复合材料中加捻纤维束的预应力效应

利用加捻纤维束的力学性能,可以制成预应力复合材料.在不受外力的情况下,这种复合材料的基体受压应力的控制.当有拉伸力作用的时候,材料所受的拉应力值会大大减少,这样,利用这种现象可以提高纤维增强复合材料的抗拉强度.本文将分析连续的加捻纤维束受拉状况并考虑到材料固化后产生的残余应力的影响.这种方法所产生的预应力取决于纤维束的加捻程度.本文将给出计算这种预应力的方法,而且还提供加捻纤维束产生预应力的光弹测试结果以及这种纤维预应力复合材料的纤维破坏的特征.     

复合材料层合板粘弹性固化残余应力分析

基于Ｓｃｈａｐｅｒｙ积分型粘弹性本构关系，推导了考虑横向剪切效应的复合材料层合板线性热粘弹性有限元分析列式，对层合板的粘弹性响应和加工成型过程中的残余应力进行了分析，给出一些有意义的结果     

纤维复合材料界面横向拉伸分析

以单纤维十字型横向拉伸试验为研究对象,对纤维/基体界面采用弹性-软化双线性内聚力模型,建立了纤维复合材料在横向拉伸作用下界面法向失效过程的解析模型。得到了沿纤维/基体圆周界面的法向应力分布,纤维/基体界面的状态与界面承载力和单纤维复合材料承载力的关系,以及内聚力参数和试件几何尺寸对它们的影响。结果表明:纤维/基体圆周界面在脱粘前经历全部弹性及弹性+软化两种状态;当界面为弹性状态时,界面法向应力随界面强度线性增加;当界面为弹性+软化状态时,界面软化范围随界面裂纹萌生位移的增加而增大;界面初始脱粘位置与拉伸荷载方向重合;界面初始脱粘时的界面承载力随界面强度及界面裂纹萌生位移的增加而增加,随界面裂纹生成位移的增加而降低;单纤维复合材料的脱粘荷载受基体截面尺寸的影响,当纤维体积含量相同时,沿荷载方向截面尺寸的增大对提高脱粘荷载更显著。     

基于静强度分布参数的复合材料剩余强度及寿命预测

为探讨剩余强度及疲劳寿命与初始静强度分布参数之间的关系,构建基于初始静强度分布参数的剩余强度和疲劳寿命计算模型。在模型构建过程中未涉及复合材料结构的层数、铺层厚度和铺层方向,适应性强。模型参数可通过静力试验和剩余强度试验获得,试验成本相对疲劳试验较低。剩余强度和疲劳寿命与初始静强度变异系数及其分布参数有关,当初始静强度服从威布尔分布时,疲劳寿命亦服从威布尔分布,可为开展疲劳可靠性提供借鉴和参考。算例表明,基于建立的模型,剩余强度计算结果最大误差为-1.58%,疲劳寿命与试验数据吻合较好。     

Residual strain measurement in composites using the cure-referencing method

This paper describes the details of a novel procedure called the cure-referencing method (CRM) to measure the strains associated with residual stresses on the surface of composite panels. The CRM involves the replication of diffraction gratings onto the surface of composite specimens during the autoclave during cycle. Residual strains associated with the curing process are measured using moiré interferometry at room temperature after the specimens have been taken out of the autoclave. The procedures for both the grating replication and the moiré interferometry experiment are described in detail. A method of high-temperature moiré interferometry was developed to resolve the residual strains due to thermal expansion from those due to chemical matrix shrinkage and stress relaxation. These procedures are demonstrated on unidirectional and multidirectional laminates and on woven textile composites.     

复合材料层合板在加工固化后期降温速率对残余热应力的影响

本文采用非线性有限元方法，对材料性质与温度有关的复合材料层合板在加工固化后期降温过程中的温度速场和热应力场进行了分析，对降温度速率对板中固化残余热应力的影响进行了研究，获得一些对层合板固化成型工艺和固化残余热应力分析模型的选取均有意义的结果。     

Z-pin复合材料细观模型固化残余应力研究

针对植入Z-pin后碳纤维增强复合材料的微观结构,通过施加Z-pin周期性边界约束条件,建立了Z-pin复合材料单层板单胞细观模型．考虑固化过程中树脂体积收缩、弹性模量随固化度变化和纤维因Z-pin进入偏转因素,运用有限单元法计算了单胞结构在固化成型工艺过程中树脂和纤维应力发展和分布,并研究了Z-pin直径和分布密度对单层板面内残余应力的影响．结果表明：凝胶点之前,树脂模量和残余应力很小,凝胶点之后,树脂模量和残余应力增加较快;残余应力分布与纤维偏转有关;Z-pin直径和分布密度增加会使固化残余应力增大．     

布里渊光纤陀螺克尔效应误差消除方法

针对克尔效应对布里渊光纤陀螺输出结果的影响,建立了基于方波调制的布里渊光纤陀螺克尔效应理论模型.分析表明,由克尔效应引起的陀螺误差不仅与光纤环内两相反方向光束的光强差有关,还依赖于两路泵浦光频率调制的幅度.通过适当调节两光束的频率调制幅度,可有效实现克尔效应误差的消除.该方法实验装置简单,对调制频率要求低,是消除布里渊光纤陀螺克尔效应的有效方法.     

