Multilayered Interphases Research Articles

A multilayered circular inhomogeneity with interfacial diffusion and sliding

We study the time-dependent and plane strain deformations of a circular inhomogeneity bonded to an infinite matrix through a multilayer interphase when subjected to uniform remote stresses. Both interfacial diffusion and rate-dependent sliding occur on all the existing interfaces between two neighboring phases. The problem is solved effectively and elegantly by means of the complex variable method together with the state-space approach. The state variables are just the unknown coefficients appearing in the analytic functions defined in all the phases of the composite. Numerical results are presented to demonstrate the obtained solution.

Fatigue Properties of SiC/SiC Composites Under Various Loading Modes

Because fatigue resistance is one of the most important issues for the blanket structural materials of the fusion reactor, the fatigue damage formation processes of the advanced SiC/SiC composite (Tyranno SA 3rd/CVI-SiC composite with SiC/C multilayer interphase) for fusion reactor applications were investigated. The fatigue tests of the SiC/SiC composite were successfully performed up to 105 cycles with no significant technical issues by using a small specimen test technique developed under the IFMIF/EVEDA. Based on the evaluation of the modulus change during the fatigue tests, the tensile loading was clarified to be a dominant factor for the degradation of the SiC/SiC composite.

A comparative study to predict the interphase modulus in polymer nanocomposites

ABSTRACTIn this study, the interphase modulus (Ei) in polymer nanocomposites is calculated by two methods and the calculated results are compared at different conditions. In the first method, the experimental moduli of samples are applied to Ji model and suitable “Ei” is calculated. In the second method, a multilayered interphase is considered, in which the Young's moduli of layers (Ek) depend to the distance between the nanoparticle surface and the polymer matrix by power function of “Y” parameter. The “Ei” is calculated for multilayered interphase assuming the same and different layer thicknesses (tk) by Parallel and Series models. Finally, the “Ei” values calculated by the explained methods are compared for two reported samples. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44076.

THERMOELASTOPLASTIC AND VIBRATION CHARACTERISTICS OF COMPOSITES WITH INTERPHASES

ABSTRACTThis paper addresses the problem of predicting the behaviors of a compositematerial, which consists of a matrix and a spherical inclusion coated by a multilayeredinterphase, under thermal and/or mechanical loading variations and basedon the micromechanics principles. The multi-layered interphase, which in generalincludes different properties for each layer, is modeled by applying the multiinclusionmodel. The considered damage mode, which is represented by theprogressive debonding of the particle from the interphase, is assumed to becontrolled by a critical energy criterion and the Weibull’s distribution function. Theeffects of the interphase parameters such as its thickness and the properties of eachlayer on the effective thermomechanical properties and the vibration characteristicsof composites with multi-layered interphases are presented and discussed. Thenatural frequencies give information about the resonance avoidance whereas modeshapes give information about observability and controllability of different structures.Therefore, the natural frequencies and mode shapes as vibration characteristics areinvestigated based on Euler and Timoshenko theories.

A micromechanical model for composites containing multi-layered interphases

This paper addresses the problem of predicting the behaviors of a composite material, which consists of a matrix phase and an ellipsoidal reinforcement coated by a multi-layered interphase, under one or more of the hygral, thermal and mechanical loading conditions and based on the micromechanics principles. The multi-layered interphase, which in general includes different properties for each layer, is modeled by applying the multi-inclusion model. The damage is considered by taking into account the progressive debonding of the reinforcement from the interphase. This damage mode is assumed to be controlled by a critical energy criterion and the Weibull distribution function. The effects of the composite parameters; interphase thickness, number of layers, properties of each layer, progressive debonding damage, reinforcement size and aspect ratio, and elastoplasticity of the matrix on the effective thermo–hygro-mechanical properties and the stress–strain response are presented and discussed. Moreover, by controlling the number of layers and their thermo–hygro-mechanical properties, composites with functionally graded interphases are investigated. To validate the predictions of the proposed microstructure-based model, results are compared to theoretical and experimental findings available in the literature and completely satisfactory agreements are obtained for both the micro-composites and nano-composites.

