Correlation Between the Fatigue-Crack Initiation at the Root of a Notch and Low-Cycle Fatigue Data
TL;DRAbstract
Fatigue-crack initiation was investigated by testing high-strength steels (AFNOR 35 NCD 16 and 35 CD 4) with 0.6-in. (15-mm) thick ASTM compact specimens having various notch-root radii between 0.003 in. (0.07 mm) and 0.04 in. (1 mm). Measuring devices were used to detect flaws with a surface area of only a few square millimetres in their propagation planes. In order to calculate the number of cycles required to initiate a crack, notch root behavior was investigated through several parameters. − ΔK/ √ρ, from linear-elastic fracture mechanics, which concentrate results when the initiation time is large; − KfEP, an experimental parameter derived from low-cycle fatigue data when Ni<105 cycles. In this case, the ratio between theoretical and experimental values of the initiation time is between one and two for a given nominal stress.
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Fatigue-crack initiation was investigated by testing high-strength steels (AFNOR 35 NCD 16 and 35 CD 4) with 0.6-in. (15-mm) thick ASTM compact specimens having various notch-root radii between 0.003 in. (0.07 mm) and 0.04 in. (1 mm). Measuring devices were used to detect flaws with a surface area of only a few square millimetres in their propagation planes. In order to calculate the number of cycles required to initiate a crack, notch root behavior was investigated through several parameters. − ΔK/ √ρ, from linear-elastic fracture mechanics, which concentrate results when the initiation time is large; − KfEP, an experimental parameter derived from low-cycle fatigue data when Ni<105 cycles. In this case, the ratio between theoretical and experimental values of the initiation time is between one and two for a given nominal stress.
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