Comparison between nonlinear FEA and notch strain analysis for modeling elastoplastic stress-strain response in crossbores

The elastoplastic stress-strain response of a crossbore geometry were evaluated using FEA and notch strain analysis based on Neuber and Glinka approaches. The stress and strain in the crossbore were predicted by FEA and analytical models for an autofrettage overload pressure, an unload, and an operating pressure cycle. An elastic FEA simulation was used to define the elastic stress concentration factors (Kt) based on von Mises and maximum normal stress using with two definitions of nominal stress. Four resulting stress concentration expressions were combined with the three forms of the Glinka notch formula and the three forms of the Neuber notch formula. This gives 24 possible expressions that were evaluated for prediction accuracy. From this comparison, the Glinka approach was found to match the FEA results most closely when the stress concentration was based on the ratio of the von Mises stress and nominal stress. However, no single notch equation was found to accurately capture the stress and strain state in the crossbore. By adopting an averaging approach using both the Neuber and Glinka predictions, the analytical model results were found to improve significantly for the entire pressure history.