Reinventing the wheel The Rise and Fall of a conceptual Mechanical support for the Atlas ITK strip Endcap by Jesse van Dongen 1

Contents Introduction to the Atlas Strip-Endcap General Concept for the spoked petal support Wheel Design/Production concepts and prototyping for the spoked petal support wheel 2

Contents Introduction to the Atlas Strip-Endcap General Concept for the spoked petal support Wheel Design/Production concepts and prototyping for the spoked petal support wheel Total of 84 slides in 30 minutes  So let’s get started 3

Goal: A new support structure to hold the petals for the Atlas InnerTracker Strip-Endcap high luminosity upgrade (2025) 4

Basic Structure 5

Interaction Point 6 Environment: ~-35 °C ~ 0% Humidity Irradiated Acceptance

Basic Structure 7

8

A shell over the structure makes it difficult to install the petals after creating the structure. 9

Basic Structure 10

Basic Structure 11

Basic Structure Trays with all required cooling and piping for the petals 12

Basic Structure Rails for insertion & Kinematic Mount 13

Basic Structure 14

Wheel Support Concept Petals are spaced 15 [mm] center to center. Some components nearly touch. Not possible to put a continuous support structure inbetween petals Mount all petals on one side of a wheel 15 mm Option Picked 15

Wheel Support Concept Petals are spaced 15 [mm] center to center. Some components nearly touch. Not possible to put a continuous support structure inbetween petals Mount all petals on one side of a wheel 15 mm Option Picked 16

Wheel Support Concept Petals are spaced 15 [mm] center to center. Some components nearly touch. Not possible to put a continuous support structure inbetween petals Mount all petals on one side of a wheel 15 mm Option Picked 17

Wheel Support Concept Petals are spaced 15 [mm] center to center. Some components nearly touch. Not possible to put a continuous support structure inbetween petals Mount all petals on one side of a wheel 15 mm Option Picked 18

Wheel Support Concept Petals Overlap Complex structure needed to support overlapping petal from the sides of the petal Support petals on top and bottom of the petal Option Picked 19

Wheel Support Concept Petals Overlap Complex structure needed to support overlapping petal from the sides of the petal Support petals on top and bottom of the petal Option Picked 20

Wheel Support Concept Petals Overlap Complex structure needed to support overlapping petal from the sides of the petal Support petals on top and bottom of the petal Option Picked 21

Wheel Support Concept Petals Overlap Complex structure needed to support overlapping petal from the sides of the petal Support petals on top and bottom of the petal Option Picked 22

Basic Structure Innertube = main element for structural stiffness Location for translational Petal Constraint X,Y,Z Constraint X Y Z 23

Basic Structure Innertube = main element for structural stiffness Location for translational Petal Constraint X,Y,Z Constraint Phi&Z constraint X Y Z 24

Basic Structure Innertube = main element for structural stiffness Location for translational Petal Constraint X,Y,Z Constraint Phi&Z constraint Z constraint X Y Z 25

Wheel Support Concept Kinematic mounts are only needed on the inner and outer radius of the wheels We want to minimize the overall material used Try to connect the inner and outer rim with as little material as possible 26

Wheel Support Concept mmmmmmmmmmmmmmmmmm Topology optimization of the static loadcase provides a shape similar to a cart wheel 27

Wheel Support Concept Thickness is limited by the compression load due to buckling Adding pretension prevents buckling and allows thinner members. Pretension 28

Wheel Support Concept Optimization of spoke orientation by finding local optimum Rotated spokes  Torsion stiffness Radial spokes  Shorter length Orientation Optimization 29

Wheel Design – Practical Desires All components  “Ease of manufacturing” Spokes  Pretensioned, stiff against elongation Rims  Stiff against in plane bending Petal Mounts  Accuracy of mounts independant of manufacturing of wheels 30

Material Selection Loadcase: Single direction (truss/spoke) Material desire: non magnetic, long radiation length Mechanical properties: high stiffness Environmental properties: low thermal expansion, and hydroscopic length derivation. Resulting Choice: Carbon Fiber Reinforced Plastic 31

