Abstract
In this study, we characterize the lateral dimension, depth, and inclination of buried tilted rectangular heat sources from time domain temperature data measured at the surface. The heat sources are representative for planar defects that emit heat in thermographic tests with internal burst excitation. We present a semi-analytical expression for the evolution of the surface temperature distribution. The emitted flux, dimensions and inclination of the heat source are determined by fitting the model to two perpendicular surface temperature profiles and the temperature history at one point of the surface. We show that the sensitivity of the data to the geometrical parameters of the heat source decreases as the angle it makes with the surface increases. The study also shows that the optimum duration of the excitation corresponds to a thermal diffusion length covering the distance from the surface to the deepest end of the heat source. The accuracy and precision of the results for different noise levels and inclinations have been tested by fitting the model to synthetic data with added noise. Fittings of experimental induction thermography data on 3D printed photo-polymeric resin samples containing calibrated Cu slabs confirm that it is possible to characterize tilted rectangular heat sources from surface temperature data.
Highlights
Thermographic techniques have proven to be very efficient nondestructive testing methods for the detection of defects in a wide variety of materials [1]
The presence of a defect distorts heat diffusion and produces an anomaly in the surface temperature distribution that is measured with an IR camera
In other thermographic modalities with ultrasonic [2] or inductive excitation [3], heat is mainly generated at the defects
Summary
Thermographic techniques have proven to be very efficient nondestructive testing methods for the detection of defects in a wide variety of materials [1]. The most common application of inductive thermography is the detection of cracks in electrically conducting parts [3] In these applications, Eddy currents induced in the material generate heat by the Joule effect and the presence of cracks may distort either heat propagation or Eddy currents distribution, which often entails an additional source of heat. In these works, the spatial extension and depth of vertical cracks was retrieved by inverting lock-in surface temperature data obtained under modulated excitation [5,6,7], as well as time domain data obtained under burst excitation [8,9,10]. The results prove that it is possible to determine the dimensions, depth, and inclination of the heat source from surface temperature data
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