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_me
chanics/beams/casestudy_display.cfm?ca
se=cantilever_endload
X = 1 in. = 0.0254 m
L = 0.0254 m
b = 1/16 in. = 0.00159 m
h = 3/32 in = 0.00238 m
E = 1.5 GPa (for PP)
Calculations for Yield Stress
Set deflection to be a maximum of 1/16 in.
I = bh3/12
The force for this deflection is .0198 N.
M = PL
Sigma = 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.
http://www.coursework.info/i/57835.html
Injection Mold Part