Fiber Reinforced Metal Matrix Composites Research Articles

Thermal Cycling Stresses in W‐Monofilament Reinforced Copper

AbstractNew materials have to be developed for fusion reactor systems to withstand the high thermal load and heavy irradiation under service conditions. The divertor element collects the residuals of the nuclear reaction and withdraws heat from the reaction chamber into a heat sink. A thermal flux of ≈20 W mK−1 can be expected in such components. A plasma facing W plate is attached to a CuCrZr heat sink suffering CTE mismatch stresses at the interface due to pulsed operation required for the Tokamak reactor design. Fiber reinforced metal matrix composites are applied as an interlayer to reduce macroscopic interfacial stresses in these components. W‐wire reinforced copper is a promising material for this application due to a good fiber‐matrix bonding strength which is further increased by surface etching or graded interface designs. Thermal stresses in between the matrix and the wires are responsible for thermal fatigue damage within the constituents and at their interface. Neutron and synchrotron diffraction was performed in situ during thermal cycling to determine the micro stress amplitudes and their changes under simulated service conditions.

Predicting the elastoplastic response of fiber-reinforced metal matrix composites

This paper aims to investigate the effect of microstructure parameters (such as the cross-sectional shape of fibers and fiber volume fraction) on the stress–strain behavior of unidirectional composites subjected to off-axis loadings. A micromechanical model with a periodic microstructure is used to analyze a representative volume element. The fiber is linearly elastic, but the matrix is nonlinear. The Bodner–Partom model is used to characterize the nonlinear response of the fiber-reinforced composites. The analytical results obtained show that the flow stress of composites with square fibers is higher than with circular or elliptic ones. The difference in the elastoplastic response, which is affected by the fiber shape, can be disregarded if the fiber volume fraction is smaller than 0.15. Furthermore, the effect of fiber shape on the stress–strain behavior of the composite can be ignored if the off-axis loading angle is smaller than 30°.

THE INVESTIGATION OF THE ELASTIC-PLASTIC BEHAVIOR USING THE PROPERTY GRADIENT OF THE INTERFACIAL REGION IN FIBER REINFORCED MMC

In this study, the interfacial perpendicular crack behavior and stress state of the unidirectional fiber reinforced Metal Matrix Composites (MMCs) are investigated by using FEA under the transverse loading. The fiber assumed as isotropic linear elastic SiC and the matrix is assumed as isotropic elastic-plastic Ti . The fiber/matrix interface is modeled as multi thin layer with different linear material properties. The behavior of perpendicular crack to the interface according to the change of the interface characteristics and thickness are evaluated.

A mean-field micromechanical study on thermal-cycling creep of short fiber-reinforced metal matrix composites: Al–Al3Ni eutectic composites

In this study, a unified mean-field micromechanical model was applied to analysis of thermal-cycling creep of short fiber-reinforced metal matrix composites subject to a wide range of external loads from compression to tension. The model considered the rate process of the local mass transfer by diffusion along the fiber/matrix interface. The thermal-cycling creep of the composites can be divided into three groups observed in high compressive stress regime, low compressive and tensile stress regime, and high tensile stress regime based on the micromechanical examination of the deformation mechanism. Numerical and experimental studies were systematically conducted with directionally solidified Al–Al3Ni eutectic composites. These studies demonstrated that even though compressive loads were applied, the elongate creep deformation occurred under given thermal-cycling conditions, and thermal-cycling creep was largely affected by the length of the fiber and temperature profile.

A mean-field micromechanical model of thermal-ratcheting behavior in short fiber-reinforced metal matrix composites

Thermal-ratcheting behavior in short fiber-reinforced metal matrix composites has been investigated. The internal stresses due to mismatch in thermal expansion coefficients between the fiber and matrix in the composites can introduce anomalous deformation under thermal-cycling conditions with or without external mechanical loads. This study has resulted in a more comprehensive understanding of such thermal-ratcheting behavior in short fiber-reinforced composites subject to a wide range of external uniaxial loads based on a mean-field micromechanical model considering the local mass transfer by diffusion along the fiber–matrix interface. The validity of the model has been verified through systematic experiments with directionally solidified Al–Al 3Ni eutectic composites.

