K-nearest neighbor driving active contours to delineate biological tumor volumes

Abstract An algorithm for tumor delineation in positron emission tomography (PET) is presented. Segmentation is achieved by a local active contour algorithm, integrated and optimized with the k-nearest neighbor (KNN) classification method, which takes advantage of the stratified k-fold cross-validation strategy. The proposed approach is evaluated considering the delineation of cancers located in different body districts (i.e. brain, head and neck, and lung), and considering different PET radioactive tracers. Data are pre-processed in order to be expressed in terms of standardized uptake value, the most widely used PET quantification index. The algorithm uses an initial, operator selected re…

Automatic photoelastic methods for the analysis of Membrane residual stresses in glass

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.

UN'EFFICIENTE PROCEDURA DI CALCOLO PER L'ANALISI DI FATICA MULTIASSIALE MEDIANTE I CRITERI BASATI SULL'APPROCCIO DI PIANO CRITICO

In multiaxial fatigue analysis using the critical plane approach, the shear stress amplitude has to be evaluate using proper numerical procedures that elaborate the points of the curve described by the tip of the shear stress vector acting in the analyzed plane. The calculation has to be carried out in several planes centred in the analyzed material plane; furthermore, in the analysis of a component, it has to be repeated in several points. In this paper a procedure that allows to noticeably reduce both the number of planes and the number of points in which it is necessary to evaluate by means of the onerous procedures, with a considerable reduction of the computational times.

La teoria dei processi analitici nel metodo della trasformata di Fourier in fotomeccanica: estensione al caso bidimensionale ed applicazionI

Review of RGB photoelasticity

Abstract 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 fr…

UNA PROCEDURA PER IL DIMENSIONAMENTO ASSISTITO DI ALBERI DI TRASMISSIONE

UN NUOVO ALGORITMO PER LA DETERMINAZIONE DELL’AMPIEZZA DELLA TENSIONE TANGENZIALE NEI CRITERI DI FATICA BASATI SUL PIANO CRITICO

I criteri di fatica multiassiale ad alto numero di cicli basati sull’approccio di piano critico richiedono la determinazione dell’ampiezza delle tensioni tangenziali di fatica a agenti sui diversi piani passanti per il punto del materiale analizzato. Tipicamente la determinazione di a viene effettuata considerando il Minimo Cerchio Circoscritto alla curva descritta dalla punta del vettore  agente nel piano nel periodo di sollecitazione. In genere tale determinazione richiede un certo sforzo computazionale. In questo lavoro viene descritta una procedura numerica per la determinazione Minimo Cerchio Circoscritto ad una curva nota per punti caratterizzato da velocità di esecuzione superiore…

RGB Photoelasticity: Review and Improvements

:  This paper considers the main developments of RGB photoelasticity with reference to the maximum measurable retardation. In this paper, a new procedure based on the standard error function evaluated on a subset of the calibration array is also proposed and experimentally tested. The experiments show that the filament lamp makes it possible to find retardations until approximately 4 fringe orders while the fluorescent lamp makes it possible to determine higher fringe orders (12 fringe orders in this paper) owing to the discrete spectrum of the source. The paper shows that, by using the incandescent lamp, the primary limiting factor is the lack of modulation of the R, G and B signals wherea…

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.

La fotoelasticità digitale in luce bianca: parte I - le equazioni dei polariscopi

A customized dental CT software for automatic correction of patient positioning error and detection of jaw midline

A critical assessment of methods for the determination of the shear stress amplitude in multiaxial fatigue criteria belonging to critical plane class

Abstract Multiaxial high cycle fatigue criteria based on the critical plane approach necessitate unambiguous definitions of the amplitude and mean value of the shear stress (τa and τm) acting on the material planes. Four of the existing definitions relate the values of τa and τm to a geometrical element of the curve described by the tip of the shear stress vector (curve Ψ), respectively, the radius of the Minimum Circumscribed Circle, the Longest Chord, the Longest Projection, the diagonal of the Maximum Rectangular Hull (MRH). In this paper a critical assessment of the above definitions is proposed, focusing on that based on the concept of MRH, which is the most recently developed. The mai…

A method for reducing the influence of quarter-wave plate errors in phase stepping photoelasticity

The phase stepping technique has recently been applied to the automated analysis of photoelastic fringes to determine the isoclinic parameter and the relative retardation. Generally, in these methods the error of quarter-wave plates, due to common manufacturing tolerances, influences the determination of the isoclinic parameter and the fringe order. In this paper a new phase stepping method in which the influence of quarter-wave plate error is null on the isoclinic parameter and negligible on the fringe order is proposed. The theoretical results have been confirmed by experimental tests.

