Design of a Monolithic Tensile Tester Fabricated and Fully Operated by a

Femtosecond Laser

C.E. Athanasiou, B. McMillen, Y. Bellouard

Mechanical Engineering Department

Eindhoven University of Technology, the Netherlands

Galatea Towards The Monolithic Integration Goal

Turning a single piece of material into a system by locally tailoring its

microstructure?

2

Fused silica (a-Si02)

3

Awazu et al, Appl. Phys. 94, 6243-6262 (2003)

(μicro)mechanics of Silica?

• Ultimate Tensile Stress of a-SiO2 Nanowires >10 GPa.

• Dependence of silica’s young modulus from surfaceeffects

• Under shear stress plastic deformation occurs

• Nanoscale plastic flow for high bending strengths

*Brambilla et al., Nano Lett. 9, 831-835(2009).

*Zheng et al., J Mater Sci. 42, 191-198 (2007)

*Rountree et al., ARL. 102, 195501 (2009)

*Bellouard, Opt. Mat. Express 5, 816-831 (2011)

The motivation…

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Capabilities of a Femtosecond Laser

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Design of a Monolithic Tensile Tester fabricated and fully operated by a

femtosecond laser

How does a Tensile Tester Works?

A sample is subjected to controlled tension until failure

7

Brittle Failure Ductile Failure

Strain Hardening

Regime

σ

ε

σ

ε

Beam Under

Test

How to perform a tensile test on micro-/nano- scale

specimens?

Requirements for a micro tensile tester for silica polymorphs

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• A fabrication method

• A loading tool

• Strain measurements

• Measurement of the stress

Femtosecond laser processing

Femtosecond laser induced volume expansion

Third Harmonic Generation Metrology

Birefringence Measurements

Fabrication methods for the micro-/nano- tensile test

Yb Fiber Amplified Laser System~270 fs pulses, 800 kHz rep-rate,low-pulse energy (200 nJ)

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Chemical Etching

Y. Bellouard et al, Optics Express, 12, 2120-2129 (2004)

Etching in low concentration HF bath

Femtosecond Laser Exposure (no ablation)

Laser induced controlled deformations in silica

By writing adjacent planes in the bulk of the material the stress of the tensile tester can be tuned!

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A. Champion et al., Opt. Mat. Express 2, 165240 (2012)

The Tensile Tester

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Part aLoading

Cell

Bars 1,2: UndergoVolume

Expansion

Bar 3: Beam underTest

Part bDisplacement Amplification

Sensor

Point C: Remote

Center of Rotation

Ground

σ=Εε

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20um1mm

20um

Measured Stress

280 MPa.

Loading the Tester

13SEM picture of the fabricated mechanism

Measured elongation after machining planesEnergy per pulse 300nJ@ 800KHz rep rate

3mm

1 1

1mm

A

B

Points A, B are the centers of rotation of thetwo stage compliant mechanism

A

B

Loading vs. Stressors

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Modeling the Loading Cell

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Modeling vs. Experiment

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Reference Surface

Undesired out of plane motion

9um

2mm

Third Harmonic Generation as an In-Situ Characterization Tool

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SiO2

ωn1,χ2

n2,χ1

• Weak process that occurs in all materials

• Surface-enhanced phenomenon

• When using focused ultrashortpulses the process is highlyoperative

T. Thomas, Physical Review A, 5, 4116–25 (1995)

3ω

Femtopulses Crossing an SiO2 Interface

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SiO2

Subsurface Edge Detection?

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SiO2Air

Subsurface Edge Detection?

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Subsurface Edge Detection?

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Subsurface Edge Detection?

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Subsurface Edge Detection?

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Subsurface Edge Detection?

SiO2 Air

Results & Perspectives

• The same femtosecond laser can be used for thefabrication, loading and dynamical characterizationof a micro tensile tester

• THG can be used for (sub)surface in-situ edgedetection in the micro scale

• Tool for characterizing silica’s polymorphic phases

C.E Athanasiou, B. McMillen, Y. Bellouard

Acknowledgements

27C.E. Athanasiou, B. McMillen, Y. Bellouard