Mechanical properties of polypropylene composites reinforced with long glass fibres and mineral fillers

Abstract

The mechanical behaviour of long discontinuous glass fibre (LGF) reinforced polypropylene (PP) composites filled with talc or calcium carbonate fillers was studied. Sample specimens were processed by injection moulding, after which tensile and impact properties were analysed. In addition, scanning electron microscopy was used to analyse the morphology of the fracture surfaces. The results showed that the use of talc as a hybrid filler in LGF reinforced PP leads to a better tensile strength and toughness than in a corresponding hybrid composite based on calcium carbonate. Furthermore, it was observed that the matrix had a dominant role at low fibre content, whereas at high fibre loading, the effect of fibres was more evident.     

Debond behavior of copper fibers in thermoset matrices and their effect on fracture toughening

Single fiber pullout experiments were conducted to determine the adhesion quality, debond behavior and subsequent matrix fracture behavior for a variety of end-modified copper fibers. The matrices were: two different epoxy resins, polyester and polyurethane; the end-modified copper fibers were: straight, flat end-impacted, flat end-impacted with release agent applied and straight end-oxidized. The goal was to determine how the bonding and debonding behavior as well as the pullout behavior of the various fiber-matrix combinations affected the composite fracture toughness increment (ΔG). Results indicate that the greatest improvement in the calculated ΔG occurred with a fiber-matrix combination that had a moderate interface bond strength with an interfacial bond failure, minor matrix damage during fiber pullout and moderate post-debond interface friction. Selective oxidation of the fiber end was performed to determine if chemical anchoring of the fiber end could be as effective as mechanical (end-shaping) anchoring of the fiber into the matrix. Improvement in the adhesion bond strength as a result of the chemical anchoring resulted in a significantly lower ΔG compared to the end-impacted fibers because interfacial failure was not possible. This indicates that for the materials tested, mechanical anchoring of the fiber was better than chemical anchoring in improving ΔG. To decrease the adhesion bond strength and allow the fibers to debond, a release agent was applied to the flat end-impacted fiber prior to embedment into the matrix. This resulted in a significantly lower ΔG compared to straight and flat end-impacted fibers for all matrices tested, because the resulting debonding force and friction were significantly reduced. Pullout curves showed that with release agent applied, the end-shape did not effectively anchor the fiber into the matrix. The reduction in the pullout work indicates that the friction at the fiber-matrix interface plays a crucial role in actively anchoring the end-shaped fiber into the matrix after debonding.     

Experimental and numerical investigation on three-point bending behaviors of unidirectional warp-knitted composites

This study develops a novel specimen model, which considers the progressive damage of the layers, the knitting yarns, and the interlaminar cohesive zone, to investigate the flexural properties and the interlaminar shear properties of the unidirectional warp-knitted composites. Three-point bending tests are conducted as verification of the numerical model. Improved strain-based Hashin criteria are proposed to analyze the shear nonlinearity. Results show that specimens with small span-to-thickness ratios exhibit obvious nonlinear behaviors and the corresponding simulation results are sensitive to the value of the shear nonlinear factor. Failure mechanism and stress distributions are analyzed based on numerical simulations. The effect of the specimen size on bending behaviors is discussed. The influence of the width is found to be negligible but that of the span-to-thickness ratio is significant. The ranges of the span-to-thickness ratio corresponding to different failure modes are given. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48132.     

Effects of patch layer and loading frequency on fatigue fracture behavior of aluminum plate repaired with a boron/epoxy composite patch

In this study, 6.125 mm cracked Al 7075-T6 plates with different patch layers of boron/epoxy composite have been fatigue tested. By using analytical and experimental methods, the variation of critical parameters in fracture mechanics, such as stress intensity factor (SIF), potential energy (PE) and energy release rate (J ^*), with patch layers were studied. According to the results of energy and driving force approaches, it was shown that both theories had good consistency using more ply numbers to repair cracked substrates. It was suggested that to investigate the effect of the patch layer on the air stream around the aircraft structure, in addition to fracture mechanics analysis, using a fluid dynamics simulation would be very helpful.     

Effects of temperature on interlaminar fracture toughness of fibre reinforced plastic composites made by newly proposed rubber pressure moulding technique

Abstract

The present paper has investigated the effect of temperatures (i.e.?70–100°C) on the interlaminar fracture toughness (ILFT) of fibre reinforced plastic (FRP) composite panels made by a recently developed process known as the rubber pressure moulding (RPM) technique. The RPM technique is based on the matching die set, where the die is made of hard metal like steel and the punch from flexible rubber like materials. The use of flexible rubber punch helps to intensify and uniformly redistribute pressure (both operating pressure and developed hydrostatic pressure due to the flexible rubber punch) on the surface of the product. Natural rubber was used to prepare rubber punch in this investigation. For performance evaluation of FRP composites made by the RPM technique, FRP composites were also made by conventional method and tested at the same temperatures. It is observed that Mode I ILFT of FRP composites decreases towards higher and lower extremes of the temperature range selected. FRP composites made by the RPM technique show a higher Mode I ILFT over the 25–100°C temperature range than those made by the conventional process.     

