The radius of bend has an effect on the strength of wire rope. In order to take this fact into account in selecting the size and design of the sheave to be used with a given diameter wire rope, the following table can be used as a guide.
For Example: Using a 1/2″ dia. wire rope with a 10″ dia. sheave, Ratio “A” = 10 ÷ 1/2″ = 20 and the strength efficiency = 91% as compared to the catalog strength of wire rope.
The repeated bending and straightening of the wire rope causes a cyclic change of stress known as “fatiguing.” The radius of bend has considerable effect on the fatigue life of wire rope and the following can be used as comparison of relative fatigue life as influenced by sheave diameter, shown in the following table.
For Example: Using a 12″ dia. sheave with a 3/4″ dia. wire rope, Ratio “B” = 12 ÷ 3/4″ = 16 and the units of fatigue life = 2.1. However, a 22.5″ dia. sheave using a 3/4” wire rope has a Ratio “B”= 225 ÷ 3/4″ = 30 and the units of fatigue life = 10. So, the expected extension of fatigue life when using a 22.5″ dia. instead of a 12″ diameter sheave would be 10 ÷ 2.1 or 4.7 times greater.
