4th Symposium Aerospace > Programme

Poster
P1	Impact Monitoring in Smart Structures Based on Gaussian Processes M.A. Torres-Arredondo, C.-P. Fritzen, Universität Siegen, Germany Abstract: Impact is a common source of in-service damage that critically compromises the safety and performan... more Abstract: minimize Impact is a common source of in-service damage that critically compromises the safety and performance of aerospace structures. For this reason, online impact detection systems are essential and require automatic and intelligent techniques providing a probabilistic interpretation of their diagnostics. On that account, a Bayesian framework within the context of Gaussian Processes is adopted in the present work for the purpose of impact magnitude estimation and localization. An aircraft fuselage from an Airbus A320 and an isotropic plate are used as examples to test the proposed approach. Firstly, structural dynamic responses captured by a piezoelectric sensor network due to impact events are recorded from simple impact experiments. In a second step, the discrete wavelet transform and multiway nonlinear principal component analysis are used and evaluated for signal filtration, feature extraction and data compression of the time histories. Afterwards, a probabilistic model is constructed and predictions can be expressed in terms of a predictive distribution that gives the probability distribution over the predicted targets, rather than simply a point estimate. At the end, the effectiveness of proposed methodology is demonstrated experimentally and discussed.
P2	Eddy Current Signal Response Predictions for Use in Model Assisted POD Estimations Based on Different Flaw Characteristics A. Rosell, GKN Aerospace, Trollhättan, Sweden G. Persson, Chalmers Univ. of Technology, Göteborg, Sweden Abstract: This work concerns the use of model based eddy current signal response predictions from various def... more Abstract: minimize This work concerns the use of model based eddy current signal response predictions from various defect characteristics. The mathematical tools based on the finite element method are used to calculate signal response regression parameters. These can then be used in combination with experimental POD curves to estimate a new curve based on the change in defect characteristics. An experimentally based POD curve is relevant for a specific procedure and also for the specific defect type used. The experimental POD assessment of eddy current procedures is often conducted on flat test objects with fatigue cracks. If the characteristics of the defects in the studied component are shown to be different from that of the test objects then the experimentally obtained POD curve can be approximate. When considering surface breaking cracks these can differ in shape resulting from the fatigue mechanisms relevant in the specific case. The crack characteristics can also vary with bridging electric contacts between crack surfaces, which has been shown to be present in closed fatigue cracks in Titanium Ti-6Al-4V, but may be absent in open cracks. This work suggests how a model can be used in order to make better estimations of POD without manufacture of additional test objects with the new type of flaw characteristics. The work also shows how to study trends and important parameters coupled to eddy current procedure capability related to probe-defect interactions using mathematical modelling.
P3	Advances in Ultrasound Longitudinal Speed Characterization of Unidirectional CFRP Laminates: Simulations and Measurements P. Pereira Junior, T. Gomes Rodovalho, R. Gonçalves, R. Junqueira Leão, A.A. Santos, Universidade Estadual de Campinas, Campinas, Brazil Abstract: Carbon Fiber Reinforced Plastic (CFRP) products are present in many commercial and scientific appli... more Abstract: minimize Carbon Fiber Reinforced Plastic (CFRP) products are present in many commercial and scientific applications, such as the fuselage of aircrafts Boeing 787, Airbus A350 or NASA rocket nuzzles. Both high thermal and weight saving applications take benefit of its advantages. This work introduces a comparison between velocity measurements of longitudinal body ultrasonic waves and calculations from Finite Element Analysis (FEA) for a specific CFRP made of AS4/8552 prepreg. This particular FEA model is composed of an epoxy resin matrix and carbon fibers as reinforcement, simulating the microstructure of the material. In this first study, we address the generation, propagation, and detection of longitudinal waves in a unidirectional laminate, i.e., each lamina having the same orientation. An innovative equation used to insert the ultrasonic pulse is proposed by the authors, considering the effects of a non-perfect coupling between transducers and material. Experimentally, we developed a 197 mm long, 197 mm wide, and 18.6 mm thick test specimen. For that, 97 layers were necessary. Afterwards, we machined this test specimen and a 24 side polygon was achieved, in order to measure the ultrasonic speed in seven different fiber orientations. Adjusting modeling parameters is very important because each composite has a unique set of characteristics, which depend on design, manufacturing process, and properties of each individual component. Our initial simulations consider an ideal model, where each layer is perfectly glued to its neighbor. Therefore, we do not take into account problems like delamination and voids. Each layer, in reality, is composed of thousands of filaments of fibers, inserted into the matrix. Here, these tows are treated as only one larger fiber. This simplified approach requires a much less refined mesh for the model. An ultrasonic pulse of 1 MHz was used to minimize the attenuation of the signal while propagating through the material. The sampling rate of the data acquisition system and the FEA were set to reach the necessary time resolution. Velocity predictions at 0º and 90º are being reported. This paper also proposes a model to simulate the wave propagation in other angles. The estimations showed a good correspondence with measurements and a great potential to simulate more realistic models. They might consider the effects of unconformities and a more heterogeneous distribution of the fibers, allowing the development of better inspection tools.
