Diagnosis Method Of Damage Probability For Complex Structures

The damage occurrence and evolution of complex structural parts,such as metal-nonmetals and special-shaped composite materials,are complicated.The regional cumulative expansion of damage is prone to cause safety accidents.It is meaningful to research and apply the monitoring of the cumulative damage.Based on the basic mechanism of diagnosing the regional damage,the probability based damage diagnosis method and was studied by using piezoelectric impedance for metal-non-metal structures.In the proposed method,the characteristic parameter of the structure-sensor electromechanical impedance spectrum is extracted which is based on the principle of electromechanical coupling.Based on the Euclid principle,the characteristic parameter under different cumulative damage states was analyzed to quantitatively determine the damage area and the cumulative degree of damage.The sparse sensing array was used to obtain the correspondence between cumulative degree of damage and the characteristic parameters.Then,a Gaussian probability diagnosis model for the cumulative degree of damage is conducted.With few sensors,the damage area and the cumulative damage could be determined.The experimental results on a real world engineering structural part showed that the damage characteristic parameter changes significantly with the propagation of the damage.The damage area and the cumulative degree of damage were detected well.The following aspects were mainly studied in this thesis:(1)The theory of structural health monitoring and the propagation mechanism of Lamb wave in special-shaped composite material structures was introduced,the principle of piezoelectric impedance,electromechanical coupling during the excitation process and the damage evaluation method based on the principle of electromechanical coupling were analyzed.(2)The signal processing methods for complex structural component damage in traditional structural health technology were analyzed and compared.The piezoelectric impedance measurement method was used to analyze the mechanism of the collected damage signals,and the damage characteristic parameters under different cumulative damage degrees were extracted.Based on the Euclid principle,the characteristic parameter under different cumulative damage states was analyzed to quantitatively determine the damage area.The cumulative degree of damage was established to confirm the property of the damage characteristic parameters.(3)A symmetric linear sparse sensor array was designed to establish the corresponding mathematical function relationship between the cumulative damage degree and the damage characteristic parameters.The original theoretical researches were broken.The Gaussian probability diagnosis of the cumulative damage degree model was constructed.(4)The solution for the cumulative damage degree was designed to realize the assessment of different cumulative damage levels,completed from hardware construction and software process.Experiments were detected on metal-non-metal composite structures.The solution was verified by the cumulative damage form of the area on the rectangular sensing arrays.Finally,the experimental results showed that the damage characteristic parameters changed significantly with the propagation of damage.The damage area and the cumulative degree of damage were detected well.The experimental results showed that the damage area and cumulative damage were detected well by the cumulative damage assessment method for complex structures.The electromechanical impedance monitoring technology was not susceptible to the influence of structural complexity in the study of damage monitoring of complex structures.The feasible path for solving the damage monitoring and damage accumulation diagnosis of complex structures was provided.It is also an important research topic in the field of nondestructive testing and structural health monitoring.