Precompression Cracking Method for Fracture Toughness Test
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概要
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Several investigations were conducted for the purpose of examining a suitable notch-tip preparation method for the fracture toughness test specimen instead of the fatigue cracking one. The materials used for investigations were three kinds of structural steels : SM41A, SM50C, and 80kg/mm^2 class high tensile steel. The fracture characteristics of notched bend specimens, on which precompression bending load had been applied, were investigated by conducting fracture tests at low temperatures. The fracture stress of a specimen precompressed at room temperature or at low temperature is lowered when the magnitude of the precompression stress exceeds that of the fracture stress of a non-compressed specimen. This lowering is caused by preliminary cracking prior to fracture. At liquid nitrogen temperature (-196℃), minute and almost continuous cracking takes place during unloading stage of a precompression load exceeding a certain value. The features of this precompression-induced crack was also investigated and a precompression-tension cracking method was proposed. This method is to extend a crack in a short length at liquid nitrogen temperature by applying a tension load after preliminary cracking during unloading stage of the compression load. Suitable crack-tip conditions for fracture toughness test are easily established by this method. The fracture toughness value of a precompression-tension-cracked specimen and that of a fatigue-cracked specimen are almost equal to each other, and the validity of precompression-tension cracking method for fracture toughness test is verified.
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関連論文
- A Study on Brittle Fracture Initiation from Inclined Cracks
- Precompression Cracking Method for Fracture Toughness Test