From bottom of page 13 of Hexcel Application Note
Total Energy of motion must
be totally absorbed by the honeycomb material.
½ mV2 =
fcr Acr s
and
“G” load = V2 /
2gs which can be derived from the
mks version for constant
acceleration
v2
= v2 init + 2ax
where G=a/g in English units, and v2 is the final velocity squared ( = 0 ), where a = acceleration, and where x =
distance
From page 15 of Hexcel Application Note
(Note that the weight is now
3000 lbs, and the max G-force is now 20)
Situation:
A 3000 pound object is
traveling at
30 mile per hour and must be
stopped.
W=3000, g=32.2
Problem: The object must not
be subjected
to more than 20 G’s.
Calculations:
V= 30 mph x 1.467 = 44.0 fps
G= V2 / 2gs where
s= feet : where G=20 is the maximum G force
s(reqd) =(44x44) /
2(32.2)(20) = 1.5 ft = 18 inches
absorbing depth required
s=70% Tc -
the honeycomb cannot be compressed to zero inches.
I add extra honeycomb to final design, so here I assume
s = 18 inches
________________________________________________________
Using ACG- ¼ - 4.8 which has crush strength of 245 psi
(I will not increase its
strength for dynamic force situation.
Increasing the strength would
help me.)
fcr static = 245
psi
Total Energy of motion must
be totally absorbed by the honeycomb material.
WV2 /2g = fcr
Acr s where s = 1.5 ft.
0.5(3000)(44x44)/32.2 = 245 (Acr)1.5
Acr = 245.4
square inches of honeycomb that is 1.5 ft. deep will completely stop the 3000 lb object.
Assume that the actual
honeycomb depth is 2.0 feet to accommodate the hardware geometry.
A block of honeycomb that is 4
feet wide and 4.26 inches high
will yield the required 245.4
square inch cross section.
If it is 2.0 feet deep, it
will have a volume of 3.4 ft sq. and will weigh
(3.4 ft sq) x (4.8 lbs/ft sq) = 16.35 lbs
This quantity of material
costs less than $400 retail.
The steel boxes to enclose
the material, and the shafts and bumpers will weigh approx. ? lbs and cost ?
If the bumpers are hit at an
oblique angle, they are unlikely to be pushed into the box.
It will be necessary to design a bumper shaft that will deform with enough force through a distance that the G forces will be kept low.