机织/针织混合铺层对复合材料力学性能的影响

为使纺织复合材料同时具有机织结构复合材料和针织结构复合材料的综合力学性能,通过混合铺层方式制备机织/针织混合结构复合材料。以芳纶机织平纹织物和针织罗纹织物为增强体,以环氧树脂为基体,调整复合材料中增强体的铺层顺序,利用真空辅助成型技术制备四层层压机织/针织混合结构复合材料。通过对复合材料拉伸性能、弯曲性能和冲击性能的测试,分析混合铺层和铺层顺序对芳纶环氧树脂复合材料力学性能的影响。结果表明,混合铺层和铺层顺序对芳纶环氧树脂复合材料的弯曲强度和冲击强度有较大影响,特别是对罗纹结构复合材料纬向弯曲强度和冲击强度的改善。当采用相同铺层方式,罗纹织物为受力面时,机织/针织混合结构复合材料具有较大弯曲强度和冲击强度。     

制备工艺对亚麻增强聚丙烯复合材料拉伸性能的影响

以亚麻纤维为增强体,与聚丙烯（PP）长丝进行丝束级共混,形成PP包覆亚麻的纱线结构,利用机织工艺织成二维机织布,作为复合材料的预制件。采用层合热压方法制备PP／亚麻复合材料板材。通过对板材拉伸性能测试及扫描电镜（SEM）拉伸断口形貌分析,研究了不同纤维体积分数、织造密度及织造组织等因素对复合材料拉伸性能的影响。结果表明,在选取最优热压温度与压力的条件下,纤维体积分数为50％的板材性能最优;经向密度相同时,拉伸性能随着纬向密度的增加而提高;经、纬向密度均相同时,斜纹3／1组织的板材性能最优,纬向最大拉伸强度可达92．42 MPa。     

Effect of stacking sequence on mechanical properties of hybrid flax/jute fibers reinforced thermoplastic composites

In this study, the hybrid composites were prepared by stacking jute/PP nonwoven and flax/MAPP woven fabrics in defined sequences. Polypropylene (PP) and maleic anhydride grafted polypropylene (MAPP) were used as matrix materials. Jute and flax fibers were treated with alkali solution in order to improve the interface properties of the resultant composites. The mechanical properties of these hybrid composites were analyzed by means of tensile, flexural, and drop‐weight impact tests. The effect of fabric stacking sequence on the mechanical properties of the composites was investigated. The stacking of nonwovens at the top and in alternate layers has resulted in maximum flexural strength, flexural stiffness, and impact force. It was also shown that hybrid composites have improved tensile, flexural, and impact properties in comparison to neat PP matrix. POLYM. COMPOS., 36:2167–2173, 2015. © 2014 Society of Plastics Engineers     

Physical and mechanical properties of kenaf/flax hybrid composites

This research investigates the physical and mechanical properties of hybrid composites made of epoxy reinforced by kenaf and flax natural fibers to investigate the hybridization influences of the composites. Pure and hybrid composites were fabricated using bi-directional kenaf and flax fabrics at different stacking sequences utilizing the vacuum-assisted resin infusion method. The pure and hybrid composites' physical properties, such as density, fiber volume fraction (FVF), water absorption capacity, and dimensional stability, were measured. The tests of tensile, flexural, interlaminar shear and fracture toughness (Mode II) were examined to determine the mechanical properties. The results revealed that density remained unchanged for the hybrid compared to pure kenaf/epoxy composites. The tensile, flexural, and interlaminar shear performance of flax/epoxy composite is improved by an increment of kenaf FVF in hybrid composites. The stacking sequence significantly affected the mechanical properties of hybrid composites. The highest tensile strength (59.8 MPa) was obtained for FK2 (alternative sequence of flax and kenaf fibers). However, FK3 (flax fiber located on the outer surfaces) had the highest interlaminar shear strength (12.5 MPa) and fracture toughness (3302.3 J/m²) among all tested hybrid composites. The highest water resistance was achieved for FK5 with the lowest thickness swelling.     

