Analysis of drift in iso-scallop planning—machining by regions

Computer-aided manufacturing (CAM) occupies an increasingly significant role in engineering with all it has to offer in terms of new possibilities and improving designer/manufacturer productivity. Our present work is devoted to the integration of a module for automatic generation of cutter paths into a CAM program to machine freeform surfaces by end milling. The study addresses the more global issue relating to the adoption of tool path planning with constant scallop height. For present purposes, the cutter geometry is taken as given and does not enter into the study’s parameter choices. The main problem posed by planning for iso-scallop tool paths lies in the management of drift in trajectories, which leads to the path looping due to the fact that global programming over the surface remains unattainable. The proposed solution is to define surface subdivision criteria (machining by regions) enabling iso-scallop planning to be implemented in each region. We conducted our study on a three-axis numerical control machine tool.     

Measurement of volume resistivity∕conductivity of metallic alloy in inhibited seawater by optical interferometry techniques

Optical interferometry techniques were used for the first time to measure the volume resistivity∕conductivity of carbon steel samples in seawater with different concentrations of a corrosion inhibitor. In this investigation, the real-time holographic interferometry was carried out to measure the thickness of anodic dissolved layer or the total thickness, U(total), of formed oxide layer of carbon steel samples during the alternating current (ac) impedance of the samples in blank seawater and in 5-20 ppm TROS C-70 inhibited seawater, respectively. In addition, a mathematical model was derived in order to correlate between the ac impedance (resistance) and the surface (orthogonal) displacement of the surface of the samples in solutions. In other words, a proportionality constant [resistivity (ρ) or conductivity (σ) = 1∕ρ] between the determined ac impedance [by electrochemical impedance spectroscopy (EIS) technique] and the orthogonal displacement (by the optical interferometry techniques) was obtained. The value of the resistivity of the carbon steel sample in the blank seawater was found similar to the value of the resistivity of the carbon steel sample air, around 1 × 10(-5) Ω cm. On the contrary, the measured values of the resistivity of the carbon steel samples were 1.85 × 10(7), 3.35 × 10(7), and 1.7 × 10(7) Ω cm in 5, 10, and 20 ppm TROS C-70 inhibited seawater solutions, respectively. Furthermore, the determined value range of ρ of the formed oxide layers, from 1.7 × 10(7) to 3.35 × 10(7) Ω cm, is found in a reasonable agreement with the one found in literature for the Fe oxide-hydroxides, i.e., goethite (α-FeOOH) and for the lepidocrocite (γ-FeOOH), 1 × 10(9) Ω cm. The ρ value of the Fe oxide-hydroxides, 1 × 10(9) Ω cm, was found slightly higher than the ρ value range of the formed oxide layer of the present study. This is because the former value was determined by a dc method rather than by an electromagnetic method, i.e., holographic interferometry with applications of EIS, i.e., ac method. As a result, erroneous measurements were recorded due to the introduction of heat to Fe oxide-hydroxides.     

Pressure-induced amorphization of zinc orthophosphate—Insight in the zinc coordination by XAS

In-situ high pressure X-ray absorption spectroscopy measurements at Zn K-edge were performed on α-Zn₃(PO₄)₂ compound, one of the model materials of the tribochemical film obtained from the ZDDP molecule. The goal of these synchrotron experiments was to investigate pressure-induced effects on the local environment of zinc atoms during a compression/decompression cycle. Modifications of the absorption spectra at Zn K-edge of α-Zn₃(PO₄)₂ show irreversible amorphization around zinc atoms and irreversible increase of the Zn–O distance. These results were identified as the signature of structural changes around the Zn atom in the pressed sample, thus suggesting an irreversible Zn coordination change with the pressure.     

Inspection of fatigue defects in endurance testing of half-axles of maneuverable aircraft’s stabilizers by means of acoustic emission and tensometry

The results obtained by acoustic-emission (AE) testing and continuous tensometry in endurance testing of half-axles of maneuverable aircrafts stabilizers are described. In order to ensure the reliability of the tests, fractography of the fractures obtained is carried out along with metallographic studies of the materials structure in the zone of fracture nucleation and propagation.Translated from Defektoskopiya, Vol. 40, No. 9, 2004, pp. 3–10. Original Russian Text Copyright © 2004 by Sereznov, Maltsev, Stepanova, Kabanov, Chaplygin, Laznenko, Kareev, Kozhemyakin.     

