Ultra-high Molecular Weight Polyethylene Research Articles

Tribological evaluation of thermoplastic polyurethane-based bearing materials under water lubrication: Effect of load, sliding speed, and temperature

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.

Enhancing the self-healing performance of engineered cementitious composites in harsh environment through cementitious matrix optimization and crack width controlling

The fragile cementitious materials can be easily cracked under service in the harsh environment, which can reduce the loading capacity of concrete structures and its expected service life. The self-curing ability of cementitious materials is thus essential for the resilience of the concrete structures in harsh environments. The purpose of the study is to enhance the self-healing ability of Engineered Cementitious Composites (ECC) in harsh environment though cementitious matrix optimization and crack width controlling. The cementitious matrix containing cement, silica fume, and fly ash is optimized based on the Simple Centroid Method. The Ultra-high Molecular Weight Polyethylene (UHMWPE) fibers have been selected as reinforcing materials due to their superior mechanical performance. The results show that the compressive strength of the ECC samples generally increases with the silica fume content, and the tensile strength rises with both the silica fume and cement content. Meanwhile, the ultimate tensile strain of the ECC samples increases and declines with the fly ash and silica fume content, respectively. The self-repairing properties of the pre-damaged ECC specimens with 5 % strain are examined through exposure in the simulated harsh environment. It is found that the exposure to the groundwater environment can improve the self-curing ability of the pre-damaged ECC specimens, while the self-curing ability can be deteriorated under exposure to the marine environment. Furthermore, the crack sealing and strength recovery ability of cementitious materials can be enhanced with higher fly ash content and lower silica fume content. Finally, the self-curing mechanism of the ECC samples is analyzed by means of the phase and microstructure analysis. Exposure to groundwater environments can promote the generation of the C–S–H gel and calcium carbonate in the self-curing product, and thus enhance the self-healing efficiency. This study can contribute the resilience enhancement of the concrete structure in harsh environments.

Ethylene Polymerizations Catalyzed by Fluorinated "Sandwich" Diimine-Nickel and Palladium Complexes.

Nickel and palladium complexes bearing "sandwich" diimine ligands with perfluorinated aryl caps have been synthesized, characterized, and explored in ethylene polymerization reactions. The X-ray crystallographic analysis of the precatalysts 16 and 6b shows differences from their nonfluorinated analogues 17 and 19, with the perfluorinated aryl caps centered precisely over the nickel and palladium centers, which results in higher buried volumes of the metal centers relative to the nonfluorinated analogues. The sandwich diimine-palladium complexes 5a and 5b containing perfluorinated aryl caps polymerize ethylene in a controlled fashion with activities that are substantially increased compared with their nonfluorinated analogues. Migratory insertion rates in relevant methyl ethylene complexes agree with the activities exhibited in bulk polymerization experiments. DFT studies suggest that facility of ethylene rotation from its preferred orientation perpendicular to the Pd-alkyl bond into a parallel in-plane conformation contributes to the higher polymerization activity for 5b relative to 18a. For these palladium systems, polymer molecular weights can be controlled via hydrogen addition (hydrogenolysis), which is unusual for late-transition-metal-catalyzed olefin polymerizations with no catalyst deactivation occurring. Sandwich diimine-nickel complexes 6a and 6b with perfluorinated aryl caps show ethylene polymerization activities that are about half of those of classical tetraisopropyl-substituted catalyst 2 but again are more active than the analogous nonfluorinated sandwich complexes. Ethylene polymerizations exhibit living behavior, and branched ultrahigh-molecular-weight polyethylenes (UHMWPEs) with very low-molecular-weight distributions (less than 1.1) are obtained. The activated nickel catalysts are stable in the absence of monomer and show good long-term stability at 25 °C.

Mechanical behavior of STF impregnation and anti-impact performances of Kevlar and UHMPWEF fabric impregnations

STF-impregnated Kevlar and ultra-high molecular weight polyethylene (UHMWPEF) fabric-impregnated bodies were prepared by using mass fraction of 34 % SiO2 with a particle size of 100 nm and PEG400 as dispersion and dispersant, respectively. When two kinds of fiber fabrics were impregnated by STF, the tensile, single fiber pull-out and single fiber tensile loads of Kevlar fabric-impregnated increased 26.63 %, 155.55 %, and 98.64 %, respectively. However, the tensile load, monofilament pull-out load and monofilament tensile load of the UHMWPEF fabric-impregnated body increased 100.14 %, 729.03 % and 51.61 %, respectively. Kevlar fiber fabric impregnated by ultrasonic vibration and smearing STF absorbs more steel projectile’s kinetic energies of 52.3 % and 27.43 % than that of the original fiber fabric, respectively. UHMPWEF fabric impregnated by using ultrasonic vibration and smearing increased 65.56 % and 47.73 % than the original fabric absorbing steel projectile’s kinetic energy. Based on the Scanning Electron Microscope (SEM) observation of the fiber fabric surface, it was found that the connection between the fibers was significantly strengthened after the STF impregnation treatment. When the fabric was subjected to impact load, STF played an important role in transmitting load and increasing friction.

The impact of boron carbide in soft and hard body armor: A comprehensive evaluation on Kevlar and UHMWPE fabrics

AbstractIn this research, an investigation was conducted to ascertain the impact of boron carbide (B4C) microparticles on soft and hard armor configurations, utilizing two distinct high‐performance fabrics namely, Kevlar and Ultra‐high Molecular Weight Polyethylene (UHMWPE), also this work discerned the optimal fabric for protection against dagger attacks and 9 mm full metal jacket (FMJ) projectiles. Initially, rheological tests on four shear thickening fluid (STF) samples revealed that 70% of nano‐silicate (SiO2) content was the optimal ratio. Besides, scanning electronic microscope (SEM) tests showed that B4C affected the nano‐silicate dispersion. Hence, the use of STF as a matrix, led to complete protection in low‐velocity stab test and behavior improvement when subjected to NIJ ballistic test for both fabric types. On the other hand, the dynamic mechanical analysis (DMA) of the thermosetting epoxy resin‐based composites reinforced by B4C indicated that the 10% ratio offered maximum rigidity, resulting in improved ballistic performance. This study revealed that Kevlar fabrics exhibit superior behavior in soft protection, while UHMWPE hard composite display further rigidity against high‐velocity impacts. Overall, this work contributes novel insights into the efficiency of B4C integration within soft and hard armor configurations using two ballistic fabrics, highlighting their performance characteristics in ballistic shielding.Highlights Investigation of B4C microparticles: The research examines the impact of B4C microparticles on soft and hard armor configurations. High‐performance fabrics: Kevlar and UHMWPE uses. The use of STF as a matrix for soft and thermosetting epoxy resin for hard armor: enhanced composite performance. Low‐velocity and high‐velocity impact tests investigations; microparticles B4C incorporation: superior mechanical characteristics. Remarkable energy absorption: promising shielding uses.

Comparison of the physico-chemical behavior of two prepregs used for body armor

The development of ultra-high molecular weight polyethylene fibers has resulted in continued improvement in ballistic protection, along with reduced weight in body armors. Prepregs from newly developed fibers are constantly available, although prepregs from older brands still remain on the market. In this work, the physicochemical properties of two successive generations of pre-impregnated materials are characterized to compare the two materials in the as-received condition and also after be consolidated in a ballistic plate. The results showed that fibers from the newer brand have a smaller diameter and greater tensile strength. This is an important result because the tensile strength of fibers is one of the variables that influence the ballistic performance of body armors. The smaller diameter of these fibers was associated with a greater degree of stretching during their manufacture, as revealed by the presence of two melting peaks in the DSC analysis.

Characterization of surface and bulk properties of α-Tocopherol blended and γ irradiated UHMWPE sandwich nanocomposites

In the present study, an unconventional approach in compression molding is chosen to fabricate Ultra High Molecular Weight Polyethylene (UHMWPE) sandwich composites with Graphene (Gr) and Nano-diamond (ND) as fillers. A unique comparison is done between the surface and bulk properties of UHMWPE nano-composites and UHMWPE sandwich composites. Influence of gamma irradiation at doses of 50, 100 kGy doses and vitamin E (vit-E) on crystal structure, mechanical, thermal and tribological characteristics of UHMWPE composites were studied through x-ray diffraction (XRD), raman spectroscopy, dynamic mechanical analysis (DMA), rheology, differential scanning calorimetry (DSC), tensile, nano-indentation and wear characterization techniques. Fracture regions and surface wear of the samples were analysed through scanning electron microscopy (SEM) to understand the dispersion behavior of fillers in matrix. The concentration of vit-E content in UHMWPE greatly influenced the crosslinks and surface properties in gamma irradiated composites. Gamma irradiation have shown significant improvement in crystallinity, viscous behavior and bulk properties of UHMWPE composites. Irradiated UHMWPE nano-composites have shown better tensile results when compared with sandwich composites, with 22 % increase in young's modulus and 16 % increase in yield stress. Wear rate has been reduced by 25 % for irradiated sandwich UHMWPE composites when compared with UHMWPE nano-composites.

Ballistic performance of flexible structures composed of UHMWPE fibers and airbag: Effects of the stacking order

A series of flexible structures incorporating an airbag and ultra-high molecular weight polyethylene (UHMWPE) fiber panels were designed as temporary architectures to offer both ballistic protective functions and lightweight constructions. Three primary structural configurations, monolithic structures (airbag or UHMWPE panel alone), bi-layer structures (airbag/ UHMWPE panel and UHMWPE panel/airbag), and sandwich structures (UHMWPE panel/airbag/ UHMWPE panel) were tested. A T12A carbon tool steel sphere with the diameter of 12.7 mm was utilized as the ballistic threat within an impact velocity range of 0–500 m/s. Investigations into the effect of stacking order on ballistic performance were carried out experimentally and numerically. The failure characteristics, ballistic limits, energy dissipations, impact processes and interaction effects of these structures are discussed. To facilitate the establishment of numerical models for impact analysis using ABAQUS, a material constitutive model of thermoplastic polyurethanes (TPU) including strain rate effect was developed. The numerical models of the monolithic single-sheet UHMWPE panel and airbag for impact analysis were subsequently verified by experiments in terms of impact processes and ballistic limits. The results reveal that arranging a few layers of UHMWPE panels in front of the airbag can improve the collapse ballistic limit while maintaining the failure ballistic limit. The inclusion of an airbag reduces the energy dissipation efficiency of composite structures. The potential to enhance ballistic protection through the combination of airbags and UHMWPE panels is highlighted. Stress dispersion and deformation restraint are identified as significant factors influencing the ballistic performance of the composite structures.

Ballistic performance of UHMWPE fiber laminates with pre-formed holes

Understanding how previous ballistic impacts affect the subsequent penetration resistance of ultra-high molecular weight polyethylene (UHMWPE) fiber laminates is crucial for their application in multi-hit scenarios. In order to investigate the effect of fiber fracture, a systematic examination of the ballistic performance of UHMWPE laminates with pre-formed holes is conducted through a combined experimental and numerical approach. Penetration resistance, dynamic penetration process, and deformation/failure modes of laminates with different configurations of pre-formed holes are tested and compared. A full three-dimensional finite element model is established, and a continuum homogenized model is utilized to simulate the laminate. The effectiveness of numerical model is validated by achieving a reasonable agreement between predictions and measurements. The presence of a single pre-formed hole will change the severity of delamination and result in tear failures, while it has minimal effect on penetration resistance until the spacing distance reaches 10 mm. When spacing distance remains the same, the change in orientation of a single pre-formed hole has little influence on the velocity history. Further, an enhancement in ballistic performance is observed when the number of pre-formed holes is increased to four, due mainly to the significant pull-in at the edge of pre-formed hole and the released fiber tensile stresses. The results of this study are valuable for comprehending the ballistic performance of UHMWPE laminate when subjected to multiple projectile impacts and have practical implications for the design of advanced protective systems.

Catalytic cyanate resin with polysulfide cation catalyst and its ultra‐high molecular weight polyethylene fiber composites for radome

AbstractCyanate (CE) resin and ultrahigh‐molecular‐weight polyethylene (UHMWPE) fiber are respectively important matrix and reinforcing material for lightweight and high wave‐transparent composites. However, the preparation and application of the composites is limited by the mismatch of molding temperature between CE resin and UHMWPE fiber. The best method to solve this problem is to catalyze the CE resin curing reaction and reduce its molding temperature from 270 to 135°C, which is the upper heat‐resistance temperature of UHMWPE fiber. In this study, the polysulfide catalyst (PSC) was used to catalyze CE resin curing reaction, reduce the curing reaction activation energy and the molding temperature. The apparent activation energy of the CE‐PSC resin decreases from 107.2 to 60.7 kJ mol−1, and the glass transition temperature of the CE‐PSC resin is 257.2°C, flexural strength and tensile strength are 120.2 and 60.8 MPa, respectively. As a result, the CE‐PSC/UHMWPE fiber composites, which are molded at the matching temperature of 135°C, have low density of 1.05 g cm−3, low dielectric constant of 2.4, low dielectric loss of 0.006, and high wave transmittance of 92.2%. Therefore, the CE‐PSC/UHMWPE fiber composites have wide application prospect in the field of light weight and high wave‐transparent composites.Highlights A novel catalytic CE resin can be cured at 135°C with low dielectric properties. The processing temperature mismatch between CE and UHMWPE fiber was solved. Catalytic CE/UHMWPE composites have lightweight and high wave‐transparent properties.

Crystallographic Texture Evolution in 3D Printed Polyethylene Reactor Blends.

In this work, crystallographic texture evolution in 3D printed trimodal polyethylene (PE) blends and high-density PE (HDPE) benchmark material were investigated to quantify the resulting material anisotropy, and the results were compared to materials made from conventional injection molded (IM) samples. Trimodal PE reactor blends consisting of HDPE, ultrahigh molecular weight PE (UHMWPE), and HDPE_wax have been used for 3D printing and injection molding. Changes in the preferred orientation and distribution of crystallites, i.e., texture evolution, were quantified utilizing the wide angle X-ray diffraction through pole figures and orientation distribution functions (ODFs) for 3D printed and IM samples. Since the change in weight-average molecular weight (Mw) of the blend was expected to significantly affect the resulting crystallinity and orientation, the overall Mw of the trimodal PE blend was varied while keeping the UHMWPE component weight fraction to 10% in the blend. The resulting texture was analyzed by varying the overall Mw of the trimodal blend and the process parameters in 3D printing and compared to the texture of conventional IM samples. The printing speed and orientation (defined with respect to the axis along the length of the samples) were used as the variable process parameters for 3D printing. The degree of anisotropy increases with an increase in the nonuniform distribution of intensities in pole figures and ODFs. All the highest intensity major texture components in IM and 3D printed samples (0° printing orientation) of reactor blends are observed to have crystals oriented in [001] or [001̅]. Overall, for the same throughput, 3D printed samples in the 0° orientation showed greater texture evolution and higher anisotropy compared to IM samples. Most notably, an increase in 3D printing speed increased the crystalline distribution closer to the 0° direction, increasing the anisotropy, while deviation from this printing orientation reduced crystalline distribution closer to the 0° direction, thus increasing isotropy. This demonstrates that tailoring material properties in specific directions can be achieved more effectively with 3D printing than with the injection molding process. Change in the overall Mw of the trimodal PE blend changed the preferential orientation distribution of the crystal planes to some degree. However, the degree of anisotropy remained the same in almost all cases, indicating that the effect of molecular weight distribution is not as significant as the printing speed and printing orientation in tailoring the resulting properties. The 3D printing process parameters (speed and orientation) were shown to have more influence on the texture than the material parameters associated with the blend.

Fourier-transform infrared spectroscopy imaging is a useful adjunct to routine histopathology to identify failure of polyethylene inlays in revision total hiparthroplasty.

The use of highly crosslinked ultra-high molecular weight polyethylene (XLPE) has significantly reduced the volumetric wear of acetabular liners, thereby reducing the incidence of osteolysis. However, contemporary components tend to generate smaller wear particles, which can no longer be identified using conventional histology. This technical limitation can result in imprecise diagnosis. Here, we report on two uncemented total hip arthroplasty cases (~7 years in situ) revised for periprosthetic fracture of the femur and femoral loosening, respectively. Both liners exhibited prominent wear. The retrieved pseudocapsular tissue exhibited a strong macrophage infiltration without microscopically identifiable polyethylene particles. Yet, using Fourier-transform infrared micro-spectroscopic imaging (FTIR-I), we demonstrated the prominent intracellular accumulation of polyethylene debris in both cases. This study shows that particle induced osteolysis can still occur with XLPE liners, even under 10 years in situ. Furthermore, we demonstrate the difficulty of determining the presence of polyethylene debris within periprosthetic tissue. Considering the potentially increased bioactivity of finer particles from XLPE compared to conventional liners, an accurate detection method is required, and new histopathological hallmarks of particle induced osteolysis are needed. FTIR-I is a great tool to that end and can help the accurate determination of foreign body tissue responses.

Effect of Nano-CuO and 2-Mercaptobenzothiazole on the Tribological Properties of Ultra-High Molecular Weight Polyethylene

In this study, the tribological properties of nanocomposites based on ultra-high molecular weight polyethylene (UHMWPE) filled with nano-CuO and 2-mercaptobenzothiazole (CuO/MBT) in mass ratios of 1:1 and 2:1 were investigated. In the supramolecular structure of UHMWPE nanocomposites, spherulites of several hundred micrometers in size are formed. The density of UHMWPE nanocomposites slightly increases relative to the pure polymer, reaching a maximum at 2 wt.% CuO/MBT in both ratios. The Shore D hardness and compressive stress of the UHMWPE nanocomposites showed an improvement of 5–6% and 23–35%, respectively. The wear resistance and coefficient of friction of UHMWPE nanocomposites were tested using a pin-on-disk configuration under dry friction conditions on #45 steel and on P320 sandpaper. It was shown that the wear rate of UHMWPE nanocomposites filled with 2 wt.% CuO/MBT decreased by ~3.2 times compared to the pure polymer, and the coefficient of friction remained at the level of the polymer matrix. Abrasive wear showed an improvement in UHMWPE nanocomposites filled with 1 wt.% CuO/MBT compared to the polymer matrix and other samples. The worn surfaces of the polymer composites after dry friction were examined by scanning electron microscopy and IR spectroscopy. The formation of secondary structures in the form of tribofilms that protect the material from wear was demonstrated. Due to this, the wear mechanism of UHMWPE nanocomposites is transformed from adhesive to fatigue wear. The developed materials, due to improved mechanical and tribological properties, can be used as parts in friction units of machines and equipment.

2.5 μm‐Thick Ultrastrong Asymmetric Separator for Stable Lithium Metal Batteries

Lithium metal batteries (LMBs) are considered the ideal choice for high volumetric energy density lithium‐ion batteries, but uncontrolled lithium deposition poses a significant challenge to the stability of such devices. In this paper, we introduce a 2.5 μm‐thick asymmetric and ultrastrong separator, which can induce tissue‐like lithium deposits. The asymmetric separator, denoted by utPE@Cu2O, was prepared by selective synthesis of Cu2O nanoparticles on one of the outer surfaces of a nanofibrous (diameter ~10 nm) ultrastrong ultrahigh molecular weight polyethylene (UHMWPE) membrane. Microscopic analysis shows that the lithium deposits have tissue‐like morphology, resulting in the symmetric lithium cells assembled using utPE@Cu2O with symmetric Cu2O coating exhibiting stable performance for over 2000 h of cycling. This work demonstrates the feasibility of a facile approach ultrathin separators for the deployment of lithium metal batteries, providing a pathway towards enhanced battery performance and safety.

Structural Evolution of Ultra-High Molecular Weight Polyethylene Low-Entangled Films with Reserved Shish Crystals During Hot Stretching

Structural Evolution of Ultra-High Molecular Weight Polyethylene Low-Entangled Films with Reserved Shish Crystals During Hot Stretching

Polymer Physics behind the Gel-Spinning of UHMWPE Fibers.

Gel-spinning of ultra-high molecular weight polyethylene (UHMWPE) fibers has attracted great interest in academia and industry since its birth and commercialization in the 1980s, due to unique properties such as high modulus, low density, and excellent chemical resistance. However, the high viscosity and long relaxation time greatly complicate processing. In industry, solvents, like decalin and paraffin oil, usually disentangle the physical networks and promote final drawability. From extruding the polymer solution to post-solid-stretching, many polymer physics problems that accompany high-modulus fiber gel-spinning should be understood and addressed. In this review, by detailed discussions about the effect of entanglements and intracrystalline chain dynamics on the mechanical properties of UHMWPE, theoretical descriptions of the structure formation of disentangled UHMWPE crystals, and the origin of high modulus and strength of final fibers are provided. Several physical intrinsic key factors are also discussed, revealing why UHMWPE is an ideal material for producing high-performance fibers.

