Current Issue : January-March Volume : 2023 Issue Number : 1 Articles : 5 Articles
This work is aimed at studying the tribological contact between a titanium–aluminu m–vanadium alloy pin (Ti6Al4V), produced by Electron Beam Melting (EBM), and a sheet of ultra high molecular weight polyethylene (UHMWPE), which are widely utilized materials for prosthetic applications. Using a “pin on disc” system, tribometric tests of different duration (up to 240 min) were carried out in order to trace the trend of the polymer mass loss as a function of test time. In this way it was possible to identify the stationary phase of adhesive friction, at which the specific wear rate, which characterizes the tribological system under different lubrication conditions, was obtained. As for the pin, no weight losses were measured, while the optical observations on the tip showed a compressive effect after the entire test campaign....
This paper introduces a novel dual-drive micro-feeding system (DDMS) to obtain precise micro-feed synthetic motion by rotating both the screw and the nut, which eliminates the effects of nonlinear friction at low micro-feeding speeds and has good resistance to external disturbances. For the DDMS system, firstly, the frictional force of the screw–ball–nut contact surface is analyzed, and the dynamic system model based on the unique frictional coupling model is established for the DDMS. Secondly, a velocity squared term is added to the Stribeck model to characterize the influence of the frictional coupling on the system. The correctness of the modified model is verified through experiments and frictional parameters identification by combining with the genetic algorithm (GA). The dynamic trend of the frictional parameters with different speed combinations is studied, and the method of fitting parameters using the modified Stribeck model is proposed. Finally, the DDMS three closed-loop error compensation model and the proportional derivative position controller with the friction feedforward compensator are put forward to realize the accurate position-tracking function. Experiment results show that the method reduces the average tracking error by about 60% compared to the conventional PD controller....
Silkiness is an extremely important attribute in high-end chocolate, and tribology is one of the commonly used methods of evaluating certain properties of the relevant food. In this study, based on three commercial chocolates of the same brand, the silky sensation was assessed by means of the professional sensation evaluation method. Artificial saliva was employed to obtain the mixed solutions with different chocolates, and their viscosity and coefficient of friction (CoF) were measured under different test parameters. The correlation of chocolate silkiness with the viscosities and average CoFs (aCoFs) are later discussed. The results showed that the silkiness of the three chocolates were negatively correlated with cocoa concentration and weakly correlated with viscosity. As the chocolate percentage decreased, the aCoF of the mixed solutions decreased, but the aCoF of the mixed solutions increased in relation to the cocoa concentration. In combination with the correlation coefficient of chocolate silkiness with the aCoFs, it was considered that 75% chocolate solutions using the Two-PDMS pair could be representative of the silkiness characteristic in oral processing at suitable operated parameters. The study results provide an insight into the rapid evaluation and development of similar attributes of high-end food....
For investigating the effect of mullite as a reinforced fiber of the non-asbestos brake friction material on the performance of brake pads, mullite reinforced composites with different contents (5% and 10%) and shapes (powder-based and fiber-based) were developed, and the physical and mechanical properties of the composites were analyzed. The tribological properties of the composites were tested by a Chase tester followed by the IS-2742 standard, and the worn surface was investigated by three-dimensional surface topography and SEM. The results show that the brake friction material with 5% powdered mullite performs best, having the highest stable friction performance (0.86), the lowest wear rate (3%), the lowest friction variation performance (0.263), and the best fade-recovery performance. With the increase of mullite content, the friction variation, wear resistance, and friction stability of the composites become worse. Meanwhile, the performance of powder-based mullite composites is better than that of fiber-based. The worn surface analysis shows that the fiber-based mullite composite has a higher surface roughness, fewer contact platforms, more wear debris, and peeling pits. In contrast, the powder-based mullite composites have a better surface performance. It provides a practical basis for mullite-reinforced non-asbestos brake friction materials....
Polymeric poly(vinyl alcohol) (PVA)-based composite hydrogels are promising materials with various biomedical applications. However, their mechanical and tribological properties should be tailored for such applications. In this study, we report the fabrication of PVA-gellan gum (GG) composite hydrogels and determine the effect of GG content on their rheological and tribological properties. The rheology tests revealed an enhanced storage (elastic) modulus with increased gellan gum (GG) concentration. The results showed up to 89% enhancement of the elastic modulus of PVA by adding 0.5 wt% gellan gum. This elastic modulus (12.1 ± 0.8 kPa) was very close to that of chondrocyte and its surrounding pericellular matrix (12 ± 1 kPa), rendering them ideal for cartilage regeneration applications. Furthermore, the friction coefficient was reduced by up to 80% by adding GG to PVA, demonstrating the increased elastic modulus improved chance of survival under mechanical shear stresses. Examining PVA/GG at different concentrations of 0.1, 0.3, and 0.5 wt% of GG, we demonstrate that at a load of 5 N, the friction coefficient decreases by increasing the GG concentration. However, at higher loads of 10 and 15 N, a 0.3 wt% concentration was sufficient to significantly reduce the friction coefficient. For PVA and PVA/GG composites, we observed a reduction in friction coefficient by increasing the load from 5 to 15 N. We also found the friction to be independent of the sliding velocity. Possible mechanisms of achieving a reduced friction coefficient are discussed....
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