RATCHETING OF INCONEL 718 AT 649°C UNDER AXIAL/TORSIONAL LOADING

Ratcheting tests have been performed on Inconel 718 at 649 degrees C for uniaxial loading, torsional loading and a few paths of axial-torsional loading. Ratcheting strain was measured to near failure cycles. The equivalent ratcheting strain is examined for different loading paths. Ratcheting strain is found to increase with cycles in the manner similar to the creep strain under static load, exhibiting steady-state behavior for much of the lifetime. The ratcheting rate depends greatly on the loading path, stress amplitude and mean stress as fatigue life does. Ratcheting rates are found higher for circular paths than for linear paths. The ratcheting strain at failure may be estimated from the steady-state ratcheting rate and cycles to failure for most test cases.