Creep characterization of vapor-grown carbon nanofiber/vinyl ester nanocomposites using a response surface methodology

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Corresponding Author: [Sullivan@ae.msstate.edu Rani W. Sulivan, Ph.D.]
 
Corresponding Author: [Sullivan@ae.msstate.edu Rani W. Sulivan, Ph.D.]
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|material model= Use a central composite design of experiments ([[Metamodeling]]) to determine the viscoelastic behavior of vinyl ester nanocomposites.
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<td colspan="2">This methodology has resulted in structures that agree with HRTEM images and grain boundary energies that agree with experimentally-measured grain boundary energies. Figure 3 shows an example plot of the grain boundary energy versus inclination angle for a complex grain boundaries in Cu (Sigma 3 asymmetric grain boundaries). This system of boundaries displays a phase transformation at the boundary to the orthorhombic 9R phase for inclination angles of 70-90 degrees. The methodology used above agrees nicely with experimental results and previous atomistic calculations of Wolf and coworkers.  
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<td colspan="2"> To model the behavioral response of the nanocomposites, creep experiments were performed at varying stress levels and temperatures. The creep strain and compliance were modeled using a Prony series representation in conjunction with the Boltzmann superposition principle (BSP). Creep strains and creep compliances were selected at varying times and modeled using a central composite design of experiments approach. This design of experiments approach allowed for the development of response surface models of the creep compliance and creep strain. These are seen in the images below.
 
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Revision as of 15:00, 1 April 2017

AbstractMethodologyMaterial ModelInput DataResultsAcknowledgmentsReferences

Abstract

Central Composite Design.

TThe effects of selected factors such as vapor-grown carbon nanofiber (VGCNF) weight fraction, applied stress, and temperature on the viscoelastic responses (creep strain and creep compliance) of VGCNF/vinyl ester (VE) nanocomposites were studied using a central composite design (CCD). Nanocomposite test articles were fabricated by high-shear mixing, casting, curing, and post curing in an open-face mold under a nitrogen environment. Short-term creep/creep recovery experiments were conducted at prescribed combinations of temperature (23.8–69.2C), applied stress (30.2–49.8 MPa), and VGCNF weight fraction (0.00–1.00 parts of VGCNF per hundred parts of resin) determined from the CCD. Response surface models (RSMs) for predicting these viscoelastic responses were developed using the least squares method and an analysis of variance procedure. The response surface estimates indicate that increasing the VGCNF weight fraction marginally increases the creep resistance of the VGCNF/VE nanocomposite at low temperatures (i.e., 23.8–46.5C). However, increasing the VGCNF weight fraction decreased the creep resistance of these nanocomposites for temperatures greater than 50C. The latter response may be due to a decrease in the nanofiber-to-matrix adhesion as the temperature is increased. The RSMs for creep strain and creep compliance revealed the interactions between the VGCNF weight fraction, stress, and temperature on the creep behavior of thermoset polymer nanocomposites. The design of experiments approach is useful in revealing interactions between selected factors, and thus can facilitate the development of more physics-based models.

Author(s): Daniel A. Drake, Rani W. Sullivan, Thomas E. Lacy, Charles U. Pittman, Jr., Hossein Toghiani, Janice L. DuBien, Sasan Nouranian, Jutima Simsiriwong

Corresponding Author: [Sullivan@ae.msstate.edu Rani W. Sulivan, Ph.D.]


Figure 1. Stages of Creep. (click on the image to enlarge).

Methodology


Material Model

Use a central composite design of experiments (Metamodeling) to determine the viscoelastic behavior of vinyl ester nanocomposites.

Input Data

{{{input deck}}}

Results

To model the behavioral response of the nanocomposites, creep experiments were performed at varying stress levels and temperatures. The creep strain and compliance were modeled using a Prony series representation in conjunction with the Boltzmann superposition principle (BSP). Creep strains and creep compliances were selected at varying times and modeled using a central composite design of experiments approach. This design of experiments approach allowed for the development of response surface models of the creep compliance and creep strain. These are seen in the images below.
Creep Compliance as a Function of Temperature and VGCNF Weight Fraction.
Creep Strain as a Function of Temperature and VGCNF Weight Fraction.

Acknowledgments

M.A. Tschopp would like to acknowledge funding provided under an NSF graduate fellowship for the initial work. Continued funding for investigating structure-property relationships in grain boundaries under the NEAMS (Nuclear Energy Advanced Modeling and Simulation) program is also acknowledged.

References

The initial methodology was used in the following papers:

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