クリープ条件下のき裂伝ぱを支配する破壊力学因子とフラクトグラフィ

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The applicability of fracture mechanics parameters to creep and fatigue crack propagation at elevated temperatures was critically examined using specimens of different geometry, and the results were discussed in the light of the electron fractography. The propagation rate of creep cracks was best correlated with the modified J integral J^^・. The stress intensity factor K failed to describe the crack propagation rate adequetly. The net section stress σ_<net> was a better correlating factor than the stress intensity factor. As for fatigue cracks, the propagation rate correlated well with the stress intensity range ΔK at low stress levels. At high stress levels, however, it correlated better with the maximum net section stress σ_<net max> or J^^・ rather than ΔK, and it was close to the value of the static test. There appeared the transition of macroscopic crack propagation. The fracture surface of creep cracks was intergranular with much reduction in area. With regard to fatigue cracks, the low stressed specimens exhibited ~at fracture surfaces with little reduction in area and, microscopically, plateaus and striation-like patterns were their characteristic features. The high stressed specimens, on the other hand, exhibited rough surfaces with much reduction in area like creep fracture. Microscopically, however, plateaus and well-defined striations were predominant in the early stage. Dimples and intergranular creep fractures appeared later in the propagation process and the transition in microscopic fracture features did not agree with that of macroscopic propagation.
社団法人日本材料学会の論文
1978-01-15

クリープ条件下のき裂伝ぱを支配する破壊力学因子とフラクトグラフィ

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