Lifetime Calculations Research Articles

Bearing capacity and life time of multielement structures exposed to corrosive wear

When in operation, a significant part of metal structures is exposed to aggressive media, causing the damage and failure of construction sites. This paper reviewed the well-known mathematical models and calculation methods of multielement metal structures, exposed to corrosive wear. Also, this paper described the solution approaches of stress-strain state and a life time evaluation of multielement rod structures. The finite element method is used for the solution of stress-strain state evaluation; the advantages of this method are also described. This paper proposes the statements of problems and solution algorithms of life time calculation of multielement rod structures, such as statically indeterminate trusses operating in the aggressive medium. This paper considered the most common corrosion wear case, where the corrosion rate is a stress function. The proposed solution methods involve the use of mathematical models and analytical formulas.

Coupling First-Principles Calculations of Electron-Electron and Electron-Phonon Scattering, and Applications to Carbon-Based Nanostructures.

We report first-principles calculations of electronic gaps, lifetimes, and photoelectron spectra of a series of molecules, performed by efficiently combining the computation of electron-electron and electron-phonon self-energies. The dielectric matrix is represented in terms of dielectric eigenpotentials, utilized for both the calculation of G0 W0 quasi-particle energies and the diagonalization of the dynamical matrix; virtual electronic states are never explicitly computed and all self-energies are evaluated over the full frequency spectrum. Our formulation enables electronic structure calculations at the many-body perturbation theory level, inclusive of electron-phonon coupling, for systems with hundreds of electrons.

A simplified formulation for calculation of minority-carrier effective lifetime

Abstract An improved simple equation to calculate the minority-carrier effective lifetime in photoconductance measurements is proposed by the perturbation method. When the given constraints are satisfied, the given formulation leads to a fast and accurate determination of effective lifetime from the bulk lifetime, surface recombination velocity, the thickness of the wafer, and diffusion coefficient.

Novel Test Facility for Investigation of the Impact of Thermally Induced Stress Gradients on Fatigue Life of Cooled Gas Turbine Components

A novel test facility has been designed and setup for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients with respect to the damage evolution of cooled gas turbine components. Thermally induced stress gradients differ from geometrically induced stress gradients. From the point of view of stress mechanics, they are independent from external loads. From the perspective of material mechanics, their impact on service life is influenced by locally different material properties and strength. However, the impact of thermally induced stress gradients on the cyclic life of high loaded, cooled components is not precisely known. In order to increase knowledge surrounding these mechanisms, a research project was launched. To achieve high temperature gradients and extended mechanical stress gradients, large heat fluxes are required. The authors developed a test bench with a unique radiant heating to achieve very high heat fluxes of q˙ ≥ 1.6 MW/m2 on cylindrical specimen. Special emphasis has been placed on homogenous temperature and loading conditions in order to achieve valid test results comparable to standard low-cycle or thermo-mechanical fatigue tests. Different test concepts of the literature were reviewed and the superior performance of the new test rig concept was demonstrated. The austenitic stainless steel 316 L was chosen as the model material for commissioning and validation of the test facility. The investigation of thermally induced stress gradients and, based on this analysis, low-cycle fatigue (LCF) tests with superimposed temperature gradients were conducted. Linear elastic finite element studies were performed to calculate the local stress–strain field and the service life of the test specimens. The test results show a considerable influence of the temperature gradient on the LCF life of the investigated material. Both the temperature variation over the specimen wall and thermally induced stresses (TIS) are stated to be the main drivers for the change in LCF life. The test results increase the understanding of fatigue damage mechanisms under local unsteady conditions and can serve as a basis for improved lifetime calculation methods.

Calculations with spectroscopic accuracy: Energies and transition parameters for lines of fusion interest in Mo XXXIX

