Predictive analysis of fracture and fatigue in polymer gear teeth: a new theory for preventing failure

Wittayapiyanon, Sutartip (2026). Predictive analysis of fracture and fatigue in polymer gear teeth: a new theory for preventing failure. University of Birmingham. Ph.D.

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Abstract

This research focuses on solving wear-related challenges in involute gear-tooth polymer materials, enhancing Buckingham's and Merritt's equations, particularly in the context of elevated frictional temperatures resulting from kinematic contact behaviour. The Mason Institute of Tribology laboratory study employs the MARK II testing machine to underscore the significant consequences of erosion and wear, leading to weight reduction and wear size increase, ultimately culminating in tooth cracking. Detailed observations of the tooth surface reveal kinematic gear contact behaviour attributed to factors such as involute gear geometry failure, changing of vibration, frictional temperature issues, tooth deflection, and bending stress, particularly under extended machine cycles and heavy work loading.
The study applies four distinct coefficient theories - Buckingham, Merritt, Benedict & Kelley, and Drozdov & Gavrikov - to determine frictional coefficients through theoretical analysis and experimental testing, establishing a correlation between these coefficients and resulting gear power losses. The research focuses on polymer gears constructed from various Polyether Ether Ketone (PEEK) grades, adhering to industrial standards. Simulated designs consider temperature variations, mechanical load conditions, and changes in polymer material stiffness, examining critical factors such as load-sharing ratio, tooth bending stress, and frictional temperature between gear pairs. The structural and thermal-dynamic geometries are analyzed using Finite Element Analysis (FEA) to predict parameters including contact pressure interface, stress distribution, and tooth bending deformation behaviour. Additionally, the study explores the impact of fluctuations in frictional coefficients on actual gear power losses, emphasizing the predictive capability of power loss in polymer gears. The research rigorously compares theoretical frictional coefficient and power loss results with experimental data to validate theoretical models.
Crack propagation analysis reveals alterations in approach lengths and recess along the un-normal contact path, leading to increased wear on tooth flanks and the onset of initial cracks. The research emphasizes the importance of Linear Elastic Fracture Mechanics (LEFM) analysis, focusing on Stress Intensity Factors (SIFs) critical for evaluating fatigue crack growth, influenced by factors including coefficient of friction, strain responses, tooth wear, and stress-induced bending deformation.
In conclusion, this comprehensive thesis contributes significantly to solving wear-related issues in involute gear-tooth PEEK gears, providing valuable insights into optimizing gear design and improving the efficiency of polymer gear systems.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):