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Binder jetting of spinel-based refractory materials - processing, microstructure and properties

ADDITIVE MANUFACTURING 2025年 102卷

作者： Freitag, Lisa Storti, Enrico Bretschneider, Leif Zeidler, Henning Hubalkova, Jana Aneziris, Christos G. TU Bergakad Freiberg Inst Ceram Refractories & Composite Mat Agr Str 17 D-09599 Freiberg Germany Tampere Univ TAU Fac Engn & Nat Sci Mat Sci & Environm Engn Korkeakoulunkatu 6POB 589 Tampere 33014 Finland Empa Swiss Fed Labs Mat Sci & Technol Lab High Performance Ceram Uberlandstr 129 CH-8600 Dubendorf Switzerland TU Bergakad Freiberg Inst Machine Elements Design & Mfg Chair Addit Mfg Agr Str 1 D-09599 Freiberg Germany

Spinel-based refractories were produced by binder jetting using a novel MgO-citric acid binder system and water as an activator of the acid-base reaction. Additionally to different amounts of binder and saturation levels, the addition of small amounts of PVA was investigated. Powder characteristics such as particle size distribution, particle shape and flowability as well as thermal behavior of the binder system were evaluated. Phase analysis by XRD conducted on dried and sintered samples indicated in situ spinel formation. Sintered samples exhibited low shrinkage (< 4%), but rather high apparent porosity (>50 vol.%) and median pore size (>25 mu m). Compressive strength of dried and sintered samples was measured both parallel and perpendicular to the printed layers with values up to 8.5 MPa in the sintered state. After thermal shock with water, microcracks were formed and the residual strength was about 1.9 MPa. Selected sintered samples were analyzed with microfocused X-ray computed tomography, revealing the orientation of larger angular-shaped particles along the printed layers. Finally, a small crucible was successfully printed and sintered.

关键词： Refractories Additive manufacturing Binder jetting Spinel Microstructure

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Wear and smearing resistance of black iron mixed oxide coated steels

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INTERNATIONAL JOURNAL OF SURFACE SCIENCE AND ENGINEERING 2010年第4-6期4卷 337-359页

作者： Mihailidis, A. Salpistis, C. Panagiotidis, K. Sachanas, C. Gatsios, S. Aristotle Univ Thessaloniki Lab Machine Elements & Machine Design Thessaloniki 54124 Greece

Surface coatings increase the wear and smearing resistance of a machine element. Nevertheless, most of the coating processes are expensive and time-consuming. By contrast, Schaeffler's Durotect (R) B coating seems attractive regarding production expenditure and price. However, the literature about the behaviour of this coating is very limited. This paper describes the experimental setup and the experiments that were carried out in order to evaluate the wear and smearing resistance of the Durotect (R) B coated 100Cr6 steel in reference to plain 100Cr6 through hardened steel. Durotect (R) B is a mixed black iron oxide coating developed by Schaeffler especially for use in machine elements. The main measured parameters (mass loss, smearing slide-to-roll ratio, friction and normal force, surface roughness and bulk temperature) are presented. Comparative charts of the monitored parameters are given and discussed. It is concluded that this coating decreases friction coefficient and improves both the smearing and wear resistance.

关键词： black iron mixed oxide coating Durotect (R) B bluing friction coefficient running-in wear rate smearing two discs test rig solid contact time percentage mixed lubrication surface coating

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Calculation of friction coefficient and temperature field of line contacts lubricated with a non-Newtonian fluid

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WEAR 1999年第2期232卷 213-220页

作者： Mihailidis, A Retzepis, J Salpistis, C Panajiotidis, K Aristotelian Univ Salonika Dept Engn Mech Lab Machine Elements & Machine Design Salonika 54006 Greece

In the present paper a model for the fast numerical prediction of the friction coefficient and the temperature field of such contacts is introduced. Motion and energy equations are numerically solved taking into consideration the non-Newtonian behavior of the lubricant assuming a power law rheological model. The viscosity is calculated in every point of the film as a function of the local temperature and pressure. The introduced model relies primarily on two simplifying assumptions. First the pressure distribution is taken semi-elliptical over the entire contact area. Consequently the film shape is assumed to be parallel having a constant film thickness. For its calculation a modified version of the Sadeghi-McClung formula is presented, which takes into account the slip rate. Second the effect of the surface roughness is neglected, since, in the operating region considered, no asperity interactions take place. In order to examine the influence of these assumptions on the accuracy of the proposed model, calculated values of the friction coefficient were compared to measured ones, obtained from experiments carried out on a two disks test rig. This comparison showed very good correlation of the calculated with the measured coefficients of friction, justifying the introduced model. (C) 1999 Elsevier Science S.A. All rights reserved.

