Sensitivity analysis and design of experiments for failure analysis in first quadrant of X-TF plane for X100 pipeline steel

Triaxiality factor (TF) and Lode angle (X) are two parameters that control failure of ductile materials. In order to determine the fracture properties of an X100 pipeline steel, the data from tension and torsion tests on round bars done in previous researches are used here to develop a simple experimental failure criterion based on these two parameter. Using this failure criterion, a series of FE analyses are done to find specimens shapes and sizes whose predicted failure occurs under different desired combinations of TF and X. The results of these analyses are used to design new experiments with unconventional specimens, to improve the failure criterion and to study the effect of each parameter separately at different levels. These analysis show that large deformations can have an important effect on the values of these two parameters during loading, which should be taken into account for the design of experiments. In order to gain a better understanding of the response of TF and X to deviations of stress, a sensitivity analysis is done on these two parameters before the start of FE analysis. This sensitivity analysis shows that the two parameters are really sensitive to stress deviations in some areas and in order to get reliable results in FE analysis; it is necessary to reduce the element size to a quarter of the element size reported in literature. This study proposes a unique approach for selection of specimens and sensitivity analysis.