A new calculation procedure for non-uniform residual stress analysis by the hole-drilling method

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 calculation methods, but the most used one is the so-called integral method. This method is characterized by some simplifications that lead to approximate results, especially when the residual stress varies abruptly. In this paper a new calculation procedure called the spline methods is proposed, which allows these drawbacks to be overcome. Numerical simulations and an experimental test have corroborated the best performance of the prop…

A kernel support vector machine based technique for Crohn’s disease classification in human patients

In this paper a new technique for classification of patients affected by Crohn’s disease (CD) is proposed. The proposed technique is based on a Kernel Support Vector Machine (KSVM) and it adopts a Stratified K-Fold Cross-Validation strategy to enhance the KSVM classifier reliability. Traditional manual classification methods require radiological expertise and they usually are very time-consuming. Accordingly to three expert radiologists, a dataset composed of 300 patients has been selected for KSVM training and validation. Each patient was codified by 22 extracted qualitative features and classified as Positive or Negative as the related histological specimen result showed the CD. The eff…

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

Abstract 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 Senarmont. The proposed methods can effectively replace manual methods of compensation (goniometric compensation of Tardy and Senarmont, Babinet and Babinet–Soleil compensators) provided by current standards on th…

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.

Automated Stress Separation Along Stress Trajectories

A procedure for the separation of principal stresses in automated photoelasticity is presented. It is based on the integration of indefinite equations of equilibrium along stress trajectories, also known as Lame-Maxwell equations. A new algorithm for precise and reliable stress trajectory calculation, which is an essential feature of the procedure, has also been developed. Automated stress separation is carried out along stress trajectories starting from free boundaries. Experimental tests were performed on a disc in diametral compression and on a ring with internally applied pressure. Full-field principal stress values were obtained and results were compared with those from the theory of e…

AN OPTIMIZED FILTERING TECHNIQUE FOR WRAPPED PHASE DATA

Determination of Nonuniform Residual Stresses Using the Ring-Core Method

This paper considers residual stress analysis using the ring-core method. In particular, the so-called integral equation method is applied to evaluate nonuniform residual stress fields. The proposed method overcomes typical drawbacks of the incremental strain method which lead to incorrect results for strongly varying stress fields. The experimental results obtained with a specimen subjected to a bending load confirm the theoretical predictions.

The influence of the quarter wave plates in automated photoelasticity

During the last decades, several methods have been proposed to automate photoelastic analyses. Some procedures are based on the circularly polarised light by using quarter wave plates. However, quarter wave plates are typically matched for a specific wavelength, and an error is introduced at different wavelengths. The error of quarter wave plates affects the measurement of isochromatic and isoclinic data. In this paper, the influence of the errors of quarter wave plates in some of the most common automated photoelastic methods is reviewed. The errors in the photoelastic data are given and the procedures to reduce, or eliminate, them are also suggested.

Fatigue life prediction under wide band random loading

In this paper, a method for the high-cycle fatigue life prediction of components subjected to gaussian, stationary, wide band random loading is presented. It allows the user to evaluate the fatigue life of components subjected to uniaxial stress states directly from the stress power spectral density (PSD), avoiding onerous simulations in time domain. The proposed method can be applied to random stress processes having PSD of any shape, and the fatigue life predictions obtained are more accurate than that provided by most of the frequency domain techniques proposed in literature.

A facile method to determine pore size distribution in porous scaffold by using image processing

Abstract Image processing permits scientists to investigate morphological properties of three-dimensional structures starting from their bi-dimensional gray-scale representation. In many cases porous structure with complex architecture has to be designed in order to attempt specific properties such in the case of scaffold for tissue engineering. Traditional morphological characterization, like scanning electron microscopy, should be coupled with quantitative information such as pore size distribution (PSD) in order to get a deeper understanding of the influence of the porous structure on tissue regeneration processes and on other related applications, it is remarkable to study a quantitativ…

Photoelastic Analysis of Edge Residual Stresses in Glass by the Automated Tint Plate Method

The analysis of residual stress in glass is usually carried out by means of photoelastic methods. This article considers the automation of the white light photoelastic method based on the use of a full-wave plate placed behind the glass plate. In particular, the method in based on the use of RGB photoelasticity in white light in conjunction with a full wave plate. The proposed method have been applied to the analysis of membrane residual stresses in tempered glass, showing that it can effectively replace manual methods of photoelastic analysis of residual stresses in glass when a low photoelastic retardation is present.

