| Popis: |
Possible variability of endpoints on the da/dN-ΔK curve is analyzed, and its influence on crack growth life is shown. Basics of the fatigue crack growth model of material with a single crack are presented. The proposed model calculates local stress at a remoted point close to the crack tip. The model establishes a relationship between the stresses and the near-threshold range of stress intensity factor. Tests were carried out for the low crack growth rates on aluminum alloy 2024-T3 and low carbon steel with rare small overloads of different sequence, and as a result, a-N and da/dN-ΔK plots were received. Fatigue predictions were done using existing Elber, Barsom, Wheeler, Willenborg models, NASGRO and FASTRAN software and the proposed model. It is shown that the proposed model of local stress calculation at the distance from crack tip is able to predict fatigue life considering load sequence of no less accurate than the best of existing models. However, application area is restricted to small overloads, high cycle ratio, and low crack growth rate at the moment. |