Crystallographic structure of human tooth enamel by electron microscopy and x‐ray diffraction: hexagonal or monoclinic?

Recently reports on the major stability of the monoclinic phase of hydroxyapatite compared with the hexagonal phase have established it as the most observable structure of hydroxyapatite in natural materials, such as hard tissues. In this work, the structural and crystallographic analysis of the inorganic component of sound human tooth enamel was done by transmission electron microscopy, electron diffraction and X-ray diffraction techniques. The results indicated that its unit cell is hexagonal not monoclinic.     

Attenuation of ultrasonic Rayleigh–Lamb waves by small horizontal defects in thin aluminium plates

The present paper illustrates how horizontal symmetric crack-like defects can be detected rapidly in thin isotropic plates by using longitudinal ultrasonic waves. The use of such longitudinal waves offers the potential of being significantly faster for non-destructively detecting defects than conventional ultrasonic techniques, which rely on transverse waves propagating through the thickness of a plate. Computational and analytical methods are used to predict reflection coefficients due to the attenuation of a longitudinal ultrasonic wave by physically small defects. It is shown that detectable attenuation (>10%), i.e. reflection coefficients, of the lowest order symmetric Rayleigh–Lamb wave (S₀) occurs for a range of small defects (sub-millimeter in length) when using high-frequency waves (MHz range).     

Influence of tool geometry on the stress–strain state of pipe in expansion by a shaped draw bar

The expansion of shaped pipe in oilfield borehole repair by means of various shaped draw bars is modeled by the finite-element method. The optimal draw-bar configuration is determined from the pressure on the tool and the effective strain. Recommendations are made regarding the shape of the draw bar.     

An ultrahigh-vacuum multifunctional apparatus for synthesis and in situ investigation of low-dimensional structures by spectral magnetoellipsometry in the temperature range of 85–900 K

This paper presents the results of modernizing an ultrahigh-vacuum multifunctional apparatus that allows one to obtain semiconductor or metallic nanostructures in a single technological cycle and to investigate their optical and magneto-optical properties in a temperature range of 85–900 K. The capabilities of the developed system were demonstrated based on the example of studying the temperature dependence of the bulk Si permittivity via spectral ellipsometric measurements.     

Digital Focusing of Aperture when Probing Test Object by All Elements of Antenna Array in One Emission–Reception Cycle

Russian Journal of Nondestructive Testing - We describe the physical meaning of the method of visualization by several sendings of probing ultrasonic waves with a plane front into the...     

Wear behaviour of in situ Cu–Al2O3 composites produced by internal oxidation of as cast alloys

Abstract

In the present study, the wear behaviour of Cu–Al₂O₃ composites and Cu–Al alloys has been investigated. The experiment involved casting of Cu–Al alloys with 0·37, 1, 2 and 3 wt-% of aluminium under inert gas atmosphere. The composites were produced by internal oxidation of alloys at 950°C for 10 h in presence of Fe₂O₃ and Al₂O₃ powders mixture. The microstructures of composites were studied using SEM and atomic force microscopy. To identify wear behaviour of specimens, dry sliding pin-on-disk wear tests were conducted according to ASTM G99-95a standard. The normal loads of 20, 30, and 40 N were applied on specimens during wear tests. The sliding speed and distances were selected as 0·5 m s^–1 and 500, 1000 and 1500 m respectively. To specify the wear mechanisms, the worn surfaces of composites were examined by SEM equipped with EDX. According to wear test results, increasing applied load and sliding distance leads to more volume loss in all specimens. Composites represent better wear resistance in comparison to alloys. Additionally, increasing the volume fraction of alumina particles in composites enhances the wear resistance, especially under high applied load. The wear mechanisms are mainly abrasion, oxidation and delamination.     

