Experimental investigation and optimization of EDM process parameters for machining of aluminum boron carbide (Al–B4C) composite

This study investigates the effect of electric discharge machining (EDM) process parameters [current, pulse-on time (T_on), pulse-off time (T_off) and electrode material] on material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) during machining of aluminum boron carbide (Al–B₄C) composite. This article also summarizes a brief literature review related to aluminum metal matrix composites (Al-MMCs) based on different process and response parameters, work and tool material along with their sizes, dielectric fluid and different optimization techniques used. The MMC used in the present work is stir casted using 5% (wt) B₄C particles of 50 micron size in Al 6061 metal matrix. Taguchi technique is used for the design of experiments (L₉-orthogonal array), while the experimental results are analyzed using analysis of variance (ANOVA). Response table for average value of MRR, EWR and SR shows that current is the most significant factor for MRR and SR, while electrode material is most important for EWR. ANOVA also confirms similar results. It is also observed that the optimum level of process parameters for maximum MRR is A₃B₁C₃D₃, for minimum EWR is A₁B₂C₃D₁, and for SR is A₁B₃C₃D₃.     

Influence of structural features of welded joints of low-alloy steels on magnetic and micromagnetic properties

Variations of magnetic (coercive force H _c , residual induction B _r , maximum magnetic permeability μ_max, maximum magnetic-permeability field H _μmax, saturation magnetization J _max) and micromagnetic (number of pulses N and RMS Barkhausen-noise amplitude U) characteristics along the parent metal-welded joint direction were studied for welds of steels 10XCHД, 15XCHД, 09Γ2C, and X70.     

SIMULTANEOUS ETHANE AND ETHYLENE DETECTION USING A CO-OVERTONE LASER PHOTOACOUSTIC SPECTROMETER: A NEW TOOL FOR STRESS/DAMAGE STUDIES IN PLANT PHYSIOLOGY

Abstract

The simultaneous measurement of the C₂H₆ and C₂H₄ emission by plant material is known to be a good stress/damage indicator. A photoacoustic spectrometer, utilizing the CO-Overtone laser, has been used for such measurements for the first time. For the simultaneous online detection of C₂H₆ and C₂H₄ in plant physiological studies, a sensitivity was achieved of 370 ppt and 2 ppb, respectively. The performance of the system has been demonstrated measuring the stress/damage behaviour of rhododendron leaves after the application of freezing stress.     

Frictionally excited thermoelastic instability in viscoelastic and poroelastic media

Friction materials commonly used in sliding applications, such as clutches and brakes, can be poroelastic and exhibit a viscoelastic behaviour. To the author's knowledge, there are no comprehensive analysis of the influence of poroelastic and viscoelastic material properties on the onset of the phenomenon of frictionally excited thermoelastic instability in sliding systems. This issue is here analysed in some details. Firstly, a linear standard model for the friction material is adopted, introducing an effective complex dynamic modulus E=|E|e^jδ and individuating three independent parameters, E₁, E₂/E₁ and c₂/E₁, that fully describe its viscoelastic behaviour. Subsequently, a similarity between viscoelastic and poroelastic formulation is presented and the three independent parameters introduced are related to the viscosity of the fluid μ_f, the permeability k_p and elastic properties M, α_B of the porous material.The linear elastic formulation proposed by Decuzzi et al. (ASME J. Tribiol. 2001;123:865) has been modified in order to take account of the new constitutive model and the variation of the critical sliding speed with the wave parameter, and viscoelastic/poroelastic properties of the material are examined.It has been found that the susceptibility towards thermoelastic instability increases by increasing both the elastic E₂/E₁ and viscoelastic c₂/E₁ parameters, or by increasing the Biot modulus M and effective stress coefficient α_B, the viscosity μ_f of the fluid, and by reducing the permeability k_p of the porous skeleton. It has been shown that for porous friction materials employed in wet clutches which are weakly viscoelastic, the neglect of its poroelastic behaviour leads to an overestimation of the critical speed smaller than 10%. However, much larger variations are predicted for elastomeric and porous materials with more pronounced viscoelastic behaviour.     

