Combined effect of fiber content and microstructure on the fracture toughness of SGF and SCF reinforced polypropylene composites

Composites of polypropylene (PP) reinforced with short glass fibers (SGF) and short carbon fibers (SCF) were prepared with extrusion compounding and injection moulding techniques. The fracture behavior of the two types of composites was studied. The fracture toughness (K _c of the composites was measured in the T-direction [main crack transverse to mould flow direction (MFD)] and in the L-direction (main crack parallel to the MFD) using compact tension (CT) specimens made from the plaques manufactured. The study was focused on the combined effect of fiber volume fraction and microstructure (fiber length and alignment) on the fracture toughness of short fiber composites. It was observed that the addition of fibers effectively enhanced the fracture toughness for both SGF/PP and SCF/PP systems in the T-direction but only improved the composite toughness in the L-direction for the case of a low fiber volume fraction (8%). The composite fracture toughness kept almost unchanged in the T-direction and decreased in the L-direction with increasing fiber volume fraction. These were explained using the combined effect of fiber volume fraction and microstructure.     

短纤维混杂增强PP复合泡沫材料的力学性能

将助剂预混与二次挤出工艺相结合制备含短纤维预发泡粒料, 并用型内二次发泡工艺制备了短炭纤维(SCF)、 短玻璃纤维(SGF)混杂增强聚丙烯(PP)复合泡沫材料。研究了在纤维总质量分数不变时, SCF与SGF的相对含量、 增强纤维与PP的界面性能及泡沫体的表观密度对PP复合泡沫材料的发泡效果和力学性能的影响。结果表明: SGF和SCF的同时加入能够改善PP的高温熔体强度, 获得孔径较小且均一的类球形的闭孔PP泡沫体。SGF和SCF混杂增强提高了PP复合泡沫材料的强度和模量, 且增强效果高于单一纤维, 当纤维总质量分数为15%, 且SGF ∶SCF为1 ∶1时(质量比), PP复合泡沫材料的抗弯强度和抗压强度最高, 而SGF ∶SCF为3 ∶1时, PP泡沫复合材料的冲击韧性和压缩模量达到最大值 。泡沫体的表观密度对PP复合泡沫材料的冲击韧性和抗压强度影响显著, 当表观密度从0.32g/cm3增至0.45g/cm3时, 冲击韧性和抗压强度分别从4.29kJ/m2和6.57MPa 提高到17.87kJ/m2和20.57MPa。      

Hybrid effects on tensile properties of hybrid short-glass-fiber-and short-carbon-fiber-reinforced polypropylene composites

Hybrid composites of polypropylene reinforced with short glass fibers and short carbon fibers were prepared using extrusion compounding and injection molding techniques. The tensile properties of these composites were investigated taking into account the effect of the hybridization by these two types of short fibers. It was noted that the tensile strength and modulus of the hybrid composites increase while the failure strain of the hybrid composites decreases with increasing the relative carbon fiber volume fraction in the mixture. The hybrid effects for the tensile strength and modulus were studied by the rule of hybrid mixtures (RoHM) using the tensile strength and modulus of single-fiber composites, respectively. It was observed that the strength shows a positive deviation from that predicted by the RoHM and hence exhibits a positive hybrid effect. However, the values of the tensile modulus are close to those predicted by the RoHM and thus the modulus shows no existence of a hybrid effect. Moreover, the failure strains of the hybrid composites were found to be higher than the failure strain of the single carbon fiber-reinforced composite, indicating that a positive hybrid effect exists. Explanations for the hybrid effects on the tensile strength and failure strain were finally presented.     

Predictions of Young’s modulus of short inorganic fiber reinforced polymer composites

An expression of Young’s modulus of short inorganic fiber reinforced polymer composites was derived based on the tensile strength equation proposed in the previous paper, and the factor affecting the Young’s modulus was analyzed. This equation was applied to estimate the Young’s modulus of short inorganic fiber reinforced polymer composites. The results showed that the relative Young’s modulus increased nonlinearly with increasing fiber volume fraction, while increased linearly with an increase of fiber length-diameter ratio. Finally, the equation was verified preliminarily by using the measured Young’s modulus of the short glass fiber (SGF) reinforced polycarbonate/acrylnitrile–butadiene–styrene copolymer composites and the polypropylene reinforced respectively with SGF and short carbon fiber reported from literature, good agreement was found between the predictions and the experimental data.     

