Fatigue of V-notched members: Short crack behavior and endurance limit

✍ Scribed by Yves Verreman; Jean-Paul Baïlon; Jacques Masounave

• Publisher: Elsevier Science
• Year: 1987
• Tongue: English
• Weight: 824 KB
• Volume: 28
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(87)90069-5

✦ Synopsis

A previous experimental investigation showed that the short crack behavior in severe V-notched geometries is essentially characterized by an initial transient variation of the crack opening level within the notch plastic zone. This result is exploited to derive a general formulation of the endurance limit of V-notched members. Analytical solutions for the stress intensity factor and the notch plastic zone extent are obtained to compute the effective crack driving force A&a as a function of notch geometry, crack length and nominal stress. Then, the endurance limit is determined as the nominal stress below which an initiated crack becomes non-propagating, i.e. by equating the minimum AK,, value at the end of the plastic zone to a threshold value. By using Irwin's redistribution principle which allows us to make relations between the V-notch elastic and plastic fields, the following results are obtained. The endurance limit can be computed only from the V-notch "stress intensity factor" and the material threshold and cyclic yield stress. The endurance limit dependence on the threshold diminishes as the notch angle increases from zero and vanishes in the limit case of a smooth surface. When the notch contains a pre-existing crack, a Kitagawa-type endurance diagram is obtained. The untracked notch endurance limit, the critical crack length and the slope of the decrease beyond this length, increase with increasing notch angle, and there is a total coincidence with the Kitagawa diagram in the limit case where the notch angle tends to 180". This result shows that a global theory should govern at one and the same time the short crack behavior in smooth and severe geometries.