In situ sem observation of self-arresting of fatigue cracks in Al-Li alloy 1420 thick plate

The effect of orientation on long fatigue crack propagation behavior was investigated for an aluminum-lithium alloy (1420) plate with 10 mm thickness at stress ratio of 0.1. The methods used are three-point bending, compact tension and in situ pulsating fatigue in SEM. The in situ fatigue observations were emphasized on crack path morphology and its closure during fatigue. It was indicated that 1420 of multi-layer microstructure can be regarded as an in situ laminated composite. The interface of the laminated metal matrix composite plays a significant role on the fatigue crack growth. The crack path is governed by the weak interface to form zigzag with groups of minor cracks within the laminated structure, which results in the increase of the closure force. The crack propagation arresting is observed in the ΔK range of 3-4 and 6-9 MPa·m^1/2 for L-T, T-S orientations, respectively.