Unidirectional hemp and flax EP‐ and PP‐composites: Influence of defined fiber treatments

In some technical areas, mainly in the automotive industry, glass fiber reinforced polymers are intended to be replaced by natural fiber reinforced polymer systems. Therefore, higher requirements will be imposed to the physical fiber properties, fiber‐matrix adhesion, and the quality assurance. To improve the properties of epoxy resins (EP) and polypropylene (PP) composites, flax and hemp fibers were modified by mercerization and MAH‐PP coupling agent was used for preparing the PP composites. The effects of different mercerization parameters such as concentration of alkali (NaOH), temperature, and duration time along with tensile stress applied to the fibers on the structure and properties of hemp fibers were studied and judged via the cellulose I–II lattice conversion. It was observed that the mechanical properties of the fibers can be controlled in a broad range by using appropriate mercerization parameters. Unidirectional EP composites were manufactured by the filament winding technique; at the PP matrix material, a combination with a film‐stacking technique was used. The influence of mercerization parameters on the properties of EP composites was studied with hemp yarn as an example. Different macromechanical effects are shown at hemp‐ and flax‐PP model composites with mercerized, MAH‐PP‐treated, or MAH‐PP‐treated mercerized yarns. The composites' properties were verified by tensile and flexural tests. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2150–2156, 2004     

Experimental assessment of the improved properties during aging of flax/glass hybrid composite laminates for marine applications

The investigation for natural fibers composites in terms of performance, durability, and environmental impact for structural applications in marine environments is a relevant challenge in scientific and industrial field. On this context, the aim of this work is to assess the durability and mechanical stability in severe environment of epoxy/glass–flax hybrid composites. For the sake of comparison, also full flax and glass epoxy composites were investigated. All samples were exposed to salt–fog environmental conditions up to 60 aging days. Wettability behavior during time was compared with water uptake evolution to assess water sensitivity of hybrid composite configurations. Moreover, quasi-static flexural and dynamic mechanical analysis were carried to evaluate as aging conditions, laminate configuration influence the surface and mechanical performances stability of the hybrid composites. The addition of glass fibers on flax laminate allows to enhance both flexural strength by 90%, and modulus by 128%, even if these properties are lower than those of full glass laminates. The results evidenced that the hybridization of flax fibers with glass ones is a practical approach to enhance the aging durability of epoxy/flax composite laminates in marine environmental conditions, obtaining a suitable compromise among environmental impact, mechanical properties, aging resistance, and costs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47203.     

Biobased composites prepared by compression molding with a novel thermoset resin from soybean oil and a natural‐fiber reinforcement

Biobased composites were manufactured with a compression‐molding technique. Novel thermoset resins from soybean oil were used as a matrix, and flax fibers were used as reinforcements. The air‐laid fibers were stacked randomly, the woven fabrics were stacked crosswise (0/90°), and impregnation was performed manually. The fiber/resin ratio was 60 : 40. The prepared biobased composites were characterized by impact and flexural testing. Scanning electron microscopy of knife‐cut cross sections of the specimens was also done to investigate the fiber–matrix interface. Thermogravimetric analysis of the composites was carried out to provide indications of thermal stability. Three resins from soybean oil [methacrylated soybean oil, methacrylic anhydride modified soybean oil (MMSO), and acetic anhydride modified soybean oil] were used as matrices. The impact strength of the composites with MMSO resin reinforced with air‐laid flax fibers was 24 kJ/m², whereas that of the MMSO resin reinforced with woven flax fabric was between 24 and 29 kJ/m². The flexural strength of the MMSO resin reinforced with air‐laid flax fibers was between 83 and 118 MPa, and the flexural modulus was between 4 and 6 GPa, whereas the flexural strength of the MMSO resin reinforced with woven fabric was between 90 and 110 MPa, and the flexural modulus was between 4.87 and 6.1 GPa. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Research on the mechanical properties prediction of carbon/epoxy composite laminates with different void contents

