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151.
Zerilli-Armstrong(Z-A)模型是基于热激活位错运动理论建立的具有物理理论基础的本构模型,但是模型建立的初始假设,降低了其预测精度.为此通过引入考虑应变率和温度耦合效应的应变强化指数对Z-A模型进行修正,拓展了其适用范围,并将修正后的Z-A模型应用于描述IC10合金在不同温度和应变率条件下的塑性流变行为.与修正前Z-A模型的预测结果及试验结果比较表明:修正后Z-A模型的预测精度有较大程度的提高,最大平均相对误差值从6.41%降低到3.65%. 相似文献
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脉冲等离子体推力器(PPT)的性能受多方面因素的影响,包括放电参数以及推力器本体结构等。通过对脉冲等离子体推力器的工作原理和物理学模型的分析,研究了PPT的效率、比冲、推力、元冲量、推功比等性能参数与电极结构、电气参数的关系,并设计了实验,对效率、比冲、元冲量等与放电能量、电极间距的关系进行了验证。结果表明,效率、比冲、元冲量均随放电能量的提高而增大,元冲量在电极间距为50 mm时大于间距为30 mm、40 mm时的值。根据实验结果,提出了设计高性能PPT的一些优化条件,对PPT的设计有参考意义。 相似文献
154.
离子辅助沉积Al膜层增强Ti811钛合金高温微动疲劳抗力 总被引:1,自引:0,他引:1
为提高Ti811钛合金高温微动疲劳抗力,利用离子辅助沉积技术在Ti811钛合金表面制备Al膜层。对比研究多弧离子镀(MIP)和离子辅助多弧沉积(IAD)Al膜层的膜基界面成分分布、膜基结合强度、显微硬度、摩擦学性能。探讨IAD铝膜层对Ti811合金微动疲劳抗力的影响。结果表明,利用离子辅助多弧沉积技术可以获得膜基结合强度高、硬度低、减摩润滑性能好的Al膜层,该膜层能够显著提高Ti811钛合金350℃时的微动疲劳抗力。 相似文献
155.
The Geology of Mercury: The View Prior to the MESSENGER Mission 总被引:1,自引:0,他引:1
James W. Head Clark R. Chapman Deborah L. Domingue S. Edward Hawkins III William E. McClintock Scott L. Murchie Louise M. Prockter Mark S. Robinson Robert G. Strom Thomas R. Watters 《Space Science Reviews》2007,131(1-4):41-84
Mariner 10 and Earth-based observations have revealed Mercury, the innermost of the terrestrial planetary bodies, to be an
exciting laboratory for the study of Solar System geological processes. Mercury is characterized by a lunar-like surface,
a global magnetic field, and an interior dominated by an iron core having a radius at least three-quarters of the radius of
the planet. The 45% of the surface imaged by Mariner 10 reveals some distinctive differences from the Moon, however, with
major contractional fault scarps and huge expanses of moderate-albedo Cayley-like smooth plains of uncertain origin. Our current
image coverage of Mercury is comparable to that of telescopic photographs of the Earth’s Moon prior to the launch of Sputnik
in 1957. We have no photographic images of one-half of the surface, the resolution of the images we do have is generally poor
(∼1 km), and as with many lunar telescopic photographs, much of the available surface of Mercury is distorted by foreshortening
due to viewing geometry, or poorly suited for geological analysis and impact-crater counting for age determinations because
of high-Sun illumination conditions. Currently available topographic information is also very limited. Nonetheless, Mercury
is a geological laboratory that represents (1) a planet where the presence of a huge iron core may be due to impact stripping
of the crust and upper mantle, or alternatively, where formation of a huge core may have resulted in a residual mantle and
crust of potentially unusual composition and structure; (2) a planet with an internal chemical and mechanical structure that
provides new insights into planetary thermal history and the relative roles of conduction and convection in planetary heat
loss; (3) a one-tectonic-plate planet where constraints on major interior processes can be deduced from the geology of the
global tectonic system; (4) a planet where volcanic resurfacing may not have played a significant role in planetary history
and internally generated volcanic resurfacing may have ceased at ∼3.8 Ga; (5) a planet where impact craters can be used to
disentangle the fundamental roles of gravity and mean impactor velocity in determining impact crater morphology and morphometry;
(6) an environment where global impact crater counts can test fundamental concepts of the distribution of impactor populations
in space and time; (7) an extreme environment in which highly radar-reflective polar deposits, much more extensive than those
on the Moon, can be better understood; (8) an extreme environment in which the basic processes of space weathering can be
further deduced; and (9) a potential end-member in terrestrial planetary body geological evolution in which the relationships
of internal and surface evolution can be clearly assessed from both a tectonic and volcanic point of view. In the half-century
since the launch of Sputnik, more than 30 spacecraft have been sent to the Moon, yet only now is a second spacecraft en route
to Mercury. The MESSENGER mission will address key questions about the geologic evolution of Mercury; the depth and breadth
of the MESSENGER data will permit the confident reconstruction of the geological history and thermal evolution of Mercury
using new imaging, topography, chemistry, mineralogy, gravity, magnetic, and environmental data. 相似文献
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从理论上建立了离子束抛光中切向定位误差对加工残差影响的模型,分析发现了该误差对加工残差的影响与面形的梯度有关.特别地分析了定位误差对不同频率成份误差的影响规律,并进行了仿真研究,验证了残差大小与相对定位误差成正比这一结论.同时利用相对定位误差对残差影响理论,评价了KDIBF1600离子束抛光机的设计精度,机床设计精度满... 相似文献
160.
草酸钠体系中Ti-10V-2Fe-3Al钛合金阳极氧化膜的制备与表征 总被引:1,自引:0,他引:1
对Ti-10V-2Fe-3Al钛合金在草酸钠为主盐的新型无氟环保电解液体系中的阳极氧化进行了研究,成功制备出阳极氧化膜。采用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)等仪器研究了氧化膜的形貌、组成和相结构。采用电化学方法研究了阳极氧化后钛合金的耐腐蚀性能。结果表明:膜层具有多孔结构,孔径范围在80nm~1μm之间。膜层的主要成分是无定形的TiO2,同时有锐钛矿相及金红石相TiO2的存在。阳极氧化后钛合金的耐蚀性有显著的提高。 相似文献