Ottimizzazione del processo di riscaldo per tempra di grandi fucinati mediante analisi FEM

In questo lavoro è presentata la simulazione del processo di riscaldo per austenitizzazione di grandi fucinatiin acciaio destinati alla tempra differenziale. In ogni trattamento termico, le grandezze controllabili a livelloindustriale sono il tempo e la temperatura. È quindi agendo su queste che si può ottimizzare il processo perottenere le proprietà e le microstrutture desiderate per l’acciaio esaminato, e in definitiva massimizzare laqualità del pezzo finale. I prodotti analizzati sono i cilindri di laminazione fucinati, la cui produzione richiede unattento ciclo termico successivo alla deformazione plastica. Infatti, dopo un ciclo termico preliminare di ricotturacon lo scopo di facilitare le lavorazioni di sgrossatura alle macchine utensili, questi pezzi vengono sottopostiad una tempra differenziale per incrementare la durezza dello strato di lavoro, il cui spessore varia in funzionedelle specifiche richieste dal cliente. L’ottimizzazione di un processo può essere implementata utilizzando leggiempiriche ed il proprio know-how in prove sperimentali. La simulazione numerica rappresenta uno strumentodi previsione che potrebbe favorire un approccio più sistematico e scientifico alla risoluzione, in fase diprogetto, di tali problematiche industriali, specialmente quando il rapporto di scala tra il provino sperimentaleed il componente reale è molto elevato, come nel caso oggetto del presente lavoro. Lo strumento numericotipicamente adottato per simulare tale processo è la modellazione e l’analisi agli elementi finiti (FEM). Avendocome possibili parametri il livello di suddivisione del modello (meshatura), le caratteristiche chimico-fisiche delmateriale ed i parametri di scambio termico (entrambe differenziabili topologicamente all’interno del modellostesso) l’approccio FEA consente di simulare sia la forgiatura che i trattamenti termici ed in particolare le fasi diriscaldo, mantenimento e raffreddamento. I risultati ottenibili sono il campo termico, la distribuzione delle variefasi ed i valori di tensioni residue derivanti dal trattamento termico stesso. I risultati sono monitorabili nell’interoarco temporale del processo. Questo tipo di analisi agli elementi finiti consente di prevedere le proprietà delpezzo nell’intero arco temporale del processo: una volta caratterizzato il materiale ed i forni di riscaldo, si haa disposizione uno strumento capace di prevedere in maniera affidabile i risultati di un trattamento termico. Ilsoftware utilizzato in questo studio è il codice FEM commerciale Forge

Analisi del processo di deformazione a caldo e dell’evoluzione microstrutturale di un acciaio al 3% Cr mediante prove di torsione

Lo studio dell’evoluzione della microstruttura durante il processo di deformazione plastica di acciai rivestefondamentale importanza. In questo lavoro è stato analizzato il comportamento a deformazione a caldo di unacciaio 3% Cr tramite prove di torsione eseguite nell’intervallo di temperatura 1000?1200°C e con e.compresatra 0.01 e 1.00s-1. L’analisi condotta ha consentito di determinare le costanti della legge di potenza che regolail processo di deformazione a caldo (A0 , Q ed n ) tramite le quali è possibile ottimizzare i processi industriali.L’evoluzione microstrutturale durante la deformazione a caldo è stata valutata in termini di grado di percentualedi fase ricristallizzata ed è analizzata attraverso microscopia elettronica a trasmissione (TEM) e microscopiaad orientazione di immagine-diffrazione da retrodiffusione elettronica (OIM?EBSD). In particolare attraversoquesta ultima tecnica viene stimata la frazione volumetrica di ricristallizzato in termini di parametro GOS (GrainOrientation Spread), che meglio sembra interpretare l’evoluzione microstrutturale dopo deformazione a caldo inmicrostrutture martensitiche

Single-shot transverse coherence in seeded and unseeded free-electron lasers: A comparison

The advent of x-ray free-electron lasers (FELs) drastically enhanced the capabilities of several analytical techniques, for which the degree of transverse (spatial) coherence of the source is essential. FELs can be operated in self-amplified spontaneous emission (SASE) or seeded configurations, which rely on a qualitatively different initialization of the amplification process leading to light emission. The degree of transverse coherence of SASE and seeded FELs has been characterized in the past, both experimentally and theoretically. However, a direct experimental comparison between the two regimes in similar operating conditions is missing, as well as an accurate study of the sensitivity of transverse coherence to key working parameters. In this paper, we carry out such a comparison, focusing in particular on the evolution of coherence during the light amplification process