We have performed high-accuracy calculations of energy levels, wavelengths, lifetimes, line strengths and radiative rates among the 250 lowest levels of the (1s2)2s2, (1s2)2s2p, (1s2)2p2, (1s2)2snl (n=3,4,5,6; l=0,1,2,3,4,5), and (1s2)2pnl (n=3,4,5,6; l=0,1,2,3,4,5) configurations of Mo XXXIX. The second-order relativistic many-body perturbation theory (MBPT) is adopted and data are provided for all electric/magnetic-dipole (E1/M1) and electric/magnetic-quadrupole (E2/M2) transitions. Similar data for the 98 lowest levels of the n ≤ 4 configurations are also determined using fully relativistic multi-configuration Dirac-Fock (MCDF) wave functions in the active space approximation with the inclusion of a finite nuclear size, the Breit interaction, self-energy, and vacuum polarization to assess the accuracy of the calculations. Based on direct comparisons between the results obtained from these two independent methods, MBPT and MCDF, as well as with the other available theoretical values and measurements, our energies are assessed to be accurate to better than 0.02%. The accuracy for strong radiative rates is estimated to be about 5%. For Mo XXXIX, only a few transition lines have been established experimentally. The present new results considerably expand the existing data sets for this ion, and should be beneficial in analysis of experimental spectra and useful for spectroscopic diagnostics and modeling of hot plasmas, in particular in fusion devices.

Relativistic large scale CI calculations of energies, transition rates and lifetimes in Ca-like ions between Co VIII and Zn XI

Energies, E1, E2 and M1 transition rates and lifetimes are reported for the lowest 134 fine-structure levels of the 3p63d2, 3p63d4s, 3p53d3 and 3p63d4p configurations in all Ca-like ions between Co VIII and Zn XI. The calculations have been performed using the multiconfiguration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction (RCI) methods. Important core–valance and core–core electron correlation effects are systematically accounted with large scale configuration interaction expansion. The Breit interaction and leading quantum-electrodynamical (QED) contributions such as the vacuum polarization and self-energy corrections are also included in the RCI calculations. The results are compared with the compiled data from the NIST ASD and other calculations to evaluate the accuracy of the present calculations. Our results have good agreement with previous relativistic many-body perturbation theory (RMBPT) calculations and the data from the NIST ASD, except for Zn XI. Present calculations provide some missing data, especially for Cu X and Zn XI, in the NIST ASD.

Out-of-Phase TMF lifetime calculation of EN-GJS-600 (ASTM 80-55-06) ductile cast iron based on strain increase tests and evaluation of cyclic deformation behavior in isothermal measuring intervals

Components of internal combustion engines not only undergo mechanical high and low-cycle fatigue but also thermally induced loadings during start-stop and load changes. Accordingly, an efficient lifetime calculation method of the ductile cast iron EN-GJS-600 for Out-of-Phase thermomechanical fatigue (OP TMF) loading was developed based on Morrow’s relation between cyclic deformation and fatigue lifetime behavior. As an alternative to established fracture mechanics based approaches, the slope of the Wöhler curve is calculated from data determined in at least one each of a TMF strain increase and TMF constant amplitude test. Based on the Physically Based Lifetime calculation (PhyBaL) method previously published for isothermal low cycle fatigue (LCF) and high cycle fatigue (HCF) loadings, and data taken from only one strain increase and at least one constant amplitude OP TMF test, the Wöhler curve can be described as according well with constant amplitude OP TMF tests performed for validation. In the present work, triangular TMF cycles were applied at 5 mHz (0.005 Hz) with a temperature range from 50 to 350 °C. Cyclic deformation behavior as input data for calculation of the slope of the Wöhler curve was determined by stepwise increases of mechanical strain amplitude in OP TMF tests. By constant amplitude tests at different mechanical strain amplitudes, the lifetime and cyclic deformation behavior at OP TMF loading were determined for validation. Moreover, applicability of measurement cycles at constant temperature and low stress amplitude applied in defined intervals of regular OP TMF cycles proved to match the OP TMF cyclic deformation behavior well. This opens up the prospect of characterizing cyclic deformation behavior in more complex, near service TMF cycles as a baseline for lifetime assessment using the PhyBaL approach outlined above.

Evaluation of the Fatemi‐Socie damage parameter for the fatigue life calculation with application of the Chaboche plasticity model

AbstractThis paper presents an approach to the evaluation of the Fatemi‐Socie parameter applied to the lifetime calculation of specimens made of CuZn37 brass. In particular, two factors affecting the calculated fatigue lives are analysed: (i) the influence of stresses calculated by applying the Chaboche plasticity model on the computed lifetime and (ii) the influence of a variability of parameter k of material sensitivity to normal stress on the calculated lifetime. The novelty of the presented research is associated with the fatigue life calculation according to the Fatemi‐Socie model with the introduced k dependence accounting for the lifetime. Underestimation of the calculated stresses results in the higher calculated fatigue lives but with acceptable scatter band. The parameter of material sensitivity to normal stress for the CuZn37 brass varies insignificantly having little impact on the calculated fatigue lives.

