## Definitions

### Stress

• It is the resistive force per unit area.
• Stress = (Applied Load, P)/(Cross-sectional area, A)
• Unit-  Newton per Sq. meter

### Strain

• It is the change in length per unit length.
• Strain = (Change in length, dl)/(Original length, l).
• It is also a dimensionless quantity.

### Elastic Limit

• A maximum unit stress to which a material can be subjected and is able to return to its original form after the removal of strength.

### Hooke’s Law

Within the elastic limit, Stress is proportional to Strain.

E = (Stress)/(Strain), E is Proportionality Constant called Young’s Modulus of Elasticity.

OR

Within the elastic limit, the extension of an elastic body is directly proportional to the force producing it.

### Ultimate Stress

• The Ratio of maximum load which a specimen sustains to its original area of cross-section.

### Yield Point

• Unit stress at which deformation first increases, without any increase in the applied load; and it is always above the proportional limit.

### Ultimate Strength

• The highest unit stress it can sustain before rupturing.

### Stiffness

• Ability to resist deformation under stress.

### The factor of Safety (FOS)

• The ratio of failure stress to the allowable stress (of the material).

#### For ductile Materials

• FOS = Ratio of Syt  to σ; where Syt is yield strength of a material
• For brittle Materials
• FOS = Ratio of Sut  to σ; where Sut is yield strength of a material

This site uses Akismet to reduce spam. Learn how your comment data is processed.