Single-sided Access Research Articles

Lightning Damage Evaluation in Carbon Fiber Composite Polymer Structure

While metallic aircraft structures are largely unaffected by lightning strikes, not the same statement could be made about carbon fibre reinforced polymer (CFRP) ones. CFRPs have low electrical conductivity and high anisotropy, and for this reason they are covered with metallic meshes, generally of aluminium or copper, to redistribute the electrical charge when the plane encounters lightning events. During these phenomena, electrical discharges could lead to physical damage, called direct effects, such as: ablation, erosion, explosion, structural weakening and degradation. Although relatively rare, when aircraft is affected by lightning strikes, structural inspections are necessary to determine the need and magnitude of repairs. Since the extent of lighting strike damage on laminated composite is difficult to determine and quantify visually, other non-destructive evaluation (NDE) techniques must be used. In this work, we complement established techniques, such as pulse-echo ultrasonics, X-ray radiography, eddy currents, and thermography with a novel investigative approach, based on planar capacitive sensing and imaging. This has the advantage of being non-contact, and requiring only single-side access to the part. The technique’s capabilities to detect dielectric changes and breakages in conductive layers make it an ideal candidate for the investigation of CFRP aircraft structure for lightning effects. The outcomes of capacitive imaging inspections on laboratory introduced lightning damage on CFRP panels are discussed along the advantages and disadvantages of the technique compared to more established ones.

Efficient data acquisition and reconstruction for air-coupled ultrasonic robotic NDE

Non-destructive evaluation of complex parts using surface scanning techniques, such as ultrasonic testing and eddy current testing, requires complex manipulation of such sensors to ensure quantitative results. A robotic arm may function as a complex manipulator for surface scanning, controlling the position and tilt between the probe and specimen’s surface. To ensure accuracy in probe manipulation, accurate geometric information of the specimen is required. This article explores a methodology that uses structured light for physical-to-virtual reconstruction, providing submillimeter scale and accurate surface geometries. Reconstruction aids in path planning through a novel ray-triangle intersection array algorithm, establishing movements for the NDE probe to orient itself on the specimen at a constant probe to specimen surface distance, or lift-off. The proposed technique is demonstrated and validated through experimental air-coupled ultrasonic inspection of automotive CFRP composite samples with simulated flaws such as interlaminar delamination. The proposed method employs guided waves and a pitch-catch configuration of air-coupled ultrasonic probes, enabling single-side access scans. A Fanuc 100ib robot arm was used to manipulate the ultrasonic probes along a sample reconstructed with a CR-Scan 01 structured light sensor. The probes were excited at 200khz from a SonoAir system, while also recovering defect vs background information synchronized with the probe’s orientation. Additionally, a framework for potential automation is proposed, with further details to be explored in future works.

Nondestructive Inspection and Quantification of Select Interface Defects in Honeycomb Sandwich Panels.

Honeycomb sandwich panels are utilized in many industrial applications due to their high bending resistance relative to their weight. Defects between the core and the facesheet compromise their integrity and efficiency due to the inability to transfer loads. The material system studied in the present paper is a unidirectional carbon fiber composite facesheet with a honeycomb core with a variety of defects at the interface between the two material systems. Current nondestructive techniques focus on defect detectability, whereas the presented method uses high-frequency ultrasound testing (UT) to detect and quantify the defect geometry and defect type. Testing is performed using two approaches, a laboratory scale immersion tank and a novel portable UT system, both of which utilize only single-side access to the part. Coupons are presented with defects spanning from 5 to 40 mm in diameter, whereas defects in the range of 15-25 mm and smaller are considered below the detectability limits of existing inspection methods. Defect types studied include missing adhesive, unintentional foreign objects that occur during the manufacturing process, damaged core, and removed core sections. An algorithm is presented to quantify the defect perimeter. The provided results demonstrate successful defect detection, with an average defect diameter error of 0.6 mm across all coupons studied in the immersion system and 1.1 mm for the portable system. The best accuracy comes from the missing adhesive coupons, with an average error of 0.3 mm. Conversely, the worst results come from the missing or damaged honeycomb coupons, with an error average of 0.7 mm, well below the standard detectability levels of 15-25 mm.

