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Ultra-high molecular weight polyethylene (UHMWPE) has an excellent performance and application value; however, as a tribological material, its main drawback is its poor performance under dry friction, impacting its ability to work in high-speed dry friction conditions. Modification of UHMWPE can be carried out to overcome these issues. A significant number of inorganic materials have been used to modify UHMWPE and provide it with good tribological performance. However, thus far, there has been no systematic investigation into the methodology of modifying UHMWPE. The authors take a quantitative approach to determine the structure tribo-ability relationship and basic principles of screening of inorganic compounds suited to modify UHMWPE.

The tribological properties of modified UHMWPE using a series of inorganic additives have been qualitatively studied by the authors’ research group previously. In this study, basic quantitative structure tribo-ability relationships (QSTRs) of inorganic additives for modifying UHMWPE were studied to predict tribological properties. A set of 15 inorganic compounds and their tribological data were used to study the predictive capability of QSTR towards inorganic additives properties.

The results show that the anti-wear and friction-reducing properties of these inorganic compounds correlate with the calculated parameters of entropy and dipole moment. Increased entropy and smaller dipole moment can effectively improve the anti-wear and friction-reducing ability of inorganic compounds as UHMWPE additives. Additives with larger molecular weight, lower hardness and lower melting and boiling points provide good tribological properties for UHMWPE. For inorganic compounds to act as UHMWPE additives, the chemical bond should be less covalent and have more ionic character.

Only 15 inorganic compounds and their tribological data were used to study the predictive capability of QSTR towards inorganic additives properties. If the samples number is more than 30, the other QSTR methodology can be used to study the modified UHMWPE, and the models finding can be more precise.

A QSTR model for modified UHMWPE has been studied systematically. While the results are not more precise and detailed, the model provides a new way to explore the modified UHMWPE characteristics and to reveal new insight into the friction and wear process.

Because the method of studying tribological materials is entirely different from others, the authors want to present the works and discuss it with colleagues.

The paper presents a new method to study the modified UHMWPE. A QSTR is used to study the tribology capability of compounds from calculated structure descriptors. This study uses the Hartree–Fock ab initio method to establish a QSTR prediction model to estimate the ability of 15 inorganic compounds to act as anti-wear and friction-reducing additives for UHMWPE.

To overcome the problem of inferior through-the-thickness mechanical properties displayed by armor-grade composites based on 2-D reinforcement architectures, armor-grade composites based on 3D fiber-reinforcement architectures have recently been investigated experimentally.

The subject of the present work is armor-grade composite materials reinforced using ultra-high-molecular-weight polyethylene fibers and having four (two 2D and two 3D) prototypical architectures, as well as the derivation of the corresponding material models. The effect of the reinforcement architecture is accounted for by constructing the appropriate unit cells (within which the constituent materials and their morphologies are represented explicitly) and subjecting them to a series of virtual mechanical tests. The results obtained are used within a post-processing analysis to derive and parameterize the corresponding homogenized-material models. One of these models (specifically, the one for 0°/90° cross-collimated fiber architecture) was directly validated by comparing its predictions with the experimental counterparts. The other models are validated by examining their physical soundness and details of their predictions. Lastly, the models are integrated as user-material subroutines, and linked with a commercial finite-element package, in order to carry out a transient non-linear dynamics analysis of ballistic transverse impact of armor-grade composite-material panels with different reinforcement architectures.

It is found that the reinforcement architecture plays a critical role in the overall ballistic limit of the armor panel, as well as in its structural and damage/failure response.

To the authors’ knowledge, the present work is the first reported attempt to assess, computationally, the utility and effectiveness of 3D fiber-reinforcement architectures for ballistic impact applications.

This paper aims to focus on studying the addition of nano-tungsten disulfide (WS₂) on fretting wear performance of ultra-high-molecular-weight-polyethylene (UHMWPE).

