Mechanical and thermal properties of sisal fiber-reinforced rubber seed oil-based polyurethane composites

The development of high-performance composite materials from locally sourced and renewable materials was investigated. Rubber seed oil polyurethane resin synthesized using rubber seed monoglyceride derived from glycerolysis of the oil was used as matrix in the composite samples. Rubber seed oil-based polyurethane composite reinforced with unidirectional sisal fibers were prepared and characterized. Results showed that the properties of unidirectional fiber-reinforced rubber seed oil-based polyurethane composites gave good thermal and mechanical properties. Also, the values of tensile strengths and flexural moduli of the polyurethane composites were more than tenfold and about twofold higher than un-reinforced rubber seed oil-based polyurethane. The improved thermal stability and the scanning electron micrographs of the fracture surface of the composites were attributed to good fiber–matrix interaction. These results indicate that high-performance “all natural products” composite materials can be developed from resources that are readily available locally.     

氧化石墨烯/再生水泥基复合材料的制备

基于建筑垃圾再生细骨料替代天然砂,进行氧化石墨烯(GO)改性再生水泥基复合材料的综合物理性能和水化机制研究。采用超声分散GO及振动搅拌制备再生水泥基复合材料,综合耐久性能测试结果表明:和不掺GO再生水泥基复合材料相比,添加0.03% GO改性7 d龄期强度的GO/再生水泥基复合材料抗折和抗压强度分别提高了16%和21%;添加0.02% GO改性的28 d龄期强度的GO/再生水泥基复合材料抗折和抗压分别提高了13.7%和13.6%。GO/再生水泥基复合材料龄期7 d耐候、50次冻融循环后力学性能均良好;氯离子含量皆小于0.06%。放射性检测结果表明:GO/再生水泥基复合材料内照射指数I_Ra和外照射指数I_r均属于A类建筑材料。通过XRD、TG-DTA、SEM等手段对GO/再生水泥基复合材料水化机制研究表明:GO促进了钙矾石(AFt)晶体的大量生成及胶凝孔中存在更多的自由水,且对后期氢氧化钙(CH)的产生有抑制作用,进而提高了GO/再生水泥基复合材料综合物理性能。      

Plant-based natural fibre reinforced cement composites: A review

The quest for sustainability in construction material usage has made the use of more renewable resources in the construction industry a necessity. Plant-based natural fibres are low cost renewable materials which can be found in abundant supply in many countries. This paper presents a summary of research progress on plant-based natural fibre reinforced cement-based composites. Fibre types, fibre characteristics and their effects on the properties of cement-based materials are reviewed. Factors affecting the fresh and hardened properties of cement-based composites reinforced with plant-based natural fibre are discussed. Measures to enhance the durability properties of cement-based composites containing plant-based natural fibres are appraised. Significant part of the paper is then focused on future trends such as the use of plant-based natural fibres as internal curing agents and durability enhancement materials in cement-based composites. Finally, applications and recommendations for future work are presented.     

Three dimensional (3D) fabrics as reinforcements for cement-based composites

This research studied the flexural behavior of cement-based elements reinforced with 3D fabrics. The effects of the through-thickness (Z direction) yarns were examined in terms of four parameters: (i) yarn properties, (ii) varying the composite content of (i.e., coverage by) high-performance aramid yarn, (iii) treatment of the fabric with epoxy, and (iv) 2D and 3D fabric composites were compared. Overall, the 3D fabric composites performed better than the 2D fabric composites, which tended to delaminate. Our results indicate that even though the Z yarns are not oriented in the direction of the applied loads, 3D fabrics still have potential applications as reinforcements for cement-based composites. Indeed, the Z yarns hold the entire fabric together, which leads to improved mechanical anchoring and mechanical properties particularly when the fabric has been treated with epoxy, i.e., to create a stiff reinforcing unit.     

氧化石墨烯增强水泥基复合材料的力学性能及微观结构

本文采用改进的Hummers法制备了氧化石墨烯（Graphene oxide,GO）悬浮液,通过FTIR、XRD和AFM等测试技术对GO晶体结构和尺寸形态进行了表征,考察了GO掺量和水灰比的变化对GO增强水泥基复合材料力学性能和微观结构的影响。结果表明：GO增强水泥基复合材料抗折抗压强度随GO掺量增加而先提高后降低,且对于抗折强度增强效果远超过抗压强度,当GO掺量为0.03%时,抗折强度达到最大值13.72 MPa;高水灰比条件下掺入GO对水泥胶砂强度的提高更显著;通过SEM对GO增强水泥基复合材料微观结构进行表征,发现GO能够优化水泥水化产物的微观结构形态,细化晶体尺寸,形成更加致密均匀的网络结构,从而改善水泥基复合材料的宏观性能。     

