Measurement of surface form of Johannesteijsmania altifrons leaf using phase-shift fringe projection

The design of thin-walled structures based on naturally occurring folded structures, such as the Johannesteijsmania altifrons leaf, is relatively unexplored. The main advantage of this particular type of folded leaf is that it is supported by a single main stem, which can be exploited in structural designs if the 3-D surface form is known. Since the leaf can deform if the surface form is measured using conventional contact methods, the non-contact phase-shifting fringe projection method was applied to determine the 3-D surface form of the leaf. The potential of the phase-shifting fringe projection method for reconstructing the 3-D surface of naturally occurring folded structures such as J. altifrons leaf has not been attempted in the past. The objective of this work is to investigate the potential of using this technique to measure the 3-D surface of the life folded leaf in its natural environment. Three fringe patterns were projected onto the leaf with phase-shifts of 0, 2π/3 and 4π/3, captured using a CCD camera and processed to obtain a phase map. The 3-D data of the leaf surface were successfully reconstructed from the phase map using a phase-unwrapping algorithm.     

THE ITD MODE-SHAPE COHERENCE AND CONFIDENCE FACTOR AND ITS APPLICATION TO SEPARATING EIGENVALUE POSITIONS IN THEZ -PLANE

The properties of a newly defined mode-shape coherence and confidence factor are discussed in detail in connection with the Ibrahim time domain method. It has been found that this factor is able to distinguish three kinds of modes, true physical modes within the frequency range (0∼f_π) (corresponding to an angular range (0∼π) of eigenvalue positions in the Z -plane), frequency folded and/or overlapped modes and computational (noise) ones. Making use of this ability gives at least two benefits; (a) it releases the limitation on the user's constant Δt₁and increases the flexibility in use of all the user's constant combinations, and (b) it extends the angular range of eigenvalue positions to a multiple of 2 π by using a large value of Δt₁and makes the identification of eigenvalue positions in the Z -plane more accurate by a sort of zoom process. Digital simulation and measurements on a gearbox were chosen as application examples to illustrate the above advantages.     

A spectrometer for seeking exotic states of pionic atoms of xenon

The parameters of a spectrometer for searching for deeply bound pionic states of xenon are presented. The main component of the spectrometer is a multilayer semiconductor telescope based on high-purity germanium detectors. A technique for calibrating the spectrometer and measuring its energy resolution using reactions p(d, ³He)π⁰ and ¹⁴N(d, ³He)¹³C is described. The energy resolution of the setup is shown to be 0.85 MeV for ³He ions with an energy of ～360 MeV.     

a study of cast alloys with partially dispersed graphite III: Characterization of high density dispersed surfaces

The characteristic features of cast alloys with partially dispersed graphite are wear resistance and toughness. The friction and wear performance, hardness and other surface characteristics of the cast alloys with a high dispersive density of 60% at the casting surfaces were studied.The reciprocating sliding wear volume of aluminium alloy AC7A containing dispersants decreases with an increase in the gravity variable G = 2π²DN²/60²g, where D (cm) is the diameter of rotation, N (rev min^?1) is the rotational speed and g (cm s^?2) is the acceleration due to gravity, but depends on the nature of the dispersants. The effect of casting temperature on the wear loss was not significant. The dispersive density at the near-surface regions which is susceptible to the magnitude of G has a direct effect on the wear loss. A dense dispersant has an adverse effect on wear resistance and lubricity. A relation between surface roughness and casting temperature is also reported.     

An approximate solution of oil film forces of turbulent finite length journal bearing

An approximate analytical method is proposed for calculating oil film forces of turbulent finite length journal bearings. The dynamic ‘π’ oil film assumption is usually taken to determine oil film forces in the dynamic analysis of hydrodynamic journal bearing-rotor systems. However oil film field is not in the ‘π’ zone, i.e. the start position of the oil film is not 0, and the termination position of the oil film is not ‘π’. Based on the variational principle, separation of variables is employed to obtain the pressure distribution in this paper. The pressure distribution of the infinitely long journal bearing model is taken as a circumferential separable function of the pressure distribution. The start and termination positions of oil film in the circumferential direction are determined by using the continuity condition. The axial separable function of the pressure distribution is obtained by the variational principle and the circumferential separable function. The results calculated by the proposed method are in good agreement with the oil film forces by the finite element method, and the computing cost is reduced greatly. Meanwhile, the influence of the parameters on the oil film forces is analyzed.     

