Characterization of thermoplastic J1 polymer and its graphite fiber AS4/J1 matrix composites
Lin, David C.
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Permalink
https://hdl.handle.net/2142/19779
Description
Title
Characterization of thermoplastic J1 polymer and its graphite fiber AS4/J1 matrix composites
Author(s)
Lin, David C.
Issue Date
1991
Doctoral Committee Chair(s)
Geil, Phillip H.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Engineering, Materials Science
Language
eng
Abstract
The objectives of this research were to study, as a representative thermoplastic system: (1) the structure-property-thermal history relationships of the J1 matrix resin (DuPont, a semicrystalline polyamide) and AS4/J1 composites, and (2) the effect of moisture absorption on mechanical properties.
At least eight different kinds of crystal structures of J1 have been found; four of which are of significance in composite materials.
In-situ FTIR, DSC, and in-situ WAXD were used to study the crystal structure and thermal behavior of J1 as a function of temperature, thermal history and processing conditions. Two crystal-crystal transformations were observed in DSC and x-ray studies, a thermally reversible one at 145$\sp\circ$C and a thermally irreversible one at 240$\sp\circ$C. An endothermic peak seen in DSC scans at ca. 145$\sp\circ$C and multiple melting peaks between 265$\sp\circ$C and 285$\sp\circ$C are due to the reversible crystal-crystal transition and a crystal melting-recrystallization-remelting process respectively. Physical aging and dynamic mechanical spectroscopy studies were conducted to explore the superposition of the glass transition, T$\sb{\rm g}$, and the crystal-crystal transition at ca. 145$\sp\circ$C.
The effect of annealing (at temperatures between T$\sb{\rm g}$ and T$\sb{\rm m}$) on crystal structure, crystallinity, and properties of quenched(prepreg), and slow cooled(laminate) J1(AS4/J1) neat resin(composite) was investigated. The mechanical properties of J1 neat resin and unidirectional graphite fiber AS4/J1 laminates, with and without annealing at 240$\sp\circ$C for 8 hours, have been examined in tension, compression and three point bend tests. The processing history dependent differences in structure lead to significant differences in mechanical properties in both neat resin and composite.
The effect of moisture absorption on mechanical properties was also examined. The diffusion behavior of J1 resin and AS4/J1 composite obeys Fick's second law. The mechanical properties of water saturated melt crystallized J1 resin and (90) $\sb{24}$ AS4/J1 laminates in tension show an increase in strain to failure and the same value of failure strength. A shear band deformation is seen in the water saturated J1 specimens in tensile tests; absorbed water molecules act as a plasticizer and soften the J1 resin. (Abstract shortened with permission of author.)
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