Determining Micromechanical Strain

Matthew Strasberg

Cornell University

Biomedical Stents

Nitinol Superelastic/Shape

Memory Half billion Cycle

lifetime Design Difficulties

http://www.xebradigital.com/img/stent_image.jpg

fracturesfractures

Continuum MechanicsForce Force

FRACTURE

Four Micromechanical Processes in Nitinol

Elastic Deformation Phase Transformation Twining Plastic Deformation

STRAIN

STRAIN

Usefulness

At what localized strain do these processes occur?

How can we determine the localized strain?

Geometry

nd sin2

Bragg’s Law

d

Strain

33

2322

131211

Tensor Transformation

coscoscossinsin

cossincossinsin

cossinsinsincos

ija

x

y

z

Q

jkjkaa 33,

Strain Calculation

o

o

d

dd

,,

3322

232

2222

1312112

,

coscos2sincossincos

2sincos2sinsinsin

Results

End Results

33

2322

131211

33

22

11

0

00

Macro Strain Medical Use

Future Research

How much information is needed to find strain?

More Complicated Strain Cases Other Micromechanical Processes

Acknowledgements

Erich Owens Apurva Mehta Sam Webb Stephanie and Adam SSRL SLAC, Department of Energy, SULI NDC