11,416 research outputs found
Basalt fibre laminates non- destructively inspected after low- velocity impacts
No full textIn this work, the use of advanced thermographic techniques for the post-impact defect detection in basalt fibre reinforced composite laminates was investigated. The laminates were previously impacted at different energies, namely 7.5, 15 and 22.5 J and then subjected to accelerated environmental aging or to a coating process in order to conceal the previous damage due to low velocity impact. In both cases the defects could be identified using infrared thermography in the mid-wave infrared (MWIR) spectrum even after the treatments. In addition, short-wave infrared (SWIR) results were employed with the aim to clearly identify unsuspected resin-rich areas. Therefore, the non-thermal part of the infrared spectrum (SWIR) can be coupled with the thermal part (MWIR) providing a complete infrared vision beyond what is perceptible to the naked eye, i.e., in the visible spectrum
Infrared vision inspection of cultural heritage objects from the city of L’Aquila, Italy and its surroundings
No full textThe city of L'Aquila, Italy has a long history of catastrophic earthquakes. The most recent devastating earthquake that caused enormous damage hit the city in April 2009. The city is also the home of a rich collection of artworks from the Romanesque, Gothic, Baroque and Renaissance periods. Cultural heritage in L'Aquila is undeniable, and the use of nondestructive testing techniques is fundamental for assuring the integrity of these valuable objects. The goal of this study was to assess the performance of infrared vision techniques for the inspection of cultural heritage objects from L'Aquila. Furthermore, processing techniques were also employed for image segmentation
Comparative Study of Impact Damage in Basalt-Carbon Hybrid Composites Using Infrared Thermography and Ultrasonic C-Scan
No full textIn this paper, infrared thermography (IRT) and ultrasonic C-scan (UT) were used to investigate basalt fiber reinforced polymer
(BFRP), carbon fiber reinforced polymer (CFRP) and basalt-carbon fiber hybrid specimens subjected to impact loading. Of
particular interest, two different hybrid structures including sandwich-like and intercalated stacking sequence were analyzed.
Three different impact energies (5 J, 12.5 J and 25 J) were applied for the evaluation of the impact damage level in the different
samples. The inspection by thermographic techniques of this type of laminates is an open matter to be discussed with the
scientific audience. The results from pulsed phase thermography (PPT), principal component thermography (PCT) and partial
least squares thermography (PLST) applied on raw thermal data were compared to understand the advantages and disadvantages
of the two hybrid structures via a comprehensive analysis
Multi-scale contrast-to-noise ratio (MS-CNR): a novel metric for quantitative defect characterisation without manual region specification
No full textSpanish National Program for Mobility of Professors and Researchers [PRX22/00165]; Spanish National Plan for Scientific and Technical Research and Innovation [PID2021-124383OB-I00
A nondestructive investigation of inserts in lightweight composite panels by ultrasonic C-scan and infrared thermography
No full textIn the aeronautical industry, there is an increasing need for lightweight composites above all for the internal design. In this regard, the final products should not contain any inclusion of foreign material in order to not compromise both the aesthetical beauty and the mechanical properties subjected to vibrational loads. In this work, the infrared thermography (IRT) and the ultrasonic C-scan (UT) methods were used to retrieve the unknown positions of sub-superficial inserts in five lightweight composite panels. They were randomly inserted during the manufacturing stage. In particular, the samples investigated herein are three glass fiber reinforced polymers (GFRP) and two carbon fiber reinforced polymers (CFRP) used as laminates or as skins for honeycombs. They were provided by the Società Elicotteristica Italiana (S.E.I.), Monteprandone (Italy). An example is reported in Fig. 1. It shows both the schematization of the cross-section and the front view of a honeycomb core (HC) covered with two skins of GFRP. A comparison between two different approaches centered on square pulse and flash thermographic scenarios is reported. The raw thermograms were processed by using advanced techniques such as the principal component thermography (PCT) and the partial least square thermography (PLST) which enhanced the visibility of the defects. In addition, the UT method applied both in reflection and in transmission modes were showed interesting advantages from a diagnostic point-of-view above all when its results are compared with the thermographic results. Fig. 2 shows the clear detection (see the blue area) of a defect realized in plastic material, having an unknown size, and positioned inside the HC. Pros and cons of both methods when applied on lightweight composite panels will be in-depth explained into the final manuscript
Post-impact damage characterization of pultruded jute/glass hybrid composites using infrared vision and optical techniques
No full textThe use of an intelligent and integrated NDT approach applied to a hybrid jute composite (JC) made
with natural fibers has been explored in this work in order to reveal emerging defects after an
indentation test. In particular, the fiber content (wt.%) of the sample investigated was 40 jute + 25
glass with a stacking sequence of Surface veil/Chopped strand/Jute/J/C/S. The sample was
analyzed by: a) near-infrared reflectography (NIRR) and transmittography (NIRT), b) short-wave
infrared reflectography (SWIR), c) infrared thermography (IT), d) holographic interferometry (HI) and
e) digital image correlation (DIC) techniques. The first two inspections, combined with the Canny
edge detector and the distance transform (DT), were useful to highlight the fibers distribution and
the areas with a low concentration of fibers, respectively. In the third inspection, two different
methods of heating were applied: pulsed thermography (PT) and square pulse thermography (SPT).
