http://yetl.yabesh.ir/yetl1/handle/yetl/19044 2026-04-04T02:21:43Z 2026-04-04T02:21:43Z Dokter, Jorn Osara, Jude A. http://yetl.yabesh.ir/yetl1/handle/yetl/4311021 2026-02-17T22:02:01Z 2025-01-01T00:00:00Z

On the Thermal Degradation of Lubricant Grease: Experiments Dokter, Jorn; Osara, Jude A. This study assesses the thermal aging of lubricant grease via five rheological, mechanical, and thermal grease properties—yield stress, storage modulus, bleed capacity, specific heat capacity, and thermal strain coefficient. Three different grease types are studied: a polyurea-thickened grease with fully synthetic ester base oil, and two lithium-thickened greases, one with a mineral base oil and the other with a semi-synthetic base oil. The properties are measured at intervals as the grease samples aged for 30 days in a vacuum oven at 130∘C. The evaporation of base oil and volatiles, which affects the grease properties, is also measured. Results show inconsistent changes in the properties throughout the aging process, with the most significant transformations occurring in the first 10 days—during which most of the evaporation occurred. In addition to evaporation, other mechanisms appear active. Various levels of discolorations are observed. About 0.5% of the polyurea-thickened grease is lost to evaporation, and about 5% of each of the lithium-thickened greases evaporates. Results from a separate thermogravimetric test show that the fully synthetic ester base oil bled from the polyurea grease has the highest latent heat of evaporation of 337.9 kJ/kg, while the mineral and semi-synthetic base oils bled from the lithium greases have comparable latent heats of evaporation of 154 kJ/kg and 137.7 kJ/kg, respectively.

2025-01-01T00:00:00Z Wang, Yuanfei Xu, Yang Sheng, Xiaowei Xie, Guosheng Zhang, Yixin http://yetl.yabesh.ir/yetl1/handle/yetl/4311020 2026-02-17T22:01:58Z 2025-01-01T00:00:00Z

Analysis of Lubrication and Wear Model With Grease for the Harmonic Reducer Wang, Yuanfei; Xu, Yang; Sheng, Xiaowei; Xie, Guosheng; Zhang, Yixin In most harmonic reducers, wear failure mainly occurs in the flex-spline and flexible bearing. However, in models like the LHD-I-25, the unique tooth profile shifts the primary wear issue to the flex-spline and circular spline contact. Since harmonic reducers like LHD-I-25 are crucial in robotic joints and prone to wear, understanding their wear mechanisms is essential for mitigating failure. This article takes the LHD-I-25 harmonic reducer as the research object and explores the tooth surface lubrication and wear of its flex-spline and circular spline. Considering the working environment of LHD-I-25 harmonic reducer, we derived the Reynolds equation for line contact grease and established the equation for oil film thickness under elastic deformation. On this basis, we derived the wear model of harmonic reducers under mixed lubrication conditions. At the same time, finite element simulation and full life cycle experiments were conducted to obtain a model applicable to the wear of LHD-I-25 harmonic reducer. This model can describe the wear of LHD-I-25 harmonic reducer over time. Through the model, we found that compared with the less sensitive effect of speed on wear, increasing the load will greatly increase the tooth surface wear, and this effect is exponential. Through experimental verification, the model's error is only 2.47%, confirming its accuracy and practicality for predicting wear and optimizing harmonic reducer durability.

2025-01-01T00:00:00Z Brown, Cora Nescio, Meg Chadha, Vimanyu Zheng, Chuyuan Abelev, Esta Chmielus, Markus Jacobs, Tevis D. B. http://yetl.yabesh.ir/yetl1/handle/yetl/4311018 2026-02-17T22:01:53Z 2025-01-01T00:00:00Z

The Difficulty of Measuring Surface Topography in Additive Manufacturing: A Comparison Between Measured and True Surface Features of Binder-Jet Printed Samples Brown, Cora; Nescio, Meg; Chadha, Vimanyu; Zheng, Chuyuan; Abelev, Esta; Chmielus, Markus; Jacobs, Tevis D. B. Surface topography represents a critical barrier to the advancement of additive manufacturing (AM). Because some internal features cannot be polished and because of the growing trend of in situ process monitoring, it is important to understand the as-built surface topography of AM components. Here we highlight the challenges of using industry-standard surface-measurement techniques on binder-jet-printed parts. We measured the topography of binder-jet-printed Inconel alloy 625 samples in their green state and over the course of sintering; this system allowed the investigation of identical starting materials undergoing systematic changes in topography. Specifically, we compared the results from industry-standard surface-measurement techniques—optical interferometry, 3D microscopy (by fringe projection), and stylus profilometry—against the “true topography,” as revealed by cross-sectional scanning electron microscopy. While the true topography changed significantly with sintering, the industry-standard techniques detected no change in the root-mean-square height because of complex surface features, including multi-scale topography, overhangs, and steep surface slopes. While these findings do not invalidate the use of industry-standard techniques for binder-jet-printed samples, they demonstrate a challenge in their application, and they motivate the development of new metrics and new techniques to more accurately describe surface topography in AM.

2025-01-01T00:00:00Z Rahman, Md Hafizur Menezes, Pradeep L. http://yetl.yabesh.ir/yetl1/handle/yetl/4311017 2026-02-17T22:01:51Z 2025-01-01T00:00:00Z

Unveiling the Effect of Electrification on Phosphonium-Based Ionic Liquid Lubrication at Tribological Interfaces for Electric Vehicle Applications Rahman, Md Hafizur; Menezes, Pradeep L. Conventional lubricants face significant challenges in electric vehicle (EV) systems due to their low electrical conductivity and inability to mitigate tribo-electrification effects which can result in increased friction, wear, and electrical discharge damage under external electrification. Consequently, conductive lubricants like ionic liquids (ILs) have emerged as promising alternatives, offering enhanced compatibility with EV applications. This study investigated the tribological behavior of four phosphonium-based room temperature ionic liquids (PRTILs) with trihexyltetradecyl phosphonium [P6,6,6,14] or tributyltetradecyl phosphonium [P4,4,4,14] cations and saccharinate [Sacc] or benzoate [Benz] anions under electrified conditions, targeting potential EV applications. Physicochemical properties, including viscosity and ionic conductivity, were measured using a viscometer and a conductivity meter, while tribological properties were evaluated using an electrified mini-traction machine and an electrified rotary ball-on-disk setup. The results revealed that all the PRTILs exhibited superior tribological (friction and wear) performance than mineral oil with or without electrification. PRTILs with the [Sacc] anion feature a double aromatic ring structure, while those with the [Benz] anion feature a single aromatic ring structure. Under low electrification (10 mA), [P6,6,6,14][Sacc] outperformed [Benz]-based PRTILs, showing a lower coefficient of friction and wear due to their higher viscosity and lower ionic conductivity. Additionally, [P6,6,6,14][Sacc] showed a power loss lower than [P4,4,4,14][Sacc] but higher than [Benz]-based PRTILs under tribo-electrification. The addition of graphene nanoplatelets (GNPs) reduced the power loss of [P6,6,6,14][Sacc] by 24% by reducing the electric contact resistance. Overall, double-ring aromatic [P6,6,6,14][Sacc] demonstrated superior tribological performance, and GNP additives enhanced their power efficiency, offering a promising pathway for IL-based lubricant development for electrified conditions.

2025-01-01T00:00:00Z