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Research Papers

Thermoviscoplastic Modeling and Testing of Shape Memory Polymer Based Self-Healing Syntactic Foam Programmed at Glassy Temperature

[+] Author and Article Information
Wei Xu, Guoqiang Li

Department of Mechanical Engineering,  Louisiana State University, Baton Rouge, LA 70803Department of Mechanical Engineering,  Louisiana State University, Baton Rouge, LA 70803;  Department of Mechanical Engineering, Southern University, Baton Rouge, LA 70813 e-mail: guoli@me.lsu.edu

J. Appl. Mech. 78(6), 061017 (Aug 25, 2011) (14 pages) doi:10.1115/1.4004554 History: Received October 19, 2010; Revised April 24, 2011; Posted July 11, 2011; Published August 25, 2011; Online August 25, 2011

Traditionally, programming of shape memory polymer (SMP) material requires initial heating above the glass transition temperature (Tg ), subsequent cooling below Tg and removal of the applied load. Therefore, the shape fixity process is inconvenient for some applications. Most recently, a new and effective approach, which programs glass transition activated SMPs directly at temperatures well below Tg ,was introduced by Li and Xu [2011, “Thermomechanical Behavior of Shape Memory Polymer Programmed at Glassy Temperature: Testing and Constitutive Modeling,” J. Mech. Phys. Solids, 59 (6), pp. 1231–1250. The 1D compression programming below Tg and free shape recovery were extensively investigated both experimentally and analytically. The current work extends this study into a shape memory polymer based self-healing syntactic foam, which was found to be capable of self-sealing structural scale damage repeatedly, efficiently, and almost autonomously [Li and John, 2008, “A Self-Healing Smart Syntactic Foam Under Multiple Impacts,” Compos. Sci. Technol., 68 (15–16), pp. 3337–3343.]. A structural-relaxation constitutive model featuring damage-allowable thermoviscoplasticity was then developed to predict the nonlinear shape memory behavior of the SMP based syntactic foam programmed at glassy temperatures. After validated by both 1D (compression) and 2D (compression in longitudinal direction and tension in transverse direction) tests, the constitutive model was used to evaluate the effects of several design parameters on the thermomechanical behavior of the SMP based syntactic foam. It is concluded that the model is a useful tool for designing and training this novel self-healing composite.

Copyright © 2011 by American Association of Physics Teachers
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References

Figures

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Figure 1

An illustration of the four-step thermomechanical cycle [programming (Step 1–Step 3) and shape recovery (Step 4)]

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Figure 2

DMA results for the SMP based syntactic foam and the pure SMP

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Figure 3

XPS spectra of the (a) the electron C (1s), pure SMP and the SMP based syntactic foam for (b) the electron O (1s)

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Figure 4

Strain-time response during the entire thermomechanical cycle for specimens programmed with (a) 30% prestrain and (b) 20% prestrain (the four steps shown in the figure are for the curve with 120 min of stress relaxation time.)

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Figure 5

Viscoelastic behavior of the foam by creep test at room temperature

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Figure 6

SEM observation of (a) pristine specimen and (b) specimen after 30% cold-compression programming

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Figure 7

Thermo-mechanical cycle in terms of (a) stress-strain-time and (b) stress-strain-temperature responses for different stress relaxation time with a prestrain level of 30% and 20%

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Figure 8

Equivalent scheme for the SMP matrix

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Figure 9

An analogous decomposition scheme for the deformation gradient

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Figure 10

An arbitrary nonlinear damage model with its linear equivalence

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Figure 11

A linear rheological illustration for stress response

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Figure 12

Comparison of numerical simulation with experimental results for the full thermomechanical cycle (a) strain evolution with 30% prestrain, (b) strain evolution with 20% prestrain, and (c) thermomechanial cycle in terms of stress-strain-time response

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Figure 13

Comparison of numerical simulation with test results for a 2D traditional thermomechanical cycle [27]

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Figure 14

Thermomechanical cycle results for specimen with different Φp

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Figure 15

Thermomechanical cycle results for specimens with different w

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Figure 16

Thermal response to a stress-free natural cooling

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Figure 17

Stress-strain response of the SMP based syntactic foam at various temperatures

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Figure 18

Stress-strain response of the SMP based syntactic foam at different strain rates

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Figure 19

Thermal response for a stress-free constant-rate heating

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