The use of generalized magnetic parameters for magnetic structural analysis and nondestructive testing

The results of studies regarding the dependence of the product of the coercive force and the initial magnetic susceptibility of a nickel single crystal with an intermediate orientation on the shear stress are analyzed. It is concluded that an increase in the aforementioned product for a nickel single crystal upon cold plastic deformation is due to refining of magnetic domains that is caused by formation of cells and subgrains within the single crystal. The tentative size of magnetic domains was determined based on the value of generalized magnetic parameter . The variations in the product and in the calculated dimensions of magnetic domains in polycrystalline nickel are analyzed using data reported by Kersten-Gottschalt. It was also shown that, the density of dislocations being constant, the generalized magnetic parameter is sensitive to changes in the sizes of nonferromagnetic inclusions, whereas in the case of small nonferromagnetic inclusions, an increase in the generalized parameter is due to an increase in the density of dislocations.Translated from Defektoskopiya, Vol. 40, No. 7, 2004, pp. 62–76.Original Russian Text Copyright © 2004 by Bida.     

Improving the Accuracy in Determining the Insulator Capacitance in Metal–Insulator–Semiconductor Structures

The results of the voltage–capacitance spectroscopy of interface states in metal–insulator–semiconductor (MIS) structures are critical functions of the accuracy in determining the insulator capacitance C _i, which is typically no higher than a few fractions of a percent. This substantially limits the energy range of the observed spectrum of the interface states (E 0.5 eV for Si-based MIS structures) and the sensitivity to the density of the interface states at the spectrum edges (N _ss 1 × 10¹⁰ cm^–2 eV^–1). We propose a method for minimizing these errors that is based on a sequential variation of the initial estimate C _i C _{i 0} C _ij, j = 0, 1, 2, ... and the identification of singular points in the dependences and on C _ij, where are the mean arithmetic values of the voltage difference between the experimental and ideal voltage–capacitance characteristic and are the rms deviations of the voltage values taken in the high-accumulation (ac) and inversion (in) regions from values. The highest (10^–4%) accuracy in determining C _i is achieved in the regions of the equidistant experimental and ideal voltage–capacitance characteristic. This method, combined with the technique of _s / _s diagrams, ensures an extension of E to 0.9 eV at N _ss 1 × 10¹⁰ cm^–2 eV^–1 and the possibility of determining the sign and density of the fixed charge in the gate insulator.     

Accuracy and strength of a joint loaded by suddenly applied torque

The influence of the required quality (fit and degree of accuracy) of prismatic joints to achieve guaranteed clearance was a speciality of experienced designers. The problem becomes quite complicated owing to stresses arising in the joint elements during torque transmission under dynamic loading.In this paper a widely used prismatic joint with a hexagonal cross-section is considered. A dynamic loading, generated by a spring mechanism is applied. D'Alambert's principle was employed in solving the kinesthetic problem.The paper presents equations for the dynamic coefficient, the angle of clearance, _i and the maximum tangential stress. It is pointed out that torque-loaded elements cannot be produced from rolled stock, obtained from drawings.The presented graphs permit selection of the steel grade in accordance with the fit and the degree of accuracy of the joint and with the permissible torsional stress.The proposed procedures may be used for computer-aided design of torque-transmitting prismatic splines, key joints and torsion mechanisms.Nomenclature d ₁ diameter of hole (see Fig. 1) - d _max D _n + es maximum limit of shaft size - d _min D _n + is minimum limit of shaft size - D _max D _n + ES maximum limit of hole size - D _min D _n + EI minimum limit of hole size - D _n nominal size of the hole and of shaft - ES, es upper deviation of hole and shaft - EI, ei lower deviation of hole and shaft - F area of hexagon - G modulus of transverse elasticity - (see Fig. 1) - I _p polar moment of intertia - polar moment of inertia of hexagon - polar moment of inertia of circle - K dynamic coefficient - l length of shaft - m number of polygon sides - M _d torque under dynamic loading - M _s torque under static loading - S _i clearance - S _max = ES-ei maximum clearance of joint - S _min = EI-es minimum clearance of joint - T tolerance - W section modulus of torsion - W _c circle section modulus of torsion - W _h hexagon section modulus of torsion - (see Fig. 1) - maximum tangential stress under dynamic loading - maximum tangential stress under static loading - _d twist angle under dynamic loading - _i angular displacement - _s twist angle under static loading     