Die sphärischen analoga zu den ϱ-Kurven von H. AltThe spherical analogy to the -curves of H. Alt

Developing planar coupler mechanisms with a dwell, H. Alt has studied for the first time the “?-curves”. A ?-curve is the sequence of those points of the moving plane, which pass through the position on the path with equal radius of curvature.In this paper the analogous locus curves called the locus cones (λ_?-curves and λ_?-cones) are investigated, which result from the spherical motions; i.e., from motions about a fixed point. These cones are found to be an important special case of the general three-dimensional motion.An introductory part of the paper gives a short survey on the kinematical theory, followed by a brief investigation of the case λ_? = π/2 ( the analogy to the inflection circles of the planar motion) and the planar problem. The general λ_?-curves and corresponding λ_?-cones are treated in detail: their general shape, as well as their curvatures, the spherical subnormals and the positions of the osculating plane of the three-dimensional locus curves for special points are described.     

Effect of tensile plastic deformations on the residual magnetization and initial permeability of low-carbon steels

The behavior of residual magnetization M _r , initial magnetic permeability μ, and coercive force H _c of steels subjected to plastic extension both in the loaded state and in the unloaded state during “slow” and “fast” loading is explained from a unified point of view. It is shown that, upon unloading, the appearance of residual compressive stresses along the direction of the applied force in a considerable portion of grains leads to an abrupt decrease in M _r and μ and to an equally sharp increase in H _c . A slow decrease in M _r and μ and an equally slow increase in H _c are observed in the loaded state with an increase in ε; this effect is caused by an increase in the dislocation density. The values of M _r , μ, and H _c in the transition region of ε ≤ ε_cr obtained under slow loading differ considerably from those obtained under fast loading. In loaded and unloaded states, the dependences of M _r , μ, and H _c on ε are identical at ε ≥ ε_cr. The results obtained will be important when the magnetic parameters analyzed in this study are used for nondestructive testing of steel structures that have plastic deformations.     

Finite difference spectral moment estimation for profiles the effect of sample spacing and quantization error

The mean square slope m₂ and curvature m₄ of surface profiles are characteristics that depend upon the frequency content of the roughness. Together with the mean square profile height m₀ they determine the microgeometrical behaviour of contacting rough surfaces. It is shown that in the absence of quantization error, the error due to finite sample spacing in estimating these spectral moments for a sinusoid is negligible when more than 8 points per cycle are used. In the presence of quantization error, large potential overestimates of m₂ and m₄ can occur. The error decreases initially with increased sample spacing and then increases. The severity of the distortion is shown to increase as the peak-to-peak range of the sine wave decreases relative to the full range of the a/d converter used in the digitization process.     

Visualization and topography of the stray magnetic field of crack-type discontinuities in magnetic materials

Configurations of the domain structure of gadolinium-cobalt amorphous films placed in spatially nonuniform magnetic fields, which are produced by cracks in steel plates, are determined. The possibility of visualization and topography of the stray fields (their normal H _z component) of cracks with openings 1.5 to 50 μm wide by the use of an applied magnetic field is shown. Strip domains, which determine the coordinates of edges of cracks with an opening width d > 20 μm (or peaks in the coordinate dependences), are formed near the saturation state under the action of the field. This result is in agreement with calculated theoretical topograms. An unusual discrepancy in the positions of peaks in experimental and theoretical topograms is observed for narrow cracks (d < 10 μm). It is likely that the observed discrepancy in the position of peaks in topograms of narrow cracks is related to the interaction of crack edges during their convergence, i.e., their partial mutual magnetization reversal. Original Russian Text ? V.E. Ivanov, V.N. Bashkinova, 2006, published in Defektoskopiya, 2006, Vol. 42, No. 1, pp. 18–25.     

Noncovalent Functionalized Graphene-Filled Polyimides with Improved Thermal,Mechanical, and Wear Resistance Properties

A facile method is proposed to prepare poly-o-phenylenediamine (PoPD) noncovalent functionalized graphene (G)-reinforced polyimide (PI) nanocomposites. PoPD-G exhibited excellent dispersibility in various organic solvents. The structures of PoPD-G were characterized by Raman and UV spectrum, which verified the π–π interactions between PoPD and G. The effective exfoliation of graphene nanosheets was investigated by observation of the morphology of PoPD-G with SEM, SPM, and TEM. Compared to PI/G composites, the interfacial adhesion between graphene nanosheets and PI matrices promoted efficient stress transfer from PI chains to PoPD-G nanofillers. Polyimide nanocomposites with different incorporations of PoPD-G exhibited outstanding thermal properties. It is interesting to note that only 0.5 wt% PoPD-G-reinforced PI composites increased by 20.8% in hardness, enhanced by 84.0% in storage modulus, and reduced by 72.8% in wear rate compared with neat PI. The eminent enhancement was attributed to the facile dispersion of graphene nanosheets and strong interface adhesion between PI and PoPD-G.     

