This is part of a series of articles on the properties of a thermoplastic polyamide matrix [PACM-12, DuPont, poly(bis-4-4'-dicyclohexylmethane) n -dodecanediamide]/graphite fiber (AS4, Hercules) composite. The structural characterization of the neat resin by differential scanning calorimetry (DSC) and X-ray diffraction as a function of processing history is described here. PACM-12, considered a representative thermoplastic matrix polymer for advanced composites, as well as an engineering plastic, is partially crystalline (ca. 20%) under normal composite processing conditions, but can be quenched to a completely amorphous state. The complex DSC results are shown to result, at least in part, from the presence of a different crystal structure in slow cooled PACM-12 than in quenched, annealed or fiber samples, to a melting-recrystallization-melting process during heating and to the effect of heating rate.
Structural characterization of AS4-graphite fiber/PACM-12§ matrix com posites was conducted using Differential Scanning Calorimetry (DSC) and Wide-Angle X-Ray Diffraction (WAXD) analyses. The DSC results indicate the significant effect of processing variables on the morphology, microstructure and crystallmity of the fiber rein forced semicrystalline thermoplastic matrix prepreg and unidirectional laminates. From WAXD results the crystallinity was determined. Time-temperature dependent thermo mechanical properties of the laminates were evaluated using dynamic mechanical spec troscopy and creep compliance measurements. Dynamic mechanical spectra revealed the matrix-dominated time-temperature dependent behavior of the laminate under torsional loading. Elevated temperature creep compliance in the longitudinal direction showed time- temperature independent behavior whereas transverse creep deformation was found to be significantly time-temperature-stress dependent.
The tensile deformation and failure behavior, dynamic mechanical properties and creep behavior of PACM-12 (DuPont, poly(bis 4-4' dicyclohexylmethane) n -dodecanediamide), a representative thermoplastic polymer for use as a matrix in advanced composites and as an engineering plastic, as a function of processing history are described. Although injection molded PACM-12 fails in a brittle fashion at room temperature, completely amorphous PACM-12 is ductile; the difference is attributed to variations in cooling in the interior of the samples due to sample thickness effects. Partially crystalline samples are brittle at room temperature, with all samples being ductile near and above T g . A master creep curve for the partially crystalline samples can be obtained by horizontal shift alone.
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