PP/POE/SGF三元复合泡沫体的压缩吸能特性研究

在准静态单向压缩条件下,测试和分析了聚丙烯(PP)/乙烯-1-辛烯共聚物(POE)/短玻璃纤维(SGF)三元泡沫复合材料的压缩性能,考察了SGF的质量分数对压缩弹性模量、屈服强度和能量吸收特性的影响.结果表明:PP/POE/SGF泡沫复合材料的压缩应力-应变曲线具有典型的弹性变形、屈服平台和致密化三个阶段;适量SGF的引入提高了压缩弹性模量、屈服强度和吸能能力,而在研究的范围内,较高含量(20%以上)的SGF才能提高泡沫复合材料的吸能效率,其增强效果不如吸能能力明显.     

Tensile,impact and dielectric properties of three dimensional orthogonal aramid/glass fiber hybrid composites

Aramid/glass hybrid composites with three different stacking sequences and their corresponding single fiber type composites have been fabricated and their tensile, impact and dielectric properties were investigated. The trend of tensile strength and modulus of the composites followed the rule of mixture (ROM) closely and a small but positive hybrid effect for tensile strength of the hybrid composites was observed. The hybrid composites in general had a higher impact resistance than the single fiber type composites and the hybrid composite in which fiber volume fractions for glass and aramid fiber were the most balanced showed the highest impact ductility. The aramid fiber composite showed a lower dielectric constant and a higher dielectric loss than the glass fiber composites. However, the dielectric constant of the hybrid composites decreased first and then increased as the volume fraction of aramid fiber increased, which did not follow the mixing rule for dielectric constants of compounds. The dielectric loss of the composites increased monotonically as the volume fraction of aramid fiber increased which agreed well with the mixing rule.     

Hybridization effect on the mechanical properties of curaua/glass fiber composites

The aim of this paper was to evaluate the effect of hybridizing glass and curaua fibers on the mechanical properties of their composites. These composites were produced by hot compression molding, with distinct overall fiber volume fraction, being either pure curaua fiber, pure glass fiber or hybrid. The mechanical characterization was performed by tensile, flexural, short beam, Iosipescu and also nondestructive testing. From the obtained results, it was observed that the tensile strength and modulus increased with glass fiber incorporation and for higher overall fiber volume fraction (%V_f). The short beam strength increased up to %V_f of 30 vol.%, evidencing a maximum in terms of overall fiber/matrix interface and composite quality. Hybridization has been successfully applied to vegetable/synthetic fiber reinforced polyester composites in a way that the various properties responded satisfactorily to the incorporation of a third component.     

PP/mPE/SGF复合材料的动态力学性能

茂金属聚乙烯弹性体(mPE)作为一种全新的弹性体品种,特别适合于PP的增韧改性。然而,和其它弹性体一样,mPE的加入不可避免地引起PP的刚性和强度降低。为了补偿因加入弹性体带来的刚性和强度的损失,采用短玻璃纤维(SGF)对PP/mPE共混物进行增强,从而制得PP/mPE/SGF三元共混复合材料。采用滞后测量法,分别对PP/mPE共混物和PP/mPE/SGF三元复合材料的动态力学性能进行了研究。结果表明,这种复合材料具有非常高的动态弹性模量和动态负荷极限。     

PET短纤维/硅灰石晶须/硅树脂混杂材料的拉伸性能表征

研究了PET短纤维和硅灰石晶须混杂增强硅树脂复合材料的拉伸性能。结果表明,相对少量硅灰石晶须加入到PET/硅树脂体系中会降低PET纤维的增强效果,材料的拉伸强度降低,但当硅灰石晶须的加入量很多时,材料的拉伸强度反而会明显提高。笔者对硅灰石晶须的加入量对PET短纤维增强系数的影响进行了定量分析。     

Tensile properties of elephant grass fiber reinforced polyester composites

Elephant grass stalk fibers were extracted using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were incorporated in a polyester matrix and the tensile properties of fiber and composite were determined. The fibers extracted by retting process have a tensile strength of 185 MPa, modulus of 7.4 GPa and an effective density of 817.53 kg/m³. The tensile strength and modulus of chemically extracted elephant grass fibers have increased by 58 and 41%, respectively. After the treatment the tensile strength and modulus of the fiber extracted by retting have decreased by 19, 12% and those of chemically extracted fiber have decreased by 19 and 16%, respectively. The composites were formulated up to a maximum of 31% volume of fiber resulting in a tensile strength of 80.55 MPa and tensile modulus of 1.52 GPa for elephant grass fibers extracted by retting. The tensile strength and the modulus of chemically extracted elephant grass fiber composites have increased by approximately 1.45 times to those of elephant grass fiber composite extracted by retting. The tensile strength of treated fiber composites has decreased and the tensile modulus has shown a mixed trend for the fibers extracted by both the processes. Quantitative results from this study will be useful for further and more accurate design of elephant grass fiber reinforced composite materials.     

