Nanoindentation
“Nanoindentation is a variety of indentation harness test applied to small volumes. Indentation is perhaps the most commonly applied means of testing the mechanical properties of materials. The nanoindentation technique was developed in the mid-1970s to measure the hardness of small volumes of material.” (Wikipedia, Nanoindentation, 6/1/2011)
“Two types of instruments have been developed to facilitate studies of thin films: the depth-sensing nanoindentor (Pethica et al. (1983) Philos. Mag. A 48:593) and the atomic force microscope (AFM) (Binnig et al. (1986) Phys. Rev. Lett 56:930). 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 can then be analyzed to obtain mechanical properties, such as hardness and elastic modulus using well established models. Using the AFM-based indentation techniques, measurements are displacement controlled--the sample is displaced against a cantilever indenter via a piezoelectric actuator--and forces are inferred from the measured deflection of the cantilever and its (nominally) known spring constant. Several different cantilever configurations and displacement detection schemes have been developed to obtain these measurements. AFM technology can be used to analyze a number of mechanical and thermomechanical properties of films including hardness, Tg or modulus.” (Bradshaw, Gotsmann and Duerig, US Patent 7,849,731; 12/14/2010
Recent US Patents
12/14/2010
7,849,731
Nanoindentation surface analysis method.
Bradshaw, Gotsmann and Duerig of IBM, New York have developed a nanoindentation method consisting of laterally scanning the surface of the film with an array of cantilever tips varying temperature, load and time to obtain a measurement of mechanical properties, such as hardness and glass transition temperature. (RDC 5/31/2011)
Recent Journal Articles
Microindentation into an epoxy composition to assess the influence of aging on mechanical properties
(2090–2094)Journal of Applied Polymer Science 123 #4 (2012)
Minster et al , Czech Republic, applied the microindentation technique for assessing the influence of two aging factors—long-term weathering and long-term laboratory aging—on the time-dependent mechanical properties of an epoxy composition on the basis of linear viscoelasticity. Four special time-dependent loading histories were applied: indentation under a step load, indentation under a constant load rate, indentation with a fixed depth of penetration, and indentation under a constant rate of penetration. The short-term histories of the viscoelastic compliance of a common epoxy composition, affected by 5-year weathering or laboratory aging, measured using a microindentation technique were compared to the data derived from standard macro measurements. The findings suggest that a qualitative assessment of the influence of the investigated aging effects on mechanical properties can be handled using short-term microindentation data, but the data has to be freed of possible attendant factors, especially of the influence of polishing procedures accompanying the microindentation techniques, before comparing it with standard measurement data. (RDC 11/2/2011)
Investigation of the effect of relative humidity on polymers by depth sensing indentation
(7551-7557) Journal of Materials Science 46 #23 (2011)
Altaf, Ashcroft and Hague of Loughborough University, United Kingdom, studied the effect of relative humidity (RH) on the mechanical behaviour of an stereolithography resin is investigated using depth sensing indentation (DSI). Hardness and modulus decreased with increasing RH and conditioning time but recovered significantly when tested after drying. (RDC 9/14/2011)
An unexpected plasticization phenomenon and a constant of the change rate of viscoelastic properties for polymers during nanoindentation test
(885–890)Journal of Applied Polymer Science 122 #2 (2011)
Tang et al of the The University of Queensland, Australia and Sichuan University, China, studied the effect of loading force, loading rate and unloading rate on the viscoelastic behavior of three representative polymers: poly(methyl methacrylate) (PMMA, amorphous polymer), polyvinylidene fluoride (PVDF, semicrystalline polymer), and epoxy (crosslinked polymer) have been investigated using nanoindentation. The results showed that the maximum indentation depth increased with the increase of loading force, and the relationship between loading force and depth became linear when the loading force is beyond 3000 μN. At the beginning, the plasticity index changed substantially with the increase of loading force, and after reaching a critical loading force, the plasticity index almost remained constant. The maximum indentation depth decreased with the increase of loading rate, which followed a power law curve. With the increase of loading rate, a plasticization phenomenon happened, and a possible reason is that the heat may accumulate and raise the local temperature. The plasticity index initially followed the power law with the increase of unloading rate and then almost remained constant. A constant, the change rate of viscoelastic properties with the unloading rate, for the three representative polymers studied in this research, around −0.033, has been obtained, which may be another manifestation of the phenomenon that many polymers have similar time/temperature shifts and that their WLF equation constants are approximately the same. (RDC 7/13/2011)
Accelerated testing of creep in polymeric materials using nanoindentation
(366-371) Polymer Testing 30 #4 (2011)
Maxwell et al of the National Physical Laboratory, United Kingdom, developed. nanoindentation test procedures to obtain creep properties directly from injection moulded components. This paper shows how creep data can be obtained from indentation experiments and how these tests can be accelerated by performing short-term indentation tests at elevated temperatures to predict long-term creep at ambient temperature. This technique can significantly reduce the length of time required to conduct indentation creep tests, allowing the creep properties of a polymer moulding to be mapped in less than a fifth of the time. (RDC 6/10/2011)
Review Articles
Comparison of the micromechanical aggregate properties of nanostructured aggregates with the stress conditions during stirred media milling
(4943-4952) Chemical Engineering Science 66 #21 (2011)\
Schilde, Beinert and Kwade of the Institute for Particle Technology, Germany, reviews the results of nanoindenter comparing the measured micromechanical properties with dispersion results in a stirred media mill. The strength of the aggregates can be changed using different primary particle sizes. Generally, the maximum achievable product fineness and the efficiency of the dispersion process increases with decrease in aggregate strength and, thus, increasing primary particle size. With the help of the calculated stress energy distribution in the stirred media mill using the discrete element method and the measured fracture distribution of the aggregates measured via nanoindentation an effective dispersion fraction can be calculated. (RDC 8/29/2011)