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

Han, Cheol E.; Sanei, Seyed Hamid Reza; Alisafaei, Farid

doi:10.1515/polyeng-2015-0030

Cited by 47 publications

(32 citation statements)

References 44 publications

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“…Therefore, strain/rotation gradient based models [22e23] would not predict h dependence in the hardness. It has been also experimentally observed that applying such a spherical tip, rotation gradients essentially do not change with h [37]. In Fig.…”

Section: Influence Of Rotation Gradients On the Depth Dependent Deformentioning

confidence: 61%

Characterization of indentation size effects in epoxy

2014

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Section: Influence Of Rotation Gradients On the Depth Dependent Deformentioning

confidence: 61%

Characterization of indentation size effects in epoxy

2014

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“…Indentation testing has been widely applied to characterize and determine properties of materials at nano-to micrometer length scales [1][2][3][4][5][6][7][8][9][10][11][12]. The deformation mechanisms and behavior at these length scales can be significantly different compared to those at the macroscopic length scale, and nanoindentation testing has been a vital tool to unravel these differences.…”

Section: Introductionmentioning

confidence: 99%

Length scale effects in epoxy: The dependence of elastic moduli measurements on spherical indenter tip radius

Chandrashekar

Han

2016

Polymer Testing

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Significant increases in the measured elastic moduli with decreasing indentation depth have been previously found in various polymers by indentation tests with a Berkovich tip at micro-to nanometer length scales. These increases in the determined elastic moduli were related to second order displacement gradients which increase with decreasing depth when a conical tip is applied.When a spherical tip is applied, such depth dependence should not be present as the second order displacement gradients remain essentially unchanged with indentation depth. However, these gradients should be proportional to the radius of the spherical tip. To examine the notion of second order displacement gradient dependence in measurements of elastic moduli, indentation experiments are conducted on epoxy with spherical tips of different nominal radii. Accounting for tip imperfections, an increase in the determined elastic moduli is found with decreasing tip radius, which corroborates the notion of second order displacement gradient dependence. 250 µm nominal radii. To address tip imperfections, the tips are examined with fused silica as a reference material. The results of these experiments are discussed in view of other possible factors and interpretations. Experiments Sample preparationEpoxy samples were prepared by mixing the commercially available liquid epoxy resin, EPON 828 (bisphenol A-epichlorohydrin), as base agent with the curing agent EPIKURE 3223, diethylenetriamine (DETA). The epoxy resin (Momentive Specialty Chemicals, USA) and DETA (Momentive Specialty Chemicals, USA) were used in the sample preparation following a procedure identical to that followed in [10], except that a curing agent content of 9 phr (parts per hundred resin) was used in the sample preparation, as opposed to 20 phr. Indentation testingThe indentation experiments were conducted at room temperature of about 23 o C with spherical tips of 3, 10, 50 and 250 µm nominal radii on an Agilent G200 nanoindenter system equipped with XP and DCM heads. The 3, 10 and 50 µm radii tips were purchased from SYNTON-MDP AG (Nidau, Switzerland) and the 250 µm tip was purchased from Micro Star Tech (Huntsville, TX, USA). The 3 µm radius tip was mounted on the DCM head and the other three tips on the XP head. The XP and DCM heads have load limits of 500 mN and 30 mN, respectively, which correspondingly limit the maximum indentation depth. The indentation experiments were conducted in two stages: 1) Tip imperfection study using fused silica as the reference material.2) Determination of elastic moduli of the epoxy sample.

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“…, a large indentation recovery occurs in LNKCP glass during unloading above T g compared with LP glass. Such recovery is unusual indentation behavior in oxide glasses, although it is known from organic glasses …”

Section: Discussionmentioning

confidence: 94%

“…Such recovery is unusual indentation behavior in oxide glasses, although it is known from organic glasses. [20][21][22] The P-h curves of LNKCP glass at 493-523 K and LP glass at 613 K were analyzed with the viscous-elastic-plastic (VEP) model, 19 which describes the sharp indentation behavior of time-dependent materials. Figure 4 shows a schematic illustration of the model.…”

Section: Discussionmentioning

confidence: 99%

Unusual Indentation Behavior of Alkali Metaphosphate Glass Above Glass Transition Temperature

et al. 2016

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The mixed alkali metaphosphate glass 12.5Li2O–12.5Na2O–12.5K2O–12.5Cs2O–50P2O5 (mol%) compressed under uniaxial stress shows unusually large recovery of its shape during heating above its glass transition temperature (Tg). To clarify the mechanism, the viscous, elastic, and plastic behavior of the metaphosphate glass was investigated with the depth‐sensing indentation method. From the load‐displacement (P–h) curves of the glass, a large recovery of the depth displacement was found during unloading above Tg. By analyzing the P–h curves with a viscous–elastic–plastic model, the large recovery was concluded to be due to larger elastic deformation than viscous deformation even above Tg. The phenomenon can be attributed to relaxation to the randomly oriented ‐P–O–P– chain structure from the oriented chain structure formed under stress in the metaphosphate glass.

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

Cited by 47 publications

References 44 publications

Characterization of indentation size effects in epoxy

Characterization of indentation size effects in epoxy

Length scale effects in epoxy: The dependence of elastic moduli measurements on spherical indenter tip radius

Unusual Indentation Behavior of Alkali Metaphosphate Glass Above Glass Transition Temperature

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