On the thermal aspect of fretting wear—temperature measurement in the subsurface layer

In fretting wear, the kinetics of the oxide film formation as well as the microstructure and the mechanical properties of the subsurface layer depend significantly on the temperature field produced in the fretted zone. Information reported in the open literature indicates contradicting values for the temperature produced at the interface. In the present study, an experimental method for direct measurement of the temperature profile in the subsurface layer has, therefore, been developed and verified. This method overcomes the limitations and the uncertainties inherent in methods of measurement used before. An error analysis indicated that the temperature gradient can be measured within ± 2.5%. The extent of the temperature measurement zone has been estimated by the theory of thermal constriction resistance and found to be in good agreement with some available experimental data.     

The Development Mechanism and the Technical Characteristics of the Modern Cutting Technology

Introduction Since 1980s cuttingtechnology has developedrapidly inthe developed countries .Uptothe end of 20 centuryor the beginningof 21 centurythe cuttingtechnology has en- teredthe development phase of modern cuttingtechnology featuringthe highcuttingspeed and high performance ma- chining.Looking back to the history of cutting technolo- gy,one century has passedsincethe metal cutting became one of the machiningtechnologiesfromthe very beginning of 20 century. Since then,cutting technology h…     

Investigation of the effect of machining parameters on the surface quality of machined brass (60/40) in CNC end milling—ANFIS modeling

Brass and brass alloys are widely employed industrial materials because of their excellent characteristics such as high corrosion resistance, non-magnetism, and good machinability. Surface quality plays a very important role in the performance of milled products, as good surface quality can significantly improve fatigue strength, corrosion resistance, or creep life. Surface roughness (Ra) is one of the most important factors for evaluating surface quality during the finishing process. The quality of surface affects the functional characteristics of the workpiece, including fatigue, corrosion, fracture resistance, and surface friction. Furthermore, surface roughness is among the most critical constraints in cutting parameter selection in manufacturing process planning. In this paper, the adaptive neuro-fuzzy inference system (ANFIS) was used to predict the surface roughness in computer numerical control (CNC) end milling. Spindle speed, feed rate, and depth of cut were the predictor variables. Experimental validation runs were conducted to validate the ANFIS model. The predicted surface roughness was compared with measured data, and the maximum prediction error for surface roughness was 6.25 %, while the average prediction error was 2.75 %.     

Development of a Setup for the Discrimination of β+ and γ Rays

Abstract

A β⁺–γ discrimination set‐up was developed and applied to the ²²Na radioisotope. The radioisotope emits positrons (β⁺) and these positrons create γ rays by annihilating with electrons. These annihilation γ rays were used here, and the discrimination between these positrons and γ rays was investigated by the coincidence measurement between time signals and the energy signals. The detection system presented here uses a 3 inch (diameter) by 3 inch (length) NaI(Tl) inorganic scintillation detector for γ detection and 3 inch (diameter) by 3 inch (length) plastic scintillation detector for β⁺ detection.     

Development of a compact and long range XYθ(z) nano-positioning stage

In this study, we describe the development of a novel, compact, and long range in-plane XYθ(z) nano-positioning stage with piezoelectric actuator and flexure mechanism. The stage is composed of an X-directional motion part and a Y, θ(z)-directional motion part, which are linked serially. The stage consists of a bridge-type amplifying mechanism for the amplification of deformation of the piezoelectric actuator, a double compound guide mechanism for performing only desired motion, and a circular hinge mechanism that permits rotational motion in the Y and θ(z)-stages. To set the design variables of the stage, optimal design is carried out. To verify the results of the optimal design process and the performance of the stage, the FEM simulation and experiment are carried out. The proposed XYθ(z) nano-positioning stage has a translational motion range of 700 μm and a rotational motion range of 0.3°; it has a closed-loop resolution of 5 nm, 5 nm, and 0.025 arcsec in the X-, Y-, and θ(z)-directional motions, respectively. The proposed stage is a novelty in that it has a compact size of 200 × 200 × 30 mm(3), and decoupled kinematic design.     

Discrimination of particles by the scintillation pulse shape (in the electron energy range of 0.5–4.0 MeV) using the zero-crossing method

The ratios of the fast to slow components of scintillation pulses produced by neutrons and γ rays have been calculated on the basis of experimental data for several energies in the range of 0.5-4.0 MeV of the electron equivalent. The procedure for discriminating between neutrons and γ rays by measuring the zero-crossing time of a bipolar pulse formed by RC circuits has been simulated for organic scintillators using the Monte Carlo method in the range of 0.012-4.000 MeV of the electron equivalent. It is shown that pulse shape discrimination of particles based on the zero-crossing technique allows rejection of γ-ray background down to a level of 10-4 at particle energies of >100 keV of the electron equivalent (for energies of <50 keV, the γ-ray background is suppressed to a level of 10^-1- 10^-2 and this technique becomes ineffective in principle).     

