
Selection criteria 411
F _3Eb
4
112 _Eb*
y~
L
3
~4Ϊ?
The mass m of the cantilever is b
2
Lp, where p is the density. Hence
(Fly)
112
_ i ^
m ~2L
5llX
~y
Thus the mass is minimized and the stiffness maximized when E
lll
jp is
maximized. This then becomes the parameter.
In determining a parameter the technique used is
1 Write down an equation for the attribute sought.
2 Eliminate, using other property equations, any terms in that equation that is
not either a property or a fixed quantity.
3 The parameter that is required is then the resulting combination of
properties.
Table 20.1 shows some of the parameters used in a number of different
situations.
20. ...