In this study, the effect of WS₂ content on fretting wear performance of UHMWPE was investigated. The fretting wear performance of the UHMWPE and WS₂/UHMWPE nanocomposites were evaluated on oscillating reciprocating friction and wear tester. The data of the friction coefficient and the specific wear rate were obtained. The worn surfaces of composites were observed. The transfer film and its component were analyzed.

With the addition of 0.5% WS₂, the friction coefficient and specific wear rate increased. With the content increased to 1% and 1.5%, the friction coefficient and specific wear rate decreased. The lowest friction coefficient and specific wear rate were obtained with the addition of 1.5% nano-WS₂. Continuingly increasing content, the friction coefficient and wear rate increased but lower than that of pure UHMWPE.

The research indicated the fretting wear performance related to the content of nano-WS₂ with the incorporation of WS₂ into UHMWPE.

The result may help to choose the appropriate content.

The main originality of the research is to reveal the fretting behavior of UHMWPE and WS₂/UHMWPE nanocomposites. It makes us realize the nano-WS₂ had an effect on the fretting wear performance of UHMWPE.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0151/

The purpose of the study was to find the best performance polymer material to be used in railway car bogies.

Wear tests and optical and scanning electron microscopy were used.

The friction coefficients of ultra-high-molecular-weight polyethylene (UHMWPE) and Nylon 6 polymers, as opposed to AISI 4140 steel, reduced with the increment of applied loads. With the increment of sliding speed, the friction coefficient increased in both UHMWPE and Nylon 6 polymers. The specific wear rate of the UHMWPE polymer was determined to be about 10-14 m2/N, whereas the rate of Nylon 6 was determined to be 10-13 m2/N.

The aim of the study was to find the best performance polymer material to be used in railway car bogies.

The friction and wear performance of UHMWPE and Nylon 6 engineering polymers were studied and compared to their AISI 4140 steel counterparts. It is an original work and it is not published in any media.

Ultra-high molecular weight polyethylene (UHMWPE) is adopted in water-lubricated bearings for its excellent performance. This paper aims to investigate the tribological properties of UHMWPE with a molecular weight of 10.2 million (g mol^‐1) under different molding temperatures.

The UHMWPE samples were prepared by mold pressing under constant pressure and different molding temperatures (140°C, 160°C, 180°C, 200°C, 220°C). The friction and wear tests in water were conducted at the RTEC tribo-tester.

The friction coefficient and wear loss decreased first and rose later with the increasing molding temperature. The minimums of the friction coefficient and wear loss were found at the molding temperatures of 200°C. At low melting temperatures, the UHMWPE molecular chains could not unwrap thoroughly, leading to greater abrasive wear. On the other hand, high melting temperatures will cause the UHMWPE molecular chains to break up and decompose. The optimal molding temperatures for UHMWPE were found to be 200°C.

Findings are of great significance for the design of water-lubricated UHMWPE bearings.

Traditionally, an armor-grade composite is based on a two-dimensional (2D) architecture of its fiber reinforcements. However, various experimental investigations have shown that armor-grade composites based on 2D-reinforcement architectures tend to display inferior through-the-thickness mechanical properties, compromising their ballistic performance. To overcome this problem, armor-grade composites based on three-dimensional (3D) fiber-reinforcement architectures have recently been investigated experimentally. The paper aims to discuss these issues.

In the present work, continuum-level material models are derived, parameterized and validated for armor-grade composite materials, having four (two 2D and two 3D) prototypical reinforcement architectures based on oriented ultra-high molecular-weight polyethylene fibers. To properly and accurately account for the effect of the reinforcement architecture, the appropriate unit cells (within which the constituent materials and their morphologies are represented explicitly) are constructed and subjected to a series of virtual mechanical tests (VMTs). The results obtained are used within a post-processing analysis to derive and parameterize the corresponding homogenized-material models. One of these models (specifically, the one for 0°/90° cross-collimated fiber architecture) was directly validated by comparing its predictions with the experimental counterparts. The other models are validated by examining their physical soundness and details of their predictions. Lastly, the models are integrated as user-material subroutines, and linked with a commercial finite-element package, in order to carry out a transient non-linear dynamics analysis of ballistic transverse impact of armor-grade composite-material panels with different reinforcement architectures.

The results obtained clearly revealed the role the reinforcement architecture plays in the overall ballistic limit of the armor panel, as well as in its structural and damage/failure response.

To the authors’ knowledge, the present work is the first reported attempt to assess, computationally, the utility and effectiveness of 3D fiber-reinforcement architectures for ballistic-impact applications.

The purpose of this paper is to investigate the fretting wear performance of ultra-high-molecular-weight-polyethene (UHMWPE) with addition of GO and SiO₂.

In this study, GO were synthesized and SiO₂ nanoparticles were grafted onto GO. The effect of nanofiller on fretting wear performance of UHMWPE was investigated.

The results indicated that GO was successfully synthesized and SiO₂ nanoparticles successfully grafted onto GO. Incorporation of GS was beneficial for the reduction in friction and the improvement in wear resistance of UHMWPE. GO was beneficial for reducing friction coefficient, while SiO₂ was good for improving wear resistance. There existed a tribological synergistic effect between GO nanosheet and SiO₂ nanoparticles.

The hybrids of GS were promising nanofiller for improving the fretting wear performance of UHMWPE.

The main originality of the research is to reveal the effect of GO and SiO₂ nanoparticles on fretting behavior of UHMWPE. The result indicated hybrids of GS were promising nanofiller for improving the fretting wear performance of UHMWPE.

Composite laminates are considered one of the most popular damage-resistant materials when exposed to impact force in civil and military applications. In this study, a comparison of composites 12 and 20 layers of fabrics Kevlar and ultrahigh-molecular-weight poly ethylene (UHMWPE)-reinforced epoxy under low-velocity impacts represented by drop-weight impact and Izod pendulum impact has been done. During the Izod test, Kevlar-based composite showed damage at the composite center and fiber breakages. Whereas delamination was observed for UHMWPE reinforced epoxy (PE). The maximum impact strength was for Kevlar-reinforced epoxy (KE) and increases with the number of laminates. Drop-weight impact test showed the highest absorbed energy for (KE) composites. The results revealed that different behavior during the impact test for composites belongs to the impact mechanism in each test.

Aramid 1414 Kevlar 49 and UHMWPE woven fabrics were purchased from Yixing Huaheng High-Performance Fiber Textile Co. Ltd, with specifications listed in Table 1. Epoxy resin (Sikafloor-156) is supplied from Sika AG. Sikafloor-156 is a two-part, low-viscosity, solvent-free epoxy resin, with compressive strength ∼95 N/mm², flexural strength ∼30 N/mm² and shore D hardness 83 (seven days). The mixture ratio of A/B was one-third volume ratio. Two types of laminated composites with different layers 12 and 20 were prepared by hand layup: Kevlar–epoxy and UHMWPE–epoxy composites as shown in Figure 1. Mechanical pressure was applied to remove bubbles and excess resin for 24 h. The composites were left in room temperature for seven days, and then composite plates were cut for the desired dimensions. Low-velocity impact testing, drop-weight impact, drop tower impact system INSTRON CEAST 9350 (see Figure 2) was facilitated to investigate impact resistance of composites according to ASTM D7137M (Test Method for Compressive, 2005). Low-velocity impact tests have been performed at room temperature for composite with dimensions 10 × 15 cm² utilizing a drop tower (steel indenter diameter 19.85 mm as shown in Figure 3), height (800 mm), drop mass (5 kg) and speed (3.96 m/s). Special impact equipment consisting of vertically falling impactor was used in the test. The energy is obtained from Drop tower impact systems, (2009) E = ½ mv² (2.1). The relationship between force–time, deformation–time and energy–time and deformation was obtained. Energy–deformation and force–deformation relationships were also obtained. The depth of penetration and the radius of impactor traces were recorded. Izod pendulum impact test of plastics was applied according to ASTM D256 (Test Method for Compressive, 2005). Absorbed energy was recorded to compute the impact strength of the specimen. The specimen before the test is shown in Figure 4.

In order to investigate two types of impact: drop-weight impact and Izod impact on damage resistance of composites, the two tests were done. Drop-weight impact is dropping a known weight and height in a vertical direction with free fall, absorbed energy can be calculated. Izod impact measures the energy required to break a specimen by striking a specific size bar with a pendulum (Test Method for Compressive, 2005; Test Methods for Determining, 2018). The results obtained with the impact test are presented. Figure 5 shows the histogram bars of impact strength of composites. It can be noticed that Kevlar–epoxy (KE) composites give higher energy strength than UHMWPE–epoxy (PE) in 12 and 20 plies. The increasing percentage is about 18.5 and 5.7%. It can be observed in Figure 6 that samples are not destructed completely due to fiber continuity. Also, the delamination occurs obviously for UHMWPE–epoxy more than for Kevlar-based composite, which may due to weak binding between UHMWPE with an epoxy relative with Kevlar.

The force–time curves for Kevlar–epoxy (KE) and UHMWPE–epoxy (PE) composites with 12 and 20 plies are illustrated respectively in Figure 7. The contact duration between indenter and composite surface is repented by the force–time curves, so the maximum force reaches with certain displacement. It can be seen that maximum force was (13,209, 18,734.9, 23,271.07 and 19,825.38 N) at the time (3.97, 4.43, 3.791 and 4.198 ms) for 12 KE, 12 PE, 20 KE and 20 PE, respectively. The sharp peaks of KE composite are due to the lower ductility of Kevlar compared with UHMWPE. These results agree with the results of Ahmed et al. (2016). Kevlar-based composites (KE) showed lower impact force and crack propagates in the matrix with fast fiber breakage compared with PE composites, whereas the latter did not suffer from fabric breakage in 12 and 20 plies any more (see Figure 8). Figure 9 illustrates force–deformation curves, for 12 and 20 plies of Kevlar–epoxy (KE) and UHMWPE–epoxy (PE) composites. Curve's slop is considered the specimen's stiffness and the maximum displacement. To investigate the impact behavior of the four different composites, the comparison was made among the relative force–deformation curves. The maximum displacement was 5.119, 3.443, 1.173 and 1.17 mm for 12KE, 12 PE, 20 KE and 20 PE, respectively. It seems that UHMWPE-based composite (PE) presents lower deformation than Kevlar-based composites (KE) at a same number of laminates, although the maximum displacement is for 12 PE and 12 KE (see Figure 8). Kevlar-based composites (KE) showed more damage than UHMWPE-based composite (PE), so the maximum displacement is always higher for KE specimens with maximum indenter trace diameter (D∼11.27 mm). The onset of cracks begins along fibers on the impacted side for 20 KE and 20 PE specimens with lower indenter trace (D∼5.42 and 5.96 mm), respectively (see Table 2). These results refer to the lower stiffness of KE composites (see the slope of the curve) relative to PE composites. This result agreed with (Vieille et al., 2013) when they found that the theoretical stiffness of laminated composite during drop-weight impact depends significantly on fiber nature (Fadhil, 2013). The matrix cracking is the first type of damage that may not change stiffness of composites overall. Material stiffness changes due to the stress concentration represented by matrix cracks, delamination and fiber breakage (Hancox, 2000). Briefly, the histogram (see Figure 10) showed that the best impact behavior was for 20 KE, highest impact force with lower deformation, indenter trace diameter and contact time. Absorbed energy–time and absorbed energy–deformation curves for composites are shown in Figures 11 and 12, respectively. The maximum absorbed energy was (36.313, 29.952, 9.783 and 6.928 J) for 12 KE, 12 PE, 20 KE and 20 PE, respectively. Test period time is only 8 ms, but the time in which composites reached maximum absorbed energy was (4.413, 3.636, 2.394 and 2.408 ms). The maximum absorbed energy was for 12 KE with lower rebound energy because part of kinetic energy transferred to potential energy kept in the composite as material damage (see Figures 3 and 4). This composite absorbs more energy as material damage which kept as potential energy. Whereas other composites 12 PE, 20 PE and 20 KE showed less damage, lower absorbed energy and higher rebound energy, which appeared in different peak behavior as the negative value of energy. Also from the absorbed energy–time curves, it had been noticed significantly the maximum contact time of indenter with composite was 4.413 ms for 12 KE, which exhibits higher deformation (5.119 mm), whereas other composites 12 PE, 20 KE and 20 PE showed less damage, contact time and deformation as (3.443, 1.173, 1.17 mm), respectively.

