What is the endurance limit of alloy steel axle under repeated load/stress?

The endurance limit of an alloy steel axle under repeated loading or stress is indeed generally considered to be equal to half the ultimate strength of the material. This concept comes from the material's behavior under cyclic loading conditions, where it experiences a significantly different failure mechanism compared to static loading.

When subjected to repeated stresses, materials can endure higher loads than the static yield strength before reaching failure. The ultimate strength represents the maximum stress the material can withstand before failure occurs, and for many steels, particularly high-strength alloy steels, the endurance limit is often approximated as half of this ultimate tensile strength. This relationship helps in designing components that can sustain repeated loading without risk of fatigue failure.

This principle is critical in machine design, particularly for applications involving rotating or oscillating elements, such as axles, where fatigue is a common failure mode. It is vital to ensure that the maximum fluctuating stress does not exceed this endurance limit to prevent premature failure during operation.