Research On Fault Diagnosis Of Plate Structure Based On Modal Curvature

With the rapid development of aerospace,civil machinery and civil engineering,the working environment of engineering structure is becoming more and more complex.Under the influence of external factors such as high temperature and high pressure,corrosion,fatigue damage and impact,local damage will inevitably occur in most engineering structures.With the continuous accumulation of damage,structural failure eventually leads to property loss or casualties.As one of the most widely used structure types,the plate structure plays an important role in engineering practice.Therefore,it is of great significance to study the damage types and damage identification of the plate structure for analyzing the working state of the structure,evaluating the service life and safety of the structure.When the structure was damaged,its physical characteristics and modal parameters(frequency,mode,etc.)will change.Among them,the damage information is more hidden in the change of modal parameters;Modal parameters are characterized by good linearity and easy measurement.Therefore,the damage identification method based on modal parameters has quickly become a research hotspot.First of all,on the basis of many studies based on the modal parameters identified by modal curvature as indicators of damage,theoretically explained the two-dimensional modal curvature can identify the slab structure damage location principle of two-dimensional modal curvature calculation formula was deduced,and the Fourier transform in frequency domain is used to calculate the two-dimensional modal curvature,greatly improving the calculation accuracy.Secondly,in order to study the effects of different damage types on the plate structure,the possible damage of the plate structure was divided into three categories:point-shaped damage,line-shaped damage and face-shaped damage according to the actual situation.The finite element models of three damage types of homogeneous thin plate structure and composite laminated plate structure are established respectively,the damage elements are characterized by reducing the elastic modulus of the element,and the damage indexes of the difference of modal curvature and the rate of change of modal curvature are proposed based on the modal curvature.The damage identification of single damage,multiple damage and mixed damage of homogeneous thin plate structure and composite laminated plate structure was carried out by using the improved damage index,and the conclusion that the damage index can identify different damage types,damage locations and damage quantities of the plate structure was obtained.Thirdly,in order to explore the influence of external factors on the recognition results in the actual situation,it is assumed that gaussian white noise is used to simulate the external interference,and the anti-noise performance of two damage indicators without noise level is studied.The influence of different damage degree and structure size on damage identification of homogeneous thin plate structure was studied.The effects of different damage degrees and layers on the structural damage identification of composite laminated plates were studied.Finally,in order to verify the accuracy and practicability of the damage index,a modal experiment of homogeneous thin plate structure was designed.The homogeneous aluminum plate was selected as the experimental object,four different damage conditions were set,and the corresponding experimental platform was built.The modal frequency and mode shape data of damage structures under different working conditions were obtained by means of hammer strike method.Damage identification is carried out with damage indexes of modal curvature difference and rate of change of modal curvature,which verifies the effectiveness of the damage indexes mentioned in this paper and provides reference for practical engineering application.