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Advance manufacturing Management

Assignment 2

Submitted by: Amer Khan

Submitted to: Dr.Bao/Dr Gawne

ID: 2827066

Date of submission: 28-05-2010



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Index

1. Methods of increasing Fracture toughness of Zirconia«««««««««««...3

1.1 Aging process««««««««««««««««««««««««««4 1.2 Modulus Transfer «««««««««««««««««««««««.«5

1.3 Pre-stressing««««««««««««««««««««««««««...5

1.4 Crack deflection or impediment ««««««««««««««««««...5

1.5 Pull-out ««««««««««««««««««««««««««««.6

1.6 Crack shielding ««««««««««««««««««««««««« 6

1.7 Transformation toughening««««««««««««««««««««...7

2. Fracture toughness of Annealed glass««««««««««««««««««.7

3. Question 2 (a)«««««««««««««««««««««««««««...8

4. Question 2 (b)«««««««««««««««««««««««««««...9

5. Question 3 (a) Gas carburizing«««««««««««««««««««««10

6. Question 3b(i)«««««««««««««««««««««««««««..13

7. Question 3b (ii)«««««««««««««««««««««««««««21

8. Question 4 (a) Stiff ness/ strength performance index«««««««««««.....22

9. Question 4(b)«««««««««««««««««««««««««««...23

10. Question 4( c )«««««««««««««««««««««««««««.24

11. Modulus density chart««««««««««««««««««««««««.25

12. Strength and density chart««««««««««««««««««««««...27

13. Fracture toughness and density chart««««««««««««««««««..28

14. R eference«««««««««««««««««««««««««««««.29



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O ptimized tetragonal precipitate of 300 nm can also be o btained by sintering zirconia at

1770°c for 3hr and su bsequently aging at 1400°C for 140 hrs. This results in a sta bilized

zirconia with 10% increase in f racture toughness. However increase in duration of aging

more than stated value results in the formation of mono-clinic which promotes a decrease in

K Ic value. The f igure given below illustrates the formation of monoclinic grains.

Fig 2: A). Increase in f racture toughness with increase in temperature

B). Formation of mono-clinic grains in Zirconia ceramic.

Fracture toughness of Zirconia can also be improved by the addition of f ibres and whiskers in

ceramic material. This increases the f racture toughness u p to 15 times. The presence of

whisker and f ibresdeflects the growth of crack formation.

Apart f rom this the f racture toughness can also be increased by the addition of small amount

of oxides such as Yttria or magnesia. And the material is said to be partially sta bilized,

varying the composition allow different pro perties to be enhanced.

The fracture toughness of Zirconia Ceramic can be increased by the following:

y Modulus Transfer

y Pre-stressing

y Crack deflection or impediment

y Bridging

y Pull-out

y Crack shielding

y Energy dissipation



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1.2 Modulus transfer:

Modulus Transfer generally involves high elastic modulus f ibres in a lower modulus matrix.

Where f ibres or polymers having higher elastic modulus than the modulus of Zirconia

composite is transferred f rom matrix of the f ibre such that the higher strength f ibres can carry

the load.

1.3 Pre-stressing:

This involves placing a portion of ceramic under residual compressive stress. A crack cannot

start or extent as long as ceramic is pre-stressed in compression. Tensile f racture only occurs

after an enough load is a pplied to exceed the compressive pre-stress and to build u p a tensile

stress large enough to initiate a crack at a critical flaw. A compressive pre-stress can be

achieved by many a pproaches; one of the a pproaches is to place the surface in compression by quenching and ion exchange

1.4 Pull-out:

Pull-out consists of f ibres, particle or grain. That de bound f rom the ad jacent micro-structure

and pull out as crack o pen, energy that would normally cause a crackpro pagation is partially

ex pended by de bonding and by f riction as the f ibers, particle or grain slides against ad jacent

micro-structure features. This caneffectively increase f racture toughness. Pull-out is often

accompanied by bridging. This a ppears to be an important mechanism for achieving o ptimumtoughening of Zirconia. The nature of f ibers reinforced ceramic matrixcomposite is critical. If

the bonding is too strong to allow the pull out. The f racture travels directly to the f iber and no

pull out or bridging occurs. The material exhibit low toughness, if the f iber matrix interface

bond is weak to allow crack deflection or de bonding. The material can exhibit high

toughness.