Ferroelastic Properties of PZT: Characterization Under Compressive and Tensile Stress, Finite-Element Simulation, and Lifetime Calculation.

Finite-element (FE) simulations, based on a phenomenological nonlinear constitutive model, were carried out to show the impact of ferroelastic switching on compressive and tensile loading of a soft and hard ferroelastic polycrystalline lead zirconate titanate ceramic (PbZr1-xTixO3, PZT). Hereby, a model assembly is used that simulates mechanical stresses generated by the contact of a ceramic element with a concave counterpart. In order to parameterize the constitutive model, the elastic and piezoelectric tensors are determined by the small signal resonance method and by the direct measurement under compressive/tensile loads. In addition, the large field ferroelectric and ferroelastic behavior of polarization and strain were characterized. The simulations show that the tensile stress level within the piezoceramic is much lower compared to a linear elastic model, which is related to ferroelastic switching. This is demonstrated to have a significant influence on mechanical lifetime predictions. To validate the parametrized FE model, a four-point bending experiment was used. The comparison of the calculated and measured strain on the compressive and tensile sides of the sample showed very good correlation.

Evaluating the Relationship between Phonon and Thermal Properties of Group IV Alloys Using Molecular Dynamics Simulation

This study examines whether mass or potential disorder is more effective at reducing the thermal conductivity and phonon properties in group IV alloys using molecular dynamics (MD) simulation. In this investigation, virtual atoms were used so that the atomic mass and the interatomic potential could be varied independently. The effects of potential disorder on the thermal conductivity and phonon properties are smaller than those associated with mass disorder. The suppression of thermal conductivity by alloying is attributed only to the effects of mass disorder. In the phonon lifetime calculation, the lifetime of the phonon determined by the scattering due to potential disorder is ten times longer than that due to mass disorder. This difference is so large that the contribution of potential disorder to phonon lifetime is effectively negligible. Thus, a binary interatomic potential is unnecessary to accurately estimate the thermal conductivity of the group IV alloys.

Calculation of Filter Lifetime Using Empirical Model Applied to Hydrodynamic Column for Phosphate Removal from Greywater

Greywater is one of the point source pollution that negatively impact water resources if not properly treated. However, improvement of greywater quality can be potentially used for irrigation purpose. The main objective of this study is to calculate the lifetime for calcined waste mussel shell (CWMS) in hydrodynamic column. This study was performed using laboratory scale hydrodynamic column filled with CWMS to determine the breakthrough curve, adsorption capacity, accumulation rate and lifetime using empirical model for the adsorption of PO4-3 onto CWMS from greywater. The bed height and flow rate that used in the experiment are 200 mm and 80 mL/h, respectively. The results demonstrate that breakthrough and exhaustion times are 12h and 18h, respectively. The empirical model was verified using experimental equilibrium data. The values of k1 and qmax calculated using model equations are 0.122 mg/g h2 and 0.0017 mg/g, respectively. On the basis of the results, CWMS can be economically basis media used as an adsorbent for the removal of PO4-3 from greywater in the hydrodynamic column.

Lifetime assessment of anisotropic materials by the example short fibre reinforced plastic

Lifetime assessment at an early stage of a development process is essential to ensure an optimal solution. Classical approaches are often limited to isotropic materials like metals. This paper presents an approach to deal with anisotropic materials using the example of short fibre reinforced plastics (sfr). Therefore, a given work flow, consisting the manufacturing process and the micro structure, is extended by the direction-depended non-linear material behaviour. Furthermore the crucial points of lifetime assessment are pointed out. Starting from a process simulation the influence of a manufacturing process on the local material properties is captured for an finite element analysis. In interaction with micro mechanical models an anisotropic stress field can be calculated which then can be used in the lifetime calculation. To characterize the material and adapt required material-models quasi static as well as cyclic tests were performed. Finally the lifetime can be calculated based on the concept of local S/N-curves. Following this enhanced method, a part equitable life time assessment can be performed independent of geometry. Compared to other methods the local material behaviour and local loads are captured over the whole structure. This provides a time and cost efficient life time prediction even on large structures. Since software tools are available for all simulation steps the presented method provides a time and cost efficient life time prediction even on big structures.

