1.5 STRESSES AND STRAINS

When a body is acted upon by external forces or loads, internal forces develop and the body is said to be in a state of stress. Considering the conditions of equilibrium, the resultant of internal forces must be equal to the resultant of external forces.

Thus, if P is the external force acting over a body of area of cross section A, then the force per unit area, p is given as

 

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This force per unit area is called the intensity of stress or for brevity, the stress. Thus, stress can be defined as the force of resistance per unit area offered by a body against deformation. The unit of stress in SI Units is N/mm2.

The ratio ...

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