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71.
Mario Ganci Wei Zhu Gianluca Buffa Livan Fratini Song Bo Chunze Yan 《The International Journal of Advanced Manufacturing Technology》2017,91(9-12):3169-3180
A numerical approach to model the selective laser sintering (SLS) of polypropylene is proposed. A 3D thermal model was developed and thus enables the prediction of the temperature fields and the extension of the sintered area in the powder bed taking into account the phase change during multiple laser passes. Powder–liquid, liquid–solid and solid–liquid phase changes were modelled during the SLS and the subsequent cooling processes. Then, a 3D thermomechanically coupled model was set up based on the temperature results of the thermal model in order to predict the distortion of the produced parts after cooling down. Different pre-heating temperatures were considered, highlighting their influence on the final part properties. 相似文献
72.
FSW of titanium alloys is nowadays one of the most challenging welding operations, even with a solid state process, due to the thermo-mechanical and thermo-chemical characteristics of such materials. Due to the relevant application of titanium alloys in the aeronautic and aerospace industries, in the recent years few attempts were carried out to develop FSW processes aimed to maximize the mechanical performances of the welded parts. In the paper a new fixture is presented allowing obtaining effective FSW joints of titanium blanks, which were investigated through mechanical and metallurgical tests highlighting the peculiarities of FSW of titanium alloys. 相似文献
73.
A few rapid tooling technologies have been recently proposed and among them Selective Laser Sintering is probably one of the most relevant and promising. In the paper, the authors report some results of a wide experimental research on the application of SLS tools in sheet metal forming. A wear test was earned out to investigate the progressive degradation of laser-sintered materials in comparison with traditional cold-work steels. In particular SLS tools were utilized in a sheet metal stamping process of S-shaped parts: their performances (in terms of tool wear and dimensional quality of the stamped part) were compared with the ones of traditional tools. 相似文献
74.
M. Filippi L. Simonelli S. Agrestini M. Fratini V. Palmisano G. Campi C. Sanipoli S. De Negri M. Giovannini A. Saccone A. Bianconi 《Journal of Superconductivity》2005,18(5-6):67-70
We have studied the variation of superconducting critical temperature T
c as a function of electron doping in the Mg10B2 system using Sc for Mg substitution. The critical temperature in the10B isotope substituted system Mg1−
x
Sc
x
10B2 increases by increasing the scandium content x in the range 0<x<0.012 up to 41.4 K, while the T
c of the natural boron system Mg1−
x
Sc
x
B2 is nearly constant. The overall difference of T
c in Mg1−
x
Sc
x
B2 as function of x between the natural B and 10B isotope system seems to indicate that the isotope effect shows large variations with electron doping as expected for the T
c enhancement driven by a shape resonance. 相似文献
75.
Carlotta Breschi Lorenzo Guerrini Paola Domizio Giovanni Ferraro Luca Calamai Valentina Canuti Piernicola Masella Alessandro Parenti Emiliano Fratini Giovanna Fia Bruno Zanoni 《European Journal of Lipid Science and Technology》2019,121(11)
Six different 300 kg batches of olive fruits are processed and the resulting six 20 kg batches of oil are collected at the end of the “decanter.” These batches of oil are subjected to four different water and solid particle separation treatments so as to obtain the following oil samples: veiled oil, filtered oil, “solid particle‐only” oil, and “water‐only” oil. The applied separation treatments show that water content has an important role in the degree of turbidity. High water content values (>0.2% w/w) are related to water activity values of >0.6 which are suitable for chemical and enzymatic reactions. The veiled oil samples are contaminated by microorganisms, but non‐proportional behavior occurs between the microbial cell count and the water and solid particle contents. Practical Applications: The results of this study recommend a multi‐approach method to characterize turbidity, based on control markers such as the degree of turbidity, water content and water activity, solid particle content, microbial contamination, and phenolic compound content. In this way, each degree of turbidity can be associated with a different level of risk of veiled extra virgin olive oil degradation during shelf life. 相似文献
76.
Material characterization for the prediction of ductile fracture occurrence: An inverse approach 总被引:2,自引:0,他引:2
The most advanced approach to the prediction of ductile fracture occurrence in metal forming processes is represented by a damage mechanics formulation. Such an approach requires a suitable evaluation of the parameters which appear in the yield condition for the damaging material and in the model which governs the evolution of microvoids (nucleation, growth and coalescence), which allow to calibrate the model with respect to the actual state and properties of the material.
