Effect of strain rate on the dynamic tensile behaviour of UHMWPE fibre laminates

Ultra-high molecular weight polyethylene (UHMWPE) fibre has great potential for strengthening structures against impact or blast loads. A quantitative characterization of the mechanical properties of UHMWPE fibres at varying strain rates is necessary to achieve reliable structural design. Quasi-static and high-speed tensile tests were performed to investigate the unidirectional tensile properties of UHMWPE fibre laminates over a wide range of strain rates from 0.0013 to 163.78 s⁻¹. Quasi-static tensile tests of UHMWPE fibre laminates were conducted at thicknesses ranging from 1.76 mm to 5.19 mm. Weibull analysis was conducted to investigate the scatter of the test data. The failure mechanism and modes of the UHMWPE fibre laminates observed during the test are discussed. The test results indicate that the mechanical properties of the UHMWPE fibre laminate are not sensitive to thickness, whereas the strength and the modulus of elasticity increase with strain rate. It is concluded that the distinct failure modes at low and high strain rates partially contribute to the tensile strength of the UHMWPE fibre laminates. A series of empirical formulae for the dynamic increase factor (DIF) of the material strength and modulus of elasticity are also derived for better representation of the effect of strain rate on the mechanical properties of UHMWPE fibre laminates.     

超高分子量聚乙烯烧结制品的链缠结调控及其对性能影响

利用新的单中心Ziegler-Natta(Z-N)催化剂,通过干预分子链的生长与聚集行为,可获得低缠结的超高分子量聚乙烯(UHMWPE)初生树脂.本研究利用这类低缠结UHMWPE,通过设置不同的烧结温度(Ts)来改变熔体缠结状态,并探讨了链缠结程度对烧结制品结构与性能的影响.实验结果表明TS=220℃下,UHMWPE样品发生显著的复缠,造成高缠结度;而Ts=170℃下,初始低缠结状态能够得以充分保留,从而获得了缠结度具有明显差别的不同样品.示差扫描量热法(DSC)测试表明,在Ts=170℃下,低缠结度有利于在随后等温及冷却结晶过程中生成高熔点(最高达141℃)晶体与高的结晶度(最高达65%).力学测试表明低缠结度制品的综合力学性能显著提升,其中屈服强度提高72%,拉伸断裂强度提升139%,弹性模量提升162%以及断裂伸长率提升36%,实现了同时增强增韧.这就提供了一种从调节链缠结温度实现UHMWPE烧结制品高性能化的新思路.     

Enhanced surface free energy of UHMWPE fibers and its interfacial adhesion behavior to PI resins

Mechanical properties of composites made up of ultra‐high‐molecular‐weight polyethylene (UHMWPE) fiber, polyimide (PI), and TiO₂ particles were investigated. The hybrid composite of 20 vol% of UHMWPE fiber with TiO₂ showed tensile strength greater than UHMWPE fiber/PI composite. A positive hybrid effect in tensile strength is obtained. It is observed that addition of small amount of TiO₂ to UHMWPE fiber/PI increased the tensile strength of the composite by 28%. With increase in TiO₂ loading to 1 to 3 vol%, the impact strength of the hybrid composite is increased from 55 KJ/m² to 69 KJ/m². This maximum value is more than one and a half times greater than the impact strength of neat UHMWPE fiber/PI composite.     

