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1.
A system for accurate real-time measurement of deflections was developed. A stable laser source is, by means of a single-mode fiber, coupled to an optical head located at one end of deformed structure. A detector circuit with a quadrant detector and processing electronics, located at the other end of the structure, communicates the resolved 2D position of the incident beam over a common digital bus. Experiments using interferometers were conducted in a climate-controlled chamber to evaluate system performance and verify the accuracy. A resolution of 0.1  m is attainable in dynamic measurements. The system was calibrated and tested to yield measurement accuracy of ± 0.8  m for ± 2σ probability over the measurement range of ± 300  m. Drift of the system in the experimental setup was determined to be less than 2  m for measurement in both degrees of freedom within the 10 h period under constant environmental conditions.  相似文献   

2.
Repeatable and accurate assembly of thin, foil optics is crucial to meeting performance goals in optical systems such as grazing-incidence X-ray telescopes and diffractive lithography tools. Our previous work in proving key technologies for assembly has been motivated by the need to meet spectral resolution goals for the NASA Constellation-X mission. We report a new generation of technology that makes strides towards simulating actual telescope assembly conditions. Our technology is based on the use of micromachined silicon tooling that we call microcombs. Theoretical error budgeting and analytical models were applied to a mechanical design with an isolated metrology frame and high-resolution actuation with feedback. Experimental testing has yielded assembly results with sub-micron repeatability and accuracy. For complete foil reassembly, placement errors are approximately 0.3  m over a 140 mm× 100 mm× 0.4 mm foil. Accuracy of assembly in pitch and yaw are 0.34 and 2.01  m, respectively. This performance meets the 1  m telescope assembly accuracy goal with the exception of yaw accuracy, which is under continued development.  相似文献   

3.
Effects of grain size on the wear of recycled AZ91 Mg   总被引:3,自引:0,他引:3  
Magnesium alloy AZ91 chips have been recycled using mechanical milling to yield samples with fine grain sizes. Together with cast samples of the same alloy, the wear behavior of these materials was studied through pin-on-disc sliding, with speeds varying from 1 to , under a normal load of 10 N. Despite the differences in grain size (0.6–) and mechanical properties, the various specimens did not differ significantly in their wear performance. Scanning electron microscopy observed abrasive wear to be dominant under low-speed sliding, and a transition to the formation of a protective mechanically mixed layer (MML) as sliding speed increased.  相似文献   

4.
F. Galliana  P.P. Capra  E. Gasparotto   《Measurement》2009,42(10):1532-1540
A national comparison of high dc resistance at and level was organized by the Electromagnetic Division of National Institute of Metrological Research (INRIM, Italy) and piloted by the high dc resistance Laboratory of the same Division. This comparison took place between January and April 2008 with the participation of 8 Secondary Laboratories accredited by the Italian Service of Accreditation of Calibration Laboratories (SIT). The travelling package included one wire-wound standard and one thick film-type standard in a wooden anti-shock container designed by INRIM. The obtained results indicate that the relative differences at and between each Laboratory’s value and the respective reference value are all within the expanded relative uncertainties of these differences at a 2σ confidence level.  相似文献   

5.
This paper presents a study concerning the influence of the amount of metallic nanoparticles on the wear behaviour of Fe0.5–Cr0.5–alumina nanocomposites rubbing on Ti–6Al–4V in fretting. Due to the elaboration process (metal–oxide nanopowder prepared by selective reduction in hydrogen of oxide solid solution and densified by spark plasma sintering), these materials generally own two sorts of nanoparticles: the intragranulars (size: ) located within the alumina grains and the intergranulars (size: ) located at the grain boundaries. This paper focuses on the role of each sort of nanoparticles with respect to the wear of the nanocomposite. Results show that the presence of intergranular nanoparticles is crucial for improving the wear resistance of nanocomposites whereas the intragranulars rather improve the mechanical properties of matrix grains. The lowest wear rate of the nanocomposite is obtained when the amount of intergranulars is about 3.5 wt%. Finally, the fretting wear mechanism of nanocomposites and the mechanism enabling to prevent it by using nanoparticles are both identified and discussed.  相似文献   

