Fracture process reconstruction method (FRASTA) and its hidden potential

Fracture surface topography analysis (FRASTA) technique reconstructs fracture process in microscopic details by matching conjugate fracture surface topographs. It produces three different results: fractured area projection plot (FAPP), cross-sectional plot (XSP), and fracture progression curve (FPC). FAPP shows graphically where the crack initiation site(s) is and how it grew. By superimposing a series of FAPPs over a scanning electron microscope image of fracture surface, we can establish relationships between fracture process and microstructures. XSP is used to characterize the crack tip opening displacement or crack opening angle. Use of these two results is seen in published papers where the crack initiation mechanisms could not be determined by regular fractographic examination. However, these two results do not indicate the kinematics of crack growth. FPC shows the relationship between fractured area and the spacing between conjugate surface topographs. This relatively unexplored relationship shows the crack growth history from the onset of microcrack initiation to the rupture of the component, and by analyzing this relationship such information as crack initiation time, crack growth rate, changes in loading conditions or environment can be learned. This paper presents some examples of use of FPC in failure analysis. © 2016 The Society of Materials Science, Japan.