Surface texturing on dry-lubricated transmissions and power systems to deliver better performance and simplified systems in aerospace engineering

Ding, Liang (2021) Surface texturing on dry-lubricated transmissions and power systems to deliver better performance and simplified systems in aerospace engineering. PhD thesis, University of Nottingham.

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Dry-lubricated contact systems are widely used in varied engineering applications, among which the spherical plain bearing (with dry-lubricating liner) in aerospace applications is one with increasing demands in performance. To achieve the improvements, the surface texturing is a propitious technique since it has seen a rapid development in the last few decades as it achieved promising effects in friction, wear and adhesion with different forms. However, to tailor the surface textures to the needs in tribological performance, it is essential to fill the gap of knowledge in the aspects such as the interaction between the liner surface and the textured counterface and the influence of the kinematics of the transmission system. Meanwhile, the relationship between the bonding strength of the liner and texturing morphology and adhesion force needs to be investigated.

The research in this thesis firstly aims at explaining the effects of surface texturing on the tribological performance of the dry contact pair (Polytetrafluoroethylene, or PTFE composite against steel surfaces), conducting systematic test series investigating the friction and wear performance with different texturing parameters (e.g. depth, coverages). To obtain understanding of the tribological phenomenon occurring with the dry contact, a novel transfer film characterisation technique based on multi-accelerating-voltage Scanning electron microscope (SEM) and Secondary ion mass spectrometry (SIMS) is developed. With this method, previous obscurity in the transfer film characterisation, particularly with worn counterface is eradicated. Combined with contact mechanics analysis using Finite Element (FE) methods, the mechanism of micro-abrasion and transfer film formation/re-distribution are identified.

Moreover, in this work a new aspect of the effects of the surface texturing on tribological performance is explored, considering the kinematics of the transmission system. With the proposed novel output-oriented modelling method of the kinematics of the transmission, a series of anisotropy tests of the tribological performance is instructed, leading to the finding that surface texturing may alter the anisotropy of the dry contact. Fundamentally, the introduced surface textures convert the contact between an anisotropic surface (composite) and a homogenous counterface into a contact between two heterogeneous surfaces.

Finally, this work investigates the effects surface texturing/roughing in bonding strength and improvement. The basic mechanism and phenomenon related with bonding strength are discussed. After identifying the inefficiency in describing the wettability of textured surfaces with conventional contact angle models, the surface free energy analysis is modified with a droplet morphology analysis. The theoretical support for anisotropic wettability of surfaces with directional surface textures is formulated.

To conclude, focusing on the physical phenomenon and working mechanism of surface textures in dry-lubricated contact system, this thesis illustrates the influence of surface texturing on tribological performance and bonding strength of bearing liner in aerospace applications. With the innovative transfer-film characterisation technique, systematic contact mechanics analysis, the output-oriented kinematic modelling and the modified surface free energy analysis for wettability, knowledge is added to the corresponding aspects that have opacity in previous research.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Axinte, Dragos
Butler-Smith, Paul
Li, Haonan
Keywords: Surface texturing, Dry-Lubricated Transmissions, Power systems, Aerospace engineering
Subjects: T Technology > TS Manufactures
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 64493
Depositing User: Ding, Liang
Date Deposited: 11 May 2021 13:56
Last Modified: 11 May 2021 14:00

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