ABSTRACT
In order to investigate what is happening inside a body in equilibrium, consider a part of the body separated from the rest by a cutting line known as a 'section'. It is evident that the body part is not accelerating and so, like the complete body, must be in equilibrium. To achieve this equilibrium, it is normally necessary for additional forces to act on the body part from the adjoining part(s) across the section. When distributed across the interface, the internal forces are called 'stresses'. They consist of normal components, 'direct stresses' and tangential components, 'shear stresses'. Whereas equilibrium conditions alone wi l l not enable stress distributions to be determined, they can be used to determine or provide information on stress resultants, otherwise known as internal forces.
