Effect of deviation on delamination by saw drill

Various cutting techniques are available to drill holes, but drilling is the most common way in secondary machining of composite materials owing to the need for structure joining. Twist drills are widely used in the industry to produce holes rapidly and economically. Since the twist drill has a chisel edge, increasing the length of a chisel edge will result in an increase in the thrust force generated. Whereas, a saw drill has no chisel edge; it utilizes the peripheral distribution of the thrust force for drilling. As a result, the saw drill can achieve better a machining quality in drilling composite laminates than twist drill. The deviation of cutting edge that occurs in saw drill would result in an increase of thrust force during drilling, causing delamination damage when drilling composite materials in particular. A comprehensive model concerning delamination induced by the thrust force of a deviation saw drill during drilling composite materials has been established in the present study. For a deviation saw drill, the critical thrust force that triggers delamination increases with increasing β. A lower feed rate has to be used with an increasing deviation saw drill in order to prevent delamination damage. The results agree with real industrial experience. A guide for avoiding the drill deviation during drill regrinding or drill wear has been proved analytically by the proposed model, especially when the deviation ratio (β) affects the critical thrust force. This approach can be extended to examine similar deviation effects of various drills.     

Development of freeform grinding methods for complex drill flank surfaces and cutting edge contours

This paper details the development of an innovative freeform grinding method that enables the generation of complex drill flank surfaces and cutting edge contours that are non-quadratic model based. This method allows a direct and independent design of drill cutting angle distributions—normal rake angle (γ_n) and relief angle (α_f). Mathematical formulations were first developed for γ_n and α_f in terms of drill geometric parameters such as helix angle, flute contour, and cutting edge contour. The developed freeform grinding methods enhance the flexibility of the grinding process by enabling the production of drills with convex and concave flank surfaces and complex cutting edge contours with standard wheel sets, eliminating the need to manufacture specially designed form grinding wheels.     

Measurement of specific cutting energy for evaluating the efficiency of bandsawing different workpiece materials

In cutting operations by multipoint cutting tools such as bandsawing, the layer of material removed per tooth (5–30 μm) is usually less than or equal to the cutting edge radius (5–15 μm). Furthermore, the bandsaw tooth is also restricted since it has to accommodate the chip in a gullet of limited size. This situation can lead to inefficient metal removal by a combination of piling up, discontinuous chip formation and ploughing action in contrast to the cutting operations by most of the single point cutting tools (e.g., turning). Specific Cutting Energy (E_SP) is a better way of measuring the efficiency of the metal cutting process compared to the other processes such as determining tool wear, cutting forces, chip ratio, etc. This paper reports on the full bandsawing tests of three different workpiece materials (Ball bearing steel, Stainless steel and Ni–Cr–Mo steel). The increase of E_SP throughout the life of the bandsaw reflected the degradation of the cutting performance due to the wear of the cutting edge geometry for Ball bearing and Stainless steels. However, there was no increase in E_SP when cutting Ni–Cr–Mo steel, which could be explained by the existence of a large protective built-up edge and/or minimal blade wear. The variation of the E_SP in different workpiece materials will also provide valuable information for bandsaw manufacturers and end users to estimate machinability characteristics for selected workpieces.     

新型微钻头横刃数控修磨的研究

为了提高新型微钻头的钻削性能,提出了一种适合于微钻头的横刃修磨原理及方法。根据刃磨的运动关系建立了新型微钻头横刃修磨的数学模型并求出了刃磨参数。仿真结果表明：提出的横刃修磨方法效果好。     

Thermodynamic properties of the ternary system InSb–NiSb–Sb in the temperature range 640–860 K

