Birefringence change in epoxy glass aged under strain

Kawakami, Hiroshi; Kishimoto, Keiji; Nanzai, Yukuo; Sato, Yoshihiro

doi:10.1016/j.jnoncrysol.2006.02.179

Cited by 3 publications

(3 citation statements)

References 7 publications

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“…However, the progress of the structural relaxation seems to be slower in sample C than in sample L, as shown in Figure 5. Such a result agrees with an experimental result from a previous study in which a change in birefringence was measured in the course of strain aging 14…”

Section: Discussionsupporting

confidence: 92%

“…The stress value at the lower yielding point (σ yl ), on the other hand, showed a different evolution: the σ yl value for C specimens increased with the aging duration, whereas for L specimens, the σ yl value was almost constant and was about the same as that of the annealed specimen. The increase in σ yl for sample C was attributed to the following phenomenon: in the crosslinked amorphous polymers, the restriction of rotational motions of the main chains increased with the progression of strain aging 14…”

Section: Resultsmentioning

confidence: 97%

“…In other words, plastic strain and strain energy become hardly frozen in the glassy structure in the course of structural relaxation under the state of strain aging. Such a structural relaxation can be rotation of side groups, which is the major change taking place in epoxy glass aged under strain 14. As a result of the freeze‐strain phenomenon, the σ yu value increases with the aging duration.…”

Section: Discussionmentioning

confidence: 99%

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Changes in the thermomechanical behavior of epoxy glasses under the state of strain aging

Kawakami

Watanabe

2007

J of Applied Polymer Sci

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Changes in thermomechanical behavior with structural relaxation taking place in epoxy glasses were studied. Differential scanning calorimetry measurements and thermostimulated strain recovery tests were performed for specimens deformed and then aged under fixed strain. In the course of heating, the specimens started to absorb thermal energy, whereas plastic strain was still stable. At higher temperatures, plastic strain started recovery, which was accompanied by exothermic behavior of the specimen. With an increase in the aging duration, the endothermic peak signified and moved to a higher temperature. These results indicated that the longer the aging duration was, the harder the plastic strain and strain energy were frozen in the glassy structure. This freeze-strain phenomenon was observed for crosslinked epoxy glass, as well as polymeric glasses with linear molecular structures, aged under strain.

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Section: Discussionsupporting

confidence: 92%

Section: Resultsmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

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Changes in the thermomechanical behavior of epoxy glasses under the state of strain aging

Kawakami

Watanabe

2007

J of Applied Polymer Sci

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Molecular Cooperativity in Large Deformation and Subsequent Structural Relaxation for Epoxy Glass

Kawakami

2007

J. Soc. Rheol., Jpn

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In the present article, results from our recent studies on effects of chemical crosslinks in epoxy glass subjected to large deformation and subsequent aging under strain are reviewed. Bis-A type epoxy monomer was cured with DDM to form a sample with a crosslinked network structure. The monomer was also polymerized with aniline to form another sample with an uncrosslinked linear molecular structure. First, change in birefringence in the course of elongation was measured, and the modified stress-optical rule was applied to the experimental results. For the crosslinked sample, both internal potential and entropy changed in a small strain range. On the other hand, for the linear molecular sample only internal potential increased in a small strain range. Another series of results was obtained through thermomechanical experiments with largely deformed specimens, and the obtained results indicated that chemical crosslinks forced more rubbery strain to recover at temperatures below T g . From these studies it was proposed that chemical crosslinks in epoxy glass enhance cooperativity between molecular motions taking place in deformation as well as in subsequent retardation process. Such an effect of chemical crosslinks was also observed in the crosslinked sample under the state of aging under strain.

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Plastic Flow of Glassy Epoxy Network

Yoshioka

Itami

Kawai

2017

J. Soc. Mat. Sci., Japan

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Steady plastic flow in specimens of tightly cross-linked glassy epoxy network was analyzed as a rate process to discuss the mechanism of nonlinear viscoelastic behavior of glassy network polymers under large deformation. Specimens were uniaxially stretched at temperatures below the glass transition temperature with various strain rates. True stress σ and birefringence in the specimen were recorded during the deformation as functions of nominal strain ε n . The glassy stress σ G was extracted from the σ-ε n relations by means of modified stress-optical rule (MSOR). The obtained σ G -ε n relations had a steady flow region, which was observed as an almost constant stress state in the post-yield strain range. The flow stress in this region was analyzed by using the Eyring equation in a special way proposed by Nanzai. The analysis gave an experimental relation between the activation enthalpy ΔH and the activation entropy ΔS, which agreed fairly well with that derived from WLF equation for the linear viscoelastic relaxation of the material in the molten state. This agreement provides an experimental evidence verifying structural change of the glass into liquid-like, highly non-equilibrium structure in the glassy network polymer under large deformation. Independently of the presence of crosslinked molecular structures, the essential mechanism of nonlinear viscoelasticity of glassy polymers is found to be strain-induced structural change.

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Birefringence change in epoxy glass aged under strain

Cited by 3 publications

References 7 publications

Changes in the thermomechanical behavior of epoxy glasses under the state of strain aging

Changes in the thermomechanical behavior of epoxy glasses under the state of strain aging

Molecular Cooperativity in Large Deformation and Subsequent Structural Relaxation for Epoxy Glass

Plastic Flow of Glassy Epoxy Network

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