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Research Papers

Cyclic Viscoplastic-Viscodamage Analysis of Shape Memory Polymers Fibers With Application to Self-Healing Smart Materials

[+] Author and Article Information
Amir Shojaei

Postdoctoral Research Associate
Department of Mechanical Engineering,
Louisiana State University,
Baton Rouge, LA 70803;
Department of Mechanical Engineering,
University College London,
Torrington Place, London WC1E 7JE, UK
e-mail: A.Shojaei.Mech.Eng@gmail.com;
A.Shojaei@ucl.ac.uk

Guoqiang Li

Professor
Department 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

George Z. Voyiadjis

Chair
Bingham C. Stewart Distinguished
Professor of Engineering
Department of Civil and Environmental Engineering,
Louisiana State University,
Baton Rouge, LA 70803
e-mail: Voyiadjis@eng.lsu.edu

1Corresponding author.

Manuscript received December 11, 2011; final manuscript received June 13, 2012; accepted manuscript posted July 16, 2012; published online October 29, 2012. Assoc. Editor: Chad Landis.

J. Appl. Mech 80(1), 011014 (Oct 29, 2012) (15 pages) Paper No: JAM-11-1467; doi: 10.1115/1.4007140 History: Received December 11, 2011; Revised June 13, 2012; Accepted July 16, 2012

The cold-drawn, programmed shape memory polymer (SMP) fibers show excellent stress recovery property, which promotes their application as mechanical actuators in smart material systems. A full understanding of the thermomechanical-damage responses of these fibers is crucial to minimize the trial-and-error manufacturing processes of these material systems. In this work, a multiscale viscoplastic-viscodamage theory is developed to predict the cyclic mechanical responses of SMP fibers. The proposed viscoplastic theory is based on the governing relations for each of the individual microconstituents and establishes the microscale state of the stress and strain in each of the subphases. These microscale fields are then averaged through the micromechanics framework to demonstrate the macroscale constitutive mechanical behavior. The cyclic loss in the functionality of the SMP fibers is interpreted as the damage process herein, and this cyclic loss of stress recovery property is calibrated to identify the state of the damage. The continuum damage mechanics (CDM) together with a thermodynamic consistent viscodamage theory is incorporated to simulate the damage process. The developed coupled viscoplastic-viscodamage theory provides an excellent correlation between the experimental and simulation results. The cyclic loading-damage analysis in this work relies on the underlying physical facts and accounts for the microstructural changes in each of the micro constituents. The established framework provides a well-structured method to capture the cyclic responses of the SMP fibers, which is of utmost importance for designing the SMP fiber-based smart material systems.

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References

Figures

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Fig. 1

Schematic representation of the biomimetic self-healing material system; (a) damaged configuration with a macroscale crack, (b) closed crack configuration due to the stress recovery process of SMP fibers, (c) diffusion of the molten thermoplastic particles (TPs) into the cracked matrix, and (d) healed configuration with magnified view of the crack interface, which shows molecular entanglement of the solidified TPs and thermosetting polymer molecular chains

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Fig. 2

Crystalline microstructure under biaxial loading condition; (a) undeformed body, (b) microcrack formation, and (c) formation of different types of dislocations due to the external loading

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Fig. 3

Amorphous polymeric network under biaxial loading condition; (a) undeformed body, (b) microcrack formation due to breakage of polymer chain, (c) stretched chains after saturation of conformational changes, and (d) conformational changes due to external loading

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Fig. 4

Schematic representation of loading-unloading process of SMP fibers

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Fig. 5

RVE; (a) nonstretched SMP fiber and (b) stretched SMP fiber

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Fig. 6

Semicrystalline morphology; (a) manufacturing-induced spherulite microstructure under isotropic conditions and (b) stress-induced crystallized microstructure

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Fig. 7

Recovery test results for the polyurethane SMP fiber with stain rate of ε·=0.0085 (sec-1) (a) after 150% cyclic tensions and (b) corresponding recoverable strains

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Fig. 8

Recovery test results for SMP fiber with stain rate of ε·=0.017 (sec-1) (a) after 300% cyclic tensions and (b) corresponding recoverable strains

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Fig. 9

Computational modules for the proposed multiscale analysis. A Message Passing Interface (MPI) is shown for parallel programming applications

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Fig. 10

Cyclic loading of SMP fiber with material parameters χ1=0.1 and χ2=1e-3 and loading cycles of ‖Δϵ‖=150% and strain rate of ε·=0.0085 (sec-1)

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Fig. 11

Cyclic loading of SMP fiber with ‖Δϵ‖=300% and strain rate of ε·=0.017 (sec-1)

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Fig. 12

Cyclic evolution of the crystalline axes (0.5,0.5,0.5)

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Fig. 13

Cyclic damage evolution of SMP fiber with loading conditions (a) ‖Δϵ‖=150% and (b) ‖Δϵ‖=300%

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Fig. 14

Experimental demonstration of the macrocrack closure and molecular level of healing for a polymer matrix composite, which is reinforced by the continuous SMP fibers, (a) OM image of a macroscale crack, (b) OM image of the sealed macrocrack, (c) SEM image of the sealed macrocrack interface, and (d) SEM image of the macrocrack interface after melting the TPs (OM and SEM images are after Ref. [87])

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