A structure metric for quantitative assessment of fracture surfaces in 3D conceived based on confocal laser scanning microscopy data

Assessment of fracture surfaces typically involves the identification of qualitative features such as dimples, grain facets, and river patterns to determine type of fracture. The present study formulates a measure termed Real-to Projected Area (RPA) ratio/metric to quantitatively assess fracture surfaces. Fracture surfaces of several metallic alloys tested monotonically and in fatigue to fracture including three Mg alloys, a Ti alloy in two conditions, and a Ni-based superalloy were observed using confocal laser scanning microscopy in 3D and quantitatively assessed using the metric. The metric successfully separated fracture surfaces obtained after fatigue testing from those obtained after monotonic tension testing. Specifically, the values of the metric were found to be in the range of 40-80 pct for fatigue fracture, while 90-140 pct for monotonic tension fracture. As a result, the metric can be used to distinguish between fracture in fatigue and fracture in monotonic tension when fracture types / loading modes are unknown. Moreover, the metric is sensitive to ductility of tested alloys as well as any presence of critical defects in the microstructure responsible for rapid fracture such as intermetallic inclusions. An added utility of the metric is also to identify outliers in the data such as invalid mechanical tests.

Automated summary

This study introduces a new metric to quantitatively assess fracture surfaces, successfully distinguishing between fracture in fatigue and fracture in monotonic tension. The metric is also sensitive to the ductility of tested alloys and the presence of critical defects.