6.
A focused ion beam (FIB) microscope has been used to simultaneously depth profile and image the γγ microstructure of a nickel base superalloy using normal incidence milling in order to characterize the precipitate microstructure in three dimensions (3D). The normal incidence milling rates of the γ and γ phases in this alloy are closely matched when the orientation of the depth-profiled surface is near , which allows for uniform material removal to depths up to a couple of microns. Depth-profiling experiments consisted of automated ion milling and collection of ion-generated secondary-electron images at specified intervals, and was demonstrated for a voxel resolution of roughly . Image-processing software was used for automated processing of the 2D image sequence to render the γ precipitate structure in 3D.  相似文献   

7.
This paper extends the analysis of Part I to investigate the influence of oil inlet pressure and its position on the dynamic characteristics of axially grooved journal bearings. Using the dynamic fluid force derived in Part I, the equations of motion are solved for the locus of the journal center. A trial-and-error method is used to identify the instability threshold speed for a given Sommerfeld number S. The effects of oil inlet pressure (in the range of ) and inlet position (in the range of 0Θi90°) on the instability threshold speed of a rotor-bearing system are investigated and discussed. It is shown that the instability threshold speed with oil inlet position Θi=0 decreases on increasing the oil inlet pressure from 0 to 1.0 while the influence of oil inlet position on the instability threshold speed depends on the steady state eccentricity ratio ε.  相似文献   

8.
This paper presents analytical expressions for the dynamic pressure and dynamic fluid force in axially grooved long journal bearings with consideration of oil inlet pressure and inlet position. The effects of oil inlet pressure (in the range of , where the dimensionless oil inlet pressure ) and oil inlet position (in the range of 0Θi90°) on the static oil film configuration, pressure distribution, and steady state journal position in axially grooved journal bearings are discussed. In this paper, Reynolds–Floberg–Jakobsson boundary conditions are assumed to account for the appropriate starting position of the cavitation, the reformation of oil film at the end of caviation, and the effect of oil inlet pressure and inlet position.  相似文献   

9.
Assuming plastic hardening of metals are specified by the stress–strain curve in the form , the material parameters σ0, k and m are identified from spherical indentation tests by measuring compliance moduli in loading and unloading of the load–penetration curve. The curve P(hp) is analytically described by a two term expression, each with different exponents. Here, εp and hp denote the plastic strain and permanent penetration. The proposed identification method is illustrated by specific examples including numerical and physical identification tests.  相似文献   

10.
Ionic liquids of α, -diimidazoliumalkylene hexafluorophosphate were synthesized. The tribological properties of the synthetic ionic liquid and the ionic liquid contained additive for contacts of steel/steel were investigated by Optimol SRV oscillating friction and wear tester under ambient conditions. The synthetic ionic liquid presented low friction coefficients and small wear volumes, especially under higher temperatures. The ionic liquid doped with benzotriazole (BTA) showed excellent anti-wear ability. The worn surfaces and chemical nature of the boundary films generated on the metal surfaces were analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). SEM results showed slight abrasion on the worn surfaces and XPS results indicated the formation of FeF2, FeF3, Fe3O4, and FePO4 by the tribochemical reactions of ionic liquid with iron during the sliding process.  相似文献   

11.
In this paper, the initial buckling loads and the corresponding buckling modes of symmetric rectangular laminated plates are investigated. The considered laminates are supposed to have a uniform thickness, are subjected to a linearly distributed inplane compressive normal load and are simply supported at the two loaded edges with one free unloaded plate edge and with one simply supported unloaded edge where elastic rotational restraints are considered. Unlike in many other investigations, the composite laminates presently under consideration may have arbitrary yet symmetric lamination schemes with bending–torsion coupling. The initial buckling loads of such plates are calculated using the RITZ-method for which some especially adjusted displacement shape functions are employed. Since a series expansion of the buckling shape is performed in the load direction only while in the perpendicular direction one single displacement function can be shown to be sufficient, the present approach is numerically very efficient when compared to approaches in which a series representation is chosen with respect to both inplane directions. Comparison with reference results and with finite element computations leads to an excellent agreement. Some new findings on the general stability behaviour of this class of laminated plates are presented as a closure.  相似文献   