Synergic Enhancement of High-density Polyethylene through Ultrahigh Molecular Weight Polyethylene and Multi-flow Vibration Injection Molding: A Facile Fabrication with Potential Industrial Prospects

General-purpose plastics with high strength and toughness have been in great demand for structural engineering applications. To achieve the reinforcement and broaden the application scope of high-density polyethylene(HDPE), multi-flow vibration injection molding(MFVIM) and ultrahigh molecular weight polyethylene(UHMWPE) are synergistically employed in this work. Herein, the MFVIM has better shear layer control ability and higher fabrication advantage for complex parts than other analogous novel injection molding technologies reported.The reinforcing effect of various filling times and UHMWPE contents as well as the corresponding microstructure evolution are investigated.When 5 wt% UHMWPE is added, MFVIM process with six flow times thickens the shear layer to the whole thickness. The tensile strength and modulus increase to 2.14 and 1.39 times, respectively, compared to neat HDPE on the premise of remaining 70% impact strength. Structural characterizations indicate that the enhancement is attributed to the improvement of shish-kebab content and lamellae compactness, as well as related to the corresponding size distributions of undissolved UHMWPE particles. This novel injection molding technology with great industrial prospects provides a facile and effective strategy to broaden the engineering applications of HDPE materials. Besides, excessive UHMWPE may impair the synergistic enhancement effect, which is also reasonably explained.     

Modified V-notched rail shear test fixture for shear characterisation of textile-reinforced composite materials

The V-notched rail shear test (VNRS) is recognised as a standard test method for the determination of shear modulus and shear strength of fibre-reinforced composite materials. This method is based on a double V-notched specimen with a large gauge section and an approximately uniform shear stress distribution between the two notches. The construction of the test device prescribed in standards was revised with the main focus of lines of force as well as precise and economic specimen clamping. Therefore, the modified test fixture has been equipped with guide units and the number of clamping bolts could be reduced. The standardised and modified VNRS fixtures were evaluated using a finite element method. It can be shown that the modified VNRS test fixture is well suited for robust and reliable material characterisation of shear property data.     

Flexural and tensile moduli of flexible FR4 substrates

A flexible FR4 substrate is not only a core part of current integrated circuit assemblies, but also a promising material for flexible electronics applications. The thin composite sheet typically contains a single-ply of glass fabric which is impregnated with epoxy resin. The single-ply reinforcement leads to large heterogeneity along the through-thickness direction, which causes different behavior in the flexural and tensile moduli. However, no comparative study between the flexural and tensile moduli has been presented for commercialized flexible FR4 substrates. In this study, the flexural and tensile moduli of flexible FR4 substrates were measured using a three-point bending test and a direct tensile test, respectively. Three FR4 substrates were prepared with a different number of glass fabric plies and different types of epoxy resin, with a total thickness ranging from 100 to 150 μm. The effect of the span-to-depth ratio on the flexural modulus was first examined in order to obtain the true flexural modulus from the three-point bending test. For comparison, the strain was accurately measured using a video extensometer to obtain the tensile modulus. In-plane anisotropy and temperature dependence were also investigated for both the flexural and tensile moduli.     

Effect of surface treatment with potassium permanganate on ultra-high molecular weight polyethylene fiber reinforced natural rubber composites

The effects of surface treatment using potassium permanganate on ultra-high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were investigated. The results showed the surface roughness and the oxygen-containing groups on the surface of the modified fibers were effectively increased. The NR matrix composites were prepared with as-received and modified UHMWPE fibers added 0–6 wt%. The treated fibers increased the modulus and tensile stress at a given elongation. The tear strength increased with increasing fiber mass fraction, attained maximum values at 4 wt%. The hardness of composites exhibited continuous increase with increasing the fiber content. The dynamic mechanical tests showed that the storage modulus and the tangent of the loss angle were decreased in the modified UHMWPE fibers/NR composites. Several micro-fibrillations between the treated fiber and NR matrix were observed, which meant the interfacial adhesion strength was improved.     