Diagnostics of Multilayered Composite Structures with the Help of a Fiber-Optic System for Strain Measurements

The paper considers a built-in fiber-optic array system for technical diagnostic of composite structures measuring local strains in hazardous cross sections of these structures. The effect of repeated microscopic bends of optical fibers on the transmitted flux in structures strained by a tensile force of up to 1 kN over a temperature range of 20 to 100°C has been investigated. The increase in the tensile stress in components of a composite structure leads to a growth in the optical losses of up to 20–23% of the initial optical flux. The loss function (F) is linear in the region of mechanical forces of up to 1 kN and temperatures up to 40°C. An explanation has been suggested for the nonlinearity of (F) at temperatures above 40°C. The conclusion is that the developed system enables one to estimate the strength of multilayered composite structures and detect their prefracture states using singular points on opto-mechanical characteristics of optical fibers.     

Modelling of Tool Wear Based on Component Forces

Polynomial and exponential wear models of the joint effect of different combinations of component forces or ratios were fitted to determine the wear model that would give the best approximation of actual tool wear rates. Statistical analysis revealed the combination of force ratios: F ₁=F _f/F _t, F ₂=F _r/F _t and F ₄ = to have the highest statistical significance with tool wear rate based on F _cal and r ² statistics for both polynomial and exponential models, with the latter giving the best approximation of the actual tool wear rates. A wear map was established using the exponential wear model of the force ratios for the machining of a nimonic C-263 nickel-base alloy with PVD TiN/TiCN/TiN-coated carbide insert grade.     

Atmospheric effects of friction,friction noise and wear with silicon and diamond. Part III. SEM tribometry of polycrystalline diamond in vacuum and hydrogen

In this part III of a multi-part paper series, the results of additional SEM tribometric experiments are described, performed with polished, mostly C(100)-oriented polycrystalline CVD diamond film [PCD_C(100) vs. PCD_C(100)] counterfaces sliding in Torr and in 0.1–0.3 Torr partial pressures of pure hydrogen gas. These tests were completed under a 28 g (0.27 N) normal load, under standard and slow thermal ramping conditions at temperatures ranging from room temperature to 1000^°C. The friction data were examined per the computer logging and analysis techniques described in part I. The treatment of the data is similar to that of Si in part II: the maximum and the average coefficients of friction (MAX.COF and COF) and their ratios (the friction noise FN) are employed to measure possible lubricative interaction of the diamond surfaces with rarefied hydrogen. The results indicate that excited species of molecular hydrogen enter into tribothermally catalyzed reactions not only with Si but with PCD_C(100) surfaces as well. Similar to the behavior of Si, the most beneficial friction-reducing regime occurs in a temperature range just before the thermal desorption of adsorbates. The general magnitudes of MAX.COF, COF and the FN are significantly lower than those of the Si crystallinities, in both vacuum and . The wear rate of the PCD_C(100) film characteristic of the standard thermal ramping test procedure performed mostly in is around , in good agreement with the wear rate previously measured in vacuum for unpolished, fine-cauliflowered diamond films. The data indicate that smooth polycrystalline diamond is a significantly better bearing material for miniaturized moving mechanical assembly applications than Si. This revised version was published online in July 2006 with corrections to the Cover Date.     

