Is there an upper limit of strength that cannot be
exceeded? The answer is “yes”.
The ideal strength or the greatest strength of a material is
proportional to its bond strength. The bonds between atoms can
be represented by springs (Fig. 2.27).
Like a spring, these bonds also have a breaking point. If we
assume that an atom occupies a cubic unit cell of size a0, then a
force F acting on the unit cell is equivalent to a stress σ = F/a02.
The force stretches the bond to a new length a, giving a strain ε
= (a-a0)/a0. The stress strain curve for a single atomic bond can
be expressed in Fig. 2.27. The peak of the curve is the bond
strength. Further increase beyond this point it will break.