head and neck safety
10-05-2010, 11:50 AM
#16
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Always at the ready. 
10-05-2010, 11:55 AM
#17
Burning Brakes
10-05-2010, 02:41 PM
#18
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Yrh... Ok...
Now my head really hurts. I can understand principles of motion and force, but not from technical explanations. I need farmer, real world, hands on examples. So if my feeble brain has this right, the shear is a linear load, like the head travelling forward and the belts holding the torso back, and the bending is a rotational one, like an offset hit where the torso hits the belts and torques the torso sideways towards the impact?
Now my head really hurts. I can understand principles of motion and force, but not from technical explanations. I need farmer, real world, hands on examples. So if my feeble brain has this right, the shear is a linear load, like the head travelling forward and the belts holding the torso back, and the bending is a rotational one, like an offset hit where the torso hits the belts and torques the torso sideways towards the impact?
10-05-2010, 03:09 PM
#19
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Fair enough, John. 
Walk over to the tool shed and grab a broom. Now hold it out in front of you, with both hands touching, such that it is horizontal. You can generate the three loads by,
1. Pulling you hands apart (axial load, tension in this case),
2. Attempting to snap the broomstick (bending load), or
3. Pushing one hand away from you while pulling the other toward you (shear).
This is three loads applied to one axis, the horizontal one. Imagine three broomsticks, each on a different axis, somehow welded together at the "origin" where they meet. Now apply the three loads simultaneously to all three axes and you get an idea how smart was Mr. Mohr that he could calculate the net stress.
(Please, no torsion comments out there. It makes my head hurt.)
Walk over to the tool shed and grab a broom. Now hold it out in front of you, with both hands touching, such that it is horizontal. You can generate the three loads by,
1. Pulling you hands apart (axial load, tension in this case),
2. Attempting to snap the broomstick (bending load), or
3. Pushing one hand away from you while pulling the other toward you (shear).
This is three loads applied to one axis, the horizontal one. Imagine three broomsticks, each on a different axis, somehow welded together at the "origin" where they meet. Now apply the three loads simultaneously to all three axes and you get an idea how smart was Mr. Mohr that he could calculate the net stress.
(Please, no torsion comments out there. It makes my head hurt.)
10-05-2010, 03:33 PM
#20
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10-05-2010, 07:12 PM
#21
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Fair enough, John.
Walk over to the tool shed and grab a broom. Now hold it out in front of you, with both hands touching, such that it is horizontal. You can generate the three loads by,
1. Pulling you hands apart (axial load, tension in this case),
2. Attempting to snap the broomstick (bending load), or
3. Pushing one hand away from you while pulling the other toward you (shear).
This is three loads applied to one axis, the horizontal one. Imagine three broomsticks, each on a different axis, somehow welded together at the "origin" where they meet. Now apply the three loads simultaneously to all three axes and you get an idea how smart was Mr. Mohr that he could calculate the net stress.
(Please, no torsion comments out there. It makes my head hurt.)
Walk over to the tool shed and grab a broom. Now hold it out in front of you, with both hands touching, such that it is horizontal. You can generate the three loads by,
1. Pulling you hands apart (axial load, tension in this case),
2. Attempting to snap the broomstick (bending load), or
3. Pushing one hand away from you while pulling the other toward you (shear).
This is three loads applied to one axis, the horizontal one. Imagine three broomsticks, each on a different axis, somehow welded together at the "origin" where they meet. Now apply the three loads simultaneously to all three axes and you get an idea how smart was Mr. Mohr that he could calculate the net stress.
(Please, no torsion comments out there. It makes my head hurt.)
I think I see. So, would I be correct in guessing you see the highest shear loads immediately after the start of negative acceleration, followed closely thereafter by the highest bending forces as the head rolls forward, and then highest axial tension near the end of the episode as the upper torso has essentially rolled into a horizontal position? I drew a diagram, and knowing what I know of biomechanics, it got me thinking.
10-05-2010, 07:26 PM
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10-06-2010, 12:23 PM
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Yes;
I think I see. So, would I be correct in guessing you see the highest shear loads immediately after the start of negative acceleration, followed closely thereafter by the highest bending forces as the head rolls forward, and then highest axial tension near the end of the episode as the upper torso has essentially rolled into a horizontal position? I drew a diagram, and knowing what I know of biomechanics, it got me thinking.
I think I see. So, would I be correct in guessing you see the highest shear loads immediately after the start of negative acceleration, followed closely thereafter by the highest bending forces as the head rolls forward, and then highest axial tension near the end of the episode as the upper torso has essentially rolled into a horizontal position? I drew a diagram, and knowing what I know of biomechanics, it got me thinking.
