Laser Interferometer Gravitational-Wave Observatory 1
Stefano TirelliUndergraduate student
University of PisaItaly
LIGO-G020441-00-R
Stress-strain behaviour of MoRuB glassy metals
ChenYang WangGraduate Student
CaltechNow at University of Stanford
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)
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
LIGO Laboratory at Caltech 4
How to measure stress?
Micro Load Cell, maximum load 1000lbs (oversized!)
Wheatstone-bridge based
Present resolution ~ 50 grams
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
LIGO Laboratory at Caltech 6
Linear response:
Present resolution: 15nm
-4
-3
-2
-1
0
1
2
3
3 4 5 6 7 8 9 10 11
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
4.7 4.9 5.1 5.3 5.5 5.7 5.9 6.1
Displacement (mm)1mm
1 V
olt
Vo
lta
ge
(V
olt
s)
Linear regime:
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)
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:Mo50.4Ru33.6B16
Cross section:3.3mm x 50um
Displacement (microns)
Lo
ad
(K
g)
Stress = load * g * 1/cross-section
LIGO Laboratory at Caltech 9
Stress/strain curves for MoRuB
Crack formation
Material hysteresis
Permanent deformationNo breakdown failure as in crystals!
Displacement (microns)
Lo
ad
(K
g)
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 thicknessMeasurement. Solution: precision-micrometerUpcoming.
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 CutLocal meltingPossible formationOf crystals on edges
Scissor cut:Very irregular and unreliable!
Electropolished cut:The best!
Nucleation of cracks causes premature failure of the material!
LIGO Laboratory at Caltech 12
Structural effects of stress: shear bands
Shear bands
Details of a MoRuB brokensample
Who knows about shear bands? I don’t, but they’re nice.
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.
LIGO Laboratory at Caltech 14
Thanks to
Riccardo DeSalvo - Mentor
Prof. Francesco Fidecaro - University of Pisa
ChenYang Wang - Graduate Student, LabMateHareem Tariq - Graduate Student
Prof. William Johnson
Robert Rogan - Materials ScienceMichael HallBrian EmmersonEric KortMaddalena MantovaniBarbara Simoni
