Extension of the Thermographic Signal Reconstruction Technique for an Automated Segmentation and Depth Estimation of Subsurface Defects

Abstract

With increased use of light-weight materials with low factors of safety, non-destructive testing becomes increasingly important. Thanks to the advancement of infrared camera technology, pulse thermography is a cost efficient way to detect subsurface defects non-destructively. However, currently available evaluation algorithms have either a high computational cost or show poor performance if any geometry other than the most simple kind is surveyed. We present an extension of the thermographic signal reconstruction technique which can automatically segment and image defects from sound areas, while also estimating the defect depth, all with low computational cost. We verified our algorithm using real world measurements and compare our results to standard active thermography algorithms with similar computational complexity. We found that our algorithm can detect defects more accurately, especially when more complex geometries are examined.

Multispectral High Temperature Thermography

“…The methods used in LWIR thermal imaging to reduce the influence of ε and environmental radiation are not applicable in high temperature thermography. Therefore, researchers from different countries show interest in multispectral thermography and create appropriate laboratory samples [10][11][12][13]. Numerical modeling and practical testing of multispectral thermography methods convince that to solve practical problems of monitoring thermal processes, it is sufficient to use the registration of thermal in three parts of the spectrum.…”

“…In large enterprises, when controlling processes with stably repeating parameters (for example, rolling mills), the deviation of the partial radiation temperature Tr from the specified values is usually used, since the parameters of thermal processes are stable. In the case of new complex thermal processes, however, it is desirable to determine the real values of T. Therefore, when the εeff, is uncertain, some authors suggest a more complex thermographic technique [10], using the measurement of thermal radiation in three [11], four [12], or even eight spectral bands [13]. Only low-cost thermographic techniques with stable methods of digital processing of registered thermal fields can have practical application in the control of high-temperature thermal processes.…”

Latest Advances in Common Signal Processing of Pulsed Thermography for Enhanced Detectability: A Review

“…A change in effective thermal diffusivity characterizes defect detection with conventional TSR. Recently, Schager et al [71] studied an extended TSR technique that can automatically segment defects into defects in the sound domain and generate defect maps by utilizing the signal characteristics of defects. They showed that the defect map provides an estimate of the depth of the defect and is inexpensive to compute.…”

In-Situ Pixel-wise Emissivity Measurement Using a Multispectral Infrared Camera

“…For example, it is employed in characterizing the thermal behavior of materials during mechanical tests such as tensile tests [1], fatigue tests [2], and machining operations [3]. Additionally, it is utilized in the detection of defective products [4][5][6][7][8], or to characterize materials [9][10][11][12]. This measurement technique is relatively simple to set up and is non-destructive.…”