Lock-in thermal wave detection of defective composite material based on phase-shifting technology

In order to improve the defect recognition ability and accuracy of the lock-in thermal wave detection technology, a temperature sequence processing method based on phase-shifting technology was proposed. A step-plate model of carbon fiber composite material with gradual thickness was established to study the relationship between thickness and phase under different modulation periods, effects of non-phase-shifting and phase-shift of temperature series in different modulation periods were numerically analyzed, the results show that the sensitivity of the phase to thickness is increased by three times after phase-shifting by 180, and the phase difference between different thicknesses is increased, which enhances the ability to identify defects. The carbon fiber plate with flat hole defects was used to verify the numerical calculation and the phase diagram obtained by non-phase-shifting and phase-shifting by 180 was compared, the results show that smaller defects can be identified after phase-shifting and the contrast near the defect was enhanced, which proved the effectiveness of phase-shifting technology to improve the ability of lock-in thermal wave for detecting defects.