Session: MF-01-01 Application of Fracture Mechanics in Failure Assessment

Paper Number: 123259

123259 - Brittle Fracture Assessment for Cold-Stamped Ellipsoidal Heads Made of Q345r 

The pressure vessels made of Chinese low alloy Q345R steel are widely used in petroleum, chemical, military, nuclear power and other industries. Cold stamping formed ellipsoidal heads are important components in these pressure vessels. However, ellipsoidal heads will produce plastic deformation due to cold forming process, thus reducing ductility and plasticity of material. Moreover, residual stress will be generated when heads are unloaded after forming and spring-back. In short, loss of plasticity and emergence of residual stress increase the tendency of brittle failure of heads. In this paper, brittle failure assessment of cold-formed ellipsoidal heads made of Q345R is performed considering the measured residual stress and fracture toughness. Firstly, cold stamping forming test of ellipsoidal heads with different thicknesses were carried out. The residual stresses were measured via portable X-ray diffraction analyzer. The yield strength and fracture toughness of Q345R were measured at different positions of the forming head. Then, the stress intensity factor was calculated by constructing finite element model of head containing cracks, considering the measured residual stress. The limit load is obtained by elastic-perfect-plastic analysis through finite element simulation, considering the measured yield strength. Finally, the brittle failure of ellipsoidal heads was evaluated by using failure assessment diagram. In this assessment, based on the stress intensity factor obtained by considering the measured residual stress, the measured fracture toughness, and limit load obtained by considering the measured yield strength, the fracture ratio and load ratio are determined. According to the results of failure assessment, it can provide reference for whether to require post forming heat treatment.

Presenting Author: Xiao Guo ZheJiang University

Presenting Author Biography: Xiao Guo is a post-graduate student at Zhejiang University

Authors:

Xiao Guo ZheJiang University
Keming Li Zhejiang University
Jinyang Zheng Zhejiang University