The ternary InSb–NiSb–Sb system has been studied by X-ray diffraction and by potentiometry. The electromotive forces (EMF) have been measured in the temperature range 640<T/K<860 by using the following galvanic cell:

with x (0.075<x<0.498) and y (0<y<0.359). The investigated samples are located on the following lines of the Gibbs triangle: InSb–Ni_0.33Sb_0.66, InSb–Ni_0.48Sb_0.52, InSb–NiSb, Sb–(InSb)_0.75(NiSb)_0.25, Sb–(InSb)_{0. 5}(NiSb)_0.5, Sb–(InSb)_0.25(NiSb)_0.75. From these measurements, the values of the partial molar thermodynamic functions (Δμ°_m,In, ΔH°_m,In, ΔS°_m,In) (data at reference pressure p⁰=10⁵ Pa), for the liquid InSb alloy, for the three solid heterogeneous regions InSb–NiSb₂–Sb, InSb–NiSb_1±δ?–NiSb₂, InSb–NiSb_1±δ, for six ternary liquid–solid alloys, have been calculated.     

Microstructural instability and embrittlement behaviour of an Al-lean, high-Nb γ-TiAl-based alloy subjected to a long-term thermal exposure in air

Both ingot-cast and forged Ti–44Al–8Nb–1B alloys were exposed at 700 °C in air for up to 10,000 h. The α₂ lamellae in the two conditions are found to be thermodynamically unstable and readily decompose through phase transformations of α₂ → γ, α₂ → B2(ω) and α₂ + γ → B2(ω). Widespread B2(ω) forms throughout the lamellar structure, resulting in a significant increase in volume fraction after 10,000-h exposure. This is attributed to the composition similarity between the transformed and parent phases. The partition coefficients for Ti/Al/Nb between B2(ω) and α₂ and between B2(ω) and α₂ + γ are all measured to be close to 1. The long-term exposure has induced embrittlement owing to oxygen releasing from α₂ decomposition. Room-temperature ductility is only 1/5 and 1/3 of the original value for the two conditions, respectively. However, no clear decreasing trend in S–N fatigue strength is observed, suggesting that the embrittlement effect of B2(ω) on the surface crack initiation is difficult to detect.     

Study of the electrical conduction behaviour of the Ba1−xLaxTi1−xNixO3 (x 0.10) system

The electrical conduction behaviour of the Ba_1−xLa_xTi_1−xNi_xO₃ (x 0.10) system has been studied by complex plane impedance analysis and measurements of a.c. conductivity in the temperature range 400–575 K. The values of the bulk resistance for these samples are obtained from a circular arc passing through the origin in their impedance plots. A.c. conductivity obeys the relation σ_a.c.αω⁸ in the temperature range of measurements. These results indicate that conduction occurs in this system because of hopping of charge carriers between localized nickel sites.     

Elastic properties of amorphous and crystalline B1−xCx and boron at low temperatures

We present measurements of the internal friction (Q⁻¹) and speed of sound variation (δ

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₀) of amorphous boron (a-B) and amorphous B₉C (a-B₉C). The elastic properties of these materials, which can only be produced as thin films, are consistent with those of other amorphous solids measured to date and exhibit good agreement with the tunneling model (TM) of amorphous solids. The TM parameter

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γ_t²/ρ

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_t² extracted from the elastic data has the same order of magnitude as that observed for all amorphous solids studied to date; a review will be presented. Using the results from the elastic measurements, we calculate the T² thermal conductivity Λ expected in the TM regime (T≤1 K) for a-B. The predicted thermal conductivity falls within the expected range for amorphous solids and agrees with the thermal conductivity of the crystalline icosahedral boride MB_68-δ (M=Y, Gd), which has been previously shown to exhibit glass-like excitations. We have also measured the internal friction and speed of sound variation of bulk polycrystalline c-B_1−xC_x at low temperatures (0.07 K<T<10 K). The elastic properties evolve towards the behavior characteristics of amorphous solids for increasingly carbon-deficient (x<0.20) specimens. The magnitude of the internal friction for the most carbon-deficient crystalline c-B_1−xC_x sample (x=0.1, c-B₉C) is comparable to that for a-B and a-B₉C, thereby confirming the inherent glass-like vibrational properties of carbon-deficient c-B_1−xC_x. Such behavior supports the glass-like character of carbon-deficient c-B_1−xC_x high temperature (T>50 K) thermal transport reported previously and provides the first experimental evidence for the presence of two-level systems (TLS) in these crystalline solids. However, discrepancies with the tunneling model are present; the data for c-B_1−xC_x bear some similarity to those for amorphous metals in which electronic relaxation channels are active, although details are still unclear. Previous studies have shown that the TM quantity C=Pγ_t²/ρ

