ポリメチルメタクリレートの環境応力割れ

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In order to investigate the mechanism of the cracking of polymethyl methacrylate (PMMA) due to enviromental stress, the propagation of the artificially induced Griffith cracks under petroleum was studied. The stress changes due to the crack propagation were also examined by the photoelastic method and the fractured surfaces were observed in the light and by electro microscopic technique. The main results are summarized as follows : (1) The growth and propagation of cracks are studied in two distinct stages. At the first stage the crack grows at high speed immediately after coming in contact with petroleum, and gradually falls until it stands at constant speed at the second stage. (2) The energy on the fractured surface is estimated at 0.40×10^5 and 0. 36×10^5 erg/cm^2 respectively under the plane stress and strain. This estimation is in coincidence with what has been derived from the Griffith crack length at the critical point where the constant of the velocity of crack propagation through the stages first and second has dropped to 0. (3) Of changes in stress patterns due to the crack propagation there have been but few cases recognized, but there have been crazings observed as made by high stress concentration at the tip of the Griffith cracks. The crack that grew at the first stage apparently passed through this crazing area. (4) The fractured surfaces are rough over extensive areas which tell of crack growth in the first stage, and a number of small parabolic marks indicate discontinuous crack initiation in the second stage.
社団法人日本材料学会の論文
1971-09-15

ポリメチルメタクリレートの環境応力割れ

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