Investigation of impact of solid particles against hardmetal and cermet targets

The objective of the present work is to investigate and discuss some features of the surface damage and material removal process during particle-wall collision of the solid particles and hardmetal and cermet targets. The restitution parameters of TiC-base cermets, WC–Co hardmetals and glass of different composition and properties have been investigated. In order to clarify the details of the impact of glass spheres and corundum particles of irregular shape on a solid half-space, the process of interaction of solid particle with target was studied using a Laser Doppler Anemometer (LDA) measuring technique. Targets were impacted with particles over the range of impact velocities (7–50 m s⁻¹) at impact angle 67°. The experimentally observed variations of the coefficient of velocity restitution as a function of the test material properties, impact velocity and hardness ratio (H_m/H_a) are adequately explained on the basis of a theoretical model. Systematic studies of the influence of the impact variables on the collision process have been carried out.     

The sectorial co-ordinate of elastic-ideally-plastic beams of three thin-walled open cross-sections

A beam lamina of thin-walled open cross-section is considered. The sectional forces are a bimoment B and a Vlasov torsional moment M_w. The material is assumed to be elastic-ideally-plastic. The change in sectorial co-ordinate with increasing bicurvature is studied for three frequently used cross-sections.     

Vlasov torsion of elastic-ideally-plastic beams of thin-walled open cross-section

Prismatic beams of thin-walled open cross-section are studied. The sectional forces are a bimoment B and a Vlasov torsional moment M_w. The material is assumed to be elastic-ideally-plastic. Special consideration is given to the monosymmetric I-section. Exact and approximate solutions are derived for a cantilevered I-beam. These solutions are compared in a numerical example.     

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.     

Standards for quantification of elements in the otolithic membrane by electron probe X-ray microanalysis: Calibration curves and electron beam sensitivity

An absolute quantitative standardization technique has been developed to measure Ca and K weight fractions (WF) in the otolithic membrane of the saccule and utricle by scanning electron microscopy and electron probe X-ray analysis using the peak-to-background (P/B) ratio method. Microcrystalline salt standards were used to calibrate Ca and K Kα P/B or Y = (P/B) · Z²/A (Z = atomic number; A = atomic weight) against WF at 10, 15, 20 and 25 kV accelerating voltage. The effect of voltage on the calibration, plotting the coefficient of correlation (r) as a function of voltage, was not dependent on the voltage in the range 10–25 kV for Ca standards. K standards were also independent when P/B was corrected for Z²/A. Background counts in the otoconia (B_o) were obtained at 5, 25, 50, 100, 200 and 500 s and used to test the electron beam sensitivity of saccular and utricular otoconia. B_o was not dependent on the spectra acquisition time, with the exception of B_o under Kα K peak in the saccule at 10 kV. Ca and K WF were determined at 10, 15, 20 and 25 kV in the saccule and utricle, showing similar values regardless of the voltage used. This method of calibration offers several advantages, such as stability, homogeneity, known composition of the standards, high reproducibility at different voltages even without Z²/A correction and the similarity between the otoconia and crystal standards. We recommend the application of this method for other elements and biomineral systems.     

Analysis of spatial vapor-phase distribution using the LIF method on multi-component fuel

We analyzed the vapor-phase distribution and behavior of each component in multi-component fuel (MCF). Evaporation characteristic of MCF was researched by laser-induced fluorescent (LIF) method. A pulsed Nd-YAG laser was used as incident light, and an experiment was performed in a constant-volume vessel so that optical measurement could be possible. MCF was injected through electronically controlled common rail injector into the vessel. I-octane (C₈H₁₈), n-dodecane (C₁₂H₂₆) and n-hexadecane (C₁₆H₃₄) were selected to be low boiling point (LO-B.P.), mid boiling point (MI-B.P.) and high boiling point (HI-B.P.) components, respectively, and Fuel A, Fuel B and Fuel C, made by compounding those components at different mass fractions, were used as MCF. Experimentation was performed under the conditions that injection pressures were 42MPa, 72MPa and 112MPa, respectively, ambient gas density was 15kg/m3 and ambient gas temperature was 700K. The spatial vapor-phase distribution, dispersion process of mixture, and vaporphase homogeneity were researched. It was ascertained that the vapor-phase of MCF showed stratified distribution and the dispersion of mixture was improved in proportion to the mass fraction of the LO-B.P. component.     

Vlasov torsion of non-linearly elastic beams of thin-walled open cross-section

A beam lamina of thin-walled open cross-section is considered. The sectional forces are a bimoment (warping moment) B and a Vlasov torsional moment M_w. A formula for the sectorial co-ordinate containing three unknowns and being suitable for numerical calculations is given. The material is assumed to be non-linearly elastic with the constitutive equation = K|σ|ⁿ sgn σ in uniaxial tension. The relation M_w = B′ is shown to hold also for n ≠ 1. The location of the centre of twist as a function of n is determined for a monosymmetric I cross-section. The torsion-bending analogue for beams is found to be valid also for n ≠ 1.     

