Ultra-high Molecular Weight Polyethylene Fibers Research Articles

Effect of various polymer fibers on spalling mitigation of ultra-high performance concrete at high temperature

Polymer fibers have been commonly used to prevent spalling of ultra-high performance concrete (UHPC) at high temperature. Although different polymer fibers have been adopted in UHPC, the critical properties of polymer fibers required for spalling resistance remained unanswered. This paper investigated the behavior of commonly used polymer fibers, including linear low-density polyethylene (LLDPE), ultra-high molecular weight polyethylene (UHMWPE), polypropylene (PP), polyamide 66 (PA) and polyester (PET) fibers, in spalling mitigation of UHPC through spalling tests, permeability measurements and microscopic characterizations. It was found that LLDPE, PP and PA could prevent spalling of UHPC, while UHMWPE and PET fibers were not effective in spalling prevention. Melting point of fiber could not determine its effectiveness on spalling prevention and empty channels left by molten fibers did not govern spalling resistance of UHPC. In fact, high coefficient of thermal expansion of polymer fibers is required for enhancing permeability of UHPC samples. Thermal expansion of polymer fibers created microcracks even before melting of fibers. This affected pore size distribution and increased permeability significantly, leading to high spalling resistance of UHPC.

Mechanical properties of pressure moulded fibre reinforced pervious concrete pavement brick

Utilising pervious concrete (PC) increases the environmental, economic and social benefits. This study aims to investigate the mechanical performance of PC paving bricks using smaller single-sized coarse aggregates with different types of fibres: Kevlar, Polyvinyl Alcohol (PVA) and Ultra-High Molecular Weight Polyethylene (UHMWPE) fibres. Four PC mixes were designed using a modified ACI method and paving bricks formed using a pressure compaction method of 2 MPa and air-curing for 28 days. Results showed that the use of smaller coarse aggregate results in reduced porosity. However, the addition of fibres at a volume fraction of 0.3 % lead to approximately 47 %, 21.5 % and 18.8 % decrease in 28-days compressive strength, and 26 %, 7.3 %, and 17.6 % reduction in tensile splitting strength for specimens containing Kevlar, PVA, and UHMWPE fibres, respectively. When compared with the control group, an optimum 9.5 % increase in the flexural strength shows the effectiveness of the fibre addition. The permeability values range between 0.15 cm/s to 0.39 cm/s, which is proportional to the porosity of the material and satisfactory according to ACI standards. Combining the pressure compaction method and the addition of fibres adversely affects the compressive and splitting tensile strength, while increasing the flexural strength slightly. An alternative forming/moulding method that can fully utilise the addition of fibres is worth further investigation.

Deciphering the structure-induced impact response of ZnO nanorod grafted UHMWPE woven fabrics

Ultra-high molecular weight polyethylene (UHMWPE) fibres, a popular choice for armour applications, have low coefficient of friction which is not favourable for good impact resistance. An attempt has thus been made in this study to increase the inter-yarn friction in UHMWPE woven fabrics by in-situ ZnO nanorod (Z-NR) grafting. The inter-yarn friction, characterised by yarn pull-out force, increased after Z-NR grafting in all fabrics irrespective of their structural variations. For all fabrics woven with 1350 denier yarn and loose fabrics woven with 400 denier yarn, Z-NR grafted fabrics outperformed their neat counterparts in terms of impact energy absorption and peak force. However, for tightly woven fabrics of 400 denier yarn, the impact energy absorption decreased in comparison to that of neat fabrics. The fabric structure induced role of Z-NR grafting was hence found to be a promising approach to augment the inter-yarn friction and consequently impact resistance of UHMWPE fabrics.

Ballistic performance of multi-layered aluminium and UHMWPE fibre laminate targets subjected to hypervelocity impact by tungsten alloy ball

Multi-layered structures have been widely used in defence, marine, aerospace and automotive engineering. It is radical to comprehend the dynamic response of such structures under impact loadings and to design optimal structures to resist ballistic penetration. In this study, hypervelocity projectile impact experiments were conducted to explore the penetration resistance of spaced multi-layered aluminium and ultra-high molecular weight polyethylene (UHMWPE) fibre laminate targets. Experimental results including crater diameter, depth of penetration (DOP) and energy absorption capacity of multi-layered targets were measured and then discussed, from which it was evident that the combined use of aluminium and UHMWPE fibre laminates was the most effective in resisting projectile impact considering both the dynamic performance and light weight. Based on the validated simulation models, further parametric studies were conducted to investigate the effect of air space between adjacent layers, number and order of layers on the ballistic performance of multi-layered aluminium and UHMWPE fibre laminate targets.