Surface modification of ultrahigh‐molecular‐weight polyethylene fibers

To prevent the loss of fiber strength, ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers were treated with an ultraviolet radiation technique combined with a corona‐discharge treatment. The physical and chemical changes in the fiber surface were examined with scanning electron microscopy and Fourier transform infrared/attenuated total reflectance. The gel contents of the fibers were measured by a standard device. The mechanical properties of the treated fibers and the interfacial adhesion properties of UHMWPE‐fiber‐reinforced vinyl ester resin composites were investigated with tensile testing. After 20 min or so of ultraviolet radiation based on 6‐kW corona treatment, the T‐peel strength of the treated UHMWPE‐fiber composite was one to two times greater than that of the as‐received UHMWPE‐fiber composite, whereas the tensile strength of the treated UHMWPE fibers was still up to 3.5 GPa. The integrated mechanical properties of the treated UHMWPE fibers were also optimum. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 463–472, 2004     

Mechanical properties and frictional resistance of Al composites reinforced with Ti_3C_2T_x MXene

Two-dimensional(2D) Ti_3C_2T_x MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti_3C_2T_x,Here we report on the use of 2D Ti_3C_2T_x to enhance the mechanical and frictional properties of Al matrix composites.Ti_3C_2T_x/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti_3C_2T_x.The Vickers hardness and the tensile strength continuously increase with increasing Ti_3C_2T_x content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt% Ti_3C_2T_x/Al composite.The frictional properties of pure Al and the Ti_3C_2T_x/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti_3C_2T_x/Al composite.Ti_3C_2T_x acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.     

The Effect of the Addition of Mg-Al LDH Intercalated with Dodecyl Sulfate on the Fire Retardancy Properties of Epoxy

Summary: Layered double hydroxides (LDH) are chemical compounds that can be added to polymeric resins to confer fire retardant characteristics. The focus of this work is to study the incorporation of LDH intercalated with dodecylsulfate anions into epoxy resins. The mechanical properties were investigated using tensile, flexural and impact mechanical tests. The flame-retardant properties were assessed using horizontal (UL 94 HB) and vertical burning (UL 94 V) tests. The highest tensile strength was obtained for the composite with 3 wt% of LDH, whereas the highest flexural strength was found by incorporating 1 wt% of LDH. All samples containing LDH showed self-extinguishing behavior in the vertical test and lower burning rate than pristine epoxy.     

Effect of thermal cycling and open-hole size on mechanical properties of polymer matrix composites

This paper investigates the effects of thermal cycling on mechanical degradation of polymer matrix composites (PMCs). Un-notched and open-hole specimens are tested using developed thermal cycling apparatus and tensile test machine. In addition, the hole-size effect of open-hole tension glass/epoxy composite laminates is investigated. The tensile strength, mass loss and surface degradation of the specimens were obtained during 250 cycles. Experimental results showed that the holes diameter is the main parameter to control the thermal cycling effects on open hole structure. Also, it is found that laminates with smaller holes have higher tensile strength variation than those with larger holes. The results showed that increment of the hole diameter and number of cycles decreases the tensile strength.     

明胶中α组分含量对明胶/羟基磷灰石复合材料力学性能的影响

选用α组分含量分别为20.5%,41%和50%的A、B、C 3种明胶作为原料,采用同时加入法制备了明胶/羟基磷灰石(HAP)复合材料.通过对干态复合物膜拉伸性能的测试和对比,发现,明胶α组分含量的变化对复合材料的弹性模量影响较大,而对拉伸强度和断裂伸长率的影响则相对较小,但总的来说,三者均随α组分含量的增加而增大.其中,α组分含量最高的复合物C的拉伸强度为86.40 MPa,弹性模量为2682.35 MPa,断裂伸长率为8.65%.另外,对复合物C基本性质的表征结果表明,该材料具有类似于自然骨的组成和结构性质,因此有望成为一种具有优异力学性能的骨替代材料.     

