Active Infrared Thermography Research Articles

Depth resolved pulse compression favourable frequency modulated thermal wave imaging for quantitative characterization of glass fibre reinforced polymer

InfraRed Thermography is an expeditiously growing non-destructive testing and evaluation technique widely used to estimate the subsurface defect details in fibre reinforced polymer materials due to its remote, fast, easy, safe and wide area monitoring abilities. In order to explore the details of subsurface anomalies in active infrared thermography, a modulated heat flux with a predefined intensity and bandwidth is employed to excite the test sample. Among various widely used active infrared thermographic techniques for non-destructive testing and evaluation applications, pulse based and modulated lock-in thermography are predominantly in use. However, these conventional techniques limits their applicability due to high peak power heat source requirements (pulse based techniques) and poor resolution (modulated lock-in thermography) for detecting the defects located at various depths of different lateral dimensions. The present paper highlights a pulse compression favourable frequency modulated thermal wave imaging which can be carried out with moderate peak power heat sources in a limited span of time with improved test resolution and sensitivity. Further the proposed experimentation is validated with the analytical as well as numerical simulations on glass fibre reinforced polymer samples having flat bottom hole defects.

Pixel-based thermal sequence processing algorithm based on R2 fractile threshold of non-linear fitting in active infrared thermography

A novel algorithm for pixel-based thermal sequences processing based on R2 (coefficient of determination, COD) fractile threshold of non-linear fitting is proposed. Original data are obtained from active laser infrared thermography inspection to an aviation CFRP laminate with artificial defects. By fitting temperature sequence of pixels in a thermogram using the 1st-order and 2nd-order Fourier function, R2 is calculated and attached to each pixel. It is found that R2 of defective pixels is greater than that of non-defective pixels. The threshold for filtering background pixels is determined by histogram analysis of R2 set in a thermogram. Then fractile thresholds of R2 set separate pixels from defect and non-defect region. The temperature value of non-defect pixels is reduced to contrast with defect pixels. The edge of defects is sharpened, and detectable defects increase. Combining the fractile thresholds of 1st-order and 2nd-order Fourier fitting, the final processed thermograms exhibit improved detection performance evaluated by simplified probability of detection (POD) analysis and signal-to-noise ratio (SNR) calculation. In this work, the tested data show huge promotion of defect detection rate. Defect with an aspect ratio of 3.0 is detected. The combine-processed thermogram possess the maximum SNR of defective area.

Comparison of Cooled and Uncooled IR Sensors by Means of Signal-to-Noise Ratio for NDT Diagnostics of Aerospace Grade Composites.

This work aims to address the effectiveness and challenges of non-destructive testing (NDT) by active infrared thermography (IRT) for the inspection of aerospace-grade composite samples and seeks to compare uncooled and cooled thermal cameras using the signal-to-noise ratio (SNR) as a performance parameter. It focuses on locating impact damages and optimising the results using several signal processing techniques. The work successfully compares both types of cameras using seven different SNR definitions, to understand if a lower-resolution uncooled IR camera can achieve an acceptable NDT standard. Due to most uncooled cameras being small, lightweight, and cheap, they are more accessible to use on an unmanned aerial vehicle (UAV). The concept of using a UAV for NDT on a composite wing is explored, and the UAV is also tracked using a localisation system to observe the exact movement in millimetres and how it affects the thermal data. It was observed that an NDT UAV can access difficult areas and, therefore, can be suggested for significant reduction of time and cost.

