Post 180 ⇒   by Gautam Shah 


Matrix-Filler Interface in Composites

A composite material is a complex entity. Understanding its constituents and their role helps in understanding of its strength and weaknesses. Here in very simple terminology this has been explained.



Plasan Sand Cat light (5t) military vehicle featuring integrated composite armoured body


In a composite material, the Filler in the form of particles, fibres and sheets, is expected to take up the stresses in unison with the Matrix, due to the strong interface provided by the later.


Composite materials with weak interfaces have low strength and stiffness, but high resistance to fracture, On the other hand materials with strong interfaces have high strength and stiffness but are brittle. The bonding between the matrix and the filler is dependent on the atomic arrangement and chemical properties of filler and on the molecular conformation and chemical constitution of the matrix.


A crack that starts in a monolithic material generally continues to propagate until that material fails, whereas the filler-matrix combination reduces the potential for a complete fracture.


Bonding at the interface: In a simple system the bonding is due to adhesion between filler and the matrix.


Adhesion can be attributed to following FIVE main mechanisms:


1 Adsorption and wetting: When two electrically neutral surfaces are brought sufficiently close, there is a physical attraction. Most solids, have surfaces that are rarely perfectly in level, blemish, and without any contamination. So a wetting agent that substantially covers all hills and valleys, displaces all air, and overcome the effects of contamination, is required.


2 Interdiffusion: It is possible to form a bond between two polymer surfaces by the diffusion of the polymer molecules on one surface into a molecular network of the other surface. The bond strength will depend on the amount of molecular entanglement and the number of molecules involved. Interdiffusion may be promoted by the presence of solvents and Plasticizing agents.


3 Electrostatic attraction: When one surface carries a net positive charge and the other surface, a net negative charge, electrostatic attraction occurs (as in acid+base reaction). Electrostatic attraction has no major role in contribution of bond strength, but has importance on how things initially begin to get mixed.


4 Chemical bonding: It is formed between a chemical group of filler and a chemical group of a matrix. The bond formation or breakage usually involves thermal activity.


5 Mechanical adhesion: Some bonding occurs by the mechanical interlocking of two surfaces (e.g. fibre shape-section).


Shocks, impact, loadings or repeated cyclic stresses can cause the Individual fibres to separate from the matrix, e.g. a fibre pull-out. In case of laminated or layered construction there could be a separation at the interface between two layers, a condition known as de-lamination.


Composite material: Radar absorbent material for stealth air craft




Post 168  ⇒  by Gautam Shah  →

The constituents of a composite are ordinarily classified as Matrix and Filler. It is the nature of relationship between the filler and matrix, or the Interface that defines the composite. Fillers serve to resist stresses, mainly tension, and the Matrix serves to resist the shear, and all materials present including any aggregates, serve to resist the compression.


Matrix and Filler each are of three types: Metals, Ceramics and Polymers.

These three provide nine possible combinations.

Composite materials’ combinations: Possibilities of combinations and type-examples.

Matrix (m) + Filler(f) = Composite Type-Examples


Metal matrix composites MMC

Metal (m)+ Metal (f) = Aluminium-Tin are non miscible metals, yet can be alloyed as a composite

Metal (m) + Ceramic (f) = Electrical semi conductors, Carbide cutting tool tips, Scissors, knives

Metal (m) + Polymer (f) = Not feasible, Metals become soft at very high temperature -unsuitable for polymer filler

Sandwiched metals

Ceramic matrix composites CMC

Ceramic (m) + Ceramic (f) = Carbon-carbon composites 

Ceramic (m) + Metal (f) = Metal sprayed optic glass fiber cables

Ceramic (m) + Polymer (f) = Not feasible, Ceramics require high temperature for formation -unsuitable for polymer filler

Brake lining

●  Polymer matrix composites PMC

Polymer (m) + Polymer (f) = Polyester or rayon fibre reinforced plastics

Polymer (m) + Metal (f) = Grinding and polishing abrasives

Polymer (m) + Ceramic (f) = Fibreglass, Fibre reinforced plastic FRP Asphalt roads, imitation granite, cultured marble sinks and counter tops

Wool fibre composite


A matrix is an environment or material within which an interface is desired. A matrix surrounds the Filler material while creating a bond with it. A matrix thus creates a network within which the filler components are supported by maintaining or reinforcing their intended positions. For a matrix to be affective, it must at some stage have a lower phase than the filler material. The lower phase may occur before or while the filler material is being formed or introduced. The matrix material may turn to a higher phase by evaporation of the solvent, removal of the heat or pressure, and polymerization or action of a catalyst. Polymer matrices are most common, followed by metals and ceramics. However, paper pulp, mud, wax, etc. are some matrix materials that do not fit into any of the above-mentioned categories. Ceramic matrix composites though difficult to form, show greatest promise in material sciences.