Automated photoelasticity in white light: Influence of quarter-wave plates

This paper deals with the influence of optical retarders on the isochromatic fringes obtained by automated white light photoelasticity using methods such as those based on spectral content analysis (SCA) and on primary colour (red, green and blue) analysis. In the following the light intensity equations of dark- and light-field polariscopes with both crossed and parallel optical retarders are reviewed. In particular, it is shown that the retardance error of the quarter-wave plates produces an attenuation of the maximum intensity in dark field and an increase of minimum intensity in light field. Experimental evidence of the influence of optical retarders is also shown.

A NEW PROCEDURE FOR THE EVALUATION OF RESIDUAL STRESSES BY THE HOLE DRILLING METHOD BASED ON NEWTON-RAPHSON TECHNIQUE

In this paper the combined use of both RGB and phase stepping photoelasticity is proposed. The method is characterised by the following features: maximum measurable order greater than that of the RGB method, ability to determine the total fringe order without necessity of unwrapping.

Review of photoelastic image analysis applied to structural birefringent materials: glass and polymers

Photoelasticity is particularly suitable for the analysis of the stress state in structural materials that are transparent and birefringent. Some techniques of digital photoelasticity (phase shifting and RGB) are applied to the analysis of stress field in two classes of structural materials. The first one consists of tempered glasses, such as those used in the automotive and architectural fields. The second one consists of thermoset polymers, typically used as matrices in fiber reinforced plastic structural composites. The birefringence of such resins is, in particular, exploited to investigate the development of swelling stresses and changes in fracture toughness as induced by water uptake…

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 analysi…

ALGORITHMS FOR THE DETERMINATION OF RETARDATION IN RGB PHOTOELASTICITY

Image processing techniques for the analysis of the micro-architecture of three-dimensional porous scaffolds

Spectral Moments and Pre-Envelope Covariances of Nonseparable Processes

A critical review of the definition of the spectral moments of a stochastic process in the nonstationary case is presented. An adequate time-domain representation of the spectral moments in the stationary case is first established, showing that the spectral moments are related to the variances of the stationary analytical pre-envelope processes. The extension to the nonstationary case is made in the time domain evaluating the covariances of the nonstationary pre-envelope showing the differences between the proposed definition and the classical one made introducing the evolutionary power.

A smart and operator independent system to delineate tumours in Positron Emission Tomography scans

Abstract Positron Emission Tomography (PET) imaging has an enormous potential to improve radiation therapy treatment planning offering complementary functional information with respect to other anatomical imaging approaches. The aim of this study is to develop an operator independent, reliable, and clinically feasible system for biological tumour volume delineation from PET images. Under this design hypothesis, we combine several known approaches in an original way to deploy a system with a high level of automation. The proposed system automatically identifies the optimal region of interest around the tumour and performs a slice-by-slice marching local active contour segmentation. It automa…

Use of the KSVM-based system for the definition, validation and identification of the incisional hernia recurrence risk factors

BACKGROUND: Incisional hernia is one of the most common complications after abdominal surgery with an incidence rate of 11 to 20% post laparotomy. Many different factors can be considered as risk factors of incisional hernia recurrence. The aim of this study is to confirm and to validate the incisional hernia recurrence risk factors and to identify and to validate new ones. METHODS: In the period from July 2007 to July 2017, 154 patients were selected and subjected to incisional hernia repair. The surgical operations were conducted under general anaesthesia. Patients received antibiotic prophylaxis when indicated, according to the hospital prophylaxis scheme. Inclusion criteria of the study…

Phase shifting photoelasticity in white light

The availability of image acquisition systems has led to the development of digital photoelasticity both in monochromatic and white light. In particular white light has been used mainly with the following methods: Spectral Content Analysis, RGB photoelasticity and phase shifting photoelasticity. Phase shifting photoelasticity in the colour domain has been used effectively for the determination of the isoclinic parameter in order to reduce the influence of the isochromatic fringes. The method has been also proposed for the determination of the isochromatic fringe order. This paper concerns the general characteristics of phase shifting photoelasticity in the colour domain. Special attention i…

A review of automated methods for the collection and analysis of photoelastic data

Photoelasticity is one of the most widely used full-field methods for experimental stress analysis. However, the collection of photoelastic parameters can be a long and tedious process. The advent of automated photoelastic systems has allowed the experimentalists to speed up the rate of analysis and to perform more complex investigations. This paper provides a survey of recent methods of automated photoelasticity developed in the last 20 years, i.e. methods of the fringe centres, half-fringe photoelasticity, phase-stepping photoelasticity, methods based on the Fourier transform, spectral content analysis (SCA) and RGB (red, green, blue) photoelasticity.

