The energy class discrimination of low velocity impacts on composite material structure by Bragg grating sensor technique

The low velocity impacts (LVI) often bring damages which cannot be detected from surface of composite material smart structure. In this paper, Bragg grating sensors were used to discriminate energy classes of LVI on composite material smart structure under constant temperature. The energy discrimination was realized by means of this characteristic that the center wave-lengths of Bragg grating sensors on composite structure under LVI are determined by strain. By analyzing the frequency spectrums of LVI signals captured by optic fiber grating demodulator, a threshold for distinguishing energy classes can be figured out after calculating frequency spectrum peak values of all energy classes. The experimental results indicate that Bragg grating sensors can be used for monitoring impacts and discriminate the energy classes of LVI on composite material structure.