Nondestructive evaluation of aircraft stealth coating by Terahertz-time domain spectroscopy: experimental and numerical investigation

ABSTRACT Particle-reinforced polymer matrix composites (PMCs) are often used as radar-absorbing materials (RAM) in aircraft stealth applications. The thickness evaluation of such multilayered coatings with micrometre-level thickness is highly challenging from single-side access. In this study, we used Terahertz Time-domain Spectroscopy (THz-TDS) in the transmission mode to extract the refractive index of the dielectric coatings for measuring the thickness using the time-of-flight method. A numerical study based on the Finite Element method (FEM) has also been developed to validate the transmission experiments. A frequency-dependent complex dielectric parameters must be considered for coatings with high absorption in the THz regime. This was addressed by performing the finite element simulations in a frequency domain. The thickness of each layer of a multi-layered coating is estimated by carrying out the experiments in reflection mode. Since the interface echoes were overlapping, a deconvolution algorithm and frequency thresholding were employed to reconstruct the signals reflected from the different interfaces. Using this technique, the thickness of each layer of coating is estimated accurately in a single measurement, which was challenging to measure using other conventional non-destructive testing (NDT) methods.

Analysis of Imaging Characteristics of Wide-field Lobster Eye Lens

The lobster-eye lens is a reflected type focusing optics. It can be used for backscattering imaging that is a single-sided access technology for homeland security, detection of improvised explosive devices, non-destructive testing, and medical imaging. The aim of this study was to investigate the imaging characteristic of meridional lobster-eye lens with a planar imaging surface. The larger the field of view, the greater the spherical aberration, and the larger the field curvature of the edge field of view. Both spherical aberration and field curvature increase the size of the focal spot, and the images become blurry. Rays with a large angle of grazing incidence have large spherical aberration and curvature. The reflectivity of these rays drops sharply as the energy of photons increases. Therefore, spherical aberration and field curvature have a greater effect on photons with low energy. These conclusions can help improve the design of a lobster-eye lens for wide-field imaging applications.

Nondestructive evaluation of cork phenolic-based aerospace structure using Terahertz time domain spectroscopy and imaging

ABSTRACT Cork phenolic sheets with thermal protection paints are used as thermal protection system in launch vehicles. Detecting debonds and inclusions at the interface of cork phenolic-composite structure and thickness measurement of multi-layer TPS is highly challenging with single-side access. In this study, Terahertz imaging in reflection mode is used to detect the defects. The sample is raster scanned in X-Y directions, and the reflected signal is measured at each pixel and consolidated to obtain a Terahertz C-scan image of the entire area. The image obtained using Terahertz time-domain spectroscopy imaging system can distinguish between the healthy and debond/inclusion areas. Terahertz time-domain spectroscopy in transmission mode is carried out to obtain the refractive index and absorption coefficient of individual layers, which is a prerequisite for thickness measurement. The time-of-flight principle is used for thickness estimation of multi-layer thermal protection systems over carbon fibre reinforced plastic samples. The Sparse deconvolution technique is used to resolve the overlapping echoes to obtain the time delay for each layer. The thickness values obtained for cork phenolic sheet and red and white thermal protection paints over carbon fibre-reinforced plastic samples using Terahertz-time domain spectroscopy are in close agreement with the actual values.

Monitoring of repaired water leaks using surface wave tomography

Cracks with water leakage have been found in an underground concrete structure, and they have been repaired by injecting waterstop agents and applying patch repair materials after V-shaped removal of existing materials. Since recurrence of the problem has been frequently reported after the repair, test construction has been made by using more proper repair materials. However, an underground structure surrounded by earth is accessible only from the inside for inspection. The authors adopted the surface wave tomography which enabled single-side access soundness evaluation of internal concrete, without requiring the source and receiving sensors to be placed on the opposing sides of an object. The results confirmed the effectiveness of the repair, with the velocity structure found to have improved from that before the repair. It was also found that the velocity has already decreased at some repaired sites, and that they were in agreement with the locations of the recurrence of water leakage detected by the visual inspection. Detection of recurrence of water leakage is important because the water ingress from the surrounding ground is one of the factors leading to reduced durability of the underground structure. The findings of this study suggested that the technique would be also useful for subsequent monitoring.

