Abstract
Explicitly considering fail-safety within design optimization is computationally very expensive, since every possible failure has to be considered. This requires solving one finite element model per failure and iteration. In topology optimization, one cannot identify potentially failing structural members at the beginning of the optimization. Hence, a generic failure shape is applied to every possible location inside the design domain. In the current paper, the maximum stress is considered as optimization objective to be minimized, since failure is typically driven by the occurring stresses and thus of more practical relevance than the compliance. Due to the local nature of stresses, it is presumed that the optimization is more sensitive to the choice of the failure shape than compliance-based optimization. Therefore, various failure shapes, sizes and different numbers of failure cases are investigated and compared on the basis of a general load-path-based evaluation scheme. Instead of explicitly considering fail-safety, redundant structures are obtained at much less computational cost by controlling the maximum length scale. A common and easy to implement maximum length scale approach is employed and fail-safe properties are determined and compared against the explicit fail-safe approach.
Highlights
During the design process of an aircraft, components with multiple and redundant load path are often required due to safety reasons
Comparing the obtained multiple load path designs to a cantilever design optimized without failure, it is observed that the worst-case stress and FSF can be improved by the maximum length scale approach
A major drawback of the original failure patch approach is that it requires an excessive amount of failure cases to be calculated per iteration
Summary
During the design process of an aircraft, components with multiple and redundant load path are often required due to safety reasons. There are alternative and computationally less expensive approaches to obtain redundant structures, e.g. the approach recently published by Wu et al (2018) They defined little subsets of the design space, mostly similar to the density filter (Bourdin 2001; Bruns and Tortorelli 2001), and applied a volume constraint to these subsets. It forces material to be evenly distributed inside the design domain and was originally designed to create bone like infill structure, but could be used to generate multiple load path and fail-safe designs Another approach is to limit maximum member size, which enforces bigger material agglomeration to split up and creating redundant load path.
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