8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for...
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![Page 1: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/1.jpg)
8th Jun. 2003 SEM X International Congress
X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications
Apurva Mehta
SSRL/ SLAC, Stanford University
Valentina Imbeni
![Page 2: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/2.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaNew Boss
![Page 3: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/3.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaCollaborators
Valentina Imbeni – SRI
Brad Boyce – Sandia Labs
Nobumichi Tamura – LBL
Xiao-Yan Gong, Alan Pelton, & Tom Duerig –
NDC
Rob Ritchie’s Group (Scott Robertson, Monica
Barney) – LBL/ UC Berkeley
![Page 4: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/4.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
Motivation:Macroscopic --- Microscopic
Understanding of Deformation and Failure of NiTi components at Local Level under Multiaxial Loading.
Validation of Design Models. Towards Improved Models that
include: Austenite to Martensitic Phase Transition Mechanics Beyond Continuum Mechanics.
In vivo loadingIn vivo loadingfracturesfractures
![Page 5: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/5.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
MotivationE.g., understanding Fatigue Tests
Location of Fracture
Increase of Fatigue Life Above 1.5% Strain !!
0.0
0.2
0.4
0.6
0.8
1.0
-4 -3 -2 -1 0 1 2 3 4
Mean Strain (%)
Hal
f Alt
ern
atin
g S
trai
n (
%)
BrokenRun Out
A. Pelton et. al. - NDC
![Page 6: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/6.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaTalk Outline
What did we do? Methodology
What did we find? Diamond in Compression Diamond in Compression Cycling Diamond in Tension
Five “New” Insights
![Page 7: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/7.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
MethodologyLoad Cell
FEA Simulations
X-ray Beam
Tension
•Nitinol Tube 4.67mm OD with 0.38mm wall
•Laser machined
•Fully Annealed – Grains ~ 20-100 microns
compression
![Page 8: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/8.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
Bend MagnetSource(250x40m)
1:1 Toroidalmirror
1:1 imageat slits
Elevation view
Plan view
4 CrystalSi(111)Monochromator
CCDcamera
Sampleon scanningXY stage
Horizontal focusing K-B mirror Vertical focusing K-B mirror
MethodologyX-ray Microdiffraction
Beam size on sample: 0.8x0.8 m2
Photon energy range: 5-14 keV
Schematic layout of the X-ray Microdiffraction
Beamline (7.3.3.) at the ALS
![Page 9: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/9.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
MethodologyX-ray Microdiffraction-1 micron spot
NiTi Diffraction Patterns
10 m Grain Map
Elastic Strain
Plastic Strain
• Ni & Ti Fluorescence
• Austenite Diff. Pattern
![Page 10: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/10.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
300
03
0
003
3'
3'
3'
332313
232212
131211
332313
232212
131211
ij
DeviatioricDeviatioric DilationalDilational
kkkb o )(lkkc o )(hkka o )(
From energy scan(Variably Monochromated X-rays)
From Laue Patterns deviations(broad bandpass (White) X-rays)
Strain Tensor
Strain TensorsIn crystal reference
frame
xx xy xz
xy yy yz
xz yz zz
+
Crystal OrientationFrom Laue Patterns
In Sample reference frame
![Page 11: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/11.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaDisplacement Strain
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8th Jun. 2003 SEM X International Congress
Findings
![Page 13: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/13.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 0 mm : F = 0 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5% 0.0 mm
xx
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
X (microns)
Y (
mic
rons
)
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%0.0 mm
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
X (microns)Y
(m
icro
ns)
xx yy
![Page 14: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/14.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 0.5 mm : F = -0.393 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
01.5%
-1.5%
Y (
mic
rons
)X (microns)
Compression 0.5 mm
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
Y (
mic
ron
s)
X (microns)
1.5%
-1.5%
Compression 0.5 mm
xx
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
xx yy
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
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8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 1.0 mm : F = -0.747 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
Y (
mic
rons
)
X (microns)
-1.5%
1.5%Compression 1.0 mm
xx
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
xx yy
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
rons
)X (microns)
Compression 1.0 mm
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
![Page 16: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/16.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 1.5 mm : F = -1.080 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
01.5%
-1.5%
X (microns)Y
(m
icro
ns)
Compression 1.5 mm
yy
-15.00
-14.00
-13.00
-12.00
-11.00
-10.00
-9.000
-8.000
-7.000
-6.000
-5.000
-4.000
-3.000
-2.000
-1.000
0
1.000
2.000
3.000
4.000
5.000
6.000
7.000
8.000
9.000
10.00
11.00
12.00
13.00
14.00
15.00
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
rons
)
X (microns)
Compression 1.5 mm
xx
-15.00
-14.00
-13.00
-12.00
-11.00
-10.00
-9.000
-8.000
-7.000
-6.000
-5.000
-4.000
-3.000
-2.000
-1.000
0
1.000
2.000
3.000
4.000
5.000
6.000
7.000
8.000
9.000
10.00
11.00
12.00
13.00
14.00
15.00
xx yy
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
![Page 17: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/17.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 2.5 mm : F = -1.465 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
0 1.5%
-1.5%
Y (
mic
rons
)X (microns)
Compression 2.5 mm
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
0 50 100 150 200 250 300 350 400500
400
300
200
100
0 1.5%
-1.5%
Y (
mic
rons
)
X (microns)
Compression 2.5 mm
xx
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
xx yy
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
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8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 3.7 mm : F = -1.543 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
rons
)X (microns)
Compression 3.7 mm
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
rons
)
X (microns)
Compression 3.7 mm
xx
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
xx yy
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
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8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 3.7 mm : F = -1.543 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
rons
)
X (microns)
Compression 3.7 mm
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
Phase Map
yy
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
Y (
mic
ron
s)
X (microns)
Compression 3.7 mm
Austenite
Martensite
![Page 20: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/20.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaInsight #1
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
ron
s)
X (microns)
