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Tiedown Straps Stiffness 1
- Thread starter ZKLCM
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MIL-W-4088 gives properties of one type of strap material used for cargo tie-downs. Might be worth giving it a read.
Getting stiffness information for textiles is nearly impossible. Even for 'engineered' fabrics the main concerns are weight, tensile strength, sometimes tear strength, and for fusible materials, peel strength.
You may try to contact strap manufacturers or be forced to perform the testing yourself.
It is an odd situation, but I suspect it has to do with the strong interaction between the raw fiber properties and the complex assembly process that goes into making fabric. Some fabrics have almost no shear resistance; others are very shear resistant.
You may try to contact strap manufacturers or be forced to perform the testing yourself.
It is an odd situation, but I suspect it has to do with the strong interaction between the raw fiber properties and the complex assembly process that goes into making fabric. Some fabrics have almost no shear resistance; others are very shear resistant.
The stretch can be significant.
Consider the barrier net that would restrain cargo in an aircraft, and picture thousands of pounds of cargo being held back at 9g's. The nets stretch a lot. Now ask yourself if the next obstacle installed in front of the net, which could be a bulkhead, or a seat, or a cabinet, installed far enough ahead of the net, that the cargo won't come in contact. If it does, how much load is added to the obstacle?
When faced with the issue, I decided to test the net. Actually, I tested a single strap, and used the stretch to calculate the deformation of the net. Plus a margin.
STF
Consider the barrier net that would restrain cargo in an aircraft, and picture thousands of pounds of cargo being held back at 9g's. The nets stretch a lot. Now ask yourself if the next obstacle installed in front of the net, which could be a bulkhead, or a seat, or a cabinet, installed far enough ahead of the net, that the cargo won't come in contact. If it does, how much load is added to the obstacle?
When faced with the issue, I decided to test the net. Actually, I tested a single strap, and used the stretch to calculate the deformation of the net. Plus a margin.
STF
Compositepro
Chemical
I would thick the logic is the same as for bolt tensioning. The straps have to be pretensioned to more than the max expected load so that the load will not move at all. This assumes a rigid floor to which to attach. If the loads are only supported by straps then the load will basically be supported be springs.
SAITAETGrad
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Parachute design information- FAA Parachaute Riggers Handbook, Knacke, Poynter, MIL guidance, OEM information, studies, etc. The information is out there.
That said, expect to validate by test.
That said, expect to validate by test.
One current cargo unit load device spec used in the US is NAS 3610. I don't have a copy, so I can't say if it has the exact information the OP needs.
Also found this FAA AC 120-85 that gives some useful information. It references AS 5385 and ARP 5596.
Also found this FAA AC 120-85 that gives some useful information. It references AS 5385 and ARP 5596.
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