相容剂对长玻纤增强热塑性聚氨酯弹性体/聚乳酸复合材料性能的影响

采用熔体浸渍工艺制备长玻纤增强热塑性聚氨酯弹性体(TPU)/聚乳酸(PLA)复合材料;以苯乙烯-丙烯腈接枝甲基丙烯酸缩水甘油酯(SAG)作为相容剂,热塑性弹性体聚氨酯作为增韧剂,聚乳酸为基体树脂,考察苯乙烯-丙烯腈接枝甲基丙烯酸缩水甘油酯用量对长玻璃纤维增强聚TPU/PLA复合材料性能的影响。结果表明,加入苯乙烯-丙烯腈接枝甲基丙烯酸缩水甘油酯能改善长玻璃纤维增强聚TPU/PLA复合材料的相容性;长玻璃纤维增强聚TPU/PLA复合材料的拉伸强度、缺口冲击强度、弯曲强度和模量等力学性能及储能模量随着苯乙烯-丙烯腈接枝甲基丙烯酸缩水甘油酯用量的增加呈先增加后降低的趋势,而长玻璃纤维增强聚TPU/PLA复合材料的损耗因子则随苯乙烯-丙烯腈接枝甲基丙烯酸缩水甘油酯含量的增加呈现降低后增加的趋势;通过复合材料的形态分析表明,加入相容剂的复合材料中玻璃纤维与基体树脂界面强度增加,且玻璃纤维表面有一层包覆的树脂基体;通过分析得出,当相容剂添加量为6%时,长玻璃纤维增强聚TPU/PLA复合材料的拉伸强度、弯曲强度和模量、缺口冲击强度等力学性能最优。     

立体多向编织结构对复合材料性能的影响

本文采用1×1,1×2和1×3三种不同的编织结构对轴向增强和非增强三维多向编织复合材料的性能进行了研究。对编织复合材料的拉伸强度、刚度和弯曲强度、刚度进行了实验分析。结果表明;三维编织复合材料具有良好的性能。编织结构对复合材料性能有较大的影响。纤维表面编织角和纤维体积比是影响复合材料性能的重要结构参数。通过轴向加入非编织增强纤维,使编织复合材料的拉伸强度和模量,弯曲强度和模量有了较大改善。     

三维正交机织复合材料的拉伸力学性能及介电性能研究

三维纺织复合材料的发展越来越广泛,其轻质,抗分层等优点是层合板式复合材料无法比拟的.本工作对自行设计并制作的五种玻璃纤维芳纶纤维混合增强的环氧树脂复合材料的拉伸力学性能和介电性能进行了研究.结果表明纯芳纶结构的三维复合材料有着最高的比强度和比模量;而在玻璃纤维含量较多的结构材料里介电性能呈现集中且稳定的趋势.在不同的应用中,可以将不同纤维混合作为增强体以发挥各种纤维的优势和特点,满足不同的设计和实际需要.     

Thermal and mechanical properties of waste grass broom fiber-reinforced polyester composites

The main focus of this study is to utilize waste grass broom natural fibers as reinforcement and polyester resin as matrix for making partially biodegradable green composites. Thermal conductivity, specific heat capacity and thermal diffusivity of composites were investigated as a function of fiber content and temperature. The waste grass broom fiber has a tensile strength of 297.58 MPa, modulus of 18.28 GPa, and an effective density of 864 kg/m³. The volume fraction of fibers in the composites was varied from 0.163 to 0.358. Thermal conductivity of unidirectional composites was investigated experimentally by a guarded heat flow meter method. The results show that the thermal conductivity of composite decreased with increase in fiber content and the quite opposite trend was observed with respect to temperature. Moreover, the experimental results of thermal conductivity at different volume fractions were compared with two theoretical models. The specific heat capacity of the composite as measured by differential scanning calorimeter showed similar trend as that of the thermal conductivity. The variation in thermal diffusivity with respect to volume fraction of fiber and temperature was not so significant.The tensile strength and tensile modulus of the composites showed a maximum improvement of 222% and 173%, respectively over pure matrix. The work of fracture of the composites with maximum volume fraction of fibers was found to be 296 Jm⁻¹.     

