Thermal Response Analysis of Lock-in Thermography Test to Identify the Delamination in Composite Materials

The delamination defects in the laminated composite structures are detected using the transient response analysis in the lock-in thermography test. The analysis procedure is implemented for the laminated composite plate subjected to harmonic heat flux in the top surface of the plate, in which the delamination defects with different sizes are located in different depths. The thermal wave propagation due to heat loading is simulated in the plate thickness along the healthy and defective regions and the amplitude and phase differences are determine in such regions. The phase difference of reflected waves is more sensitive to the defects than the amplitude of the waves. The results show that the phase difference between reflected waves from healthy and defective regions increases up to specific frequency value and the optimum frequency is determined using the present simulation. The results also show that the logarithmic phase difference depends linearly on the depth of delamination and such dependency can be used to determine the defect depth. The simulation results of lock-in thermography test are used to determine the optimum parameters required to detect the delamination in the laminated composite materials.