Fabrication Review Board FRB SearchCoil Magnetometer SENSOR S/N 4 Ferrite cores cracks

1. Fabrication Review BoardFRBSearchCoil MagnetometerSENSOR S/N 4 Ferrite cores cracks P. LEROY MMS SCM FRB, 20 APR 2012

2. Introduction • History: • S/N QM SENSOR ferrite cores broke during the first vibration campaign, cracks located at the end of the cores • S/N EM4 SENSOR fully qualified at protoflight levels (change in vibration levels and in the test protocol, notching applied) • S/N FM1 SENSOR fully qualified at protoflight, delivered at UNH • S/N FM2 SENSOR fully qualified at protoflight, calibrated, to be delivered soon at UNH • S/N FM4 SENSOR chosen for the SCM FM3 delivery jointly with the S/N FM4 PREAMP • Cracks detected at the center of the ferrite cores during post-vibration thermal cycle validation at LPP (see next slide for workflow) • ambient pressure • Cycle [°C]: 22 – 30 – 40 – 50 – 60 – 50 – 40 – 30 – 22 • Plateau of 5 minutes at each step • Investigations have shown that the torque value used for S/N FM4 (1.4N.m) was different from the requested one (1.2N.m) due to a bad calibration of the screw-driver. This is the only difference we saw between the previous models • NCR documented: MMS-SCM-NC-TRI-139_FM4_SENSOR_cracks_after_vibration.doc MMS SCM FRB, 20 APR 2012

3. SCM Sensor Manufacturing Workflow SENSOR S/N FM4 cracks detected at this step MMS SCM FRB, 20 APR 2012

4. 3 cycles have been performed at LPP on the S/N FM4 sensor => 2 cores broke • X cracked during cycle 1 • Crack not seen during the X-ray inspection performed between after cycle 1 • Cycle 2 launched for validation => Z cracked • Tubes removed from the holder => crack detected at X-ray inspectio • Cycle 3 performed without the screws 1 2 3 MMS SCM FRB, 20 APR 2012

5. Cycles on S/N FM3 and FMS, the try to fasten S/N FM3 to 1.2N.m failed FM3 FMS MMS SCM FRB, 20 APR 2012

6. Limits of secondary coil S/N FM4 X-ray inspection • The PEEK tubes have been removed from the holder to see the cracks • The crack is under the jaw MMS SCM FRB, 20 APR 2012

7. New run of thermoelastic analyses • Coefficient of thermal expansion of the Mapsil resin updated after characterization at CNES(real value 20 times larger than the one used in the previous simulations, 15E-6 => 349E-6) • Ultimate constraint for the ferrite cores measured at CNES and used in the simulations • Different torque values applied (0.8, 1.2 and 1.4N.m) • SY00728_RP_1445_12_MMS_Mechanical_Analysis.pdf • No crack seen in simulation at 60°C, margins are quite high => this does not meet the experimental results • The simulation will be updated with the 2216 solution, the geometry of the PEEK tubes will also be updated slightly • Conclusion: • Thermoelastic effects are the source of the cracks • The fastening of the screws add constraints where the cores actually crack • The cores have never cracked when not fastened (either alone or mounted in the holder without fastening the screws as tested on S/N FM3 and S/N FMS) • Thus, we propose to reduce the torque value (0.35N.m instead of 1.2N.m) and to add glue to avoid sliding during vibration qualifications => solution tested on the QM MMS SCM FRB, 20 APR 2012

8. Configuration tested in vibration • Tested at protoflight levels along the Z axis (highest levels) • 2216 glue added on both sides of the PEEK tubes • Screws fastened at 0.35N.m (instead of 1.2N.m) • No sliding detected • The screws do not moved MMS SCM FRB, 20 APR 2012

9. Update of the Workflow MMS SCM FRB, 20 APR 2012