Roberto Marsili

Measurement of the dynamic normal pressure between tire and ground using PVDF piezoelectric films

In this paper, an application of piezoelectric polyvinylidene fluoride (PVDF) films is presented, for the eval- uation of the dynamic normal pressure exchanged between the ground and the tire of a moving car. A low-cost prototype matrix made of PVDF films has been dynamically characterized and its measurement uncertainty was evidenced. The sensorized platform was eventually inserted in a typical asphalt road and proved in the real conditions. The goal of this research will be the realization of a higher dimension matrix of sensing elements in order to measure the distribution of the pressure under the pneumatic tire in operating conditions. The research activity has been started to develop new techniques, together with the dynamic measurement of the tire crushing using a triangulation laser sensor, for contributing to the trim of a racing F3 car.

Measurement on Rotating Mechanical Component by Thermoelasticity

In this paper a new measurement technique to perform thermoelastic stress analysis on rotating mechanical component is proposed. The idea is to use a particular realization of the Dove prism optical system, optimized to work width infrared radiation, able to give a fixed output image of a rotating surface on where a normal thermoelastic measurement system can be applied. The realization of a first prototype of this optical system is described. First results on a test case are illustrated.

Vibration measurements of tools inside fluids by laser Doppler techniques: uncertainty analysis

In this work a technique based on a laser vibrometer is examined for the vibration measurement of bodies with fluids between the measurement point and vibrometer head. Some mathematical models have been considered and the causes of uncertainty have been correlated with the optical characteristics of the various fluids employed and with their thickness. Optical test benches have been set up and comparative measurements with accelerometers have been carried out in order to verify the mathematical models and estimate other uncertainty sources. Results of the analysis have been used to perform forced vibration measurements on a machine shaft with special care in order to minimize the effect of the noise sources analysed.

Development and experimental characterization of a new non contact sensor for blade tip timing

Performances of blade tip timing measurement systems (BTT), recently used for non contact turbine blade vibration measurements, in terms of uncertainty and resolution are strongly affected by sensor characteristics. The sensors used for BTT generate pulses, to be used also for precise measurements of turbine blades time of arrival. All the literature on this measurement techniques do not address this problem in a clear way, defining the relevant dynamic and static sensor characteristics, fundamental for this application. Till now proximity sensors used are based on optical, capacitive, eddy current and microwave measuring principle. Also pressure sensors has been used. In this paper a new sensing principle is proposed. A proximity sensor based on magnetoresistive sensing element has been assembled end tested. A simple and portable test bench with variable speed, blade tip width, variable clearance was built and used in order to characterize the main sensor performances.

Image Analysis Technique for Material Behavior Evaluation in Civil Structures

The article presents a hybrid monitoring technique for the measurement of the deformation field. The goal is to obtain information about crack propagation in existing structures, for the purpose of monitoring their state of health. The measurement technique is based on the capture and analysis of a digital image set. Special markers were used on the surface of the structures that can be removed without damaging existing structures as the historical masonry. The digital image analysis was done using software specifically designed in Matlab to follow the tracking of the markers and determine the evolution of the deformation state. The method can be used in any type of structure but is particularly suitable when it is necessary not to damage the surface of structures. A series of experiments carried out on masonry walls of the Oliverian Museum (Pesaro, Italy) and Palazzo Silvi (Perugia, Italy) have allowed the validation of the procedure elaborated by comparing the results with those derived from traditional measuring techniques.

Uncertainty analysis of vibration measurements of tools inside fluids by laser Doppler techniques

In this work a technique based on a laser vibrometer is examined for the vibration measurement of bodies with fluids between the measurement point and vibrometer head. Some mathematical models have been considered and the causes of uncertainty have been correlated with the optical characteristics of the various fluid employed and with their thickness. Optical test benches have been set up and comparative measurements with accelerometers have been carried out in order to verify the mathematical models and estimate other uncertainty source. Results of the analysis have been sued to perform forced vibration measurements on a machine shaft with special care in order to minimize the effect of the noise sources analyzed.

Measurement of contact and grip force as reference for human hand transmitted vibration evaluation by laser scanning vibrometers

As illustrated in previous works a laser scanning vibrometer can be used to detect vibration transmitted to human body, in particularly vibration velocity on hand skin. The problem still open to investigation of hand mechanical impedance, i.e. the ratio between force and velocity. This parameter, and its distribution on the hand, is of paramount importance for example to build multi input - multi output models or develop and test insulating devices. Another well known fact is that vibration transmission to human hands depends on the overall grip force applied by the subject. In this work film sensors to detect local contact pressure has been analyzed and tested in different situations. The signals of those sensors are then used to calculate mechanical impedance maps of human hands using also results obtained by a scanning laser Doppler vibrometer.

Fibre Bragg Gratings for the Monitoring of Wooden Structures

The aim of this work was to develop and validate an experimental methodology suitable for analysing on-site the behaviour of fibre-reinforced wooden structures. The proposed measurement method is based on the application of fibre Bragg grating (FBG) strain sensors. An analysis of adhesive behaviour was performed preliminarily, which provided indications for choosing the type of adhesive and for the fibre bonding length in accordance with the volume of measurement. The first series of tests was carried out on wood samples to verify the coupling between the measuring sensor and the wood support when the latter is subject to mechanical stresses. The second investigation was done on site to test the behaviour of a historical wood floor before and after reinforcement by means of a series of tests performed using optical fibres with the Bragg grating. The optical fibre system measurements were compared to those obtained using a laser vibrometer, a measurement system of proven stability and precision. The comparison makes it possible to confirm the validity of the results and the reliability of the system for the monitoring of historic wooden structures.

A New Measurement and Testing Procedure Based on Thermoelasticity for Motorcycle Frame Prototype Development

Motorcycle frames are mechanical components that need to be optimised in terms of performance and costs but with a limited amount of resources compared to, for example, car frames. Fatigue testing of the component is required for qualification and this is typically performed by using rotating drums with steps or servo-controlled hydraulic actuator based test benches. Therefore a fast and simple measurement and testing technique that operates during the fatigue tests will be a very useful tool. In this paper the possibility of analysing these components by measuring the stress levels and stress concentration in critical parts by thermoelasticity is investigated. The development of a multibody model, useful to simulate the typical working conditions of the motorcycle frame, is also described.

Comparison between accelerometer and laser vibrometer to measure traffic-excited vibrations on bridges

The use of accelerometer based measurement techniques for evaluating bridge forced vibrations or to perform bridge modal analysis is well established. Some of the goals of this experimental approach and typical results are here reviewed. It is well known to all researchers who have experience in vibration measurements that values of acceleration amplitude can be very low at low frequencies and that a limitation to the use of accelerometer can be due to the threshold parameter of this kind of transducer. Under this condition the measurement of displacement seems more appropriate. On the other hand laser vibrometer systems detect relative displacements as opposed to the absolute measures of accelerometers. In this paper the results of some in field measurements on a highway little bridge, excited by traffic, under normal operating conditions, are analyzed. Vibrations have been measured simultaneously by a typical accelerometer for civil structures and by a laser vibrometer equipped with a fringe counter board in terms of velocity and displacements. The accelerations calculated from the laser vibrometer signals and the one directly measured by the accelerometer has been compared. The advantages of the use of a laser vibrometer at low frequency are relevant and it appears possible to open up new possibility to analyze bridge loads in operating conditions, monitoring bridge health state, predict fatigue life and improve the bridge design.