| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1993: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1992: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
For the purpose of finding a possivility of non-destructive detection of fatigue damage, that is accumulated in a member of a welded structure due to fatigue loading, a series of experimental investigation was made on initiation and extesion behaviors of surface micro cracks during strain cycling fatigue loading. The smmoth and solid cylinder specimens, 8 mm in test section diameter and 12.5 mm in gage length, were machined out from base metals and transverse butt-welded joints of four kinds of steel : mild steel, 600 MPa class and 800 MPa class high tensile steels and SUS316NG stainless steel. During completely reversed strain cycling fatigue up to 10&7& cycles at the longest, micro cracks on the specimen surface were replocated on readily soluble 0.08 mm thick cellulose acetate films by stopping the fatigue testing machine for a few minutes, the dried films were wxamined by an optical microscope, that was connected to a TV camera and an image analyzing system.
Both the crack density in a unit area and the total crack length in a unit area, that is the summation of lengths of all cracks in the area, showed monotonic increase as a function of increasing fatigue cycle ratio, and the curves for both parameters were arranged in an order of the magnitude of strain amplotude, respectively. the normalized crack density, that is the crack density at any cycle ratio devided by that at the visible crack initiation life, increased exponentially against the cycle ratio. A similar tendency was obserbed in the relation between the normalozed total crack length and the cycle ratio. It was concluded that both the crack density and the summation of all crack lengths are promising indications for the estimation of an accumulated fatigue damage in a stractural steel, and, in other words, these two parameters may be usufull for estimation of survival fatigue life.
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