LONGITUDINAL COMPRESSION THERAPY FOR SMALL BOWEL STRICTURE CROHN'S DISEASE: DURABLE RESOLUTION IN SWINE MODEL

Abstract INTRODUCTION Small bowel stricture is common in Crohn’s disease (CD), both de novo and after resection. With all standard treatments having high recurrence rates, CD patients would benefit greatly from a novel and highly durable non-surgical intervention. We report the first long-term study of longitudinal compression therapy (LCT) for the treatment of anastomotic strictures in an animal CD stricture model. LCT entails progressive endoluminal compression of stricture tissue between two flange-like device components. The goal is to gradually bring about necrosis of fibrotic tissue interposed between the two flanges while allowing remodeling with minimal iatrogenic inflammation around the periphery. METHODS Stable anastomotic strictures with hallmarks of CD small bowel strictures were created in 6 pigs, using an established method entailing ileocolonic anastomosis creation with a bypassed ileal segment to maintain patency of the gastrointestinal tract followed by serial injections of phenol/trinitrobenzenesulfonic acid at the anastomosis site. Instead of using LCT devices deployed wholly endoscopically, to best study stricture response to LCT in this model, we used devices with magnetic elements for compressive force generation and integrated ultraminiature sensor arrays for monitoring treatment progression; one 23 mm diameter device component was placed via a surgical enterotomy and a second was deployed endoscopically. Animals were followed for 9 weeks after LCT to gauge post-treatment stricture response. RESULTS LCT device placement was successful in all animals. Five animals reached the 9-week timepoint. One animal was sacrificed on day 12 due to urinary tract complications unrelated to the device. The initial therapeutic response took place over a 3-hour period after device placement, with LCT devices applying increasing force from 3 to 10 Newtons. In endoscopic assessments, widened lumens were noted, with openings 3.3-fold larger at 2 weeks and 3.7-fold larger at 9 weeks. In comparison, for endoscopic balloon dilation in the same animal stricture model, the openings were 2.3-fold larger at 2 weeks, declining to 1.9-fold at 9 weeks. Endoscopic and macroscopic evaluation after euthanasia demonstrated newly patent lumens after excision of stricture tissue, with healthy-appearing mucosa and no macroscopic findings of stricture. CONCLUSION Prior work by our group and others--in animal models and in a small number of treated patients--has provided favorable indications of efficacy of LCT for treating refractory strictures. To the best of our knowledge, this is the first study to include long-term follow-up of LCT in a validated animal model of Crohn’s stricture. This work provides strong preliminary support that LCT’s combination of resection and neo-epithelialization can durably resolve CD stricture. LCT clinical studies are planned as a next step. Design and operation of device systems for longitudinal compression therapy for small bowel stricture in Crohn’s. (a) Longitudinal compression therapy device systems incorporate a dual-flange design, with a mechanism for drawing the flanges together to longitudinally compress the stricture. For single-sided access, expanding flange designs can be used (inset, top left). The LCT device systems used in this study are pairs of discrete non-expanding flange components, with one flange component placed proximal to the strictured region via laparotomy; magnetic elements in the flange components supply the compressive force. This design facilitates incorporation of ultraminiature sensor arrays into the flange components for monitoring stricture response to treatment (inset bottom right). (b)-(d) Steps in longitudinal compressive therapy: (b) advancing the LCT device through the stricture; (c) stricture compression between distal flange and expanded proximal flanges; (d) completion of therapy. Representative result for LCT in the porcine model of Crohn’s small bowel stricture. (a) Before treatment, a length of bowel 15 mm long is badly strictured, with the lumen less than 10 mm at its narrowest point. (b) At 2 weeks after LCT treatment, the narrowest point is markedly larger. (c) At 9 weeks post LCT treatment—a time after which balloon dilated strictures tend to have recurred—the LCT treated stricture is even more open than at 2 weeks post, consistent with the LCT intervention having spurred healing instead of exacerbating fibrosis. Three-dimensional anatomy of strictured segments determined by impedance-based measurement (Endoflip, Medtronic).

Protecting the edge: Ultrafast laser modified C-shaped glass edges

A procedure and optical concept is introduced for ultrashort pulsed laser cleaving of transparent materials with tailored edges in a single pass. The procedure is based on holographically splitting a number of foci along the desired edge geometry including C-shaped edges with local 45° tangential angles to the surface. Single-pass, full-thickness laser modifications are achieved requiring single-side access to the workpiece only without inclining the optical head. After having induced laser modifications with feed rates of ∼1m/s, actual separation is performed using a selective etching strategy.

