1. E. P. Papadakis J. Acoustic Soc. Amer. 37 (1965) 711.
2. W. J. Bratina Int. J. Nondestr. Test. 2 (1970) 229.
3. A. Vary,Mater. Eval. 36 (1979) 55.
4. R. Klinman, G. R. Webster, F. J. Marsh andE. T. Stephenson,ibid. 38 (1980) 26.
5. A. Vary, in ?Fracture Mechanics? edited by C. W. Smith, ASTM STP number 677 (ASTM, Philadelphia, 1979) p. 563.