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Structural optimization of components and joints in assemblies considering fail-safety
Citation Link: https://doi.org/10.15480/882.4618
Publikationstyp
Doctoral Thesis
Date Issued
2022
Sprache
English
Author(s)
Ambrozkiewicz, Olaf
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2022-09-30
Institut
TORE-DOI
Citation
Technische Universität Hamburg (2022)
Structural optimization has become an increasingly important part of product development, especially in the aerospace industry, where weight savings due to lightweight design have a particularly strong impact on efficiency and thus economy and environmental compatibility. One area of structural optimization is topology optimization, which offers maximum design freedom and thus enables the greatest improvements. However, load-adapted designs obtained by topology optimization are usually highly sensitive to an unpredictable local loss of stiffness, like e.g. for the case of randomly inflicted damage to individual load paths of the structure. Therefore, these designs are not considered fail-safe.
This thesis presents a two-stage procedure for density-based optimization towards a fail-safe design. Existing approaches are either computationally extremely expensive or do not explicitly consider fail-safe requirements in the optimization. The presented method trades off both aspects by employing a two-stage optimization approach to provide redundant designs that offer robustness to the failure of single load paths. In the first stage, a topology optimization with local volume constraints is performed. The second stage is referred to as "density-based shape optimization" since it only alters the outline of the structure while still acting on a fixed voxel-type finite element mesh with pseudo-densities assigned to each element. The performance gain and computational efficiency of the proposed method are demonstrated by application to various 2D and 3D examples. The results show, that the presented method can be carried out with reasonable computational effort, in contrast to existing approaches with explicit consideration of fail-safety in topology optimization. For the 2D examples considered, the number of analyses for a fail-safe optimization is reduced by three orders of magnitude compared to existing methods and is at most 5.6 times higher than for a standard topology optimization. Consequently, the proposed method is also applicable for large-scale models in an industrial context.
With the possibility to compute and manufacture single optimized components, the question of how to optimize the connections between different components in an assembly arises. This thesis therefore also provides a method for the simultaneous optimization of the topology of components and their corresponding joint locations in an assembly. Therein, the joint locations are not discrete and predefined, but continuously movable. The underlying coupling equations allow for connecting dissimilar meshes and avoid the need for remeshing when joint locations change. The presented method models the force transfer at a joint location not only by using single spring elements but accounts for the size and type of the joints. When considering e.g. riveted or bolted joints, the local part geometry at the joint location consists of matching holes that are surrounded by material. For spot welds, the joint locations are filled with material and may be smaller than for bolts. The presented method incorporates these material and clearance zones into the simultaneously running topology optimization of the components. Furthermore, failure of joints may be taken into account at the optimization stage, yielding assemblies connected in a fail-safe manner. Finally, by embedding the above-mentioned efficient method for fail-safe optimization of single components in the presented assembly optimization framework, damage tolerant assemblies can be obtained that are robust to the failure of joints and single load paths of each component.
This thesis presents a two-stage procedure for density-based optimization towards a fail-safe design. Existing approaches are either computationally extremely expensive or do not explicitly consider fail-safe requirements in the optimization. The presented method trades off both aspects by employing a two-stage optimization approach to provide redundant designs that offer robustness to the failure of single load paths. In the first stage, a topology optimization with local volume constraints is performed. The second stage is referred to as "density-based shape optimization" since it only alters the outline of the structure while still acting on a fixed voxel-type finite element mesh with pseudo-densities assigned to each element. The performance gain and computational efficiency of the proposed method are demonstrated by application to various 2D and 3D examples. The results show, that the presented method can be carried out with reasonable computational effort, in contrast to existing approaches with explicit consideration of fail-safety in topology optimization. For the 2D examples considered, the number of analyses for a fail-safe optimization is reduced by three orders of magnitude compared to existing methods and is at most 5.6 times higher than for a standard topology optimization. Consequently, the proposed method is also applicable for large-scale models in an industrial context.
With the possibility to compute and manufacture single optimized components, the question of how to optimize the connections between different components in an assembly arises. This thesis therefore also provides a method for the simultaneous optimization of the topology of components and their corresponding joint locations in an assembly. Therein, the joint locations are not discrete and predefined, but continuously movable. The underlying coupling equations allow for connecting dissimilar meshes and avoid the need for remeshing when joint locations change. The presented method models the force transfer at a joint location not only by using single spring elements but accounts for the size and type of the joints. When considering e.g. riveted or bolted joints, the local part geometry at the joint location consists of matching holes that are surrounded by material. For spot welds, the joint locations are filled with material and may be smaller than for bolts. The presented method incorporates these material and clearance zones into the simultaneously running topology optimization of the components. Furthermore, failure of joints may be taken into account at the optimization stage, yielding assemblies connected in a fail-safe manner. Finally, by embedding the above-mentioned efficient method for fail-safe optimization of single components in the presented assembly optimization framework, damage tolerant assemblies can be obtained that are robust to the failure of joints and single load paths of each component.
Subjects
fail-safety
joint optimization
topology optimization
shape optimization
DDC Class
620: Ingenieurwissenschaften
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