Finite Element Modeling of Tube Piercing and Creation of a Crack

From the issue entitled "Proceedings of the 11th ESAFORM Conference on Material Forming, Lyon (France), 23-25 April 2008, edited by P. Boisse, F. Morestin, E. Vidal-Sallé, LaMCoS, INSA de Lyon)" - http://esaform2008.insa-lyon.fr/proceedings/MS06/p_Ch_571.pdfInternational audienceA 3D simulation of Mannesmann tube piercing is performed using the finite element software Forge 2005®. The sensitivity of the simulation results to numerical methods and physical parameters is discussed. Advanced numerical schemes and refined time discretizations are required to obtain correct descriptions of the material flow. In this study, one concentrates on the stress state and damage development before the material comes in contact with the plug. Indeed, the crack is to appear prior to the action of the plug. The description of the material behaviour is found to be a key information to predict the crack development. Predictions based on a modified Lemaitre damage law and a normalised Latham and Cockroft criterion are compared

Saving temporary exhibitions in virtual environments: The Digital Renaissance of Ulisse Aldrovandi – Acquisition and digitisation of cultural heritage objects

As per the objectives of Project CHANGES, particularly its thematic sub-project on the use of virtual technologies for museums and art collections, our goal was to obtain a digital twin of the temporary exhibition on Ulisse Aldrovandi called “The Other Renaissance”, and make it accessible to users online. After a preliminary study of the exhibition, focusing on acquisition constraints and related solutions, we proceeded with the digital twin creation by acquiring, processing, modelling, optimising, exporting, and metadating the exhibition. We made hybrid use of two acquisition techniques to create new digital cultural heritage objects and environments, and we used open technologies, formats, and protocols to make available the final digital product. Here, we describe the process of collecting and curating bibliographical exhibition (meta) data and the beginning of the digital twin creation to foster its findability, accessibility, interoperability, and reusability. The creation of the digital twin is currently ongoing

Modelling of the Mannesmann Effect in Tube Piercing

Seamless tube manufacturing utilises continuous cast cylindrical billets that, after piercing, are rolled until a specified diameter, thickness and length are reached. The hollow part can be industrially obtained through cross roll piercing. The main characteristic of this process is the local failure at the billet centre due to the so-called Mannesmann Effect. In general the cylindrical billet is introduced into the piecing mill after a pre-heating stage, it is dragged and radially deformed by two skew conical rolls that create the stress state generating the internal cavity and then it is effectively pierced by a plug that enlarges the axial crack. The knowledge of the industrial parameters, which determine the beginning and the propagation of the axial fracture, is crucial because it determines the optimal position of the plug in order to grant the best quality of the tube and service life of the plug. Despite the vast industrial experience, the scientific knowledge of the Mannesmann Effect is quite limited. Fracture initiation has been widely studied at room temperature and many contributions can be found in scientific literature, but there is a substantial lack in fracture modelling when applied to forming operations at elevated temperatures. The objective of this work is to develop a reliable numerical model capable to describe the industrial conditions that lead to Mannesmann fracture through the implementation into a commercial FE code of a damage law appropriately calibrated on experimental material behaviour. experimentally it can be noted that the solidification phase of steel after the continuous casting process provokes a differentiation of the billet material in terms of the amount of voids fraction and phase distribution that is reflected on its behaviour during the forming operation. Material workability under process conditions is investigated through hot tensile tests carried out on specimens machined from a continuous cast billet and microscopic observations are performed in order to correlate the sample location in the billet section with its micro-structural characteristics. The fracture condition characterization is possible using a damage model according to the Lemaitre formulation and the identification of damage parameters is based on the inverse analysis on hot tensile test results. In particular, a modification to the standard damage law is adopted in order to describe the different behaviour of the material in the billet section and to take into account the effect of porosity and phase distribution on the initial material state. Finally, the developed numerical model is validated, through the comparison between numerical results and industrial trials of non-plug piercing, showing that there is a good agreement in regards to the length and initiation site of the Mannesmann cone fracture.La produzione di tubi in acciaio senza saldatura si basa sull’utilizzo di barre cilindriche ottenute per colata continua che, dopo aver subito il processo di perforazione, vengono sottoposte a diverse operazioni di laminazione per l’ottenimento delle caratteristiche specificate in termini di lunghezza e spessore del tubo finale. Industrialmente il forato è ottenuto mediante il processo di perforazione obliqua, la cui caratteristica principale è una frattura lungo l’asse longitudinale della billetta che si crea per il cosiddetto Effetto Mannesmann. Nel processo industriale, in seguito a una fase di riscaldamento, la billetta cilindrica viene introdotta nell’impianto di perforazione, trascinata e deformata dall’azione di due rulli tronco-conici ad assi sghembi che generano lo stato di sollecitazione caratteristico per la comparsa della frattura interna. Solo a questo punto la billetta viene effettivamente perforata da un mandrino che svolge la funzione di allargare la cavità ottenuta longitudinalmente e laminare le pareti interne del forato. La conoscenza delle condizioni industriali di laminazione che determinano la comparsa e della frattura lungo l’asse della billetta e la sua propagazione, è di fondamentale importanza in quanto essa determina la posizione ottimale del mandrino perforatore al fine di garantire un’elevata qualità del prodotto laminato e massimizzare la durata della punta. Nonostante l’elevata esperienza dei produttori industriali, la conoscenza scientifica sull’effetto Mannesmann e sulle condizioni che lo determinano è notevolmente limitata. In generale, la letteratura tecnico-scientifica raccoglie numerosi studi sull’insorgere della frattura nei processi di deformazione in condizioni di lavorazione a freddo, c’è invece una sostanziale assenza di modellazione della rottura nel materiale in deformazione per quanto riguarda le lavorazioni ad elevata temperatura. L’obiettivo di questo lavoro sta nello sviluppare un modello numerico in grado di riprodurre in modo affidabile le condizioni che industrialmente provocano la frattura per effetto Mannesmann nel processo di perforazione, mediante l’implementazione in un codice di calcolo di una legge di danneggiamento opportunamente calibrata sulla base del reale comportamento del materiale. Mediante studi di carattere sperimentale, si dimostrato come la fase di solidificazione del’acciaio dopo l’operazione di colata continua provochi una forte differenziazione del materiale della billetta in termini di porosità e distribuzione delle diverse fasi che si riflette nel suo comportamento durante l’operazione di formatura. La lavorabilità del materiale in condizioni di processo è esaminata mediante prova di trazione ad elevata temperatura su provini estratti da billetta ottenuta per colata continua e osservazioni a microscopio sono svolte al fine di correlare la posizione dei campioni sulla billetta con le sue caratteristiche microstrutturali. La caratterizzazione delle condizioni di frattura è possibile grazie all’utilizzo di un modello di danno secondo la formulazione di Lemeitre e l’identificazione dei parametri di danno dipendenti dal materiale è basata sull’uso di tecniche di analisi inversa in riferimento ai risultati sperimentali dei test di trazione a caldo. In particolare, una modifica alla legge di danno è introdotta al fine di descrivere correttamente le differenze nel comportamento del materiale nella sezione della billetta e considerare quindi l’effetto di porosità e distribuzione di fasi nello stato del materiale iniziale. Al termine, il modello numerico sviluppato è validato mediante il confronto dei risultati da simulazione e fermi-macchina in impianto perforatore industriale in assenza del mandrino, che dimostra la bontà del modello per quanto riguarda la previsione del sito di frattura e della lunghezza del cono Mannesmann