The HANS neck tension plot is not smooth; it peaks at ~45ms and spikes again at the 65ms mark. The peak shear is at ~60ms.
The dampers in the Isaac design cause a tension, compression, tension sequence to occur, which slows things down. All three peak loads -- tension, bending and shear -- occur around the 80ms mark.
The best way to illustrate all this would be to overlay the time plot(s) on the crash video, but I don't have that capability at hand.
10-06-2010, 01:31 PM
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Ah yes, timing. In a baseline test (no H&N restraint) the neck tension peaks at about ~50-60 milliseconds post impact, at the same time the peak rear bending force occurs. Peak forward bending occurs, along with peak shear, ~ 80ms.
The HANS neck tension plot is not smooth; it peaks at ~45ms and spikes again at the 65ms mark. The peak shear is at ~60ms.
The dampers in the Isaac design cause a tension, compression, tension sequence to occur, which slows things down. All three peak loads -- tension, bending and shear -- occur around the 80ms mark.
The best way to illustrate all this would be to overlay the time plot(s) on the crash video, but I don't have that capability at hand.
The HANS neck tension plot is not smooth; it peaks at ~45ms and spikes again at the 65ms mark. The peak shear is at ~60ms.
The dampers in the Isaac design cause a tension, compression, tension sequence to occur, which slows things down. All three peak loads -- tension, bending and shear -- occur around the 80ms mark.
The best way to illustrate all this would be to overlay the time plot(s) on the crash video, but I don't have that capability at hand.
That brings more questions...
10-06-2010, 03:23 PM
#27
Three Wheelin'
Am I the only one wondering what sobering accident occurred at VIR last weekend? I hope everyone's OK ...
Scott
Scott
10-08-2010, 01:07 PM
#28
Burning Brakes
From what I've read, there was a big off at T-1 to the inside. Both driver & instructor had to be medevaced. Instructor was released same or next day, no detail on injuries. Driver was in ICU for several days, sustained brain injury and may be released soon.
10-08-2010, 09:55 PM
#29
GBaker,
What if the ultimate SFI38.1 hans type device just had dampers on it? It seems like lack of single release is the big problem with Issac which I have always liked by the way. Why can't you make a HANSish device like defNder, and hutchins hybrid and put dampers on it? So you would design your own non-patent infinging collar to hold dampers. Then you would have all the qualities a damper provides and single release all the sactioning bodies want. What is so special about rolling anchors connected to the shoulder belts? Sorry for being a simple mind but I just don't get it.
What if the ultimate SFI38.1 hans type device just had dampers on it? It seems like lack of single release is the big problem with Issac which I have always liked by the way. Why can't you make a HANSish device like defNder, and hutchins hybrid and put dampers on it? So you would design your own non-patent infinging collar to hold dampers. Then you would have all the qualities a damper provides and single release all the sactioning bodies want. What is so special about rolling anchors connected to the shoulder belts? Sorry for being a simple mind but I just don't get it.
10-09-2010, 08:42 AM
#30
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GBaker,
What if the ultimate SFI38.1 hans type device just had dampers on it? It seems like lack of single release is the big problem with Issac which I have always liked by the way. Why can't you make a HANSish device like defNder, and hutchins hybrid and put dampers on it? So you would design your own non-patent infinging collar to hold dampers. Then you would have all the qualities a damper provides and single release all the sactioning bodies want. What is so special about rolling anchors connected to the shoulder belts? Sorry for being a simple mind but I just don't get it.
What if the ultimate SFI38.1 hans type device just had dampers on it? It seems like lack of single release is the big problem with Issac which I have always liked by the way. Why can't you make a HANSish device like defNder, and hutchins hybrid and put dampers on it? So you would design your own non-patent infinging collar to hold dampers. Then you would have all the qualities a damper provides and single release all the sactioning bodies want. What is so special about rolling anchors connected to the shoulder belts? Sorry for being a simple mind but I just don't get it.
I'm not GBaker, but I did talk to him on the phone the other day.
The baseline problem with the HANS concerning its performance is that you can't necessarily keep it under the belts. To adopt that design platform is to defeat the bedrock performance advantage of the Isaac. I would guess this is a compromise that Isaac is not willing to make. To some extent, that might be a shame, as the Isaac certainly has many other advantages in performance beyond that. If the yoke would stay in place, the addition of the Isaac dampers would be an improvement of the breed. I'm studying some three axis load graphs right now, and it is enlightening. Neat stuff!