Development of a new constitutive model considering the shearing effect for anisotropic progressive damage in fiber-reinforced composites

A corrected Linde's criterion considering the shearing effect for anisotropic progressive damage is developed to describe the elastic-brittle behavior of fiber-reinforced composites. Based on this criterion, a new three-dimensional (3D) nonlinear finite element model for static damage of unidirectional fiber-reinforced composites is proposed within a framework of continuum mechanics. The model is validated by taking 3D braided composites as example to study the relationship between the damage of materials and the effective elastic properties. The impregnated unidirectional composites are treated as homogeneous and transversely isotropic materials, whose properties are calculated by the Chamis' equations. The more accurate failure mechanisms of composites are revealed in the simulation process, and the effects of braided parameters on the uniaxial tensile behavior of 3D braided composites are investigated. Comparison of numerical results and experimental data is also carried out, which shows a better agreement than that of former study using the 3D Hashin's criterion.     

纤维编织网增强混凝土补强隧道衬砌力学性能研究

纤维编织网增强混凝土(TRC)是一种新型高性能纤维增强水泥基复合材料,用它补强隧道衬砌可以有效地克服粘贴碳纤维布法的缺点。该文提出了纤维编织网增强混凝土补强隧道衬砌正截面受力全过程分析方法,并开展了验证试验。在此基础上,分析了衬砌截面偏心距、配网率、前期受力历史、钢筋和混凝土强度对纤维编织网增强混凝土补强隧道衬砌正截面承载性能的影响,最后探讨了纤维编织网补强隧道衬砌的破坏模式并给出了合理配网率区间。研究结果表明:衬砌截面偏心距、配网率和混凝土强度越大,前期受力历史和钢筋强度越小,补强效果越明显。     

连续纤维增韧陶瓷基复合材料可持续发展战略探讨

连续纤维增韧陶瓷基复合材料(CMC)是航空航天等高科技领域发展不可缺少的材料。其中, 连续纤维增韧碳化硅陶瓷基复合材料(CMC-SiC)是研究最多、 应用最成功的一种。本文作者以CMC-SiC为例, 介绍了该材料的战略需求与应用领域, 详细分析了国内外的应用研究现状及发展趋势, 并对我国陶瓷基复合材料面临的机遇与挑战, 以及发展战略进行了探讨。      

Crack growth resistance of hybrid fiber reinforced cement composites

Crack propagation in cement-based matrices carrying hybrid fiber reinforcement was studied using contoured double cantilever beam (CDCB) specimens. Influence of fiber type and combination was quantified using crack growth resistance curves. It was demonstrated that a hybrid combination of steel and polypropylene fibers enhances the resistance to both nucleation and growth of cracks, and that such fundamental fracture tests are very useful in developing high performance hybrid fiber composites. The influence of number of variables which would otherwise have remained obscured in normal tests for engineering properties become apparent in the fracture tests. The paper emphasizes the desired durability characteristics of these composites and discusses their current and future applications.     

Reliability of fiber-reinforced composite laminate plates

Many engineering structures ranging from aircrafts, spacecrafts and submarines to civil structures, automobiles, trucks and rail vehicles, require less weight and more stiff and strong materials. As a result of these requirements, the use of composite materials has increased during the past decades. In fact during the past five years, we have witnessed exponential growth in research and field demonstrations of fiber-reinforced composites in civil engineering. Manufacturers and designers have now access to a wide range of composite materials. However, they face great problems with forecasting the reliability of composites materials. Due to the differences among the properties of materials used for composites, manufacturing processes, load combinations, and types of environment, the prediction of reliability of composites is a very complex task. In this study, the reliability of fiber-reinforced composite laminate plates under random loads is investigated. The background of the problem is defined, the failure criterion chosen is presented, and the probability of failure is computed by Monte Carlo simulation.     

