Abstract: Based on the variational principle of potential energy, displacement jump condition which depends only on material strength is derived. Moreover, the connection of displacement jump and uniqueness of governing equations is built; and equivalent scopes are verified. Uniqueness of governing equations uses constitutive/acoustic tensor to deal with material stable problem caused by stiffness degeneration, which could be equal to displacement jump condition; but it is less straightforward than the displacement jump condition described by material strength, especially, those materials whose strength can be tested easily at lab.

Key words: displacement jump condition, uniqueness, material strength, acoustic tensor