Modelling of the interphase in polymer-matrix composite material systems

The interphase, or transition region between fibre and matrix in composite material systems, is known to play an essential role in the performance of composite components. In fact, it has recently been discovered that the interaction and cooperative action of the constituents in the system control the durability of such systems, in stark contrast to other behaviour characteristics such as stiffness and quasi-static (or ‘instantaneous’) properties wherein the constituents contribute to the properties, essentially, in proportion to their presence. Hence, this ‘systems effect’ has become the focus of much attention, and the object of modelling efforts. However, modelling the interphase with properly set boundary value problems is a considerable challenge, especially because the properties in these transition regions are often a function of spatial position, i.e., they are non-uniform as a function of position. The author has constructed models of the interphase region which admit this non-uniformity, and has achieved solutions to several classes of these problems. The present paper will describe the general problem of the ‘systems effect’, discuss the practical issues of how the interface enters micromechanical models of strength and durability, and present models for the interphase region that include the variability of material properties in those transition regions. Special attention will be given to the contrasts between these considerations and the rule-of-mixtures concepts that currently pervade the field, and to the importance of these differences to the practical opportunities offered by the ability to properly model and “design’ interphase regions in polymer-matrix composites.     

The role of the SnO2 interphase in an alumina/glass composite: a fractographic study

The role of tin dioxide (SnO₂) interphase for the alumina/glass composite system was investigated using fractography. Alumina (Al₂O₃) and glass form a strong chemical bond which is undesirable for toughness in a ceramic matrix composite. SnO₂ interphase was incorporated to prevent this strong bond between alumina and glass. SnO₂ was deposited on Al₂O₃ substrates via chemical vapour deposition and bonded with glass. The role of the interphase was then studied by characterizing the fracture surfaces of the bend test and special composite disc samples loaded in diametral compression. Bend tests results showed that the SnO₂ interphase and/or the SnO₂/Al₂O₃ interface acted as a plane of weakness. Secondary cracking at 90° to the major crack direction was observed along this plane of weakness, which appears to be in accord with the Cook and Gordon model. Crack deflection and secondary cracking were also observed in the SnO₂ region of the compression samples. These results indicate the suitability of SnO₂ interphase for the alumina/glass composite system.     

Combined micro- and macromechanical considerations of layered composite shells

This contribution deals with a computational treatment of the non-linear behaviour of composite sandwich shells with extremely thin face layers and a relatively thick orthotropic core, and multi-layered fiber reinforced polymer or metal matrix composite shells. Special emphasis is laid on algorithms which allow the consideration of local effects, like face layer wrinkling in sandwich shells and progressive damage or microplasticity in fibre composites, by semi-analytical approaches implemented into a finite element formulation. This leads to the advantage that the shell structure must be discretized only up to an element mesh density which is sufficient for describing the global deformation and stability behaviour.     

Surface,interphase and composite property relations in fibre-reinforced polymers

The aim of this study is to demonstrate the relations between surface, interphase and different composite properties in composites of carbon and glass fibres and thermosets (epoxy resin) or thermoplastics (polyamide, polypropylene). The surface characteristics of variously treated carbon and glass fibres have been determined by contact angle measurements, using a capillary penetration technique, and zeta potential measurements. Micromechanical tests (single-fibre pull-out) have been applied to model composites to establish the interphase properties. Bulk composites have been manufactured by impregnation with resins and curing by hot pressing or pressing of commingled yarn samples (continuous reinforcing fibres) or twin-screw extrusion and injection moulding (short reinforcing fibres). The composite properties have been tested by tensile and shear tests. Contact angle and electrokinetic measurements permit detection of differences in the surface treatment of glass and carbon fibres. Measurements of shear strength by pull-out, fibre fragmentation and yarn tensile shear tests show comparable results and correlate to the macromechanical properties.     

Effects of interphase properties in unidirectional fiber reinforced composite materials

A micromechanical study has been performed to investigate the mechanical properties of unidirectional fiber reinforced composite materials under transverse tensile loading. In particular, the effects of different properties of interphase within the representative volume element (RVE) on both the transverse effective properties and damage behavior of the composites have been studied. In order to evaluate the effects of interphase properties on the mechanical behaviors of unidirectional fiber reinforced composites considering random distribution of fibers, the interphase is represented by pre-inserted cohesive element layer between matrix and fiber with tension and shear softening constitutive laws. Results indicate a strong dependence of the RVE transverse effective properties on the interphase properties. Furthermore, both the damage initiation and its evolution are also clearly influenced by the interphase properties.     

