Validation of Macro Fiber Composites for Strain Measurements in Structural Health Monitoring Applications of Complex Aerospace Structures

摘要

The use of piezoelectric sensors for Structural Health Monitoring is in a continuous expansion not only due to their low costs but also to their proven versatility to be used in a wide range of applications. The development of the sensors/actuators relying on piezoelectric materials, especially lead zirconate titanate (PZT), have followed closely the development of structural integrity assessment methods that have been developed through the years. Recently, a new type of piezoelectric transducer, the macro fibre composite (MFC), was developed at NASA Langley laboratory. The MFCs have been initially intended for the use in elastic wave based diagnostic procedures, which rely on the raw time history data, rather than on accurate measurements of strain or force. The latter, are usually required in modal based structural identification. The present research analyses the possibility to use these piezoelectric sensors for accurate strain measurements, opening the path towards the unification, under the same sensorial network, of continuous modal-based low frequency methods with triggered high-lrequency guided waves methods. The theoretical challenges regarding the prediction of the strain field based on the piezoelectric effect are reviewed and discussed. Experiments have been conducted in order to obtain the sensitivities of the MFCs with respect to strain in dynamic conditions. The MFCs strain was compared to that obtained from fibre Bragg (FBG) strain sensors. Two sets of experiments were performed, one on a fixed-free aluminium beam, for preliminary evaluation of the sensitivities and one on a free-free Sokol W3 helicopter main rotor blade for a frequency-response model based structural identification. The results of all tests are presented and the capability of the MFCs to be used as strain sensors is analysed.