Experimental and theoretical studies on the adjustable thermal properties of epoxy composites with silver‐plated short fiberglass

This article investigates the evolution of the thermal conductivity and the coefficient of thermal expansion (CTE) of epoxy composites filled with different silver‐plated short glass fibers (Ag@GFs) treated by electroless plating. After electroless plating, the results of X‐ray diffraction and scanning electron microscopy showed that glass fibers were coated with pure silver shells whose thickness was controlled via the repetition of electroless plating cycle, and calculated by weighting method. The optical photographs showed that Ag@GFs are randomly oriented and uniformly dispersed in the composites. HotDisk thermal constant analyzer and dilatometer were used to further characterize the thermal conductivity and the CTE of the composites, respectively. The results revealed that the thermal conductivity of Ag@GF/epoxy composites increased with the increase of Ag@GF content, and was adjusted by changing the thickness of silver shell. But the CTE of the composites drops sharply as the Ag@GF content increases compared with neat epoxy. Based on Agari model with fitted factors of C_p and C_f, the calculated thermal conductivity values of Ag@GF/epoxy composites agreed well with the experimental results, and C_p kept almost unchanged, but C_f varied with the change of the thickness of silver shell, despite increasing filler content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45555.     

含裂隙煤体抗压性能的试验研究与模拟计算

煤体内部天然存在的裂隙是瓦斯流动的主要通道和影响煤矿安全的重要因素。为考察不同原生裂隙分布形态的煤体抗压缩强度与裂纹演化规律,对原煤试样进行初始裂隙的提取和室内三轴压缩试验,结合数值模拟方法进一步研究了含裂隙试样在围压分别为1, 3, 5, 7, 9 MPa和加载速率在0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.0 m/s下的峰值应力及破坏形态。结果表明,煤样的峰值应力随围压增加呈指数形式增大。垂直方向延伸的原生裂隙对裂纹扩展带的影响较小,当原生裂隙的延伸角度倾向于对角线方向时,裂纹容易在裂隙端部萌生和扩展。试样2的“V”型裂纹带在低围压(1, 3, 5 MPa)时受原生裂隙影响较大,高围压(7和9 MPa)下的破坏特征与试样1相似。随着加载速率逐渐递增,试样的抗压强度变化经历先缓慢上升,后迅速增加,最终趋于平缓的过程。低加载速率下的裂纹多聚集在原生裂隙延伸方向上,较高的加载速率容易造成裂纹集中于试样的角部位置,裂纹数目也迅速增多。     

Experimental and theoretic studies on sound transmission loss of laminated mica‐filled poly(vinyl chloride) composites

The effects of dioctyl phthalate and inorganic filler, mica, on the sound insulation property of poly(vinyl chloride) (PVC) were investigated in this work. The stiffness and mass laws, which are the common theoretic tools to predict the soundproof properties of materials, were used to analyze the sound transmission loss (STL). The experimental results revealed that the stiffness and mass laws can describe well the sound insulation property of PVC/mica composites. The stiffness and surface density are important factors influencing the improvement of STL. With the increase of content of mica, STL and resonance frequency, f_mn, of PVC/mica composites increase. Moreover, the change of STL in the stiffness‐ controlled region is more obvious than that in the mass‐controlled region, because the addition of mica in PVC leads to a greater increase in the stiffness. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

旋流板上流场的LDA实验研究

在φ３００ｍｍ塔内，实现了用二维激光多普勒测速仪对旋流板上气体速度场的测定，获得了不同高度剖面的切向、轴向及径向速度分布的数据，探明了板上气流场的基本特点；还采用气－固流模拟湿板操作，测定了模拟液滴的流场。实验结果证实了旋流板的传统设计思想。     

内置转子换热管强化传热性能实验研究

针对光管中加入3种不同导程的洁能芯转子后的换热特性及流体动力学特性进行了实验研究,壳程和管程的工作介质分别为热水和冷水,研究表明:插入转子后,努赛尔数Nu和阻力系数f均增加,并且二者均随转子导程的增大而增大;对插入转子的换热管进行了强化传热性能评价分析,其传热性能评价因子η的数值均大于1,证明其具有强化传热的应用价值,转子导程为150 mm时,实验范围内η最大值为2.01,强化传热效果最好。     

Experimental studies of air-blast atomization on the CO2 capture with aqueous alkali solutions