Increasing inter-yarn friction to ultra-high molecular weight polyethylene yarns for ballistic application by sol-gel treatment

Ultra-high molecular weight polyethylene fibre is popularly used in military for ballistic protection owing to its low density but high modulus and high tenacity. However, the inter-yarn friction in the corresponding ballistic fabric is too low and thus the yarns in the fabric are easily pulled out, in which lowers down the ballistic performance. This paper aims to improve the inter-yarn friction in the fabric by sol-gel method using TiO2/ZnO hydro-sols and investigate the ballistic performance of fabric treated. The results from the coefficient of friction test have showed that the inter-yarn friction treated with TiO2/ZnO hydro-sol can be increased 40%. Moreover, tensile test indicates that the tenacities of yarns after different treatments are increased whereas the strains and moduli of the yarns almost kept unaffected. Through ballistic performance test, the treated fabric displays higher ballistic energy absorption compared with the original one, indicating that higher inter-yarn friction is beneficial to fabric against ballistic impact.

Tensile behavior of strain-hardening geopolymer composites (SHGC) under impact loading

Strain-hardening geopolymer composites (SHGC) exhibit remarkable ductility, crack control and high energy dissipation capacity when subject to quasi-static tensile loading. However, their mechanical performance under dynamic loading has not yet been explored. A comprehensive assessment of possible rate effects is required to facilitate a targeted material design for various practical applications. The article presents the results of an experimental investigation on the mechanical behavior of two types of SHGC under both quasi-static and impact tensile loading. The composites were reinforced with 2% of either short polyvinyl alcohol (PVA) fiber or ultra-high molecular-weight polyethylene (UHMWPE) fiber. The experiments were performed both at the composite scale and at the fiber level. The impact tests on the plain geopolymer matrix and SHGC were performed in a gravity-driven split-Hopkinson tension bar (SHTB) at strain rates of up to 300 s−1. The tests were accompanied by optical measurements to assess specimen deformation and multiple cracking by means of Digital Image Correlation (DIC). The dynamic fiber-matrix bond properties were investigated in a miniature split Hopkinson bar. Both under quasi-static tensile loading and impact tensile loading, the SHGC made with UHMWPE fibers exhibited superior mechanical performance compared to the composite made with PVA fibers. When comparing the impact tensile performance of SHGC with normal-strength SHCC from previous studies, SHGC demonstrated higher dynamic tensile strength and energy dissipation capacity, making SHGC promising for strengthening/prospective applications against highly dynamic actions.

Delamination process in cross-ply UHMWPE laminates under ballistic penetration

Cross-ply unidirectional laminates made of ultra-high molecular weight polyethylene fibers are widely used as components of bullet-proof vests. To simulate the delamination process of the material under penetration, we constructed a numerical mechanical model, which was validated by tests using 7.62 × 39 mm rifle bullets penetrating laminates of different thicknesses. The results show that the delamination region is essentially diamond-shaped. The simulated delamination region is in good agreement with the experimental data. It is found that the delamination region increases with the compression modulus along the fiber direction. The delamination region increases when the shear strength between the fabric layers decreases; However, it is little influenced by the normal strength. The delamination region of the front face of the laminate is little influenced by the failure strain of the material and the initial velocity of the bullet. The delamination region of the back face increases with the failure strain and decreases with the initial velocity.

Functional Characteristics and Mechanical Performance of PCU Composites for Knee Meniscus Replacement.

The potential use of fiber-reinforced based polycarbonate-urethanes (PCUs) as candidate meniscal substitutes was investigated in this study. Mechanical test pieces were designed and fabricated using a compression molding technique. Ultra-High Molecular Weight Polyethylene (UHMWPE) fibers were impregnated into PCU matrices, and their mechanical and microstructural properties evaluated. In particular, the tensile moduli of the PCUs were found unsuitable, since they were comparatively lower than that of the meniscus, and may not be able to replicate the inherent role of the meniscus effectively. However, the inclusion of fibers produced a substantial increment in the tensile modulus, to a value within a close range measured for meniscus tissues. Increments of up to 227% were calculated with a PCU fiber reinforcement composite. The embedded fibers in the PCU composites enhanced the fracture mechanisms by preventing the brittle failure and plastic deformation exhibited in fractured PCUs. The behavior of the composites in compression varied with respect to the PCU matrix materials. The mechanical characteristics demonstrated by the developed PCU composites suggest that fiber reinforcements have a considerable potential to duplicate the distinct and multifaceted biomechanical roles of the meniscus.

Fast, Light-Responsive, Metal-Like Polymer Actuators Generating High Stresses at Low Strain

Summary Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultra-high molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzene-doped UHMWPE films have high Young's moduli (∼100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast ( 6 × 104 Pa (kg m−3)−1) to UV or visible light at a low strain (∼0.06%). The actuator responds to rotating linearly polarized light, causing a photo-induced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics.

High-Strength Fiber-Reinforced Composite Hydrogel Scaffolds as Biosynthetic Tendon Graft Material.

The development of suitable synthetic scaffolds for use as human tendon grafts to repair tendon ruptures remains a significant engineering challenge. Previous synthetic tendon grafts have demonstrated suboptimal tissue ingrowth and synovitis due to wear particles from fiber-to-fiber abrasion. In this study, we present a novel fiber-reinforced hydrogel (FRH) that mimics the hierarchical structure of the native human tendon for synthetic tendon graft material. Ultrahigh molecular weight polyethylene (UHMWPE) fibers were impregnated with either biosynthetic polyvinyl alcohol/gelatin hydrogel (FRH-PG) or with polyvinyl alcohol/gelatin + strontium-hardystonite (Sr-Ca2ZnSi2O7, Sr-HT) composite hydrogel (FRH-PGS). The scaffolds were fabricated and assessed to evaluate their suitability for tendon graft applications. The microstructure of both FRH-PG and FRH-PGS showed successful impregnation of the hydrogel component, and the tendon scaffolds exhibited equilibrium water content of ∼70 wt %, similar to the values reported for native human tendon, compared to ∼50 wt % water content retained in unmodified UHMWPE fibers. The tensile strength of FRH-PG and FRH-PGS (77.0-81.8 MPa) matched the range of human Achilles' tendon tensile strengths reported in the literature. In vitro culture of rat tendon stem cells showed cell and tissue infiltration into both FRH-PG and FRH-PGS after 2 weeks, and the presence of Sr-HT ceramic particles influenced the expression of tenogenic markers. On the other hand, FRH-PG supported the proliferation of murine C2C12 myoblasts, whereas FRH-PGS seemingly did not support it under static culture conditions. In vivo implantation of FRH-PG and FRH-PGS scaffolds into full-thickness rat patellar tendon defects showed good collagenous tissue ingrowth into these scaffolds after 6 weeks. This study demonstrates the potential viability for our FRH-PG and FRH-PGS scaffolds to be used for off-the-shelf biosynthetic tendon graft material.

Hierarchical Mechanisms of Lateral Interactions in High-Performance Fibers.

The processing conditions used in the production of advanced polymer fibers facilitate the formation of an oriented fibrillar network that consists of structures spanning multiple length scales. The irregular nature of fiber tensile fracture surfaces suggests that their structural integrity is defined by the degree of lateral (interfacial) interactions that exist within the fiber microstructure. To date, experimental studies have quantified interfacial adhesion between nanoscale fibrils measuring 10-50 nm in width, and the global fracture energy through applying peel loads to fiber halves. However, a more in-depth evaluation of tensile fracture indicates that fiber failure typically occurs at an intermediate length scale, involving fibrillation along interfaces between fibril bundles of a few 100s of nanometers in width. Interaction mechanisms at this length scale have not yet been studied, due in part to a lack of established experimental techniques. Here, a new focused ion beam-based sample preparation protocol is combined with nanoindentation to probe interfaces at the intermediate length scale in two high-performance fibers, a rigid-rod poly(p-phenylene terephthalamide) and a flexible chain ultrahigh molecular weight polyethylene fiber. Higher interfacial separation energy recorded in the rigid-rod fiber correlated with less intensive fibrillation during failure and is discussed in the context of fiber chemistry and processing. Power law scaling of the total absorbed interfacial separation energy at three different scales in the polyethylene fiber is observed and analyzed, and distinct energy absorption mechanisms, featuring a degree of self-similarity, are identified. The contribution of these mechanisms to the overall integrity of the fiber is discussed, and the importance of the intermediate scale is elucidated. Results from this study provide new insights into the mechanical implications of hierarchical lateral interactions and will aid in the development of novel fibers with further improved mechanical performance.

