Research On Structural Health Monitoring Method For Fatigue Crack Growth Monitoring

Structural Health Monitoring (SHM) is a leading subject covering many different technologies. SHM system has the ability of real-time on-line detecting compared with Non Destructive Testing (NDT) technology. Lots of damage happened in structures are usually caused by non-appearance cracks at the initial state. It is very important to detect the crack correctly and immediately to ensure the safety of the structure. The crack monitoring is a difficult topic in the area of SHM and has become a research focus.This paper adopts active Lamb wave technology to monitor the crack initiation and growth. The main works can be generalized as following:1. The process of fatigue crack propagation was studied. With the characteristic of real fatigue crack damage, the SHM method to monitor crack growth was researched theoretically.2. The basic theory regarding the piezoelectric component was researched first. Then the ways to excite Lamb wave were experimentally studied, in which circle and single exciting methods, one-side and double-side exciting methods were particularly compared.3. An integrated experimental system was developed for crack growth monitoring research. The study of the system hardware mainly included the design of experimental specimens, selection of fatigue testing equipment and construction of wave generation and data acquisition subsystem. The software research included the design of user interface of wave generation and data acquisition subsystem and the signal processing program.4. The growth of side crack and hole-edge crack were monitored in-situ. A method was put forward to use the first-half wave packet energy of the S0 mode of the Lamb wave received as damage signature to represent different crack growth grades. Experiments were designed to research the relationship of the energy differences with the real crack growth. A signature index was defined to represent the crack growth grade. The relationship of the Lamb wave changing with the growth of fatigue crack was obtained in the research.