Wood Particles in Resin Matrix

  • Portland cement, Gypsum plaster, mud (clay), and Bitumens are widely used matrix materials. Polymer matrix materials are thermosetting resins such as polymers, poly-amides, epoxies, or thermoplastic resins such as polycarbonate or polysulphones. Typically a polymer matrix composite of Epoxy and carbon fibres is of two thirds the weight of aluminium, and two and a half times as stiff.
  • For metal matrices most commonly used metals are aluminium, titanium, magnesium, and copper. Composites with metal matrices generally have metal or ceramic as filler materials. Aluminium reinforced with fibres of the ceramic silicon carbide is a classic example of a metal matrix with ceramic filler. The composite material combines the strength and stiffness of a silicon carbide with the ductility of aluminium. Metal to metal composites consist of two immiscible metals (metals that do not form alloys), such as magnesium and titanium. Such metal-metal composites with bronze matrices have been in use since Bronze Age to create many useful materials.


Next article in the series -about FILLERS in COMPOSITES



Post 156   by Gautam Shah ➔

Natural and manufactured raw materials are invariably compounds, made of many materials. These raw materials are formed into products by a method of assimilation -the COMPOSITE or the raw materials are organized into a geometric form -the COMPOSITION.


1 Composite (Cloth+Gypsum) (Wikipedia image by JanSLWC)  2 Composition -geometric arrangement (Wikipedia image by Viapastrengo at En Wikipedia)

Many of the raw materials are naturally compounded materials, in the form of Composites. The composite materials come into being, by putting together natural and manufactured materials in such a special way that the strength and other qualities are different from the constituents, individually and cumulatively. The term different, is considered here as an improved quality, because man-made composites are designed and created towards specific performance requirements only.



Man-made composition -Howrah Bridge Kolkota

Similarly natural and man-made materials have an inherent organization of geometric arrangements which endow unique structural behaviour capacities. Some of the simplest examples are hives of honey bees or birds’ netted nests. At a complex level a truss, bicycle frame, a hull of a boat, are all Structural Compositions or geometric arrangements.

Natural and manufactured materials, and their composites, all are further shaped, re-formed and geometrically integrated to create secondary components as well as Structural Compositions.

1- 640px-PCCB_Wiki_9949


A composite is a natural or designed material entity with potential utility, but has no operational functionality. On the other hand, a component is a configuration of many materials into a utilitarian product. Component manufacturing involves processes that are many times similar to a composite formation. As a matter of fact for component manufacturing, the ‘composite formation’ and the ‘component creation’ both occur simultaneously. Structural compositions (trusses, bridges, buildings) are geometric-configuration of materials, often assisted by components (nuts, rivets, pins, bearings, etc.). Structural compositions use composites to form the constituent elements.

A Layered composite -Plywood

Various Definitions of Composites:

# Consisting of two or more physically distinct and conceptually separable or visually identifiable materials.

# Products that can be made by mixing separate materials, so the dispersion of one material in the other can be done in a controlled way to achieve optimum properties.

# Products with properties that are superior and possibly unique in some specific respects compared to the properties of their individual components.

Particulate composite


Cement Aggregate composite -Mozaic tile

Classes of Composites:

Natural composites               Wood, Bamboo, Bone, Muscle and other tissues

Macro composites                 Galvanized steel,

Engineered products           Reinforced cement concrete (beams, etc.), Helicopter blades Skis, Tennis rackets.

Microscopic composites     Metallic alloys, Toughened plastic (impact polystyrene, ABS), Reinforced plastics.

Nano composites                   Electronics circuits, diodes, transistors

Toys Object Sport Ping Pong Ping-pong Table Tennis

Some natural composites are easy to identify, such as: wood, bamboo, bones, muscles, etc. First man-made composites related to the bronze, as man tried to fix natural stones and ceramic pieces by hammering into the bronze. Layered wood composites have been used by Egyptians. Mud bricks reinforced with hay, hair, and rice husk have been used in prehistoric times. Cow-dung is also reinforced with granular sand particles for wall plaster. Gypsum (Plaster of Paris) has been applied on a lattice of jute, papyrus and such other fibres.

1 - 640px-Textolite

Macro, Micro and Nano Composites: Composites can be categorized in terms of the size of constituent particulate matter. Ingredients of macro composites can be distinguished by naked eye, whereas one may need an electron microscope to understand the constituents of micro composites and nano composites. Nano composites are created by introducing nano-particulate, which drastically add to the electrical, thermal, and mechanical properties of the original material.

1 -Composite_laminate_specimen

Basic Constituents of a Composite:     MATRIX and FILLERS

The constituents of a composite are ordinarily classified as Matrix and Filler. It is the nature of relationship between the filler and matrix, or the Interface that defines the composite. Fillers serve to resist stresses, mainly tension, and the Matrix serves to resist the shear, and all materials present including any aggregates, serve to resist the compression.

Fibres -used as FILLER in composite

Categorization of Composites on the basis of strengthening mechanisms.

Composite materials can be distinguished into three categories based on the strengthening mechanism.

These categories are:

1. Dispersion strengthened,

2 Particle reinforced

3 Fiber reinforced.

Dispersion Strengthened Composites have a fine distribution of secondary particles (fillers) in the matrix of the material. These particles impede the mechanisms that allow a material to deform. Many Metal-matrix composites would fall into the dispersion strengthened composites’ category.

Particle reinforced composites have a large volume of particles dispersed in the matrix. The load is shared by the particles and the matrix. Most commercial ceramics and many filled polymers are particle-reinforced composites.

Fiber-reinforced composites have fibre as the main load-bearing component. Fiberglass and carbon fibre composites are examples of fiber-reinforced composites.