Fiber tortuosity and its effects on shock transfer characteristics of Ultra High Molecular Weight Polyethylene (UHMWPE) fibers embedded in a polyurethane composite structure

Low density, high strength, and flexibility of ultra-high molecular weight polyethylene (UHMWPE) fibers have made them a topic of intensive research in many fields. More specifically, UHMWPE has been extensively used in shock damping applications. However, little is known about the effects of fiber tortuosity and fiber wetting on the shock transfer characteristics of these fibers. Herein, focus is placed on studying the effects of tortuosity and fiber wetting on the shock transfer characteristics of UHMWPE fiber braid embedded in a polyurethane matrix. Shock transfer characteristics of these fibers are identified by generating a longitudinal shock on one end of the fiber, while simultaneously measuring the transferred force overtime on the other side of the fiber. From the experiments it is found that the force versus time response of these structures show an underdamped response. Analyzing the maximum force transfer and the rate of decay, it is seen that tortuosity has a significant effect on the shock transfer characteristics of these structures. Given the nature of these results, it is strongly believed that the presented work provides a creative strategy for designing, developing, and characterizing, new composite structures with improved impact attenuation characteristics.

Enhanced Performance in Uranium Extraction by Quaternary Ammonium-Functionalized Amidoxime-Based Fibers

Acrylonitrile and 2-(dimethylamino)ethyl methacrylate were grafted onto ultrahigh molecular weight polyethylene fibers, and a series of quaternary ammonium (Q)-functionalized amidoxime (AO)-based f...

Damage tolerance of 2-dimentional UHMWPE/CF hybrid woven laminates subjected to low-velocity impact

Carbon fiber reinforced polymer composite laminates (CFRPs) with weak impact damage tolerance were toughened with Ultra-high Molecular Weight Polyethylene (UHMWPE) fiber in the form of two-dimensional hybrid weaving in this paper. The effects of hybrid woven on impact behaviour and residual flexural stiffness of CFRPs, compared with plain carbon-fiber woven laminates, were investigated by drop weight impact and four-point bending experimental tests, together with finite element analysis (FEA). Indentation measurement and X-ray tomography, together with Scanning Electron Microscope (SEM) were employed for a comprehensive inspection of external and internal damage of specimens subjected to impact previously. A significant increment of 71.43% in penetration energy revealed the lower sensitivity of hybrid laminates to impact events in comparison with the pure carbon fiber reinforced ones, while post-impact flexural tests demonstrated that two-dimensional hybrid weaving was capable of bringing about a promotion of 10.1% in damage tolerance. The suppression mechanism of damage propagation in impact test, which lead to an enhancement in damage tolerance and structural integrity, was explained.

Residual Solvent in Highly Oriented Ultrahigh Molecular Weight Polyethylene Fibers

The use of a solvent, Vaseline oil, for the orientational drawing of high-strength and high-modulus UHMWPE fibers is considered. Since the side effect of the residual solvent during orientational drawing of UHMWPE fibers is the formation of pores that reduce the packing density of macromolecules, then at a certain stage of drawing the fiber, the solvent is removed from it by washing in n-heptane. The task of monitoring the residual solvent is studied by wide-line 1H NMR and ATR IR spectroscopy. In terms of methodology, the task is complicated by the accumulation of low molecular weight fragments of broken UHMWPE macromolecules, which are difficult to distinguish from short solvent molecules, in highly oriented fibers.

Study on the blast resistance of concrete beams reinforced with ultra-high-molecular-weight polyethylene (UHMWPE) fibers

Experiments and numerical simulations were performed to investigate the blast resistance of concrete beams reinforced with ultra-high-molecular-weight polyethylene (UHMWPE) fibers under close-in blast loads. The blast tests were carried out on fiber- reinforced concrete beams with a volume content of 0.7% at three scaled distances (i.e., 0.36, 0.40, and 0.47 m/kg1/3) and the damage results were compared with the characteristics of normal reinforced concrete beams. The results show that the UHMWPE fibers can decrease the damage degree of the beams, hinder the generation and development of cracks, and prevent spalling on the back surface, indicating that the blast resistance of UHMWPE-fiber-reinforced concrete beams is better than that of normal reinforced concrete beams with the same strength grade. Due to the addition of fibers, the improvement in the damage resistance to blast loads at the bottom surface of the beam is better than that at the top surface. A 3D blast-test model was established and calculated using the LS-DYNA software. A numerical study of the extended scaled distances was carried out to determine the change law of the damage features based on it. When the scaled distance is greater than 0.41 kg/m1/3, the damage mode of the beam begins to change from the mode of large damage at the bottom and small damage at the top to the mode involving large damage at the top and small damage at the bottom.

