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A Uniaxial Hysteretic Superelastic Constitutive Model Applied to Additive Manufactured Lattices
(John Wiley & Sons, 2024-11-29) Schasching, Marius; Červinek, Ondřej; Koutný, Daniel; Pettermann, Heinz; Todt, Melanie
Lattice materials with superelastic properties offer great potential for engineering applications, as they are able to undergo large deformations while ensuring the reversibility of the deformations due to stress-induced phase transformation. Adequate prediction of the mechanical response of lattice materials requires models that properly capture the deformation mechanisms of the internal architecture and the material response of the parent material. To analyze large-scale lattices by means of the finite element method, numerical efficiency becomes crucial. For this purpose, we propose a simple approach relying on beam-based modeling in combination with a uniaxial superelastic constitutive material model. The latter is based on polynomial functions, which make it easy to take customer-based material data into account being especially important for additive manufactured materials. To verify our constitutive model, a comparison with a well-established standard model is performed. The capabilities of the beam-based model to predict the mechanical response of lattice materials are evaluated by the comparison to high-fidelity models using continuum elements. We show that beam-based modeling is able to capture the governing deformation mechanisms of the investigated lattices and that our constitutive model is able to capture the smooth stress–strain response of the experimental data that are not available to the standard model.
Case Study: Correlations Between Curve Squeal, Weather Conditions, and Traction in a Tram Loop
(Faculty of Engineering, University of Kragujevac, Serbia, 2024-12-15) Valena, Martin; Omasta, Milan; Klapka, Milan; Galas, Radovan; Navrátil, Václav; Křupka, Ivan; Hartl, Martin
This study explores the relationship between the coefficient of traction (CoT) and squeal noise parameters on a tram line loop, focusing on the influence of weather conditions. An automatic noise module was placed near a tram loop known for noise complaints. This module distinguishes between squeal and flange noise, recording their duration, root mean square (RMS) sound pressure level, and maximum sound pressure level when a threshold in the appropriate frequency band is exceeded. Concurrently, weather conditions were monitored, and the CoT on the rail was measured using a BUT rail tribometer. The findings reveal a notable correlation between the CoT and the duration of squeal noise, while the association with sound pressure levels was less pronounced. An increase in CoT was observed with rising relative humidity, which may be attributed to increasing temperature throughout a sunny April day, while absolute humidity remained almost constant. Furthermore, noise parameters rose with higher relative humidity and showed an inverse relationship with temperature. These findings suggest that weather conditions, particularly relative humidity and temperature, influence both the CoT and noise parameters on tram lines.
Performance and stability comparison of hydrostatic bearing pad geometry optimization approaches
(Springer Nature, 2025-04-30) Michalec, Michal; Foltýn, Jan; Svoboda, Petr; Křupka, Ivan; Hartl, Martin
Hydrostatic bearings are commonly used across a range of applications, yet their reliance on externally pressurized lubricants presents significant energy consumption challenges. This research aims to experimentally assess various approaches for optimizing the geometry of hydrostatic bearing pads. Utilizing a two-pad hydrostatic tester equipped with online diagnostics, we analyzed optimized multi-recess pads developed through both analytical methods and computational fluid dynamics (CFD). Our results demonstrate that the CFD method achieves a substantially greater film thickness recess pressure compared to the analytical method under similar experimental conditions. Additionally, the CFD approach reduces pumping power losses by 14%. However, this improvement in performance is accompanied by a reduction in film stiffness and an increased sensitivity to eccentric overload or misalignment, as highlighted in our findings. While the adoption of CFD-optimized geometries offers significant potential for lowering energy consumption, maintaining precise alignment especially in large-scale applications remains essential. In summary, our study suggests that employing CFD optimization can effectively reduce the service costs associated with hydrostatic bearings, but optimal outcomes necessitate careful alignment considerations.
Uncertainty analysis of hydrostatic bearing working conditions with experimental, CFD, and analytical approach
(SPRINGER HEIDELBERG, 2025-05-02) Foltýn, Jan; Maccioni, Lorenzo; Michalec, Michal; Concli, Franco; Svoboda, Petr
The design and real-time control of hydrostatic bearings (HS) require precise models capable of accurately predicting bearing behaviour under diverse operational conditions. Traditional analytical models have been found to be inadequate to simultaneously estimating critical parameters, including carrying capacity, recess pressure, film thickness, and flow rate. To overcome these limitations, Computational Fluid Dynamics (CFD) has emerged as a powerful tool in recent years. However, the accuracy of operational data used to calibrate the numerical and analytical models significantly influences the propagation of uncertainty. This study focusses on an experimental campaign and the development of a CFD model within the OpenFOAM® environment. Numerical and analytical models were calibrated using various input parameters, such as flow rate and recess pressure, to replicate experimental conditions while accounting for extreme operational scenarios and the inherent uncertainties in the experimental data. The results indicate that although average CFD predictions exhibit consistent errors in estimating operational parameters, the uncertainty ranges of the experimental and numerical data overlap under the conditions examined. On the contrary, analytical predictions show notable discrepancies, even when measurement uncertainties are considered. In particular, recess pressure emerged as the most effective input parameter to accurately estimating carrying capacity. These findings highlight the critical importance of incorporating measurement uncertainties into the calibration of numerical and analytical models for HS bearings, offering valuable information for their precise design and effective real-time control. Moreover, this paper demonstrates how CFD enables the consideration of misalignments measured during experimentation, a factor that is not accounted for in current analytical models.
On the Friction and Lubrication of 3D Printed Ti6Al4V Hip Joint Replacement
(Springer Nature, 2025-04-28) Rebenda, David; Odehnal, Lukáš; Uhrová, Simona; Nečas, David; Vrbka, Martin
The present study investigates the tribological performance of 3D printed Ti6Al4V total hip replacements (THR) compared to conventionally produced THRs from CoCrMo and FeNiCr alloys. The objective was to evaluate the suitability of 3D printed titanium alloy, with and without DLC coating, for THR rubbing surfaces and to investigate the potential benefits of 3D printing technology for friction and lubrication. A pendulum hip joint simulator was employed to replicate the swinging motion of a hip joint, thereby enabling the measurements of coefficient of friction (COF) and the observation of lubricant film formation under realistic conditions between the metal femoral head and acetabular cup. The experiments demonstrated that additive manufacturing enables the creation of specific surface topographies that can enhance protein adsorption, but also introduce surface imperfections negatively affecting tribological properties. The elevated surface roughness of additively manufactured femoral heads did not inevitably result in an increase in COF and was comparable to that of conventionally manufactured femoral heads. The additively manufactured Ti6Al4V head without DLC coating also exhibited a more rapid increase in lubricant film thickness during dynamic motion. In conclusion, the findings indicate that while 3D printing offers promising advancements in implant customization and material properties, its application requires careful consideration of surface finishing and coating methods to achieve optimal tribological performance.

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