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> Seam welding chassis, Video on how effective it is
Tdskip
post Dec 13 2018, 03:05 PM
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QUOTE(screenguy914 @ Dec 13 2018, 03:47 PM) *

I added a link to your YouTube video of a discussion I started some time ago on that other Porsche forum:
http://forums.pelicanparts.com/porsche-911...nforcement.html

While not directly applicable to a 914, anything helps since 914 sheet metal is not as robust as on a 911.

Sherwood


Sherwood! Didn't know you where here too, you've been a big help on my 911 over on Pelican.

Very worthwhile thread.
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gereed75
post Dec 13 2018, 07:20 PM
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Interesting that I just read a Motortrend article on the new Honda Civic Type R. It gets more seam adhesive and where welds are used they are spaced .8” apart vice the 1.6” apart for the normal Civic. That equates to two additional hours in the weld shop.

The article does not mention the resultant increase in stiffness, but This technique obviously works and their concern for altered crush zones does not trump their desire for performance

I realize that the crash protection in these modern cars utilize many measures not incorporated in our 60’s designed structures, but it is an interesting point to consider
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tperazzo
post Jan 13 2019, 11:00 PM
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Attached Image
New homemade strut bar brackets and strut tower plates welded in! Who thinks the front strut bar will improve the torsional stiffness? I have my doubts, so I've instrumented a temporary strut bar with an inline load cell and a data acquisition system to monitor forces in the bar. My hunch is that the strut bar won't improve torsional stiffness much, but it may help with cornering and suspension loads.

Unfortunately, my car isn't driveable but I have a few tests in mind to play around with.

Stay tuned for more results.
Tom
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Tdskip
post Jan 14 2019, 12:00 PM
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Very tidy work. Keen to learn what you discover.
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914_teener
post Jan 14 2019, 12:23 PM
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QUOTE(tperazzo @ Jan 13 2019, 09:00 PM) *

Attached Image
New homemade strut bar brackets and strut tower plates welded in! Who thinks the front strut bar will improve the torsional stiffness? I have my doubts, so I've instrumented a temporary strut bar with an inline load cell and a data acquisition system to monitor forces in the bar. My hunch is that the strut bar won't improve torsional stiffness much, but it may help with cornering and suspension loads.

Unfortunately, my car isn't driveable but I have a few tests in mind to play around with.

Stay tuned for more results.
Tom



I don.t think it will do much for torsional rigidty of the chasisis.

Good Luck.
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tperazzo
post Jan 19 2019, 08:09 PM
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This week I did some experimentation with the forces in the front strut bar. I thought the results were quite surprising! Maybe not very relevant to the 914 because it already has better front strut support than the 911.

1) Increased torsional rigidity is about 10%
2) Max load in the horizontal bar was measured at 70 lbs
3) The loads alternate between tension and compression
4) Changes in camber are very small with or without the strut bar


This video is a bit long, but I did everything I could to make the strut brace look good. At the end of the day it didn't impress me much.

https://youtu.be/QjGYaeYew8s

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TravisNeff
post Jan 20 2019, 06:39 AM
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Thanks for putting that video together, we all love the data!
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jd74914
post Jan 20 2019, 07:36 AM
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QUOTE(tperazzo @ Jan 19 2019, 09:09 PM) *

1) Increased torsional rigidity is about 10%
...
At the end of the day it didn't impress me much.

This is very cool stuff-super impressed!! Please note, I haven't watched watched the video yet, so please ignore if you covered the questions below. Just curious on your thoughts.

To me, 10% stiffness gain is a lot. I would have killed to have gained that with minimal weight in the tube chassis cars I've designed. Why aren't you happy with that number?

Out of your scope, but it'd be interesting to see if there would be a difference if the strut bar was more of a strut panel with two wide spaced vertical attachment points and a larger vertical dimension (more box that bar) to make it more like a shear panel. I feel like something that could resist twisting loads might more effective than what's effectively a pure tension/compression member.

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tperazzo
post Jan 20 2019, 08:36 AM
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QUOTE(jd74914 @ Jan 20 2019, 05:36 AM) *

QUOTE(tperazzo @ Jan 19 2019, 09:09 PM) *

1) Increased torsional rigidity is about 10%
...
At the end of the day it didn't impress me much.

This is very cool stuff-super impressed!! Please note, I haven't watched watched the video yet, so please ignore if you covered the questions below. Just curious on your thoughts.

To me, 10% stiffness gain is a lot. I would have killed to have gained that with minimal weight in the tube chassis cars I've designed. Why aren't you happy with that number?

Out of your scope, but it'd be interesting to see if there would be a difference if the strut bar was more of a strut panel with two wide spaced vertical attachment points and a larger vertical dimension (more box that bar) to make it more like a shear panel. I feel like something that could resist twisting loads might more effective than what's effectively a pure tension/compression member.

Thank you!
The ten percent increase is measureable and I'm happy. If I compare the 10% to seam welding, I think was 19%, I prefer seam welding with even less weight added. So overall I'm happy with that improvement but the 10% comes from the diagonal bar and not the strut bar. I measured a torsional stiffness with a two point strut bar and a three-point strut bar configuration.
The two point strut bar did nothing to improve torsional rigidity.


Your idea of a strut panel is very good. That's exactly what I learned from this test. Rather than a solid panel I think two bars with a shape of an X in the same plane as the strut towers would do the the most to improve structural chassis rigidity. It's easy for me at this point to add two more tabs to the lower corner where it attaches to the bottom of the strut tower. These bars pictured were temporary so the actual bars that I will use will be in the shape of an X. A X shape is almost the same as a solid sheer panel.
Cheers,
Tom
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