Michael Sinapius

Bio: Michael Sinapius is an academic researcher from Braunschweig University of Technology. The author has contributed to research in topics: Lamb waves & Structural health monitoring. The author has an hindex of 18, co-authored 186 publications receiving 1337 citations. Previous affiliations of Michael Sinapius include German Aerospace Center & Otto-von-Guericke University Magdeburg.

Quantitation of the reinforcement effect of silica nanoparticles in epoxy resins used in liquid composite moulding processes

Abstract: Epoxy–silica nanocomposites are investigated for their suitability as a new type of matrix for fibre-reinforced polymers (FRP) using injection technology (LCM). The key focus is the determination of the processing characteristics of the nanocomposites. The silica nanoparticle content varies between 0 and 25 wt% for the high performance epoxy resin. Photon Cross Correlation Spectroscopy (PCCS) and Scanning Electron Microscopy (SEM) analysis performed on the liquid and cured epoxy–silica nanocomposites indicate a nearly homogeneous distribution of the nanoscaled silica in the epoxy matrix, even at rather high weight percentages. Depending on the silica content of the composite, its stiffness, strength and toughness can be increased significantly compared with neat resin. Moreover, resin shrinkage and the thermal expansion (CTE) can be significantly reduced and the thermal conductivity increased. Concomitant the glass transition temperature remains nearly constant. The initial viscosity of the resin increases slightly depending on the nanoparticle content, while the gel-time slightly decreases. The injectability of the nanocomposite for the purpose of lamination using the LCM technology is nearly unaffected. The optimum filler content is at approx. 25 wt% silica. Epoxy–silica nanocomposites are now proven to be a new high performance polymer matrix for FRP structures manufactured by the low cost LCM techniques.

Lamb-Wave based Structural Health Monitoring in Polymer Composites

Abstract: Deutsche Forschungsgemeinschaft: "Integrierte Bauteiluberwachung in Faserverbunden durch Analyse von Lambwellen nach deren gezielter Anregung durch piezokeramische Flachenaktoren"

Analysis of swept-sine runs during modal identification

Abstract: Experimental modal analysis of large aerospace structures in Europe combine nowadays the benefits of the very reliable but time-consuming phase resonance method and the application of phase separation techniques evaluating frequency response functions (FRF). FRFs of a test structure can be determined by a variety of means. Applied excitation signal waveforms include harmonic signals like stepped-sine excitation, periodic signals like multi-sine excitation, transient signals like impulse and swept-sine excitation, and stochastic signals like random. The current article focuses on slow swept-sine excitation which is a good trade-off between magnitude of excitation level needed for large aircraft and testing time. However, recent ground vibration tests (GVTs) brought up that reliable modal data from swept-sine test runs depend on a proper data processing. The article elucidates the strategy of modal analysis based on swept-sine excitation. The standards for the application of slowly swept sinusoids defined by the international organisation for standardisation in ISO 7626 part 2 are critically reviewed. The theoretical background of swept-sine testing is expounded with particular emphasis to the transition through structural resonances. The effect of different standard procedures of data processing like tracking filter, fast Fourier transform (FFT), and data reduction via averaging are investigated with respect to their influence on the FRFs and modal parameters. Particular emphasis is given to FRF distortions evoked by unsuitable data processing. All data processing methods are investigated on a numerical example. Their practical usefulness is demonstrated on test data taken from a recent GVT on a large aircraft. The revision of ISO 7626 part 2 is suggested regarding the application of slow swept-sine excitation. Recommendations about the proper FRF estimation from slow swept-sine excitation are given in order to enable the optimisation on these applications for future modal survey tests of large aerospace structures.

