排序方式: 共有16条查询结果,搜索用时 15 毫秒
1.
本文对星载光学系统遮光罩消杂光结构的优化设计做了初步探讨。提出了遮光罩和挡光环消杂光设计的基本原则。给出了一种二级遮光罩结构寸的优化设计方法和一种遮光罩内壁上挡光环位置优化设计方法,并对一级和二级遮光罩进行了初步的分析比较。 相似文献
2.
Solder pastes used in surface mount soldering techniques (SMT) are very complex suspensions containing high volumes of metallic powder in a carrier fluid. The rheological complexity results largely from the carrier fluid itself, which is a suspension of colloidal particles. In this work, we have characterized the rheological properties of a typical carrier fluid and its solder paste containing 64 vol.% metallic powder. A six-blade vane geometry was used to avoid wall slip and sample fracture. All measurements were carried out following pre-shearing and rest time in order to obtain reproducible results. Steady shear experiments showed that the solder paste was highly shear-thinning and thixotropic. In oscillatory shear, the linear viscoelastic domain was found to be very narrow for both the suspending fluid and the paste. Frequency sweep tests in the linear domain revealed a gel-like structure with a nearly constant G′ for the suspending fluid and a slightly increasing G′ for the solder paste. From creep experiments, a yield stress of about 40 Pa was determined for the suspending fluid at temperatures between 25 and 40°C, and of 100 Pa at 4°C. A much larger yield stress, 480 Pa, was determined for the solder paste at 25°C. 相似文献
3.
The present work describes the development of a novel robotic vane shear test tool for characterization of soil parameters with high precision and accuracy. The tool automates industrial standards for testing procedures. The proposed system is capable of performing high resolution torque measurements, which are then used to estimate the shear strength of the soil. The design of the instrument and its advantages over traditional manual instruments are discussed, after which error sources, calibration, and test procedures are described. The developed tool was successfully validated against high-end commercial equipment. The built unit was employed for characterizing mine waste in a laboratory setting and also deployed in the field on board an Unmanned Ground Vehicle for remote soil characterization. 相似文献
4.
G. H. Meeten 《Rheologica Acta》2008,47(8):883-894
The rheology and slip of a dry shaving foam are investigated using squeeze-flow and rotating-vane methods. Constant-force
squeeze flow between planar surfaces is used to study the effect of surface roughness on slip and to obtain the yield stress.
Non-slip vane measurements are used to obtain the linear shear viscosity and elasticity at small strains, and the yield stress
and strain at large strains. Data are compared with the small-strain Maxwell and Kelvin–Voigt linear-viscoelastic models.
An apparent dependence of the yield stress and elasticity on the rotational speed of the vane is shown to result from time-dependent
rheological parameters as the foam ages. The effect of viscosity in the pre-yield region may give an erroneous identification
of yield. 相似文献
5.
在气动和化学强激光器系统研制中,压力恢复系统扩压器设计技术研究具有重要的工程应用价值。介绍了常温空气介质情况下若干型式扩压器试验件的数值模拟和实验研究结果,针对扩压器扩张角大小、壁面之间加隔板和边界层吹气等因素对其扩压性能的影响作了对比分析。初步研究表明:激光器系统的光腔段和压力恢复系统扩压器采用较小扩张角,扩压器内腔宽度方向设置适当厚度的竖隔板,扩压器左右侧壁采用附面层吹气等措施能有效提高扩压器的扩压效率。而由于压力恢复系统扩压器宽高比很大,在扩压器内腔使用水平隔板对扩压效率没有明显提高,并且当扩压器扩张角度很小时,水平隔板反而降低了扩压器扩压效率。 相似文献
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7.
Ternary blends of PLA/PBS/CSW with different weight fractions were prepared using a vane extruder. The mechanical properties, morphology, crystallization behavior and thermal stability of the blends were investigated. For the PLA/CSW blend, the tensile strength decreased, the flexural strength and modulus increased compared with pure PLA. For PBS, the addition of CSW had little influence on the mechanical properties. For the ternary blends PLA/PBS/CSW, the tensile strength, flexural strength and modulus decreased compared with pure PLA, while the elongation at break and the impact strength increased significantly. The brittle-ductile transition of the blends took place when the PBS weight fraction reaching 30 wt%. As a soft component in the blends, PBS was beneficial to improve the tensile ductility and the toughness of PLA. SEM measurements reveal that PLA/PBS/CSW blends were immiscible. When the weight fraction of PBS was 50 wt%, significant phase separation was observed, and CSW had preferential location in the PBS phase of the blend. DSC measurement and POM observation reveal that CSW had a heterogeneous nucleation effect on PLA and PBS matrix. The addition of PBS improved the crystallization of PLA and the thermal resistance of the PLA/PBS/CSW blends significantly. 相似文献
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9.
Vane viscometers are often used to investigate the low shear rate properties of plastic fluids. The shear stress is determined by assuming that the material is held in the space between the vane blades so that it behaves like a rigid cylinder. Experimental evidence supports this assumption and the aim of the present study is to model numerically the yield process in a vane rheometer using viscoelastic and plastic fluids. The finite element method has been used to model the behavior of Herschel-Bulkley (Bingham), Casson and viscoelastic (Maxwell type) fluids. The penalty function approach for the pressure approximation and a rotating reference frame are used together with fine meshes containing more than 1300 elements. The results show that for Herschel-Bulkley (Bingham), and Casson fluids a rotating rigid cylinder of fluid is trapped inside the periphery of the vane, the shear stress is uniformly distributed over the surface of the cylinder. Finally a modified second order fluid is used to simulate the viscoelastic behaviour, anticipated to be an intermediate between the elastic deformation and the plastic flow, to provide a more realistic simulation of the yield process about a vane. In this case, contrast with the concentration of the elastic strain rate at the blade tips, a nearly uniform distribution of the plastic shear rate is still found. This implies that the plastic shear always distributes uniformly during the entire yielding process. Evidently the assumption of uniform shear on a rotating cylinder of material occluded in the blades of a vane is a valid and useful model for many types of fluid possessing a yield stress. 相似文献
10.
A two-stage Tikhonov regularisation procedure has been used to obtain rheological properties for a high internal phase emulsion
from gap-dependent steady-state parallel plate shear data. This method is beneficial in that it can convert the steady shear
data into rheological property functions. The built-in regularisation parameters of the method are able to keep noise amplification
under control. The two-stage method is able to obtain not only the shear stress–shear rate function but also the apparent
slip velocity as a function of wall shear stress. The method is such that it obtains the rheological functions over the maximum
range of shear rate covered by the data. The results obtained using the new method are compared to those obtained using the
vane geometry with good agreement being observed. 相似文献