Effect of laminated structure design on the mechanical properties of bamboo-wood hybrid laminated veneer lumber

The effects of veneer orientation and loading direction on the mechanical properties of bamboo-bundle/poplar veneer laminated veneer lumber (BWLVL) were investigated by a statistical analysis method. Eight types of laminated structure were designed for the BWLVL aiming to explore the feasibility of manufacturing high-performance bamboo-based composites. A specific type of bamboo species named Cizhu bamboo (Neosinocalamus affinis) with a thickness of 6 mm and diameter of 65 mm was used. The wood veneers were from fast-growing poplar tree (Populus ussuriensis Kom.) in China. The bamboo bundles were obtained by a mechanical process. They were then formed into uniform veneers using a one-piece veneer technology. Bamboo bundle and poplar veneer were immersed in water-soluble phenol formaldehyde (PF) resin with low molecular weight for 7 min and dried to MC of 8–12 % under the ambient environment. All specimens were prepared through hand lay-up using compressing molding method. The density and mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), and shearing strength (SS) of samples were characterized under loading parallel and perpendicular to the glue line. The results indicated that as the contribution of bamboo bundle increased in laminated structure, especially laminated on the surface layers, the MOE, MOR and SS increased. A lay-up BBPBPBB (B-bamboo, P-poplar) had the highest properties due to the cooperation of bamboo bundle and poplar veneer. A higher value of MOE and MOR was found for the perpendicular loading test than that for the parallel test, while a slightly higher SS was observed parallel to the glue line compared with perpendicular loading. Any lay-up within the homogeneous group can be used to replace others for obtaining the same mechanical properties in applications. These findings suggested that the laminated structure with high stiffness laid-up on the surface layers could improve the performance of natural fiber reinforced composites.     

The effect of hydrophilic (polyvinyl alcohol) fiber content on the flexural behavior of engineered cementitious composites (ECC)

This paper investigates the effect of hydrophilic polyvinyl alcohol (PVA) fiber’s content (1.2–2.0% volume of composite) on the flexural behavior of engineered cementitious composites (ECC) materials. Different parameters of flexural behavior such as strength at first-cracking and post-cracking stages, deflection at ultimate load, toughness indices according to ASTM 1018, flexural modulus, and energy absorption were determined. Test results showed that the flexural strength and flexural modulus of composites significantly increases by increment in fiber content. However, flexural strength of composites varies from 8.5 to 14 MPa depending on amount of PVA fibers. The toughness indices, deflection at max load and energy absorption were decreased by further increase in the fiber content from 1.6 to 2%. It was indicated that there was an indirect relationship between flexural strength and ductility of composite in higher amount of fiber content.     

二维三轴向编织混杂层合复合材料的冲击性能

为探讨混杂结构与破坏机制关系。本文研究了在铺层数目相同时,4组二维三轴编织碳纤维/玻纤纤维混杂层合复合材料受到低速冲击后的冲击性能。实验结果表明,在相同铺层数目情况下,编织混杂层合复合材料冲击后表面产生裂纹均比纯碳纤或纯玻纤编织层合复合材料多,且正面裂纹纵向扩展范围较大,而背面裂纹横向扩展范围较大;碳纤+玻纤+碳纤编织层合复合材料单位厚度吸收的能量比纯碳纤编织层合复合材料提高7.61%;玻纤+碳纤+玻纤编织层合复合材料单位厚度吸收的能量比纯玻纤编织片层合复合材料提高2.21%;编织混杂层合复合材料冲击后在厚度方向产生的损伤扩展较少;编织层合复合材料在低速冲击作用下不易分层,通过合适的铺层方式及纤维组合能够实现正的混杂效应,并能有效改善材料的抗冲击性能。     

Mechanical properties and microstructure of 3D sinking woven quartz fiber-reinforced silica composites by silicasol-infiltration-sintering

Three-dimensional (3D) sinking woven quartz fiber-reinforced silica composites were successfully prepared by silicasol-infiltration-sintering process at a low temperature of 450°C. The density of the composites was 1.74?g/cm³. The characteristics of 3D sinking woven structure were determined. Flexural strength and shear strength of the composites were investigated along the warp and weft directions. Both flexural stress–displacement curves in warp and weft directions had two fractural points, e.g. matrix fracture point and fiber fracture point. The shear stress–displacement curves exhibited mostly nonlinear behavior. The composite in warp and weft direction reflects different shear behavior. Microstructural observations revealed that the adhesion strength between the fibers and the matrix was weak. There was a good state without serious degradation of quartz fibers during the preparation. Apart from these, the composites exhibited an extensive and long fiber pullout in the fracture surface. Crack deflection and fiber pullout contributed to the good toughness of the composites under the loading.     

