NiTi纤维表面处理及其树脂基复合材料的界面特性

NiTi纤维表面呈惰性,表面能低,NiTi纤维与树脂间界面粘结性差.为了提高界面性能,采用硅烷偶联剂、表面涂层和低温冷等离子体技术等方法对NiTi纤维表面进行处理,改善纤维表面的浸润性,达到纤维与树脂界面良好的粘结.对复合材料进行界面剪切强度的测定,并利用扫描电镜观察拔脱纤维表面形貌的变化.研究表明:NiTi纤维经不同方法处理后,纤维的浸润性和界面的粘结强度均有不同程度的改变,其中冷等离子体处理的纤维再经硅烷处理,其复合材料IFSS提高2.94倍,ILSS提高1.45倍,且纤维与树脂粘合较好.     

Scaling global fracture behavior of structures-sized laminated composites

The propagation of damage in laminated fiber composites similar to a crack-like configuration is studied experimentally. Of particular interest is the behavior of a `macro-crack' or `global crack' that propagates through a large scale structure (e.g., airplane fuselage or wing) with the potential interaction of stringers or other reinforcements. The question is considered whether such damage propagation can be understood in terms of classical fracture mechanics. Because the damage zone (wake width) can be very extensive and may be measured in terms of inches, the question arises as to the scalability of associated `fracture' phenomena. An integral part of this investigation is thus an examination of the size of the test specimens to establish whether a minimum size is required to relate fracture at larger scales by laboratory specimens. Using (globally anisotropic) 32-lamina composite specimens, proportioned like compact tension specimens, it is found that test `coupons' on the order of 45 to 50 cm on a side (18×18 in.²) or larger are needed to begin simulating large scale structures for establishing a global equivalent of a fracture energy for `crack propagation' simulations. Displacement controlled tests on groups of three specimen sizes (15, 30 and 46 cm on a side) indicate that scaling can be accomplished through the square root of the linear specimen or crack dimension. In certain lay-ups `run-away delamination' severs the surface laminae so that the reinforcement action of stringers is jeopardized. Damage at the `global crack front' is quantified through an effective area relation, with a characteristic value for the mostly intra-laminar initiation of damage (intra-lamina cracks) at a sharp notch, and another value conceived of as governing the onset of unstable growth.     

单丝断裂双树脂法研究碳纤维/环氧树脂界面粘结性能

建立了单丝断裂双树脂体系法,利用外层树脂的韧性使包埋于内层脆性树脂中的纤维单丝断裂达到饱和,解决了断裂伸长率较低的树脂基体采用传统的单丝断裂法无法测得界面剪切强度的问题.分别采用界面剪切强度和界面断裂能作为表征参量,考察了干态及湿热条件下两种T300级和两种T800级碳纤维/环氧树脂的界面性能,并与单丝断裂单树脂体系的界面性能进行比较.结果表明:单丝断裂双树脂体系与单树脂体系在表征碳纤维/环氧树脂的界面性能上定性规律一致;双树脂体系界面断裂能和界面剪切强度均可评价界面的耐湿热性能,且二者得到的变化规律一致;湿热处理后界面粘结性能均呈下降趋势,国外碳纤维体系的界面耐湿热性能明显优于国产碳纤维体系.     

Effect of fibre/matrix adhesion on residual strength of notched composite laminates

Effects of fibre/matrix adhesion and residual strength of notched polymer matrix composite laminates (PMCLs) and fibre reinforced metal laminates (FRMLs) were investigated. Two different levels of adhesion between fibre and matrix were achieved by using the same carbon fibres with or without surface treatments. After conducting short-beam shear and transverse tension tests for fibre/matrix interface characterisation, residual strength tests were performed for PMCLs and FRMLs containing a circular hole/sharp notch for the two composite systems. It was found that laminates with poor interfacial adhesion between fibre and matrix exhibit higher residual strength than those with strong fibre/matrix adhesion. Major failure mechanisms and modes in two composite systems were studied using SEM fractography. The effective crack growth model (ECGM) was also applied to simulate the residual strength and damage growth of notched composite laminates with different fibre/matrix adhesion. Predictions from the ECGM were well correlated with experimental data.     

BN-SiC层状复合陶瓷的断裂行为研究

以SiC、BN粉为原料,采用热压法制作了BN-SiC层状复合陶瓷,并对层状复合陶瓷的断裂行为进行了研究,发现层状材料通过层间界面优先开裂使横向裂纹扩展路径明显曲折化,断裂从一次性脆断变为对裂纹损伤具有一定容忍能力的逐次多级断裂,裂纹张开位移显著增大,断裂韧性显著提高.     

