On the causes of the formation of a maximum in the dependences of the coercive force of simple carbon steels on the tempering temperature

The dependences of the coercive force H _c of quenched specimens made of simple carbon steels on the tempering temperature T _t were measured at room and liquid-nitrogen temperatures. These studies showed that the formation of the character of H _c(T _t) dependences for the mentioned steels within the region of medium and high tempering temperatures is caused by the content of cementite and its magnetic hysteresis properties.     

Magnetic Testing of Stressed State of Hydrotested Gas-Separator Wall

The stressed state of a hydrotested gas separator has been studied by magnetoelastic demagnetization. Correlation dependences are obtained between the level of magnetoelastic demagnetization of a complex-loaded gas-separator wall and the magnitude of hoop, meridian, and equivalent stresses it experiences. The magnetoelastic demagnetization of a residually magnetized test-object wall, loaded with internal pressure, was estimated from the change in the strength of its magnetic stray field measured along the normal (H_n) and tangent (H_τ) to the surface. It has been established that the growth of mechanical stresses in the separator wall to half the value of the yield strength of steel it is made of causes a noticeable irreversible decrease in the normal (H_n) and tangential (H_τ) components of the strength of its magnetic stray field in the residually magnetized area. It is shown that the method of magnetoelastic demagnetization has the highest sensitivity to mechanical stresses and is easiest to implement and most prompt compared with coercimetry and tensometry.

     

Analysis of force patterns and tool life in milling operations

The paper describes the practical effects of the operating parameters in the milling operation. Experiments have been conducted to measure cutting force and tool life under dry conditions. Based on the experimental results, three mathematical models have been developed: Force, TLife and Force/TLife. Further analyses have been conducted on the cutting force patterns: seasonal pattern and nonlinear trend. A process optimisation that is based on the minimum production cost has been applied to relate Force model, TLife model and machinability criteria, such as power consumption, cutting parameters and surface roughness.Nomenclature C _w cost of workpiece ($) - C _s set-up cost ($) - C _m machining cost ($) - C _o overhead cost ($) - C _r tool replacement cost ($) - C _t tool cost ($) - D diameter of the cutter (inch) - d depth of cut per pass (inch) - d ₀ required depth (inch) - e _t random error attth sample - F cutting force (N) - f feedrate (ipm) - L length of workpiece (inch) - N spindle speed (r.p.m.) - n number of teeth - P power of the motor (h.p.) - R surface roughness (µm) - R _e real part of a complex function - T tool life (min) - t sample number - t _m machining time (s) - t ₀ overhead time (s) - t _r tool replacement time (s) - t _s set-up time (s) - U _i unit cost of itemi ($/unit)v - v cutting speed (i.p.m.)     

The Additive Action of Some Organic Chlorides and Sulfides in the Four-Ball Lubricant Test

When tested by the four-ball extreme-pressure procedure, oil solutions of t-octyl chloride at the 2 percent chlorine level rated approximately equal to oil solutions of di-t-octyl disulfide at the 2 percent sulfur level, and both of these additive blends rated better than n-octyl chloride in oil at the 2 percent chlorine level or di-n-octyl disulfide in oil at the 2 percent sulfur level. n-Octyl chloride and di-n-octyl disulfide in oil at corresponding concentrations of active element were approximately equivalent in additive action. t-Octyl chloride was almost as good at the 1 percent as at the 2 percent chlorine level. Mixtures of di-t-octyl disulfide and t-octyl chloride in oil at the level 1 percent S-1 percent Cl rated approximately twice as well as di-t-octyl disulfide (2 percent S) or t-octyl chloride (2 percent Cl). Some finer points of the action of these additives were investigated by studying time-connected behavior at 50-kg and 100-kg loads. The action of the additives cannot be explained on the basis of their chemical structures only; interactions with the rubbing process in the four-ball machine also must be considered.     