P4	Corrosion Steel Inspection under Steel Plate Using Pulsed Eddy Current Testing D. Suh, Raynar, Daejon, South Korea J.E. Jang, K.S. Jang, D.H. Lee, SAE-AN, Seoul, South Korea Abstract: Although the conventional eddy current testing is a powerful method to detect flaws of surface, it ... more Abstract: minimize Although the conventional eddy current testing is a powerful method to detect flaws of surface, it is difficult to measure the deep depth differences of the testing materials because eddy current density has changed its magnitude with distance from the surface. But the pulsed eddy current (PEC) system can control the depth of eddy current. In this paper, we used the PEC technique to improve the capability of depth of eddy current and studied multi-pointing method to evaluate the thickness with variation of resistivity. The present paper relates to a defect impedance measurement using PEC. The PEC signals were stored with a program for time-sharing and displaying the PEC signal on a graph, which processes a resultant value to be displayed. A display unit connected to the measurement unit, that displays the resultant value being output from the measurement unit, and an input unit connected to the measurement unit, that sets a phase (a value selected from an arbitrary location by time-sharing the measured PEC signal), frequency (a frequency value of the input PEC signal) and gain (a time axis range of the reflected PEC signal) of the PEC signal irradiated to the object. So, in this study, we have investigated performance of pulsed eddy current testing method by measuring impedance variation of fabricate of specimens. From the investigation results, pulsed eddy current test can be one of corrosion detect method for inspection of corrosion. Thus, we apply PEC testing method inspecting the bar corrosion under steel plate.
P5	A Hybrid Formulation Using Transition Matrix Method and Finite Elements in a 2D Eddy Current Interaction Problem L. Larsson, Chalmers Univ. of Technology, Göteborg, Sweden A. Rosell, GKN Aerospace, Trollhättan, Sweden Abstract: A hybrid formulation of the eddy current interaction problem using transition matrix method coupled... more Abstract: minimize A hybrid formulation of the eddy current interaction problem using transition matrix method coupled to a finite element formulation of the defect is presented in a 2D geometry. The applied analytical method involves use of the free space Green’s function to generate a system of boundary integral relations. The defect is enclosed in a circular region in the conductive material and this region is resolved and formulated using linear finite elements. The approach allows a complex defect to be described with a finite element contribution to the transition matrix representing the defect in the analytical analysis of the problem. The result combines the fast analytical computation with the possibility to describe a complex shaped internal defect with finite elements. The total transition matrix with the finite element contribution is calculated one time initially and afterwards used in the analytical approach for calculation of impedance response at various positions of the conductor generating the magnetic fields.
