Modelling of pseudoplastic deformation of carbon/carbon composites with a pyrocarbon matrix (original) (raw)
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Deformation and failure of a carbon fibre composite under combined shear and transverse loading
Acta Metallurgica et Materialia, 1995
The in-plane shear and transverse properties are measured for T800-924C carbon fibre reinforced epoxy unidirectional material. Non-linearity in the shear response is ascribed partly to plasticity and partly to micro-crack growth within the matrix. The stress-strain response under proportional and non-proportional stressing supports the use of a deformation theory of plasticity. A failure envelope is measured and presented in both stress space and in strain space for the composite; failure is associated with distributed tensile micro-cracking within the matrix.
Effect of architecture on mechanical properties of carbon/carbon composites
Composite Structures, 2008
Three-directional orthogonal, 3-directional plain-woven and 4-directional in-plane composites are three architectures commonly used in components made of carbon/carbon composites. Homogenization and finite element analysis of a three-dimensional periodic unit cell characterizing the structure of the composite and periodic boundary conditions are used to compute the elastic moduli of carbon/carbon composites for different architectures. First, the mechanical properties of a fiber bundle are predicted assuming the fiber bundle to be a perfectly bonded uni-directional composite. Second, these properties are used to predict the mechanical properties of the multidirectional composite. Cohesive zone models are used to simulate the interfacial debonding at the fiber bundle/matrix interfaces. The application of cohesive zone model when there are debonds at the interface between the fiber bundle and the matrix results in a remarkable change in the values of shear modulus when compared to that obtained for perfectly bonded composites. The analysis predicts a significant effect of architecture on the properties of composite.
Micromechanical modelling of finite deformation of thermoplastic matrix composites
The prediction of the constitutive behavior of thermoplastic matrix composites from quasi-static up to impact rates demands a detailed understanding of the behavior of the polymeric constituents of these materials; this is due to the pronounced rate dependence of the polymeric matrix. This paper is an attempt at approaching the prediction of finite deformation of thermoplastic matrix composites, using a multi-scale approach in which the fibre and the matrix are separately modelled and combined within a finite element scheme to determine the constitutive response of the test composite. A micromechanical model comprising a finite element implementation of constitutive laws for the fibre and matrix constituents are discussed. The robust formulation for predicting the behavior of the semicrystalline polymer was successfully developed, including the techniques of generating the 3D representative volume element (RVE) of composites as well as prescribing the periodic boundary conditions on the 3D RVE. Finally, the validation studies for predicting the elastic properties of the composite using the Finite Element (FE) methods and the effect of spatial arrangement of the fibre inclusions within the matrix at finite strains are illustrated.
A micromechanically based model for strain rate effects in unidirectional composites
Mechanics of Materials, 2020
This article addresses dynamic behaviour of fibre reinforced polymer composites in terms of a transversely isotropic viscoelastic-viscoplastic constitutive model established at the unidirectional ply level. The model captures the prelocalized response of the ply in terms of rate dependent elasticity and strength without damage. A major novelty is that the model draws from computational homogenization, with matrix and fibre materials as subscale constituents for a representative volume element of the ply. The micromechanics of the strain rate dependent polymer matrix is represented by an isotropic pressure sensitive viscoelastic-viscoplastic prototype model. For the fibre material, transverse elasticity is assumed. The constituents are homogenized via the fluctuating strain of the subscale, where a simple ansatz is applied to allow for constant stress in the plane transverse to the fibre orientation. Despite the relatively simple modelling assumptions for the constituents, the homogenized model compares favourably to experimental data for an epoxy/carbon fibre based composite, subjected to a variety of challenging uniaxial off-axis tests. The model response clearly reflects observed strain rate dependencies under both tensile and compressive loadings.
Computational Materials Science, 2014
A computational study of the effect of microstructure of hybrid carbon/glass fiber composites on their strength is presented. Unit cells with hundreds of randomly located and misaligned fibers of various properties and arrangements are subject to tensile and compression loading, and the evolution of fiber damages is analyzed in numerical experiments. The effects of fiber clustering, matrix properties, nanoreinforcement, load sharing rules on the strength and damage resistance of composites are studied. It was observed that hybrid composites under uniform displacement loading might have lower strength than pure composites, while the strength of hybrid composites under inform force loading increases steadily with increasing the volume content of carbon fibers.
Numerical modeling of the microstructure of carbon/carbon composites on different length scales
Carbon/carbon composites produced by chemical vapour infiltration consist of carbon fibers embedded in a matrix of pyrolytic carbon with anisotropic mechanical properties. Microscopic studies show that the production process facilitates formation of a matrix consisting of cylindrically shaped pyrolytic carbon layers. The matrix layers may have different textures, which induce different mechanical properties in the axial, radial and circumferential directions. By modifying the production process parameters, it is possible to control the order, approximate width and degree of texture of the layers. Depending on the infiltration conditions pores with different geometry, size and orientations are formed between fibers with pyrolytic carbon coating. One of the goals of the present study is the microstructure characterization and the statistical description of the matrix texture, the fibers orientation distribution and the porosity. Furthermore, a micromechanical modeling using homogenization methods of the material on different length scales is performed. Correlation between calculated and experimentally obtained material properties is also discussed.
