Tribology of Polyurethane Graphene Composite.

Open Defense on DissertationBy

Atul Kumar VermaUnder the Supervision of

Prof. Pralay Maiti

School of Materials Science & Technology Indian Institute of Technology(Banaras Hindu University)

Varanasi

Roll No. 14112003

Content

Introduction. Literature survey. Synthesis. Experimental data. Conclusion. Future work. Reference.

IntroductionWhat is Tribology ?

Tribology is study of interaction through the surfaces in relative motion.

Originated from the Greek word tribos meaning rubbing. It is interdisciplinary performance where relative motion between

surfaces is involved. It leads to surface interactions of a solid surface exposed face to

face and environmental condition that causes loss of material from the surface.

Examples are bearings, gears, cams and tappets, tyres, brakes, and piston rings.

Approximately one-third of the world's energy resources in present use appear as friction in one form or another.

The aim tribology is the minimization and elimination of unnecessary waste at all levels of technology where the rubbing of surfaces is involved.

Major objectives in tribology is the regulation of the magnitude of frictional forces.

Surface contact.

Fig.1 Contact between basebody and counterbody.

Applications:

Fig.2 Different application of polymer in tribology.

Literature survey Wear test has been utilized by numerous analysts as a part of

examining wear rate and erosion’s coefficient. Riadh, E., et al. have worked on thermoplastic polyurethane. The wear conduct tried on sliding contact wear machine. Outline of results got by Riadh, E., et al.

Fig.3 Riadh E., et al. “Tribological behavior of thermoplastic polyurethane elastomers”, Materials and design. 28, 824-830, 2007.

Two mechanism shearing junction by adheshion and dissipation of mechanical energy due to deformationFig.4 Wear volume against the product of applied normal load and distance (Archard,s factor) for TPU and TPUG (Tribol Letter (2012) 48:209–216).

S.No Material

Load(N)

Wear(mm3/Nm)

(µ) No of cycle

Sliding speed (m/s)

PLATE

REFRENCE

1. PU 5 3×10E-6 0.5 6000 0.3 St.steel

Tribo.lett(2012)48(209-216)

2. PA66 19.6 1.2×10E-8

.66 2000 2.0 St.steel

Tribo.online,10,2(2015)213-219

3. PA66/RBC

19.6 0.3×10E-8

0.48 2000 2.0 St. sttel

Tribo.online,10,2(2015)213-219

4. PI 50 0.78×10E-8

0.5 5000 0.2 Steel disc

Tribo.interntnl 92 (2015) 162-171

5. PP 100 125×10E-6

0.67 100 1 Steel disc

J.Aurrekoexteaetat wear 265(2008)606-611

6. PMMA 2 107×10E-6

0.44 18000 0.1 Artificial.teeth

 J Prosthet Dent.2015 Aug;114(2):286-92

Table.1 Wear of Different Polymers

Butane di-ol (BD) HO ̶ (CH2)4 ̶ OH Di-isocynate (HMDI) OCN ̶ (CH2)6 ̶ NCO Polytetra methylene glycol(PTMG) HO ̶ [ (CH2)4-O-)] n - H

Polyurethane: Polyurethanes are most versatile polymer constituted by hard and soft segments. They can be repeatedly melted and processed due to the

absence of the chemical networks that normally exist in rubber and, therefore, are used in many fields.

Due to their moderate cost, excellent mechanical properties(higher elasticity, flexibility, toughness etc.) high resistance to tear, oxidation and humidity.

Graphene: Graphene can be described as a one- atom thick layer of graphite.  It is the basic structural element of other allotropes, including

graphite, charcoal, carbon nanotubes and fullerenes. Graphene is an atomic-scale honeycomb lattice made of 2D carbon

atoms having sp2 hybridization and it is bound to its three neighbors.

Fig.5 Single atomic layer of graphene (Castro-Neto, et al. Rev. Mod. Phys) 81 (2009) 109..

It is chemically the most reactive form of carbon. Only form of carbon (and generally all solid materials) in

which each single atom is in exposure for chemical reaction from two sides (due to the 2D structure).

C-atoms at the edge of graphene sheets have special chemical reactivity and commonly modified with oxygen- and nitrogen- containing functional groups.

Synthesis:

Fig.6

Types of Wear

Adhesive wear. Abrasive wear. Surface fatigue wear. Tribo-chemical or corrosive wear.

Fig.7 Wear mechanism where (Fn normal force , Ff friction force , Fn, as normal force on asperity contact, ∆v relative velocity) (KRAGELSKI, J.W. Reibung und Verschleiß (VEB Technik, Berlin 1971), in German).

Preparation of Sample For Wear Test: Samples were prepared by melt cast method. PUs were melted in a

predetermined sized mold. Casted sample dimensions 10mm × 3mm × 3mm.Experimental Procedure : The experimental parameters were carried out to study the effects of

load, velocity, travel distance and temperature on the tribological behavior of TPU material against steel disc plate.