The main goal of the current study is to evaluate the performances of armor composite made off of Kevlar and UHMWPE fabrics reinforced epoxy thermosetting resin under the low-velocity impact. Several plates of composites were prepared by hand layup. Izod and drop-weight impact tests were facilitated to get an indication about the absorbed energy and strength of the armors.

The purposes of this paper are to investigate the biotribological behaviour of Vitamin E-blended highly cross-linked ultra-high molecular weight polyethylene (HXL-UHMWPE) under multi-directional motion by using a CUMT II artificial joint hip simulator and compare it with HXL-UHMWPE and conventional UHMWPE.

The biotribological behaviour of conventional, highly cross-linked and Vitamin E-blended highly cross-linked UHMWPE acetabular cups counterfaced with CoCrMo alloy femoral head under multi-directional motion were investigated by using CUMT-II artificial hip joint simulator for one-million walking cycles. The test environment was at 36.5 ± 0.5°C and 25 per cent bovine serum was used as lubricant. A Paul cycle load with a peak of 784 N was applied; the motion and loading were synchronized at 1 Hz.

The wear resistance of Vitamin E-blended highly cross-linked UHMWPE was significantly higher than that of highly cross-linked and conventional UHMWPE. The wear marks observed from the worn surface of UHMWPE were multi-directional, with no dominant wear direction. Only abrasion occurred on the surface of Vitamin E-blended highly cross-linked UHMWPE, while yielding and accumulated plastic flow processes occurred on the surface of conventional UHMWPE and flaking-like facture and abrasion occurred on the surface of highly cross-linked UHMWPE.

Besides the prevention of oxidative degradation, blending with Vitamin E can also reduce the incidence of fatigue crack occurred in the surface layer of HXL-UHMWPE samples. Therefore, the wear resistance of HXL-UHMWPE under multi-directional motion can be further enhanced by blending with Vitamin E.

This study aims to fabricate and investigate the tribological performance of ultra-high molecular weight polyethylene (UHMWPE)-based composite materials reinforced with 0.5, 1 and 2 weight percentage of graphene nanoplatelets (GNPs) while keeping the weight percentage of vitamin C constant at 2% for each composite.

In this paper, the composites were fabricated using hot pressing, and the dispersion of GNP/vitamin C/UHMWPE hybrid composite was investigated by X-ray diffraction. Experimental trials were performed according to ASTM F732 on a reciprocating sliding tribometer (pin-on-disc) at human body temperature of 37 ± 1 °C, for a load of 52 N, to assess the role of these fillers on the tribological properties of UHMWPE against Ti6Al4V counter body material under dry and lubricating (human serum) environment.

In this study, it has been observed that friction and wear behavior of the developed composites improve with increase in weight percentage of GNP, and human serum adheres to the surface of the composite pins upon sliding, resulting in the formation of a film, which results in better wear resistance of the composite pins under human serum lubrication than dry sliding. Scanning electron microscope was used to investigate the worn surface morphological examination of the composite materials. Specific wear rate of 0.76 × 10⁻⁷ mm³/Nm was attained for 2 Wt.% GNP-filled composite under human serum lubrication.

The results indicate the compatibility of the composite material used in this study and suggested the in vitro implant application.

The presented work includes novel study of synergistic effect of GNP (which acts as a solid lubricant) and vitamin C (added as an antioxidant) on the tribological performance of UHMWPE under dry and human serum lubrication.