三维正交机织复合材料的冲后压缩性能

为揭示纱线张力对三维机织复合材料抗冲击及冲后压缩性能的影响规律,基于多剑杆织造工艺,配置不同接结纱张力(25、50、100 cN)织造三维正交机织物,通过真空辅助树脂传递模塑成型工艺制备复合材料,并在室温下进行低速冲击及冲后压缩性能测试。结果表明：当接结纱张力为100 cN时,试样在冲击载荷下发生表层树脂大面积破裂和剥离并使纬纱失去支撑,同时,试样表层纬纱发生较大卷曲,促使压缩载荷发生屈曲失效;接结纱张力为100 cN试样的压缩性能相比接结纱张力为25 cN试样下降约50%;接结纱张力较高时易导致纬纱卷曲增大和树脂富集,并由此降低试样的弯曲刚度和冲后压缩性能。     

Influence of Kevlar Hybridization on Dielectric and Conductivity of Bamboo Fiber Reinforced Epoxy Composite

In a motive to develop a natural fiber-based dielectric material, bamboo fiber-reinforced epoxy composite is fabricated using hand layup technique and hybridized with Kevlar K29 fiber to enhance its properties. Dielectric and conductivity studies are performed using LCR meter on the composite samples as a function of frequency (100 Hz-1 MHz) and temperature (22–120°C). From the experiment, it is observed that the dielectric properties of bamboo-based natural composite are significantly enhanced by Kevlar hybridization. And also the influence of variation in frequency and temperature on the electrical properties i.e. dielectric and conductivity of the fabricated composite was studied. The morphological study is also carried out using scanning electron microscope (SEM).     

竹原纤维/聚氨酯复合材料的隔音性能

为充分发挥天然竹原纤维的可再生性和生物分解性,减少隔音复合材料对环境的负荷,并进一步改善竹原纤维/聚氨酯复合材料的隔音性能,以天然环保和可再生的竹原纤维为增强材料,以聚氨酯为基体,制备了一系列不同方式复合的隔音复合材料。研究了竹原纤维的排列方式与质量分数、及氢氧化钠溶液表面处理对复合材料隔音性能的影响。结果表明：竹原纤维采用直铺法制成的复合材料隔音性能最好;竹原纤维经氢氧化钠溶液处理后制成的复合材料其隔音性能显著提高;随着竹原纤维质量分数增加,复合材料的隔音性能增大。     

Effect of Chemical Treatment on Thermal,Mechanical and Degradation Behavior of Banana Fiber Reinforced Polymer Composites

ABSTRACT

The current research endeavor, explores the thermal, mechanical, and degradation behavior of alkaline treated banana fibers reinforced polypropylene composites. Composites incorporating BF (20% w: w) treated with NaOH (5% w: v) aqueous solution were developed using extrusion-injection molding processes. After chemical treatment, the tensile, flexural and impact strength of the composite increases by 3.8%, 5.17%, and 11.50%, respectively. Scanning electron microscope (SEM) observations of tested specimens confirm the fiber pull out and fiber fracture as the main reasons for failure of developed composites under tensile and impact loading. The specimens were exposed to two different environments, water immersion and soil burial for 5 weeks for the degradation studies. The degradation behavior of composites was measured in terms of variation in weight and mechanical properties (tensile, flexural, and impact). The maximum degradation in mechanical properties was observed for the composites buried under soil. The composite lost 7.69%, 12.06%, and 3.27% of tensile, flexural, and impact strength, respectively.     

Investigation of mechanical behavior of woven/knitted hybrid composites

The objective of this research is to develop the woven/knitted hybrid composites for improved in plane as well as out of plane mechanical properties. Two different type of structures and two different materials were used in this study. Firstly, the woven and knitted fabrics were developed with glass and Kevlar yarn. Secondly, the laminated composite samples were fabricated with different stacking sequence of fabric plies. The epoxy resin was used as matrix. The cured samples were characterized for impact, tensile and dynamic mechanical properties. The behavior of composite materials was then analyzed with percentages of different fiber and fabric types. The samples with higher percentages of knitted reinforcement gave better impact strength but failed to provide better tensile properties. Moreover, the samples with higher percentages of woven structure and glass materials gives better modulus values.     