Modeling of Damage Evolution and Failure in Fiber-Reinforced Ductile Composites Under Thermomechanical Fatigue Loading

In this article, a methodology based upon micromechanical analysis of multiple damage-plasticity events is developed to predict nonlinear cyclic stress-strain response and fatigue failure of continuous fiber-reinforced metal matrix composites under cyclical thermomechanical loading. Microscopic damage-plasticity events in composite are described by fiber fracture, local cyclic plasticity of matrix and interface as well as interfacial debonding. A superposition method under the framework of shear-lag arguments is developed to analyze cyclic stress and deformation in the composites. A simulation scheme coupled with Monte-Carlo method is proposed to investigate evolution of damage-plasticity, cyclic behavior, and fatigue life of the composites. The statistic variations in fiber strength, local thermoplasticity of matrix properties, and interface characters between fiber and matrix have been taken into account. The model can predict the crossover behavior of the S-N curves observed in experiments for the in-phase and out-of-phase thermomechanical fatigue loads. The underlying mechanisms controlling the cross-over behavior have been revealed by the simulation.

Damage Detection in Fibre Reinforced Ceramic and Metal Matrix Composites by Acoustic Emission

In this work damage micro-mechanisms of two different types of fibre reinforced composites are investigated by acoustic emission, AE. Ceramic based oxide fibre reinforced mullite matrix composite and metallic based SiC fibre reinforced titanium matrix composites exhibit different fracture mechanisms during loading and AE technique could pinpoint these damage mechanisms based on the AE responses detected simultaneously. The results show that in a ceramic matrix composite, the identification of fibre fracture and matrix cracking requires careful analysis of the AE data as both fibres and matrix break in brittle manner. Whereas the separation of fibre fracture from the ductile tearing of matrix ligaments could be easier in metallic based composites, such as titanium matrix composites.

Effect of Short Fiber Reinforcement on the Fracture Toughness of Metal Matrix Composites

Evaluation of fracture toughness of short fiber reinforced metal matrix composites (MMCs) becomes important for their application as structural materials. Therefore, in this study static and dynamic fracture toughness of MMCs manufactured by squeeze casting process were investigated. A number of MMCs were tested with various matrix alloy, volume fractions and specifically types of reinforcements. It was found that static and dynamic fracture toughness of MMCs was remarkably decreased by the addition of ceramic reinforcements. Compared with static fracture toughness, the mean cause of the decrease difference of dynamic fracture toughness and notch dynamic fracture toughness is due to the effect of dynamic velocity under impact loading. The toughness of ceramic reinforced MMCs is controlled by a complex interaction between the matrix alloy and reinforcement. Important properties which influence toughness include the type of reinforcement (appearance, size), volume fraction and combination of reinforcement and the matrix alloy. Notch fracture toughness of MMCs for simple evaluation was also discussed.

Effect of imperfect interfaces on Elastothermodynamic Damping of fibre-reinforced MMCs

Elastothermodynamic Damping (ETD) is a source of damping present in all thermoelastic materials. Most of the works related to the evaluation of ETD in fibre-reinforced Metal-Matrix Composites (MMCs) assume perfect interfaces between reinforcement and matrix. On the contrary, composite materials do have imperfect interfaces because of debonding between the reinforcement and matrix. In recent years, the effect of imperfect interfaces on ETD of particulate MMCs has been analysed. In this work, imperfect interface model for the particulate composites has been extended to a continuous unidirectional fibre-reinforced composite. The investigations of imperfect mechanical and thermal interface on the ETD capacity have been carried out.

Modeling of Progressive Failure in Ductile Matrix Composites Including Local Matrix Yielding

In this article a theoretical model based upon micromechanical analysis of damage is developed to predict nonlinear stress-strain response and progressive failure of continuous fiber-reinforced metal matrix composites (MMCf). A micromechanically analytical model using an influence function superimposition technique is developed to derive stress profiles for any configuration of breaks in MMCf under tensile loading, by considering local matrix tensile yield and interface yield (or sliding). Several hundred Monte Carlo simulations including these failure mechanisms have been executed to simulate failure process and determine statistically the ultimate strength distributions of the composites. Site discretization, material sizes and shape parameter in Weibull distribution are studied to investigate the dependence of ultimate strength on these factors. It is shown that the size dependence of composite ultimate strength is dominated by fiber strength statistics and stress redistribution due to progressive microdamage.

Fiber push-out study of a copper matrix composite with an engineered interface: Experiments and cohesive element simulation

The fiber push-out test is a basic method to probe the mechanical properties of the fiber/matrix interface of fiber-reinforced metal matrix composites. In order to estimate the interfacial properties, parameters should be calibrated using the measured load–displacement data and theoretical models. In the case of a soft matrix composite, the possible plastic yield of the matrix has to be considered for the calibration. Since the conventional shear lag models are based on elastic behavior, a detailed assessment of the plastic effect is needed for accurate calibration. In this paper, experimental and simulation studies are presented regarding the effect of matrix plasticity on the push-out behavior of a copper matrix composite with strong interface bonding. Microscopic images exhibited significant local plastic deformation near the fibers leading to salient nonlinear response in the global load–displacement curve. For comparison, uncoated interface with no chemical bonding was also examined where the nonlinearity was not observed. A progressive FEM simulation was conducted for a complete push-out process using the cohesive zone model and inverse fitting. Excellent coincidence was achieved with the measured push-out curve. The predicted results confirmed the experimental observations.

