Numerical predictions of the anisotropic viscoelastic response of uni-directional fibre composites

Finite Element (FE) simulations are conducted to predict the viscoelastic properties of uni-directional (UD) fibre composites. The response of both periodic unit cells and random stochastic volume elements (SVEs) is analysed; the fibres are assumed to behave as linear elastic isotropic solids while the matrix is taken as a linear viscoelastic solid. Monte Carlo analyses are conducted to determine the probability distributions of all viscoelastic properties. Simulations are conducted on SVEs of increasing size in order to determine the suitable size of a representative volume element (RVE). The predictions of the FE simulations are compared to those of existing theories and it is found that the Mori-Tanaka (1973) and Lielens (1999) models are the most effective in predicting the anisotropic viscoelastic response of the RVE

Impact hammer-based analysis of nonlinear effects in bolted lap joint

This work presents an experimental investigation into the dynamic behavior of a bolted joint beam configuration. The impact hammer is chosen as an alternative to classical harmonic excitation methods. The structural responses are explored for a range of the joint tightening toques and various levels of impulse hammer excitations. A symmetric beam assembly made of two nominally identical steel beams is studied. Symmetric modes are found to be sensitive to the test parameters. For given torque, impact-based varying joint loading conditions are used to induce the nonlinear joint effects. A linear data processing strategy is used to observe the nonlinear behavior indirectly. The dynamic joint behavior is described in the form of the modal frequency-damping ratio performance maps represented by the two-parametric approximating quadratic response surface models. This model maps the joint conditions on the corresponding dynamic characteristics of interest and it will serve as a basis for the parametric linear joint model developmen

Novel parametric reduced order model for aeroengine blade dynamics

© 2015 Elsevier Ltd. All rights reserved.The work introduces a novel reduced order model (ROM) technique to describe the dynamic behavior of turbofan aeroengine blades. We introduce an equivalent 3D frame model to describe the coupled flexural/torsional mode shapes, with their relevant natural frequencies and associated modal masses. The frame configurations are identified through a structural identification approach based on a simulated annealing algorithm with stochastic tunneling. The cost functions are constituted by linear combinations of relative errors associated to the resonance frequencies, the individual modal assurance criteria (MAC), and on either overall static or modal masses. When static masses are considered the optimized 3D frame can represent the blade dynamic behavior with an 8% error on the MAC, a 1% error on the associated modal frequencies and a 1% error on the overall static mass. When using modal masses in the cost function the performance of the ROM is similar, but the overall error increases to 7%. The approach proposed in this paper is considerably more accurate than state-of-the-art blade ROMs based on traditional Timoshenko beams, and provides excellent accuracy at reduced computational time when compared against high fidelity FE models. A sensitivity analysis shows that the proposed model can adequately predict the global trends of the variations of the natural frequencies when lumped masses are used for mistuning analysis. The proposed ROM also follows extremely closely the sensitivity of the high fidelity finite element models when the material parameters are used in the sensitivity

Novel frame model for mistuning analysis of bladed disc systems

The work investigates the application of a novel frame model to reduce the computational cost of the mistuning analysis of bladed disc systems. A full-scale finite element (FE) model of the bladed disc is considered as benchmark. The single blade frame configuration is identified via an optimization process. The individual blades are then assembled by 3D springs, whose parameters are determined via calibration process. The dynamics of the novel beam frame assembly is also compared to those obtained from three state-of-the-art FE-based reduced order models (ROMs): a lumped parameter approach; a Timoshenko beam assembly, and component mode synthesis (CMS) based techniques with free and fixed interfaces. The development of these classical ROMs to represent the bladed disc is also addressed in detail. A methodology to perform the mistuning analysis is then proposed and implemented. A comparison of the modal properties and forced response dynamics between the aforementioned ROMs and the full-scale FE model is presented. The case study demonstrates that the beam frame assembly can predict the variations of the blade amplitude factors with results being in agreement with the full-scale FE model. The CMS based ROMs underestimate the maximum amplitude factor, while the results obtained from beam frame assembly are generally conservative. The beam frame assembly is 4 times more computationally efficient than the CMS fixed-interface approach. This study proves that the beam frame assembly can efficiently predict the mistuning behavior of bladed discs when low order modes are of interest

Measurements and predictions of the viscoelastic properties of a composite lamina and their sensitivity to temperature and frequency

We perform finite element analysis of the mechanical response of random RVEs representing the microstructure of a unidirectional (UD) fibre composite, predicting its anisotropic stiffness and damping properties and their sensitivity to temperature and frequency, using as inputs only the measured response of the constituents. The simulations are validated by DMTA measurements on a UD composite; then, the numerical predictions are compared to those of previously published theoretical models. New equations are proposed to predict the viscoelastic constants, providing better accuracy than existing models. The accuracy of these new equations is tested, over wide ranges of fibre volume fractions and stiffness ratios of the constituents, against the numerical predictions

Preparation and use of maize tassels’ activated carbon for the adsorption of phenolic compounds in environmental waste water samples

The determination and remediation of three phenolic compounds bisphenol A (BPA), ortho-nitrophenol (o-NTP), parachlorophenol (PCP) in wastewater is reported. The analysis of these molecules in wastewater was done using gas chromatography (GC) × GC time-of-flight mass spectrometry while activated carbon derived from maize tassel was used as an adsorbent. During the experimental procedures, the effect of various parameters such as initial concentration, pH of sample solution, eluent volume, and sample volume on the removal efficiency with respect to the three phenolic compounds was studied. The results showed that maize tassel produced activated carbon (MTAC) cartridge packed solid-phase extraction (SPE) system was able to remove the phenolic compounds effectively (90.84–98.49 %, 80.75–97.11 %, and 78.27–97.08 % for BPA, o-NTP, and PCP, respectively) . The MTAC cartridge packed SPE sorbent performance was compared to commercially produced C18 SPE cartridges and found to be comparable. All the parameters investigated were found to have a notable influence on the adsorption efficiency of the phenolic compounds from wastewaters at different magnitudes

Probabilistic dynamics of mistuned bladed disc systems using subset simulation

© 2015 Elsevier Ltd.abstract The work describes an assessment of subset simulation (SubSim) techniques to increase the computational efficiency for the predictions of probabilistic dynamic behaviour in mistuned bladed disc systems. SubSim is an adaptive stochastic procedure to efficiently compute small failure probabilities, which are expressed as a product of large conditional failures probabilities by introducing intermediate failure events. The original version of SubSim with a classical modified Markov chain Monte Carlo (MCMC) method is used in this work to generate samples related to intermediate failure events. A 2-DOFs model with lumped parameters identified from a high-fidelity finite element model is used to represent a bladed disc. The statistics associated to the maximum forced frequency response amplitudes are evaluated from different levels of the blade mistuning using stiffness perturbations of the blades. Direct Monte Carlo simulations (MCS) are used to benchmark the results from the SubSim. The proposed methodology is shown to capture efficiently the statistical properties of the mistuned blades with less than 5% samples compared to the direct MCS method. Trade-off parametric studies of the SubSim method indicate that 2000 samples at each level yield an overall good computational efficiency and accuracy for the bladed disk system considered in this work. The study confirms that SubSim techniques can be effectively used in stochastic analysis of bladed disc systems with uncertainty related to the blade configurations

Extraction of dynamic characteristics from vibrating structures using image sequences

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