Effect of an interphase region on debonding of a CNT reinforced polymer composite

The effect on stiffness and debonding of an interphase zone of altered polymer properties surrounding each carbon nanotube (CNT) in a CNT reinforced polymer composite is investigated. The interphase zone has position dependent material properties that merge with those of the polymer at a sufficiently large distance from the inclusion. There is evidence that such an interphase zone must be included in models in order to represent the overall composite properties. The analyses are based on an axisymmetric unit cell model of the composite. An elastic–viscoplastic conventional continuum constitutive relation (a size-independent relation between stress, strain and strain rate) is taken to characterize the bulk polymer material and the interphase, with the material properties being position dependent in the interphase. The interface between the polymer and the CNT is modeled by a phenomenological cohesive relation that allows for complete separation and the creation of new free surface. The effect of varying interface strength on the composite stress–strain response and on debonding is analyzed both with and without an interphase. The presence of an interphase increases the composite stiffness but promotes debonding which ultimately reduces composite stress carrying capacity. The compliance of the interface also affects the stress–strain response prior to debonding and leads to stress redistributions within both the fiber and the matrix (and/or interphase) which can affect the fracture mode that occurs.     

直流电机复合定位控制系统性能分析及系统优化

在直流电机复合定位控制系统(CPCS)设计过程中,发现电机速度等动态响应曲线发生振荡,表现出一定程度的不稳定性.为探究这一振荡与控制系统内在结构之间的关联性,使用MATLAB对PID及CPCS系统动态响应、根轨迹及频率特性等进行分析、比较.结果显示：高阶控制系统的传递函数总可以通过降阶等方式简化为具有1个实数零点、1个实数极点和2对复共轭极点的基本形式.其中离原点位置较近处的一对复共轭极点的移除是造成CPCS系统稳定性下降,产生振荡的根本原因.该振荡可通过增大另一对复共轭极点实部或减小虚部的方法予以降低或消除.这一结论对提高控制系统的定位精度和稳定性具有重要的参考意义.     

Effect of interphase on fibre-bridging toughness of a unidirectional FRP composite thin plate

A parametric analysis of the toughening mechanisms in a uniaxially fibre reinforced polymer (FRP) thin plate with a power-law hardening shear interphase is presented. An interfacial shear-lag model is used to analyse the relationship between the crack surface traction exerted by the intact fibres and the crack opening displacement (COD). Numerical solutions of the equations governing bridge-toughening are given. Two special kinds of interphase, i.e. linearly elastic and perfect plastic, are discussed. The results demonstrate that the toughening ratio of the composite thin plate is sensitive to several parameters, e.g. the thickness of the interphase between fibre and matrix, the hardening parameter of the interphase, the interfacial shear properties (stiffness and strength), the fibre radius and the far-field load. The results of this investigation will be beneficial to the selection of constitutive materials, the improvement of mechanical behaviour and the fabrication process of FRP composites.     

微污染水处理中投加粉末炭减缓膜污染的机理研究

采用MBR(膜生物反应器)及MBR-PAC(PAC,粉末活性炭)组合工艺处理微污染湖水.试验考察了各工艺条件下的膜污染状况,发现投加PAC降低了膜阻力,利于减缓膜污染.为了进一步研究相应的机理,采用空间排阻液相色谱(SELC)法对粉末炭投加前后膜污染物的分子量分布(MWD)进行了直接和间接的测定.结果表明,在MBR应用于微污染湖水处理时,小分子物质是一类重要的膜污染物质.PAC对大量小分子污染物(MW<3 000)的有效吸附去除是投加PAC后膜污染状况改善的重要原因.     

复合催化剂对聚酰胺纳滤膜结构和性能的影响

以聚砜(PSf)为基膜,间苯二胺(MPD)和均苯三甲酰氯(TMC)为反应单体,通过界面聚合制备聚酰胺复合纳滤膜.考察了复合催化剂三乙胺(TEA)和樟脑磺酸(CSA)及反应条件对纳滤膜功能层结构和性能的影响.结果表明:在反应体系中,TEA和CSA的质量比为1/2时,随着复合催化剂中TEA的质量分数从0.5％增加到3％,纳滤膜功能层密度增大,表面粗糙度和水接触角下降,膜通量明显升高,但纳滤膜的截留率及其对盐的选择顺序基本不变.在TEA质量分数为2％、反应时间40 s、热处理温度80℃和热处理时间3 min的最优条件下,所得复合纳滤膜对2 g/L MgSO4溶液的截留率为93.2％,通量为16 L/(m2·h).在0.2～1.0 MPa的操作压力下,聚酰胺复合纳滤膜分离性能稳定.     

