Strength of Materials

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Define stress.
When an external force acts on a body, it undergoes deformation. At the same time the body resists deformation. The magnitude of the resisting force is numerically equal to the applied force. This internal resisting force per unit area is called stress.
Stress = Force/Area     N/m2
Define strain
When a body is subjected to an external force, there is some change of dimension in the body. Numerically the strain is equal to the ratio of change in length to the original length of the body.
Strain = Change in length/Original length
e = δL/L

Define- elastic limit
Some external force is acting on the body, the body tends to deformation. If the force is released from the body it regain to the original position. This is called elastic limit.

State Hooke’s law
It states that when a material is loaded, within its elastic limit, the stress is directly proportional to the strain.
Stress α Strain
σ α e

Define – Young’s modulus
The ratio of stress and strain is constant within the elastic limit.
E = Stress/ Strain


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