关键词： friction coefficient temperature field non-Newtonian lubricant thermal EHD lubrication

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Modeling and fatigue assessment of weld start-end locations based on the effective notch stress approach

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MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK 2011年第4期42卷 298-305页

作者： Malikoutsakis, M. Savaidis, G. Aristotle Univ Thessaloniki Fac Mech Engn Lab Machine Elements Machine Design Thessaloniki 54124 Greece

The present paper contains a methodology for modeling and life assessment of fatigue loaded welded components providing distinct weld start and end locations. The proposed methodology follows the IIW recommendation regarding modeling and finite element meshing of weld toe and root by means of an effective notch radius and uses the corresponding Wohler curve (FAT class) to assess the durability. Geometrical singularities and, therewith, numerical discontinuities, can be overcome especially when 3D weld root problems are treated. The fatigue life assessment is performed on the basis of normal stresses acting at the failure-critical weld toe and root locations. Comprehensive experimental database containing stress and fatigue life results derived from motor truck's hypoid rear axles providing complex 3D welds subject to vertical, longitudinal, and torsional loading is used to verify the calculation accuracy of the proposed methodology. The agreement between experimentally determined and calculated fatigue results is satisfactory.

关键词： Fatigue Welds Local Concepts Weld-Ends

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EHL film thickness and load dependent power loss of cycloid reducers

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 2016年第7-8期230卷 1303-1317页

作者： Mihailidis, Athanassios Athanasopoulos, Emmanouil Agouridas, Konstantinos Aristotle Univ Thessaloniki Fac Engn Dept Mech Engn Lab Machine Elements & Machine Design Thessaloniki 54124 Greece

Robotic arms, space joints and micro-medical devices demand high positioning accuracy, high efficiency, lightweight reducers which often are required to be lubricated for life. Cycloid drives have been gaining popularity in recent years due to their compact form, high reduction ratio and stiffness. Energy loss minimization and ensured good lubrication are vital for those applications. Total power loss is commonly computed as sum of two parts. The first is the zero or minimum-load, which is caused mainly by oil churning and drag as well as contact seals friction. The second part is load dependent and is related to the transmitted power. It is dominated by the friction in all sliding contacts. Geometry parameters of the meshing surfaces affect the load distribution as well as the rolling and sliding velocity of the contacting bodies. The study utilizes meshing equations and an ideal load distribution model to calculate pressure, rolling and sliding at the contacts of a typical 1-disc cycloid reducer. The conditions are characterized by severe slip and counter-turning. A comparison with established EHL models revealed high discrepancy at areas of counter-turning. The ultimate aim of the present study is to calculate the local film thickness and friction. Due to the shortcomings of the aforementioned models, an advanced numerical EHL solver was employed. The determined conditions of the contact points were used as input for the solver. In order to demonstrate the method, calculations were performed for four different load cases as a way of showing the effect of input speed and torque on the efficiency.

关键词： EHL cycloid reducers central film thickness FVA reference oils power loss efficiency friction coefficient

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Fatigue assessment of thin-welded joints with pronounced terminations

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FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES 2014年第7期37卷 782-799页

作者： Malikoutsakis, M. Savaidis, G. Aristotle Univ Thessaloniki Lab Machine Elements & Machine Design Dept Mech Engn Thessaloniki 54124 Greece

The present paper reviews and contains simple modifications to extend the applicability of global and local fatigue concepts to thin-welded specimens with pronounced weld terminations (starts/ends). Experimental fatigue data reported by Kaffenberger and Vormwald have been used for the validation of the proposed procedures. Special attention is paid to the notch strain concept. The material state is explicitly considered by means of corresponding strain-life curves in conjunction with PSWT, PMorrow or the experimental mean stress sensitivity factors proposed by Olivier. The accuracy of Neuber's sharp and mild notch formulas, Seeger-Beste's formulation and Glinka's strain energy density rule within the context of the notch strain approach has been investigated. Simple rules accounting for stress relaxation effects have been additionally proposed and implemented into the calculations. Comparison of experimental with theoretical fatigue lives validates the accuracy and robustness of the proposed procedures to calculate fatigue design S-N curves.

关键词： fatigue effective notch stress notch strain approach thin-welded joints weld terminations

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Influence of run-in procedures and thermal surface treatment on the anti-wear performance of additive-free lubricant oils in rolling bearings

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WEAR 2015年 328卷 309-317页

作者： Burghardt, Gero Waechter, Florian Jacobs, Georg Hentschke, Chistoph Rhein Westfal TH Aachen Inst Machine Elements & Machine Design D-52062 Aachen Germany ETH Inorgan Chem Lab CH-8093 Zurich Switzerland

When rolling bearings are operated in the boundary and mixed friction regime, there is a risk of wear which can be minimized by the application of suitable lubricants with anti-wear additives. These lubricants form surface-bound additive-based tribolayers under tribological strain. The trend towards a reduction of additive concentration requires new methods of effective wear protection. In this study, two additive-free lubricants were investigated using highly wear-critical cylinder roller thrust bearings. The results show that both oils exhibit insufficient wear protection. This protection can be increased for one of the oils by an iron oxide-based tribolayer which is built up during a suitable run-in procedure. Furthermore, it is shown how the run-in tribolayer can be reproduced by a thermal treatment of the bearings. The increase in wear protection can be explained by a better lubricant-surface interaction due to the tribolayers, which leads to a better separation of the steel surfaces. The tribolayers are characterized using EPMA, FIB-TEM, and nano-indentation analyses. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Bearings Wear testing Boundary lubrication Tribochemistry Surface analysis Nanoindentation

