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991.
Virtual manufacturing based on through-process modelling becomes an evolving research area which aims at integrating diverse simulation tools to realize computer-aided design, analysis, prototyping and manufacturing. Numerical prediction of the as-cast microstructure is an initial and critical step in the whole through-process modelling chain for engineering components. A commercial software package with the capability of calculating important microstructure features for aluminium alloys is used to simulate a G-AlSi7MgCu0.5 laboratory casting. The simulated microstructure, namely grain size, secondary dendrite arm spacing and diverse phase fractions are verified experimentally. Correspondence and discrepancies are reported and discussed. 相似文献
992.
Daixin LiTianran Zhang Siqi YangZhanliang Tao Jun Chen 《Journal of Alloys and Compounds》2011,509(32):8228-8234
A systematic consideration of the compounds made up of Li, Mg and H has been taken with respect to the structural, electronic, and thermodynamic properties, by means of density functional theory (DFT). Through the database mining approach, the ground state structures of LiMgH3 and Li2MgH4 are identified to be R3c and Pbam, respectively. The Li-Mg-H ternary hydrides are insulators dominated by ionic bonds besides some covalent components between Mg and H. Energies of different formation pathways have been calculated at finite temperature. Hydrides synthesized from Li, Mg and H2 possess obvious energetic advantage, but may be inhabited kinetically by pure phase separation. Thermodynamically reversible decomposition to LiH and MgH2 brings about another issue for the actual preparation and stable existence of the ternary hydrides. Inserting H atoms to the sites of the ordered alloys with high electric density has been taken as another way to explore possible structures of this system. As H uptakes stepwise, the resulted compounds turn from conductors to insulators. The present results shed light on the design of Li-Mg-H ternary hydrides. 相似文献
993.
994.
本文分析了再制造系统风险管理与知识需求的关系,提出了提高再制造系统风险管理水平的知识需求链,并通过对再制造过程实践的分析,识别出风险管理实施过程中存在的6大知识缺口的原因,构建基于知识管理的再制造风险管理模式,该模式能从根源上弥补风险管理中的知识缺口,并为再制造风险管理实践提供了知识来源和控制流程。 相似文献
995.
996.
非金属垫片螺栓法兰连接寿命评价 总被引:2,自引:0,他引:2
分析非金属垫片密封的时效特性,考虑高温条件下材料退化和垫片载荷松弛过程对密封性能的影响,依据多孔介质理论,建立非金属垫片密封的时效泄漏模型.将螺栓法兰连接系统寿命划分为密封寿命和部件寿命.提出密封寿命试验方法,在考虑垫片泄漏特性变化的基础上,基于指标泄漏率分析螺栓法兰连接系统密封寿命;基于蠕变和疲劳损伤准则分析高温螺栓的剩余寿命,探讨螺栓法兰连接系统的密封寿命和各部件寿命之间的关系.建立螺栓法兰连接系统的寿命预测最弱环模型,将垫片的变形特性和泄漏特性统一于螺栓法兰连接系统中进行研究,提出基于指标泄漏率和结构完整性的螺栓法兰连接系统寿命评价方法. 相似文献
997.
998.
介绍了时间序列预测法中的灰色预测模型和指数平滑法,并用这两种预测方法运用于广西客运需求的预测,根据预测的结果,对两种预测方法进行了分析。 相似文献
999.
Jun Sun 《岩石力学与岩土工程学报(英文版)》2011,3(4):289-301
Durability problem of reinforced concrete for underground structures is a hot issue in the field of structural engineering.For underground structures,the prediction of structural service life and methodology for durability design are needed to estimate structural durability.Taking the case of Xiamen Xiang’an subsea tunnel as background,which is designed to meet the requirement of 100-year service life,the influential factors on tunnel lining durability are analyzed.Under the criteria of crack controlling and bearing capacity of lining structures,the theoretical service life of Xiamen Xiang’an subsea tunnel lining is studied.The regulations,which are needed for the diffusion capability of chloride ions in concrete by the relevant diffusion tests,are proposed.After a quick corrosion test,the bearing capacity test on eccentric short columns is implemented to investigate the variation rules in the bearing capacity of models with time.Influence of the corrosion degree of steel bars on the bearing capacity of models is also investigated.Based on the results of model tests,the acceleration ratio between the quick corrosion in laboratory test and the natural corrosion environments is established.Thus,the natural service life of subsea tunnel lining structures can be obtained by means of laboratory tests.Then,the proposed method using this modified model is employed to predict the service life of tunnel lining structures.Finally,the design and construction measures for improving the durability of lining structures of subsea tunnel are introduced.The proposed method in the present study based on a real engineering project is superior to those with only theoretical assumptions,and would be more suitable for similar projects. 相似文献
1000.
将改进的层次分析法和模糊综合评判方法相结合,深入分析影响公路滑坡灾害危险性的影响因素,建立了综合评判指标体系并划分危险性等级.评价过程中首先确定了不同降雨情况下指标体系的动态权重系统,然后应用“梯形”隶属函数公式和专家经验赋值法分别测算连续型和离散型指标的隶属度,最终通过所构建的3级模糊综合评判模型进行了实例研究.研究... 相似文献