Study On Quantitative Damage Detection Method Of Layered Composites

With the rapid development of science and technology,layered composites have been widely used in various engineering fields for their superior mechanical properties.In the process of manufacturing and service,due to the long-term impact of load and mutation of external factors,it is easy to cause structural strength reduction and fatigue damage,if as a key stress component,it will bring great hidden dangers to production and safety.Therefore,it is of great significance to detect the structure state and discover the possible damage in time for the safety of the structure.The damage detection method based on vibration signal is an effective structural damage detection technology,which has been widely studied and applied.The general steps of structural damage identification are as follows: firstly,determine whether the structure has damage,and then determine the damage location(positioning)and damage degree(quantification).In this paper,based on vibration signals,the corresponding damage detection algorithm is developed for typical layered composites under different damage conditions,and the damage identification,location,and quantitative calculation are carried out.The main research contents and results are as follows:(1)A damage detection method is proposed to identify the exact location of the desoldering damage of laminated sandwich plate by identifying the damaged cell.Firstly,a damage detection method based on cell-matrix correlation was proposed according to the periodic characteristics of sandwich plates.The improved surface smoothing algorithm solved the problem of the method's dependence on the original health model,but the damage index decreased by more than 50%.Secondly,a damage identification method based on a twodimensional continuous wavelet transform is proposed,which not only solves the dependence of the method on the original health model but also improves the anti-noise ability of the damage identification method.Finally,the validity of the proposed methods is verified by processing the numerical simulation and experimental test data.(2)A two-stage damage quantitative detection method based on difference method and improved particle swarm optimization algorithm was proposed to solve the structural damage problems of laminates during processing and service.Firstly,the structural damage element was defined by the method of element elastic model reduction.The modal parameters of the numerical model of laminates under different damage conditions were obtained by the analysis of structural vibration characteristics,and the approximate damage area was identified by the difference method.Secondly,an improved particle swarm optimization(PSO)algorithm is used to accurately locate and calculate the damage based on the objective function constructed by the flexibility matrix of the structure.The numerical analysis results show that the errors of the damage degree identification results are all less than 1%.Finally,the feasibility of the proposed method for damage location identification and quantitative calculation of damage degree is verified by experiments.(3)To solve the problem of the dependence of the damage quantitative detection method in the above two stages on other methods and health model parameters in the first stage,a new damage quantitative detection method based on improved particle swarm optimization algorithm was proposed.By improving the population initialization and optimizing the boundary element,and directly processing the damage data with the new method,the precise position and damage degree of the damage element can be identified effectively,and the rapid quantitative calculation of the damage can be realized.However,with the large increase in the number of variables,the convergence times also increase about 2 times.Finally,the effectiveness of the proposed method is verified by numerical simulation.