The first parameter considers the effect of load at room temperature (21°C) with a sliding speed v of 0.209 m/s over a traveled distance L of 62.83m and time 300s at constant normal loads were chosen at 5N and 10N.

The second parameter concerns the effect of velocity and travel distance with a constant load of 10N at room temperature further process repeated for each sample.

Wear Test: Friction and wear experiments were carried out on tribometer (Winducom 2010 pin on disc). Polymeric pin were mounted vertically on a pivoted arm which was connected to a disc made of steel and loaded against liver by a dead weight. The test were performed under the ambient condition. Friction and wear test was carried out at 50 rpm and normal load (Fn) 5 N and track diameter 80mm for 5 min. Formula used to determine the coefficient of friction (COF),

COF = Ff / Fn

 Where, Ff = Frictional force, and Fn = Normal load. Fig.8 Pin on Disc

Calculation of Wear Rate: A common used equation to compute the wear rate is (Archard,1953).  Vi = kiFs where, F is the normal load, s the sliding distance, Vi the wear volume and ki the specific wear rate coefficient. Index i identifies the surface considered.The k value is given in m3/Nm or m2/N, sometimes in mm3/Nm. From design view the wear displacement h is more convenient than V. With hi =Vi /A, the contact pressure P=F/A where A is the area subjected to wear then 

hi =ki p s

The sliding distance s can be replaced by s = v.t where v is the mean value for the slide rate and t the running time. Because the k value depends just like the friction coefficient on a lot of parameters this factor is to be find experimentally (www.tribologyabc.com).

0 50 100 150 200 250 3000

500

1000

1500

Wea

r/µm

t/sec.

50 rpm / 5N

PU

PUGC

PUGP

0 50 100 150 200 250 3000.0

0.5

1.01.52.0

2.5

3.03.5

4.0

Ff/N

t/sec.

50 rpm / 5N

PU

PUGC

PUGP

Fig. 9 (A) Wear vs Time Graph (B) Friction Force vs Time Graph

0 50 100 150 200 250 3000.0

0.2

0.4

Coe

ffic

ient

of f

rict

ion/

µ

t/sec.

50 rpm / 5N

PU

PUGC

PUGP

0 50 100 150 200 250 3000.0

0.1

0.2

0.3

0.4

0.5

Wea

r ra

te (m

3 /Nm

)

t/sec.

50rpm/5N

PU

PUGC

PUGP

(C) Coefficient Of Friction (µ) vs Time (D) Wear Rate vs Time

0 50 100 150 200 250 3000

400

800

1200

1600 50rpm/10N

Wea

r(m

3 /Nm

)

t/sec.

PU

PUGC

PUGP

0 50 100 150 200 250 3000

1

2

3

4

5

50rpm/10N

Ff/N

t/sec.

PU

PUGCPUGP

Fig.10 (A) Wear vs Time Graph (B) Friction Force vs Time Graph

0 50 100 150 200 250 3000.0

0.2

0.4

0.6

50rpm/10N

Coe

ffic

ient

of f

rict

ion/

µ

t/sec.

PUPUGCPUGP

(C) Coefficient Of Friction (µ) vs Time

0 50 100 150 200 250 3000.0

0.1

0.2

0.3

0.4

0.5

Wea

r ra

te (m

3 /Nm

)

t/sec.

PU

PUGC

PUGP

50rpm/10N

(D) Wear Rate vs Time

0.0

2.0x10-4

4.0x10-4 Sliding Speed

Wea

r fa

ctor

(m3 /N

-m)

PU PUGC PUGP

Fig.11 (A) Wear Factor at constant Load (B) Wear Factor at constant Sliding Speed

0.0

2.0x10-4

4.0x10-4 50 rpm/ 5N

Wea

r fa

ctor

(m3 /N

-m)

PU PUGC PUGP

S. No Material

Load(N) Wear(m3/Nm) (µ) No of Sliding Plate

          cycle speed              (m/s)                 

1. PU 5 6.740×10E-6 0.5 3000 0.209 St. steel

               

2. PUGP 5 1.709×10E-6 0.23 3000 0.209 St. steel

               

3. PUGC 5 1.728×10E-6 0.26 3000 0.209 St. steel

               

4. PU 10 8.78×10E-6 0.5 3000 0.209 St. steel

               

5. PUGP 10 2.5×10E-6 0.4 3000 0.209 St. steel

               

6. PUGC 10 2.10×10E-6 0.6 3000 0.209 St. steel

               

Table 3. Experimental Data

Barwell Curve Fitting:  Barwell suggested that wear rates may be explained by one of three equations. (H.C. Meng, K.C. Ludema 1 Wear 181-183 (1995) 443457).   V = /{1 – exp(-t)}………. (1) V = t …………………. (2) V = exp(t )……….. (3)  Where, is the probability of metal contact. is constant. V is volume and, t is the time. 