Developing Algorithms for Estimating Strength on the Base of Imitating Structural Model of Acoustic Emission. II. Effect of Structural Inhomogeneity of a Material

The first part was dedicated to the theoretical basis for estimating strength characteristics of materials developed from the ideas that had been put forth in the earlier publications [1–5]. A formalized technique based on the earlier studies [2, 3] was also discussed. Its main assumption was that the material was homogeneous, and it enabled one to process real experimental data on a computer. This paper is devoted to the effect of structural inhomogeneities of materials, which is identified with a large spread of the parameter . This factor must be taken into account in a number of cases when the assumption that a tested body is structurally homogeneous does not apply.     

Cyclic Scheduling of Operations for a Part Type in an FMS Handled by a Single Robot: A Parametric Critical-Path Approach

We consider two problems of periodic scheduling of parts in a robotic production system functioning under a given repetitive robot's route. The objective is to determine the starting times and durations of processing operations so as to minimize the cycle length. We reduce the problems to finding parametric critical paths in networks with varying arc lengths. In contrast to previously known methods, which solve these cyclic scheduling problems in cubic time, the parametric network approach solves the problems in time, m being the problem size.     

Application of symbolic manipulation to inverse dynamics and kinematics of elastic robots

An inverse dynamics and kinematics of a flexible manipulator is derived in symbolic form based on the recursive Lagrangian assumed mode method. A PC-based program has implemented the algorithm to automatically generate the inverse dynamics and kinematics for an elastic robot in a symbolic form. A case study is given to illustrate how to use this program for inverse dynamic and kinematic generation. Simulation results for a case study by considering different mode shape are compared with the rigid case.Nomenclature A _i joint transformation relates systemi to systemi-1 - E _i link transformation relates the deflection of systemi to systemi - F _i joint torque acting on jointi - g gravity vector expressed at the base coordinates - J inertia = - K kinetic energy of the system - l _i length of linki - M _i a mass concentrated at the joint i - m _i number of modes used to describe the deflection of link i - n number of links - q _h joint variable of thehth joint - q _hk time-varying amplitude of mode k of link h - R vector of remaining dynamics and external forcing terms = - r _i vector locating the centre of mass of linki - R _j dynamics from the joint equation j, excluding second derivatives of the generalized coordinates - R _if dynamics from the deflection equation jf, excluding second derivatives of the generalized coordinates - V potential energy - W _i transformation from the base to theith link - transformation from the base to the systemî - z the vector of generalised coordinates = - link density     

Optimising tolerance allocation for mechanical components correlated by selective assembly

Selective assembly can enlarge the tolerances of mechanical components for easier manufacturing. However, the non-independent dimensions of correlated components make it difficult to optimise tolerance allocation for an assembly. This paper proposes a solution for this constrained optimisation problem consisting of tolerances and non-independent dimensions as design variables. The approach is to develop a simplified algorithm applying a Lagrange multiplier method to evaluate the optimal tolerances efficiently. The solution is shown to be a global optimum at the given correlation coefficients. The correlation coefficients are key elements in determining the optimal solution, which is demonstrated in the given examples. The results are helpful in designing tolerances for selective assembly.Notation A _j coefficient matrix off _j - B _i coefficient of cost function - C total manufacturing cost function - C _i manufacturing cost function forx _i - F _j thejth dimensional constraint function - f _j thejth quadratic constraint function - f quadratic constraint vector - H _j thejth Hessian matrix - J _kj element ofn×m Jacobian matrix - L Lagrangian - m number of assembly dimensions - n number of component dimensions - p number of equality dimensional constraints - T tolerance vector of component dimensions [mm] or [°] - tolerance ofx _i [mm] or [°] - tolerance ofZ _j [mm] or [°] - x component dimension vector - x midpoint vector - x _i component dimension [mm] or [°] - x _i midpoint ofx _i [mm] or [°] - Z _j assembly dimension [mm] or [°] - _j confidence coefficient forZ _j - _i confidence coefficient forx _i> - _j given design value ofZ _j [mm] or [°] - Lagrange multiplier vector - _j thejth Lagrange multiplier - * Lagrange multiplier vector at the optimum solution - correlation coefficient forx _i andx _k - _x standard deviation vector - _x ^* standard deviation vector at the optimum solution - _x ⁰ candidate point satisfying the constraintsf( _x ^* )=0 - standard deviation ofx _i      

