WRC Deaths

Nevermind.

One observation I wanted to point out about fiber-behaviour in an earlier post, was covered in a later one.

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Edited 2 time(s). Last edit at 09/29/2013 10:55PM by Creech.

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Iowa999
Yeah, as we continue, I'm getting more confused and unsure. According to my old notes, there are two very different ways to measure belts. One is the classic stress/strain, where the device has effectively infinite ability to produce tension and "walks" one end back in steps of .001% of original length, measuring the tension transmitted to the other end. The other pulls one end to a certain level of tension and measures the total length. The former seems to produce plots like the one I posted above, but the latter produces plots with two straight zones before the curve to final breakage. I can accept that the two methods produce different plots, but I can't wrap my head around the relationship between the two.

From your description, do you mean method 1 pulls the belt out and then measures the stress-strain as the tension is released? Which direction is "walks one end back"? Increasing or decreasing length? If I understand your method 2 right, does that produce a plot of points by repeatedly stretching the material to increasing lengths wh relaxation in between each measurement?

If indeed the plot you scanned represent one full cylce of tension and release of tension, that seems to be what we need for best understanding.

Thanks Gene; good info on the material differences and the breakage.

One question is at how much lower a tension point does the belt break when it is bent over something versus when it is straight out? If the tension is still super high if the webbing breaks over a bend, i.e., so high that the associated G's are marginally or totally unsurvivable, then it begs the question of how much it matters? If it is a difference of 5%, I would guess no; but if a difference of 50%, then yes.

And what is the radius of the edge over which it is bent where it makes a difference, and how many degress of bend? Perhaps knowing the bend radius used for the particular test is good to know. That seems to be important; after all, a shoulder harness is 'bent' over a HANS device.......


And, if you don't mind my saying so, no one ever said that SFI does not do testing....

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heymagic
Material Width(in.)BreakingLoad(lbs.)Elongation(%)Load@ElongationMeasurement(lbs.) Spec

Nylon , ------ 3.0" --- 10,101 --- 13.2 --- 2,500 --- both
Polyester, --- 3.0" --- 10,656 ---- 8.46 --- 2,500 ---both
Nylon, ------ 2.0" ----- 6,375 --- 13.35 --- 1,500 ---16.1
Polyester, --- 2.0" ----- 7,079 ---- 7.5 ----- 1,500 ---16.1
Nylon, ------ 1.75" ----- 6,587 --- 18.05 --- 2,500 ---16.5
Polyester, --- 1.75" ----- 6,921 --- 15 ------ 2,500 ----16.5


From the company who never tests... This is a summary of the last couple years testing belts. I have about 4 pages of specifics (without names) in a pdf I can send. Looks like nylon stretchs about twice what poly does. In a dead straight pull the hardware usually fails before the webbing. In any angular pull, like real life sometimes sees, the material experiences rapid breaking of the fibers one at a time known as dumping. The webbing fails before the hardware. This is why we harp on keeping belts straight and not being redirected. I also think (myself) that maybe we should install the mounting hardware on a shouldered bolt so it can pivot to increase the possibility of a straight load.

Hmmm. Interesting that a 2" belt is now allowed for Hans use. Seems like much lower spec.
I know I try to set up my lower belts so that they go straight toward the seat and use the clip in ones.
There was some video distributed a few years ago about making sure the shoulder belt harnesses were straight after tightening. If they are angled you get a single point of stress and dramatically reduce the strength and give a place for tearing to start.

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Grant Hughes

I've been told that belts need to be tight and that the more stretch and movement in a seat the more the peak loads on the body are, both chest and neck. maybe a whiplash effect? The body stretches plenty on its own, the small amount of 'cushioning' from belt stretch wouldn't be noticed from a comfort standpoint.

I'd guess the difference in a curved belt and a straight belt is pretty small, as it's curved over the flat side. The big deal is when you curve it on the edge, that is when the dumping becomes a factor and the danged things break. Just like when we tear paper, grab opposite edges and pull, pretty tough. Grab the same edge and rip, not so tough.

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heymagic
I'd guess the difference in a curved belt and a straight belt is pretty small, as it's curved over the flat side.

Exactly. Just look at the average D-ring that your shoulder belt passes over in a street car. The belt comes up from a retractor mounted low in the B-pillar, passes up over the D-ring at the shoulder anchorage and then down at quite a sharp angle to fit across your chest.

As long as the belt is lying flat over whatever it is bending across, there's no issue. You just don't want to knick the edges of the webbing strap which will start it to tear across.

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mulik52
I think you want the maximum length of the belt which would still prevent you from hitting the steering wheel or anything else that is hard. Therefore for each seating set up it would be different. A reasonable load would probably be 3500 lb, as that is the required strength of the anchors. So, if we would have the stress-strain plot of a particular belt, belt's cross-section and the distance between a persons head and the steering wheel, we should be able to calculate the optimal length of the belt.
Klim

In order to do this theoretical calculation, you must first know exactly how much energy you are planning to put into loading the belts. That is relatively easy to predict in the standard laboratory crash test into a flat wall, but it's impossible to predict beforehand for any particular rally car crash.

