Brittle matrix

There is another interesting difference between the two irons. Ni-Hard (nominally 1 A Cr, 4 A Ni, 3C) has a matrix of the iron carbide that suiTounds the areas of the steel constituent. This brittle matrix provides a continuous path if a crack should start thus the alloy is vulnerable to impact and is weak in tension. In contrast, HC 250 (nominally 25 Cr, 2 AC) has the steel portion as the matrix that contains island crystals of chromium carbide. As the matrix is tougher. HC 250 has more resistance to impact and the tensile strength is about twice as high as that of Ni-Hard. jMoreover, by a suitable annealing treatment the... 

There is increasing evidence in recent years in the fragmentation test of some brittle fiber-brittle matrix composites that a matrix crack is developed at the position of the fiber break. The presence of the matrix crack and its physical size are shown to alter the stress distributions at the fiber-matrix interface. As the applied strain... 

Lee, J.W. and Daniel, I.M. (1992). Deformation and failure of longitudinally loaded brittle matrix composites. In Composite materials Testing and Design (Tenth Voi). ASTM STP 1120, (G.C. Grimes, ed.), ASTM, Philadelphia, P.A., pp. 204-221. 

Marshall, D.B. (1992), Analysis of fiber debonding and sliding experiments in brittle matrix composites. Acta Metall. Mater. 40. 427-442. 

Sigl, L.S. and Evans, A.G. (1989). Effects of residual stress and frictional sliding on cracking and pull-out in brittle matrix composites. Mech. Mater. 8, 1-12. 

Evans. A.G., Zok, F.W. and Davies, J. (1991). The role of interfaces in fiber-reinforced brittle matrix composites. Composites Sci. Technoi. 42, 3-24. 

Ac can be approximated to Cf if Cm is neglected in brittle matrix composites (Harris, 1980). It is shown that Rd( contributes substantially to the total fracture toughness of glass fiber-polymer matrix composites (Harris et al, 1975 Kirk et al., 1978 Beaumont and Anstice, 1980 Munro and Lai, 1988). 

The descriptions presented in the foregoing sections are concerned mainly with composites containing brittle fibers and brittle matrices. If the composite contains ductile fibers or matrix material, the work of plastic deformation of the composite constituents must also be taken into account in the total fracture toughness equation. If a composite contains a brittle matrix reinforced with ductile libers, such as steel wire-cement matrix systems, the fracture toughness of the composite is derived significantly from the work done in plastically shearing the fiber as it is extracted from the cracked matrix. The work done due to the plastic flow of fiber over a distance on either side of the matrix fracture plane, which is of the order of the fiber diameter d, is given by (Tetelman, 1969)... 

Morton J. and Groves G.W. (1974). The cracking of composites consisting of discontinuous ductile fibers in a brittle matrix-effect of fibre orientation. J. Mater. Sci. 9, 1436-1445. 

Figure 5.91 Schematic illustration of tensile strength versus fiber volume fraction for continuous, unidirectional ductile fibers in a brittle matrix. Adapted from N. G. McCrum, C. P. Buckley, and C. B. Bucknall, Principles of Polymer Engineering, 2nd ed., p. 269. Copyright 1997 by Oxford University Press.

Fibres are added to a plastic or metal matrix, mainly to increase the strength of the material. In case of a ceramic matrix this is done to increase the fracture toughness of the brittle matrix. 

In addition, it has been shown (Boccaccini etal., 2001 Chlup etal., 2001) that the chevron-notched specimen flexural technique (the CN-technique) can be a reliable method of assessing fracture properties (fracture toughness, work of fracture) in thermally shocked brittle matrix composites reinforced by brittle fibres. 

Boccaccini, A.R. (1998), Predicting the thermal shock resistance of fibre reinforced brittle matrix composites , Scripta. Mat., 38(8), 1211-1217. 

Hansson, T., Warren, R. (2000), Particle and whisker reinforced brittle matrix composites , in Kelly, A., Zweben, C. (editors-in-chief), Comprehensive Composite Materials, Vol. 6 (R Warren, editor), Elsevier. 

Pagano, N.J., Kim, R.Y. (1994), Progressive microcracking in unidirectional brittle matrix composites , Mech. Compos. Mater. Struct., 1(1), 3-29. 

Data regarding the effects of cyclic loading and creep on the life of brittle matrix composites are limited. The concepts to be developed thus draw upon knowledge and experience gained with other composite systems, such as metal matrix composites (MMCs) and polymer matrix composites (PMCs). The overall philosophy is depicted in Fig. 1.7. 

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