Application of rock wool waste in cement-based composites

This study investigates the properties of cement-based composites with addition of various rock wool wastes. The rock wool wastes are an insulating material. This study used rock wool waste with a cylindrical size distribution ranging from 17 to 250 μm, 30% of which is less than 150 μm. Rock wool waste can be used as a suitable substitute for coarse and fine aggregates, saving on the cost of natural aggregates and minimizing the environmental impact of solid waste disposal. In addition, because the composition of rock wool waste is similar to other pozzolan materials such as fly ash, ground granulated blast-furnace slag (GGBS), and silica fume, it can be considered as a supplementary cementitious material. Experimental results show that partially replacing natural aggregates with rock wool wastes improves the compressive strength, splitting tensile strength, abrasion resistance, absorption, resistance to potential alkali reactivity, resistivity, and chloride-ion penetration of cement-based composites. These improved properties are the result of the dense structure achieved by the filling effect of pozzolanic product. Pozzolanic strength activity index (PSAI) results and scanning electron microscope (SEM) observations confirm these findings. Therefore, rock wool wastes can act as either a cementitious material or inert filler in cement-based composites, depending on the particle size. The critical size appears to be 75 μm.     

Calcium phosphate cement scaffolds with PLGA fibers

The use of calcium phosphate-based biomaterials has revolutionized current orthopedics and dentistry in repairing damaged parts of the skeletal system. Among those biomaterials, the cement made of hydraulic grip calcium phosphate has attracted great interest due to its biocompatibility and hardening “in situ”. However, these cements have low mechanical strength compared with the bones of the human body. In the present work, we have studied the attainment of calcium phosphate cement powders and their addition to poly (co-glycolide) (PLGA) fibers to increase mechanical properties of those cements. We have used a new method that obtains fibers by dripping different reagents. PLGA fibers were frozen after lyophilized. With this new method, which was patented, it was possible to obtain fibers and reinforcing matrix which furthered the increase of mechanical properties, thus allowing the attainment of more resistant materials. The obtained materials were used in the construction of composites and scaffolds for tissue growth, keeping a higher mechanical integrity.     

石墨烯及其衍生物掺配水泥基材料研究进展

石墨烯及其衍生物因其独特的结构及优异的性能在改善基水泥材料的抗拉强度、韧性、耐久性及赋予水泥基材料功能性等方面表现出良好的应用前景.本文简述了石墨烯、氧化石墨烯(GO)的结构特点及性能,归纳了各自的制备方法;对石墨烯及其衍生物在水泥基材料中的分散进行了综述;重点综述了石墨烯及其衍生物掺配水泥基材料的力学性能、流变性能、...     

Modeling of interface cracks in fiber-reinforced composites with the presence of interphases using the boundary element method

An advanced boundary element method (BEM) with thin-body capabilities was developed recently for the study of interphases in fiber-reinforced composite materials (Y.J. Liu, N. Xu and J.F. Luo, Modeling of interphases in fiber-reinforced composites under transverse loading using the boundary element method, ASME J. Appl. Mech. 67 (2000) 41–49). In this BEM approach, the interphases are modeled as thin elastic layers based on the elasticity theory, as opposed to spring-like models in the previous BEM and some FEM work. In the present paper, this advanced BEM is extended to study the interface cracks at the interphases in the fiber-reinforced composites. These interface cracks are curved cracks between the fiber and matrix, with the presence of the interphases. Stress intensity factors (SIFs) for these interface cracks are evaluated based on the developed models. The BEM approach is validated first using available analytical and other numerical results for curved cracks in a single material and straight interface cracks between two materials. Then, the interface cracks at the interphases of fiber-reinforced composites are studied and the effects of the interphases (such as the thickness and materials) on the SIFs are investigated. As a special case, results of the SIFs for sub-interface cracks are also presented. It is shown that the developed BEM is very accurate and efficient for the interface crack analyses, and that the properties of the interphases have significant influences on the SIFs for interface cracks in fiber-reinforced composites.     

Matrix solidification and the resulting residual thermal stresses in composites

The disparate thermal expansion properties of the fibres and matrices in high-performance composites lead to an inevitable build up of residual thermal stresses during fabrication. We first discuss the thermal expansion behaviour of thermoplastic and thermoset polymers that may be used as high-performance composite matrices. The three classes of polymers considered are epoxies, amorphous thermoplastics, and semicrystalline thermoplastics. The relevant thermal expansion data for prediction of the magnitude of the residual stresses in composites is the zero (atmospheric)-pressure thermal expansion data; these data are plotted for a range of thermoplastics and a typical epoxy. Using the technique of photoelasticity, we have measured the magnitude of the residual stresses in unidirectional graphite composites with an amorphous thermoplastic matrix (polysulfone) and with an epoxy matrix (BP907). The temperature dependence of the residual stress build up and the resulting magnitude of the residual stresses correlate well with the thermal and physical properties of the matrix resin.     