Axial compressive behaviour of reinforcing fibres and interphase in glass/epoxy composite materials

Axial compressive behaviour of reinforcing fibres and interphase in glass fibre/epoxy resin composites were examined. Axial compressive strengths of glass fibres were evaluated by the tensile recoil method. The effects of silane-based coupling surface treatment agent on the fibre compressive strengths were investigated. The glass fibres showed higher compressive strengths when coated by the surface treatment. Interphase behaviour was also investigated by means of the single-fibre embedded compressive test. The particular stress and strain distributions inside the specimen were examined by a three-dimensional finite element analysis. The parameter interfacial transmissibility instead of the conventional critical fibre length theory was introduced as an index of interfacial properties. This parameter was useful to estimate the interfacial properties at the elastic state apart from the complicated critical state. It was confirmed that the surface treatment improved the glass/epoxy interphase under axial compressive load.     

Effects of hybrid fillers based on micro- and nano-sized silver particles on the electrical performance of epoxy composites

In the present study, electrically conductive adhesives produced from hybrid fillers based on micro- and nano-sized silver (Ag) was developed. The influence of the hybrid filler composition on the electrical properties of the hybrid system was studied. The electrical conductivity of the epoxy composites filled with micro- and nano-silver was correlated with their morphologies. A positive effect was observed in the electrical conductivity result when the composition of micro- and nano-sized Ag particles reached a 50:50 weight ratio. The nano-sized Ag particles became interconnecting particles in the interstitial spaces between micro-sized particles. Micrograph scanning shows that the particles were well distributed and dispersed, the separation between lumps of Ag filler by the insulating matrix was significantly reduced, leading to the formation of continuous linkages. The increased electrical conductivity resulted in a charge around the particle distribution, which led to the high capacity. Hence, these particles increased the conductivity of the system.     

壳聚糖-聚己内酯复合膜的制备及其性能研究

为综合壳聚糖(CS)和聚己内酯(PCL)的性能,将CS和PCL在醋酸溶液中进行共混,利用流延法制备5/95,10/90,15/85,20/80 4种不同比例的壳聚糖-聚己内酯复合膜.采用元素分析、FTIR、XRD和SEM对膜的组分、结构和形貌进行了表征,证明了壳聚糖和聚己内酯在复合膜中有一定的相容性.探讨了体系中壳聚糖含量对多孔膜的力学性能和吸水率、溶胀比、孔隙率的影响,结果表明:在实验范围内随壳聚糖含量的增加,复合膜的刚度从4 188.17N/m提高到20 436.00 N/m;杨氏模量亦从30.52 MPa增加到69.69 MPa;断裂伸长率降低.吸水率可达76.39%,孔隙率亦可增加到约35%,而溶胀比几乎不变.     

Numerical analysis of composite systems by using interphase/interface models

The paper considers two classes of approaches for the numerical analysis of composite systems: the first one discretizes the assumed interphase (between matrix and fibre) as volumic elements and uses material models that degenerate from Continuum Damage Mechanics. The second one introduces interface elements that relate non linearly the normal and tangential tractions to the corresponding displacement discontinuities, incorporating a progressive decohesion, following the lines of Needleman (1987) and Tvergaard (1990). The respective capabilities of these two approaches are discussed on the basis of some numerical results obtained for a unidirectional metal matrix composite system. When the models are consistently adjusted they are able to reproduce the same kind of results. The advantages of the second class of method is underlined and two new versions of interface models are proposed that guarantee the continuity and the monotonicity of the shear stiffness between the progressive decohesion phase and the subsequent contact/friction law that plays role under compressive shear after complete separation.     

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.     

Role of the micro- and nanostructure in the performance of surface-enhanced Raman scattering substrates assembled from gold nanoparticles

Highly active and stable substrates for surface-enhanced Raman scattering (SERS) can be fabricated by using colloidal crystals to template gold nanoparticles into structured porous films. The structure-dependent performance of these SERS substrates was systematically characterized with cyanide in continuous flow microfluidic chambers. A matrix of experiments was designed to isolate the SERS contributions arising from nano- and microscale porosity, long-range ordering of the micropores, and the thickness of the nanoparticle layer. The SERS results were compared to the substrate structure observed by scanning electron microscopy (SEM) and optical microscopy to correlate substrate structure to SERS performance. The Raman peak intensity was consistently highest for nanoporous substrates with three-dimensionally ordered micropores, and decreases if the micropores are not ordered or not templated. Removing the nanoscale porosity by fusion of the nanoparticles (without removing the large micropores) leads to a drastic plunge in substrate performance. The peak intensity does not strongly correlate to the thickness of the nanoparticle films. The results make possible the efficient controlled fabrication of stable, reproducible, and highly active substrates for SERS based chemical sensors with continuous sampling.