Prosthetic limbs must be able to sustain large magnitudes of stress, therefore the materials selected for their construction is extremely important. Most are now made of an nonliving solid because they are subject to deformation, and thus, must demonstrate elastic qualities. |
Flex-Foot, inc. |

Physical Concepts for Prosthetic Limb Design.

*Young's
Modulus:

Y,
measures the tension or compression of the object. This modulus is
used in deciphering

the material(s) to use for the prosthetic device.

Y= __tensile stress__
= F/A
__ __
tensile strain
= L/Lo

Common Materials | Characteristics |

Aluminum | Sturdy, durable, non bulky, withstands drastic temperature changes, and can support heavy weights. |

Fiberglass | Easily
manipulated, natural looking, is
compressible, can withstand moderate to heavy weights. |

Wood | Not frequently used, inexpensive, bulky, natural looking, can withstand heavy weights, but must be replaced often. |

*
Shear Modulus:

Measures the elasticity of Shape. This modulus
is used in designing the

appropriately shaped limb for a particular person.

S= __shear stress.__ = __F/A__

shear strain. X/h

These moduli can determine and predict the necessary size and shape of
a prosthetic limb based on the weight and activity level of the amputee.
This can be done by finding a particular material that can withhold the
person's weight(mg) and will respond with compressions and elasticity to
the movement of the person.

Problems encountered in the
field.

*when deciding what
material to use for a person of particular weight, or activity level, the
person's height, weight, and size(dimensions), must be known.

* Height
= 66inches=1.68m

*length of
desired limb= 19inches=.48m

* desired
cross sectional area=( 7E-3m)

(the
area of the limb they wish to match)

*Maximum
weight to carry = 350lbs ,1550N

(weight of the person, and weight they can hold)

*Using
Aluminum first, the distance compressed will be measured.

Using Young's modulus: Y=FLo/A(delta)L

delta L= FLo/YA

=__(1550N)(.48m)__

(7E10) (7E-3m)

= 1.5E-6m

*We thus find that aluminum is a suitable source for the limb*