Guided A0 wave mode interaction with interfacial disbonds in an elastic-viscoelastic bilayer structure

The study reports on the characterization of interfacial disbonds in an elastic-viscoelastic (steel-rubber) adhesively bonded bilayer structure where the elastic material (steel) has a significantly higher impedance than the viscoelastic material (rubber). The study uses the A0 mode guided wave at a low frequency of 100 kHz, which was generated and detected using non-contact air-coupled ultrasound. The A0 mode could be generated and detected from both steel and rubber sides, despite the high viscoelasticity of the rubber layer. However, the A0 mode guided wave propagation is sustained only in the steel layer and not in the rubber layer. The mode travelling along the steel layer leaks into the rubber layer and hence can be detected from the rubber side in the bonded region. When the disbond is below either the transmitter or the receiver, a better sensitivity in the disbond detection was achieved from the rubber side rather than the steel side. Using the experimental and 2D frequency-domain finite element simulation results, a linear correlation between the extent of disbond and the amplitude, time-of-flight (ToF) difference of the A0 mode arrival in the disbond region on the steel side was also established. The results show the potential to characterize interfacial disbonds regardless of the position with respect to the transmitter or receiver in elastic-viscoelastic multilayered structures using air-coupled guided wave inspection from single-side access.

Comparison of Ultrasonic Non-Contact Air-Coupled Techniques for Characterization of Impact-Type Defects in Pultruded GFRP Composites.

This article compares different air-coupled ultrasonic testing methods to characterize impact-type defects in a pultruded quasi-isotropic glass fiber-reinforced plastic (GFRP) composite plate. Using the air-coupled transducers, comparisons among three methods were performed, namely, bulk-wave through transmission, single-side access using guided waves, and ultrasonic-guided wave tomography. The air coupled through transmission technique can determine the size and shape of impact-type defects with a higher resolution, but with the consequence of time consumption and, more importantly, the necessity of access to both sides of the sample. The guided wave technique on the other hand, allows a single-side inspection and is relatively fast. It can be used to determine the size of the defect using ultrasonic B-scan, but the exact shape of the defect will be compromised. Thus, in this article, to determine the shape of the defect, application of the parallel beam tomographic reconstruction technique using guided Lamb waves is demonstrated. Furthermore, a numerical finite element simulation was performed to study the effects of guided wave propagation in the composite sample and interaction with the internal defect. Lastly, the results from the experiments of different techniques were compared according to possibilities of defect sizing and determination of its shape.

High-Contrast and -Resolution 3-D Ultrasonography with a Clinical Linear Transducer Array Scanned in a Rotate-Translate Geometry

We proposed a novel solution for volumetric ultrasound imaging using single-side access 3-D synthetic aperture scanning of a clinical linear array. This solution is based on an advanced scanning geometry and a software-based ultrasound platform. The rotate-translate scanning scheme increases the elevation angular aperture by pivoting the array (−45° to 45°) around its array axis (axis along the row of its elements) and then scans the imaged object for each pivoted angle by translating the array perpendicularly to the rotation axis. A theoretical basis is presented so that the angular and translational scan sampling periods can be best adjusted for any linear transducer array. We experimentally implemented scanning with a 5-MHz array. In vitro characterization was performed with phantoms designed to test resolution and contrast. Spatial resolution assessed based on the full-width half-maximum of images from isolated microspheres was increased by a factor of 3 along the translational direction from a simple translation scan of the array. Moreover, the resolution was uniform over a cross-sectional area of 4.5 cm2. Angular sampling periods were optimized and tapered to decrease the scan duration while maintaining image contrast (contrast at the center of a 5-mm cyst on the order of −26 dB for 4° angular period and a scan duration of 10 s for a 9-cm3 volume). We demonstrated that superior 3-D ultrasound imaging can be obtained with a clinical array using our scanning strategy. This technique offers a promising and flexible alternative to development of costly matrix arrays toward the development of sensitive volumetric ultrasonography.

