Pulsed Phase Thermography Research Articles

Safety issues in cultural heritage management and critical infrastructures management

Safety issues in cultural heritage management and critical infrastructures management

Through-the-thickness identification of impact damage in composite laminates through pulsed phase thermography

In this paper we demonstrate through-the-thickness imaging of barely visible impact damage in a two-dimensional woven, carbon fiber epoxy laminate using pulsed phase thermography (PPT). Specifically we calibrate the defect depth with blind frequency for the particular material system using a specimen with simulated defects in the form of polymer foam inclusions. The calibrated depth versus blind frequency relation is then applied to specimens with barely visible impact damage due to low-velocity impacts. The polymer foam reproduces the irregular boundaries and thin nature of the delaminations, but does not reproduce through-the-thickness variations. The extent of delamination at different depths was reconstructed as a function of depth for varying levels of impact energy. The extent of damage imaged using PPT corresponded well with visual observations and microscopy images.

Eddy current pulsed phase thermography for subsurface defect quantitatively evaluation

This Letter verified eddy current pulse phase thermography through numerical and experimental studies. During the numerical studies, two characteristic features, blind frequency and min phase, were extracted from differential phase spectra, and their monotonic relationships with defects' depth under different heating time were compared. According to the numerical studies, 100 ms was employed as heating time during the improved experimental studies. The experimental results agreed with the numerical results. Based on their linear relationship with defects' depths, both features can be used to measure the defect's depth.

Current injection phase thermography for low-velocity impact damage identification in composite laminates

An innovative non-destructive evaluation (NDE) technique is presented based on current stimulated thermography. Modulated electric current is injected to Carbon Fibre Reinforced Plastics (CFRP) laminates as an external source of thermal excitation. Pulsed Phase Thermography (PPT) is concurrently employed to identify low velocity impact induced (LVI) damage. The efficiency of the proposed method is demonstrated for both plain and with Carbon Nanotubes (CNTs) modified laminates, which are subjected to low-velocity impact damaged composite laminates at different energy levels. The presence of the nano reinforcing phase is important in achieving a uniform current flow along the laminate, as it improves the through thickness conductivity. The acquired thermographs are compared with optical PPT, C-scan images and Computer Tomography (CT) representations. The typical energy input for successful damage identification with current injection is three to four orders of magnitude less compared to the energy required for optical PPT.

Eddy current pulsed phase thermography and feature extraction

This letter proposed an eddy current pulsed phase thermography technique combing eddy current excitation, infrared imaging, and phase analysis. One steel sample is selected as the material under test to avoid the influence of skin depth, which provides subsurface defects with different depths. The experimental results show that this proposed method can eliminate non-uniform heating and improve defect detectability. Several features are extracted from differential phase spectra and the preliminary linear relationships are built to measure these subsurface defects' depth.

Improvement of compressive strength after impact in fibre reinforced polymer composites by matrix modification with thermally reduced graphene oxide

In this study fibre reinforced laminates with a graphene oxide modified epoxy matrix were manufactured using a filament winding technology for prepreg production. Dispersion of the nano-particles was achieved with a three roll mill. Cross-ply laminates with carbon and glass fibres and different nano-particle loadings were produced. Impact damage was introduced with an instrumented drop weight tower. Prior to mechanical testing damage size was determined using ultrasonic c-scans and pulse phase thermography. The defect size was reduced significantly with increasing graphene oxide loading in the matrix. Residual compressive properties of the laminates improved significantly for the modified specimen, with the glass fibre laminates showing the highest improvement of 55% when compared to unmodified specimens. In addition to the improved mechanical properties the matrix modification also improved the phase contrast of the thermography data thus enabling better detection of defects and improved detection limits.

Defect Detection Using Pulse Phase Thermography - Repeatability and Reliability of Data

A study has been carried out to characterize the effect of variation of processing parameters on the phase contrast data between defective and defect-free areas obtained through the use of pulse phase thermography (PPT). Processing parameters used to implement the fast Fourier transform (FFT) have been varied. Phase contrast was maximized when the datum used as the start point for the FFT was taken as the frame just after the pulse. Optimum recording duration was found when the surface temperature had returned to its initial temperature. A truncation shorter than this resulted in a reduced phase contrast. Sampling interval and range is required to be balanced against the quantity of data produced and the computational expense. A sampling frequency of 0.06 Hz was suggested for the sample studied as this allowed peak phase contrast to be captured without unnecessarily increasing data size. Repeatability of tests was also investigated. It was found that PPT phase contrast results have been found to be repeatable with a maximum standard deviation of 6°.

