Vanita Arora

Pulse Compression with Gaussian Weighted Chirp Modulated Excitation for Infrared Thermal Wave Imaging

This paper proposes a novel signal processing approach to thermal non-destructive testing by incorporating Gaussian window function onto the linear frequency modulated incident heat ∞ux to achieve better pulse compression properties. The present work highlights a flnite element analysis based modeling and simulation technique in order to test the capabilities of the proposed windowing scheme over the conventional frequency modulated thermal wave imaging method. It is shown that by using Gaussian weighted chirp thermal stimulus, high depth resolution can be achieved.

Pulse Compression Approach to Nonstationary Infrared Thermal Wave Imaging for Nondestructive Testing of Carbon Fiber Reinforced Polymers

Infrared thermography (IRT) is one of the promising remote and whole field inspection techniques for nondestructive characterization of various solids. This technique relies on the mapping of surface temperature response to detect the presence of surface and subsurface anomalies within the material. Due to its fast and quantitative testing capabilities, the IRT has gained significant importance in the testing of fiber reinforced polymers (FRP). A carbon FRP sample with flat bottom holes is considered for inspection using nonstationary digitized frequency modulated thermal wave imaging technique. Furthermore, depth scanning performance using frequency domain-based phase approach has been compared with recently proposed time domain phase approach.

Numerical approach to binary complementary Golay coded infrared thermal wave imaging

A novel binary complementary (Golay) coded infrared thermal non destructive testing and evaluation approach is introduced for characterization of mild steel sample having flat bottom holes as defects. The resultant correlation results of these individual Golay complementary codes used to reconstruct a short duration high peak power compressed pulse to extract the subsurface features hidden inside the test sample. In this paper, a finite element method has been used to model a low carbon steel sample containing flat bottom holes as sub-surface defects located at different depths. Results show the depth scanning capabilities of the proposed Golay complementary coded excitation scheme as a promising testing and evaluation method to detect the subsurface defects with improved resolution and sensitivity.

Theory, modeling, and simulations for thermal wave detection and ranging

Active infrared thermography for nondestructive testing and evaluation is a rapidly developing technique for quick and remote inspection of subsurface details of test objects. Sinusoidal modulated thermal wave imaging such as Lock-in thermography (LT) significantly contributed to this field by allowing low power controlled modulated stimulations and phase based subsurface detail extraction capabilities. But demand of repetitive experimentation required for depth scanning of the test object, limits its applicability for realistic applications and demands multi frequency low power stimulations. Non-stationary thermal wave imaging methods such as frequency modulated thermal wave imaging (FMTWI), digitized FMTWI and coded thermal wave imaging methods permitting multi frequency stimulations to cater these needs and facilitate depth scanning of the test object in a single experimentation cycle. This contribution highlights theory, modeling and simulation for non-stationary modulated thermal wave imaging methods for non-destructive characterization of solid materials.

Recent advances in thermal wave detection and ranging for non-destructive testing and evaluation of materials

Thermal Wave Detection and Ranging (TWDAR) for non-destructive testing (TNDT) is a whole field, non-contact and non-destructive inspection method to reveal the surface or subsurface anomalies in the test sample, by recording the temperature distribution over it, for a given incident thermal excitation. Present work proposes recent trends in nonstationary thermal imaging methods which can be performed with less peak power heat sources than the widely used conventional pulsed thermographic methods (PT and PPT) and in very less time compared to sinusoidal modulated Lockin Thermography (LT). Furthermore, results obtained with various non-stationary thermal imaging techniques are compared with the phase based conventional thermographic techniques.

Pulse compression approach to digitized frequency modulated infrared imaging for non-destructive testing of carbon fibre reinforced polymers

InfraRed Thermal Wave Imaging (IRTWI) is one of the promising non-contact and full field inspection technique for non-destructive characterization. This technique relies on the mapping of surface temperature distribution to visualize the presence of surface and subsurface anomalies in the test material. Due to its fast and quantitative evaluation capabilities, IRTWI has gained significant importance in the characterization of Carbon Fiber Reinforced Polymers (CFRP). A CFRP specimen having flat bottom holes is considered for inspection using non-stationary Digitized Frequency Modulated Thermal Wave Imaging (DFMTWI) technique. Further depth scanning performance by using frequency domain based phase approach has been compared with recently proposed time domain phase approach.

Complementary Coded Thermal Wave Imaging Scheme for Thermal Non-Destructive Testing and Evaluation

Abstract Infrared thermography is a well-established technique for the non-destructive characterisation of various materials. This technique relies on the analysis of acquired temperature profile over the test sample to evaluate the presence of surface and sub-surface anomalies within the material. Over past decade coded thermal excitation schemes and associated post processing (signal/video processing) schemes have gained vital attention in infrared thermographic community in various fields. However, in thermal non-destructive testing the usage of coded excitations are still relatively uncommon. This paper explores the feasibility of using complementary Golay coded excitation in active thermography. The newly developed technique is shown to be effective in increasing temporal signal to noise ratio by suppressing side lobes of the compressed pulse. The present experimental investigation emphasises the defect detection capabilities of Golay coded thermal wave imaging to characterise a carbon fibre reinforced plastic material having blind holes and inclusions as defects. An investigation of spatial signal to noise ratio is also presented.

Non-stationary thermal wave imaging for nondestructive testing and evaluation

Among various widely used Infrared Thermal Non-destructive Testing (IRTNDT) modalities, non-stationary thermal wave imaging (NSTWI) methods have proved to be an indispensable approach for the inspection and evaluation of various materials. Growing concerns of surface and subsurface defect detection capabilities with moderate peak power heat sources than the widely used conventional pulse based thermographic methods and in a reasonably less testing time compared to sinusoidal modulated lock-in thermography, make these NSTWI techniques invaluable for this field. The present work highlights a comparative study on various NSTWI techniques, further experimental results are presented to find their defect detection capabilities by taking signal to noise ratio (SNR) into consideration.

Nondestructive testing and evaluation of composites by non-invasive IR Imaging techniques

InfraRed Thermography (IRT) is one of the promising technique for non-destructive testing method for characterization of materials. This technique relies on evaluation of the surface temperature variations to detect the presence of surface and subsurface anomalies within the material. Due to its whole field and remote testing capabilities, IRT has gained significant importance in testing of Glass Fiber Reinforced Plastic (GFRP) materials. A GFRP sample with defects of various sizes at a given depth was inspected using non-stationary thermographic techniques. In order to highlight the defect detection capabilities of the proposed non-stationary schemes, a comparison has been made using matched excitation energy in frequency domain by taking signal to noise ratio into consideration.

Non-destructive testing of steel sample by non-stationary thermal wave imaging

This contribution demonstrates an application of non-stationary frequency modulated thermal wave imaging technique for the numerical characterization of a mild steel sample containing random shape defects. Frequency and time domain based phase analysis schemes are implemented on the recorded thermal profiles and their detectabilities are compared by taking signal to noise ratio into consideration.