Karsten Stahl - Academia.edu (original) (raw)
Papers by Karsten Stahl
Frontiers in Mechanical Engineering
Lubricants with a functional water portion have demonstrated a drastic reduction in friction unde... more Lubricants with a functional water portion have demonstrated a drastic reduction in friction under elastohydrodynamic lubrication conditions. With water-containing polyalkylene glycols, superlubricity with coefficients of friction <0.01 have been measured in model and gear contacts. In addition to the low friction, their calorimetric properties make them particularly interesting for application in electrified vehicles because the liquid can simultaneously serve as lubricant for the gearbox and coolant for the electric motors and the power electronics. In this study, the influence of water content between 8 wt% and 40 wt% of water-soluble polyalkylene glycols on friction and film thickness in elastohydrodynamically lubricated rolling-sliding contacts such as in gears and bearings is investigated. A polyalphaolefine oil is used as a reference. Friction has been measured on a ball-on-disk tribometer and film thickness on an optical tribometer. For a water content of 40 wt%, superlub...
Tribologie und Schmierungstechnik
In large gear drives, through-hardened ring gears or internal gears are often in contact with cas... more In large gear drives, through-hardened ring gears or internal gears are often in contact with case-hardened pinions. This offers economic advantages, but involves an increased risk of wear during its operation. Various test methods exist to evaluate the expected wear of the used gear-lubricant-system, but typically with case-hardened gears only. A direct transfer of the test results to the application in field is not known so far. In this study, influences from different surface hardness and surface roughness values as well as lubricating conditions were systematically investigated on a FZG back-to-back test rig. The results prove a higher risk for strong wear for hard-soft gear pairings. Based on these results, a calculation method for the wear lifetime of gears was extended to allow an estimation of the wear lifetime of gear pairings with different surface hardness based on standard wear tests.
Applied Sciences
The circular layout and the kinematics of planetary gearboxes result in characteristic oil flow p... more The circular layout and the kinematics of planetary gearboxes result in characteristic oil flow phenomena. The goal of this paper is to apply a new remeshing strategy, based on the finite volume method, on the numerical analysis of a planetary gearbox and its evaluation of results as well as its validation. The numerical results are compared with experimental data acquired on the underlying test rig with high-speed camera recordings. By use of a transparent housing cover, the optical access in the front region of the gearbox is enabled. Different speeds of the planet carrier and immersion depths are considered. A proper domain partitioning and a specifically suited mesh-handling strategy provide a highly efficient numerical model. The open-source software OpenFOAM® is used.
Tribology Letters
The goal of this work is to evaluate the potential of diamond-like carbon (DLC) coatings on therm... more The goal of this work is to evaluate the potential of diamond-like carbon (DLC) coatings on thermoplastic polymers for friction and wear reduction in highly stressed rolling–sliding contacts. Therefore, hydrogen-containing DLC coatings were deposited on the polymer surface by a low-temperature high power pulsed magnetron sputtering (HPPMS) physical vapor deposition (PVD) process. The rolling-sliding contact between coated polyamide 66 (PA66) or coated polyether ether ketone (PEEK) against case-hardened steel 16MnCr5 is investigated in a twin-disk tribometer at normal loads up to FN = 1,000 N, sum velocities between 1 m/s ≤ vΣ ≤ 16 m/s and slip ratios up to s = 50%. Results show a friction reduction with the application of DLC on the considered polymers compared to uncoated polymers under specific lubrication conditions. High solid losses caused by the polymer’s internal damping properties dominate the temperature behavior of the polymer, even when coated with DLC. Regarding the wear...
Springer eBooks, Aug 6, 2022
Forschung im Ingenieurwesen
For the development of high power density gearboxes the knowledge of the gear mesh behavior is im... more For the development of high power density gearboxes the knowledge of the gear mesh behavior is important. Especially, the tooth deflection influences flank load distribution and is the basis for the design of flank modifications. Analytical and numerical approaches are suitable to evaluate the behavior. Since numerical methods are complex, elaborate and time-consuming, fast and accurate analytical methods are still important and are worth to be further developed and assessed.An analytical method for calculating tooth deformation for gears goes back to Weber and Banaschek from 1953. In the initial work the final equations are given without many intermediate steps in the plane strain assumption for materials with Poisson’s ratio ν = 0.3. This paper derives the tooth deflection equations in a more detailed and general manner for any linear material. The final equations are valid for the plane stress and plane strain state in one new closed representation and are therefore suitable for ...