Registration of Alfvén resonances in TCABR tokamak by the scanning reflectometer at sideband frequencies

A frequency scanning O-mode reflectometer was used for studies of plasma density oscillations during local Alfve?n wave (LAW) excitation in the Tokamak Chauffage Alfve?n Bre?silien (TCABR) at the frequency f(A) = 5 MHz. It was found that the spectrum of the reflectometer output signal, which consists mainly of the "beat" frequency f(B), is modified by the LAW excitation, and two additional frequency peaks appear, which are symmetrical in relation to the LAW excitation frequency f = f(A) ± f(B). This result opens the possibility to improve the efficiency of studying the LAW induced density oscillations. The symmetry of these frequency peaks yields the possibility of finding the microwave frequency at which the reflectometer cutoff layer coincides with radial position of the LAW resonance zone in the TCABR tokamak.     

Evaluation of a digital data acquisition system and optimization of n-γ discrimination for a compact neutron spectrometer

A compact NE213 liquid scintillation neutron spectrometer with a new digital data acquisition (DAQ) system is now in operation at the Physikalisch-Technische Bundesanstalt (PTB). With the DAQ system, developed by ENEA Frascati, neutron spectrometry with high count rates in the order of 5×10(5) s(-1) is possible, roughly an order of magnitude higher than with an analog acquisition system. To validate the DAQ system, a new data analysis code was developed and tests were done using measurements with 14-MeV neutrons made at the PTB accelerator. Additional analysis was carried out to optimize the two-gate method used for neutron and gamma (n-γ) discrimination. The best results were obtained with gates of 35 ns and 80 ns. This indicates that the fast and medium decay time components of the NE213 light emission are the ones that are relevant for n-γ discrimination with the digital acquisition system. This differs from what is normally implemented in the analog pulse shape discrimination modules, namely, the fast and long decay emissions of the scintillating light.     

Significant improvement of wear properties by creating micro/nano dual-scale structure in Al–Sn alloys

We present in this work evidence that significant improvement of wear behavior can be achieved by creating a dual-scale structure. An Al–12 wt%Sn bearing alloy consisting of mixtures of nanocrystalline (NC) Al–Sn powder and coarse-grained (CG) Al–Sn powder was produced by a combination of mechanical alloying and conventional powder sintering. The extent of the improvement in wear properties was related to the ratio of NC/UFG to CG, and the best properties were achieved at a ratio of 30 wt% CG. With this ratio, this dual-scale Al–Sn (CG-30) alloy had a wear resistance about 1.5 times greater than that of the monolithic NC/UFC alloy prepared by mechanical alloying, about twice that of the monolithic CG alloy. The friction coefficient decreased by nearly 13% of the CG alloy. The detailed wear mechanism investigation revealed that an optimized combination of hardness and toughness is a key for the improvement of wear properties in the dual-scale material.     

Influence of thermoelectric junctions on the electrical signals generated by the tool–workpiece thermocouple system in machining

This work investigates the influence of the electrical circuits on TMF (total thermoelectromotive force) response signals captured from the rotating workpiece generated by the tool–workpiece thermocouple system in turning process considering four different thermoelectrical circuits – Ec namely: C₁ – bronze pin, C₂ – aluminum pin, C₃ – graphite brush and C₄ – liquid mercury contact. The tests were carried out under different cutting conditions. A multifactorial analysis of variance was performed using the 2^k factorial design, always considering the C₄ as the lower level. In addition, a single factor analysis of variance was performed, keeping the cutting speed, Vc, the feed rate, f, the depth of cut, doc, and the lubri-coolant system, Lub, constants while varying the Ec in order to validate the results found with the factorial design. The results indicated that there was no statistical significant difference in the TMF responses of the tool–workpiece thermocouples C₁ and C₄ as well as C₂ and C₄. However, when comparing the TMF generated by C₃ and C₄ a significant difference was detected, indicating that graphite brushes is not recommended for such application, while the bronze and aluminum pins can be thought as an advantageous substitute for the laborious liquid mercury system.