Magnetic-Powder Inspection of the Crystallographic Texture of Electrical Steel

A theoretical model of the formation of rhombic (in the case of an edge texture) or square (on cubic texture) indicator patterns upon magnetization of single crystals of electrical steel orthogonally to the (110) and (100) planes is described. The model is based on a solution of Maxwell's equations for a magnetostatic problem, with magnetic permeability introduced as a tensor. Two field sources are considered as limiting cases: (a) loop, short coil; (b) semi-infinite magnet, long coil. Two cases of permanent magnet diameters are considered: thin, d = 4 mm; thick, d = 20 mm. Two cases of density of magnetic charges are considered: (a) = const; (b) = ₀/ .     

The Contribution of a Soft Thin (Metallic) Film to a Friction Pair in the Running-In Process

Analytical and experimental studies have been conducted on silver-film-covered and uncoated metallic surfaces to investigate the role of the soft, thin, metallic film in the running-in process. The experimental results have shown that a low coefficient of friction of about 0.22 and especially low wear can be obtained at the inception of sliding when there is a thin film. The analysis has shown that for the coated case the improvements can be obtained owing to the increase of the true area of contact and thus the reduction of contact pressures. In the presence of such a thin film, it has been pointed out that the friction force arises due to shear of the film and substrate instead of solely shearing of the film. Based on the experimental and analytical results, a new physical model for the film-covered case was proposed where a plastic deformation for the thin film was assumed. To account for the role of the film in preventing the substrate/pairing materials from wear, the effect of the coefficients of friction on the maximum shear stresses and maximum tensile stresses in the subsurface was calculated in light of the von Mises yield criterion .     

Atmospheric effects of friction,friction noise and wear with silicon and diamond. Part II. SEM tribometry of silicon in vacuum and hydrogen

Scanning electron microscope (SEM) tribometric data on polycrystalline silicon (poly-Si) vs. poly-Si, Si(100) vs. Si(100) and Si(111) vs. Si(111) interfaces, obtained in Torr and in 0.2 Torr partial pressure of hydrogen gas ( ) from room temperature to 850^°C, were performed under standard and much slower thermal ramping rates. The friction data were analyzed per the methodology described in part I of this paper series. The results indicate a highly beneficial friction- and wear-reducing regime within a relatively narrow thermal region. This desirable region coincides with some chemisorption of excited species of molecular hydrogen just before the mass thermal desorption of surface hydrides. These data represent the tribochemical equivalent of a method routinely used in electronics, whereby deep electron traps (dangling Si bonds) are passivated by baking in molecular hydrogen. The also exerts a moderating influence on the size of the friction noise at all test temperatures. However, the general level of friction beyond the beneficial thermal region is high. In parallel, the general wear rate of Si representative of the entire range of standard thermal ramping in both atmospheric environments is in the extremely high 10^-12m³/(N m) range. Operating strictly in the beneficial, low-friction thermal regime resulted in a several orders-of-magnitude reduction in the wear rate over those measured under standard thermal ramping conditions. Although the results confirm previous findings that Si is not a good material of construction for miniaturized moving mechanical assemblies (e.g., microbearings and gears), there seems to be some limited possibility of gas-phase lubrication of Si micromechanisms with rarefied hydrogen at surface temperatures between 100 and 300^°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of the diamond sawing process