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_t² (“tunneling strength”) is essentially independent of the material's shear modulus G=ρ

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_t² over a factor of 17. The elastic data presented in this work now extend the observed independence of the tunneling strength, C, over a factor of 70 in shear modulus.     

Kinetics of phase separation in iron-based ternary alloys. I. Theoretical analysis of phase separation behavior in iron-based ternary alloys

Phase sepation behavior in an Fe-based ternary system was investigated by using a model based on the Cahn–Hilliard equation. The asymptotic behavior of the minor element, Y, in an Fe–X–Y ternary alloy along a trajectory of a peak top of the major element, X, is classified into three groups according to the sign of the second derivative of the chemical free energy f₁ with respect to the concentration of X, c_X and the concentration of Y, c_Y, f′_XY≡∂²f₁/∂_CX∂_CY. If f′_XY>0,, the value of c_Y along the trajectory of the peak top of Y decreases with time. When f′_XY<0 at 0t<∞, peaks of c_Y formed at the peak tops of Y. The amplitute of the peak increases with time. In the case that f′_XY<0 at 0t<t₀and f′_XY>0 at t₀<t<∞, peaks of c_Y formed at the peak tops of Y at the initial stage. Bifurcation of peaks occurs. The concentration of the major element, c_X, along the trajectory of its peak increases with time regardless of the sign of f′_XY.     

Conductive molecular solids: partial iodine oxidation of octaethylporphyrins

We report e.p.r. and resonance Raman spectra, and electrical conductivity for polycrystalline samples of the M(OEP)(I)_x, where M = “H₂”, Ni, Cu; OEP = 1,2,3,4,5,6,7,8-octaethylporphinato; x 5.8. These materials are shown by resonance Raman spectrometry to be properly formulated as . The electrical conductivities depend strongly on ρ = x/5 and M. In some cases (e.g., Ni(OEP)(I)_x, x > 1.4) the ambient temperature polycrystalline conductivities (0.03 S cm⁻¹) and the activation energies (0.10 eV) are comparable with those of polycrystalline samples of materials whose single crystal conductivities are 500 Sm⁻¹ with a metal-like temperature dependence (dσ/dt < 0).     

The edge force components in oblique cutting

It is shown that in an oblique cutting operation two of the edge force components can be derived on the basis of the hypotheses: (a) that there exists an equivalent orthogonal cutting operation which is such that the depth of the layer of workpiece material which is extruded below the cutting edge in oblique cutting, h, is equal to that which would be extruded below the cutting edge in this equivalent orthogonal cutting operation, and (b) the area of contact between the flank face and the extruded layer in oblique cutting is that which would exist in the equivalent orthogonal cutting operation.By applying these hypotheses, expression for the edge force component acting normal to the generated surface, F_v′, and that acting along the cutting speed direction, F_c′, are derived and are verified using empirical cutting data. It has not proved possible to formulate a model from which the edge force component acting along the cutting edge direction, F₂′, can be deduced. However, on the basis of conjecture, a simple-minded argument is advanced which leads to an expression for F₂′. This expression is verified using empirical force data.     