Analysis of data processing methods for pulsed thermal imaging characterisation of delaminations

Pulsed thermal imaging is a commonly used infrared thermal imaging technology for non-destructive evaluation of engineering materials. It provides a complete interrogation and, therefore, a potentially complete quantification of the thermal properties and structures of a test material. The quantity and quality of material parameters that can be extracted depend mostly on the data processing methods. Although thermal property measurement is one important area for thermal imaging, this study is focused on the methods used mainly for subsurface flaw detections, including pulsed phase thermography, principal component thermography, derivative and a recently developed thermal tomography method. The characteristics of these methods were analysed and compared based on theoretical solutions and experimental data from a ceramic matrix composite plate with simulated delaminations. It was identified that although all methods have similar detection sensitivity and accuracy for delamination characterisation, there is a clear advantage in the interpretation of detailed flaw configurations when using spatially-resolved three-dimensional (3D) results from thermal tomography.

Inspection on SiC coated carbon–carbon composite with subsurface defects using pulsed thermography

An investigation on SiC coated carbon–carbon (C/C) composite plates has been undertaken by pulsed thermography. The heat transfer model has been built and the finite element method (FEM) is applied to solve the thermal model. The simulation results show that defects with DA/DP smaller than one can hardly be detected by an infrared camera with the sensitivity of 0.02°C. Certificated experiments were performed on the built pulsed thermography system. The thermal wave signals have been processed by subtracting background image method (SBIM), pulsed phase thermography (PPT), and temperature–time logarithm fitting method (TtLFM). The limit DA/DP of defects in SiC coated C/C composite plates with the thickness of 6mm that can be detected by pulsed thermography with the presented signal analysis algorithms has been obtained.

Characterizing Influence Parameters in Pulsed Phase Thermography for Defect Detection in Sheet Metal Parts

Pulsed phase thermography (PPT) is a common infrared technique for quantitative nondestructive testing and evaluation (NDT&E). PPT was initially applied in the aeronautical and aerospace engineering to the detection and quantification of defects in materials with either high or low thermal conductivity, such as aluminium and composite materials. This paper presents for the first time the application of PPT-technique for defect inspection in sheet metal parts, attempting to provide a solution for an alternative quality control rather than the traditional optical survey in the press shop. The inspected defects in this paper were produced in deep drawing cups, to effectively creating various crack lengths and depths respectively in both steel and aluminium alloys. The approach of the characterizing influence parameters is primarily based on the particular parameters of the PPT-technique. These parameters were firstly classified into various categories, and a DoE model was subsequently designed to define the required experiments for a process window analysis. According to the defined process window, more accurate conclusions of defect detecting effects were achieved. Studies in the paper present the fundamental perceptions for defect inspecting in the sheet metal parts by using PPT-technique in the press shop.

Image Processing for Automated Flaw Detection and CMYK model for Color Image Segmentation using Type 2 Fuzzy Sets

Infrared (IR) thermography has evolved in recent years from being an emerging nondestructive testing (NDT) technique to a viable approach for both aerospace manufacturing and in-service inspections. One of the drawbacks of thermography techniques is that no standard signal processing has been universally adopted and that different algorithms yield different sizing results. Additionally, the data interpretation is not as simple as with other NDT techniques. In this paper the most common signal processing techniques applied to pulsed thermography, which include derivative processing, pulsed phase thermography and principal component analysis, are applied in an attempt to simplify the damage detection and sizing process. The pulsed thermography experiments were carried out on 25 impacted panels made of carbon fiber epoxy material. Despite using similar panels and the same experiment parameters, the damage detection and sizing processes are not straight forward. It is concluded that some algorithms provide easier detection capability than others. However, on their own, the different algorithms lack the robustness to make the damage detection and sizing processes reliable and fully automated. And Optimization of the similarity measure is an essential theme in medical image registration. In this paper, a novel continuous medical image registration approach (CMIR) is proposed. This is our extension work of the previous one where we did a segmentation part of any particular image with a custom algorithm .The CMIR, considering the feedback from users and their preferences on the trade-off between global registration and local registration, extracts the concerned region by user interaction and continuously optimizing the registration result. Experiment results show that CMIR is robust, and more effective compared with the basic optimization algorithm. Image registration, as a precondition of image fusion, has been a critical technique in clinical diagnosis. It can be classified into global registration and local registration. Global registration is used most frequently, which could give a good approximation in most cases and do not need to determine many parameters. Local registration can give detailed information about the concerned regions, which is the critical region in the image. Finding the maximum of the similarity measure is an essential problem in medical image registration. Our work is concentrating on that particular section with the synergy of Tpe-2 fuzzy logic invoked in it.

