Damage Identification Of Structures Based On Experimental Modal Analysis

Health monitoring of the structure and damage identification have a great significance on theanalysis of the working condition of structure, the evaluation of the working life of the structure andits security. The method of structural damage identification which is based on the structural dynamicscharacteristics and experiment modal analysis has been a hot topic of the academic and engineering. Itincorporates many subjects including system identification, vibration theory, testing and measurementtechniques, signal acquisition technology, and it has been widely used in aerospace and precisionmachine tools and so on.This paper introduces the vibration theory and the finite element theory of the beam and platestructure which have been usually used in our daily life，and also the damage location index the modalstrain energy based on the perturbation theory. This paper puts forward a weighted element modalstrain energy change rate as an improved damage location index to reduce the influence of noise, andanalysis the reduction of noise of the index through the simulation. During the actual process of anexperiment, we can not get the modal vectors of all degree of freedoms. An dynamic extended ordermethod which is referred to Guyan expanding order method is put forward to solve this problem. Atlast, this paper introduces the concept of element damage variable D, and theoretical derivation theprinciple for damage degree evaluation.In this paper the basic idea of damage identification can be summarized as the following twosteps: First is select the element strain energy change rate and the improved weighted element strainenergy change rate as the index of damage location; Second is use the element damage variable D toevaluate the damage degree. A numerical simulation experiment of beam and an actual experiment ofa plate are arranged during this paper. In order to find the advantages and disadvantages of thisdamage identification method and evaluate the useful scope a large amount damage cases aresimulated. A software on damage locating is developed finally, which is supposed to provide areference for practical engineering application.