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Meola C.,University of Naples Federico II | Toscano C.,Cira Italian Aerospace Research Center
Materials | Year: 2014

It is a fact that the presence of porosity in composites has detrimental effects on their mechanical properties. Then, due to the high probability of void formation during manufacturing processes, it is necessary to have the availability of non-destructive evaluation techniques, which may be able to discover the presence and the distribution of porosity in the final parts. In recent years, flash thermography has emerged as the most valuable method, but it is still not adequately enclosed in the industrial enterprise. The main reason of this is the lack of sufficient quantitative data for a full validation of such a technique. The intention of the present work is to supply an overview on the current state-of-the-art regarding the use of flash thermography to evaluate the porosity percentage in fiber reinforced composite materials and to present the latest results, which are gathered by the authors, on porous carbon fiber reinforced polymer laminates. To this end, several coupons of two different stacking sequences and including a different amount of porosity are fabricated and inspected with both non-destructive and destructive testing techniques. Data coming from non-destructive testing with either flash thermography or ultrasonics are plotted against the porosity percentage, which was previously estimated with the volumetric method. The new obtained results are a witness to the efficacy of flash thermography. Some key points that need further consideration are also highlighted. © 2014 by the authors.

Toscano C.,Cira Italian Aerospace Research Center | Toscano C.,University of Naples Federico II | Meola C.,University of Naples Federico II | Iorio M.C.,University of Naples Federico II | Carlomagno G.M.,University of Naples Federico II
Advances in Optical Technologies | Year: 2012

The ever wide use of composite materials in the aeronautical industry has evidenced the need for development of ever more effective nondestructive evaluation methodologies in order to reduce rejected parts and to optimize production costs. Infrared thermography has been recently enclosed amongst the standardized non destructive testing techniques, but its usefulness needs still complete assessment since it can be employed in several different arrangements and for many purposes. In this work, the possibility to detect slag inclusions and porosity is analyzed with both lock-in themography and pulse thermography in the transmission mode. To this end, carbon-fiber-peinforced polymers different specimens are specifically fabricated of several different stacking sequences and with embedded slag inclusions and porosity percentages. As main results, both of the techniques are found definitely able to reveal the presence of the defects above mentioned. Moreover, these techniques could be considered complementary in order to better characterize the nature of the detected defects. © 2012 C. Toscano et al.

Toscano C.,Cira Italian Aerospace Research Center | Lenzi F.,IMAST Scarl
Civil-Comp Proceedings | Year: 2010

In this work, specific viscoelastic materials characterized by different complex modulus have been selected, embedded and co-cured into the graphite/epoxy structure composites in order to study the impact behaviour of the obtained structures. Therefore, an impact test campaign at the same energy has been performed on the embedded panels as well as on simple graphite/epoxy laminates. The effects of the impact have been examined via Non Destructive Testing (NDT) using the Ultrasound Pulse-Echo technique, and by optical microscopy analysis, then the results have been compared. The presented work allows to establish that the impact behaviour of graphite/epoxy laminates could be highly influenced by the presence of damping layers. In particular the damping layers seems to strongly limit the damaged area, effectively reducing the inter-lamina damage propagation. © Civil-Comp Press, 2010.

Riccio A.,Cira Italian Aerospace Research Center | Giordano M.,CNR Institute of Composite and Biomedical Materials | Zarrelli M.,CNR Institute of Composite and Biomedical Materials
Journal of Composite Materials | Year: 2010

In this article, a simplified linear analysis-based approach to simulate the delamination growth initiation in stiffened composite panels, suitable as preliminary design and optimization tool implemented into a finite element code, is presented. The proposed approach is based on the determination of the delamination buckling and on the evaluation of the energy released during the delamination propagation by means of eigenvalue and linear static analyses. Stiffened composite panels with circular embedded bay delaminations, under compression loads, were adopted as a benchmark to test the simulation capabilities of the method. Obtained results, in terms of delamination growth initiation load and energy release rate distributions along the delamination front, have been compared to nonlinear results obtained by the virtual crack closure technique and experimental data for preliminary validation purposes. Comments and considerations upon the applicability of this methodology are, finally, provided with particular focus on delamination sizes and locations within the considered structural elements. © The Author(s), 2010.

Amoroso F.,University of Naples Federico II | Pecora R.,University of Naples Federico II | Ciminello M.,Cira Italian Aerospace Research Center | Concilio A.,Cira Italian Aerospace Research Center
Smart Structures and Systems | Year: 2015

Today, as railways increase their capacity and speeds, it is more important than ever to be completely aware of the state of vehicles fleet's condition to ensure the highest quality and safety standards, as well as being able to maintain the costs as low as possible. Operation of a modern, dynamic and efficient railway demands a real time, accurate and reliable evaluation of the infrastructure assets, including signal networks and diagnostic systems able to acquire functional parameters. In the conventional system, measurement data are reliably collected using coaxial wires for communication between sensors and the repository. As sensors grow in size, the cost of the monitoring system can grow. Recently, auto-powered wireless sensor has been considered as an alternative tool for economical and accurate realization of structural health monitoring system, being provided by the following essential features: On-board micro-processor, sensing capability, wireless communication, auto-powered battery, and low cost. In this work, an original harvester device is designed to supply wireless sensor system battery using train bogie energy. Piezoelectric materials have in here considered due to their established ability to directly convert applied strain energy into usable electric energy and their relatively simple modelling into an integrated system. The mechanical and electrical properties of the system are studied according to the project specifications. The numerical formulation is implemented with in-house code using commercial software tool and then experimentally validated through a proof of concept setup using an excitation signal by a real application scenario. Copyright © 2015 Techno-Press, Ltd.

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