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Physics of Prosthetics

present May 7
by

Morgan LePoire

on 7 May 2013

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Transcript of Physics of Prosthetics

Spring-like motion: How a prosthetic leg functions like a spring Creation Process: trial and error Spring-like action Stress Forces of Stress: Compression
Tension
Shear Friction Problems: How socket irritation is reduced Advancements the physics behind the prosthetic leg Prosthesis Revealed: Friction Advancements ELASTIC MODULUS: a substance's tendency to be deformed elastically, but non-permanently when a force is applied to it. It is the slope of a stress–strain graph in the elastic deformation region. Also, a stiffer material will have a higher elastic modulus. Things to Consider in a prosthetic: lightweight
tension
compression
flexibility
stiffness
durability
stress resistance
cost effectiveness
application Materials used in production: Materials used for creating a prosthetic vary according to each leg; however most are made from fiberglass due to cost-effectiveness. Other commonly used materials include Kevlar and carbon (graphite). fiberglass is often used because it is created similarly to the way bone is composed in order to maintain a similar gait for the amputee. Fiberglass is essentially fine pieces of glass embedded in a plastic resin and bone is essentially calcium phosphate embedded in collagen fibers. When we look at a prosthetic as a whole, it proves to act like a spring. Due to this, when someone looks for material to use, he must think of the spring constant "k." One must realizes that The spring constant is important due to the
amount of energy the leg can produce for the
amputee. Because fiberglass has a high spring
constant,it as higher potential energy. The
elasticity of the material used in the new leg is imperative for the most successful and comfortable use. The weight of the material must also be considered due to stress and strain. This is important because elastic energy is lost due to the release of energy as heat when it is bent and recoils--like running. The Spring Modulus is similar to a spring constant due to the When a structure is compressed or stretched beyond its elastic modulus, it can have permanent effects. This graph shows stress versus strain (change in length versus force). The elastic region is the area where the material will maintain its former shape. Any more force and change in length will lead to permanent damage. fact that . However the Spring Modulus is different because Young's Modulus is only used for compression or tension, while a shear modulus is used for shear stress. Friction is caused by rubbing of the residual stump and the sock that slips around it. When moving, the sock can slip like the back of a heel slips in a shoe, which causes pain and irritation due to friction. The force of friction is determined through . Because of this, most prosthetic limbs are attached through suction. Suction is created when the pressure inside the area between the stump and the prosthetic must be less than the atmospheric pressure surrounding the limb. Friction is also reduced by a light weight mass to provide a high center of gravity which eases acceleration. The foot is also shorter to control acceleration and ultimately reduces friction. Irritation can be reduced through lowering the coefficient of friction. One can find the coefficient of friction by using this equation: . Slippery surfaces have lower coefficients whereas rough surfaces have higher coefficients. Because of this fact it becomes clear why in history prosthesis have been extremely painful due to being made from wood, and why today they are attached with a gel-like sleeve for comfort. Prostheses in the world today: There has been extreme advancements in the
world of prosthesis. The history of prosthesis comes from the Egyptians from 2750-2625 B.C. Prosthesis originated from a wooden peg like a pirate peg leg. Today a man with two prosthetic legs is able to compete in the Olympics. The technology involved in creating an artificial limb includes using internal computers to read a person's gait and duplicate the motion. Details such as freckles, hair, and skin tone can be added to the false limb. The prosthesis begins to read muscle movements of residual muscles and mimic the desired motion through electrodes. These advancements prove that we have come a long way, but where could we go from here? The need now comes in the form of affordability and availability. Third world countries are in desperate need of artificial limbs and one way to account for this is recycling old models when we upgrade to a new and better prosthesis. This could be possible if the newer models were made more cost-effective for the mainstream population. This would be possible if a new easier and faster process for making the limb was possible, which causes a need for more research. from humans to animals, but what about our present problems? These equations are used for determining stress and strain, which will ultimately provide the elastic modulus through the slope when graphed. This is useful for determining the proper material for a prosthetic limb.
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