Coercive Force as a Function of Uniaxial Stresses (Part 2)

The relative anisotropy of the coercive force is investigated as a function of the tensile stress. A generalized calculated curve with coefficients averaged over all the low-carbon steels tested is constructed. A mechanism for determining the effective magnetostriction λ ₁₀₀ ^* and λ ₁₁₁ ^* from the field dependence λ(H) is proposed. The magnetoelastic sensitivity ΔH _c coefficients are determined as functions of the magnetostriction λ ₁₀₀ ^* .     

Increasing the signal-to-noise ratio during joint use of the spectrum extrapolation and splitting methods

The possibility of increasing the signal-to-noise ratio by the method of echo-signal spectrum splitting jointly with spectrum extrapolation is considered. The essence of the method proposed is that the echo-signal spectrum known within a given frequency range (f _min, f _max) is divided into several subranges (f _min ⁱ , f _max ⁱ ). The construction of the AR model of the echo-signal spectrum allows the spectrum extrapolation from each subrange by an interval (f _min ^e , f _max ^e that far exceeds the initial interval. This means that, with the use of one echo signal, a set of signals can be obtained, the adding together of which increases the signal-to-noise ratio and ensures an ultrafine beam resolution for flaw images. The presented results of processing echo signals, which were obtained in numerical and model experiments, confirm the efficiency of the proposed technique for processing echo signals.     

Thermomechanical wear during quasistationary heat generation by friction

The known criterial relationships of thermomechanical wear are adapted to the case of spatial quasistationary temperature and stress-strain state of the triboelement. The original data used are the distribution of temperature and stresses in the semispace exposed to the heat flux and normal pressure in the region moving over the surface with constant velocity. The dimensionless parameters Pe, G _th and p ₀/?? _f ⁰ are used to plot the maps of thermomechanical wear which take into account the tribosurface plastic fracture (steel; ShKh15) or brittle and plastic fracture (aluminum oxide Al₂O₃) in response to the temperature.     

Atomic structure of extended defects in boron-implanted silicon layers

The structure of extended defects introduced into Si by means of boron implantation followed by thermal annealing at T = 900 °C is studied by the method of high-resolution transmission electron microscopy and computer modeling for different values of the implantation dosage (D) and concentration of boron atoms in substitutional positions B₀ \((C_{B_0 } )\) injected into the Si lattice before implantation. It is shown that the Frank dislocation loops of both interstitial (I) and vacancy (V) type at a ratio of 4: 1 are observed in Si samples with D = 10¹⁶ cm^?2 up to \(C_{B_0 } \) = 0.8·10²⁰ cm^?3. The atomic structure of the I-type Frank dislocation loops is heavily deformed, which suggests segregation of finely dispersed boron in the defect plane. At the same time, the structure of the V-type Frank dislocation loops tends to be reconstructed due to interaction with self-interstitials. At \(C_{B_0 } \) = 2.5·10²⁰ cm^?3, the I-type Frank dislocation loops are found to transform to perfect dislocation loops, and boron precipitates with a high density appear in Si. Based on the results obtained, probable reasons for vacancy deficit formation in boron-implanted Si are discussed.     

Similarity and approximate solutions of laminar film condensation on a flat plate

Laminar film condensation of a saturated pure vapor in forced flow over a flat plate is analyzed as boundary layer solutions. Similarity solutions for some real fluids are presented as a function of modified Jakob number (C _pl ΔT/Prh _fg ) with property ratio ( $\sqrt {\sigma _l \mu _l /\rho _v \mu _v } $ ) andPr as parameters and compared with approximate solutions which were obtained from energy and momentum equations without convection and inertia terms in liquid flow. Approximate solutions agree well with the similarity solutions when the values of modified Jakob number are less then 0.1 near 1 atmospheric pressure.     

Effects of structure and defect on fatigue limit in high strength ductile irons

In this paper, the influence of several factors such as hardness, internal defect and non-propagating crack on fatigue limits was investigated with three kinds of ductile iron specimens. From the experimental results the fatigue limits were examined in relation with hardness and tensile strength in case of high strength specimens under austempering treatment; in consequence the marked improvement of fatigue limits were not showed. The maximum defect size was an important factor to predict and to evaluate the fatigue limits of ductile irons. And, the quantitative relationship between the fatigue limits (σ _w ) and the maximum defect sizes ( $\sqrt {area} _{\max } $ ) was expressed as $\sigma _w ^n \cdot \sqrt {area} _{\max } = C_2 $ . Also, it was possible to explain the difference for the fatigue limits in three ductile irons by introduction of the non-propagating crack rates.     