Modeling of fatigue crack growth closure considering the integrative effect of cyclic stress ratio, specimen thickness and Poisson’s ratio

Key components of large structures in aeronautics industry are required to be made light and have long enough fatigue lives.It is of vital importance to estimate the fatigue life of these structures accurately.Since the FCG process is affected by various factors,no universal model exists due to the complexity of the mechanisms.Most of the existing models are obtained by fitting the experimental data and could hardly describe the integrative effect of most existing factors simultaneously.In order to account for the integrative effect of specimen parameters,material property and loading conditions on FCG process,a new model named integrative influence factor model(IIF) is proposed based on the plasticity-induced crack closure theory.Accordingly to the predictions of crack opening ratio(γ) and effective stress intensity factor range ratio(U) with different material under various loading conditions,predictions of γ and U by the IIF model are completely identical to the theoretical results from the plane stress state to the plane strain state when Poisson’s ratio equals 1/3.When Poisson’s ratio equals 0.3,predictions of γ and U by the IIF model are larger than the predictions by the existing model,and more close to the theoretical results.In addition,it describes the influence of R ratios on γ and U effectively in the whole region from-1.0 to 1.0.Moreover,several sets of test data of FCG rates in 5 kinds of aluminum alloys with various specimen thicknesses under different loading conditions are used to validate the IIF model,most of the test data are situated on the predicted curves or between the two curves that represent the specimen with different thicknesses under the same stress ratio.Some of the test data slightly departure from the predictions by the IIF model due to the surface roughness and errors in measurement.Besides,based on the analysis of the physical rule of crack opening ratios,a relative thickness of specimen is defined to describe the influence of material property,specimen thickness and so forth on FCG characteristics conveniently.In conclusion,the relative thickness of specimen simplifies the expression of FCG characteristic and provides a general parameter to analyze the fatigue characteristics of different materials with various thicknesses under different loading conditions.The IIF model describes the integrative effect of existing influence factors explicitly and quantitatively,and provides a helpful tool for fatigue property estimation of practical component and experiment design.     

The optimization of annealing and cold-drawing in the manufacture of the Ni�CTi shape memory alloy ultra-thin wire

In this paper, the mechanical properties of the Ni?C50.5?at.%?CTi alloy super-elastic wires manufactured by a conditioned multi-passed process of annealing and cold-drawing have been studied. The annealing temperature of 450~800°C, time of 20?min~3?h and the cold-drawing amount of 6.9%~39% were chosen. Their effects on the thermo, mechanical, and surface morphology of the Ni?CTi wires have been studied. The differential scanning calorimetry and tensile-recovery tests were adopted to obtain the phase transformation temperatures and mechanical hysteresis of the Ni?CTi SMA wires with different treatment conditions. The results show that the phase transition temperature of Ni?CTi wire can be changed by varying the annealing temperature and time; cold-drawing deformation and subsequent annealing have a great influence on the super-elasticity. The process with 39% cold-drawing amount, 600°C and 20?min annealing is shown to be effective in the manufacturing.     

Discrimination of particles by the scintillation pulse shape in the range of low energies (6–100 keV for electrons) using the linear filters

The use of the linear filters for particle discrimination by the scintillation pulse shape is considered. The particle separation process has been simulated by the Monte Carlo method, taking into account that the slow scintillation component decays according to the hyperbolic law and that its relative contribution is energy dependent. The best figures of merit of particle discrimination attainable with this technique have been obtained assuming that the PMT and electronic noises are zero. It is shown that, by contrast to the zero crossing method, pulse shape discrimination of particles using the linear filters can ensure rejection of the γ-ray background to a level of ∼10⁻⁴ at particle energies of up to 12 keV of the electron equivalent. For energies of <24 keV, it is expedient that the signal acquisition time be increased to a few microseconds.     

Formulation,rheology and thermal ageing of polymer greases—Part I: Influence of the thickener content

The aim of this work is to show the correlation between polymer greases’ rheology and its formulation. The tested polypropylene (PP) thickened greases were evaluated regarding their thickener content and its effect on the rheological properties. An artificial ageing procedure was performed by heating fresh grease samples in an oven to study the thermal degradation. The ageing evaluation was performed through rheological measurements, FT-IR spectra, oil loss, bleed-oil viscosity changes and bleed rate. The rheology measurements were performed on a rotational rheometer, emphasizing on the storage and loss moduli values at the Linear Visco-Elastic (LVE) region. The flow curve of each grease was also measured. A modified Herschel–Buckley model was applied and the data was correlated to the thickener content.     

