Denis Benasciutti

Harvested power and sensitivity analysis of vibrating shoe-mounted piezoelectric cantilevers

This paper presents a preliminary investigation on energy harvesting from human walking via piezoelectric vibrating cantilevers. Heel accelerations during human gait are established by correlating data gathered from the literature with direct experimental measurements. All the observed relevant features are synthesized in a typical (standard) acceleration signal, used in subsequent numerical simulations. The transient electromechanical response and the harvested power of a shoe-mounted bimorph cantilever excited by the standard acceleration signal is computed by numerical simulations and compared with measurements on a real prototype. A sensitivity analysis is finally developed to estimate the mean harvested power for a wide range of scavenger configurations. Acceptability criteria based on imposed geometrical constraints and resistance strength limits (e.g. fatigue limit) are also established. This analysis allows a quick preliminary screening of harvesting performance of different scavenger configurations.

On thermal stress and fatigue life evaluation in work rolls of hot rolling mill

The paper proposes an approach for thermal stress evaluation and fatigue life assessment of work rolls in hot rolling mills. Temperature and thermal stress distributions are calculated with a simplified finite element approach, based on a plane model of work roll loaded on its boundary by rotating thermal actions for a typical hot rolling configuration. A transient of one hour is simulated and the calculated temperature field is next applied as thermal loading in elastic–plastic mechanical simulation, to get thermal stresses and elastic–plastic strains in work roll. Calculated cyclic stresses and strains are finally used to estimate work roll service life, based on Universal Slopes equation that is modified to account for the multiaxial stress state. A comparison of results by three multiaxial fatigue criteria is provided. The obtained results show that, according to such multiaxial criteria, stress multiaxiality would have a great effect on fatigue life, despite it is generally neglected in approaches usually adopted in literature.

Vibration analysis of Sendzimir cold rolling mill and bearing fault detection

Abstract The presence of several rolls in cluster cold rolling mills makes on-line vibration monitoring and failure analysis difficult. The dynamic behaviour of rolls strongly depends on the rolling pressure in the roll bite. Strip vibration applies a dynamic component on the rolling force acting on the work roll and may excite the resonance of the mill stand. This problem motivates predicting the cluster mill dynamics by using a numerical model. It may help in planning the maintenance operation of rolls and bearings and in reducing the service costs. A complete dynamic analysis of the cluster mill layout has seldom been proposed in the literature. In this article, the authors investigate the dynamic behaviour of a Sendzimir mill. A numerical simulator developed in the Matlab/Simulink environment is used to distinguish the effects of chattering, rolls unbalance, motor dynamic irregularities, and bearing fault. Analytical approaches proposed to compute the dynamic component of the rolling force are used as an input to excite the rolls vibration in the cluster mill simulator. Numerical results are used to interpret some preliminary experimental measures performed on the operating Sendzimir mill. Some goals were achieved. This investigation allowed the distinguishing of the dynamic effects due to the rolls from those related to the motor and bearings fault. Critical parameters used in the numerical model were identified. To complete this study, a fully instrumented cold rolling mill has to be used in order to measure all the dynamic signals required to detect the relevant phenomena that have to be prevented.

Fatigue damage assessment of a car body-in-white using a frequency-domain approach

This work presents an application of a frequency-domain methodology developed for the fatigue damage and service life assessment of mechanical components under multiaxial random loadings. The road-induced random loadings in a virtual laboratory bench test (four post test rig) are determined using an integrated Multi-Body/Finite Element (MB/FE) analysis. A method (i.e. the variance method) based on the statistics of the observed multiaxial loadings is used to determine the critical direction. The shear stress resolved in the critical direction is then assumed as the reference loading for the subsequent fatigue analysis. A frequency-domain approach recently proposed in the literature (i.e. the non-Gaussian TB method), capable to include the load non-normality into the fatigue assessment procedure, is used to estimate the loading spectrum. A comparison between the observed and the estimated loading spectrum, extrapolated from shorter to longer time (e.g. the entire vehicle service life), is shown. The presented results show how the proposed methodology could be a very useful tool for the reliable and quick analysis of components under multiaxial random loadings.

Estimation of Material Parameters in Nonlinear Hardening Plasticity Models and Strain Life Curves for CuAg Alloy

This work investigates the cyclic response and low-cycle fatigue behaviour of a CuAg alloy used in crystallizer for continuous casting lines. Therefore isothermal strain-based fatigue tests are first performed on CuAg specimens at different temperature levels (20 °C, 250 °C, 300 °C). The evolution of stress-strain loops recorded during the cyclic tests is used for the parameter identification of several nonlinear hardening models (nonlinear kinematic, nonlinear isotropic). Cyclic stress-strain data from experiments are compared with results from numerical simulations with the identified material parameters, showing a satisfying agreement. Critical examination of numerical results from different models is also performed. Finally, the strain- life fatigue curves estimated from experimental data are compared with approximate strain-life equations (Universal Slopes Equation, 10% Rule) which are obtained from simple tensile tests. The material parameters determined in this work can conveniently be used as inputs in a elasto- plastic finite element simulations of a crystallizer.

