Nanoindentation Study of Yielding and Plasticity of Poly(methyl methacrylate)

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

doi:10.1021/acs.macromol.5b01064

Cited by 45 publications

(31 citation statements)

References 62 publications

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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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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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“…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: 62%

“…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%

“…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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“…In the case of polymerization processes, the molar mass distribution (MMD) of a polymer is one of the most important quality control variables since many of the polymer end-use properties are directly dependent on the MMD. Some examples include the mechanical properties such as stiffness, strength and viscoelasticity [1][2][3]. Optimal operation in polymerization usually involves computing and accurately maintaining the optimal policies that can lead to a product with desired MMD and final conversion, while minimizing the total operation time.…”

Section: Introductionmentioning

confidence: 99%

Combining On-Line Characterization Tools with Modern Software Environments for Optimal Operation of Polymerization Processes

et al. 2016

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This paper discusses the initial steps towards the formulation and implementation of a generic and flexible model centric framework for integrated simulation, estimation, optimization and feedback control of polymerization processes. For the first time it combines the powerful capabilities of the automatic continuous on-line monitoring of polymerization system (ACOMP), with a modern simulation, estimation and optimization software environment towards an integrated scheme for the optimal operation of polymeric processes. An initial validation of the framework was performed for modelling and optimization using literature data, illustrating the flexibility of the method to apply under different systems and conditions. Subsequently, off-line capabilities of the system were fully tested experimentally for model validations, parameter estimation and process optimization using ACOMP data. Experimental results are provided for free radical solution polymerization of methyl methacrylate.

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Nanoindentation Study of Yielding and Plasticity of Poly(methyl methacrylate)

Cited by 45 publications

References 62 publications

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

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

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

Combining On-Line Characterization Tools with Modern Software Environments for Optimal Operation of Polymerization Processes

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