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排序方式: 共有142条查询结果,搜索用时 78 毫秒
1.
Andreas Förner Jan Vollhüter Anna Krapf Abdullah Jamjoom Daniel Hausmann Benjamin Wahlmann Zongwen Fu Carolin Körner Steffen Neumeier Mathias Göken 《Advanced Engineering Materials》2023,25(15):2300407
By increasing the density of interfaces in NiAl–CrMo in situ composites, the mechanical properties can be significantly improved compared to conventionally cast material. The refined microstructure is achieved by manufacturing through electron beam powder bed fusion (PBF-EB). By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate-like or an interconnected network of the (Cr,Mo) reinforcement phase which is embedded in a NiAl matrix. The microstructure of the different cell morphologies is investigated in detail using scanning electron microscope, transmission electron microscopy, and atom probe tomography. For both morphologies, the mechanical properties at elevated temperatures are analyzed by compression and creep experiments parallel and perpendicular to the building direction. In comparison to cast NiAl and NiAl–(Cr, Mo), the yield strength of the PBF-EB fabricated specimens is significantly improved at temperatures up to 1,027 °C. While the columnar morphology exhibits the best improved mechanical properties at high temperatures, the equiaxial morphology shows nearly ideal isotropic mechanical behavior, which is a substantial advantage over directionally solidified material. 相似文献
2.
Although the deterministic flow shop model is one of the most widely studied problems in scheduling theory, its stochastic
analog has remained a challenge. No computationally efficient optimization procedure exists even for the general two-machine
version. In this paper, we describe three heuristic procedures for the stochastic, two-machine flow shop problem and report
on computational experiments that compare their effectiveness. We focus on heuristic procedures that can be adapted for dispatching
without the need for computer simulation or computer-based search. We find that all three procedures are capable of quickly
generating solutions close to the best known sequences, which were obtained by extensive search. 相似文献
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In the field of forging the production processes are subject to extreme influences. This leads to failures in process steps or part qualities. To guarantee a high product quality and process stability it is necessary to measure and evaluate the process parameters during the manufacturing process. Online monitoring systems are especially required to avoid high scrap costs. In this paper an innovative concept for monitoring the spray field of massive forming processes is presented. So far a practical method to monitor the lubrication process for purpose of quality assurance and process fault diagnosis in forging processes does not exist. With the sensor system developed at the Institute of Forming Technology and Machines a qualitative and quantitative assessment of spray fields used for cooling and lubrication of forging die processes is possible. The sensor system operates on the basis of current flow measurements and is able to realize a local determination of the spray field. Furthermore an artificial neuronal network (ANN) was programmed to collect, evaluate and analyze the signal of the sensors automatically. Such networks have already been proven to detect and analyze process failures. Especially in the analyses of systems depending on many parameters and their interactions with each other ANN offer the advantage to deliver the desired statements on the basis of suitable test series. 相似文献
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Astrid Heckl Samir Cenanovic Mathias G?ken Robert F. Singer 《Metallurgical and Materials Transactions A》2012,43(1):10-19
The phase stability of nickel-base superalloys has been investigated using a new in-house-designed alloy series with stepwise
increased additions of Re and Ru at otherwise fixed atomic fractions of alloying elements. Results presented in this study
are focused on the lesser-known topologically closed packed (TCP) formation of columnar colonies or so-called discontinuous
precipitation. A detailed investigation of these colonies allowed for identifying compositional changes during the growth
process and for providing a three-dimensional (3-D) illustration of the TCP phases within these colonies. The results were
used to compare the colony growth process with existing growth models. Furthermore, the influence of Re and Ru on the appearance
of discontinuous precipitation has been investigated by means of colony width and the effect on creep properties. Larson-Miller
plots are given to illustrate the creep strength of directionally solidified samples with and without TCP colonies compared
with single crystalline samples free from TCP colonies. 相似文献
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9.
Michael Lüken Ottmar EdenhoferBrigitte Knopf Marian LeimbachGunnar Luderer Nico Bauer 《Energy Policy》2011
The impacts of the availability of low-carbon technologies on the regional distribution of mitigation costs are analyzed in a global multi-regional integrated assessment model. Three effects on regional consumption losses are distinguished: domestic measures, trade of fossil energy carriers and trade of emission permits. Key results are: (i) GDP losses and a redirection of investments in the energy system towards capital-intensive technologies are major contributions to regional consumption losses. (ii) A devaluation of tradable fossil energy endowments contributes largely to the mitigation costs of fossil fuel exporters. (iii) In case of reduced availability of low-carbon technologies, the permit market volume and associated monetary redistributions increase. The results suggest that the availability of a broad portfolio of low-carbon technologies could facilitate negotiations on the permit allocation scheme in a global cap-and-trade system. 相似文献
10.
M.?Paland?ken M.?Aksoy M.?TümayEmail author 《Electrical Engineering (Archiv fur Elektrotechnik)》2003,86(1):9-16
This paper introduces a single-phase voltage source current-controlled pulse width modulation rectifier model, acting as an active power filter (APF), with a fuzzy logic controller in the inner loop and a simple proportional-integral (PI) d.c. link voltage controller in the outer loop to compensate reactive power and current harmonic components simultaneously from nonlinear loads. The proposed scheme operates with a fixed switching frequency. The control scheme of the APF is simple, since it has fewer control inputs for determining the desired action. It is easily tunable for different performance criteria and can be achieved by means of low-cost of hardware installation, as it does not need to use more sensitive and accurate measuring devices. The model can also compensate both reactive and harmonic current components from nonlinear loads. 相似文献