Experimental and theoretical investigation on transverse vibration of delaminated cross-ply composite beams

• The effect of delamination parameters is investigated on natural frequencies.
• Analytical, FE and experiments are compared for delaminated composite beams.
• .The free mode frequencies are comparatively lower than the constrained modeones.
• The first mode has the minimum frequency changes.
• As delamination moves from nodes to antinodes, the effect of delamination reduced.

Delamination is a major damage mode in laminated composite structures which causes reduction in stiffness and strength and affects their vibration characteristics. This paper deals with the effects of delamination size and its thickness-wise and lengthwise location on the vibration characteristics of cross-ply laminated composite beams. Free and constrained mode models are introduced and compared in the analytical and finite element methods for the first three modes and a comprehensive discussion among these results is done. To verify the results, modal tests were carried out on the delaminated specimens. Unlike the available experimental research, the proportion of delamination size to the beam length (a/L) is relatively small (i.e., a/L=0.20, 0.10 and 0.05). Moreover, these experiments are focused on the effect of the axial location of delamination on the first three natural frequencies. All results are considered under both the clamped-free and clamped-clamped boundary conditions. Finally, some interesting relationships are presented between the frequencies reduction and their corresponding mode shapes, which can be useful for delamination detection.