NDT, NDI, crack check is essential to being competitive in any form of racing. There are 2 types that are commonly used in off road racing, magnetic particle (mag., magnaflux) and penetrant inspection.
Let’s start with magnetic particle which is used most often. Mag. Is used on materials that are magnetic, such as 300M, 4340, 4130, etc. Mag. Inspection will reveal indications that can be indicative of a crack, or other anomalies in the material. The part should be subjected to inspection in both the longitudinal and circular directions. A circular field is created by putting the part between the head stock (head shot) and putting current in a straight direction to create a magnetic field. The straight field is created by putting the part in the coil (coil shot) and inducing a circular current. As the parts are subjected to the current load a oil, which contains magnetic particles, is flooded over the part. A crack or discontinuity will create a flux leakage in the magnetic field which will attract the magnetic particles. The part will then be inspected visually in a dark area under a black light. An indication will appear as a bright line where the fluorescent particles have been attracted to the discontinuity by a break in the magnetic field. To properly test the part, the field created should be between 30 to 60 Gauss when measured on a Tesla meter, or background or false indications could be seen.
Penetrant can be either liquid or spray can type. Pen. Inspection is used on non magnetic materials such as aluminum, titanium, or most stainless steels. Liquid pen. Is most commonly either water washable or post emulsified. These differing types have different sensitivity levels. For post emulsified (PE), the part(s) are submerged in the liquid penetrant, removed, and then it should sit on the part for a dwell time of around 15 minutes minimum. The part is then submerged in the emulsifier, and dwelled for around 2 minutes minimum. The parts are then washed with water under a black light to remove the exterior penetrant. Once all the pen. has been removed, the parts are placed into an oven to dry. Once dry, they are placed into a chamber with a dry developer powder which will be air agitated. The parts then dwell for 10 minutes minimum, and are then inspected in a dark area under a black light. If there are any cracks or discontinuities, the penetrant will have permeated into the crack or discontinuity, and will now have been drawn out and appear as a bright fluorescent indication under a black light in a dark room.
Most racers today have their major suspension components, spindles, hubs, transmission internals, engine components, and other critical items non destructive tested after each race. NDT can detect a problem before it becomes catastrophic, and ends your day.