Fig. 1. Calculation flowchart for the large-deformation model of lower head

Fig. 2. Schematic of the lower head

Fig. 3. Stress analysis of the lower-head node

Fig. 4. Stress analysis of the center node of the wall thickness of the lower head

Fig. 5. Numerical simulation of the FOREVER experiment

Fig. 6. Experimental data and simulation results for the 70° (a) and 80º (b) inner wall temperature of the lower head (color online)

Fig. 7. Experimental data and simulation results for the external wall temperature at 300 min

Fig. 8. FOREVER pressure experimental data and simulation results (color online)

Fig. 9. Stress distribution in the middle node of the wall thickness at failure

Fig. 10. Equivalent stress along the wall thickness at the failure position of the lower head

Fig. 11. Shape of the lower head before and after deformation (color online)

Fig. 12. Experimental data and simulation results for elongation at the bottom of the lower head

Fig. 13. Failure fraction at each position of the lower head