AC conductivity and dielectric measurements of bulk magnesium phthalocyanine (MgPc)

The AC conductivity, σ_ac(ω) for bulk magnesium phthalocyanine (MgPc) in the form of compressed pellet in the frequency range of 1–500 kHz and in a temperature range of 303–443 K with evaporated ohmic Au electrodes have been investigated. The frequency dependence of the impedance spectra plotted in the complex plane shows semicircles. The Cole–Cole diagrams have been used to determine the DC conductivity. The AC conductivity, σ_ac(ω), is found to vary as ω^s in the frequency range of 1–500 kHz. At high range of frequency, s < 1 and it decreases with increasing the temperature. The variation of s with temperature suggests that the AC conduction is due to the correlated barrier hopping (CBH). The dielectric constant, ′, and dielectric loss, ″, for bulk MgPc were decreased with increasing frequency and increased with increasing temperature.     

A neutron diffraction study of the hexagonal pseudo-ternary compounds ErMn6−xFexSn6 (x = 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0)

The hexagonal ErMn_6−xFe_xSn₆ solid solution (0.2 < x < 4) has been studied by magnetisation measurements and neutron diffraction. The ordering temperature of the T = (Mn,Fe) sublattice almost continuously increases from T = 386 K for x = 0.2 to T = 498 K for x = 4. The T sublattice orders in the successive magnetic structures helimagnetic H1, antiferromagnetic AF2, helimagnetic H2 and antiferromagnetic AF1 with increasing iron content. While structures AF2 and H1 were already observed in ternary Mn compounds and AF1 in ternary iron compounds, the structure H2 is of a new kind characterized by an AF slab around the Er(1a) site. At low temperature, a change of the easy direction of the Er moment from easy plane to easy axis is observed. The iron-rich compounds display a ferromagnetic order of the Er sublattice. A new kind of magnetic structure characterized by a sine-wave modulated arrangement with a propagating vector Q = (0, 0, q_z) is also observed. The evolution of the magnetic properties (enhancement of the AF character of the (Mn,Fe) sublattice and magnetocrystalline anisotropy of erbium) is discussed.     

Mathematical model for helical drill point

Helical drill points provide a superior cutting performance in drilling operations, particularly in micro-hole drilling. This paper presents a comprehensive and straightforward method for the design of helical drill points. The proposed method has three particular features. Firstly, a mathematical model of the helicoid grinding surface is developed. This model allows the normal and tangential vectors of the abrasive wheel to be obtained explicitly. Secondly, the mathematical models of the flute and flank surfaces are integrated and therefore the cutting and chisel edges can be obtained by numerical calculation. Finally, the derivation of the model is straightforward and expresses the drill's characteristics (e.g. the semi-point angle, chisel edge, lip clearance angle, heel clearance, angle tool cutting edge inclination, normal rake angle and normal clearance angle) in accordance with all current international standards. The proposed model is capable of describing a wide range of helical drills. The methodology presented in this study facilitates the production of helical drills on a 6-axis CNC grinding machine.     

Devitrification phase transformations in amorphous Al85Ni7Gd8 alloy

Non-isothermal devitrification phase transformations in amorphous Al₈₅Ni₇Gd₈ over the temperature range from 100 to 1300 °C were systematically investigated using differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) techniques. Continuous heating DSC scans revealed that the crystallization proceeds through multiple stages. The only crystalline phase formed in the first two stages is fcc-Al, appearing exclusively as dendritic single crystals. A metastable phase (τ_n) is formed in the 3rd stage, and another metastable phase (τ_u) is formed in the 4th stage, together with the equilibrium ternary compound τ₁. The equilibrium “binary” compound M₃Gd (M=Al, Ni) with 0.4 at.% Ni solubility is formed only in the 5th stage. Further heating initiates eutectic melting at 635 °C, followed by other melting events at higher temperatures, until fully liquid when T>919 °C. Isothermal annealing at 260 °C readily induces formation of another metastable phase (τ_m) and fcc-Al. Fcc-Al nanocrystal development and interpretation of isothermal DSC technique is discussed.     