Ionic liquids as lubricants of polystyrene and polyamide 6-steel contacts. Preparation and properties of new polymer-ionic liquid dispersions

Room-temperature ionic liquids (ILs) have been used as external lubricants in polystyrene (PS) and polyamide 6 (PA6)-steel contacts and as internal lubricants in new polymer-IL dispersions. 1−C _n H_2n+1−3−CH₃-imidazolium X⁻ [X=BF₄; n=2 (IL1), 6 (IL2), 8 (IL3). X=PF₆; n=6 (IL4). X=CF₃SO₃; n=2 (IL5). X=(4−CH₃C₆H₄SO₃); n=2 (IL6)] ionic liquids give low friction and extremely mild wear in PS/AISI 316L stainless steel contacts, independently of IL composition. For AISI 52100 steel pins a tribocorrosion reaction produces FeF₂ and increases friction. PS+IL1 (1; 1.35; 3 wt.% IL1) dispersions show lower dry friction and wear against AISI 52100 as IL1 proportion increases, but the lowest friction, with a one order of magnitude reduction with respect to PS, is reached for PS+1%IL1 once the skin layer has been worn out. Increasing IL1 content to 10 wt.% produces an heterogeneous material with non-uniform IL distribution. IL4 reduces friction and wear in PA6+3%IL4 dispersions against AISI 316L, although the lowest values are obtained with IL4 as external lubricant. The cryofracture surfaces of the polymers have been examined and the thermal stability of the polymers in the presence of ILs has been determined.     

Resistive loss compensation in the power supply system of the toroidal field winding in the TUMAN-3M tokamak

In the tokamak, in which the winding generating the toroidal field with induction B _t is powered from an inductive energy storage, resistive losses are the main factor that causes B _t to decrease during a discharge. Upgrading of the power supply circuit of the toroidal magnetic field winding (TFW) in the TUMAN-3M tokamak is aimed, primarily, at increasing B _t in the injection heating phase and, second, at maintaining B _t quasi-stationarity during the whole tokamak discharge. To do this, an additional two-section capacitive storage commuted by two thyristor switches has been introduced into the available circuit. Either section of the storage is characterized by a charging voltage of 0.25 kV, a capacitance of 4.32 F, and an energy capacity of 135 kJ. The maximum discharge current of the section is 40 kA. The upgraded circuit compensates for the resistive loss in the TFW and ensures thereby a 50% increase in the magnetic field during injection heating relative to the old circuit: B _t = 1.0 T instead of 0.68 T. In this case, the circuit maintains a TFW current of 110 kA with an accuracy of 10% for ∼60 ms.     