Quantification by Signal to Noise Ratio of Active Infrared Thermography Data Processing Techniques

In this paper, the use of a signal to noise ratio (SNR) is proposed for the quantification of the goodness of some selected processing techniques of thermographic images, such as differentiated absolute contrast, skewness and kurtosis based algorithms, pulsed phase transform, principal component analysis and thermographic signal reconstruction. A new hybrid technique is also applied (PhAC—Phase absolute contrast), it combines three different processing techniques: phase absolute contrast, pulsed phase thermography and thermographic signal reconstruction. The quality of the results is established on the basis of the values of the parameter SNR, assessed for the present defects in the analyzed specimen, which enabled to quantify and compare their identification and the quality of the results of the employed technique.

Detecting deeper defects using pulse phase thermography

Detectable defect depth by pulse phase thermography (PPT) is reportedly improved when using phase at low frequency. This study was conducted to identify mechanisms detecting deeper defects by the PPT, and to determine the optimum frequencies for detecting defects with various depths and sizes. One-dimensional and finite element analyses reveal that the optimum frequency decreases continuously with increasing defect depth, and that the amplitude of noise appearing in phase data decreases with decreased frequency. These engender a large signal-to-noise ratio for deep defects in a lower-frequency range. The analytical results were verified by experiments for a polymethylmethacrylate specimen having artificial defects. The experimental results at the optimum frequency demonstrated that defects with up to 5–6mm depth were detected, which is a significant improvement compared with the reported detectable defect depth of 3.5mm.

Experimental study of inspection on SiC coated high-temperature alloy plates with defects using pulsed thermographic technique

The pulsed thermographic technique was used to detect flat-bottomed hole defects in SiC coated high-temperature alloy plates. Temperature–time Logarithm Fitting Method (TtLFM), Principal Component Analysis (PCA) and Pulsed Phase Thermography (PPT) were used to extract the characteristic information of the thermal wave signal generated by thermal pulse. It is found that PCA algorithm is available for analyzing the thermal wave signal generated by thermal pulse due to higher signal–noise ratio. Experiments were performed to investigate the effect on the thermal contrast by the pulse intensity, frame rate and analysis moment, respectively. Experimental results show that larger pulse intensity and frame rate are benefit to get larger thermal contrast thermogram, and optimal analysis moment selected is helpful to detect the defects of SiC coated high-temperature alloy plates using pulsed thermographic technique.

Scanning pulse phase thermography with line heating

Thermographic investigations with a line heating source have been carried out, to localise small subsurface defects. The object is moved along the heating source, i.e. an induction coil in our experiments. The infrared camera is recording the temperature distribution either in reflection or in transmission mode. From the recorded images, the pixel columns are extracted and a new image sequence is created. After adjusting the images according to the shift between two consecutive recorded images, the sequence represents the temporal change of the temperature after a short homogeneous heating pulse. With Fourier transformation a phase image is created, therefore the technique is called scanning pulse phase thermography. In order to find the optimal parameters, as inspection time and motion speed, finite element simulations and analytical calculations are carried out. Experimental results on ferromagnetic steel samples are presented, showing that in reflection mode a 6 mm defect in a 9 mm thick slab in a depth of 7 mm can be detected (aspect ratio = 6/7). In contrast, in transmission mode, even a 4 mm defect in 8 mm depth could be made visible (aspect ratio = 0.5).

Applications of chirp z transform and multiple modulation zoom spectrum to pulse phase thermography inspection

The fine spectrum structure is required when some key frequencies are estimated; however the implementation may be hindered due to insufficient frequency resolution. In this work, two types of transforms were introduced into Pulse Phase Thermography (PPT), the first was Chirp Z Transform (CZT), which was used for the badly sampled or short truncated data, and the other was Multiple Modulation Zoom spectrum Analysis (ZFFT), used for the long duration data. The CZT can refine the spectrum and improve the frequency resolution; consequently the subtle spectral structure of the selected local band can be observed for purchasing the precise frequency; furthermore time consumption for long point FFT calculation can be greatly alleviated by the ZFFT without worsening the resolution. The comparative test results demonstrate that the proposed CZT can obtain more accurate characteristic frequencies; in addition, the reconstructive images from the developed method are better than the ones by conventional technique, simultaneously ZFFT can save calculation time and storage space largely.

Defect Recognition in Thermosonic Imaging

This work is aimed at developing an effective method for defect recognition in thermosonic imaging. The heat mechanism of thermosonic imaging is introduced, and the problem for defect recognition is discussed. For this purpose, defect existing in the inner wall of a metal pipeline specimen and defects embedded in a carbon fiber reinforced plastic (CFRP) laminate are tested. The experimental data are processed by pulse phase thermography (PPT) method to show the phase images at different frequencies, and the characteristic of phase angle vs frequency curve of thermal anomalies and sound area is analyzed. A binary image, which is based on the characteristic value of defects, is obtained by a new recognition algorithm to show the defects. Results demonstrate good defect recognition performance for thermosonic imaging, and the reliability of this technique can be improved by the method.

Materials and Corrosion 3/2012

Cover: Grinding surface pattern of steel, coated with thick‐film E‐coat (40 μm) after a stone chipping defect exposed in an accelerated corrosion test (BMW AA‐0224) showing blistering and a corrosion progress. The small image represents a cross section of the sample which was carried out on the FEI Nanolab Nova200 dual‐beam focused ion beam (DB‐FIB – FEI company, Eindhoven, The Netherlands). For the single wide cut (1350 μm by 30 μm) a beam current of 20nA at an acceleration voltage of 20kV was used. Afterwards the part in front of the cross section was removed manually with a scalpel blade. Additional ion beam cross section cleaning with 7nA at 20kV was performed and images were taken with the electron beam using the Everhart‐Thornley detector at 52° tilt angle and an acceleration voltage of 5kV.Grinding surface pattern and analyzes were investigated at the Austrian Centre for Electron Microscopy and Nanoanalysis (ZFE‐Graz), Graz‐Austria, by Dr. J. Wagner.More detailed information can be found in: A. Schönberger, S. Virtanen, V. Giese, H. Schröttner, C. Spießberger, Non‐destructive detection of corrosion applied to steel and galvanized steel coated with organic paints by the pulsed phase thermography, Materials and Corrosion 2012, 63, 195.

Effect of Anisotropic Properties on Defect Detection by Pulse Phase Thermography

The influence of anisotropic thermal diffusivities on non-destructive testing of CFRP laminates using pulse phase thermography (PPT) was studied analytically. The results show that the optimum frequency for maximizing detectable depths of defects increases concomitantly with the increase in the ratio of the thermal diffusivities in the through-thickness direction to that in the in-plane direction . Furthermore, the phase difference between sound and defective areas decreases significantly with decreased . These predicted tendencies were verified through experiments. Experimental results also demonstrated that defects of 10 mm in diameter can be detected up to around 5 mm depth in CFRP with lower but only to around 1 mm in CFRP with higher

NDT inspection of plastered mosaics by means of transient thermography and holographic interferometry

In this research work, experimental procedures by means of Transient Thermography and Holographic Interferometry were performed in order to detect subsurface tesserae areas of plastered mosaics. A mosaic sample consisted of various types of tesserae and covered with hydraulic lime mortar was evaluated in the laboratory with various transient thermal processing techniques such as Pulsed Phase Thermography, Thermographic Signal Reconstruction and Principal Component Thermography, as well as Holographic Interferometry in both real-time and double-exposure configurations. Results from the non-invasive investigation are presented and discussed, revealing that the above approaches can obtain a seeing through investigation of plastered mosaics.