Indentation Depth Dependent Hardness in Polydimethylsiloxane

2011 ◽  
Author(s):  
Chung-Souk Han ◽  
Andrew J. Wrucke ◽  
Partha Majumdar
Keyword(s):  
Experimental Data ◽  
Size Effects ◽  
Indentation Depth ◽  
Berkovich Indenter ◽  
Indentation Size ◽  
Size Dependent

Size dependent deformation in polymers has been observed in various experiments including microbeam bending, foams, composites and indentation. For indentation depths from 100 microns down to hundreds of nanometers strong increases in the hardness has been observed where the hardness has been determined with a Berkovich indenter tip on polydimethylsiloxane. These observations are related to other existing experimental data of the literature and possible rationales for these indentation size effects are discussed.

scholarly journals Indentation Depth Dependent Mechanical Behavior in Polymers

2015 ◽  
Vol 2015 ◽  
pp. 1-20 ◽  
Author(s):  
Farid Alisafaei ◽  
Chung-Souk Han
Keyword(s):  
Size Effect ◽  
Mechanical Behavior ◽  
Size Effects ◽  
Indentation Depth ◽  
Common Ground ◽  
Experimental Studies ◽  
Experimental Methods ◽  
Indentation Size ◽  
Size Dependent ◽  
Nanoindentation Testing

Various experimental studies have revealed size dependent deformation of materials at micro and submicron length scales. Among different experimental methods, nanoindentation testing is arguably the most commonly applied method of studying size effect in various materials where increases in the hardness with decreasing indentation depth are usually related to indentation size effects. Such indentation size effects have been observed in both metals and polymers. While the indentation size effects in metals are widely discussed in the literature and are commonly attributed to geometrically necessary dislocations, for polymer the experimental results are far sparser and there does not seem to be a common ground for their rationales. The indentation size effects of polymers are addressed in this paper, where their depth dependent deformation is reviewed along with the rationale provided in the literature.

BLUNTNESS MEASUREMENT OF A BERKOVICH INDENTER

2011 ◽  
Vol 25 (31) ◽  
pp. 4273-4276 ◽  
Author(s):  
YUN-HEE LEE ◽  
BYUNG-GIL YOO ◽  
JAE-IL JANG
Keyword(s):  
Size Effects ◽  
Indentation Depth ◽  
Three Dimensional ◽  
Image Data ◽  
Curvature Radius ◽  
Berkovich Indenter ◽  
Indentation Size ◽  
Atomic Force ◽  
Observation Method ◽  
Direct Observation Method

Indenter blunting is inevitable in nanoindentations and results in unexpected contact properties. Both relaxation of the indentation size effects and deepening of the substrate effects under a blunted indenter cause a change of the bathtub-shaped hardness with indentation depth in a soft film on hard substrate. Thus an identification of three-dimensional morphology of an indenter apex is necessary for precise measurements of hardness in thin films. We observed an actual Berkovich indenter using an atomic force microscope (AFM). Through a quantitative analysis on the AFM image, data pairs of contact area versus contact depth were obtained; curvature radius of the apex was estimated by searching a sphere well-fitted to the indenter apex morphology. The estimated curvature radius and blunted height were 1043.9±50.9 nm and 44.4 nm, respectively. By comparing with the result from the modified Kick's law, both blunted heights were comparable each other within a 7 nm difference. This confirms validity of the direct observation method with the AFM.