1.5 Crack shielding:

Crack shielding is a stressed induced micro-structural change. That results in a reduction in

stress at the crack tip. The effect occurs around the crack tip and extends along the crack. The

thickness of zone and the extent of the wake both affect the degree of stress shielding at the

crack tip.

Several ty pe of crack shielding has been identif ied.



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Micro-Cracking:

This result in crack shielding by locally reducing the elastic modulus and s preading the

a pplied stress over many cracks rather than one primary crack.

Ductile Zone:

A ductile zone results in crack shielding by allowing plastic deformation around crack tip.

1.6 Transformation toughening:

Transformation toughening is a relatively new a pproach to achieve high toughening in

Zirconia, where a Zirconium oxide goes through a martensitic phase transformation f rom

tetragonal to monoclinic crystal. While cooling through a temperature of a pproximately

1150

o

C. By control of composition, particle size and heat treatment cycle. Zirconia can be densif ied at higher temperature and cooled such that tetragonal phase is maintained as

individual grain or as precipitate to room temperature. The f igure given below ex plains the

transformation of Zirconia f rom tetragonal to monoclinic crystal distribution.

Fig 3. Zirconia Transformation f rom Tetragonal to monoclinic crystal.

1.b). Fracture toughness of annealed Glass:

Given 2a = 1.1 m

A = 0.55m

Stress = 125 Mnm-2

Y = 1.0

We know that f racture toughness

K lc = Y¥a



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1.0*125*¥*0.55

164.3 Mn-3/2

Therefore f racture of toughness of f reshly annealedglass is found to be 164.3 Mnm-3/2

1(ii).

Given

= 41 MN m-2

We know that

R ate of f ractureoccurrence= (Af-Ai)/t

Where Ai = 1.1m

Af = (K lc/Y)²*1/

Af = 5.092m

R ate of f racture = (Af -Ai)/t

(15.092-0.55)/9

0.50477m/ day

Therefore rate of f racture over 9 day period is found to be 0.50477m/day.

Question 2:

2. a) The mechanism for lu brication of piston ring and the consequent wear phenomenon

have been a su bject extensive investigation for some considera ble time. A recent advance

in technological review indicates that,during the lu brication of piston ring and cylinder

linear, a region is encountered. Where hydrodynamic lu brication fails because of

increased load, high temperature and decreased s peed thus squeezes out of oil. However

as per recent investigation the f riction increases suddenly whentransition temperature is

reached. Which is def ined as the temperature at which lu brication tend to lose its a bility

to lu bricate. The piston ring ru bs against the wall of linear and this result an increase in

wear. However a recent investigation revealed that when metal surfaces are heated in the

presence of lu brication. The a bsorbed layer softens whichin turn de pend u pon nature of

lu brication.



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Under poor running condition the piston ring is always heated at same s pot, whereas the

same f riction energy is dissipated over a much greater surface of linear. The bulk

temperature at ru bbing s pot is higher on piston ring than on linear.

Methods to reduce wear and increase performance:

A common technician found that by matching the molecular chain length of polar

additives to the chain length of the base fluid, wear resistance and maximum loading

could be increased safely. Apart f rom this, to minimize the wear the piston ring can be

made u p of wear resistance material such as cast iron and steel, which can also be coated

or treated to enhance the wear resistance.

Ty pically the compression ring or oil ring can be coated with ³chromium or nitride´

possible plasma s prayed or by physical va pour de posit.

This result in enhanced scuff resistance and further improvement in wear resistance.

For example: The modern diesel engine have to p ring coated with modif ied chromium

coating known as CKS or GDC. A patent coating f rom Goetz, which has aluminium

oxides or diamond particles res pectively included in chromium surface. Where the lower

oil ring is designed to leave a lu bricated flux, a few micrometres thick or bore, as piston

descend and this maintains the lu brication of linear at all time.

Question no.2

2.b). Ty pe of wear = oxidative wear

Activation energy = 268 Kj/ mol= 268000 j/mol

T1= 250 °c

T2 = 300 °c

Arrhenius equation for wear rate = Aex p(-Q/RT)

Where Q = Activation energy

R = universal gas constant = 8.314 j/molK

T = temperature in K elvin

A = ex ponential constant = 1016



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R ate of wear at 250°C = 1016ex p (-268000/8.314*523)

1.708148*10-11m

Wear rate at temperature T2 = 300°C

1016ex p( -268/8.314*573)

3.700*10-9m

The relative increase in wear rate due to increase in temperature f rom 250oC-300°C is

found to be

3.700*10-9 ± 1.708148*10-11

3.68 3*10-9

m

Question No.3:

Gas carburizing:

Gas carburizing is a case hardening process in which carbon is dissolved on to the surface

layer of steel part at a temperature suff icient to render the steel austenitic characteristics.

Followed by quenching and tempering to form a martensitic micro-structure. The

resulting gradient in carbon content below the surface of part causes a gradientin

hardness, producing a strong wear résistance surface layer on material. High productionrate gas carburizing is commonly carried out on highly stressed component. Such as

gears, bearing and shafts. Ma jority of gears are gas carburized as it offers acce pta ble

control of case hardening, surface carbon content and pro perdiffusion of carbon into

steel.

Effect of carburizing on gear materials:

A carburized gear tooth may be regarded as a composite structure consisting of lower

carbon in centre and high carbon content on the surface.

Increasing carbon content on the surface increases wear resistance andresistance to

fatigue life.

As the carbon level increases a bove 0.8%. There is a tendency to retain austenite. This

produces carbide network in the u pper case. A recent study showed that a level of 15-



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20% retain austenitic is desira ble both for sliding wear resistance ad resistance to pitting

fatigue.

In general case de pth of a carburized tooth is a function of diametric pitch. The bigger the

tooth the more case is needed to carry the load that will be imposed on the tooth. Too

much case hardening makes the tooth brittle with a tendency to shatter off the to p of the

tooth. However too thin case hardening reduces tooth resistance to pitting. The diagram

given below illustrates the diffusion of carbon on to the surface of gear tooth increasing

the wear ca pacity.

Fig:A Fig: B

Fig: 4 a)A gas carburized Gear b)Diffusion of carbon on to the surface of tooth.

The wear resistance increases by increase in hardness. The wear rate can better be

ex plained by the following mathematical ex pression.

Wear rate = KW/H

Where k = constant

H = hardness

W = load

The following diagram shows increase in hardness in conjunction with case de pth for 135

modif ied steel, 4340 which were carburized for 45 hours.



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Fid 5: R elationship between hardness and wear resistance.

As the carbon content of steel increases it compresses the steel structure. Which

inevita ble increases the fatigue strength of steel structure. The diagram given below

illustrate as how the fatigue strength increased by gas carburizing.

Fig6 : Gas carburizing increasing fatigue strength by compressing the structure.



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3. B) Given Co = 0.2 wt%

Cs = 0.8 wt%

(i) Condition 1

Conditions A1 A2 A3

Temperature 840 840 840

Time 1 5 8

We know that

(Cx-Co)/ (Cs-Co) = 1-erf (x/2¥Dt)

Where Do = Do ex p (-Q/RT)

Diff usion coefficient for the corresponding temperature D1, D2, D3.

D1 = Doex p (-Q/RT)

2.3*10-5ex p(-148000/8.314*1113)

26.03*10-3

D2 = 2.3*10-5ex p (-148000/8.314*1153)

4.5352*10-12

D3=2.3*10-5ex p (-148000/8.314*1203)

8.615*10-12

D1 D2 D3

Diffusion

coeff icient

value

2.60*10-12 4.5352*10-12 8.615*10-12



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Carbon content at X=0.1mm for condition A1 time = 3600 sec

The distance can be taken into meters= 0.1*10-3m

Cx-0.2 /0.8-0.2 = 1-erf (0.1*10-3/2¥2.60*10-12*3600)

Cx-0.2 / 0.6 = 1-erf (0.5168)

Cx- 0.2/0.6 = 1-0.5205 Cx-0.2/ 0.6 =0.4795

Cx-0.2 = 0.2877

Cx = 48 wt%

Condition A1 at X= 0.2= 0.2*10-3m

Cx-0.2/0.6 = 1- erf (0.2*10-3¥26.03*10-3*3600)

Cx-0.2/ 0.6 = 1-erf (1.0336)

Cx-0.2/0.6 = 1-0.8427 Cx = 29wt%

Condition A1 at X= 0.3= 0.3*10-3 m

Cx-0.2/ 0.6 = 1- erf (0.3*10-3/2¥26.03*10-3*3600)

1-erf (1.55044)

1- 0.971622

Cx = 0.21 wt %

Condition A1 at X = 0.5mm = 0.5*10-3m

Cx-0.2/0.6 = 1- erf (0.5*10-3¥26.03*10-3*3600)

Cx-0.2/ 0.6 = 1-erf (2.5840)

Cx-0.2/0.6 = 1-0.9993

Cx = 0.204 wt%



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Similarly the carbon content at x = 0.2*10-3m, 0.5*10-3m is given in the ta ble given below.

Condition B: Temperature = 880oc + 273

1153oF

Diffusion coeff icient = 4.5352*10-12

Conditions B1 B2 B3


Time 1 5 8

Condition B1 at X= 0.1*10-3 at a duration of 1 hours = 3600 sec

Cx-0.2 /0.8-0.2 = 1-erf (0.1*10-3/2¥4.5352*10-12*3600)

Cx-0.2 / 0.6 = 1-erf (0.3913)

Cx- 0.2/0.6 = 1-0.428

Cx-0.2/ 0.6 = 0.572

Cx = 54wt%

Similarly the carbon content at X= 0.2*10-3m, 0.5*10-3m for the surface of gear su bjected to a

carburizing for 1 hour is given in the ta ble below.

Carbon content for condition A3 at 28800 sec duration.

Distance f rom

surface

Percentage of carbon content for A3

X = 0.1*10-3m 68 wt %

X = 0.2*10-3m 57wt%

X = 0.5*10-3m 33wt%



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Condition B2 at X= 0.1*10-3 at a duration of 5 hours = 18000 sec

Cx-0.2 /0.8-0.2 = 1-erf (0.1*10-3/2¥4.5352*10-12*18000)

Cx-0.2 / 0.6 = 1-erf (0.1749)

Cx- 0.2/0.6 = 1-0.195468

Cx-0.2/ 0.6 = 00.8045

Cx = 68wt%

Similarly the carbon content at x = 0.2*10-3m, 0.5*10-3m is given in the ta ble given below.

Condition B3 at X= 0.1*10-3

at a duration of 8 hours = 28800 sec

Cx-0.2 /0.8-0.2 = 1-erf (0.1*10-3/2¥4.5352*10-12*28800)

Cx-0.2 / 0.6 = 1-erf (0.1375)

Cx- 0.2/0.6 = 1-0.1403162

Cx-0.2/ 0.6 = 0.8596

Cx = 71wt%

Carbon content for condition B1 at 3600 sec duration.

Distance f rom

surface Percentage of carbon content for B1

X = 0.1*10-3m 54wt %

X = 0.2*10-3m 36wt%

X = 0.5*10-3m 20wt%


Distance f rom

surface Percentage of carbon content for B

2

X = 0.1*10-3m 68wt %

X = 0.2*10-3m 57wt%

X = 0.5*10-3m 33wt%



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Similarly the carbon content at x = 0.2*10-3m, 0.5*10-3m for the a bove condition is given in

the ta ble given below.

Condition C

Given Temperature = 930oc+273

= 1203

Diffusion coeff icient = 8.615*10-12

Conditions C1 C2 C3


Time 1 5 8

For the conditionC1 at a subjectedto a duration of 1 hour = 3600

At X = 0.1*10-3m

Cx-0.2 /0.8-0.2 = 1-erf (0.1*10-3/2¥8.615*10-12*28800)

Cx-0.2 / 0.6 = 1-erf (0.2839)

Cx- 0.2/0.6 = 1-0.3026

Cx-0.2/ 0.6 = 0.6974

Cx = 61wt%


Distance f rom

surface Percentage of carbon content for B3

X = 0.1*10-3m 71wt %

X = 0.2*10-3m 61wt%

X = 0.5*10-3m 40wt%



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For the conditionC2 subjectedto a duration of 5 hour = 18000 sec

At X = 0.1*10-3m

Cx-0.2 /0.8-0.2 = 1-erf (0.1*10-3/2¥8.615*10-12*18000)

Cx-0.2 / 0.6 = 1-erf (0.1269)

Cx- 0.2/0.6 = 1-0.1403

Cx-0.2/ 0.6 = 0.8596

Cx = 71wt%

Similarly the carbon content at x = 0.2*10-3m, 0.5*10-3m for the a bove condition is given inthe ta ble given below.

Carbon content for condition C1 at 3600 sec duration.

Distance f rom

surface Percentage of carbon content for C1

X = 0.1*10-3m 71wt %

X = 0.2*10-3m 44wt%

X = 0.5*10-3m 22wt%


Distance f rom


X = 0.1*10-3m 71wt %

X = 0.2*10-3m 63wt%

X = 0.5*10-3m 42wt%



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For the conditionC3 subjectedto a duration of 8 hour = 28800 sec

At X = 0.1*10-3m

Cx-0.2 /0.8-0.2 = 1-erf (0.1*10-3/2¥8.615*10-12*28800)

Cx-0.2 / 0.6 = 1-erf (0.100) Cx- 0.2/0.6 = 1-0.2227

Cx-0.2/ 0.6 = 0.7773

Cx = 66wt%



Carbon profile of steel gear with respect to different conditions

Z33\

0

10

0

30

40

¡

0

60

70

¢

0

90

100

0 0.£ 0.4 0.6 0.¤ 1 1. £ 1.4 1.6

%

o

f

C

a

r

b

o

n

Distance from the surface in "x" mm

Carbon profile for 1st condition at 840 degrees


Distance f rom


X = 0.1*10-3m 73wt %

X = 0.2*10-3m 66wt%

X = 0.5*10-3m 48wt%



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3b. (ii):

Given Cx = 0.3 wt %

X = 0.5 mm

X = 0.5*10-3mts

From the carbon prof ile as plotted a bove where a steel gear is su bjected to different temperature and time combinations

The most suita ble condition to reach a de pth of 0.5mm with a concentration of 0.3wt%

carbon is found to be A3

0

20

40

¥ 0

¦

0

§ 00

0 0.2 0.4 0. ¥ 0.̈ © © .2 © .4 © .¥

%

o

f

C

a

r

b

o

n

Distance from the surface "X" mm

Carbon profile for the 2nd condition at 880 c

0

10

20

30

0

50

60

70

80

90

100

0 0.2 0. 0.6 0.8 1 1.2 1. 1.6

%

o

f

c

a

r

b

o

n

Distance from the surface "x" in mm

Carbon profile for 3rd Condition at 930C

C1 for 1 hr

C2 for hr

C3 for 8 hr



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Where

Temperature is found to be = 840oC

Duration of carburising = 5 hours

This can better be ex plained f rom the f igure given below.

Question No. 4:

4.a) Stiffness performance Index:

Given deflection = 5FL / 32Ewt³««««««1

Tensile stress () = 3FL/4wt²««««««««.2

Ste p 1: Identif ication of function, f ree varia bles and o bjective

Function: to su pport weight

Free varia ble: ³t´ thickness

O bjective: minimize weight

We know that performance equation m = AL

Where area = w*t

Therefore the performance equation can be written as

M = w*t*L*««««««««««««««««««.3



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We know that = 5FL³/ 32Ewt²

t³ = 5FL³/ 32E

t = (5FL³)1/3 / (32Ew)1/3«««««««««««««««««..4

Inserting equation 4 into equation eq 3 we get

M = w*L*(5FL³)1/3/(*32wE)1/3

M = (5F)1/3/ (*32)1/3*(w*L²)/w1/3*(/E1/3)

Therefore the performance index is found to be

P1 = E1/3/

Strength performance index:

We know that tensile stress = 3FL/ 4wt²

t² = 3FL/4w t = (3FL)1/2

/ (4w)1/2«««««««««««««««««««««««««..5

Su bstituting equation 5 in equation 3 we get

m = (3F/4) 1/2*(w*L3/2) / w1/2*[/1/2]

Therefore the performance index is found to be P2= () 1/2/ .

4.b) From the charts provided following materials were selected with strength performance index greater than 1.50 mpa and stiff ness performance index greater than 6.0 Gpa

Stiffness performance chart

Diamond Sic SL3 N4

Sialoons Alumina¶s Silicon

Laminates GFRP, KFRP

Magnesium alloy Beo



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Strengthperformance chart

Diamond Sic A2LO3 ZrO3

Mgo B Glass Laminates

KFRP, CFRP Silicon

Please refer to the charts attached for design guide lines.

4.c) Selection of material on the basis of Strength and performance index. The followingf ive materials where selected on the basis of their performance indices values.

Material Stiff ness performance

index Strength performance index

Be (450)1/3/2.1 = 3.6 Sqrt(5000)/2.1= 33.67

Diamond (1000)1/3/ 3.22 = 3.22 Sqrt(10000)/3.1 = 32.25

Sic (600)1/3/3 = 2.81 Sqrt(9000)/3 = 31.6

GFRP(laminates) (60)1/3/1.5 = 2.60 Sqrt(1000)/ 1.5 = 21.08

Sailoon (500)1/3/3 = 2.64 Sqrt(7000)/3.2 = 26.14

As f racture toughness of plate is concern, which has to be a bove 20 mpa

I select GFRP laminates as it has f racture toughness of 80 mpa.

Stiff ness performance Index= 2.60

Strength performance index = 21.08.

GFRP laminate proves to be the best material as it has low density and high performance index in relation to the f racture toughness which is a bout 80 mpa.



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Modulus and Densitry chart:

The design guide line was o btained by the following calculation:

Point 1:

Since it is given that the strength performance indices should be greater than 6 Gpa

½/= 6

½/ 3 = 6



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Point 1

= 324 M pa

Point 2:

½/= 6

Taking density as 1(mg/m3)

½/ 1 = 6

Point 2

= 36M pa

Strength and Density Chart:

For strength and density chart the two points where calculated by the following methods

Since it is given in the assignment that the stiff ness performance indices should be greaterthan 1.50

E1/3/ = 1.50

Point 1:

Taking the density as 1mg/m3

E1/3/1 = 1.50

E= 3.375 Gpa

Point 2:

Taking the density as 3mg/m3

E1/3/ = 1.50

E1/3/3 = 1.5

E = 91.1125 Gpa



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Strength and density Chart



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Fracture toughness and density chart:



R eference:

1. Dr Bao. 2010. London south bank university. Availa ble: online, Date of access: 15-

05-2009.

2. D. w Richardson. 2006. ³Modern ceramics engineering. Pro perties processing and

uses in design´. 3rd edition, CR C press. Taylor and Francis grou p.

3. D. w. Richardson. 1992. ³Modern ceramic engineering´ 1st edition. Fracture

toughness. Pu blished by MarcelDekker.

4. J.s Burnell, P.K Dutta,2004. ³Surface engineering´. Case book. 1st edition. Wood

head pu blishing limited-uk.

5. Stan grainer, J Blunt, 1998. ³Engineering Coating´. Design and a pplication, 2nd

edition. Abington limited-uk.

6. Dr Gawne, 2010. ³Tribology´. London south bank university. Availa ble online: Black

Board. Date of access: 12-05-2010.

7. B. Bhushan. 2002. ³Introduction to Tribology´ 1st edition, wear mechanism. John

weily and son¶s ± UK.

8. P. C. Nautiyal, S. Singhal and J. P. Sharma. 2007. ³Friction and wear processes in

piston rings´ Journal of *Indian Institute of Petroleum, Mo pkampur, Dehra Dun,India.

Volume 12. Page no. 23-40. Availa ble Online: www.sciencedirect.com. Date of

access: 25-05-2010.

9. D. Casellas, Adrian Freder,Luis Llanes. 2001. ³Fracturetoughness and mechanical

strength of Y-TZP/ PSZ Ceramic´. Journal of material science. Volume 45, page no.

213-220. Availa ble online: www.sciencedirect.com Date of access: 25-05-2010.

10. Hannah J. Yount. 2006. ³Hardness and f racture toughness of heat treated advance

ceramics for use in fuel coating´. Thesis. University of Wisconsin- Madison.

Availa ble online: www.scribd.com date of access: 25-05-2010.

11. James F. Shackel ford. 2005.. ³ introduction to material science for engineers´.

Seventh edition. Pearson pu blication. NJ-USA.

12. Myer K utz. 2002. ³Hand book of material selection´. 1st

edition. John Wiley and son¶s. New York.

13. G. T Murray. 1997. ³Hand book of material selection for engineering a pplication´. 3rd

edition. Marcel Dekker Inc. USA.

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