The sectorial co-ordinate of non-linearly elastic beams of three thin-walled open cross-sections

A beam lamina of thin-walled open cross-section is considered. The sectional forces are a bimoment B and a Vlasov torsional moment M_w. The material is assumed to be non-linearly elastic with the constitutive equation = K|σ|ⁿ sgn σ in uniaxial tension. A slight redefinition of the generalized sectorial moment of inertia I⁽ⁿ⁾_ω is given. The sectorial co-ordinate as a function of n is determined for three commonly used cross-sections.     

Dependence of the Detectability of Flaws on the Distribution of the Magnetizing Field in the Vicinity of a Flaw

It is shown that the flaw detectability of the magnetic-powder inspection method depends on the ratio of the normal H _n and tangential H _t components of the field in the flaw's vicinity and that H _n/H _t < 3 is a condition that ensures the detectability of surface flaws.     

Third-order aberration theory of Wien filters for monochromators and aberration correctors

Third-order aberrations at the first and the second focus planes of double focus Wien filters are derived in terms of the following electric and magnetic field components – dipole: E₁, B₁; quadrupole: E₂, B₂; hexapole: E₃, B₃ and octupole: E₄, B₄. The aberration coefficients are expressed under the second-order geometrical aberration free conditions of E₂ = −(m + 2)E₁/8R, B₂ = −mB₁/8R and E₃R²/E₁ − B₃R²/B₁ = m/16, where m is an arbitrary value common to all equations. Aberration figures under the conditions of zero x- and y-axes values show very small probe size and similar patterns to those obtained using a previous numerical simulation [G. Martínez & K. Tsuno (2004) Ultramicroscopy, 100 , 105–114]. Round beam conditions are obtained when B₃ = 5m²B₁/144R² and (E₄/E₁ − B₄/B₁)R³ = −29m²/1152. In this special case, aberration figures contain only chromatic and aperture aberrations at the second focus. The chromatic aberrations become zero when m = 2 and aperture aberrations become zero when m = 1.101 and 10.899 at the second focus. Negative chromatic aberrations are obtained when m < 2 and negative aperture aberrations for m < 1.101. The Wien filter functions not only as a monochromator but also as a corrector of both chromatic and aperture aberrations. There are two advantages in using a Wien filter aberration corrector. First, there is the simplicity that derives from it being a single component aberration correction system. Secondly, the aberration in the off-axis region varies very little from the on-axis figures. These characteristics make the corrector very easy to operate.     

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.     

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.

     

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.     

The Model of a Surface Flaw and the Calculation of the Topography of Its Magnetic Field for Normal Magnetization by an Alternating Field. A Quasi-Stationary Case

A surface flaw model is proposed. The model describes the magnetic field topography H _d for normal magnetization by an alternating field H of frequency . It is shown that H _d can be presented as two cofactors: one cofactor describes a dependence of the topography on coordinates x, z and parameters of a flaw (depth h, opening width 2b), and another cofactor describes its dependence on the electrophysical properties of a tested material containing the surface flaw (specific conductivity , and the relative magnetic susceptibility ). Transition from the magnetostatic field of a flaw = 0 to a quasi-stationary field for magnetization under an alternating field H _0s of frequency is carried out using the model proposed for the magnetic field of a surface flaw under normal magnetization.     

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.     

Environmental scanning electron microscopy studies of diffusion mechanism of boron particle combustion

This investigation was performed to resolve long-term contradicting theories regarding the mechanisms which govern the species diffusion across the liquid B₂O₃ layer covering a single boron particle during the combustion of boron. An environmental scanning electron microscope (ElectroScan E-3) was used to observe the liquefaction characteristics of the boron oxide layer and to examine boron dissolution and species diffusion processes in real time. Using a hot stage, crystalline boron particles were heated from 25 to 950°C in O₂, H₂O, or Ar environments. Pure B₂O₃ particles were also heated in an O₂ environment and examined. In situ observations showed that the diffusion of dissolved boron into molten B₂O₃₍₁₎ is much more dominant at elevated temperatures than the diffusion of gaseous O₂ through the B₂O₃₍₁₎ layer. Dissolution of solid boron into the boron oxide layer caused the liquefaction of boron particles at relatively low temperatures (940°C). The chemical composition of liquid boron oxide, coated on the surface of boron particles, was identified as a polymeric vitreous (BO)_n complex through the reaction between dissolved boron and molten B₂O₃₍₁₎.