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CHAPTER-7 WEAR STUDIES

7.1 INTRODUCTION

Wear is the progressive loss of material due to relative motion between a surface and

the contacting substance or substances [1]. The wear damage may be in the form of

micro-cracks or localized plastic deformation. Wear may be classified as adhesive

wear, abrasion wear, surface fatigue wear and tribo-chemical, fretting, erosion and

cavitation wear. Wear is a complex phenomenon in which real contact area between

two solid surfaces compared with the apparent area of contact is invariably very

small, being limiting to the points of contact between surface asperities. The load

applied to the surfaces will be transferred through these points of contact and the

localized forces can be very large. The material intrinsic surface properties, the

surface finish, load, speed and temperature and properties of the opposing surfaces

are important in determining the wear rate. Wear, the progressive loss of substance

from the operating surfaces of the mechanically interacting element of a tribo-system

may be measured in terms of weight loss or volume loss. Commonly available test

apparatus for measuring sliding friction and wear characteristics in which, sample

geometry, applied load, sliding velocity, temperature and humidity can be controlled

are Pin-on-Disc, Pin-on-Flat, Pin-on-Cylinder, Thrust washers, Pin- into-Bushing,

Rectangular Flats on a Rotating Cylinder and such others. In laboratories, wear

tests are conducted at ambient temperature by varying loads and speeds under varying

environments and frictional force, wear height loss and temperature are monitored.

7.2 TYPES OF WEAR

A fundamental scheme to classify wear was first outlined by Burwell and Strang [2].

Later Burwell [3] modified the classification to include five distinct types of wear,

namely (1) Abrasive (2) Adhesive (3) Erosive (4) Surface fatigue (5) Corrosive

7.2.1 Abrasive Wear

Abrasive wear can be defined as wear that occurs when a hard surface slides against

and cuts groove from a softer surface. It can be account for most failures in practice.

Hard particles or asperities that cut or groove one of the rubbing surfaces produce

abrasive wear. This hard material may be originated from one of the two rubbing

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surfaces. In sliding mechanisms, abrasion can arise from the existing asperities on one

surface (if it is harder than the other), from the generation of wear fragments which

are repeatedly deformed and hence get work hardened for oxidized until they became

harder than either or both of the sliding surfaces, or from the adventitious entry of

hard particles, such as dirt from outside the system.

Fig. 7.1 Schematic representations of the abrasion wear mechanism

Two body abrasive wear occurs when one surface (usually harder than the second)

cuts material away from the second, although this mechanism very often changes to

three body abrasion as the wear debris then acts as an abrasive between the two

surfaces. Abrasives can act as in grinding where the abrasive is fixed relative to one

surface or as in lapping where the abrasive tumbles producing a series of indentations

as opposed to a scratch.

7.2.2 Adhesive Wear

Adhesive wear can be defined as wear due to localized bonding between contacting

solid surfaces leading to material transfer between the two surfaces or the loss from

either surface. For adhesive wear to occur it is necessary for the surfaces to be in

intimate contact with each other. Surfaces, which are held apart by lubricating films,

oxide films etc. reduce the tendency for adhesion to occur.

Fig .7.2 Schematic representations of the adhesive wear mechanism

7.2.3 Erosive Wear

Erosive wear can be defined as the process of metal removal due to impingement of

solid particles on a surface. Erosion is caused by a gas or a liquid, which may or may

not carry, entrained solid particles, impinging on a surface. When the angle of

impingement is small, the wear produced is closely analogous to abrasion. When the

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angle of impingement is normal to the surface, material is displaced by plastic flow or

is dislodged by brittle failure

Fig. 7.3 Schematic representations of the erosive wear mechanism

7.2.4 Surface Fatigue Wear

Wear of a solid surface caused by fracture arising from material fatigue. The term

‘fatigue’ is broadly applied to the failure phenomenon where a solid is subjected to

cyclic loading involving tension and compression above a certain critical stress.

Repeated loading causes the generation of micro cracks, usually below the surface, at

the site of a pre-existing point of weakness. On subsequent loading and unloading, the

micro crack propagates. Once the crack reaches the critical size, it changes its

direction to emerge at the surface, and thus flat sheet like particles is detached during

wearing. The number of stress cycles required to cause such failure decreases as the

corresponding magnitude of stress increases. Vibration is a common cause of fatigue

wear.

Fig. 7.4 Schematic representations of the surface fatigue wear mechanism

7.2.5 Corrosive Wear

Most metals are thermodynamically unstable in air and react with oxygen to form an

oxide, which usually develop layer or scales on the surface of metal or alloys when

their interfacial bonds are poor. Corrosion wear is the gradual eating away or

deterioration of unprotected metal surfaces by the effects of the atmosphere, acids,

gases, alkalis, etc. This type of wear creates pits and perforations and may eventually

dissolve metal parts.

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The expeditious advancement of technology in the past decades has resulted in the

need for new multifunctional materials which possess characteristics not obtainable

from any individual material. Aluminum metal matrix composites (AMMCs) possess

much higher specific strength and stiffness, higher wear resistance and lower thermal

expansion coefficient in comparison to their base alloy matrices due to the

incorporation of suitable particles or fibers into the metal matrix [4, 5]. Wear

properties of aluminum alloys can be improved by the addition of a second ceramic

phase provided there is good interface bonding between the ceramic and metal

phases [6]

One third of our global energy consumption is consumed wastefully in friction. In

addition to this primary saving of energy, very significant additional economics can

be made by the reduction of the cost involved in the manufacture and replacement of

prematurely worn out components. The dissipation of energy by wear impairs

strongly the national economy and the life style of most of people. So, the effective

decrease and control of wear of metals are always desired [7].

The current study provides a new insight into the wear and friction properties of an

A356 /HSA(P) composite.

7.3: LITERATURE REVIEW

Considerable amounts of research on the dry sliding wear behaviour of aluminum

metal matrix composites (AMMCs) have been carried out. The comprehensive

reviews of this research were done by P. K. Rohatgi, A.P. Sannino, R.L. Deuis [8–

10].

P.K. Rohatgi et.al [11] reported the abrasive wear resistance of Aluminum alloy

(A356) containing fly-ash particles. Their results show that the wear resistance of

specimen containing fly ash is comparable to that of alumina fiber-reinforced alloy

and superior to that of base A356 alloy.

Dry sliding wear behavior of silicon particles-reinforced aluminum matrix composites

was reported by Sun Zhiqiang, et.al [12]. In their work, a ring on rock wear testing

machine was used to study the wear properties of powder metallurgy aluminum

matrix composites 9Si/Al-Cu-Mg. Quartz (SiO2p) reinforced chilled metal matrix

composites for automotive applications were developed by Joel Hemanth [13].

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Dry sliding wear behavior of aluminum syntactic foam was discussed by D. P.

Mondal et.al. [14], K.M.Shorowordi et.al [15] studied the effect of velocity on the

wear, friction and tribochemistry of aluminum MMC sliding against phenolic brake

pad. Their results show that higher sliding velocity leads to lower wear rate and lower

friction coefficient for Al-B4C and Al-SiC metal matrix composites

I.M. Hutching [16] studied the tribological properties of metal matrix composites and

has the opinion that under certain conditions MMCs show high wear resistance but

this is not the case always and is some time depended on the wear mechanism.

Axen et.al [17] studied the friction and wear behaviour of an Al-Si, Mg-Mn aluminum

alloy reinforced with 10%, 15%, and 30% volume of alumina fibers. Their results

shows that fiber reinforcement increases the wear resistance in milder abrasion

situations and the coefficient of friction decreases with increasing fiber content and

matrix hardness of composites. Wear of metals depends on many variables, so wear

research programs must be planned systematically. Therefore researchers have

normalized some of the data to make them more useful.

Several investigators have proposed that wear resistance of a material depends on

its hardness, strength, ductility, toughness, the kind of reinforcement, its volume

fraction (Vf) and the particle size [18-26]. The particle reinforcements are the most

effective in improving the wear resistance of MMCs [27] provided that good

interfacial bonding between the reinforcement and the matrix exists.

The wear resistance of the composites is improved by preventing direct metallic

contacts that induce subsurface deformation [28]. The addition of hard ceramic

particles improves the resistance to seizure at elevated temperatures.

Barwell and Strang [29] in 1952: Archard [30] in 1953: developed the adhesion

theory of wear and proposed a theoretical equation identical in structure with Holm’s

equation. In 1957, Kragelski developed the fatigue theory of wear. Because of the

Asperities in real bodies their interactions on sliding is discrete and contact occurs at

individual locations, when taken together, form the real contact area. Under normal

force the asperities penetrate into each other or are flattened out and in the region of

real contact points Corresponding stress and strain rise. In sliding, a fixed volume of

material is subjected to the many times repeated action, which weakens the material

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and leads finally to rupture. Though all the theories are based on different

mechanisms of wear, the basic consideration is the frictional work. Hence friction is

the prime consideration

Kirit J. Bhansali and Robert Mehrabian [31] have studied the abrasive wear resistance

of aluminum matrix composites containing Al2O3 and SiC using a dry sand/rubber

wheel abrasion tester. Their results show that composites containing Al2O3 were

found to be superior to those containing SiC.

G.Wang and I.M. Hutching [32] reported the investigations of the response of

alumina fiber- aluminum metal matrix composites systems to wear by two-body

abrasion. Their results show that wear resistance of the composites was found to range

from almost two to six times that of the unreinforced matrix alloy.

A.T. Alpas and J.Zhang [33] studied the dry sliding wear of aluminum matrix

composites and determined how the micro structural parameters such as volume

fraction of particulate and particulate size affect the wear resistance of these materials.

V.Constantin et.al [34] investigated the sliding wear behaviour of Aluminum Silicon

Carbide metal matrix composites reinforced with different volume fraction of

particulate against a stainless steel slider. Their results show that addition of

reinforced particles increases the resistance of the composites to sliding wear under

dry conditions, even for small volume fraction of particles.

T.Miyajima and Y.Iwai [35] studied the effect of reinforcements on sliding wear

behaviour of aluminum matrix composites. Their results show that the degree of

improvement of wear resistance of metal matrix composites (MMC) is strongly

dependent on the kind of reinforcement as well as its volume fraction. Aluminum

metal matrix composites are emerging as promising friction materials. One of the

important applications that are being considered for MMCs is as rotor (disc/drum)

material in automotive brake system.

Liang.Y.N et.al [36] studied the effect of particle size on the wear behaviour of SiC

particulate reinforced 2024 Al composites investigated using three tests, sliding wear

test, impact abrasion test, and erosion test. Their results show that the wear behavior

of particulate reinforced aluminum composite is significantly affected by particle size.

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Composites contain large particles exhibited excellent wear under sliding wear

conditions with steady applied load.

Yoshiro.Iwai et.al [37] studied the wear properties of Sic whisker reinforced 2024 Al

alloy with volume fraction of whiskers ranging from 0 to 16% produced by Powder

Metallurgy technique. Their results show that SiC whisker reinforcement can improve

the wear resistance of aluminum alloy for both severe and mild wear.

D. Huda et.al. [38, 39] reported that a particular fabrication technique depends on the

type of the proper matrix and reinforcement materials to form the MMC.

Sannino and Rack [40] however showed that the effect of the shape of reinforcement

depends on the sliding velocity. It is difficult to deduce the effects of reinforcement

from the literature because in the reported studies experimental conditions such as

contact load and sliding velocity spread over very wide ranges and these studies

employ different kinds of test apparatus. The effects of sliding velocity on the

frictional and wear behavior of aluminum MMC sliding against ferrous counter body

have been studied by a number of researchers [41-42]. Their studies revealed that the

frictional and wear characteristics of aluminum MMC depend on the sliding speed in

a complicated way. Depending upon the sliding velocity range, both increase and

decrease in wear rate with sliding velocity were reported.

M.K. Surappa et.al [43] studied the tribological behaviour of stir-cast Al–Si/ SiCp

composites against automobile brake pad material was studied using Pin-on-Disc

tribotester. The Al-metal matrix composite (Al-MMC) material was used as disc,

whereas the brake pad material forms the pin. It has been found that both wear rate

and friction coefficient vary with both applied normal load and sliding speed. With

increase in the applied normal load, the wear rate was observed to increase whereas

the friction coefficient decreases. However, both the wear rate and friction

coefficients were observed to vary proportionally with the sliding speed. During the

wear tests, formation of a tribolayer was observed, presence of which can affect

the wear behavior, apart from acting as a source of wear debris. Tribolayer formed

over the worn disc surfaces was found to be heterogeneous in nature. It has also

investigated the morphology and topography of worn surfaces and debris were studied

using scanning electron microscope (SEM).

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7.4: EXPERIMENTAL WORK

In the present work, studies have been carried out to assess the wear behaviour of

A356/HSA(P) composites under controlled laboratory conditions. A comprehensive

picture of wear under different working conditions has been presented by conducting

laboratory tests in pure sliding mode using a pin-on-disc machine; and further

characterization was carried out by using scanning electron microscopy to know the

wear mechanism

7.4.1 Dry Sliding Wear Tests

Dry sliding wear tests have been carried out on a pin- on- disc apparatus (Model:

Ducom TR- 20 LE) by sliding a cylindrical pin against the surface of hardened steel

disc (with a hardness value of HRC 62) under ambient condition, as shown in Figure

7.5. The disc was ground to a smooth surface finish and renewed for each test. The

wear test specimens were prepared by wire cut EDM from the composite castings in

the dimensions of 8 mm diameter and 30 mm length, figure 7.6. The samples were

placed on the wear disc and the sliding wear tests were carried out at various loads,

time and sliding distance. The wear rate (K) was defined as the volume loss (V),

divided by the sliding distance (L). Hence, the volumetric from the weight loss

measurement and expressed wear rate (K). The friction force (F) was continuously

monitored during the wear test for determining the coefficient of friction (µ).

The friction force was measured for each pass and then averaged over the total

number of passes for each wear test. The average value of coefficient of fricition (µ)

of composite was calculated from the following expression.

µ=Ff/Fn

where: Ff is the average fricition force and Fn is applied load

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Figure 7.5 Experimental setup of wear machine

Figure 7.6 Wear samples, by wire cut EDM

In the present experimental, the parameter speed is kept constant by varying time

and load throughout for all the experiments. These Parameters are given in the

following Table 7.1.

Table 7.1: Parameter taken during sliding wear test

Load 4.9, 9.8 and 14.7 N

Speed (V) 2.345 m/s

Total Time 15, 30 and 45 min

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7.5 RESULTS AND DISCUSSION

Figure 7.7 shows the sliding wear behavior of A356 alloy and the composites. The

normal loads applied were 0.5, 1.0 and 1.5 Kgf. Wear test was conducted for a period

of 45 min at a sliding speed of 640 rpm on a steel disc with 70 mm track diameter and

the track velocity was 2.34 m/sec. In all the cases it was evident that the resistance to

wear increases with increasing reinforcement content. Alloy exhibits higher wear, and

the composite with 15% wt HSA(P) fraction showed lower wear.

Kamalpreet Kaur and O. P. Pandey [44] have reported, the wear behaviour of Al–

Si/zircon sand composite and base Al–Si alloy at various applied loads and constant

sliding velocity of 1.6 m/s (zircon sand as reinforcement and Al–Si alloy as a base

material). The wear rate and volume loss showed the two stages of wear for all the

applied loads. At the initial stage run-in wear occur up to 1 km sliding distance and in

later stage wear approaches a steady state. The results confirmed that spray formed

Al–Si/zircon sand composite is clearly superior to base Al–Si alloy in delaying the

transition to severe wear at higher loads as well as showing greater resistance to wear

at lower loads also.

J.Babu Rao et.al, [45], has studied the dry sliding wear behaviour of Fly-Ash as a

reinforcement and A2024 alloy as a base material. In all the results it was evident that

the resistances to wear increases with increasing fly ash content. With increasing fly

ash content, the amount of particle present strengthens the matrix and hence more

wear resistance was observed.

All the composites exhibit better wear resistance compared to the alloy. Presence of

reinforcement strengthens the matrix, resulting in increased wear resistance.

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(a)

(b)

(c)

Figure 7.7: Comparative graphs of A356 alloy and A 356 alloy-HSA(P) composites

showing the amount of wear as a function of sliding times for an applied load of 0.5,

1.0 and 1.5 kg (Process parameters: Speed: 640rpm, Time: 45min, Track dia: 70mm.).

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7.5.1 Effect of Load on Coefficient of Friction (µ)

Figure 7.8 shows the change in the friction coefficient (µ) with varying loads for the

alloy and composites. For both alloy and the composites, µ found to be decreasing

with increasing applied load. Also µ decreases with increasing reinforcement content.

Figure 7.8 Variation of coefficient of friction (µ) as a function of load (a) 0.5 Kgf

(b) 1.0 Kgf (c) 1.5 Kgf

M. Ramachandra et al [46] reported similar behaviour of decrease in coefficient

friction with increasing reinforcement content and also at higher applied loads. The

decrease of coefficient of friction with increase of the load was attributed to

increasing amounts of wear debris particles coming out from the wear surface and

filling in the empty spaces between fly ash particles. An addition TiC in A356 alloy

exhibited the lowest wear rate and an increase in the load at which the transition from

low wear rate to high wear rate and also the coefficient of friction is reduced [47].

M.K.Surappa, et al. [48] has reported similar trend in their study on dry sliding wear

of fly ash particle reinforced with A356. Coefficient of friction varies from 0.45 to

0.14 in this study, the higher coefficients of friction in case of composites containing hard

particles was due to the formation of tribofilm at the interface between pin and disc.

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7.5.2 Effect of Load on Wear Rate�

The variation of wear rate of alloy and the composites with loads of 0.5, 1.0, and 1.5

Kgf was shown in figure 7.9. It was observed that the wear rate increases with

increase in loads.

Figure 7.9 wear rate of alloy and composites with load (Sliding distance=2.1km)

Kapoor et.al [49], reported that, as the load increases, the proportion of metallic wear

debris was also increased and the size of the delamination increased for the

composite resulting in increase of wear rate. At the highest load, the worn surface of

the materials could be described as classical rachetting wear.�

Ferhat Gul, et.al [50] reported, that the wear rate increases with increased applied

loads, because the oxidation of aluminium plays a significant role in formation of the

wear debris and hence the tribolayer. At higher applied loads, high wear rates are

observed. The wearing surface is characterized by a significant transfer of material

between the sliding surfaces; a delamination wear mechanism has been inferred for

this wear regime, where the tribolayer is removed by sub-surface plastic deformation

and fragmentation of the silicon particles.

Alpas and zhang et.al [51], investigated the effect of SiC particle reinforcement on

the dry sliding wear of an A356 alloy under different applied loads, the wear

behaviour of an A356 alloy reinforced with SiC 20 vol% was compared to that of

unreinforced alloy, and found the increase in wear rate due to the SiC particles acted

as a load bearing phase.

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7.5.3 Effect of Sliding Distance on Wear Rate

Figure 7.10, shows the effect of sliding distance on wear rate of the alloy and

composites. Wear rate decreases with increasing in sliding distance, at all loads.

(a)

(b)

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(c)

Figure 7.10 Variation of wear rate as a function of sliding distances of A356 alloy and

HSA(p) composites at normal load of (a) 0.5 Kgf (b) 1.0 Kgf (c) 1.5 Kgf

S. Basvarajappa, G. Chandra Mohan et.al, [52], reported, that the wear rate of the

A356/25SiCp composites is less than the matrix alloy for all loads. The wear rate of

composites with coarse fly ash particles exhibits better wear resistance than

composites with fine particles. This may be due to the fact that smaller particles tend

to get ploughed away from the surface of the matrix easily, thus increasing the wear.

In composites with coarse particles, the particles get fragmented into small particles

and continue to restrict the particle removal, thereby decreasing the wear.

Presence of reinforcement enhances the wear resistance of the resultant composite.

And the wear resistance increases with increase in reinforcement contents. It is self-

explanatory that, presence of particulate material not only strengthens the matrix

(mechanisms discussed in chapter 4 page no. 53), for also reinforce the matrix. A

good interface between the matrix and reinforcement causes effective transfer of load

to the reinforcement resulting in increased wear rate due to the presence of hard

reinforcements.

At initial stages of testing, both matrix and the reinforcement were in contact with the

disc resulting high wear rate and high coefficient of friction values. The wear rate

decreases with increase in time / sliding distance, shows that matrix has worned out

and particulates were taking the load, resulting in decreased contact area (decrease in

µ) and offering increased wear resistance

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This phenomenon is much truer with decreased µ values at increasing reinforcement

contents. Figure shows the banding nature of the reinforcement reflecting continuous

supply of reinforcements to the contact area, even when the particulate which was in

contact with the rotating disc, either worn out or pulled off. This discussion further

holds good, at decreased wear rate due to increased area of reinforcement at the

contact area. The same explanation holds good with increasing sliding distance, as

well.

7.5.4 Microstructure Studies

Figure 7.11 shows the wear track photographs of the alloy and composites. Alloy

shows a rough and worn surface with coarser and deeper grooves. Composites exhibit

a smoothened worn surface.

Varun Sethi [53], reported, that by incorporating ceramic particles in A356 matrix

results in weakening of the interfacial bonding and eventually resulting in the pull-out

of the SiC particle, because of the lattice straining in the surrounding areas of the

particles, there will be a reduction in the extent of plastic deformation that these areas

can undergo, which will make them more susceptible to cracking. These cracks will

result in the removal of the matrix from adjacent areas of the particles, thereby

decreasing the strength of interfacial bond. Some of the particles also underwent

fracture. These fractured particles must also become detached from the matrix. In

both the above cases, the strength of the bond between the matrix and the particle is

expected to play a critical role in determining wear.

With reference to dry sliding wear of A356 reinforced with SiCp Pramila Bai

[54] observed that with increasing applied loads the wear behavior of the

unreinforced alloy was dominated by extensive plastic flow of the alloy surface and

significant wear debris formation.

It was also observed that at higher loads the wear loss in composites was less as

compared to the matrix alloy. And it is evident from the microstructures that no

particle was cracked or pulled out from the matrix. This is due to good interfacial

bond between the alloy and the matrix. These findings suggest that a metal-metal

composite system gives better and wear resistant properties, compared to metal-

ceramic composite system.

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Figure 7.11: SEM image of worn surface at 1.5 kgf applied load and 2.7 km sliding

distance (a) A356 alloy

Figure 7.12: SEM image of worn surface at 1.5 kgf applied load and 2.7 km sliding

distance (a) A356/5% wt HSA(P) composite

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Figure 7.13: SEM image of worn surface at 1.5 kgf applied load and 2.7 km sliding

distance (a) A356/10% wt. HSA(P) composite

Figure 7.14: SEM image of worn surface at 1.5 kgf applied load and 2.7 km sliding

distance (a) A356/15% wt. HSA(P) composite

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7.5 CONCLUSIONS

1. Dispersion of HSA(P) in A356 matrix improves the wear resistance of the resultant

composites.

2. Wear resistance increases with increasing reinforcement content.

3. Composites exhibit decreased coefficient of friction compared to that of alloy.

4. Coefficient of friction decreases with increase in reinforcement content.

5. No particle pullout or cracking during test was observed with the composite,

reflecting, good bonding between the matrix and reinforcement.

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.

AUTHOR’S PROFILES

GOPI KRISHNA MALLARAPU was born on 24th

November 1980. He had

completed his graduation in Mechanical Engineering from Nagarjuna University,

Andhra Pradesh in the year 2002. He received post graduate degree in Computer

Aided Design, from Anna University, Chennai in the year 2004. He started the career

as Lecturer in KL college of Engineering Vijayawada in 2005, also worked as

Lecturer in RVR & JC College of Engineering Guntur from 2006 to 2009. Presently

he is working as Assistant Professor in the Department of Mechanical Engineering,

University College of Engineering and Technology, Acharya Nagarjuna University

Guntur, since 2009. Between 2004 and 2005, he worked as Project Assistant at

BHEL (R&D), Hyderabad in Fracture Mechanics Lab.

Publications of the author with regard to the present thesis:

(i) International Journal Papers

1. J Babu Rao, M.Gopi Krishna, K.Praveen Kumar and NRMR Bhargava

“Microstructure and Mechanical properties of Al-20%Cu-10%Mg alloy

particles reinforced AA 2024 Composites – International Journal of Materials

and Design (Elsevier publication, ISSN. 0261-3069) –Under review. (Impact

factor: 2.2)

(ii) National /International Conferences

1. Gopi Krishna M, K.Praveen Kumar, Babu Rao J, and NRM Bhargava, “Fabrication

and Characterization of CuMgAl2/A356 Reinforced Metal-Matrix Composites, at

National Symposium on M A T E R I A U X - 2 0 1 2 held a t Andhra University,

Vishakhapatnam.(Secured best paper award)

2. Gopi Krishna M, K.Praveen Kumar, Babu Rao J, and NRM Bhargava, “Synthesis

and Characterization of CuMgAl2/AA2024 Reinforced Metal-Matrix Composites.”

at National Symposium on M A T E R I A U X - 2 0 1 2 held a t Andhra University,

24-25 Febraury2012 Vishakhapatnam.

3. Gopi Krishna M, K.Praveen Kumar, Krishna Kishore, Babu Rao J, and NRM

Bhargava, “Studies on machinability properties of Aluminium based composites.”

at National Symposium on M A T E R I A U X - 2 0 1 2 held a t Andhra University,

Vishakhapatnam

4. Gopi Krishna M, K.Praveen Kumar, J.Babu Rao, and NRM Bhargava, Structure

Property Relations of Al-Cu-Mg Ternary Alloys National Symposium on N C A M E

held a t National Institute of Technology Surat, Gujarat.