Electronic transport properties of liquid Ga–Zn alloys

In the present work, the electrical resistivity and the absolute thermoelectric power (Seebeck coefficient) of the liquid Ga_x–Zn_1−x alloys have been measured at different concentrations as functions of temperature. The liquid alloy is contained in a quartz cell fitted with tungsten and tungsten-rhenium electrodes. The thermal conductivity is deduced using Wiedemann–Franz law. To interpret our experimental data, we used a quantum mechanical calculation of the electrical resistivity ρ and of the thermoelectric power S of Ga_x–Zn_1−x alloys known as the “Faber–Ziman” formalism.     

Isothermal section at 1673 K of the Mo–Ru–Si diagram and crystallographic structures of ternary phases

Efforts to improve the high temperature behavior of MoSi₂ in oxidizing environments led to the investigation of the Mo–Ru–Si phase diagram. The isothermal section at 1673 K was determined by X-ray diffraction, optical and scanning electron microscopies and EPMA. Five new silicides were identified and their crystallographic structure was characterized using conventional and synchrotron X-ray as well as neutron powder diffraction. Mo₁₅Ru₃₅Si₅₀, denoted α-phase, is of FeSi-type structure, space group P2₁3, a=4.7535 (5) Å, D_x=7.90 g. cm⁻³, Bragg R=7.13. Mo₆₀Ru₃₀Si₁₀ is the ordered extension of the Mo₇₀Ru₃₀ σ-phase with space group P4₂/mnm, a=9.45940(8) Å, c=4.94273(5) Å, D_x=6.14 g. cm⁻³, Bragg R=5.75.     

A thermodynamic approach to assess glass-forming ability of bulk metallic glasses

According to the Gibbs free energy difference between liquid and crystal, a thermodynamic glass-forming ability(GFA) parameter related to characteristic temperatures, onset crystallization temperature(T_x) and liquidus temperature(T_l), was proposed for evaluating the GFA of bulk metallic glasses(BMGs). The new parameter defined as ω=T_l(T_l+T_x)/(T_x(T_l−T_x)) has good correlation with the critical section thickness(Z_c) of Ca-Mg-Cu BMGs. Being verified by the glasses data, including oxide glasses, which were used to validate the former GFA parameters, ω is one of the most reliable and applicable GFA parameters among T_rg (=T_g/T_l), γ(=T_x/(T_l+T_g)), α (=T_x/T_l), δ (=T_x/(T_l−T_g), and so on. Finally, predicting GFA of Cu-Ag-Zr-Ti and Cu-Zr-Ti-Al BMGs using ω was compared with the experimental results.     

Monitoring the tensile deformation in real unidirectional Kevlar-epoxy composites

Two acoustic emission (AE) parameters, event count rate (ER) and the skewness of the peak amplitude distribution (PAD), were found to correlate with mechanical and damage mechanisms in unidirectional Kevlar-epoxy composites loaded in tension. The ER of the AE reached a local maximum at about 0.3σ_cu (σ_cu= composite tensile strength), a minimum at about 0.6–0.7σ_cu, and increasing ER rates were noted as failure stress approached, with a peak at final failure.Along with our proposed approach to evaluate the PAD as a tool for characterizing processes, damage mechanisms and failure modes, the third statistical moment of the PAD, the skewness, was found to be able to distinguish between various mechanisms. From the beginning of loading until completion of the fibre straightening process, 0.6–0.7σ_cu, the value of the skewness steadily decreased, and then gradually increased to final failure. This behaviour is explained by a model based on the non-elastic mechanisms which contribute to the monitored AE. At final failure, the PAD's skewness value was affected by macroscopic failure modes. When this mode comprises fibre fracture with little matrix and interface splitting, the skewness decreased; when fibre failure was accompanied by matrix and interface splitting, its value changed slightly or even increased.     

Transport anisotropy and pseudo-gap state in oxygen deficient ReBa2Cu3O7−δ (Re = Y, Ho) single crystals

The temperature dependence of the transport anisotropy of ReBa₂Cu₃O_7−δ (Re = Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δ_c increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa₂Cu₃O_7−δ, the temperature dependence of the anisotropy of the resistivity ρ_c/ρ_ab(T) for the HoBa₂Cu₃O_7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity.