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Dissertation - CI ZHANG.pdf (3.85 MB)

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ELECTROMECHANICAL DEFORMATION AND FAILURE OF LAYERED POLYMERIC FILMS

Zhang, Ci
http://orcid.org/0000-0002-7646-2274
http://rave.ohiolink.edu/etdc/view?acc_num=case1600528144785256

Abstract Details

2021, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science and Engineering.
This study focused on the investigation of electromechanical deformation and failure of monolithic and multilayered polymeric films when subjected to an instantaneous voltage using a needle-plane electrode setup. The first and the second chapters concentrated on the electromechanical deformation on monolithic films, including polycarbonate (PC), poly (vinylidene fluoride (PVDF), polystyrene (PS), polypropylene (PP) and high-density polyethylene (HDPE). The third chapter focused on the effect of layer thickness on the electromechanical deformation of PC/PVDF multilayered films. The strong effect of scaling, layer thickness, was elucidated on the complex damage mechanisms. In Chapter One, electrically induced mechanical stress was applied on monolithic PC films. Three different experimental methods were used to investigate the electrically induced mechanical deformation on the glassy PC film, namely, morphological observation, energy loss analysis, and dielectric hysteresis. The PC film exhibited reversible elastic behavior at electric field below 200 MV/m, showing no indentation on the film surface. When the field was above 200 MV/m, an irreversible spherical indentation was created at the needle tip. Subsequent thermal annealing of the deformed film revealed a recoverable “delayed elastic” and an irreversible “plastic” deformation. A three-stage mechanism was proposed based on these experimental results, which includes the correlation between the energy loss and the deformed volume. Chapter Two investigated the electromechanical deformation on other polymers and compared with PC. The additional amorphous materials, PS, and two semi-crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar onset of observable deformation. However, PVDF, having a dielectric constant of 12.0, showed an onset at very low electric field. The depth and diameter of the deformation for all polymers increased with increasing electric field. Thermal annealing of the deformed films again revealed a recoverable “delayed elastic” component and an irreversible “plastic” component. The correlation of the energy loss with deformed volume for amorphous and semi-crystalline polymers was also determined. In Chapter Three, layer thickness was found to have a significant effect on the irreversible electromechanical deformation and the failure mechanism in polycarbonate (PC)/poly (vinylidene fluoride) (PVDF) multilayered films. Three distinct regions of behavior were observed. Region I comprised thick layer systems that exhibited only irreversible center deformation. The improvement to failure resistance compared to the monolithic films was attributed to the interphase between the two components. Region II films with an intermediate layer thickness showed both irreversible center deformation and the unique surface treeing mechanism which occurred simultaneously. It was suggested that the two dimensional treeing mechanism, similar to the lightning phenomena in nature, occurs only at impact rates. The tree morphology showed large amounts of ploughing, indicating that this damage mechanism dissipates a large amount of energy prior to electromechanical fracture of the film. Region III films which comprise ultrathin layers in the nanoscale showed no treeing. The unique interphase region between these ultrathin layers was estimated to be at least ten percent of the overall layered structure. When the layer thickness decreased into the nanoscale region, interactive craze array was observed instead of single craze. These films with ultra thin layers behaved similar to monolithic materials with improved electromechanical failure characteristics.
Eric Baer (Committee Chair)
Lei Zhu (Committee Member)
Gary Wnek (Committee Member)
Ya-Ting Liao (Committee Member)
155 p.
Materials Science; Plastics; Polymers
delayed elastic deformation; electromechanical behavior; energy dissipation; plastic deformation; multilayered films; dielectric constant; treeing pattern; fracture initiation

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Citations

  • Zhang, C. (2021). ELECTROMECHANICAL DEFORMATION AND FAILURE OF LAYERED POLYMERIC FILMS [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1600528144785256

    APA Style (7th edition)

  • Zhang, Ci. ELECTROMECHANICAL DEFORMATION AND FAILURE OF LAYERED POLYMERIC FILMS. 2021. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1600528144785256.

    MLA Style (8th edition)

  • Zhang, Ci. "ELECTROMECHANICAL DEFORMATION AND FAILURE OF LAYERED POLYMERIC FILMS." Doctoral dissertation, Case Western Reserve University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1600528144785256

    Chicago Manual of Style (17th edition)

case1600528144785256
238
© 2021, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.