International Journal of Fracture
Lightweight design has had an important role to play in recent gear developments. One way of redu... more Lightweight design has had an important role to play in recent gear developments. One way of reducing gear weight is to apply a shot-peening process in addition to the usual case-hardening because the higher compressive residual stresses within the material mean that the same torque values can be transmitted with smaller gears. However, due to the compressive residual stresses, fisheye failures at non-metallic inclusions can occur, which have an effect on the endurance fatigue strength of high-strength gears, especially in the very high cycle fatigue range. This paper presents a detailed FEM simulation of the stress state at a non-metallic inclusion in the tooth root fillet of such high-strength gears. The aim is to explain certain fracture characteristics, which differ from fisheye failures of standard specimens. With the results of the simulation und taking into consideration the fracture characteristics determined in a SEM, a fracture analysis for fisheye failures in the tooth ro...
Lubricants
Low-loss gears are an interesting design approach for increasing the efficiency and thermal load ... more Low-loss gears are an interesting design approach for increasing the efficiency and thermal load limits of gearboxes. The loss-optimized gear geometry concentrates sliding around the pitch point, which results in low load-dependent gear power losses. In this study, a method for modeling transient EHL (elastohydrodynamically lubricated) contacts in gear mesh considering mixed lubrication and thermal effects is introduced and applied to analyze the tribological behavior of a low-loss gear geometry. Special focus is placed on local frictional losses to analyze the role of the thermal effects of the gear mesh. Although a thermal reduction in fluid friction is observed, the overall effect on total frictional losses of the low-loss gear geometry is evaluated to be very small. The edge geometry strongly influences the lubricant film thickness and frictional power losses.
HTM Journal of Heat Treatment and Materials
Globalization and international supply chains constantly challenge gear- and steel manufacturers.... more Globalization and international supply chains constantly challenge gear- and steel manufacturers. In the case of large gear units in particular, expensive alloy contents have a direct impact on the material price. Steels with lower alloy contents and therefore cheaper steels are therefore becoming the focus of attention in order to further improve competitiveness. This article therefore compares two materials with different alloying elements and contents and thus different hardenability behaviour. For this purpose, extensive material characterizations as well as pulsator tests were carried out on case-hardened large gears. The aim of these tests was to determine the tooth root load-bearing capacity of the two material variants. Finally, the results are compared, discussed and recommendations for industrial application are derived, taking into account the hardenability of large gears. ◼
Proceedings of the VII European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS Congress 2016), 2016
International Conference on Gears 2015 International Conference on High Performance Plastic Gears 2015 International Conference on Gear Production 2015, 2015
Maschinenelemente 1, 2019
Planetary gear stages have an increased power density compared to gearboxes with cylindrical gear... more Planetary gear stages have an increased power density compared to gearboxes with cylindrical gear stages. Due to their power density gear failures could lead to a malfunction of the whole gear box. Condition monitoring helps to detect gear failures. Pitting on the flanks of gear wheels are one mechanism of gear failure. Pitting do not lead to an instant failure, but increase during running time. Hence the characteristic of Transmission Error is worsening during running time. Due to rotating planet shafts, measurements on separate gear meshes are connected with great effort. Measurement results for Transmission Error of a single stage, e.g. Transmission Error of the stage sun-planet, are usually not available. Hence it is more common to measure the Total Transmission Error (TTE) of planetary stages. It is challenging to implement condition monitoring for planetary stages by using TTE. Therefore, the influence of pitting on TTE are analysed by simulation in a first step. At FZG there ...
Mechanism and Machine Theory, 2017
The operational behavior and, in particular, the bending strength of thermoplastic gears are subs... more The operational behavior and, in particular, the bending strength of thermoplastic gears are substantially influenced by the significant increase in contact ratio under load. According to current analytic calculation standards and guidelines, this effect is neglected when tooth root stress is calculated. Using numerical methods, such as the finite element method (FEM), a consideration of deflections is possible but the usage is complex and extensive in engineering practice compared to recomputing guidelines or standards like VDI 2736 or ISO 6336. In this work, a method is presented for calculating the nominal tooth root stress based on existing analytic guidelines, taking the actual contact ratio into account. Based on the example of three test gear geometries, the results are compared to existing guidelines, as well as numerical computations, showing that the presented method correlates well with the latter.