The influence of pre-treatment of Spartium junceum L. fibres on the structure and mechanical properties of PLA biocomposites

Different chemical pre-treatments of Spartium junceum L. fibres using alkali (NaOH), nanoclay (MMT) and Citric acid (CA) with the aim of producing biodegradable composite material are discussed. As environmental requirements in processing technologies have been higher in recent years, the Polylactic acid (PLA) is used in this research as a matrix, due to its renewability, biodegradability and biocompatibility. Biocomposites are prepared by reinforcing PLA with randomly oriented, short Spartium junceum L. fibres in order to increase material strength. The effects of different pre-treatments of Spartium junceum L. fibres on the mechanical properties of final biocomposite material are examined. Fibre tenacity is studied using Vibroscop and Vibrodyn devices. Tensile strength of biocomposite material was measured on the universal electromechanical testing machine Instron 5584. The results indicate that biocomposites reinforced with fibres modified with MMT and CA show upgraded mechanical properties of the final composite material in comparison with the composite materials reinforced with referenced (nontreated) fibres. Infrared spectra of tested fibres and biocomposites were determined with Fourier transform infrared spectroscopy using Attenuated total reflection (FT-IR ATR) sampling technique and the influence of fibre modifications on the fibre/polymer interfacial bonding was investigated. The interface of Spartium/PLA composites was observed with scanning electron microscope (SEM) and it was clearly visible that biocomposites reinforced with fibres modified by MMT and CA showed better interaction of fibres and matrix.     

The mechanical properties of surface treated UHMWPE fibers and TiO2 reinforced PMMA composite

Mechanical properties of hybrid PMMA composites reinforced with UHMWPE fiber and nano‐titanium dioxide (2, 4, 6, and 8 wt%) was investigated. In this work, the effect of UHMWPE fiber surface treatment on tensile, flexural, and impact properties of PMMA composites was studied. The fiber loadings were varied from 0% to 20%. The addition of UHMWPE fiber had caused a decline in the tensile strength of the PMMA composite. Results revealed that the presence of titanium dioxide on the surface treated UHMWPE fiber has further enhanced the efficiency of stress transfer from the matrix to the fiber thus improved the interfacial adhesion between the UHMWPE fiber and PMMA matrix.     

Mechanical properties degradation of polyimide films irradiated by atomic oxygen

Mechanical properties of polyimide films are degraded by exposure to a low earth orbit environment. The main environmental factor for that degradation is atomic oxygen (AO). Using tensile tests, AO-irradiated surface topography observations, and fracture surface analyses, this study investigated the degradation behavior of polyimide films’ mechanical properties by increased AO fluence and its accompanying degradation mechanisms. Tensile strength and elongation of polyimide films were reduced concomitantly with increased AO fluence. Furthermore, AO-irradiated polyimide films fractured from the AO-irradiated surfaces, of which roughness became marked as AO fluence increased. These results reflect that reduction of mechanical properties is attributable to the roughness increase in AO-irradiated surfaces. Polyimide films coated with indium tin oxide (ITO) were also evaluated to confirm the degradation behavior of AO protective films. Surfaces of ITO-coated polyimide films remained smooth even after AO irradiation. However, undercut cavities were formed at ITO coating defect sites. Rupture of ITO-coated polyimide films initiates from the undercut cavities, engendering large reduction of tensile strength and elongation. The degradation of the mechanical properties of ITO-coated polyimide films increased substantially until the undercut cavities fully penetrated the film.     

Experimental investigation on mechanical properties of unidirectional and woven fabric glass/epoxy composites under off-axis tensile loading

Mechanical properties of unidirectional (UD) and woven fabric glass/epoxy composites under off-axis tensile loading were experimentally investigated. A number of off-axis tests considering different fibre orientations were performed to study the character and failure mechanisms of the composite laminates. The experimental results indicated that both off-axis elastic moduli and strength degrade with increasing off-axis angle in all cases, and the woven fabric composites present nonlinear stress-strain behaviour under off-axial tension loading. The Tsai-Wu criteria used for failure analysis of the UD and woven fabric composites were compared and discussed, especially considering different values of interaction coefficient F₁₂. The prediction results demonstrated that the Tsai-Wu criterion can be used successfully to analyse failure properties of the woven fabric composites under multiaxial stress conditions, where the criterion with the modified coefficient F₁₂ obtained from the 45° off-axial tension tests is better and has higher accuracy. Finally, the specific failure modes were compared in the UD and woven fabric composites. The selected fracture surfaces were also observed by scanning electron microscopy (SEM), and the corresponding failure mechanisms of the woven fabric composites under off-axis tensile loading were identified.     

