Fatigue strength of mechanical parts of amusement equipment.Under variable stress conditions, the damage form of amusement equipment parts is fatigue fracture.Fatigue fracture has the following characteristics: the maximum stress of fatigue fracture is much lower than the strength limit of the material under static stress;No matter brittle material or plastic material, the fatigue fracture of the material is brittle and sudden fracture without obvious plastic deformation;Fatigue fracture is the accumulation of damage. Its initial phenomenon is the formation of micro-cracks on the surface or surface of amusement equipment parts. This micro-crack gradually expands with the increase of the number of stress cycles until the remaining uncracked cross-sectional area is insufficient. When subjected to an external load, the part breaks suddenly.This is clearly seen on the fracture of the part (Please check Figure 2-67).There are obviously two areas on the fracture: one is the smooth surface area formed by mutual friction on both sides of the crack under the repeated action of variable stress, and the other is the coarse-grained area where brittle fracture eventually occurs.

The main factors affecting the fatigue strength of amusement equipment parts are the following:

1) Stress concentration: When the part is loaded, the local stress at the sudden change of its section geometry (such as fillets, holes, grooves, threads, etc.) is much larger than its nominal stress. This phenomenon is called stress concentration.

2) Geometric size: When other conditions are the same, the larger the size of the part, the lower the fatigue strength. This is due to the fact that the larger the size, the coarser the grains of the material, the greater the probability of defects, and the relative thinning of the cold-work hardened layer on the surface after machining.

3) Surface state: When other conditions are the same, the rougher the surface of the part, the lower the fatigue strength.