Experimental Investigation on Thermal Diffusivity of PM Steels

The scanty literature data on thermal diffusivity of P/M steels seems contradictory, if the cooling speed on quenching is the evaluation parameter. Due to the basic importance of diffusivity on the response of P/M steels to heat-treating, an experimental survey has been carried out, to collect data on various P/M steels, based on prealloyed, or diffusion-bonded, or admixed powders. The study has also covered the influence of processing parameters, such as compaction pressure and sintering temperature. The flash method has been used to measure the thermal diffusivity of P/M steels. This method directly measures the thermal diffusivity of a sample in slab shape. A plane-parallel sample is inserted in the test apparatus and then a short light pulse, produced by a laser or a flash lamp, heats the front surface of the sample. The heat diffuses through the sample, leading to a temperature rise on the sample rear surface. An infrared detector measures this temperature rise, versus time, and thermal diffusivity is derived from the least square regression on the whole temperature trend, using the analytical solution of heat conduction. The results show that thermal diffusivity increases as density increases. This achievement can be justified by a simple theoretical analysis of the thermal conductivity on thermal diffusivity. The collected data also enable us to ascertain the influence of sintered material composition and carbon content on thermal diffusivity. The results should contribute to clarify some uncertainties and perplexities on the behavior of properly elaborated P/M steels, to be hardened by heat treatment, conventional – such as oil quenching – or innovative, such as sinter -hardening

Aqueous phase reforming of the residual waters derived from lignin-rich hydrothermal liquefaction: investigation of representative organic compounds and actual biorefinery streams

Secondary streams in biorefineries need to be valorized to improve the economic and environmental sustainability of the plants. Representative model compounds of the water fraction from the hydrothermal liquefaction (HTL) of biomass were subjected to aqueous phase reforming (APR) to produce hydrogen. Carboxylic and bicarboxylic acids, hydroxyacids, alcohols, cycloketones and aromatics were identified as model compounds and tested for APR. The tests were performed with a Pt/C catalyst and the influence of the carbon concentration (0.3–1.8 wt. C%) was investigated. Typically, the increase of the concentration negatively affected the conversion of the feed toward gaseous products, without influencing the selectivity toward hydrogen production. A synthetic ternary mixture (glycolic acid, acetic acid, lactic acid) was subjected to APR to evaluate any differences in performance compared to the tests with single compounds. Indeed, glycolic acid reacted faster in the mixture than in the corresponding single compound test, while acetic acid remained almost unconverted. The influence of the reaction time, temperature and carbon concentration was also evaluated. Finally, residual water resulting from the HTL of a lignin-rich stream originating from an industrial-scale lignocellulosic ethanol process was tested for the first time, after a thorough characterization. In this framework, the stability of the catalyst was studied and found to be correlated to the presence of aromatics in the aqueous feedstock. For this reason, the influence of an extraction procedure for the selective removal of these compounds was explored, leading to an improvement in the APR performance

Direct Evidence of a Slow‐Slip Transient Modulating the Spatiotemporal and Frequency‐Magnitude Earthquake Distribution: Insights From the Armutlu Peninsula, Northwestern Turkey

Earthquakes and slow‐slip events interact, however, detailed studies investigating their interplay are still limited. We generate the highest resolution microseismicity catalog to date for the northern Armutlu Peninsula in a ∼1‐year period to perform a detailed seismicity distribution analysis and correlate the results with a local, geodetically observed slow‐slip transient within the same period. Seismicity shows a transition of cluster‐type behavior from swarm‐like to burst‐like, accompanied by an increasing relative proportion of clustered (non‐Poissonian) relative to background (Poissonian) seismicity and gradually decreasing b‐value as the geodetically observed slow‐slip transient ends. The observed slow‐slip transient decay correlates with gradually increasing effective‐stress‐drop values. The observed correlation between the b‐value and geodetic transient highlights the influence of aseismic deformation on seismic deformation and the impact of slow‐slip transients on local seismic hazard

An extended assessment of bowel habits in a general population.

Bowel habits are difficult to study, and most data on defecatory behaviour in the general population have been obtained on the basis of recalled interview. The objective assessment of this physiological function and its pathological aspects continues to pose a difficult challenge. The aim of this prospective study was to objectively assess the bowel habits and related aspects in a large sample drawn from the general population

A Stochastic Multi-scale Approach for Numerical Modeling of Complex Materials - Application to Uniaxial Cyclic Response of Concrete

In complex materials, numerous intertwined phenomena underlie the overall response at macroscale. These phenomena can pertain to different engineering fields (mechanical , chemical, electrical), occur at different scales, can appear as uncertain, and are nonlinear. Interacting with complex materials thus calls for developing nonlinear computational approaches where multi-scale techniques that grasp key phenomena at the relevant scale need to be mingled with stochastic methods accounting for uncertainties. In this chapter, we develop such a computational approach for modeling the mechanical response of a representative volume of concrete in uniaxial cyclic loading. A mesoscale is defined such that it represents an equivalent heterogeneous medium: nonlinear local response is modeled in the framework of Thermodynamics with Internal Variables; spatial variability of the local response is represented by correlated random vector fields generated with the Spectral Representation Method. Macroscale response is recovered through standard ho-mogenization procedure from Micromechanics and shows salient features of the uniaxial cyclic response of concrete that are not explicitly modeled at mesoscale.Comment: Computational Methods for Solids and Fluids, 41, Springer International Publishing, pp.123-160, 2016, Computational Methods in Applied Sciences, 978-3-319-27994-