Maschinenelemente 1, 2019
In der Produktentwicklung sind verschiedene Berufsbilder zu finden, wie z. B. Konstruktionsingeni... more In der Produktentwicklung sind verschiedene Berufsbilder zu finden, wie z. B. Konstruktionsingenieure, Berechnungsingenieure, Versuchsingenieure, Normeningenieure oder Systemingenieure, welche sich unter dem Begriff des Ingenieurs in der Produktentwicklung zusammenfassen lassen. Je nach Berufsbild ergeben sich unterschiedliche Tatigkeiten, die mehr Synthese- oder Analyse-orientiert sein konnen. Ingenieure in der Produktentwicklung von heute sind Entwickler, Treiber und Gestalter im Entstehungsprozess neuer Produkte. Sie denken - unter Berucksichtigung samtlicher Phasen des Produktlebenszyklus - neue Produkte im Unternehmen vor, entwickeln diese und erstellen einen grosen Teil der Produktdokumentation. Damit beeinflussen sie in direkter Weise den Unternehmenserfolg produzierender Unternehmen, da sie den Grosteil der Kosten eines Produktes festlegen und verantworten.
Maschinenelemente 1, 2019
Dudley's Handbook of Practical Gear Design and Manufacture, 2021
Forschung im Ingenieurwesen, 2021
Demands on modern gearboxes are constantly increasing, for example to comply with lightweight des... more Demands on modern gearboxes are constantly increasing, for example to comply with lightweight design goals or new CO2 thresholds. Normally, to increase performance requires making gearboxes and powertrains more robust. However, this increases the weight of a standard gearbox. The two trends therefore seem contradictory. To satisfy both of these goals, gears in gearboxes can be shot-peened to introduce high compressive residual stresses and improve their bending fatigue strength. To determine a gear’s tooth root bending fatigue strength, experiments are conducted up to a defined number of load cycles in the high cycle fatigue range. However, investigations of shot-peened gears have revealed tooth root fracture damage initiated at non-metallic inclusions in and above the very high cycle fatigue range. This means that a further reduction in bending load carrying capacity has to be expected at higher load cycles, something which is not covered under current standard testing conditions. ...
DRITEV – Drivetrain for Vehicles 2021, 2021
Frontiers in Mechanical Engineering
Lubricants with a functional water portion have demonstrated a drastic reduction in friction unde... more Lubricants with a functional water portion have demonstrated a drastic reduction in friction under elastohydrodynamic lubrication conditions. With water-containing polyalkylene glycols, superlubricity with coefficients of friction <0.01 have been measured in model and gear contacts. In addition to the low friction, their calorimetric properties make them particularly interesting for application in electrified vehicles because the liquid can simultaneously serve as lubricant for the gearbox and coolant for the electric motors and the power electronics. In this study, the influence of water content between 8 wt% and 40 wt% of water-soluble polyalkylene glycols on friction and film thickness in elastohydrodynamically lubricated rolling-sliding contacts such as in gears and bearings is investigated. A polyalphaolefine oil is used as a reference. Friction has been measured on a ball-on-disk tribometer and film thickness on an optical tribometer. For a water content of 40 wt%, superlub...
Tribologie und Schmierungstechnik
In large gear drives, through-hardened ring gears or internal gears are often in contact with cas... more In large gear drives, through-hardened ring gears or internal gears are often in contact with case-hardened pinions. This offers economic advantages, but involves an increased risk of wear during its operation. Various test methods exist to evaluate the expected wear of the used gear-lubricant-system, but typically with case-hardened gears only. A direct transfer of the test results to the application in field is not known so far. In this study, influences from different surface hardness and surface roughness values as well as lubricating conditions were systematically investigated on a FZG back-to-back test rig. The results prove a higher risk for strong wear for hard-soft gear pairings. Based on these results, a calculation method for the wear lifetime of gears was extended to allow an estimation of the wear lifetime of gear pairings with different surface hardness based on standard wear tests.
Applied Sciences
The circular layout and the kinematics of planetary gearboxes result in characteristic oil flow p... more The circular layout and the kinematics of planetary gearboxes result in characteristic oil flow phenomena. The goal of this paper is to apply a new remeshing strategy, based on the finite volume method, on the numerical analysis of a planetary gearbox and its evaluation of results as well as its validation. The numerical results are compared with experimental data acquired on the underlying test rig with high-speed camera recordings. By use of a transparent housing cover, the optical access in the front region of the gearbox is enabled. Different speeds of the planet carrier and immersion depths are considered. A proper domain partitioning and a specifically suited mesh-handling strategy provide a highly efficient numerical model. The open-source software OpenFOAM® is used.
