Papers by Keyword: Friction

Abstract: A new ultra-precision positioning system is introduced in this paper. Experiment results show that using oblique impact drive, stage can be positioned in one axis as well as rotated around one axis by one actuator, that is, 'One-actuator-two-motion'. This means that simpler positioning system is possible, resulting in compact system, less components, more reliability, less costly system, which lead to SDGs.

Abstract: Maintenance due to the replacement of damaged wheels and rails due to rolling contact fatigue (RCF) and wear has been found to be the major problem to rail operating companies. This problem tends to lead to unavailability of railway networks. To solve this problem, costly wear simulators are developed to predict the wear behaviour of the rails and wheels to improve the preventive maintenance in pursuit of operational efficiency. Therefore, more studies that simulate a combination of rolling and sliding wear, together with RCF, are required, specifically for the Southern African, where good and cost-effective rail wear simulators are not readily available. The problem with wear and RCF simulators is high production costs, so this work aims to solve this problem by developing a cost-effective wear test rig that is capable of simulating RCF, sliding and rolling wear as experienced by the train wheel while moving along railway tracks. For this work, it was decided that twin-disc concept would be used, since literature clearly shown that the method was able to simulate the three damage mechanisms mentioned. The developed twin-disc wear simulator was able to simulate both rolling and sliding wear and parameters including contact load and slip ratio could be changed with ease so to simulate the actual contact conditions between the wheel and rail. Outputs such as coefficient of friction and wheel disc temperature were obtained. The results showed that the severity of wear is heavily dependent on slip ratio i.e., increased with slip ratio, with both coefficient of friction and wear rate increasing with slip ratio.

Abstract: A wear test was performed under the long-used machine oil sliding environment on Cu-based alloys Al-bronze and α-brass. A pin-on-disc wear testing method was applied where normal pressure of 0.255 to 2.55 MPa and a constant sliding speed of 0.641 m/s were considered. For the assessment dry and fresh machine oil sliding environments were also conducted. The results from the experiment demonstrated that the wear rate and friction coefficient in dry sliding condition were much greater for their direct contact but lower under machine oil due to the reduced roughness by the sealing effect as oil forms a thin lubricating film between the contact surfaces. Used oil displayed some degree of higher wear rate along with friction coefficient due to heavy and harmful chemical compounds in it. Al-bronze performed the better wear properties with lower wear rate and coefficient of friction for all the environments as it achieved the strength through different intermetallic formations. In case of α-brass, it had little effect on wear characteristics. Examined by optical microscopy and SEM analysis, worn surfaces showed that Al-bronze improved wear resistance through mild and smooth abrasive grooves filled with oxides in dry sliding conditions. In case of oil sliding environment, smooth surfaces were created by the resistance of the oil film to the direct contact between the surfaces. Used oil sliding conditions reduced the surface smoothness of the Cu and Cu-based alloys for the presence of damaging chemical compounds.

Abstract: The methods of influence on the material using different energy sources are considered. The role of friction in several technological processes is emphasized. The technological process of heat treatment is proposed, which allowed to restore the properties of rolled rolls that were lost due to incorrect grinding conditions. Application of the proposed technological process has shown that: 40X steel can be hardened to martensite in oil, water, and in a 10 % aqueous solution of NaCI salt, but with different results (i); the most effective hardening mode for 40X steel rolls is quenching with cooling in a 10 % aqueous solution of NaCI salt and subsequent high-temperature tempering, which is necessary to remove dangerous residual stresses (ii); the structure of the surface working layer of 40X steel rolls, after the selected optimal heat treatment regime, consists of fine-needle martensite and a small amount of Cr carbides (iii); closer to the core of the rolls, in addition to martensite, there are areas of troostite-bainite structure (iv); the resulting structure of the rolled rolls is capable of ensuring their efficient and long-term operation, but under optimal conditions, when the rolls' heating temperatures do not exceed 200 °C, and the proposed temperature conditions are recommended for both operation and routine maintenance associated with periodic restorative grinding of the working surfaces of the rolled rolls (v).

Abstract: We present our recent study on adhesive contacts of viscoelastic materials sliding against rigid substrates. Ultimately, the theory addresses the combined effect of viscoelasticity and adhesion in sliding contacts, with specific focus on the sliding frictional behavior. Compared to the adhesiveless case, we show that a significant enhancement of hysteretic friction occurs in the presence of adhesion, in agreement with long-standing experimental evidence. The presented formulation allows to investigate the effect of sliding velocities ranging from extremely slow to very high, thus taking into for local viscoelasticity, occurring at the edges of the contacts (crack tips), and bulk viscoelasticity, occurring in the bulk deformable material.

Abstract: Usually, contact mechanics focus on semi-infinite solids, so that any interaction between normal and in-plane deformation is commonly disregarded. However, when dealing with layers of finite thickness, this assumption is no longer valid, and the specific geometry of the contact pair plays a key role in determining the normal-tangential coupling. In this study, we focus on the exemplar case of a thin deformable layer in frictional sliding contact with a rough profile, where the interplay between tangential friction and normal pressure may lead to significantly different contact behavior compared to the uncoupled case, both in terms of contact area size and frictional response.

