钢纤维对水泥基复合材料抗起裂特性的影响

通过不同钢纤维体积分数及不同试件尺寸的预制缺口三点弯曲梁断裂试验,研究了普通乱向及定向钢纤维增强水泥基复合材料的抗起裂特性。利用试验测得的荷载-裂缝口张开位移曲线,分析了钢纤维对水泥基复合材料断裂性能的影响,并基于线性相关系数陡降法计算了起裂韧度。结果表明,定向钢纤维增强水泥基复合材料的起裂韧度明显高于普通乱向钢纤维增强水泥基复合材料;起裂韧度随钢纤维体积分数的增加而逐渐增大,当钢纤维体积分数达到0.9%左右时,定向钢纤维增强水泥基复合材料的起裂韧度值趋于稳定;在本试件高度范围内(40~100mm),起裂韧度随试件尺寸增加而逐渐增大,且定向钢纤维增强水泥基复合材料的增长趋势较为平缓。此外,从裂缝尖端夹杂改变其应力强度因子的角度解释了钢纤维的掺入及定向对起裂韧度的提高作用。     

Mechanical behaviour and microstructural characterization of 3D four‐directional braided SiO2f/SiO2 composites

In this paper, SiO_2f/SiO₂ composites reinforced by 3D four‐directional braided quartz preform were prepared by the silica sol‐infiltration‐sintering method in a relatively low sintering temperature (450 °C). To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural and shear loading. The microstructure and the fracture behaviour of the 3D four‐directional braided SiO_2f/SiO₂ composites were studied. The tensile strength, flexural strength and the in‐plane shear strength were 30.8 MPa, 64.0 MPa and 22.0 MPa, respectively. The as‐fabricated composite exhibited highly nonlinear stress–strain behaviour under all the three types of loading. The tensile and flexural fracture mechanisms were fully discussed. The fracture mode of the 3D four‐directional braided SiO_2f/SiO₂ composite in the Iosipescu shear testing was based on a mixed mechanism because of the multi‐directivity of the composite. Owing to low sintered temperature, the fibre/matrix interfacial strength was weak. The SiO_2f/SiO₂ composites showed non‐catastrophic behaviour resulting from extensive fibre pull‐out during the failure process.     

微胶囊自修复复合材料断裂力学实验研究

测试了微胶囊自修复复合材料的基体和胶囊壳材料的断裂韧性,并分析了夹层模拟试件和含模拟胶囊试件的断裂特性,研究了胶囊壳材料与基体材料断裂韧性的匹配关系.结果表明:当基体材料与胶囊壳材料的断裂韧性差值小于107754.45 Pa·m1/2时,裂纹扩展时胶囊壳能够破裂.     

Comparison of Interlaminar Fracture Toughness in Unidirectional and Woven Roving Marine Composites

This paper investigates the effect of fibre lay-up and matrix toughness on mode I and mode II interlaminar fracture toughness (G_Ic and G_IIc) of marine composites. Unidirectional and woven roving fibres were used as reinforcements. Two vinyl ester resins with different toughness were used as matrices. Results from both modes showed toughness variation that is consistent with matrix toughness. Values of G_Ic were not significantly influenced by fibre lay-up except at peak load points in the woven roving/brittle-matrix composite. Each peak load point, caused by interlocked bridging fibres, signified the onset of unstable crack growth. For unidirectional specimens, crack growth was stable and G_Ic statistically more reliable than woven roving specimens, which gave fewer G_Ic values due to frequent unstable crack growth. Mode II tests revealed that, except for crack initiation, G_IIc was higher in woven roving composites. This was due to fibre bridging, perpendicular to the crack growth direction, which encouraged stable crack growth and increased energy absorption. Mode II R-curves were obtained for the woven roving specimens. These R-curves provide additional information useful for characterising delamination resistance. The paper concludes that composites with woven roving fibres show similar mode I delamination characteristics to the unidirectional composites; but their mode II delamination characteristics, after crack initiation, are quite different.     

