单向不连续CF／PEEK复合材料结构参数与力学性能关系研究

采用有限元法建立了有关的单胞模型和相关的边界条件。着重研究了复合材料的结构参数与单向不连续碳纤维增强聚醚醚酮（ＣＦ／ＰＥＥＫ）复合材料的细观弹塑性应力应变的关系,分析了纤维重叠比、纤维中的不连续性对复合材料中纤维与纤维、纤维与周围基体相互作用以及应力场变化的影响。此外利用体积平均法预测了在外载荷作用下不同结构参数的单向不连续碳纤维增强复合材料的弹塑性应力－应变关系。     

热机械循环载荷下短纤维增强金属基复合材料性能分析

从复合材料内部组分的细观力学关系人手,选取代表体积元,基于Eshelby椭圆夹杂理论和瞬时体积平均的概念,通过集中张量描述纤维与基体以及纤维与纤维间的相互作用,并把在弹性范围内得到的各集中张量推广到弹塑性范围内,建立能够在弹塑性范围内分析热机械循环载荷作用下短纤维增强金属基复合材料的性质的模型。为了接近工程实际,假设纤维始终保持线弹性,对基体材料采用能反映bauschinger效应的混合硬化模型,依据基体的弹塑性状态决定复合材料整体的弹塑性状态。在塑性范围内,从各向异性的角度出发,采用增量法迭代得出每个加载步结束时复合材料整体以及各相的应力应变增量。编写控制应变和温度加载条件下,计算复合材料应力应变响应的程序,着重讨论纤维的外形、空间分布、体积百分比以及温度载荷对复合材料宏观性质的影响,并与相关的实验结果和数值结果进行比较。     

Al2O3-SiO2／AZ91D复合材料蠕变行为的研究

研究了Al2O3-SiO2短纤维增强AZ91D复合材料在不同温度下的蠕变性能。结果表明,Al2O3-SiO2／AZ91D复合材料具有良好的抗高温蠕变性能。显微分析发现,复合材料在蠕变过程中部分纤维发生断裂。纤维／基体界面处的缺陷和微裂纹在加载应力的作用下逐渐扩展,最终导致复合材料的蠕变断裂。     

湿热老化对纤维增强树脂基复合材料性能的影响及其机理

总结了纤维增强树脂基复合材料湿热条件下的吸湿行为及影响吸湿的因素;综述了湿热老化对复合材料耐热性能和力学性能的影响,分析了其作用机理。多数树脂基复合材料吸湿的初期阶段符合费克定律,吸湿会造成树脂基体的塑化、水解,产生裂纹以及纤维/树脂基体界面破坏,从而降低材料的性能。最后对纤维增强树脂基复合材料湿热老化研究提出了几点建议。     

陶瓷基复合材料低循环拉—拉疲劳寿命预测

采用细观力学方法建立预测纤维增强陶瓷基复合材料低循环拉—拉疲劳寿命的模型。该模型考虑初始加载到疲劳峰值应力时,基体出现裂纹,纤维/基体界面发生脱粘,部分纤维将发生断裂,并采用统计方法得到初始加载到峰值应力时的纤维失效体积分数;在后续循环过程中,考虑纤维相对基体在界面脱粘区滑移造成界面切应力下降,纤维失效模型与Evans界面磨损模型相结合,得到循环过程中纤维失效体积分数与界面切应力、循环数之间的关系;当纤维失效导致剩余强度下降,并小于疲劳峰值应力时,判断材料失效。采用剩余强度方法对陶瓷基复合材料的S-N曲线进行预测,并将预测的S-N曲线与试验数据进行对比,结果吻合较好。     

三维编织复合材料界面应力传递机理的数值分析

针对三维编织复合材料,在纤维/基体界面受力分析的基础上,以小段纤维的结构而建立的拉拔模型为理论依据,采用有限元分析软件对拉拔模型进行分析,得到了纤维/基体界面分别在不同载荷与不同埋入深度时出现的应力、应变和位移变化规律.结果与理论吻合,对于进一步改进三维编织复合材料的工艺流程及提高使用性能有一定的指导作用.     

纤维增强复合材料的刚性圆柱夹杂双周期分布模型的平面问题

对于硬夹杂一软基体的单向纤维增强复合材料，将纤维束看成刚性圆柱状夹杂，考虑夹杂间的相互影响，采用复变函数和坐标变换的方法，构造呈双周期分布且相互影响的刚性圆柱夹杂的复应力函数，同时满足夹杂的边界条件，利用围线积分将求解方程组化为线性代数方程组，推导出受到远场均匀拉应力的作用，双周期分布的刚性圆柱夹杂的界面应力表达式，算例给出双周期夹杂模型的界面应力值，并与单夹杂模型的界面应力最大值进行对比。     

