Travel Hair Comb

Janet Ryu

12.12.05

3.064

Product Design Goals

Some give in the material.

Sufficient stiffness and toughness.

Can withstand some heat.

Does not absorb water.

Cheap and easy to produce in bulk.

Choose polypropylene (33 MPa).

Usability Goals

Small size for discrete portability.

Rounded, large teeth so it does not damage the hair.

Smooth finish.

Stress Analysis

Use cantilever beam theory. Calculate force on a tooth of

the comb with:http://www.efunda.com/formulae/solid_mechanics/beams/casestudy_display.cfm?case=cantilever_endload

X = 1 in. = 0.0254 mL = 0.0254 mb = 1/16 in. = 0.00159 mh = 3/32 in = 0.00238 mE = 1.5 GPa (for PP)

Calculations for Yield Stress

Set deflection to be a maximum of 1/16 in.I = bh3/12The force for this deflection is .0198 N.M = PLSigma = Mc/I, where c is distance from

neutral axis to extreme fibers. (c=y/2).33 MPa (well under the yield stress)Hair can withstand .8 N before breaking.

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Injection Mold Part