On initial defects of externally pressurized shells
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To analyze the stability of externally pressurized spherical shells using geometric nonlinear methods, the buckling modes are first determined using the eigenvalue method; thereafter, initial defects are introduced into these modes. The value of these initial defects has a significant impact on the results obtained from geometric nonlinear analysis. So, what should be the appropriate value for these initial defects? Some suggest it should be equal to the thickness of the sphere shell, while others suggest it should be half the thickness of the sphere shell. What is the correct value to use?
The initial defects are determined by the manufacturing tolerances that can be guaranteed by the shell plate pressing manufacturer and the on-site welding manufacturer; they are not values that can be chosen arbitrarily.
But the factory I contacted cannot provide this figure
Personal opinion: 1/2 shell thickness.
This needs to be discussed with the manufacturer to determine an appropriate precision level they can achieve. The precision is too high; manufacturers cannot achieve it, and it’s not practical to have such high standards ； Too low precision also affects the quality of the device, which is not good. It’s best to find a balance between the two