Le, C. I., Q. D. Tran, V. N. Pham, and D. K. Nguyen. “Free Vibration and Buckling of Bidirectional Functionally Graded Sandwich Plates Using an Efficient Q9 Element”. Vietnam Journal of Mechanics, vol. 43, no. 3, July 2021, pp. 277-95, doi:10.15625/0866-7136/15981.