Stress-life fatigue behavior of a Zr-based bulk metallic glass

Fatigue damage was characterized for a Zr-based bulk metallic glass to elucidate damage initiation and growth mechanisms. Damage was observed to initiate as shear bands or mixed-mode cracks propagating at ∼49° to the maximum applied stress axis after only a few stress cycles. The apparent lack of a damage initiation stage may account for the low endurance limit reported. The damage was often observed to initiate from pre-existing defects. At a characteristic length, the initial shear bands or mixed-mode cracks abruptly changed growth direction and propagated orthogonal to the maximum stress axis. The resulting “small” fatigue crack-growth rates were carefully characterized and shown to be consistent with “long” crack-growth rate behavior. Fatigue life was estimated from the observed initial defect sizes and small crack-growth rate behavior and life predictions were found to be consistent with measured stress life data.