Prediction of tool failure rate in turning hardened steels

This paper presents a stochastic model for predicting the tool failure rate in turning hardened steel with ceramic tools. This model is based on the assumption that gradual wear, chemical wear, and premature failure (i.e. chipping and breakage) are the main causes of ending the tool life. A statistical distribution is assumed for each cause of tool failure. General equations for representing tool-life distribution, reliability function, and failure rate are then derived. The assumed distributions are then verified experimentally. From the experimental results, the coefficients of these equations are determined. Further, the rate of failure is used as a characteristic signature for qualitative performance evaluation. The results obtained show that the predicted rate of ceramic tool failure is 20% (in the first few seconds of machining) and it increases with an increase in cutting speeds. These results indicate that there will always be a risk that the tool will fail at a very early stage of cutting. Such a possibility should not be overlooked when developing proper tool replacement strategies. Finally, the results also give the tool manufacturers information which can be used to modify the quality control procedures in order to broaden the use of ceramic tools.Nomenclature c constant - ch chamfer width of the tool, mm - d depth of cut, mm - h _i hardness value at theith location on the workpiece during machining - h mean ofh ₁,h ₂,h ₃, ...,h _nn - n hardness mean location - m Meyer exponent determined experimentally to define the nonlinear relation between the cutting force and the ratioh _i/h - f feedrate, mm rev^–1 - f(t) probability density function of tool failure - f ₁(t) probability density function of tool failure due to breakage caused by tool quality - f ₂(t) probability density function of tool failure due to breakage caused by workpiece condition - f ₃(t) probability density function of tool failure due to tool chipping caused by chemical wear - f ₄(t) probability density function of tool failure due to flank wear - f ₅(t) probability density function of tool failure due to crater wear - O() error - t cutting time, min - x ₁,x ₂,...,x _n independent variables - A _i instantaneous area of contact between the tool and the workpiece - C ₁ chip load, which can be determined as a function of the cutting conditions and tool geometry - K _I crater wear index - K _T maximum depth of crater wear on tool face, mm - K _M crater centre distance, mm - N number of failures - P(t) probability function of tool failure - P _j(t) corresponding probability of failure, such that 1j5 - R tool nose radius, mm - R(t) reliability function - R _j(t) corresponding reliability function, such that 1j5 - T _V estimate of tool life for a set value of average flank wear (V _B ^* ) - T _K estimate of tool life for a set value of maximum depth of crater wear (K _T ^* ) - V cutting speed, m/min - V _B average tool wear, mm - Z(t) instantaneous failure rate or hazard function - ₃ shape parameter in the Weibull probability density function - rake angle - ₃ scale parameter in the Weibull probability density function, min - failure rate of the cutting tool - mean of a logarithmic normal distribution function - standard deviation of a logarithmic normal distribution function - tool wear function - time corresponding to the occurrence of tool failure - (.) standard logarithmic normal distribution function     

An extrapolation method for the determination of Cliff-Lorimer kAB factors at zero foil thickness

An extrapolation method is proposed to be useful for the determination of the Cliff-Lorimer k_AB factor at zero foil thickness. The method consists of measuring k_AB factors as a function of the measured foil thickness, t_M, and extrapolating the relationship toward t_M=0. The intersection between the extrapolated line and the ordinate of t_M=0 gives (k_AB)₀ which is free from the effect of absorption. The straight line extrapolation that can be achieved by a linear-least squares method is particularly developed to eliminate arbitrariness introduced in the extrapolation process. The extrapolation method is applied to data available in the literature. It is shown that the method yields the (k_AB)₀ factors compatible with those predicted from the theoretical calculation. It is also shown that this method can circumvent several problems which make it complex and difficult to determine accurate values of the absorption-free k_AB factors. Using the straight line extrapolatioin, it is possible to estimate the degree of the thickness overestimation which arises when the foil thickness is measured by the contamination spot separation (CSS) method. Validity of the straight line extrapolation is further discussed.     

Effect of Hardness Ratio on the Wear Performance and Subsurface Evolution of Ni3Al Matrix Composites

A favorable hardness ratio (H_disk/H_pin = H_d/H_p) could lead to a transition to mild wear during sliding contact. To determine a more appropriate H_d/H_p value for the sliding wear, the dry sliding pin-on-disk wear tests of Ni₃Al matrix composites (NMCs) with multilayer graphene (MLG) are undertaken at H_d/H_p values of 0.99, 0.83, 0.42, and 0.35 at sliding speeds of 0.1, 0.3, 0.5, and 0.7 m/s. It is found that the tribological properties of NMCs are strongly affected by the various hardness ratios. At 0.1 m/s, the friction coefficient decreases with a decrease in H_d/H_p value. The low friction coefficient is 0.14 and the wear rate is 0.9 × 10^?5 mm³ N^?1m^?1 under the ceramic counterpart with H_d/H_p of 0.35. At 0.7 m/s, the tribological properties show the opposite trend with a decrease in H_d/H_p. At an H_d/H_p of 0.35, the smooth compact layer on the worn surface could decrease the friction at 0.1 m/s, and the improved hardness in the subsurface by strain hardening would play an important role in the improvement of wear resistance. Under the metal counterpart with H_d/H_p of 0.99, plastic deformation only occurs on the contact surface and the MLG could suppress further shear deformation in the subsurface, leading to a low wear rate (2.4 × 10^?5 mm³ N^?1m^?1) and friction coefficient (0.15) at 0.7 m/s.     

