A research in different types and applications of the composite materials in engineering Report 2022

Chapter 1: A research in different types and applications of the composite materials in
engineering
Introduction
With the rapid advancements in technology, requirement for materials with unusual
combinations of properties is increasing too. These properties are hard to be met by the
traditional ceramics, metal allows and polymeric materials that have been in use. Application
areas like underwater, transportation and aerospace, especially, have created a demand for
materials with these properties. One prime example can be found in the aircraft industry
wherein the search for structural materials, with properties such as increased strength,
stiffness, impact resistance but low densities and not easily corroded, is on the rise. With
these challenging combination of properties, composite materials are being developed to cater
to these requirements. In general, a combination of two materials in multiphase and have a
considerable proportion of the properties of the constituent phases and improved properties,
is a composite material. A composite material is artificially made material and the constituent
phases have different/dissimilar physical and chemical properties. Most of the composite
materials consist of two phases, one is matrix and other is dispersed phase. Matrix phase is
continuous and surrounds the dispersed phase. Composite materials can be classified in the
following way:
Fig. 1. Classification of Composites(Composites, 2005)
Applications of composites include transportation, aerospace, sporting goods, marine goods,
construction , and in recent times infrastructure, with transportation and construction being
the largest.
Composite Materials
Metal-Matrix Composites
A ductile metal is used as matrix in Metal-Metal composites. Utility at higher operating
temperatures, than their constituent metals counterparts, is a feature of these materials,

moreover these materials have improved creep resistance, specific strength, specific stiffness,
thermal conductivity and dimensional stability due to reinsforcement. A few advantages of
metal-metal composites over polymer-matrix composites are increased resistance to
deprivation by organic fluids, nonflammability and higher operating temperatures. The matrix
materials used in these materials are alloys of copper, titanium, aluminium and magnesium
and superalloys too. The reinforcement could be discontinuous and continuous fibers, and
whiskers. Some of the materials used for continuous fibres are boron, silicon carbide,carbon,
refractory metals and aluminium oxide. The discontinuous reinforcements can be silicon
carbide whiskers, chopped fibres of carbon and aluminium oxide and aluminium oxide and
silicon carbide particulates. They are being used in automobiles, for example, aluminium
oxide and carbon fibres reinforced aluminium –alloy have started to be used in some engine
components. Apart from this, in aerospace industry MMCs find application as structural
applications(Composites, 2005).
Carbon-Carbon Composites
Carbon fibre reinforced carbon matrix composites are showing great promise among the
composite materials and among most advanced materials. They are often called carbon-
carbon composites. In these materials both matrix and reinforcement material is carbon.
These composites have properties like high tensile strengths, relatively large fracture
toughness values and high tensile moduli which can be retained to temperatures which are in
excess of resistance to creep. Moreover, these materials have relatively high thermal
conductivities and low coefficients of thermal expansion; these properties are coupled with
high strengths make these materials relatively low susceptible to thermal shock. These
materials have a drawback of being susceptible to oxidation at high temperatures. Further,
these materials are used for advanced turbine engines components, hot-pressing molds, in
rocket motors, as ablative shields for re-entry vehicles and as friction materials in high-
performance automobiles and aircraft (Composites, 2005).
Manufacturing methods
i) Pultrusion
The components which have a constant cross-sectional shape ( beams, rods, tubes etc.),and
continuous lengths are manufactured using the process of pultrusion process . In this method,
first thermosetting resins are used to impregnate continuous fiber rovings or tows; then they
are pulled through a steel die that provides the required shape and also sets the ratio
resin/fibre. This stock is then passed through a curing die which is precision machined so that
it can give the final shape to it. This die is also heated to start curing of the resin matrix. The
stock is then drawn with the help of a pulling device through the dies, and by this the
production speed is determined too. Aramid fibres, glass and carbon are primary
reinforcements, usually added in concentrations of approximately ranging from 40 and 70 vol
%. The matrix materials commonly used in this process are vinyl esters, polyesters and epoxy
resins.

ii) Prepreg Production processes
In this process, continuous fiber is reinforced by preimpregnating it with a polymer resin
which is only partially cured. The composite material which is formed is delivered in tape
form. The manufacturer after receiving the material molds the material directly and without
the need of adding any resin, fully cures the product. Structural applications are where this
material is used widely. Common reinforcements used are glass, carbon and aramid fibers,
and resins used are thermosetting and thermoplastic resins.
The advantages of using composites are many. These are namely resistance to corrosion, the
ability to customise the layup for optimum stiffness and strength, lighter weight , fatigue life
betterment, and, reduced assembly costs due to lesser number of fasteners and detail parts
and also using with good design practice. High strength fibers (especially carbon) have
higher specific modulus (modulus/density) and specific strength (strength/density) than those
of other comparable aerospace metallic alloys(Introduction to Composite Materials, 2010).
There are few disadvantages of the composites as well such as usually high fabrication and
assembly costs and high raw material costs; prone to impact damage and delaminations or ply
separations, bad effects of both moisture and temperature; lesser strength in the out-of plane
direction where the matrix carries the primary load, and greater difficulty in repairing them in
comparison to metallic structures.
Some of the common steps for maintenance and repair of composite materials include the
following(Ilcewicz, Cheng, Hafenricher and Seaton, 2009):
i) Initial inspection of composite components and perform initial damage
assessments using basic tap and visual inspection techniques
ii) Monitoring repair materials like adhesives, prepregs, resins which are perishable.
Their shelf lives should be monitored and storage conditions must be correctly
maintained.
iii) For components with temporary, time-limited repairs, a review of component
records for previous repairs, should be done to know if repairs need to be replaced
with permanent repairs
iv) Some of the worksheets with repair and related records to be maintained are
a. Materials record sheet
b. Component master worksheet
c. Component record card
v) The various techniques for any damage assessment should be suitably adopted.
Some of these techniques are:
a. Visual inspection
b. Tap test
c. Ultrasonic inspection
d. Pulse echo
e. X-ray

f. Eddy-current inspection
g. Thermography
h. Bond testers
i. Moisture Meters
Recycling of Composites
Recycling of composites properly is still challenging due to their characteristic of
heterogeneity. However, few of the methods used for recycling some of the composite
materials could be as follows(Yang et al., 2012).
Few composites which are recycled are thermoplastic and thermosetting. To recycle
thermoplastic composites, finished parts are grinded into small particles which can then be
fed into an injection moulding machine with virgin thermoplastic material. To recycle
thermosetting composites, special equipments are used to grind them. During this process, the
filler part and resin separate from the reinforcing fibres. The filler and resin part is used again
as filler in many other applications. Further, in few other applications, the fibre part can be
reused as reinforcing material(Kasper, 2008).