International Journal of Applied Engineering Research ISSN 0973-4562 Volume 8, Number 2 (2013) pp. 157-170 © Research India Publications http://www.ripublication.com/ijaer.htm Effect of the Thickness-wise Location Delamination on Natural Frequency for Laminate Composite R. Sultan, S. Guirguis, M. Younes and E. El-Soaly * Libyan air force, Libya mig23yb@yahoo.com ‡ Egyptian Armed Forces, Egypt samer_guirguis_2000@yahoo.com † Egyptian Armed Forces, Egypt myounes27@yahoo.com § 10 th of Ramadan Higher Institute of Technology, Egypt, eldessouky@hotmail.com Abstract The laminated composite plates are basic structural components used in a variety of engineering structures. An important element in the dynamic analysis of composite laminate structure is the computation of their natural frequencies. The present study involves extensive experimental works to investigate the free vibration of square woven fiber Glass/Epoxy composite plates with two opposite simply supports edges and the remaining two edges are free boundary conditions. The specimens of woven glass fiber and epoxy matrix composite plates were manufactured by the hand-layup technique. Elastic parameters of the plate were also determined experimentally by tensile testing of specimens. Finite element modelling was employed to simulate the dynamic response of composite laminates plates with delamination and extract their vibration parameters. Present experiments were used to validate the results obtained from the FEM numerical analysis. In this paper, the effect of delamination on free vibration through thickness- wise direction was introduced. First natural frequency was investigated theoretically by using energy method and compared with numerical and experimental results. Good agreement was found between theoretical, numerical and experimental results. Results show that the delamination has considerable effect on the natural frequencies.