Matrix materials 4

Matrix Materials - 4
By,
D. B. Naga Muruga,
Dept of Mechanical Engineering,
Sriram Engineering College

 Although it is undoubtedly true that the high strength of composites is
largely due to the fibre reinforcement, the importance of matrix
material cannot be underestimated as it provides support for the fibres
and assists the fibres in carrying the loads. It also provides stability to
the composite material.
Matrix Materials

In selecting matrix material, following factors may be taken into
consideration:
 The matrix must have a mechanical strength commensurate with that
of the reinforcement i.e. both should be compatible. Thus, if a high
strength fibre is used as the reinforcement, there is no point using a low
strength matrix, which will not transmit stresses efficiently to the
reinforcement.
 The resultant composite should be cost effective.
Factors considered for Matrix Selection

 The matrix must stand up to the service conditions, viz., temperature, humidity,
exposure to ultra-violet environment, exposure to chemical atmosphere, abrasion
by dust particles, etc.
 The matrix must be easy to use in the selected fabrication process.
 Smoke requirements.
 Life expectancy.

 Thermodynamically stable dispersoids are essential for the use of
metal matrix composites for high temperature applications.
 Aluminium and magnesium alloys are regarded as widely used
matrices due to low density and high thermal conductivity.
 Composites with low matrix alloying additions result in attractive.
 Reducing the tensile ductility of the composite.
Matrix Selection

Role of Matrices in Composites
 Transfer stresses between the fibers.
 Provide a barrier against an adverse environment.
 Protect the surface of the fibers from mechanical abrasion.
 Determine inter-laminar shear strength.
 Determine damage tolerance of composites.
 Determine in-plane shear strength.
 Determine the processibility of composites.
 Determine heat resistance of composites.
1.Role of Matrix

 The primary roles of the matrix alloy then are to provide efficient transfer of load to the
fibers and to blunt cracks in the event that fiber failure occurs and so the matrix alloy for
continuously reinforced composites may be chosen more for toughness than for strength.
 On this basis, lower strength, more ductile, and tougher matrix alloys may be utilized
in continuously reinforced composites.
 For discontinuously reinforced composites, the matrix may govern composite
strength.
Then, the choice of matrix will be influenced by consideration of the required
composite strength and higher strength matrix alloys may be required.
2.Role of Matrix

 Additional considerations in the choice of the matrix include potential reinforcement/matrix reactions,
either during processing or in service, which might result in degraded composite performance; thermal
stresses due to thermal expansion mismatch between the reinforcements and the matrix; and the
influence of matrix fatigue behavior on the cyclic response of the composite.
 In composites intended for use at elevated temperatures, an additional consideration is the difference in
melting temperatures between the matrix and the reinforcements. A large melting temperature difference
may result in matrix creep while the reinforcements remain elastic, even at temperatures approaching the
matrix melting point. However, creep in both the matrix and reinforcement must be considered when
there is a small melting point difference in the composite.

In a composite material, the matrix material serves the following functions:
 Holds the fibres together.
 Protects the fibres from environment.
 Distributes the loads evenly between fibres so that all fibres are subjected to the same
amount of strain.
 Enhances transverse properties of a laminate.
 Improves impact and fracture resistance of a component.
 Helps to avoid propagation of crack growth through the fibres by providing alternate failure
path along the interface between the fibres and the matrix.
 Carry interlaminar shear.
Functions of Matrix

The needs or desired properties of the matrix which are important for a composite
structure are as follows:
 Reduced moisture absorption.
 Low shrinkage.
 Low coefficient of thermal expansion.
 Good flow characteristics so that it penetrates the fibre bundles completely and
eliminates voids during the compacting/curing process.
 Must be elastic to transfer load to fibres.
Desired Properties of a Matrix

 Reasonable strength, modulus and elongation (elongation should be greater than fibre).
 Strength at elevated temperature (depending on application).
 Low temperature capability (depending on application).
 Excellent chemical resistance (depending on application).
 Should be easily processable into the final composite shape.
 Dimensional stability (maintains its shape).
 Reasonable strength, modulus and elongation (elongation should be greater than fibre).
 Strength at elevated temperature (depending on application).
 Low temperature capability (depending on application).
 Excellent chemical resistance (depending on application).
 Should be easily processable into the final composite shape.
 Dimensional stability (maintains its shape).

Matrix materials 4

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