ABSTRACT
First, to describe the wave motion, we afœx a Cartesian coordinate xi (i = 1, 2, 3) to the continuum elastic body of interest, where the coordinate xi is also used to label the material particle that was located at xi in the initial (undeformed) conœguration. This way of describing the wave motion is called the Lagrangian description, and xi is called the Lagrangian coordinate. At any given time t, the displacement of the particle xi from its initial location is denoted by ui = ui(x, t). The deformation of the continuum can then be described by the Lagrangian strain
1 2 ( ),, , , ,
(8.1)
where, and in the rest of this chapter, the summation convention has been adopted.