Effects of fibre/matrix adhesion on carbon-fibre-reinforced metal laminates—II. impact behaviour

Quasi-static, low-hanging and high-velocity impact tests have been conducted in order to study the effect of fibre/matrix adhesion on the impact properties of fibre-reinforced metal laminates. Differences in fibre/matrix adhesion were achieved by using treated or untreated carbon fibres in an epoxy resin system. Chemical removal of the aluminium layers and a sectioning technique were applied to examine and characterize the impact damage in the laminates. The results show that the laminates with the weaker fibre/matrix adhesion exhibit larger damage zones, although the back face crack length and permanent indentation after impact are smaller for a given impact energy. Residual tensile strength after impact is also higher for the untreated fibre laminates due to increased fibre/matrix splitting in the composite layer.     

A tensile strength model for unidirectional fiber-reinforced brittle matrix composite

A model for the ultimate tensile strength of unidirectional fiber-reinforced brittle matrix composite is presented. In the model, transverse matrix crack spacing and change in debonding length between the fiber and the matrix is continuously monitored with increasing applied load. A detailed approximate stress analysis, together with a Weibull failure statistics for fiber fracture, are used to determine the probability of fiber fracture and fiber fracture location in the composite. Results of the model are consistent with experimental data. It is suggested from the results that the strength and toughness of the composite are significantly influenced by the Weibull modulus of the fiber and the fiber/matrix interfacial shear stress. A higher fiber Weibull modulus results in a lower composite strength while a higher fiber/matrix interfacial shear stress results in a composite with higher strength but lower toughness. A moderate variation in matrix strength and fiber/matrix interfacial shear strength does not significantly affect the strength of the composite.     

Influence of ultrasonic treatment on the characteristics of epoxy resin and the interfacial property of its carbon fiber composites

To enhance the interfacial property between a carbon fiber and epoxy matrix, an ultrasonic technique was used to treat the resin liquid and the impregnated fibers respectively. The effects of the treatments on the characteristics of the resin system and the fiber surface, as well as fiber/matrix interfacial bonding strength, were analyzed and discussed. The results indicated ultrasonic treatments significantly decreased the viscosity and surface tension of the resin system, and increased the wettability and the oxygen content of the fiber surface due to the ultrasonic cavitation effects. Microbond tests revealed much more increase of interfacial shear strength when the ultrasound was applied to the impregnated fibers, and combination failures of interface and matrix layer were observed from the pulled-out fiber surface.     

Determination of fiber/matrix adhesion using the Outwater–Murphy single fiber specimen

Fiber/matrix (F/M) interface toughness values of carbon/vinylester 411 and glass/vinylester 411 has been determined using the Outwater–Murphy (OM) single-fiber compression test specimen. The OM test specimen consists of a rectangular block of matrix with a centrally embedded fiber with a hole drilled through the specimen and the fiber. Upon loading of the specimen in compression, the fiber may debond at the hole edge. The interface toughness can be determined from the measured values of the critical load for debonding. The fiber/matrix debond toughness values for dry carbon/vinylester and glass/vinylester were 51.2 and 38 J/m², respectively, in reasonable agreement with previously published data determined using other test methods. Testing of water immersed carbon/vinylester 411 and glass/vinylester 411 OM specimens revealed significant reductions of the fiber/matrix adhesion.     

The interaction between matrix cracks and delaminations during quasi-static impact of composites

This paper discusses the investigation of the impact process for beam-like composite specimens. The research is focused on the initiation of delaminations at matrix cracks and on the interaction of delaminations with matrix cracks. The research is based on experiments and on finite element calculations. This study improves the fundamental understanding of the impact process in composite laminates, and gives clear indications on the relative influence of different material properties (transverse strength, interlaminar fracture toughness) on the damage development during impact.     

