Surface detection errors cause overestimation of the modulus in nanoindentation on soft materials

Kaufman, Jessica D.; Klapperich, Catherine M.

doi:10.1016/j.jmbbm.2008.08.004

Cited by 80 publications

(51 citation statements)

References 34 publications

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“…Recently, instrumented nanoindentation has arisen as an interesting technique to characterize the mechanical properties and viscoelastic behavior of soft materials such as polymers, gels and biological tissues (Deuschle, 2008;Pruitt, 2004, 2006;Franke et al, 2007;Herbert et al, 2009;Herbert et al, 2008;Kaufman and Klapperich, 2009;Kaufman et al, 2008;Liu et al, 2009;Oyen, 2006;Oyen and Cook, 2009). In this technique, a sample is locally compressed by an indenter with known geometry, while load, displacement and time are constantly recorded and then used to calculate materials properties (Oyen, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…In standard nanoindentation methods, initial contact is usually identified as the point when a small increase in force or stiffness is detected. Although this works well for hard materials such as metals or ceramics, even small forces can lead to extensive displacements in soft materials, thereby leading to zero-point errors and, consequently, to wrong determinations of contact area and material properties (Kaufman and Klapperich, 2009;Oyen, 2013). Furthermore, the large displacements usually imposed during mechanical loading of compliant materials require the tip area function to be calibrated for large indentation depths.…”

Section: Introductionmentioning

confidence: 99%

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Mechanical characterization of oligo(ethylene glycol)-based hydrogels by dynamic nanoindentation experiments

Guglielmi

Herbert

Tartivel

et al. 2015

Journal of the Mechanical Behavior of Biomedical Materials

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Oligo(ethylene glycol)-based hydrogel samples (OEG hydrogels) of varying cross-link densities and degrees of swelling were characterized through dynamic nanoindentation testing. Experiments were performed using a non-standard nanoindentation method which was validated on a standard polystyrene sample. This method maximizes the capability of the instrument to measure the stiffness and damping of highly compliant, viscoelastic materials.Experiments were performed over the frequency range of 1 to 50 Hz, using a 1 mm diameter flat punch indenter. A hydration method was adopted to avoid sample dehydration during testing. Values of storage modulus ‫)'ܧ(‬ ranged from 3.5 to 8.9 MPa for the different OEGhydrogel samples investigated. Samples with higher OEG concentrations showed greater scatter in the modulus measurements and it is attributed to inhomogeneities in these materials.The ‫'ܧ‬ values did not show a strong variation over frequency for any of the samples. Values of loss modulus ‫)''ܧ(‬ were two orders of magnitude lower than the storage modulus, resulting in very low values of loss factor ‫'ܧ/''ܧ(‬ < 0.1). These are characteristics of strong gels, which present negligible viscous properties.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanical characterization of oligo(ethylene glycol)-based hydrogels by dynamic nanoindentation experiments

Guglielmi

Herbert

Tartivel

et al. 2015

Journal of the Mechanical Behavior of Biomedical Materials

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“…[12][13][14][15] In this study, after shifting the data by h 0 by using the least-square errorfitting algorithm, the indentation depth associated with the smallest force during loading is approximately 0.03 lm. For more adhesive materials, the indentation depth associated with the lowest load could be far larger than the 0.03 lm found for PDMS.…”

Section: Discussionmentioning

confidence: 79%

“…In addition to surface forces, longer range attractive forces such as van der Waals and electrostatic forces can mask the onset of contact between the AFM probe and the specimen, which creates uncertainty in the location of the contact point. Several studies have shown that contact point uncertainty can cause significant error in the calculation of the specimen's modulus on both soft [12][13][14][15] and hard 16,17 materials, and these studies have accounted for this uncertainty by shifting the measured indentation depth data by some constant. However, no standardized method of shifting the data has been adopted.…”

Section: Introductionmentioning

confidence: 99%

“…As a result of some of these difficulties, many previous nanoindentation studies on soft materials have ignored the effects of adhesion, assuming them to be minimal. 12,15 The objective of this paper is to properly account for adhesion in a nanoindentation experiment with an AFM on soft materials by applying the well-known JohnsonKendall-Roberts (JKR) model. 21 The reduced modulus E* of the material is computed and compared with the modulus measured using a uniaxial tension experiment.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of nanoindentation of soft materials with an atomic force microscope

2011

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Nanoindentation is a popular experimental technique for characterization of the mechanical properties of soft and biological materials. With its force resolution of tens of pico-Newtons, the atomic force microscope (AFM) is well-suited for performing indentation experiments on soft materials. However, nonlinear contact and adhesion complicate such experiments. This paper critically examines the application of the Johnson-Kendall-Roberts (JKR) adhesion model to nanoindentation data collected with an AFM. The use of a nonlinear least-square error-fitting algorithm to calculate reduced modulus from the nanoindentation data using the JKR model is discussed. It is found that the JKR model fits the data during loading but does not fit the data during unloading. A fracture stability analysis shows that the JKR model does not fit the data collected during unloading because of the increased stability provided by the AFM cantilever.

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Length scale dependent deformation in natural rubber

Chandrashekar

Alisafaei

Han

2015

J of Applied Polymer Sci

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Strong length scale dependent deformation has been previously observed in the elastomer polydimethylsiloxane by indentation type experiments at micro-to nanometer length scales with a sharp conical tip. To examine if other nonsilicone based elastomers exhibit similar length scale dependent deformation behavior, natural rubber has been chosen in this study. Performing indentation type tests with a nanoindentation system, the universal hardness and the elastic modulus are determined at different probing depths ranging from about 90 to 5 lm to characterize length scale dependent deformation behavior in natural rubber. The testing with a Berkovich tip resulted in an amazing increase in the universal hardness with decreasing probing depth indicating that the deformation mechanisms at the micrometer length scales are significantly different as compared to those at the macroscopic length scales. The observed length scale dependent deformation is associated with an increase in rotation gradients with decreasing probing depth.

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Surface detection errors cause overestimation of the modulus in nanoindentation on soft materials

Cited by 80 publications

References 34 publications

Mechanical characterization of oligo(ethylene glycol)-based hydrogels by dynamic nanoindentation experiments

Mechanical characterization of oligo(ethylene glycol)-based hydrogels by dynamic nanoindentation experiments

Analysis of nanoindentation of soft materials with an atomic force microscope

Length scale dependent deformation in natural rubber

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