Modeling the Effect of Active Fiber Cooling on the Microstructure of Fiber-Reinforced Metal Matrix Composites

A modified pressure infiltration process was recently developed to synthesize carbon-fiber-reinforced aluminum matrix composites. In the modified process, the ends of carbon fibers are extended out of the crucible to induce selective cooling. The process is found to be effective in improving the quality of composites. The present work is focused on determining the effect of the induced conductive heat transfer on the composite system through numerical methods. Due to the axisymmetry of the system, a two-dimensional (2-D) model is studied that can be expanded into three dimensions. The variables in this transient analysis include the fiber radius, fiber length, and melt superheat temperature. The results show that the composite system can be tailored to have a temperature on the fiber surface that is lower than the melt, to promote nucleation on the fiber surface. It is also observed that there is a point of inflection in the temperature profile along the particle/melt interface at which there is no temperature gradient in the radial direction. The information about the inflection point can be used to control the diffusion of solute atoms in the system. The result can be used in determining the optimum fiber volume fraction in metal matrix composite (MMC) materials to obtain the desired microstructure.

An elastoplastic damage model for metal matrix composites considering progressive imperfect interface under transverse loading

An elastoplastic damage model considering progressive imperfect interface is proposed to predict the effective elastoplastic behavior and multi-level damage progression in fiber-reinforced metal matrix composites (FRMMCs) under transverse loading. The modified Eshelby’s tensor for a cylindrical inclusion with slightly weakened interface is adopted to model fibers having mild or severe imperfect interfaces [Lee, H.K., Pyo, S.H., 2009. A 3D-damage model for fiber-reinforced brittle composites with microcracks and imperfect interfaces. J. Eng. Mech. ASCE. doi:10.1061/(ASCE)EM.1943-7889.0000039]. An elastoplastic model is derived micromechanically on the basis of the ensemble-volume averaging procedure and the first-order effects of eigenstrains. A multi-level damage model [Lee, H.K., Pyo, S.H., 2008a. Multi-level modeling of effective elastic behavior and progressive weakened interface in particulate composites. Compos. Sci. Technol. 68, 387–397] in accordance with the Weibull’s probabilistic function is then incorporated into the elastoplastic multi-level damage model to describe the sequential, progressive imperfect interface in the composites. Numerical examples corresponding to uniaxial and biaxial transverse tensile loadings are solved to illustrate the potential of the proposed micromechanical framework. A series of parametric analysis are carried out to investigate the influence of model parameters on the progression of imperfect interface in the composites. Furthermore, a comparison between the present prediction and experimental data in the literature is made to assess the capability of the proposed micromechanical framework.

Hygrothermal Stresses in Coated Hollow/Solid Fibers Reinforced Polymer Matrix Composites (PMCs)

Using composite cylinders assembly (CCA) model, a generalized algorithm has been developed to evaluate the micro stresses developed in the constituent phases of multiply (N-phases) coated hollow/solid fiber reinforced polymer matrix composites (PMCs) under different hygrothermal loading conditions. In the formulation all the N-phases are considered to be transversely isotropic. Results have been presented for S-glass/epoxy and AS-graphite/epoxy composites treating them as a five-phase (fiber, coating, matrix, and the composite) composite, void being the fifth phase along the centre line of the fiber. Results reveal the differences in the nature and the magnitude of stresses developed when solid fibers are replaced by the hollow ones. The algorithm can be utilized for evaluating the stresses in the constituent phases of multiply coated fiber reinforced metal matrix composites also where more than one coating layer and reaction zones, each with different constituent properties, are to be considered and the composite has to be treated as multiphase composite.

