1. The bolt fracture is not due to the tensile strength of the bolt:
Take an M20×80 grade 8.8 high-strength bolt as an example, its weight is only 0.2 kg, and its minimum tensile load is 20 tons, which is as high as 100,000 times its own weight. Generally, we will only use it Fasten a 20 kg component and only use one-thousandth of its maximum capacity. Even if it is the action of other forces in the equipment, it is impossible to break through a thousand times the weight of the component, so the tensile strength of the threaded fastener is sufficient, and it is impossible to damage it due to insufficient strength of the bolt.
2. The fracture of the bolt is not due to the fatigue strength of the bolt:
Threaded fasteners can be loosened only one hundred times in the transverse vibration loosening test, and one million times in the fatigue strength test. In other words, threaded fasteners loosen when using one ten-thousandth of its fatigue strength, and we only use one ten-thousandth of its maximum capacity, so the loosening of threaded fasteners is not due to the fatigue strength of bolts .
3. The real reason for the damage of threaded fasteners is looseness:
After the threaded fastener is loosened, a huge kinetic energy mv2 is generated. This huge kinetic energy directly acts on the fastener and the equipment, resulting in damage to the fastener. After the fastener is damaged, the equipment cannot work in a normal state, which further leads to Equipment damage. For fasteners subjected to axial force, the threads are destroyed and the bolts are pulled off. For fasteners subjected to radial force, the bolts are sheared and the bolt holes are punched into ellipses.
4. The root of the problem is to choose the thread anti-loosening method with excellent anti-loosening effect:
When stainless steel bolts are broken, the easiest conclusion people can draw is that the strength is not enough, so most of them adopt the method of increasing the strength grade of the bolt diameter. This method can increase the pre-tightening force of the bolt, and its friction force has also been increased. Of course, the anti-loosening effect can also be improved, but this method is actually a non-professional method. Its investment is too large and its benefit is too small. In short, the bolt is: "If it is not loose, it will break when it is loose."
