Institute of Fundamental Technological Research

This paper is concerned with numerical modeling of deformation and fracture of a metal ligament bridging the crack faces in ceramic-metal composites, as a prerequisite for the determination of the J integral for composites with interpenetrating microstructure. A finite element model is proposed of an elasto-plastic crack-reinforcing fiber undergoing large plastic deformations and progressive debonding from the elastic matrix through a cohesive matrix-fiber interface. The σ-u relationships are derived first in the case of pullout of an elasto-plastic fiber embedded in an elastic matrix and then in uniaxial tension of the elasto-plastic fiber bridging the crack faces in elastic matrix. The obtained numerical results are discussed and compared with the theoretical predictions reported by other authors.

ceramic–metal composites, fracture modeling, crack bridging, fiber pullout, cohesive interface, fiber debonding, finite element simulations

This paper presents a simple way of using X-ray micro-computed tomography (micro-CT) in numerical modeling of material properties of metal-ceramic composites. It shows step by step the proposed methodology with details of the finite element mesh creation, so that it can easily be reproduced by interested researchers. Two case studies are considered to show the proposed approach at work: i) determination of processing-induced residual stresses in hot pressed Cr/Al2O3 and NiAl/Al2O3 particulate composites and ii) determination of J-integral for an interpenetrating phase composite made of porous alumina preform infiltrated with molten copper. The method is straightforward and effective but has its limitations that are pointed out.

The metal-ceramic interpenetrating phase composites (IPC) are usually processed by pressure assisted or pressureless infiltration of molten metals into porous ceramic performs. They have characteristic microstructure different than typical MMC or CMC with particulate or fiber reinforcement. The main difference is that both metal and ceramic phases are spatially continuous forming complementary 3D skeletons of non-zero stiffness. The uniform microstructure, enhanced mechanical and thermal properties are the main advantages of IPC. A state-of-the art in fracture and damage modelling of IPC can be found in [1], while models of effective properties in [2] and [3]. The objective of this paper is twofold: (i) to model the effective elastic properties of IPC, and (ii) to model the fracture in IPC with the crack bridging being the major toughening mechanism. The developed models are verified on the example of Al2O3-Cu infiltrated composites.

[1] Basista M. and Weglewski W. (2006). Modelling of damage and fracture in ceramic-matrix composites – an overview, J. Theor. Appl. Mech., 44, 455-484.
[2] Feng X., Tian Z., Liu Y. and Yu S. (2004). Effective elastic and plastic properties of interpenetrating multiphase composites, Appl. Comp. Mater., 11, 33-55.
[3] Poniznik Z., Salit V., Basista M. and Gross D. (2008). Effective elastic properties of interpenetrating phase composites, Comp. Mat. Sci., 44, 813-820.

Interpenetrating phase composites, effective elastic properties, crack bridging

Objective of this paper is to estimate the effective elastic properties of metal-ceramic interpenetrating phase composites (IPC). To this end, approximate analytical models such as Feng’s and Tuchinskii’s model were employed and checked against Voigt, Reuss, and Hashin–Shtrikman bounds. On the other hand, the overall elastic properties of IPC were determined by means of some numerical models suitable for the interpenetrating networks with model microstructures. A real Al2O3–Cu microstructure acquired from the computer tomography images was also used for numerical simulations.

Interpenetrating phase composites, Metal-ceramic composites, Effective elastic moduli, Finite element method, Micromechanics, Microstructure

In processing of metal-ceramic composites thermal residual stresses may result from different CTEs of the constituent materials, variable cooling rates inside the bulk material, or irregular pore shapes causing thermal stress concentrations.This paper investigates the interplay between material microstructure and processing-induced thermal residual stresses (TRS) in particulate bulk metal-matrix composites (MMC) and infiltrated phase composites (IPC) with the main objective to explore thecombined effect of TRS and microstructure on the macroscopic mechanical properties (E modulus, bending strength, fracture toughness) of the composite. The main focus is on numerical modelling of TRS, fracture toughness and effective elastic properties, while taking into account the real material microstructure from micro–computed tomography (micro-CT) experiments. The modelling methodology will be developed on examples ofa hot pressed chromium-alumina bulk MMCdoped with rheniumand on an IPC obtained by squeeze casting infiltrationof an alumina porous preform with molten Al alloyor Cu. Our interest in these particular compositesis motivated by their potential applications in transport and energy sectors. The paperwill includehighlights on the processingtechnologies used(HP, SPS, ceramic tape casting/squeeze casting infiltration), microscopic analysis of material microstructure with special focus on micro-CT scanning, measurements of TRS by neutron diffraction (ND) method, and numerical modelling of TRS by FEM using micro-CT images of real material microstructure. A numerical micro-CT based model developed to predict the TRS, Young’s modulus with account of TRS-induced damage of the ceramic phase will be shown (cf. Fig. 1). The grain size effect on TRS and Young’s modulus will be addressed. A good predictive capability of these TRS models was achieved which may become important considering the cost of beam time for ND experiments at neutron sources. Another model to be presented is concerned with micro-CT FEM modeling of fracture in infiltrated metal-ceramic composites. The model accounts for crack bridging toughening mechanism, large plastic deformations of metal ligaments, and matrix-ligament decohesion. Here the results on J integralin the case of compact-tensiontest specimen made of real interpentrating phase composite will be discussed. Finally, the large pool of obtained experimental data and modelling results will be wrapped up and conclusions will be drawn.