Tensioning spokes Youngs Modulus * Area Force = * Elongation Initial Length High enough to ensure no compressive force High enough to ensure stiffness requirements are met Large enough to keep pretension under changing environmental conditions 32

Tensioning spokes – Apply an Elongation 33

Tensioning spokes – Apply an Elongation 34

How much Pretension is needed? 35

Spokes – Side view 36

Spokes – Side view 37

Spokes – Side view 38

Spokes – Side view 39

Lower Pretension  Easier to manipulate 40

Tensioning spokes – Apply a force 100N  225µm Spokes are stiff & Required force is low  short elongation 41

Tensioning spokes – Apply a force 100N  225µm Spokes are stiff & Required force is low  short elongation 100N  5mm 42

Tensioning spokes – Apply a force 43

Tensioning spokes – Apply a force 44

Tensioning spokes – Apply a force 45

Tensioning spokes – Apply a force 46

Tensioning spokes – Apply a force 47

Tensioning spokes – Apply a force 48

Tensioning spokes – Apply a force Structure stiffness is lost! 49

Tensioning spokes – Apply a force Structure stiffness regained! 50

Producing a full wheel Create Inner and outterrim Hold Innerrim and outerrim in place Drill holes using jig Mount spoke tensioning devices & petal mounts Reinforce wheel at spoke feedthroughs Apply wet spokes, through the spoke tensioning device Postprocess all Petal Mounts 51

Rims Stiff against in-plane bending & low width  T-profile Mostly unidirectionally wound to optimize stiffness 52

Rims Stiff against in-plane bending & low width  T-profile Mostly unidirectionally wound to optimize stiffness 53

Spool carbon fiber 50k filament's 0.007[mm] Wetting/wire tensioning tool D1900[mm] +/-1[m/min] 54

Mold for coiling inner wheel Wetting/wire tensioning tool Teflon wheels Silicone rubber wheelRemovable segments Epoxy level D760[mm] 55

Winding Tooling 56

Rim Winding Jig InnerRimOuterrim 57

Rim Winding InnerRimOuterrim 58

Produced Rims InnerRim 2 rims made (~60/40 volume fraction) Outerrim 2 rims made (~60/40 and 50/50 volume fraction) 59

Producing a full wheel Create Inner and outterrim Hold Innerrim and outerrim in place Drill holes using jig Mount spoke tensioning devices & petal mounts Reinforce wheel at spoke feedthroughs Apply wet spokes, through the spoke tensioning device Postprocess all Petal Mounts 60

Hold Rims in Place 61

Producing a full wheel Create Inner and outterrim Hold Innerrim and outerrim in place Drill holes using jig Mount spoke tensioning devices & petal mounts Reinforce wheel at spoke feedthroughs Apply wet spokes, through the spoke tensioning device Postprocess all Petal Mounts 62

Drill holes using jig Holes for petal mounts Holes for spoke tensioner Holes for spoke feedthrough Note: In final production to obtain higher accuracy some of these holes w ould be drilled using the large CNC milling Cern 63

Producing a full wheel Create Inner and outterrim Hold Innerrim and outerrim in place Drill holes using jig Mount spoke tensioning devices & petal mounts Reinforce wheel at spoke feedthroughs Apply wet spokes, through the spoke tensioning device Postprocess all Petal Mounts 64

Glue all torlon pieces on the wheel Petal Mount (both glued and mechanically fixed) Spoke Tensioner 65

Producing a full wheel Create Inner and outterrim Hold Innerrim and outerrim in place Drill holes using jig Mount spoke tensioning devices & petal mounts Reinforce wheel at spoke feedthroughs Apply wet spokes, through the spoke tensioning device Postprocess all Petal Mounts 66

Reinforce the spoke feedthroughs 67

Producing a full wheel Create Inner and outterrim Hold Innerrim and outerrim in place Drill holes using jig Mount spoke tensioning devices & petal mounts Reinforce wheel at spoke feedthroughs Apply wet spokes, through the spoke tensioning device Postprocess all Petal Mounts 68

