240z - fabbing new front rails

[ConVerTT]

Moving right along ....

 

 

 

 

This will go a LOT faster than the frame rails ....

 

 

[ConVerTT]

Excited to finish fitting these ???

 

 

Tired ...tomorrow ...

 

 

[ConVerTT]

Got the driver’s side fitted, trimmed and cleco’d in ....

 

 

 

 

Decided to butt the inner rocker to the wheel well instead of tapering it in (factory). ...

vs factory taper ....

 

And test fitting the outer rocker and wheel housing (Tabco) and DIY lower door patch ...

 

 

So much cleaner ...

Feels like progress!!! ?

[Patcon]

I wonder why they tapered it originally? There must have been a reason

[ConVerTT]

3 minutes ago, Patcon said:

I wonder why they tapered it originally? There must have been a reason

Agreed and I don’t know the answer.  But I can’t see it being stronger than maintaining  the section.  

[Patcon]

11 minutes ago, ConVerTT said:

Agreed and I don’t know the answer.  But I can’t see it being stronger than maintaining  the section.  

I'm not sure. One of our engineers want to weigh in?

Tapering it together makes all three pieces act like one but I'm not sure of the forces acting on the area. Tying it to the inner wheel well requires that piece of metal to be in tension to prevent the rocker panel (beam) from opening up. You obviously have the skills to replicate the factory design. I think with out more information I would default to the factory design. They would have done it in a simpler (ie. cheaper) way if it had made sense.

[ConVerTT]

2 minutes ago, Patcon said:

I'm not sure. One of our engineers want to weigh in?

Tapering it together makes all three pieces act like one but I'm not sure of the forces acting on the area. Tying it to the inner wheel well requires that piece of metal to be in tension to prevent the rocker panel (beam) from opening up. You obviously have the skills to replicate the factory design. I think with out more information I would default to the factory design. They would have done it in a simpler (ie. cheaper) way if it had made sense.

Occupation:  retired engineer ...

Good points and it would be easy to replicate but I’m not too worried about it.  The rocker also has a internal brace with a heavy bead to box it and add strength.  (I haven’t made it yet).

The main reason I did it is that all the layered metal in that corner is a brutal rust trap.  It was an almost indistinguishable lump when I first cut into it.

[wheee!]

Sounds like a steak I had at my brother in-laws .... indistinguishable lump...

[Namerow]

18 hours ago, Patcon said:

I'm not sure. One of our engineers want to weigh in?

I can never resist a good structural engineering puzzle. Of course, unibody structures are not simple affairs to analyze as the load points and paths are complicated.  And automotive design decisions can also be influenced (if not, dictated) by manufacturability and cost. 

From a structural perspective, we're looking at a long closed-box section that acts as an outboard rib for the floor panel.  The floor panel has an equally strong inner rib, in the form of the open-box section created by the transmission tunnel.  The rocker structure connections to the A and B-posts have to transfer/resist both axial loads and torques (and not just in simple bending mode, but also torsion, such as when a single wheel hits a pothole or a ridge). 

After staring at diagrams and photos of the rockers and the (very complicated) dogleg area, think the design solution used by Nissan at the ends of the rocker structures reflects all three considerations: 

1. Structural:  I think the structural decision was premised on a desire to have all of the loads from the rocker structure to the A and B posts transferred/resisted in shear through a single plane (vertical-longitudinal in this case).  It's elegant and simple. It also means that...

2. Manufacturability:  The spot welds all occur in that same plane and can be accomplished without the need to rotate the welder electrodes, and...

3. Cost:  The inner rocker can be stamped with a single-shot (not need to fold flanges are the rear end to allow joining with the wheel housing.  This might also assist in stacking the parts for shipment and storage.

This is all just educated guessing, offered by an engineer who should be retired but still needs the money. 

To assist in further speculation, here are a couple of photos for your consideration (as usual, with apologies to the original posters whose names I failed to record)...

 

[ConVerTT]

I agree with all three of your points, although I would reverse the order of priority as follows:

1) cost: single stamp is always cheaper - agreed

2) manufacturing (really cost point 2):  spot weld through multiple layers without adjusting position is cheaper - agreed

3) structural;  meh.  ( Understand that the top and bottom edges of mine are in exactly the same point as factory and the top edge of the curved section is about 1 inch inboard.  But even if I concede that) the factory design was better on day  1 ....On day 1200,  it’s a rust trap and arguably much worse.  But at day 1200 who cares ? (...well off warranty) .  So ... See 1 and 2 above ???

That said, I do like how the factory design tranfers the seat belt load to the corner ....

Edited March 31, 2019 by ConVerTT
More typos

[Namerow]

16 hours ago, ConVerTT said:

I do like how the factory design tranfers the seat belt load to the corner

There's that, too.  Even at an occupant crash decel rate of just 3g, the forces generated by a strapped-in 200-pounder through the seat belt attachment points are compelling.  And the resulting stresses in the sheet metal can jump even higher if the local panel(s) starts to deform.

[ConVerTT]

Agreed.  That backing plate is the least discussed and most important piece.  Given that I am (slightly LOL) over 200 lbs, I will likely overbuild that plate and tie it back to the corner.