metal-ceramic composites, processing, thermal residual stresses, Youngs' modulus, microCT imaging, numerical modelling

The motivation for research on interpenetrating phase composites and possible applications of these novel materials were given in [1]. A rationale behind designing an IPC is to achieve a highly durable material that would combine the most desirable properties of the constituent phases: the high hardness and wear resistance of ceramic and improved fracture toughness and thermal conductivity due to the metal content. The interpenetrating metal-ceramic composites may have remarkable applicability in different sectors of industry, e.g. automotive and aerospace. They should, thus, be carefully investigated in terms of processing routes, material properties and modeling of material response to service conditions.
A 3D FEM model in ABAQUS of the fracture parameters and crack growth in bi-continuous metal-ceramic composites with interpenetrating microstructure (IPC) is proposed. The crack is modeled using the extended finite element method (XFEM) [4]. The J-integral and fracture toughness KIc are determined for a real IPC microstructure obtained from micro-CT images. The fracture parameters (i.e. fracture toughness KIc, J integral, crack opening displacement) are key mechanical characteristics of IPC composites because of the brittleness of the ceramic phase. The main effects occurring in metal-ceramic IPC during fracture are described (cf. [2], [3]).

Ceramic-metal composites, interpenetrating microstructure, fracture toughness, crack growth, numerical modeling, XFEM

A 3D FEM model for crack growth in bi‐continuous metal‐ceramic composites with interpenetrating microstructure (IPC) is proposed. The results for the load‐displacements relationship in a plastically deformable reinforcing fibre computed by means of different material models will be shown. The J‐integral and fracture toughness will be determined for a simplified IPC microstructure with reinforcing ligaments modeled as axisymmetric fibres, and for real IPC microstructure obtained from micro‐CT images

interpenetrating phase composites, bi‐continuous composites, metal‐ceramic composites, crack bridging, crack growth, fracture toughness, finite element method

The paper is focused on modeling of the overall elastic properties and crack toughening mechanism by bridging in metal-ceramic interpenetrating phase composites (IPC). The Tuchinskii-Feng analytical model (Feng 2004) especially devised for IPC microstructures is further developed. Numerical FEM models of the effective elastic constants are implemented for the simplified 3-D cross microstructure and real microstructures based on micro-CT scans. The energy release rate increase due to crack bridging (Mataga 1989) is modeled numerically. The stress-displacement relationships in the reinforcing fibers undergoing large strains and delamination from the matrix materials are obtained and then applied as material models for the bridging reinforcements in compact-tension test specimen of the fracture toughness determination. The J integral for this specimen is calculated by FEM (Abaqus) with reinforcing ligaments modeled as truss and cohesive elements. The growth of a bridged crack is also modeled numerically.

Effective elastic constants, Fracture toughness, Crack toughening, Crack bridging, Metal-ceramic composites, FEM

The objective of this paper is the analytical and numerical modelling of the overall elastic properties and the crack bridging toughening mechanism in metal-ceramic composites with interpenetrating phase microstructure (IPC). The specific microstructure of the IPC makes the effective media/field models based on Eshelby's solution inapplicable to the estimation of the effective elastic properties of the IPC. The effective material constants were calculated analytically extending the Tuchinskii-Feng models devised for the IPC microstructure. Numerical FEM models were developed for two types of IPC microstructure: simplified 3-D cross structure and real microstructure obtained with computer micro-tomography scans. The micro-CT scans were transformed into FEM meshes using the Simpleware ScanIP/FE commercial software. The crack bridging mechanism was investigated assuming the metal ligament undergoing large plastic deformations (necking) and delamination from the surrounding elastic material (ceramic matrix). As a first step towards the numerical determination of J integral from the simulation of the CT (compact tension) test. the s-u relationship in the metal fiber was determined numerically and applied to compute the stress and displacement fields in the CT specimen. The numerical solution agrees well with the analytical one obtained by Mataga et al. [4].

Interpenetrating phase composites, metal-ceramic composites, overall material properties, crack bridging, finite element method, micromechanics, microstructure