界面脱粘对正交铺设SiC/CAS复合材料基体开裂的影响

采用细观力学方法研究了正交铺设SiC/CAS复合材料在单轴拉伸载荷作用下界面脱粘对基体开裂的影响。采用断裂力学界面脱粘准则确定了0°铺层纤维/基体界面脱粘长度, 结合能量平衡法得到了主裂纹且纤维/基体界面发生脱粘(即模式3)和次裂纹且纤维/基体界面发生脱粘(即模式5)的临界开裂应力, 讨论了纤维/基体界面剪应力、 界面脱粘能对基体开裂应力的影响。结果表明, 模式3和模式5的基体开裂应力随纤维/基体界面剪应力、 界面脱粘能的增加而增加。将这一结果与Chiang考虑界面脱粘对单向纤维增强陶瓷基复合材料初始基体开裂影响的试验研究结果进行对比表明, 该变化趋势与单向SiC增强玻璃陶瓷基复合材料的试验研究结果一致。     

界面相性态对纤维增强复合材料内应力传递的影响

本文用有限元法研究了具有基体裂纹的纤维增强复合材料内的应力传递问题.假设纤维与基体的界面为非理想的,文中运用“弹簧层”模型首先分析了在不同的组分弹性模量比、纤维体积含量与边界约束条件下,界面相性态对复合材料内的应力传递的影响,然后进一步考察了在几种典型的损伤模式下界面附近的应力分布情况.     

拉应力对玻璃纤维增强聚合物基复合材料介电强度的影响

在拉应力条件下, 测试了聚合物基体和单向玻璃纤维增强聚合物基复合材料的介电强度, 探索了聚合物基体和玻璃纤维/聚合物复合材料的介电强度与拉应力的关系, 提出并证明了聚合物基体的介电强度与拉应力呈负指数关系, 复合材料中纤维与基体的界面是影响材料介电强度的主要因素。     

单纤维VS复合物纤维应力传递

纤维复合材料的力学特性很大程度上依赖于纤维和基体的应力传递。本文建立了单纤维和复合物纤维平面拉伸轴对称有限元模型，它考察了纤维拉伸时伴随基体破裂、界面分离以及基体破裂与界面分离同时发生时的应力传递特性，计算结果给出具有参考价值的有益结论。     

纤维与基体界面剪切强度研究

采用微脱粘法,在改装的光学显微镜下测得复合材料单根纤维与基体界面发生微脱粘时的微脱粘力。在建立单根纤维—基体—复合材料的层套细观力学模型基础上,依据复合材料最大应力失效判据,使用自行设计的专门有限元分析程序,对已发生微脱粘界面进行分析,从而得到单根纤维与基体界面剪切强度。      

多向细编碳／碳复合材料界面力学性能测试与表征

本文用自制装置研究了多向细编Ｃ／Ｃ复合材料纤维束性能，分析了工艺过程的影响。同时用界面微脱粘实验技术研究了Ｃ／Ｃ复合材料界面性能，给出了相应的理论模型和界面应力分布，提出了由界面脱粘力，纤维、基体和复合材料性能表征界面剪切强度的方法，为Ｃ／Ｃ复合材料优化设计提供了定量参数。结果表明：织物结构、织物编织工艺以及织物／基体复合对纤维的强度影响很大，降为原始纤维的２０％左右，对模量影响小。不同界面层次，纤维／基体的界面结合情况和界面剪切强度不同，Ｚ向纤维束中纤维／基体结合好，具有最高的结合强度，ＳＥＭ观察证实有大量基体碳在纤维上枝联。     

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     

云母和纤维组合增强聚丙烯复合材料Ⅱ.界面性能研究

用单丝拔出法测定了云母和纤维组俣增强聚丙烯合材料中纤维与基体之间的界面结合强度，测定了云母和纤维组合增强聚丙烯复合材料的结晶温度，动态储存模量和线膨胀系数，并计算了纤维因基体体积收缩而形成的径向热残余压缩应力和基体与纤维之间的摩擦系数，研究了云母对纤维和基体界面性能的影响，结果表明，云母的加入使纤维受到的残余应力增加，摩擦系数显著下降，导致基体与纤维界面的结合强度随云母含量的增加先上升后下降。     

