1. Design and Plans for Introducing Flexible End Parts Steve Krave 15 October 2013

2. Background During coil winding, difficulties are encountered in fitting end spacers to coil as the geometry has not yet assumed its final position. End parts need to be able to compensate for initial winding inconsistencies. –Traditionally through manual material removal May allow turns to not take proper shape resulting in degradation Not possible with plasma coating –Single slit parts Reduces dependence on material removal Fit ranges from OK to very poor Large discontinuity at slit location

3. Accordion Parts Reduce or eliminate fit issues during installation. Are highly flexible for winding, but remain rigid in longitudinal direction. Are rigid after impregnation in all directions. Legs can be matched exactly to straight section. Take final location after curing / reaction.

4. Accordion Part Design Currently exist as a feature added to existing part geometry –Slits are simply predefined pattern cut through part vertically. –Slits can be added as secondary operation using EDM or similar technique. Two step process allows for part inspection before modification –Slits can be modeled in part and fabricated through additive manufacturing with no additional post processing. Flexible parts are difficult to inspect, perhaps just check key features. –Go/No-Go surface check, Wedge transition inspection. –Flexibility may negate the necessity of a detailed inspection. Easy to simplify as a set of beams. –Approximations of stiffness can be made for different loading conditions to predict flexibility. Azimuthal Direct: Series of beams with fixed rotation at supports. Azimuthal Bending: Series of cantilever beams (single total element length beam). Axial: Beam loaded in torsion. –Modulus modeled as parallel or series springs.

5. Spring Values for Different Loading Directions

6. Buckling Buckling was a concern on initial EDM Part. –Critical Pressure for this part with very thin elements was ~90MPa. –New parts significantly higher from shorter and thicker elements. Minimum 200MPa. –Does not account for epoxy fill/bonding which would significantly improve performance.

7. Part Modulus After Potting After potting, space between slits is filled with epoxy and modulus is restored to near solid part levels. –Slit area modulus is set of series or parallel springs. Assuming 20GPa for modulus of GFRP: –Axial modulus: 150GPa –Radial Modulus: 150GPa –Azimuthal Modulus: 62GPa

8. Trial EDM Part Installation was very easy. EDM slits were filled with 7 mil S-2 glass. Part Installed surrounded by 7mil S-2 glass to make up for missing plasma coating. Part was too sharp, glass was not cured. –Cured glass is recommended.

9. 3D Printable Slits are easily 3D printable, as long as process is good. Reduction in volume = reduction in cost.

10. Plasma Coating Plasma Coating has been tested on 3d printed part with slits. –Coating successfully applied without bridging gaps. It does not appear that any masking was used. –Coating adheres well and allows standard motion without cracking or chipping. –Coating improves surface finish to some extent on 3d printed parts. Small steps are smoothed by coating. –Part will be run through next available reaction cycle, but it is not expected to show any degradation.

11. Plans for Introduction An HQ Coil has been proposed as the ideal test bed for Accordion End Parts. –More rapid iteration could allow earlier adoption in QXF. –Existing end parts have been modified and would be ready to 3D print, drawings could be quickly created for other manufacturing processes. Possible implementation in SQXF Practice Coil.