# Presentation: 788507

## Stave and Support Mechanics

- W. Miller
- iTi
- M. Cepeda, S. Dardin, M. Gilchriese, C. Haber and R. Post
- LBNL

## Reminder of Prototype Concept

- Precision mechanical core
- High-modulus facings
- Honeycomb
- Embedded cooling tube
- Flattened(-> for evaporative cooling)
- Round with POCO foam for thermal contact(-> CO2 cooling)
- Side closeouts(carbon-fiber) and end closeouts(aluminum with supporting pins)

_**Prototype dimensions**_

## Stave Geometry-10cm Silicon Modules

## Goals

- Build prototype stave mechanical/cooling “cores”
- For both C3F8 and C02 requirements
- Different support conditions(end supports only or shell-like support)
- Provide 1m core for module mounting
- Other cores for thermal and mechanical measurements
- Design and FEA of cores
- Mechanical(sag, distortion upon cooldown, etc)
- Thermal(vary properties, thermal runaway,etc)
- Compare to prototype measurements to validate FEA
- Initial study of stave support options
- End-supported
- Shells with rings
- Flat panel with rings

## Prototype Stave Core Assembly

|  | Length (m) | Facing  Material | # of Plys  Facing | Tube       Type | Purpose | Status |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 0.35 | CN60 | 10 | Flattened | Assembly trial | Complete |
| 2 | 0.35 | K13D2U | 10 | Flattened | Short, thermal prototype | Complete |
| 3 | 1.0 | K13D2U | 10 | Flattened | For modules | Complete |
| 4 | 0.35 | K13D2U | 3 or 4 | 4.8 mm round/  POCO foam | Foam bonding, thermal prototype | In progress |
| 5 | 0.35 | K13D2U |  3 or 4 | 2.8 mm  round/   POCO foam | CO2 thermal prototype | Not started |
| 6 | 1.0 | K13D2U | 3 or 4 | 2.8 mm  round/   POCO foam | TBD | Not started |

## Short Prototype

- Same as 1m except for length
- Will be used for thermal measurements
- Gluing on “cable”, silicon, dummy hybrids now

## 1m Prototype Complete

- _[http://www-physics.lbl.gov/~gilg/StavePrototypes/FirstFullLengthPrototype/](http://www-physics.lbl.gov/~gilg/StavePrototypes/FirstFullLengthPrototype/)_

## POCO Foam/4.8mm Tube

- POCO foam(or K-foam) bonded with CGL to 4.76mm tube.
- In turn will be bonded with CGL to faceplates
- Note for smaller tube(Items #5,6) foam will completely cover tube(bonded to foam with CGL) but will bond then foam to faceplates with more rigid thermal epoxy.

## Prototype Weights(gms)

- Measured

- Extrapolated

## Approximate Radiation Length Comparison

- Averaged over stave area
- Very stiff stave, end supported only e.g. as measured prototype weight
- About 0.9% without end supports, about 1.05% with supports
- Thinner, less stiff but with mid-support e.g. for possible 10 cm design
- About 0.4% without end(or mid) supports, very roughly 0.6% with end and mid-supports
- Note 0.5mm shell(see later) is about 0.3% so total  as good as or better than end support

## Thermal Analysis

- Sensor temperature obviously depends strongly on chip power
- Also on many other parameters
- Studied mostly with “short” model, although some with other more detailed models.
- Also have looked at thermal runaway in some detail.

## Thermal FEA Summary

- Not so sensitive to fiber type, orientation or layup. Cable and heat flux into tube dominate.
- Obviously T sensitive to IC power(and detector power, temperature dependence taken into account above)

## Detector Thermal Runaway

- Thermal Runaway Prediction
- Assess stave composite facing thickness reduction from 0.7mm to 0.21mm: *1m stave length*
- 0.70mm thickness: W/mK
- 352 axial, 89 transverse
- 0.21mm or 0.28mm thickness: W/mK
- 221 axial, 221 transverse
- Result
- Insignificant effect, higher transverse K’s offset thickness reduction
- Significant headroom at 0.25W/IC even for C3F8

- 10 layers 0.7mm 90/0/0/0/0/s versus
-       3 layers 0.21mm 90/0/0 *or*
-       4 layers 0.28mm 90/0/0/90

- _[http://www-](http://www-physics.lbl.gov/~gilg/ATLASUpgradeRandD/Analysis%20of%20Silicon%20Module%20Thermal%20Runaway%20for%20Stave%20Geometry%20with%20Embedded%20Cooling%20Tubes.pdf)__[physics.lbl.gov/~gilg/ATLASUpgradeRandD/Analysis](http://www-physics.lbl.gov/~gilg/ATLASUpgradeRandD/Analysis%20of%20Silicon%20Module%20Thermal%20Runaway%20for%20Stave%20Geometry%20with%20Embedded%20Cooling%20Tubes.pdf)__[ of Silicon Module Thermal Runaway for Stave Geometry with Embedded Cooling ](http://www-physics.lbl.gov/~gilg/ATLASUpgradeRandD/Analysis%20of%20Silicon%20Module%20Thermal%20Runaway%20for%20Stave%20Geometry%20with%20Embedded%20Cooling%20Tubes.pdf)__[Tubes.pdf](http://www-physics.lbl.gov/~gilg/ATLASUpgradeRandD/Analysis%20of%20Silicon%20Module%20Thermal%20Runaway%20for%20Stave%20Geometry%20with%20Embedded%20Cooling%20Tubes.pdf)_

