When a large number of atoms come together to form a metallic solid, such as an iron nail, they settle equilibrium Positions in a three-dimensional lattice. a repetitive arrangement in which each atom has a well-defined equilibrium distance from its nearest neighbors. The atoms are held together by inter atomic forces that are modeled as tiny springs.
If you hang two cars from the rod, the rod will be permanently stretched and will not recover its original length when you remove the; load. If you hang three cars from the rod, the rod will break. Just before rupture,elongation of the rod w’ill be less than 0.2%. Although deformations of this size seem small, they are important in engineering practice. (Whether a wing under will stay on an airplane is obviously important.)
In a standard test of tensile properties, i.he tensile stress on a test cylinder (like that in is slowly increased from zero to the point at which the cylinder fractures, and the strain is carefully measured and plotted. The result is a graph of stress versus strain like that in range of applied stresses, the stress-strain relation is linear, and the; specimen recovers its original dimensions when the stress is removed.