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In-situ observations of microscale ductility in a quasi-brittle bulk scale epoxy

Olivier Verschatse (UGent) , Lode Daelemans (UGent) , Wim Van Paepegem (UGent) and Karen De Clerck (UGent)
(2020) POLYMERS. 12(11).
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Abstract
Fiber reinforced composite materials are typically comprised of two phases, i.e., the reinforcing fibers and a surrounding matrix. At a high volume fraction of reinforcing fibers, the matrix is confined to a microscale region in between the fibers (1–200 µm). Although these regions are interconnected, their behavior is likely dominated by their micro-scale. Nevertheless, the characterization of the matrix material (without reinforcing fibers) is usually performed on macroscopic bulk specimens and little is known about the micro-mechanical behavior of polymer matrix materials. Here, we show that the microscale behavior of an epoxy resin typically used in composite production is clearly different from its macroscale behavior. Microscale polymer specimens were produced by drawing microfibers from vitrifying epoxy resin. After curing, tensile tests were performed on a large set of pure epoxy microfiber specimens with diameters ranging from 30 to 400 µm. An extreme ductility was observed for microscale epoxy specimens, while bulk scale epoxy specimens showed brittle behavior. The microsized epoxy specimens had a plastic deformation behavior resulting in a substantially higher ultimate tensile strength (up to 380 MPa) and strain at break (up to 130 %) compared to their bulk counterpart (68 MPa and 8%). Polarized light microscopy confirmed a rearrangement of the internal epoxy network structure during loading, resulting in the plastic deformation of the microscale epoxy. This was further accompanied by in-situ electron microscopy to further determine the deformation behavior of the micro-specimens during tensile loading and make accurate strain measurements using video-extensometry. This work thus provides novel insights on the epoxy material behavior at the confined microscale as present in fiber reinforced composite materials.
Keywords
Scanning Electron Microscopy (SEM), micromechanical testing, microscale, yielding, plasticity, COMPOSITE-MATERIALS, FRACTURE-TOUGHNESS, TENSILE PROPERTIES, STRENGTH, RESIN, POLYMER

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MLA
Verschatse, Olivier, et al. “In-Situ Observations of Microscale Ductility in a Quasi-Brittle Bulk Scale Epoxy.” POLYMERS, vol. 12, no. 11, 2020, doi:10.3390/polym12112581.
APA
Verschatse, O., Daelemans, L., Van Paepegem, W., & De Clerck, K. (2020). In-situ observations of microscale ductility in a quasi-brittle bulk scale epoxy. POLYMERS, 12(11). https://doi.org/10.3390/polym12112581
Chicago author-date
Verschatse, Olivier, Lode Daelemans, Wim Van Paepegem, and Karen De Clerck. 2020. “In-Situ Observations of Microscale Ductility in a Quasi-Brittle Bulk Scale Epoxy.” POLYMERS 12 (11). https://doi.org/10.3390/polym12112581.
Chicago author-date (all authors)
Verschatse, Olivier, Lode Daelemans, Wim Van Paepegem, and Karen De Clerck. 2020. “In-Situ Observations of Microscale Ductility in a Quasi-Brittle Bulk Scale Epoxy.” POLYMERS 12 (11). doi:10.3390/polym12112581.
Vancouver
1.
Verschatse O, Daelemans L, Van Paepegem W, De Clerck K. In-situ observations of microscale ductility in a quasi-brittle bulk scale epoxy. POLYMERS. 2020;12(11).
IEEE
[1]
O. Verschatse, L. Daelemans, W. Van Paepegem, and K. De Clerck, “In-situ observations of microscale ductility in a quasi-brittle bulk scale epoxy,” POLYMERS, vol. 12, no. 11, 2020.
@article{8679816,
  abstract     = {{Fiber reinforced composite materials are typically comprised of two phases, i.e., the reinforcing fibers and a surrounding matrix. At a high volume fraction of reinforcing fibers, the matrix is confined to a microscale region in between the fibers (1–200 µm). Although these regions are interconnected, their behavior is likely dominated by their micro-scale. Nevertheless, the characterization of the matrix material (without reinforcing fibers) is usually performed on macroscopic bulk specimens and little is known about the micro-mechanical behavior of polymer matrix materials. Here, we show that the microscale behavior of an epoxy resin typically used in composite production is clearly different from its macroscale behavior. Microscale polymer specimens were produced by drawing microfibers from vitrifying epoxy resin. After curing, tensile tests were performed on a large set of pure epoxy microfiber specimens with diameters ranging from 30 to 400 µm. An extreme ductility was observed for microscale epoxy specimens, while bulk scale epoxy specimens showed brittle behavior. The microsized epoxy specimens had a plastic deformation behavior resulting in a substantially higher ultimate tensile strength (up to 380 MPa) and strain at break (up to 130 %) compared to their bulk counterpart (68 MPa and 8%). Polarized light microscopy confirmed a rearrangement of the internal epoxy network structure during loading, resulting in the plastic deformation of the microscale epoxy. This was further accompanied by in-situ electron microscopy to further determine the deformation behavior of the micro-specimens during tensile loading and make accurate strain measurements using video-extensometry. This work thus provides novel insights on the epoxy material behavior at the confined microscale as present in fiber reinforced composite materials.}},
  articleno    = {{2581}},
  author       = {{Verschatse, Olivier and Daelemans, Lode and Van Paepegem, Wim and De Clerck, Karen}},
  issn         = {{2073-4360}},
  journal      = {{POLYMERS}},
  keywords     = {{Scanning Electron Microscopy (SEM),micromechanical testing,microscale,yielding,plasticity,COMPOSITE-MATERIALS,FRACTURE-TOUGHNESS,TENSILE PROPERTIES,STRENGTH,RESIN,POLYMER}},
  language     = {{eng}},
  number       = {{11}},
  pages        = {{14}},
  title        = {{In-situ observations of microscale ductility in a quasi-brittle bulk scale epoxy}},
  url          = {{http://doi.org/10.3390/polym12112581}},
  volume       = {{12}},
  year         = {{2020}},
}

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