A novel method for failure analysis based on three-dimensional analysis of fracture surfaces

The fractured surfaces include a lot of useful information that can help investigate the reasons that caused metal materials to break. For example, the details on the processes that lead to failure can be determined from these surfaces, making it useful to investigate their morphology. The principle of the fracture-surface topography analysis (FRASTA) was used in this research and some progresses have been made on quantitative reverse deduction of metal fracture surfaces. In FRASTA, the fracture surfaces are scanned by laser microscope and the elevation data is recorded for analysis. The crack-tip opening angle (CTOA) was firstly determined by the cross-sectional plots. Simple bar hypothesis was then proposed. As for the hypothesis, the fracture surfaces can be assumed to be composed of independent rectangular bars. After dividing the plastic deformation left on the fracture surfaces into such single bars, the original lengths of these bars were calculated and then the global strains of these bars during the course of failure were calculated, and finally the J-integral was calculated. Then, the relationship between J-integral and crack opening displacement (COD), and the relationship between J-integral and fracture surface average profile for plain strain were deduced. Furthermore, according to the relationship between true stress and true strain for the material, the normal stress on the cross section of each single bar was determined. Summing up all the loads on all bars provided the total applied load of the specimen. Some experiments have been performed and the proposed methods have been verified to some extent. At the same time, software, namely fracture surface analyst (FSA) was developed as per the proposed methods and was used for analysis successfully.