Characterizing shear transformation zones in polycarbonate using nanoindentation

Samadi-Dooki, Aref; Malekmotiei, Leila; Voyiadjis, George Z.

doi:10.1016/j.polymer.2015.11.049

Cited by 36 publications

(16 citation statements)

References 48 publications

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“…It is also worth noting that the material pile‐up around the indenter can alter the contact area and affect the measured hardness especially at shallow depths of the indentation. The calculated hardness in Figure is obtained from the direct measurement of the indentation strain rate (

\dot{h} / h true)

, therefore is not affected by the pile‐up, while the measured hardness in this figure could be affected by the pile‐up. Hence, another contributing parameter for the discrepancy of the calculated and measured hardness could be the pile‐up of the material around the tip.…”

Section: Resultsmentioning

confidence: 88%

“…Since the yield behavior of the rate dependent materials like polymers is highly dependent on the applied strain (loading) rate, one expects the higher value of hardness (which is proportional to yield stress) at shallow indentation depths where the strain rate is higher. Figure shows the variation of the hardness during the nanoindentation of PC and PMMA at three different set

\dot{P} / P

values.…”

Section: Resultsmentioning

confidence: 99%

“…Based on the authors' previous studies (and many other articles), the yield stress (or hardness) of glassy polymers varies linearly with the logarithm of the strain rate. Based on the authors' nanoindentation evaluation, explicit relations have been obtained for this variation for PC and PMMA.…”

Section: Resultsmentioning

confidence: 99%

“…A short summary on sample preparation is given in this part; for details readers are referred to the authors' previous studies on poly(methyl methacrylate) (PMMA) and polycarbonate (PC) . The glassy polymers used in this investigation are commercially produced (Goodfellow, Cambridge, U.K.) PMMA and PC, 2.0 and 5.0 mm‐thick sheets, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…Since time related parameters such as loading and strain rates can be easily adjusted in the nanoindentation experiments, the effect of their variations on the mechanical response of time dependent materials like polymers has been investigated in numerous studies . However, the heterogeneity of the induced stress and strain fields in the material due to the loading by a self‐similar tip necessitates a closer look at the strain (loading) rate variation during the indentation.…”

Section: Introductionmentioning

confidence: 99%

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Variation of the strain rate during CSM nanoindentation of glassy polymers and its implication on indentation size effect

Voyiadjis

Malekmotiei

2016

J. Polym. Sci. Part B: Polym. Phys.

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The indentation strain rate is currently assumed to remain unvaried during continuous stiffness measurement (CSM) nanoindentation where _ P =P is imposed to remain constant. To probe the validity of this assumption for the nanoindentation of glassy polymers, a series of experiments have been performed at different set _ P =P values on poly(methyl methacrylate) and polycarbonate using CSM technique. It is firstly shown that the actual _ P =P value changes drastically at shallow indentation depths and it takes a considerable depth, which is material independent, for this parameter to attain a stabilized value. Furthermore, the strain rate is measured directly as the descent rate of the indenter divided by its instantaneous depth ( _ h=h), and indirectly via considering the variations of the load and hardness during the test. Both of these approaches reveal that the strain rate is considerably larger at shallow depths, and the depth beyond which it becomes constant is material and _ P =P ratio dependent. Finally, by considering the relationship between the hardness and strain rate, it is observed that although the strain rate variation alters the hardness, its contribution is not able to justify the observed indentation size effect; hence, other contributing factors for this phenomenon are discussed for their possible effects.

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\dot{h} / h true)

Section: Resultsmentioning

confidence: 88%

\dot{P} / P

values.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Variation of the strain rate during CSM nanoindentation of glassy polymers and its implication on indentation size effect

Voyiadjis

Malekmotiei

2016

J. Polym. Sci. Part B: Polym. Phys.

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Mechanical test and friction‐mapping on recycled polypropylene beads using atomic force microscopy

Koç

Çağlayan

2021

Microscopy Res & Technique

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Mechanical tests at sub‐micron scales using force microscopy are often used for the characterization of materials. Here we report the mechanical, tribologic, and morphological characterization of recycled polypropylene beads using force spectroscopy and lateral‐force microscopy. The compression‐elastic moduli calculated using the Hertzian model for polypropylene beads was between 0.448 ± 0.010 and 1.044 ± 0.057 GPa. The grain size analysis revealed a significant correlation between the grain size and measured compression‐elastic moduli. Friction‐maps of recycled polypropylene beads obtained using lateral‐force microscopy were also reported for 25 μm2 scanning areas.

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Effect of annealing temperature on interrelation between the microstructural evolution and plastic deformation in polymers

Malekmotiei

Voyiadjis

Samadi-Dooki

et al. 2017

J. Polym. Sci. Part B: Polym. Phys.

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The mechanical loading induced flow of glassy polymers is triggered by the nucleation of shear transformation units, and strongly depends on the initial microstructural state of the material. Therefore, investigation of the possible relationship between the microstructural state variables and plastic deformation is required for a better understanding of the macroscopic response of this class of materials during large deformation. In this study, free volume content is considered as a state variable and thermal treatment is selected as a process through which the accelerated and forced evolution of the free volume can be imposed. For two well-known glassy polymers, poly(methyl methacrylate) and polycarbonate, the free volume content alteration upon annealing is monitored via positron annihilation spectroscopy, and the changes of the micro-and macromechanical properties are also obtained by utilizing nanoindentation technique and employing the homogeneous amorphous flow theory. The correlation between the microstructural state variable, that is, free volume, and the micromechanical state variable, that is, shear activation volume, is then investigated. The results reveal opposite direction of alterations of free volume and shear activation volume with annealing temperature. Accordingly, the possibility of the existence of an interrelation between these two state variables is critically discussed.

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Characterizing shear transformation zones in polycarbonate using nanoindentation

Cited by 36 publications

References 48 publications

Variation of the strain rate during CSM nanoindentation of glassy polymers and its implication on indentation size effect

Variation of the strain rate during CSM nanoindentation of glassy polymers and its implication on indentation size effect

Mechanical test and friction‐mapping on recycled polypropylene beads using atomic force microscopy

Effect of annealing temperature on interrelation between the microstructural evolution and plastic deformation in polymers

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