Comments for Evaluation of flex joint vs floating clamp

                            July 10, 2001

                    from Kris Anderson
                        ------------------------


1.  Overall Remarks
In general, the current flex joint appears to meet the mechanical flexible
criteria.  The current design results in load at the horn terminals of only a
few hundred pounds when the horn is moved from the neutral to the extreme
position.  The  modal analysis shows that even though one of the natural
frequencies of the flex stripline is near that of the horn inner conductor,
this mode is very localized and some distance from the horn terminals.  Based
on the deflected shape, it appears that minimal energy will be transferred to
the horn inner
conductor. The rocking clamp is an interesting concept to allow limited
"slip" motion along the conductor length between adjacent conductors.

2.  Itemized Comments
-  Considering fabrication, it is questionable whether or not one will be
able to wire EDM the slot in the exact location shown in the drawing.  Given
that the bend radius will likely not be exactly that shown in the drawing
(from natural fabrication tolerance of bending in a fixed radius die) and
that the plate may have some natural bow/bend associated with it, the wire
slit may not be centered in the conductor.  Will a non-centered slit
condition result in an increase in stress?  The non-centered condition may
vary from one assembly to another.

-  The welding operation to close the EDM entry point will most likely result
in weld shrinkage of the conductor at that point, as well as a possible
stress concentration from not having a smooth surface on the underbead of the
weld.  Will this weld distortion be acceptable in terms of fabrication of the
overall shape?  Will surface imperfections in the weld region lead to fatigue
failures?
(Note that the fatigue limit in welded regions is about 1/2 that of virgin
material, and point discontinuities could lead to further reductions in
fatigue limit).

-  A more comprehensive fatigue analysis should be undertaken which accounts
for magnetic load + thermal load + DC component of stress from moving to the
extreme position.  Fatigue in welded areas and locations of stress
concentration should be considered.

-  Should we consider electroless nickel plating of the entire stripline
section?  This part is most likely small enough to fit in most vendors
processing tanks.  Alex Chen has conducted fatigue testing (albeit with small
sampling size) of electroless nickel plated aluminum spider support struts
for the horn that suggest that this process enhances fatigue life.  It may be
worthwhile to get a quotation or two to evaluate cost vs. benefit.

-  Since the review, a cost estimate of the stripline has been completed that
indicates that the design as presented represents a significant amount of
money.  Alternative designs should be considered to minimize fabrication
costs while assuring a robust design.  For example, could one consider making
the entire flex line out of say quantitiy of three 1/8" thick plates instead
of a single 3/8" thick line?  Or alternatively, could one wire EDM a 1" or 2"
wide strip by drilling a 0.031" diameter hole as the entry point for the
wire, thus eliminating the welds?  With such an alternative, the 8" wide
stripline would be "built up" of either eight - 1" wide pieces or four - 2"
wide pieces.

-  A few test pieces should be constructed ASAP that investigate the above
fabrication comment to determine the most cost effective manner of
fabrication.

-  Can this section of stripline be fabricated out of 6061-T6 instead of
6101-T6?  Fatigue benefits may be better with the 6061, at the cost of
slightly higer resistivity.  Are there any other materials that we should
consider (e.g., copper, Be/copper)?

-  I agree with Mike May's comment that a ceramic tube placed through the
clamp to encapsulate the clamp bolt may be more robust (and less expensive)
in terms of electrically isolating the clamp bolt from adjacent conductors
than the ceramic bushings.

-  As a more radical design consideration, should we investigate using a
quantity of 2 or possibly 4 conductor plates below the remote clamp as
opposed to the 8 conductors that exist in current designs?  Fabrication of 2
or 4 plates will most like cost less money at the expense of additional
design time.