Plastic deformation of 25CrMo4 steel during wear: Effect of the temperature,the normal force,the sliding velocity and the structural state

This article follows a previous study on friction and wear of 25CrMo4 steel [N. Khanafi-Benghalem, K. Loucif, E. Felder, F. Delamare, Influence de la température sur les mécanismes de frottement et d’usure des aciers X12NiCrMoSi25-20 et 25CrMo4 glissant sur du carbure de tungstène, Matériaux et techniques 93 (2005) 347–362]. The aim of our work is to study in more details the process of plastic deformation and the wear rate of this steel in lubricated sliding against cemented tungsten carbide, process observed in the previous work. The considered parameters are the temperature T (from 20 to 200 °C), the normal force P (from 500 to 1500 N), the steel structure (normalised HV 220 and quenched/tempered HV 480 states) and the sliding velocity v (from 0.05 to 0.3 m/s). We measured the friction coefficient and the sample total volume loss. A displacement sensor follows the volume loss evolution during the test; this follow-up is approximate because of the sample plastic flow which leads to the formation of peripheral burrs. All the tests conditions generate a significant plastic deformation of the sample steel, even in the quenched/tempered state: it produces a marked increase of the surface hardness, the work hardened layer being much finer for the quenched/tempered state (15 μm) than for the normalised state (40 μm at 20 °C). For temperatures T ≤ 100 °C in normalised state, the wear follows the Archard's law with an increasing rate with temperature. For T ≥ 120 °C, the wear rate decreases during the test, the global volume of wear being a decreasing function of T. For the quenched/tempered state, the wear rate decreases with the increase of the normal force, this decrease is less than 30% of the normalised state value. The material heating during the wear tests is well correlated with the friction dissipated power, but remains small, except in extreme cases (v maximum, great friction at high temperatures). These results suggest the existence of two wear mechanisms: abrasion by sample debris and burrs emission by plastic flow. The abrasion is probably the dominating mechanism for the tests carried out at the lowest temperatures. The plastic flow becomes a significant component at the highest temperatures. Using a contact model, we discuss to what extent the influence of the temperature and the strain rate on the steel hardness and ductility could explain the temperature and the sliding velocity effect on wear. Other phenomena are probably present: the influence of the steel microstructure and the lubricant on the size and/or the number of particles responsible for abrasion.     

The FLINT setup for studying cumulative processes with photon production

A setup is developed at the Institute for Theoretical and Experimental Physics for studying cumulative processes in hA and AA interactions with photon and π ⁰-meson production in the central region of rapidities at high transverse momenta. Lead glass calorimeters and a charged particle rejection system are the main components of the setup. A fast trigger for a high-energy cumulative particle, based on detection of Cherenkov radiation in the lead glasses, is realized in the setup.     

Dry sliding wear of epoxy/cenosphere syntactic foams

Dry sliding wear behavior of epoxy matrix syntactic foams filled with 20, 40 and 60 wt% fly ash cenosphere is reported based on response surface methodology. Empirical models are constructed and validated based on analysis of variance. Results show that syntactic foams have higher wear resistance than the matrix resin. Among the parameters studied, the applied normal load (F) had a prominent effect on wear rate, specific wear rate (w_s) and coefficient of friction (μ). With increasing F, the wear rate increased, whereas w_s and μ decreased. With increase in filler content, the wear rate and w_s decreased, while the μ increased. With increase in sliding velocity as well as sliding distance, the wear rate and w_s show decreasing trends. Microscopy revealed broken cenospheres forming debris and extensive deformation marks on the wear surface.     

Relaxation capacity and cracking resistance of nitrous coating produced by electron-beam facing of 0.6C-24Cr-0.7N-16Mn steel powder during wear by hard abrasive under heavy loads

Specific features of the topography of friction tracks formed during the sliding of a WCo6 ball over an austenitic nitrous coating at various velocities of sliding under various loads using the ball-on-disc arrangement are studied and compared with those for the WCo6 ball-110Mn13 steel pair. It has been found that the wear resistance of nitrous austenite is due to its capacity to relax frictional stresses. The correlation between the H ₃/E ₂ parameter of the friction surface and the wear rate has been shown.     