The influence of the porosity on the static mechanical strength of the carbon fiber fabric reinforced epoxy composites laminates was investigated. The tensile, compressive, bending, and interlaminar strength test on the CFRP laminates with porosity of 0.33% and 1.50% were conducted and simulated by a finite element analysis model. The article proposes the failure criterion of the static mechanical strength of the fabric fiber reinforced composites based on the improved Hashin failure criterion that is suitable for the undirectional composite laminates. The basic composite strength parameters are used to evaluate the mechanical properties of CFRP laminates with different porosities. A finite element analysis model is established by using software ABAQUS™ combined with the sudden stiffness degradation model. The experiment results show that the tensile, compressive, bending, and interlaminar strength decrease with the increasing porosities. The tensile, compressive, bending, and interlaminar strength of the fabric carbon fiber reinforced epoxy composites laminates are simulated accurately by the finite element model. POLYM. COMPOS., 14–20, 2016. © 2014 Society of Plastics Engineers     

制备工艺对亚麻增强热塑性复合材料拉伸力学性能的影响

将增强体亚麻纱线和基体丙纶复丝制成pp/亚麻包覆纱后,进行织造,织物用层合热压法制成复合材料.制备工艺中,包覆纱法对复合材料的拉伸强度最好;麻含量50%的复合材料的拉伸强度达到最佳;当纬纱密度相同时,随着经纱密度的增大经向的拉伸强力和拉伸弹性模量也随之增大,而纬向的却随之减小,当经纱密度相同时,随着纬纱密度的增大,经向的拉伸强力和拉伸弹性模量随之减小,纬向的随之增大.     

Tribological Performance of Bamboo Fabric Reinforced Epoxy Composites

Bamboo fiber is one of the strongest natural fibers with high strength-to-weight and stiffness-to-weight ratios and can be used economically for manufacturing fiber-reinforced composites. In this paper, bamboo fabric-reinforced epoxy composite is manufactured and its tribological properties for load-bearing applications are investigated. Sliding wear tests are conducted using a linear reciprocating tribometer and the effect of dry and lubricated contact conditions, applied load, sliding speed, temperature, and woven fabric direction on the coefficient of friction and wear rate are investigated. A scanning electron microscope is used to define the wear mechanisms at room and elevated temperatures. It is observed that the fabric orientation influences the mechanical and tribological performances of the composite material. Wear rate increases at higher loads and working temperatures; however, the effect of sliding speed is not remarkable, especially under lubricated contact conditions. The results present in this paper can be used for designing bamboo-reinforced epoxy composites for load-bearing applications, under different working conditions.     

Effects of heat accelerated aging on tensile strength of three dimensional braided/epoxy resin composites

The tensile tests of three‐dimensional (3Dim) and four‐directional (4Dir) carbon fiber braided/epoxy resin composites and carbon fiber woven plain fabric laminated/epoxy composites after heat accelerated aging at 150 and 180°C for 60, 120, and 180 h were carried out respectively. The reason of the changes of tensile property of these composites after different aging period of time at different high temperature was explained. The results of two‐way ANOVA analyzing indicate that the aging time has a significant effect on tensile strength of these composites. With the increase of accelerated aging period of time at high temperature, the tensile strengths of these composite samples decreased compared with that of composite samples without aging. However the decrease of tensile strength of 3Dim and 4Dir braided composites is less than that of laminated composites. One of the reasons is after aging for a long time at high temperature, the resin is damaged and becomes brittle which make the bonding force between fiber and resin decrease. Another reason is the structure of reinforcement of composites. After aging, the structure of 3Dim and 4Dir braided/epoxy resin composites still keeps the integrity which makes the 3Dim and 4Dir composites have less tensile performance degradation (3Dim and 4 Dir: three‐dimensional and four‐directional). POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Improvement of mechanical properties of structural thermoplastic composites using a reactive (low molecular weight) matrix component

An innovative manufacturing process for continuous fiber composites with the polymeric matrix made up of polypropylene and epoxy resin, as a model reactive low molecular weight component, was developed; variable process parameters give rise to different morphologies of matrix components surrounding the woven fabric reinforcement. Furthermore, the combination of both thermoplastic and thermosetting polymers permitted intimate fibers impregnation, typical of thermosetting matrix composites, with short process cycle time, which usually occurs in manufacturing process of thermoplastic matrix composites. Polypropylene (PP) films, glass fibers fabric, and epoxy resin film were used to produce flat composite through film‐stacking technique. The preparation process focused on control of both epoxy resin cure process and polypropylene melting. The process was able to induce the two matrix components to form either a planar (sandwich‐like) structure or a three‐dimensional (3D) network by means of controlling the process parameters such as pressure and heating rate. The strong enhancement of the mechanical properties (Young's modulus and tensile strength of the composites with the 3D structure were almost twice as high of those of the composites with sandwich‐like matrix structure) was due to the different microstructures produced by the interplanar flow of the thermoplastic polymer. POLYM. COMPOS., 31:1762–1769, 2010. © 2010 Society of Plastics Engineers.     