A New Procedure for the Evaluation of Non-Uniform Residual Stresses by the Hole Drilling Method Based on the Newton-Raphson Technique

The hole drilling method is one of the most used semi-destructive techniques for the analysis of residual stresses in mechanical components. The non-uniform stresses are evaluated by solving an integral equation in which the strains relieved by drilling a hole are introduced. In this paper a new calculation procedure, based on the Newton-Raphson method for the determination of zeroes of functions, is presented. This technique allows the user to introduce complex and effective forms of stress functions for the solution of the problem. All the relationships needed for the evaluation of the stresses are obtained in explicit form, eliminating the need to use additional mathematical tools. The t…

Analisi fotoelastica delle tensioni residue nel vetro

IL METODO DI PROVA “AIAS - TR” PER LA MISURA DELLE TENSIONI RESIDUE COSTANTI O VARIABILI CON LA TECNICA DEL FORO INCREMENTALE

Viene presentata una sintesi dell’attività svolta dal Gruppo di lavoro AIAS “Tensioni Residue” nel periodo dal 2006 al 2009. Lo scopo dell’attività è stata l’elaborazione del metodo AIAS - TR 01 per la misura delle tensioni residue con il metodo del foro incrementale. La normativa tecnica esistente sull’argomento (ASTM E 837-08) [1] ha un campo di applicabilità ristretto; infatti essa non considera alcuni effetti che possono influenzare l’accuratezza della misura. Il metodo di prova (AIAS - TR 01) fornisce una visione d’insieme del metodo della rosetta forata, aggiornata all’attuale stato dell’arte (2009) sia a livello tecnologico che a livello teorico. Le principali innovazioni riguardano …

ANALISI DELLE TENSIONI RESIDUE NEL VETRO MEDIANTE LA FOTOELASTICITÀ CON FRANGE DI RIFERIMENTO

L’analisi delle tensioni residue nei vetri viene di solito effettuata con metodi fotoelastici dato che il vetro è un materiale birifrangente. Questa memoria considera l’automazione del cosiddetto "test fringes” metodo che si basa sull’impiego di un compensatore di Babinet o di un provino inflesso. In particolare si propongono due metodi automatici basati sull’impiego del metodo del centro frangia in luce monocromatica e sull’impiego della fotoelasticità RGB in luce bianca. I metodi proposti possono efficacemente sostituire i metodi manuali.

UN NUOVO METODO PER LA PREVISIONE DELLA VITA A FATICA DI COMPONENTI SOGGETTI A SOLLECITAZIONI RANDOM A BANDA LARGA

In this paper a new method for the high cycle fatigue life prediction of components subjected to random processes of stress, simply using data from the PSD of the stress process is presented. The method is easy to use and more precise than the existing ones.

Developments in RGB photoelasticity

In this paper the combined use of both RGB and phase stepping photoelasticity is proposed. The method is characterised by the following features: maximum measurable order greater than that of the RGB method, ability to determine the total fringe order without necessity of unwrapping.

Electrochemical treatments of aluminium alloys surfaces: a way to improve the performance of structural adhesives

PROPAGAZIONE DELLA FRATTURA IN COMPONENTI SOLLECITATI DA PROCESSI ALEATORI A BANDA LARGA

In this paper a method for estimating the crack propagation in components subjected to wide band random processes of loading is presented. The analysis has been carried out considering uniaxial stresses and stationary and gaussian processes. The method uses as input one parameter of the power spectral density (PSD) of the stress process, its variance and 2 parameters of the material and eliminate the need of the integration of the equation of Paris in time domain. The method has been developed by carrying out a significant amount of numerical simulations in which about a thousand different PSDs of different shapes and spectral parameters have been considered.

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 no…

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 …

Una nuova tecnica per l’unwrapping di mappe di fase

Full field automated evaluation of the quarter wave plate retardation by phase stepping technique

Quarter wave plates are optical elements commonly used in photoelasticity to obtain circularly polarized light. They divide the incident light field into two linearly polarized orthogonal components with a phase difference of a quarter of the light wavelength. Due to the tolerance in manufacturing, however, the actual phase shifting produced by the plates is affected by an error, which noticeably influences the photoelastic measurements performed by means of various automated methods. This paper presents a technique, based on the phase stepping method, for the full field automatic evaluation of the quarter wave plate error.