0 50 100 150 200 250 3000

2

4

6

8

10

12 50 rpm / 5N

Wea

r/µm

t /sec.

PU Exp2PMod1 of PU

0 50 100 150 200 250 3000.0

0.1

0.2

0.3

0.4

0.5

0.6 50 rpm / 5NEquation y = a*exp(b*x)Adj. R-Square 0.98708

Value Standard ErrorPUGC a 0.05014 0.00739PUGC b 0.00864 5.71356E-4

Wea

r/µm

t / sec.

PUGC Exp2PMod1 of PUGC

Fig.12 (A) Curve Fitting of PU (B) Curve Fitting of PUGC.

0 50 100 150 200 250 300

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

50 rpm / 5N

W

ear/

µm

t / sec.

PUGP Exp2PMod1 of PUGP

Equation y = a*exp(b*x)Adj. R-Square -1.94925

Value Standard ErrorPUGP a 0.01075 0.19324PUGP b -1.31613 2.47708E28

0 50 100 150 200 250 300

0

3

6

9

1250 rpm / 5N

W

ear/

µm

t / sec.

PU PUGC PUGP Exp2PMod1 of PUGC Exp2PMod1 of PUGP Exp2PMod1 of PU

Equation y = a*exp(b*x)Adj. R-Square 0.98708 -1.94925 0.97687

Value Standard ErrorPUGC a 0.05014 0.00739PUGC b 0.00864 5.71356E-4PUGP a 0.01075 0.19324PUGP b -1.31613 2.47708E28PU a 1.22801 0.20041PU b 0.00749 6.23004E-4

(C) Curve Fitting of PUGP (D) Fitting Graph

Table 3. Curve fitting values:S.no

Equation y = *exp(*x)

     

1 Adj. R-Square 0.98708 -1.94925 0.976872     Value Standard Error3 PUGC a 0.05014 0.007394 PUGC b 0.00864 5.71356E-45 PUGP a 0.01075 0.193246 PUGP b -1.31613 2.47708E287 PU a 1.22801 0.200418 PU b 0.00749 6.23004E-4

According to Barwell equation the graph nature is true and it shows the exponential value of wear with time and characteristics values are true. Basically these values are fully depending upon the contact of metal surface and this cause wear and friction.

Polarized Optical Microscopy (POM)

3) PU 10N Worn Surface2) PU 5N Worn SurfaceFig.13 1) PU Unworn Surface Wear

4) PUGC Unworn 5) PUGC 5N Worn Surface 6) PUGC 10N Worn SurfaceWear

7)PUGP Unworn 8) PUGP 5N Worn Surface 9) PUGP 10N Worn SurfaceWear

Scanning Electron Microscopy (SEM):

Fig. 14. 1)PU Unworn 2) PU Worn 5N 3) PU Worn 10NWear

4) PUGC Unworn 5) PUGC 5N Worn 6) PUGC 10N WornWear

1)PUGP Unworn 2) PUGP 5N Worn 3) PUGP 10N WornWear

From the wear observation of polyurethane and graphene composite we can conclude that with increasing load wear debris of the surface increases and due friction force frictional heat generated that causes plastic deformation in the wear surface.

As we increase the load from 5N to 10N the wear increases rapidly and due to frictional heating continuous film form on the counter surface due to this worn surface is not uniform.

In virgin polyurethane maximum wear seen on comparing to physical and chemical polyurethane composite as load increases. In physical composite wear is more than the chemical composite material and it can be easily observed from the worn surfaces.

Conclusion:

On increasing load wear of polymer increases rapidly in case of polyurethane and its composite.

Maximum wear in pure polymer and minimum wear in chemical composite while moderate wear in physical composite.

On comparing with literature the results are almost same.

Future workDifferent composite can be made for analysis of wear

behavior of polyurethane and granphene composite.

Application of polymer in different sector can be tested.

Wear property can be check with higher load and change in temperature of base body and counterbody.

Reference.

1.Riadh E., et al. “Tribological behavior of thermoplastic polyurethane elastomers”, Materials and design. 28, 824-830, 2007.2. (Tribol Lett (2012) 48:209–216).3. Castro-Neto, et al. Rev. Mod. Phys. 81 (2009) 109.4. KRAGELSKI, J.W. Reibung und Verschleiß (VEB Technik, Berlin 1971), in German.5.www.tribologyabc.com6. H.C. Meng, K.C. Ludema 1 Wear 181-183 (1995) 443457.7.J. Phys. Chem. B 2010, 114, 5292–5300.10.www.elsevier.com/locate/matdes.9.www.seminarlinks.blogspot.com8.www.google.com[fig.1, fig.2].