竹原/亚麻复合材料力学性能的模糊评判

采用竹原纤维、亚麻纤维作为增强体,低熔点聚酯纤维(LMPET)及丙纶纤维(PP)做基体,通过非织造工艺制作混合纤维预成型件,采用模压成型工艺制作植物纤维增强复合材料。用模糊综合评判的方法,探讨增强相与基体相选用的纤维种类及纤维质量百分率对材料力学性能的影响。利用扫描电镜研究了复合材料拉伸断口的形貌。结果表明:LMPET/40%竹原纤维复合材料的力学性能最优,纵、横向拉伸强度分别为136.00 MPa和87.58 MPa;纵、横向弯曲强度分别为534.00 MPa和470.00 MPa,超过了普通工程塑料的水平。     

锯齿形三维机织间隔复合材料的弯曲性能

为解决层合间隔复合材料易开裂和整体性差的问题,采用绿色环保的玄武岩低捻长丝作为经、纬纱,合理设计经向截面图和组织图,并在普通织机上织造3种不同间隔高度的锯齿形三维机织间隔织物。以所织得的锯齿形三维机织间隔织物作为增强材料,环氧乙烯基树脂作为基体,利用真空辅助成型工艺,制备锯齿形三维机织间隔复合材料,同时对三维机织间隔复合材料进行三点弯曲性能测试,得到弯曲载荷-位移曲线、能量吸收图和破坏模式。结果表明:复合材料的纬向是主要承力方向;组织循环个数越多的材料表现出更好的弯曲性能;在一定间隔高度范围内,间隔高度越高的锯齿形三维机织间隔织物承受的弯曲载荷和吸收的能量也越高;锯齿形三维机织间隔复合材料的破坏模式是材料上表层受压,下表层受拉,而连接层受压;在作用力下材料只是出现明显的变形,但并未出现材料整体的破坏。     

剪切增稠液/纤维复合材料防弹性能的研究进展

为促进对剪切增稠液(STF)与高性能纤维复合形成具有高效力学响应和能量吸收机制的智能抗冲击防护材料的性能研究和应用,综述了STF流变性能、STF/纤维复合材料力学性能及其抗弹道冲击机制的研究进展,分析了STF原料选择、复合材料体系构建原理及制备方法。针对STF/纤维复合材料的弹道冲击过程和特点及其在高速冲击下的反应机制,探讨影响弹道冲击性能的因素并提出解决方案。展望了高响应度的柔性智能STF/纤维防弹复合材料的研究发展方向,指出对柔性智能STF/纤维防弹复合材料的表征和评价方法尚需完善,基于三维自增强结构、纤维材料与STF界面结合性、流变滑移及摩擦特性是未来防弹复合材料的研究重点。     

Exploring the potential of milkweed stalk in wood plastic manufacture

The physical and mechanical properties of milkweed composites based on different loads of milkweed flour and maleic anhydride grafted polypropylene (MAPP) using polypropylene as matrix are investigated in this study. There levels of milkweed fibers (30, 40, and 50 wt.%), one level of mixed milkweed flour (20:20 wt.% fiber:bark), and two levels of MAPP (4 and 6 wt.%) were used to prepare natural fiber-reinforced composites. Physical and mechanical properties including flexural, tension, impact, and thickness swelling were evaluated according to ASTM standards. The result demonstrated that addition of milkweed flour fluctuates mechanical properties of reinforced composite. However, the optimum load of milkweed flour was different in each test. Generally, 40 wt.% mixed flour composite in comparison with 40 wt.% milkweed composite showed lower mechanical results and higher thickness swelling. MAPP as a coupling agent improved physical and mechanical properties of milkweed-filled composites in most properties. The results of this study depicted positive effects of lignocellulose fibers and coupling gent and also negative effect of bark flour as a function of lower cellulose and higher extractive contents on physical and mechanical properties of milkweed-reinforced composites.     

Improving the stiffness of multilayer 3D woven composites by the integration of shape memory alloys (SMAs) into structures

Abstract

Shape memory alloys (SMAs) are capable of shape-retaining and stress generation when activated. SMA wires are embedded in laminated composites for improving the properties of the composites. Laminated composites have low through-the-thickness properties and poor delamination resistance. 3D composites are well known for having higher through-the-thickness properties. In 3D woven composites, a set of yarn is in through-the-thickness direction that improves through-the- thickness properties and provides resistance to delamination of layers. As in multilayer 3D woven structures, yarns are distributed from in-plane to through-the-thickness direction, so in-plane properties are reduced with the same number of yarns compared to 2D laminated composites. In this research, SMA wires are embedded into different types of 3D woven structures for utilising stress generation property of SMA wires for improving in-plane properties, specifically stiffness of the composites. Three types of 3D orthogonal interlocking composites: layer-to-layer, through-the-thickness, and modified multilayer interlock structures are fabricated with and without SMA wires. From the tensile test, results show that embedding SMA wires into structures significantly improves the stiffness of the structures due to the stress-induced martensite phase of SMA wire when subjected to load. When these SMA wires are activated, stresses are generated by SMA wires due to phase transformation from martensite to austenite that further gives remarkable higher values of stiffness. This results in a composite structure that has higher in-plane properties due to embedded SMA wire and through-the-thickness properties due to 3D structure of composite reinforcement. The interlocking pattern in the through-the-thickness direction of 3D structures was also found to have an effect on the extent of the improvement in stiffness.     

