Real Strength of Nylon Straps

[cruiser97eric]

I have a 2 inch wide self-recovery Nylon strap for my truck. The label claims it is a 20000 lb strap, which I assume is the breaking strength.

I took some measurements and found it to be 1.92 inch wide by 0.155 inch thick. The cross section therefore is 1.92 inch * 0.155 inch = 0.298 square inches. If it really has a breaking strengh of 20000 lb, the material it's made of would need to have an ultimate tensile strength of 20000 lb / 0.298 square inch = 67Ksi. So basically it has to be as strong as low carbon steel.

After doing some research on plastics I found Nylon 6/6 has an ultimate tensile strength of only 12Ksi. Even the glass reinforced grades don't come anywhere close to 67Ksi tensile strength. WTF?????

At 12ksi tensile strength, my strap should be breaking with just 12ksi * 0.298 square inch = 3500 lb!!!

So is there some major fraud going on with the way these self-recovery Nylon straps are specified, or are they made of some super magical grade of Nylon I have never heard of?

[GatorTaco]

Yea, I've seen so many of those stupid straps bust I can't even remember. I ended up getting ahold of a strap that was formerly used for something regarding jets, but it is about 3x as thick as normal straps, and about 4" wide. So far so good...

[hunter4runner]

I've broken 4 straps and now on 5 and its a harbor freight one and it works the best

[sasaholic]

im using a sling that for hanging shit from helicopters. been using it for 2 years without any problems.

[TacoDell]

http://en.wikipedia.org/wiki/Elastic_deformation

http://en.wikipedia.org/wiki/Tensile_strength

http://en.wikipedia.org/wiki/Flexural_strength

http://en.wikipedia.org/wiki/Yield_%28engineering%29

I'm not intellectual enough to spend time discussing things that don't matter much.

I have several straps... if one breaks... I use another ;)

[hytenor]

never broken a 2" 20k# strap...worn out two but never broken one.

[Avsfreak1234]

never broken a 2" 20k# strap...worn out two but never broken one.

X2

you also have to take into account the modulus of elasticity of the nylon. that increases the force required to break a material. I could send you a technical report on elasticity of cast vs. milled aluminum if you want to see how much it actually increases to allow a little give (if I can find it?). cant remember which had a higher modulus but it required much greater force to break in pure tension.

[trifenix]

i snapped a 2x20k last month....then again i was trying to straighten out my bumper from a tree :D

[cruiser97eric]

I haven't broken any straps yet, but I saw a 3" wide one break right in front of me while taking a video.

http://good-times.webshots.com/video/3038768900102424377ehTmCQ

[sasaholic]

and that right there is why you should never be standing anywhere close to a recovery when u dont HAVE to be. also never try to pull someone out in reverse when u dont have to

[cruiser97eric]

X2

you also have to take into account the modulus of elasticity of the nylon. that increases the force required to break a material.

No. The ultimate tensile strength (UTS) is by definition the maximum resistance to fracture. It is equivalent to the maximum load that can be carried by one square inch of cross-sectional area when the load is applied as simple tension. It's only 12Ksi for Nylon 6/6.

The modulus of elasticity gives you an idea of how much elastic deformation to expect in the material when you apply a load to it. It has nothing to do with breaking point in tension.

[terryj5]

Interesting thread on EP
http://expeditionportal.com/forum/showthread.php?t=22367
Check out the vid.

[Gerdo]

For those of you that use things like construction slings and silly big straps... Bigger is not better. If you are doing static pulls, then big is fine. but if you are doing any yanking, big isn't going to give and will do damage.

If you are going to yank then get a strap or rope made for that and the proper size.

[HIRunna]

For those of you that use things like construction slings and silly big straps... Bigger is not better. If you are doing static pulls, then big is fine. but if you are doing any yanking, big isn't going to give and will do damage.

If you are going to yank then get a strap or rope made for that and the proper size.

Juts curious what you mean damage? To the vehicle?


And back to OP, I would think the way they weave the material gives a lot more strengh. Do you calculations take that into account?

[cruiser97eric]

And back to OP, I would think the way they weave the material gives a lot more strengh.

What makes you think that? What I have heard is that fibers loose strength due to the bending of the fibers caused by the weaving pattern and due to the abrasion caused by the weaving process. Sure, some weaving types are stronger than others, but I don't have reason to believe any kind of weaving makes fibers stronger than unwoven ones.

[HIRunna]

What makes you think that? What I have heard is that fibers loose strength due to the bending of the fibers caused by the weaving pattern and due to the abrasion caused by the weaving process. Sure, some weaving types are stronger than others, but I don't have reason to believe any kind of weaving makes fibers stronger than unwoven ones.

So you're telling me rope is not wrapped like the way it is for no reason? Did you not watch the episode of mythbusters where tory climbed down the building with essentially wrapped up toilet paper?