The expected volume of a random polytope in a ball*

For any convex body K in d-dimensional Euclidean space E^d(d≥2) and for integers n and i, n ≥ d + 1,1 ≤ i ≤ n, let V^(d)_n-ii(K) be the expected volume of the convex hull H_{n-i, i} of n independent random points, of which n-i are uniformly distributed in the interior, the other i on the boundary of K. We develop an integral formula for V^(d)_{n-i, i}(K) for the case that K is a d-dimensional unit ball by considering an adequate decomposition of V^(d)_n-i, i into d-dimensional simplices. To solve the important case i = 0, that is the case in which all points are chosen at random from the interior of B_d, we require in addition Crofton's theorem on mean values. We illustrate the usefulness of our results by treating some special cases and by giving numerical values for the planar and the three-dimensional cases.     

Baseline correction of AFM force curves in the force–time representation

This note reports on the proper correction of force data acquired with an atomic force microscope (AFM). The force–time representation is hereby used to obtain the correction factors for the overall offset and slope for a single force–time curve, as the initial force, F₀ = F(t₀), and the rate of change in the force per unit of time, dF/dt, respectively. The report shows that a complete set of force data, including the approach, delay and retraction regions, can be simultaneously corrected in the force–time representation by subtracting the line CL_t = F₀ + dF/dt·t to the experimental data. The method described here outperforms the one commonly employed in the correction of AFM force curves and highlights the convenience of using the force–time representation for force data processing wherein the artifactual behavior can be expressed as a single, differentiable function of time.     

Problems of Evaluation of the Flaw Parameters in the Magnetic Nondestructive Testing

The magnetic leakage fields are investigated experimentally on rectangular-slit aw models for various magnetizing fields H ₀. It is shown that in certain cases the aw parameters can be incorrectly classified as a result of coincidence of their leakage fields. This is associated with both the choice of the magnetizing fields H ₀ and the effect of the aw width on the dependence of the aw field on H ₀: for wide aws this dependence is close to a linear function, whereas for narrow aws the dependence tends to the magnetization curve of the sample.     

Solute-enriched surface layers and X-ray microanalysis of thin foils of a commercial aluminium alloy

Thin foils of the commercial Al alloy 7075 were subjected to X-ray microanalysis in a Jeol 100 CX TEMSCAN using a modified double-tilting stage. The ratio of the Cu K_x and Al K_x peaks, I_cu/I_Al, was found to decrease rapidly with increasing foil thickness, t, in regions thinner than about 200 nm. This was attributed to the formation of surface layers enriched in Cu during electropolishing, consistent with the findings of other investigators. An equation predicting the variation of I_B/I_A with t in an A-rich alloy in which B (or additional solute elements) is dilute is derived for a sample with surface layers enriched in B. The derivation predicts that I_B/I_A should vary linearly with t^?1, and that the intercept of such a plot should be positive. It is suggested that consistency with this prediction serves as a criterion for true surface enrichment. Our data on Cu obey these predictions, and further analysis indicates that the layers on both surfaces are enriched by a factor of about 5.6. The ratio of the intensities of the Zn K_x and Al K_x X-ray peaks was found to be nearly independent of foil thickness to t?400 nm. This result, combined with additional analysis, indicates that the apparent enrichment observed by other investigators is most likely due to the influence of instrumental factors.     

Optimization of micro-EDM drilling of inconel 718 superalloy

In this study, the gray relational analysis method was used to optimize the micro-electrical discharge machining (EDM) drilling process of Inconel 718 nickel-based superalloy with multiperformance characteristics. In order to determine the best factor level conditions, a full factorial experimentation was performed based on the micro-EDM parameters of discharge current and pulse duration. The hole taper ratio (H _t) and hole dilation (H _d) were the measured performances. By analyzing the used optimization results, it was observed that the pulse current was more efficient on performance characteristics than pulse duration. The characteristics of drilled surfaces and tool electrodes were also investigated by using optical and scanning electron microscopy. A linear regression model was developed to estimate the performances. The measured and model results were in a good agreement with correlation coefficients of R ²?=?0.897 and R ²?=?0.929 for H _t and H _d, respectively. It is concluded that the EDMed hole quality can be improved effectively through this approach.     