接触爆炸对底部有土垫层纤维混凝土板破坏效应试验研究

采用钢纤维混凝土、聚丙烯纤维混凝土、钢筋混凝土3种材料共24块板试件进行了接触爆炸试验。对试验现象进行了描述,由迎爆坑尺寸拟合分析得到了3种材料的爆炸介质压缩系数。采用ЛяхоB公式对试验测得的土压峰值进行了拟合分析,结果表明,随试件厚度的增加,砂土中应力波峰值衰减更显著,相同比例爆距的土压值明显减小,并由试验结果得到了底部有土垫层介质情况下混凝土板临界爆炸贯穿厚度计算公式。     

Numerical analysis of interface fatigue of fiber reinforced composites

A numerical analysis of the interface debonding process is carried out for fiber–matrix composites under cyclic loading. The results show that the interface friction plays an important role in resisting debonding under fatigue. The degradation coefficient of interface friction influences the debonding velocity. An approximate formula of interface friction is found for fatigue debonding.     

Elastic wave scattering and dynamic stress in composite with fiber

IntroductionTheproblemofscatteringofelasticwavesinsolidstructureshasnotonlytheoreticalsignificancebutalsowideoutlookinengineering .Thisproblemhasabsorbedmanypeople’sattentionsinmanyfieldssuchasaeronautics,compositemechanics,civilengineeringandearthquakeengineering[1～ 3 ] .Thepropagatingvelocityanddirectionofelasticwaveareinvariableasitpropagatesinaninfiniteuniformmedium .Butscatteringofelasticwavescanoccurifthereexistsincontinuitysuchasinclusion ,crackandcavityinelasticmedium .Fiber_reinfor…     

The homogenization method for the study of variation of Poisson's ratio in fiber composites

Summary Materials with specific microstructural characteristics and composite structures are able to exhibit negative Poisson's ratio. This fact has been shown to be valid for certain mechanisms, composites with voids and frameworks and has recently been verified for microstructures optimally designed by the homogenization approach. For microstructures composed of beams, it has been postulated that nonconvex shapes (with reentrant corners) are responsible for this effect. In this paper, it is numerically shown that mainly the shape, but also the ratio of shear-to-bending rigidity of the beams do influence the apparent (phenomenological) Poisson's ratio. The same is valid for continua with voids, or for composites with irregular shapes of inclusions, even if the constituents are quite usual materials, provided that their porosity is strongly manifested. Elements of the numerical homogenization theory and first attempts towards an optimal design theory are presented in this paper and applied for a numerical investigation of such types of materials. Received 11 March 1997; accepted for publication 12 September 1997     

湿热环境对挖补修理后复合材料层合板振动特性的影响

通过对湿热环境下阶梯挖补胶接修理后碳纤维/双马树脂(T300/QY8911)层合板振动特性的分析,探究了挖补修理后碳纤维/双马树脂层合板在不同湿热效应下的振动特性。基于Mindlin-Reissner板理论与最小势能变分原理,在考虑湿热效应前提下,推导了正交各向异性复合材料层合板的本构关系及四边简支条件下的自由振动控制方程;其次,利用ABAQUS软件建立了三维黏弹性有限元挖补修理模型,应用Fortran语言将湿热耦合下的应力-应变本构关系编入UMAT二次开发文件中,采用三维八节点五自由度等参单元进行了离散。通过与参考文献对照,验证了胶接修理后T300/QY8911层合板有限元模型和编译的湿热环境下UMAT子程序的合理性与有效性。算例结果表明:湿热环境对挖补修理后层合板固有频率的影响比对完整层合板严重;温度对材料性能的影响大于湿度;相比于材料性能变化对振动特性的影响,湿热残余应力对胶接修理后层合板振动特性的影响占主导;参考环境下,胶接修理后层合板的固有频率增大;湿应力对层合板固有频率的影响大于热应力。     

Measurement of residual internal stresses in optical fiber preforms

A non-destructive experimental procedure is presented which enables the determination of residual thermal stresses in optical fiber preforms. The procedure is based on integrated photoelasticity. We carry out the measurement of the optical retardation using the traditional Sénarmont compensation method combined with a fringe shifting technique. The radial distribution of the axial stress is reconstructed using Abel transform. We have investigated two different refractive-index profiles, adopted in the realization of monomode and multimode optical fibers. It was shown that in both cases the results obtained experimentally and those analytically predicted by the Timoshenko elastic model were in good agreement. To obtain accurate experimental results, it was necessary to apply a correction procedure to take into account the fact that the trafectories of the light rays inside the preforms are not straight lines.     

