Clemente Ibarra-Castanedo

Comparative Study of Active Thermography Techniques for the Nondestructive Evaluation of Honeycomb Structures

In this article, the theoretical and experimental aspects of three active thermography approaches: pulsed thermography (PT), lock-in thermography (LT), and vibrothermography (VT), are discussed in relation to the nondestructive evaluation (NDE) of honeycomb sandwich structures. For this purpose, two standard specimens with simulated defects (delaminations, core unbonds, excessive adhesive, and crushed core) were tested, and results were processed, examined, and compared. As will be pointed out, the similarities and differences between these active approaches allow conclusions to be made about the most suitable approach for a particular application. In addition, results from NDE inspection by X-rays and c-scan ultrasounds are provided and discussed for reference.

Pulsed phase thermography reviewed

Pulsed Phase Thermography has considerably evolved since it was originally introduced in 1996. In this paper, a general review of the technique is presented. The different types of uncertainties related to data acquisition and processing are identified. Equivalence between discrete and continuous Fourier Transforms when applied to thermographic data is discussed in detail. As will be pointed out, the optimal solution for a Pulsed Phase problem, qualitative or quantitative, arises from a compromise between sampling rate, truncation window size and the available computer power. The theoretical concepts introduced here are reinforced with a variety of experimental results.

Advanced surveillance systems: combining video and thermal imagery for pedestrian detection

In the current context of increased surveillance and security, more sophisticated surveillance systems are needed. One idea relies on the use of pairs of video (visible spectrum) and thermal infrared (IR) cameras located around premises of interest. To automate the system, a dedicated image processing approach is required, which is described in the paper. The first step in the proposed study is to collect a database of known scenarios both indoor and outdoor with a few pedestrians. These image sequences (video and TIR) are synchronized, geometrically corrected and temperature calibrated. The next step is to develop a segmentation strategy to extract the regions of interest (ROI) corresponding to pedestrians in the images. The retained strategy exploits the motion in the sequences. Next, the ROIs are grouped from image to image separately for both video and TIR sequences before a fusion algorithm proceeds to track and detect humans. This insures a more robust performance. Finally, specific criteria of size and temperature relevant to humans are introduced as well. Results are presented for a few typical situations.

Interactive Methodology for Optimized Defect Characterization by Quantitative Pulsed Phase Thermography

ABSTRACT Pulsed phase thermography is a nondestructive evaluation processing technique based on the discrete Fourier Transform. The time-frequency duality plays a critical role in the selection of the sampling and truncation parameters and has to be addressed experimentally as a function of the inspected depth. To characterize a wide range of depths in a single test, the ideal solution is to sample at the maximum available frame rate for the longest possible time and to process all this data at once. Nevertheless, two factors restrict this operation. First, the maximum frame rate and storage capacity in any acquisition system are limited and so is the span of potentially detected depths. Second, although limited, the storage capacity generally exceeds the ordinary PCs capabilities to handle simultaneously all the collected information. As a result, a compromise between sampling and storage capacity, processing capabilities and range of potentially detected depth needs to be made. A four-step interactive methodology is proposed to deal with this problem. The idea is to perform a first partial processing with a fraction of the recorded data for visualization purposes only and then to individually manage selected (defective) areas, now visible, without repeating any test.

Nondestructive testing with thermography

Thermography is a nondestructive testing (NDT) technique based on the principle that two dissimilar materials, i.e., possessing different thermo-physical properties, would produce two distinctive thermal signatures that can be revealed by an infrared sensor, such as a thermal camera. The fields of NDT applications are expanding from classical building or electronic components monitoring to more recent ones such as inspection of artworks or composite materials. Furthermore, thermography can be conveniently used as a didactic tool for physics education in universities given that it provides the possibility of visualizing fundamental principles, such as thermal physics and mechanics among others.

Delamination detection and impact damage assessment of GLARE by active thermography

GLAss REinforced (GLARE) is a fibre metal laminate (FML) consisting of alternating layers of thin aluminium and glass fibre reinforced prepregs, whose improved physical properties confer it an interesting advantage over aluminium and composite materials for a number of aerospace applications. On the other hand, contrary to monolithic structures, GLARE can suffer from internal damage either during fabrication or in-serve stages. Non-destructive testing and evaluation (NDT&E) of GLARE is still a challenge, especially considering that large structures are typically sought (e.g., aircraft fuselage). In this paper, we investigated the use of infrared thermography for the inspection of GLARE. The experimental results presented herein demonstrate that it is possible to detect delamination-type defects and to assess the impact severity on GLARE through active thermography techniques, specifically pulsed thermography and vibrothermography. C-scan ultrasonic testing was performed as well with the intention of providing supplementary results.

Qualitative and quantitative assessment of aerospace structures by pulsed thermography

Pulsed thermography (PT) is an NDT&E technique allowing the remote examination of materials and systems. PT is particularly interesting for the inspection of aerospace structures since it can be used to perform safe inspection of large structures in a fast manner and without having to remove the components from the aircraft. Pulsed thermographic data however, is contaminated by noise of many forms. Fortunately, numerous signal processing techniques are available to perform qualitative and quantitative data analysis of data. In this paper, we present three processing techniques that have shown very promising results. We provide the theoretical background and experimental details as well as some representative results that highlight the pros and cons of each technique. As it will be pointed out, an interesting approach is the combination of existing processing techniques in order to use the most attractive features from each technique while reducing the non-desirable characteristics.

Diagnostics of panel paintings using holographic interferometry and pulsed thermography

Holographic and thermographic techniques have been recently applied in artwork diagnostics for the quantitative evaluation of defect size and depth in laboratory samples of artworks. The aim of this study is a comparison between holographic interferometry (both double exposure and real time), and pulsed thermography (PT) processing techniques such as differential absolute contrast (DAC) and pulsed phase thermography (PPT) for the detection of the subsurface flaws on wooden panel paintings. The performance of holographic techniques can be reserved for investigation of particular defects (cracks, detachments) at incipient stages, where high resolution/sensitivity is required, while PT can provide interesting quantitative results in situ.

Inspection of aerospace materials by pulsed thermography, lock-in thermography, and vibrothermography: a comparative study

Inspection of aerospace components has always been a challenge. Infrared thermography has demonstrated to be a useful tool for this matter. In this paper, we offer a comparative study involving three active techniques: pulsed thermography, lock-in thermography and vibrothermography. Some of these techniques have proven to be more effective than others for a specific type of system. We compare the experimental results from these three techniques as applied to two typical aerospace parts: honeycomb structures and Glare. The later is perhaps the most challenging of all as will be pointed out. Some insights are provided regarding the most suitable technique for a number of typical situations.

From the experimental simulation to integrated non-destructive analysis by means of optical and infrared techniques: results compared

In this work the possibility of modeling manufacturing ceramic products is analyzed through the application of transient thermography, holographic interferometry and digital speckle photography, in order to identify the subsurface defects characteristics. This integrated method could be used to understand the nature of heterogeneous materials (such as plastic, sponge simulating a void, wood, aluminum) potentially contained within ceramic materials, as well as to predict crack formation due to them. The paper presents the analysis of green ceramic tile containing defects of different types and sizes located at different depths. The finite element method is used for solving the problem of transient heat transfer occurring in experimental conditions. Unknown parameters of the numerical model (such as convective heat transfer coefficients and sample surface emissivity) were adjusted to obtain numerical simulation results as close as possible to those obtained experimentally. Similarities and differences between experimental and simulated data are analyzed and discussed. Possibilities for improving the results and further developments are proposed.