Characteristics of continuous unidirectional kenaf fiber reinforced epoxy composites

Kenaf fibers generally has some advantages such as eco-friendly, biodegradability, renewable nature and lighter than synthetic fibers. The aims of the study are to characterize and evaluate the physical and mechanical properties of continuous unidirectional kenaf fiber epoxy composites with various fiber volume fractions. The composites materials and sampling were prepared in the laboratory by using the hand lay-up method with a proper fabricating procedure and quality control. Samples were prepared based on ASTM: D3039-08 for tensile test and the scanning electron microscopy (SEM) was employed for microstructure analysis to observe the failure mechanisms in the fracture planes. A total of 40 samples were tested for the study. Results from the study showed that the rule of mixture (ROM) analytical model has a close agreement to predict the physical and tensile properties of unidirectional kenaf fiber reinforced epoxy composites. It was also observed that the tensile strength, tensile modulus, ultimate strain and Poisson’s ratio of 40% fiber volume content of unidirectional kenaf fiber epoxy composite were 164 MPa, 18150 MPa, 0.9% and 0.32, respectively. Due to the test results, increasing the fiber volume fraction in the composite caused the increment in the tensile modulus and reduction in the ultimate tensile strain of composite.     

炭纤维增强明胶复合材料的性能研究

制备了不同形式炭纤维增强的明胶复合材料,对不同复合材料的力学性能进行了测量与分析,并对复合材料的拉伸断口进行了观察,研究表明,长炭纤维增强明胶（CL/Gel)复合材料具有最高的拉伸强度,剪切强度和模量,而炭纤维毡增强明胶（CF/Gel)复合材料因内部存在较多的孔隙使其力学性能最差,因此,炭纤维毡不能用于增强明胶材料,由于纺织炭纤维布增强明胶（Cw/Gel)复合材料的纤维维束内亦有孔隙,炭纤维布的增强效果不及长炭纤维。     

Modeling the effect of reinforcement discontinuity on the tensile strength of UD flax fiber composites

To exploit the potential of natural fibers as reinforcement of polymer matrix composites, aligned bast fiber composite materials are being produced and studied. Bast fiber reinforcement is discontinuous due to the limited length of natural fibers, which needs to be reflected in predictive models of mechanical properties of composites. The strength in tension in the fiber direction of an aligned flax fiber-reinforced composite is modeled assuming that a cluster of adjacent fiber discontinuities is the origin of fracture. A probabilistic model of tensile strength, developed for UD composites containing a microdefect, is applied. It follows from the theoretical analysis that the experimental tensile strength as a function the fiber volume fraction can be described with acceptable accuracy assuming the presence of a cluster of ca. 4 × 4 elementary fiber discontinuities.     

Tensile properties of VGCF reinforced carbon composites

Carbon composites based on vapor grown carbon fibers prepared by a fixed catalyst method were fabricated using a pitch infiltration technique. The composites have both unidirectional and bi-directional fiber reinforcement, and different fiber volume fractions ranging from 25% to 56%. Specimens were prepared from these composites for tensile testing at room temperature, and tensile modulus and strength were determined. The composite modulus was then used to estimate the fiber modulus.     

Interfacial properties and microfailure degradation mechanisms of bioabsorbable fibers/poly-l-lactide composites using micromechanical test and nondestructive acoustic emission

Interfacial properties and microfailure degradation mechanisms of the bioabsorbable composites for implant materials were investigated using micromechanical technique and nondestructive acoustic emission (AE). The tensile strength of absorbable fibers with hydrolysis was analyzed statistically using either uni- or bimodal Weibull distribution. As hydrolysis time increased, the tensile strength, the modulus and the elongation of poly(ester-amide) (PEA) and bioactive glass fibers decreased, whereas those of chitosan fiber almost did not change. Interfacial shear strength (IFSS) between bioactive glass fiber and poly-l-lactide (PLLA) was much higher than PEA or chitosan fiber/PLLA systems using dual matrix composite (DMC) specimen. The decreasing rate of IFSS was the fastest in bioactive glass fiber/PLLA composites whereas that of chitosan fiber/PLLA composites was the slowest. Work of adhesion, W_a between bioactive glass fiber and PLLA was the highest, and the wettability results were consistent with the IFSS. AE energies of PEA fiber decreased gradually, and their distributions became narrower than those in the initial state with hydrolysis time. In case of bioactive glass fiber, AE energies in tensile failure were much higher than those in compression. In addition, AE parameters at the initial state were much higher than those after degradation under both tensile and compressive tests. Interfacial properties and microfailure degradation mechanisms can be important factors to control bioabsorbable composite performance.     

立体多向编织结构对复合材料性能的影响

本文采用1×1,1×2和1×3三种不同的编织结构对轴向增强和非增强三维多向编织复合材料的性能进行了研究。对编织复合材料的拉伸强度、刚度和弯曲强度、刚度进行了实验分析。结果表明;三维编织复合材料具有良好的性能。编织结构对复合材料性能有较大的影响。纤维表面编织角和纤维体积比是影响复合材料性能的重要结构参数。通过轴向加入非编织增强纤维,使编织复合材料的拉伸强度和模量,弯曲强度和模量有了较大改善。