Non-destructive evaluation of the yield stress for low carbon steel by ultrasound measurements

The non-destructive evaluation method for yield stress assessment in low carbon steels based on ultrasonic measurements of the longitudinal and transversal velocities and the longitudinal attenuation coefficient is proposed. First, the mean grain size $\bar D$ is calculated from the measured acoustic parameters and then the yield strength is estimated from these three parameters using the Hall-Petch relationship. Comparative non-destructive and destructive tests for yield stress evaluation are elaborated. The results obtained allow to be concluded that the accuracy of non-destructive evaluation of σ _y is reliable enough.     

A UV lamp based on a Kr-Xe mixture with Br2 and I2 molecules

A small-size broadband ultraviolet lamp with an emission spectrum of 206–390 nm, which is excited by a dc glow discharge, is described. The discharge was ignited in a quartz discharge tube with an inner diameter of 1.4 cm and an anode-cathode spacing of 10 cm. The tube was filled with a Kr/Xe/Br₂/I₂ working mixture, the total pressure being 0.5–2.0 kPa. The lamp’s emission spectrum consisted of a 206.2-nm iodine atomic line 0.1 nm wide at half-height and a continuum in a spectral region of 210–390 nm. The continuum resulted from overlapping of wide emission bands with peaks at 221 nm for XeBr(D-X), 253 nm for XeI(B-X), 282 nm for XeBr(B-X), 289 nm for Br ₂ ^* , 342 nm for I ₂ ^* , and 386 nm for IBr*. The total power of the ultraviolet emission was no more than 8–12 W, the power injected into the discharge being 10–100 W. The lamp lifetime in the gas-static mode was 300–400 h.     

Effects of a blade profile, the Reynolds number, and the solidity on the performance of a straight bladed vertical axis wind turbine

This study investigates the effects of parameters such as a blade profile (changing the digit of the 4-digit NACA00xx airfoil), the Reynolds number, and the solidity on the performance characteristics of a straight bladed vertical axis wind turbine (VAWT). A numerical analysis, adopting the multiple stream tube (MST) method, is carried out to evaluate the performance depending on the parameters. The numerical result shows that the variation of a blade profile directly influences the power production, i.e., the high-digit NACA00xx airfoil provides higher power in a low speed zone (BSR < 3; BSR: blade speed ratio (ΩR/U _f ), Ω: angular velocity of blade, R: radius of a straight Darrieus wind turbine, U _f : free stream velocity) than the low-digit NACA00xx profile. On the contrary, the low-digit NACA00xx airfoil produces higher power in a high speed range (BSR > 5) than the high-digit NACA00xx profile. An enhancement of the power production is observed with increasing the Reynolds number on the whole tested blade speed ratio range (1 < BSR < 12). In particular, the rate of the enhancement of the power is rapidly decreased with the increases of the Reynolds number ( $Re = {{\rho \bar U_r c} \mathord{\left/ {\vphantom {{\rho \bar U_r c} \mu }} \right. \kern-0em} \mu }$ , ρ: air density, $\bar U_r$ : mean resultant velocity acting on a blade with variable rotating speeds in a uniform free stream velocity (U _f ), c: blade chord length, µ: air viscosity). For the effect of the solidity on the power production, a marked reduction of the range of the blade speed ratio that can provide the power is observed with increasing the solidity. A pattern of very steep variation of the power around the peak in the low speed zone (BSR < 3) is found in a high solidity range (σ > 0.3; σ: solidity (N _c /R), N: number of blade, c: chord length of an airfoil), and this tendency is conspicuously different from that of the eggbeater-type Darrieus VAWT, which is interpreted as a gradual variation of the power around the peak.     

Determining the optimum process parameter for grinding operations using robust process

We applied combined response surface methodology (RSM) and Taguchi methodology (TM) to determine optimum parameters for minimum surface roughness (Ra) and vibration (Vb) in external cylindrical grinding. First, an experiment was conducted in a CNC cylindrical grinding machine. The TM using L ₂₇ orthogonal array was applied to the design of the experiment. The three input parameters were workpiece revolution, feed rate and depth of cut; the outputs were vibrations and surface roughness. Second, to minimize wheel vibration and surface roughness, two optimized models were developed using computer-aided single-objective optimization. The experimental and statistical results revealed that the most significant grinding parameter for surface roughness and vibration is workpiece revolution followed by the depth of cut. The predicted values and measured values were fairly close, which indicates (R _Ra ² =94.99 and R _Vb ² =92.73) that the developed models can be effectively used to predict surface roughness and vibration in the grinding. The established model for determination of optimal operating conditions shows that a hybrid approach can lead to success of a robust process.     

