Presentation at the World Tribology Conference WTC2013, Torino, Italy

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Evaluation and prediction of the effect of load frequency on the wear properties of pre-cracked nylon 66

Authors:

A. Abdelbary, M. N. Abouelwafa, I.M. El Fahham and A. H. Hamdy

Dr. Ahmed Abdelbary

Presented by:

Mechanical Eng. Dept., Faculty of Eng., Alexandria, EGYPT

WE2-FW7- 81

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1. Introduction

2. Experimental Work

3. Results & Discussion

4. Conclusions

ContentsCONTENTS

Microscopic investigation of nylon 66 worn surface showed

a number of transverse vertical cracks, which suggested

that the surface cracks play an important role in SFW [1].

3[1] Y.K. Chen, S.N. Kukureka, C.J. Hooke, M. Rao, Surface topography and wear mechanisms in

polyamide 66 and its composites, J. of Mat. Sci. 35(2000) 1269–1281.

1. INTRODUCTION

In cyclic loading, loading-unloading cycles generate

subsurface stress regions that increase the

tendency to initiate surface and subsurface cracks

[2].

Under cyclic loading, the wear rate was about 30%

larger than under a constant load of the same

magnitude [3].

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[2] J.R. Cooper, D. Dowson, J. Fisher, Macroscopic and microscopic wear mechanisms in UHMWPE, Wear 162-164 (1993) 378–384.

[3] A. Abdelbary, M.N. Abouelwafa, I. El Fahham and A. I. Gomaa, The influence of cyclic loading parameters on the wear of nylon 66, Proc. 8th International Conference on Production Engineering and Control PEDAC (2004) Egypt.

1. INTRODUCTION

5[4] K. Furber, J.R. Atkenson, and D. Dowson, The mechanisms for nylon 66: Paper II, Proc. of the 3rd

Leeds-Lyon Symposium on Tribology, 1976.

Volume loss versus sliding distance for Nylon 66 loaded at 67 N, Ref [4].

A

B

1. INTRODUCTION

Section B wear was introduced

[4] as a third wear regime

characterized by marked

increase (10:30%) in WR and

transverse cracks on the

rubbing surface.

It was suggested that section is

SFW takes place after a number

of cycles to failure proportional

to the sliding distance.

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1. INTRODUCTION

The present study aimes to: Investigate the influence of load frequency on wear of

nylon 66 with a pre-existing defect on its rubbing

surface.

Explore the relation between SFW and section B wear

regime.

Predict WR of the tested polymer using ANN wear

model.

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2. EXPERIMENTAL WORK

The dry wear tests under constant and cyclic loads

were performed using reciprocating tribometer of dual

six-station wear tracks.

Sliding speed: 0.25 m/s

Sliding stroke: 310 mm

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Tribometer: (1) motor; (2) machine frame; (3) chain drive mechanism; (4) U-beam guide; (5) reciprocating carriage; (6) spring; (7) eccentric cam; (8) dead weights; (9) pin holder.

1700 mm

1100

m

m

1

2

3

4

5

6

79

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Cyclic load Constant load

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All tests were carried out using Nylon66 sliding on

steel counterface AISI 1050, Ra = 0.2 µm.

The imposed cracks were generated by a sharp razor

applied vertically to the surface of the test specimen.

2.5

mm

Wear pin with imposed

vertical crack


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The effect of load frequency on Pre-cracked

polymer:

Cyclic load tests: at two frequencies:

f = 0.25, 1.50 Hz, Fmean= 90 N

Constant load tests: at two loads: F = 90 , 135 N

The influence of surface imperfections:

explored by introducing three parallel cracks on the

polymer rubbing face.

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Relation between surface cracks and section B

wear:

Tests start using un-cracked pin; subsequently, surface

crack was imposed after 80 km, and tests were run

again for 40 km.

ANN model:

Constructing and training the wear model using the

experimental results.

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3. RESULTS & DISCUSSION

CONSTANT LOAD

Tes

t

F

N

surfac

e

cracks

X

km

WR x10-4

mm3.m-1

1 90 - 110 13.3

2 90 1 80 14.8

3 90 3 80 25.2

4 135 - 90 18.1

5 135 1 90 30.7F Applied force [N]X Sliding distance [km]WR Wear Rate [m m3/m]

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CYCLIC LOAD

Test

Freq.f

Hz

surfac

e

cracks

X

km

WR x10-

4

mm3.m-1

7 0.25 - 80 13.7

8 0.25 1 80 21.8

9 0.25 3 80 29.7

10 1.50 - 100 15.8

11 1.50 1 80 30.1Fmean= 90 N, Fmin/Fmax = 0.06

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Effect of frequency

test fHz

cracks RCW

12 0* 1 1.11

13 0* 3 1.89

78 0.25 1 1.59

79 0.25 3 2.17

1011 1.50 1 1.90

* Constant load tests

RCW Relative Change in WR

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Un-cracked polymer

wear pin surface after 60 km sliding, showing wear grooves parallel to the sliding direction

steel counterface after 20 km sliding, showing transfer film formed

300 µm

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wear pin surface, test 11 after 20 km sliding, showing trapped wear debris inside the crack mouth

steel counterface after 20 km sliding, showing transfer film formed

Pre-cracked polymer

300 µm

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Optical micrograph of nylon 66 rubbing surface, test 2 after 20 km sliding, showing trapped wear debris, pitting.

Pre-cracked polymer

300 µm


Sliding direction

1 mm

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wear pin surface of test (3) after 20 km sliding, showing wear pin surface with high density of wear grooves

steel counterface of test (3) after 10 km sliding, showing transfer film formed

Pre-cracked polymer, 3 surface cracks

300 µm


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Relation between SFW and section B wear

TestX

km

WR A x10-4

mm3.m-1

Xof sec. B

km

WR B x10-4

mm3.m-1

*6 120 12.7 80 14.6

**12 125 25.1 80 27.6

10 to15% increase

Test (6)


* F= 90 N** Fmean= 90 N, f= 0.25 Hz

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ANN wear model

Hidden layers Output layer

Wear Rate

WR

Input layer

Load (F or Fmean)

Maximum load (Fmax)

Frequency (f)

Cracks (n)


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ANN wear model

Ref. ANNNeurons Type

Training algorithmI/P Hidden O/P

Z. Zang {9[15105]3 1} tan-sigmoid tan-sigmoid pure-linear LM

A. Lada {7[93 ]2 1} tan-sigmoid tan-sigmoid pure-linear CGB

A. Abdelbary {5[201010]3 1} tan-sigmoid tan-sigmoid pure-linear LM

X. Liu {2[8]1 1} - tan-sigmoid pure-linear LM

Z. Jiang {9[1263]3 1} - - - CGB

A. Helmy {35[85]2 1} tan-sigmoid pure-linear pure-linear LM

Configuration of ANNs adopted from literatures

LM Levenberg-Marquardt algorithm CGB Powell–Beale conjugate Gradient algorithm


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ANN wear model

Comparison of the prediction quality for various ANNs

configurations

[201010]3


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ANN wear model

[201010]3


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3. CONCLUSIONS

1) Transverse crack(s) on the polymer rubbing face

is responsible for significant increase in wear

rate.

2) Frequency of cyclic load has an important role in

wear behaviour of surface cracked polymer.

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3. CONCLUSIONS

4) Performing a single transverse crack during the

steady state wear phase resulted in a

generation of section B wear characterized by a

relatively higher wear rate.

5) Introduction of ANNs is beneficial in predicting

the wear rate of nylon 66.

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Thank You

Technology

Presentation at the World Tribology Conference WTC2013, Torino, Italy