Vibration Analysis of Cracked Composite Laminated Plate: A Review

Composites are one of the rapidly consuming materials due to their utmost attractive applications ranging from the aerospace to the agricultural products. The composite structures usually experience vibration during service. Experiments showed that presence of delamination in composite structures is one of the major causes of failures in laminated structures. Presence of delamination in a structure not only significantly impacts the stiffness of the structure with declining trends but also affect their vibration properties. The purpose of this paper is to review the literature studies on the effect of vibration on composite delaminated structures subjected to different boundary conditions. The literature studies have been classified on the basis of methodology adpated to analyze the problem i.e experimental work, analytical approaches and finite element methods. In this review particular attention has been given to the study of results attained from the analytical analysis, finite element and experimental works. Comparison of the results conducted by other researchers in the field of the free and forced vibration behavior of the composite laminates subjected to delamination or cracked structures has also been studied. Studies have shown that the location and size of delamination in composite structures significantly impacted the natural frequencies and mode shapes.


INTRODUCTION
F iber-reinforced composites have gained wide use in many aspects of engineering applications [1].
For example, they have been applied in ship building, mechanical, aerospace, etc. They are preferred because of the advantages they have such as superior mechanical characteristics, high-strength, their stiffness ratio to weight is excellent [2].
The characteristics of the CFRP (Carbon-Fiber-Reinforced Polymers)formed depend on the Reinforcement and the particular matrix used. The reinforcement components like elasticity and stress determines the rigidity and strength of the CFRP. This is why the property strength of CFRP is usually described as directional and distinct from isotropic structures like aluminum. It must not be forgotten that the carbon-fiber layout also has the ability to influence the CFRP properties. Laminates are formed by stacking different laminates (usually two or more) with different or similar fiber orientation under global direction [3]. Different or similar composite materials with varying thicknesses can be used to form the laminate under any stacking sequence. Stacking sequence optimization of composite laminates requires the use of least amount of layers, highest fiber quality and highest possible thickness for each of the layers [4].
The composite structures usually experience vibration during service. The consequences of vibration have a wide impact range from minor issue, such as development of noise in an automobile component, to significant damage occurrences to the structure or its parts [5][6][7].
Presence of delamination in a structure affects the stiffness of the composite structure and also vibration properties. Delamination length and size decrease the natural frequencies and therefore to find effect of delamination on vibration characteristics is quite important for highly sensitive applications [8][9]. Experiments proved that in the presence of delamination, mode shapes of the composite materials were changed [10]. A Comprehensive review study of vibration analysis of cracked composite laminated is lacking. The objective of this paper is to present a comprehensive review of the state of the art studies on the vibration analysis of cracked composite plate.

VIBRATION OF COMPOSITE WITH CRACK OR DELAMINATION
The literature studies has been classified according to the techniques i.e. analytical, experimental and finite element analysis. The next sections critically describe the prominent studies according to the above theme.

Experimental Techniques
Hammami et. al. [25] conducted experiments to find the  [26] concluded that presence of delamination reduced the natural frequencies by 10 Bangade et. al. [10] carried out experimental and numerical analysis to find the effect of delamination on the natural frequencies of composite beam.

Finite Element Method
Gowda et. al. [31]   Interestingly, delamination size equivalent to one fourth of the total length of structures, has no significant impact on the fundamental and higher frequency modes subjected to all boundary conditions. It clearly shows that shorter crack is ignorable for ordinary structures.
Delamination lengths along with diameter alone also impacts non-linearity behavior in composite plate. Also increase in the bending stiffness caused an increase in the frequency. Natural frequency decreased as the thickness ratio increased and natural frequencies increased with an increase in constrained modes.
By the above discussion, it is important that delamination lengths, widths and depths have different impacts on the natural frequencies and mode shapes of the composite structures.