Sorry if this subject is posted in the wrong part of the forum, but I could find anywhere else to post it. I was reading on another forum about somebody who was discussing seat belt defects and the members seemed to be argumentative rather than helpful to the person who asked for professional feedback. The poster asked about seat belt webbing in a damaged condition and wanted to know how to define the standard significantly weakened. I searched the internet and found seat belt manufactuers who show how seat belts are put together and tested, but nobody shows how the polyester webbing is actually put together? Looking at a modern seat belt the webbing appears to be in five sections woven or weaved together, but I would be interested in seeing how they do it? I would also be interested in knowing if there is actually a recommended standard applied to a seat belt for accepting when it is actually significantly weakened? If we talk about cuts laterally, how deep across the belt would be significant? If we talk about damage to the belt, i.e. the fibres separate across the belt laterally, how far across the belt would be significant? I assume that it must be something to do with load testing and how much strength is actually left in the belt before agreement is reached to say the damage is significant? Any advise much apreciated Thanks
http://www.thomasnet.com/articles/materials-handling/what-is-webbing - explains a bit about the manufacturing processes involved in producing nylon webbing. But it is pretty much stitched to shape once the initial webbing strap has been produced. Inspection is odd, not sure about automotive standards, but for lift straps ASME B30.9 is a inspection/rejection criteria, you can start there. You can always check out everyspec.com and search under Nylon Webbing, it will bring up quite a few specifications that may help out. Best of luck.
It's been a few years since I was involved, but as and OEM there had to be no visible defects. Because oof the nature of the 'weave' and the patterns it generates, discrepencies were quite obvious. If the belt had been in an accident, and had restrained the occupent, there was a maximum stretch that cold be allowed. I forget the figure, but it was something like 10%. So you needed to know the original manufactured length and compare it to the post impact length. !)5 stretch meant that it wouldn't do it's job again and subsequent stresses would cause injury. I successfully argues this case after a road accident where the belt stretched 8%. the insurers didn't want to replace the belt until informed that any subsequent personal injury would be attributable, at least partly, to the previously stretched belt. They gave in, reluctantly! In all probability, Automotive seat belt webbing has some very specific criteria that asking an appropriate manufacturer would give some general information, provided it didn't infringe their IPR.
OEM webbing is dictated by strict regulations such as FMVSS, CMVSS, and guidelines by SAE. They are usually rated by maximum tensile load, such as 10,000-15,000 N. Try looking more deeply in those regulations. Personally, I haven't seen or heard about anything that would define what "significantly weakened" would be, and am curious as to why somebody would like to know. Webbings are usually used for applications where any defect would/should result in replacement. The cost of webbing is very low so it usually isn't an issue. I certainly would never want to wear a seat belt that had a small tear in it, nor would I lift a heavy object over my head with a belt that has cuts in it. The nature of most weaves has it so that any small cuts and tears are immediate weak points where complete separation would propagate from. I also agree with Bob_S's remarks concerning stretch. In the applications I've used webbing on, we were told that the webbings stretch anywhere from 2-5% under high loads. However, our testing did not get close enough to the max loads of the belts to see anything of significance.