P7	High Resolution Single Crystal Scintillator Plates Used for Light Weight Material X-Ray Radiography J. Tous, Crytur, Turnov, Czech Republic M. Nikl, Academy of Sciences of the Czech Republic, Institute of Physics, Prague, Czech Republic K. Blazek, Crytur, Turnov, Czech Republic Abstract: Recently, very thin single crystal scintillator imaging plates became of great interest. Such thin ... more Abstract: minimize Recently, very thin single crystal scintillator imaging plates became of great interest. Such thin screens are mainly used in micro-CT and nano-CT systems with either micro-focus X-ray tubes or with synchrotron sources. This work deals with a high resolution CCD camera in conjunction with different optical systems and different single crystal scintillators for low energy X-ray micro-radiography applications. The thin screens used were prepared by mechanical polishing from Y3Al5O12 single crystal material. YAG:Ce inorganic crystal scintillator material is characterized by good mechanical and chemical stability, non-hygroscopicity, high scintillation efficiency and fast decays. The light distribution on the screen is transferred by an optical system to a high-resolution CCD chip. Thin YAG:Ce screen absorbs and converts low X-ray energies very efficiently and thus is highly suitable for use in NDT of low weight materials. These materials consist mainly of carbon and hence are transparent for higher energies. A high resolution open type micro-focus X-ray tube was used to achieve high spatial resolution radiographs. The results show that the single crystal plates exhibit high spatial resolution and high sensitivity to low energy X-rays resulting in high image contrast. The plates are highly suitable for light-weight material X-ray radiography. The high resolution and contrast are demonstrated on single carbon fibers. Several other light-weight objects are also imaged.
P8	On the Application of X-Ray Computed Tomography for the Investigation of Aerospace Materials A. Zorrilla, C. Galleguillos, N. Gutiérrez, F. Lasagni, CATEC, La Rinconada, Spain Abstract: The evaluation of the inspectionability of novel aerospace components by Non-Destructive Testing (N... more Abstract: minimize The evaluation of the inspectionability of novel aerospace components by Non-Destructive Testing (NDT) is considered as one of the key factors at design level. Although both the design and manufacturing techniques would allows many times the fabrication of parts with complex geometry which accomplish the structural requirements, the capabilities of positioning (e.g. wedge and coupling media in ultrasonics) or possibilities for image recording (e.g. free-access zones for infrared thermography or laser shearography) would determine the future of that component. In the last decades, X-Ray Computed Tomography (XCT) has became important in many industrial sectors since avoids the inconvenient listed above and providing high detail information. XCT is a technique which allows the three dimensional (3D) characterization of materials and components providing quantitative information. In this way it is possible to obtain local or global information of the material like density, metrology and its defects (e.g. delaminations, debondings, porosity, etc for CFRP). The present work, shows an XCT study performed in different aerospace materials and components for the demonstration of the technique capabilities. Different examples are presented using Carbon Fiber Reinforced Polymers (CFRP) laminates and sandwich structures. Furthermore, 2D and 3D results for the quantification of micro porosity are included as well.
P9	Determination of Damage Evolution in CFRP by Thermoelastic Stress Analysis at Dynamic Low Frequencies A. Zorrilla, R. Fernandez, N. Gutiérrez, F. Lasagni, CATEC, La Rinconada, Spain Abstract: Thermoelastic Stress Analysis (TSA) is a non-contact, full field and non-destructive technique whic... more Abstract: minimize Thermoelastic Stress Analysis (TSA) is a non-contact, full field and non-destructive technique which measure thermal stresses generated by mechanical loads using an infrared camera. A quantitative strains/stresses map, damage assessment and fracture mechanics can be measured and displayed. However, in order to avoid heat transfer effects within the components (introducing error in the measurements), the technique is mainly used only under high frequency loading conditions. Aerospace structures are tested in a wide variety of conditions. Low frequency fatigue testing of large structures is a standard procedure on the validation process. At present the available dynamic testing technology is limited for detecting damage evolution at not “expected” positions. For instance, extensometric or FBG measurements are recorded only at sensor locations. Digital image correlation techniques are capable to measure local strain and damage appearance in the whole sample surface, but presents problems for data storage during long term fatigue testing. This paper aims to develop a thermoelastic stress analysis procedure applied to low frequency fatigue testing. A feasibility study using Carbon Fiber Reinforced Polymers (CFRP) laminates with at different damage and load conditions has been carried out. Two and three dimensional analysis for thermal and stress maps on the components is presented as well as local strain measurements performed by digital image correlation (DIC) for validation of the test.
