Modular Ratio:

Consider the composite bar shown in Figure in that an aluminum bar is encased just snug within a copper tube which in itself is encased just snug in a steel tube. Let us analyze how the three various components of the composite bar share the load applied axially on the composite bar.

Figure

The primary requirement in such a case is that all the three elements of the bar should undergo the similar amount of deformation although carrying the load. Otherwise, the bar that shortens the least alone will be in contact with the load that is physically impossible, because a component which looses its contact will not be carrying any load and therefore there could be no shortening of that component that contradicts the assumption that it shortens more. Therefore, it is logically essential that all the three bars should undergo the same amount of deformation. This condition is called the compatibility condition or condition of consistent deformation. Satisfaction of this condition is the basis on which the problem of composite bars is analysed.