Size Dependent Hardness of Polyamide/Imide

Tatiraju, Ramajaneyulu V.S.; Han, Cheol E.; Nikolov, S.

doi:10.2174/1874158400802010089

Cited by 21 publications

(14 citation statements)

References 13 publications

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“…Such behavior is well known and widely observed in other material tests such as simple tensile tests [Lemaitre and Chaboche 1990]. The values in Figure 3, however, also show a decrease of η e with decreasing h, and therefore the dissipation of the indentation work increases with decreasing h. Similar tendencies have also been observed in other polymers [Briscoe et al 1998;Tatiraju et al 2008]. The magnitude with which η e decreases is more pronounced at shorter loading times.…”

Section: Indentation Experimentssupporting

confidence: 82%

Rate dependence of indentation size effects in filled silicone rubber

Tatiraju

Han

2010

JOMMS

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Indentation experiments at the nanometer and micrometer range reported in the literature have shown that the deformation of polymers is -similarly to metals -size-dependent. In addition its size dependence, the deformation behavior of polymers is also known to be rate-dependent. Here silicone rubber is considered. In order to characterize the relation between size and rate-dependent deformation indentation tests of silicone at indentation depths of between 30 and 300 microns and loading times of between 1 and 1000 seconds are performed. In these experiments the hardness and dissipation increased with decreasing loading time and decreasing indentation depth. These experimental results are analyzed with a recently suggested indentation model which incorporates a Frank energy-related nonlocal deformation work. It is found that the indentation model is in good agreement with the experimental data. Evaluation of the experimental data indicates that the rate effects are mostly related to the nonlocal, size-dependent deformation.

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Section: Indentation Experimentssupporting

confidence: 82%

Rate dependence of indentation size effects in filled silicone rubber

Tatiraju

Han

2010

JOMMS

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“…Depth sensing indentation testing has been widely applied to determine hardness, elastic modulus, as well as to study deformation mechanisms at micro-and nanometer length scales. Numerous indentation experiments conducted on metals [1][2][3] and polymers [4][5][6][7][8][9][10][11][12][13][14][15][16] demonstrated that the hardness is significantly higher at small probing depths. In [11,13,17] the length scale dependence in polymers has been experimentally observed in elastic deformation, which is in contrast to metals, where length scale effects were observed in plastic deformation and usually attributed to geometrically necessary dislocations [2].…”

Section: Introductionmentioning

confidence: 99%

“…In [11,13,17] the length scale dependence in polymers has been experimentally observed in elastic deformation, which is in contrast to metals, where length scale effects were observed in plastic deformation and usually attributed to geometrically necessary dislocations [2]. Although there is mounting experimental evidence for size effects in polymers [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], compared to metals, length scale dependent deformation in polymers is arguably not well understood and there are only few length scale dependent theories suggested in the literature [5,6,21,22] for polymers.…”

Section: Introductionmentioning

confidence: 99%

Length scale dependence in elastomers – comparison of indentation experiments with numerical simulations

Garg

Han

Alisafaei

2016

Polymer

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Probing depth dependent deformation at nano-and micrometer length scales has been observed in indentation experiments of polymers. Unlike in metals, where size effects are observed in plastic deformation and are attributed to geometrically necessary dislocations, the origin of size dependence in polymers is not well understood. As classical continuum theories are unable to describe such phenomena, higher order gradient theories have been developed to capture such size dependent deformation behavior. The present study adopts the penalty finite element approach for a couple stress elasticity theory under axisymmetric conditions to numerically simulate and analyze the probing depth dependent deformation. Polydimethylsiloxane (PDMS) and natural rubber have been used as model materials to analyze the depth dependent deformation at different probing depths. Simulations were performed on PDMS using spherical indenter tips of different radii to show the influence of strain/rotation gradients on elastic modulus. To capture the experimentally observed increase in hardness with decreasing probing depth, simulations applying a conical indenter tip were performed and compared with experimental data.

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“…What we observed, however, appears at best weak effects whereas there are obvious difference in the pressure beneath the tips. Further the gradient elasticity approach of Han and co workers suggest no depth dependence for the spherical geometry and for the wedge tip geometry which is a cylindrical shape. Hence, while one might expect a tip effect on absolute modulus values at a given depth, the sphere and wedge shapes should not show depth dependence.…”

Section: Discussionmentioning

confidence: 96%

“…One recent proposal for depth-dependent moduli comes from the idea of a strain gradient elasticity [58][59][60][61][62][63], for which the Berkovich tip seems to exhibit a very large effect in soft materials. Hence, a Berkovich indenter was also used to probe the mechanical properties of the PETN single crystals.…”

Section: Indentation Measurements With the Berkovich Shaped Tipmentioning

confidence: 99%

Mechanical properties of pentaerythritol tetranitrate(PETN) single crystals from nano‐indentation: Depth dependent response at the nano meter scale

Zhai

McKenna

2016

Crystal Research and Technology

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The current work presents the results from an investigation of the mechanical behavior of single crystals of the energetic material pentaerythritol tetranitrate (PETN) using a nano‐indentation technique. The indentation tests have been performed on the maximum growth habit face (110) of the PETN, using a spherical, Berkovich and an anisometric (wedge‐shaped) tip. The load displacement curves along with analysis have been used to extract the mechanical properties and identify the anisotropic indentation modulus for the PETN. The indentation moduli of the PETN single crystal were found to decrease as indentation depth increases and become independent of indentation depth for depths greater than 200 nm for the spherical indenter and 300 nm for the anisometric wedge indenter and Berkovich tip. The indentation modulus obtained from spherical tip indentation is compared with the results calculated by using literature values of the elastic constants. The wedge indenter measurements and Berkovich indentation at various tip orientations are different due to the anisotropy of the PETN. The yield behaviors of the PETN single crystal were also explored using both spherical and wedge tip indentation and the differences are discussed.

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Size Dependent Hardness of Polyamide/Imide

Cited by 21 publications

References 13 publications

Rate dependence of indentation size effects in filled silicone rubber

Rate dependence of indentation size effects in filled silicone rubber

Length scale dependence in elastomers – comparison of indentation experiments with numerical simulations

Mechanical properties of pentaerythritol tetranitrate(PETN) single crystals from nano‐indentation: Depth dependent response at the nano meter scale

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