3,306 research outputs found
Experimental Identification of the Constitutive Model of Viscoelastic Non-Standard Materials
No full textThere is an increasing interest towards the use of
non-conventional material such as Functionally Graded
Materials (FGM) for aerospace and automotive mechanical
applications. Classical material models, e.g. Kelvin or Zener,
can show some limitations in describing the viscoelastic
behavior of these materials. A numerical and experimental
approach to identify the optimal model order and the
parameters of the constitutive material relationship in the
frequency domain is proposed. The constitutive equation is
modeled by means of a generalized Kelvin model and
expressed in the form of a rational function. To describe the
complex material behavior, high order polynomials are needed
for the rational function and the problem of finding the function
coefficients can be ill-conditioned. Different approaches for the
rational function parameters identification are compared. A
least square error identification technique adopting Forsythe
orthogonal polynomials is proposed. The selected procedure is
first applied on numerically estimated measurements with
noise, and then on real measurement data obtained by forced
vibration testing of Polytetrafluoroethylene specimens
Identification of the extended standard linear solid material model by means of experimental dynamical measurements
No full textA novel algebraic procedure for the non-parametric identification of the material model by means of dynamical test measurements is proposed. An extended Standard Linear Solid (SLS) material model is taken into account to model the material linear visco-elastic behavior. It consists of the series arrangement of fractional Kelvin model elements adopting real parameters and integer and non-integer order time differential operators, and of hysteretic Kelvin model elements adopting complex parameters and integer order time differential operators. Hysteretic Kelvin model elements are introduced to take account of the material hysteretic behavior. The material E(j center dot omega) complex modulus, is analytically modeled as the ratio of pseudo polynomials (non-integer power terms) in the j center dot omega Fourier variable. A multi-step, iterative, material model identification technique is here proposed to identify the unknown polynomial coefficients and the non-integer exponent values starting from E(j center dot omega) material discrete estimates from input-output dynamical measurements made on a beam specimen at different omega frequency values. Computational, nonphysical SLS elements resulting from the application of the identification procedure can be found and eliminated, so that a low order optimal model result. Some results obtained by applying the proposed identification technique with real experimental measurements are shown and discussed
An effective coating material solution and modeling technique for damping oriented design of thin walled mechanical components
No full textA multi-layer coating beam model is proposed to find, at the modelling stage, optimal coating architectures to be applied to mechanical components, in order to maximize the vibration damping in industrial operating conditions. Recent experimental works showed that application of coatings may influence vibration damping, and that dissipative actions can be mainly localized at the interlaminar interface. The aim of this paper is to present a mechanical model for numerically simulating the response of a uniform, multi-layered composite beam specimen taking into account of these interlaminar dissipative actions, so that reducing the need to experimentally evaluate the effectiveness of many candidate coating solutions. The model is based on a modified third order zig zag beam theory, where the contribution of the frictional actions is modelled by means of complex, elasto-hysteretic distributed actions localized at the layer interfaces. The resulting multi layered beam model degrees of freedom do not depend on the number of the coating layers and the proposed technique showed to be computationally effective to simulate the damping behaviour of different virtual specimens. A frequency and application dependent damping estimator is proposed and some application examples are presented and critically discussed
Robust identification of the mechanical properties of viscoelastic non standard materials by means of frequency domain experimental measurements
No full textThis work presents an identification procedure for the constitutive model of viscoelastic non-standard materials, such as Functionally Graded Materials (FGM). A generalized Kelvin model of arbitrary order is selected, making it possible to define the material constitutive relationship by means of the ratio of polynomials in the frequency domain. Since ill-conditioning may occur at the numerical identification stage of high order model parameters, a novel approach to identify the model optimal order and parameters, mainly employing a orthogonal polynomial basis, is proposed in this paper. Least square error fitting techniques employing a classic monomial and a Forsythe orthogonal polynomial basis are compared by starting from numerically estimated measurements with noise. The selected approach is used to fit dynamical measurement data obtained from real test specimens in a wide excitation frequency range. The optimal model results obtained by fitting real experimental data are presented and discussed
Virtual prototyping of high damping multilayer coating solutions for industrial applications
No full textSpecifically designed and optimized multi-layered coating solutions can be adopted to obtain composite components with high stiffness, high resistance and effective vibration damping capabilities.
