DESIGN SPACE EXPLORATION FOR OPTIMISATION OF DAMAGE TOLERANT STRUCTURES

DESIGN SPACE EXPLORATION FOR OPTIMISATION OF DAMAGE TOLERANT STRUCTURES

Das, R.; Jones, R.

Full Article:

In parametric design studies, the strength of a structure is often considered as the primary design criteria, and consequently the optimal (best) structural design is often chosen as the one that minimises the maximum stress generated. However, for structures whereby failure is governed by fracture or fatigue, the residual strength, as distinct from stress, needs to be considered as the explicit design objective. In this study, the design space for the distribution of residual strength for different structural configurations is evaluated to demonstrate the utility of design space exploration for damage tolerance design optimisation. This was illustrated using the problem of the optimum design of a cutout shape under biaxial load. The geometry of the cutout was represented parametrically, and numerous flaws/cracks were assumed to be located along the structural boundaries. The maximum stress intensity factors associated with the flaws along the boundary were evaluated for each cutout geometry. Finite element modelling was used to calculate the stress field, and a semi-analytical method was used for computation of the stress intensity factors. The design surface for residual strength was found to resemble a ‘ship hull’. This shape confirms that a design based on residual strength indeed poses a well-behaved optimisation problem, i.e. a well-defined minimum/maximum region exists. The flatness of the design space for residual strength was demonstrated. The optimum values of the stress intensity factor obtained from the design space agreed well with those determined using various optimisation methods in the literature. It is shown that the residual strength optimised shape can be quite different from the corresponding stress optimised solution. This emphasises the need to explicitly consider residual strength as the design objective. It is shown that a design space exploration can provide a systematic way to reduce the weight of a structure by adopting a ‘feasible non-optimal’ solution that meets the design criteria, rather than aiming for the ‘optimal’ (best) solution.

In parametric design studies, the strength of a structure is often considered as the primary design criteria, and consequently the optimal (best) structural design is often chosen as the one that minimises the maximum stress generated. However, for structures whereby failure is governed by fracture or fatigue, the residual strength, as distinct from stress, needs to be considered as the explicit design objective. In this study, the design space for the distribution of residual strength for different structural configurations is evaluated to demonstrate the utility of design space exploration for damage tolerance design optimisation. This was illustrated using the problem of the optimum design of a cutout shape under biaxial load. The geometry of the cutout was represented parametrically, and numerous flaws/cracks were assumed to be located along the structural boundaries. The maximum stress intensity factors associated with the flaws along the boundary were evaluated for each cutout geometry. Finite element modelling was used to calculate the stress field, and a semi-analytical method was used for computation of the stress intensity factors. The design surface for residual strength was found to resemble a ‘ship hull’. This shape confirms that a design based on residual strength indeed poses a well-behaved optimisation problem, i.e. a well-defined minimum/maximum region exists. The flatness of the design space for residual strength was demonstrated. The optimum values of the stress intensity factor obtained from the design space agreed well with those determined using various optimisation methods in the literature. It is shown that the residual strength optimised shape can be quite different from the corresponding stress optimised solution. This emphasises the need to explicitly consider residual strength as the design objective. It is shown that a design space exploration can provide a systematic way to reduce the weight of a structure by adopting a ‘feasible non-optimal’ solution that meets the design criteria, rather than aiming for the ‘optimal’ (best) solution.

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DOI: 10.5151/meceng-wccm2012-16703

Referências bibliográficas

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Como citar:

Das, R.; Jones, R.; "DESIGN SPACE EXPLORATION FOR OPTIMISATION OF DAMAGE TOLERANT STRUCTURES", p-225-238. In: In Proceedings of the 10th World Congress on Computational Mechanics [= Blucher Mechanical Engineering Proceedings, v. 1, n. 1]. São Paulo: Blucher, 2014.
ISSN 23580828, DOI 10.5151/meceng-wccm2012-16703