Indentation size effects in polymers and related rotation gradients

2007 ◽  
Vol 22 (6) ◽  
pp. 1662-1672 ◽  
Author(s):  
Chung-Souk Han ◽  
Svetoslav Nikolov
Keyword(s):  
Experimental Data ◽  
Size Effects ◽  
Indentation Size Effect ◽  
Polymer Chains ◽  
Indentation Size ◽  
Proposed Model ◽  
Dislocation Densities ◽  
Model Size ◽  
Depth Ranges ◽  
Plastic Extension

Similar to metals, the hardness of many polymers increases with decreasing indentation depths at depth ranges from several microns down to several nanometers. While for metals such phenomena are commonly attributed to geometrically necessary dislocation densities, such an explanation cannot be applied to polymers. To provide a micromechanically motivated model for the indentation size effect in polymers, here we propose an elasto-plastic extension of the higher order elasticity model recently developed by the authors. In this model, size effects in polymers (as well as in nematic liquid crystals) are related to Frank elasticity arising from bending distortions of the polymer chains and their interactions. On the basis of this theory, we derive a simple model for indentation size effects in polymers. Unlike other models, our model includes only elastic size effects due to rotational gradients. It is shown that the proposed model can explain the experimentally observed size effects in polymers. Together with the existing experimental data mentioned here, new experimental data for silicon rubber are also presented and discussed.

Depth-Dependent Hardness Characterization by Nanoindentation using a Berkovich Indenter with a Rounded Tip

2005 ◽  
Vol 875 ◽  
Author(s):  
Ju-Young Kim ◽  
David T. Read ◽  
Dongil Kwon
Keyword(s):  
Single Crystal ◽  
Size Effects ◽  
Function Method ◽  
Characteristic Length ◽  
Berkovich Indenter ◽  
Indentation Size ◽  
Height Difference ◽  
Force Microscopy ◽  
Atomic Force ◽  
Fused Quartz

AbstractThe height difference Δhb between the ideally sharp Berkovich indenter tip and a Δhb rounded tip was measured by direct observation using atomic force microscopy (AFM). The accuracy of the indirect area function method for measuring h was confirmed. The Δhb indentation size effects (ISE) in (100) single crystal copper, (100) single crystal tungsten, and fused quartz were characterized by applying the ISE model considering the rounded tip effect. The model fits the data these materials well, even though fused quartz does not deform by dislocations. However, a very small value of the ISE characteristic length h' was obtained for fused quartz. The present h' value for (100) copper is 32% larger than a previously-measured value for polycrystalline copper. This may indicate that grain boundaries suppress the dislocation activity envisioned in the ISE model.

On the Time Dependence of Size Effect in Polydimethylsiloxane

2013 ◽  
Author(s):  
F. Alisafaei ◽  
Seyed Hamid Reza Sanei ◽  
E. J. Smith ◽  
Chung-Souk Han
Keyword(s):  
Size Effect ◽  
Time Dependence ◽  
Size Effects ◽  
Indentation Depth ◽  
Applied Force ◽  
Experimental Results ◽  
Time Dependent ◽  
Deformation Mechanisms ◽  
Indentation Size ◽  
Hardness Model

Nanoindentation tests at the nano-micrometer scales are conducted to investigate the depth and time dependent deformation mechanisms of polydimethylsiloxane (PDMS). Astonishing indentation size effects observed in these experiments are analyzed with an existing theoretical hardness model, and the effects of loading time on the hardness and indentation stiffness of PDMS are studied. The change in the indentation recovery with respect to indentation depth and loading time are analyzed. Furthermore, it is shown that the stiffness of PDMS obtained at the maximum applied force can be efficiently applied to validate the applied theoretical hardness model with the experimental results.

scholarly journals Indentation Size Effect in Pressure-Sensitive Polymer Based on A Criterion for Description of Yield Differential Effects and Shear Transformation-Mediated Plasticity

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 412 ◽  
Author(s):  
Hui Lin ◽  
Tao Jin ◽  
Lin Lv ◽  
Qinglin Ai
Keyword(s):  
Size Effects ◽  
Indentation Depth ◽  
Yield Criterion ◽  
Strain Rates ◽  
Depth Range ◽  
Pressure Sensitivity ◽  
Indentation Size ◽  
Strength Differential ◽  
Two Factors ◽  
Shear Transformation

