Stress–Strain Curve
StressStrain

Yield Strength

The stress at which a material begins to deform plastically. Below this point, the material can generally return to its original shape after unloading.

Symbol
σᵧ
Design Role
Serviceability and plastic-deformation limit

Engineering Interpretation

Elastic Limit

Permanent deformation begins. In design practice, the selected allowable stress is normally reduced from material strength using an appropriate factor of safety and the relevant design standard.

Stress–Strain Curve
StressStrain

Ultimate Tensile Strength

The maximum engineering tensile stress a material can withstand before necking and eventual fracture. UTS is a key measure of the material's overall tensile capacity.

Symbol
σᵤ
Design Role
Failure resistance and material comparison

Engineering Interpretation

Maximum Tensile Capacity

Maximum tensile stress. In design practice, the selected allowable stress is normally reduced from material strength using an appropriate factor of safety and the relevant design standard.

Stress–Strain Curve
StressStrain

Fracture Strength

The engineering stress recorded when the specimen finally fractures. For ductile materials, fracture occurs after the stress has passed through the UTS and the specimen has necked.

Symbol
σ𝒇
Design Role
Failure investigation and damage tolerance

Engineering Interpretation

Rupture Point

Final rupture point. In design practice, the selected allowable stress is normally reduced from material strength using an appropriate factor of safety and the relevant design standard.