3D-C/SiC复合材料的损伤机理

陶瓷基复合材料在热结构中潜在着许多用途 ,但对 3D C/SiC材料高温损伤尚不完全清楚。本工作用T3 0 0碳纤维编织为三维四向编织体 ,编织角 2 2° ,用CVI化学气相渗法在 95 0℃～ 10 0 0℃沉积热解碳界面层、SiC基体。最终得到纤维体积分数约为 40 %、热解碳界面层厚度约 0 .2微米和空隙率为 17%的复合材料 ,表面SiC涂层厚度为 5 0 μm。基体由于热应力和外力会产生许多微裂纹 ,用单向陶瓷基复合材料裂纹计算公式可大致估算出 3D C/SiC的基体开裂应力和裂纹间距。纤维束间的孔隙在蠕变中变形 ,孔隙表面基体易产生微裂纹 ,而且纤维束间的夹角不断改变。蠕变是损伤引起的 ,属于损伤蠕变机理。弯曲、断裂韧度、蠕变及疲劳等试验中 ,纤维束力图沿拉应力方向伸直 ,纤维束间相对滑动并产生损伤是细观主要的损伤机理。室温及疲劳循环应力低、循环周次多的断口粗糙度大 ,纤维拔出较长 ;高温及高应力、循环周次少的断口相对齐平 ,纤维拔出较短。纤维束与基体界面和纤维与基体界面的脱粘和滑动产生损伤中 ,以纤维束与基体之间的磨损产生的损伤为主要的 ,因此纤维束编织交叉处的损伤更大     

超声铣削复合材料应力场分析与试验研究

为解决复合材料难加工问题,本文采用超声铣削和普通铣削加工方法对复合材料进行试验研究。试验结果表明,在超声加工条件下,由于外加的周期性振动使铣削力大大减小,使得已加工表面产生较小的应力场,则纤维束和碳基体交界处微裂纹扩张速度减慢和分层不明显;而在普通加工条件下,由于产生较大的铣削力,则纤维束和基体交界处裂纹扩展迅速,且分层也十分明显,工件表面纹理质量很差。     

铸态Al18B4O33W/Al复合材料中基体的实际性能

根据X射线应力测量的基本原理，建立了复合材料基体拉伸应力与应变关系的试验方法，研究了铸态25%（体积分数）Al18B4O33W/6061Al复合材料中基体力学性能。结果表明：复合材料基体屈服强度及加工硬化系数明显高于单一基体材料，从而地复合材料基体实际性能及强化效应有了直接的认识。     

Effects of fiber aspect ratio evaluated by elastic analysis in discontinuous composites

An elastic stress analysis to investigate the effects of fiber aspect ratio in short fiber reinforced discontinuous composite materials has been done for different fiber volume fractions. In order to examine the elastic internal behavior, an evaluation of the load bearing capacity of discontinuous reinforcements is needed in advance. Accordingly, analytical derivation of composite mechanics has been carried out to predict fiber stresses and fiber/matrix interfacial shear stresses in discontinuous composites. The model is based on the theoretical development of conventional shear lag theory developed by Cox. However, the major shortcoming of the Cox model is due to the calculation without normal stress transfer from the end of fibers. In order to overcome the shortcoming, both of the normal and shear stress transfer mechanisms between the fiber and the matrix are accounted for with the stress concentration effects as well as material and geometrical properties. Results of predicted stresses concerning the various fiber aspect ratios are described by using the present model that is the closed form solution and compared with the Cox model and Taya model. It is found that the effect of fiber aspect ratio is significant to composite strengthening through load transfer from the matrix to the fiber, whereas the effect of fiber volume fraction is not so sensitive, relatively. It is also found that the present model has the capability to correctly predict the values of fiber stresses and fiber/matrix interfacial shear stresses.     

Analytical study on the elastic-plastic transition in short fiber reinforced composites

In discontinuous composites, the fiber end effects can be neglected when the length of fiber is much greater compared to the diameter. Thus, conventional shear lag theory is very useful for predicting composite properties deduced from each constituent. However, in the case of short fiber or whisker reinforced composites, the end effects cannot be neglected, and the composite properties are functions of material and geometrical parameters since the fiber end effects significantly influence the behavior of composites. For a good understanding of the behavior of short fiber or whisker reinforced composites, it is necessary to first understand the mechanism of stress transfer and it has well been modified before. However, the modification was limited to the basic elastic stress calculation of the fiber and matrix in a micromechanical model. Accordingly, the former modification of the shear lag model has been extended to predict the overall elastic composite behavior and elastic-plastic behavior of which result can predict the stress concentration in the matrix as well as the onset of matrix yielding. The extended modification results showed that it gives a good agreement with finite element analysis as well as with experimental data. It was also found that the local matrix yielding is initiated in the vincinity of the fiber ends which produces local plasticity and an elastic-elastic transition before the composite stress reaches matrix yield stress.     

