SEDL / STP / STP631-EB / STP35534S

Correlation Between the Fatigue-Crack Initiation at the Root of a Notch and Low-Cycle Fatigue Data

Baus, A
Institut de Recherches de la Sidérurgie Francaise, Saint Germain en Laye,

Lieurade, HP
Institut de Recherches de la Sidérurgie Francaise, Saint Germain en Laye,

Sanz, G
Institut de Recherches de la Sidérurgie Francaise, Saint Germain en Laye,

Truchon, M
Institut de Recherches de la Sidérurgie Francaise, Saint Germain en Laye,

Pages: 16    Published: Jan 1977

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Abstract

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.