Stress Strain Plot
The below properties can be observed in a stress-strain plot.
- Elastic region
- Yield point
- Proof stress
- Plastic portion - steadily decreasing slope
- Ultimate tensile strength
- Localization of the deformation
- Young’s modulus
- Upper and lower yield stresses
- Fractural strength
Yield stress point
The point where plastic deformation starts in stress-strain diagram.
Yield strength
Stress at yield stress point. Denoted by
True yield stress point is very difficult to find practically. Therefore strain offset method is used to find an approximate yield strength.
Strain offset method
A straight line is constructed parallel to the elastic portion of the
stress-strain curve at some specified strain offset. The stress corresponding to
the intersection of this line and the stress-strain curve is defined as the
yield strength
0.2% proof stress
Yield strength when
Observables
Ductility
Higher strain at fracture or failure strain.
Implies:
- Greatest percentage elongation
Stiffness
Slope of the elastic region. Steeper line means more stiffness.
Strengthness
- For ductile materials: yield stress
- For brittle materials: fracture stress
Flexibility
Higher strain in elastic region.
Toughness
Area under the curve, until the breaking point. Higher area means the higher toughness.
Tensile strength
After yielding, the stress necessary to continue plastic deformation increases to a maximum, and then decreases.
Ultimate tensile strength (UTS)
The maximum stress that can be sustained by a material in tension.
Necking starts after UTS point.