VALUTAZIONE DEL GRADO DI DIFFUSIONE DEL NICHEL IN SINTERIZZAZIONE MEDIANTE METODI STATISTICI

È ben noto che le proprietà meccaniche di un materiale sinterizzato, a parità di altre condizioni, dipendonofortemente dal grado di sinterizzazione. Una definizione rigorosa ed universalmente accettata del terminegrado di sinterizzazione non è ancora disponibile ed anche le normative più frequentemente richiamate edaggiornate, come ad esempio le norme MPIF, non ne riportano ancora una definizione univoca, né fornisconoelementi utili per arrivare ad un’idea condivisa.In questo lavoro sperimentale sono state messe a confronto quattro polveri di tipo diffusion-bonded, su baseatomizzata, che, per lo meno in Europa, sono state presentate come equivalenti tra loro. In questo rapportosi presentano i risultati del confronto, effettuato mediante analisi locali del tenore di nichel attraversomicroanalisi EDS, a parità di condizioni di sinterizzazione, effettuata in un impianto industriale, fra le quattrodifferenti polveri prese in considerazione. I dati sperimentali sono stati elaborati e analizzati mediante tecnichestatistiche diverse e mettono in evidenza alcune interessanti differenze tra polveri nominalmente uguali

Predictive modeling of die filling of the pharmaceutical granules using the flexible neural tree

In this work, a computational intelligence (CI) technique named flexible neural tree (FNT) was developed to predict die filling performance of pharmaceutical granules and to identify significant die filling process variables. FNT resembles feedforward neural network, which creates a tree-like structure by using genetic programming. To improve accuracy, FNT parameters were optimized by using differential evolution algorithm. The performance of the FNT-based CI model was evaluated and compared with other CI techniques: multilayer perceptron, Gaussian process regression, and reduced error pruning tree. The accuracy of the CI model was evaluated experimentally using die filling as a case study. The die filling experiments were performed using a model shoe system and three different grades of microcrystalline cellulose (MCC) powders (MCC PH 101, MCC PH 102, and MCC DG). The feed powders were roll-compacted and milled into granules. The granules were then sieved into samples of various size classes. The mass of granules deposited into the die at different shoe speeds was measured. From these experiments, a dataset consisting true density, mean diameter (d50), granule size, and shoe speed as the inputs and the deposited mass as the output was generated. Cross-validation (CV) methods such as 10FCV and 5x2FCV were applied to develop and to validate the predictive models. It was found that the FNT-based CI model (for both CV methods) performed much better than other CI models. Additionally, it was observed that process variables such as the granule size and the shoe speed had a higher impact on the predictability than that of the powder property such as d50. Furthermore, validation of model prediction with experimental data showed that the die filling behavior of coarse granules could be better predicted than that of fine granules

Acciaio sinterizzato trattato a vapore: Caratteristiche e propriet\ue0 degli strati ossidati

Nella metallurgia delle polveri le finalit\ue0 del trattamento a vapore possono essere diverse: dall\u2019aumento della durezza, e conseguentemente della resistenza all\u2019usura da strisciamento, all\u2019aumento della massa volumica, all\u2019impermeabilizzazione ai fluidi tramite occlusione della porosit\ue0 intercomunicante. Il risultato tecnologico del trattamento di ossidazione a vapore dipende dai parametri di processo ma anche dalla natura e dalle caratteristiche del materiale trattato, in particolare dalla sua composizione e massa volumica. La ricerca qui presentata \ue8 volta alla caratterizzazione chimica, fisica, morfologica e strutturale dello strato ossidato ottenuto trattando a vapore, in condizioni industriali, un acciaio ferritico sinterizzato con aggiunta di MnS. Tra le diverse tecniche di indagine utilizzate particolare importanza ha avuto la microspettroscopia Raman di cui si \ue8 riscontrata l\u2019efficacia per questa particolare applicazione. Lo strato ossidato sviluppatosi a seguito del trattamento di vaporizzazione, sia sulla superficie esterna sia all\u2019interno delle porosit\ue0 di tutto il componente, \ue8 risultato costituito prevalentemente da magnetite. Lo strato superficiale, nella sua parte pi\uf9 esterna, \ue8 costituito da ematite mescolata a porzioni variabili di magnetite. Negli strati ossidati interni alle porosit\ue0 si \ue8 identificata la presenza di solfuro di ferro circondato da aree di magnetite contenenti piccole percentuali di zolfo e manganese. I risultati esposti in questo lavoro costituiscono un punto di partenza per la valutazione degli effetti del trattamento a vapore sulla resistenza alla corrosione