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Influence of the bushing geometry on the thermohydrodynamic performance of a misaligned journal bearing

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY 2010年第J1期224卷 37-53页

作者： Mihailidis, A. Bakolas, V. Panagiotidis, K. Poulios, K. Sachanas, C. Aristotle Univ Thessaloniki Lab Machine Elements & Machine Design Thessaloniki 54124 Greece Schaeffler KG Corp Basic Projects & Long Term Qual Bearing Fundamentals Herzogenaurach Germany

Often journal bearings have to support shafts that run misaligned into the bushing bore because of the combined effect of elastic deformations and manufacturing tolerances. In such cases, the thermo-hydrodynamic behaviour of the bearing needs to be investigated in detail in order to ensure the safe operation of the device, or, in other words, to avoid asperities contact. The difficulties to model the thermal phenomena comprise one of the main reasons for the limited contribution of theoretical models to the designing efforts. In this article an accurate thermo-hydrodynamic simulation of journal bearings operating under misalignment conditions is introduced at first. Then, the computed film thickness, pressure and temperature distribution, as well as the friction coefficient are shown for several variations of hour-glass profiled bearings operating under a misalignment of up to 5'. From the results shown it can be concluded that the load-carrying capacity of journal bearings can be greatly enhanced if a properly selected hourglass design is applied. The results show further that a three-dimensional thermo-hydrodynamic analysis, as the one shown here, should always be carried out in order to verify the bushing design.

关键词： journal bearing thermo-hydrodynamic lubrication misalignment multi-grid method

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Finite element method based analysis of planetary gear systems considering backlash and manufacturing deviations

Finite element method based analysis of planetary gear syste...

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International Conference on Gears

作者： Mihailidis, A. Korbetis, G. Drivakos, N. Nerantzis, I. Aristotle Univ Thessaloniki Lab Machine Elements & Machine Design Thessaloniki Greece BETA CAE Syst Thessaloniki Greece

ISBN: (纸本)9783180922942

The load carrying capacity of gear transmissions depends strongly on design, material and operation conditions. Modern analysis methods, such as the Finite Element Analysis, consider the above parameters with more or less sufficient accuracy. But it is still a challenging task to account for backlash and manufacturing errors although they have a crucial impact. There are several difficulties to overcome: First, the contact footprints as well as backlash and errors are some orders of magnitude smaller than the dimensions of the gears. Therefore, an extremely fine mesh is required. On the other hand, the total number of DOF's should be kept as small as possible to keep the computational effort manageable. Less stressed areas should be coarsely meshed, while the transition must be as smooth as possible. Moreover, in order to generate and mesh three-dimensional tooth flanks taking into considerations the above mentioned geometrical deviations is extremely time consuming. In this paper, new techniques and tools are introduced aiming to facilitate the modelling procedure. They include automatic generation of 3D gear flanks and selective meshing. A simple planetary gear system featuring helical gears with backlash and manufacturing errors is used to demonstrate the effectiveness of the proposed procedure, since it features multiple contacts and floating members. Results shown include stress distribution and deformation, as well as load sharing under quasi-static conditions.

关键词： Finite element method

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Overload capacity of high transmission ratio speed reducers

Overload capacity of high transmission ratio speed reducers

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3rd International Conference of Engineering Against Failure, ICEAF 2013

作者： Mihailidis, A. Nerantzis, I. Athanasopoulos, E. Aristotle University of Thessaloniki Department of Mechanical Engineering Lab of Machine Elements and Machine Design Greece

ISBN: (纸本)9789608810433

This paper presents a study on the overloading capacity of a Wolfrom type gear planetary system. Such systems are used as reducers when high transmission ratio and power concentration is needed. When they operate as reducers, the efficiency is acceptable. However, when they operate as increasers, the efficiency ratio is very low. Therefore, in many cases such systems can be used when reverse operation is unwanted. Wolfrom reducers are common in aircrafts, robotic arms, nacelles of wind energy converters and cranes among others. In this paper a Wolfrom planetary system with transmission ratio equal to 19.2 is modelled and simulated using the finite element method. This model has the characteristic that multiple contacts occur between complex geometric pairs. The load distribution from the sun to the three planets is unknown. Even for a single gear with double contact the load distribution between the two teeth pairs cannot be determined analytically. In the model each gear engagement is defined as a contact interaction. A single loading torque is applied at the input shaft and the load distribution derives from the solution when equilibrium is achieved. The load transmitted through gear contacts develops surface pressure which is a key factor that determines the load carrying capacity of the reducer and safety against pitting. The root region of the gear teeth is also a critical area because the bending stress determines the safety against tooth breakage. The aim of the present paper is to investigate the overloading capacity of the reducer. A model with balanced element length at the two regions of interest was built with respect to low solution duration and result accuracy.

关键词： Finite element method

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