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 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.

scholarly journals The Correlation of Indentation Size Effect Experiments with Pyramidal and Spherical Indenters

2001 ◽  
Vol 695 ◽  
Author(s):  
J. G. Swadener ◽  
E. P. George ◽  
G. M. Pharr
Keyword(s):  
Size Effect ◽  
Work Hardening ◽  
Size Effects ◽  
Indentation Size Effect ◽  
Experimental Results ◽  
Indentation Size ◽  
Depth Of Penetration ◽  
Wide Range ◽  
Sphere Radius

ABSTRACTExperiments were conducted in annealed iridium using pyramidal and spherical indenters over a wide range of load. For a Berkovich pyramidal indenter, the hardness increased with decreasing depth of penetration. However, for spherical indenters, hardness increased with decreasing sphere radius. Based on the number of geometrically necessary dislocations generated during indentation, a theory that takes into account the work hardening differences between pyramidal and spherical indenters is developed to correlate the indentation size effects measured with the two indenters. The experimental results verify the theoretical correlation.

Study of the Size Effects and Friction Conditions in Microextrusion—Part II: Size Effect in Dynamic Friction for Brass-Steel Pairs

2007 ◽  
Vol 129 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Lapo F. Mori ◽  
Neil Krishnan ◽  
Jian Cao ◽  
Horacio D. Espinosa
Keyword(s):  
Grain Size ◽  
Friction Coefficient ◽  
Size Effect ◽  
Contact Pressure ◽  
Size Effects ◽  
Numerical Models ◽  
Kolsky Bar ◽  
Experimental Results ◽  
Material Response ◽  
Dynamic Coefficients

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material (211μm) showed a tendency to curve, whereas those fabricated from billets having a small grain size (32μm), did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size (32μm) and a large grain size (211μm) at low contact pressure (22MPa) and high contact pressure (250MPa) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

Indentation Size Effect on Hardness of Nanostructured Thin Films

2006 ◽  
Vol 312 ◽  
pp. 363-368 ◽  
Author(s):  
Chun Sheng Lu ◽  
Yiu Wing Mai ◽  
Yao Gen Shen
Keyword(s):  
Thin Films ◽  
Plastic Deformation ◽  
Grain Boundary ◽  
Size Effect ◽  
Indentation Depth ◽  
Indentation Size Effect ◽  
Indentation Size ◽  
Nanostructured Thin Films ◽  
Measured Hardness

Based on nanoindentation techniques, the evaluation of hardness of two nanostructured thin films, AlN and Ti-Al-N, is discussed. In the case of AlN films, the indentation size effect of hardness can be modeled using the concept of geometrically necessary dislocations, whereas in the case of Ti-Al-N films, the measured hardness increases exponentially as the indentation depth decreases. The results show that, as thin films approach superhard, dislocation-based plastic deformation is gradually replaced by grain-boundary mediated deformation.

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.

Indentation Size Effects in Ductile and Brittle Materials

2013 ◽  
Vol 586 ◽  
pp. 51-54
Author(s):  
Jaroslav Menčík ◽  
Martin Elstner
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Indentation Size Effect ◽  
Brittle Materials ◽  
Indentation Hardness ◽  
Indentation Size ◽  
Homogeneous Materials

Indentation hardness of homogeneous materials should be constant. However, at very small depths, the apparent hardness often increases with decreasing imprint size. The paper discusses various cases of this indentation size effect in metals and ceramics and explains the extrinsic and intrinsic reasons.

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.

YUKAWA CORRECTIONS TO THE NEWTONIAN GRAVITATIONAL POTENTIAL: FINITE SIZE EFFECTS IN A RECENT EXPERIMENT

2011 ◽  
Vol 26 (22) ◽  
pp. 3742-3751 ◽  
Author(s):  
C. R. JAMELL ◽  
R. S. DECCA
Keyword(s):  
Size Effect ◽  
Gravitational Potential ◽  
Size Effects ◽  
Recent Experiment ◽  
Finite Size ◽  
Experimental Results ◽  
Finite Size Effect ◽  
Finite Size Effects ◽  
Yukawa Term

We provide a formalism to calculate the effect of the finite size of the sample on hypothetical Yukawa-like corrections to the Newtonian gravitational potential. It is explicitly shown that finite size effect contributions are negligible when the extent of the sample is larger than the range of the Yukawa term. In particular we show that these contributions are small in the configuration of a recent experiment. In the experiment a gold coated sphere was moved across the interface between two materials with different mass densities. In view of these new experimental results, we analyze the situation when the error on the hypothetical correction could result to be significant.

Nanoindentation Size Effects for Calcium Silicate Hydrate

2010 ◽  
Vol 177 ◽  
pp. 537-540
Author(s):  
Wu Yao ◽  
Kang Liang
Keyword(s):  
Size Effect ◽  
Size Effects ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Indentation Size Effect ◽  
High Density ◽  
Nanoindentation Test ◽  
Low Density ◽  
Indentation Size ◽  
Basic Composition

Hardness of Calcium Silicate Hydrate (CSH) at different ages was measured by nanoindentation test. The results show obvious indentation size effect in hardness of CSH. Hardness decreases with increasing depth. Moreover, both low density CSH and high density CSH follow the same size effect law in hardness. This phenomenon further indicates that two types of CSH are of the same basic composition but different packing densities.

Nanomechanical Characterization on Zinc and Tin Oxides Nanobelts

2002 ◽  
Vol 740 ◽  
Author(s):  
Minhua Zhao ◽  
Scott Mao ◽  
Zhong Lin Wang ◽  
Fengting Xu ◽  
John A Barnard
Keyword(s):  
Size Effect ◽  
Cross Section ◽  
Indentation Depth ◽  
Indentation Size Effect ◽  
Indentation Size ◽  
Tin Oxides

ABSTRACTNanobelts are a group of materials that have a rectangle-like cross section with typical widths of several hundred nanometers, width-to-thickness ratios of 5 to 10, and lengths of hundreds of micron meters. In this paper, nanoindentations were made on individual ZnO, SnO2 nanobelts and (0001) bulk ZnO by using AFM and Hysitron Triboscope indenters. It was shown that the indentation size effect was still obvious for the indentation depth under 50 nm. It is also demonstrated that nanomaching is possible on nanobelt using AFM tip.

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