Flexural Strength,Performance, and Cost Analysis of Multiaxial Warp-Knitted Preforms for Composite Reinforcements

In the scope of this study, performance analysis of industrial fabrics for composite reinforcement was evaluated from the cost point of view. For the production of composite structures, major considerations can be summarized as stiffness, strength, weight, and cost. In general, manufacturing costs of composites consist of material, labor, overhead, and development costs. The priorities and demands will determine characteristics of the material and process. Specific strength per cost relation is in favor of multiaxial warp-knitted (MWK) fabric. In order to evaluate fiber reinforcements within the group, MWK fabric laminate was compared with woven fabric laminate from the cost/performance point of view. To do so, laminate comparison was performed between MWK fabric and woven fabric reinforced composites. It was found that relative to woven reinforced composite, MWK fabric reinforced composite has lower resin weight, overall composite weight, and labor cost and higher flexural moment with slightly higher material cost.     

Mechanical and thermal properties of compatibilized polypropylene reinforced by woven doum

In this work, the development and the mechanical characterization of a doum textile composite based on a polypropylene matrix were carried out. Mechanical and rheological tests were effectuated, to illustrate the effect of woven fibers on the mechanical and viscoelastic properties at 0°, 15°, 30°, and 45° directions. The woven fibers were treated and the matrix was melted to a coupling agent to assure compatibility between the fibers and the polymer. The composites with long fiber are generally used as film and the main properties is the tensile. In this study, our goal was to improve the tensile properties. Results have shown that tensile properties exhibited a significant increase when compared to the polypropylene. However, it was observed that the stress direction has no influence on the thermal properties of the composite. Also, this article evaluates models that predict the stiffness of the composites at different stress directions to be compared to the experiments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4347–4356, 2013     

Tensile,flexural and impact properties of jute fibre-based thermosetting composites

Abstract

The present study reports static and impact mechanical properties of jute fibre-based thermosetting composites using woven and flat braided jute fabrics. Tensile, three-point flexural and low-to-medium energy drop-weight impact tests were conducted and mechanical properties were evaluated to study their dependence upon surface modifications of the fibre materials due to bleaching and coating treatments. Full-bleaching (longer and rigorous) treatments improved interfacial bonding and tensile strength properties of the woven jute composites compared to unbleached and half-bleached counterparts. Bleaching treatments did not seem to improve the flexural strength of composites. Unbleached (natural) jute composites have relatively better flexural strength due to reduced microstructural waviness or fibre crimping to facilitate flexural failure. With coated jute yarns, the tensile properties of the resultant flat braided composites slightly degraded, whereas the flexural properties showed clear improvements. The changes in the mechanical properties were broadly related to the accompanying modifications and to the state of microstructural imperfections, namely fibre/matrix interfacial adhesion, severity of resin matrix shrinkage during the curing process, fibre/matrix debonding and distribution of disbonds within the matrix region, and also to the relative fibre filament density along the loading axis, in the cured composite structure. There was a clear indication that natural woven jute composites could be more effective in applications requiring better impact damage resistance, energy absorption capability and improved progressive crushing behaviour.     