- See link above for more details

## Mechanical Summary

- Example: 1m Stave, K13D2U 4/1 fiber Orientation, 4.6mm core height, graphite fiber HC, semi-flatten Al tube (12mil wall, U-Tube shape), Al end caps, steel pins
- Gravity sag and deflection
- Gravity sag purely horizontal and vertical : 55.5μm and 3.5μm respectively(FEA)
- Simple deflection measurements on 1m prototype agree with estimate within 15%
- Thermal distortion(FEA)
- Thermal strain *5μm out-of-plane*: 50oC temperature change plus 0.5W per chip
- Thermal strain *6.2μm out-of-plane*: 60oC temperature change only
- Coolant Tube Pressure
- 4.6mm semi-flat tube: 1.5μm out-of-plane for 100psi (6.9bar C3F8)
- For CO2 use small diameter round tube, deflections and stresses become non-issue
- Sag for lower-mass/lower-stiffness staves not an issue with mid-point support eg. 20-30 microns horizontal, worst case(does not include support-shell sag).

## Preliminary look at different options(all for 2m long barrels)
End supported
Ultra-stiff stave(10 ply facings)
Not first choice, but likely possible
Endplates/midplates hard(holes)
Thin-shell with rings
“Thin” stave – 4 ply(or less) facings and mid-point support
Thin shell(0.5mm) with external rings or external and internal rings => support two layers, possibly
Cutouts(ala pixel shells) an option
Compatible in general with staves, not just integrated stave. 
Current choice for more work
Flat-panel shell with rings
Backup to thin-shell for now

- End supported
- Ultra-stiff stave(10 ply facings)
- Not first choice, but likely possible
- Endplates/midplates hard(holes)
- Thin-shell with rings
- “Thin” stave – 4 ply(or less) facings and mid-point support
- Thin shell(0.5mm) with external rings or external and internal rings => support two layers, possibly
- Cutouts(*ala *pixel shells) an option
- Compatible in general with staves, not just integrated stave.
- Current choice for more work
- Flat-panel shell with rings
- Backup to thin-shell for now

- Support Options

## Stave Support Shell/Ring Concept

- Shell Concept: Single layer
- Avoid sandwich construction complexity
- Shell stiffness enhanced with radial rings
- Staves are mounted to rings
- Five rings chosen for 2m shell design
- Provides a mid-span support for stave
- Rings although sandwich members are modeled as single thickness laminate
- Concept offers potential for supporting two detector layers
- Could conceive of half-shells, although adds complexity but easier to mount staves

- Mean shell radius 595cm

## FEA of Support Options - Single Layer

- Example #1---One Silicon Layer
- 0.5mm thick composite, ring reinforced shell, 2m long at radius of 595mm
- Rings used as primary support for 1m staves, 38 staves for a total of 76 to make 2m length
- Mass of support shell and outer rings 6.64kg
- Rings as modeled are 5cm deep, 1mm thick facings
- From a practical sense the rings would be constructed as a sandwich, whereas the shell is not
- Mass of 76 staves is ~51.15kg
- Deflection at highest point of the rings is < 30microns

- Composite: M55J fiber/cyanate ester resin, 60% fiber fraction ρ=1.64g/cc

- Shell support: simple constraint, mid-plane at four corners

- Max sag at rings <30microns

## FEA of Support Options - Two Layers

- Example #1---Two Silicon Layers
- 0.5mm thick composite, ring reinforced shell, 2m long at radius of 595mm
- Added inner rings, 5cm depth, same as outer
- Mass of support shell and outer rings 7.98kg
- Inner surface has 64 staves to populate 2m, whereas the outer was 76
- Total stave mass ~94.2kg
- Deflection at highest point of the rings is < 14microns
_*Inner rings increased total stiffness significantly*_
- Without inner staves, but with outer staves the deflection is <8 microns

- Total mass: structure plus staves 102.2kg

- Max sag at rings <14microns

## Outlook

- Complete assembly of prototypes and simple mechanical and thermal measurements(with water) and continue to compare with FEA.
- Is anyone ready to test thermally with C02?
- Integrated “thin” stave and shell/ring support conceptual design and FEA for 2m long barrel
- Complete “proof-of-principle” design by Fall, await feedback from stave with modules.
- Longer-term(should all head in this direction)
- Complete relook at stave design/fabrication to minimize cost/material and updated requirements e.g. what is coolant(critical)
- Production plan for stave
- Has to be coupled with choice of overall support => in parallel design