CONSIDERAZIONI TEORICHE E PRATICHE SUL METODO DEL MASSIMO RETTANGOLO CIRCOSCRITTO PER LA VALUTAZIONE DELL’AMPIEZZA DELLA TENSIONE TANGENZIALE NEI CRITERI DI FATICA MULTIASSIALE BASATI SULL'APPROCCIO DI PIANO CRITICO

The multiaxial fatigue criteria based on the approach of the critical plane require the determination of the amplitude of the alternating shear stress τ aacting on different planes passing through the point of the material analyzed. In the case of non-proportional stresses the shear stress vector varies both in modulus and direction and its tip describes a curvedefined loading path. In these cases τ ais identified and evaluated by means of special procedures the most recent, and apparently more effective, of which is that of the Maximum Circumscribed Rectangle (MCR) to the loading path itself. In particular τ ais equal to the length of the diagonal of the MCR. In this paper, the MCR method is analyzed comparing it with other existing methods in terms of results obtained and computational effort. Furthermore two procedures that help to optimize the performance ofthe method are proposed, then some critical aspects of the method itself are highlighted for future development of the technique.I criteri di fatica multiassiale basati sull’approccio di piano critico richiedono la determinazione dell’ampiezza della tensione tangenziale alternata a agente sui diversi piani passanti per il punto del materiale analizzato. Nel caso di sollecitazioni di tipo non proporzionale il vettore della tensione tangenziale varia sia in modulo che in direzione e la sua punta descrive una curva definita percorso di carico. In questi casi a viene valutato mediante apposite procedure delle quali la più recente ed apparentemente più efficace è quella del Massimo Rettangolo Circoscritto (MRC) al percorso di carico stesso. In questo lavoro viene effettuato un confronto tra il metodo MRC e i principali altri metodi in termini di risultati ottenuti e di onere computazionale, vengono proposte due procedure di applicazione del metodo MRC che consentono di ottimizzarne l'esecuzione, infine vengono evidenziati alcuni aspetti critici del metodo stesso al fine di ispirarne opportune future modifiche

Improvements in the algorithms for the determination of the shear stress components in critical plane class fatigue criteria

This paper presents two improvements in the procedure for the evaluation of the amplitude and mean values of the shear stress in critical plane class fatigue criteria, when the method of the Minimum Circumscribed Circle (MCC) to the path of the tip of the vector is used. In particular, the paper shows how it is possible to reduce the number of material planes passing through the point of interest in which the MCC has to be determined and the number of points of each curve that has to be considered for the determination of the MCC, noticeably reducing the computational time

Manganese-containing mixed oxide electrodes as anode materials for degradation of model organic pollutants

Mixed oxide thin film electrodes have been prepared by thermal decomposition from alcoholic solution on Pt substrate. In particular, three different anodes have been obtained by co-deposition of Ru (Ruthenium) and Mn (Manganese) oxides, Ru, Mn and Cu (Copper) oxides and co-deposition of Ru, Mn and Co (Cobalt) oxides. The electrochemical behaviour of the prepared electrodes was evaluated by potentiodynamic polarization curves and cyclic voltammetry tests. We also tested and compared their oxidizing ability in the degradation of aqueous solutions containing methyl orange as model compound and small amount of chloride. Galvanostatic experiments were conducted in a membrane-free reactor. The treatment extent was assessed by detection of color and TOC decay. The electrogeneration of active chlorine, chlorate and perchlorate was also monitored. The preliminary results show that ternary oxides coated electrodes exhibit enhanced electrocatalytic activity without producing undesired chlorinated by-products

Una nuova procedura per il calcolo delle tensioni residue con il metodo della rosetta forata basata sulla tecnica di Newton-Raphson

The hole drilling method is one of the most used semi-destructive techniques for residual stress analysis in mechanical parts. In the presence of non-uniform residual stress, the stress field can be determined from the measured relaxed strains using several methods, but the most used one is the so called integral method. This method is characterised by some simplifications that lead to approximate results especially when the residual stress varies abruptly. In this paper a new calculation procedure based on the Newton-Raphson method for the determination of zeroes of functions is presented. The advantages of the method are also explained and validated by the application to simulated stress fields

