Application of Characteristic Parameters of Ultrasonic Power Spectrum in Testing for Composite Porosity

The relationship between porosity of carbon fiber reinforced polymer from 0.03% to 2.3% and characteristic parameters, such as principle frequency, central frequency, frequency of weighted power spectrum, energy for limited frequency band(ELFB)and energy for principle frequency(EPF), was investigated based on the ultrasonic testing system model and the power spectrum analysis method for composite materials. The correlation between porosity，ELFB and EPF was mainly analyzed quantitatively. The results showed that ELFB decreased linearly when the porosity increased from 0.03% to 0.67%, while ELFB decreased according to quadratic equation when the porosity increased from 0.67% to 2.3%; the correlation between porosity and EPF changes from linear to quadratic curve when the porosity exceeded 0.64%; The changing of CFRP porosity can be characterized by ELFB and EPF effectively.