"Alan Legerlotz 508.486-5744" <legerlotz@smaug.enet.dec.com>
writes on Repairing holes in MGA inner frame rails....
>Option 1 is to cut out the areas of the frame that are damaged
>and butt weld replacement pieces in place of the areas cut out. Option 2 is
>to take a pre cut overlay, which covers the entire area, and weld it on top of
>the damaged area. Option 2 will, in effect, seal the area and the inside of
>the frame will have a double wall and some added strength.
One potential technical problem with option 2---this is in effect an abrupt
change in the cross-sectional properties of the
original member, and such changes can (and in welded steel structures often do)
result in unpleasant side effects. The
possibility of a fatigue crack in the transverse (perpendicular to the axis of
the longitudinal member) weld is increased
by this option. This results from the fact that there is the aforementioned
discontinuity plus high (probably nearly at
yield) residual stresses from welding, and is only a problem if there are
significant (a few ksi) cyclic stresses at that site
resulting from vibration or ground motion. I would opt for option 1, or at
least option 3, which is to cut a hole almost as
large as the required patch, but leaving room for lap and fillet welds (or
maybe brazing?) rather than butt welds. The
hole will serve to reduce the effect of the change is cross section, and the
fillet welds will be easier for most welders to
control quality.
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Name: Ray W. James, Texas A&M Univ, Texas Transportation Inst.
E-mail: Ray James <rwj4123@sigma.tamu.edu>
Date: 08/15/94
Time: 16:41:58
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