圧縮予荷重により発生する亀裂を用いた破壊靱性評価法に関する研究

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It is known that pre-compressed bend specimen exhibits lower fracture toughness than that without pre-compression. In order to apply pre-compressed bend specimen for fracture toughness testing, fracture characteristics of such specimen have been studied. From this study, it is found that a crack is initiated at the tip of the notch and extends a short length when a certain amount of compression bending load has been applied and unloaded at a temperature exhibiting only small scale yielding. The crack front configuration is almost straight except the portions adjacent to the specimen surfaces. The applicability of compression induced crack to fracture toughness testing is verified by conducting a series of four-point bend fracture toughness tests for specimens with fatigue crack and compression induced crack. Simply prepared one described in the following is found to give practically the same result as compared with specimen with fatigue crack. The proposed notch tip preparation is ; firstly apply compression bening load to initiate and extend a crack during unloading stage, then apply tension bending load to extend the crack furthermore at liquified nitrogen gas temperature (-196). The applicabilities of machined notch and fatigue cracks which are extended under large K_f (max) to fracture toughness testing have been also investigated experimentally and it is shown that such notch and cracks application is not so suitable.
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圧縮予荷重により発生する亀裂を用いた破壊靱性評価法に関する研究

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