Improvement in electrical and thermal behavior of polystyrene/multiwalled carbon nanotubes nanocomposites

Polystyrene (PS)/multiwalled carbon nanotubes (MWCNTs) nanocomposite has been prepared by solvent evaporation technique  and . Tetrahydroforan (THF) has been used as a solvent. Its electrical and thermal properties have been investigated by using LCR meter, 2-probe mechanism and Thermo Gravimetric Analysis Differential Thermal Calorimeter (TGA/DTA) respectively. Increase in dielectric constant and loss is observed with the increase of MWCNTs content in the nanocomposites. Frequency dependent AC conductivity follows the universal power law. Increase in AC conductivity with temperature has been attributed to hopping of π electrons in the MWCNTs. Temperature dependent DC conductivity was found to be a typical of a semi conducting behavior following Mott’s 3-D variable range hoping model. Best fitted Mott’s parameters were determined from the observed data.     

Approximate Entropy as a diagnostic tool for machine health monitoring

This paper presents a new approach to machine health monitoring based on the Approximate Entropy (ApEn), which is a statistical measure that quantifies the regularity of a time series, such as vibration signals measured from an electrical motor or a rolling bearing. As the working condition of a machine system deteriorates due to the initiation and/or progression of structural defects, the number of frequency components contained in the vibration signal will increase, resulting in a decrease in its regularity and an increase in its corresponding ApEn value. After introducing the theoretical framework, numerical simulation of an analytic signal is presented that establishes a quantitative relationship between the severity of signal degradation and the ApEn values. The results of the simulation are then verified experimentally, through vibration measurement on a realistic bearing test bed. The study has shown that ApEn can effectively characterise the severity of structural defect, with good computational efficiency and high robustness.     

Minimum centroid neighborhood for minimum zone sphericity

The minimum zone sphericity tolerance is derived from the ANSI and ISO standards for roundness and has extensive applications in the tribology of ball bearings, hip joints and other lubricated pairs. The worst-case proposed in this paper provides theoretical evidence that the minimum zone center of the two (circumscribed and inscribed reference) spheres with minimum radial separation containing the sampled spherical surface is included in a spherical neighborhood centered in the centroid of radius 2π⁻²E_C, where E_C is the sphericity error related to the centroid, which can be determined in closed form.     

A hybrid clustering approach for multivariate time series – A case study applied to failure analysis in a gas turbine

A clustering problem involving multivariate time series (MTS) requires the selection of similarity metrics. This paper shows the limitations of the PCA similarity factor (SPCA) as a single metric in nonlinear problems where there are differences in magnitude of the same process variables due to expected changes in operation conditions. A novel method for clustering MTS based on a combination between SPCA and the average-based Euclidean distance (AED) within a fuzzy clustering approach is proposed. Case studies involving either simulated or real industrial data collected from a large scale gas turbine are used to illustrate that the hybrid approach enhances the ability to recognize normal and fault operating patterns. This paper also proposes an oversampling procedure to create synthetic multivariate time series that can be useful in commonly occurring situations involving unbalanced data sets.     

干涉式大气垂直探测仪中面弹簧的有限元分析

面弹簧是干涉式大气垂直探测仪中的精密部件,系统要求其在工作过程中具有较大刚度比和足够的轴向行程。利用有限元分析方法对面弹簧进行了优化设计。通过对比不同缝形面弹簧在轴向拉伸过程中的轴向刚度、径向刚度、刚度比,确定了螺旋缝形是相对最优缝形。进一步对螺旋缝形面弹簧做了系统分析,得到了螺旋缝形面弹簧中的基圆半径 、螺距 、旋转角度 、指数 、直径 、开缝数 、簧片厚度 、材料的杨氏模量等参数在面弹簧轴向拉伸过程中,对其轴向刚度、径向刚度、刚度比的影响规律。根据有限元分析结果最终确定一组最优参数值 r₀=20mm,a=20／π²mm/rad,θ₁=πrad,b=2,=200mm,n=3,t=0.2mm,E=1.3 e11Pa,并据此加工成实物。对实物的实测结果表明,螺旋缝形面弹簧具有的轴向行程和较大的刚度比达到了设计目标,验证了有限元分析结果的准确性和合理性。