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CivilComp Proceedings
ISSN 17593433 CCP: 83
PROCEEDINGS OF THE EIGHTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping, G. Montero and R. Montenegro
Paper 269
Predicting the Macroscopic Behaviour of MetalMatrix Composites Embedding an Interphase A. Taliercio
Department of Structural Engineering, Politecnico di Milano, Milan, Italy A. Taliercio, "Predicting the Macroscopic Behaviour of MetalMatrix Composites Embedding an Interphase", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Eighth International Conference on Computational Structures Technology", CivilComp Press, Stirlingshire, UK, Paper 269, 2006. doi:10.4203/ccp.83.269
Keywords: fibre reinforced composites, metalmatrix, interphase, homogenization, finite elements.
Summary
A numerical model previously developed by Taliercio [2] is applied to the prediction of the macroscopic
nonlinear behaviour of unidirectional metalmatrix composites (MMCs) reinforced by a regular array of long,
parallel fibres, considering the presence of an interphase region between the fibres and the matrix.
The interphase can be either originated by the manufacturing process, which often involves high temperatures and
pressures, or purposely inserted between the fibres and the bulk matrix to improve their adhesion.
As the interphase has properties different from the neighbouring materials, a threephase composite is actually
considered.
The direct evaluation of the mechanical properties of the interphase is nearly unfeasible. Indirect testing techniques
(fiber pushin, fiber pushout ) have been proposed, as well as ultrasonic methods
or identification procedures in conjunction with micromechanical models.
The proposed numerical model is based on the finite element method in its displacement formulation. The overall response of the composite is predicted through the analysis of a single 2D unit cell, which is the crosssection of a prismatic representative volume element of unlimited length. Generalized plane strain conditions have to be assumed in the analysis of the unit cell, To this end, special finite elements are employed capable of describing 3D deformation modes invariant along the fibre axis [1]. To make the mechanical response of the unit cell representative of the macroscopic behaviour of a material element under arbitrary stresses, suitable periodicity conditions at the boundary of the cell have to be prescribed. The three phases of the composite are supposed to be isotropic, elasticperfectly plastic, and to conform with plasticity. The compatibility matrix of the finite elements is modified, according to proposals of other authors, to avoid locking phenomena near the fully plastic range.
Some numerical applications are carried out to investigate the influence of a weakening interphase
on the macroscopic mechanical behaviour of Ti/SCS,
with particular attention to the macroscopic yield strength. To this end, the unit cell was subjected to
particular macroscopic stresses of increasing intensity, namely, transverse tension, transverse shear and
longitudinal shear. In the applications, the interphase was given decreasing strength values,
,
expressed as a fraction of the matrix strength,
. The predicted macroscopic yield strength of
the composite, normalized to the strength of the composite with matrix perfectly bonded to the fiber
(i.e., with
), is reported in Table 1. The decrease in transverse tensile and shear strength
with the interphase strength is nearly similar.
The most detrimental effect of a weakening interphase is observed under longitudinal shear.
The theoretical results presented in the foregoing now await an experimental validation. The literature is quite sparse in terms of test data on MMCs embedding a weakening interphase. Another problem is that the interphase material exhibits a brittle behaviour under several stress conditions, such as tension and shear. This is why an extension of the present model has been started to accommodate damage phenomena at the interphase region: the ensuing results will be presented in a forthcoming paper. References
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