Process of Nanoindentation and use of finite element modelling for results analysis

1. By- D.R. Kartikayan

2. Topics to be covered
Initial
• Introduction to some characteristic material
properties
• Why Nanoindentation (NI)?
Intermediate
• The requirements and the procedure of NI
• Analysis of Nanoindentation results
Conclusion
• Factors affecting Nanoindentation
• Scope of Finite Element Method (FEM) in
interpreting the results

3. Characteristic Material
Properties
Hardness
(On the Basis of Load and
Depth of Penetration)
Macro Hardness
Micro Hardness
Elastic Modulus
It is a measure of the stiffness
of the Material
For Metallurgical Purposes – Determined
through Indentation Experiments
“ Resistance to the penetration of a hard
indenter upon application of load”

4. Nanoindentation
What is Nanoindentation
• Such an indentation testing in which both load and
the depth of penetration are in the micro scale or
lower.
• Gives real time measurement of Load and Depth
Why Nanoindention?
• Can be readily used in the measurement of
mechanical properties of thin films and surface
layers.
• Less error prone and less time consuming

5. Conventional Hardness testing Vs
Nanoindentation
Conventional
Hardness
Testing
Nanoindentation
Testing

6. Requirements of
Nanoindentation
Unlike Conventional hardness
testing Nanoindentation requires
some conditions to be fulfilled:
High accuracy, precision
equipments for recording the
small load and displacement
Analytical modeling for
utilizing the load
displacement curve data for
determining the various
mechanical properties.
Total included angle: 142.3˚ with
an half angle of 65.35˚
Average radius of curvature
between 100 and 200 nm

7. Procedure
Loading and then Unloading is
done on the material surface
Loading considered to have
elastic plastic deformations
while unloading is considered
fully elastic
Maximum load is so selected
that a fully developed plastic
zone is formed in the material
The maximum value
of mean contact
pressure obtained
during loading is
called HARDNESS
The data obtained
during unloading
forms the basis for
contact area
during Maximum
load
Stiffness
obtained from
the unloading
curve

8. Load Displacement curve analysis
Load Displacement curve consists
of two parts:
Loading part
Unloading Part
Analysis of the curve can give us:
1) Hardness
2) Elastic Modulus
3) Strain rate sensitivity
4) Activation volume

9. Contd….
Analysis of the unloading curve:
The slope of the unloading curve is a measure of the
stiffness of contact
Such analysis can be done by two methods
a)Doerner-Nix Method: Less complicated,Linear curve
fit
b)Oliver-Pharr method: More complicated, non-linear
curve fit, more accurate results
Such analysis has:
a) Deformation upon unloading to be purely elastic
b) Contact modeled as rigid indenter of defined shape with homogenous elastic
half space.
c) The compliance of sample and indenter tip can be thought of as combination of
springs in series.

10. Indentation Mechanics
Specimen
Surface
Indenter
Tip
Nanoindentation
Result
Some Models to explain the Indenter-
Specimen interaction
Elastic
Model
Rigid
Plastic
Model
Spherical
cavity
model
Elastic and
perfectly
plastic
model

11. Factors affecting Nanoindentation
Thermal Drift
Instrument
Compliance
Indenter Geometry
Indentation Size
effect
Piling up and
Sinking In
Initial Penetration
Depth
Surface
Roughness
Tip Rounding etc

12. Indentation size effect
Increase in
Hardness
(ISE)
Decrease in
Hardness
(RISE)
Decrease in
Load
Hinders the Use of Hardness as a
Characteristic material property
Various Models proposed to explain ISE
•Minimum resistance model
•Proportional specimen resistance
•Energy balance approach
•Combined approach
•Elastic plastic deformation model
•Indentation induced cracking
•Strain gradient plasticity
•Dislocation mechanics

13. Piling up
Raised Surface
at Edge of the
indentation
Support for
Indenter
Indenter
penetrates lesser
Hardness and
Elastic Moduli
are
Overestimated

14. Finite element Analysis of Load
indentation data
Factors affecting NI not considered  More error prone results
Deformed Indenter
Tip Less
penetration depth
Calculated contact
region different
from the actual
contact region
The results are
error prone
ISE can be
accounted for
Empirical and
analytical
methodologies
Higher accuracy
of results as well
as other
advantages
FEM Analysis

15. FEM applied for contact between the indenter
tip and material surface.
FEM applied to study the deformation of
Indenter tip upon indentation.
FEM applied to the surface under the indenter
to account for piling up or sinking down.
All of the above makes FEM a very
efficient tool for analyzing NI Results

16. References
1) M.F. Doerner and W.D.Nix, ‘A method for interpreting the data from depth-sensing
indentation instruments’, J. Mater. Res 1 (1986)
2) W.C. Oliver and G.M. Pharr, ‘An improved technique for determining hardness and elastic
modulus using load and displacement sensing indentation experiments’, J.Mater. Res 7
(1992)
3) W.C. Oliver, R Hutchings and J.B. Pethica ,(American society for testing and materials) ASTM
STP (1986)
4) N.K.Mukhopadhyay and P.Paufler, Micro and Nanoindentation techniques for mechanical
characterisation of materials, IMR 453.3d (2005)