In a rally car you do NOT want to come out of your seat, whether it is because your belts are too loose or stretch too far or whether your seat has collapsed.

In the US government five-star rating crash tests, the car's manufacturer knows exactly how much the test dummies weigh, precisely how they are positioned in their seats, exactly the shape of the crash pulse generated as the front of the car collapses after connecting with the flat wall, and exactly how and where the dummies will move during that crash pulse.

For this precisely controlled and repeatable scenario it is possible to "fine tune" the restraint system to perform admirably in all the criteria that are measured to score well on the five-star scale. The test procedure defines what is to be measured, and what is not, therefore it is possible to cheat.

For example, one of the performance measurement criteria is chest-deflection, i.e. how far the sternum is pressed back toward the spine. With the dummy sitting upright and restrained by a lap belt and a single shoulder belt passing over the sternum, the shoulder belt will compress the rib-cage during the crash pulse. One of the ways to cheat on this measurement is to allow the shoulder belt to stretch. As the dummy pitches forward, restrained by the lap belt, the shoulder belt loads on the sternum are relieved and transferred instead to the clavicle and shoulder, thereby driving forces downward onto the shoulder where there are no load cells monitoring the forces in this test.

Bravo. The results show very little chest-deflection. But now the forces are instead being directed into compressing the spine, which is exactly what we don't want.

Was told by a long time EMT that back in the 80's she came upon lots more deaths from shoulder belts tearing the arota from the heart. I would much rather have a broken clavical, back then be dead. The results may look wrong but really its more of pick your injury.

Why all the talk of belt stretch? Did there belts brake in this wreck?

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First rally 2013
Rally car type AWD subaru
Total rallies as driver 6
Total rally cars built 2
Total rally cars caged 3
Total rally cars repaired from offs 4
Total years racing exp other then rally 19 yrs
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Dunno Jeff, I skipped the middle part of this thread. I think it just spun off into a discussion....I'm finding it educational; belts are an area I don't know enough about. Mark B.

I'd guess many of us could learn a bit more about belts and stuff. I had one very mild frontal impact when the lights went out during a stage. One slow roll onto the side. One big crash but landed bottom first against a tree and slid down to the ground. One big roll down a bank and landed on wheels (broke one outside mirror). One 80 mph plus spin and tree smacking but with left front tire and land in ditch. I definitely benefitted from belts but certainly never stressed them. More strain on the seat mounts for the most part.

I know one competitor hit hard enough to actually crack the harness bar (in a homolgated cage). Olson's wreck back east a few years ago (big rock head on) was pretty dramatic. It really is a crap shoot. So much depends on luck when you hit.

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Reamer
Was told by a long time EMT that back in the 80's she came upon lots more deaths from shoulder belts tearing the aorta from the heart. I would much rather have a broken clavicle, back, than be dead.

A torn aorta is typically caused by a blunt impact to the chest, i.e. an unrestrained driver landing on the steering wheel, or even from sitting too close to the steering wheel and then getting punched in the chest by the air bag deployment.

The heart is relatively free-floating suspended within your chest, whereas the aorta is fixed in place against the back of your chest cavity. In a severe frontal impact the heart can tear away from the aorta.

It is not the shoulder belt doing the tearing -- at least not directly.

It is the sudden deceleration of a severe frontal impact that's doing that. I suppose you could say the shoulder belt is indirectly implicated, because if you were unrestrained by the belt your body wouldn't be subjected by the belt to that sudden deceleration. But then you'd be hit with a much more severe deceleration upon contacting the steering wheel.

The idea of wearing a seat belt harness is that it ties you to the safety cell of the occupant compartment. As the front of the car crumples and absorbs the impact of hitting the wall, the safety cell decelerates "gradually". If you are firmly attached to the safety cell, you will decelerate at a similar rate. If you are NOT attached, you will continue flying along at your original speed until contacting the steering column which, by that time, will already have come to a full stop. Upon contact you will be decelerated to a stop much more suddenly than you would have if you had been properly restrained to "ride down" the collision using the full benefit of the vehicle's crumple zone.

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Reamer
The results may look wrong but really its more of pick your injury.

Unfortunately there are limits to what the body can endure. You're basically a big bag of blood and guts hanging off a skeletal frame. There's a limit to how much load can be safely transferred to that skeleton via seat belt webbing. Worn improperly, the lap belt can cut you in half and the shoulder belt can crush your rib cage. If that bag of blood ruptures, important stuff spills out. Even if the bag stays intact, important soft stuff slaps around inside like a big bowl of pudding. Vehicle crashes are seriously dangerous.