碳纤维增强铜基复合材料制备方法研究进展

综述了碳纤维增强铜基复合材料的主要制备方法及其发展现状,重点讨论了粉末冶金法、热压扩散烧结法、熔渗法、PVD法、CVD法及电镀法等常用制备工艺的原理及特性,分析了不同制备方法的优缺点及适用领域,提出了现有方法中存在的问题,并展望了碳纤维增强铜基复合材料的发展趋势及在输变电领域的应用前景。     

Effect of matrix sub-layer interfacial fracture on residual strength improvement of the fatigued carbon/carbon composites

In the present study, flexural behavior of carbon fiber reinforced pyrolytic carbon matrix composites (C/C composites) before and after fatigue tests had been studied. The results showed that the residual flexural strengths of the samples had been improved after fatigue tests, and the fracture mechanisms of the original and post-fatigue specimens had some differences. Fracture mechanism of the original specimens could be described as fiber/matrix interfacial de-bonding, and the dominant damage of the post-fatigue specimens could be regarded as pyrolytic carbon sub-layers’ step-delamination. The degradation of matrix sub-layer interfacial bonding strength was beneficial to improve the mechanical properties of C/C composites.     

Compressive strength of unidirectional fiber composites with matrix non-linearity

A study has been made of the effect of fiber misalignment and non-linear behavior of the matrix on fiber microbuckling and the compressive strength of a unidirectional fiber composite. The initial fiber misalignment constituted the combined axial and shear stress state in the matrix, and the state of stress just prior to the buckling was considered to be the initial state of stress in bifurcation analysis. The expression for the critical microbuckling stress was found to be the same as that for the elastic shear-mode microbuckling stress except that the matrix elastic shear modulus was replaced by the matrix elastic-plastic shear modulus. Incremental theory of plasticity and deformation theory of plasticity were used to model the matrix non-linearity. The analysis results showed reasonable correlation with available experimental data for AS4/3501-6 and AS4/PEEK graphite composites with 2° to 4° range of initial fiber misalignment.     

Tensile fracture behavior of notched fiber reinforced titanium metal matrix composite

The static fracture behavior of a titanium based metal matrix composite (MMC) with a central hole or a straight notch was investigated. The MMC used was SCS-6/Ti-β21-S with a quasi-isotropic lay-up. Different sizes of hole or notch were used which provided cut-out size to specimen width ratios from 0·1 to 0·4. Two test temperatures were used: ambient and 650°C. At both temperatures, the tested MMC showed a mild hole size effect or notch sensitivity. The failure mechanisms involved the debonding of fibers followed by failure of fibers, and then by failure of the matrix.     

Control of interfacial adhesion in continuous carbon and kevlar fiber reinforced polymer composites

Carbon fiber surfaces were treated by cold plasmas of oxygen, nitrogen, argon, ammonia, and propylene. A two-component bismaleimide, an epoxy, and a model thermoplastic resin polypropylene were used as the matrices for composites. The effectiveness of various plasmas in improving the interfacial adhesion between carbon fibers and matrix resins was demonstrated. Predominant adhesion promotion mechanisms as influenced by various plasma treatments were determined. Oxygen and argon plasmas were found to promote mechanical keying by increasing the level of fiber surface roughness and porosity. The wettability of carbon fiber surface by the matrix resin was also enhanced by oxygen plasmas and argon plasmas (to a lesser extent), as evidenced by the increased total surface energies and their polar components. These surface energy increases are mainly due to the various oxygen-containing functional groups observed on the oxygen plasma-treated surface. For the cases of ammonia and combined ammonia/argon plasma treatments, possible chemical bonding between bismaleimide and the plasma-deposited amine groups is one important promoter of interfacial bonding. In these cases increased wettability was also observed. Ammonia and ammonia/argon plasmas appear to be the more appropriate treatments for carbon-fiber/thermoset resin composites considering that they generally do not induce any appreciable reduction in fiber strength. In contrast, excessively prolonged exposure of carbon fibers to oxygen, nitrogen or argon plasma could lead to a significant reduction in fiber strength. The plasma-polymerized polypropylene deposited on the fiber surface was capable of improving the compatibility and adhesion between the fiber and the polypropylene matrix.     

Transverse elastic moduli of unidirectional fiber composites with fiber/matrix interfacial debonding

An elastic contact model is developed to predict the transverse Young's modulus, Poisson's ratio and shear modulus of unidirectional fiber composites with interfacial debonding. The elastic deformation formulae of the fiber under contact pressure are derived by the use of elasticity theory. These results are then used in the formulation of an analytic boundaryelement method for solving the interfacial debonding problem. The two extreme cases of perfect bonding and the fiber-like void are also studied. On the basis of this theory, the upper and lower bounds of the transverse moduli for unidirectional fiber composites with imperfect fiber/matrix interfaces are provided. Numerical calculations of parametric studies are conducted for four composites, and some basic characteristics of the transverse elastic moduli of unidirectional fiber composites with interfacial debonding are presented.     

