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Prosthesis Device for paraplegic people Jorge J. Corujo Javier Cruz Irvin De La Paz Francisco Torres

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Design and usage: Prosthesis Device for paraplegic people to use for running Unlike normal prosthesis, which allow for its user to accomplish normal basic movement, this one allows the user to participate in sporting events, such as running. A similar device was use by paralympic’s athlete Tony Volpentest

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Design and usage:

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A little bit of History: 1981- The Seattle foot revolutionizes sport prosthetics with the introduction of key elements: New stronger and light materials (Derlin, carbon fibers) energy storing prosthetic foot (ESPF)

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Why choose this design? This design provided us with the opportunity to design and analyze an atypical product, which although simple in design it encompasses many engineering aspects, and proved to be a challenge Our concentration will be the lower component; the flexed toe.

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Important engineering considerations: Design Process: Determine target runner: Max. weight of runner –> F=200 lbs. Person with transtibial amputation (above the foot but below the knee) Determine acting forces (static & dynamic) Dynamic model Alternates from: F to -3F

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Important engineering considerations: Direction of runner Applied force by runner Friction force Ground reaction Attachment to socket and runner Critical point for Bending

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Important engineering considerations:

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Bending Find critical point Determine actual maximum (absolute) magnitude during the cycle. This is the first parameter for choosing the material.

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Important engineering considerations: Stress due to bending in a curved beam M = The internal moment, determined from the method of sections and the equations of equilibrium and computed about the neutral axis for the cross section. A = the cross-sectional area of the member R= the distance measured from the center of curvature to the neutral axis r (bar) = the distance measured from the center of curvature to the centroid of the cross-sectional area r = the distance measured from the center of curvature to the point where the stress is to be determined

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Important engineering considerations: For a rectangular cross-sectional area:

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Important engineering considerations: Fatigue For the desired part we want an infinite life. Determine all stress concentrators K size, K temp =1, K load, K reliability (99.99%), K surf This is the second parameter for choosing the material.

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Important engineering considerations: Material selection We need a material that is: Strong and Light Utilize both previously determined parameters: Max. Bending and Desired Fatigue Endurance With each candidate the resulting deflection has to be considered. Some deflection (spring action) is desired for absorbing impact and giving extra boost.

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Important engineering considerations: Deflection for curved beams:

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Important engineering considerations: Static analysis: V=-5.28lb Normal=-813.54 lb

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Chosen material: Deutsche Titan® Tikrutan RT 18 Pd Low-Alloyed Titanium For the Purpose of this design, cost was not considered. Price can be improved with available polymers, but all the needed information for a proper analysis wasn’t reliably available. Provides a lightweight design 1.28 lbs. per spring toe for the weight of the whole design add weight of socket Safety factor of n=2.04 (Goodman)

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Design challenges and weaknesses Our main challenges appeared at the moment of material selection. Finding (information for) a lightweight material with the required strength really limited our options. The main weak spot is at the center of curvature. However, as long as design parameters are followed the user is within acceptable safety limits (n=2.04)

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What did we learn? Simple design ≠ simple calculations Differences in analyzing curved and linear beams. Moments Deflection Small, apparently insignificant, material property changes can amount to huge problems (and consequences) in the design as a total. Material sciences have become part of the forefront in engineering design.

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Questions? Thanks for your attention and your time

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