Scanning Electron Microscopy


Fracture surfaces of austenitic samples tested at room temperature show a correlation between fracture characteristics, Δ K-value and R-ratio: 1) at low Δ K-values up to 400 N/mm3/2 and stress ratios of R = 0.1 and R = 0.7, no fatigue striations but fan-like features and flat facets can be seen; 2) fatigue striations, but no facets exist at Δ K-values greater than 900 N/mm3/2 and R = 0.1; 3) at a higher stress ratio of R = 0.7 the facets disappear already at lower Δ K-values of about 650 N/mm3/2.

Applied to failure analysis, this correlation permits an estimate of operating level of fatigue stress as a result of the evaluation of fatigue fracture characteristics.

Fracture characteristics of samples tested at 200°C differ from those tested at room temperature, but do not show any appreciable changes in fracture features dependent on the Δ K-value and R-ratio.

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