Tap testing: Why it's not a reliable choice for the cycling industry
Most cyclists are familiar with the tap test (or coin test), in which a specialised tap hammer or coin are gently tapped against their frame or component while the user listens for audible changes in sound, signifying the presence or lack thereof of underlying damage or defects.
This method is logical and stems from the non-destructive testing (NDT) industry. However, there are many aspects and limitations which are often overlooked in the cycling industry, likely due to the availability and practicality of this method, and the inaccessibility of more robust methods.
1. The accuracy of this method is limited by the auditory processing skills of the individual. Most individuals could only tell the presence of large damages or defects where a substantial change in sound occurs.
2. The accuracy of tap testing is also limited by the technique of the user i.e. the ability to create a reliable sound via their tapping motion.
3. Soundwaves (waves detectable by human hearing) by definition only have a limited wavelength and limited properties when it comes to penetrating various materials.
4. The presence (or lack thereof) for some damages such as large disbonds maybe detectable, but not smaller damages or defects such as voids, in which the carbon fibres may be in tact but not in the manufacturer’s intended composition.
5. In order to accurately classify the type of damage (e.g. a delamination or a bridging void), a multidimensional approach is needed i.e. we need to know the position, orientation, length, width, and depth of the damage. Only with all of these pieces of information can we attempt to accurately classify damage, understand the risks, and determine whether a repair is possible and how to go about it. Tap testing only enables us to determine whether there may or may not be some types of (typically large) damage.
Cycle Inspect suggests that more effective methods such as Ultrasonic Testing should be used to determine the presence of damage and defects, and the characteristics and risk imposed by these in bicycle components.
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