1. Nanoindentation

2. Nanoindentation

3. Why nanoindentation over tension/ compression testing?
Tension and Compression are destructive to the specimen
Clinical Applications
Macroscopic vs microscopic failure

4. Principles of Indentation
A small stiff probe applies a small load into the specimen, and the deformation is observed
Time
Displacement
Hold
Load
Unload

5. Larger contact area, averaged material property, assumes homogeneity
Traditional hardness testing
Nanoindentation
Millimeter scale
Larger contact area, averaged material property, assumes homogeneity
Measure: Projected area
Material Properties: Hardness
Nano- micrometer scale
Smaller contact area, finer spatial precision for heterogeneous materials
Measure: Indentation depth, force response
Material Properties: Hardness, load- displacement data, Young’s Modulus
Additional tests: creep, stress relaxation, strain rate sensitivity, fracture toughness

6. How do we get this extra data?
MEMS Probe
Cantilever Probe

7. Difficulties in Nanoindentation
Cannot image during indentation
Limited depth of indentation
Sensitivity and accuracy of measurements
Complex calibration
Difficult to detect the surface of the sample in soft tissues
Material pile-up

8. Indenter Geometries te Berovich Tip used in Lab maybe
Conincal and pyramid get down to 20 nanometer, a few micron
Spherical and cylindrical typically micron
Interface Focus Apr 6; 4(2):
Berovich Tip used in Lab maybe

9. Specimen Parameters As level of surface as possible
Boundary Conditions
Width and height
Thickness
Typically 1:10 indentation depth to thickness
As level of surface as possible
As Smooth of surface as possible, minimize surface Roughness

10. Resulting curve Load Displacement S = dP/dh
Hold
Unload
Pmax
hmax
S = dP/dh
Resulting curve
Small strain within elastic limit
continuous and non-conforming
elastic half-space
Frictionless surface
Time
Displacement
Hold
Load
Unload
Can get force, displacement, and elastic properties of a material
Assumptions of elastic contact theory
Small strain within elastic limit
Surfaces are continuous and non-conforming (i.e. semi-infinite plate)
Each body can be considered an elastic half-space
Frictionless surface

11. ε = 0.75
Geometric const.
S = contact stiffness

12. Young’s Modulus Contact Stiffness Effective Modulus
The slope of the unloading curve evaluated at Pmax
We will give you
Effective Modulus
Young’s Modulus
Other Material properties: Hardness, Strain Rate sensitivity, Creep, Stress Relaxation, Fracture toughness
β = 1.03
geometric constant
Assume Poisson’s Ratio of 0.3

13. Intermediate Calculations:
Test Data:
Force
displacement
Intermediate Calculations:
Contact Stiffness
Contact Height
Contact Area
Effective Modulus
Final Analysis:
Young’s Modulus
Indenter parameters