UN NUOVO METODO PER LA DETERMINAZIONE DELL’AMPIEZZADELLA TENSIONE TANGENZIALE NEI CRITERI DI FATICA MULTIASSIALE BASATI SULL'APPROCCIO DI PIANO CRITICO

Nel caso di sollecitazioni di fatica multiassiale di tipo non proporzionale il vettore della tensione tangenziale varia sia in modulo che in direzione e la sua punta descrive una curva definita percorso di carico. In questi casi l’ampiezza della tensione tangenziale alternata τ a viene valutata mediante apposite procedure, quali quella del Minimo CerchioCircoscritto e la più recente ed apparentemente più efficace, relativa al Massimo Rettangolo Circoscritto. Entrambe le procedure presentano tuttavia dei difetti che fanno ritenere che la definizione da cui si originano non sia del tutto corretta. In questo lavoro viene proposta una nuova definizione di tensione tangenziale alternata. Essa non presenta i difetti degli altri metodi e, utilizzata con alcuniefficaci criteri di piano critico, fornisce risultati più congruenti con i dati sperimentali disponibili in letteratura. La procedura di calcolo è di semplice implementazione.In the case of multiaxial non proportional fatigue stresses, the shear stress vector varies both in modulus and direction and its tip describes a curvedefined loading path. In these cases τa is identified and evaluated by means of special procedures like the Minimum Circumscribed Circle method and the most recent, and apparently more effective, Maximum Circumscribed Rectangle method. However, both definitions present drawbacks suggesting that the definition from which they have been developed are not entirely correct. In this paper, a new definition of alternating shear stress has been proposed. It does not present the flaws of the other methods and, applied with some effective critical plane based criteria, provides results more consistent with the experimental data available in the literature than the existing methods. The procedureis also easy to be applied

ANALISI DELLE TENSIONI RESIDUE NEI VETRI MEDIANTE FOTOELASTICITÀ RGB E LASTRA A TINTA SENSIBILE

L'analisi delle tensioni residue nel vetro viene solitamente effettuata mediante metodi fotoelastici. Questo lavoro considera l'automazione del metodo fotoelastico in luce bianca basato sull'uso congiunto della fotoelasticità RGB e di una lastra a tinta sensibile (full wave plate o tint plate), che manifesta il ritardo di un ordine di frangia, posta in serie alla lastra di vetro. Il metodo proposto è stato applicato all’analisi delle tensioni residue membranali in un vetro temperato

A critical assessment of automatic photoelastic methods for the analysis of edge residual stresses in glass

The measurement of residual stresses is of great importance in the glass industry. The analysis of residual stresses in the glass is usually carried out by photoelastic methods since the glass is a photoelastic material. This article considers the determination of membrane residual stresses of glass plates by digital photoelasticity. In particular, it presents a critical assessment concerning the automated methods based on gray-field polariscope, spectral content analysis, phase shifting, RGB photoelasticity, ‘‘test fringes’’ methods and ‘‘tint plate’’ method. These methods can effectively automate manual methods currently specified in some standards

Photoelastic Analysis of Edge Residual Stresses in Glass by Automated “Test Fringes” Methods

Since the glass is a birefringent material, the analysis of residual stress in glass is usually carried out by means of photoelastic methods. This paper considers the automation of the “test fringes” method which is based on the use of a Babinet compensator or of a beam subjected to bending. In particular, two automated methods are proposed: the first one is based on the use of the centre fringe method in monochromatic light and the second one is based on the use of RGB photoelasticity in white light. The proposed methods have been applied to the analysis of membranal residual stresses in some tempered glasses, showing that they can effectively replace manual methods of photoelastic analysis of residual stresses in glass

Review of RGB photoelasticity

Automatic methods of photoelasticity have had a significant progress with the development of automatic acquisition and image processing methods. This article concerns RGB photoelasticity, which allows the determination of the photoelastic retardation using, usually, a single acquisition of the isochromatic fringes in white light by a colour camera. In particular, the article presents an overview of the main characteristics of RGB photoelasticity that is influence of the quarter-wave plate error, number of acquisitions, type of light source, determination of low and high fringe orders, methods for searching the retardation, scanning procedures, calibration on a material different from that under test, combined use of the RGB and phase shifting methods. A short section on the applications of RGB photoelasticity completes the article