Tensioning spokes -> Endpoints Clamping endpoints  possibly unequal engagement of fibers Continuously wound endpoints  equal engagement of fibers 69

Spoke the wheel using wetted CFRP 70

Tensioning spokes -> Endpoints Clamping endpoints  possibly unequal engagement of fibers Continuously wound endpoints  equal engagement of fibers 71

How to pretension spokes? 72 Wet Spokes are tensioned with force using springs When under tension device is locked, by putting glass filled epoxy in locking hole. After device is locked, metal springs get cut away and removed Small 2mm radius

Prototyping – Individual Spokes Multiple spokes made with ~ 60/40 Fiber/Epoxy ratio 73

Producing a full wheel Create Inner and outterrim Hold Innerrim and outerrim in place Drill holes using jig Mount spoke tensioning devices & petal mounts Reinforce wheel at spoke feedthroughs Apply wet spokes, through the spoke tensioning device Postprocess all Petal Mounts 74

With all locking points glued on The final X,Y,Z position of the pins & slideguide get machined in a single step on a COMPLETED wheel 75

76 Peek M3 Torlon part glued to Carbon fiber rim In one plane Final machining on produced wheel M4 nut

Petal Mount Prototyping 77

Petal Locking Points X,Y,Z Constraint Phi&Z constraint Z constraint X Y Z 78

Petal Locking Points X,Y,Z Constraint Phi&Z constraint Z constraint X Y Z 79

Petal Locking Points X,Y,Z Constraint Phi&Z constraint Z constraint X Y Z 80

Single wheel FEA Results: Remaining calculated force with 50 [N] prestress, under effects of gravity, dryout and temperature 81

Maintaining pretension Spokes & Rim are made of unidirectional carbon fiber & same material Spoke & Rim total length change linearly with an increase in rim radius. Size changes due to thermal expansion and hydroscopic swelling should in theory not affect the pretension of the system. Spokes not connecting to the thermal center of the rim profile & uneven cooldown/dryout will cause some additional tension being lost/ building up. For pretension use a length safety factor ~ 100µm stretch above the required stretch to prevent buckling. Test a full wheel in a climate chamber and test the spoke frequencies, and stiffness, to estimate the pretension that was lost. And feed that info back into calculations Extensive material testing on effects like creep & relaxation 82

And that finalizes a Wheel  To be Continued 83

Spoked Wheel Team: 84 Physicist: M. Vreeswijk, N. Hessey, A.P. Colijn Mecanical engineering: M. Doets, J. van Dongen Mechanical production: A. Rietmeijer

Some Backup Slides 85

Material used for Rims and spokes Slow curing epoxy Epoxy Resin L + Harder W300 T50 Unidirectional tow 24k 86

Material used for Rims and Spokes Same material for Rims and Spokes to minimize thermal or moisture based expansion mismatches. Epoxy Long curing time ( spokes are cured under tension in a wheel, slow curing time gives time to finish an entire wheel before the curing process stops). Ability to cure under room environment without an autoclave to be able to cure at room temperature. Stable, not extremely exothermic Carbon fiber 16 spokes & ~2 [mm] thickness per spoke is something that is still doable for manufacturing. Minimum pretension desired, while environmental effects should not negate the pretension. Balance between stiffness of material, and physical stretch. Desire to have fibers with a relatively high stretch so we can bend them around a small radius (before curing). 87

Materials for Petal mounts & Spoke tensioner Petal mounts Peek for elements that are mechanically fixed Torlon for parts that need to be glued Spoke Tensioner Glass filled Torlon Regular springs that get cut away 88

Thermal and Hydroscopic CTE/CME Sources Hydroscopic Dryout CME unidir 23.5um, parallel unidir 1250um  Dimensional stability characterization of carbon fiber with epoxy and cyanate ester resin laminates due to moisture absobrtion – J. Trigo Thermal Expasion CTE (Average over range of +20°C to -40°C) unidir -0.22um*K-1*m-1,, parallel unidir 36 µm*K-1*m-1  The thermal expansion of carbon fibre-reinforced plastics, Part 1 The influence of fibre type and orientation, K.F. Rogers et all and B. Yates et all 89