Tribology Letters
The goal of this work is to evaluate the potential of diamond-like carbon (DLC) coatings on therm... more The goal of this work is to evaluate the potential of diamond-like carbon (DLC) coatings on thermoplastic polymers for friction and wear reduction in highly stressed rolling–sliding contacts. Therefore, hydrogen-containing DLC coatings were deposited on the polymer surface by a low-temperature high power pulsed magnetron sputtering (HPPMS) physical vapor deposition (PVD) process. The rolling-sliding contact between coated polyamide 66 (PA66) or coated polyether ether ketone (PEEK) against case-hardened steel 16MnCr5 is investigated in a twin-disk tribometer at normal loads up to FN = 1,000 N, sum velocities between 1 m/s ≤ vΣ ≤ 16 m/s and slip ratios up to s = 50%. Results show a friction reduction with the application of DLC on the considered polymers compared to uncoated polymers under specific lubrication conditions. High solid losses caused by the polymer’s internal damping properties dominate the temperature behavior of the polymer, even when coated with DLC. Regarding the wear...
Springer eBooks, Aug 6, 2022
Forschung im Ingenieurwesen
For the development of high power density gearboxes the knowledge of the gear mesh behavior is im... more For the development of high power density gearboxes the knowledge of the gear mesh behavior is important. Especially, the tooth deflection influences flank load distribution and is the basis for the design of flank modifications. Analytical and numerical approaches are suitable to evaluate the behavior. Since numerical methods are complex, elaborate and time-consuming, fast and accurate analytical methods are still important and are worth to be further developed and assessed.An analytical method for calculating tooth deformation for gears goes back to Weber and Banaschek from 1953. In the initial work the final equations are given without many intermediate steps in the plane strain assumption for materials with Poisson’s ratio ν = 0.3. This paper derives the tooth deflection equations in a more detailed and general manner for any linear material. The final equations are valid for the plane stress and plane strain state in one new closed representation and are therefore suitable for ...
International Journal of Fracture
Lightweight design has had an important role to play in recent gear developments. One way of redu... more Lightweight design has had an important role to play in recent gear developments. One way of reducing gear weight is to apply a shot-peening process in addition to the usual case-hardening because the higher compressive residual stresses within the material mean that the same torque values can be transmitted with smaller gears. However, due to the compressive residual stresses, fisheye failures at non-metallic inclusions can occur, which have an effect on the endurance fatigue strength of high-strength gears, especially in the very high cycle fatigue range. This paper presents a detailed FEM simulation of the stress state at a non-metallic inclusion in the tooth root fillet of such high-strength gears. The aim is to explain certain fracture characteristics, which differ from fisheye failures of standard specimens. With the results of the simulation und taking into consideration the fracture characteristics determined in a SEM, a fracture analysis for fisheye failures in the tooth ro...
Lubricants
Low-loss gears are an interesting design approach for increasing the efficiency and thermal load ... more Low-loss gears are an interesting design approach for increasing the efficiency and thermal load limits of gearboxes. The loss-optimized gear geometry concentrates sliding around the pitch point, which results in low load-dependent gear power losses. In this study, a method for modeling transient EHL (elastohydrodynamically lubricated) contacts in gear mesh considering mixed lubrication and thermal effects is introduced and applied to analyze the tribological behavior of a low-loss gear geometry. Special focus is placed on local frictional losses to analyze the role of the thermal effects of the gear mesh. Although a thermal reduction in fluid friction is observed, the overall effect on total frictional losses of the low-loss gear geometry is evaluated to be very small. The edge geometry strongly influences the lubricant film thickness and frictional power losses.
