The laws of structural mechanics are well established in recognised elastic theory using the following assumptions:
• the material is homogeneous which implies its constituent parts have the same physical properties throughout its entire volume.
• the material is isotropic which implies that the elastic properties are the same in all directions.
• the material obeys Hooke's Law, i.e. when subjected to an external force system the deformations induced will be directly proportional to the magnitude of the applied force.
• the material is elastic, which implies that it will recover completely from any deformation after the removal of load.
• the modulus of elasticity is the same in tension and compression.
• plane sections remain plane during deformation. During bending this assumption is violated and is reflected in a non-linear bending stress diagram throughout cross-sections subject to a moment; in most cases this can be neglected.
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