P10	Ultrasonic Phased Array Inspection of CFRP Radii F. Lasagni, M.d. Santamaria, CATEC, La Rinconada, Spain J.M. Gallardo, Universidad de Sevilla, Spain Abstract: Phased Array (PA) is an ultrasonic technique widely used for qualification of CFRP (Carbon Fiber Re... more Abstract: minimize Phased Array (PA) is an ultrasonic technique widely used for qualification of CFRP (Carbon Fiber Reinforced Polymer) parts in the aerospace industry. A PA device includes multi-elements point-source transducer which is used for generating a front-wave acoustic beam. The resulting ultrasonic wave can be guided at different angles and focused. In this work, a detailed study for the detection and quantification of artificial defects in CFRP radii is presented. Samples with artificial Teflon® were fabricated according to the standards of the European aircraft manufacturer. The influence of the part geometry and probe positioning is studied, as well as the problematic derived from automation inspection system. According to the indications found on the UT cartographies, the gates configuration was also optimized to improve the results interpretation. Defects’ characterization and a reproducibility analysis were included as well. As conclusion, a summary for inspection recommendations is also included.
P11	Practical Applications of Air-Coupled Ultrasonic Technique W. Hillger, L. Bühling, D. Ilse, Hillger NDT, Braunschweig, Germany Abstract: Since more than 20 years the air-coupled ultrasonic technique already exists. Problems caused by th... more Abstract: minimize Since more than 20 years the air-coupled ultrasonic technique already exists. Problems caused by the large acoustic mismatch between solids and air are solved with special transducers, a powerful excitation as well as a hard- software signal processing. The USPC 4000 AirTech includes a powerful burst-pulser, an ultra-low pre-amplifier and a band pass filter amplifier. The combination of hard- and software filters increases the signal-to noise ratio up to 50 dB. The software imaging Hillgus for Windows enables an easy control of the system and of the different manipulators as well as evaluation and measuring functions of the C-scans. Air-coupled ultrasonic testing requires separate transducers as a sender and receiver on opposite sides of the component. Pitch and catch technique require only a single sided access. Because of critical adjustments this method is preferable only for laboratory applications. However, a robust inspection requires a two sided access. This paper presents details of automated scanning systems for tube-shaped- and flat CFRP- and CFRP honeycomb components.
P12	Practical Comparison and Requirements Using UV-LED-Lamps instead of Bulb-Based UV-Sources for Fluorescent Stimulation in Magnetic and Penetrant Testing M. Breit, RIL-CHEMIE, Kleinblittersdorf, Germany Abstract: UV-A-LED-Sources for Fluorescent Stimulation are more and more established in NDT and will complete... more Abstract: minimize UV-A-LED-Sources for Fluorescent Stimulation are more and more established in NDT and will completely substitute conventional Bulb-Based-UV-A-Sources in the future. Actually the standardization just started to standardize this new technique, why there are many open questions and insecurity in practice. This presentation will answer the practitioner’s questions and shows the state of the art about UV-LED-sources as a secure and reliable substitute for all classical bulb-based UV-A-sources, when used high-quality and well qualified and parameterized UV-LED-Lamps. It gives some prospects for the future, an overview about the technical differences, informs about the advantages and the practical differences for the testing practice, the enhanced technical requirements and the massively enhanced safety at work. Further it will explain some new important parameters and give practical suggestions to help users and responsibles to select the best source from a growing offer of UV-LED-sources for his specific application to ensure a better testing than using conventional UV-A-Sources.
