Page 99 - Plastics Engineering

82 Mechanical Behaviour of Plastics

area, I, will quantify the stiffening effect of the cross-section and if this is
related to the I value for the flat sheet of the same length and thickness then it
is possible to define a stiffness enhancement factor, q, as

2 2
q=- { mh+- (7- 4> +ph+ (7- (nh+ :))
L
+- sin a + - q)lJ (2.25)
24n
2nh
(7-
h
sin
a
where 7 = distance to centre of area from the base of the cross-section, i.e.
+
0.5m + pn + 0.5~ -
y=h
p+m+-
tana
and
b B D
m=- p=- n=-
h ' h ' h
Clearly there are many permutations of D, b, h, a, etc and Fig. 2.31 shows
how the stiffness enhancement factor, q, changes with various values of these
parameters. In each case the angle a has been fixed at 85" and the corrugation
dimensions have been expressed as a function of the wall thickness, h.

Fig. 2.31 Stiffness of cormgations as function of dimensions