Minimizing thermal residual stresses in ceramic matrix composites by using Iterative MapReduce guided particle swarm optimization algorithm

The thermal residual stresses (TRSs) induced in ceramic matrix composites (CMCs) with multi-layered interphases when cooling down from the processing temperature, have a significant influence on the mechanical behavior and lifetime of CMCs. The objective of this work is to minimize the TRS of the unidirectional CMCs with multi-layered interphases by controlling the interphases thicknesses. The unit cell finite element models of CMCs with multi-layered interphases are generated and finite element analysis is implemented to determine the TRS. The MapReduce is extended to a new iterative MapReduce which is then combined with classical particle swarm optimization (PSO) algorithm to develop an iterative MapReduce guided PSO (IMPSO) algorithm. The IMPSO algorithm is interfaced with finite element code to find an optimal design for minimizing the TRS within CMCs. Satisfactory results are obtained for a variety of design cases by comparing IMPSO and PSO.

Mechanical behavior of SiCf/SiC composites with alternating PyC/SiC multilayer interphases

In order to tailor the fiber–matrix interface of continuous silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites for improved fracture toughness, alternating pyrolytic carbon/silicon carbide (PyC/SiC) multilayer coatings were applied to the KD-I SiC fibers using chemical vapor deposition (CVD) method. Three dimensional (3D) KD-I SiCf/SiC composites reinforced by these coated fibers were fabricated using a precursor infiltration and pyrolysis (PIP) process. The interfacial characteristics were determined by the fiber push-out test and microstructural examination using scanning electron microscopy (SEM). The effect of interface coatings on composite mechanical properties was evaluated by single-edge notched beam (SENB) test and three-point bending test. The results indicate that the PyC/SiC multilayer coatings led to an optimum interfacial bonding between fibers and matrix and greatly improved the fracture toughness of the composites.

Evaluation of Damage Tolerance of Advanced SiC/SiC Composites after Neutron Irradiation

Silicon carbide composites (SiC/SiC) are attractive candidate materials for structural and functional components in fusion energy systems. The effect of neutron irradiation on damage tolerance of the nuclear grade SiC/SiC composites (plain woven Hi-Nicalon™ Type-S reinforced CVI matrix composites multilayer interphase and unidirectional Tyranno™-SA3 reinforced NITE matrix with carbon mono-layer interphase) was evaluated by means of miniaturized single-edged notched beam test. No significant changes in crack extension behavior and in the load-loadpoint displacement characteristics such as the peak load and hysteresis loop width were observed after irradiation to 5.9 × 1025 n/m2 (E > 0.1 MeV) at 800°C and to 5.8 × 1025 n/m2 at 1300°C. By applying a global energy balance analysis based on non-linear fracture mechanics, the energy release rate for these composite materials was found to be unchanged by irradiation with a value of 3±2 kJ/m2. This has led to the conclusion that, for these fairly aggressive irradiation conditions, the effect of neutron irradiation on the fracture resistance of these composites appears insignificant.

Electrohydrodynamics of Soft Polyelectrolyte Multilayers: Point of Zero-Streaming Current

We report a comprehensive formalism for the electrokinetics (streaming current, I(str)) at soft multilayered polyelectrolyte films. These assemblies generally consist of a succession of permeable diffuse layers that differ in charge density, thickness, and hydrodynamic softness. The model, which extends one that we recently reported for the electrokinetics of monolayered soft thin films (Langmuir 2010, 26, 18169-18181), is valid without any restriction in the number and thickness of layers, or in the degree of dissociation and density of ionizable groups they carry. It further covers the limiting cases of hard and free draining films and correctly compares to semianalytical expressions derived for I(str) under conditions where the Debye-Hückel approximation applies. The flexibility of the theory is illustrated by simulations of I(str) for a two-layer assembly of cationic and anionic polymers over a large range of pH values and electrolyte concentrations. On this basis, it is shown that the point of zero streaming current (PZSC) of soft multilayered interphases, defined by the pH value where I(str) = 0, generally depends on the concentration of the (indifferent) electrolyte. The magnitude and direction of the shift in PZSC with varying salinity are intrinsically governed by the dissymmetry in protolytic characteristics and density of dissociable groups within each layer constituting the film, together with the respective film thickness and hydrodynamic softness. The fundamental effects covered by the theory are illustrated by streaming current measurements performed on two practically relevant systems, a polyelectrolyte bilayer prepared from poly(ethylene imine) (PEI) and poly(acrylic acid) (PAA) and a polymer-cushioned (PEI) bilayer lipid membrane.