Materials Letters, 2002
By incorporating small amounts (0 5 5 at%) of transition metals (TM) of Cr, Mo, Fe and Ta into Pd 40 Cu 30 Ni 10 P 20 alloy that has been considered to be the best glass former so far, in-situ composites consisting of a glassy phase and nano-and/or micro-sized crystalline particles were prepared by copper-mold casting. The nano-and micro-sized particles identified to be phosphides are homogeneously dispersed in a glassy matrix. The formation of such a characteristic structure is attributed to a primary crystallization reaction with high nucleation rate and limited growth rate in the undercooled Pd 40 Cu 30Àx Ni 10 P 20 TM x melt. The TM atoms interact preferentially with the clusters of Pd-Ni-P, one kind of atomic units in the deeply undercooled Pd-Cu-Ni-P liquid, and result in the formation of the TM-Ni-P or TM-Ni-P-Pd clustered units in the undercooled melt, which act as nucleation sites during solidification. With the addition of Cr, Mo, Fe and Ta atoms into Pd 40 Cu 30 Ni 10 P 20 alloy, the first phosphide phases precipitated from these melts are Ni 33 Cr 33 P 34 , MoNiP, Fe 33 Ni 33 P 34 , and (Pd,Ta)NiP, respectively. These phases possess the same hexagonal structure as Fe 2 P (hP9). The dispersed particles have a volume fraction ranging from 9 to 18% for the alloys investigated. The compressive strength and ductility of these glassy composites are not significantly improved by the dispersion of the nano-and micro-sized particles. These glassy composites deformed by an inhomogeneous shear slip mode and fractured by an adiabatic shear mechanism. The nucleation behavior and the effect of dispersed particles on the deformation and fracture behavior are discussed.
2001
The role of the interphase in the failure of carbon fibre/epoxy composites has been investigated using elasto-plastic finite element (FE) analysis. It has been found that the interphase has little effect on the fibre stresses but a significant effect on matrix strains. Plastic strains in the matrix material were found to decrease when an interphase was included in the model. Failure in a short fibre composite was investigated using the Rice and Tracey voidgrowth model and slow crack growth was assumed. A crack initiation criterion was developed to predict the initiation angle for the matrix crack and the applied strain at failure. In a long fibre composite, a high strain rate near the fibre fracture location induced by the fibre recoil makes catastrophic failure involving rapid crack-growth in the matrix material more likely. The semi-cone angle of a matrix crack was predicted to be about twice the value for a short fibre system using the minimum strain energy criterion. It was also found that the fibre stress profiles are characteristic of the matrix crack geometries. 4p The effects of the inter-fibre spacing and the presence of a matrix crack on the stress redistribution in a planar array and hexagonal array of fibres composite have been investigated using 3-D elasto-plastic FE analysis. Matrix cracks were found to have a significant effect in determining the stress amplification factor (SAF) in planar array composites but have less effect in hexagonal array composites. The presence of a matrix crack was also found to increase the positively affected length (PAL) and better agreement for the fibre stress profiles with the LRS results was obtained.
Composite Structures, 2018
A multi-scale computational analysis based on representative volume element (RVE) modeling and molecular dynamics (MD) simulations is developed to investigate the microscopic failure mechanisms of unidirectional (UD) carbon fiber reinforced polymer (CFRP) composites. The average properties of the 200-nm thickness interphase region between fiber and matrix are characterized through MD simulations and an analytical gradient model. The results demonstrate that the interphase region has higher Young's modulus and strength, compared to the bulk matrix. This stiffened interphase region influences the composite response significantly. Specifically, the traditional two-phase model with zero-thickness interface fails to capture the stress-strain behavior compared to the experimental data. However, by adding the interphase region to a modified RVE model, the accuracy of simulation results will be improved significantly. Furthermore, a coupled experimental-computational micromechanics approach is adopted to calibrate and validate the cohesive parameters of the interface. By including the cohesive interface, our modified RVE model accurately captures the failure strength of the composites. Finally, different failure mechanisms for specimens are investigated using our multi-scale computational framework. The results show that the failure modes of UD CFRP composites are very complex and multiple failure mechanisms co-exist depending on the loading conditions, agreeing well with our experimental analyses.
Micromechanical Modeling of Porous Carbon/Carbon Composites
Mechanics of Advanced Materials and Structures, 2005
A procedure to model fiber-reinforced composites containing pores of irregular shapes is presented. Closed-form expressions for contributions of fibers and pores into effective elastic moduli are provided. The procedure is applied to predict the transverse elastic properties of unidirectional carbon/carbon composites (carbon fibers in pyrolytic carbon matrix) densified by chemical vapor infiltration. Infiltration treatment results in the formation of irregularly shaped pores randomly oriented in the plane perpendicular to the direction of fiber (transverse plane). These pores are analyzed using a numerical conformal mapping technique, and their contribution to the effective elastic properties is expressed in terms of the cavity compliance contribution tensor. Components of this tensor are found for a variety of typical pore shapes.