Influence of tooth profile and oil formulation on gear power loss

Nowadays power losses are a main concern in transmission systems and the friction between gear teeth during the meshing cycle is one of the main sources. The friction losses reduction is mandatory to promote lower energy consumption, lower operating temperatures, lower oil oxidation and lower risk of failures.In this study the power losses reduction is obtained using two different approaches: using lower modulus helical gears and significant positive profiles shifts and using gear oil formulations with different base oils.The adopted geometries proved to reduce the power losses considerably, promoting a reduction of oil operating temperature up to 20 K.     

Dynamics of a viscoelastic rotor shaft using augmenting thermodynamic fields—A finite element approach

Modelling viscoelastic materials is always difficult since such materials store energy as well as dissipate it to the thermal domain. Whereas modelling the elastic behaviour is easy, modelling the energy dissipation mechanism poses difficulty. This paper presents a theoretical study of the dynamics of a viscoelastic rotor-shaft system, where the internal material damping in the rotor-shaft introduces a rotary force well known to cause instability of the rotor-shaft system. An efficient modelling technique that assumes coupled (thermo-mechanical) augmenting thermodynamic field (ATF) to derive the constitutive relationships is found more suitable in comparison with the viscous and hysteric damping models, and is used to model the viscoelastic rotor material. Dynamic behaviour of an aluminium rotor is predicted through viscoelastic modelling of the continuum to take into account the effect of internal material damping. Stability limit speed (SLS) and unbalance response (UBR) amplitude are used as two indices to study the dynamics. It is observed that, the ATF approach predicts more reliable SLS and UBR amplitude in comparison with the viscous and hysteretic model of rotor-internal damping. Composite rotor-shaft assumed by reinforcing the aluminium matrix with carbon fibre is found to postpone the critical speeds and thus make available, higher speed of rotor operation and lower UBR amplitude in comparison with pure aluminium rotor-shaft. Finite element method is used for modelling and analysis.     

New pathways for improved quantification of energy‐dispersive X‐ray spectra of semiconductors with multiple X‐ray lines from thin foils investigated in transmission electron microscopy

Theoretical approaches to quantify the chemical composition of bulk and thin‐layer specimens using energy‐dispersive X‐ray spectroscopy in a transmission electron microscope are compared to experiments investigating (In)GaAs and Si(Ge) semiconductors. Absorption correctors can be improved by varying the take‐off angle to determine the depth of features within the foil or the samples thickness, or by definition of effective k‐factors that can be obtained from plots of k‐factors versus foil thickness or, preferably, versus the K/L intensity ratio for a suitable element. The latter procedure yields plots of self‐consistent absorption corrections that can be used to determine the chemical composition, iteratively for SiGe using a set of calibration curves or directly from a single calibration curve for InGaAs, for single X‐ray spectra without knowledge of sample thickness, density or mass absorption coefficients.     

Demonstration of aluminium in polyphosphate of Laccaria amethystea (Bolt. ex Hooker) Murr. by means of electron energy-loss spectroscopy

Toxic aluminium species in acidified soil damage the rootlets of trees. The symbiotic association with ectomycorrhizal fungi may, however, protect the rootlets by sequestration of aluminium in polyphosphates. Electron energy-loss imaging and spectroscopy was used to identify the relative amount of aluminium in the polyphosphate of the mycelium of the ectomycorrhizal fungus Laccaria amethystea. A three-window method at the L_2,3 edge yielded results which were in agreement with the spectra obtained at the aluminium K edge. The aluminium net distribution images were recorded at 85 eV, the backgrounds at 70 eV and 60 eV, setting the energy selecting slit to 5 eV and the beam current to 15 μA. The method can be used to study the sequestration of aluminium in mycelia of ectomycorrhizal fungi under different stress situations.     

Dynamic indentation and penetration of aluminium foams

Failure of metal foams caused by dynamic indentation and penetration is very common in practice, such as light-weight structural sandwich panels, packing materials and energy absorbing devices. Rational application of these materials requires a sound understanding of deformation and energy absorption mechanisms of the aluminium foams as well as the effect of impact velocity. In this study, following experimental investigations into compression, tension, sharing and indentation of CYMAT aluminium foams of various densities, a finite element (FE) analysis using ABAQUS is conducted for dynamic indentation process of aluminium foams under a rigid, flat-headed indenter. Two methods of applying impact velocities are considered: the indenter is pushed into the foam at a constant velocity through the whole process or with an initial velocity which then decreases with indentation. Two energy dissipation mechanisms are considered: compression of the foam ahead of the indenter and fracture along the indenter edge. Effect of impact velocity is noted on the size of a localized deformation and the total energy absorbed. A plastic structural shock theory developed by previous researchers is applied to calculate the resistance force with indentation depth during indentation process and fair agreement is obtained between the analytical and numerical results.     