Abstract: A lubricating oil additive for armored vehicle engine was synthesized by ultrasonic dispersion and physical blending with polyisobutylene and poly alpha olefin as polymer matrix, nanoBN and nanoALN as antifriction materials and polyisobutylene succinimide as surfactant. Polymer-based lubricating oil additive, hydroxyl magnesium silicate powder additive, commercial anti-wear repairing agent Goldway and commercial anti-wear protective agent Chief were dispersed into 10W-40 armored vehicle engine special lubricating oil according to a certain mass fraction. The dissolution stability of different lubricating oil additives in lubricating oil was investigated by standing test. The effects of ultrasonic time and temperature on the dispersion of different kinds of lubricating oil additives in lubricating oil are investigated by using ultrasonic disperser and particle size analyzer. The MDW-5G multifunctional end-face friction and wear tester is used to simulate the actual working process of cylinder liner-piston ring in armored vehicles during driving, and tribological tests were carried out under conventional working conditions to evaluate the tribological properties of different lubricating oil additives. Scanning electron microscope was used to measure and analyze the wear surface morphology and friction interface elements after tribological test, and the lubrication mechanism of lubricating oil additives is revealed. The results show that the polymer-based lubricating oil additive has good dissolution stability and dispersion in lubricating oil. Compared with pure lubricating oil, the average friction coefficient of lubricating oil containing 3wt% polymer-based additives is 0.085, and the friction coefficient decreases by 38.8%. During the friction process, polymer-based lubricating oil additives form a self-repairing oil film to cover the surface of the sample through a series of complex physical and chemical reactions, which reduces the friction and wear between the grinding pairs and improves the lubricating performance of lubricating oil.

Abstract: Single point incremental forming process, which is also known as SPIF, that forms from one direction. SPIF process was used for milling an aluminum metallic sheet. In this paper, an aluminum (A5052) sheet was formed in a conical shape by the SPIF process. The A5052 sheet was deformed by the computer numerical control (CNC) technology in the T60 series milling machine. The conical shape was deformed by the spiral toolpath in the T60 series milling machine. At the surface of the A5052, lubricant grease was continuously applied manually for reducing the friction generated due to milling. Also, for decreasing the tool rotational force friction on the A5052 sheet there was the use of lubricant. Moreover, 0.1mm step-down is used for the tool path because it takes more time for forming a metallic sheet, however, it deformed the sheet smoothly. The 0.5mm step-down g-code was extracted from fusion 360. Then the metallic sheet A5052 surface was compared before and after deformation. For testing a metallic sheet A5052 the formability parameter was analyzed in the experiment part. The experiment was performed to find the optimal smooth surface from the CNC milling machine. The initial roughness value and the microscopic image were presented in the investigational part. Likewise, the comparison of points for the highest and lowest rough point was further discussed and compared throughout the experiment.

Abstract: Ti15Mo7Zr15Ta1.00Si titanium alloy contained higher concentration of silicon and better elastic properties, excellent biocompatibility and lower processing cost. To investigate the influence of texture shapes and parameters of joint surfaces on the friction and wear properties under bionic lubrication conditions, three types of texture morphologies (circular, elliptical, and equal-width grating) with the same pit depth and surface coating rate were processed on a Ti15Mo7Zr15Ta1.00Si titanium alloy using a picosecond laser processing system in this study. Then, the "ceramic–metal" friction and wear tests of textured and smooth samples under lubrication with bovine serum protein were performed using a UMT-3 multifunctional friction and wear testing machine. The results showed that the surface micro-texture morphology could improve the anti-friction properties of titanium alloy artificial joint materials. The wear resistance of the circular micro-dimples improved with an increase in the circular diameter. In the elliptical micro-dimple texture morphology, the vertical arrangement of the ellipses could provide the maximum bearing capacity and best friction reduction effect, followed by the elliptical morphology and the transverse ellipse arrangement. The denser the arrangement of the equal-width bars, the better the friction reduction effect was.

Abstract: The single point incremental forming (SPIF) process is a high-trend method for forming a metal in a desirable shape. Forming parameters is an important part of deforming metal sheets. So, while reshaping a metal sheet parameters like tools, toolpath, material properties, sheet thickness, and lubricant were considered. Since the Aluminum sheet is used world widely for the body parts of machines for manufacturing parts. So, an A5052 metallic sheet was formed for the improvement of the depth deforming through the SPIF process. While forming an A5052 sheet lubricant was used constantly. After deforming through the SPIF process, further evaluations of the formed part were examined with the nanoprofiling machine to evaluate the deformed areas. Moreover, the deformed part was analyzed for the nana profiling for the deformation occurs on the surface. Likewise, before forming a part, the A5052 design was computer analysis. The simulation part was studied for fixing the maximum depth.