Mechanical properties of advanced SiC fiber composites irradiated at very high temperatures

Six different composite materials of various near-stoichiometric silicon carbide (SiC) fiber reinforcements and pyrolytic carbon or SiC/pyrolytic carbon multilayer interphases were neutron-irradiated to ∼6×1025n/m2 (E>0.1MeV) at nominal temperatures of 800°C and 1300°C, and tested for tensile properties at room temperature. Only insignificant or very minor modifications to the tensile strength were realized. However, statistical analysis on relatively large specimen populations revealed minor but statistically significant strength degradation for some composites. From 50 to 150nm appeared to be within the optimum PyC interphase thickness range for the SiC fibers used in terms of tensile properties. The misfit stresses present in the unirradiated samples were significantly reduced after irradiation. The change in misfit stress may be attributed to the irradiation-induced modification of coefficient of thermal expansion or potential differential swelling between the fibers and the matrix. True matrix cracking stress estimated from the proportional limit stress and misfit stress did not appear to degrade by neutron irradiation.

Thermophysical and mechanical properties of near-stoichiometric fiber CVI SiC/SiC composites after neutron irradiation at elevated temperatures

Thermophysical and mechanical properties of high purity chemically vapor-deposited (CVD) SiC and chemically vapor-infiltrated SiC matrix, pyrocarbon/SiC multilayered interphase composites with Hi-Nicalon™ Type-S and Tyranno™-SA3 SiC fibers were evaluated following neutron irradiation. Specimens including statistically significant population of tensile bars were irradiated up to 5.3 displacement-per-atom at ∼220 to ∼1080 °C in the Advanced Test Reactor at Idaho National Laboratory and High Flux Isotope Reactor at Oak Ridge National Laboratory. Thermal diffusivity/conductivity of all materials decreased during irradiation. The reciprocal thermal diffusivity linearly increased with temperature from ambient to the irradiation temperature. The magnitude of defect thermal resistance was distinctively different among materials and its ranking was Hi-Nicalon™ Type-S > Tyranno™-SA3 > CVD SiC regardless of irradiation condition. Dynamic Young’s modulus decrease for the irradiated CVD SiC exhibited explicit correlation with swelling. No significant effects of neutron irradiation on tensile properties of the composites were revealed, except for an anomaly case for the Hi-Nicalon™ Type-S composite irradiated in a specific condition. According to the single filament tensile evaluation, fibers of both types retained the original strength during irradiation at intermediate temperatures but significantly deteriorated during bare fiber irradiation at ∼910 °C. However, fiber strength deterioration was not observed when irradiated in composite form. Irradiation effects on the fiber–matrix interface properties were discussed based on results from the composite and single filament tensile tests, the hysteresis analysis, and the fracture surface examination.

The effect of neutron irradiation on the fiber/matrix interphase of silicon carbide composites

Given the good stability of mechanical properties of silicon carbide (SiC) under neutron irradiation, the ultimate irradiation tolerance of SiC composite materials may be limited by the fiber/matrix interphase, which is critically important to the performance of these composites. This study investigates the irradiation stability of pyrolytic carbon (PyC) monolayer and PyC/SiC multilayer interphases by tensile and single fiber push-out test techniques. Neutron irradiation was performed to doses of 0.7–7.7 dpa at temperatures from 380 to 1080 °C. Both interfacial debond shear strength and interfacial friction stress apparently decrease by irradiation, although this is not so dramatic when T irr < 1000 °C. In contrast, the interfacial shear stresses are most affected by the higher temperature irradiation (>1000 °C). Noteworthy, these irradiation effects depend on the type of interphase material, i.e., for the pyrolytic carbon or multilayer SiC variants studied. In the range of irradiation temperature and dose, the degradation in interfacial shear properties, while measurable, is not of a magnitude to degrade the mechanical performance of the composites. This was observed for both interphase types studied. In particular, the proportional limit tensile stress decreases slightly by irradiation while the tensile fracture strength undergoes very minor change.

