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Entwicklung eines NXOpen-basierten Optimierungsvorgehens zur belastungsgerechten Anpassung von Stabdurchmessern in Gitterstrukturen

 
: Heinrichs, Michael

Augsburg, 2012, 110 S.
Augsburg, Hochschule, Bachelor Thesis, 2012
Deutsch
Bachelor Thesis
Fraunhofer IWU ()
additive Fertigung; Gitterstruktur; Optimierung; Leichtbau

Abstract
Additive manufactured lattice structures show a high potential for lightweight design. Currently, these structures have a periodical build-up, which leads to disadvantageous stress states. On the one hand, unfavorable bending loads on the single struts appear. This can be avoided by an adaption of the course of the structure to the main stress directions inside the part. On the other hand, different stress values are appearing inside the single struts. Therefore, a procedure for the optimization of the struts diameters is presented. Thus, it becomes possible to achieve equal stresses in the whole structure and gain a better lightweight performance.
The initial structure with uniform strut diameters has a mass of 104 g, and the force at which the limit of elasticity is reached for this structure is 518.5 N. From these values, a characteristic coefficient of 8,891 N/g can be calculated for the ratio of load capacity to mass. To realize the optimization of the strut diameters, two tools have been created for the software Siemens NX 7.5 32 bit by using the NX Open .NET API. With the help of these tools, it was possible to generate three differen optimized structures.
The first structure has been build up with CBEAM elements, which have fixed connections among each other in the respective nodes and it was optimized with a maximum von-Mises stress as optimization goal. The resulting structure is very inhomogeneous, has a mass of 106 g, a maximum stress of 31.38 N/mm² and a characteristic coefficient of 4.96 N/g. Furthermore, it can be seen that the distribution of the stress over the structure is very inhomogeneous.
The second structure was build up with released rotational degrees of freedom at the nodes and constraint and it was optimized with a maximum von-Mises stress as optimization goal. The result has a mass of 58.1 g, a maximum von-Mises stress of 31.94 N/mm², a characteristic coefficient of 8.891 N/g and the distribution of the stress over the structure is way more homogeneous than for the optimization presented before. However, the manual effort is quite big for this method.
The third structure has been build up with fixed connections among each other in the respective nodes and it was optimized with an average von-Mises stress as optimization goal. With the help of this structure was it possible to run an automated optimization which led to a good result. The resulting structure has a mass of 57.5 g, a maximum von-Mises stress of 31,95 N/mm², a characteristic coefficient of 8,891 N/g and the distribution of the stress over the structure is also almost homogeneous. This means an improvement of 79% compared to the initial structure.

: http://publica.fraunhofer.de/dokumente/N-229109.html