There are three methods in use for separating diamonds, i.e. by cleaving, by laser beam and by sawing. Sawing is one of the main methods used for this purpose. This operation is carried out on special sawing machines equipped with a sawing disk blade, 0.04–0.14 mm thick and 76 mm initial diameter. The rotational velocity (n) of the disk is between 6000 and 12 000 r.p.m. Diamond powder is embedded in the periphery of the disk. The outcome surface of a diamond after the sawing operation must be flat and smooth, Whenever such a surface is actually obtained, the polishing time and the loss in size and weight of the diamonds are reduced.In the present work, the positioning of the diamond to be sawed, with respect to an embedded particle in the disk, to create a favourable cutting angle is discussed. This would make it possible to reduce the rake angle () to near-zero, and thereby the cutting forces. Furthermore, a method to control the morphology and grain size of the diamond powder to be used in the cutting was developed.In the diamond industry, two modes of sawing operations are in practice. One uses the periphery of the disk for the sawing while the other employs a circular hole in the centre of the disk. Analysis of the two modes showed that the hole mode is more promising, as the design in that case requires tensioning of the disk and makes for better lateral stability during the sawing process. In addition the tangential and the radial stresses, developed in both sawing methods, were calculated. To support the above, data was obtained from existing literature and analysed.Nomenclature n rotational velocity of the disk, r.p.m. - rake angle, degrees - back clearance angle, degrees - cutting angle, degrees - m relative frequency - f feed - b disk radius, mm - a disk hole radius, mm - r current disk radiusb>r>a, mm - density of disk material, kg m^–3 - angular velocity - Poisson ratio of disk material - g acceleration of gravity, m s^–2 - _r radial stress, kg cm^–2 - _{r max} highest radial stress, kg cm^–2 - _t tangential stress, kg cm^–2 - tangential stress at outside circumference, kg cm^–2 - tangential stress at inside circumference, kg cm^–2     

The effect of fluorination on the surface chemistry of alkyl ethers on Cu(111)

By using small fluorinated ethers as models for perfluoropolyalkylether (PFPAE) lubricants, we have been able to determine the effect of fluorination on the bonding of the alkyl ethers adsorbed on the Cu(111) surface. The desorption energies have been determined by using temperature programmed desorption (TPD). The model compounds studied were dioxolane , diethyl ether ((CH₃CH₂)₂O), dimethoxymethane ((CH₃O)₂CH₂), dimethyl ether ((CH₃)₂O) and their perfluorinated analogues. All of the molecules studied adsorb molecularly and reversibly on the Cu(111) surface exhibiting first-order desorption kinetics. Upon fluorination of the alkyl ethers, the adsorbate-metal bond was weakened by 14 to 8 kcal/mol. The intermolecular interaction parameters for the hydrogenated ethers indicated repulsive adsorbate-adsorbate interactions, while the fluorinated ethers have attractive adsorbate-adsorbate interactions.     

Chatter stability analysis for end milling via convolution modelling

This research discusses the methodology of developing a symbolic closed form solution that describes the dynamic stability of multiflute end milling. A solution of this nature facilitates machine tool design, machining parameter planning, process monitoring, diagnostics, and control. This study establishes a compliance feedback model that describes the dynamic behavior of regenerative chatter for multiflute tool-work interaction. The model formulates the machining dynamics based upon the interconnecting relationship of the tool geometry and the machining system compliance. The tool geometry characterises the cutting forces as a function of the process parameters and the material properties, while two independent vibratory modules, the milling tool and the workpiece, represent the machining system compliance. The compliance feedback model allows the development of a corresponding characteristic equation. By investigating the roots of the characteristic equation, this research symbolically expresses the stability of the system as a function of the cutting parameters, the tool geometry, the workpiece geometry, and the vibrational characteristics of the machine tool. Machining experimentation examining the fidelity of the regenerative chatter model is discussed. The dynamic cutting forces, cutting vibration, and surface finish of the machining process confirm the validity of the analytical prediction.Nomenclature b damping coefficient: mass-spring-damper representation - b _e equivalent damping coefficient: mass-spring-damper representation - C compliance element - CWD chip with density function - D diameter of cutter - d _a axial depth of cut - d _r radial depth of cut - average total cutting force - K _r radial specific cutting pressure constant - K _t tangential specific cutting pressure constant - k spring constant - k _e equivalent spring constant - m mass: mass-spring-damper representation - m _e equivalent mass: mass-spring-damper representation - n number of flutes on the cutter - p _x,y elemental cutting forces - P _1,2 elemental cutting force functions - R cutter radius - s Laplace variable - TS tooth sequencing function - chip thickness - t _c average chip thickness - t _x feed per tooth - helix angle - _x actual displacement of cutter tip - unit impulse function - _d damped circular frequency of vibration - damping ratio - spindle speed     

