Autonomous inspection and repair of aircraft composite structures

This paper deals with the development of an innovative approach for inspection and repair of damage in aeronautical composites that took place in the first two years of the H2020 CompInnova project which. The aim is a newly designed robotic platform for autonomous inspection using combined infrared thermography (IRT) and phased array (PA) non-destructive investigation for damage detection and characterization, while integrated with laser repair capabilities. This will affect the increasing societal need for safer aircraft in the lowest possible cost, while new and effective techniques of inspection are needed because of the rapidly expanding use of composites in the aerospace industry

Fast, accurate, and reliable detection of damage in aircraft composites by advanced synergistic infrared thermography and phased array techniques

This paper presents an advanced methodology for the detection of damage in aircraft composite materials based on the sensor fusion of two image-based non-destructive evaluation techniques. Both of the techniques, phased-array ultrasonics and infra-red thermography, are benchmarked on an aircraft-grade painted composite material skin panel with stringers. The sensors systems for carrying out the inspections have been developed and miniaturized for being integrated on a vortex-robotic platform inspector, in the framework of a larger research initiative, the Horizon-2020 ‘CompInnova’ project

Intrinsic Parameters in the Fracture of Carbon/Carbon Composites

The R-curve, bridging stress profile and the corresponding bridging law of C/C woven composites were calculated for two different specimen configurations: compact tension (CT) and double-edge-notch (DEN). Monotonic tensile loading as well as cyclic loading was performed on CT specimens and the R-curve was evaluated from the change of specimen compliance in the presence and absence of the bridging zone by quantifying the total damage in the material through an effective crack length approach. The bridging stresses and laws for the DEN specimens tested under monotonic tension were calculated directly through the elastic correction of the measured displacement. The comparison of the R-curves and bridging laws between the two configurations was performed after identification of a common damage extent measure, the local crack opening displacement. The rising part of the R-curve was found similar for the two configurations, with the mean initiation and plateau values being Ro~1.3 and Roo~9.5 kJ/m2, respectively. In contrast, the bridging laws evaluated for the two configurations were in disagreement. It was concluded that the investigated material, although characterised as Class-III in the literature, exhibits crack growth and bridging, however of a Small rather of a large scale and that the calculated R-curve can serve as an intrinsic parameter that characterises the fracture behaviour of the material independently of configuration, and - thus - independently of dimensions and geometry. Keywords: A. Ceramic-matrix composites; B. Fracture; C. Crack; Fibre bridgingJRC.F.2-Cleaner energie

Assessment of Fatigue Damage and Crack Propagation in Ceramic Matrix Composites by Infrared Thermography

The initiation and propagation of damage in SiC fiber-reinforced ceramic matrix composites under static and fatigue loads were assessed by infrared thermography (IRT). The proposed thermographic technique, operating in lock-in mode, enabled early prediction of the residual life of composites, and proved vital in the rapid determination of the materials’ fatigue limit requiring testing of a single specimen only. IRT was also utilized for quantification of crack growth in the materials under cyclic loads. The paper highlights the accuracy and versatility of IRT as a state-of-the art damage assessment tool for ceramic composites

A Micromechanical Bridging Law Model for CFCCs

In the present work, a methodology is presented for the assessment of bridging laws for continuous fibre-reinforced ceramic matrix composites based on material properties as well as micromechanics of fibre deformation and failure. A load–displacement model is initially formulated that utilizes weakest-link statistical concepts to analyse and relate the individual contributions of matrix, intact/bridging and failed/pull-out fibres during the composite fracture process. The total and individual contributions to the bridging law and crack growth resistance of the material are determined by identifying the non-elastic part of displacement as crack opening. The model is validated against the experimentally recorded load–displacement behaviour of a notched SiC-fibre-reinforced glass–ceramic matrix composite tested under monotonic tension. The output parameters of the converged regression procedure remain within a small scattering range from the corresponding mean values that compare favourably with known material properties. A parametric analysis of the effect of fibre volume fraction, Weibull modulus of fibres and interfacial shear stress in overall composite performance is presented in view of the ability of the model to serve as an a priori fracture prediction tool.JRC.F.2-Cleaner energie

Mechanical Properties of Alumina Nextel-TM 720 Fibres at Room and Elevated Temperatures: Tensile Bundle Testing.

