Pop-in Phenomena in an Al-Li Alloy
Pop-in (PI) cracking was studied as a function of temperature, test velocity and orientation in Weldalite-049 Al-Li alloy. It was found that local crack instability is characterized by a cumulative damage mechanism as reflected by AE activity. In addition, PI behavior in fracture is controlled by mechanical and microstructural factors. First, the mechanical effect is expressed by the increase of PI crack velocity as the excess local stored elastic energy increases (due to consecutive PI, and also by increasing test speed), while in the case of extreme conditions resulting from warm-prestressing or cold-prestressing, PI events are almost eliminated. Second, a microstructural effect is reflected by the behavior of various crack extension orientations; PI is diminished in S-T orientation (crack delamination), due to a lack of barriers for crack arrest. For two other orientations, T-S (crack arrester) and L-T (crack divider), blunting accompanied by a concurrent crack delamination process, causes crack arrest even at high test velocities at low temperatures. Thus, PI phenomena reflect in some way the dynamic toughness and crack arrest properties of materials.
KeywordsFracture Toughness Acoustic Emission Crack Extension Crack Arrest Acoustic Emission Activity
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