Mechanical properties of natural fiber hybrid composites based on renewable thermoset resins derived from soybean oil,for use in technical applications

Natural fiber composites are known to have lower mechanical properties than glass or carbon fiber reinforced composites. The hybrid natural fiber composites prepared in this study have relatively good mechanical properties. Different combinations of woven and non‐woven flax fibers were used. The stacking sequence of the fibers was in different orientations, such as 0°, +45°, and 90°. The composites manufactured had good mechanical properties. A tensile strength of about 119 MPa and Young's modulus of about 14 GPa was achieved, with flexural strength and modulus of about 201 MPa and 24 GPa, respectively. For the purposes of comparison, composites were made with a combination of woven fabrics and glass fibers. One ply of a glass fiber mat was sandwiched in the mid‐plane and this increased the tensile strength considerably to 168 MPa. Dynamic mechanical analysis was performed in order to determine the storage and loss modulus and the glass transition temperature of the composites. Microstructural analysis was done with scanning electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A study on the moisture sorption characteristics in woven sisal fabric reinforced natural rubber biocomposites

Textile biocomposites were prepared by reinforcing natural rubber with woven sisal fabric. Sisal fabric was subjected to various chemical modifications like mercerization, silanization, and thermal treatment. The moisture uptake of the textile composites was found to depend upon fiber content as well as architecture. The mechanism of diffusion in the composites was found to be fickian in nature. The effect of chemical modification of sisal fabric on moisture uptake was also analyzed. Mercerization was seen to increase the water uptake in the composites while thermally treated fabric reinforced composites exhibited lower water uptake. The influence of temperature on water sorption of the biocomposites is also analyzed. The thermodynamic parameters of the sorption process were also evaluated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 416–423, 2006     

Zum Verhalten von Jute- und Flachsfaser-Epoxidharz-Verbunden mit alkalibehandelten Fasern bei Feuchteexposition

Investigations on the influence of exposure to water on the physical properties of untreated and alkali-treated jute and flax fibers and their composites with an epoxy resin were carried out. The moisture uptake led to a strong anisotropic swelling which was more significant for the alkali treated fibers. In general, jute fibers lost roughly 30% of their tenacity after this water exposure, while the tenacity of flax fibers remained unaffected. Due to this, the tensile strength of jute-epoxy composites decreases with increasing water content, while the strength of comparable flax-epoxy composites increases slightly. The dynamic strength of the composites was improved by the use of alkali-treated fibers, the loss of this characteristic value after a 49-days water storage was influenced by the type of fiber and their treatment.     

Properties of Isoprene Rubber Reinforced with Treated Bleached Kraft Cellulosic Fibers or Rayon Fibers

Abstract

Both native and regenerated (rayon) cellulosic fibers are potential reinforcing elements in rubbers due to their relatively good mechanical properties, suitable aspect ratio, low cost and low density. The properties of the cellulosic fibers can also be changed fairly easily by chemical treatment. The effects of two treatments, mercerization (NaOH-immersion) and benzylation, on the mechanical properties of a rubber-cellulose composite are here reported. The rubber matrix was isoprene and the fiber content 20% by volume (27% by weight). Mercerization of bleached kraft fibers gave a composite with a higher modulus and strength than was attained when untreated kraft fibers were used, whereas benzylation of both kraft fibers and rayon fibers caused a reduction in the strength and stiffness of the rubber composites. This is interpreted as being due to a decrease in the degree of interaction between the cellulose fiber and the matrix due to the benzylation. The effect of these treatments on the mechanical properties of single rayon fibers is also reported.     

Tensile Fracture and Failure Behavior of Thermoplastic Starch with Unidirectional and Cross‐Ply Flax Fiber Reinforcements

Thermoplastic starch (MaterBi®) based composites containing flax fibers in unidirectional and crossed‐ply arrangements were produced by hot pressing using the film stacking method. The flax content was varied in three steps, viz. 20, 40 and 60 wt.‐%. Static tensile mechanical properties (stiffness and strength) of the composites were determined on dumbbell specimens. During their loading the acoustic emission (AE) was recorded. Burst type AE signal characteristics (amplitude, width) were traced to the failure mechanisms and supported by fractographic inspection. The mechanical response and failure mode of the composites strongly depended on the flax content and the flax fiber lay‐up. It was established that the tensile strength increases until 40 wt.‐% flax fiber content but stays almost constant above this value. In the case of 40 wt.‐% unidirectional fiber reinforcement, the tensile strength of the composite was 3 times greater than that of the pure starch matrix. The flax fiber reinforcement increased the tensile modulus of the pure starch by several orders of amplitude.

SEM picture of the fracture surface of a composite with UD flax reinforcement.