In recent years, aperiodic, transient pulse compression favourable infrared imaging methodologies demonstrated as reliable, quantitative, remote characterization and evaluation techniques for testing and evaluation of various biomaterials. This present work demonstrates a pulse compression favourable aperiodic thermal wave imaging technique, frequency modulated thermal wave imaging technique for bone diagnostics, especially by considering the bone with tissue, skin and muscle over layers. In order to find the capabilities of the proposed frequency modulated thermal wave imaging technique to detect the density variations in a multi layered skin-fat-muscle-bone structure, finite element modeling and simulation studies have been carried out. Further, frequency and time domain post processing approaches have been adopted on the temporal temperature data in order to improve the detection capabilities of frequency modulated thermal wave imaging.
Reinforced concrete structures (RCS) have budding applications in civil engineering due to their high strength, durability, sustainability and flexibility in making complex shapes. However, loss of durability of constructed structures due to premature corrosion of rebar is a major constraint. An initial stage of cracking and corrosion of rebar in concrete is not detectable by visual inspection. With a view to avoid catastrophic failure and massive repair of structures, it is essential to determine damage at low levels. Growing concern about the safety of structure due to premature deterioration has led to a significant demand for advancement of non-destructive testing and evaluation (NDT&E) techniques for monitoring and assessing health of RCS. This paper highlights a whole-field, remote, non-destructive testing and evaluation method based on infrared thermography for identifying hidden corrosion of rebar in a concrete structure. Results shown for both time and frequency domain transform techniques prove the effectiveness of the proposed approach for identification of corrosion in rebar in the concrete specimen.
Among the widely used active infrared non-destructive testing and evaluation methods, coded thermal wave imaging modalities have proved to be an efficient testing and evaluation methods for characterization of various solid materials. These techniques makes use of relatively low peak power heat sources in a moderate time compared with the conventional pulsed based and sinusoidal modulated thermographic approaches respectively. This present work introduces a 11-bit Barker coded thermal wave imaging approach for characterization of mild steel sample having flat bottom holes as defects. Capabilities of the proposed approach has been studied on a mild steel sample containing flat bottom holes as sub-surface defects located at different depths and it has been modeled using a finite element method. Results show the defect detection capabilities of the proposed 11-bit Barker coded excitation scheme as a promising testing and evaluation method to detect the subsurface defects.
Glass Fibre Reinforced polymer (GFRP) composites are being used in a wide range of application areas since these materials are less affected by corrosive environmental conditions and provide longer life with less maintenance. However, there are still some concerns about reinforced polymers, such as the presence of surface and sub-surface defects which influence their in service applications. To detect these defects, InfraRed Thermographic (IRT) methods show their potential usage for Non-Destructive Testing and Evaluation (NDT&E) of composite materials due to their inherent testing capabilities such as remote, whole field, quantitative and qualitative to detect surface and sub-surface defects. Thermal NDT&E is broadly categorized into passive or active approach. In passive approach, the test sample's temperature distribution is monitored in the absence of any external heat stimulus at ambient conditions. However, this may not provide ample thermal contrast to detect the defects located at deeper depths. In order to detect deeper defects inside the test specimen, an active thermography is preferred. This can be carried out by applying an external heat stimulus, to induce enough thermal contrast over the test object. The thermal gradients appear over the material during the active heating due to the changes in thermal properties of defective and sound region leading to the detection of subsurface defects. This present work highlights a spectral reshaping by introducing a Gaussian window on the captured thermal profile in a frequency modulated thermal wave imaging and named as Gaussian Windowed Frequency Modulated Thermal Wave Imaging (GWFMTWI) technique. Further various multi-transform techniques (time and frequency domain based) have been introduced in order to test sub-surface defect detection capabilities in chosen GFRP sample. Comparison has been made with the non-stationary linear frequency modulated thermal wave imaging technique in terms of depth scanning capability. Results obtained from GWFMTWI clearly show better detection potential with improved test resolution and sensitivity.
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.
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.
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.
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.
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.
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.
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