how to check a carbon bike frame for cracks | EWIG

Whether a crash occurs on the road or on the field, the first thing you need to protect is your own safety, followed by equipment. After confirming that you are in a safe condition, the steps to check whether the equipment is damaged are critical. So how can we predict whether the 29inch carbon fiber mountain bike frame has cracked or hidden dangers in the first place? Next, the content of this article is to teach you how to judge the health of the frame from different materials such as carbon fiber, aluminum alloy and titanium alloy.

For metal frames, if the front fork is damaged after a frontal collision, the frame will also be damaged. Although the carbon fiber frame is not so sure, it should be checked according to the situation. Because the frame and the front fork are damaged together, it mainly depends on the ductility of the frame material, which determines whether the frame tube is elastically deformed or exceeds its elastic limit during a collision.

The carbon fiber frame is actually made of carbon fiber composite materials, and the difference between them depends on the type of carbon fiber used, the stacking direction and the resin used. Snowboards are also made of composite materials. This is a good example, because snowboards made of composite materials will bend under pressure, while bicycle frames are often the opposite. It is very strong, so when under pressure, It is often not obvious. Therefore, if the carbon fiber frame is subjected to an impact force sufficient to break the front fork, the frame may be damaged even if there is no visible damage.

In the case of damage to the carbon fiber frame, there is a certain chance that the inner deep layer of carbon cloth has cracked, and the appearance does not appear to be damaged. This situation is usually called "dark damage." Fortunately, the "coin test" can be used to detect whether this happens.

The "coin test method" is to use the edge of the coin to tap the frame, especially around the upper tube, the tee of the head tube, and the bottom tube of the frame. The sound of the knock is compared with the sound of the knock near the headset. If the sound More dull, it proves that the carbon fiber frame has been damaged. However, it is worth noting that passing the coin test does not necessarily mean that the frame is safe, and further professional frame X-ray inspection is needed to finally determine the frame health value.

How to check cracks by coin?

We do this kind of inspection quite a bit. We clean the frame and look closely for cracks. A coin tap test is very effective. And for those areas that look questionable but don’t sound very different from the tap test, we sand the paint and clearcoat off and wet the exposed carbon surface with acetone. You can quickly see where acetone stays wet in a crack as it evaporates. Similar to the flouro-dye test but without the flashy colors. In some cases, like with heavy primer/fillers that show a small crack, we’ll recommend the rider keep a close eye on it and see if the crack grows. A tiny mark is placed at the end of the crack with a razor blade. 90% of the time, it’s a paint crack that doesn’t grow. 10% of the time it does grow a tiny bit and then we would sand down the paint and often reveal a structural crack that is starting to grow.

 How to check cracks by X-ray technology ?

When you have been in a crash, there might be a visible crack on the surface of the carbon fiber  bike, which makes it unsafe for use and either needs repair or (in most cases) replacement. Some cracks might not be visible on the surface and might lead to unsafe use of a crashed bike.How do you know when there is a crack inside the carbon fiber bicycle or not?

One method is using state of the art X-ray technology - in particular X-ray tomography - also known as microCT or CT scanning. This technique uses X-rays to look inside parts and see if there are cracks or even manufacturing flaws. This article summarizes a case study where CT was used to image cracks in two crashed carbon fibre bikes.

How to protect the carbon fiber frame?

No high temperature exposure

Although carbon fiber has high temperature resistance, long-term sunlight exposure may cause damage to the external paint, so please do not expose the bicycle to outdoor high temperature exposure or place it in a higher temperature indoor or vehicle.

 Clean regularly

Regular cleaning of the frame is also an opportunity to inspect the bicycle. When cleaning the frame, you should check whether it is damaged or scratched. Do not use non-professional chemical solvents to clean the frame. It is recommended to use professional bicycle cleaners.Do not use strong acid, strong alkali (cleaner, sweat, salt) and other chemical-containing cleaning agents to clean the carbon fiber car to avoid damage to the frame paint.

Post time: Nov-01-2021