engleski

Plastic Collapse Analysis of Surface Cracked Steam Generator Tubes

The objective of this work is to obtain new analytical approximation of the plastic limit pressure and estimation equation of J-integral for thick tubes with axial semi-elliptical surface cracks which are subjected to internal pressure. The plastic limit pressure solutions are developed on the basis of the finite element limit load analyses employing elastic-perfectly plastic material behavior. The results for the stress intensity factor and J-integral are generated and expressed as the GE/EPRI influence functions for a wide range of tube and crack geometries as well as strain hardening indices for the Ramberg-Osgood material. It is found that the GE/EPRI results can be very sensitive to how the stress-strain data are fitted using the Ramberg-Osgood relation. For application to general stress-strain laws the developed GE/EPRI-type solutions are then re-formulated using the concept of the reference stress approach where the reference stress is defined based on the plastic limit load. The proposed reference stress based J estimation equation is compared with three-dimensional finite element results using actual experimental uniaxial stress-strain data of austenitic steel 08X18H10T, with incremental plasticity. The developed J estimation and analytical approximation of limit pressure provide very useful tools for assessing of the integrity of pressurized thick tubes.

finite element method; tubes; surface cracks; fracture analysis; plastic limit analysis; J-integral; plastic limit pressure

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