Significant advances have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions from practical and theoretical standpoints. This approach has enabled the aerospace industry to cope with constant introduction of new materials that allow the engine temperature to increase at a rate of 10 °C per annum since the 1950s. Improvements achieved from research and development activities in this area have particularly enhanced the machining of difficult-to-cut nickel base and titanium alloys that have traditionally exhibited low machinability due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation, etc. A good understanding of the cutting tool materials, cutting conditions, processing time and functionality of the machined component will lead to efficient and economic machining of nickel and titanium base superalloys. This paper presents an overview of major advances in machining techniques that have resulted to step increase in productivity, hence lower manufacturing cost, without adverse effect on the surface finish, surface integrity, circularity and hardness variation of the machined component.

Key improvements in the machining of difficult-to-cut aerospace superalloys

https://cyberleninka.org/article/n/544115.pdf

Hydrodynamic lubrication of textured surfaces: A review of modeling techniques and key findings

http://research.me.udel.edu/~dlburris/papers/JA9.pdf

A low friction and ultra low wear rate PEEK/PTFE composite

Recent advances in engineering design optimisation: Challenges and future trends

http://research.me.udel.edu/~dlburris/papers/JA8.pdf

Improved wear resistance in alumina-PTFE nanocomposites with irregular shaped nanoparticles

This study presents an engineering approach for optimizing performance of fluid-film lubricated bearings. Unconstrained nonlinear programming methods, lattice search and simplex method, were used as the optimization schemes to improve the merit of studied bearings with two or more design variables. The analysis of elliptical bearings shows high eccentricity ratio and two large pressure zones for high-speed stability can be obtained by maximizing film pressures in the upper and lower lobes. In this study, lattice method exhibits slightly more efficient search compared with that of simplex method in several two-variable optimum designs. The automatic mesh generation technique used in the pocket-shaped bearing analysis makes the numerical optimization as a flexible design tool. The effect of side flow restrictions on the load-carrying capacity of an optimized pocket-shaped slider bearing is clearly verified. The analysis of the aerostatic bearing explains an example of multi-objective minimization. A similar...

Engineering optimum design of fluid-film lubricated bearings©

This study deals with the development of a computational procedure for solving the isothermal compressible Reynolds equation as the governing equation of air-bearing analysis. Newton's method is used to linearize Reynolds equation and an iterative successive relaxation process is adopted to solve for the air film pressure. The optimal value of relaxation factor for the cases studied is suggested in this report for numerical stability and computational efficiency. The model is verified numerically by examining the conservation of mass flow of the lubricant. The dimensional analysis of the governing equation permits the model to be readily applied to any given film geometry. The computer model developed can evaluate the air film pressure distribution, load capacity, frictional force, and mass flow of an air bearing. The proposed computational scheme efficiently analyzes the performance of air-lubricated journal bearings at large eccentricity ratios. A similar procedure can be employed to investigate the per...

An Application of Newton's Method to the Lubrication Analysis of Air-Lubricated Bearings

A feasible solution must be obtained in a reasonable time with high probability of global optimum for a complex tribological design problem. To meet this decisive requirement in a multi-objective optimization problem, the popular and powerful genetic algorithms (GAs) are adopted in an illustrated air bearing design. In this study, the goal of multi-objective optimization is achieved by incorporating the criterion of Pareto optimality in the selection of mating groups in the GAs. In the illustrated example the diversity of group members in the evolution process is much better maintained by using Pareto ranking method than that with the roulette wheel selection scheme. The final selection of the optimal point of the points satisfied the Pareto optimality is based on the minimum–maximum objective deviation criterion. It is shown that the application of the GA with the Pareto ranking is especially useful in dealing with multi-objective optimizations. A hybrid selection scheme combining the Pareto ranking and roulette wheel selections is also presented to deal with a problem with a combined single objective. With the early generations running the Pareto ranking criterion, the resultant divergence preserved in the population benefits the overall GA's performance. The presented procedure is readily adoptable for parallel computing, which deserves further study in tribological designs to improve the computational efficiency.

Application of the Genetic Algorithm to the Multi-Objective Optimization of Air Bearings

A mixed elastohydrodrynamic (EHL) model for journal bearings considering an axial flow due to shaft axial motion and misalignment is developed for lubrication performance evaluation A new, faster mixed EHL computing technology utilizing the odd–even successive overrelaxation (OESOR) parallel numerical iterative method is proposed based on the red–black successive overrelaxation (RBSOR) method to minimize the execution time prolonged by the complexity caused by the axial flow and misalignments The multithreaded computing scheme conducted by the OpenMP directive using different meshes and threads suggests that the OESOR method exhibits better efficiency A series of transient analyses was conducted to solve the mixed EHL model with the parallel OESOR method The results show that the axial flow and misalignments significantly affect the average pressure, hydrodynamic and asperity contact pressure, elastic deformation, and other characteristics of the journal bearings

Nenzi Wang

Papers

Engineering optimum design of fluid-film lubricated bearings©

An Application of Newton's Method to the Lubrication Analysis of Air-Lubricated Bearings

Application of the Genetic Algorithm to the Multi-Objective Optimization of Air Bearings

Effects of Shaft Axial Motion and Misalignment on the Lubrication Performance of Journal Bearings Via a Fast Mixed EHL Computing Technology

Optimum design of externally pressurized air bearing using Cluster OpenMP