Indentation depth sensing

Indentation has been used for over 100 years to determine hardness of materials [8J. For a given indenter geometry (e.g. spherical or pyramidal), hardness is determined by the ratio of the applied load to the projected area of contact, which was determined optically after indentation. For low loads and contacts with small dimensionality (e.g. when indenting thin films or composites), a new way to determine the contact size was needed. Depth-sensing nanoindentation [2] was developed to eliminate the need to visualize the indents, and resulted in the added capability of measuring properties like elastic modulus and creep. 

Fig. 9. (a) Depth-sensing nanoindenter model and (b) simple mechanical model for force controlled indentation assuming purely elastic contact mechanics. 

Kranenburg JM, van Duin M, Schubert US (2007) Screening of EPDM cure states using depth-sensing indentation. Macromol Chem Phys 208 915-923... 

K.W. McElhaney et al Determination of indenter tip geometry and indentation contact area for depth-sensing indentation experiments. J. Mater. Res. 13, 1300-1306 (1998)... 

The measurement of local mechanical properties is an important step in understanding of the macroscopic behavior of multiphase materials. The indentation hardness test is probably the simplest method of measuring the mechanical properties of materials. Figure 12.2b shows the evolution of the microhardness as a function of the thermal treatment temperature of a Nasicon sample. The use of load-controlled depth-sensing hardness testers which operate in the (sub)micron range enables the study of each component of the composite more precisely. 

Mechanical and Chemical Characterization Enamel has often been viewed as a homogeneous solid [2, 3], but Knoop microhardness tests [4, 5] and compression tests [6] have shown that the Young s modulus (E) and hardness (H) are higher for cusp (or surface) enamel than for side (or subsurface) enamel. Depth-sensing Vickers indentation [7] has shown that the H and E obtained from an occlusal section of enamel are higher than those for an axial section. The variations in mechanical properties with location have been explained in terms of the degree of tissue mineralization. Notably,... 

Doemer MF, Nix WD A method for interpreting the data from depth-sensing indentation instruments. JMaterRes 1986 1 601-609. 

Nanoscratch tests have been used to simulate the effect of third-body particulate wear debris on component surface scratching during use. The load at which the co-efficient of friction or friction force suddenly increases is identified as the critical load, and is used to evaluate scratch resistance and adhesion strength. The depth-sensing nanoindenter, usually equipped with a conical indenter, can elucidate the mode of failure, whether elastic/plastic deformation, cracking, or delamination. 

In general, the available indentation techniques are based either on scanning force microscopy (SFM) or on dedicated indentation setups providing well-defined tip geometries. The two approaches are described in Sections 8.2.1 and 8.2.2, respectively. Issues related to potential artifacts in IP characterization are discussed in Section 8.3. Finally, examples of epoxy IP characterization by means of SFM-based stiffness mapping as well as depth-sensing micro-indentation (DSI) are given in Sections 8.4.1 and 8.4.2, respectively. 

Baker, S. P.. The analysis of depth sensing indentation data, MRS Srmp, Proedgs.. 308. 209 216 (1993). 

Fig. 21. Characteristic events observed in the depth-sensing indentation of silicon during unloading (a) pop-out and (b) elbow. Indentations were made at the loading rate of 3 mN/s and maximum load of 50 mN.

Giro-Paloma, J. Roa, J.J. Diez-Pascual, A.M. Ray6n, E. Flores, A. Martinez, M. Chimenos, J.M. Fernandez, A.I. Depth-sensing indentation applied to polymers A comparison between standard methods of analysis in relation to the nature of the materials. Eur Polym J 49 (2013) 4047-4053. 

As additional information, the curve of the indentation size eflFect of sapphire in Fig. 8 was complemented by data measured and analyzed by Oliver and Pharr [19] on a (0001) plane. It is very remarkable that neither the different crystals and orientations, nor the different (depth sensing) measurements (Vickers-Berkovich) and the very different data analyses affect the character of the size effect observed in sapphire it can be described by one curve according to Eq. (3)/(3a) for available data in an extremely wide range of testing loads between 1 mN and 100 N. 

Sel Seltzer, R., Mai, Y.-W. Depth sensing indentation of linear viscoelastic-plastic solids A simple method to determine creep compliance. Eng. Fract. Mech. 75 (2008) 4852-4862. 

Kucheyev SO, Hamza AV, Satcher Jr JH, Worsley MA (2009) Depth-sensing indentation of low-density brittle nanoporous solid. Acta Mater 57 3472-3480... 

Indentation studies on different polymeric materials suggest that the hardness values derived from continuous depth-sensing recording compare fairly well with the hardness numbers derived from the direct measurement of the size of indentation (35,43,44). This result suggests that hardness numbers determined from the contact area imder load are comparable to post-indentation hardness values. 

For depth-sensing nanoindentation, a controlled, variable force is applied to a sample by the indenter and the resulting displacement of the indenter is measured. The resulting load vs. displacement data, together with the indenter geometry, can be analyzed to obtain hardness and elastic modulus using well established mechanical models (14). The simultaneous measurement of load and displacement also allows study of creep (time dependent strain response due to a step change in stress) (15,16). 

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