► A temperature modified Dirlik (TMDK) model is validated successfully. ► The validation is performed on standard specimens made of aluminium alloy AlSi9Cu3. ► The model enables fatigue damage ...estimation for combination of the frequency based fatigue with the temperature effect. ► The TMDK model enables computationally fast fatigue damage estimation.
The paper presents the validation of a temperature modified Dirlik method. This method enables an estimation of high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from a known power spectral analysis with the temperature effect. High cycle fatigue properties of high pressure die-cast aluminium alloy AlSi9Cu3 are investigated at elevated temperatures. Standard fatigue tests are performed to determine the temperature dependent S–N curves. In the next step special fatigue tests are developed and performed to validate the temperature modified Dirlik method. Finally, the numerical simulation results are compared with the experimental results. The temperature modified Dirlik method is tested successfully. Besides, it enables a computationally fast fatigue damage estimation of random stress loadings and temperature histories.
This paper details an advanced method of continuous fatigue damage prediction of rubber fibre composite structures. A novel multiaxial energy‐based approach incorporating a mean stress correction is ...presented and also used to predict the fatigue life of a commercial vehicle air spring. The variations of elastic strain and complementary energies are joined to form the energy damage parameter. Material parameter α is introduced to adapt for any observed mean stress effect as well as being able to reproduce the well‐known Smith‐Watson‐Topper criterion. Since integration to calculate the energies is simplified, the approach can be employed regardless of the complexity of the thermo‐mechanical load history. Several numerical simulations and experimental tests were performed in order to obtain the required stress‐strain tensors and the corresponding fatigue lives, respectively. In simulations, the rubber material of the air spring was simulated as nonlinear elastic. The mean stress parameter α, which controls the influence of the mean stress on fatigue life, was adjusted with respect to those energy life curves obtained experimentally. The predicted fatigue life and the location of failure are in very good agreement with experimental observations.
► The original Dirlik model is modified to estimate the high cycle fatigue damage. ► The model combine the frequency based fatigue and the temperature effect. ► The modified model enables ...computationally fast fatigue damage estimation.
This paper proposes a temperature modified Dirlik method to estimate the high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from a power spectral analysis. Besides, the methodology for combining the frequency based fatigue analysis with the temperature effect is represented. This approach is based on a new definition of loading as a random Gaussian process. The fatigue damage estimation of the high pressure die-cast aluminium alloy AlSi
9Cu
3 is investigated at elevated temperatures. Finally, numerical simulations on the known power spectral densities with different shapes at different temperatures are performed in order to establish proper dependence between the temperature modified Dirlik method, the rainflow cycle counting, the linear cumulative fatigue damage and the spectral bandwidth parameters. The proposed method enables computationally fast fatigue damage estimation for the random loadings and the temperature histories.
► The Prandtl type operator is used to determine dissipated energy. ► Key equations of the multiaxial operator approach are introduced. ► Operator approach is compared to the traditional integration ...approach by simulations. ► Integral approach cannot be justified due to cycle identification problem. ► The approach can be used under any rate independent thermomechanical fatigue loading.
The paper presents an approach to the energy dissipation calculation under arbitrary multiaxial thermomechanical fatigue (TMF) loading. In such an approach the total area of plastic hysteresis loops is taken as a measure of dissipated energy. The calculation is based on the concept of the developed temperature dependent Prandtl type operator. Energy dissipation is associated to irreversible dislocation movements represented by slider shifts of three independent operators. The dissipated energy is then obtained continuously at any time by collecting dissipated energy increments of each operator. It is shown that the multiaxial operator approach gives us the same total energy of plastic deformation as compared to the classical integration approach. Furthermore, the presented approach enables to automatically split the obtained dissipated energy between the “true” dissipated energy and the elastically “stored” energy. In order to satisfy the request for a minimum number of dedicated material tests, the approach assumes fixed principal directions. Therefore, the proportional as well as non-proportional loading conditions are addressed in the same manner, which is currently the main deficiency of the approach.
The paper concerns the metallic material lifetime calculation under arbitrary multiaxial thermo-mechanical fatigue loading. An energy-based damage operator approach (eDOA) is introduced. In such an ...approach, fatigue lifetime is continuously computed by the Prandtl type damage operator. The dissipated energy of plastic deformation is applied as a damage parameter that is obtained at any moment by the recently developed multiaxial energy operator approach. Strain-life curves are transformed into energy-cycle damage curves in order to associate the damage parameter with the fatigue lifetime. The present approach is validated on turbocharger housing. A satisfactory evaluation of the fatigue lifetime is obtained even though visco-plasticity and mean stress correction are not addressed yet.
► The Prandtl type operator is used to determine dissipated energy. ► Key equations of the operator approach are introduced. ► Operator approach is compared to the traditional integration approach by ...simulations. ► Both approaches give the same dissipated energy after a closed cycle. ► The operator approach can be used under arbitrary rate independent TMF loading.
The paper presents a numerical approach to compute the total amount of dissipated energy under arbitrary rate independent uniaxial thermomechanical fatigue (TMF) loading. Such an approach is based on the stress controlled Prandtl type operator enabling continuous energy dissipation calculation. It focuses on non-isothermal stress–strain conditions of a spring–slider segment, and relates slider movements to irreversible energy dissipation. The correct amount of dissipated energy is computed at any moment (online), without the need of ‘waiting’ the cycle to finish. The operator approach guaranties monotonically increasing progress of energy dissipation, which is within the framework of thermodynamics. It is also shown that the operator approach results in the same dissipated energy after closed isothermal cycle as the traditional integration approach.
We monitored trends of severe COVID-19 morbidity in Slovenia during weeks 13 to 37 2021. National weekly rates of severe acute respiratory infections (SARI) cases testing positive for SARS-CoV-2 at ...admission in all hospitals varied between 0.2 and 16.3 cases per 100,000 population. Of those without previous COVID-19 diagnosis, SARI COVID-19 admission rates ranged between 0.3 and 17.5 per 100,000 unvaccinated, and 0.0 and 7.3 per 100,000 fully vaccinated individuals. National SARI COVID-19 surveillance is essential in informing COVID-19 response.
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