模型氧化铝单纤维复合材料的界面应力传递

用热压方法制作了模型氧化铝单纤维复合材料，使用激光荧光光谱研究了拉伸状态下纤维和基体间界面的应力传递行为。     

单向纤维增强陶瓷基复合材料单轴拉伸行为

采用细观力学方法对单向纤维增强陶瓷基复合材料的单轴拉伸应力-应变行为进行了研究。采用Budiansky-Hutchinson-Evans（BHE）剪滞模型分析了复合材料出现损伤时的细观应力场,结合临界基体应变能准则、应变能释放率准则以及Curtin统计模型三种单一失效模型分别描述陶瓷基复合材料基体开裂、界面脱粘以及纤维失效三种损伤机制,确定了基体裂纹间隔、界面脱粘长度和纤维失效体积分数。将剪滞模型与3种单一失效模型相结合,对各个损伤阶段的应力-应变曲线进行模拟,建立了准确的复合材料强韧性预测模型,并讨论了界面参数和纤维韦布尔模量对复合材料损伤以及应力-应变曲线的影响。与室温下陶瓷基复合材料单轴拉伸试验数据进行了对比,各个损伤阶段的应力-应变、失效强度及应变与试验数据吻合较好。     

Load carrying characteristics of short fiber composites containing a heterogeneous interphase region

A micromechanics finite element model has been developed for the stress transfer in short fiber composites, incorporating a heterogeneous interphase region. The specimen consists of a single fiber under stress embedded in an epoxy matrix. Considering a heterogeneous and compliant interphase, a generalized computational procedure has been developed that enables imperfect adhesion or loss of interphasial strength simulations. Varying the global variables of the problem, parametric studies were performed to study the influence of the model parameters on the load transfer characteristics from the fiber to matrix. Numerical results of the stress distribution have been determined as a function of geometric and material variables. The effect of both the imperfect adhesion between the fiber and the matrix, and the loss of interphase compliance on stress state were demonstrated and discussed. The results showed that the interphase plays a significant role in stress transfer characteristics of fibrous composites, and extension of the load transfer zone is restricted very close to the loaded fiber end.     

陶瓷基复合材料多层界面相应力传递的有限元模拟

针对陶瓷基复合材料（CMCs）多层界面相的应力传递进行了有限元模拟。采用圆柱单胞模型描述CMCs的细观结构,按相应界面相亚层的实际厚度建立明确的界面相,并假设界面相亚层之间及界面相与纤维、基体之间初始完好结合,然后赋予各界面相亚层不同的材料参数,并采用轴对称有限元法进行求解,最终建立了多层界面应力传递的模拟方法。分别对比了不同厚度热解碳（PyC）界面相、PyC和SiC两种不同成分界面相及（PyC/SiC）和（SiC/PyC）两种结构界面相的应力传递模拟结果。从剪应力沿纤维方向分布及径向分布特点可以看出,通过合理配置CMCs内部多层界面相的结构、成分和厚度,可以实现界面相应力传递及失效模式的控制和优化。     

Micromechanics of stress transfer through the interphase in fiber-reinforced composites

A micromechanical model to predict the interphasial/interfacial stress transfer in a three-phase fiber-reinforced composite is presented. The axisymmetric system consists of a fiber embedded in a compliant matrix having an interphase between them. Each constituent of the composite is regarded as a linear elastic continuum. The matrix is treated as an isotropic material while the fiber and interphase are considered as a transversely isotropic material. Traction-free boundary conditions are strictly enforced. It is assumed that the interfaces are perfect and strong. A pair of uncoupled governing partial differential equations is obtained in terms of unknown displacements. Furthermore, assuming that the Eigenvalues exist for this system of equations, Eigenfunction expansion method is employed to derive an exact solution in terms of the Bessel functions. Analytical solutions are obtained for free boundary conditions at the external surface of the matrix cylinder to model a single fiber pull-out problem, and for fixed boundary conditions to approximately model a hexagonal array of fibers in the matrix material. This formulation provides an analytical framework for the analysis of interphasial and interfacial stresses as well as displacements in the entire 3D axisymmetric system. Finite element (FE) analysis was also performed to simulate stress transfer from the fiber to the matrix through the interphase. Analytically obtained stress fields are verified with FE results. Shear and radial interphasial stresses provide insight into the design of engineered interfaces/interphases.     

Matrix-fiber stress transfer in composite materials: Elasto-plastic model with an interphase layer

The matrix-fiber stress transfer in glass-epoxy composite materials was studied using analytical and experimental methods. The mathematical model that was developed calculates the stress fields in the fiber, interphase, and neighboring matrix near a fiber break. This scheme takes into account the elastic-plastic behavior of both the matrix and the interphase, and it includes the treatment of stress concentration near the discontinuities of the fibers. The radius of the fibers and the mechanical properties of the matrix were varied in order to validate the mathematical model. The computed values for the lengths of debonding, plastic deformation, and elastic deformation in the matrix near the fiber tip were confirmed by measurements taken under polarized light on loaded and unloaded single fiber samples.     

