Variable pulse width pulsed thermography: theoretical model and experimental validation

As an advanced non-destructive testing (NDT) technology, pulsed thermography (PT) plays a crucial role in fields such as aviation, automotive transportation, and construction. The classical PT theoretical model uses the Dirac delta function to describe the temporal distribution of heat source power density. However, the duration of this highly singular function is infinitesimal, which not only oversimplifies the actual heat input conditions but also violates the applicability conditions of Fourier's law of heat conduction. This results in significant discrepancies between theoretical predictions and experimental results. To address this issue, this paper proposes an improved temporal distribution function for the pulse heat source power density. The work incorporates the effects of optical absorptivity and defect depth on the detection results. The Laplace transform method was employed to solve the one-dimensional (1D) transient heat conduction equation, leading to an improved PT theoretical model with a variable pulse width. To validate the accuracy and applicability of this model, PT detection experiments were conducted on metal additive manufacturing (MAM) components. The experimental results showed that the theoretical model more accurately reflects real-world conditions than the classical theoretical model. This work provides a more reliable theoretical foundation for optimizing PT system performance in practical NDT scenarios.