In particular the adoption of multi-layer coating solutions, designed to maximize dissipative actions at the interface between different layers, offers significant advantages with respect to a single layer coating approach. The use of single layer coating technology often results in thick coating layers that produce undesired alterations in the geometrical and mechanical properties of the component. By maximizing the dissipative actions between relatively thin layers high damping multi-layer coating solutions can be obtained, with limited alteration of the uncoated component geometry, stiffness and strength properties.
In this work different high damping multi-layer coating solutions are presented and a virtual prototyping and experimental validation design procedure is discussed. An extensive measurement campaign, consisting on estimating the frequency response function of coated and uncoated slender beam test specimens, is made in order to investigate the effectiveness of different coating material choices, to be adopted in multi-layer coating solutions. Different coating material solutions, such as single and dual component epoxy resin, cyanoacrilate based, ceramic-based polymeric, metal oxide and nitrides coating solutions are taken into account. The various solutions are applied by means of different manufacturing methods such as screen printing, anodization and plasma based deposition technologies. Some frequency
dependent damping estimators, defined by the authors in previous works, are evaluated over a wide frequency range. An identification procedure, making use of a multi-layer beam model that takes into account of the dissipative actions at the interface between the layers, is applied to the measurement data in order to find the unknown parameters modeling the inter-layer hysteretic dynamical actions at the interface between two different layers. The identification procedure is first tested on numerically simulated specimen examples with the addition of noise to evaluate the robustness of the identification technique before applying it to true experimental measurements. Then the coating materials property
estimates and the damping experimental estimates, obtained from reference tri-layer symmetric beam specimens, are used as input of the previously validated numerical identification procedure. The optimal value of the parameters that define slipping and dissipative actions at the interface between different layers, modeled by means of complex interlaminar impedances, are identified. The identified parameters are used with a multi-layer beam virtual prototype model to simulate the damped free and forced vibrational response of different multi-layer composite beam specimen architectures. Different coating solution virtual prototypes, obtained by varying the coating layer architecture, i.e. the number of layers, materials and thickness values, are compared by means of the evaluation of the previously
cited damping estimator. The more effective coating solutions are selected, some multi-layer beam specimens are prepared accordingly and tested by means of dynamic mechanical measurements. The experimental measurement results are used to validate the proposed prototyping procedure. Some industrial application examples, consisting on the application of some of the effective coating solution previously found on the casing of a mechanical pump are presented. The vibrational and acoustic response of these coated solutions working in real operating conditions is experimentally evaluated and compared with respect to the same results obtained from within the uncoated solutions. A discussion
and a critical analysis is presented
Robust identification of material model by means of forced sinusoidal excitation measurements
No full textRobust identification of material model by means of forced sinusoidal excitation measurements
Dynamic Mechanical Analysis (DMA) test instruments are commonly employed to identify the mechanical behaviour of materials at different temperatures and frequencies. In a typical dynamic measurement, a sinusoidal excitation is applied to a beam specimen of known geometry and the displacement response is obtained. The DMA output can be processed to obtain the D(ω) material stress (σ) versus strain (ε) relationship, i.e. σ (ω)=D(ω)× ε (ω), by means of the Timoshenko or Euler Bernoulli beam model assumption. Nevertheless, the approach shows some limitations since these model assumptions do not take into account of the many other factors influencing the measurement output: the effective boundary conditions, the structural instrument frame model coupling, the inertial and dissipative contribution of the excitation moving substructure, so that a multi-DOF (MDOF) system results. Many techniques are known for identifying a MDOF system model typically requiring measurements being done in some experimental DOFs, and requiring data not directly available from within the typical DMA set-up, so that an additional test measurement system is needed, being not synchronized with the DMA measurements. Some calibration procedures are commonly proposed by the many commercial instrument firms, but the related accuracy is generally poor, as it is shown in this work in some identification examples related to a harmonic steel specimen.