A methodology for assessing manufacturing cost due to tolerance of aerodynamic surface features on turbofan nacelles

A component of the direct operating cost of aircraft is that associated with the manufacturing cost. This affects depreciation, interest, insurance and maintenance charges. By relaxing the requirements for aerodynamic surface smoothness the manufacturing cost can be reduced at the expense of an increase in drag and corresponding fuel costs. This work is part of a study to examine this multidisciplinary problem. Only isolated turbofan nacelles are considered. The costs associated with assigning different tolerance levels to the feature dimensions on nacelles are assessed. A statistical procedure is employed to estimate the cost-tolerance relationship for eleven features involving gaps, steps, surface profile and fastener flushness. This procedure requires actual manufacturing and cost source data. A knowledge of the cost-tolerance relationships is useful in a concurrent engineering context. It will allow aerodynamicists to optimise surface smoothness in consultation with production engineers, thus achieving the best compromise between cost and drag.Nomenclature A ₁ statistic distribution area to the left ofL ₁ - A _u statistic distribution area to the right ofL _u - C manufacturing cost (£/piece) - C _a assembly process manufacturing cost (£/piece) - C _c cost per concession (£/concession) - C _ci interface component edgei manufacturing cost (£/piece) - C _i interface manufacturing cost (£/piece) - C _lmh labour man hour cost (£/piece) - C _ma management cost (£/piece) - C _mh man hour cost (£/h) - C _mmh management man hour cost (£/piece) - C _nr non-recurrent cost (£/piece) (cost of all the jigs and tools used in the assembly process divided by the number of units produced) - C _rd redeployment cost (£/piece) - C _smh skilled worker man hour cost (£/h) - C _su support cost (£/piece) - C _sumh support man hour cost (£/h) - C _usmh unskilled worker man hour cost (£/h) - C ₀ initial manufacturing cost (£/piece) - d _tma t _ma parameter - d _{N c} N _c parameter - d _{O f} O _f parameter - d _{t r} t _r parameter - d _{t rd} t _rd parameter - d _{t su} t _su parameter - E _i interface edgei - F _i featurei - G interface gap (mm) - G _n interface gap normal to air flow (mm) - G _p interface gap parallel to air flow (mm) - L _ef production line loss of efficiency factor due to redeployment - L ₁ dimension lower specified limit (mm) - L _u dimension upper specified limit (mm) - M mean - N dimension nominal value (mm) - N _c number of concessions (concession/piece) - O _f worker overtime fraction - P surface profile deviation (mm) - R _on ratio between the worker overtime and the normal man hour cost - S interface step or fastener flushness (mm) - standard deviation - S _n interface step normal to air flow (mm) - S _p interface step parallel to air flow (mm) - T manufacturing tolerance (mm) - T _a assembly process manufacturing tolerance (mm) - t _bw basic work time (hour/piece) - T _ci interface component edgei manuacturing tolerance (mm) - T _i interface tolerance (mm) - t _ma management time (hour/piece) - T _p performance tolerance - t _r rework time (h/piece) - t _rd worker redeployment time to other production line stations different to the usual one (h/piece) - t _su support time of the methods, quality and design departments to the line (h/piece) - T _t tolerance threshold between skilled and unskilled worker employment (mm) - T ₀ initial manufacturing tolerance (mm)     

Evaluation of the Current Condition and the Residual Lifetime of Forming Rolls Using the Magnetic Method of Nondestructive Testing Based on the Coercive Force

The magnetic method on the basis of the coercive force H_c is proposed to use for estimating the current condition and the residual lifetime of forming rolls. Sixty rolls have been tested. It is shown that H_c increases almost twice in exploiting the roll from the beginning of the operation to reaching the limit of its lifetime. Results of observation of the degree of nonuniformity of the H_c distribution over the roll surface in the operation process are given. The results of investigation make it possible to optimize the path of each roll through the mill stands in order to avoid the stress concentration at the same depth of the roll operating (magnetic) coating in the roll change process. Using the magnetic testing method based on H_c makes it possible effectively to estimate the current condition of accumulation of the fatigue in the roll operating (magnetic) coating.     

