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RESEARCH PAPERS

Polycarbonate and a Polycarbonate-POSS Nanocomposite at High Rates of Deformation

[+] Author and Article Information
A. D. Mulliken

Department of Mechanical Engineering,  Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 1-304, Cambridge, MA 02139

M. C. Boyce1

Department of Mechanical Engineering,  Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 1-304, Cambridge, MA 02139mcboyce@mit.edu

1

Corresponding author.

J. Eng. Mater. Technol 128(4), 543-550 (Apr 21, 2006) (8 pages) doi:10.1115/1.2345446 History: Received August 15, 2005; Revised April 21, 2006

Polymeric materials are known to exhibit strong time-dependent mechanical behavior, as evidenced by rate-dependent elastic moduli, yield strength, and post-yield behavior. The nature of the rate sensitivity is found to change between different temperature regimes as various primary (α) and secondary (β, γ, etc.) molecular mobility mechanisms are accessed. The ability to tailor these molecular-level mechanics through the incorporation of nanoscale particles offers new opportunities to design polymer-based material systems with different behaviors (elastic, yield, post-yield) in different frequency∕rate regimes. In this study, the macroscopic rate-dependent mechanical behavior of one particular polymer nanocomposite—polycarbonate compounded with TriSilanolPhenyl-POSS® particles—is compared with that of its homopolymer counterpart. The experimental and theoretical techniques follow those established in previous research into the rate-dependent mechanical behavior of amorphous homopolymers over a wide range of strain rates. On the experimental side, dynamic mechanical analysis tension tests were used to characterize the viscoelastic behavior of these materials, with focus on the rate-dependent shift of material transition temperatures. Uniaxial compression tests on a servohydraulic machine (103s1to0.3s1) and an aluminum split-Hopkinson pressure bar (1000s1to3000s1) were used to characterize the rate-dependent yield and post-yield behavior. The behaviors observed in these experiments were then interpreted within the theoretical framework introduced in previous work. It is concluded that, for this particular material system, the POSS has little influence on the polycarbonate α regime. However, the POSS clearly enhances the mobility of the β motions, significantly reducing the resistance to high rate elastic and plastic deformation. Furthermore, it is shown that the continuum-level constitutive model framework developed for amorphous homopolymers may be extended to this polymer nanocomposite material system, simply by accounting for the reduced deformation resistance in the β process.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 8

PC and PC-POSS nanocomposite true stress-true strain behavior at low (10−3s−1) and high (∼2400s−1) strain rates. Reported high strain rates are approximate averages over the course of the tests.

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Figure 9

PC and PC-POSS nanocomposite true yield stress as a function of strain rate (logarithmic scale); low to high strain rates, model versus experiment. The model-predicted yield curves are developed from discrete predictions spaced at semidecade intervals.

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Figure 10

PC-POSS nanocomposite true stress-true strain behavior in uniaxial compression at low, moderate, and high strain rates: model prediction (dotted lines) and experiment (solid lines).

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Figure 1

(a) PC storage modulus and loss tangent as a function of temperature at 3.2×10−3s−1(1Hz). (b) Predicted PC storage modulus as a function of temperature at four strain rates.

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Figure 2

A one-dimensional rheological interpretation of the Mulliken and Boyce constitutive model for amorphous polymers.

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Figure 3

PC true stress-true strain behavior (a) and yield behavior (b) in uniaxial compression at low, moderate, and high strain rates; model prediction and experiment (data from (33)). Model-predicted yield curve in (b) is developed from discrete predictions spaced at semidecade intervals.

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Figure 4

TriSilanolPhenyl-POSS: C42H38O12Si7 (www.hybridplastics.com)

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Figure 5

PC and PC-POSS nanocomposite storage modulus as a function of temperature at 1Hz (average strain rate of 10−3s−1)

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Figure 6

PC and PC-POSS nanocomposite loss tangent in the region of the β transition; 1, 10, and 100Hz

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Figure 7

PC-POSS nanocomposite true stress-true strain behavior at four low, moderate, and high strain rates. The reported high strain rate is an approximate average over the course of the test.

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