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Re: More Rants on Rods...+ Rod stress and Strains

To: tigers@Autox.Team.Net
Subject: Re: More Rants on Rods...+ Rod stress and Strains
From: DrMayf@aol.com
Date: Thu, 8 Oct 1998 16:53:54 EDT
Excuse me on this one folks. I got tangled up in an AOHell flash session and
this went out befor I completed it. But, the bottom line is that even the
ch*vy guys test things strangely and prognisticate get results. I'll finish
this one day and sent it out again. 

I find fallacy in some of the comments to Dr. Bob. When the rod piston is
reaching the top and bottom of the stroke, the velocity is approaching zero,
but the acceleration is approaching the maximum. Simple sinsusoidal motion. At
max acceleration you get max stress/ strains. Why would we expect this? Well
as the piston is driving upward it has lots of inertia and so it has to be
stopped or it goes right out through the cylinder head. Same on the down
stroke, lots of inertia to load the rod in compression yeilding high stresses,
plus if this is the power stroke the forces on the rod are additive (eg
inertia plus pressure times piston area). This I would think would be the
design load condition that automotive engineers consider. And since the piston
is pinned to the rod as is the crank, all forces go through the rod centerline
in the direction of rotation. Uneven pressure on the top of the piston could
cause bending of the rod in the cross axis. When the engineer considers this
he/she would likely do a vector addition of the forces for combined bending
and column buckling. I can take some time to develop this if there are non-
believers out there.

Class dismissed.

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