A near-wall reynolds stress model for backward-facing step flows

A near-wall Reynolds stress model has been used in numerical computations for two-dimensional, incompressible turbulent flows over backward-facing steps. Numerical results are compared with Direct Numerical Simulation data as well as experimental data for flow quantities such as the skin friction, wall pressure,U-velocity and the Reynolds stress. Budgets of the transport equations for theU-velocity, turbulence kinetic energy,k and the Reynolds shear stress,— are also calculated and compared with the Direct Numerical Simulation data. The comparison reveals that the near-wall Reynolds stress model predicts the reattachment length fairly accurately. The near-wall Reynolds stress model also predicts the development of the boundary layer downstream of the reattachment point correctly when the Reynolds number is low. However, the model generally predicts a weak separation bubble and a slowly developing boundary layer when the Reynolds number is high.     

Determining the process tolerances based on the manufacturing process capability

An efficient approach has been developed for determining the process tolerances. This approach simplifies the traditional procedures of tolerance chart balancing and takes into account the capability of the process producing the workpiece. A mathematical model, based on the modified rooted tree chart, has been established. By using the model, the process tolerance can be obtained effectively and accurately without the effort of finding the additional tolerances. The work done previously by Ngoi is examined and several drawbacks are identified. A comparison between the results generated by the proposed method and by Ngoi is also made.Notation d _i additional tolerance to be added - f _j jth functional relationship betweent _i andd _i - m the number of blueprint specifications - n the number of operations - r _i the failure rate - estimated standard deviation ofith operation - T _i initial tolerance - TB _j blueprint tolerance - TP _i upper limit of process tolerance - _i process tolerance for operationi - x _i standardised process tolerance - w _i weighting value - Z the minimum value amongx _i      

Feasibility of NDT of Ferromagnetic Steel Structures Based on Measurements of Residual Magnetization as a Function of Elastic Stress

Algorithms for estimating elastic stress in ferromagnetic steel structures are based on measurements of the residual magnetization M _r as a function of tensile and compressive stress ₀ after quenching and tempering at different temperatures T _tem. The suggested testing technique is highly sensitive because the range of M _r (₀) is fairly wide (for the interval 0.6_{y 0} –0.6_y, where _y is the yield limit, the range is 600–800 kA/m). The necessary condition for using this testing technique is the availability of calibration curves for the selected testing algorithm measured on samples of steels to be tested (i.e., of the same sort of steel tempered at the same temperature). All the testing algorithms suggested in the paper enable one to determine both the magnitude and sign of the stress in the material.     

Procedures for testing manufacturing precision Cpbased on (\bar{x},R) or (\bar{x},S) control chart samples

Process precision index C_p has been widely used in the manufacturing industry for measuring process potential and precision. Estimating and testing process precision based on one single sample have been investigated extensively. In this paper, we consider the problem of estimating and testing process precision based on multiple samples taken from ( ,R)or ( ,S)control chart. We first investigate the statistical properties of the natural estimator of C_p and implement the hypothesis testing procedure. We then develop efficient MAPLE programs to calculate the lower confidence bounds, critical values, and p-values based on m samples of size n. Based on the test, we develop a step-by-step procedure for practitioners to use in determining whether their manufacturing processes are capable of reproducing products satisfying the preset precision requirement.