Calculations of energies, transition rates, and lifetimes for the fluorine-like isoelectronic sequence with [formula omitted

Employing two state-of-the-art methods, multiconfiguration Dirac–Hartree–Fock and second-order many-body perturbation theory, highly accurate calculations are performed for the lowest 200 fine-structure levels arising from the 2l7,2l63l′ and 2l64l′ configurations of the fluorine-like isoelectronic sequence with Z=31−35. Complete and consistent atomic data, including excitation energies, lifetimes, wavelengths, and E1, E2, M1, M2 line strengths, oscillator strengths, and transition rates among these 200 levels are provided. Comparisons are made between the present two data sets, as well as with other available experimental and theoretical values. The present data are accurate enough for identification and deblending of emission lines involving the n=3,4 levels, and are also useful for modeling and diagnosing fusion plasmas.

Theoretical Calculations of Economic Life of Firefighting Appliances Based on Chassis Tatra in the South Moravian Region

This paper is focused on the evaluation of economic data obtained from operational records of firefighting equipment with a focus on firefighting and rescue appliances, especially on exit vehicles based on the chassis CAS 20 – TATRA T815-231R55 18 325 4x4.2. These vehicles have been operated by professional units of the Fire and Rescue Service in the South Moravian Region since September 2013. The producer of firefighting superstructures WISS GROUP, Bielsko-Biala, Poland, was a supplier of all these vehicles. The paper’s aim is to specify the optimum lifetime of the firefighting vehicles by the analysis of firefighting vehicles’ economical operation. Theoretical calculations of the optimum lifetime have been processed with implementing both the method of exponential trends and the Brown method. The residual value of vehicles has been calculated both according to the current Czech tax law, and to the Expert Standard Valuation of motor vehicles in force in the Czech Republic.

Assessing the reproducibility of quartz OSL lifetime determinations derived using isothermal decay

Signal stability is a key consideration when using luminescence dating techniques. The stability, or lifetime, of a signal is one of the factors determining the upper age constraint for luminescence dating, and it has been suggested that the signal being used for dating should have a lifetime at least ten times the age being dated in order to limit age underestimation to an upper loss of 5%. Accurate derivations of signal stability and associated kinetic parameters, such as trap depth and frequency factor, are also important parameters for constraining rock cooling histories in thermochronometric techniques. This paper aims to assess the reproducibility of lifetime determinations derived using isothermal decay measurements. Variability arising from changing the isothermal decay protocol used is tested. Simulating Arrhenius plot from fixed trap depth and frequency values shows that whilst trap depth can be relatively well constrained, significant variability in the frequency factor, hence signal lifetime, should be expected. This paper also uses luminescence signals measured using different wavelengths to better understand the impact of signal from non-fast quartz OSL components in lifetime calculations. The presence of contributions from non-fast OSL components in the initial part of the OSL signal can result in the lifetime being calculated from charge contributions from multiple traps, not solely the 325 °C TL peak, as has been previously assumed. This effect can be reduced however by stimulating luminescence signals with longer wavelengths to better isolate signal from the fast component.

A stress distribution modelization of a neat fit pin-loaded hub

PurposePin-loaded hubs with fitted bush are used in industrial connector-type elements. They are subjected to varying radial forces leading to variable stress distribution. The literature provides various pressure distribution expressions adapted essentially for symmetric geometries and fixed load condition (circular hubs, half-infinite geometries, axial load, tangential load, etc.). This study aims to take into account the geometrical conditions of industrial connector-type elements and presents a model for pressure distribution based only on geometric parameters, maximal pressure and contact angle value for the case of fit pin-loaded hub.Design/methodology/approachThe finite element computation for the contact problem shows that the pressure distribution of the pin-loaded hub under various inclined forces (from 0° to 180°) is a parabolic distribution. This distribution can be defined by three parameters which are θA, θB and Pmax. The study assumes that the distribution is symmetric and that Pmax can be modeled using force F, hub radius R, hub thickness b and the half contact angle are θA.FindingsThe new proposal pressure distribution parameters are easy to identify. Even for the non-symmetric pressure distribution, the study denotes that the errors on evaluating θA and θB keep the analytical model still in good agreement with finite element computations.Research limitations/implicationsOnly the neat fit case was studied.Practical/implicationsPin-loaded joints are connector-type elements used in mechanical assemblies to connect any structural components and linkage mechanisms such as connecting rod ends of automotive or shear joints for aircraft structure.Originality/valueThe good correlation between finite element computations and model results shows the validity of the assumptions adopted here. Analytical fatigue models, based on this stress distribution, could be derived in view of a fatigue lifetime calculation on connecting hub. Friction, pin deformation and local plastic effects under pin-loading are the main phenomena to take into account to further enrich this model.

