the video, the ultrasound scan clearly shows that this fork should not be used.

The bike was involved in a crash where the handlebar swung around and hit the top tube of the frame. If you have had a similar accident we recommend that the fork steerer be thoroughly inspected.

 

 

 

Ultrasound scans are very useful for carbon composite inspection and is the primary method used in aerospace to determine the structural integrity of these parts.

Carbon composite structures are made up with a number of layers called plies, stacked on top of each other. Each ply needs to be bonded to the adjacent ply so it can transfer load. If this bond is compromised the structural integrity is significantly reduced.

Typical defects include:

Delaminations - where the plies are separated and can no longer transfer load. Very common after an impact or other failure.
Unbond - an unbond is when the plies or other fittings were not bonded properly during manufacture.
Porosity - dispersed air trapped in the resin during cure causing a reduction on mechanical properties. Aerospace standards are typically 2% max. porosity.
Void - a large air bubble trapped in the part.
Cracks - broken fibres and/or matrix.

Ultrasonic inspection is very sensitive to all these defects, it works by sending a high frequency sound wave into the part and then measuring what sound comes back. It takes very specialised equipment and knowledge.

Often highly loaded carbon composite parts such as aircraft components get 100% inspected by ultrasound methods during manufacture. This is usually conducted by automated inspection machines specific to the part and is very expensive. For aircraft repairs portable ultrasound systems are used to determine the damage prior to repair and most importantly to verify the structural integrity after repair.

Back to bikes!

So as carbon bikes become lighter and closer to the design limit it becomes very important to know that the structural material is made properly and capable of meeting the loads it was designed for. And just like aerospace, to repair high performance bikes you need to know what the damage is and that it has been repaired successfully.

 

 

We stress the importance of using resins with a high Tg (Glass transition temperature), which basically means the temperature that the resin can still provide structural performance. We only use aerospace approved repair resins that  have a Tg of over 120 deg C when cured properly, which is typical of the resin used during frame manufacture.

This is really important because if a lower Tg resin is used, the mechanical properties such as strength are reduced when the repair is at a higher temperature. This can happen if you have the bike in the car on a hot day and then go and ride. With a low Tg resin the repair can fail in this situation.

The thing is that the higher Tg resins need to be cured at elevated temperature to achieve these properties, so room temperature curing resins with lower Tg are generally not suitable for repair (unless you never ride in warm weather!)

So make sure when you get a carbon repair the correct resin and cure cycle is used to ensure correct performance, and avoid any repairs using general purpose resins such as those often used in boat building or other industrial applications.

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.