Simplified numerical approach for the thermo-mechanical analysis of steelmaking components under cyclic loading: an anode for electric arc furnace

ABSTRACT The need of a strong improvement of productivity and reliability led the adoption of advanced modeling techniques in the design of steelmaking plants components. In this work a procedure based on a finite element simulation is proposed in order to perform a durability analysis of an anode for electric arc furnace. This component undergoes cyclic thermal loads, which also produce a partial melting of one part, meanwhile the other is maintained at almost constant temperature by a cooling system. A simplified, but effective, procedure is developed to take into account steel melting during the heating phase. Considering the cyclic loading conditions, several material cyclic plasticity models, and their effect on the thermal fatigue behavior, are also systematically investigated. The proposed approach permits the component fatigue life to be assessed by a simple and fast uncoupled thermo-mechanical simulation in steady-state conditions.

A harmonic one-dimensional element for non-linear thermo-mechanical analysis of axisymmetric structures under asymmetric loads: The case of hot strip rolling:

This work presents a one-dimensional harmonic finite element for the transient elasto-plastic analysis of axisymmetric structures loaded by non-axisymmetric thermal and mechanical loads. The one-dimensional element exploits a semi-analytical approach, based on Fourier series decomposition of the applied loads. The initial stress method is used for the non-linear solution of elasto-plastic analysis. As a case study, the proposed one-dimensional harmonic element is applied for modelling a two-dimensional circle under thermal and mechanical loadings rotating over its surface, which is used as an approximation of a work roll in hot strip rolling. With the one-dimensional harmonic element, the cyclic thermo-mechanical behaviour of the work roll can be simulated by considering localized plasticity caused by thermo-mechanical loads representative of strip and back-up roll. Compared to two-dimensional models already used in the literature, the one-dimensional element allows a significant reduction in the computational time to be achieved; it follows that the whole transient thermo-mechanical response can be simulated, thus permitting a more complete evaluation of the stress–strain response that is necessary for fatigue life assessment.

Analytical characterization and experimental validation of performances of piezoelectric vibration energy scavengers

One of the main requirements in wireless sensor operation is the availability of autonomous power sources sufficiently compact to be embedded in the same housing and, when the application involves living people, wearable. A possible technological solution satisfying these needs is energy harvesting from the environment. Vibration energy scavenging is one of the most studied approaches in this frame. In this work the conversion of kinetic into electric energy via piezoelectric coupling in resonant beams is studied. Various design approaches are analyzed and relevant parameters are identified. Numerical methods are applied to stress and strain analyses as well as to evaluate the voltage and charge generated by electromechanical coupling. The aim of the work is increasing the specific power generated per unit of scavenger volume by optimizing its shape. Besides the conventional rectangular geometry proposed in literature, two trapezoidal shapes, namely the direct and the reversed trapezoidal configuration, are analyzed. They are modeled to predict their dynamic behavior and energy conversion performance. Analytical and FEM models are compared and resulting figures of merit are drawn. Results of a preliminary experimental validation are also given. A systematic validation of characteristic specimens via an experimental campaign is ongoing.

A numerical approach for the analysis of deformable journal bearings

This paper presents a numerical approach for the analysis of hydrodynamic radial journal bearings. The effect of shaft and housing elastic deformation on pressure distribution within oil film is investigated. An iterative algorithm that couples Reynolds equation with a plane finite elements structural model is solved. Temperature and pressure effects on viscosity are also included with the Vogel-Barus model. The deformed lubrication gap and the overall stress state were calculated. Numerical results are presented with reference to a typical journal bearing configuration at two different inlet oil temperatures. Obtained results show the great influence of elastic deformation of bearing components on oil pressure distribution, compared with results for ideally rigid components obtained by Raimondi and Boyd solution.

Energy Harvesting with Vibrating Shoe-Mounted Piezoelectric Cantilevers

This chapter presents a study on energy harvesting from human walking via piezoelectric vibrating bimorphs. Heel accelerations are measured and compared with data from literature. All relevant features are summarized in a typical (standard) acceleration signal, used as a reference input in numerical simulations. The transient electromechanical response (beam deflection, output voltage, and average output power) of a shoe-mounted rectangular scavenger excited by the standard acceleration is calculated by numerical simulations. Step-by-step numerical integration is used, as the input is a non-sinusoidal signal and explicit analytical solution is not available. Results from simulations are also validated with measurements on a real shoe-mounted device. A sensitivity analysis is finally performed to find alternative scavenger configurations that could provide increased power levels. Acceptability criteria based on imposed geometrical constraints and material strength limits are also checked. This analysis allows a rapid screening of harvesting performance among a wide set of different scavenger configurations, which allows finding the one providing the largest output power.