As a long time member of EAA, I agree that 4130 makes great airplane
parts. But a welded fuseage does not have 100,000 PSI yield strength in
the joint clusters. It drops off to around 50,000 after annealing with
the torch. The middle of the tube span where the material has not been
subjected to post manufacturing heat, the yield strength is still up
there, but not in the weld zone. Most people use mild steel weld rod.
The still air annealing is to remove residual weld stresses which can be
quite high. By definition, annealing removes all heat treat effects used
to increase the yield strength.
Aircraft fuselages are similiar to towers in that the design concern is
compressive buckling of the unsupported span, so the lower available
yield in weld clusters is not a problem. The limiting factor is the
buckling resistance, which is proportional to yield strength, in the
middle of the span.
de n0yvy steve
CQK8DO@aol.com wrote:
>
> In a message dated 97-10-10 21:36:01 EDT, you write:
>
> << Do not weld on 4130 in the high temper states ie yield strength over
> 100,000 PSI. The weld arc will locally destroy the high yeild strength
> you paid for and provide a discontinuity that provides a site for cracks
> to start.
> >>
>
> Just got to reading the mail... I have to take issue with this as welding
> 4130 is how we build aircraft fuselages, race car frames, etc.... After
> welding is finished the steel is re-tempered in the area of the weld by a
> process called normalizing... This is a simple reheating of the weld area
> with a gas torch to a specific color and allowing it to air cool (very still
> air)... Any manual on aircraft welding will have specific instructions, many
> with color photos... Check with the EAA (Experimental Aircraft Association)
> to get a manual...
>
> Denny
>
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