12.
Effect and mechanism of additives for ionic liquids as new lubricants   总被引:4,自引:0,他引:4  
Ionic liquids are unique compounds, which exhibit low viscosity, non-flammability, low vapor pressure, and extremely high thermal stability. Therefore, they are expected as candidates for advanced lubricants. Several ionic liquids, derived from cations such as imidazolium, pridinium, ammonium, and anions such as , bis(trifluoromethylsulfonyl)imide (TFSI-) were examined under boundary conditions. It was found that tribological properties of ionic liquids are better than those of conventional lubricants such as synthetic hydrocarbons, synthetic esters, and fluorinated ethers. Careful analysis of worn surface revealed that tribochemical reactions of ionic liquids take place under these conditions. For example, organic fluoride, iron fluoride, iron sulfate derived from anionic moiety of the ionic liquids were detected by the instrumental surface-analysis with TOF-SIMS and XPS. Tricresylphosphate (TCP) and dibenzyldisulfide (DBDS) were found to improve anti-wear properties of ionic liquids to some extent. Interestingly, both additive-derived compounds and anionic moiety derived ones were detected on the worn surface. Moreover, additive response of ionic liquids was found to be superior to those for conventional lubricants. It was speculated that the unique tribochemical reactions will lead us to design tailor-made lubricants. Lubrication mechanism of ionic liquids is discussed from the viewpoint of tribochemistry.  相似文献   

13.
In this paper the validation of a fiber-fed heterodyne laser interferometer with nanometre uncertainty is presented. The achievable displacement measurement uncertainty is investigated for different polarisation maintaining fibres used in these interferometers. Measurement results are shown for both a range of m as well as a range of 300 mm. It is shown that a (selected) PM-fibre with an extinction ratio of 1:1650 and the use of an external reference allows realising a fibre-fed laser interferometer able to measure displacements with the same uncertainty as a laser interferometer system without fibre. Tests were performed with fibres ranging in length up to 50 m.  相似文献   

14.
The properties of ceramic materials (high hardness, high-temperature capability, low coefficient of thermal expansion) are of interest to rolling element materials. One of the most interesting materials is silicon nitride.The paper presents an experimental study of the influence of oil additives (Cl, S, P, cerium dioxide (CeO2)) on spread cracks in silicon nitride. The additives Cl, S, P are bound in molecules in liquid form soluble in the base oil. The CeO2 is purely in powder form in suspension. The use of CeO2 powder was made based on the good results of polishing of silicon nitride. A ceramic angular contact ball bearing was modelled using a four-ball machine. Silicon nitride, -in diameters balls were artificially damaged with pre-cracks. Ring formed pre-cracks were propagated on the ball surface by a blunt impact load using a tungsten carbide ball under five various impacts.Rolling contact fatigue failure modes were studied under high contact stresses and speed. The surface of silicon nitride balls before and after failure was examined using scanning electron microscopy.The research of the present paper shows that fatigue failure under rolling contact loading is markedly sensitive on the size of pre-cracks and oil additives. Propagations of surface pre-cracks takes place under fatigue load. Primary and secondary surface crack propagation are described.  相似文献   

15.
This work describes the theoretical study concerning the effect of non-linear behaviour of the lubricant on the performance of a slot-entry journal bearing. The analysis considers the generalized Reynolds equation governing the flow of lubricant having variable viscosity in the clearance space and the three dimensional elasticity equations governing the displacement field in the bearing shell, and equation of flow of lubricant through slot restrictor. The non-Newtonian lubricant is assumed to follow the cubic shear stress law ( ). Bearing performance characteristics have been presented for a typically selected values of non-linearity factor ( ) and deformation coefficient ( ). It has been observed that the combined effect of non-linearity factor ( ) and bearing flexibility ( ) affects the performance characteristics of slot-entry journal bearing quite significantly.  相似文献   

