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.

scholarly journals Investigation on the Influences of Hygrothermal Aging on the Indentation Size Effects and Micro-Indentation Measurements of PMMA. Part I: Experimental Results

2020 ◽  
Vol 10 (16) ◽  
pp. 5454 ◽  
Author(s):  
Hui Lin ◽  
Lin Lv ◽  
Tao Jin
Keyword(s):  
Elastic Modulus ◽  
Aging Time ◽  
Size Effects ◽  
Companion Paper ◽  
Strain Rates ◽  
Indentation Size ◽  
Hygrothermal Aging ◽  
Shear Transformation ◽  
Micro Indentation ◽  
Indentation Strain

The polymethyl methacrylate (PMMA) subjected to hygrothermal aging was applied to nanoindentation tests under different indentation strain rates. The influences of hygrothermal aging on the indentation behaviors of PMMA are discussed. Results show that the indentation elastic modulus and hardness decrease with increasing aging time. Furthermore, the indentation size effects (ISE) can be observed in aged PMMA specimens as they are sensitive to aging time as well as to the indentation strain rate. The quantitative analysis of ISE is proposed on the basis of shear transformation-mediated plasticity and was presented in our companion paper.

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.

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.

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.

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.

Localized Necking in a Round Tensile Bar with HCP Material Considering Tension-Compression Asymmetry in Plastic Flow

2013 ◽  
Vol 535-536 ◽  
pp. 164-167
Author(s):  
Jonghun Yoon ◽  
Oana Cazacu ◽  
Jung Hwan Lee
Keyword(s):  
Yield Criterion ◽  
Matrix Material ◽  
Ductile Failure ◽  
Material Behavior ◽  
Strength Differential ◽  
The Matrix ◽  
Void Evolution ◽  
Hcp Materials ◽  
Spherical Voids ◽  
Tension Compression Asymmetry

In spite of this progress in predicting ductile failure, the development of macroscopic yield criteria for describing damage evolution in HCP (hexagonal close-packed) materials remains a challenge. HCP materials display strength differential effects (i.e., different behavior in tension versus compression) in the plastic response due to twinning. Cazacu and Stewart [1] developed an analytic yield criterion for a porous material containing randomly distributed spherical voids in an isotropic, incompressible matrix that displays tension-compression asymmetry. The matrix material was taken to obey the isotropic form of the Cazacu et al. [2] yield criterion, which captures the tension-compression asymmetry of the matrix material. In this paper, finite element calculations of a round tensile bar are conducted with the material behavior described by the Cazacu and Stewart [1] yield criterion. The goal of these calculations is to investigate the effect of the tension-compression asymmetry on the necking induced by void evolution and propagation.

Plastic Analysis of Metal Sheet Forming with SD Effects

2013 ◽  
Vol 299 ◽  
pp. 216-220
Author(s):  
Zhen Yu Chen ◽  
Chun Du Wu ◽  
Zhong Xian Wang
Keyword(s):  
Shear Stress ◽  
Yield Criterion ◽  
High Strength ◽  
Sheet Forming ◽  
Metal Sheet ◽  
Film Stress ◽  
Strength Differential ◽  
Thin Film Stress ◽  
Plastic Analysis ◽  
Tension And Compression

Generally, many high-strength alloy materials used in aerospace, power and chemical industries have strength differential effect in tension and compression (SD effects). Usually, in mechanical calculations of sheet metal forming, Treasca yield criterion and Mises yield criterion are applied. Because the yield criterions don’t take SD effects into consideration, the calculation result may have errors for certain materials. However, generalized twin shear stress yield criterion, which takes into account the influence of the intermediate principal stress, is more suitable for most metal materials than Mohr-Coulomb strength theory. Therefore, this article has made plastic analysis on thin film stress issues of metal sheet forming with generalized twin shear stress yield criterion. We have obtained a unified plastic solution to the internal and external stretching issue of thin material with rounded holes and different tension and compression ratio. Providing a new result with wider applicability is very significant.

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.

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