T.D. Ta

Tribological Behavior of Aqueous Copolymer Lubricant in Mixed Lubrication Regime.

Although a number of experiments have been attempted to investigate the lubrication of aqueous copolymer lubricant, which is applied widely in metalworking operations, a comprehensive theoretical investigation at atomistic level is still lacking. This study addresses the influence of loading pressure and copolymer concentration on the structural properties and tribological performance of aqueous copolymer solution of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) at mixed lubrication using a molecular dynamic (MD) simulation. An effective interfacial potential, which has been derived from density functional theory (DFT) calculations, was employed for the interactions between the fluids molecules and iron surface. The simulation results have indicated that the triblock copolymer is physisorption on iron surface. Under confinement by iron surfaces, the copolymer molecules form lamellar structure in aqueous solution and behave differently from its bulk state. The lubrication performance of aqueous copolymer lubricant increases with concentration, but the friction reduction is insignificant at high loading pressure. Additionally, the plastic deformation of asperity is dependent on both copolymer concentration and loading pressure, and the wear behavior shows a linear dependence of friction force on the number of transferred atoms between contacting asperities.

Numerical evaluation of a high speed steel work roll during hot strip rolling process

Hot strip rolling process is one of the most promising industrial processes to fabricate finished or semi-finished bulk products. Numerical analysis on the temperature and thermal stress distributions in a high speed steel work roll during hot rolling has been conducted based on a transient thermo-mechanical model. Influence of initial work roll body temperature on temperature and thermal stress has been discussed in detail by assuming different rolling stages. Compared to the work roll surface, stress is much smaller at depth of 2.1 mm and 5.0 mm, respectively. Results showed similar maximum circumferential thermal stress at both depths of 2.1 mm and 5.0 mm when the roll has initial temperature of 25 °C and 100 °C, but they are about 3 times and 8 times larger than at depth of 2.1 mm and 5.0 mm, respectively, when the initial temperature is 200 °C.