Efficiency of NDT techniques to detect voids in grouted post-tensioned concrete ducts

ABSTRACT Variations in the design requirements of prestressed concrete girders lead to variations in their geometry and section profile, thereby influencing the characteristics of the waves which form the working principles of the various NDT techniques, and thus possibly shield the presence of air void. Thus, an experimental plan was adopted to study the effect of the changes in parameters like the cover to the duct, the material of the duct, the number of strands, and diameter of the duct on the efficiency of Ultrasonic Pulse Velocity (UPV), Ground Penetrating Radar (GPR) and Infrared Thermography (IRT) (active and passive) to detect a simulated void in a grouted duct. Seven 150 × 150 x 750 mm specimens were prepared with duct embedded in concrete. Both steel (inner diameter 106.6 mm) and plastic (inner diameter 105 mm and 86 mm) ducts were used. Three specimens had 3 strands, three specimens had 5 strands, and one specimen had 8 strands. It was found that the efficiency of GPR increased with the increase in the number of strands and duct diameter. Active IRT is highly efficient for the detection of voids than Passive Thermography. The presence of steel strands influenced UPV results.

Complementary Use of Active Infrared Thermography and Optical Coherent Tomography in Non-destructive Testing Inspection of Ancient Marquetries

Imaging-based inspection techniques have practical advantages in the study and/or rehabilitation of artworks. They provide in some cases internal information on the status of the sample to be inspected. On the one hand, techniques based on active infrared thermography (IRT) are advantageous to obtaining complete images of the inspected parts, although a technical interpretation performed by a team of experts in non-destructive testing (NDT) techniques is needed above all when the target is composed, as in our case, by different materials. On the other hand, optical coherence tomography (OCT) is slow when inspecting complete parts, but it has great level of structural detail in subsurface measurements up to 3 mm. The complementary use of these two techniques, and its application to a very ancient marquetry sample with an unusual tessellatum layer, is presented herein. The plan size of the sample is 208 × 212 mm, while the tessellatum is 1.5 mm thick. Starting from thermal imaging inspections, using step-heating (SH) and pulsed thermography (PT), a defect map has been defined. Structural details of these defects using OCT will help the restorer in charge of the restoration process to perform a satisfactory work.

Investigation of reconstructed three-dimensional active infrared thermography of buried defects: multiphysics finite elements modelling investigation with initial experimental validation

In this paper, we use a Multiphysics approach in COMSOL™ Platform to develop and validate a finite element model that simulates thermal images obtained in active thermography mode. This approach allows variation in material properties, the selection of active thermography methods such as Flash, Pulse Phase & Lock-in techniques, source wavelength, depth and dimensions of defect. We then take experimental thermography images of a defect embedded into a PLA block to compare with simulated images generated by the Multiphysics model. Our work shows the feasibility of real-time three-dimensional (3D) active infrared thermography (IRT) of buried defects. Such imaging can be hugely beneficial not only in quality control and process optimisation in additive manufacturing but also determination of shape and outline of tumours and plaques in medical applications.

Thermographic imaging for early detection of biocolonization on buildings

ABSTRACT Biofilms developed on historical heritage buildings are made of various microbial communities settled and anchored in a substrate. They provide a good medium to the development of macroscopic vegetation which causes irreversible and physical damage to stone structure. Infrared thermography (IRT) measurements have been performed in laboratory scale to investigate the applicability of this non-destructive technique to an early detection of microbial biofilms on stone surface. Detecting biofilms before stone soiling is important in Cultural Heritage conservation to avoid both irreversible damage and building restoration costs. Active IRT was set up on a French limestone used in many French buildings and monuments. Samples were collected after six-months of exposure in an outdoor biofouling test during which they were colonized by microbial biofilms. They have been compared with controls with no biofilm. Experimental set-up has been carried out in dry and damp conditions to simulate different climatic conditions. First results displayed a different thermal response: stone surfaces with biofilm reached higher temperatures and they cooled down faster than row stones. Biofilm entailed a change of the stone thermal behaviour similar to a monolayer. IRT detected biofilm with a better efficiency in dry than in damp condition.

