Modelling of spur gear contact using a local adaptive finite element mesh

The gear drive is a critical part of a power transmission system. Modelling and simulating of the gear pairwith finite element method (FEM) take important role as a part of the design process to estimate stresses,deformations, and damage risks in various operating conditions. A parameterized calculation model for theanalysis of stresses in the gear contact and the gear root was developed. A local adaptive FE mesh was used,where a dense FE mesh zone around the contact point moves along the line of action to speed up thecomputation. The adaptive FE mesh, the rotation of the gear pair, and the accurate surface profile based ongear hobbing process were created in Matlab environment to obtain a good control of the flank profile andthe meshing parameters. These were integrated with a commercial FEM software to calculate deformationsand stresses. The developed FE mesh approach was validated successfully against analytical Hertzian theory.In addition, the developed spur gear model was compared to the gear standard ISO 6336 and a commercialgear calculation software resulting in relatively good correspondence with the maximum contact pressureand the maximum tooth root stresses

A numerical model for the calculation of fretting fatigue crack initiation for a smooth line contact

A numerical model for the calculation of fretting fatigue crack initiation in smooth elastic contact is presented. The model is focused on cylinder-on-plane contact and it can be applied in partial and gross slip conditions by using a constant normal force, a reciprocating tangential force and a cyclic bulk stress. The model is based on explicit stress equations, the multi-axial Dang Van and Findley fatigue criteria and a statistical size factor concept. The model allows non-symmetric traction distribution caused by cyclic bulk stress and the calculation of relative tangential surface displacement. The results from the model correlate well with the corresponding FE-results. The model developed is fast

On the fretting fatigue behavior of quenched and tempered steel in smooth point contact

Fretting fatigue can lead to a rapid decrease in the life of machine components when their contact surfaces have to transfer high tractions. Fretting fatigue was studied in partial, mixed and gross slip conditions made on quenched and tempered steel 34CrNiMo6. Measurements were made with sphere-on-plane contact geometry for smooth surfaces to detect macroscopic cracks. The fretting map type test series outlined a certain zone in partial and mixed slip conditions, where cracking occurred. The parameters affecting cracking threshold values and crack initiation are discussed

On the violation of a local form of the Lieb-Oxford bound

In the framework of density-functional theory, several popular density functionals for exchange and correlation have been constructed to satisfy a local form of the Lieb-Oxford bound. In its original global expression, the bound represents a rigorous lower limit for the indirect Coulomb interaction energy. Here we employ exact-exchange calculations for the G2 test set to show that the local form of the bound is violated in an extensive range of both the dimensionless gradient and the average electron density. Hence, the results demonstrate the severity in the usage of the local form of the bound in functional development. On the other hand, our results suggest alternative ways to construct accurate density functionals for the exchange energy.Comment: (Submitted on 27 April 2012

Response functions in TDDFT: Concepts and implementation

Many physical properties of interest about solids and molecules can be considered as the reaction of the system to an external perturbation, and can be expressed in terms of response functions, in time or frequency and in real or reciprocal space. Response functions in time-dependent densityfunctional theory (TDDFT) can be calculated by a variety of methods. Timepropagation is a non-perturbative approach in the time domain, whose static analogue is the method of finite differences. Other approaches are perturbative and are formulated in the frequency domain. The Sternheimer equation solves for the variation of the wavefunctions, the Dyson equation is used to solve directly for response functions, and the Casida equation solves for the excited states via an expansion in an electron-hole basis. These techniques can be used to study a range of different response functions, including electric, magnetic, structural, and k·p perturbations. In this chapter, we give an overview of the basic concepts behind response functions and the methods that can be employed to efficiently compute the response properties within TDDFT and the physical quantities that can be studied.DAS acknowledges support from the US National Science Foundation, Grant No. DMR10-1006184 and a graduate fellowship. LL and MALM acknowledges support from the French ANR (ANR-08-EXC8-008-01). AR acknowledges funding by the European Research Council Advanced Grant DYNamo (ERC-2010-AdG -Proposal No. 267374) Spanish MICINN (FIS2010-21282-C02-01), ACI-promociona project (ACI2009-1036), “Grupos Consolidados UPV/EHU del Gobierno Vasco” (IT-319-07), and the European Community through e-I3 ETSF project (Contract No. 211956). SGL was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, U.S. Department of Energy under Contract No. DEAC02-05CH11231.Peer reviewe

Any order imaginary time propagation method for solving the Schrodinger equation

The eigenvalue-function pair of the 3D Schr\"odinger equation can be efficiently computed by use of high order, imaginary time propagators. Due to the diffusion character of the kinetic energy operator in imaginary time, algorithms developed so far are at most fourth-order. In this work, we show that for a grid based algorithm, imaginary time propagation of any even order can be devised on the basis of multi-product splitting. The effectiveness of these algorithms, up to the 12$^{\rm th}$ order, is demonstrated by computing all 120 eigenstates of a model C$_{60}$ molecule to very high precisions. The algorithms are particularly useful when implemented on parallel computer architectures.Comment: 8 pages, 3 figure

Development of a test device for the evaluation of journal bearings

Journal and thrust bearings are widely used in heavy industry. Today, there is a growing need for studying different kinds of new bearing material and coating solutions in operating conditions where full film lubrication cannot be achieved or sustained. A test device for the evaluation of journal bearings was developed. The device consists of a rotating shaft and four stationary test bearings. This scheme eliminates the need for support bearings, allowing an accurate measurement of friction. The initial tests were carried out with a variety of loads and sliding speeds in mixed and full film regimes. The friction results in the form of a Stribeck curve were obtained and found to be in line with general trends. The results also indicate that the bearing lift-off speed occurs when the value of the non-dimensional ηen / ppro - parameter is in the range of 0.5·10-8 - 1.0·10-8

The crystal structure of cold compressed graphite

Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp3 bonds and is the only carbon allotrope which provides an excellent match to unexplained features in experimental X-ray diffraction and Raman spectra of graphite under pressure. The transition from graphite to Z-carbon can occur through simple sliding and buckling of graphene sheets. Our calculations predict that Z-carbon is a transparent wide band gap semiconductor with a hardness comparable to diamond.Comment: 4 pages, 5 figure