Fatigue Crack Growth in Notched Thin-walled Tubes Under Non-proportional Mixed Mode Loads

摘要

The present paper introduces the typical results from a series of fatigue tests under non-proportional mixed mode loads. Three groups of load conditions are covered, namely cyclic mode I plus steady or quasi steady mode II, cyclic mode II plus steady mode I and, cyclic mode I plus cyclic mode II with varied loading path. The tests were performed with notched thin-walled tubes in mild steel. Two types of crack growth mechanism are recognized. The mode I type propagation occurs to the tests where the cyclic portions of the fatigue loads are proportional. The non-mode I type propagation occures to the tests where the cyclic portions of the fatigue loads are non-proportional. Crack surface fractograph, crack growth direction and crack growth rate are presented, for which significant differences are noticed voer the two growth mechanisms.