EXOCROSS: a general program for generating spectra from molecular line lists

EXOCROSS is a Fortran code for generating spectra (emission, absorption) and thermodynamic properties (partition function, specific heat, etc.) from molecular line lists. Input is taken in several formats, including ExoMol and HITRAN formats. EXOCROSS is efficiently parallelized showing also a high degree of vectorization. It can work with several line profiles such as Doppler, Lorentzian and Voigt and support several broadening schemes. Voigt profiles are handled by several methods allowing fast and accurate simulations. Two of these methods are new. EXOCROSS is also capable of working with the recently proposed method of super-lines. It supports calculations of lifetimes, cooling functions, specific heats and other properties. EXOCROSS can be used to convert between different formats, such as HITRAN, ExoMol and Phoenix. It is capable of simulating non-LTE spectra using a simple two-temperature approach. Different electronic, vibronic or vibrational bands can be simulated separately using an efficient filtering scheme based on the quantum numbers.

Load distribution in a roller-type rotor blade bearing

Pitch bearings of wind turbines are large, grease-lubricated rolling bearings that connect the rotor blades with the rotor hub. Rolling bearings are the standard bearing type for this application. Most blade bearings are four-point bearings with one or two rows. Three-row roller bearings with two axial rows and one radial row have higher costs, but are an increasingly used alternative. Both rotor blade and rotor hub have a varying stiffness along the circumference of the bearing rings. This results in rotationally non-symmetric load sharing (load distributions) of the bearing rollers. The load distribution depends on the pitch angle, the load magnitude and the load angle. In this paper, we evaluate the load sharing of such a three-row bearing for a reference wind turbine of the 3 MW-class, taking account of the stiffness of the interface parts hub and rotor blade. A set of finite-element simulations with varying loads, load angles and pitch angles has been executed to determine the influence of the named parameters on the loads of the individual rollers. Curve fits of these discrete load points allow the determination of roller loads for any given parameter combination. One application of the results is the determination of the overall bearing load which is a key input for fatigue lifetime calculations.

Damage Tolerance Evaluation of Rotorcraft Horizontal Tail Under Variable Amplitude Service Loading Conditions

To ensure the safe operation of the helicopter throughout its lifetime, the primary structure has to be designed taking into account damage tolerance criteria. This has been considered in the design process, for example, by using multiple load paths as well as by taking into account the presence of certain structural defects like impacts or manufacturing defects in composite parts when performing the dimensioning and lifetime calculations. This paper describes and presents an effort performed for damage tolerance (DT) aspects of rotorcraft horizontal tail (HT) through multi-scale (MS) modeling computational approach to assess the growth rate of damages from fatigue under spectrum loading from rotorcraft mission profile and consideration of the effects of material variability to assess structural advantages. Main emphasis was laid on the design of the cyclic loaded components in order to achieve unlimited life with high flaw tolerance. A micromechanics-based multi-scale progressive failure analysis (MS-PFA) approach that detects damage and fracture evolution is carried out to assess the durability and damage tolerance (DD (2) fiber waviness exhibited in thick sections; and (3) void shape, size, distribution. Fatigue life is estimated under service spectrum block loading conditions in critical mission by determining the material stiffness and strength degradation, failure load and cycles.

Fatigue life calculation procedure for the rotor of an embedded magnet traction motor taking into account thermomechanical loads

Abstract Working cycle and load fluctuation have to be considered in the design process of traction motors in order to be able to optimize the size, life cycle, and performance of the electric drive. The total stress and fatigue life of an electric motor rotor are determined to a large extent by centrifugal forces, tangential forces caused by torque, and the temperature gradient along the rotor. Rapid increase in heat as a result of sudden variation in the electric current and the differing thermomechanical characteristics of the components leads to non-uniform stress in the assembly. By applying the principle of superposition to the transient mechanical and thermal stress, a multidisciplinary method is proposed for the calculation the equivalent von Mises stress for a fatigue life analysis. This paper presents a fatigue life calculation procedure considering the mechanical and thermal stresses. The method is presented using the rotor of the Electric RaceAbout (ERA) traction motor as a case example. The presented approach is validated by comparing simulated and measured temperature data from ERA drive tests at the Nurburgring Nordschleife track. The results indicate the great importance of taking into consideration both mechanical and thermal loads in lifetime calculation.