Title Abstract "Emerging Technologies in Non-Destructive Testing VI" "The 6th International Conference on Emerging Technologies in Nondestructive Testing (ETNDT6) took place in Brussels, Belgium, May 27–29, 2015 (www.etndt6.be). It was organized by the Department of Mechanics of Materials and Constructions (MEMC) of the Vrije Universiteit Brussel (VUB).The conference gathered world-wide leading experts and covered all fields of Non-Destructive Testing (NDT) in materials and structures. This is a subject of great significance, with great social impact as it is strongly related to detection of damage in engineering structures, such as buildings, bridges, aircrafts, pressure vessels, monuments etc. using non-invasive techniques (among others ultrasound, X-rays, Radar, neutrons, thermography, vibrations, acoustic emission). Health monitoring of structures and components is in close connection to the developments in the field of nondestructive testing. Information on the structural condition is important for planning maintenance and overall management of structures. Fast, reliable and low cost methodologies for evaluation are certainly in demand in the life cycle engineering of the structures.The ETNDT6 conference aimed to provide the latest developments in these techniques, contribute to the exchange of ideas among scientists and industry and disseminate significant knowledge. The conference attracted more than one hundred participants from 22 countries showing that the area of NDTreceives continuously more attention due to its importance in safety and engineering. The conference featured the following excellent plenary talks:• “Neutron techniques for NDT”, by Prof. Helena Van Swygenhoven-Moens from Paul Scherrer Institute & EPFL, Switzerland• “Basics and Applications of NDE based on Elastodynamics towards Infra-Dock for Concrete Structures” by Prof. Masayasu Ohtsu from Kumamoto University, Japan• “Resonant Defects: A New Approach to Highly-Sensitive Defect-Selective Imaging” by Igor Solodov from University of Stuttgart, Germany.Substantial keynote presentations were contributed by A. Moropoulou, A. Saisi, N. Lammens, H. Pfeiffer, M. Bentahar, E. Gruyaert, N. Godin, T. Shiotani, M. Ioannides, T. Suzuki, P. Rizzo, M. Gresil, G. Chiesura, T. Kek.The present volume is a collection of the submitted papers grouped in different sections according to the session they were presented. We believe that it represents the current trends in nearly all fields of NDT with cutting edge applications." "Compressed sensing mm-wave SAR for non-destructive testing applications using multiple weighted side information" "Mathias Becquaert, Edison Cristofani, Van Huynh Luong, Marijke Vandewal, Johan Stiens, Nikos Deligiannis" "This work explores an innovative strategy for increasing the efficiency of compressed sensing applied on mm-wave SAR sensing using multiple weighted side information. The approach is tested on synthetic and on real non-destructive testing measurements performed on a 3D-printed object with defects while taking advantage of multiple previous SAR images of the object with different degrees of similarity. The tested algorithm attributes autonomously weights to the side information at two levels: (1) between the components inside the side information and (2) between the different side information. The reconstruction is thereby almost immune to poor quality side information while exploiting the relevant components hidden inside the added side information. The presented results prove that, in contrast to common compressed sensing, good SAR image reconstruction is achieved at subsampling rates far below the Nyquist rate. Moreover, the algorithm is shown to be much more robust for low quality side information compared to coherent background subtraction." "Compressed sensing mm-wave SAR for non-destructive testing applications using side information" "Mathias Becquaert, Edison Cristofani, Gokarna Pandey, Marijke Vandewal, Nikos Deligiannis" "This paper evaluates the applicability of an innovative strategy for applying compressed Sensing (CS) on Synthetic Aperture Radar (SAR) imaging, in the mm-wave range, using prior or structural side information. The studied technique adds the side information to the conventional CS minimization problem using an l1-l1 minimization approach, allowing for lower sub-Nyquist sampling than standard CS predicts. The applicability of this strategy on ultra-wideband SAR measurements is tested through simulations and real Non-Destructive Testing (NDT) experiments on a 3D-printed polymer object." "Performance monitoring of large-scale autonomously healed concrete beams under four-point bending through multiple non-destructive testing methods" "G Karaiskos, E Tsangouri, D G Aggelis, Kim Van Tittelboom, Nele De Belie" "Concrete is still the leading structural material due to its low production cost and great structural design flexibility. Although it is distinguished by such a high durability and compressive strength, it is vulnerable in a series of ambient and operational degradation factors which all too frequently result in crack formation that can adversely affect its mechanical performance. The autonomous healing system, using encapsulated polyurethane-based, expansive, healing agent embedded in concrete, is triggered by the crack formation and propagation and promises material repair and operational service life extension. As shown in our previous studies, the formed cracks on small-scale concrete beams are sealed and repaired by filling them with the healing agent. In the present study, the crack formation and propagation in autonomously healed, large-scale concrete beams are thoroughly monitored