On-line measurement of material properties for composite wing structures

Structures will encounter degradation of material properties in changing service environments. To improve structural safety and prevent accident, it is necessary to examine material properties of structures in nondestructive ways. Although several nondestructive evaluation techniques have been developed in the literature, most of them detect local damages not global material properties. In this paper, an on-line and real-time detection system is developed through the concept of inverse analysis. In this system, the detectors are selected to be natural frequencies and static strains whose relations with material properties can be obtained from analytical solution or commercial finite element software or experimental data. Transferring their relations into training patterns of artificial neural networks, the elastic properties of composite wing structures can be determined on-line with frequency and strain sensors embedded into structures. To illustrate this on-line measurement system, an example of NACA 2412 composite wing is provided in this paper. This example shows that the material properties determined through this on-line system well agree with the values obtained from the conventional testing methods. The difference is that the present method determines the properties on-line and real-time without cutting any specimen on the structures and testing specimens in the laboratory.