Compression 3.7 mm
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
Finite Elem. Analysis Microdiffraction
3.7 mm compression
Qualitative agreement with FEA
But – Granular and Speckled
X. –Y. Gong et al.
![Page 21: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/21.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaInsight #2
Local Strain Never exceeds 1.5 %
NiTi Superelastic because the Aust. And Mart. Elastic region separated by a large region of Transformation Strain
Mar
tens
ite
Aust
enit
e
Molar vol ~ strain 1.5%
Aust + Mart2 phase region
Transformation strain @
const. Stress
![Page 22: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/22.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaInsight #3
Strain relief on transformation
Strain reversal
140 145 150 155 160
150
140
130
120
110
100
yy
X (microns)
Y (
mic
rons
)
Aust
enit
eMolar vol ~ strain
1.5%
Nucleation energy
![Page 23: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/23.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 2.5 mm unload : F = -1.037 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
X (microns)
Y (
mic
rons
)
xx
Compression 2.5 mm on unload
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
rons
)X (microns)
Compression 2.5 mm on unload
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
xx yy
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
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8th Jun. 2004 SEM X International Congress
Apurva Mehta
CompressionD = 0.0 mm unload : F = +0.282 N
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
-1.5%
1.5%
Y (
mic
rons
)X (microns)
Compression 0.0 mm on unload
yy
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
Y (
mic
rons
)
X (microns)
-1.5%
1.5%Compression 0.0 mm on unload
xx
-15.00-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
xx yy
-4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
For
ce (
N)
Displacement (mm)
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8th Jun. 2004 SEM X International Congress
Apurva MehtaLoad Cycling @3.7 mm
0 50 100 150 200 250 300 350 400500
400
300
200
100
0
Y (
mic
rons
)
X (microns)
Compression 3.7 mm
0 50 100 150
100
0
Martensite map
X (microns)
Y (
mic
rons
)
0 50 100 150
160
140
120
100
80
60
40
20
0
yy
X (microns)
Y (
mic
rons
)
0 20 40 60 80 100 120 140 160 180
160
140
120
100
80
60
40
20
0
Martensite map
X (microns)
Y (
mic
rons
)
0 20 40 60 80 100 120 140 160 180
140
120
100
80
60
40
20
0
yy
X (microns)
Y (
mic
rons
)
0 20 40 60 80 100 120 140 160 180
140
120
100
80
60
40
20
0
Martensite map
X (microns)
Y (
mic
ron
s)
0 20 40 60 80 100 120 140 160 180
140
120
100
80
60
40
20
0 yy
X (microns)
Y (
mic
rons
)
-5 -4 -3 -2 -1 0
-1.5
-1.0
-0.5
0.0
0.5
Force
(N)
Displacement (mm) Zero Cycles0 – 3.7 mm
One Cycles3.7- 0- 3.7 mm
Eleven Cycles4.9 – 2.5 - 3.7 mm
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8th Jun. 2004 SEM X International Congress
Apurva MehtaInsight #4
On cycling Martensitic region grows.
Growth Pattern unpredictable from FEA
Strain relief as Martensite grows
Explanation for increased Fatigue Life for macroscopic strains > 1.5 %
![Page 27: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/27.jpg)
8th Jun. 2004 SEM X International Congress
Apurva Mehta
Tension : yy
-200 -100 0 100 200 300-150
-100
-50
0
50
100
150
200
250
300
350
400
Tension 3.0 mm
yy
-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
X (microns)
Y (
mic
rons
)
-200 -150 -100 -50 0 50 100 150 200 250 300
-100
0
100
200
300
400
Tension 2.0 mm
yy
-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
X (microns)Y
(m
icro
ns)
-200 -100 0 100 200 300
-100
0
100
200
300
400
Tension 0.3 mm
yy
-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
X (microns)
Y (
mic
ron
s)
-200 -100 0 100 200 300
-100
0
100
200
300
400
Tension 6.0 mm
yy
-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
X (microns)
Y (
mic
rons
)
-200 -100 0 100 200 300
-100
0
100
200
300
400
Tension 5.0 mm
yy
-14.00-13.00-12.00-11.00-10.00-9.000-8.000-7.000-6.000-5.000-4.000-3.000-2.000-1.00001.0002.0003.0004.0005.0006.0007.0008.0009.00010.0011.0012.0013.0014.0015.00
X (microns)
Y (
mic
rons
)
![Page 28: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/28.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaInsight #5
Transformation front and hence stress “hotspot” changes direction, and traverses down the stem of the diamond.
Failure occurs when the “hotspot” encounters a defect or weakness in the material. Location of failure maybe different from FEA prediction.
![Page 29: 8 th Jun. 2003 SEM X International Congress X-Ray Microdiffraction on Diamond-shaped NiTi for Biomedical Applications Apurva Mehta SSRL/ SLAC, Stanford.](https://reader035.fdocuments.in/reader035/viewer/2022062804/56649d405503460f94a1aaa7/html5/thumbnails/29.jpg)
8th Jun. 2004 SEM X International Congress
Apurva MehtaSummary
Insights: Strain map granular, martensite evolution speckled. In the superelstic region max stress doesn’t exceed
stress corresponding to 1.5% Austenite strain. Strain relief and strain reversal at the transformation
front. On load cycling, the martensite region grows. Overall
stress drops. Transformation and max stress front changes directions.
Further Questions: What is the crystallographic relationship between the
Martenite and the Austenite phase? What happens around a crack tip?
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8th Jun. 2004 SEM X International Congress
Apurva Mehta
Crystallographic Relationships
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8th Jun. 2003 SEM X International Congress
Thanks !