Abstract not availableJRC.F-Institute for Energy (Petten

A novel processing route for carbon nanotube reinforced glass-ceramic matrix composites

Conference on Smart Sensor Phenomena, Technology, Networks, and Systems Integration, San Diego, CA, MAR 09-10, 2015International audienceThe current study reports the establishment of a novel feasible way for processing glass-and ceramic-matrix composites reinforced with carbon nanotubes (CNTs). The technique is based on high shear compaction of glass/ceramic and CNT blends in the presence of polymeric binders for the production of flexible green bodies which are subsequently sintered and densified by spark plasma sintering. The method was successfully applied on a borosilicate glass/multi-wall CNT composite with final density identical to that of the full-dense ceramic. Preliminary non-destructive evaluation of dynamic mechanical properties such as Young's and shear modulus and Poisson's ratio by ultrasonics show that property improvement maximizes up to a certain CNT loading; after this threshold is exceeded, properties degrade with further loading increase

Σύνδεση δευτεροβάθμιας και τριτοβάθμιας εκπαίδευσης. Ο ρόλος του Εθνικού Οργανισμού Εξετάσεων (ΕΟΕ)

<p>H ανεξάρτητη διοικητική αρχή με την επωνυμία «Εθνικός Οργανισμός Εξετάσεων» (ΕΟΕ) και διεθνή ονομασία «National Exams Organization», με έδρα την Αθήνα, αποτελεί επιτελικό επιστημονικό φορέα αρμόδιο για ζητήματα που αφορούν στις εξετάσεις εισαγωγής στην τριτοβάθμια εκπαίδευση. Αποστολή του Οργανισμού είναι η υποστήριξη του Υπουργείου Παιδείας και Θρησκευμάτων για τη διασφάλιση της υψηλής ποιότητας των εξετάσεων εισαγωγής στην τριτοβάθμια εκπαίδευση. Οι έρευνες και μελέτες του ΕΟΕ στηρίζονται στα δεδομένα της αποτύπωσης, καθώς και στην εύρεση και αξιοποίηση βέλτιστων πρακτικών από τα διάφορα εξεταστικά συστήματα για την πρόσβαση στην τριτοβάθμια στον ελλαδικό, ευρωπαϊκό και διεθνή χώρο. Οι έρευνες αυτές εμπίπτουν σε τρεις διακριτούς ερευνητικούς κύκλους, ήτοι: Εξεταστικά συστήματα στις χώρες της Ευρώπης, Ελληνικό εξεταστικό σύστημα και Ολιστική θεώρηση του συστήματος των Πανελλαδικών Εξετάσεων. Οι έρευνες αυτές αποτελούν παραδείγματα σύνδεσης του σχολείου με την τριτοβάθμια εκπαίδευση μέσω των εξετάσεων πρόσβασης. Στη συνέχεια γίνεται αναφορά στον μελλοντικό σχεδιασμό του ΕΟΕ με γνώμονα την ενίσχυση της σύνδεσης ανάμεσα στο σχολείο και την τριτοβάθμια εκπαίδευση μέσω των εισαγωγικών εξετάσεων στην Ελλάδα και διεθνώς. </p&gt

Synergistic Effect of Carbon Micro/Nano-Fillers and Surface Patterning on the Superlubric Performance of 3D-Printed Structures

Superlubricity, the tribological regime where the coefficient of friction between two sliding surfaces almost vanishes, is currently being investigated as a viable route towards the energy efficiency envisioned by major long-term strategies for a sustainable future. This current study provides new insights towards the development of self-lubricating systems by material and topological design, systems which tend to exhibit near-superlubric tribological performance, by reporting the synergistic effect of selective surface patterning and presence of carbon micro/nano-fillers on the frictional coefficients of additively manufactured structures. Geometric and biomimetic surface patterns were prepared by fused deposition modelling (FDM), using printing filaments of a polymeric matrix infused with graphene nanoplatelets (GNPs) and carbon fibers (Cf). The calorimetric, spectroscopic, mechanical and optical microscopy characterization of the starting materials and as-printed structures provided fundamental insights for their tribological characterization under a ball-on-disk configuration. In geometrically patterned PLA-based structures, a graphene presence reduced the friction coefficient by ca. 8%, whereas PETG exhibited the lowest coefficients, in the vicinity of 0.1, indicating a high supelubric potential. Biomimetic patterns exhibited an inferior frictional response due to their topologically and tribologically anisotropy of the surfaces. Overall, a graphene presence in the starting materials demonstrated great potential for friction reduction, while PETG showed a tribological performance not only superior to PLA, but also compatible with superlubric performance. Methodological and technical challenges are discussed in the text