Destruction Products from Gel Spinning of Ultrahigh-Molecular-Weight Polyethylene Fibers

Mechanical and thermal oxidative destruction was observed during gel spinning of ultrahigh-molecular-weight polyethylene (UHMWPE) high-modulus fibers. Destruction products (DPs) were observed in the solvent and on the surface of finished UHMWPE fibers using optical and scanning electron microscopy. IR spectra of the DPs were compared with those of UHMWPE reactor powder, solid paraffin, and the mineral oil used in the gel-spinning process to show that absorption bands corresponding to terminal aldehydes and acids and unsaturated hydrocarbons and ethers in the UHMWPE were strengthened by the destruction.

Transverse compressive characteristics of fiber reinforced cementitious composites tubes

Abstract Fibre reinforced cementitious composites (FRCC) hollow tube is a kind of promising high-toughness energy absorption structure. As this structure absorbs energy via the transverse deformation of tube, it is necessary to investigate the transverse compressive behavior and failure mode of the FRCC tubes. In this study, the transverse compressive response of cementitious composites tubes reinforced by Polyvinyl alcohol (PVA) fiber and ultra-high molecular weight polyethylene (PE) fibre, respectively, has been experimentally investigated, numerically simulated and dimensionally analyzed. According to the transverse compression tests, the FRCC tubes failed with four-hinge fracture. The FRCC tubes presented ductile fracture while the plain cement-based material (P0) tube presented brittle fracture. The numerical simulation based on extended finite element method (XFEM) has a good agreement with the experimental measurements, and both the crack development at the hinges and stress distribution on the crack section are predicted. The fibre reinforcements remarkably enhanced the mechanical properties of tubes, including the transverse force resistance and deformation capacity. The peak force and maximum energy absorption of FRCC tube is 2 times and 60 times higher than those of P0 tube, respectively. The dimensional analysis suggested that the specific energy absorption per unit volume was principally dominated by the ratio of tube thickness to average radius, whereas the stroke efficiency was governed by the ratio of tube thickness to average radius and the ratio of average radius to tube length. This work provides a guidance for developing FRCC tubes with high specific energy absorption, and is expected to widen the applicability of FRCC tubes in protection engineering.

The Failure Mechanisms of Ultra-high Molecular Weight Polyethylene Fibre Composites Under In-plane Compression

The in-plane compressive characteristics of the ultra-high molecular weight polyethylene (UHMWPE) fibre (Dyneema®) reinforced composites, both in 0/90° and ±45° fibre orientations with respect to the loading direction, have been investigated. The composite made from unidirectional high modulus fibres (volume fraction 83%) and low strength polyurethane matrix (volume fraction 17%) is layered in an orthogonally alternating manner. The different failure mechanisms for the composites with 0/90° and ±45° fibre orientations have been detected with the methods of experimental measurement, SEM observation and theoretical analysis. The composites specimens of 0/90° fibre orientation failed with macro-buckling of the high-modulus UHMWEP fibre layers with the matrix damage, whereas the specimens of ±45° fibre orientation failed with the shearing of the soft matrix. Hence, the composite specimens in 0/90° fibre orientation had higher stiffness as well as compressive strength than those in ±45° fibre orientation. The failure criteria of the composites under in-plane compression was employed to characterize the failure mechanism. Compared with the traditional thermoset matrix, the soft thermoplastic matrix leads to lower strength and higher failure strain of fibre reinforced composites under in-plane compression. In addition, the composite specimens cut by waterjet machine exhibited higher stress levels than those cut by bandsaw that introduced more initial imperfections with the temperature rising and tensile shocking. The comparison between the methodologies for cutting the tough composites can provide a valuable suggestion to obtain required composite structures without reducing the mechanical properties.

Manufacturing of Single-Polymer Composite Materials Based on Ultra-High Molecular Weight Polyethylene Fibers by Hot Compaction

This paper describes the manufacturing process and properties of single-polymer composites based on ultra-high molecular weight polyethylene fibers produced by hot compaction. The hot compaction results in partial surface melting of the initial fibers, and melted part after cooling forms a matrix of the self-reinforced composites. Using high pressure during hot compaction allows to increase the fibers’ melting point and allows to avoid relaxation processes. Moreover, the fiber-to-matrix ratio may be changed using this approach by varying pressure and temperature. The flexural test was carried out to determine the mechanical properties. Samples obtained at 160 °C and 50 MPa have optimum properties (flexural strength and Young’s modulus were equal to 116.5 MPa and 15.3 GPa, respectively). It was found that mechanical properties of the obtained composites depend on both matrix amount and preservation of oriented fibers structure. The small amount of melted fibers does not allow to form matrix for load transferring. But the excessive melting of the fibers can result in a significant decrease in the fibers’ mechanical properties.