Prospects for longitudinal phase-space measurements at the MAX IV linac

Knowing the longitudinal phase space of an electron beam is one of the most important and crucial issues in short-pulses linacs. To achieve this task expensive and rather complicated setups (like transverse deflecting cavities) are usually implemented. The MAX IV linac is a 3GeV accelerator which will be used to inject into two rings and to drive a short pulse facility. Nevertheless, a more deep understanding of the beam quality would be useful especially in view of an upgrade as FEL driver. Another interesting aspect is to evaluate how the double-achromat bunch compressors are performing. We are studying how to implement off-phase acceleration: one part of the linac will be set at zero-crossing phase and the following transfer line could be used as energy spectrometer to retrieve the bunch profile. In the present configuration of the MAX IV linac this procedure will allow to check the bunch length after the first bunch compressor. Since it is work in progress, in this contribution we present a sketch of the measurement and the feasibility of the method will be explored by means of simulations

Beam performance of the photocathode gun for the MAX IV LINAC

The MAX IV facility in Lund (Sweden) is under construction and conditioning of the electron guns for the injector is ongoing. There are two guns in the injector, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. In this paper we report on the beam performance tests of the photocathode gun. The measurements were performed at the MAX IV electron gun test stand [1] during spring 2014. Parameters that were studied includes quantum efficiency, emittance and emittance compensation. Results from the measurements are also compared to particle simulations done with ASTRA

Characterization of longitudinal wakefields in the MAX IV linac

In the second part of 2014, the 3 GeV linac at the MAX IV laboratory will enter its commissioning stage. Equipped with two guns, the linac will act as a full energy injector for the two storage rings and at the same time provide high brightness pulses to a Short Pulse Facility (SPF). Compression in the linac is done in two double achromats with fixed R56 that relies upon the RF phase introduced energy chirp, which in this case is strongly enhanced by the longitudinal wakefields. Since the longitudinal wakefields play a major role in the compression and bunch shaping they need to be carefully investigated during the commissioning. In this proceeding we will discuss a measurement technique that will be used during commissioning to characterize the longitudinal wakefields in the MAX IV linac and their precise effects on e.g. the bunch shape and the energy spread. Predictions obtained from particle tracking will be presented

Analysis of Emissions into Atmosphere of the Cogeneration and District Heating Plant in Norcia (Italy)

District heating enables to recover heat produced simultaneously with electricity in combined heat and power generation plants, which would be wasted and dissipated into environment, in order to supply residential and commercial heating requirements; the distribution of this energy is realized close to production site, minimizing losses associated with transportion. The European-wide Authorities identify in urban district heating systems a great opportunity for rationalizing energy use and a very interesting way to decrease harmful emissions, in order to reduce local pollution as well as greenhouse gas emissions. In this paper the district heating plant built in Norcia (Perugia, Italy) is described: it is located in the area of Sibillini, a mountain range that divides anche and Umbria regions, in the centre of Italy. The system is powered by a natural gas cogeneration plant characterized by three engines for an overall electric power of 1050 kW and a thermal power of 1500 kW. The plant supplies heat to about forty industrial and civil users Objective of this study is to correlate the data recordered by monitoring emissions of cogeneration system following several load profiles, in order to optimize simultaneously system management and the trend in emissions into atmosphere. Different emissions are processed through a flue gas analyzer, installed permanently at the poer generator, able to monitor real-time (range of programmable recording from 250ms) concentration of CO, NOx, CO2 and the temperature of the flue gases. Data recording has enabled to compare current situation with the pre-existing one, before plant's realization, in terms of air quality

Maximum entropy principle and coherent harmonic generation using a single-pass free-electron laser

Single-pass free-electron lasers constitute an example of systems with long-range interactions. The light-particle interplay leading to the power growth and successive relaxation towards a quasi-stationary state is governed by the Vlasov equation. A maximum entropy principle inspired to Lynden-Bell's theory of “violent relaxation" for the Vlasov equation can be invoked to analytically characterize the behaviour of the saturated system. In particular, we here concentrate on the case of coherent harmonic generation obtained from an externally seeded free-electron laser and provide a simple strategy to predict the laser intensity as well as the final electron-beam energy distribution. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200705.45.-a Nonlinear dynamics and chaos,

Advanced concepts in the design for the soft X-ray FEL at Max IV

A Soft X-ray FEL (the SXL) is currently being designed at the MAX IV Laboratory. In the work to adapt the FEL to the scientific cases several advanced options are being studied for coherence enhancement, generation of short pulses and two-color pulses. We will discuss the current status and initial results of the schemes studied, especially regarding the FEL performance with the features of the MAX IV linac, including a positive energy chirp