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

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

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

Measurement of edge residual stresses in glass by the phase-shifting method

Control and measurement of residual stress in glass is of great importance in the industrial field. Since glass is a birefringent material, the residual stress analysis is based mainly on the photoelastic method. This paper considers two methods of automated analysis of membrane residual stress in glass sheets, based on the phase-shifting concept in monochromatic light. In particular these methods are the automated versions of goniometric compensation methods of Tardy and Sénarmont. The proposed methods can effectively replace manual methods of compensation (goniometric compensation of Tardy and Sénarmont, Babinet and Babinet–Soleil compensators) provided by current standards on the analysis of residual stresses in glasses

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

Effetti del raggio di raccordo al fondo foro nella analisi delle tensioni residue con il metodo della rosetta forata

Il metodo della rosetta forata è una delle tecniche di analisi delle tensioni residue più utilizzati in campo industriale. Il metodo è abbastanza accurato per tensioni costanti, mentre nel caso di tensioni variabili nello spessore del componente esaminato diverse cause di incertezza devono essere attentamente esaminate. Poiché nella valutazione numerica dei coefficienti di influenza il foro è considerato perfettamente cilindrico e privo di raccordo, una sorgente di errore è costituita dal raggio di raccordo al fondo foro. In questa memoria viene studiato l’effetto che il raggio di raccordo ha sulle deformazioni misurate e sulle tensioni calcolate. E’ cosi mostrato come anche piccoli raggi di raccordo possono essere causa di errori significativi sulle tensioni calcolate. Inoltre, è proposto un metodo semplice di correzione degli errori sulle tensioni calcolate

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

RGB photoelasticity applied to the analysis of membrane residual stress in glass

The measurement of residual stresses is of great relevance in the glass industry. The analysis of residual stress in glass is usually made by photoelastic methods because glass is a photoelastic material. This paper considers the determination of membrane residual stresses in glass plates by automatic digital photoelasticity in white light (RGB photoelasticity). The proposed method is applied to the analysis of membrane residual stresses in some tempered glass. The proposed method can effectively replace manual methods based on the use of white light, which are currently provided by some technical standards

SVILUPPI DELLA FOTOELASTICITÀ RGB

Questa memoria considera le caratteristiche della fotoelasticità RGB con riferimento al massimo ordine di frangia rilevabile che dipende dalla modulazione del segnale, dalla sorgente luminosa, dalla presenza di colori simili e dal gradiente delle frange. Le esperienze mostrano che la lampada ad incandescenza consente di rilevare ritardi fino a circa 4 ordini di frangia mentre la lampada a fluorescenza consente di determinare ordini di frangia ben più elevati (12 in questa memoria) grazie alla natura discreta della sorgente