Sulla misura delle tensioni residue con il metodo del foro: metodi di calcolo per le tecniche sperimentali a campo intero

The hole drilling technique is a well known experimental method for residual stress investigation. This technique is usually used in combination with electrical strain gages but there is no reason to enforce this choice and other approach are possible. In particular some optical measurement techniques (grating interferometry, speckle interferometry, holographic interferometry, shearography) can be advantageously used. Since all these optical techniques give a full field information, it becomes important to properly use their data to increase the robustness and reliability of the analysis. In this work, various well known approaches to this problem will be investigated using a known displacement field as a reference. In this way it will be possible to discover the best performing algorithm in terms of robustness and reliability

Un nuovo algoritmo di Phase Unwrapping basato sulla crescita competitiva di regioni

The phase unwrapping problem arises every time one has to analyse experimental data acquired by means of techniques based on periodical phenomena, from the opto-interferometric ones to some geologycal or medical techniques. This paper presents a new phase unwrapping algorithm based on the competitive region growing: starting from an equipotential condition, it makes an area to absorb its neighbours by mean of a quality parameter based on the extension and the coherency of the regions. After a short description of the phase unwrapping problem and of some of the most used techniques, this paper describes the working principle of the algorithm and the implementation details. The paper ends with some examples of applications of the algorithm on synthetic images

Sviluppo di un sensore interferometrico per il controllo del posizionamento di un rugosimetro ottico

The optical profilometer that is under development at the Mechanical Engineering Department of the University of Cagliari (DiMeCa) requires a translation stage able to displace part of the optical system with sub-micrometric resolution. This work describes the development of an interferometric displacement sensor which enables, by its feedback, to accurately control an otherwise open loop controlled electrostrictive translation stage. After a short description of the optical system, the mechanical assembly, the electronic module and the software interface will be described. At the end some experimental result, showing the performances of the sensor will be illustrated

Sulla interferometria olografica digitale

The holographic interferometry is a well-known experimental technique which allows for measuring the displacements field of a sample in a relatively simple way. In its classical implementation, this technique uses high sensitivity photographic plates as recording media; nevertheless there is no reason why a different recording support, for example a CCD camera, can not be used (obviously in this case the reconstruction step has to be performed in numerical form). Since most of the industries producing holographic plates have stopped their lines, the digital version of holographic interferometry is becoming more than an option: this work aims to establish the limitation and the technical aspects that have to be taken into account when using a camera as the recording media. In fact, the low spatial resolution of the hardware requires special precaution to be taken both while building the setup and while performing the measurement

Sull'uso del phase shifting spaziale nella ricostruzione di campi di spostamento con tecniche ottiche

The Spatial Phase Shifting technique makes possible to reconstruct the displacement field using the Fourier analysis of a single image. However, in its “classical” version it presents various problems—first of all the residual component of the carrier fringe field—which seriously limits its usability. This work proposes to combine some techniques, either well known, either new, with the classical spatial phase shifting algorithm so as to enlarge its working field. After illustrating these techniques and their synergic effect, a series of test problems are analyzed showing the reliability of the proposed methodology