Perspective Measurement of the Out‐of‐plane Displacement and Normal Strain Field Distributions Inside Glass Fibre‐reinforced Resin Matrix Composite

A depth‐resolved wavenumber‐scanning interferometer (DRWSI) was built up to measure the out‐of‐plane displacement and normal strain field distributions on the front surface, rear surface and internal glass fibres of a glass fibre‐reinforced resin matrix composite before and after loading. Series of the fringe patterns were recorded, while the wavenumber of the laser, monitored online by an optical wedge, was scanned by tuning the temperature. Random sampling Fourier transform is used to overcome the non‐linearity of the wavenumber series. In the end, the distributions of the out‐of‐plane displacements and normal strain field are presented as the applied loads were 10 µm, 20 µm and 30 µm, respectively. In conclusion, DRWSI is a suitable method to measure the mechanical properties inside resin composite non‐destructively.     

Interlaminar Fracture Toughness of CF/PEI and GF/PEI Composites at Elevated Temperatures

An experimental study has been conducted to assess temperature effects on mode-I and mode-II interlaminar fracture toughness of carbon fibre/polyetherimide (CF/PEI) and glass fibre/polyetherimide (GF/PEI) thermoplastic composites. Mode-I double cantilever beam (DCB) and mode-II end notched flexure (ENF) tests were carried out in a temperature range from 25 to 130°C. For both composite systems, the initiation toughness, G _IC,ini and G _IIC,ini, of mode-I and mode-II interlaminar fracture decreased with an increase in temperature, while the propagation toughness, G _IC,prop and G _IIC,prop, displayed a reverse trend. Three main mechanisms were identified to contribute to the interlaminar fracture toughness, namely matrix deformation, fibre/matrix interfacial failure and fibre bridging during the delamination process. At delamination initiation, the weakened fibre/matrix interface at elevated temperatures plays an overriding role with the delamination growth initiating at the fibre/matrix interface, rather than from a blunt crack tip introduced by the insert film, leading to low values of G _IC,ini and G _IIC,ini. On the other hand, during delamination propagation, enhanced matrix deformation at elevated temperatures and fibre bridging promoted by weakened fibre/matrix interface result in greater G _IC,prop values. Meanwhile enhanced matrix toughness and ductility at elevated temperatures also increase the stability of mode-II crack growth.     

玻纤增强尼龙6的断裂研究

通过对不同玻纤含量的玻纤增强尼龙复合材料(GFPA)的性能及断口形貌的研究,得出GFPA的宏观力学性能的变化可由断面形貌特征来定量表征。拉伸强度随拉伸断口断面平坦区面积与断面总面积之比AP/A0的变小而提高,Izod缺口冲击强度随GFPA的断面粗糙度参数RS的提高而线性提高。断面形貌的变化与玻纤在基体树脂中的应力集中作用及对裂纹扩展的阻碍作用有关。     

Effects of Fibre Geometry and Volume Fraction on the Flexural Behaviour of Steel‐Fibre Reinforced Concrete

Abstract: This work aims in studying the mechanical behaviour of concrete, reinforced with steel fibres of different geometry and volume fraction. Experiments include compression tests and four‐point bending tests. Slump and air content tests were performed on fresh concrete. The flexural toughness, flexural strength and residual strength factors of the beam specimens were evaluated in accordance with ASTM C1609/C1609M‐05 standard. Improvement in the mechanical properties, in particular the toughness, was observed with the increase of the volume fraction of steel‐fibres in the concrete. The fibre geometry was found to be a key factor affecting the mechanical performance of the material.     

增强双马来酰亚胺树脂基复合材料研究

石英纤维增强双马来酰亚胺树脂复合材料具有低介电损耗、耐高温、耐湿热及良好的力学性能。本文介绍了改性双马来酰亚胺树脂的分子结构与性能,及复合材料的模压成型工艺。     

中国聚酰胺生产、科研和市场概况

本文对国内聚酰胺 (尼龙 )工程塑料的生产、科研和市场现状作了调查统计 ,并分析了发展走向     

关于横观各向同性体在其各向同性面内弹性问题的一个常数

研究了在平面应力和平面应变情况下, 横观各向同性材料在其各向同性面内的应力2应变关系以及用位移表达的平衡方程可以被表示成与各向同性材料完全相同的形式。这种等同关系是通过引入一个与横观各向同性材料的泊松比有关的常数得到的。该常数的引入消除了已发表的文献中求解横观各向同性材料平面问题时出现的矛盾。这个常数的引入也便于正确计算单向纤维增强复合材料的横向切变模量。      