In the paper this aim is pursued employing an inverse identification approach based on an optimization technique which permits to adjust the material variables so that the numerical response matches the experimental one. In particular the load vs. displacement curve during a tensile test has been used to optimise the comparison between the numerical and the experimental results and to develop a full damage characterisation of the material. 相似文献
77.
Cesta A. Cortellessa G. Fratini S. Oddi A. Denis M. Donati A. Policella N. Rabenau E. Schulster J. 《Intelligent Systems, IEEE》2007,22(4):12-19
Deep-space missions carry an ever larger set of different and complementary onboard payloads. Each payload generates data, and synthesizing it for optimized downlinking is one way to reduce the ratio of mission costs to science return. This is the main role of the Mars-Express scheduling architecture (Mexar2), an Al-based tool in daily use on the Mars-Express mission since February 2005. Mexar2 supports space mission planners continuously as they plan data downlinks from the spacecraft to Earth. The tool lets planners work at a higher abstraction level while it performs low-level, often-repetitive tasks. It also helps them produce a plan rapidly, explore alternative solutions, and choose the most robust plan for execution. Additionally, planners can analyze any problems over multiple days and identify payload overcommitments that cause resource bottlenecks and increase the risk of data losses. Mexar2 has significantly increased the data return over the whole Mars-Express mission duration. It's effectively become a work companion for mission planners at the European Space Agency's European Space Operations Center (ESOC) in Darmstadt, Germany. 相似文献
78.
R De Paulis L Sommariva L Colagrande GM De Matteis S Fratini F Tomai C Bassano A Penta de Peppo L Chiariello 《Canadian Metallurgical Quarterly》1998,116(4):590-598
OBJECTIVE: Stentless biologic aortic valves are less obstructive than stented biologic or mechanical valves. Their superior hemodynamic performances are expected to reflect in better regression of left ventricular hypertrophy. We compared the regression of left ventricular hypertrophy in 3 groups of patients undergoing aortic valve replacement for severe aortic stenosis. Group I (10 patients) received stentless biologic aortic valves, group II (10 patients) received stented biologic aortic valves, and group III (10 patients) received bileaflet mechanical aortic valves. METHODS: Echocardiographic evaluations were performed before the operation and after 1 year, and the results were compared with those of a control group. Left ventricular diameters and function, left ventricular wall thickness, and left ventricular mass were assessed by echocardiography. RESULTS: Group I patients had a significantly lower maximum and mean transprosthetic gradient than the other valve groups (P = .001). One year after operation there was a significant reduction in left ventricular mass for all patient groups (P < .01), but mass did not reach normal values (P = .05). Although the rate of regression in the interventricular septum and posterior wall thickness differed slightly among groups, their values at follow-up were comparable and still higher than control values (P = .002). The ratio between interventricular septum and posterior wall and the ratio between wall thickness and chamber radius did not change significantly at follow-up. CONCLUSIONS: Because the number of patients was relatively small, we could not use left ventricular mass regression after I year to distinguish among patients undergoing aortic valve replacement for aortic stenosis by means of valve prostheses with different hemodynamic performances. 相似文献
79.
80.
Guillaume Schweicher Gabriele D'Avino Michael T. Ruggiero David J. Harkin Katharina Broch Deepak Venkateshvaran Guoming Liu Audrey Richard Christian Ruzi Jeff Armstrong Alan R. Kennedy Kenneth Shankland Kazuo Takimiya Yves H. Geerts J. Axel Zeitler Simone Fratini Henning Sirringhaus 《Advanced materials (Deerfield Beach, Fla.)》2019,31(43)
Molecular vibrations play a critical role in the charge transport properties of weakly van der Waals bonded organic semiconductors. To understand which specific phonon modes contribute most strongly to the electron–phonon coupling and ensuing thermal energetic disorder in some of the most widely studied high‐mobility molecular semiconductors, state‐of‐the‐art quantum mechanical simulations of the vibrational modes and the ensuing electron–phonon coupling constants are combined with experimental measurements of the low‐frequency vibrations using inelastic neutron scattering and terahertz time‐domain spectroscopy. In this way, the long‐axis sliding motion is identified as a “killer” phonon mode, which in some molecules contributes more than 80% to the total thermal disorder. Based on this insight, a way to rationalize mobility trends between different materials and derive important molecular design guidelines for new high‐mobility molecular semiconductors is suggested. 相似文献