界面相多重开裂对纤维强度的影响

当纤维表面的界面相(如涂层)较脆时,纤维发生断裂之前界面相一般会发生多重开裂的损伤,这种损伤裂纹垂直于纤维轴向,故能导致纤维强度下降.本文以四相(纤维,界面相,基体,复合材料)圆柱体模型为基础,并假设界面脱粘后不再传递剪应力.首先用剪切滞后理论求得了界面相发生多重开裂后,纤维、界面相中的应力集中系数,以及界面上的剪应力,并同时考虑了纤维与界面相间界面部分脱粘的影响;然后,假设纤维强度统计特性用Weibull分布函数表示,从而根据界面相多重开裂在纤维中引起的应力集中系数K_f得到广纤维破坏概率的变化.最后利用界面脱粘区的大小,定性研究了界面剪切强度τ0对纤维强度的影响,结果表明:存在一个最佳的界面剪切强度τ0,使界面相多重开裂对纤维强度的影响最小.     

The effect of temperature on the behavior of the interphase in polymeric composites

The single-filament fragmentation method for measuring the fiber/matrix stress transfer was used for the identification of interphase perturbations. This technique is based on the measurement of the fiber length resulting from the multiple fracture of a single fiber embedded in a resin specimen during tensile loading. A series of single-fiber fragmentation experiments was conducted over a wide range of temperatures on the AS4-carbon-fiber/Epon-828/PACM20-epoxy-resin system. Critical aspect ratios, the magnitude of which is considered to be inversely proportional to the square root of the matrix modulus, showed a significant increase from ambient to elevated temperatures, at temperature levels much lower than the glass transition point of the bulk matrix. This increase was consistent with the existence of an interphase of lower glass transition temperature than the bulk matrix. A three-concentric-cylinder elastic model was employed to correlated the effect of material properties.     

Control of strength anisotropy of metal matrix fiber composites

Summary This paper examines theoretically the stress distribution around fiber breaks in a unidirectional reinforced metal matrix composite, subjected to axial loading when plastic yielding of the matrix is allowed to occur. The composites considered have a ductile interphase, bonding the matrix to the fiber. The likelihood of failure of a fiber adjacent to the existing broken fiber is considered. Detailed and systematic results are given for composites with a wide range of fiber volume fractions, Young's modulus of the fibers and the matrix, interphase properties and Weibull modulus for the strength of the fibers. The objective is the optimization of these material and geometric variables to ensure global load sharing among the fibers in the longitudinal direction, which will give the composite good longitudinal strength. Calculations are carried out for transverse loading of the composite to determine the effect of the ductile interphase on the yield strength. Characteristics of the ductile interphase are determined that will provide good longitudinal strength through global load sharing and a relatively high yield strength in the direction transverse to the fibers. This, in turn, will allow control of the strength anisotropy of uniaxially reinforced metal matrix composites.     

The effect of the interphase and material properties on load transfer in fibre composites

An interphase between a fibre and a matrix is modelled with its own mechanical properties to study the load transfer through this crucial region. The effect of material properties on the maximum shear stress during the load transfer is investigated. The results indicate an optimum point where the shear stress would be the lowest at the interphase. With the help of this model, the effect of crack initiation at the interphase on the stresses is illustrated. It is shown that cracks are likely to initiate at the fibre/interphase interface rather than at the interphase/matrix side.     

Microstructural investigations of the pyrocarbon interphase in SiC fiber-reinforced SiC matrix composites

The microstructure of the pyrocarbon interphase in SiC fiber-reinforced SiC matrix (SiCf/SiC) composites and its transformations during fiber/matrix debonding were studied. The phenomena of bridging and delamination within the pyrocarbon interphase are found during fiber/matrix debonding. A new phenomenon of ‘stress orientation’ of the basal planes of the pyrocarbon in the bridging region is discovered. It is found that the microstructural features of the pyrocarbon interphase are in favor of the toughness improvement of the SiCf/SiC composites.     

Effect of the interphase microstructure on the behavior of carbon fiber/epoxy resin model composite in a thermal environment

The effect of the interfacial microstructure on the stress transfer for a single-fiber carbon fiber/epoxy matrix composite with two different levels of fiber–matrix adhesion for a temperature range between 25 and 115 °C was studied. The heterogeneity of the matrix in the neighborhood of the fiber on the effective mechanical properties of the composite and the possible interactions fiber–matrix that could lead to the development of an interphase dissimilar to the bulk matrix were also analyzed. The preferential absorption of one component of the matrix on the carbon fiber surface is considered to play a key factor on the interfacial behavior for a varying temperature. The matrix-interphase amine-resin stoichiometry is considered to be the main parameter controlling the single-fiber composite behavior when exposed to high temperature.