Attendees: Emma Gautheron, Ariel Haziot, Roland Piccin, Gianluca Vernassa

Discussion

• Who is measuring what?
  • Global measurements (Ginchard): small stacks, mechanical measurements include a strong effect from contact. Strain is concentrated on the contact surfaces.
  • Local measurements (Wolf/Sheuerlein): measure with extensometer, no contact effect, pure material reaction/response. 
  • It has been shown that a FE model considering stress-strain measurements from Wolf and real geometry at the contacts gives a good fit with the experimental data of the mock-up (strain gauges, Fuji and peak stresses)” 
• What has been done so far?
  • MQXF: linear, eleastic, isotropic
  • 11T (2D model from SMT): isotropic material, bi-linear elastic-plastic, with isotropic hardening (tangent or virgin modulus after linear fit on Guinchard’s plot but excluding the contact area so the first 15 MPa).
  • A. Bertarelli (11T mock-up, 12T today): 2 components material (insulation & cable) with 2 input properties both as isotropic material, multi-linear elastic-plastic, with isotropic hardening; such as simple reference stack produces the Wolf-stress-strain curve in total. Very sensitive to a specific case.
  • G. Vernassa's approach: Giving to the coil pack mechanical properties issued from independent material properties and bench-marked on a 10 stack (without contact), add contact in the model

• What should be assessed in order to define the best way to measure 10 stacks?
  • strategy: material vs structural (ie including contacts or not in the measurement)
  • strategy: CTE under load or not
  • sample configuration: compensated vs non-compensated
• List of measurements required on 10 stacks.
  • Dimension at RT, under load
  • Stress/strain curve at RT
  • Stress/strain curve at LT (cycling)
  • Thermal contraction (300/77 K) or Thermal contraction under load (300/77K)
  • Thermal expansion at reaction Temp. (this is too much of an open question and should not be listed for now)

Conclusion

ideally, G. Vernassa's approach seems to be the goal we all would like to reach. But there could be unexpected surprises and still unknown. In the meantime we need to define our strategy and determine the best way of measuring the 10 stacks. But we still have some time before making any hard decision.

One could work the 2 things in parrallel

1. As part of his thesis G. Vernassa keeps on bench-marking and validating his approach focusing on simple tests that will help on defining the strategy
2. We keep on relaunching the 10 stacks measurements campaign as much as possible with the information we can gather today

Actions list

• meet with M. Guinchard to have his vision
• meet with C. Sheuerlein to have his vision
• meet with D. Tommasini to have his vision
• G. Vernassa set-up a series of simple test with M. Guinchard in the framework of his thesis
• Start to look for a universal testing machine (ideally with nitrogen dewar, cf 288 C. Barth), 220 Mpa on 15x15 mm requires 50 kN.