STUDY THE EFFECT OF ANGLE DORSIFLEXION ON BENDING STRESS OF PROSTHETIC PYLON

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STUDY THE EFFECT OF ANGLE

DORSIFLEXION ON BENDING STRESS

OF PROSTHETIC PYLON

MUSLIM M. ALI

Technical Institute-Babylon Babylon, IRAQ

ALI I. AL-MOSAWI

Technical Institute-Babylon

Babylon, IRAQ

alibrahim76@yahoo.com

JABBAR H.MOHMMED

University of Technology Baghdad, IRAQ

ALI R. YOUSIF

Technical Institute-Babylon Babylon, IRAQ

Abstract:

Affecting millions of people worldwide, artificial limbs and prosthetics are major topics in the field of bio mechatronics. This paper will examine and describe in effect of angle dorsiflexion on bending stress limb technology, in particular focusing on prosthetic pylon. The theoretical part includes; analytical solution to find dorsiflexion angle and bending stress. In the numerical method, the finite element is used by employing ANSYS package to find bending stress with angle dorsiflexion with gait cycle and Von Misses stresses. Thus the prosthetic pylon was angle dorsiflexionthe value of stress bending will be increased with increasing of angle dorsiflexion.

Keyword: Prosthetic, Pylon, ANSYS Program, Bending stress. 1. Introduction

Every year, hundreds of thousands of people lose a limb due to diseases such as diabetes and cancer, as well as to the trauma associated with automobile collisions and violence. In the United States over 130,000 people had a lower limb amputated in 1997 [1]. Of those amputations, 67% were as a result of complications due to diabetes. In 2001, the International Committee of the Red Cross (ICRC) fitted a total 7,418 people with their first prostheses and distributed 9,779 prostheses to land mine survivors in fourteen post-conflict countries [2].As of 2008, about 100 individuals with amputation have had abutments for attaching leg prostheses implanted in their residuum [3].Current prosthetic foot designs do not replicate the exact characteristics of a normal human foot. A human foot is a multi - functional device that can be used to perform a wide range of activities, however, a prosthetic foot is limited to only a few. More recently manufacturers of prosthetic feet have looked into the characteristics of a prosthesis that may be adjustable. The amputee may then be able to perform a number of activities without requiring a different prosthesis [4].

2. Dorsiflexion

Once the foot has become flat, the leg rolls over the foot until it reaches a peak dorsiflexion of 8 to 10 degrees. As the heel raises off the ground the ankle plantar - flexes to a position of 18 to 23 degrees. In the later part of the stance the amount of plantar-flexion reaches up to 30 degrees [5]. Table .1 shows Dorsiflexion of normal foot at various walking speeds [4] .

Table .1: Dorsiflexion of normal foot at various walking speeds

Walking Speed ( km/h) Dorsiflexion ( Degrees)

1-3 km/hr 3-4° 3-5 km/hr 5° 7-8 km/hr 7-10°

Muslim M. Ali et al. / International Journal of Engineering Science and Technology (IJEST)

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3. Stresses in pylon

Forces and couples acting on the pylon cause bending (flexural stresses) and shearing stresses on any cross section of the pylon and deflection perpendicular to the longitudinal axis of the pylon. If couples are applied to the ends of the pylon and no forces act on it, the bending is said to be pure bending. If forces produce the bending, the bending is called ordinary bending.

4.Assumptions

In using the following formulas for flexural and shearing stresses, it is assumed that a plane section of the pylon normal to its longitudinal axis prior to loading remains plane after the forces and couples have been applied, and that the pylon is initially straight and of uniform cross section and that the module of elasticity in tension and compression are equal.

5. Flexure formula

Stresses caused by the bending moment are known as flexural or bending stresses. Consider a beam to be loaded as shown.

Fig.1. Loaded beam

Bending stress can be obtained from the following formula:

σ=32 M πD3 1 M=FLsin 2 Where:

σ = Bending stress (N / m2) M = Bending moment (N-m ) F=Ground reaction force (N)

L=Length of the exposed part of pylon (m)

α=Angle of dorsiflexion.

Fig.2 shows an analytical solution of prosthetic pylon .

Fig.2 . Analytical solution of prosthetic pylon

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6. Results and discussion

From the results obtained on bending stress from angle dorsiflexion by analytical solution and in the numerical method, the finite element is used by employing ANSYS package, we can see.

Fig.3 represents the relationship between dorsiflexion angle and bending stress which calculated by equations. From figure we note at zero angle there is no bending stress value since there is no moment, but by increasing the angle to (1°) we find bending stress results from the moment generated by ground reaction force. By increasing these angle the bending will increase directly to the same cause (i.e. there is direct relationship between bending value and dorsiflexion angle which the bending moment increase by its increasing).

Fig.3 . Mathematic equations bending stress with dorsiflexion angle

Fig.4 . Represents the relationship between the angle and bending stress which calculated by ANSYS simulation, where at angle increasing the bending stress in the pylon increase as a result of moment which causes reaction in the foot. Bending stress increases by increasing the angle as shown in figures (5 to 18). By comparing between mathematic equations and ANSYS simulation, shows more precision in ANSYS simulation from thus calculated by equations. This is interpreted that ANSYS program calculates the bending stress in each point of body, whereas equation takes the effect of force on gross body.

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Fig.4 . relationship between the angle 1º and bending stress which calculated by ANSYS simulation

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7. Conclusions

The aim of this paper we concluded that:

1-Increasing the angle dorsiflexion as the bending stress increased. 2-The diameter of the pylon is increase as the bending stress decreased. 3-The length of the pylon is increase as the bending stress increased.

4-Using for the comparison of bending stress between numerical methods ( Finite element methods) and the theoretically methods.

8. References

[1] Centers for Disease Control and Prevention. (2001): Hospital Discharge Rates from Non-Traumatic Lower Extremity Amputation by Diabetes Status, Morbidity and Mortality Weekly Report, 50(4) ,pp. 954-958.

[2] Walsh, N. E. and Walsh, W. S. (2003): Rehabilitation of Landmine Victims – the Ultimate Challenge, Bulletin of the World Health Organization, 81(9) ,pp. 665-670.

[3] Frossard L, Stevenson N, Smeathers J, Häggström E, HagbergK, Sullivan J, Ewins D, Gow DL, Gray S, Brånemark R. (2008): Monitoring of the load regime applied on the Osseo integratedfixation of a trans-femoral amputee: A tool for evidence- based practice. ProsthetOrthot Int.,32(1),pp. 68–78.

[4] Daniel Jimeneze l and Ivan Polizzi .(1998): Prosthetic Foot Design, Mech. Eng.Dept. Victoria University Press . [5] Zatsiorsky, V. M.(2002): Kinetics of Human Motion. Human Kinetics .