Evaluation of fracture initiation in the Mannesmann piercing process

One of the challenging objectives in studying the Mannesmann piercing process is to predict the fracture initiation, known as "Mannesmann effect", in order to design and optimize the working parameters of the piercing process. The objective of the paper is to investigate the workability of a tube steel tested in the same conditions of the Mannesman piercing process. The stress and strain states as well as temperature fields arising during the process are identified through numerical simulations. The hot tensile test is chosen for fundamental studies on fracture initiation, as a tensile state of stress in the centre of the billet in the first stages of the piercing process before the plug arrival seems to be one of the main causes of the crack initiation. The material constants of energy-based models implemented in FEM codes are calculated and numerical results are compared with non-plug piercing tests carried out on the industrial plant

Prediction of the fracture due to mannesmann effect in tube piercing

none3noMannesmann piercing process is a well-known hot rolling process used for seamless tube production. Its special feature is the so-called Mannesmann effect, that is the cavity formation in the center of the cylindrical billet and its propagation along the axis due to stress state caused by the rolls in the early stages of the process. The cavity is then expanded and sized in its internal diameter by an incoming plug. The industrial requirement is to know quite precisely the characteristics of the cavity especially in terms of its location along the billet axis in order to minimize the plug wear and the oxidation of the pierced bar. However, the scientific knowledge about the fracture mechanism leading to the Mannesmann effect is still limited, even if several theories have been proposed; this lack makes the design and optimization of the process through numerical simulations still a challenging task. The aim of this work is then to develop a suitably calibrated FE model of the piercing process in its first stage before the plug arrival, in order to investigate the Mannesmann effect using different damage criteria. Hot tensile tests, capable to reproduce the industrial conditions in terms of temperature, strain rate, and stress states, are carried out to investigate the material workability and to determine the parameters of the damage models on specimens machined from continuous-casting steel billets. The calculated parameters are implemented in the numerical model of the process and a sensitivity analysis to the different criteria is carried out, comparing numerical results with non-plug piercing tests conducted in the industrial plant.restrictedFanini, S; Ghiotti, A.; Bruschi, S.Fanini, Silvio; Ghiotti, Andrea; Bruschi, Stefani

Prediction of the fracture due to Mannesmann effect in tube piercing

Mannesmann piercing process is a well-known hot rolling process used in industry for seamless tube production. Its special feature is the so-called Mannesmann effect, that is the cavity formation in the center of the cylindrical billet and its propagation along the axis due to stress state caused by the rolls. The cavity is then expanded and sized in its internal diameter by an incoming plug. The industrial requirement is to know quite precisely the characteristics of the cavity especially in terms of its location along the billet axis in order to minimize the plug wear and the oxidation of the pierced bar. However, the scientific knowledge about the fracture mechanism leading to the Mannesmann effect is limited, even if several theories have been proposed; this lack makes the design and optimization of the process through numerical simulations still challenging [1]. The aim of this work is then to develop a suitably calibrated FE model of the piercing process in its first stage before the plug arrival, in order to investigate the Mannesmann effect using both energy-based criteria and continuous damage mechanics [2]. Different workability tests, capable to reproduce the industrial conditions in terms of temperature, strain rate, and stress states, are proposed and carried out to determine the parameters of the damage models on specimens machined from continuous-casting steel billets. The calculated parameters are implemented in the model of the process and a sensitivity analysis to the different criteria is carried out. Numerical results are then compared with non-plug piercing tests conducted in the industrial plant, allowing the choice of the most suitable test and damage criterion

Modelling of the Mannesmann effect

The paper presents a new model of the Mannesmann effect. The model is based on a novel damage law that takes into account the effects of pre-existing defects in the working material. Thanks to this feature, the model is capable of making accurate predictions of the location where the fracture will appear under the action of external loading as well as of the time it takes to be generated. An application of the model to a rotary tube piercing operation carried out at elevated temperature is presented and commented