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991.
J. POKLUDA P. ANDERA J. HORNÍKOVÁ 《Fatigue & Fracture of Engineering Materials & Structures》2004,27(2):141-157
A new theoretical concept is introduced to describe the roughness‐induced shielding effects in metallic materials. This approach is based on the statistics of the local ratio between the characteristic microstuctural distance and the plastic zone size. A general equation involving both the crack branching and the crack closure phenomena is derived in the frame of linear elastic fracture mechanics under the assumption of remote mode I loading. It enables the determination of the intrinsic values of both the fracture toughness and the fatigue crack growth threshold. Moreover, the roughness‐induced component can be separated from other closure components, such as the plasticity or oxide‐induced closure. In order to estimate the total roughness‐induced shielding effect only standard materials data such as the yield stress, the mean grain size, the surface roughness and the fracture mode are necessary. Examples of applications concerning static fracture and fatigue are presented for selected metallic materials. 相似文献
992.
The paper reports an investigation into the effect of interfacial friction law during the forging of a powder circular disc
with large slenderness ratio(L/D), between two flat dies. The deformation pattern during the operation is influenced by many factors, which interact with each
other in a complex manner. The relative velocity between the work piece material and the die surface, together with high interfacial
pressure and/or deformation modes, creates the conditions essential for adhesion in addition to sliding. The decisive factors
are the interfacial conditions, initial relative density of the preform and geometry of the preform. An attempt has been made
to determine the most realistic interfacial friction law and die pressures developed during such forging using an upper bound
approach. The results so obtained are presented graphically and discussed critically to illustrate the interaction of various
interfacial friction laws involved. 相似文献
993.
针对低合金含铬钢中Cr成分不稳、回收率较低的状况,从温度制度、终点控制、助熔方法、转炉操作等方面采取了一系列措施进行工艺优化,使钢中铬的回收率从66.30%提高到90.65%,含铬钢的熔炼成分合格率达到98.49%,提高了钢板质量,使济钢生产的低合金含铬钢的各项性能等技术指标全部达到标准要求。 相似文献
994.
论述了低渣比冶炼锰硅合金的条件和操作要点,阐明了炉料中Al2O3与电炉工艺参数、焦炭粒度之间的相互关系及其对电耗等指标的影响。 相似文献
995.
本文分析了槽下返矿率高的原因及其不利影响。烧结厂通过加强各方面的管理和进行设备技术改造,使槽下返矿率明显下降,取得了明显的效果和经济效益。 相似文献
996.
The standard Pearson correlation coefficient is a biased estimator of the true population correlation, ρ, when the predictor and the criterion are range restricted. To correct the bias, the correlation corrected for range restriction, rc, has been recommended, and a standard formula based on asymptotic results for estimating its standard error is also available. In the present study, the bootstrap standard-error estimate is proposed as an alternative. Monte Carlo simulation studies involving both normal and nonnormal data were conducted to examine the empirical performance of the proposed procedure under different levels of ρ, selection ratio, sample size, and truncation types. Results indicated that, with normal data, the bootstrap standard-error estimate is more accurate than the traditional estimate, particularly with small sample size. With nonnormal data, performance of both estimates depends critically on the distribution type. Furthermore, the bootstrap bias-corrected and accelerated interval consistently provided the most accurate coverage probability for ρ. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
998.
基于Boosting方法的人脸检测 总被引:3,自引:0,他引:3
该文提出一种基于Boosting方法的人脸检测算法。先用特征脸方法构造一个基于重建图像信噪比的阈值函数用于人脸检测,在此基础上,该文利用Boosting方法构造一个基于信噪比阈值的检测函数序列,然后以一定的方式将它们组合成一个总检测函数,据此判别一幅图像是否为人脸图像。实验结果显示,这种方法明显提高了检测性能。 相似文献
999.
提出了基于球环类型的先进氚生产堆概念设计,它是聚变能发展的中间应用。与传统托卡马克氚生产堆不同,设计中利用了球形环的先进等离子体物理性能和紧凑的结构特征,并尽量利用真空室内的空间安置氚生产包层以减少氚泄露而增加氚增殖率,达到年生产氚1000 g的目标,相应的堆利用因子为40%。在2D中子学计算的基础上提出了较为完整的初步概念设计。逐项进行了分析,同时对设计的风险、不确定性和后备方案也做了概括的解释。为下一步更详细、具体的概念设计提供了直接的依据和重要的参考价值。 相似文献
1000.
TAN Zhiyi & HE Yong . Department of Mathematics Zhejiang University Hangzhou China 《中国科学F辑(英文版)》2004,47(2):161-169
Consider a resource allocation problem on the following system. A system consists of m identical parallel machines and is alive only when all the machines are alive. To keep a machine alive, it requires resources (material, fuel, etc.). Resources with various sizes arrive one by one and the goal is to keep the system alive as long as possible. The problem has applications in many areas such as sequencing of maintenance actions for modular gas turbine aircraft engines[1]. Using scheduling term… 相似文献