Current Status and Future Trends on Environmental Strength of Metals

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This paper deals with the current topics of environmental strength of metallic materials and its methodology from the theoretical and practical viewpoints, including cyclic stress corrosion cracking (cyclic SCC), dynamics SCC, corrosion-product-induced wedge effects, and the mechanical factors controlling crack initiation. Low-frequency variation (stress ratio being near zero)causes cyclic SCC even in materials insensitive to static SCC under a sustained load. Also, the dependence of the waveform on cyclic SCC is opposite that on corrosion fatigue (CF). Small, high-frequency vibratory stresses cause dynamic SCC, with a lower threshold than that of static SCC, K_<ISCC>; the effects of the vibratory stress range, stress cycle frequency, solution temperature, and crack length on dynamic SCC are discussed. The corrosion-product-induced wedge effects (crack closure) have great potential in influencing CF crack growth, and the mechanisms are discussed. In the case of crack initiation at the bottom of a corrosion pit, the stress intensity factor, calculated on the assumption of a pit being a sharp crack, dominates its crack initiation. The image processing technique, including three-dimensional analyses and the region segmentation according to fracture surface morphology, provide us with powerful tools to investigate the environmental strength of materials.
一般社団法人日本機械学会の論文
1989-01-15