Effect of neutron irradiation on tensile properties of unidirectional silicon carbide composites

Tensile properties of unidirectionally reinforced Hi-Nicalon™ Type S SiC fiber, chemically vapor-infiltrated (CVI) SiC-matrix composites, with either pyrolytic carbon (PyC) or multilayered PyC/SiC interphase, were characterized following neutron irradiations to the maximum fluence of 7.7 × 10 25 n/m 2 at 380 and 800 °C. The stress–strain behavior of the multilayered interphase composites remained unmodified after irradiation. The PyC interphase composite increased in ultimate tensile stress and strain to failure following neutron irradiation, whereas the proportional limit stress exhibited a slight decrease. Potential mechanisms for these changes include accommodation of misfit stress through irradiation creep, reduced interfacial friction, and differential swelling among individual composite constituents.

Microstructure of multi‐layered interphases processed by temperature‐pulsing chemical vapor infiltration

AbstractWe demonstrate for the first time to our knowledge the method of temperature‐pulsing chemical vapour infiltration to process multilayered interphases of the carbon/silicon carbide composites. Transmission electron microscopy was employed to investigate the microstructure of the interphases. Finely alternate layered microstructures in nanoscale were proved to be prepared successfully via the route. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The material force acting on a screw dislocation in the presence of a multi-layered circular inclusion

In this paper, we study the interaction of a screw dislocation with a multi-layered interphase between a circularly cylindrical inclusion and a matrix. The layers are coaxial cylinders of annular cross-sections with arbitrary radii and different shear moduli. The number of layers may also be arbitrary. Continuity of traction and displacement across all interfaces is assumed. We extend Honein et al.’s solution of circularly cylindrical layered media in anti-plane elastostatics to the case where all the singularities reside inside the inclusion core. The solution to this heterogeneous problem is given explicitly, for arbitrary singularities, as a rapidly convergent Laurent series, whose coefficients are expressed in terms of those of the complex potential of a corresponding homogeneous problem with the same singularities. We then consider the two particular cases of a screw dislocation, where, in the first instance, the dislocation resides inside the matrix, while, in the second instance, it is located in the inclusion core. In both instances, the Peach–Koehler force acting on the dislocation is calculated explicitly as a rapidly convergent series. We present several examples, where the effect of the layers on the material force is examined.

Recent advances in the field of ceramic fibers and ceramic matrix composites

Progress achieved during the last decade in the field of ceramic fibers and related ceramic matrix composites is reviewed. Both SiC-based and alumina-based fine fibers have been improved in terms of thermal stability and creep resistance with temperature limit of about 1400 and 1200°C, respectively. Two concepts for achieving damage-tolerant ceramic matrix composites have been identified : (i) that of non-oxide composites with a dense matrix in which matrix cracks formed under load are deflected and arrested in a weak fiber coating referred to as the interphase and (ii) that of all-oxide composites with a highly porous matrix with no need of any fiber coating. The lifetime under load of non-oxide composites in oxidizing atmospheres, is improved through the use of multilayered self-healing interphases and matrices deposited from gaseous precursors by chemical vapor infiltration (CVI). Lifetime ranging from 1000 to 10,000 hours at 1200°C under cyclic loading in air are foreseen. Alumina-based composites although attractive for long term exposures in oxidizing atmospheres up to 1200°C. are still experimental materials.