The first one linked to a mid-wave IR camera, while the second one combined to a long-wave IR
camera. IRT data were processed using different algorithms, such as: principal component
thermography (PCT) and thermographic signal reconstruction (TSR). Comparing the TSR and the
optical results, two zones invisible to the naked eye and surrounding the indented area can be
identified (Figure 2). These zones were quantitatively confirmed using the MOIRE Software package
(DIC script) described in the final paper, illuminating the sample by means of a speckle pattern
induced by a laser Nd : Yag 250 mW
Monitoring of jute/hemp fiber hybrid laminates by non-destructive testing techniques
No full textDamage following static indentation of jute/hemp (50 wt.% total fiber content) hybrid laminates was detected by a number of nondestructive testing (NDT) techniques, in particular, near (NIR) and short-wave (SWIR) infrared reflectography and transmittography, infrared thermography (IRT), digital speckle photography (DSP), and holographic interferometry (HI), to discover and evaluate real defects in a laminate with a complex structure. A comparative study between thermographic data acquired in the mid- (MWIR) and long-wave infrared (LWIR) spectrum bands, by pulsed (PT) and square pulse (SPT) thermography, is reported and analyzed. A thermal simulation by COMSOL (R) Multiphysics (COMSOL Inc., Burlington, MA, USA) to validate the heating provided is also added. The robust SOBI (SOBI-RO) algorithm, available into the ICALAB Toolbox (BSI RIKEN ABSP Lab, Hirosawa, Japan) and operating in the MATLAB (R) (The Math Works, Inc., Natick, MA, USA) environment, was applied on SPT data with results comparable to the ones acquired by several thermographic techniques. Finally, segmentation operators were applied both to the NIR/SWIR transmittography images and to a characteristic principal component thermography (PCT) image (EOFs) to visualize damage in the area surrounding indentation
Integrated approach between pulsed thermography, near-infrared reflectography and sandwich holography for wooden panel paintings advanced monitoring
No full textThe durability of an exterior finish is affected by the characteristics of the wood. Satisfactory finish life is usually more difficult to achieve on woods of higher density. All wood shrinks as it loses moisture and swells as it absorbs moisture, but some species are more stable than others. Species that shrink and swell the most cause more stress on paint films than woods that are more stable [1]. To this end, let us recall that a painting on wood can be considered as a layered structure: The wood support is coated with a number of superposed priming layers made from mixtures of gesso and glue. A frequent fault resulting from such a system is the formation of detached regions inside the layered structure caused by the shrinkage process of the wood support [2]. Obviously, wood deteriorates more rapidly in warm, humid regions with respect to cool or dry places [3]. The influence of wood conditions on surface coatings is a critical point that should be monitored and that depends on environmental parameters such as microclimate. To prevent and control the effects, keeping costs down, a non-destructive monitoring of wood support behavior under thermal stress is needed. In this work, an integrated approach based on traditional and innovative (HI, PT and NIR) techniques was conducted on a primed support of poplar wood with a complex-shape surface containing areas of artificial defects at several depths due to the influence of the support on the various layers. The obtained results could be arranged, if integrated into a multidisciplinary approach, in order to define and design the conservation of the wooden artifacts
Robust quantitative depth estimation on CFRP samples using active thermography inspection and numerical simulation updating
No full textAbstract: A quantitative evaluation of delaminations in composite laminates encounters multiple difficulties due to the anisotropic behaviour of the laminate. Extensive calibrations for each structure are required and each depth needs certain manual modifications for optimal performance of the estimation routines. In this manuscript, a robust technique is developed using a numerical model to estimate the thermal diffusivity through the anisotropic material which improves defect depth estimation between each layer. Three different calibration depths are necessary to compute the diffusivity through a certain stacking sequence of a multi-layered composite laminate. The results are compared with the state-of-the-arts experimental evaluation techniques and with a regular numerical model. It is seen that especially for deeper defects, the optimised numerical model delivers more accurate results due to the considered anisotropic diffusivity
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