Boron nitride inclusions within adhesive joints: Optimization of mechanical strength and bonded defects detection

Non Destructive Testing (NDT) by active InfraRed Thermography (IRT) of bonded Carbon Fibers Reinforced Plastic (CFRP) laminates is a very challenging issue. Adding Boron Nitride (BN) particles within the joint material provides an interesting solution to better capture bonding defects. Though increasing additives leads to the improvement of NDT, the validation of this solution requires the mechanical characterization of the new joint material. In this way, the influence of particles on the mechanical properties of the adhesive joint is first investigated via double strap lap shear tests for different BN volume fraction. At the same time, controlled size void inclusions are generated within composite assemblies in order to evaluate the IRT ability to detect bonded defects inside BN-based adhesives. It is demonstrated that thermal data post-processing methods such as Singular Values Decomposition (SVD) and Principal Component Thermography (PCT) help to get the best trade-off between mechanical performance and defect detection.

Comparison between air-coupled ultrasonic testing and active thermography for defect identification in composite materials

ABSTRACT Glass or carbon fibre-reinforced polymer (FRP) structures have attained a relevant role in modern production thanks to their lightweight, high resistance to corrosion and fatigue, and relative ease of manufacturing complex shapes. Nevertheless, several types of defects, such as voids, matrix fractures, delaminations and impact damages, which might significantly reduce the useful life of composite-made structural components, are often difficult to be identified. Conventional non-destructive methods, such as ultrasonic testing, are routinely used to monitor composite constructions with good results. However, an inspection of large structures requires alternative and faster NDT methods. Among these, air-coupled ultrasonic testing (ACUT) and active infrared thermography (AIRT) are generally considered the most promising ones. In this paper, ACUT and AIRT have been compared by performing experimental tests on two reference composite panels with synthetic defects. Polytetrafluoroethylene (PTFE) and aluminium inserts with different sizes and located at various depths have been used as artificial defects. The relative merits and drawbacks of the two techniques have been highlighted in terms of defect size sensitivity, maximum depth that can be detected, and thermo-physical properties of the reflector. A qualitative and quantitative analysis has been carried out to evaluate the ability of the two techniques in retrieving the actual size of the subsurface defects.

Termografía infrarroja (TI) para detectar los defectos internos causados por los insectos xilófagos en los culmos de bambú

Infrared Thermography (IRT) is a technique used in the inspection of constructive elements in buildings. It has a great potential for the investigation of pathological manifestations because it is a strictly non-destructive procedure that could be rapidly applied in fieldwork. This research analyzes the possibility of using active IRT to detect internal defects caused by xylophagous insects in bamboo culms, in order to apply it in the fieldwork for the inspection of pathological manifestations in buildings. In laboratory, samples of bamboo culms of Bambusa tuldoides and Phyllostachys bambusoides species were submitted to a thermographic experiment using a thermographic camera and FLIR B400 software. Subsequently, the potential for using this technique in the fieldwork was evaluated. The results point the limitations of both, technique and method used, to identify perforations of diameter less than or equal to 3 mm located in the inner wall of the bamboo culms.

Numerical Simulation of Non-Destructive Characterization of CFRP Composite Through Frequency Modulated Thermal wave Imaging

Non-destructive testing plays a vital role in industrial and biomedical applications. Non-stationary stimulation based active Infrared thermography is an emerging area of interest in subsurface defect detection and visualization. In present article, frequency modulated thermal wave imaging is employed on a numerical simulation to detect defects of CFRP specimen and applied various post processing techniques such as FFT phase, Pulse compression, principal component analysis and random projection transform for better defect detection. Defect Signal to noise ratios considered as merit of analysis.

Infrared (IR) thermography-based quantitative parameters to predict the risk of post-operative cancerous breast resection flap necrosis

Despite intraoperative clinical evaluation, development of post-breast reconstruction surgery flap necrosis is not uncommon. This results in prolonged healing or the need for a secondary corrective procedure to remove the necrosis part. In the present study, to predict the post-operative necrosis risk (within 24 h), novel passive and active dynamic thermography-based quantitative parameters were tested. Thirty-two patients, undergoing breast reconstruction surgery, were recruited, on whom, post-surgery passive and active infrared (IR) thermography examinations were performed. Using the resultant quantitative parameters, a cut-off value-based classification model was tested that resulted in a highest sensitivity, specificity, and accuracy of 89%, 87%, and 88%, respectively, for the passive thermography examination performed just after the surgery.