压力作用下横向短纤维与基体间应力传递机理研究

在短纤维增强复合材料的研究中,弄清界面应力传递机理对于认识短纤维的增强机理及短纤维复合材料的力学性能是十分重要的。但传统的观点认为,在钢纤维混凝土中纤维对混凝土抗压强度的增强作用甚微,故对压力下纤维与基体界面应力传递没有进行过研究。作者最近的试验研究与近年来的研究[1,3]均表明,中、高含量短钢纤维对混凝土的立方体抗压强度有大幅度提高。基于这一新的试验事实,作者在本文中对压力作用下横向短纤维与基体之间界面的应力传递进行了理论分析,得出了短纤维端部附近的应力分布。     

Interfacial damage in fibre‐reinforced composites subjected to tension fatigue loading

ABSTRACT The interfacial behaviour of fibre‐reinforced composites subjected to tension fatigue loading is studied based on the shear‐lag model. The governing equations of this problem are obtained and solved. In order to describe the interfacial debonding, the Paris fatigue crack growth formula as well as a modified degradation model for the coefficient of friction is adopted. Finally some important values related to interfacial debonding are obtained. In the present investigation, Poisson's contraction is considered.     

TiO2中性水溶胶的制备及其在玻璃纤维增强水泥基材料表面的光催化自洁性能研究

最近实现建筑幕墙的自清洁已经受到了人们的极大关注。首先使用Ti(SO4)2作为原料,采用H2O2解胶法在回流条件下合成了具有光催化活性的TiO2中性光触媒溶胶。同时将TiO2溶胶在玻璃纤维增强水泥基材料(GRC)表面涂覆成膜,研究了其光催化降解罗丹明B的能力。通过实验证明:制备的二氧化钛水溶胶光触媒活性组分TiO2的粒径仅为几纳米且分布均匀,溶胶的稳定性很好,长时间存放后不会沉淀。合成的纳米二氧化钛水溶胶呈中性,可以很好地涂覆于GRC表面,并且在紫外光下具有较好的光催化能力和自清洁性能。     

Rehabilitation of Composite Steel Bridges Using GFRP Plates

The current study is a part of an extensive research program conducted to assess the use of Glass Fibre Reinforced Plastic (GFRP) sheets in enhancing the flexural capacity of steel beams. The properties of a heavy-duty adhesive system that can be used to bond GFRP sheets to the flanges of steel beams were experimentally determined in a previous study. The excellent performance of a W-shaped steel beam strengthened using GFRP sheets has encouraged the authors to assess the applicability of this technique to composite steel bridges.The dimensions and cross section properties of a real composite steel plate girder bridge are considered in a case study analysis. A detailed nonlinear numerical model is developed for the bridge before and after attaching GFRP sheets to the bottom flange of its steel girders. Nonlinear moving load analyses are first conducted to determine the critical truck locations that will lead to maximum GFRP axial stresses, and maximum adhesive shear and peel stresses. Using these configurations, nonlinear analyses are then conducted to assess the increase in the bridge capacity that can be achieved by bonding 38 mm GFRP sheet to the bottom flange of its steel girders.     

Interlaminar Fracture Toughness of Carbon Fibre‐Reinforced Polymer Laminates With Nano‐ and Micro‐Fillers

Abstract: Vapour growth carbon nanofibres (CNF) and lead zirconate titanate (PZT) piezoelectric particles were added in the matrix of carbon fibre‐reinforced polymer laminates. The fracture toughness of the modified composites was measured under mode I and mode II loading and compared with plain epoxy carbon fibre‐reinforced composites. The mode I fracture toughness of the composites improved with the incorporation of the carbon nanofibres and deteriorated with the incorporation of PZT piezoelectric particles. When both fillers were added in the composite matrix, the mode I fracture toughness improved but to a lesser extend. The mode II fracture toughness of the modified composites was improved in all three cases. The aforementioned behaviour was attributed to competing fracture mechanisms instigated by the different fillers, and backed by fractographic evidence from the failed composite coupons; during the tests, the acoustic emission activity of the coupons was monitored and classified in three major energy absorbing mechanisms which were attributed to the failure of distinct composite phases.