Introduction
Engineers need to be extremely cognizant of the properties of the materials that they use in 
their designs. When subject to a particular stress, or force per unit area, materials will respond 
with a particular strain, or deformation. If the stress is small enough, the material will return 
to its original shape after the stress is removed, exhibiting its elasticity. If the stress is greater, 
the material may be incapable of returning to its original shape, causing it to be permanently 
deformed. At some even greater value of stress, the material will break or fracture. The 
particular values of stress that cause these three situations differ for every material.