This work deals with specimens in the form of slender, uniform, homogeneous beams with clamped double pendulum boundary conditions excited by means of a sinusoidal flexural force at different frequencies at the mobile free beam end, where both excitation and displacement response are measured at the same time, i.e. in the single cantilever experimental set-up. A single experimental DOF is measured with respect to both input and output, frequency range [0.01-200] Hz. In this work a calibration technique for dynamic mechanical analysis (DMA) experimental systems, using only data obtained from tests made within the commercially available instrument itself, is adopted and it is shown as a part of the identification procedure. The calibration technique is based on an optimisation algorithm and deals with the identification of a 2 DOFs frame model coupled to the specimen beam model by using as input the single beam DOF force and displacement measurements made on some reference uniform specimens. The aim is to obtain measurement estimates being filtered from the contribution of the experimental system. The robustness of the proposed technique is tested on some numerical model cases with added noise. A sensitivity based numerical technique is also proposed to evaluate the contribution of each identification unknown during the optimisation process. The technique is applied to some dynamical measurements made on material specimens whose model is known in advance and then to some non standard material configurations. The technique is also applied on two DMA systems made by two different manufacturers. The results are shown and critically discussed
Dynamical Calibration of a Standard Sensor-Based Experimental Test Apparatus for Accurate Material Model Parametric Identification
No full textAbstract: A signal processing-based procedure is proposed for calibrating an experimental
sensor-based test system used to identify material model parameters. A standard dynamic
mechanical analyzer (DMA) sensorized test apparatus is considered, enabling the measurement of dynamic excitation and displacement response in a specimen under flexural
conditions. To account for the dynamic contributions of the system frame and fixtures to
the measured response, a novel calibration procedure is introduced, mainly differing from
the techniques used in standard test applications. A multi-degree-of-freedom dynamic
model of the instrument frame, coupled with the beam specimen under test, is considered,
and a frame identification procedure is described. The proposed procedure requires measurements from at least three beam specimens made of a known material but with different geometries. It is shown that an accurate frame model can be identified using an algebraic numerical technique. It is shown that the accuracy of the material model identification can be improved by applying the proposed calibration technique. Some experimental application examples are presented and discussed
Separazione e valutazione funzionale dei linfociti circolanti nelle leucemie linfatiche croniche.
No full textMechanical modelling and experimental identification of the model parameters of multilayer coated specimens for high damping industrial applications
No full textCoating technology may be adopted to produce composite mechanical components with high vibration damping behavior, but thick coating layers, significantly modifying the geometry and the mechanical properties of the component, may generally result. An alternative approach is to use multilayer coatings designed to maximize the interlaminar dissipative actions. By adopting this approach relatively thin coatings may result, while the composite component geometry, stiffness and strength properties do not greatly change with respect to the uncoated solution. Preliminary experimental tests made by our research group on multilayer coating applied by means of different technologies such as reactive plasma vapour deposition (RPVD), anodization, screen printing of inhorganic polymer and cianoacrilate based coatings, showed some interesting but still not fully satisfying results. In order to reduce time and costs of the development process of new coating solutions a multi-layered beam model was proposed for numerically simulating the response of a composite beam specimen, taking into account of the slipping occurring at the interface between the layers and of distributed dissipative actions modelled by means of a complex interlaminar impedance. By adopting a discretization procedure based on a spectral approach, a linear, second order system of discrete equations result, involving complex Hermitian matrices. The damping behaviour of the composite beam can be evaluated by means of different estimators based on the complex eigenvalues resulting from the eigenproblem associated to the system homogeneous equations (free vibration) and on a real, frequency dependent, normalized functional based on the system frequency response function. Nevertheless, since the application of this model strongly depends on the values of the interface parameters, a numerical identification procedure based on experimental tests done on reference bilayer beam specimens is presented, and results are critically discussed. Some interesting results are obtained by virtual prototyping by means of the proposed model and the interface identified parameters. New multilayer architectures showing useful damping behaviour, are obtained and experimentally validated as well, and presented herein
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