Engineering Report: Composite Materials, Welding, and Failure Analysis

This report, prepared for the MOD002634 module, delves into composite materials, welding processes, and failure analysis. Chapter 1 examines the various types and applications of composite materials in engineering, including metal-matrix and carbon-carbon composites, their advantages, disadvantages, manufacturing methods (pultrusion and prepreg processes), maintenance, and recyclability. The chapter provides a comprehensive overview of the properties and applications of composite materials. Chapter 2 focuses on welded and brazed specimens, detailing different welding types (arc, resistance, gas, solid-state, and energy beam welding) and analyzing the soundness of various welded joints, identifying defects like porosity and cracks. Chapter 3 explores defects and failures in engineering components, specifically addressing corrosion in aluminum collets and stainless steel pipes, as well as the failure of a cast cam shaft, providing a detailed understanding of material degradation in various environments. The report incorporates images and references to support its findings, offering a detailed analysis of materials and processes.

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).

Chapter 2 - WELDED AND BRAZED SPECIMENS
The various types of welding are as follows:
1) Arc welding- In this type of welding, an electric arc is maintained between a base
material and an electrode by using a power supply. This arc melts the metals at the
welding point. The commonly used types of arc weldings are:
a. Shielded metal arc welding
b. Gas Tungsten arc welding
c. Gas Metal arc welding
2) Resistance welding- in this welding technique, a high current (1000-10000A) is used
to generate heat. The current is passed through the resistance. The contact between the
metals causes this resistance. It leads to the formation of pools of molten metals at the
weld area.
3) Gas Welding- This type of welding utilises a focuses high temperature flame to melt
the workpieces together.Gas combustion is used to generate high temperature flame.
4) Solid state welding-In this method, there is no melting of the metals. The common
types include electromagnetic pulse welding, ultrasonic welding, friction welding.
5) Energy beam welding- This method of welding utilises a focused high-energy beam to
melt and then join the work pieces(Introduction to Welding Technology, n.d.).
1. Specimens Single pass arc weld in plain low carbon steel – In this joint, a single pass
arc weld is made. It can be seen that the filler material has completely filled the joint
in the centre of the workpiece. However, there is overlap of the material from the joint
onto the workpiece as can be seen from the extruded material.
4. Bronze in brass weld
In this weld, it is seen that the filler has completely filled the weld joint. The black spots seen
on the weld joint are due to the porosity defect in the joint wherein filler material has left
some spaces unfilled leading to porosity in the weld joint (What is Welding Defects - Types,
Causes and Remedies? - The Welding Master, 2017).

In this top view of the weld joint, it is seen that the filler has completely filled the gap of the
joint resulting in good welded joint.
7 Multi pass weld in low carbon steel.
In this sample, a multipass weld has been performed on low carbon steel. However it is also
seen that there is development of small cracks also in the workpiece as given in the following
images.

9. Submerged Arc weld in large sectioned low carbon steel plate – In this welded joint, it is
seen the joint made is good joint as there is not any defects and it is levelled.

5. Fusion weld between pipe and plate (compensation plate).
Sample 68: Friction weld in carbon steel

The friction weld in the carbon steel made in the given specimen is good weld. Both the parts
have fused well by the friction welding. Small lumps of melted metals can be seen on the
edge of the workpiece as weld defects.
Fusion welding- It refers to the type of welding in which the base metals are melted using
heat. Most of the fusion welding operations use a filler metal during the welding operation.
Non-fusion welding –In this type of welding , there is no melting of the parent material
during the welding operation.
Solid-state welding – In this type of welding, the amalgamation results from the applications
of pressure alone or combination of pressure and heat(FUNDAMENTALS OF WELDING,
n.d.).
The metallurgical aspect of the welds is effected by the temperature variations that the weld
joint has to undergo(Metallurgical aspect of welding, 2015). The two types of welding
process, fusion and non-fusion have a little distinct effect on it. In fusion welding, the
maximum temperature exceeds the local melting point and a pool of weld if formed. The
unmolten material attains a maximum temperature, , this temperature depends on the distance
from the fusion boundary. During cooling, the liquid weld metal solidifies again, forming the
weld. In non-fusion welding, the process is simpler. However, in both type of welding, the
temperature cycle has influence on the properties and structure of the material.

Chapter 3: Defects and Failures
1. Cast aluminium collet for attached to a steel rope immersed in seawater.
Sea water is a corrosive environment. In this case , less resistant material, aluminium
becomes anodic and steel becomes cathodic. Ionised metal electrons leave anode , free
electrons move towards cathode. The potential difference between the two metals drives the
current. Thus this flow of current results in corrosion of the anode which is aluminium and
causes failure.
2 Stabilised Stainless Steel pipe carried Chlorine at 120oC. Failure occurred in 9 months

Here, the corrosive environment is the hot chlorine flowing at 120 degree C. due to the hot
chlorine there could be pits formation inside of the pipe. The formation of pits and resistant
stress on the pipe , both could have been the causes of failure of the part.
5 Cast cam shaft.
A cam shaft is used as a moving part in various machines and is thus subjected to various
stresses. These stresses are developed due to the varying forces and can lead to stress
concentration and fatigue. The stress concentration can generate a crack and which then led
to the breaking of the part.
6 Mazak torque test specimen. Aluminium/Zinc alloy

In this case, the sample is subjected to twisting motion and hence under torque which lead to
rotational stresses or torsion. This torsion resulted in principal stress in the part and this led to
the failure of the sample.
7 Slave spring for refuse vehicle
In this sample, the part was used to hold load under stress. It was subjected to elastic stresses
which could have exceeded the elastic region. Due to continuous bends, the part could have
failed due to brittle failure. The rust indicates the presence of corrosive environment too.