Manufacturing and mechanical characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/β-TCP/TiO<Subscript>2</Subscript> biocomposite as a potential bone substitute

This paper focuses on the mechanical characterization of a bioceramic based on commercial alumina (Al₂O₃) mixed with synthesized tricalcium phosphate (β-TCP) and commercial titania powder (TiO₂). The effect of β-TCP and TiO₂ addition on the mechanical performance was investigated. After a sintering process at 1600 °C for 1 h, various mechanical properties of the samples have been studied, such as compressive strength, flexural strength, tensile strength, elastic modulus, and fracture toughness. The measurements of the elastic modulus (E) and the tensile strength (σ _t ) were conducted using the modified Brazilian test while the compressive strength (σ _c ) was determined through a compression test. Also, semi-circular bending (SCB) specimens were used to evaluate the flexural strength (σ _f ) and the opening mode fracture toughness (K _IC). From the main results, it was found that the best mechanical performance is obtained with the addition of 10 wt.% TCP and 5 wt.% TiO₂. Alumina/10 wt.% tricalcium phosphate/5 wt.% titania composites displayed the highest values of mechanical properties and a good combination of compressive strength (σ _c ?≈?352 MPa), flexural strength (σ _f ?≈?98 MPa), tensile strength (σ _t ?≈?86.65 MPa), and fracture toughness (K _IC?≈?13 MPa m^1/2).     

The run sum t control chart for monitoring process mean changes in manufacturing

The $ \overline{X} $ type charts are not robust against estimation errors or changes in process standard deviation. Thus, the t type charts, like the t and exponentially weighted moving average (EWMA) t charts, are introduced to overcome this weakness. In this paper, a run sum t chart is proposed, and its optimal scores and parameters are determined. The Markov chain method is used to characterize the run length distribution of the run sum t chart. The statistical design for minimizing the out-of-control average run length (ARL₁) and the economic statistical design for minimizing the cost function are studied. Numerical results show that the t type charts are more robust than the $ \overline{X} $ type charts for small shifts, in terms of ARL and cost criteria, with respect to changes in the standard deviation. Among the t type charts, the run sum t chart outperforms the EWMA t chart for medium to large shifts by having smaller ARL₁ and lower minimum cost. The run sum t chart surpasses the $ \overline{X} $ type charts by having lower ARL₁ when the charts are optimally designed for large shifts but the run sum $ \overline{X} $ and EWMA $ \overline{X} $ prevail for small shifts. In terms of minimum cost, the $ \overline{X} $ type charts are superior to the t type charts. As occurrence of estimation errors is unpredictable in real process monitoring situations, the run sum t chart is an important and useful tool for practitioners to handle such situations.     

Prediction of fatigue strength in HSS-Co, S55C and the friction welded materials based on statistical evaluation of inclusion size

In this paper, the effects of nonmetallic inclusions on the fatigue strength of medium and high strength steels are quantitatively investigated by considering the relationship between the Vickers hardness, Hv and the maximum size of nonmetallic inclusion, $\sqrt {(area)_{\max } } $ . The maximum size of nonmetallic inclusion defined by the square root of the projected area in an inclusion can be estimated by the statistics of extreme values with a definite number of specimens or structural components. While most of other studies using the parameter $\sqrt {(area)_{\max } } $ have performed the experiments with the specimens with small artificial defects or notches, this study investigates the possibility of prediction on fotigue strength in the unnotched smooth specimens. The results show that strength of the friction welded joints of HSS-Co to S55C carbon steel is almost equal to that of the weaker material in the optimum welding conditions. Under the limiting condition for the nonpropagating cracks emanating from defects or inclusions, the threshold stress intensity factor range °K_th and the lower limit of fatigue strength σ_w1 were successfully estimated from the largest inclusion size $\sqrt {(area)_{\max } } $ . From the analysis of SEM fractographs, it can be concluded that the fatigue fractures of the specimens are associated primarily with the inclusions located at the outer periphery of the specimens.     

A Model of the Calibration Blocks of the Magnetic Susceptibility of Disperse Materials for Devices Intended for Magnetic Susceptibility Measurements: I. Calculation of a Calibration Specimen with the Normalized Magnetic Susceptibility of a Disperse Material

Calculated parameters of large-volume calibration specimens are presented. The specimens are made of a disperse ferromagnetic mixture with the magnetic susceptibility χ_c ≥ 1 400 SI units encased in a spherical shell made of a dielectric with the magnetic susceptibility χ _m ^d ? 1. The normalized magnetic susceptibility is determined for the calibration specimens. Its limiting value, equal to χ _c ^c = 1.99 SI units, is determined by their spherical form and the volume concentration C _V = 0.9, which corresponds to the volume fraction of the ferromagnetic component in the disperse medium. Relative error δ in the measurement of the specimen's magnetic susceptibility does not exceed ±1%.     