Metodo automatici per l'analisi fotoelastica delle tensioni residue nel vetro

Nei manufatti in vetro sono generalmente presenti tensioni residue provocate dalle lavorazioni. In tali componenti, il controllo delle tensioni residue riveste grande importanza; a tal fine si impiegano diversi metodi di analisi, codificati anche dalla normativa internazionale. Poiché il vetro è un materiale birifrangente, le tecniche sviluppate per l’analisi delle tensioni residue sono basate principalmente sul metodo fotoelastico. In questo lavoro vengono proposti due metodi automatici di analisi delle tensioni residue di tipo membranale nei vetri basati rispettivamente sulla fotoelasticità RGB, in luce bianca, e sul metodo a variazione di fase, in luce monocromatica. I suddetti metodi po…

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.

La fotoelastIcità digitale in luce bianca: parte II - il metodo a variazione di fase

Phase shifter calibration for phase stepping interferometry

Micro-architecture of three-dimensional porous scaffolds evaluated via image processing technique

Deep learning approach for the segmentation of aneurysmal ascending aorta.

Diagnosis of ascending thoracic aortic aneurysm (ATAA) is based on the measurement of the maximum aortic diameter, but size is not a good predictor of the risk of adverse events. There is growing interest in the development of novel image-derived risk strategies to improve patient risk management towards a highly individualized level. In this study, the feasibility and efficacy of deep learning for the automatic segmentation of ATAAs was investigated using UNet, ENet, and ERFNet techniques. Specifically, CT angiography done on 72 patients with ATAAs and different valve morphology (i.e., tricuspid aortic valve, TAV, and bicuspid aortic valve, BAV) were semi-automatically segmented with Mimic…

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.

Una procedura generale per la valutazione delle tensioni residue con il metodo del foro

Il metodo della rosetta forata è una delle più note tecniche semidistruttive di analisi delle tensioni residue su componenti meccanici. In presenza di tensioni non uniformi, il campo delle tensioni può essere determinato a partire dalle deformazioni rilassate utilizzando varie procedure di calcolo basate sulla stessa equazione, chiamata equazione integrale. In questo lavoro viene presentata una nuova procedura di calcolo basata sul metodo di Newton-Raphson per la determinazione degli zeri di una funzione. La tecnica proposta presenta due importanti vantaggi rispetto alle altre tecniche: 1) è basata su una teoria piuttosto generale che permette di ottenere le principali tecniche esistenti co…

A NOVEL APPROACH TO FULLY CHARACTERIZE FIBER NETWORK MORPHOLOGY OF PLANAR FIBROUS TISSUES AND SCAFFOLDS

Comprendere come la struttura di uno scaffold influenzi la morfologia cellulare e predirne il comportamento meccanico sono divenuti obiettivi fondamentali nello sviluppo dei tessuti ingegnerizzati. In questo studio si presenta un algoritmo innovativo basato su analisi d’immagine. Vengono introdotti descrittori di micro architettura che identificano univocamente la topologia della rete di fibre: orientamento delle fibre, connettività, densità spaziale delle intersezioni e diametro. Le prestazioni dell’algoritmo sono state valutate utilizzando immagini di microscopio a scansione elettronica (SEM) di (1) scaffolds in poliestere uretano-urea prodotti per elettrospinning, (2) gel di collagene se…

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 …

Computer aided photoelasticity by an optimum phase stepping method

In this paper an automated photoelastic method based on the phase stepping technique is described. It provides full-field maps of the isoclinic parameter and the relative retardation. The technique is based on processing six images of a photoelastic specimen acquired using plane and circularly polarized light. The number of acquisitions and the type of polariscope used in this approach have been chosen with the aim at reducing the influence of quarter wave plate errors and obtaining raw photoelastic data in a periodic form suitable for easy applications of automatic unwrapping routines.

Full-field automatic evaluation of an isoclinic parameter in white light

In this paper, a technique for full-field evaluation of the isoclinic parameter is presented. It combines the phase-shifting method with true color imaging technology to minimize the interaction between isoclinic and isochromatic fringes. The paper also shows how the proposed technique can be suitably integrated with known methods for evaluating the retardations. Furthermore, a digital algorithm for filtering wrapped phase data obtained by general phase-shifting techniques is presented.

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