1. Dove-Tail Tack Block Design
Colin Narug
6/27/2019

2. Tack Block Tack blocks used as a base to weld shell to
cold mass
While there will be a pre-stress in the shell design
if misalignment occurs that removes the pre-stress,
can the structure survive this loading condition?
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3. Previous Work
Previous work by Bob Wands and Heng Pan have shown issues with tack block.
When thermal contraction occurs, displacement will cause high stress in tack block
Slots added to allow for deformation
Expensive to make and does not work well
Slack in connection helps, does not fix major issues
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H. Pan, “Stress Analysis on Tack Blocks with Axial Compliance”, LBNL

4. Current Design
A majority of the stress in the tack block occurs due to thermal contraction
To absorb the deformation, the tack block was broken into two pieces
Connected through a dovetail joint
To prevent galling, a coating will be used
Hard Chrome Plating or similar coating
Tolerances on connection still in progress
Will need to be tested
Fixed tack block will be used on both cold masses
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5. Slot to allow for airflow/gas flow
Current Design
Dovetail Connection
Bolts attached to lower piece, slot to allow for access prior to welding
Slot to allow for airflow/gas flow
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6. Simulation Setup Two loading conditions used for simulations
Centered and Offset Positions
Loads from another simulation to determine how the cold mass is distributed across blocks
Largest values used
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7. Simulation Results, Tack Block
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8. Simulation Results, Offset Tack Block
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9. Simulation Results, Thin Tack Block
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10. Simulation Results, Offset Thin Tack Block
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11. Cold Mass Behavior
When cold mass is offset from shell, tack blocks will be only connection
Under just the effects of gravity, the shell will deform less than 1 mm
If contact is not reestablished, during the shipment of the cold mass, the shell and/or the tack block will fail
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12. Summary Tack block is sufficiently strong to survive normal operation
Conservative loads used
If tolerance is significantly off on the magnet shell, the structure will fail in shipment
Critical failure, significant bends in shell
Shell is not designed to be load bearing
Deformation of shell under 1g load will cause deformation which will reengage contact with cold mass body and the shell
Due to the weight of the cold mass, assuming the shell is not significantly out of tolerance, the magnet will remain in contact with the bottom of the shell
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