成型ベークライト曲げ試験片の残留応力

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It happens sometimes that mechanical engineers have to deal with the mechanical behavior of high polymeric substances. In most cases, however, they must reconcile themselves to much qualitative estimation, with all the knowledge of advanced chemistry and chemical physics, because of the different nature of the problems of mechanics from those in the laboratories of chemists and chemical physicists. One of these cases is the evaluation of the residual stress in a molded article of phenol resin, for which it may be necessary to resort to rules-of-thumb in designing molds, as the inherent stress seems to be related definitely to the spontaneous cracking in course of time as well as immediately after taking the article out of the molds. As the first foothold for dealing with more general cases of residual stress, those of bending test specimens are, at in present work, evaluated numerically in accordance with the approximate formula established for this investigation. Preliminary experiments were carried out and Young's moduli at room temperature obtained in relating to the variation of the temperature and the pressing time on molding. Then, the variation of the warping of specimens due to the relaxation of the surface stress by taking off the surface layer of small depth from the specimen was measured. The locked-in stress distribution is naturally characteristic of the cooling rate of the specimen. The results are reproduced in the accompanying diagrams for air-cooled and oil-cooled specimens. Oil cooling causes a steeper gradient of the stress in the neighborhood of the surface than in natural cooling in the air, and the greatest residual stress reaches 200 kg/cm^2 compression at the edges. In such a state of stress, the apparent modulus of flexure must be 10 per cent higher than that of the naturally cooled case and this the fact was ascertained experimentally.
一般社団法人日本機械学会の論文
1952-03-15

著者

樋口正一
九州大学応用力学研究所

成型ベークライト曲げ試験片の残留応力

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