09:00
3D Volume Measurements
Chair: Nandini Bhattacharya
09:00
20 mins
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STUDY OF DAMAGE MECHANISMS IN A319 ALUMINIUM ALLOY BY X-RAY TOMOGRAPHY AND DIGITAL VOLUME CORRELATION
Nora Dahdah, Nathalie Limodin, Ahmed El Bartali, Jean-François Witz, Rian Seguir, Eric Charkaluk, Jean-Yves Buffiere
Abstract: In the cylinder heads produced by the Lost Foam Casting process, the microstructure consists of hard intermetallic phases and large gas and microshrinkage pores. In order to study the influence of this complex 3D microstructure on fatigue crack initiation and propagation, an experimental protocol using laboratory and synchrotron tomography, Finite Element simulation and 3D Digital Volume Correlation has been used. Tests performed at low temperatures (room temperature and 150°C) revealed the initiation of 3D cracks at large pores and a propagation along the hard inclusions towards the free surface. At temperatures characteristics of in-service conditions (above 200°C), an additional damage mechanism was observed: cracks were detected in silicon particles around the main pore that drove to failure but also in other areas of the specimen gauge length.
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09:20
20 mins
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IN SITU CRACK INITIATION AND PROPAGATION IN SEMICRYSTALLINE POLYAMIDE 6 REAVEALED BY 3D SYNCHROTRON LAMINOGRAPHY
Yin Cheng, Lucien Laiarinandrasana, Lukas Helfen, Henry Proudhon, Olga Klinkova, Laurent Corte, Tilo Baumbach, Thilo F. Morgeneyer
Abstract: Micro-damage mechanisms in semicrystalline PolyAmide 6 polymer were characterized by in situ synchrotron radiation computed laminography (SRCL) on compact-tension like specimen. SRCL allows for quantifying the cavity nucleation, growth and coalescence in a flat 2 mm-thick notched specimen at micrometer resolution in 3D during the in situ loading. The maximum damage occurred at mid-thickness and located at a small distance ~160 um from the notch root. It is shown that damage is distributed in distinct zones, that can be linked to different stress triaxiality states. Penny shaped cracks are found after some loading. Their diametre is a function of the distance of the notch root: In a layer of about 30 µm limited damage is found. In the adjacent layer of 50 µm pennyshaped cracks are found with diametrees in the order of average spherulite sizes (6 µm). The next region 20-50 µm long cracks are found correspondingly. Our observation has been compared with smooth and notched round bar samples, respectively. Finally, the position of the main crack was found to be largely dependent on the roughness of the machined notch surface by comparing two samples with the same loading conditions.
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09:40
20 mins
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OPTICAL COHERENCE TOMOGRAPHY FOR ANALYSIS OF COATINGS ON WOOD
Liesbeth Dingemans, Ping Liu, Vassilis Papadakis, Roger Groves, Aurele Adam
Abstract: This paper discusses a novel application of optical coherence tomography (OCT) by using it as a way to study and characterize coatings on wood for a variety of applications and research fields. The coatings studied in this work are transparent layers applied to protect the wood from external influences. OCT can be used to assess the quality or damages of such a coating, to monitor its penetration into the wood structure and to measure its thickness. This study will apply OCT as a non-destructive technique that can both be used to test the quality of applied coatings as well to lay a basis to study coatings on wood in the field of cultural heritage. Measurements of deteriorated coated wood and reference coated wood show that both time-domain and Fourier-domain OCT are successful in imaging the coated layer. In order to deal with noise and to fully utilize information provided by the obtained data, post-processing plays an important role. Results from the two OCT techniques and their comparison will be presented and discussed.
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10:00
20 mins
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HIGH-RESOLUTION TERAHERTZ HOLOGRAPHY FOR PROFILOMETRY IN TRANSMISSION
Erwin Hack, Peter Zolliker
Abstract: We describe a setup for digital Terahertz holography based on a high-power THz gas laser and a high-resolution uncooled micro-bolometer array detector. Amplitude and phase of the diffraction pattern of test objects in transmission is obtained from phase-stepped digital holograms. The object thickness profile is reconstructed using numerical Fourier transform algorithms. A lateral resolution of around 0.2 mm and a relative phase sensitivity of about 0.5 rad corresponding to a depth resolution of 20 µm are estimated from the measurement of a test structure in polypropylene. We apply this holographic surface profilometry to the measurement of a fingertip imprint.
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