Application of numerical procedure for thermal diagnostics of the delamination of strengthening material at concrete construction

PurposeLarge structural objects, primarily concrete bridges, can be reinforced by gluing to their stretched surface tapes of fiber-reinforced polymer (FRP). The condition for this technology to work requires the quality of the bonding of FRP and the concrete to be perfect. Possible defects may arise in the phase of construction but also as a result of long-term fatigue loads. These defects having different forms of voids and discontinuities in the bonding layer are difficult to detect by optical inspection. This paper aims to describe the development of a rapid and nondestructive method for quantitative assessment of the debonding between materials.Design/methodology/approachThe applied technique belongs to the wide class of active infrared (IR) thermography, the principle of which is to heat (or cool) the investigated object, and determine the properties of interest from the recorded, by an IR camera, temperature field. The methodology implemented in this work is to uniformly heat for a few seconds, using a set of halogen lamps, the FRP surface attached to the concrete. The parameter of interest is the thermal resistance of the layer separating the polymer tape and the concrete. The presence of voids and debonding will result in large values of this resistance. Its value is retrieved by solving an inverse transient heat conduction problem. This is accomplished by minimizing, in the sense of least squares, the difference between the recorded and simulated temperatures. The latter is defined as a solution of a 1D transient heat conduction problem with the already mentioned thermal resistance treated as the only decision variable.FindingsA general method has been developed, which detects debonding of the FRP tapes from the concrete. The method is rapid and nondestructive. Owing to a special selection of the compared dimensionless measured and simulated temperatures, the method is not sensitive to the surface quality (roughness and emissivity). Measurements and calculation may be executed within seconds. The efficiency of the technique has been shown at a sample, where the defects have been artificially introduced in a controlled manner.Originality/valueA quantitative assessment procedure which can be used to determine the extent of the debonding has been developed. The procedure uses inverse technique whose result is the unknown thermal resistance between the member and the FRP strip.

Comparative study of active infrared thermography, ultrasonic laser vibrometry and laser ultrasonics in application to the inspection of graphite/epoxy composite parts

ABSTRACT Three nondestructive testing techniques, namely, optically- and ultrasonically stimulated infrared thermography, ultrasonic laser vibrometry and laser ultrasonics, have been comparatively investigated in the inspection of a graphite-epoxy sample characterized by a complicated geometry to demonstrate advantages and drawbacks of each technique in the detection of different types of defects.

Thermal response of building stones contaminated with salts

The accumulation of salts in building stones can lead to weathering features such as scaling, sanding or even slab detachment. To detect salts in walls at the early stages and to predict their evolution, the non-destructive technique (NDT) Infrared Thermography (IRT) was tested in a stimulated way. The main objective was to trial this technique in order to obtain more information such as the type of salt, its precise location and its concentration in building stones.Three building materials were studied, including two natural limestones and a reconstituted stone. Samples were submitted to immersion/drying tests in water and in salt solutions of Na2SO4, NaCl and MgSO4 at 7%, 14% and 26% in weight during 20 cycles of 24 h. The weight of the samples and the surface colour were recorded after each cycle. After 1, 5, 10 and 15 cycles, 3 samples were taken out for active IRT measurements.The results showed that when the porosity and the capillarity are low, the intake of salts into the porous network is low and the thermal response of the stone to heating (ΔTmax) corresponds to the salt thermal signature and has no relation with concentration. On the other hand, when the initial porosity is high, salts crystallize inside the porous network and porosity decreases. Hence, the thermal response of the porous stone is related to salt concentration and the ΔTmax increases until the stone starts to disaggregate.Active IRT is a promising NDT adapted to identify and quantify salts within building stones during the first states of accumulation.

