| Budget Amount *help |
¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1995: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1994: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
Microstructure of crazes appearing as precursors to fracture in engineering plastics and its variation with strain during uniaxial elongation at well below their glass transmission temperatures have been investigated by real-time small-angle X-ray scattering (SAXS), electron microscopy, and low-angle and wide-angle electron diffraction.
The real-time small-angle X-ray scattering measurements has revealed that (i) the fibrillar structure bridging the interior of the crazes in polypropylene grows in width by its elongation, maintaining its thickness and spacing unaltered, and that (ii) the above result suggests that the fibril grows in length by being supplied with molecular chains from active zones formed in the craze/bulk boundaries, and that the breakdown of the fibril occurs when this molecular supply is interrupted. Selected-area wide-angle electron diffraction patterns observed for the inside of crazes indicate that the crystallites in the fibrils are highly oriented in such a way t
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hat the molecular chains in the crystallites lie in the longitudinal direction of the fibrils. From this result we are lead to the conclusion that the initiation of fracture does not occur only within the amorphous regions or amorphous/crystalline boundaries but also occurs within crystalline regions, and that on crazing spherulites flow into the fibrils after fragmenting into small pieces, suggesting that the confinement of the molecular chains within crystals is not a major reason for the fibril breakdown in semicrystalline polymers.
Transmission electron microscopic observation on polysulfone and polyarylate has revealed that the fibrils in crazes formed in these polymers break around their centers by creeping. This mechanism fo fibril breakdown is completely different from that observed for many general-purpose amorphous polymers, in which molecular chains flow into the fibrils during the growth of crazes. The thickness and the spacing of the fibrils measured by SAXS are approximately the same as those for general-purpose amorphous polymers, suggesting that the high strength of amorphous engineering plastics has close reration to the mobility of molecular chains, which is affected by the regidity of the chains, in the ductile deformation that occurs microscopically even in brittle fracture. Less
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