Extended fine structure in electron energy loss spectra of MgO crystallites

EXAFS-like features in energy loss spectra (known as EXELFS) were observed by using an imaging energy filter built into an electron microscope. Single crystal micro-platelets of MgO were used as test samples. Extended fine structures were obtained reproducibly in the energy range up to 150 eV beyond the OK, MgK and MgL edges. Comparison with single scattering calculations for the K edges showed a fair agreement, indicating the feasibility of this type of analysis.     

Butt autogenous laser welding of AA 2024 aluminium alloy thin sheets with a Yb:YAG disk laser

Higher productivity, lower distortion and better penetration are the main advantages provided by laser welding in comparison with conventional processes. A Trumpf TruDisk 2002 Yb:YAG disk laser is used in this work to increases productivity and quality. Aluminium alloys lead to many technological issues in laser welding, resulting in shallow penetration and defects. In particular, AA 2024 aluminium alloy in a thin sheet is investigated in this paper, being it is used extensively in the automotive and aerospace industries. Bead-on-plate and butt autogenous laser welding tests with continuous wave emission on 1.25 mm thick AA 2024 aluminium alloy sheets were examined morphologically and micro-structurally. The geometric and mechanical features of the welding bead were evaluated via a three-level experimental plan. In addition to the power and speed which are traditionally referred to, beam defocusing was considered as an additional governing factor in a central composite design scheme because it massively affects keyhole conditions. Softening in the fused zone is discussed via Vickers micro-hardness testing and magnesium loss through energy dispersive spectrometry. After properly performing the modelling and optimisation of the fused zone and the cross-section shape factor as the response variables, the laser welding conditions for thin sheets of AA 2024 aluminium alloy are suggested. X-ray and tensile tests were conducted on the specimens obtained with the recommended processing parameters to characterise the AA 2024 disk laser welded beads.     

Failure modes during uniaxial deformation of magnesium alloy AZ31B tubes

This study examines magnesium alloy AZ31B circular tubing subject to uniaxial compressive loading and compares their performance to steel (ASTM A106 Grade B) and aluminium alloy AA6061T6 circular tubing at both low and high strain rates. Quasi-static tests were undertaken using a hydraulic testing machine for a range of tube lengths and thicknesses for tubes with an outside diameter of approximately 48 mm. To examine the effects of higher strain rate, a drop test rig was used. It was found that magnesium alloy AZ31B outperforms both the steel and aluminium alloys in terms of energy absorption for equivalent mass when subject to uniaxial compressive loads for the thicker sections. This is further enhanced by alloy AZ31B’s strain rate sensitivity, as there is a dramatic increase in the energy absorption at higher strain rates. However, the AZ31B tubes usually fail by fracturing, which generally involves a shear fracture mode, unlike the aluminium and steel tubes, which generally retained their structural integrity to a higher degree. The greatest energy absorption was obtained when the AZ31B failed via fine sharding. This failure mode appeared to be related to the presence of micro-cracks on the surface of the section obtained by overheating during extrusion. At higher strain rates, much greater plasticity and compaction are present in the fracture modes for the thicker AZ31B tubing. Some of the fracture modes have been discussed and the failure/fracture modes are compared with a typical aluminium alloy tube failure mode classification chart.     

材料断裂韧度与试样厚度关系研究

研究试样厚度对材料断裂韧度的影响，通过采用格利菲斯表面能理论和巴林布拉特吸附力理论，结合达格代尔塑性准则，给出有关断裂韧度与试样厚度关系的数学描述。并通过两种试验材料LY12CZ（L－T）与TC4（L－T）进行了验证。     

Characteristics of a hybrid journal bearing with one recess: Part 2: Thermal analysis

A thermal analysis is made of a fluid-film hybrid journal bearing with one recess under steady-state and adiabatic conditions. The coupled Reynolds equation and energy equation are solved simultaneously by a finite difference method with a successive under-relaxation method. The results for isothermal conditions with effective temperature and feed oil temperature are also obtained for comparison. The load capacity for the adiabatic condition is lower than that for the isothermal condition due to temperature gradients as well as the higher temperature distribution in the high pressure zone. Moreover, the high pressure recess works as a cooling source, so that the maximum temperature occurs at the edges of the bearing and near the position of minimum film thickness. The side flow decreases as the eccentricity increases in the adiabatic condition. This is caused by the rapid decrease in film thickness when eccentricity increases, which dominates the effect of pressure-induced flow.     