Microstructure and physicochemical properties of the anisotropic moso bamboo (Phyllostachys pubescens) surface

European Journal of Wood and Wood Products - The surface of moso bamboo (Phyllostachys pubescens) was commonly removed in the mechanical processing for bamboo-based composites because of its poor...     

Fabrication and Characterization of MWCNT Filled Hybrid Natural Fiber Composites

Hybrid composites are fabricated by the combination of two or more fibers using a single matrix. It can be fabricated either with all of its constituents as natural fibers or with one or more constituents belonging to artificial fiber. The stacking sequence of the fibers in a hybrid composite can be altered resulting in a varying mechanical properties. In the present study the MWCNT filled banana-jute-flax fiber reinforced composites are investigated for its mechanical behavior by varying the stacking sequence of the fiber layers and weight % of Multi-Walled Carbon Nano Tube (MWCNT). A Modified resin was prepared by adding MWCNT in the epoxy resin using ultrasonic probe sonicator and a hybrid composite is fabricated with it by using compression moulding processes. The mechanical properties are evaluated as per the ASTM standards. The incorporating of MWCNT and the stacking sequence of fiber layers shows the greater impact on the mechanical properties. The composites of jute fibers at the extremities (JBFBFBFJ) exhibiting the enhancement of tensile, compressive and hardness properties than the flax fiber at the extremities (FBJBJBJF) and it could be used in various automobile applications. Microstructure of the samples are investigated by Scanning Electron Microscope (SEM)with Energy dispersive X-ray (EDS). The results indicate that increasing the weight % of MWCNT and varying the stacking sequence of fibers improves the mechanical properties of hybrid natural fiber composites.     

我国竹材材性与加工利用研究新进展

简要介绍了竹类资源,竹材材性和加工利用的研究现状;重点分析了毛竹和其它竹种的材性,材性与培育和加工利用的相关关系;比较了现有竹质人造板产品、竹炭、竹纤维、竹醋液等研究概况.提出了关于竹材材性研究和利用的几点建议.     

竹木复合是高效利用竹材的重要途径

介绍了竹材人造板工业发展的现状,简要分析了目前竹材人造板工业发展中存在的几个主要问题,在此基础上,提出了竹木复合是高效、合理地利用竹材的重要途径的观点。     

ThermoMechanical Characterization of Calotropis gigantea Stem Powder-Filled Jute Fiber-Reinforced Epoxy Composites

Filler performs key tasks in enhancing the strength of the composites. Calotropis gigantea is a weed waste typically called White Madar, widely grown in Asian countries. It is ground to powder and used as filler. Thus the present work deals with the development of three different jute fiber reinforced epoxy composite filled without and with various weight proportion of Calotropis gigantea stem powder namely 5 and 10 weight percentage using conventional hand lay-up technique. The developed composites are tested for its mechanical properties as per ASTM standards and thermal stability using the Thermo Gravimetric Analyzer. The composite which is filled with 10 weight percentage Calotropis gigantea powder filler showed superior properties in both thermal and mechanical characteristics due to its higher filler content which possess constituents like cellulose, lignin, etc. Scanning Electron Microscopy helped to analyze the fiber pullout, fractured interface, filler distribution, voids of the composites.     

Experimental study on the bending fatigue behaviors of 3D five directional braided T-shaped composites

The static three-point bending properties and cyclic bending fatigue performances of three-dimensional five-directional braided T-beam composite (3D5DBTC) have been investigated at room temperature. The fatigue life of 3D5DBTC under different stress levels was analyzed based on the obtained S–N curves. The load–displacement hysteresis loops curves and stiffness degradation curves were recorded to reveal the relationship between stiffness degradation and damage evolution. It is shown that there were three distinct stages corresponding respectively to matrix cracks, interface debonding, and fiber breaking in the whole fatigue loading. In addition, to understand the ultimate fracture failure mechanism of 3D5DBTC under the different fatigue loading conditions, the damage morphologies of 3D5DBTC after fatigue testing were observed by macrographs and SEM micrographs. The matrix crack and the resin–yarns interface debonding occurred on the flange while fiber breakages occurred in the web. Meanwhile, macrographs and SEM images confirm that fiber breaking is the dominant damage under the high stress level, while matrix cracking and interfacial debonding are the main failure modes at low stress level.