Material ratio curve as information on the state of surface topography—A review

This study deals with the analysis and usefulness of the material ratio curve. The parameters obtained from this curve are presented. The most popular of these parameters include two groups that are derived from this curve and provided in the ISO 13565–2 (Rk) and ISO 13565–3 (Rq) standards. They are compared by considering their practical significance and sensitivity to measurement errors. The parameters in the Rk family can easily be calculated but are ambiguous, which leads to errors in their calculation. The Rq group, which is based more on theoretical logic, must be applied with great care because of the problems with the Rpq parameter calculation and approximation of the material ratio probability plot. The methods of obtaining the correct oil capacity and its relation with the transition point between the central and valley surface parts are presented. The application of the material ratio curve in low-wear assessment is discussed.     

Development and Evaluation of Greases for High Temperature—High Speed Applications

Greases capable of lubricating antifriction bearings in aircraft accessory components operating at temperatures up to 600 F and at speeds between 20,000 and 45,000 rpm under light loads are required by the military. Some of the phases of a development program on greases for this application are discussed. The phases covered include criteria and methods of evaluation for the fluid and thickener components for greases, test equipment, and methods of test for determining the performance life of greases, and the current status of the development program.     

Coke Formation from Aircraft Turbine Engine Oils: Part I — Deposit Analysis and Development of Laboratory Oil Coking Test

The authors report here the results of a study undertaken to determine how aircraft engine oil degrades to form coke in static films on engine components and the impacts of additives and surface materials upon the coke production processes. The research is presented in two parts. This first paper deals with the initial research to develop a simple laboratory oil-coking test capable of monitoring antioxidant depletion, oil degradation, and coke formation of stressed aircraft turbine engine oils. Details of the analytical chemistry experiments performed on the stressed samples to quantitate the percentage of oil, polymer dissolved in the oil, and insoluble coke are also presented. The second paper (Part 2) (I) deals with more quantitative measurements of the degradation of thin layers of oil on heated surfaces. Effects of different oils and surfaces are explored.

The results presented in Part I show that simple open-vial laboratory tests involving thin films of oil produce polymer and coke similar to the deposits seen on failed face seals taken from operating aircraft engines and isolated from used engine oils. Coking reactions require oxygen to deplete the antioxidant package and to polymerize/decompose the ester basestock of the oil. After the antioxidant package is depleted, the ester basestock polymerizes to form small oil-soluble polymers. As the oil spends additional time at elevated temperature, these polymers increase in molecular weight and change in chemical composition becoming insoluble in the oil, producing deposits. Although the antioxidants inhibit the polymer/coke reactions, the antioxidants are incorporated in the formed deposits increasing the deposit amount. Consequently, these results indicate the proper concentration and choice of antioxidants will allow elimination, not just reduction, of deposits on engine components coated with thin layers of static oil films.     

Effect of matrix/reinforcement particle size ratio (PSR) on the mechanical properties of extruded Al–SiC composites

This paper studied the combined effects of matrix-to-reinforcement particle size ratio (PSR) and SiC volume fraction on the mechanical properties of extruded Al–SiC composites. A powder metallurgy technique (PM) of cold pressing at 500 MPa followed by hot extrusion at 580 °C was adopted to produce Al/SiC composite. Aluminum powder of size 60 μm and silicon carbide with different sizes, i.e., 50, 20, and 8 μm, were used. Three different volume fractions of SiC were employed, i.e., 5, 10, and 15 %, for each investigated size using a constant extrusion ratio of 14.36. The effect of matrix-to-reinforcement PSR on the reinforcement spatial distribution, fabricability, and resulting mechanical properties of a PM-processed Al/SiC composite were investigated. It has been shown that small ratio between matrix to reinforcement particle size resulted in more uniform distribution of the SiC particles in the matrix. As the PSR increases, the agglomerations and voids increase and the reinforcement particulates seem to have nonuniform distribution. In addition, the agglomerations increased as the volume fraction of the SiC increased. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength, and elongation. Yield strength and ultimate tensile strength of the composite reinforced by PSR (1.2) are higher than those of composite reinforced by PSR (7.5), while the elongation shows opposite trend with yield strength and ultimate tensile strength.     

Design of spherical and planar crank-rockers and double-rockers as function generators—I

The design of crank-rockers may be considered as a special case of synthesizing a function generator to match two prescribed velocity ratios, in which these velocity ratios are zero. The conception is based on the equations of relative poles. Like in the well-known planar case, where the loci of A₁ (crack-pin centre) and B₁ (rocker-pin centre) are both circles and straight lines, these loci in the spherical case are ellipses and great circles. Synthesis equations in simple trigonometric forms are presented for the spherical case, which are analogous to those in the planar case. Ranges of rotation angle φ₃ of the crank and those of the parameter φ₀, the initial position angel of the crank, are discussed. Simplified procedure for optimizing the transmission angles in both spherical and planar cases are described. Examples are given.     