The effects of volume percent and aspect ratio of carbon fiber on fracture toughness of reinforced aluminum matrix composites

Carbon fiber reinforced aluminum matrix composites are used as advanced materials in aerospace and electronic industries. In order to investigate role of aspect ratio of carbon fiber on fracture toughness of aluminum matrix composite, the composite was produced using stir casting. Al–8.5%Si–5%Mg selected as a matrix. The samples were prepared with three volume fractions (1, 2 and 3) and three aspect ratios (300, 500 and 800). Three-point bending test was performed on the specimens to evaluate the fracture toughness of the materials. The results showed that the fracture toughness of composites depends on both fiber volume fraction and aspect ratio. Scanning electron microscopy (SEM) was employed to elucidate the fracture behavior and crack deflection of composites. The study also, showed that the toughening mechanism depends strongly on fiber volume fraction, aspect ratio and the degree of wetting between fiber and matrix.     

Formation of interfacial voids in composites with a weakly bonded viscoplastic matrix

The formation and evolution of interfacial voids are investigated in the case of metal matrix composites (MMCs) reinforced by ceramic fibres and subjected to high compressive loads. The resulting compression flows of a viscoplastic aluminum matrix around rigid fibres are described by a nonlinear free-boundary problem. A new finite element model with boundary-fitted mesh motion is introduced to simulate the formation of interfacial voids. The fibre–matrix interface is weak and allows yielding and sliding with separation at a dynamic contact line connecting three phases. The fibre–matrix interaction is simulated via a modified O'Donovan–Tanner constitutive model and a phenomenologically defined interface potential. The shape of the interfacial surface undergoing large deformation is not known a priori and found as a part of the solution. The influence of hydrostatic stress and constitutive characteristics of the matrix on the evolution of interfacial voids and their growth rates are examined. As the transverse strain increases, the evolution of interfacial voids occurs through a sequence of convex profiles. Numerical simulations are carried out for a special case involving small values of the yield stress and the viscosity of yielded matrix in order to compare them with similar results for linear viscous solids. The numerical results are also compared with the experiments involving similar compression flows of viscoplastic model materials.     

Role of controlled debonding along fiber/matrix interfaces in the strength and toughness of metal matrix composites

In metal matrix composites toughness is derived primarily from the plastic work of rupture of ductile matrix ligaments between the fractured fibers and from the plastic work of simple shear separation along steps connecting major fracture terraces. In the optimization of tensile strength in the longitudinal and transverse directions together with the respective works of fracture the most important factor is the control of the extent of debonding along interfaces between the fibers and the matrix, which develops locally in the course of deformation in a continuously changing mix of modes. In Al alloy matrix composites reinforced with Al₂O₃ fibers an effective means of controlling the key interface fracture toughness is through coarsening of Al₂Cu intermetallic interface precipitates which prescribe a ductile fracture separation layer. A combined experimental approach and micromechanical modeling, utilizing a specially tailored novel tension/shear: traction/separation law provides the means for further optimization of overall behavior. This revised version was published online in July 2006 with corrections to the Cover Date.     

Compressive fracture behavior of 3D needle-punched carbon/carbon composites

Compressive fracture behavior under transverse and longitudinal compressive loading are determined for 3D needle-punched carbon/carbon (C/C) composites with single rough laminar (RL) pyrocarbon matrix or dual matrix of RL pyrocarbon and resin carbon. The results of Weibull statistics analysis indicate that scale parameter σ₀ of transverse and longitudinal compression of the composites with single matrix are 153.41 and 94.26 MPa, and σ₀ of the composites with dual matrix are 205.16 and 105.33 MPa, respectively. The mean compressive strength of both composites is nearly equal to σ₀ under each experimental condition. Failure modes of both composites under transverse and longitudinal compressive loading are shear and extension, respectively. Both composites exhibit quasi-ductile fracture behavior under transverse compression. Many small fragments of fibers and matrix carbon on the fracture surface of the composites are observed for single matrix composites. And the fiber bundle breakage with extensive debonding occurs for dual matrix composites. Under longitudinal loading, the composites with single matrix show quasi-ductile fracture behavior and delamination and splitting of non-woven long carbon fiber cloth layers are observed. The composites with dual matrix exhibit catastrophic failure behavior and crack runs through the composites along compressive loading direction.