P13	AvizoFire® for NDT in Large-Scale Production P. Westenberger, FEI, Düsseldorf, Germany Abstract: Computed tomography (CT) has evolved tremendously in the fields of material sciences and Non-Destru... more Abstract: minimize Computed tomography (CT) has evolved tremendously in the fields of material sciences and Non-Destructive-Testing (NDT) over the past years. Especially in aerospace industries it is mandatory that each component has to follow certified procedures in order to guarantee for safety. But, what if not the procedure itself but the enormous number of parts becomes the bottleneck in the process chain? What if thousands of small parts need to be tested before they get mounted on the aircraft? There are already solutions available that try to answer these questions. Robots accelerate the loading and unloading process of the parts. Some solutions provide CT devices where the robot is mounted inside the acquisition chamber. These robots process palettes of parts without the need to open and shut the chamber for each single part. The approach described in this paper also takes palettes into consideration but in a different application. The parts are paletted in a suitable holding fixture and processed by the CT in a single scan. After the acquisition process and the accompanying reconstruction of the tomography images have been finished, the NDT procedure needs to process a palette of unregistered and unaligned parts: AvizoFire® by VSG uses its quantification tools for isolating and for registering each individual part versus a reference model. This reference model can be a CAD model or a reference volume. Each isolated part is then processed with all the predefined NDT plans that are necessary to decide if the part is compliant or not. These test plans may include procedures for: - Defect detection (Pores, Inclusions, etc.) - Wall thickness analysis - Nominal-Actual-Comparison - Fiber orientation analysis - Metrology All these steps like isolating, registering, testing, deciding, and reporting can be run fully automatically without the need for user interaction. Thanks to the massive parallelization of the processing techniques this reduces the time-to-usage-factor by order of magnitude.
P14	Linear- and Nonlinear Ultrasonic Testing of Carbon-Fiber-Composites Combined with a Newly Developed Ultrasonic Fatigue System U. Rabe, C. Boller, T. Helfen, M. Weikert-Müller, Fraunhofer IZFP, Saarbrücken, Germany S. Hirsekorn, Saarbrücken, Germany D. Backe, F. Balle, D. Eifler, TU Kaiserslautern, Germany Abstract: Carbon fiber reinforced plastics (CFRP) are widely used as structural materials in the aerospace in... more Abstract: minimize Carbon fiber reinforced plastics (CFRP) are widely used as structural materials in the aerospace industry because of their high stiffness and strength to weight ratio. CFRP components are exposed to dynamic loads while in service which can sum up to 1011 loading cycles corresponding to a time in service of 20 years or more. Compared to metallic structural materials where a lot of experience has been gained even up into the very high cycle fatigue (VHCF) regime, CFRP have so far rarely been tested at more than 107 cycles due to a lack of appropriate high frequency testing concepts. In a joint project with the Institute of Materials Science and Engineering at the University of Kaiserslautern (WKK), a three point bending ultrasonic fatigue testing system is being developed at WKK. The system with a loading frequency of f = 20 kHz was newly designed for CFRP. In order to avoid overheating of the samples, a pulse-pause operation scheme was chosen. VHCF experiments up to 109 loading cycles were carried out with a carbon fiber reinforced polyphenylensulfide (CF-PPS) used as reference material. The ultrasonic oscillation at the operating frequency of the system (20 kHz) is used at the same time as ultrasonic excitation for in-situ monitoring of the fatigue processes in the material. Contact-free sensors are used to measure the ultrasonic sample vibration. The local sample surface velocity is measured by an optical laser vibrometer. Furthermore the vibrating sample emits ultrasonic signals into the air which are detected by a special broadband microphone. The time-signals are digitized and stored, and their spectral content is calculated by Fast Four, Short Time Fourier and Hilbert Huang Transformation in order to evaluate the linear and nonlinear signal content. In addition, the samples were characterized with non-destructive testing methods in their initial state and after the fatigue experiments. The spectral content of the ultrasonic signals acquired during the loading process is discussed in reference to the detected fatigue damage.

Poster