Numerical Derivation of Buckling Knockdown Factors for Isogrid-Stiffened Cylinders with Various Shell Thickness Ratios

Table 5

Postbuckling analysis results of the isogrid-stiffened cylinders with various shell thickness ratios (, 356, 244, and 122).

Thickness ratio, ()	536 (441)	356 (300)	244 (200)	122 (100)
Global buckling load without initial imperfection,
Detailed model (kN)	5,560	5,400	5,460	5,630
Equivalent model (kN)	5,490	5,450	5,570	5,750
Relative error (%)	-1.26	0.93	2.01	2.13
Global buckling load with initial imperfection,
Detailed model (kN)	3,600	3,900	4,330	4,480
Equivalent model (kN)	3,730	3,990	4,430	4,500
Relative error (%)	3.61	2.31	2.31	0.45
Knockdown factor,
NASA SP-8007 [4]	0.31	0.38	0.44	0.47
Detailed model	0.647	0.722	0.793	0.796
Equivalent model	0.679	0.732	0.795	0.783
Relative error (%)	4.93	1.37	0.29	-1.65
Computation time
Detailed model (min.)	64	67	46	40
Equivalent model (min.)	38	27	26	25
Equivalent model/detailed model (%)	59.4	40.3	56.5	62.5