In this work, an air-blast atomizing column was used to study the CO₂ capture performance with aqueous MEA (mono-ethanol-amine) and NaOH solutions. The effects of gas flow rate, the liquid to gas ratio (L/G), the CO₂ concentration on the CO₂ removal efficiency (η) and the volumetric overall mass transfer coefficient (K_Ga_v) were investigated. The air-blast atomizing column was also compared with the pressure spray tower on the studies of the CO₂ capture performance. For the aqueous MEA and NaOH solutions, the experimental results show that the η decreases with increasing gas flow rate and CO₂ concentration while it increases with increasing L/G. The effects on K_Ga_v are more complicated than those for η. When the CO₂ concentration is low (3 vol%), K_Ga_v increases with increasing gas flow rate while decreases with increasing L/G. However, when the CO₂ concentration is high (9.5 vol%), as the gas flow rate and L/G increases, K_Ga_v increases first and then decreases. The aqueous MEA solution achieves higher η and K_Ga_v than the aqueous NaOH solution. The air-blast atomizing column shows a good performance on CO₂ capture.     

Synergetic effects on the mechanical and fracture properties of epoxy composites with multiscale reinforcements: Carbon nanotubes and short carbon fibers

The ball‐milling/liquid‐phase oxidation (BMLPO) method was used to fabricate surface‐modified short carbon fibers (SCFs). Multiscale epoxy composites reinforced with a combination of SCFs and multiwalled carbon nanotubes (MWNTs) were prepared. Atomic force microscopy observations and contact angle measurement were used to investigate the modification effect of the BMLPO method. Mechanical tests and scanning electron microscopy observations were used to study the effects of the SCFs, MWNTs, and their combination on tensile properties, impact strength, and fracture toughness of the epoxy composites. The results show that the surface roughness of the SCFs after BMLPO treatment increased, and the wettability of the SCFs was improved as well. The combined use of the SCFs and MWNTs had a synergetic effect on the tensile strength, fracture toughness, and impact strength of the epoxy composites. The addition of MWNTs promoted the plastic deformation of the epoxy matrix and decreased the stress‐concentration level near the SCF/matrix interface; these were considered the main causes of the synergetic effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43500.     

Experimental studies on gasification of the Shenmu coal char with CO2 at elevated pressures

The gasification rates of Shenmu coal chars with CO₂ were experimentally studied with a pressurized thermo- gravimetric analyzer (PTGA). Shenmu coal is a typical Chinese coal, and the coal char was prepared by a fixed-bed reactor in nitrogen at 900 °C. The experiments were carried out in the dynamic heating segments from 750 °C to 1,000 °C, and the reaction pressure increased from 0.1MPa to 3.1MPa with pure CO₂. The external diffusion resistances were minimized by increasing the flow rates and decreasing the thickness of sample layer before the test, to ensure the reactions were under kinetic control. The results show that the gasification rates increase proportionally to the 0.1 power of the CO₂ partial pressure. The unreacted-core shrinking model was applied to predict the reaction rate by changing the molar fraction of CO₂ at 0.6Mpa and 1.6Mpa total pressures, which showed a good match with experimental data. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

换热管内置螺旋形扭带阻力与传热特性的实验研究

为了研究螺旋形扭带阻力与传热特性,选取了不同宽度（6、7和8 mm）的3种扭率（2.0、3.0、4.0）、3种螺距比（1.5、2.0、2.5）的参数组合下共27根螺旋形扭带插入换热管内进行实验.实验结果表明,插入螺旋形扭带后换热管内流动阻力和传热效果都有明显提高.通过对实验数据的多元线性回归分析,建立了相应的阻力系数和努赛尔数关联式.并且由强化传热综合性能评价分析,在实验雷诺数范围内得出强化传热综合性能评价因子φ=1.063～1.587,证明了实验研究的扭带具有强化传热的应用价值.     

Experimental and theoretical studies about the adsorption of toluene on ZSM5 and mordenite zeolites modified with Cs

In this work, we studied the adsorption capacity and thermal stability of toluene on ZSM5 and mordenite zeolites with different exchange cations (H, Na and Cs). The interaction of the hydrocarbon molecules with the adsorption sites was also addressed with both experimental and theoretical techniques. Flow-adsorption measurements were carried out in order to obtain breakthrough curves as well as TPD experiments. Molecular simulations were performed using the Density Function Theory (DFT). The results show that, in general, mordenite samples have a better adsorption capacity than ZSM5 samples and that the thermal stability of the adsorbed toluene is more influenced by the exchanged cations than by the zeolite structure. The overall basicity of the samples depends on the exchanged cations, following the Cs > Na > H order. The main interaction of toluene takes place between the π electrons of the aromatic ring and the Lewis sites generated, and another interaction takes place between C-H groups and the zeolite network oxygen.The increase of the Cs loading decreases the surface area and pore volume of the zeolites, thus decreasing the available sites for the overall toluene adsorption at 100 °C. Through TPD experiments both the Φ parameter, which represents the fraction of toluene retained at temperatures higher than 100 °C, and the temperature at which the toluene desorbs were measured. It was observed that in the Cs exchanged samples, Φ is higher but the thermal stability (temperature of the maximum desorption rate on TPD) follows the order NaMOR = NaZSM5 > CsNaZSM5 > CsNaMOR > CsHMOR = CsHZSM5 > HMOR > HZSM5. The molecular calculations for the NaMOR structure determined that the interaction energies were higher for NaMOR when compared with the HMOR structure and increased even more when Cs was exchanged. These facts are in line with the experimental results.     