through a combination of non-destructive testing (NDT) methods. The ultrasonic pulse velocity (UPV), using embedded low-cost and aggregate-size piezoelectric transducers, the acoustic emission (AE) and the digital image correlation (DIC) are the NDT methods which are comprehensively used. The integrated ultrasonic, acoustic and optical monitoring system introduces an experimental configuration that detects and locates the four-point bending mode fracture on large-scale concrete beams, detects the healing activation process and evaluates the subsequent concrete repair." "Compressed sensing and defect-based dictionaries for characteristics extraction in mm-wave non-destructive testing" "Edison Cristofani, Mathias Becquaert, Gokarna Pandey, Marijke Vandewal" "In ultra-wideband non-destructive testing of large multilayered polymers, data collection and reduction can be achieved by applying compressed sensing techniques. In this work, using effective modelling of possible defects, such as air gaps between layers, we construct defect dictionaries and use them as support data for a signal similarity-based classifier, which will automatically extract the main characteristics of the inspected defect." "Non-destructive testing techniques for the observation of healing effects in cementitious materials: an introduction" "CU Grosse, Kim Van Tittelboom, Nele De Belie" "To develop an appropriate method of self-healing for cementitious materials including the right composition and amount of suitable healing agents it is required to investigate the healing efficiency for certain material mixtures. While some researchers evaluate the regain in compressive strength by means of destructive load tests, this method is obviously second best in particular for field applications. In a large EU project the best candidates among the non-destructive testing methods are investigated to be applied in small and large laboratory experiments as well as at real structures in-situ. The paper is giving an introduction to these techniques and addresses also issues of structural health monitoring used for example to monitor the healing effects on a long term basis and to assess the condition of the structure, where self-healing techniques are applied." "Homogenized eddy current model for non-destructive testing of metallic cables" "Valdemar Melicher, Peter Sergeant" "Non-destructive testing of composites by ultrasound, local defect resonance and thermography" "Mathias Kersemans, Erik Verboven, Joost Segers, Saeid Hedayatrasa" "Towards in-plane local defect resonance for non-destructive testing of polymers and composites" "Joost Segers, Mathias Kersemans, Saeid Hedayatrasa, Javier Andres Calderon Tellez" "An optimized non-destructive protocol for testing mechanical properties in decellularized rabbit trachea" "M. Den Hondt, B.M. Vanaudenaerde, E.F. Maughan, C.R. Butler, C. Crowley, E.K. Verbeken, J.J. Vranckx" "Successful tissue-engineered tracheal transplantation relies on the use of non-immunogenic constructs, which can vascularize rapidly, support epithelial growth, and retain mechanical properties to that of native trachea. Current strategies to assess mechanical properties fail to evaluate the trachea to its physiological limits, and lead to irreversible destruction of the construct. Our aim was to develop and evaluate a novel non-destructive method for biomechanical testing of tracheae in a rabbit decellularization model. To validate the performance of this method, we simultaneously analyzed quantitative and qualitative graft changes in response to decellularization, as well as in vivo biocompatibility of implanted scaffolds. Rabbit tracheae underwent two, four and eight cycles of detergent-enzymatic decellularization. Biomechanical properties were analyzed by calculating lumina] volume of progressively inflated and deflated tracheae with microCT. DNA, glycosaminoglycan and collagen contents were compared to native trachea. Scaffolds were prelaminated in vivo. Native, two- and four-cycle tracheae showed equal mechanical properties. Collapsibility of eight-cycle tracheae was significantly increased from -40 cm H2O (-3.9 kPa). Implantation of two- and four-cycle decellularized scaffolds resulted in favorable flap-ingrowth; eight-cycle tracheae showed inadequate integration. We showed a more limited detergent-enzymatic decellularization successfully removing non cartilaginous immunogenic matter without compromising extracellular matrix content or mechanical stability. With progressive cycles of decellularization, important loss of functional integrity was detected upon mechanical testing and in vivo implantation. This instability was not revealed by conventional quantitative nor qualitative architectural analyses. These experiments suggest that non-destructive, functional evaluation, e.g. by microCT, may serve as an important tool for mechanical screening of scaffolds before clinical implementation. Statement of Significance Decellularization is a front-running strategy to generate scaffolds for tracheal tissue-engineering. Preservation of biomechanical properties of the trachea during this process is paramount to successful clinical transplantation. In this paper, we evaluated a novel method for biomechanical testing of decellularized trachea. We detected important loss of functional integrity with progressive cycles of decellularization. This instability was not revealed by our quantitative nor qualitative analyses. These experiments suggest that the technique might serve as a performant, non-destructive tool for mechanical screening of scaffolds before clinical implementation. (C) 2017 Published by Elsevier Ltd on behalf of Acta Materialia Inc."