Steels - Endurance Limits and Fatigue Stress | MEPKit Engineering Tools

Steel Type	BS Standard	Treatment	Tensile Strength σu (MPa)	Endurance Limit σe (MPa)	σe / σu Ratio
0.4% Carbon	BS970 080M40	Normalized	540	270	0.5
0.4% Carbon	BS970 080M40	Hardened and tempered	700	340	0.49
Carbon, manganese	BS970 150M19	Normalized	540	250	0.46
Carbon, manganese	BS970 150M19	Hardened and tempered	700	325	0.53
3% Chrome molybdenum	BS970 709M40	Hardened and tempered	1000	480	0.48
Spring steel	BS970 735A50	Hardened and tempered	1500	650	0.43
18.8 Stainless	N/A	Cold rolled	1200	490	0.41

Key Definitions

Fatigue - When a material is subjected to repeated cycles of stress or strain and its structure breaks down, ultimately leading to fracture. Fractures due to fatigue occur at stress levels less than the material's Yield Stress.

Endurance Limit (Fatigue Limit) - The amplitude or range of cyclic stress that can be applied to a material without causing fatigue failure. Most steels have an endurance limit approximately half the Tensile Strength.

Tensile Strength (Ultimate Tensile Strength) - The limit stress at which the material actually breaks, with sudden release of the stored elastic energy.

Yield Strength - The amount of stress that a material can undergo before moving from elastic deformation into plastic deformation.

Creep - Time-dependent deformation due to heavy loads over extended periods. Both stress and temperature influence the creep rate.

Unit Conversion

1 MPa = 10⁶ Pa = 1 N/mm² = 145.0 psi (lbf/in²)