Experimental and theoretical studies on NIR luminescence of titanate-germanate glasses doped with Pr3+ and Tm3+ ions

Near-infrared (NIR) luminescence of Pr³⁺ and Tm³⁺ ions in titanate-germanate glasses has been studied for laser and fiber amplifier applications. The effect of the molar ratio GeO₂:TiO₂ (from 5:1 to 1:5) on spectroscopic properties of glass systems was studied by absorption, luminescence measurements, and theoretical calculations using the Judd–Ofelt theory. It was found that independent of the TiO₂ concentration, intense NIR emissions at 1.5 and 1.8 μm were observed for glasses doped with Pr³⁺ and Tm³⁺ ions, respectively. Moreover, several spectroscopic and NIR laser parameters for Pr³⁺ and Tm³⁺ ions, such as emission bandwidth, stimulated emission cross-section, quantum efficiency, gain bandwidth, and figure of merit, were determined. The results were discussed in detail and compared to the different laser glasses. Systematic investigations indicate that Pr³⁺-doped system with GeO₂:TiO₂ = 2:1 and Tm³⁺-doped glass with GeO₂:TiO₂ = 1:2 present profit laser parameters and could be successfully applied to NIR lasers and broadband optical amplifiers.     

换热管内插入间隔自旋扭带流阻与传热特性的实验研究

通过实验研究了内置间隔自旋扭带的换热管的传热和流阻特性。实验结果表明,间隔扭带的换热系数和摩擦系数都低于全长扭带;扭转比越大,间距对换热管阻力和传热特性的影响越小。此外,作者还建立了包含间隔扭带结构参数在内的流阻与传热特性的经验关联式。     

Experimental studies on heat transfer and friction factor characteristics of turbulent flow through a circular tube fitted with helical screw-tape inserts

Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and increasing and decreasing order of twist ratio set have been studied with uniform heat flux under turbulent flow conditions. The Reynolds number was varied from 2700 to 13 500. The experimental data obtained are compared with those obtained from plain tube published data. The maximum Nusselt number for the twist of 1.95 was obtained. The performance of the helical twist insert was compared with the twisted tape performance reported in the literature and found that it is better than twisted tape performance. The heat transfer augmentation for helical twist of increasing and decreasing order twist were also presented. The empirical correlations developed relating twist ratio and Reynolds number, are fitting the experimental data within ±13% and ±15% for Nusselt number and friction factor, respectively. The performance evaluation study has been presented to check the potential of using the helical twist insert.     

Effect of gas expansion on the velocity of individual Taylor bubbles rising in vertical columns with water: Experimental studies at atmospheric pressure and under vacuum

This study was designed to determine the effect of gas expansion on the velocity of Taylor bubbles rising individually in a vertical column of water. This experimental study was conducted at atmospheric pressure or under vacuum (33.3 and ) using three different acrylic columns with internal diameters of 0.022, 0.032, and 0.052 m, and more than 4.0 m high. A non-intrusive optical method was used to measure velocity and length of Taylor bubbles at five different locations along the columns. The operating conditions used correspond to inertial controlled regime.In experiments performed under vacuum, there is considerable gas expansion during the rise of Taylor bubbles, particularly when they approach the liquid free surface where the pressure drop (due to the hydrostatic pressure) is of the order of magnitude of the absolute pressure. The liquid ahead of the bubble is displaced upward by an amount proportional to the gas expansion resulting in increased bubble velocity. The calculated Reynolds number suggests a laminar regime in the liquid ahead of the bubble. However, the experimentally determined velocity coefficient C for each column was much smaller than 2, which would be expected for laminar flow. The value of C obtained ranges from 1.13±0.09, for the narrowest column, to 1.40±0.24, for the widest column. This suggests that a fully developed laminar flow in the liquid ahead of the bubble is never achieved due to continuous bubble expansion at a variable rate, regardless of column height.The velocity coefficient C can be used to calculate the contribution of liquid motion to bubble velocity. Subtracting this contribution from the measured bubble velocity defines a constant value which is nearly identical to the bubble rise velocity measured in the same column operated as a constant volume system (two ends closed) where gas expansion is absent.