Eco-efficiency assessment of manufacturing carbon fiber reinforced polymers (CFRP) in aerospace industry

Abstract: Carbon fiber reinforced polymers (CFRP) are frequently used in aerospace industry. However, the manufacturing carbon footprint and direct cost are obstacles in the way of adopting CFRP in further aerospace structures. Therefore, the development of a combined ecological and economic assessment model for CFRP manufacturing is demonstrated in this paper. This model illuminates the proper developments for the decision-makers. In this work, the eco-efficiency assessment model (EEAM) is developed based on life cycle assessment (LCA) and life cycle cost analysis (LCCA). EEAM is an activity-based bottom-up decision support tool for the manufacturing process of fiber reinforced polymer (FRP). This paper discuses a case study of manufacturing CFRP wing ribs for a modern commercial aircraft as a part of the project LOCOMACHS. Ecological results of EEAM conclude that the carbon footprint of manufacturing wing rib made of CFRP thermoset by the technique of in-autoclave single-line-injection (SLI) is around 109 kg CO2-equivalent for each kg of CFRP. Moreover, fiber material is the main contributor in this carbon footprint. On the other hand, the economic assessment shows that the studied rib has a direct manufacturing cost of about 584 €/kg. In these results, labor work dominates the direct cost with 49%, while fiber and matrix compensate about 35%. As an activity-based assessment model, EEAM guides the decision-makers toward sustainable direct applications. It is concluded that direct applications for fiber waste reduction are beneficial for both eco-efficiency aspects. Energy consumption reduction is ecologically beneficial, while labor work reduction on the other hand is cost relevant. In aerospace industry, there is a clear potential for eco-efficient direct applications that satisfy both aspects.

Detection and description of non-linear phenomena in experimental modal analysis via linearity plots

Abstract: Ground vibration tests (GVTs) on aircraft prototypes are mainly performed to experimentally identify the structural dynamic behaviour in terms of a modal model This assumes a linear dynamic behaviour of the structure However, in the practice of ground vibration testing it is often observed that structures do not behave in a perfectly linear manner Non-linearities can be determined, for example, by free play in junctions, hydraulic systems in control surfaces, or friction This paper compiles measured, typical, non-linear phenomena from various GVTs on large aircraft The standard procedure in GVTs nowadays is the application of the Harmonic Balance method which linearizes the dynamic behaviour on the level of excitation The procedure requires a harmonic excitation of the structure which is usually performed during phase resonance testing The non-linear behaviour is investigated in terms of linearity plots in which the resonance frequency of a mode is plotted as a function of the excitation level The experimental data is then compatible with all post-processing procedures for the measured results, eg updating of the finite element model or flutter calculations This paper shows measured linearity plots for some typical non-linear phenomena In the second part of the paper analytical linearity plots for different non-linear stiffness and damping models are considered in order to investigate whether the type of non-linearity can be identified from measured linearity plots The analytical linearity plots are discussed with respect to their application limits The analytical linearity plots are used to interpret the experimental linearity plots stemming from various GVTs on different aircraft prototypes Finally, the observability of non-linear stiffness and non-linear damping characteristics via linearity plots is assessed

Hilbert transform in vibration analysis

Abstract: This paper is a tutorial on Hilbert transform applications to mechanical vibration. The approach is accessible to non-stationary and nonlinear vibration application in the time domain. It thrives on a large number of examples devoted to illustrating key concepts on actual mechanical signals and demonstrating how the Hilbert transform can be taken advantage of in machine diagnostics, identification of mechanical systems and decomposition of signal components.

Composites Part A: Applied Science and Manufacturing

Abstract: Reference EPFL-ARTICLE-184271doi:10.1016/j.compositesa.2012.08.001View record in Web of Science Record created on 2013-02-27, modified on 2017-05-10

Nonlinear system identification in structural dynamics: 10 more years of progress

Abstract: Nonlinear system identification is a vast research field, today attracting a great deal of attention in the structural dynamics community. Ten years ago, an MSSP paper reviewing the progress achieved until then [1] concluded that the identification of simple continuous structures with localised nonlinearities was within reach. The past decade witnessed a shift in emphasis, accommodating the growing industrial need for a first generation of tools capable of addressing complex nonlinearities in larger-scale structures. The objective of the present paper is to survey the key developments which arose in the field since 2006, and to illustrate state-of-the-art techniques using a real-world satellite structure. Finally, a broader perspective to nonlinear system identification is provided by discussing the central role played by experimental models in the design cycle of engineering structures.