A four-parameters model for fatigue crack growth data analysis

A four-parameters model for interpolation of fatigue crack growth data is presented. It has beenvalidated by means of both data produced by the Authors and data collected from Literature. The proposedmodel is an enhanced version of a three-parameters model already discussed in a previous work that has beensuitably modified in order to overcome some drawbacks raised when applied to a quite wider experimental dataset. Results of validation study have also revealed that the new model, besides interpolating accurately crackgrowth data, allows to identify the presence of anomalies in the data sets. For this reason, by a suitable filter tobe chosen depending on the size and number of anomalies, it can be used to remove them and obtain sigmoidalcrack propagation curves smoother than those obtained when the current analysis techniques are used. In theend, possible model parameters correlations are analysed

About the certification of railway rails

When the compliance with the European Code of some rail steel has to be verified, the need ofcarrying out the experimental activities in accordance with several testing Standards forces the operator both tosolve the problems related to the choice of a suitable testing practice and often to interpret subjectivelyStandards guidelines. This does not facilitate the comparability and/or the quality of the results produced byseveral laboratories. With reference to a series of fatigue, fracture toughness and fatigue crack growth testscarried out by the authors on specimens extracted from rails, the main lacks in the current standards, related toboth the choice of the control parameters and the testing procedures, are pointed out. Regarding the crackgrowth testing, several procedures to compute the crack growth rates to be compared with the limits prescribedby the Code are proposed. These procedures have been applied to a data set produced during theaforementioned testing activity, in order to highlight, by comparison of the results obtained by them, thesignificant differences in the crack growth rate estimates and the magnitude of the errors that can be done dueto the lacks in the standard practices currently adopted

About the certification of railway rails

When the compliance with the European Code of some rail steel has to be verified, the need of carrying out the experimental activities in accordance with several testing Standards forces the operator both to solve the problems related to the choice of a suitable testing practice and often to interpret subjectively Standards guidelines. This does not facilitate the comparability and/or the quality of the results produced by several laboratories. With reference to a series of fatigue, fracture toughness and fatigue crack growth tests carried out by the authors on specimens extracted from rails, the main lacks in the current standards, related to both the choice of the control parameters and the testing procedures, are pointed out. Regarding the crack growth testing, several procedures to compute the crack growth rates to be compared with the limits prescribed by the Code are proposed. These procedures have been applied to a data set produced during the aforementioned testing activity, in order to highlight, by comparison of the results obtained by them, the significant differences in the crack growth rate estimates and the magnitude of the errors that can be done due to the lacks in the standard practices currently adopted

A three-parameter model for fatigue crack growth data analysis

A three-parameters model for the interpolation of fatigue crack propagation data is proposed. It has been validated by a Literature data set obtained by testing 180 M(T) specimens under three different loading levels. In details, it is highlighted that the results of the analysis carried out by means of the proposed model are more smooth and clear than those obtainable using other methods or models. Also, the parameters of the model have been computed and some peculiarities have been picked out

a continuous model for the railway track analysis in the lateral plane

Abstract This paper deals with a mechanical model for the analysis of the railway track behaviour built by exploiting the periodicity of the track-structure. The starting point of this study is the analysis of the inner forces transferring modes. They have been determined by the unit principal vectors analysis of the base cell transfer matrix. The proposed model is able to reproduce accurately the track behaviour in transferring its inner forces. However, solutions that are equilibrated but not kinematically admissible are obtained from it when transversal loads are applied. In additions, only boundary conditions compatibles with the track transferring modes can be satisfied. This inconsistency is eliminated by superposition of a corrective deformed shape. This is derived from the eigenvectors of the transfer matrix pertaining to self-equilibrated systems of bending moments decaying along the track. The application field of the proposed track model is also discussed and the results of a validation study carried out by F.E. analysis are finally presented

A three-parameter model for fatigue crack growth data analysis

A three-parameters model for the interpolation of fatigue crack propagation data is proposed. It has been validated by a Literature data set obtained by testing 180 M(T) specimens under three different loading levels. In details, it is highlighted that the results of the analysis carried out by means of the proposed model are more smooth and clear than those obtainable using other methods or models. Also, the parameters of the model have been computed and some peculiarities have been picked out

