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Shock Cords
Last updated 07/09/2008
Small "Twisted Strands" Kevlar
Small Braided Tubular Kevlar
| Test Series # |
Type |
Source |
Description |
Peak Load (lbs) |
Other Picture |
| Knotted 1 |
TKM |
Pratt Hobbies |
Overhand knots on each end |
261.473 |
|
| Knotted 2 |
TKM |
Pratt Hobbies |
Overhand knots on each end |
180.290 |
|
| Knotted 3 |
TKM |
Pratt Hobbies |
Overhand knots on each end |
271.299 |
|
| Knotted 4 |
TKM |
Pratt Hobbies |
Overhand knots on each end |
228.208 |
|
| RDeH8 Method |
TKM |
Pratt Hobbies |
2" / 3" inserted |
517.782 |
After Test |
In addition to showing the strength of this cord, this test shows the the RDeH8 method of securing Kevlar works well and shows that tying a knot to secure shock cords is a bad idea. (More RDeH8 coming) |
* In all of the cases, The knot pulled tighter so elongation
data is irrelevant. The failure of the knots was the result of the knot
squeezing the cord while under tension.
11mm Flat Kevlar Ribbon
These samples were very tough to test. The coating made them slip in the fixtures. Samples #11 and #12 were the only two samples to actually break. Since there was not at least 3 samples with acceptable testing criteria, I have to consider this an invalid test. It does show what the material may be capable of.
| Test Series # |
Type |
Average Thickness (in.) |
Average Width (in.) |
Average Area in^2 |
Stress At Offset Yield (psi) |
Peak Stress (psi) |
Peak Load (lbs) |
| 1 |
FKR |
0.03250 |
0.39800 |
0.01293 |
18716.922 |
33606.45965 |
434.70093 |
| 2 |
FKR |
0.03250 |
0.39800 |
0.01293 |
36609.538 |
48645.62115 |
629.23309 |
| 3 |
FKR |
0.03250 |
0.39800 |
0.01293 |
18799.587 |
29373.85481 |
379.95201 |
| 4 |
FKR |
0.03250 |
0.39800 |
0.01293 |
**** |
15117.91351 |
195.55083 |
| 5 |
FKR |
0.03250 |
0.39800 |
0.01293 |
14370.764 |
26457.28646 |
342.22608 |
| 6 |
FKR |
0.03250 |
0.39800 |
0.01293 |
8375.233 |
24664.76714 |
319.03977 |
| 7 |
FKR |
0.03250 |
0.39800 |
0.01293 |
14505.408 |
16331.65382 |
126.89735 |
| 8 |
FKR |
0.03250 |
0.39800 |
0.01293 |
18395.941 |
35626.52237 |
276.81895 |
| 9 |
FKR |
0.03250 |
0.39800 |
0.01293 |
27828.334 |
35489.96321 |
275.75788 |
| 10 |
FKR |
0.03250 |
0.39800 |
0.01293 |
36189.031 |
54966.06103 |
427.08764 |
| 11 |
FKR |
0.03250 |
0.39800 |
0.01293 |
80961.471 |
97586.86933 |
758.25236 |
| 12 |
FKR |
0.03250 |
0.39800 |
0.01293 |
105355.067 |
112086.27996 |
870.91314 |
This test is of the 11mm Flat Kevlar Ribbon from John Cox at rinconrocketry.com. Also available on the Rocketry Planet Auctions. Samples provided by Jim Urrata. |
Ken's Cords tested with a 6" gauge length
| Test Series # |
Type |
Width" |
Description or Source |
Peak Load (lbs) |
Elongation in 6" |
| SC-1 |
T-Ny |
0.590 |
Aardvark Rockets |
479.164 |
1.106 |
| SC-1 |
T-Ny |
0.590 |
" |
717.726 |
0.961 |
| SC-1 |
T-Ny |
0.590 |
" |
772.883 |
1.142 |
| Mean |
0 |
0.590 |
" |
656.591 |
|
| Std Dev |
0 |
0 |
0 |
156.111 |
|
| Test Series # |
Type |
Width" |
Description
or Source |
Peak Load (lbs) |
Elongation in 6" |
| SC-2 |
T-Ny |
0.230 |
Sporting Goods Store |
96.184 |
2.324 |
| SC-2 |
T-Ny |
0.230 |
" |
97.224 |
2.759 |
| SC-2 |
T-Ny |
0.230 |
" |
92.058 |
1.699 |
| Mean |
0 |
0.230 |
" |
95.155 |
|
| Std Dev |
0 |
0 |
0 |
