The Influence of Deformation under Tension on Some Mechanical and Tribological Properties of High-Density Polyethylene

Abstract

Polymer materials are increasingly being used for sliding machine elements due to their numerous advantages. They are used even where they are deformed and in such a state that they interact frictionally, e.g., in machine hydraulics or lip seals. Few publications deal with the influence of deformation, which is the effect of, e.g., assembly on tribological properties of polymeric material. This deformation can reach up to ε ≈ 20% and is achieved without increasing the temperature of the polymer material. The paper presents the results of investigations in which high-density polyethylene (PE-HD) was maintained in deformation by means of a special grip (holder). The wear of the sample was significantly higher than that of the undeformed sample. This effect persisted even after partial relaxation of the stress in the sample after 24 h. Additional investigations were carried out to explain the obtained results. There were the microscopic observations of the surface after friction, measurements of microhardness, and surface free energy. Changes in the value of surface free energy and a significant decrease in microhardness with deformation under tension were observed. Deformed materials have a different surface appearance after friction and a different size and form of wear products. It was indicated that it is probable that the cohesion of the material will decrease and that the character of the wear process will change as a result of tension. Deformation under tension without heating of polymeric material (PE-HD), e.g., as a result of assembly, has been qualified as a threat to be taken into account when designing and analysing polymeric sliding elements.

Research on Deformation of Hydraulic Cylinders Made of Plastics

“…Through control of the hydraulic systems, the movement and loads of the tested cylinder were realized. Hydraulic parameters were measured using pressure transducers (7,8) and a flow rate meter. The movement of the piston rod was monitored using a displacement transducer (9) and the force on the piston rod using a sensor located in the connector (4).…”

“…In this method, it was shown that the choice of plastic material has an impact on the design, manufacturing technology, exploitation and application areas of cylinders made of plastics. This is due to the lower strength and greater elasticity of plastic compared to metal materials [7]. Less strength and greater elasticity leads to greater deformations.…”

Wear Resistance of Selected Anti-Wear Coatings Used in Multi-Material Composite Hydraulic Cylinders

“…Plastics are widely used in the design of machine components (Skowrońska et al, 2021). Their satisfactory mechanical properties, combined with good tribological properties, self-lubrication and the possibility of modifying the composition, allow them to be used in elements such as gears, pumps and others (Chihai et al, 2019;Krawczyk, 2021;Kujawa et al, 2019;Li et al, 2021;Majdič & Strmčnik, 2019;Zhang et al, 2021). Manufacturing large sliding surfaces, such as the inner surface of a cylinder, from thermoset materials, requires specialised manufacturing methods.…”