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Optimal Weight of Cracked Composite Panels By An Equivalent Strain Constraint

An equivalent strain constraint can be used instead of a crack propagation constraint based on the value of the stress intensity factor, when the latter constraint is not available in a structural optimization package. The approach is demonstrated at two levels of fidelity for minimum weight design of a composite blade-stiffened panel with a crack. The low-fidelity approach utilizes a closed form solution of stress intensity factor while the high-fidelity approach computes it from the stress distribution around the crack. Results are compared with a direct approach that implements stress intensity factor as a constraint in the structural optimizations. The equivalent strain was computationally efficient, but did not converge to the optimum design when started from a very different initial design. Using the low-fidelity direct approach to obtain initial design for optimization based on the highfidelity model reduced computational cost for both direct optimization and the equivalent-strain approach, and it eliminated the problem of convergence to the wrong design for the latter approach.