2.732 |
|
| Test Series # |
Type |
Width" |
Description
or Source |
Peak Load (lbs) |
Elongation in 6" |
| SC-3 |
T-Ny |
1.02 |
All Hobbies |
1217.586 |
1.312 |
| SC-3 |
T-Ny |
1.02 |
" |
1331.671 |
1.196 |
| SC-3 |
T-Ny |
1.02 |
" |
1337.548 |
1.145 |
| Mean |
0 |
1.02 |
" |
1295.601 |
|
| Std Dev |
0 |
0 |
0 |
67.627 |
|
| Test Series # |
Type |
Width" |
Description
or Source |
Peak Load (lbs) |
Elongation in 6" |
| SC-4 |
T-Ny |
0.250 |
Sporting Goods Store |
175.645 |
1.683* |
| SC-4 |
T-Ny |
0.250 |
See "*" Below |
* |
4.853* |
| SC-4 |
T-Ny |
0.250 |
See "*" Below |
* |
1.969* |
| Mean |
0 |
0.250 |
0 |
* |
* |
| Std Dev |
0 |
0 |
0 |
* |
* |
| Test Series # |
Type |
Width" |
Description or Source |
Peak Load (lbs) |
Elongation in 6" |
| SC-5 |
T-Ny |
0.240 |
Sporting Goods Store |
126.184 |
1.529 |
| SC-5 |
T-Ny |
0.240 |
" |
133.592 |
1.234 |
| SC-5 |
T-Ny |
0.240 |
" |
129.613 |
1.207 |
| Mean |
0 |
0.240 |
" |
129.796 |
1.198 |
| Std Dev |
0 |
0 |
0 |
3.707 |
0.041 |
| Test Series # |
Type |
Width" |
Description
or Source |
Peak Load (lbs) |
Elongation in 6" |
| SC-6 |
T-Ny |
0.337 |
Sporting Goods Store |
280.740 |
1.824 |
| SC-6 |
T-Ny |
0.337 |
" |
293.882 |
1.618 |
| SC-6 |
T-Ny |
0.337 |
" |
298.209 |
1.683 |
| Mean |
0 |
0.337 |
" |
290.944 |
1.709 |
| Std Dev |
0 |
0 |
0 |
9.098 |
0.105 |
| Test Series # |
Type |
Width" |
Description
or Source |
Peak Load (lbs) |
Elongation in 6" |
| SC-7 |
T-Ny |
0.474 |
Sporting Goods Store |
406.955 |
1.647 |
| SC-7 |
T-Ny |
0.474 |
" |
447.798 |
2.172 |
| SC-7 |
T-Ny |
0.474 |
" |
433.832 |
1.818 |
| Mean |
0 |
0.474 |
0 |
429.529 |
1.879 |
| Std Dev |
0 |
0 |
0 |
20.759 |
0.268 |
| Test Series # |
Type |
Width" |
Description
or Source |
Peak Load |
Elongation in 6" |
| SC-8 |
Underwear |
0.978 |
Could not be tested** |
* |
* |
* The SC-4 test pieces gave me grief. It has a core material
that broke at a different point than the outer material. As a result, the
data from two of the tests "did not compute". Look at the graph
from the second SC-4 test.
** The bungee type cords could not be tested. The amount of travel to break
the cord was more than my actuator travels, Even with the upper and lower
fixtures starting out touching.
Rick's 9/16 Tubular nylon*
| Test Series # |
Type |
Width" |
Description or
Source |
Peak Load (lbs) |
Elongation at break (in) |
| SC-9 |
T-Ny |
0.587 |
Unknown |
1308.430 |
4.274 |
| SC-9 |
T-Ny |
0.587 |
" |
1321.005 |
2.964 |
| SC-9 |
T-Ny |
0.587 |
" |
1388.228 |
2.856 |
| SC-9 |
T-Ny |
0.587 |
" |
1412.359 |
3.009 |
| SC-9 |
T-Ny |
0.587 |
" |
1391.675 |
3.109 |
| SC-9 |
T-Ny |
0.587 |
" |
1377.904 |
3.116 |
| Mean |
0 |
0 |
" |
1366.599 |
3.221 |
| Std Dev |
0 |
0 |
" |
41.907 |
0.525 |
* 2 foot lengths tested with cam type fixture
John's Kevlar*
| Test Series # |
Type |
Width" |
Description or
Source |
Peak Load (lbs) |
Elongation at break (in) |
| SC-10 |
Tube
Kevlar |
0.576 |
Unknown |
3666.899 |
1.632 |
| SC-10 |
Tube Kevlar |
0.576 |
" |
3401.456 |
1.519 |
| SC-10 |
Tube Kevlar |
0.576 |
" |
3563.127 |
2.004 |
| SC-10 |
Tube Kevlar |
0.576 |
" |
3653.450 |
2.048 |
| Mean |
0 |
0.576 |
0 |
3571.233 |
1.801 |
| Std Dev |
0 |
0 |
0 |
122.204 |
0.265 |
* 2 foot lengths tested with cam type fixture
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