Stress analysis of a composite material with short elastic fibre in power law creep matrix

An approximate stress analysis of a composite material, power law creep material (matrix) reinforced by an elastic short fibre is performed by modifying the Cox model, elastic monofibre in a unit cell of an elastic matrix. The numerical calculation is performed by using aluminium (6061)-SiC (whisker aspect ratio of 10). The result obtained by using the analysis is compared with that obtained by experiments performed by a previous investigator. The result shows that composite stress obtained by the analysis is compatible with that obtained by the experiment in order of magnitude, while stress exponent obtained by the experiment is much higher than that obtained by the analysis. A correction factor relating analytical to experimental results is found and the physical meaning of the factor associated with the actual deformation process is discussed. In addition to this analysis, a rigid fibre in power law creep material (matrix) is analysed. The fibre stress distribution obtained by the analysis is compatible with that obtained by the previous investigator.     

Analytical study on elastic transition in short-fiber composites for plane strain case

An analytical approach for short-fiber-reinforced composites is developed for three-dimensional (3D) elastic stress field distribution subjected to an applied axial load. Two sets of exact displacement solutions for matrix and fiber, which are respectively called far-field and transient solutions, are derived based on the theory of elasticity. The superposition state of these solutions are then used to obtain the analytical expressions for the 3D stress field components over the entire composite system, including the fiber end region, through the adding imaginary fiber technique. The fiber/matrix 3D stress field components fully satisfy the equilibrium and compatibility conditions in the theory of elasticity. The stress field components also satisfy the overall boundary, interface continuity, and axial force equilibrium conditions. The analytical results obtained are then validated by finite element method modeling.     

间断式复合材料结构参数和性能数学模型分析

在分析间断式纤维增强复合材料应力应变场理论模型的基础上，利用虚位移原理，建立了复合材料内在几何结构参数与其弹生模量间的解析表达式，分析了有关结构参数对复合材料弹性模量的影响；理论解与有限元解对比分析表明，两种计算方法获得的纤维长径比R、纤维重叠比η与复合材料弹性模量关系的变化趋势有好的一致性。表达式的建立对分析间断式复合材料本构关系具有重要意义。     

Ductile damage micromodeling by particles’ debonding in metal matrix composites

The elastic–plastic behaviour of particle-reinforced metal matrix composites undergoing ductile damage is modelled using a two-level micro-structural approach. The considered heterogeneous material is a polycrystal containing intra-crystalline elastic particles. Ductile damage is initiated by the matrix/particle interface debonding and the subsequent voids growth with plastic straining of the crystalline matrix. Homogenization techniques are used twice: first at mesoscale to derive the equivalent grain behaviour and then to obtain the macroscopic behaviour of the material. Plastic deformation of the crystalline matrix is due to crystallographic gliding on geometrically well-defined slip systems. The associative plastic flow rule and the hardening law are described on the slip system level. The evolution of micro-voids volume fraction is related to the plastic strain. The elastic–plastic stress–strain response of particle composite is investigated. Predictions of the proposed model are compared to experimental data to illustrate the capability of the suggested method to represent material behaviour. Furthermore, specific aspects such as the stress triaxiality and yield surfaces are discussed.     

An elastic-plastic stress analysis in silicon carbide fiber reinforced magnesium metal matrix composite beam having rectangular cross section under transverse loading

In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as 0°, 30°, 45°, 60° and 90°, The plastic zone expands more at the upper side of the composite beam than at the lower side for 30°, 45° and 60° orientation angles. Residual stress components ofσ _x andτ _xy are also found in the section of the composite beam.     

三维编织C/SiC复合材料弹性常数预报

基于纤维倾角模型 ,根据层合板理论推导出其弹性常数计算公式。三维编织C/SiC复合材料不同于树脂基复合材料 ,一是纤维模量低于基体模量 ,二是碳纤维在高温沉积热解碳和碳化硅后模量有较大幅度的下降 ,还有较多的空洞存在。考虑到这些因素对三维编织C/SiC复合材料弹性性能的影响 ,编制了相应的C语言计算程序 ,预报了三维编织C/SiC复合材料的纵向弹性性能 ,对程序计算结果进行了分析讨论。另外 ,通过力学实验来验证了理论分析的可靠性。     

金属材料的平面应力非连续分叉

对已有弹塑性体非连续分叉结果进行了修正 ,使其更为合理。在此基础上 ,基于统一屈服准则 ,得出了金属材料非连续分叉的起始方位角以及相应的硬化模量的统一解析解 ,并且分析了不同程度的中间主应力对结果的影响。进而发现所得的结果与屈服准则的选取有关 ,揭示了在分叉研究中正确选取符合金属材料特性的强度准则的重要性。     

MoS2/C复合涂层在不同对磨副下的冲击磨损行为研究

在基于动能控制的冲击磨损设备上,以球-平面接触的方式,探究304不锈钢基体和MoS_2/C复合涂层在不同对磨副冲击下的磨损行为,并分析摩擦界面响应及磨损机制。结果表明:随着冲击副材料的弹性模量增加,冲击接触峰值力以及能量吸收率逐渐上升,对应的磨损量及磨损率也随之提高;MoS_2/C复合涂层的接触应力、能量吸收率以及磨损均要低于304不锈钢基体;涂层的冲击磨损形式主要为材料的剥落与磨屑堆积,磨损机制为塑性变形以及摩擦氧化。