An electrochemical methanol actinometer and its application to measurements of the intensity of vacuum UV radiation of a Xe 2 * excilamp

A methanol actinometer is used for measuring the intensity of vacuum UV radiation of a Xe ₂ ^* excilamp. The absorbed radiation dose is determined by measuring the concentration of formaldehyde, which is the decay product of methanol illuminated by UV radiation, with the use of amperometric titration.     

Modeling of surface roughness effect on dry contact friction in metal forming

Interfacial conditions such as friction and roughness substantially affect the process characteristics of metal forming. This study developed a dry friction model that accounted for the adhesion and interference effects of surface roughness. A sliding friction coefficient was suggested to provide fundamental information about the interfacial conditions of the contact surface. The proposed model was easily verified by published experiments and predicted values agreed with experimental results. Accordingly, friction coefficient ?? clearly increased as relative roughness R _m (=?roughness of tool $ R_a^T $ /roughness of workpiece $ R_a^M $ , measured as interference effect) increased. Simulations confirmed that the friction coefficient ?? decreased as dimensionless stress S _m (=?contact pressure p _m /tensile strength $ \sigma_u^0 $ ) increased at small strain hardening exponent n-values. Under the conditions of large n and small R _m values, the friction coefficient ?? initially decreased and then increased. It then slightly decreased as dimensionless stress S _m increased. However, this trend became less apparent as relative roughness R _m increased since friction coefficient ?? simply decreased.     

Plastic depth and load-bearing capacity of autofrettaged cylinders

Autofrettage technology is usually adopted to even out and reduce stresses as well as improve the load-bearing capacity of a variety of cylindrical ultra-high mechanical apparatuses. The autofrettage of cylinders is theoretically investigated based on maximum shear stress theory or the Tresca criterion to establish the general law for autofrettage theory. The equation for the optimum plastic depth for a certain load and radius ratio is derived to ensure that the equivalent stress of the total stress does not exceed the yield limit and the absolute value of the equivalent stress of the residual stress at the internal surface likewise does not exceed the yield limit. Through this equation, a set of concise equations for total stress and residual stresses are obtained. The safe and optimum load-bearing conditions for cylinders are presented. Results show that, provided the pressure contained in a cylinder is equal to the autofrettage pressure, irrespective of k _j, the equivalent total stress, σ_e, equals the yield limit everywhere in the entire plastic zone, that is, σ_e is a constant. In the elastic zone, σ_e is always lower than the yield limit, but if k _j is outside the quasi-infinite area enclosed by the curves of the sense and possible plastic depth, then either compressive yield occurs or k _j is meaningless. The results based on the Mises criterion and Tresca criteria are compared.     

Plastic deformation depth modeling on grinding of gamma Titanium Aluminides

This work reports on the subsurface plastic deformation depth (PDD) as a result of grinding of γ-TiAl, where the effects of grit size and shape, workpiece speed, and wheel depth of cut were studied. A grinding model based on a stochastic distribution of the chip thickness was used to estimate the expected maximum normal force per grit ( ${F''_{n\:{\rm max}}}$ ), which was correlated to the PDD. It was found that the PDD shows a linear correlation with ${F''_{n\:{\rm max}}}^{0.5}$ . The results suggest that the indentation model is still valid for grinding if ${F''_{n\:{\rm max}}}^{0.5}$ is used as a PDD predictor variable instead of the total grinding force.     

Shear Thinning of Nanometer-Thick Liquid Lubricant Films Measured at High Shear Rates

Viscosities of liquid films that were confined and sheared in a nanometer-scale gap were higher than those in the bulk state, and decreased with increasing shear rate, which is called shear thinning. However, the previous findings were based on the experimental results obtained at shear rates of 10^?1–10⁶ s^?1 by using a surface force apparatus (SFA). In this study, we succeeded in measuring shear rate dependence of viscous friction at the high shear rates of 10⁵–10⁸ s^?1. To measure the viscous friction at high shear rates, we used a fiber wobbling method that is a highly sensitive shear force measurement method we developed. The confined polymer lubricant (PFPE Z03) showed shear thinning behavior even at high shear rates up to 10⁸ s^?1, and the relationship between effective viscosity η and shear rate $\dot{\gamma }$ was well expressed by the equation that was $\log_{10} \eta = C - n\log_{10} \dot{\gamma }$ where C ≈ 4.6 ± 0.6 and n ≈ 1.1 ± 0.1. This equation agreed well with the universal curve of shear thinning determined based on the SFA measurements conducted at shear rates of 10^?1–10⁶ s^?1. This result indicates the measured shear thinning behavior was consistent at wide range of shear rates from 10^?1–10⁸ s^?1.