Separation of overlapping core edges in electron energy loss spectra by multiple-least-squares fitting

A multiple-least-squares fitting procedure for quantitating electron energy loss spectra is demonstrated on some strongly overlapping core edges. The method, first applied by Shuman and Somlyo [Ultramicroscopy 21 (1987) 23], takes into account plural inelastic scattering and can be applied under conditions of non-uniform sample thickness where Fourier deconvolution techniques are invalid. By using appropriate reference spectra generated from pure compounds, quantitation of potassium and calcium (L23 edges) is possible in the presence of carbon (K edge), and sulfur in the presence of phosphorus (L23 edges). Some of the advantages and limitations of the multiple-least-squares approach are discussed.     

An experimental and numerical study of necking initiation in aluminium alloy tubes during hydroforming

In this paper, a combined experimental and numerical investigation of free hydroforming of aluminium alloy tubes is conducted. The tubes are subjected to different loading histories involving axial compression and internal pressure. The circumferential and axial strains experienced by the tubes are continuously recorded along with the pressure and axial load. The numerical simulations are carried out using both 2D axisymmetric and 3D finite-element formulations by applying the experimentally recorded axial load and internal pressure. In the latter, a geometric imperfection is introduced in the form of wall thickness reduction at the tube mid-length in order to trigger necking which happens after significant bulging and beyond the stage of peak pressure. The strain histories and peak pressures obtained from the simulations agree well with those determined from the experiments. Further, the forming limit curve predicted by the simulations as well as from a M–K analysis incorporating the computed strain paths corroborate well with the experimental data. The role of nonproportional straining on the mechanics of failure of the tubes due to bulging and necking is studied in detail.     

Electron-specimen interactions in low-voltage scanning electron microscopy

Measurements of the electron range R, and the backscattering coefficient η and the secondary electron yield δ at normal and tilted incidence for different elements show characteristic differences for electron energies in the range of 0.5 to 5 keV, compared with energies larger than 5 keV. The backscattering coefficient does not increase monotonically with increasing atomic number; for example, the secondary electron yield shows a lesser increase with increasing tilt angle. This can be confirmed in back-scattered electron (BSE) and secondary electron (SE) micrographs of test specimens. The results are in rather good agreement with Monte Carlo simulations using elastic Mott cross-sections and a continuous-slowing-down model with a Rao Sahib-Wittry approach for the stopping power at low electron energies. Therefore, this method can be used to calculate quantities of BSE and SE emission, which need a larger experimental effort. Calculations of the angular distribution of BSEs show an increasing intensity with increasing atomic number at high takeoff angles than expected from a cosine law that describes the angular characteristics at high electron energies. When simulating the energy distribution of BSEs, the continuous-slowing-down model should be substituted by using an electron energy-loss spectrum (EELS) that considers plasmon losses and inner-shell ionizations individually (single-scattering-function model). The EELS can be approached via the theory for aluminium or from EELS spectra recorded in a transmission electron microscope for other elements. Measurements of electron range Rα Eⁿ of 1 to 10 keV electrons are obtained from transmission experiments with thin films of known mass thickness. In agreement with other authors the exponent n is lower than at higher electron energies.     

The effect of aluminium coating on elemental standards in X-ray microanalysis

The standardisation of frozen hydrated bulk biological specimens using gelatin standards is described. The relationship between corrected elemental X-ray counts and ionic concentration was found to be linear, and minimum detectable limits for each element are stated. Variations in uncorrected standard curves were found to be due to changes in aluminium coating thickness. There was an inverse relationship between coating thickness and elemental X-ray counts. The factors causing this are discussed. To avoid errors arising from inconsistent aluminium thickness, experimental material should only be compared with standards of similar aluminium net counts. This can be achieved most easily by mounting and analysing specimen and standard together.     

