Tribological behavior of UHMWPE in water lubrication: the effect of molding temperature

Purpose 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. Design/methodology/approach 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. Findings 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. Originality/value Findings are of great significance for the design of water-lubricated UHMWPE bearings.

Graphite/epoxy composite for building Bipolar Plates

Bipolar plates (BPs) are important components of Proton Exchange Membrane Fuel Cells (PEMFC). Graphite-epoxy composites, having a better corrosion resistance than metal-based BPs and better mechanical properties than graphite BPs, are a promising alternative. In this study, we tried to develop graphite-epoxy composites meeting the technical US DOE targets for 2020, with a proper choice of manufacturing conditions that ensure a good compromise between conductivity, flexural strength, and gas permeability. In particular, we studied the influence of the filler to binder ratio, changed the molding temperature and time, and investigated the effects of increasing pressure both on in-plane conductivity and on helium permeability. We found that both formulation and molding pressure are crucial in determining the permeability of the graphite-epoxy composites, whereas molding temperature and time seem to play a minor role.

Optimization of Process Parameters for Friction Materials Using Multi-Criteria Decision Making: A Comparative Analysis

Friction materials, mainly made of reinforced composites, should possess excellent physical and tribological properties, such as a higher coefficient of friction, minimum wear, adequate surface hardness, and higher porosity for various automotive brake applications. Attainment of those properties greatly depends on the settings of different input parameters, such as molding pressure, temperature and time, temperature and time of heat treatment/sintering, etc., during the processing of friction materials. In this article, four multi-criteria decision-making (MCDM) tools, i.e., technique for order of preference by similarity to ideal solution (TOPSIS), evaluation based on distance from average solution (EDAS), VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR), and multi-objective optimization on the basis of ratio analysis (MOORA) are applied to identify the optimal parametric combinations for two different friction materials. A comparative analysis of the derived results suggests the same optimal parametric mixes for all the MCDM techniques for both case studies. Thus, for the considered case studies, the optimal parametric combinations as molding time = 8 min, molding temperature = 175 °C, molding pressure = 27 MPa, sintering time = 10 h and sintering temperature = 225 °C, and molding pressure = 27.90 MPa, molding temperature = 170 °C, curing time = 8 min, and heat treatment time = 1 h, respectively, would help in attaining the most desired properties of friction materials. Improvements in the predicted response values prove the efficacy of the adopted MCDM techniques in determining the optimal combinations of various process parameters for friction materials.

Investigation of Wood Flour Size, Aspect Ratios, and Injection Molding Temperature on Mechanical Properties of Wood Flour/Polyethylene Composites

In the present research, wood flour reinforced polyethylene polymer composites with a coupling agent were prepared by injection molding. The effects of wood flour size, aspect ratios, and mold injection temperature on the composites’ mechanical properties were investigated. For the preparation of the polymer composites, five different formulations were created. The mechanical properties including tensile strength and the modulus, flexural strength and the modulus, and impact energy were measured. To investigate the changes in the properties resulting from different compositions, mechanical static and impact testing was performed. The obtained results indicate that by reducing the flour size, the tensile strength and modulus, flexural strength, and impact energy were reduced. In contrast, the flexural modulus increased. Furthermore, with the increment of injection molding temperature, the tensile strength and the modulus and the impact energy of the specimens were reduced. On the other hand, the flexural strength and the modulus increased. Thus, an optimized amount of injection molding temperature can provide improvements in the mechanical properties of the composite.

Establishment of Rutting Model of Wheel-Tracking Test for Real-Time Prediction of Rut Depth of Asphalt Layers

The construction process control of asphalt layers directly affects the road service life and quality. The objective of this study was to establish a rutting model of the wheel-tracking test used for the real-time prediction of the rut depth of asphalt layers in the construction process. The gradation of asphalt mixture, asphalt content, and molding temperature were considered in the development of the new rutting model of the wheel-tracking test. The effects of these three factors on the high-temperature performance of asphalt mixture were analyzed. The order of importance of the factors affecting the high-temperature performance of asphalt mixture is the gradation of asphalt mixture, asphalt-aggregate ratio, and molding temperature. Overall, the predicted values of the rut depth of the wheel-tracking test are very close to the measured values. Furthermore, the difference between the rut depths of asphalt layers of the test group and the control group is small. These comparison results indicate that the new rutting model of the wheel-tracking test has high accuracy and good applicability for the test road.

Flax fiber reinforced polylactic acid composites for non-structural engineering applications: Effect of molding temperature and fiber volume fraction on its mechanical properties

Owing to its biodegradability, durability, low cost and potential material to replace existing commercial products in the field of engineering applications, nowadays there is a lot of interest in the field of green composites. It is formed by a mixture of biodegradable polymers and natural fibers and has a potential to replace synthetic polymer based composites. In this research work flax fibers are used as reinforcement and Poly-lactic acid (PLA) as matrix material for the development of Flax/PLA composites. The effects of processing parameters such as fiber volume fraction ranging from 25% to 50% and molding temperature ranging from 160°C to 180°C on mechanical properties of flax/PLA composites were investigated. It is concluded from the results that maximum tensile and flexural strength are recorded at 35% fiber volume fraction of flax/PLA composites developed at 170°C molding temperature. SEM analysis validated the findings obtained from the mechanical characterization.

Fabrication and Optical Characterization of Polymeric Aspherical Microlens Array Using Hot Embossing Technology

Hot embossing has been widely used in fabricating microlens arrays because of its low cost, high efficiency, and high quality. The process parameters such as molding temperature, molding pressure, and holding temperature affect the microlens array’s replication quality. This work selected the stainless steel S136H tool steel as the mold material to process an aspheric microlens array structure through ultra-precision milling. Polymethyl methacrylate (PMMA) microlens arrays with different surface replication were prepared by controlling the molding temperature, molding pressure, and holding temperature. By analyzing the surface quality, contour replication, and optical imaging of hot-embossed samples, the optimal molding temperature of PMMA for optimal replication of aspheric lens arrays was determined as 130 °C. Besides, the internal elastic recovery of PMMA affected the dimensional accuracy and optical performance of the lens. The results showed that, at the molding pressure of 400 N and the holding temperature of 60 °C, the surface defects were eliminated, and the aspheric lens array had perfect replication with a profile deviation of only 4 μm. The aspheric microlens array with good quality was eventually achieved by these optimal process parameters, which provides a foundation for producing aspheric microlens arrays in a low-cost and high-efficiency way.

Optimization of molding process parameters for CF/PEEK composites based on Taguchi method

In this article, nine groups of laminates were prepared according to the Taguchi L9(33) test array to study the influence of three process parameters, including molding pressure, molding temperature, and holding time on the performance of unidirectional carbon fiber/polyetheretherketone (CF/PEEK) laminates. A differential scanning calorimetry test was employed to select a reasonable process parameters range. The transverse tensile strength of the laminates was measured, and the fiber–matrix interfacial bonding behavior of the tested samples was analyzed by scanning electron microscopy. The results showed that the significance of factors to transverse tensile strength were molding temperature, holding time, and molding pressure in sequence. The optimal molding process parameters for CF/PEEK composite laminate were molding temperature of 400°C, molding pressure of 3 MPa, and holding time of 30 min. The optimization results were meaningful for the extension and application of thermoplastic composites.