Prosthesis device (flexed toe part)

University of Puerto Rico
Mayagüez Campus
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INME 4011 Machine Component Design 1, 2007-I
Prosthesis Device (Flexed Toe Part)
Jorge Corujo Sandín
Francisco Torres
Irvin de la Paz
Javier Cruz
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Department of Mechanical Engineering
University of Puerto Rico at Mayagüez
May 7, 2007

Objective

The project outline is to design and analyses loads and stressconcentrations for the flexed toe part of the prosthesis of Tony Volpentest. At the same time thinking in properties of materials, design and safety.

Description

The project consists of an existing design involving a prosthetic device already in use by runners like Tony Volpentest. The goal of our team is to rethink and if possible improve upon the current design. If no substantial new design can befound we will concentrate our project on the existing design and how the combine loads affect it as well as what material it should be in order to fulfill its engineering and economical demands and specifications. The entire project (the whole prosthesis) consist of various part but only one will be considered for the full in depth design. As expressed before we will concentrate on the flexed toepart.  The focus of our design would be based on the standards already establish to created a device that will be use under the diverse loads. Because we are designing prosthesis for use in sport, it will be subjected to heavy a quick changing loads, thus we need to choose a material which would be durable and can resist fatigue.   The other important detail when choosing a material for designingsport prosthesis is the weigh, this needs to be strong and flexible but as light as possible.
     As mention, the flexed toe will be subjected to combine loads. Some of these, which we are expecting to find during our analysis (but not limited to only these), will be; Bending, sheer and normal compressive in the region where the socket meets the flexed toe.  Also there should be sheer and normalcompressive forces at the bottom of the toe (where the feet's toes should be).  This would be cause

by the individual's weight and friction with the floor.  We are currently not expecting any mayor torsion force, since our
Preliminary analysis shows that for torsion to act it would require for part of the flexed toe to somehow jam (get stuck) and for the individual to fall to his/her side.Design Details
The design process first consisted in generating enough information, so we could have a solid base of data to select the appropriate material. Several consideration were taken into count, in our design the important aspects were weight and the ability of the material to be flexible but still be strong enough to resisted the alternating loads. The relationship of density withrespect to tensile stress was the major criteria. Using this has a departure point we were able to come up with and equation to minimize mass by reducing this relation.

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Where F is the maximum forces apply at the beam and L is the length. This two are assumed constant for the purpose of this analysis. The value of the force was 600 lb. and L was chosen to be 19 in. In thecase of the other two variables a different approach was taken, first it consists of presuming a minimum value of tensile stress which was 29.00 psi. With the use of a graph of strength-density, a range of materials were selected.
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At the end we finish with four materials for which we after choose the best that will fit our necessities. The four materials are a selecting of athermoplastic, titanium alloy, nickel alloy and a SRCR 6100. A thermoplastic is a kind of material that is able to be deforming plastically, it becomes more brittle at lower temperatures, but it has a great strength against fatigue. A titanium alloy “Deutche Titan Tikrutan RT 18 Pd Low-Alloyed Titanium”, titanium is a material that has a high YS value, but it has a higher density value than other material...