Three-dimensional shakedown analysis of fiber-reinforced metal matrix composite (FRMMC) layered plasma-facing component for high heat flux loading

Copper alloys have been considered as a structural material for the heat sink substrate of a plasma-facing component (PFC) due to their excellent thermal conductivity. However, insufficient high temperature strength and large thermal expansion set the limitations to structural applications. Fiber-reinforced metal matrix composites (FRMMCs) can be a candidate for a structural material for the future PFCs due to the excellent high temperature strength. Since the FRMMCs of the PFCs are exposed to thermal and mechanical loads, the resulting stress fields in mesoscopic level are highly heterogeneous and often exceed the yield limit of the matrix. The shakedown limit was investigated as the safety criterion of the FRMMCs considering the fusion-relevant thermomechanical loads. In this work, the shakedown theorems were formulated with FEM and the large-scale nonlinear optimization program. The shakedown formulation was extended to three-dimensional models. The shakedown limits were determined for SiC fiber and Cu alloy FRMMC composite system. The stress and temperature loading paths of FRMMC components were determined in the fusion-relevant loading. The thermomechanical loading paths were compared with the shakedown limits. The results showed that the loading paths in the high heat flux (HHF) operation condition were partly covered by the area of shakedown limits. It was interpreted that the FRMMC layers may undergo low cycle fatigue.

Shakedown analysis of fibre-reinforced copper matrix composites by direct and incremental approaches

Plastic failure caused by variable loads is a critical design concern for fibre-reinforced metal matrix composites when the matrix is very soft. Shakedown analysis provides a quantitative prediction regarding the safe loading domain. In this article, shakedown analysis of fibre-reinforced copper composites is presented. For a comparative study both the FEM-based direct method and the incremental method were applied, which were based on the shakedown theorem combined with an optimisation process and FEM cyclic plasticity simulations, respectively. In addition to unidirectional lamina, a cross-ply laminate was also investigated using three dimensional unit cell models subjected to bi-axial loads. The shakedown predictions obtained from the two theoretically independent approaches showed a nice agreement each other for both lamina and laminate. Effects of loading condition, fibre volume fraction, unit cell architecture and plastic hardening laws are discussed. The trend of the lamina shakedown behaviour was interpreted in terms of the Mori–Tanaka mean field theory.

Micromechanical Elastoplastic Damage Mechanics for Elliptical Fiber-Reinforced Composites with Progressive Partial Fiber Debonding

By considering progressive interfacial partial debonding, a multi-level elastoplastic damage formulation is proposed to predict the overall transverse behavior of continuous elliptical fiber-reinforced metal matrix composites within the framework of micromechanics and homogenization. Based on the method of equivalent inclusion and taking the evolutionary interfacial debonding angle into consideration, partially debonded isotropic elliptical fibers are replaced by equivalent orthotropic yet perfectly bonded elliptical fibers. Three interfacial damage modes are considered. The Weibull’s probabilistic function is employed to describe the varying probability of progressive partial fiber debonding. The effective elastic moduli of four-phase composites, consisting of a ductile matrix and randomly located yet unidirectionally aligned elliptical fibers are derived via a micromechanical formulation. Further, the explicit exact exterior-point Eshelby’s tensor for an elliptical fiber is presented to investigate its effects upon inelastic responses of composites due to the cross-sectional shapes of fibers. In order to characterize the overall transverse elastoplastic damage behavior, an effective yield function is derived based on the ensemble-area averaging and the first-order effects of eigenstrains upon the overall yielding. Finally, comparisons between the present predictions and experimental data, and biaxial simulations are performed to illustrate the potential of the proposed framework.

In Situ Measurements of Local Strain in Heterogeneous Materials

In this study, the local deformation of an Al-7wt.% Si alloy, a 10 vol.% particle reinforced and 20 vol% short fibre reinforced metal matrix composites is studied. The strain field at the surface of the materials during tensile testing inside a scanning electron microscope is determined by image analysis and compared with FEM simulations.

Influence of the infiltration pressure on the properties of MMC wires

MMC wires are ceramic fibre reinforced metal matrix composites produced by continuous infiltration method (Blucher process). During the MMC (Metal Matrix Composite) wire production it is possible to change the applied infiltration pressure which overcomes the poor wetting behaviours between the ceramic reinforcement and the molten metal. The changing of infiltration pressure has influence on the mechanical properties by the porosity of MMC wires.

Numerical analysis of influence of micro-parameters on macro-micromechanical properties of fiber reinforced metal matrix composites

The properties of fiber reinforced metal matrix composites (MMCs) are anisotropic. These properties can be more appropriately evaluated in polar coordinate. In this paper, the elastic–plastic mechanics model of MMCs is presented based on the combination of macroscopic and meso-scopic analysis in polar coordinate. The influence of micro-parameters such as matrix materials, the fibers and fiber volume fraction of Al/Mg metal matrix composites (MMCs) on the tensile properties of MMCs is also investigated numerically by the representative volume element (RVE) and the numerical results are compared with the experimental data. The results show that the model built in polar coordinate is suitable to the real constructs of MMCs; the fiber plays a major role of load supporting during MMCs stretched. And there is little distinction of the value of maximum stress of MMCs between tests and the numerical analysis.