On the Crack Propagation by Cyclic Stresses below the Fatigue Limit in Specimens with a Pinhole

Abstract

The fatigue crack propagation by the cyclic stress below the fatigue limit in specimens with a pinhole is investigated after the crack initiation by the over-stress. The test results show that the critical condition for the start of crack propagation in a cracked specimen is indicated by σ³1 = 1.6 × 10³ ( (kg/mm²)³mm) as the relation between the crack length and the applied stress value. In some cases, a fatigue crack propagates under a cyclic stress below the fatigue limit and afterwards stops to propagates under a cyclic stress below the fatigue limit 1*__2 is greater in the case when the crack initiating stress is higher. When the cyclic stress over the fatigue limit is applies after a crack propagation has been stopped by the under-stress, the crack propagating rate is reduced in the first period of crack propagation.