The problem of phase velocity of longitudinal impact wave in a solid elastic bar has a very important significance as a basic theory to determine the natural frequency of vibrations in various engineering frame-warks.
The exact theory as to the phase velocity of longitudinal impact wave in an elastic bar which has been hitherto approved is the Pochhammer-Chree theory.
However the author considers that the traditional Pochhammer-Chree theory is not correct and that a large error not tolerable even in engineering sense will be inevitably included in the analytical result of natural frequency obtained by the application of traditional theory.
This paper is the summary of author's presented paper to the 14th IUTAM Congress 1976 (Congress 1976 of the International Union of Theoretical and Applied Mechanics) in Delft, the Netherlands. However the author has paid all the effort not to omit as far as possible the essential parts necessary for readers to understand the outline of his theory.