Experimental Study of Crackling Noise
as Micro-mechanics of Flow
Kla Karava
Mentors: Xiaoyue Ni, Julia Greer, and Rana Adhikari
Part of the LIGO SURF programme 2015
California Institute of Technology
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Motivation for Crackling Noise
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Barkhausen noise in magnetisation
Wikimedia Commons
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Stochastic
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Crackling Noise in aLIGO
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Potential Source?
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Potential Source?
Non-linear collective behaviour of pinned dislocations
Orowan Bowing
X. Ni ,What is Crackling Noise:
a Study of Micro-mechanics of
Flow in Metals (2015)
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Then, how to study?
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Pure Copper > Maraging Steel
fcc > bcc
Well-defined slip planes
{111}
{110}
MSM Part IA Course D Handout, University of Cambridge (2014)
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Then, how to study?

Monocrystalline Cu nanopillars: 500x1500 nm (1:3)
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Why Nanopillars?
Nanopillar
Bulk
MSM Part IA Course D Handout,
University of Cambridge (2014)
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Focused Ion Beam (FIB)
X. Ni, What is Crackling Noise:
a Study of Micro-mechanics of
Flow in Metals (2015)
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Focused Ion Beam (FIB)
FEI® Versa 3D
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Well, what’s the problem?

Too much noise
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Alternative approach?
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Energy dissipation
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Dynamic Mechanical Analysis (DMA)
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Dynamic Mechanical Analysis (DMA)
𝜎 𝑡 = 𝜎0 sin(𝜔𝑡)
𝜀 𝑡 = 𝜀0 sin(𝜔𝑡 − 𝜙)
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Dynamic Mechanical Analysis (DMA)
Continuous DMA
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Dynamic Mechanical Analysis (DMA)
X. Ni , What is Crackling Noise:
a Study of Micro-mechanics of
Flow in Metals (2015)
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Dynamic Mechanical Analysis (DMA)
Hysitron® Triboindenter
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Dynamic Moduli
𝐸 = 𝐸𝑠𝑡𝑜𝑟𝑎𝑔𝑒 + 𝑖𝐸𝑙𝑜𝑠𝑠
𝜎0
𝐸 ≡ (cos𝜙 + 𝑖sin𝜙)
𝜀0
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Standard Linear Model of Solids
Frame Stiffness
𝑘1
Indenter Stiffness
Machine Damping
Contact Stiffness
Material Stiffness
Leaf Spring Stiffness
Contact Damping
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A.R. Maloney & W.D. Nix ,
An Improved Analysis for Viscoelastic
Damping in Dynamic Nanoindentation
(2007)
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Results for Cu 500nm
Theoretical results
1 Hz
10 Hz
200 Hz
Experimental results
1 Hz
10 Hz
200 Hz
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But…how can we be sure?
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Machine artefacts: thermal drift?
Calibration?
Are machine parameters actually constant?
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Fused Silica Nanopillars
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Amorphous
No dislocation
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Result for Fused Silica
1 Hz
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Size Effect
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Cu 1 µm nanopillars
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Comparing Results
500 nm
1 Hz
10 Hz
200 Hz
1 µm
1 Hz
10 Hz
200 Hz
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Conclusion
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Non-constant loss moduli in the elastic regime
Not from machine artefacts
Non-trivial microstructure evolution
Existence of crackling noise?
Need a theoretical model to confirm
Further experiments
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