APPLICATIONS AND MODELLING CHALLENGES OF METAL-MATRIX COMPOSITES

Metal-matrix composites find application in several industrial sectors, where either the homogenized material and the component phases can be designed and optimized by multiscale simulations performed on realistic numerical models of the actual microstructure. This approach benefits of nowadays commonly available image processing and micro-computed tomography techniques, as well as of authomatic mesh generation procedures for non-linear finite element analysis.The related computing costs can be reduced significantly by analytical approximations, which retain the essential features of the investigated system response and make the transition between micro and macroscale potentially feasible even in industrial practice. The present chapter reviews recent contributions in this research area

The influence of imperfect interfaces on the measurable effective properties of ceramic composites

This work evaluates the influence of the interface characteristics on the measurable quantities that reflect the overall response of ceramic composites. The situations that may lead to the misinterpretation of the experimental results are evidenced. The study is carried out on representative volume elements (RVEs) of periodic microstructures with either perfect adhesion or pure frictional coupling between the matrix and the reinforcement. These alternatives may constitute the initial and the final material configuration in the presence of damaging processes. The mechanical response to common characterization tests is reproduced by numerical analyses, and measurable quantities are evaluated by computational homogenization procedures. Different material combinations with fiber or particle inclusions are analyzed. The case of porous composites is also introduced for comparison purposes. Overall stresses and strains are not proportional in the presence of frictional interfaces. It is however shown that the deviation from linearity is slight and prone to be confused with experimental inaccuracies, e.g. due to the initial adjustment of the testing devices. The effect on the effective material proprieties is significant, though

The influence of imperfect interfaces on the overall mechanical response of metal-matrix composites

A systematic study of the overall mechanical response of strongly or weakly bonded periodic composites has been performed. Results have been recovered in the extreme conditions of perfect adhesion and pure friction. The aim of this investigation is to evaluate the sensibility of the overall material behavior to the interface characteristics and to evidence the load transfer mechanisms between the matrix and the inclusions. The problem is particularly relevant for metal-ceramic composites, due to low chemical affinity and difficult production processes that can prevent the desirable coupling between the components

A Numerical Investigation of the Influence of the Material Microstructure on the Failure Mode of Metal Ceramic Composites

Metal failure is often initiated by strain localization in narrow bands. In metal matrix composites, the occurrence and the consequences of this phenomenon are influenced by the material microstructure. This dependency has been numerically investigated by considering periodic and quasi-periodic arrangement of ceramic fibers in a metal matrix, with reinforcement content varying between 10% and 50% in volume. The constitutive response of the metal has been simulated by the widely used GTN (Gurson-Tvergaard-Needleman) continuum damage-plasticity model with evolution law based on local porosity. The onset of failure for the composite has been identified with the critical growth of micro voids that induce softening at the macro scale. An extensive study has been performed in order to distinguish the effects of the material microstructure, the role of the imperfections and the influence of the simulation details. The main results of this investigation are summarized in this paper

Surrogate analytical models of damage localization in metal matrix composites

Several parameters entering the constitutive laws of metal matrix composites are not amenable to direct measurement. Their determination is therefore demanded to indirect identification procedures, based on the comparison between the output of some experimental works and the results of the iterative simulation of the performed tests. Largely repetitive numerical analyses can also support the optimized design of composite microstructures, the understanding of the actual stress-transfer mechanisms, and virtual testing. Surrogate analytical models can replace effectively non-linear finite element (FE) computations in parametric studies and identification procedures, reducing execution times and costs without compromising the accuracy of the results. In this context, a frequently used approach consists of the interpolation, by means of radial basis functions (RBFs), of data filtered by proper orthogonal decomposition (POD). This methodology is often used to reproduce the smooth output of different mechanical systems. This work is rather focused on the homogenized response of damaging metal matrix composites subjected to strain localization phenomena, and explores the accuracy achievable in these situations by the POD-RBF approximation of more traditional FE analyses. In all considered cases, the POD-RBF results are accurate, and able to distinguish between apparently similar situations. The approach is flexible, and the performance of the surrogate models can be tailored to the requirements of each application. In particular, various analytical approximations can be introduced to support the design of new microstructures and material couplings, and to understand the role of any material and/or geometry imperfections resulting from the production processes

Experimental and Numerical Investigation of the Deformation and Fracture Mode of Microcantilever Beams Made of Cr(Re)/Al2O3 Metal–Matrix Composite

This work presents a combined experimental and computational study of the deformation and fracture of microcantilever specimens made of chromium(rhenium)-alumina metal–matrix composite (MMC), with a particular focus on the failure properties of the metal–ceramic interfaces. The obtained experimental results show that the bending strength of microcantilevers containing alumina particles in critical cross-sections near specimen’s fixed end is considerably higher than that of unreinforced chromium(rhenium) samples. Brittle cracking along chromium–alumina interfaces is the dominant fracture mode of the composite microcantilevers. The interface characteristics are determined in an indirect way by numerical simulations of the experiment with account of the actual specimen microstructure from the scanning electron microscope (SEM) images. A parametric study demonstrates that the overall material response may be reproduced by different sets of model parameters, whereas the actual failure mode permits to discriminate among the possible alternatives. Using this approach, the in situ values of the chromium–alumina interface cohesive strength and the fracture energy are estimated