Indentation size effects in poly(methyl methacrylate) (PMMA) were studied through nanoindentation. Two factors of indentation size effects in PMMA, namely yield criterion and shear transformation-mediated plasticity, were analysed in detail. The yield criterion that considers strength differential (SD) effects and pressure sensitivity was constructed by performing the combined shear-compression experiments. The relationship between hardness and normal stress can then be obtained based on Tabot’s relation. Shear transformation-mediated plasticity was also applied to model the measured hardness as a function of the indentation depth at different strain rates. Results show that the yield criterion contains the terms of SD effects and pressure sensitivity gives the best description of the yielding of PMMA. Additionally, the volume of single shear transformation zone calculated through the presented criterion agrees well with simulation and exhibits increases with increasing strain rate. Indentation size effects in PMMA under different strain rates were discussed and an appropriate indentation depth range was suggested for calculating the hardness and modulus.

On the origin of indentation size effects and depth dependent mechanical properties of elastic polymers

2016 ◽  
Vol 36 (1) ◽  
pp. 103-111 ◽  
Author(s):  
Chung-Souk Han ◽  
Seyed H.R. Sanei ◽  
Farid Alisafaei
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Size Effects ◽  
Indentation Depth ◽  
Second Order ◽  
Indentation Size

Abstract Indentation size effects have been observed in both polymers and metals but, unlike in metals, the origin of size effects in polymers is not well understood. To clarify the role of second order gradients of displacements, a model polymer is examined with spherical and Berkovich tips at probing depths between 5 and 25 μm. Applying different theories to determine the elastic modulus, it is found that with a pyramidal tip, the elastic modulus increases with decreasing indentation depth, while tests with the spherical tip yielded essentially constant values for the elastic modulus independent of indentation depth. The differences between these tips are attributed to second order displacement gradients, as they remain essentially constant with a spherical tip while they increase in magnitude with decreasing indentation depth applying a Berkovich tip.

A study of indentation work in homogeneous materials

2006 ◽  
Vol 21 (6) ◽  
pp. 1363-1374 ◽  
Author(s):  
Mengxi Tan
Keyword(s):  
Plastic Deformation ◽  
Elastic Modulus ◽  
Elastic Energy ◽  
Size Effects ◽  
Unit Volume ◽  
Plastic Work ◽  
Total Work ◽  
Indentation Size ◽  
Scaling Relationships ◽  
Homogeneous Materials

The work of indentation is investigated experimentally in this article. A method of using the elastic energy to extract the elastic modulus is proposed and verified. Two types of hardness related to the work of indentation are defined and examined: Hwtis defined as the total work required creating a unit volume of contact deformationand Hwp is defined as the plastic work required creating a unit volume of plastic deformation; experiments show that both hardness definitions are good choices for characterizing hardness. Several features that may provide significant insights in understanding indentation measurements are studied. These features mainly concern some scaling relationships in indentation measurements and the indentation size effects.

On the Indentation Modulus of Sintered Materials

2013 ◽  
Vol 586 ◽  
pp. 190-193
Author(s):  
Miriam Kupková ◽  
Martin Kupka
Keyword(s):  
Experimental Data ◽  
Indentation Size Effect ◽  
Displacement Curve ◽  
Indentation Modulus ◽  
Indentation Size ◽  
Depth Sensing ◽  
Nano Indentation ◽  
Individual Grains ◽  
Theoretical Results ◽  
Sintered Materials

When the depth-sensing (nano)indentation is applied to sintered samples, measured properties, which are expected to represent the material of an individual grain, seem to depend on the overall porosity of the macroscopic sample. To understand such a result, it is assumed that while the nanoindenter penetrates into the surface grain and probes the properties of its material, the grain itself serves as another, larger indenter indenting the rest of sample and probing the properties that represent the bulk of material rather than individual grains. Load vs. displacement curve reflects the synergetic response of these two “indenters” and so it contains information about the sample’s mechanical properties at both microscopic and macroscopic scales. Obtained theoretical results agree qualitatively with the experimental data (the dependence of the indentation modulus on the porosity of sample; the indentation size effect).

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