Summary of first round of testing of shim concept for modular coil assembly

Problem Shear loading in the inboard regions has no manner in which to be resolved

From Art and H.M. modeling Bottom Line: friction alone will not prevent sliding. (how much sliding that would ultimately result is unanswered)

Linear 20° H.M E = 8.5 Mpsi Freudenberg

Further Checking The stress plots between the two models agree well with each other. However, It appears that turning one coil non-linear at a time produces different compressive forces at coil joints (unbalanced) then cases where all coils exhibit like properties.

Concept to resolve shear forces Add shear pins to prevent this motion from occurring

Calculation for size and number based on largest shear force from shim abinb

What an individual shim would look like 53 pins on approx 2.5” centers 70 pins on approx 2” centers Design will be similar to the left figure (with 50 pins per section)

Pins and shims (up-close) Large clearance holes are needed to allow for alignment

SST Shims, G-10 Shims, bushings and pins

Test Fixture A prototype fixture containing 4 pins was designed and loaded

Stycast not shown Pins are 2” apart.625 Fixture

Welded stud bushing epoxy G-10 shim Steel shim Outer pull plate is invisible

Stud Welding The four half inch studs were welded on at the MDL laboratory onto the two pull plates. The pins had very little tilt to them and were fairly normal to the plates. The weld bead was then ground off and the studs were cut back to 3/8” long. This procedure can be performed at PPPL in the same manner as was done at MDL. All other parts of the fixture (excluding the studs), were machined at a local machine shop.

Sample Preparation (Awaiting Insertion of the Stycast) Imagine from cell phone (poor quality) 1/32” Groove for Stycast run off (two places)

Sample Preparation (Insertion of the Stycast) Mixed Stycast 2850 with catalyst 23LV Extracted using Walgreens syringe Stycast was inserted from the top filling all four holes in this orientation

Stycast Support Weight First two holes (with pins up) were filled with 3cc’s of Stycast to the top 3cc’s were then placed in the other two holes and the top plate was placed down.

More Preparation pictures pool Final Step (assembling top pull plate onto fixture) Another View of Stycast Pool

Shim Test Fixture loaded into pull fixture Independent measuring extensometer installed on outer lower block via magnetic mount Max Load tested so far = 15,000 lbs (3750 lbs/pin) Stroke and load are measured by the 5-0 kip load cell on top of the machine (just outside the picture)

The “one armed bandit” Hard to see, but the probe touches the bottom of the shim piece here. Close up of the bandit

Prototype testing Max loading of 15,000 lbs

First test

2 mil offset

Test Setup #2: left and right side measuring All tests showed approximately 6-7 mils of deflection at 15,000 lbs

Finite Element Analysis Experimental demonstrated in deflection for 15,000 lbs (3750 lbs/pin)

FEA Loading and setup 200 lb preload applied to bolts 15,000 lb tension load (top hole) Model is fixed at bottom hole Mesh Frictionless contact between g-10 shims and outer pulling plates Elastic Modulus SST = 28 Mpsi G-10 = 7 Mpsi Stycast 2850 = 1.05 Mpsi from Fermilab paper (TM-2339-E)

Deformation Deflection (x 1e-2 in ) Stycast has frictionless contact with bushing, thus only compressive loading is seen by the Stycast. Upward movement of 1.75 mils.

Stress Intensity on pins Very Localized peak stress near the root of the pin, σ nom approx 14 ksi

Post testing Observations The analysis underestimated the experimentally observed deflection by a factor of 3.5. Why did this happen?

Post test Pictures Top Pull Plate removed

Pictures of Stycast and bushings Top View: Bushing are not concentric No cracking is seen. ISO view: Large gaps 1/8” are seen in the level of the stycast compared to the sst shim,

Pictures of Stycast and bushings More gap pictures and a view of the relief groove milled into the shim.

Air Bubbles After removing bottom pull plate and breaking the stycast, Multiple air bubbles were observed throughout the material (largest bubble approx dia = 3/16”) Bubble Bubbles

Updated Analysis [Model changes to reflect post test observations] Gaps Introduced around pins on one side (see pictures above). Modulus reduced by 50% (estimate) to account for bubbles. Resulting Deflection is 7.35 mils gaps No gaps on reverse side

Solutions and Path Forward. Inject Stycast from the side of each hole (instead of top) using Zerc fittings and hypodermic needle. Two holes will be drilled to allow for insertion and vacuum pulling of stycast around each bushing. Deair stycast until bubbling has ceased using vacuum (Use prototype to test Stycast mixture for presence of bubbles) Limit stirring of Stycast Test Stycast samples in LN2 environment to test compressive strength.

Appendix: Bubble Solution To ensure a void-free embedment, vacuum deairing should be used to remove any entrapped air introduced during the mixing operation. Vacuum deair mixture at 1-5 mm mercury. The foam will rise several times the liquid height and then subside. Continue vacuum deairing until most of the bubbling has ceased. This usually requires 3-10 minutes. To facilitate deairing in difficult to deair materials, add 1-3 drops of an air release agent, such as ANTIFOAM 88, into 100 grams of mixture. Gentle warming will also help, but working life will be shortened.