[Gerdo]

Juts curious what you mean damage? To the vehicle?


If you yank on a strap, chain or cable that will not give or stretch, all of the energy that is produced will transfer into the vehicle being yanked. This energy can yank the vehicle and damage it.

[cruiser97eric]

So you're telling me rope is not wrapped like the way it is for no reason? Did you not watch the episode of mythbusters where tory climbed down the building with essentially wrapped up toilet paper?
IMO, the fibers in a strap need to be weaved to just make it practical to use the thing, not because of the fibers somehow being stronger that way.

As for mythbusters, I like those guys, but half the time they don't know what the heck they are doing. Thanks god they have Kari and Jessy around to save the day and keep them alive. In any case, wrapped toilet paper isn't the same as weaved toilet paper, and toilet paper isn't made of Nylon.

[Wgasa84]

I have a 2 inch wide self-recovery Nylon strap for my truck. The label claims it is a 20000 lb strap, which I assume is the breaking strength.

I took some measurements and found it to be 1.92 inch wide by 0.155 inch thick. The cross section therefore is 1.92 inch * 0.155 inch = 0.298 square inches. If it really has a breaking strengh of 20000 lb, the material it's made of would need to have an ultimate tensile strength of 20000 lb / 0.298 square inch = 67Ksi. So basically it has to be as strong as low carbon steel.

After doing some research on plastics I found Nylon 6/6 has an ultimate tensile strength of only 12Ksi. Even the glass reinforced grades don't come anywhere close to 67Ksi tensile strength. WTF?????

At 12ksi tensile strength, my strap should be breaking with just 12ksi * 0.298 square inch = 3500 lb!!!

So is there some major fraud going on with the way these self-recovery Nylon straps are specified, or are they made of some super magical grade of Nylon I have never heard of?

The only time I've broken a 2" 20K strap was when a buddy and myself were tandem towing a basically dead rig (no front drive, no locker/lsd in the rear and two tires almost off the rims on the drivers side, and an overheating transmission). The dead rig got wedged on some rocks and with both of our rigs in 200:1+ we snapped the strap between the dead rig and the middle rig.

I have a 2" strap that's been attached to the back of my rig for probably over 6 years. It's torn and tattered, never washed, and left out in the sun all the time. I've pulled on that strap more than any other recovery strap/point. Will it break?

You're over thinking a recovery strap!

[TacomaJD]

If you yank on a strap, chain or cable that will not give or stretch, all of the energy that is produced will transfer into the vehicle being yanked. This energy can yank the vehicle and damage it.

That's why you always pull from a secure, firm point on both vehicles. I don't see any more damage being done regardless of what strap, rope, or even chain being used if its securely hooked to a receiver hitch, D-rings reinforced to the frame or even oem tow hook mounts. You can do damage to anything hooking a strap up in the wrong place.

[camogonewild]

tug boat rope is excelltent for snatchin run the rope till it dont stretch any more an hit the brakes an let it spring back to u but any rope of an caliber of strenth is great id rather have a rope then a strap imo just more compact

[TacomaJD]

I once recovered a Matchbox truck from a puddle with dental floss because of its elasticity.....

[Wgasa84]

That's why you always pull from a secure, firm point on both vehicles. I don't see any more damage being done regardless of what strap, rope, or even chain being used if its securely hooked to a receiver hitch, D-rings reinforced to the frame or even oem tow hook mounts. You can do damage to anything hooking a strap up in the wrong place.
A yanking strap takes the initial shock from the yank. If I was pulling someone by getting much speed I would think twice about using a tow strap. You'll cause problems down the road to either the rig or the strap... probably both.

Yanking straps stretch to a certain amount and then use the stored energy to pull the vehicle from being stuck (great in mud/snow/sand).

[WallyP226]

Nylon stretches, polyseter and steel do not, thats why they are not used for making a snatch strap where dynamic forces are the norm.


http://www.youtube.com/watch?v=FkHng7n6BBU

http://www.youtube.com/watch?v=f5BJpYqfjRo

Wally

[camogonewild]

if u cant use a rope or snatch strap u sir are a ratard an who ever says u cant use a resse hitch is retarded just dont use the pull point on the front of toyotas they suck ass an break same as chevy

[TacomaJD]

Leave it stuck, burn it, collect insurance.... Win/win.

[Gerdo]

That's why you always pull from a secure, firm point on both vehicles. I don't see any more damage being done regardless of what strap, rope, or even chain being used if its securely hooked to a receiver hitch, D-rings reinforced to the frame or even oem tow hook mounts. You can do damage to anything hooking a strap up in the wrong place.

If I see you stuck on the trail, lets use my snatch strap or kinetic rope to get you out.

[TacomaJD]

If I see you stuck on the trail, lets use my snatch strap or kinetic rope to get you out.

If you see me stuck on the trail, you'll be a long way from home ;)