HTM Journal of Heat Treatment and Materials
Globalization and international supply chains constantly challenge gear- and steel manufacturers.... more Globalization and international supply chains constantly challenge gear- and steel manufacturers. In the case of large gear units in particular, expensive alloy contents have a direct impact on the material price. Steels with lower alloy contents and therefore cheaper steels are therefore becoming the focus of attention in order to further improve competitiveness. This article therefore compares two materials with different alloying elements and contents and thus different hardenability behaviour. For this purpose, extensive material characterizations as well as pulsator tests were carried out on case-hardened large gears. The aim of these tests was to determine the tooth root load-bearing capacity of the two material variants. Finally, the results are compared, discussed and recommendations for industrial application are derived, taking into account the hardenability of large gears. ◼
Proceedings of the VII European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS Congress 2016), 2016
International Conference on Gears 2015 International Conference on High Performance Plastic Gears 2015 International Conference on Gear Production 2015, 2015
Maschinenelemente 1, 2019
Planetary gear stages have an increased power density compared to gearboxes with cylindrical gear... more Planetary gear stages have an increased power density compared to gearboxes with cylindrical gear stages. Due to their power density gear failures could lead to a malfunction of the whole gear box. Condition monitoring helps to detect gear failures. Pitting on the flanks of gear wheels are one mechanism of gear failure. Pitting do not lead to an instant failure, but increase during running time. Hence the characteristic of Transmission Error is worsening during running time. Due to rotating planet shafts, measurements on separate gear meshes are connected with great effort. Measurement results for Transmission Error of a single stage, e.g. Transmission Error of the stage sun-planet, are usually not available. Hence it is more common to measure the Total Transmission Error (TTE) of planetary stages. It is challenging to implement condition monitoring for planetary stages by using TTE. Therefore, the influence of pitting on TTE are analysed by simulation in a first step. At FZG there ...
Mechanism and Machine Theory, 2017
The operational behavior and, in particular, the bending strength of thermoplastic gears are subs... more The operational behavior and, in particular, the bending strength of thermoplastic gears are substantially influenced by the significant increase in contact ratio under load. According to current analytic calculation standards and guidelines, this effect is neglected when tooth root stress is calculated. Using numerical methods, such as the finite element method (FEM), a consideration of deflections is possible but the usage is complex and extensive in engineering practice compared to recomputing guidelines or standards like VDI 2736 or ISO 6336. In this work, a method is presented for calculating the nominal tooth root stress based on existing analytic guidelines, taking the actual contact ratio into account. Based on the example of three test gear geometries, the results are compared to existing guidelines, as well as numerical computations, showing that the presented method correlates well with the latter.
Maschinenelemente 1, 2019
In der Produktentwicklung sind verschiedene Berufsbilder zu finden, wie z. B. Konstruktionsingeni... more In der Produktentwicklung sind verschiedene Berufsbilder zu finden, wie z. B. Konstruktionsingenieure, Berechnungsingenieure, Versuchsingenieure, Normeningenieure oder Systemingenieure, welche sich unter dem Begriff des Ingenieurs in der Produktentwicklung zusammenfassen lassen. Je nach Berufsbild ergeben sich unterschiedliche Tatigkeiten, die mehr Synthese- oder Analyse-orientiert sein konnen. Ingenieure in der Produktentwicklung von heute sind Entwickler, Treiber und Gestalter im Entstehungsprozess neuer Produkte. Sie denken - unter Berucksichtigung samtlicher Phasen des Produktlebenszyklus - neue Produkte im Unternehmen vor, entwickeln diese und erstellen einen grosen Teil der Produktdokumentation. Damit beeinflussen sie in direkter Weise den Unternehmenserfolg produzierender Unternehmen, da sie den Grosteil der Kosten eines Produktes festlegen und verantworten.
Maschinenelemente 1, 2019
Dudley's Handbook of Practical Gear Design and Manufacture, 2021
Forschung im Ingenieurwesen, 2021
Demands on modern gearboxes are constantly increasing, for example to comply with lightweight des... more Demands on modern gearboxes are constantly increasing, for example to comply with lightweight design goals or new CO2 thresholds. Normally, to increase performance requires making gearboxes and powertrains more robust. However, this increases the weight of a standard gearbox. The two trends therefore seem contradictory. To satisfy both of these goals, gears in gearboxes can be shot-peened to introduce high compressive residual stresses and improve their bending fatigue strength. To determine a gear’s tooth root bending fatigue strength, experiments are conducted up to a defined number of load cycles in the high cycle fatigue range. However, investigations of shot-peened gears have revealed tooth root fracture damage initiated at non-metallic inclusions in and above the very high cycle fatigue range. This means that a further reduction in bending load carrying capacity has to be expected at higher load cycles, something which is not covered under current standard testing conditions. ...
DRITEV – Drivetrain for Vehicles 2021, 2021