Tensile, Flexural, and Shear Properties of Neutron Irradiated SiC/SiC Composites with Different Fiber-Matrix Interfaces

Abstract Unidirectional SiC/SiC composites fabricated with highly-crystalline and stoichiometric fibers and matrix, but with three different interfacial types (single-layer pyrolytic carbon (PyC), multilayered SiC/PyC, and pseudo porous SiC interfaces) were irradiated up to 1.0 × 1025 n/m2 (E &amp;gt; 0.1 MeV) at 1073 and 1273 K. Tensile, inter-laminar shear, and flexural properties were evaluated to compare the role of different interfaces on neutron irradiation behavior. There was nearly no significant degradation in tensile and flexural strength after high-temperature neutron irradiation, except for porous SiC interphase composite. Moreover, no meaningful reduction of tensile modulus was identified regardless of interphase types, although 20–40% degradation in flexural moduli occurred due to a reduction in inter-laminar shear modulus. In contrast, matrix cracking stress was significantly dependent on interfacial properties. Multilayer interphase composites exhibited the best irradiation stability. Irradiation instability of thick PyC and porous SiC interphase resulted in 20% and 40% degradations of matrix cracking stress, respectively.

Fabrication of advanced SiC fiber/F-CVI SiC matrix composites with SiC/C multi-layer interphase

SiC/SiC composite with SiC/C multi-layer interphase coated on advanced SiC fibers was fabricated by the forced thermal-gradient chemical vapor infiltration (F-CVI) process. SEM and TEM observations verified that SiC/C multi-layer interphase was formed on SiC fibers. Both flexural and tensile strengths of SiC/SiC composite with SiC/C multi-layer interphase were approximately 10% higher than composites fabricated with single carbon interphase. The SEM observation of fracture surface for the composite with SiC/C multi-layer interphase revealed cylindrical steps formed around the fiber. Apparently several crack deflections occurred within SiC/C multi-layer interphase. Moreover, the SiC/C multi-layer applied in this study operated efficiently to improve the mechanical properties.

Microstructural stability of SiC and SiC/SiC composites under high temperature irradiation environment

Silicon carbide continuous fiber-reinforced silicon carbide matrix composites (SiC/SiC composite) are attractive as the structural material of advanced energy systems, including nuclear fusion. The irradiation may affect the fiber/matrix interphases which are responsible for the pseudo-ductile fracture behavior of SiC/SiC composites. In this work, the investigation of the microstructural evolution of SiC/SiC composites in a fusion environment is performed by the dual-ion irradiation method. Reinforcements were Tyranno™-SA and Hi-Nicalon™ Type-S. The displacement damage rate was up to 100 dpa. The irradiation temperature and He/dpa ratio were up to 1673 K and 60 appm, respectively. The microstructural modification induced by the dual-ion irradiation especially occurred in the interphase. The advanced SiC fiber did not shrink and the C/SiC multilayer interphase showed a superior microstructural stability against the dual-ion irradiation at high temperatures.

Flame‐retarded polyolefin systems of controlled interphase

AbstractThe principle of multilayer interphases was proposed earlier for modifying the mechanical properties and UV stability of various multicomponent polymer systems. This paper focuses on the applicability of this principle for improving the performance of intumescent flame‐retardant systems using melamine‐treated ammonium polyphosphate, silicone modified polyol + ammonium polyphosphate, and silicone modified nanoparticles in polypropylene. The structure–property relationship of the formed systems was studied. A melamine layer of 1.45 nm thickness was formed around ammonium polyphosphate in order to improve the hygrothermal stability, but this layer was not shear‐resistant enough. An interphase formed using a special silicone additive is more stable and acts with the intumescent flame‐retardant system synergistically. The advantageous interfacial structure is quite complex in this case: polyphosphate particles are surrounded with a macromolecular layer formed from polyol, silicone, and reactive surfactant in order to ensure good stability, efficiency and compatibility. AFM, XPS and a Cone Calorimeter were used for determining the structure and flame‐retardancy of these systems. Nanocomposites combined with silicone‐containing intumescent system were developed in order to avoid dipping at ignition in the vertical position. SAXS and µ‐TA methods were used for determining the structure of this material. Copyright ­© 2003 John Wiley &amp; Sons, Ltd.