Stress & Strain: Stress-Strain Graph

 Stress-Strain Graph

When a sample of ductile material is tested under Tensile load in the lab, the stress vs strain graph is plotted. Strain is plotted on the X- axis while on the Y-axis Stress is plotted. There are mainly five limiting points on the graph which are more significant than others. Those are discussed below:

Point A - 

Proportionality Limit: Limiting Value of stress up to which the stress is proportional to strain.

Elastic Limit: Limiting Value of stress up to which the material shows elasticity i.e. deformation due to some applied load vanishing when the applied load is removed and regains its original shape. It is assumed to be within the 0.2% offset to the original graph up to the Proportionality Limit.

Point B - 

Upper Yield Point: This is the point in the graph when the strain is increasing but the stress starts decreasing slowly. This is called the YIELDING of the material.

Point C - 

Lower Yield Point: This is the point in the graph when the strain is increasing but the stress remains constant for some duration.

Point D - 

Ultimate Point: Ultimate point on the graph where stress is maximum. After this stage, the stress starts reducing.

Point E - 

Breaking Point: The point at which the specimen fails ultimately. At this stage, strain is almost 20% to 25%.