Micro-mechanical approximation to the stress field around an inclined fiber of FRCC

Matrix spalling or crushing is one of the important mechanisms of fiber-matrix interaction of fiber reinforced cementitious composites (FRCC). The fiber pullout mechanisms have been extensively studied for an aligned fiber but matrix failure is rarely investigated since it is thought not to be a major affect. However, for an inclined fiber, the matrix failure should not be neglected. Due to the complex process of matrix spalling, experimental investigation and analytical study of this mechanism are rarely found in literature. In this paper, it is assumed that the load transfer is concentrated within the short length of the inclined fiber from the exit point towards anchored end and follows the exponential law. The Mindlin formulation is employed to calculate the 3D stress field. The simulation gives much information about this field. The 3D approximation of the stress state around an inclined fiber helps to qualitatively understand the mechanism of matrix failure. Finally, a spalling criterion is proposed by which matrix spalling occurs only when the stress in a certain volume, rather than the stress at a small point, exceeds the material strength. This implies some local stress redistribution after first yield. The stress redistribution results in more energy input and higher load bearing capacity of the matrix. In accordance with this hypothesis, the evolution of matrix spalling is demonstrated. The accurate prediction of matrix spalling needs the careful determination of the parameters in this model. This is the work of further study.     

SMA复合材料在热载条件下的残余应力分析

本文基于三相复合圆柱模型发展了增量型的分析方法,讨论在ＳＭＡ复合材料中由于ＳＭＡ材料相变以及各相材料热特性随温度变化引起的残余应力。研究基体与过渡恸介面和纤维与过渡界面间的残余应力,同时讨论由于基体相的变化对残余应力的影响。特别研究了涂层和复合材料基体间界面处的残余应力受纤维体积比、涂层厚度、纤维最大相变应以及基体中纤维取向等影响,而且讨论了计及应力对相就运动方程的影响时对ＳＭＡ复合材料相变温度和     

分块法研究圆柱绕流升阻力

 使用新的分块耦合方法，分别对单圆柱和串列双圆柱绕流进行了数值 模拟. 对于单圆柱绕流，低$Re$下计算所得到的定常涡尺寸与实验非常接近. 对于 串列双圆柱绕流，研究分析了改变双圆柱中心间距对上下游圆柱的升阻力系数和脉动频率所 产生的影响，计算结果与实验非常吻合，为进一步研究涡致振动提供了依据.     

Compression-induced stiffness in the buckling of a one fiber composite

We study the buckling of a one fiber composite whose matrix stiffness is slightly dependent on the compressive force. We show that the equilibrium curves of the system exhibit a limit load when the induced stiffness parameter gets bigger than a threshold. This limit load increases when the stiffness parameter is increasing and it is related to a possible localized path in the post-buckling domain. Such a change in the maximum load may be very desirable from a structural stand point.     

Self-consistent methods in the problem of axial elastic shear wave propagation through fiber composites

Summary Two self-consistent schemes (effective medium method and effective field method) are applied to the problem of monochromatic elastic shear wave propagation through matrix composite materials containing cylindrical unidirected fibers. Dispersion equations of the mean wave field in such composites are derived by both methods. In the long-wave and short-wave ranges, analytical solutions of these equations are obtained and compared with each other, while numerical solutions are constructed for a wide range of frequencies. In particular, velocities and attenuation factors of the mean wave fields obtained by the two methods are compared for various volume concentrations, elastic properties and densities of inclusions in a wide range of frequencies of the incident field. The main discrepancies in the predictions made by the two methods are indicated, analyzed and discussed.     

聚酯纤维对透水沥青混凝土冲击压缩性能的影响

为研究聚酯纤维对透水沥青混凝土冲击压缩性能的影响,采用?74 mm钢质分离式霍普金森压杆装置对掺杂不同质量分数的聚酯纤维透水沥青混凝土进行冲击压缩实验。在静态和4个应变率下的实验结果表明,透水聚酯纤维沥青混凝土是应变率敏感性材料,具有较强应变率效应。透水聚酯纤维沥青混凝土具有较好的延展性,动态应力应变曲线分为3个阶段:弹性变形阶段、塑性变形阶段和破坏阶段。当应变率相同时,随着掺杂聚酯纤维质量分数的增大,透水沥青混凝土的冲击抗压强度呈现出先升高后降低的变化规律,掺杂聚酯纤维的质量分数为0.40%时,冲击抗压强度达到最大。冲击抗压强度约为静态抗压强度的8~13倍。