1. B. Koplik and Y. Y. Yu, ?Axisymmetric vibrations of homogeneous and sandwich spherical caps,? Trans. ASME, E,34, No. 3, 668?673 (1967).
2. J. S. Kao and R. J. Rossi, ?Fundamental natural frequencies of circular sandwich plates,? AIAA J.,7, No. 12, 2353?2355 (1969).
3. S. Mirsa and A. V. Singh, ?Axisymmetric vibration of circular sandwich plares, ? AIAA J.,12, No. 10, 1418?1420 (1974).
4. K. K. Pujara, ?Vibrations of circular sandwich plates.? J. Inst. Eng. Mech. Eng. Div.,49, No. 4, 226?229 (1969).
5. É. I. Grigolyuk and P. P. Chulkov, Stability and Vibrations of Three-Layer Shells [in Russian], Mashinostroenie, Moscow (1973).