ポリマーアロイにおける応力集中の緩和機構の塑性力学による解析
Plastical Analysis of the Mechanism of Relaxation of Stress Concentration on the Polymer Alloy
久松徳郎・中野 哲・石川 優・岩倉賢次
Hisamatsu, Tokuro / Nakano, Satoshi / Ishikawa, Masaru / Iwakura, Kenji
It is well known that the technique of polymer alloying, in which an elastomer is blended in the matrix, is effective for the improvement of toughness. It has been proposed by one of the authors that the mechanism of toughening results from the relaxation of stress concentration by the release of constraint of strain, which is caused by void formation. In this study, a qualitative discussion has been made using slip line field theory for the stress distribution in the plastic zone, which is formed at the top of a notch, and using the condition for general yielding of a polymer alloy. The criterion for yielding of a plastic body containing voids has close resemblance to that for polymers with a hydrostatic pressure dependence. Therefore, for the case of plain strain, the shear yield stress is given by the following equation. (τ0 : shear yield stress when hydrostatic pressure ρ is equal to zero, μ: void density) (σ1 _ σ3)/2 = τ0 _ μρ = τ
Use of this equation leads to the conclusion that the relaxation of stress concentration results from the release of constraint of strain followed by void formation. When the maximum stress in the plastic zone is smaller than the craze strength, general yielding takes place in the polymer alloy and toughness increases greatly.
Key words: Polymer alloy / Improvement of toughness / Relaxation of stress concentration / Slip line field theory / Plastic zone / Craze strength / General yielding