Hooke’s Law

Robert Hooke first stated the connection between load and extension. According to his law, the force needed to extend or compress a spring is directly proportional to the deforming force or load, where stiffness is a constant factor. It takes twice as much force to stretch a spring twice as far.

F_spring = -kx

        The graphical representation forms a straight line graph up to a limit of proportionality and then starts to curve when the change in no longer proportional to the load. And the point at the material stops to be elastic is known as elastic limit. If the elastic limit exceeds, the material will never return to its original length.

        A tensile force is applied to establish the elastic limit of a metal using a test piece. The values are recorded at regular intervals until the test piece fails with its final load bearing limit. The data is then represented in a graph called load-extension graph or stress-strain graph. Many metals will not show the limit of proportionality and the straight line starts curving without obvious point of elastic limit.