Convergence characteristics of the Crank-Nicolson-Galerkin scheme for linear parabolic systems

This paper is concerned with the investigation on the stability and convergence characteristics of the Crank-Nicolson-Galerkin scheme that is widely being employed for the numerical approximation of parabolic-type partial differential equations. Here, we present the theoretical analysis on its consistency and convergence, and we carry out the numerical experiments to examine the effect of the time-step sizeΔ _t on theh- and ρ-convergence rates for various mesh sizesh and approximation ordersρ. We observed that the optimal convergence rates are achieved only when Δt,h andρ are chosen such that the total error is not affected by the oscillation behavior. In such case,Δ _t is in linear relation with DOF, and furthermore its size depends on the singularity intensity of problems.     

Determination of the Minority Carrier Surface Thermogeneration Rate in Metal-Oxide-Semiconductor Structures

A metal-oxide-semiconductor (MOS) structure with the common field electrode insulated from the semiconductor by oxide layers h of different thicknesses allows the surface generation rate of minority charge carriers from current I(t) of nonequilibrium depletion state relaxation to be found. At the same time, it is possible in similar structures to observe the kinematics of electron-hole pair generation at the periphery of the field electrode (the edge generation effect). Measurements performed on an n-Si MOS structure with a stepwise change in oxide layer thickness (h ₁ = 100 Å and h ₂ = 3200 Å) allowed the generation rate at both the initial transient (t ∼ 10⁻⁵ s) stage of surface generation (4.34 × 10¹⁰ cm⁻² s⁻¹) and at the basic extremely slow stage (10.4 cm⁻² s⁻¹) to be reliably determined for the first time. The estimated peripheral generation rate of minority charge carriers (holes) was 7.8 × 10¹¹ cm⁻² s⁻¹.__________Translated from Pribory i Tekhnika Eksperimenta, No. 4, 2005, pp. 84–88.Original Russian Text Copyright © 2005 by Chucheva, Zhdan, Akhmedov, Kukharskaya.     

The effect of tempering temperature on the coercive force of high-carbon steels measured at room temperature and a temperature above the curie point of cementite

The role of cementite in the formation of the H _c of carbon steels after quenching and tempering is determined based on analysis of dependences of the coercive force of У9A steel in the measurement temperature range from the temperature of liquid nitrogen to the cementite Curie point. It is shown that the key contribution to the formation of the maximum in the H _c (T _temp) dependence measured at room temperature is due to the magnetic hardness of cementite, whose maximum lies at T _temp = 500°C. The coercive force measured at 250°C is mainly related to the interaction of the domain walls of the ferrite matrix with nonferromagnetic inclusions of cementite, the maximum of which is at T _temp = 400°C, thus causing a shift of the maximum in the H _c (T _temp) dependence measured at the temperature above the cementite Curie point toward lower tempering temperatures.     

The effect of cementite on the formation of the magnetic hysteresis properties of thermally treated carbon steels

The role of cementite in the mechanisms of formation of the coercive force of high-purity 60 and 13 model steels and 9A and 12A industrial steels after quenching and subsequent medium- and high-temperature tempering is determined from the analysis of the temperature dependences of the coercive force. It is shown that cementite as a hard-magnetic phase plays an important part in the formation of the dependence H _c (T _temp) measured at room temperature. The maximum contribution caused by the coercivity of cementite to H _c of the model steels is proportional to the volume content of cementite. In the industrial steels, an effect on the coercivity of cementite is produced by carbideforming unavoidable impurities.