FINITE ELEMENT ANALYSIS OF HUMAN FEMUR

4TH INT. CONFERENCE OF MULTIPHYICS, LILLE, FRANCE, 9-11 DEC 09

H. A. KHAWAJA (PhD Student, Dept. of Engineering)

A. NAIK (PhD Student, Dept. of Material Sciences)

K. PARVEZ

(Professor; Research Centre for Modelling & Simulation)

POINTS FOR DISCUSSION

INTRODUCTION

FEMUR CAD DEVELOPMENT

Laser 3-D Scanning

CAD Model

Marrow Cavity (Approx.)

FINITE ELEMENT ANALYSIS

Finite Element Modelling

Material Properties and Assumptions

Loading and Boundary Conditions

Finite Element Analysis Results

SUMMARY & CONCLUSION

REFERNCES

ACKNOWLEDGEMENTSH. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 2

INTRODUCTION

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 3

FEMUR

Largest Human Bone

Single Support Member

Less Flexible (Stiff)

Anisotropic Material

This work addresses:

Load Bearing limit of Femur

Natural Safety Factor

Results will aid in deciding substitute material for bone

FEMUR CAD DEVELOPMENT

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 4

Laser 3-D Scanning:

OBJECT LASER SCAN

ROTATION

COORDINATES CLOUD

CAD Model:

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 5

FEMUR CAD DEVELOPMENT

Marrow Cavity is developed based on approximation

FINITE ELEMENT MODELLING

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 6

Finite Element Mesh: Tetrahedral 20-noded 186 structural solid element has been used Mesh sensitivity analysis is carried out to ensure the quality of results

Mesh has been refined in the regions of high Gradients

FINITE ELEMENT MODELLING

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 7

Material Properties & Assumptions: Originally Bone material is anisotropic but assumed to be isotropic

because complete femur was taken for analysis; a piece of bone could be solved for anisotropic solution but not the complete bone.

The bone Young’s modulus varies between 10 to 20 GPa. The Poisson’s ratio is about 0.3 *. “For linear static analysis stresses doesn’t depend on modulus of elasticity”

Physiological conditions has been ignored for time being; e.g. muscle stresses.

x

y

z

*BAOHUA, J., HUAJIN, GAO., (2004). Journal of Mechanics and Physics of Solids, 52, 1963-1990.

FINITE ELEMENT MODELLING

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 8

Loading & Boundary Conditions: Axial Load

Bending Load Based on its position w.r.t. Its orientation

Load is varied until failure

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 9

FINITE ELEMENT MODELLING

Finite Element Results (Compression): Displacement Contour Plot

1 Units = 1 metres

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 10

FINITE ELEMENT MODELLING

Finite Element Results (Compression): Von-Mises Stress Contour Plot

1 Units = 1 Pascal

Max. Stress regions coincides under axial and bending load

FLUIDIZED BED

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 11

FINITE ELEMENT MODELLING

Finite Element Results (Based on 70 Kg Human Weight):

69 Kg is limit load under bending load and 414 Kg is limit load under axial load.

*Failure limit is 100 MPa (BAOHUA, J., HUAJIN, GAO., (2004). Journal of Mechanics and Physics of Solids, 52, 1963-1990.)

Loading (Kg) Max. Stress (Compression)

Max. Stress (Bending)

25 6.04 36.31

35 (Design Value) 9.31 51.22

69 24.23 100.30*

150 36.41 217.93

250 60.01 363.11

414 99.83* 601.93

500 121.12 733.31

SUMMARY & CONCLUSION

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 12

Summary:

3-D CAD Model has been developed via Laser Scanning

Approximations have been applied on material and model

Finite Element Analysis has been conducted

Results are evaluated

Conclusion:

Natural Margin of Safety under 35 Kg Design Load (70Kg average

Human) of compression is 9.74.

Natural Margin of Safety under 35 Kg Design Load (70Kg average

Human) of bending is 0.952.

Human Femur is designed to bear 10 times more load compared to load at normal conditions. It has also

been found out Femur resistance to fracture under compression is approx. 5 times to the bending.

FUTURE WORK

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 13

Evaluated results are the indicative of the mechanical properties of

substitute material for bones.

Physiological conditions may be involved to increase the accuracy of

results.

Whole human bone structure may be solved via FEM under the

availability of computational resources.

REFERENCES

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 14

•ALBERT. H., ET AL, (1972). Journal of Biomechanics, 5, 35-44.

•ANSYS® Multiphysics FEM Package, Release 11.0

•ANSYS® Technical Manuals, Release 11.0 Documentation for ANSYS®

•BAOHUA, J., HUAJIN, GAO., (2004). Journal of Mechanics and Physics of Solids, 52, 1963-1990.

•CURREY, J., D., (1979). Journal of Biomechanics, 12, 313-319.

•CURREY, J., D., (1988). Journal of Biomechanics, 21, 2, 131-139.

•LAWRENCE, J., (1984). IEEE Transactions on Biomedical Engineering, 31,12.

•WEINER, S., WAGNER, H., D., (1998). Annual Review Material Science, 28.

ACKNOWLEDGEMENTS

Institute of Space Technology (IST) – Pakistan

Cambridge Commonwealth Trust – Cambridge, UK

Research Centre for Modelling & Simulation, National University

of Sciences & Technology (NUST) - Pakistan

H. A. KHAWAJA MULTIPHYSICS 2009, LILLE, FRANCE, 9-11 DEC 09 15

THANK YOU

CONTACT

HASSAN KHAWAJA

Email: hak23@cam.ac.uk

Webpage: http://hassanabbaskhawaja.blogspot.com