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Reamer
Why all the talk of belt stretch? Did their belts break in this wreck?

We've strayed way off topic in this discussion. None of this has anything to do with the original post.

I supose the 80's were pre seat belt laws so her seeing more aorta deaths would be more likly from the lack of wearing a seat belt at all.

It is good to learn more about safty. Just wondered why it went 4 pages on belt stretch. I thought maybe I missed them saying there belts broke.

Unrelated but it was kind of neat to put a face to JVL in the movie Matt Johnston produced. Easier said then done. JVL's wording makes a lot more sense when you actually here his tone of voice! Funny guy!

Also a small plug for Matt but I really enjoyed the movie. I think he did a good job and recommend buying the dvd!

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First rally 2013
Rally car type AWD subaru
Total rallies as driver 6
Total rally cars built 2
Total rally cars caged 3
Total rally cars repaired from offs 4
Total years racing exp other then rally 19 yrs
Like 31motorsports on FB!
Check out 31motor sales on ebay for used Subaru parts

FYI, car seat belts became required in 1963 and shoulder belts some time after that, may around 1970. Some of the early shoudler and lap belts did not have a retractor; you adjusted it to your fit. The early shoulder belt retractors would seem to just lock rock-solid hard at a point after you started hurtling towards the dash, and did not have any sort of deceleration control (that I could tell). So perhaps that type of sudden belt stoppage was the cause.

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starion887

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Reamer
I suppose the 80's were pre seat belt laws so her seeing more aorta deaths would be more likely from the lack of wearing a seat belt at all.

FYI, car seat belts became required in 1963 and shoulder belts some time after that, maybe around 1970.

I believe Jeff was referring to the laws introduced requiring people to wear the seat belts.

Seat belts were available long before the 80's, yes. But as late as 1984 only 14% of Americans bothered to wear them. By 1990 that had climbed to a mere 49%, and today it seems to have peaked at a hard ceiling of 85%. Seat belt usage rates in the United States

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starion887
Some of the early shoulder and lap belts did not have a retractor; you adjusted it to your fit.

You adjust it just like you do with your racing harness today to ensure a snug fit with no slack. People didn't like that because it meant they couldn't reach their glove compartment doors to get at their handguns whenever Road Rage occurred.

Belt retractors were introduced as a comfort and convenience feature, with the consequence of introducing slack in the system due to weak spooling springs in the retractor. People wouldn't wear the belts if the spring pulled back too tightly. So now you have several extra feet of unused webbing wound loosely on the retractor spool.

The only safety benefit was that the retractor kept unused seat belts from falling out the door where they'd get pinched, dragged, cut, dirty, etc, with the mud making the belt less attractive to use to those few people who would otherwise have chosen to wear them.

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starion887
The early shoulder belt retractors would seem to just lock rock-solid hard at a point after you started hurtling towards the dash, ...

Early-style retractors had either a fly-weight mechanism that locked the retractor if the belt webbing was pulled out too suddenly, and/or a pendulum mechanism that swung to lock the retractor under sudden decelerations (or if you parked nose down on a steep hill).

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starion887
... and did not have any sort of deceleration control (that I could tell). So perhaps that type of sudden belt stoppage was the cause.

Deceleration control is provided by the deformable structures of the car as the crush space is used up. You only benefit from this if you are securely tied to the safety cell of the occupant compartment. Slack in the belt webbing introduces a delay, meaning you begin to decelerate much later and at a much more severe rate compared to the rest of the occupant compartment.

Modern belt systems have pre-tensioners that are triggered by the same sensors that fire air bags. The pre-tensioner removes slack in the belt in order to couple you to the occupant compartment as early as possible in the crash pulse.

To limit chest compression, modern restraint systems also incorporate tension relief mechanisms that allow the webbing to spool out once a maximum belt load is reached. But from there on those systems rely on an air bag to catch you instead. If for any reason the air bag does not deploy, the spooled out belt webbing will not prevent you from doing a face-plant into the dashboard.

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Reamer
Why all the talk of belt stretch? Did there belts brake in this wreck?

As far as I know, no actual details about the deaths in Germany have been released. But, the belt stretch discussion grew like this:
- the idea that the HANS device may have contributed to the deaths was raised, based on observations of an increase in the number of broken backs since mandatory HANS use. (in s study that was rejected by the FAI)
- HANS discussions almost always include a tangent about short vs. long shoulder belts
- Someone linked to crash test pix showing belt stretch and HANS vs. no HANS head position
- Someone else asked about the 'data' behind the sled tests, suggesting the pictures were propaganda without the supporting data.
- Yet another person asked for clarification on a measurement standard for belt stretch that was suggested.
- This is Rally Anarchy, so add some drama and colorful language
- Voila, much talk ensued about belt stretch and stretch testing.

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First Rally: 2001
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Last Updated, January 4, 2015

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john vanlandingham
Blame is for idiots. losers.