SMC 複合材料の破壊じん性と微視的破壊

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The paper is concerned with the fracture toughness and microfractures of a sheet molding compound polyester composite at room and low temperatures. Fracture toughness tests were performed by using compact tension specimens of the composite at room temperature and liquid nitrogen temperature,77K. Acoustic emission signal were monitored during the fracture toughness tests. The microscopic observation of the fractures surfaces and the spectrum analysis of the acoustic emission signals were made in order to obtain a reasonable explanation of the fracture mechanism. The results are summarized as follows: (1) The load-crack mouth displacement curves at liquid nitrogen and room temperatures became nonlinear at about the same load level and the maximum load observed at liquid nitrogen temperature increased by about three times that observed at room temperature. The acoustic emission activity for the specimen tested at liquid nitrogen temperature was higher than that at room temperature. (2) The fracture toughness K_<AE> at liquid nitrogen temperature, obtained as the stress intensity factor which corresponds to th. e onset of abrupt increase of the accumulated acoustic emission energy, was extremely larger than that at room temperature. (3) At room temperature the fracture toughness K_<AE> was in good agreement with the fracture toughness K_Q obtained by the 5% offset procedure of ASTM E399, and at liquid nitrogen temperature K_<AE> was larger than K_Q. (4) From the microscopic observation, it was found that the fracture of a sheet molding compound composite accompanies the microfractures of four types, i. e. fiber. breakage, fiber debonding, resin cracking and delamination. (5) The spectrUm analysis indicated that the acoustic emission signals could be classified into three types for the specimens tested at room temperature and four types for the specimens tested at liquid nitrogen temperature. An attempt was made to assign each type of the frequency spectra to the microfracture, and the fracture mechanism of the SMC composite was discussed.
社団法人日本材料学会の論文
1986-09-15

SMC 複合材料の破壊じん性と微視的破壊

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