Simultaneously enhanced antioxidation and wear resistance in UHMWPE molded plastic by adding natural polyphenol antioxidant

Ultrahigh-molecular-weight polyethylene (UHMWPE), with its excellent wear resistance and biocompatibility, has important application as artificial joints. The most commonly used method to improve its wear resistance is to introduce crosslinking through irradiation. However, free radicals are introduced after radiation, which are easy to cause inflammation in the human body. Some antioxidants, such as vitamin E (VE), need to be added. However, the addition of VE could reduce the crosslinking density of UHMWPE and worsen the wear resistance of the material. Therefore, obtaining new antioxidants that could eliminate free radicals without affecting or even improving the crosslinking density of materials during irradiation is an important subject worth exploring. In this paper, a kind of natural polyphenol substance, resveratrol (RSV), was introduced as a new antioxidant and crosslinking promoter during irradiation crosslinking of UHMWPE. RSV can better eliminate free radicals than VE and further improve the crosslinking density to obtain UHMWPE materials with excellent oxidation resistance and high wear resistance. The multi-active phenolic hydroxyl structure of RSV molecule provides its free-radical trapping ability, and the appropriate molecular size of RSV may promote the H-type crosslinking of UHMWPE, thereby increasing the crosslinking density. This work provides a new pathway for developing high-performance artificial joint prosthesis materials.

Thermal aging behavior and heat resistance mechanism of ultraviolet crosslinked ultra‐high molecular weight polyethylene fiber

AbstractAs advances in heat resistant ultrahigh molecular weight polyethylene (UHMWPE) fiber via ultraviolet (UV) crosslinking, it is worth paying attention to its thermal aging behavior and heat resistance mechanism. UHMWPE fibers in different forms, the fully drawn yarn (FDY) and the UV crosslinked FDY (UVFDY), are subjected to isothermal aging at 135°C. The effects of thermal aging on their surface morphology and mechanical properties are studied and compared initially. The results demonstrate that UVFDY is a kind of a heat‐resistant fiber. Subsequently, to reveal the heat resistance mechanism of UVFDY, its crystalline and orientation structure evolution during thermal aging are further studied. It is indicated that the formation of dense‐packing crystals and disorientation behavior lead to fiber shrink, so that a number of grooves appear on the fiber surface. Since the crosslinked stucture of UVFDY hinders its molecules movement, the crystallization and disorientation behavior of UVFDY are weaker than those of FDY, resulting in UVFDY possesses slighter thermal shrinkage (Ts), fewer grooves and better mechanical properties than those of FDY. Therefore, the heat resistance of the fiber improves effectively after UV crosslinking. This work provides insights into the structure–property relationship of UVFDY during thermal aging, and offers basis data for its application in specific conditions.

Effect of impact spacing on the dynamic response of UHMWPE fiber composites under two-point high velocity impacts

The impact from multiple bullets leads to more severe damage to fiber composite laminates, and the dynamic response becomes more complex. However, current research has focused on studying the ballistic limit and single impact response of materials. In this study, an experimental method to investigate the dynamic response and damage modes of fiber composite materials under multi-point asynchronous impacts is proposed. The aim is to reveal the mechanisms behind the differences in ballistic limits and energy absorption of UHMWPE (Ultra-High Molecular Weight Polyethylene) fiber composite panels at different impact distances. Through CT scanning and DIC (Digital Image Correlation) techniques, the delamination area and dynamic response of the laminates were quantitatively analyzed. The results show that the ballistic limit of the second impact is increased by 3.05 % when the impact distance is 2.5 times the diameter of the bullet. The maximum difference of energy absorption compared to the first impact was only 3.7 % at an impact spacing of 5 times the diameter of the bullet, despite the interference in the damage region. From the perspective of energy absorption, the two impacts are independent. Multiple impact tests are critical for protective materials, and the results of this study provide important insights into UHMWPE fiber laminates in terms of multi-point impact.

A low-cost design approach to vanadium redox flow test cell

Vanadium redox flow batteries (VRFB) will be essential in maximizing the large-scale use of renewable energy after achieving technical maturity. But as the test cells needed to conduct VRFB research are very expensive, the cost factor can prevent participation of developing countries in critical research. To address such issue, this work presents a novel low-cost design for laboratory VRFB cell yielding good performances. This design relies on sturdy ultra-high molecular weight polyethylene (UHMWPE) end plates with flow channels to provide the strength needed to seal other components while properly distributing electrolyte. This simpler design uses a reduced number of components compared to traditional cells, thus resulting in easier manufacturing and assembly while keeping costs low. This novel design approach achieved performances that are comparable to a commercial VRFB test cell in various testing conditions, but at roughly a third of the cost. Performances have been further improved by 3D printing end plates with optimized flow channels, with the added benefit of avoiding the complexity and costs of computer numerical control (CNC) milling. This novel design approach can thus be useful to many researchers in developing countries for their VRFB test.