Tribological performance of an ionic liquid as a lubricant for steel/aluminium contacts

The wear and friction behaviour of an ionic liquid 1‐ethyl‐3‐hexylimidazolium tetrafluoroborate (L206) was investigated as a lubricant for steel/aluminium contacts using an Optimol SRV® oscillating friction and wear tester. The elemental composition and chemical nature of the antiwear films generated on the aluminium surface were analysed using a scanning electron microscope with a Kevex energy dispersive X‐ray analyser attachment (SEM/EDS) and X‐ray photoelectron spectroscopy (XPS). A low friction coefficient (˜0.05) was recorded when lubricating with L206; a small amount of water (5 wt. %) in L206 effectively reduced the wear volume and greatly increased the microhardness of the aluminium alloy, but had little effect on the friction coefficient. The SEM/EDS results showed that severe corrosive wear occurred on the aluminium alloy when lubricating with neat L206, which could be avoided by the addition of water in L206. The XPS results indicated that the species AlF₃, Al₂O₃, AlO(OH), and Al(OH)₃ formed during friction; there was no indication of boron on the worn surfaces.     

Mechanical behaviour and failure modes of metal to composite adhesive joints for nautical applications

In this paper, the influence of several parameters on the mechanical behaviour and failure modes of hybrid bonded joints aluminium/composite was investigated. Particularly, the effects of metallic surface condition, adhesive properties and thickness on single-lap joint resistance were analysed. To these aims, two adhesives were used and, for each adhesive, two different adhesive thicknesses (0.5 and 1.5?mm) have been investigated. Furthermore, two sets of joints for each adhesive kind and thickness were investigated: the former was obtained using aluminium blanks which were previously mechanically treated with sandpaper (P60) and the latter using aluminium treated with sandpaper and with presence of fillets in the ends of the overlap area. In order to improve the adhesion strength between polymeric adhesive and aluminium, two metal surface treatments have also been performed using a silane coupling agent, ??-glycidoxypropyltrimethoxysilane (??-GPS). The mechanical performances and failure modes were found to be significantly increased using the chemical pre-treatments with ??-GPS silane coupling agent unlike other parameters investigated. As regard the thickness of the adhesive layer, the better value is found to be equal to 0.5?mm, for both adhesives investigated.     

On springback of double-curved autobody panels

The springback of double curved autobody panels is studied theoretically and experimentally. Both steel and aluminium sheets are included in this investigation. The obtained results show that the springback is decreased with increasing binder force, increasing curvature, increasing sheet thickness and decreasing yield strength. This paper comprises also a discussion on the plastic strains and their influence on the springback.     

Spectroscopy of the cross section of inelastic scattering of electrons in SiO2/Si(100) layered systems

Spectra of the cross section of inelastic scattering of electrons (product of the mean free path of inelastic scattering and its differential cross section) are obtained for SiO₂/Si(100) layered structures from experimental spectra of energy losses of reflected electrons with different energies of primary electrons. Computer simulations of the spectra of the cross section of inelastic scattering of reflected electrons for these layered structures are performed with the use of the dielectric function of the film and substrate materials. It is found that the SiO₂ layer thickness determined through comparisons of experimental and model spectra agrees with results of ellipsometric measurements.     

Fundamental understanding of the interaction of continuous wave laser with aluminium

In welding, the depth of penetration, weld profile and the corresponding thermal cycle are the three basic outcomes that a user wishes to control flexibly. In laser welding applications, controlled application of power and energy density is the key to achieve predictable control of these characteristics. Creation of an analytical model is an important step towards understanding the underpinning science of laser metal interaction in controlling the depth, bead geometry and thereby temperature profile of a weld. The “power factor model”, which correlates the power applied per unit length to the laser metal interaction time, has been originally developed and validated for mild steel, guides a user on the selection laser system parameters, to achieve specific weld profile. This study is performed to extend the power factor–interaction time model to aluminium alloys by understanding the underpinning laser aluminium interaction parameters in terms of power density, interaction time, specific point energy and their correlation with the weld bead profiles. Although the power factor and interaction time showed a rectangular hyperbolic relationship, as observed in low carbon steel, for a specific weld depth and profile, the absolute magnitude and the characteristic profile of the curve is different due to the intrinsic differences in physical and thermal properties of aluminium as compared to steel. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of power and travel speed by keeping the energy input per unit length constant.     

On-line recording and processing of CTEM images

The direction dependence of electron energy losses was measured with a Möllenstedt energy analyzer which was attached to a convergent beam electron diffraction camera. High energy losses could be observed by adjusting the potential of the middle electrode. The investigations were performed with perfect MgO single crystal platelets of about 400 Å thickness. K-losses of oxygen and magnesium were analyzed. The greatest effect of the direction dependence was observed for the K-loss of Mg. By these results the validity of the reciprocity theorem was confirmed even for higher energy loss electrons up to at least 1.3 keV for 40 keV primary electrons.