Low-velocity flexural impact response of fiber-reinforced aerated concrete

Impact response of fiber-reinforced aerated concrete was investigated under a three-point bending configuration based on free-fall of an instrumented impact device. Two types of aerated concrete: plain autoclaved aerated concrete (AAC) and polymeric fiber-reinforced aerated concrete (FRAC) were tested. Comparisons were made in terms of stiffness, flexural strength, deformation capacity and energy absorption capacity. The effect of impact energy on the mechanical properties was investigated for various drop heights and different specimen sizes. It was observed that dynamic flexural strength under impact was more than 1.5 times higher than the static flexural strength. Both materials showed similar flexural load carrying capacity under impact, however, use of 0.5% volume fraction of polypropylene fibers resulted in more than three times higher flexural toughness. The performed instrumented impact test was found to be a good method for quantifying the impact resistance of cement-based materials such as aerated concrete masonry products.     

Effect of compressive strain on electrical resistivity of carbon black-filled cement-based composites

This paper investigates the strain sensing properties of carbon black (CB)-filled cement-based composites which were prepared with 120 nm CB. A linear relationship between the fractional change in resistivity and compressive strain was observed for cement-based composites containing a large amount of CB, suggesting that this kind of composite was a promising candidate for strain sensors used in concrete structures. Tunneling effect theory and percolation theory are employed to interpret the conductivity and electromechanical properties of CB-filled cement-based composites.     

Can nanotechnology be ‘green’? Comparing efficacy of nano and microparticles in cementitious materials

The use of nano-sized particles in cementitious materials introduces a myriad of potential innovations from new functionality to enhanced mechanical performance, but such materials can be energy-intensive to manufacture. With increasing emphasis on sustainable development, it is important to investigate and understand benefits and costs of using nanomaterials compared to relatively less energy-intensive microparticles. The current research investigates the effect of chemically inert nano and microparticles (i.e., titanium dioxide (TiO₂) and calcium carbonate (limestone)) on early age properties and behavior of cement-based materials. Results indicate that the early age hydration rates, shrinkage, and pore structure of cement-based materials can be modified and optimized by tailoring the size of fillers. Life cycle analysis indicates that photocatalytic reactivity of TiO₂ could offset initial higher environmental impacts. Thus, optimally sized nanoparticles could revolutionize the construction industry by allowing tailoring of structure and properties of cement-based composites, with environmental sustainability preserved through the selection of lower embodied-energy particles.     

先驱体浸渍-裂解法制备SiBN纤维增强SiBN陶瓷基复合材料

连续纤维增强氮化物陶瓷基复合材料是耐高温透波材料的主要发展方向,纤维是目前制约耐高温透波复合材料发展的关键,而SiBN陶瓷纤维是一种兼具耐高温、透波、承载的新型陶瓷纤维。以聚硅氮烷为陶瓷先驱体,以SiBN连续陶瓷纤维为增强体,采用先驱体浸渍-裂解法制备了SiBN陶瓷纤维增强SiBN陶瓷基复合材料,研究了复合材料的热膨胀特性、力学性能、断裂模式以及微观结构。结果表明:SiBN陶瓷纤维增强SiBN陶瓷基复合材料呈现明显的脆性断裂特征,复合材料的弯曲强度和拉伸强度分别为88.52 MPa和6.6 MPa,纤维的力学性能仍有待于提高。     

Friction and wear behavior of carbon fiber reinforced brake materials

A new composite brake material was fabricated with metallic powders, barium sulphate and modified phenolic resin as the matrix and carbon fiber as the reinforced material. The friction, wear and fade characteristics of this composite were determined using a D-MS friction material testing machine. The surface structure of carbon fiber reinforced friction materials was analyzed by scanning electronic microscopy (SEM). Glass fiberreinforced and asbestos fiber-reinforced composites with the same matrix were also fabricated for comparison. The carbon fiber-reinforced friction materials (CFRFM) shows lower wear rate than those of glass fiber- and asbestos fiber-reinforced composites in the temperature range of 100°C-300°C. It is interesting that the frictional coefficient of the carbon fiber-reinforced friction materials increases as frictional temperature increases from 100°C to 300°C, while the frictional coefficients of the other two composites decrease during the increasing temperatures. Based on the SEM observation, the wear mechanism of CFRFM at low temperatures included fiber thinning and pull-out. At high temperature, the phenolic matrix was degraded and more pull-out enhanced fiber was demonstrated. The properties of carbon fiber may be the main reason that the CFRFM possess excellent tribological performances.