Study of the thermomechanical behavior of UHMWPE yarns under different loading paths

UHMWPE viscoelastic fibers show great interest as reinforcement within composites and especially when used in SRPs (Self-Reinforced Polymers). They provide ductility, lightness and recyclability, benefits that glass or carbon fibers cannot provide. It is, therefore, necessary to increase knowledge about the behavior of UHMWPE fibers. Before the thermomechanical characterization of these yarns, an experimental protocol is proposed, validated and it supplements the existing standard. Monotonous, load-unload and creep tensile tests were carried out on Doyentrontex® yarns. Temperature and strain rate dependencies were observed. A time-temperature superposition is used to reconstruct the evolutions of modulus at 0.5%, maximum strength, and strain at break at 23 °C over a wide range of strain rates. The behavior of the yarns studied appears to be complex. Indeed, at low temperatures, a hyperelastic type of behavior, combined with plasticity, predominates whereas a more elasto-viscoplastic one emerges at 100 °C. From creep tests, a time-temperature-stress level superposition leads to the reconstruction of the yarns creep behavior over a long period at the reference temperature 23 °C and the reference stress level, which is 40% of the stress at break in tensile tests at any given test temperature.     

Experimental study on the 3D‐printed plastic parts and predicting the mechanical properties using artificial neural networks

This study investigates the mechanical properties of 3D‐printed plastic parts fabricated using Fused Deposition Modeling (FDM). For this purpose, a 3D printer named KASAME was designed and built by the researchers. The test samples were fabricated using polylactic acid (PLA). The experiments were conducted using three melt temperatures (190°C, 205°C, and 220°C), four layer thickness values (0.06 mm, 0.10 mm, 0.19 mm, and 0.35 mm), and three raster pattern orientations (+45°/?45° [the crisscross pattern], horizontal and vertical). Tensile strength tests were performed to determine tensile strength values of the samples and fracture surfaces were also analyzed. Using artificial neural networks, a mathematical model for the tensile test results was generated corresponding to the raster pattern employed in 3D fabrication. Tensile strength tests indicated that melt temperature, layer thickness, and raster pattern orientation had a significant effect on the tensile strengths of the samples. According to the result of the experiment, the maximum average tensile strength values were observed for the samples fabricated using the crisscross raster pattern. The analysis of variance (ANOVA) table shows the raster pattern (PCR) value of 48.68% was obtained with the highest degree of influence. With respect to R ², the best performing artificial neural network model, with test and training values of 0.999199 and 0.999997, respectively, was observed to be the crisscross raster pattern. Copyright © 2016 John Wiley & Sons, Ltd.     

Tensile strength and fracture of glass fiber-reinforced plastic (GFRP) plate with an eccentrically located circular hole

In this paper, tensile strength and fracture of finite glass fiber-reinforced plastic GFRP (glass/polyester) composite materials with a through-the-thickness eccentrically located circular hole are experimentally studied. The strain response histories near the hole boundary for different eccentrically located holes during the whole damage and fracture process of the notched specimen are recorded. The effects of off-center distance and hole diameter on strength and fracture of the notched specimen are analyzed. The tensile fracture strength of the notched specimen with an eccentrically located hole is determined. Also, the initial stress concentrations in the composite laminate due to the presence of the eccentrically located hole are understood. These results play an important role for predicting strength and evaluating lifetime of laminate composite with complex geometrical cutouts.     

Towards efficient electromagnetic interference shielding performance for polyethylene composites by structuring segregated carbon black/graphite networks

An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.