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Nanoindentation Lecture 1 Basic Principle

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Nanoindentation Lecture 1 Basic Principle

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    1. Nanoindentation Lecture 1 Basic Principle Do Kyung Kim Department of Materials Science and Engineering KAIST

    2. Indentation test (Hardness test) Hardness resistance to penetration of a hard indenter

    3. Hardness Hardness is a measure of a materials resistance to surface penetration by an indenter with a force applied to it. Hardness Brinell, 10 mm indenter, 3000 kg Load F /surface area of indentation A Vickers, diamond pyramid indentation Microhardness Vickers microindentation : size of pyramid comparable to microstructural features. You can use to assess relative hardness of various phases or microconstituents. Nanoindentation

    5. Microhardness - Vickers and Knoop

    6. Microindentation

    7. Nanoindentation Nanoindentation is called as, The depth sensing indentation The instrumented indentation Nanoindentation method gained popularity with the development of, Machines that can record small load and displacement with high accuracy and precision Analytical models by which the load-displacement data can be used to determine modulus, hardness and other mechanical properties.

    8. Micro vs Nano Indentation Microindentation A prescribed load appled to an indenter in contact with a specimen and the load is then removed and the area of the residual impression is measured. The load divided by the by the area is called the hardness. Nanoindentation A prescribed load is appled to an indenter in contact with a specimen. As the load is applied, the depth of penetration is measured. The area of contact at full load is determined by the depth of the impression and the known angle or radius of the indenter. The hardness is found by dividing the load by the area of contact. Shape of the unloading curve provides a measure of elastic modulus.

    9. Basic Hertzs elastic solution (1890s)

    10. Schematics of indenter tips

    11. 4-sided indenters

    12. 3-sided indenters

    13. Cone indenters

    14. Indenter geometry

    15. Stress field under indenter - contact field

    16. Sharp indenter (Berkovich)

    17. Blunt indenter - spherical tip

    18. Data Ananlysis P : applied load h : indenter displacement hr : plastic deformation after load removal he : surface displacement at the contact perimeter

    19. Analytical Model Basic Concept Nearly all of the elements of this analysis were first developed by workers at the Baikov Institute of Metallurgy in Moscow during the 1970's (for a review see Bulychev and Alekhin). The basic assumptions of this approach are Deformation upon unloading is purely elastic The compliance of the sample and of the indenter tip can be combined as springs in series The contact can be modeled using an analytical model for contact between a rigid indenter of defined shape with a homogeneous isotropic elastic half space using where S is the contact stiffness and A the contact area. This relation was presented by Sneddon. Later, Pharr, Oliver and Brotzen where able to show that the equation is a robust equation which applies to tips with a wide range of shapes.

    20. Analytical Model Doerner-Nix Model

    21. Analytical Model Field and Swain They treated the indentation as a reloading of a preformed impression with depth hf into reconformation with the indenter.

    22. Analytical Model Oliver and Pharr

    23. Continuous Stiffness Measurement (CSM) The nanoindentation system applies a load to the indenter tip to force the tip into the surface while simultaneously superimposing an oscillating force with a force amplitude generally several orders of magnitude smaller than the nominal load. It provides accurate measurements of contact stiffness at all depth. The stiffness values enable us to calculate the contact radius at any depth more precisely.

    24. Analysis result

    25. One of the most cited paper in Materials Science

    26. Material response

    27. Nanoindenter tips

    28. Berkovich indenter

    29. Berkovich vs Vickers indenter

    30. Commercial machines

    31. Commercial machine implementation

    32. Force actuation

    33. Displacement measurement

    34. Factor affecting nanoindentation Thermal Drift Initial penetration depth Instrument compliance Indenter geometry Piling-up and sinking-in Indentation size effect Surface roughness Tip rounding Residual stress Specimen preparation

    35. Thermal drift Drift can be due to vibration or a thermal drift Thermal drift can be due to Different thermal expansion in the machine Heat generation in the electronic devices Drift might have parallel and/or a perpendicular component to the indenter axis Thermal drift is especially important when studying time varying phenomena like creep.

    36. Thermal drift calibration

    37. Machine compliance Displacement arising from the compliance of the testing machine must be subtracted from the load-displacement data The machine compliance includes compliances in the sample and tip mounting and may vary from test to test It is feasible to identify the machine compliance by the direct measurement of contact area of various indents in a known material Anther way is to derive the machine compliance as the intercept of 1/total contact stiffness vs 1/ sqrt(maximum load) plot, if the Youngs modulus and hardness are assumed to be depth-independent

    38. Machine compliance calibration

    39. Real tip shape Deviation from perfect shape

    40. Area function calibration Ideal tip geometry yields the following area-to-depth ratio: A = 24.5 hc2 Real tips are not perfect! Calibration Use material with known elastic properties (typically fused silica) and determine its area as a function of contact

    41. Surface roughness As sample roughness does have a significant effect on the measured mechanical properties, one could either try to incorporate a model to account for the roughness or try to use large indentation depths at which the influence of the surface roughness is negligible. A model to account for roughness effects on the measured hardness is proposed by Bobji and Biswas. Nevertheless it should be noticed that any model will only be able to account for surface roughnesses which are on lateral dimensions significantly smaller compared to the geometry of the indent

    42. Pile-up and Sinking-in

    43. Phase transition measurement Nanoindentation on silicon and Raman analysis

    44. Creep measurement

    45. Fracture toughness measurement

    46. High temperature measurement Nanindentation with or without calibration

    47. Nanomechanical testing Tests Nanohardness/Elastic modulus Continuous Stiffness Measurements Acoustic Emmisions Properties at Various Temperature Friction Coefficient Wear Tests Adhesion NanoScratch Resistance Fracture Toughness Delamination

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