About the certification of railway rails

When the compliance with the European Code of some rail steel has to be verified, the need of carrying out the experimental activities in accordance with several testing Standards forces the operator both to solve the problems related to the choice of a suitable testing practice and often to interpret subjectively Standards guidelines. This does not facilitate the comparability and/or the quality of the results produced by several laboratories. With reference to a series of fatigue, fracture toughness and fatigue crack growth tests carried out by the authors on specimens extracted from rails, the main lacks in the current standards, related to both the choice of the control parameters and the testing procedures, are pointed out. Regarding the crack growth testing, several procedures to compute the crack growth rates to be compared with the limits prescribed by the Code are proposed. These procedures have been applied to a data set produced during the aforementioned testing activity, in order to highlight, by comparison of the results obtained by them, the significant differences in the crack growth rate estimates and the magnitude of the errors that can be done due to the lacks in the standard practices currently adopted

Effect of different boundary conditions on the crack growth mechanism under cycling bending loads

Sometimes, structural components are subjected to service conditions that have not taken into account at the design stage. If it is assumed that an initial flaw exists, according to damage tolerance philosophy the analysis of such components needs to be corroborated by accurate Stress Intensity Factor (SIF) solutions, in order to determine both the crack propagation life and the appropriate inspection intervals. In this study, the effects of the boundary conditions on both the SIF and the crack propagation life have been evaluated for a surface crack existing at the root of a shoulder fillet notch in a round bar under bending. The SIF distribution along the crack front has been calculated for the component object of the study by using the Virtual Crack Closure Technique, whereas a two parameters propagation law has been employed to evaluate the evolution of the crack shape. The results show that, under the same loading conditions, the way the component is constrained strongly influences the fatigue crack growth, due to additional SIF fluctations that might contribute to the crack growth and, in turn, affecting both the number of cycles to failure and the frequency of the inspection intervals

Caratterizzazione di giunzioni ibride composito pultruso/metallo con l’ausilio di tecniche di digital imaging correlation

Il perfezionamento delle tecnologie produttive dei materiali compositi ad alto contenuto volumetrico di fibre come la pultrusione, sia in vetro che in carbonio, ha reso questi materiali competitivi con i materiali tradizionali anche in settori dove il risparmio in peso non è una priorità assoluta. In ambito più propriamente industriale o strutturale la diffusione di materiali compositi è spesso ostacolata dalla necessità di studiare e adottare accorgimenti particolari per le giunzioni ibride con parti metalliche. In questo lavoro è stata studiata la resistenza di una giunzione mediante perno di un profilato pultruso in composito a fibra di carbonio. Una verifica al rifollamento è stata condotta secondo normativa mentre l’uso di boccole speciali metalliche per migliorare l’efficienza della giunzione è stato validato mediante la tecnica di misura delle deformazioni a distanza con correlazione d’immagine

SISTEMA DI COLLEGAMENTO DI GIUNTI A SEMPLICE SOVRAPPOSIZIONE CON CALETTAMENTO AUTOMATICO

Il brevetto propone un sistema per collegare due semigiunti di grosso spessore, dotati di foro opportunamente sagomato, con calettamento automatico ed irreversibile nei riguardi delle azioni che si trasmettono l’un l’altro i semigiunti in esercizio. Esso consta essenzialmente di una spina sagomata, ad un’estremità, a forma di calettatore, realizzato in tre segmenti uguali ed equidistanziati quanto la loro dimensione trasversale, sulla quale può scorrere, in posizione contrapposta al precedente, un secondo calettatore, anch’esso realizzato in tre segmenti uguali, ma contigui, quando viene azionato il meccanismo biella-manovella per il bloccaggio del giunto. Il sistema manovella-biella presenta un’articolazione a ginocchio, azionata da un attuatore a camma, che rende il meccanismo, quando è chiuso, irreversibile sotto i carichi di esercizio. L’attuatore, a sua volta, è contenuto in una guida che lo fa ruotare di 60°, nella fase di innesto e disinnesto della spina nel giunto, per consentire al calettatore fisso di raggiungere o lasciare le superfici coniugate del foro. Il tutto è chiuso in un carter che garantisce rigidità, protezione e guida al sistema, oltre a presentare i riscontri necessari al funzionamento del meccanismo