Rheological Behavior of Greases: Part I—Effects of Composition and Structure

The aim of this work is to show the correlation between grease rheological behavior and its composition and structure (base oil viscosity, soap nature, and concentration).

A rheological investigation was carried out under the controlled stress mode. The results, obtained over different time intervals, show that grease behaves like a non-Newtonian viscoelastic material, with a narrow linear domain.

The soap nature and concentration are the dominant parameters when grease is submitted to low shearing. This was confirmed by TEM observations: the closer networks gave the highest rheological properties. Base oil viscosity influenced grease behavior only under high strain rates.

Some properties are discussed with respect to their influence on the contact replenishment, which is a critical point for mechanism lifetime prediction.

Finally, the authors suggest using rheometry as an alternative technique to standardized methods. Yield stress varies in the same way as penetration does, but is further influenced by the sample macrostructure.     

Modeling and analysis of the effects of processing parameters on the performance characteristics in the high pressure die casting process of Al–SI alloys

The high pressure die casting (HPDC) process has achieved remarkable success in the manufacture of aluminum–silicon (Al–SI) alloy components for the modern metal industry. Mathematical models are proposed for the modeling and analysis of the effects of machining parameters on the performance characteristics in the HPDC process of Al–SI alloys which are developed using the response surface methodology (RSM) to explain the influences of three processing parameters (die temperature, injection pressure and cooling time) on the performance characteristics of the mean particle size (MPS) of primary silicon and material hardness (HBN) value. The experiment plan adopts the centered central composite design (CCD). The separable influence of individual machining parameters and the interaction between these parameters are also investigated by using analysis of variance (ANOVA). With the experimental values up to a 95% confidence interval, it is fairly well for the experimental results to present the mathematical models of both the mean particle size of primary silicon and its hardness value. Two main significant factors involved in the mean particle size of primary silicon are the die temperature and the cooling time. The injection pressure and die temperature also have statistically significant effect on microstructure and hardness.     

Fabrication,characterization and evaluation of the effect of PLGA and PLGA–PEG biomaterials on the proliferation and neurogenesis potential of human neural SH-SY5Y cells

In recent years with regard to the development of nanotechnology and neural stem cell discovery, the combinatorial therapeutic strategies of neural progenitor cells and appropriate biomaterials have raised the hope for brain regeneration following neurological disorders. This study aimed to explore the proliferation and neurogenic effect of PLGA and PLGA–PEG nanofibers on human SH-SY5Y cells in in vitro condition. Nanofibers of PLGA and PLGA–PEG biomaterials were synthesized and fabricated using electrospinning method. Physicochemical features were examined using HNMR, FT-IR, and water contact angle assays. Ultrastructural morphology, the orientation of nanofibers, cell distribution and attachment were visualized by SEM imaging. Cell survival and proliferation rate were measured. Differentiation capacity was monitored by immunofluorescence staining of Map-2. HNMR, FT-IR assays confirmed the integration of PEG to PLGA backbone. Water contact angel assay showed increasing surface hydrophilicity in PLGA–PEG biomaterial compared to the PLGA substrate. SEM analysis revealed the reduction of PLGA–PEG nanofibers' diameter compared to the PLGA group. Cell attachment was observed in both groups while PLGA–PEG had a superior effect in the promotion of survival rate compared to other groups (p < .05). Compared to the PLGA group, PLGA–PEG increased the number of Ki67⁺ cells (p < .01). PLGA–PEG biomaterial induced neural maturation by increasing protein Map-2 compared to the PLGA scaffold in a three-dimensional culture system. According to our data, structural modification of PLGA with PEG could enhance orientated differentiation and the dynamic growth of neural cells.     

Exploring Operation Mechanisms of the Flexible Metal-to-Metal Face Seal: Part I—Numerical Modeling and Validations

A numerical model was developed for a special type of metal-to-metal face seal to evaluate its performance under various operating conditions. The model considers interactions among surface deformations due to thermomechanical twists, oil transport in the sealing band, and heat transfer in the seal pair simultaneously. In the meantime, experimental efforts have been made to measure the friction coefficients and seal temperatures during different operations. The model predictions were then compared with the experiment results through the two above-mentioned quantities. The comparisons show that the numerical simulations consistently overestimate the friction by 15–20%. However, the overall trend of friction variation with speed and some details of the friction have been captured, indicating that the current models are able to properly predict tribology of seal operations.