High-Frequency Guided Waves for Corrosion Thickness Loss Monitoring

Abstract Adverse environmental conditions result in corrosion during the life cycle of marine structures such as pipelines, offshore oil platforms, and ships. Generalized corrosion leading to the loss of wall thickness can cause the degradation of the integrity, strength, and load bearing capacity of the structure. Nondestructive detection and monitoring of corrosion damage in difficult to access areas can be achieved using high-frequency guided waves propagating along the structure. Using standard ultrasonic wedge transducers with single-sided access to the structure, specific high-frequency guided wave modes (overlap of both fundamental Lamb wave modes) were generated that penetrate through the complete thickness of the structure. The wave propagation and interference of the guided wave modes depend on the thickness of the structure and were measured using a noncontact laser interferometer. Numerical simulations using a two-dimensional finite element model were performed to visualize and predict the guided wave propagation and energy transfer across the plate thickness. During laboratory experiments, the wall thickness was reduced uniformly by milling of one steel plate specimen. In a second step, wall thickness reduction was induced using accelerated corrosion for two mild steel plates. The corrosion damage was monitored based on the effect on the wave propagation and interference (beating effect) of the Lamb wave modes in the frequency domain. Good agreement of the measured beatlengths with theoretical predictions was achieved, and the sensitivity of the methodology was ascertained, showing that high-frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations.

Application of Dual Focused Ultrasonic Phased Array Transducer in Two Orthogonal Cross-Sections for Inspection of Multi-Layered Composite Components of the Aircraft Fuselage.

Our previous studies have shown that the application of the proposed technique of a dual focused ultrasonic beam in two orthogonal cross-sections in passive (elevation) and active (azimuth) apertures of linear ultrasonic phased array transducer (ULPAT) enhances the 3D spatial resolution in the case of the inspection of conventional defects (flat bottom holes) or measurement of thickness of multi-layered metal composites. The objective of this work is to apply the proposed technique to enhance the spatial resolution of the ULPAT in the cases of detection and sizing demonstration of internal defects possessing spatially complex geometry, and during the inspection of defective multi-layered thin composite components (e.g., GLARE) of the aircraft fuselage. The specially prepared aluminium specimen possessing an internal defect of complicated geometry (crescent-shaped) was investigated. The simulation results and experiments demonstrate the resolution enhancement, higher amplitude of the reflections (e.g., 2.5 times or +8 dB) and spatial improvement in the defect detection even in the case of the non-perpendicular incidence of ultrasonic waves to the complex geometry surface of the internal defect. During the experiments, the multi-layered GFRP-metal based composite sample GLARE 3-3/2 was investigated in the case of the single-side access to the surface of the sample. The internal artificial delamination type defect of 25 mm was detected with a higher accuracy. Compared to the limitations of conventional ULPAT, the relative error (32%) (at the −6 dB level) of lateral defect dimensions estimation was completely reduced.

Capacitive sensing for the detection of tile misalignment in ceramic armor arrays

The capacitive nondestructive technique uses a planar, two- or multi-terminal device to detect dielectric changes in its proximity. The technique has the advantages of being non-contact and requiring single-side access to the inspected test-piece. In this work, it is employed to determine the misalignment of ceramic tiles in two-dimensional array arrangements, as used for armored vehicles. Ceramic materials provide protection against projectile penetration in military and security applications. Tile assemblies are manufactured as protective add-on layers to armored vehicles. To provide effective protection, arrangements of rectangular or hexagonal tiles have to minimize potential misalignment, such as inter-tile gaps and out-of-plane mismatch. In this study, three planar capacitive probes with triangle-shaped terminals are used for the investigation of linear arrays of rectangular alumina tiles. Numerical simulations were employed to understand the probe's design parameters, as well as coupling aspects. It was found that the size of the capacitive probe and the separation between terminals provide a balance between spatial resolution, penetrability, and sensitivity to dielectric changes. Inter-tile gaps down to at least 0.5 mm, as well as out-of-plane tile misalignment as small as 0.25 mm were successfully discriminated.

Small-animal 360-deg fluorescence diffuse optical tomography using structural prior information from ultrasound imaging

.We demonstrate dual modality of free-space fluorescence diffuse optical tomography (FDOT) and handheld ultrasound (US) imaging to reveal both functional and structural information in small animals. FDOT is a noninvasive method for examining the fluorophore inside an object from the light distribution of the surface. In FDOT, a 660-nm continuous wave diode laser was used as an excitation source and an electron-multiplying charge-coupled device (EMCCD) was used for fluorescence data acquisition. Both the laser and EMCCD were mounted on a 360-deg rotation gantry for the transmission optical data collection. The structural information is obtained from a 6- to 17-MHz handheld US linear transducer by single-side access and conducts in the reconstruction as soft priors. The rotation ranges from 0 deg to 360 deg; different rotation degrees, object positions, and parameters were determined for comparison. Both phantom and tissue phantom results demonstrate that fluorophore distribution can be recovered accurately and quantitatively using this imaging system. Finally, an animal study confirms that the system can extract a dual-modality image, validating its feasibility for further in vivo experiments. In all experiments, the error and standard deviation decrease as the rotation degree is increased and the error was reduced to 10% when the rotation degree was increased over 135 deg.

