Effect of Molecular Weight and Orientation on Fatigue Crack Propagation of Polyimide Resin.

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  • ポリイミド樹脂の疲労き裂進展特性に及ぼす分子量と配向の影響
  • ポリイミド ジュシ ノ ヒロウ キレツ シンテン トクセイ ニ オヨボス ブンシリョウ ト ハイコウ ノ エイキョウ

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The effects of molecular weight and orientation on crack propagation property of polyimide (PI) are investigated. The specimens which have four kinds of molecular weight (Mw) from 2.5×104 g/mol to 3.8×104 g/mol are prepared. The crack propagation resistance increased with increasing Mw. The discontinuous crack growth (DCG) bands were observed on the fracture surfaces except for that of the specimen with the highest Mw. The reason that the DCG disappears for high Mw is attributable to the decrease of ductility. The width of DCG bands is almost constant until transition of DCG to continuous crack growth. The critical craze stress for cyclic loading given by Dugdale model decreases with the increase of Mw since the damage of the craze region is accumulated until breaking down. From the results of miniature CT specimens, the crack propagation resistance increased when the direction of crack propagating was perpendicular to the orientation of PI molecular chains.

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