U-value time series analyses: Evaluating the feasibility of in-situ short-lasting IRT tests for heavy multi-leaf walls

A gap in standardization of quantitative infrared thermography (IRT) directly leads to a lack of measurement pattern for determining in-situ U-values of heavy multi-leaf walls. Three groups of causal factors might influence the estimation of this build quality indicator: operating conditions, thermophysical properties and technical conditions. Focusing on the last one, previous studies underlined the difficulties of measuring below 3 h. In contrast to active IRT, no algorithms have been found to process images, despite playing an important role in the effectiveness and robustness of IRT. The traditional approach involves analysing from 120 to 7200 thermograms with a data acquisition interval of 1 min up to 1 s respectively. The aim of this paper was to critically assess the test duration that is traditionally used. Six real heavy multi-leaf walls were tested under a stationary regime as a stochastic process of underlying data. For the first time, a research based on two U-value time series analyses (statistical tests and a signal modelling technique by MATLAB) demonstrated the feasibility of short-lasting IRT tests. Moreover, this research posed an innovative data management tool to automate this non-destructive testing (NDT) in mid-term, stopping IRT tests in real time once the right level of accuracy was achieved.

Coded thermal wave imaging technique for infrared non-destructive testing and evaluation

ABSTRACTActive InfraRed Thermography (IRT) is one of the promising Non-Destructive Testing (NDT) and evaluation method for inspection of various solid materials. Its inherent inspection capabilities such as remote, wide area monitoring, fast, quantitative and safe deployment in field test makes active IRT as a vital testing technique in NDT community. The present work introduces a novel application based on recently proposed Golay Coded Thermal Wave Imaging (GCTWI) to examine mild steel and carbon fibre reinforced polymer (CFRP) test samples having sub-surface defects. Further defect detection capability of the proposed approach is compared with the conventional frequency domain phase approach on each sequence by considering the signal-to-noise ratio as a figure of merit.

Effectiveness of phased array focused ultrasound and active infrared thermography methods as a nondestructive testing of Ni-WC coating adhesion

ABSTRACTThe substrate/coating adhesion is a crucial parameter conditioning the quality of coating and its durability in service. For this reason, an inspection of the coating integrity, in particular, the presence of adhesion defects will be of great importance. The adhesion inspection is usually ensured by destructive methods, such as traction, interfacial indentation, four-point bending, testing scratch, etc. However, it is currently hampered by the absence of a satisfactory non-destructive method. Among the non-destructive testing technologies widely used in the industrial field, there are X-ray diffraction, ultrasonic inspection, and infrared thermography. In this paper, two methods are investigated: ultrasonic inspection, which becoming more efficient, especially with the emergence of phased array systems that allow to investigate different inspection angles and focusing depths, and the active infrared thermography. Experiments were performed on metallic coatings deposited on a mild steel substrate. Coatings were containing artificial defects (flat bottom holes with different diameters) at the interface and others were exempts of defects. Longitudinal waves with specific delay laws were generated through a phased array contact transducer (5 MHz of central frequency). Experimental results show that the ultrasonic method allows detecting and sizing defects with a diameter of 1 mm located in thick coatings.

Nondestructive evaluation for adhesion region of automotive body with active infrared thermography.

Nondestructive evaluation for adhesion region of automotive body with active infrared thermography.

Imaging and condition diagnosis of underground sewer liners via active and passive infrared thermography: A case study in Singapore

This paper presents a case study of customizing an in-house built In-pipe Infrared Thermographic System (IPITS), which makes use of thermo-images for imaging and diagnosis of pipe crown condition in underground sewer pipelines. Active and passive infrared thermography (IRT) were attempted in two gravity sewer pipes in Singapore in July 2017. The results show that images captured with active IRT (with heating) can image and reveal invisible lining defects not readily revealed by traditional visual inspection using CCTV. These defects include bubbles, wrinkling and delamination, or construction details (like anchor knobs in HDPE material), for which sizes were estimated using an image processing algorithm customized in an in-house program. While images captured by passive IRT (without heating) can be used to identify suspected water seeping points, this paper also reports the design of instrumentation and appropriate parameter settings. The results of this case study are believed to pave the way for parallel inspections using a combination of CCTV and infrared cameras.