Challenges and opportunities in laser welding of 6xxx high strength aluminium extrusions in automotive battery tray construction

Laser welding has been increasingly adopted into the automotive sector due to its competitive processing speed, less restrictive single-sided access requirements and improved process flexibility. These benefits notwithstanding, laser welding still remains susceptible to the weld cracking especially for 6xxx high strength aluminium extrusions, which are widely used in the automotive industry for body-in-white and battery tray manufacturing. This paper reviews current challenges and opportunities for construction of battery tray using aluminium alloys with laser welding process. It aims to provide a view on the selection of welding equipment in terms of beam oscillation, power modulation, beam shaping, filler wire and shielding gas, and analyze their impact on joint integrity for 6xxx grades aluminium extrusions. The driving idea is to control the thermal history in and around the molten pool and to modify the chemical composition in the fusion zone to reduce the formation of solidification cracks. Results of the study have shown that the modification of chemical composition by the use of filler wire is currently the most efficient approach to improve joint strength. Further results evidences also showed that beam shaping with adjustable ring mode laser helps to stabilize the keyhole and achieve a wider molten pool and weld interface width. Manufacturing implications are reviewed and discussed throughout the paper.

Single-sided access remote imaging via resonant airborne activation of damage

The feasibility of remote imaging of damage by using resonant airborne acoustic activation combined with laser vibrometry is studied experimentally. Two-step optimization to stimulate the damage vibration comprised resonant oblique incidence followed by frequency selective local resonance in the damaged area (LDR). The methodology is applied to a wide variety of flaws from artificial planar defects to real damages in composite parts. Various types of damage are shown to manifest LDR in two different ways depending on the structure of the damage. The resonance is activated either as in-phase vibration over a total damaged area at a single frequency (normal LDR) or includes weakly coupled resonant vibrations of its parts at different frequencies. In the latter case, LDR is a combination of multiple so-called fractional resonances. Both kinds of the resonances enhance the sensitivity of remote defect-selective imaging and are applicable to a wide range of flaws from clearly visible to barely visible and even virtually invisible damage in composites.

Experimental analysis of the flow drill screw driving process

Flow drill screw (FDS) driving is a thermomechanical assembly process that allows for single-sided access multi-material joining, with a high application potential for modern lightweight vehicle design. The process combines three consecutive operations which partially overlap: flow drilling, thread forming, and tightening. The paper extensively investigates the process parameter effects on the flow drilling operation of thin sheet AA5182-O 2.5-mm thick and DP600 1.4-mm thick. Drilling defects have been associated with specific ranges of control parameters. Mechanical tests have shown that the drilling defects do not have a significant impact on the mechanical strength of the assembly under static loading. These results were used to determine both the optimal joining parameters and the robust process window. The variation of all process-relevant mechanical quantities was recorded over the whole available process window. This data may further serve for process simulation validation, or alternatively for the construction of data-driven meta-models.

Enhancement of damage identification in composite structures with self-heating based vibrothermography

The self-heating vibrothermography non-destructive testing method is a promising approach for testing polymeric composite structures with a single-side access or inability of application of external heating sources for thermal excitation. The method is based on excitation of low-frequency mechanical vibrations with multiple resonant frequencies, which allows for local heating of a tested structure, and based on a captured thermal response, identification of structural damage. Although the method is quite sensitive for damage, the resulting damage signatures in thermograms are often blurred or invisible due to the measurement noise and non-uniform temperature evolution on the surface of a tested structure. In this paper, the authors examine various post-processing techniques applied for infrared thermograms in order to enhance damage detectability in polymeric composite structures. Three types of methods were examined: methods based on statistical features, a new method based on trend estimation of the temperature profiles, and a method based on similarity maps. The results of the processing reveal visible enhancement of the damage detectability using the proposed methods, which allow detecting and identifying more damage signatures compared to single raw thermograms.