1,721,057 research outputs found
Rolling contact fatigue damage detected by correlation between experimental and numerical analyses
No full textA study on vibrations related to rolling contact fatigue test bench and a possible way to correlate this mechanical behavior and damage of the specimens is presented. In particular it has been evaluated the possibility to detect and quantify, thanks to vibration analysis, the damage on two discs subjected to rolling contact fatigue in different working conditions. Paper is divided in two parts. In the first part there is a description of test bench and results of its static and modal analyses. Then, some tests were carried out changing working conditions and specimens' parameters and a procedure that allowed both to monitor the specimen's damage state and to record accelerometric data was implemented. A set of piezoaccelerometers was placed on the machine and a virtual instrument for automatic data handling and analysis was performed. Taking into account the FEM results derived from the first part of work, data were analyzed both using a standard approach and by implementing custom digital weighting filters for a windowed RMS in order to define, real-time during the measurement, a good estimator for the specimen damage state development
Analisi teorico-preliminare e sperimentale del sistema di riposizionamento delle testing mass nell’esperimento L.I.S.A.
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Wireless Instrumented Crutches for Force and Movement Measurements for Gait Monitoring
No full textThis paper describes the design, development, and characterization of two wireless instrumented crutches for gait monitoring in order to provide clinicians quantitative parameters of upper limbs’ contributions during walking. These parameters could be used to teach orthopedic patients to correctly use these supports and minimize problems connected to their usage. These instrumented crutches allow monitoring axial forces and shear forces, tilt angles, and time of impact on the ground in real time. Each crutch is composed of three strain-gauge bridges for measuring axial and shear forces, a conditioning circuit with transmission module, a triaxial accelerometer, a power management circuit, two batteries, and a biofeedback. The data are wirelessly transmitted via Bluetooth without needing any further readout unit, from the crutches to a personal computer, where the data are processed and displayed by a program created in LabVIEW. Each instrumented crutch was tested to assess the response of the accelerometer and the three strain-gauge bridges using a setup designed ad hoc. The mean experimental standard deviation was about 42 mV for axial forces corresponding to about 8 N and about 35 mV for shear forces corresponding to about 4 N. Hysteresis, linearity, and drift were calculated, and the obtained accuracy was about 8–9 N for axial forces and 4–5 N for shear forces. Furthermore, the crutches were tested during a walking activity of ten healthy subjects along a straight path for several trials. These crutches were used for a common analysis usually reported in the literature for weight bearing evaluation. The subjects were monitored performing a nonweight bearing (NWB) and a partial weight bearing (PWB) during a three-point gait. The results showed a mean of 102%±16% for NWB tests and a mean of 19%±14% for 10% PWB tests; these values are in agreement with similar studies in the literature. The simplicity that includes only constitutive strain gauges and a separable circuit board allows the achievement of the objectives of simplicity, ease of use, and noninvasiveness. Therefore, these crutches could be used as a support tool for controlling the use of crutches during walking not only in hospitals but also at home
Discrete models for the simulation of rubber components dynamics
No full textThis contribution deals with improvements which have been undertaken on a modelling
and simulation tool (developed by the authors), aimed to numerically characterize the
dynamic behaviour of rubber to metal devices (such as: engine mountings, shock absorbers,
vibration dampers, etc.). The adopted approach allows designing such devices in a CAD like
environment, meshing them and simulating their dynamics; materials constitutive equations
modelling is operated by a neural network, working directly on numerical data supplied by
experimentation. The peculiar properties of rubber, in terms of non-linearity, viscoelasticity
as well as frequency, temperature and static strain dependence, are taken into account in the
numerical analysis.
The proposed method avoids the implementation of finite elements models (as proposed by
many authors) in order to produce a light and easy-to-use modelling and simulation tool, to
be adopted by industrial technicians in the design optimization of the mentioned devices. To
achieve this point, discrete models, constructed by a multi-body particle based approach, are
applied. Several models of such a kind have been taken into account during this research project,
from discrete concentrated parameters models to a chosen hybrid particle based model,
where local finite elements stiffness is computed directly by the continuum constitutive equations.
Simulative results are successfully compared with experimental data for some existing devices,
provided by CF Gomma S.p.A (Brescia, ITALY)
Enhancing micropositioning accuracy of a six axis hexapod through uncertainty evaluation
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