The Journal of the Acoustical Society of America

Composites science and technology

Hilbert transform in vibration analysis

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

Composites Part A: Applied Science and Manufacturing

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

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.

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

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

Lamb-Wave based Structural Health Monitoring in Polymer Composites

Analysis of swept-sine runs during modal identification

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

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

Michael Sinapius

Papers

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

Lamb-Wave based Structural Health Monitoring in Polymer Composites

Analysis of swept-sine runs during modal identification

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

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