16.
The roughness effect on the frequency of frictional sound   总被引:2,自引:0,他引:2  
Dry sliding of two bodies in contact generates a wide range of effects like friction, wear, heat and sound among others. The main interest of this study is in the frequency characteristics of the generated sound.In the past, frequency spectrum and sound pressure level with relation to surface topography (surface roughness in particular), have been studied mainly for concentrated contacts like stylus or hemispherical tip pin on a rough surface. Studies on flat–flat contacts were mainly focused on the topography of contacting surfaces and its relation to occurrence or non-occurrence of squeal (high pitch, high sound pressure level sound) in brake systems.The present study aims to clarify the effect of surface roughness on the frequency of non-squealing frictional sound generated in dry flat–flat sliding contact.Sound was generated by the dry contact in rubbing by hand of two rectangular cross-section stainless-steel plates having similar surface roughness. The roughness of the contacting surfaces varied in the range Rz=0.8–12.4 μm. The sound spectra had 5 peaks (P1, P2, P3, P4 and P5) in order of increasing frequency and it was found that the peak frequency was shifted when the roughness of the rubbed surfaces changed. The first peak P1 was most sensitive to change of surface roughness and it shifted from 3.0 to 4.5 kHz when the maximum surface roughness changed from Rz=10.9 to . When the surface was relatively rough, this peak was close to the first bending natural frequency of the plate at 2.377 kHz.  相似文献   

17.
The elastic–plastic stress distribution of a solid disk due to nonuniform heat source under external pressure is investigated in this work. The nonuniform heat generation rate is taken to be a function of the radial position in the form , where a denotes radius of the solid disk; q0, n and s are constants. The exact solution presented is based on the usual assumptions of plane stress, Tresca's yield condition, its associated flow rule and linear strain hardening material behaviour. According to this analysis, the plastic core in the general case consists of three parts with different forms of the yield condition. The present solution is illustrated by numerical results and is compared with uniform heat generation case. This work provides the basis for a comprehensive investigation of the influence of nonuniform heat generation.  相似文献   

18.
Numerical tensile tests of an elastoplastic cylindrical bar at various high strain rates are performed by the use of a dynamic explicit FEM code (DYNA3D, a public domain version). The effects of mass (inertia) of the body, strain rate and strainrate sensitivity exponent (m-value) on the deformation pattern and the load curve are investigated. As for the material, strain-dependent nth power work hardening property is given by where is strain rate. The range of the prescribed average strain rate is 50–1000/s where the tensile tests with constant average strain rate and with constant tensile velocity are performed. Materials with higher density exert a greater influence on deformation mode at a high strain rate. Even if the tensile speed is less than that of plastic wave propagation, the deformation becomes non-uniform remarkably due to mass effect. It is unexpected that double necking occurs at certain computational conditions. The strain at maximum load point predicted by the numerical simulation does not coincide with the analytically predicted one. Maximum rate of decrease in cross sectional area within the straight portion of the bar is compared with Hart's instability criterion based on the imperfection in the cross section. In high-rate tension over , deformation behavior is chaotic in the sense that it varies very sensitively with a trivial change in material properties and/or in the prescribed strain rate.  相似文献   

19.
The stability of ideal orientations and texture evolution was investigated for FCC sheet metals during deep drawing. Lattice rotation fields around ideal orientations were numerically predicted using a rate-sensitive polycrystal model with full constraint boundary conditions. In order to evaluate the strain path during deep drawing of an AA1050, simulations using a finite element analysis were carried out. The stability of orientations and texture formation was examined at sequential paths such as flange deformation, transition and wall deformation. Depending on the initial location in the blank, the deviation from the plane strain state in the flange deformation path decreased the orientation density around P and shifted the final stable end orientation from P to Yf near . The texture evolution in AA1050 sheet metals during deep drawing was experimentally investigated. The change of orientation density around ideal orientations in the RD and TD samples was in good agreement with the rate-sensitive polycrystal model.  相似文献   

20.
A dynamic behaviour of thin periodic plates interacting with an elastic periodic foundation is analysed. The main aim is to investigate free vibrations and calculate frequencies for these plates. The presented modelling approach to the linear-elastic plates, having periodic structure in planes parallel to the midplane, is adopted from the tolerance averaging method developed by Woźniak and Wierzbicki (Averaging techniques in thermomechanics of Composite Solids, Wydawnictwo Politechniki Cz stochowskiej, Cz stochowa, 2000) for periodic composites. The obtained plate model describes the effect of the periodicity cell size on the overall plate behaviour. In this paper this effect is analysed in the free vibrations problem. Two special cases are taken into account: a square plate with a periodic thickness interacting with a homogeneous foundation and a square plate with a constant thickness interacting with a periodic foundation. A certain justification of the model is also presented.  相似文献   

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