1. Laser Interferometer Gravitational-Wave Observatory 1 Stefano Tirelli Undergraduate student University of Pisa Italy LIGO-G020441-00-R Stress-strain behaviour of MoRuB glassy metals ChenYang Wang Graduate Student Caltech Now at University of Stanford

2. LIGO Laboratory at Caltech 2 Physical properties studied Young’s Modulus Mechanical hysteresis Yield Point High yield point allows THINNER suspensions and less energy dissipation Structural modifications Shear bands Crack propagation (upcoming)

3. LIGO Laboratory at Caltech 3 How to study stress/strain of MoRuB? Load frame and cell courtesy of Robert Rogan, Materials Science Load frame, operational setup

4. LIGO Laboratory at Caltech 4 How to measure stress? Micro Load Cell, maximum load 1000lbs (oversized!) Wheatstone-bridge based Present resolution ~ 50 grams

5. LIGO Laboratory at Caltech 5 How to measure strain? LVDT: Linear Variable Differential Transformer Custom designed micro-LVDT and holders Differential measurement = high resolution, rejection of noise Current flow

6. LIGO Laboratory at Caltech 6 Linear response: Present resolution: 15nm Displacement (mm) 1mm 1 Volt Voltage (Volts) Linear regime:

7. LIGO Laboratory at Caltech 7 The stress/strain chart The stress\strain chart give us a clear picture of many properties of the material: Slope: Young’s modulus Breaking point Plastic deformation (not present in Glassy metals) Yield point Ductile deformation (not present in Glassy metals)

8. LIGO Laboratory at Caltech 8 Stress/strain chart for MoRuB First cycles: low load Non-rigidity of the system Hysteresis NOT due to sample Sample tested: Mo 50.4 Ru 33.6 B 16 Cross section: 3.3mm x 50um Displacement (microns) Load (Kg) Stress = load * g * 1/cross-section

9. LIGO Laboratory at Caltech 9 Stress/strain curves for MoRuB Crack formation Material hysteresis Permanent deformation No breakdown failure as in crystals! Displacement (microns) Load (Kg)

10. LIGO Laboratory at Caltech 10 Why low values for yield point? Young’s modulus: Boron 16: 174 GPa Yield point (lower limit!): Boron 16: 1.34 Gpa (upper limit: 5.2GPa) Non-uniformity of stress: effective cross- section is LOWER than the measured one. Solution: self-aligning swivel holders (already in production): LVDT Sample holder Rotating swivel Two LVDT’s for detecting torsion! Error: ~15% mainly due to poor thickness Measurement. Solution: precision-micrometer Upcoming.

11. LIGO Laboratory at Caltech 11 Why low values for yield point? Nucleation of cracks. To take good measurements we need regular borders without weak point for crack nucleation: EDM Cut Local melting Possible formation Of crystals on edges Scissor cut: Very irregular and unreliable! Electropolished cut: The best! Nucleation of cracks causes premature failure of the material!

12. LIGO Laboratory at Caltech 12 Structural effects of stress: shear bands Shear bands Details of a MoRuB broken sample Who knows about shear bands? I don’t, but they’re nice.

13. LIGO Laboratory at Caltech 13 What needs to be done: Testing on electropolished samples to obtain a value close to the one calculated by Vicker hardness test (5.2GPa). Study of crack propagation. Poisson’s modulus. Observation of shear bands during formations: load frame is designed to fit into an SEM casing.

14. LIGO Laboratory at Caltech 14 Thanks to Riccardo DeSalvo - Mentor Prof. Francesco Fidecaro - University of Pisa ChenYang Wang - Graduate Student, LabMate Hareem Tariq - Graduate Student Prof. William Johnson Robert Rogan - Materials Science Michael Hall Brian Emmerson Eric Kort Maddalena Mantovani Barbara Simoni