DAMAGE IDENTIFICATION IN CYLINDRICAL SHELLS WITH FUNCTIONALLY GRADED MATERIALS RESTING ON ELASTIC FOUNDATION

Identification of damage location in a structure is an important issue in structural health monitoring. Most of the structures are exposed to major threats due to decrease in their efficiency and also, unpredictable loads. These problems are aggravated by induced loads due to natural or artificial dangers such as earthquakes and explosions. The main objective of this paper is to investigate the free vibration of cylindrical shell structures with functionally graded materials, FGM, on the elastic foundation in undamaged and damaged conditions. Functionally graded materials are a new type of composite materials and are characterized by gradual variations in composition, resulting in desired changes of the characteristics of the material in different directions. For this purpose, an analytical method based on first-order shear deformation theory is used. The corresponding equations which are extracted through the Maclaurin series are implemented using the MAPLE software and the corresponding frequencies and modal shapes are obtained. The numerical verification of the model is carried out by comparing the results with those of other researches in the literature and also with the results of modeling in ABAQUS software. The comparisons show good agreement between these results, indicating the accuracy and applicability of the applied numerical method. In order to investigate the effectiveness of the proposed method in identification of the damaged location in the structure, different single and multiple damage scenarios are applied to the structure resting an elastic base condition, considering various supporting conditions such as clamped and simply supports. The corresponding damage scenarios are applied through a reduction in the elasticity modulus of the interested cylindrical layers materials. In the damage identification process, modal shape derivatives are used. The results show the efficiency of the proposed model in detecting the damaged zone of the structure. The proposed method is capable of expanding real structures.